A preliminary study on potential of developing shower and laundry

Chemosphere 52 (2003) 1451–1459 www.elsevier.com/locate/chemosphere

A preliminary study on potential of developing shower/laundry wastewater reclamation and reuse system Weizhen Lu *, Andrew Y.T. Leung Department of Building and Construction, City University of Hong Kong, Kowloon, Hong Kong, HKSAR, PR China

Abstract With the ever-increasing urban population and economic activities, water usage and demand are continuously increasing. Hence, finding/re-creating adequate water supply and fully utilizing wastewater become important issues in sustainable urban development and environmental benign aspect. Considering Hong KongÕs situation, e.g., lack of natural fresh water, domination of municipal wastewater, etc., developing wastewater reclamation and reuse system is of specific significance to exploit new water resource and save natural fresh water supplied from Mainland China. We propose and have carried out some preliminary studies on the potential of categorizing municipal wastewater, developing grey and storm water recycling system in public housing estate, investigating the feasibility and potential of using reclaimed grey water, etc. Since there is very limited experience in grey water recycling, such initial studies can help to understand and increase knowledge in utilizing grey water, to foresee the feasibility of developing new water resource, to estimate the cost-effectiveness of reclaiming grey water in metropolitan city.
2003 Elsevier Ltd. All rights reserved. Keywords: Potable; Potential; Shower/laundry water; Water resource; Wastewater reclamation and reuse

1. Introduction Water is a limited and, in the mean time, the most strategically important resource on earth (Spivy, 2002). Water is essential for urban, industrial, and agricultural needs. It is estimated that the consumption of fresh water by domestic usage takes up to 70–80% of the total volume of wastewater globally (Harrison, 1999; Asano, 2002). Such ration in Hong Kong is even higher due to the migration of major industries further north to Mainland China in recent years. Besides, Hong Kong itself is almost totally lacking in natural water resources due to the hard granite base yields no appreciable underground water and there are no sizable lakes or rivers. Finding adequate water supplies has always been a problem for Hong Kong over the past 150 years. This

*

Corresponding author. Tel.: +852-2784-4316; fax: +8522788-7612. E-mail address: [email protected] (W. Lu).

densely populated international world-trading center (with population density of 6000 persons/km2 ) has suffered water shortage for most of its 160-years history. Currently, the major single source of fresh water comes from Guangdong Province, Mainland China. Such supply system can be traced back to 1960 when it was first formulated for receiving a supply of 22.7 million cubic meters a year. It provides and annually increases by 30 million cubic meters from 690 million cubic meters in 1995 to 840 million cubic meters in 2000. During 1986, water from Guangdong represented only about 52% of the total demand. In 1996, the annual supply has been raised to 720 million cubic metres, which is over 70% of Hong KongÕs demand. Such ratio keeps increasing in recent years and the demand for fresh water is also raised continuously. Besides, since 1863, Hong Kong government has established series rainfall catchment reservoirs for collecting and storing the rainfall water as reservation, e.g., Pok Fu Lam reservoir 1863 (9000 m3 capacity), Wong Nai Chung reservoir 1899 (150 000 m3 capacity), Tai Tam Byewash reservoir 1904

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2003 Elsevier Ltd. All rights reserved. doi:10.1016/S0045-6535(03)00482-X

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(1.36 million m3 capacity), New Kowloon reservoir 1906, Shek Lei Pui reservoir 1925, Kowloon Byewash reservoir 1931, Tai Lam Chung reservoir 1957, Shek Pik reservoir on Lantau Island 1963, Plover Cove reservoir 1973 (170 million m3 capacity), High Island reservoir 1978 (281 million m3 capacity), etc. Although the completed reservoirs can supply certain amount of fresh water to urban use, such resources are unstable and uncontrollable due to the seasonal variations and the uneven distribution of rainfall. Hence, seeking and developing new water resources are significant to stabilize the water supply and further improve the living standard in Hong Kong (WSD annual report, 2001). In fact, to save the fresh (potable) water resource, Hong Kong has two water supply systems to complement the daily urban needs. One is the fresh water supply system for potable usage. The other is the sea water supply system for flushing usage. As a metropolitan city with the highest population density in the world, the daily sewage amount generated by the community exceeds 2.3 million cubic meters. Among this, domestic usage takes up 53%, non-domestic 21% (e.g., hotel, hospital, schools, sports centre, etc.), restaurants 17%, government 4%, bleaching and dyeing 2%, food manufacturing 1%, textile industry 1%, laundries 1%, see Fig. 1 (DSD annual report, 2001). It can be seen that the domestic and non-domestic wastewater mainly contribute to the sewage discharge in Hong Kong. These two kinds of sewages provide large sources for reclamation and may be used as new water resources. The treated wastewater, especially shower and laundry water after first usage of fresh water, is a valuable resource, which can be available for secondary usage, and, if under good purification, for potable purpose again. This article reports a preliminary investigation and discusses the potential of development of wastewater recycle system to collect, filter, and purify domestic wastewater from

Fig. 1. Distribution of water consumptions by sewage accounting in Hong Kong (2001).

shower and laundry discharges to reuse level. The study aims to arouse the attention of relevant parties (both official and social organizations) to promote and support the development and processing of municipal wastewater for reuse in Hong Kong territory.

2. Background information and previous studies Population growing and scarcely increase of new water sources have stipulated a variety of water management measures during the last few decades, including the processing and reuse of water for many purposes. These measures include the use of highly treated municipal wastewater to augment and conserve the raw water supply. Such investigation has special significance to excavate the new water resource and improve the built environment in metropolitan city like Hong Kong. Wastewater utilization is closely related to the generation, collection, transfer and transport, treatment, disposal and reuse of wastewater that is in accordance with the principles of public health, economics, engineering conservation, aesthetics, and other environmental factors along with political constraints. It also encompasses all administrative, financial, legal, planning, and engineering functions in solving problems related to wastewater (Cheremisinoff and Cheremisinoff, 1993; NRC, 1998; Al-Sulaim and Asano, 2000; Bryan, 2000; Henze et al., 2002). Problems associated with wastewater utilization in todayÕs society are complex because of the quantity and diverse nature of the domestic and industrial wastewaters generated. Wastewater discharges are classified based on whether they are from municipalities or industries (Burton and Stensel, 2002). In Hong Kong, municipal wastewater dominates and is usually discharged from residences, commercial and institutional facilities. Domestic water usage, and, the resultant wastewater, is affected by climate, community size, development density, community affluence, dependability and quality of water supply, and water conservation requirements or practices. Hence, any wastewater utilization programme should include the monitoring of the quality and quantity of wastes produced. Tables 1–3 show the typical wastewater flow rates from residential, commercial, and institutional sources in Hong Kong. It can be seen from these tables that large amount of municipal wastewater is generated daily from various users in Hong Kong. Among these users, 7 out of 13 sources (over 50%) contain shower/laundry activities. It can be seen that the unit percentages of shower/laundry discharge in residential, commercial, and institutional sources are quite high, e.g., the unit percentage of laundry in commercial source is about 53% to the total unit consumption of commercial usage, the unit percentage of shower/laundry in institutional source achieves about 80% to the total unit consumption, etc.

W. Lu et al. / Chemosphere 52 (2003) 1451–1459 Table 1 Typical wastewater flow rates from residential sources (DSD; WSD annual report, 2001) Source

Unit

Flowrate (l/unit, day) Range

Apartment High-rise Low-rise

Person (shower/ laundry) Person (shower/ laundry)

Individual residence Typical home Person (shower/ laundry) Better home Person (shower/ laundry) Luxury home Person (shower/ laundry) Older home Person (shower/ laundry)

189

189–302

246

170–340

264

227–378

302

283–567

360

113–227

170

Total

Table 3 Typical wastewater flow rates from institutional sources (DSD; WSD annual report, 2001) Source

Unit

Hospital

Bed (shower/ laundry) Employee

Typical

132–283

1531

Source

Unit

Flowrate (l/unit, day) Range

Typical

Airport

Passenger

7.5–15

11.3

Automobile service station

Vehicle served Employee Customer

26.5–49 34–56 4–19

38 45 11

Bar

Employee Toilet room (laundry)

38–60 1040–1520

49 1280

Department store

Employee Customer

30–45 34–56

38 40

Hotel

Guest (shower) Employee Laundry/ machine

151–212 26–49 1700–2460

181 38 2080

Office

Employee

26–60

49

Restaurant

Meal

7.5–15

11.3

Shopping center

Employee Parking space

26.5–49 3.8–7.6

38 7.6

Total

3917

Tables 1–3 also imply that, in Hong Kong, not only the municipal wastewater dominates, also the abundant,

Flow rate (l/unit, day) Range

Prison

School, daily With cafeteria, gym, shower With cafeteria only Without cafeteria and gym Total

Table 2 Typical wastewater flow rates from commercial sources (DSD; WSD annual report, 2001)

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473–908 19–57 284–567

Typical 624 38

Inmate (shower/ laundry) Employee

435

19–57

38

Student (shower)

57–113

95

Student

38–76

57

Person

19–64

42

1319

stable sources of shower/laundry discharge exist. The shower/laundry wastewater possesses the potential, from both qualitative and quantitative aspects, for reclamation and reuse as secondary usage at least. Such reclamation and reuse of shower/laundry discharge is important to save/augment water supply, and of significance to improve urban environment. Wastewater reclamation and reuse is one element of water resource development and management, which provides an innovative and alternative option for agriculture, municipality, and industries. The water pollution control efforts in many countries have made treated effluent from municipal wastewater available that may be an economical augmentation to the existing water supply when compared to the increasingly expensive and environmentally destructive new water resources development. In the planning and implementation of wastewater reclamation and reuse, the intended wastewater reuse applications govern the degree of wastewater treatment required and the reliability of wastewater treatment processing and operation. It is necessary to investigate the potentials of reuse of municipal wastewater and the corresponding constraints. In principle, wastewater or any marginal quality waters can be used for any purpose provided that they meet the water quality requirements for the intended use. Table 4 lists the identification of seven categories of reusing municipal wastewater along with the potential constraints (Olsson and Newell, 1999). Fig. 2 shows the types and volume of wastewater reuse in California and Japan in 1996 (Al-Sulaim and Asano, 2000). It can be seen that, among these seven

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Table 4 Categories of municipal wastewater reuse and potential constraints Wastewater reuse categories

Potential constraints

Agricultural irrigation Crop irrigation Commercial nurseries

Effect of water quality, particularly, salts on soils and crops; Public health concerns related to pathogens (bacteria, viruses and parasites)

Landscape irrigation Park, school yard Freeway median Golf course Cemetery Greenbelt Residential Industrial reuse Cooling Boiler feed Process water Heavy construction Groundwater recharge Groundwater replenishment Salt water intrusion Subsidence control Recreational and environmental uses Lakes and ponds Marsh enhancement Streamflow augmentation Fisheries Snowmaking Non-potable urban uses Fire protection Air conditioning Toilet flushing Potable reuse (repurified water) Blending in water supply Pipe to pipe water supply

Surface and groundwater pollution if not properly managed; Marketability of crops and public acceptance; Reclaimed wastewater constituents related to scaling, corrosion, biological growth, and fouling

Public health concerns, particularly aerosol transmission of organics and pathogens in cooling water and pathogens in various process water

Trace organics in reclaimed wastewater and their toxicological effects

Health concerns of bacteria and viruses; Eutrophication due to nutrients; Esthetics including odor

Public health concerns about pathogen transmission by aerosols; Effect of water quality on scaling, corrosion, biological growth and fouling; Potential crossconnections with potable water systems Trace organics in reclaimed wastewater and their long-term toxicological effects; Esthetics and public acceptance; Public health concerns on pathogen and viruses transmission

categories, the target of potable reuse demands the highest standard of water quality of wastewater reclamation and is not yet completely achieved to date. Although the situations are different from case to case, the usage of reclaimed water presents potentials, to certain degree, in various purposes. Agricultural irrigation is the most commonly target for reusing wastewater. From Table 4 and Fig. 2, it can be foreseen that the reclamation and reuse of wastewater proposes significant challenges in addressing the environmental problems relating to the management of water, especially to water scarcity area like Hong Kong. Considering situations in Hong Kong, i.e., no industrial and agricultural demands of wastewater, and no need of groundwater recharge, etc., the potential wastewater reuses may include landscape irrigation (limited), non-potable urban use, and, the most potential

usage, potable use. Such target proposes a challenging task and an exciting research area. Many sound studies need to be carried on further.

3. Proposed scheme of wastewater reclamation As mentioned above, the most potential applications of wastewater reclamation in Hong Kong include landscape irrigation (limited), non-potable urban use, and, the most challenging target, potable reuse. Such wastewater reclamation and reuse planning require the support of whole society including public recognition, financial aid, and, sometimes, legislation through government. Municipal wastewater contains many chemicals, which present known or potential health risks if ingested (Haller, 1995). Hence, wastewater reclamation

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Fig. 2. Types and volumes of wastewater reuse in Japan and California (Al-Sulaim and Asano, 2000).

and reuse involve considerations of public health and also require close examinations of infrastructure and facilities of planning, wastewater treatment plant site, treatment reliability, economic and financial analyses, and water utility management involving effective integration of water and reclaimed wastewater. Whether wastewater reuse is appropriate or not depends upon careful economic considerations, potential uses for the reclaimed water, stringency of waste discharge re-

quirements, and public policy wherein the desire to conserve rather than develop available water resources may override economic and public health considerations. Through integrated water resources planning, the use of reclaimed wastewater may provide sufficient flexibility to allow a water supply agency to respond to short-term needs as well as increase long-term water supply reliability without constructing additional storage or conveyance facilities at substantial economic and

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environmental expenditures. Thus, wastewater reuse has a rightful place and an important role in optimal planning and more efficient management and use of water resources for society (White, 1987; Rowe and Abdel-Magid, 1995; Burton and Stensel, 2002). Planning for wastewater reuse can be divided into three stages: • conceptual planning, • feasibility investigation, • facilities planning. 3.1. Conceptual planning During conceptual planning stage, a potential project is sketched out, rough costs are estimated, and a potential reclaimed water market is identified. Some initial surveys and site investigations are required to obtain the records of wastewater amount from main residential sites, crowded commercial building groups (e.g., Central, Causeway Bay, Mong Kwok), public altitudes to the idea of wastewater reclamation, etc. If the concept appears worthwhile, feasibility investigation takes place next. 3.2. Feasibility investigation The feasibility investigation includes: (a) performing a market assessment for reclaimed wastewater; (b) assessing the existing water supply facilities and developing some preliminary alternatives; (c) developing or identifying the alternative non-reclamation facilities, such as wastewater treatment for stream discharge or constructing dams and reservoirs for future water supply, with which to compare a proposed water reuse option; and (d) performing a preliminary screening of wastewater reuse alternatives to consider technical, economic and financial attractiveness, and other constraints such as public health protection. If wastewater reclamation and reuse appear viable, then detailed actual planning can be pursued, refined facilities alternatives developed, and a final facilities plan proposed. 3.3. Facilities planning A key task in planning a wastewater reclamation project is to find potential customers who want and know how to use reclaimed wastewater for their applications. Whether a user is capable of using reclaimed wastewater depends on the quality of effluent available and its suitability for the type of use involved. Although technical, environmental, and social factors are considered in project planning, monetary factors usually override other issues when decisions are made

about whether and how to implement a water reuse project. Monetary analysis falls into two aspects: economic analysis and financial analysis. Economic analysis focuses on the value of the resources invested in a project to construct and operate it, measured in monetary terms and computed in the present value. The basic result of the economic analysis is to answer the question: Should a water reuse project be constructed? The financial analysis addresses whether a water reuse project is financially feasible. The project sponsor will need a source of capital and sources of revenue to pay for debt service and operation costs for both the proposed wastewater reuse project and any existing facilities. Thus, the equally important question to answer in the financial analysis is: Can a water reuse project be constructed? A common misconception in planning for wastewater reuse is that reclaimed wastewater represents a low-cost new water supply. This assumption is generally true only when wastewater reclamation facilities are conveniently located near large users and when no additional treatment is required beyond the water pollution control facilities from which reclaimed water is delivered. The conveyance and distribution systems for reclaimed water represent the principal cost of most proposed water reuse projects. Recent experience in California indicates that approximately four million dollars in capital cost are required for each one million m3 per year of reclaimed water made available for reuse. Assuming a facility life of 20 years and a 9% interest rate, the amortized cost of this reclaimed water is US$0.5/m3 , excluding operation and management costs (Al-Sulaim and Asano, 2000). The main steps in wastewater reclamation and reuse plan include: (a) study area characteristics, (b) water supply characteristics and facilities, (c) wastewater characteristics and facilities, (d) treatment requirements for discharge, reuse and other restrictions, (e) potential water reuse customers, (f) project alternative analysis, (g) recommended plan, (h) constructing financing plan and revenue program. Fig. 3 shows the outlines of wastewater reclamation and reuse plan. The wastewater reclamation project is a complicated one that involves many parties from the society to contribute together. Considering Hong KongÕs situations, assessments on current or potential water resources has been carried out and results are listed in Table 5. Table 5 presents the results of a preliminary study on current available and potential water resources. The results indicate that the water from Dongjiang River is still a major fresh water resource to Hong Kong in next decade; the municipal wastewater may become another water source due to its abundant supply and relatively low cost; the purification of sea water and increase of rainfall catchment areas would claim higher costs, good quality land resources, etc., and may not be suitable to be considered as alter-

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Fig. 3. Outline of wastewater reclamation and reuse plan.

natives of water supply augment in Hong Kong. The HKSAR government intends to proceed the scheme of municipal wastewater reclamation. The paper presented here aims to invoke the awareness and attention of whole society to protect and save our water resources, to promote challenging research topics, and to suggest possible way to achieve the targets.

4. Proposed processes of shower/laundry wastewater reclamation In Hong Kong, wastewater mainly comes from domestic, commercial, and rainfall sewer, etc. These wastewater resources need to be collected to a combined sewer first, and then pumped into wastewater treatment plant

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Table 5 Assessment of current/potential water resources Sources

Unit price (HK$/m3 )

Advantage

Disadvantage

Dongjiang River, Canton province, PRC

4.5 currently

Stable

Worry of water quality upstream

Cheapest at moment Reclamation of municipal wastewater

5.3 approximately

Abundant resources

Long-time to be accepted by public

Purification (Reclamation) of sea water

7.7 approximately

Unlimited sea water resource

High cost Occupy high quality land resource on coast

Increase of rainfall catchment areas

9.1 approximately

NA

Unstable resource Occupy quality land resource Highest cost

for further treatment before discharge. Similar to category of solid wastes, we propose to categorize the wastewater from domestic/commercial buildings first, i.e., separate shower/laundry water from other wastewater, collect shower/laundry water to combined sewer, and then pump into treatment plant. The proposed scheme can be started from the design stage of a newly developed residential/town site. Figs. 4 and 5 present the schematic processes of shower/laundry wastewater reclamation. It can be seen that the quality control is a key step to guarantee the quality of reclaimed water in the wastewater reclamation system. It should be mentioned that quality control also includes the monitoring of bio-organics growth and migration, which proposes a challenging task to such wastewater treatment system (Leggett, 2001).

Shower/laundry wastewater collection from domestic sites

Shower/laundry wastewater collection from commercial sites

Combined sewer (Basin for secondary water)

Fig. 4. Wastewater collection system.

Fig. 5. Treatment processes of wastewater.

Rainfall stream

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5. Conclusions This paper proposes a challenging topic of development of shower/laundry wastewater reclamation and reuse to the society. The topic concerns the public awareness of limited natural water resource, the reservation of natural water resources, the potential solution to augment water resource, and the promotion of better urban environment. It involves many factors relating to different parties in the society. The feasibility and practicability of the scheme mainly depend on the public altitude and the support of whole society, which is almost in the half way if such support acquired. Further studies are required to deeply understand the water resource and usage target in Hong Kong. Acknowledgements The work described in this paper was supported by Strategic Research Grants # 7001371 (BC) and 7001463 (BC) from, City University of Hong Kong, HKSAR. References Al-Sulaim, J., Asano, T., 2000. Wastewater Reclamation and Reuse. New Age International (P) Ltd. Asano, T., 2002. Water from (waste) water––the dependable water resource. Water Science and Technology 43 (1), 24–33.

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Bryan, E.H., 2000. Research needs for developing innovative water and wastewater treatment technologies. Water Science and Technology 42 (12), 61–64 (special issue). Burton, F.L., Stensel, H.D., 2002. Wastewater Engineering: Treatment and Reuse. McGraw-Hill Ltd., USA. Cheremisinoff, N., Cheremisinoff, P., 1993. Water Treatment and Wastewater Recovery. PTR Prentice Hall, Inc., A Simon & Schuster Company, Englewood Cliffs, NJ, USA. Drainage Services Department, HKSAR: 2001, Annual report. Haller, E.J., 1995. Simplified Waster Water Treatment Plant Operations. Technomic Publishing Co. Inc., USA. Harrison, R.M., 1999. Understanding Our Environment––An Introduction to Environmental Chemistry and Pollution. The Royal Society of Chemistry, Redwood Books Ltd., UK. Henze, M., Harremo€es, P., Cour Jansen, J.L., Arvin, E., 2002. Wastewater Treatment––Biological and Chemical Processes. Springer-Verlag, Berlin, Heidelberg, Germany. Leggett, D.J., 2001. Rainwater and Greywater use in Buildings: Best Practice Guidance. CIRIA Publishing, UK. National Research Council (NRC), 1998. In: Dobbs, D.A. (Ed.), Issues in Potable Reuse. National Academy Press, Washington DC, USA. Olsson, G., Newell, B., 1999. Wastewater Treatment Systems–– Modelling, Diagnosis and Control. IWA Publishing, UK. Rowe, D.R., Abdel-Magid, I.M., 1995. Handbook of Wastewater Reclamation and Reuse. Lewis Publishers, USA. Spivy, W., 2002. There is no new water, US Water News, 3–5. Water Services Department, HKSAR: 2001, Hong KongÕs water, Annual report. White, J.B., 1987. Wastewater Engineering. Edward Arnold Publisher, UK.