Techniques for water and wastewater management a review of

Urban Water 2 (2000) 197±221

www.elsevier.com/locate/urbwat

Review

Techniques for water and wastewater management: a review of techniques and their integration in planning Roland Burkhard a,*, Ana Deletic b, Anthony Craig c a Colenco-Holinger AG, Mellingerstrasse 207, 5405 Baden, Switzerland Engineering Department, University of Aberdeen, Aberdeen AB24 3UE, UK Scottish Centre for Environmental Design Research, Robert Gordon University, Faculty of Design, Aberdeen AB10 7QB, UK b

c

Received 8 July 2000; received in revised form 13 July 2000; accepted 25 October 2000

Abstract This paper presents a review of techniques in wastewater management and a discussion as to how they can be integrated in future water-planning issues. Three technical areas are dealt with: rainwater management, domestic wastewater management, and water and waste re-use. Each approach is reviewed from a technical perspective with a further commentary on economic and social factors that underpin the di€erent techniques that each approach has to o€er. This is followed by a discussion on how integrated assessment can lead to the design and implementation of more sustainable approaches to wastewater management. Ó 2001 Elsevier Science Ltd. All rights reserved. Keywords: Rainwater; Sustainability; Wastewater; Water and waste re-use; Water and wastewater management

Contents 1.

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.1. Sustainability in water management . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.2. Social aspects in water management . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.3. Social acceptability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

198 198 198 199

2.

Review methodology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

199

3.

Rainwater management . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.1. Techniques . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.2. Eciency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.2.1. Suspended solids . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.2.2. Heavy metals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.2.3. Land use . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.3. Economic aspects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.4. Social aspects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

199 199 201 201 202 202 203 203

4.

Domestic wastewater management . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.1. Techniques . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.2. Eciency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.2.1. TSS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.2.2. BOD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.2.3. Land use . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.3. Economic aspects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.4. Social aspects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

204 205 207 207 208 209 209 211

*

Corresponding author. Tel.: +41-056-483-1824; fax: +41-056-483-1875. E-mail address: [email protected] (R. Burkhard).

1462-0758/01/$ - see front matter Ó 2001 Elsevier Science Ltd. All rights reserved. PII: S 1 4 6 2 - 0 7 5 8 ( 0 0 ) 0 0 0 5 6 - X

198

R. Burkhard et al. / Urban Water 2 (2000) 197±221

5.

Water and waste re-use . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.1. Techniques . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.2. Water quality and health issues in re-use techniques. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.3. Eciency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.3.1. Greywater and rainwater harvesting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.3.2. Solid and liquid waste re-use . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.4. Economic aspects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.4.1. Rainwater. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.4.2. Greywater. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.4.3. Human waste recycling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.5. Social aspects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

211 212 213 214 214 215 215 215 215 216 216

6.

Discussion and conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.1. Techniques . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.2. Eciency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.3. Economic aspects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.4. Social aspects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.5. Planning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

217 217 217 217 217 218

Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

218

References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

218

1. Introduction If future generations are not to be constrained even further, we must develop a coherent `holistic' approach to the planning, speci®cation, costing and evaluation of water and wastewater options in the domestic context, such as where the demand for new housing developments is forecast to have signi®cant and widespread environmental impact. It requires a balance of technical, economic, environmental and social goals, while satisfying the demands of developers, planners, environmental protection agencies and customers. The decisionmaking process is therefore complex, requiring the identi®cation and evaluation of mutual and con¯icting interests of stakeholders. 1.1. Sustainability in water management Before dealing with sustainability in wastewater management, it is helpful to review some de®nitions of sustainability and thus to place it in context. According to Otterpohl, Albold, and Grottker (1996), the World Commission on Environment and Development (WCED, 1987, also known as Brundtland Report) made the most popular de®nition of sustainability. Sustainable development is de®ned as ``development that meets the needs of the present without compromising the ability of future generations to meet their own needs''. According to Tages-Anzeiger (1995), the word sustainability has long been used in forestry where it means that volume and mass taken out is replaced and hence the mass balance accounts to zero. This is nowadays

known as `natural sustainability', whose criteria are based on mass ¯ux and the ability of a technique to recycle nutrients and other valuable resources from wastewater before they are lost. Another aspect is `®nancial sustainability'. It can be argued that the success and survival of business follows natural laws as well, i.e. money spent on production, wages and interest has to be replaced by money earned for services or goods. However, the costs and use of raw materials included in the processes to produce the goods or deliver a service may seriously a€ect the mass balance. The instability that can thus be created by applying di€erent economic criteria is one of the principal reasons why the issue of sustainability is raised at all. Hence, the quest for sustainability is intimately linked to the quest for economic models, which take the natural mass ¯uxes into account. A third and important factor in sustainability considerations is the potential users of a system. Their behaviour and commitment to participate in the water management process make a method sustainable, because the occurrence of pollution in the water cycle is mostly due to human behaviour. This third factor may be called `social sustainability'. In this review, sustainability will be discussed in the context of the above three distinct interpretations. 1.2. Social aspects in water management Of the many criteria which may be used to assess the feasibility of water and wastewater systems, it is likely that ``the social aspects will be the most dicult issues''

R. Burkhard et al. / Urban Water 2 (2000) 197±221

(Harremoes, 1997). This oft-neglected `social' side of systems can provide a wealth of information regarding the appropriateness of a technology in a given setting, along with any potential barriers to its implementation. The scope for interdisciplinary co-operation in this area is large and the role of the engineer and the social scientist may converge, thereby reducing the tendency towards ``expertocracy'' (Fismer & Wendler, 1996). The distinction made between social acceptability and social sustainability throughout this paper is discussed below. 1.3. Social acceptability The `awareness' criteria have to be included in the investigation on ecological systems, as lack of awareness in¯uences acceptance. The extent to which people are required to alter their everyday behaviour will probably have the largest e€ect on acceptability. Disgust sensitivity is also likely to have an e€ect on acceptance of water and waste re-use systems (Bixler & Floyd, 1997). Furthermore, research into risk perception (Slovic & MacGregor, 1994; Renn, 1998; Lofstedt, 1997) has shown that people are more likely to accept risks if they are seen to be familiar, voluntary, and of negligible catastrophic potential. Simply being `environmental' does not necessarily determine public acceptance. To be sustainable, wastewater technology assessment should include community participation within the decision-making process. The need for institutional involvement in the installation and maintenance of wastewater systems will also a€ect the social sustainability, along with the potential for local development, in the form of jobs, amenity enhancement, and correspondence with local ethics (Balkema, Weijers, & Lambert, 1998). One of the biggest positive in¯uences that many alternative wastewater treatment systems may have is the ``environmental education'' component and the potential for further interdisciplinary communication and active partnership. 2. Review methodology Three main areas in planning of wastewater in urban areas are tackled: · rainwater management; · domestic wastewater management; · management of water re-use (both domestic and rainwater). Three aspects have been analysed in each area regarding eciency, economic, and social aspects of the techniques, as listed below. Techniques: Both traditional and novel will be presented with a brief description of their design requirements.

199

Eciency: For all techniques, the eciency is presented with respect to their purpose (e.g. SS and BOD removal). Economics: Cost data are hard to ®nd. Whenever possible, real costs were used, but in all cases qualitative costs were systematised. They may include values, which are subjective to the user, e.g. environmental bene®ts. Social aspects: The social impact of the di€erent techniques will di€er largely. The subjective importance of various social-sustainability criteria (based on Balkema et al., 1998) will be discussed brie¯y for systems a€ected by that criterion. 3. Rainwater management 3.1. Techniques 1. Traditional storm drainage systems consist of inlet structures (inlets with gully-pots or catch-basins), and drainage pipes which transport water to the nearest outfall. A number of ancillary structures may be included in such systems, such as silt traps, storage tanks and controllable structures. This form of drainage is still the most widely used technique. A distinction between combined and separate drainage systems (Escritt, 1984) needs to be made: 1(a) CSS: Combined sewer systems convey both wastewater (domestic/industrial) and storm runo€. 1(b) SSS: Separate sewer systems collect and convey the wastewater and runo€ in separate colection systems. This requires two parallel pipe systems. 2. In®ltration and collection systems have been used in urban drainage for centuries, however they were almost forgotten in the era of high urbanisation. These methods are now experiencing a renaissance and are being increasingly used in the planning of new developments. In®ltration systems help limit peak runo€ in sewer systems and can thus reduce over¯ow from combined systems. Extensive literature exists in several countries (Watkins, 1995; Bettess, 1996; Bettess, Davis, & Watkins, 1996; Hydro Research, 1993; AGW, 1991, 1996; AfU, 1994; WEF, 1998, ATV, 1997b). Bettess et al. (1996) distinguish between plane in®ltration systems and 3-D in®ltration systems. To design in®ltration systems, the required inputs are listed in Table 1. The design procedures vary from country to country. The main requirement is the establishment of enough storage for a speci®ed storm event. Safety factors attempt to minimise risks and result in larger systems. 2(a) PP: Permeable pavement is used for surfaces on parking lots and residential roads. Permeable macadam is an option, but is very expensive and tends to clog after 1±3 years. It needs considerable maintenance e€ort. Also in widespread use are lattices of blocks with the in®l-

200

R. Burkhard et al. / Urban Water 2 (2000) 197±221

Table 1 Input requirements for in®ltration systems q (m/h)

AD …m2 †

n …m3 =m3 †

i (m/h), D (h)

Ad …m2 †

In®ltration coecient from test (>0.001)

Area to be drained

Porosity of ®ll material (0.2±0.5)

Intensity and duration of rainfall events

Drainage area of in®ltration system

Table 2 Design criteria of permeable block pavement Base layer depth (mm), material, porosity

Top layer (Filter) depth (mm), material, porosity

n/a, Porous ®ll material, n/a

50±100, ®lter or geotextile, n/a

Pavement

Porous Macadam, concrete blocks 300, coarse gravel (3.5±5.0 cm), 100, ®ne graded gravel (0.3±2.0 cm), Modular block, blocks of 0.3±0.4 0.2±0.3 lattices, etc. 200±300, clean stone (25±150 50, geotextile, n/a; 50, gravel 15±25 50 mm Macadam, 80 mm mm), 0.3±0.4 mm; n/a concrete block

tration surface below the load-bearing surface. In some countries, surface in®ltration does not need any hydraulic design considerations when rainfall is in®ltrated. Table 2 shows some guidelines in the selection of PPs. 2(b) IB: In®ltration basins (Fig. 1) are allocated grassed areas that can be ¯ooded at times of rain when water can slowly drain into the ground. During dry weather intervals, the in®ltration basins are empty and can be used for other purposes. Table 3 shows some general design considerations. Bettess (1996) suggests that attention should be paid in handling the soil, as this is important for the support of the plants growing in the basin as well as the in®ltration capacity. Plant selection and plant community according to local microclimate is also an important issue. Cutting grass prevents shrub invasion.

Fig. 1. In®ltration basin (after AGW, 1991).

Fig. 2. Combination of two soakaways and a French drain (after AGW, 1991).

Distance to groundwaterlevel (m)

Literature source

n/a

Bettess (1996)

>0.9

WEF (1998)

n/a

Leonard and Sherri€ (1992)

2(c) Sw: Swales are grassed ditches, taking up runo€ from roads or parking lots. The runo€ slowly runs through the grass swale and in®ltrates into the ground. There is no stagnant water in a carefully designed swale. Table 4 shows some design guidelines and their ®gures. 2(d) So: Soakaways or in®ltration trenches (Fig. 2) are underground structures, which normally are circular shafts or trenches. They are ®lled with a gravel medium into which runo€ is discharged. Circular soakaways normally consist of precast concrete manhole elements ®lled with gravel. The concrete elements are often solid on top and perforated at the bottom. However, this varies from guideline to guideline (AGW, 1996; WEF, 1998; Bettess, 1996). Combinations of circular soakaways with trenches are used, and soakaways can be linked which enlarges the in®ltration area (Bettess, 1996). Table 5 shows some design ®gures. 3. Detention systems have been used to control runo€ peaks and for treatment of combined-sewer over¯ows (CSOs) for a number of years, usually at the outlet of a conventional system. However they are now increasingly used for catchment management. 3(a) P: Ponds act as detention or retention structure where the rainfall runo€ enters straight from the drained surface. The pond also acts as a settlement structure. Any over¯ow from the pond can be directed via an outlet structure, into a receiving watercourse, a soakaway, or drainage pipe. The pond can easily be integrated into the landscaped surrounding of a new housing estate and can serve as a habitat for wildlife. Table 6 shows some design data for a dry pond. Wet detention ponds also exist. 3(b) CW: Constructed wetlands can act as detention and puri®cation ponds. They can also be used for cleaning wastewater spilled through CSOs. Table 7 shows some design data.

R. Burkhard et al. / Urban Water 2 (2000) 197±221

201

Table 3 Design criteria of in®ltration basins Max depth (m)

Distance to groundwaterlevel (m)

Layout

Vegetation

Literature source

0.3

>1.2

Several small basins instead of one large

Grasses that will survive prolonged inundation

WEF (1998)

Table 4 Design criteria of swales Minimum length (m)

Min/max bottom width (m)

Recommended slope (%)

Max ¯ow velocity …m sÿ1 †

30

0.6/2.4

n/a n/a

n/a 1

2.0 (0.5 minimum, 6.0 <0.3 maximum) <4.0 without berms n/a n/a n/a

n/a

n/a

<6.0

n/a

<0.5

Roughness, k …m1=3 sÿ1 †

Max depth of ¯ow (mm)

Literature source

5/4.17

75

WEF (1998)

n/a n/a

n/a 250±1000 (total depth) n/a

Bettess (1996) Leonard and Sherri€ (1992) FRPB (1995)

Table 5 Design criteria of soakaways and in®ltration trenches Porosity of ®lling …m3 mÿ3 †

Maximum depth

Layout con®guration

Dist to seasonal high groundwaterlevel (m)

Literature source

0:15±0:30

f(Wall stability, groundwaterlevel) 3±6 m

Long and deep

>1.2

WEF (1998)

Depth excavation <3  depth to invert of drain

Mention of caution

Leonard and Sherri€ (1992)

n/a

Table 6 Design criteria of ponds Storage volume

Layout

Basin side slopes

Literature source

Capture volume + 20%

Expand from inlet, contract toward outlet, top stage 0.6±1.8 m deep, bottom slope 2%; bottom stage 0.5±0.9 m

<4:1

WEF (1998)

Detain storm runo€ for a few hours, capture of ®rst foul ¯ush

Careful inlet and outlet design to prevent scouring, ori®ce control for outlet

n/a

FRPB (1995)

n/a

O€- and on-line detention tanks, ¯ow storage

n/a

Luker and Montague (1994)

3(c) OR: On-site retention systems may consist of grassed roofs or other roof areas where runo€ can temporarily be stored. These may be parking lots, sports grounds and other suitable areas. 3.2. Eciency For rainwater control systems eciency of water quality control (qualitative eciency) and the eciency of ¯ood control (quantitative eciency) were examined.The qualitative eciency of these systems is as-

sessed with regard to the removal of suspended solids (SSs) and heavy metals (HMs) from the runo€. 3.2.1. Suspended solids Data from the literature on removal eciency of SS for the techniques presented are shown in Fig. 3. The minimum eciency recorded in the literature for a certain technique is presented as `low', while the highest ®gures are presented as `high'. The following remarks concern each studied technique:

202

R. Burkhard et al. / Urban Water 2 (2000) 197±221

Table 7 Design criteria of constructed wetlands DWF depth variation (m)

Wet weather storage

Open water area

Length to width ratio

Literature source

0.1±1.2

Design as detention pond, surcharge depth 0.6 m above DWF depth, drawdown 24 h

<50% total wetland area

>3:1, 2:1 recommended

WEF (1998)

1(a) CSS: Depending on the inlet structure and the particle size, sediment traps need maintenance to be ecient (Luker & Montague, 1994; Bettess, 1996). 1(b) SSS: As above (Luker & Montague, 1994; Bettess, 1996). 2(a) PP: Removal eciency is high and amounts to almost 100%, removal ˆ f(in®ltration media) (FRPB, 1995). 2(b) IB: As above (FRPB, 1995; Luker & Montague, 1994). 2(c) Sw: Research restricted to laboratory conditions, no interaction between natural environment and sediment studied (FRPB, 1995; Deletic, 1998; White, 1987; Gray, 1989; Escritt, 1984). 2(d) So: As PP and IB (Mehler & Ostrowski, 1998; FRPB, 1995). 3(a) P: From low to very high, depending on design and hydraulic loading of ponds (Mehler & Ostrowski, 1998; FRPB, 1995; Bettess, 1996; WEF, 1998; Luker & Montague, 1994). Long-term wet detention pond performance was found to be very good according to Maristany (1993), suggesting consistent removal of particulate constituents. 3(b) CW: Most extensive data, removal eciency depending heavily on hydraulic loading and hence design of system (Bettess, 1996; WEF, 1998; Luker & Montague, 1994; Knight, Ruble, Kadlec, & Reed, 1993; Sapotka & Bavor, 1994; Kadlec & Hey, 1994).

Fig. 3. Removal eciency of rainwater control techniques: suspended solids (SS).

3(c) OR: No data found, OR techniques are combination of di€erent techniques, hence good removal eciency likely. 3.2.2. Heavy metals Other signi®cant pollutants include heavy metals (HMs). There is research on HM removal, but this is mainly for heavily polluted runo€ from special mining and industrial processes (Eger, 1994). Data on removal of HM in urban runo€ can be found in Luker and Montague (1994) and FRPB (1995). For all techniques, the removal eciency is governed by design. Maintenance is also crucial for the e€ective functioning of a technique. The performance of almost all techniques with regard to SS removal can be improved by using sediment traps (AGW, 1996) and generously designed inlet structures (Ellis & Revitt, 1991). It is not possible to conclude from the literature whether low performing techniques were badly designed. 3.2.3. Land use The quantitative removal of storm water runo€ in urban areas is determined by the design return period (RP) storm, imperviousness of the catchment, slope of the catchment, the surface/underground on/in which the technique will be applied, the vegetation cover, the use of the catchment and the available space. A simple example is presented to illustrate the typical land use of each technique as a percentage of a newly developed site. A hypothetical catchment was located in Aberdeen. The parameters for the design storm were chosen for the Aberdeen area (NERC, 1974; Bettess, 1996; Leonard & Sherri€, 1992), and the site speci®cations were adopted according to the literature. The chosen site and storm characteristics are presented in Table 8. The following was assumed for each technique: 1(a) CSS: Assumed all underground structures under access roads. 1(b) SSS: Assumed all underground structures under access roads. 2(a) PP1: Permeable pavement with subgrade material of porosity n ˆ 0:325. 2(a) PP2: Permeable pavement without subgrade material, hence porosity n ˆ 1. 2(b) IB: In®ltration basin with maximum water depth of 0.4 m. 2(c) Sw: Swales with base width of 2.4 m, embankment slope of 1:4 and base slope of 0.5%.

R. Burkhard et al. / Urban Water 2 (2000) 197±221

203

Table 8 Design constraints BMPs Site

Rainfall eventa

Soil type, k b

Dwelling typec

Runo€ coecientc

Estate size

Distance GWL

Aberdeen, UK

10 Year RP

Loamy sand, 0.3 m/h

Detached, semidetached

0.45

2 ha

2m

a

Bettess (1996). Data from AGW (1996). c Data from Heierli (1991). b

2(d) So: Soakaway with ®lling material of porosity n ˆ 0:35. 3(a) P: Detention pond with length:width ratio 2:1. 3(b) CW: Constructed wetland with length:width ratio 2:1. 3(c) OR: Other retention measures with an average depth of 0.2 m. Using the recommendations from Bettess (1996), AGW (1996), WEF (1998), NERC (1974) and Leonard and Sherri€ (1992), the data on land use presented in Fig. 4 were obtained. The ®gure shows that the detention BMP techniques use most land. OR seems to be particularly problematic. However, if we take into account that the OR techniques include roof and parking lot retention, allocation of new land for their construction becomes less than for P and CW. In®ltration techniques are from a land-use point of view least problematic, but they hardly contribute to amenity value.

lower enhancement costs of downstream systems. Bettess also stresses the distinction between economic and ®nancial appraisal. Economic appraisal is often dicult, as many aspects cannot be measured in cash terms, such as the impact of in®ltration on groundwater levels. Financial appraisal concerns only the ¯ow of money, which arises from the system. Table 9 shows a qualitative economic comparison of the various rainwater management techniques (based on Luker & Montague, 1994). It should be noted that such a comparison is inherently subjective and therefore hard to generalise from. A qualitative assessment however does provide the means to balance con¯icting criteria. McKissock (1999) gathered information on capital costs of rainwater control techniques. These are presented in Fig. 5(a) and (b).

3.3. Economic aspects

The social science literature of rainwater management is extremely limited and would clearly bene®t from further quantitative research. Nevertheless, some qualitative analysis can be helpful. The di€erent criteria and degree of interdependence are listed below.  Social acceptance of rainwater management systems will generally be high, as there is usually little awareness of such systems. However, in the case of ponds, perceived safety to children might in¯uence acceptance, and thus deter their use (McKissock, Je€ries, & D'Arcy, 1997). Acceptance may be in¯uenced by a perception of ¯ood risk for swales and in®ltration basins, as they may be designed to ¯ood public areas. Acceptance of constructed wetlands could be in¯uenced if people have similar safety worries, or think that there might be a problem with insects. Perception of tighter land use control may also in¯uence acceptance (WEF, 1998).  The added Amenity value of a rainwater management system will depend largely on how well landscaped the systems are (e.g. how much involvement landscape architects have). In a recent study, where a range of people involved with BMPs were questioned, it has been found that only 12% believed that runo€ control could have amenity objectives (McKissock et al., 1997). Houses that are built near water tend to be preferred by the public. Emmerling-DiNovo (1995) found that the residents in her study valued wet detention basins sig-

Economic comparisons exist in several CIRIA publications (Luker & Montague, 1994; Bettess, 1996). While Luker and Montague valued the BMPs for highway drainage only qualitatively, Bettess saw the necessity for an appraisal of costs. He proposed to compare the prices of the conventional drainage system with the on-site in®ltration schemes. Costs for the conventional system include construction costs and enhancement of downstream systems, whereas costs for in®ltration systems comprise construction costs and

Fig. 4. Land use of di€erent BMP techniques.

3.4. Social aspects

204

R. Burkhard et al. / Urban Water 2 (2000) 197±221

Table 9 Economic aspects of rainwater management Technique

Capital cost

Operation and maintenance costs

Environmental bene®t

Remarks

1(a) CSS 1(b) SSS 2(a) PP

High High High

Low±medium Low±med High

Negative Negative Positive

2(b) IB 2(c) Sw

High Low±medium

Low±medium Medium

Positive Positive

2(d) So

Med

Medium

Positive

3(a) P

High

Low

Positive

3(b) CW 3(c) OR

High Low±high

Medium Low±high

Positive Positive

*** *** High maintenance costs, sweeping. Also, may have a limited life (10 years) Require periodic refurbishment Cost high when land has to be acquired. Require periodic refurbishment High maintenance and refurbishment costs. Require periodic refurbishment Cost high due to land acquisition, lower maintenance costs, wet ponds cheaper than drier *** ***

ni®cantly higher than dry detention basins. EPA (1995) found that well-designed runo€ controls can provide signi®cant economic bene®ts in the form of increased property values.  Community participation is important, especially for those systems that might a€ect the amenity and landscape value of an area. People tend to be especially concerned about landscape changes that might a€ect the value of their property (EPA, 1995). However, public

(a)

(b) Fig. 5. (a) Costs of rainwater control per housing unit, low, high and average prices. (b) Costs of rainwater control per hectare, low, high and average prices.

education is a prerequisite to public participation (see WEF, 1998; Pateman, 1970).  Awareness of rainwater management systems is generally rather low. Educational interventions are required to increase awareness, such as storm drain stencilling (this is where community groups stencil slogans on storm drains or nearby signs, such as ``when you rubbish the streets, you rubbish the river'' (Melbourne Water, 1997) which makes potential polluters aware of the connection between the drain and the river).  Institutional requirements will vary from site to site, depending on the size of the development in question and the land availability. By and large, however, the developer will be responsible for providing the land, meeting the capital costs, and landscaping costs of BMPs. Legal arguments around who is responsible for long term maintenance are common (Maxwell, 1997). Lack of guidance, rather than general ignorance seems to be the cause for a lack of uptake of BMPs by developers, who prefer to stick to traditional drainage structures (McKissock et al., 1997). Monitoring of discharge standards will require the same institutional involvement (from the relevant environmental protection agency) for each of the di€erent systems.  Local development potential of the di€erent systems will depend largely on who is responsible for installation and maintenance (i.e. are local people employed).  There is potential for Stimulation of sustainable behaviour, especially for ponds and wetlands, to which visits could be incorporated into school curricula. Various examples exist in Australia of such educational programmes (e.g. Melbourne Water, 1997).

4. Domestic wastewater management Domestic wastewater management in urban and semi-urban Europe is based on the conventional ap-

R. Burkhard et al. / Urban Water 2 (2000) 197±221

205

proach of collecting the wastewater in one of the traditional drainage systems discussed in the section above and transferring it to a treatment works. However, a variety of decentralised methods exist, which are applicable for both rural and suburban areas. Decentralised and also ecological methods generally provide simple, low-cost and low maintenance methods of treating domestic wastewater. 4.1. Techniques 1. Centralised conventional sewage treatment works consist of several stages, of which the primary and secondary stages are the bare minimum nowadays, and the focus is on these two stages. Tertiary stages exist where there are known problems of water eutrophication, where wastewater needs advanced treatment or where it is discharged into a sensitive environment. Conventional treatment systems produce considerable amounts of sludge and they are generally very energy consuming (Gujer, 1996). The primary stage is similar for most conventional treatment works. The incoming wastewater is screened before it enters the primary stage of the treatment process. Primary treatment consists of a settlement area where grit and other solids can settle out and fats, oils and greases (FOG) are removed. Secondary stages are more diverse and they are usually the focus of alternative methods. The centralised conventional systems are listed below without any explanation because these techniques are widely known (see, for example, White, 1987; Gray, 1989; Metcalf & Eddy, 1991; Escritt, 1984; Salvato, 1982): 1(a) AS: Activated sludge. 1(b) PF: Percolating ®lters or trickling ®lters. 1(c) RBC: Rotating biological contactors. 1(d) OP: Oxidation ponds (aerobic ponds, anaerobic ponds, and facultative ponds). 2. Decentralised conventional systems are used for one or a few remote houses. Some of the methods have been abandoned, as they can be a threat to ground or surface water. This is especially true for group 2(a). The reason why they are listed here is their possible use as cost-effective pre-treatment methods for decentralised treatment. 2(a) NB: Non-biological treatment Cesspools, as shown in Fig. 6, are watertight underground plastic tanks in which the wastewater is collected and stored until emptied by a tanker. This solution is very costly and the waste is transported over long distances for ®nal disposal (Grant et al., 1996; Grant & Moodie, 1997; Metcalf & Eddy, 1991; VSA, 1995). They are useful where no other options are available or are costlier, and where intermittent use does not allow for biological treatment systems.

Fig. 6. Cesspool (after Grant, Moodie, & Weedon, 1996).

Septic tanks are also underground structures that collect wastewater. They generally have two chambers, separated by a ba‚e. In the ®rst chamber the sediments in the raw sewage settle out, while in the second chamber some secondary treatment processes may take place. The sewage can become fully anaerobic. Technically, they are very unproblematic and hence require little maintenance. They are a low-cost primary treatment solution and can be used in combination with leach®elds, where the wastewater is fully treated. Settlement tanks have a similar function to septic tanks. However, they are a lot smaller. The sewage stays in the tank for a much shorter time and therefore does not become septic. The objective is separation of solids and foam from the sewage. The e‚uent from the settlement tank is passed on to secondary treatment. They are extremely low cost constructions and require little maintenance except for the removal of sludge. 2(b) PB: Package biological plants Recirculating biological ®lter (RBF): The treatment principle is the same as in a percolating ®lter. The ®lter is contained within a plastic shell and the wastewater is spread over the ®lter via a pump from the well. Once through the ®lter, the water ¯ows back in the well. An over¯ow ensures the out¯ow of the treated wastewater. Regular cleaning of the distribution channels is required for some systems (Grant et al., 1996; Metcalf & Eddy, 1991). Submerged aerated biological ®lter (SABF): This system is a combination of an activated sludge treatment system and a recirculation ®lter system (Fig. 7). After an inlet chamber, the wastewater passes through a chamber with aerated activated sludge where it is broken down. It then discharges into a settlement chamber where part of the ¯ow is recirculated back into the inlet chamber while the other part leaves the treatment SABF. This helps to enhance the treatment process but also makes it more costly (Grant et al., 1996; Metcalf & Eddy, 1991). Activated sludge package plants or sequence batch reactors (SBR): This process is the smaller equivalent of the large-scale treatment works. There are several different package versions available, some of which consist of di€erent chambers through which the wastewater

206

R. Burkhard et al. / Urban Water 2 (2000) 197±221

Fig. 8. Leach®eld (after Klargester, 1999). Fig. 7. SABF (after Grant et al., 1996).

¯ows and within which the activated sludge process and the settlement of the sludge take place. Other systems consist of just one chamber, where a batch of wastewater is treated with activated sludge, i.e. oxygen is blown into the chamber and suspends the sludge. When the wastewater is puri®ed, the aerator switches o€ and the sludge settles at the bottom of the chamber. The sediment-free water is then pumped out and replaced by a new batch of wastewater. Hence the name sequence batch reactors (Grant et al., 1996; Metcalf & Eddy, 1991). Bio disc units: These are self-contained units, which include, similarly to RBCs, a rotating disc. The disc is powered by a low-energy electric motor. The sizing is a function of the pollutant load, daily sewage volume and ¯ow. They are designed to deal with domestic sewage only. Table 10 provides design considerations for bio disc units. 2(c) LF: Leach®elds as shown in Fig. 8, and soakaways are used in remote areas where e‚uent from septic tanks is in®ltrated into the soil via an underground network of pipes. Any aquifer has to be a minimum distance away from the in®ltration pipes and a bioactive layer of soil is generally required to provide ample treatment for the pre-treated sewage (Grant et al., 1996; Metcalf & Eddy, 1991; VSA, 1995; Kennedy, 1997). Table 11 provides design criteria for leach®elds. 3. Ecological treatment methods are generally also decentralised systems. Most of them try to make use of natural puri®cation processes that happen in the zones of interaction between water and soil or plants. Any ¯ow that is treated in them undergoes primary treatment, which is usually screening and settlement. 3(a) Constructed wetlands (Fig. 9) can be used for secondary treatment of domestic sewage. They consist of a watertight pool, ®lled with a medium and planted with aquatic plants (macrophytes), which are able to grow in

a water-saturated root zone. At the upstream end of the wetland, an inlet structure distributes the in¯ow either over or into the top section of the bed. At the downstream end, an outlet structure collects the treated wastewater (Grant et al., 1996; Nutall, Boon, & Rowell, 1997; Kowalik, 1995; Cooper, 1990; Cooper, Job, Green, & Shutes, 1996; Schimid & Z ust, 1995; Haberl, Per¯er, Laber, & Cooper, 1996; Wissing, 1995). Some design criteria are provided in Table 12. 3(b) Living machines are a relatively new method of treating domestic wastewater. Their layout consists of a preliminary septic tank where sedimentation takes place. The water then enters, where required, a greenhouse, where the ®rst phase of aerobic treatment takes place in a closed tank. The water then ¯ows into open aerobic reactors. Floating on plant racks, macrophytes grow with their large root system submerged in the wastewater. In this phase, BOD and TSS are reduced and ammonia is nitri®ed. Oxygen is constantly bubbled into the reactors. Clari®ers then settle solids left in the ef¯uent from the aerobic reactors. Denitri®cation takes place in the subsequent stage, the ecological ¯uidised beds. Live ®sh in the ®nal e‚uent ensure an automatic quality control. (Findhorn Foundation, 1996; Todt, 1997) 3(c) Aquaculture is a good measure to directly recycle human waste. Being used for centuries all over the world, they were abandoned in Europe towards the end of the 20th century (Prein, 1996). This was due to their extensive nature, the need to employ ®shkeepers and their locations on the fringes of expanding cities where land prices rose signi®cantly, rendering them economically unattractive. The only remaining large aquaculture in Europe is the basin in Munich that serves as a polishing treatment stage for the refurbished treatment works. Aquaculture consists of large ponds in which di€erent plants and ®sh live. The plants feed on the nutrients from either raw, screened sewage or secondary treated

Table 10 Design criteria of bio disc units Size ˆ f( )

Use

Desludge

People

Discharge

Literature source

Daily sewage volume

Permanent occupation, remote areas

Depends on size: every half year or annually

<12

Soakaway, watercourse

Klargester (1999)

R. Burkhard et al. / Urban Water 2 (2000) 197±221

207

Table 11 Design criteria of leach®elds Floor area trench …m2 †

Use

Trench width (m)

Min/max length

Literature source

P  Vp  0:25; P ˆ No of persons; Vp ˆ percolation (s mmÿ1 ) 4±20 PEÿ1

Suitable soil and groundwater environment Clay±medium sand

0.6±0.9

30/200 m

Klargester (1999)

n/a

n/a

VSA (1995)

3(d) Sand ®lters can be vertical ¯ow ®lters as well as pressure ®lters. The wastewater that is applied is usually tertiary e‚uent. (Metcalf & Eddy, 1991; Gray, 1989; White, 1987; Escritt, 1984). Table 13 provides some design criteria for sand ®lters. 4.2. Eciency

Fig. 9. Wetland for domestic wastewater treatment.

e‚uent. The ®sh in the pond feed on the plants and normally grow to full size in one vegetative season. They are then harvested and sold. Plants for human consumption can also be reared in aquacultures (Guterstam, 1997; Staudenmann, 1994; Ghosh, 1997; Ol ah and Pekar, 1997).

The eciency with regard to wastewater treatment is assessed using the literature data. For all treatment systems, the eciency is only as good ± or as bad ± as the design. However, the design of conventional systems is better understood since the technology has developed over the past century and is hence well researched. Figs. 10 and 11 show the removal eciency of TSS and BOD. 4.2.1. TSS The following remarks refer to the data presented in Fig. 10. 1(a) AS: The values are for two-stage treatment works. AS plants can be designed to remove a high

Table 12 Design criteria of wetlands Sealing

Medium

Velocity …mhÿ1 †

Area …m2 †

Depth (m)

Literature source

None if clay; concrete; plastic container; liner; bentonite; clay

Sandy gravel

0.36±3.6

Horizontal: min 20; P 5.0 PEÿ1 vertical: min 10; P 2.5 PEÿ1

Horizontal: 0.5; vertical: 0.8

ATV (1998)

If clay available, puddled clay; plastic liner or membrane

Gravel, pulverised fuel ash

n/a

4±5; ˆ f(sewage strength)

0.3 (inlet)±0.6 (average)

Cooper (1990)

Compacted clay; bentonite; plastic membranes

surface: local soil subsur.: gravel

ˆ f(hydraulic conductivity; cross section; gradient)

ˆ f(¯ow; in¯uent, e‚uent BOD5 ; reaction rate constant; water depth; porosity)

surface ¯ow: 0.10±0.45 subsur. ¯ow: 0.3±0.6

Kowalik (1995)

n/a

Gravel sand

0.1

6±10 PEÿ1

0.3±0.8

VSA (1995)

Table 13 Design criteria of sand ®lter Type

Hydr loading per area …mdÿ1 †

Loading frequency …dÿ1 †

Media: depth (m); diamenter (mm)

Area …m2 PEÿ1 †

Literature source

Covered ®lter Open ®lter

0.04±0.08 0.12±0.20

2±4 4±10

0.6±0.9; 0.5±4 0.6±0.9; 0.5±4

4±6 2

ATV (1998)

208

R. Burkhard et al. / Urban Water 2 (2000) 197±221

Fig. 10. Removal eciency for domestic treatment methods: TSS. (Values show range and average found in the literature.)

percentage of pollutants, removal of SS mainly depends on settlement tanks (Tiefbauamt der Stadt Z urich, 1993; Metcalf & Eddy, 1991; Grant et al., 1996; Gray, 1989; White, 1987; Escritt, 1984). 1(b) TF: The values are for two-stage treatment works. Low loaded TF plants remove a high percentage of pollutants, removal of SS mainly depends on settlement tanks (Metcalf & Eddy, 1991; Grant et al., 1996; Gray, 1989; White, 1987; Escritt, 1984). 1(c) RBC: High removal eciency, although not very robust as many mechanical parts can fail (Metcalf & Eddy, 1991; Gray, 1989). 1(d) OP: Poor eciency due to algae growth, usually needs ®nal settlement (Metcalf & Eddy, 1991; Gray, 1989; White, 1987; Escritt, 1984). 2(a) NB: Robust, but low removal eciencies. They are normally combined with other treatment facilities. Suitable for small remote housing (Metcalf & Eddy, 1991; Grant et al., 1996; Gray, 1989; White, 1987; Escritt, 1984; VSA, 1995). 2(b) PB: Little information on removal eciency. Mechanical parts make them failure prone (VSA, 1995; Salvato, 1982). 2(c) LF: When used in the right place, they virtually remove all SS as the e‚uent ®lters through soil with high ®ltering capacity (Grant et al., 1996). 3(a) CW: Good removal eciency with little maintenance requirements. Robust on shock loadings (B orner, 1992; Vyzamal, 1995; Nuttall et al., 1997). 3(b) LM: Very good removal eciency, however requires external energy source for operation in UK.

Fig. 11. Removal eciency of domestic treatment methods: BOD5 . (Values show range and average found in the literature.)

3(c) AC: Can be very ecient in removing pollutants with the additional incentive of income. (Ghosh, 1997; Olah & Pekar, 1997; Tchobanoglous, 1997; Guterstam, 1997; Govindan, 1996). 3(d) SF: Usually used for e‚uent polishing. Good performance of pressurised ®lters (Gray, 1989; White, 1987; Escritt, 1984). 4.2.2. BOD The following remarks refer to the data presented in Fig. 11: 1(a) AS: Can achieve very high removal eciency if properly designed. (Metcalf & Eddy, 1991; Grant et al., 1996; Gray, 1989; White, 1987; Escritt, 1984). (b) TF: Removal of BOD in TF depends strongly on the BOD loading. In heavily loaded TF, the removal eciency can be as low as 45% (Metcalf & Eddy, 1991; Grant et al., 1996; Gray, 1989; White, 1987; Escritt, 1984) 1(c) RBC: RBC perform within a relatively small ¯ow range. They are designed for highly predictable sewage ¯ow from small settlements (Metcalf & Eddy, 1991; Gray, 1989). 1(d) OP: Can have excellent performance, depends on detention time in the pond (Metcalf & Eddy, 1991; Gray, 1989; White, 1987; Escritt, 1984). 2(a) NB: Worst performance, however normally used in conjunction with leach®elds or soakaways. (Metcalf & Eddy, 1991; Grant et al., 1996; Gray, 1989; White, 1987; Escritt, 1984; VSA, 1995).

R. Burkhard et al. / Urban Water 2 (2000) 197±221

2(a) NB: Worst performance, however normally used in conjunction with leach®elds or soakaways. (Metcalf & Eddy, 1991; Grant et al., 1996; Gray, 1989; White, 1987; Escritt, 1984; VSA, 1995). 2(b) PB: Little information. Can be very e€ective though. Maintenance required (VSA, 1995; Salvato, 1982). 2(c) LF: When used in the right place, they virtually remove all BOD as the e‚uent ®lters through soil with high microbial activity (Grant et al., 1996). 3(a) CW: Good removal eciency if properly designed. They can fail with improper loading. Robust (B orner, 1992; Vyzamal, 1995; Nuttall et al., 1997). 3(b) LM: Very good removal eciency achieved by gearing the plant to very speci®c purposes. Requires a lot of oxygen. 3(c) AC: Very good removal eciency with the additional bene®ts of crops. Very sustainable technique, but labour intensive (Ghosh, 1997; Ol ah & Pek ar, 1997; Tchobanoglous, 1997; Guterstam, 1997; Govindan, 1995). 3(d) SF: Variable performance, di€erences due to di€erent types of SF (Gray, 1989; White, 1987; Escritt, 1984; Heeb & Z ust, 1997). Good performance even in very cold climates (Thompson & Reese, 1985). Removal eciencies depend strongly on the design of the di€erent treatment techniques. For small settlements, ecological techniques present a valuable alternative to traditional treatment techniques, which are often costly and require a considerable amount of supervision by highly quali®ed sta€. 4.2.3. Land use Fig. 12 shows the land requirement for di€erent techniques that are suitable for small-scale wastewater treatment (VSA, 1995; Nuttall et al., 1997), given as square meter per person equivalent (m2 PEÿ1 ). All systems need preliminary treatment. Leach®elds appear to consume most land, however as they are underground structures, they cannot be seen. Their size depends largely on the subsoil conditions through which the preliminary treated wastewater percolates. The following remarks refer to the data in Fig. 12: 1(d) OP-no O2: Non-aerated sewage pond with aerobic treatment process where oxygen enters via water surface into water body. 2±3 ponds in series. 1(d) OP-O2: Aerated sewage pond where oxygen input is supplied. Various methods exist for aeration. 2±3 ponds in series. 2(c) LF min Leach®eld minimum area, depending on soil conditions. 2(c) LF max Leach®eld maximum area, as above. 3(a) CW VF min Constructed wetlands vertical ¯ow, minimum depends on strength of sewage. 3(a) CW VF max as above.

209

Fig. 12. Land requirement for selected techniques (small treatment plants). (Data:  VSA, 1995;  Nuttall et al., 1997.)

3(a) CW HF min Constructed wetlands horizontal ¯ow minimum area. 3(a) CW HF max as above. 3(d) SF cov: Covered sand®lter with carefully selected ®ltermedia of diameter 0.5±1.2 mm. For nitri®cation lime-containing media used. 3(d) SF open: Open sand®lters, same as above, wastewater must be applied evenly over the surface. 4.3. Economic aspects Table 14 provides a qualitative economic comparison of the di€erent domestic wastewater management techniques. These ratings are purely illustrative. Further research needs to be carried out in order to undertake an objective comparison, such as life cycle costing analyses. For example, 80% of costs in conventional systems is attributed to transportation of sewage (Jenssen, 1996). This fact has also to be considered when conventional treatment systems are assessed. An example of quantitative evaluation of economic aspects was made between conventional treatment systems and wetland systems using the literature data. North of Scotland Water Authority's (NOSWA, 1999b) data on conventional treatment were obtained for the wastewater treatment works (RBCs) in Culbokie, Black Isle, at a cost of £725,000 for a population of 1000 or £725 per head. Another conventional scheme by NOSWA for the towns of Inverness and Fort William, serving a population of 61,000 will cost £45 million or £740 per head. Capital costs per head (£PEÿ1 ) of a few wetland systems installed in the UK (Nuttall et al., 1997) are presented in Fig. 13. The high costs of the Oakland Park wetland are due to the high standard to which the ef¯uent had to be treated (i.e. nitri®cation) but are still

210

R. Burkhard et al. / Urban Water 2 (2000) 197±221

Table 14 Economic aspects of domestic wastewater management Technique

Capital cost

Operation & Maintenance costs

Environmental bene®t

Remarks

1(a) AS 1(b) PF 1(c) RBC 1(d) OP no O2 1(d) OP O2 2(a) NB

Mediuma ±higha Mediuma ±higha Mediuma ±higha Mediuma Mediuma ±higha Low±medium

Higha Higha Higha Very lowa Mediuma Low±high

Negative Negative Negative Zero Zero±negative Negative

2(b) PB 2(c) LF 3(a) CW

High Low Lowa

Medium Low Mediuma

Zero Zero Positive

3(b) LM 3(c) AQ 3(d) SF

High High Medium

High High Medium

Positive Positive Zero±negative

*** *** *** Costs depend on land requirements High electricity costs for oxygenation* Cesspools expensive due to high maintenance costs. Septic- and settlement tanks provide cheap pre-treatment options *** Very cheap, when combined with 2(a) NB Cost depends largely on the size of settlement served *** Revenue possible Usually vertical ®lter

a

ATV (1997a).

Fig. 13. Cost of several wetland treatment systems installed in the UK (Nuttall et al., 1997).

within the range of the two aforementioned conventional Scottish treatment works. The other wetlands have considerably lower capital costs. The Wetwang wetland is for secondary e‚uent polishing and hence not directly comparable, but it gives an idea of the PE costs for tertiary treatment wetlands. Information on capital costs from several consultants for some ecological treatment systems is provided in Table 15. All Water Utilities were very secretive and

reluctant to release any data at all and in most cases did not even respond. Operation and maintenance costs are as important as the capital costs. Figures from the US (Nuttall et al., 1997) suggest that £400±£600 per ha annually is a reasonable estimation for surface ¯ow wetlands. Smerdon et al. (1997) expect running costs to amount to approximately £50 per year and the savings to be around £170. The costs of maintaining vegetated beds are no more than for landscape maintenance per unit area. Severn Trent Water has compared the operation of a small RBC works combined with tertiary wetland treatment and a conventional biological ®ltration works. The former required 68 min and the latter 4±6 h maintenance e€ort per week. Non-technically trained personnel can carry out wetland maintenance whereas conventional treatment works required technically trained sta€. The layout of a wetland can demand additional costs for electricity, which is needed for pumping, raking and sometimes aeration. Harvesting can add to the costs (Nuttall et al., 1997). There are diculties in undertaking comparative studies because water companies do not break down speci®c and isolated costs at treatment sites for di€erent treatment methods. An indepth comparison was conducted by Fife Regional Council for the Valley®eld reed bed treatment system.

Table 15 Capital costs of ecological wastewater techniques Consultants

Reed beds …£PEÿ1 †

Oxidation ponds …£†

Other …£PEÿ1 †

Iris water Cress water Elemental solutions Reed Bed Technologies Smerdon, Wagget, and Grey (1997)

The larger the cheaper 900 (1±5 PE); 375 (40 pe); 215 (140 PE) 500 (>12 PE) 200±300 (after primary treatment) 2400 (£ per house)

40±60 (mÿ2 ) (for 20±50 PE) 400±600 (PEÿ1 ) n/a n/a n/a

n/a n/a 400 (sand ®lters) n/a n/a

R. Burkhard et al. / Urban Water 2 (2000) 197±221

For this system, whole life costs were compared with a conventional treatment plant and the wetland was found to be the more economic option. Package sewage treatment systems were analysed by Smerdon et al. (1997). For a cluster of houses (<50 houses), the capital cost per house amounts to £2000± £5000 and the running costs approximately £30, with a saving of £170 per year because there are no extra sewerage costs for conventional systems. For a village (<500), the capital costs would reduce to £1500±£5000, the running costs would amount to £25 and the savings to £170. Economic data on aquaculture are dicult to obtain. The only system that is working on a large scale in Europe is the one used as tertiary stage in Munich. Most economically bene®cial aquacultures are in Asia and India in particular (Ghosh, 1997; Ol ah & Pek ar, 1997). One small system is implemented in Stensund (Guterstam, 1997), Sweden and another small system where secondary treatment e‚uent is used for commercial aquaculture is Oakland Park in the UK. 4.4. Social aspects The relative importance of the various social±environmental criteria for di€erent domestic wastewater systems is presented below:  Social acceptance. People are usually unaware of conventional domestic wastewater treatment systems, and will probably have little opinion, and therefore be fairly accepting. Further research is needed to ascertain the public awareness and acceptability of the more ecological systems (CW, LM, and AC). Most likely, acceptance will be in¯uenced primarily by institutional factors, as these are still `end of pipe' systems (Shields, 1999). Individuals often still adopt an `out of sight, out of mind' attitude.  Amenity value. Only the ecological treatment systems (CW, LM, OP and AC) have the potential for amenity enhancement. However, this is only the case if careful planning is carried out.  Community participation. This will depend largely on the extent to which public participation is used generally in a given locality ± this is important for social sustainability (see e.g. Uzzell, 1982). An important related point here is the cost of such measures. People do not tend to be motivated to participate in matters that will have no direct impact on their everyday lives, but if for example, a small-scale ecological wastewater treatment works required a change in behavioural patterns, people might well be more vocal.  Awareness. Unless they live fairly close by, people do not tend to be very aware of conventional domestic wastewater treatment systems, and will probably have little opinion. The more ecological systems however, have the potential to make the issue of wastewater

211

management more salient. Craig (1999) found that people who lived in a village next to a constructed wetland were more likely to know where their sewage was treated than people in a peri-urban settlement served by a conventional treatment works.  Institutional requirements. For all systems, this will depend largely on the local situation, and will be speci®c to the legislative, political and social climate of the area in question.  Local development. For all systems, this will probably depend on who is responsible for installation (and maintenance). More research is needed in this area, but ecological systems will usually have more potential to be managed locally.  Stimulation of sustainable behaviour . The educational potential of sustainable wastewater systems is large. There are many opportunities for visiting both conventional and non-conventional wastewater treatment plants (NOSWA, 1999b), which could be extremely useful in making the issues surrounding wastewater treatment more salient. However, it must be stressed that in order to be e€ective, educational approaches should place the issue at hand in its broader social context (Uzzell, 1994).

5. Water and waste re-use Water and waste re-use techniques come closest to what was earlier described as natural sustainability. These techniques enhance the local water cycle and reapply nutrients from domestic wastewater to the local environment. If we consider water usage in the average household in the UK as shown in Fig. 14, we see that some 67% of

Fig. 14. Water usage in household (from Griggs, Shouler, & Hall, 1997; Mustow, Grey, Smerdon, Pinney, & Waggett, 1997).

212

R. Burkhard et al. / Urban Water 2 (2000) 197±221

all water used is theoretically not contaminated by human faeces, although small amounts of faeces can occur in baby bathing water. This water leaves the average household as the so-called greywater and can potentially be re-used for purposes where drinking water quality is not required, such as toilet ¯ushing. Similarly, a considerable amount of lightly polluted water from impervious areas, namely roofs can be harvested and used for various purposes, including washing and watering the garden. Waste re-use may also include recycling of the organic matter at the very beginning of the water cycle before it even has the chance to get into contact with water. 5.1. Techniques 1. Greywater is normally collected from hand washbasins, bathtubs, washing machines and dishwashers. Several ®ltering methods are available to treat the greywater before it is collected in a storage facility. This facility could be located in the cellar or outside the house. From there, water is pumped into a loft storage facility and then distributed by gravity. Greywater contains less organic matter and pathogens (Jenssen & Etnier, 1997) than wastewater containing a mixture of sink and toilet waste residue. Thus, greywater can be re-used for domestic purposes if treated accordingly: for toilet ¯ushing, for washing machines in the domestic environment, and irrigation (both on the surface and underground). Greywater re-use systems (Fig. 15) are being investigated (Dixon, Butler, & Fewkes, 1999; Jenssen & Etnier, 1997; Sayers, 1998a; Nolde, 1995) and, in several countries, there are also systems in the market which allow houses to be retro®tted with greywater recycling systems (Sims, 1998). The technology used varies among di€erent countries. Greywater is usually treated to higher levels and applied to larger housing estates in Germany than in the UK (Nolde, 1996; Kennedy, 1997; Sims, 1998; Dixon et al., 1999; Sayers, 1998a). Some features of greywater systems include (from Mustow et al., 1997):

Fig. 15. Greywater System (adapted from Nolde, 1995).

· Bypass of greywater system to restore original supply, backup supply for greywater tank. · One- or two-stage treatment of greywater and safety mechanism to ensure storage 6 2 days. · Air gap between backup system and maximum over¯ow water level of greywater tank. · Labelling of cisterns and taps where greywater is applied. 2. Rainwater harvesting (Fig. 16) has been practised over thousands of years. Most water harvesting takes place in arid climates where surface water is scarce and groundwater is dicult to abstract (Pacey & Cullis, 1986). Growth in freshwater demand in all regions (usually due to our lifestyle) could sometimes be met by rainwater re-use. Rainwater harvesting is certainly a viable option when it comes to watering gardens and the techniques can range from simple to sophisticated technical solutions. For example, rainwater harvesting is used in an autonomous housing project in Nottingham, where some of it is treated to potable standard (Mustow et al., 1997). Brechb uhl (1998) sees the main uses of rainwater being for domestic purposes in ¯ushing toilets, watering gardens and washing. Design recommendations for the storage facilities are listed in Table 16 (Mustow et al., 1997; Brechb uhl, 1998; Referat f ur Gesundheit und Umwelt, 1998). Storage size considerations are given by Referat f ur Gesundheit und Umwelt (1998). They base the estimation of the harvesting tank on the average water yield per year and the water consumption of the household. The relation between water yield and consumption indirectly results in a factor, which is then multiplied with the total average water yield per year. The result is the volume of the storage facility. Smerdon et al. (1997) base their storage considerations on available rainfall, runo€ area and anticipated days of drought. 3. Solid waste re-use concerns both organic and human body wastes. The re-use of human body wastes was practised in Europe well into the last century when the waste was thrown out into the backstreets and then collected on carts and recycled on ®elds. Solid waste reuse systems include compost toilets where the waste is collected in large composting facilities (Kennedy, 1997; Otterpohl et al., 1996). Small systems where the waste is

Fig. 16. Rainwater harvesting (after AGW, 1991).

R. Burkhard et al. / Urban Water 2 (2000) 197±221

213

Table 16 Design considerations of rainwater harvesting facilities Location

Material

Layout

Separation

Size

Filters

Dark, cool, secure from frost, easily accessible for cleansing

Plastic tanks for best easiest cleansing. Concrete with paintcoat to prevent algae growth in pores

Drain at lowest point to allow easy cleansing, U-shaped pump suction pipe to avoid pumping sediments

Two tanks or more allow cleansing without interrupting rainwater use (large systems)

Dependent on usage, content to be replaced 10±30 times per year

500 lm into tank, sucient for domestic use; 100 lm to pump

collected in bin liners and enhanced with carbon-rich material also exist (Rohrer & Geiger, 1998; einblick, 1995, 1999). Solid human wastes can be anaerobically digested with other organic household wastes (Otterpohl et al., 1996). The end products are nutrient-rich water, compost earth and methane which can be used for gasfuelled lorries, cars and decentralised heating systems. Rohrer (1998a) has shown that agricultural applications can also bring bene®ts without compromising risk. The handling of the waste can be problematic as it contains a considerable amount of faecal coliforms. A certain degree of education is hence necessary to apply this kind of waste management. Farmers could be part of this solution as they are often used to handling excreta and are potential users of the nutrient-rich compost, even as a substitute for commercially available fertiliser. Huber (1999) suggests that the collection and distribution of this kind of fertiliser from small settlements does not cause problems for farmers. He nevertheless predicts problems with the even application of the fertiliser to the land. Compost facilities that are easy to handle are available in the market. Some of them depend on ventilation via electric fans. The stirring mechanism of the compost, which is contained in a drum within the toilet, is driven by an electric motor. Larger facilities with external drums or compost facilities in cellars are also available. (Peuser GmbH, 1999; Sun-Mar, 1998). Jenssen and Skjelhaugenen (1994) describe a composting facility for tenement buildings in Norway that not only composts the faeces of the residents, but also other organic kitchen waste. Design of composting toilets depends on the use of the facility. A variety of versions for weekend as well as residential use are available in the market. The compost toilets for continuous use have larger storage facilities, which are often situated in the cellar. 4. Liquid waste re-use is about collecting and using urine separately. When faeces are composted, the humidity level has to be relatively low if constant ventilation and dehydration of the compost heap is to be avoided. Hence the need to separate urine at the location of origin. According to Rohrer (1998b), urine adds approximately 88% of Nitrate and 57% of Phosphate to the domestic wastewater. Jenssen (1996) quotes slightly lower ®gures (81% Nitrate and 48% Phosphate). Both

are important fertilisers, which are produced (nitrate) and mined (phosphate) using large amounts of fossil fuels. Seen in this light, separate collection and storage of urine for the use as a fertiliser may become an option for new housing developments. Urine separation can be achieved by using urinals, which are restricted to male use only, or by a small, inserted bowl in the main bowl of the toilet, which collects the urine from both men and women. Jarl ov (1996) reports on a trial in Falun where a urine separation system was retro®tted during renovation works on a large housing estate. Storage can cause loss of nitrogen and hence loss of fertiliser according to Hellstr om and Karrmann (1996), but if the basic conditions of cool storage and low pH are ful®lled, storage is unproblematic. Gujer (1996) presents an alternative to storage. He suggests collecting the urine in tanks during the day and releasing it at night, when the ¯ow in sewer systems is at its lowest. It can then be captured at the sewage treatment works, treated separately from other sewage and recycled. Adamsson and Dave (1996) investigated the toxicity that ammonium from human urine may pose to Daphnia Magna, a plant used in the food chain of aquaculture. Rohrer (1998b) designed guidelines for using urine as a fertiliser. Few examples can be found in the UK where the separation of urine is practised. It may be practised to a certain extent by gardeners who are aware that urine is a valuable fertiliser. 5.2. Water quality and health issues in re-use techniques Given the clear bene®ts and long-standing practice of water harvesting and waste re-use, issues of water quality do need to be considered, although the hazard is generally lower than that many people expect. Problems can occur where water is stored for a long time in warm conditions. Bacteriological laboratory tests have shown that stored rainwater does not meet the EU drinking water standards, but the quality of bathing water can be matched (implying no health hazard for a person if he/ she swallows small quantities). Consideration must be given as to which surface rainwater is harvested from. Metal roofs can lead to a signi®cant increase of heavy metals in the water and should be avoided (AGW, 1996). People who build their own systems are generally

214

R. Burkhard et al. / Urban Water 2 (2000) 197±221

less concerned about these issues (Burkhard, 1999). Where people have little or no knowledge of these systems, there is concern that they might carry some kind of health hazards (Craig, 1999; Naisby, 1997). However, laboratory tests have shown that the total bacterial count in 20 l of rainwater is no higher than the one in a cream pastry displayed in a bakery for a day (Brechb uhl, 1999). If storage, ®ltering, appropriate use and labelling are undertaken sensibly, these systems pose little risk. For the UK, there are no quality guidelines. Dixon et al. (1999) and Mustow et al. (1997) state however, that application-speci®c water quality standards should be appropriate. As a guideline, EU bathing water standards as shown in Table 17 could be applied where water is of such a standard that small indigestion does not cause a health hazard. Trials into greywater quality conducted by Naisby (1997) and data from Rasmussen, Jenssen, and Weatlie (1996) con®rm that greywater can be treated to EU bathing water standards. Rainwater can be treated to drinking water standard. This is done in countries that depend on rainwater as a drinking water source (Alghariani, 1998; Pacey & Cullis, 1986) and also in the UK (Mustow et al., 1997; Naisby, 1997). Using harvested rainwater for washing purposes has the additional bene®t of reducing washing powder consumption, as the rainwater is often softer than drinking water from the tap. Greywater quality varies greatly, according to Rasmussen et al. (1996). Gerba et al. (1995) suggest that this may be in¯uenced by habit and lifestyle of the residents producing the greywater. It contains considerably less plant nutrients than blackwater and can be treated to a high standard using septic tanks, preliminary ®lters and sand- and soil-based ®lters as main treatment. These methods eliminate most hazardous elements in greywater (Nolde, 1995, 1996; Gl ucklich, 1996; Rasmussen et al., 1996). Membrane treatment systems are also considered (Demboski, Benson, Rossi, Leavitt, & Mull, 1997). Anderson, Siegrist, and Boyle (1981) found that

greywater may be routinely contaminated with faecal material, which would require the treatment system prior to re-use to address this fact. Gerba et al. (1995) investigated ®ve di€erent treatment methods, which all led to acceptable quality of greywater for re-use in terms of faecal coliforms, total coliforms, pH, nitrate, suspended solids and turbidity. Olivieri and Cooper (1982) designed a health risk table based on interviews with health experts, which listed the health risk of using compost from toilets and greywater for di€erent applications (e.g. fertiliser for food crops, irrigation, etc.) against geographic conditions (e.g. climate, groundwater). Enferadi (1982) reports that mesophilic stabilisation and one year's time of composting of faeces would eliminate most pathogens, which is also con®rmed by research carried out at the Ecocentre Schattweid (einblick, 1995). Strauss (1991) discusses the health protection issues with regard to reusing wastewater for di€erent applications (e.g. irrigation, aquaculture) and describes a model, which assesses the health risk of the end-user of a product where reused wastewater was applied. 5.3. Eciency 5.3.1. Greywater and rainwater harvesting The success and eciency of greywater and rainwater harvesting can be measured in volumetric (litres of water saved) and monetary terms. Studies were conducted by Naisby (1997), Mustow et al. (1997) and Nolde (1995, 1996) into the eciency of these systems. The savings in the use of drinking water depend largely on the size of the storage tank and the intended purpose of the water. Theoretically, rain or grey water can replace all drinking water for toilet ¯ushing. This can constitute up to 34% of the total water consumption. Sims (1998) reports a drinking water reduction of 39% while trials with members of the EA show a reduction of 5.2±30.6% (Sayers, 1998a). Sayers suggests that giving an average

Table 17 Water quality for di€erent uses Parameter

Concentration bathing watera

Concentration drinking waterb

Concentration rainwaterc

Concentration greywaterd

Total coliforms Faecal coliforms Salmonella Entero viruses

10,000 (100 mlÿ1 ) 2000 (100 mlÿ1 ) Absent in 1 l No plaque forming units in 10 l 6±9

0 0 n/a n/a

3340±250,000 (mlÿ1 ) 0!500 (100 mlÿ1 ) n/a 1±300 (100 mlÿ1 )

103 ±107 (100 mlÿ1 ) 103 ±105 (100 mlÿ1 † 0 (chlorination) 0 (chlorination)

5.5±9

6.6±7.85

3.8±5.7 0±0:02 …mg lÿ1 † 0:02±0:16 …mg lÿ1 †

PH Ammonia Reactive phosphorus a

EU bathing water standard. UK drinking water quality. c Laboratory test results CH. d Naisby (1997). b

R. Burkhard et al. / Urban Water 2 (2000) 197±221

value is not very reliable because the range of savings is quite large. Karpiscak, Brittain, Gerba, and Foster (1991) describe a desert house in the US where water conserving ®xtures, greywater recycling and water harvesting can reduce potable drinking water use by up to 50% without major expense or change in lifestyle. 31% of the total water budget is recycled as greywater and represents the largest source of water savings (Karpiscak, Foster, & Schmidt, 1990). Smerdon et al. (1997) estimate that some 30% of water usage can be saved if a greywater system was installed. They also consider the application of greywater systems to single units as less complicated than several dwellings. The evidence shows that use of rainwater does not deteriorate our lifestyle in an unacceptable way and can lead to considerable potable water savings for households. Current research in the UK (Dixon et al., 1999) on the use of rainwater for toilet ¯ushing suggests considerable water savings due to rainfall harvesting only. 5.3.2. Solid and liquid waste re-use Regarding waste reduction, solid and liquid waste recycling is the only method that reduces nutrient and BOD loading to wastewater treatment works signi®cantly. Keeping human waste away from treatment works has the same removal eciency as a treatment work that removes 60% of TOC, 99% of total Nitrate and 72% of total Phosphate. Fig. 17 shows a comparison between a three-stage treatment works (WWTP) and separation of human waste (einblick, 1999). The e‚uent that leaves a household with human waste separation is greywater, which has a signi®cantly lower nutrient content than normal blackwater. 5.4. Economic aspects As can be seen from Table 18, all water and waste reuse techniques are environmentally bene®cial, and can

Fig. 17. Removal eciency and e‚uent quality of WWTP and separation techniques.

215

be economically viable, provided appropriate consumer tari€ structures are in place, and that they are designed with reasonable payback periods in mind. 5.4.1. Rainwater According to Mustow et al. (1997), rainwater harvesting systems can cost anything between £20 for a water butt and £2000±£3000 (retro®t ¯ats) for customised systems. Smerdon et al. (1997) estimate savings of £20±£50 per person and year. Mustow et al. (1997) calculate with a payback period between 6 and 210 years when rainwater is used for external purposes only and 29±31 years when rainwater is used for external and internal purposes. For ¯ats, Mustow et al. estimate a payback period of 23±34 years when rainwater is used for external and internal purposes. An example from Switzerland (Brechb uhl, 1995, 1998) estimates a payback period of 50 years (external and internal use: garden watering, toilet ¯ushing, washing machine). Payback periods depend on the following parameters: · Amount of water saved. · Water price (water metering). · Standard of solution, plumbing. · Number of uses, number of users per system. · New or retro®t system. 5.4.2. Greywater Large systems that serve several households and where installation cost can be saved are more cost effective than small systems that are installed in just one household. According to Smerdon et al. (1997) the costs of a retro®tted greywater system costs up to £1000 or around £750 if installed during construction. The British systems from Aquasaver (Sims, 1998) and Water Dynamics (1998) are three times more expensive per household than the German system used in Berlin (Nolde, 1995), although dwelling type may account for this variation. The system in Berlin has the additional advantage of treating the greywater to a higher hygiene standard, which makes it less hazardous to health. Assuming that 33% of drinking water usage per year can be saved, a reduction in the water bill of £25 in Britain and £43 in Germany (1998 prices) can be achieved. Smerdon et al. (1997) estimate a reduction in the water bill up to £75. The payback period for systems serving several people is better, but due to the housing structure is more dicult to implement in Britain. The payback period for the German system is 8 years and for the British system 10±46 years. Hence it may be viable to investigate ways of how to share greywater re-use systems in Britain. Greywater systems in the UK are not economic due to the low water prices (Naisby, 1997; Sayers, 1998b). Mustow et al. (1997) estimate a payback period for greywater and rainwater re-use system for internal and external use for houses of 35±49 and 48±890 years for external use only. For ¯ats, the payback period for in-

216

R. Burkhard et al. / Urban Water 2 (2000) 197±221

Table 18 Economic aspects of water and waste re-use Technique

Capital cost

Operation and maintenance costs

Environmental nene®t

Remarks

Greywater

Medium±high

Low±medium

Positive

Rainwater harvesting

Low±high

Low±medium

Positive

Solid re-use Liquid re-use

Low±medium Medium

Low±medium Low±medium

Positive Positive

Savings occur when water is metered Savings occur when water is metered Revenue possible Revenue possible

ternal use is 28±33 years. However, the EA would like to see an increase in water prices to ease the pressure on the environment (Sayers, 1998b). Butler and Dixon (1997) suggest that greywater re-use (combined with rainwater) can signi®cantly contribute to water and cost savings. This scenario would be particularly applicable for areas where drinking quality water supply for all domestic use is metered. Greywater systems can be viable, as the German example has shown. 5.4.3. Human waste recycling Table 19 provides the price range of some compost toilet systems. Systems where user involvement is larger are cheaper, whereas the more luxurious ones are equipped with fans and electric motors, which inevitably push prices up. A study into recycling human waste by Rohrer and Geiger (1998) has shown that in the waste of the decentralised areas in Switzerland, there are SFr 0.2 million (approximately £88000) worth of nitrate and SFr 0.2 million worth of phosphate for agricultural use contained in approximately 2.4 million m3 wastewater per annum. According to Jenssen and Skjelhaugenen (1994) a reduction of 15±20% of arti®cial fertiliser imports for Norway's farmers can be achieved, if all human faeces of the whole Norwegian population are recycled into agriculture. A cost analysis between a sophisticated compost toilet produced by Peuser costs approximately £300, and a standard toilet sold by a local bathroom retailer that costs £120±£200. If the compost toilet is used, the savings in wastewater costs are around £80 per year (Band C wastewater charge of North of Scotland Water Au-

thority, NOSWA, 1999a). This means that in three years time, the ®rst one becomes ®nancially more sustainable. 5.5. Social aspects As can be seen from the list below, greywater and rainwater systems are more socially acceptable to the end-user than solid waste and liquid waste re-use systems. However, it should be stressed that ratings of acceptability, awareness, and other factors are highly subjective, and vary greatly depending on the commentators (see, for example, Griggs et al., 1997).  Social acceptance. Naisby (1997) found that the public was generally accepting the idea of greywater and rainwater recycling, although such studies need replication. Results of a recent survey (Craig, 1999) also showed a general acceptance towards such systems, although people have concerns about using greywater in their gardens. Economic factors seem to have an in¯uence in both cases (Naisby, 1997; Craig, 1999). There is a scarcity of work in the area of solid and liquid waste reuse, but acceptability is arguably one of the biggest barriers to the implementation of such ecological systems (Shields, 1999; see also Fittschen & Niemczynowicz, 1997). Results of a recent survey (Craig, 1999) suggest a general interest in such new systems, but many concerns about odour, hygiene, and cleaning. Religious and cultural beliefs will also have an impact on acceptability (Warner, 1999).  Amenity value. Not applicable on a household scale.  Community participation. Examples of water and waste re-use systems in the UK tend to be small scale, with end-users usually consciously opting to install such

Table 19 Economic aspects of compost toilets Type

Use

No. of users

Price …£†

Composting

Source

Kompakt Humus-2000 Humus-exclusiv Self contained Self contained, mobile Central composting system

Weekend Residential Residential Residential Weekend Residential

2±4 2±4 2±4 1±5 1±2 3±6

120 300 420 820±998 874±902 800±1195

External compost External compost External compost Drum in toilet Drum in toilet Container in cellar

Peuser GmbH (1999) Peuser GmbH (1999) Peuser GmbH (1999) Sun-Mar (1998) Sun-Mar (1998) Sun-Mar (1998)

R. Burkhard et al. / Urban Water 2 (2000) 197±221

systems. Research needs to ascertain whether or not the general public would accept an extensive retro®t programme of such systems (see, for example, Jarl ov, 1996; Fittschen & Niemczynowicz, 1997). All too often, only an interested minority of the public ever get involved in any form of water planning (Syme & Nancarrow, 1992), so extensive public education programmes would be required.  Awareness. By their very nature, all water and waste re-use systems require more awareness than conventional systems, as they tend to require some change in behaviour. Greywater and rainwater harvesting can be a fairly passive intervention, whereas solid waste and liquid waste re-use would require something of a re-evaluation of cultural norms, and hence an increase in awareness.  Institutional requirements. This depends largely on the scale of the system, although the environmental health department would most likely be involved in all cases.  Local development. Local plumbers may bene®t from work involved in retro®tting greywater systems, etc. Farmers and gardeners could bene®t from a local supply of cheaper fertiliser from urine separation toilets, although a lack of knowledge about urine probably plays a role in the acceptance of this idea.  Stimulation of sustainable behavior. There is a large potential for environmental education, as the user is directly involved at source, and is thus empowered to some degree. Again though, the issue must be placed in its broader social context if it is to act as a form of educational catalyst (Uzzell, 1994). 6. Discussion and conclusions 6.1. Techniques With respect to planning for water and wastewater management, there is a wealth of techniques available and yet most of them are hardly known by the mainstream engineer. In civil engineering undergraduate courses in higher education, ecological treatment systems are not included in water modules and students study conventional techniques. Only in specialised courses, do students have a chance to learn about new techniques. This fact makes the application of ecologically sound solutions more dicult. Similar observations can be made for other people who in¯uence water and wastewater management, namely planners and site developers. Their attention is slowly drawn to these issues, but there is still a long way to go until there is greater awareness of water problems. That said, the UK Royal Academy of Engineering has recently decided to place ``sustainable design'' at the heart of its courses, to address social and environmental problems (THES,

217

1999). Similarly, a course was introduced almost three decades ago by the University of Connecticut's Civil Engineering Department (Laak, 1982) taking the above aspects into consideration. 6.2. Eciency Most ecological techniques match the performance of the well-established techniques. In some cases, they require more land, which can become a ®nancial issue. Looking at the eciency factor from a natural sustainability angle, the ecological techniques tend to fare better because they are designed to use less embodied energy in both building and running processes. Often, ecological techniques enhance the environment, create new habitats, replenish groundwater and can have a social function. Hence the eciency aspect could easily be expanded into these ®elds and may have to be considered. 6.3. Economic aspects Further investigations into cost and life cycle analysis regarding wastewater management options are necessary. This is the case for conventional treatment systems where costs are not entirely broken down. This is also the case for novel techniques where costs are often dif®cult to obtain. The construction costs may change considerably over the next few years as the implications of the greenhouse e€ects may start to be felt. This may result in rising prices for construction and transportation, in case carbondioxide taxes on fossil fuels are levied in future. Hence construction of wastewater treatment works, which consume a large amount of embodied energy, may turn out to be more costly than at present and this may tip the balance to less energy intensive ways of treating wastewater or even reducing domestic wastewater. Some techniques may even generate revenue and jobs. Looking at the economic issue from this angle, ecological techniques may be seen in a better light, especially when there is the chance to partially or wholly substitute non-renewable energy and fertilisers. Jobs may be generated in building and maintenance of these techniques (with money saved from investing in conventional techniques), in further development of techniques, and in the marketing of eventual by-products. 6.4. Social aspects Most conventional techniques have little or no in¯uence on the behaviour of users. For each of the areas discussed in this paper (rainwater management, domestic wastewater, and water-and-waste re-use), the more ecological techniques have a greater in¯uence on the end-user. While it is clear that ecological rainwater

218

R. Burkhard et al. / Urban Water 2 (2000) 197±221

management techniques are less likely to have an impact than for example compost toilets (apart from the earlier mentioned safety fears), the relationship between awareness and acceptance is not clear. Social acceptance and social sustainability are two areas in which further research is needed to ascertain the relative importance of the di€erent criteria for the various techniques. The theory of participatory democracy holds that ``individuals and their institutions cannot be considered in isolation from one another'' (Pateman, 1970). Thus, a diverse range of opinions should be accommodated and considered within any planning decision. These opinions should include those which advocate the use of innovative ecological techniques, and also the multitude of views held in the public sphere. Moreover, public opinion should not only be sought out, but an attempt at understanding it should also be made, rather than simply dismissing it as `irrational public opinion', as is so often the case. There is also a clear need to develop e€ective educational strategies to develop environmental awareness and action competence (having the understanding and the tools necessary for environmentally friendly behaviour) at all levels, be it at home, in a primary school, in higher education, in planning departments, or developers oces. Such attempts are actively made in Los Angeles, where demonstration gardens were set up to show residents that it is possible to have a nice garden without using excess water (Harasick, 1990). 6.5. Planning Alongside this need for greater public participation, consideration should also be given to the planning system as a whole if `holistic planning' is to be achieved. Thus, land use planning and control legislation which are sensitive to the requirements of such pollution prevention techniques such as those discussed herein will go a long way towards achieving sustainability, howsoever it is de®ned. Planning of integrated water and waste management requires thoughtful consideration, because of the complexity of the process. Asano (1991) listed elements of water re-use planning. However, to integrate all the above issues, a new planning approach has to be developed in the form of participatory integrated assessment, as suggested by Schlumpf, Behringer, D urrenberger, and Pahl-Wostl (1999). Smerdon et al. (1997) show ways to plan and implement decentralised water supplies and sewage. They assess the application of ecological techniques to single units as well as clusters of houses, villages and towns and recommend the most appropriate technique for each size. To integrate all the above techniques and aspects, it is important to develop a tool that is capable of incorporating all aspects of water and wastewater management.

Acknowledgements We would like to thank Mr Graeme Slaver of Robert Gordon University who found the necessary ®nancial resources to fund this research.

References Adamsson, M., & Dave, G. (1996). Toxicity of human urine, its main nitrogen excretory and degradation products to Daphnia Magna. In C. Etnier, J. Staudenmann, & A. Sch onborn (Eds.), Environmental research forum (Vols. 5±6). Switzerland: Transtec Publications. AfU, Amt f ur Umweltschutz Luzern (1994). Versickerung und Retention im Liegenschaftsbereich. Kantonales Amt f ur Umweltschutz Luzern. AGW, Amt f ur Gew asserschutz und Wasserbau (1991). Retention und versickerung von meteorwasser im liegenschaftsbereich. Baudirektion des Kantons, Z urich. AGW, Amt f ur Gew asserschutz und Wasserbau (1996). Today Amt f ur Wasser, Energie und Luft des Kantons Z urich (AWEL). Die Versickerung von Regenabwasser auf der Liegenschaft. Baudirektion des Kantons, Z urich. Alghariani, S. A. (1998). Rainwater collection and utilisation as a  Maksimovic potential resource for urban areas. In D. Butler, & C. (Eds.), Proceedings of the fourth international conference on development in urban drainage modelling, UDM'98, London. Anderson, D. L., Siegrist, R. L., & Boyle, W. C. (1981). Performance evaluation of greywater recycle systems. In Proceedings of the water re-use symposium 2: water re-use in the future. Denver. Asano, T. (1991). Planning and implementation of water re-use projects. In R. Mujeriego, & T. Asano (Eds.), Water Science and Technology, 24(9), 1±10. ATV (Abwassertechnische Vereinigung, e.V.) (1997a). Arbeitsblatt ATV ± A 200: Grunds atze f ur die Abwasserentsor gung in l andlich strukturierten Gebieten. Gesellschaft zur F orderung der Abwassertechnik. Hennef. ATV (Abwassertechnische Vereinigung, e.V.) (1997b). Versickerung von Regenwasser. Gesellschaft zur F orderung der Abwassertechnik. Hennef. ATV (Abwassertechnische Vereinigung, e.V.) (1998). Arbeitsblatt ± A 262: Grunds atze f ur Vermessung, Bau und B e trieb von P¯anzenbeeten f ur kommunales Abwasser bei Ausbaugr ossen bis 1000 Einwohnerwerte. Hennef. Balkema, A. J., Weijers, S. R., & Lambert, F. J. D. (1998). On methodologies for comparison of wastewater treatment systems with respect to sustainability. In Proceedings of conference ``options for closed water systems'', Wageningen, The Netherlands. Bettess, R. (1996). In®ltration drainage, manual of good practice. CIRIA Report 156, London. Bettess, R., Davis, A., & Watkins, D. (1996). In®tration drainage ± hydraulic design. CIRIA Project Report 23, London. Bixler, R. D., & Floyd, M. F. (1997). Nature is scary, disgusting and uncomfortable. Environment and Behaviour, 29(4), 443±467. B orner, T. (1992). Ein¯ussfaktoren f ur die Leistungsfahigkeit von P¯anzenkl aranlagen. Ph.D. Thesis TU Darmstadt, Darmstadt. Brechb uhl, B. (1995). Planung und Betrieb von Regenwassernutzungsanlagen. Amt f ur technische Anlagen und Lufthygiene des Kantons, Z urich. Brechb uhl, B. (1998). Verminderung der Wasser- und Abwasserkosten ± Einsatz und Planung von Regenwassernutzungsanlagen. Hochbauamt des Kantons, Z urich. Brechb uhl, B. (1999). Personal communication. Burkhard, H. R. (1999). Personal communication.

R. Burkhard et al. / Urban Water 2 (2000) 197±221 Butler, D., & Dixon, A. (1997). Assessing the viability of the household greywater and rainwater reuse. 21AD water: Architectural digest for the 21st century. Oxford Brookes University. Cooper, P. F. (Ed.) (1990). European design and operations guidelines for reed bed treatment systems. WRc Swindon. Cooper, P. F., Job, G. D., Green, M. B., & Shutes, R. B. E. (1996). Reed beds and constructed wetlands for wastewater treatment. WRc Swindon. Craig, A. (1999). Psychological aspects of sustainable domestic water and wastewater management. The Robert Gordon University, Aberdeen, Unpublished internal report. Deletic, A. (1998). The ®rst ¯ush load of urban surface runo€. Water Research, 32(8), 2462±2470. Demboski, D. J., Benson, J. H., Rossi, G. E., Leavitt, N. S., & Mull, M. A. (1997). Evolutions in US navy shipboard sewage and greywater programs. American Society of Naval Engineers (ASNE) Environmental Symposium '97. Dixon, A. M., Butler, D., & Fewkes, A. (1999). Guidelines for greywater re-use: health issues, water and environment management. Journal of the Chartered Institution of Water and Environmental Management, 13(5), 322±326. Eger, P. (1994). Wetland treatment for trace metal removal from mine drainage: the importance of aerobic and an aerobic processes. Water Science and Technology, 29(4), 249±256. einblick (1995). Ausgabe Nr 13, April. Zentrum f ur angewandte  Okologie Schattweid. Steinhuserberg. einblick, (1999). Ausgabe Nr 21, April. Zentrum f ur angewandte  Okologie Schattweid. Steinhuserberg. Ellis, J., Revitt, D. (1991). Drainage from roads: control and treatment of highway runo€. National Rivers Authority, Reading. Emmerling-DiNovo, C. (1995). Stormwater detention basins and residential locational decisions. Water Resources Bulletin, 31(3), 515±521. Enferadi, K. M. (1982). A ®eld evaluation of the waterless toilet as an alternative to the failing soil absorption system. In L. Waldorf, & J. L. Evans (Eds.), Proceedings of eighth national conference on individual onsite wastewater systems, Ann Arbor. EPA (US Environmental Protection Agency) (1995). Economic bene®ts of runo€ controls. website: http://www.epa.gov/owowwwtr1/NPS/ runo€.html. Escritt, L. B. (1984). Sewerage and sewage treatment. Chichester: Wiley Interscience. Findhorn Foundation (1996). Why chose a living machine? Information brochure provided by Findhorn Foundation, Forres, Scotland. Fismer, R., & Wendler, L. (1996). Case study: analysing the planning process. Environmental Research Forum, 5±6, 467±470. FRPB (Forth River Puri®cation Board) (1995). A guide to surface water best management practices. Edinburgh. Fittschen, I., & Niemczynowicz, J. (1997). Experiences with dry sanitation and greywater treatment in the ecovillage Toarp, Sweden. Water Science and Technology, 35(9), 161±170. Ghosh, D. (1997). Ecosystems approach to low cost sanitation in India: where people know better. In C. Etnier, & B. Guterstam (Eds.), Ecological engineering for wastewater treatment. Boca Raton: CRC Press. Gerba, C. P., Straub, T. M., Rose, J. B., Karpiscak, M. M., Foster, K. E., & Brittain, R. G. (1995). Water quality study of graywater treatment systems. Water Resources Bulleting, American Water Resources Association, 31(1). Gl ucklich, D. (1996). Water re-use: techniques, concepts and management In Proceedings of the IChemE one day conference: `water recycling, technical and social implications'. Govindan, V. S. (1996). Pisciculture and biomagni®cation of cadmium in a wastewater ecosystem. In C. Etnier, J. Staudenmann, A. Sch onborn (Eds.), Environmental research forum (Vols. 5±6). Switzerland: Transtec Publications. Grant, N., & Moodie, M. (1997). Septic tanks: an overview (2 ed.).

219

Grant, N., Moodie, M., & Weedon, C. (1996). Sewage solutions ± answering the call of nature. Centre for Alternative Technology Publications, Machynlleth. Gray, N. F. (1989). Biology of wastewater treatment. Oxford: Oxford Science Publications. Griggs, J. C., Shouler, M. C., & Hall, J. (1997), Water conservation and the built environment. 21AD water: Architectural digest for the 21st century. Oxford Brookes University. Gujer, W. (1996). Comparison of the Performance of Alternative Urban Sanitation Concepts. In C. Etnier, J. Staudenmann, A. Sch onborn (Eds.), Environmental research forum (Vols. 5±6). Switzerland: Transtec Publications. Guterstam, B. (1997). Ecological engineering for wastewater treatment: theoretical foundations and practical realities. In C. Etnier, & B. Guterstam (Eds.), Ecological engineering for wastewater treatment. Boca Raton: CRC Press. Haberl, R., Per¯er, R., Laber, J., & Cooper, P. (1996). In Proceedings of the ®fth international conference on wetland systems for water pollution control, Vienna, September 1996. Harasick, R.F. (1990). Water conservation in Los Angeles. In H. R. French (Ed.), Proceedings of the international symposium on hydraulics/hydrology of arid lands, ASCE, New York. Harremoes, P. (1997). Integrated water and waste management. Water Science and Technology, 35(9), 11±20. Heeb, J., Z ust (1997). Sand plant ®lter systems. In C. Etnier, & B. Guterstam (Eds.), Ecological engineering for wastewater treatment. Boca Raton: CRC Press.  berblick  Heierli, R. (1991). U uber die Abwassertechnik, Lecture Notes. Swiss Federal Institute of Technology, Z urich. Hellstr om, D., & K arrmann, E. (1996). Nitrogen and phosphorus in fresh and stored urine. In C. Etnier, J. Staudenmann, A. Sch onborn (Eds.), Environmental research forum (Vols. 5±6). Switzerland: Transtec Publications. Huber, C. (1999). Farmer, personal communication. Hydro Research (1993). Urban drainage ± the natural way. Clevedon, UK: Hydro Research and Development. Jarl ov, L. (1996). Nutrient circulation with innovative toilets in multifamily dwellings. In C. Etnier, J. Staudenmann, & A. Sch onborn (Eds.), Environmental research forum (Vols. 5±6). Switzerland: Transtec Publications. Jenssen, P. D. (1996). Ecological engineering for wastewater treatment: fundamentals and examples. In C. Etnier, J. Staudenmann, & A. Sch onborn (Eds.), Environmental research forum (Vols. 5±6). Switzerland: Transtec Publications. Jenssen, P. D., & Etnier, C. (1997). Ecological engineering for wastewater and organic waste treatment in urban areas. Water saving strategies in urban renewal ± European approaches. Berlin: Dietrich Reimer Verlag. Jenssen, P. D., & Skjelhaugen, O. J. (1994). Local ecological solutions for wastewater and organic waste treatment: a total concept for optimum reclamation and recycling. In Proceedings of the seventh international symposium on individual and small community sewage systems. Kadlec, R. H., & Hey, D. L. (1994). Constructed wetlands for river quality improvement. Water Science and Technology, 29(4), 159± 168. Karpiscak, M. M., Brittain, R. G., Gerba, C. P., & Foster, K. E. (1991). Demonstrating residential water conservation and re-use in the sonoran desert: Casa del Agua and desert house. In R. Mujeriego, & T. Asano (Eds.), Wastewater Reclamation and Reuse. Water Science and Technology, 24(9), 323±330. Karpiscak, M. M., Foster, K. E., & Schmidt, N. (1990). Residential water conservation: Casa del Agua. Water Resources Bulletin, American Water Resources Association, 26(6), 939±948. Kennedy, M. (1997). Decentralised water supply and biological wastewater puri®cation in an ecological settlement in bielefeld. Water saving strategies in urban renewal. Berlin: Dietrich Reimer Verlag.

220

R. Burkhard et al. / Urban Water 2 (2000) 197±221

Knight, R. L., Ruble, R. W., Kadlec, R. H., Reed, S. (1993). Wetlands for wastewater treatment: performance database. In G. A. Moshiri (Ed.), Constructed wetlands for water quality improvements. Lewis Publishers. Klargester (1999). O€ mains wastewater treatment for domestic applications. Promotional Brochures. Kowalik, P. (1995). Constructed wetlands for wastewater treatment from small communities. Gdansk: Politechnica Gdansk. Laak, R. (1982). Integrating onsite system design into sanitary and environmental curricula. In L. Waldorf, & J. L. Evans (Eds.), Proceedings of eighth national conference on individual onsite wastewater systems, Ann Arbor. Leonard, O. J., & Sherri€, J. D. F. (1992). Scope for control of urban runo€: guidelines (Vol. 3). CIRIA Report 124, London. Lofstedt, R. E. (1997), Risk assessment and management. In D. Brune, D. V. Chapman, M. D. Gwynne, & J. M. Pacnya (Eds.), The global environment, science, technology and management (Vol. 2). Scandinavia Science Publisher. Luker, M., & Montague, K. (1994). Control of pollution form highway drainage discharges. CIRIA Report 124. London. Maristany, A. E. (1993). long-term performance of wet detention ponds. In K. Hon (Ed.), Water management in the 1990s, proceedings of the 20th anniversary conference, ASCE. Maxwell, J. (1997). ``Scotland's ®rst ``BEST MANAGEMENT PRACTICE'' surface water treatment: the developers perspective. In Proceedings of an engineering foundation conference `sustaining urban waters in the 21st century', Malmo, Sweden. McKissock, G. (1999). University of Abertay Dundee. Personal communication, June. McKissock, G., Je€ries, C., & D'Arcy, B. (1997). An assessment of drainage best management practices in Scotland. CIWEM, 13(1), 47±51. Mehler, R., & Ostrowski, M. W. (1998). Comparison of the eciency of best stormwater management practices in UDS. In D. Butler &  Maksimovic (Eds.), Proceedings of the fourth international C. conference on development in urban drainage modelling, UDM '98, London. Melbourne Water (1997). Website: http://www.greenweb.com.au/melbwater/html/drains_to_the_bay.html. Metcalf, , & Eddy, (1991). Wastewater engineering treatment, disposal and re-use (3rd ed.). New York: MacGraw-Hill. Mustow, S., Grey, R., Smerdon, T., Pinney, C., & Waggett, R. (1997). Water conservation: implications of using recycled greywater and stored rainwater in the UK. Bracknell: BSRIA. Naisby, C. (1997). Greywater recycling and rainwater harvesting. a viable means of domestic water conservation?. Unpublished Masters Thesis, Department of Geography and Civil Engineering, University of Leeds. NERC (1974). Flood studies report. London: Natural Environment Research Council. Nolde, E. (1995). Betriebswassernutzung im Haushalt durch Aufbereitung von Grauwasser. Wasserwirtschaft und Wassertechnik. Nolde, E. (1996). Greywater re-use in households: experience from Germany. In C. Etnier, J. Staudenmann, A. Sch onborn (Eds.), Environmental research forum (Vols. 5±6). Switzerland: Transtec Publications. NOSWA (North of Scotland Water Authority) (1999a). 1999±2000 Water and Wastewater Charges; Information for Domestic Customers. NOSWA (North of Scotland Water Authority) (1999b). http:// www.noswa.co.uk/html/edu_2.htm. Nutall, P. M., Boon, A. G., & Rowell, M. R. (1997). Review of the design and management of constructed wetlands. CIRIA Report 180, London. Olah, J., & Pekar, F. (1997). Waste water fed ®sh cultures in Hungary. In C. Etnier, & B. Guterstam (Eds.), Ecological engineering for wastewater treatment. Boca Raton: CRC Press.

Olivieri, A. W., & Cooper, R. C. (1982). Public health evaluation of onsite systems. In L. Waldorf, J. L. Evans, & Ann Arbor (Eds.), Proceedings of eighth national conference on individual onsite wastewater systems. Otterpohl, R., Albold, A., & Grottker, M. (1996). Integration of sanitation into natural cycles: a new concept for cities. In C. Etnier, J. Staudenmann, & A Sch onborn (Eds.), Environmental research forum (Vols. 5±6). Switzerland: Transtec Publications. Pacey, A., & Cullis, A. (1986). Rainwater harvesting: The collection of rainfall and runo€ in rural areas. London: IT Publications. Pateman, C. (1970). Participation and democratic theory. Cambridge: Cambridge University Press. Peuser, (1999). Humustoiletten. Westerwald: Promotional Lea¯et. Prein, M. (1996). Water-fed aquaculture in Germany. In C. Etnier, J. Staudenmann, J., A. Sch onborn (Eds.), Recycling the resource; environmental research forum (Vols. 5±6). Switzerland: Transtec Publications. Rasmussen, G., Jenssen, P. D., & Weatlie, L. (1996). Graywater treatment options. In C. Etnier, J. Staudenmann, & A. Sch onborn (Eds.), Environmental research forum (Vols. 5±6). Switzerland: Transtec Publications. Referat f ur Gesundheit und Umwelt (1998). http://www.muenchen.de/ referat/rgu/frames/regnutz/, Munich. Renn, O. (1998). The role of risk communication and public dialogue for improving risk management. Risk Decision and Policy, 3(1), 5± 30. Rohrer, T. (1998a). Biogene Abf alle und N ahrsto€e ± Wertsch opfungsm oglichkeiten f ur die Landwirtschaft. Steinhuserberg:  Zentrum f ur angewandte Okologie Schattweid. Rohrer, T. (1998b). Mitmachprojekt Urin als n utzlicher P¯anz end unger. Steinhuserberg: Zentrum f ur angewandte Okologie Schattweid. r Rohrer, T., & Geiger, M. (1998). Komposttoiletten ± Information f u  die Praxis. Steinhuserberg: Zentrum f ur angewandte Okologie Schattweid. Salvato, J. A. (1982). Environmental engineering and sanitation. NewYork: Wiley Interscience. Sapotka, D. P., & Bavor, H. J. (1994). Gravel media ®ltration as a constructed wetland component for the reduction of suspended solids from maturation pond e‚uent. Water Science and Technology, 29(4), 55±66. Sayers, D. (1998a). A study of domestic greywater recycling. Interim Report. National Water Demand Management Centre, Environment Agency. Worthing, West Sussex. Sayers, D. (1998b). Personal communication, December 98. Schlumpf, C., Behringer, J., D urrenberger, G., & Pahl-Wostl, C. (1999). The personal CO2 calculator: a modelling tool for participatory integrated assessment methods. Environmental modelling and assessment. Baltzer Science Publishers BV. Schmid, M., Z ust, B. (1995). Informationen und Tips zu naturnahen Kl  a  ranlagen. Zentrum f ur angewandte Okologie Schattweid. Shields, J. (1999), Living Water, Edinburgh, Scotland. Personal communication, May, 1999. Sims, B. (1998). Liquid asset ± services for housing grey water recycling. Building Services Journal, p. 30. Slovic, P., MacGregor, D. G. (1994). The social context of risk communication. Decision research. Eugene, Oregon. Smerdon, T., Wagget, R., & Grey, R. (1997). Sustainable housing ± options for independent energy, water supply and sewage. BracknellBracknell: BSRIA. Staudenmann, J. (1994). Abwasserreinigung in Aquakulturanlagen ± Ein Beitrag zu einem nachhaltigen Ressourcen-Haushalt? Diplomarbeit Swiss Federal Institute of Technology, Z urich. Strauss, M. (1991). Human waste use: health protection practices and scheme monitoring. In R. Mujeriego, T. Asano (Eds.), Wastewater Reclamation and Reuse. Water Science and Technology, 24(9), 67± 79.

R. Burkhard et al. / Urban Water 2 (2000) 197±221 Sun-Mar, (1998). Composting toilets 1998±1999 catalog. Tonawanda: Promotional Lea¯et. Syme, G. J., & Nancarrow, B. E. (1992). Predicting public involvement in urban water management and planning. Environment and Behaviour, 24(6), 738±758. Tages-Anzeiger. (1995). Was ist Nachhaltigkeit? Tages-Anzeiger, edition of Wednesday, 21 September 1995, Z urich. Tchobanoglous (1997). Land based systems, wetlands and aquatic plant systems in the United States: an overview. In C. Etnier, & B. Guterstam (Eds.), Ecological engineering for wastewater treatment. Boca Raton: CRC Press. Thompson, D. B., & Reese, L. E. (1985). Cold climate performance of recirculating sand ®lters. In Proceedings of fourth national symposium on individual and small community sewage systems, ASAE, Michigan. Tiefbauamt der Stadt Z urich (1993). Kl aranlage Z urich Werdh olzli; Information Brochure. Times Higher Education Supplemment (THES). Analysis. 29 October 1999. Todt, D. (1997). Analyse von bestehenden Aquakulturanlagen bez uglich Eignung zur Reinigung des Prozesswassers der Kompogasanlage Otel®ngen. Wadenswil: Ingenieurschule W adenswil. Uzzell, D. L. (1982). Environmental pluralism and participation: a coorientational perspective. In J. R. Gold, & J. Burgess (Eds.), Valued environments. London: Allen and Unwin.

221

Uzzell, D. L. (1994). Action competence: some theoretical issues and methodological problems. In B. B. Jenson, & K. Schnack (Eds.), Action and action competence as key issues in critical pedagogy. Copenhagen: The Royal Danish School of Educational Studies. VSA (Verband Schweizerischer Abwasser- und Gew asserschutzfachleute) (1995). Kleinkl aranlagen. Vyzamal, J. (1995). Constructed wetlands wastewater treatment in the Czech Republic. Wiener Mitteilungen Wasser Abwasser Gew asser. P¯anzenkl aranlagen Stand der Technik, Zukunftsapekte; Wien. Warner, W. S. (1999), The in¯uence of religion on blackwater treatment. In Proceedings of the fourth international conference on  Norway. ecological engineering for wastewater treatment. As, Water Dynamics (1998). Supply management recycling; information brochure. Watkins, D. C. (1995). In®ltration drainage ± literature review. CIRIA Project Report 21, London. WCED (The World Commission on Environment and Development) (1987). Our common future. Geneva: Oxford University Press. WEF (Water Environment Federation) (1998). Urban runo€ quality management. USA: Alexandria. White, J. B. (1987). Wastewater engineering (3rd ed.). Edward Arnold. Wissing, F. (1995). Wasserreinigung mit p¯anzen. Stuttgart: Ulmer Verlag.