GREYWATER REUSE IN ARID COUNTRIES: PROBLEMS AND POSSIBILITIES

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1 GREYWATER REUSE IN ARID COUNTRIES: PROBLEMS AND POSSIBILITIES MUSHTAQUE AHMED College of Agricultural & Marine Sciences, Sultan Qaboos University, O Box 34 Al-Khod 123, Oman SANMUGAM PRATHAPAR College of Agricultural & Marine Sciences, Sultan Qaboos University, Box 34 Al-Khod 123, Oman AHMAD AL-JAMRAH College of Engineering, Sultan Qaboos University,PO Box 34 Al-Khod 123, Oman AHMED AL-MASKIRI College of Agricultural & Marine Sciences, Sultan Qaboos University, PO Box 34 Al-Khod 123, Oman ABDULLAH AL-BELUSHI College of Agricultural & Marine Sciences, Sultan Qaboos University, PO Box 34 Al-Khod 123, Oman A large portion of the domestic wastewater is considered greywater, which is defined as water that has been used for washing dishes, laundering clothes or bathing. Under most conditions, it may be possible to reuse greywater with minimum treatment. Reuse of greywater will reduce the demand for freshwater, reduce the volume of wastewater entering sewer and septic system and will have positive environmental and economic benefits. Water for domestic use in Oman is produced at a very high cost. Increasing water availability by treating and reusing wastewater is a government policy in Oman, which suffers from serious shortage of water. The constraints associated with greywater reuse may significantly reduce the chances of successful implementation of any reuse strategy. Constraints in greywater reuse include: negative attitude of public, variability of supply/production of greywater, existing government regulations that may be very stringent as they deal with mainly wastewater without differentiating between greywater and blackwater (toilet water), costs and absence of infrastructures. Preliminary data from an ongoing study show variability of greywater production is extremely high on a daily, weekly and monthly basis from public buildings. Quality of the greywater also varies within a single household depending on its source. A survey has indicated that support for greywater reuse is not overwhelming. Existing Omani standards for wastewater reuse will require greywater to be treated like regular domestic wastewater, which must be treated sufficiently before reuse. The cost of domestic water (drinking water) supplied by 1

2 the municipalities is relatively low and this subsidy will work as a disincentive for public to make necessary investment in greywater treatment and reuse systems. INTRODUCTION Most arid countries have been trying to supplement their freshwater with treated wastewater and desalinated water. According to FAO [1] contribution of these two sources in overall water supply ranges from negligible to substantial (0.408% in Egypt to 52.6% in Kuwait). Increasing water availability by treating and reusing wastewater particularly for irrigation is a government policy in Oman, which suffers from serious shortage of water [2]. Greywater reuse reduces the amount of freshwater needed to supply a household and reduces the amount of wastewater entering sewer or septic system. Likely benefits include water savings, reduction in wastewater treatment costs and reduction in the threat to groundwater pollution from septic tanks. With proper management, greywater reuse will bring significant environmental and economic benefits. GREYWATER AS AN ALTERNATIVE SOURCE OF WATER Greywater definition It has been already mentioned that greywater is considered as the water that has been used for washing dishes, laundering clothes, or bathing. In other words, except for toilet wastes, all water draining form a household is greywater. Toilet wastes are termed as blackwater. DWI/BSRIS [3] defines greywater as all wastewater from domestic (nonprocess) appliances and fittings with the exception of that from WCs and bidets. Surendran and Wheatly [4] reported that in United Kingdom, on average there are approximately equal volumes of greywater and lavatory flush water. Although Hodges [5] reported that about two thirds of domestic water is greywater. Shouler and Griggs [6] reported that problems associated with greywater reuse are: storage, contamination and separation from existing drinking water supply. Hill [7] describes an innovative greywater treatment system using reed beds. Hodges [5] suggests that untreated greywater should not be kept for longer than one day, unless it is disinfected. Griggs et al. [8] identified greywater reuse for irrigation and WC flushing as a major water conservation measure. Mustow [9] suggested that: adequate care must be taken to avoid the contamination of underlying aquifers and neighbouring water courses and systems must be designed in such a manner that inadequately serviced systems will not harm the environment. Greywater treatment Although the basic design requirements of greywater treatment systems are the same, individual designs will be site specific. Nolde [10] reported that biological treatment of the greywater is indispensable in order to guarantee a risk free service of water for reuse applications other than potable water. The final design will depend on quality, quantity 2

3 and timing of greywater generated, soil and climatic conditions, legal requirements and cost-benefit analysis. During storage of untreated greywater, suspended solids settle, aerobial microbial activities increase, anaerobic release of soluble COD increases, and atmospheric reaeration occurs. Storing greywater for 24 hours may improve the water quality by rapid settlement of solid particles, however, storage beyond it leads to depleted dissolved oxygen levels and other aesthetic problems [11]. Greywater may be treated sequentially as below [4, 6]. 1. Storage of Greywater: It is recommended that the size of the storage tank is at least 2.4 times the maximum expected flow to allow sludge accumulation and sludge loading. 2. Balancing and screening: The greywater can be acidic or alkaline, depending on its contaminants. This requires ph balancing. Furthermore, greywater may contain solid particles including hair, which has to be screened. 3. Aerobic treatment: This may include aeration, flotation, dilution, and addition of chemicals such as alum, lime, or chlorine. 4. Slow filtering: Filtering may include slow sand filters and carbon filters to remove odor and toxins. 5. Storage of freshwater In Japan small to medium sized bio-film type facilities are receiving various kinds of greywater. This type of compact bio-film treatment became popular because of its inexpensive construction and energy saving characteristics [12]. Jefferson et al. [13] evaluated advanced biological unit operations from recycling of greywater, and found the membrane bioreactor (MBR) demonstrated the greatest efficacy towards water recycling in terms of all the quality parameter determinants. Likely savings and implications Under most conditions, it would be possible to reuse greywater with little treatment. Reusing greywater serves two purposes; it reduces the amount of freshwater needed to supply a household, and reduces the amount of wastewater entering sewer or septic system. In Oman, like many other countries, septic systems are designed to handle combined flow of greywater and blackwater. It has been observed that greywater contains only one-tenth of the nitrogen contained in blackwater ( Nitrogen as nitrite and nitrate are considered pollutants posing risks to human health. As such separation of greywater and blackwater will result in septic tanks of smaller sizes lowering costs. Greywater decomposes much faster than does blackwater. Therefore it is easier to treat greywater. Greywater also contains far fewer pathogens. Lower cost of treatment and increase in water conservation are also other beneficial aspects of separation of greywater and blackwater. 3

4 The Omani context The Sultanate of Oman, located in the South East corner of the Arab peninsula, is an arid country with a mean annual rainfall of less than 100mm. The net annual natural recharge to the groundwater is estimated to be around 1260 million cubic meters (MCM). The total water demand is put around 1650 MCM of which 90% is used for agriculture. The deficit of 390 MCM is drawn from the groundwater reserves, thus lowering the water tables and leading to seawater intrusions and salinization in Al Batinah coast [14]. About 51 MCM of water is annually desalinated for domestic use and 27MCM of wastewater are treated for use in agriculture. Many reasons are attributable for overexploitation of groundwater resources, but a fundamental one is the perception that freshwater is required to meet all demands for water, whether it is for drinking or gardening. This paradigm of water management ought to shift towards a new one, which aims to provide adequate amounts of water of acceptable quality. Such a paradigm shift will convert freshwater uses and users to water uses and users, and therefore reduce pressure on freshwater reserves of the sultanate of Oman. CONSTRAINTS IN GREYWATER REUSE Variability in greywater production: quality and quantity High variability in terms of quantity and quality can pose serious complications in design, operation and maintenance of treatment facilities. Two mosques are being investigated as part of a greywater reuse research project at SQU, Oman. Weekly greywater productions at the Al Hail South mosque and at the SQU mosque since October 2003 are presented in Figures 1 and 2. 4 Weekly greywater production at Al-Hail South mosque Greywater Produced (m 3 ) Week Figure 1. Weekly greywater production at Al Hail South mosque Weekly greywater produced at the Al Hail South mosque ranged from 4.1 m 3 to 17.6 m 3. Average weekly greywater production was 10.5 m 3 with a coefficient of variation of 0.3. Greywater production was high during weeks when the mosque hosted a community event.

5 5 Weekly Greywater Production at SQU mosque Greywater Produced (m 3 ) Week Figure 2. Weekly greywater production at SQU mosque Average weekly greywater production at the SQU mosque was 46 m 3, with a coefficient of variation of The primary reason for the wide range of greywater production at the SQU mosque was that, the students were on leave for a period of 5 weeks during the data collection period. Average daily greywater production at the Al Hail mosque was 1.22 m 3, with a coefficient of variation of Average daily greywater production during the holidays at the SQU mosque was 2.05 m 3, with a coefficient of variation of Daily data from SQU mosque during semester Greywater Production (m 3 ) Day Figure 3. Daily greywater production at SQU mosque during semester Daily greywater produced at the SQU mosque during semester ranged from 1.31m 3 to 15.4 m 3 (Figure 3) averaging 6.6 m 3, with a coefficient of variation of Analysis of daily and weekly greywater production data from both mosques indicates a high degree of variability in the amount of water produced. This makes the supply of greywater an unreliable one. However, reliability of treated greywater can be increased if it is stored before use although which is not recommended [15]. Preliminary water quality data from Al Hail South mosque and from SQU mosque are presented in Table 1. Results from greywater quality analysis and comparison with wastewater reuse guidelines in Oman show BOD 5, COD, Coliform and E.Coli levels exceed permissible concentrations, requiring treatment before reuse.

6 Table 1. Quality of greywater determined from grab samples at Al Hail South mosque and at SQU mosque. Parameter Unit SQU Al Hail South n Mean S.D. n Mean S.D. ph E.C. µs cm BOD 5 mg l COD mg l Coliform N/100 ml TSS mg l TDS mg l E.Coli. N/100 ml Turbidity NTU D.O. mg l TC mg l Water samples collected from an Omani household showed high degree of variability with regards to quality parameters (Table 2) depending on its source within the household as well as time of the day and day of sampling. Table 2. Water quality parameters of various types of greywater produced from an Omani household. 6 Source ph EC ds/m BOD 5 mg/l Turbidity NTU DO mg/l WK 1 WK 2 WK 1 WK 2 WK 1 WK 2 WK 1 WK 2 WK 1 WK 2 Fresh Hand Low Basin Shower Washing Machine Kitchen Morning Kitchen Noon Kitchen Night Public s attitude towards greywater reuse Some think that greywater reuse is not allowed by Islam. But Faruqui et al. [16] noted a special fatwa, issued in 1978, in which wastewater reuse after treatment was made permissible for all purposes, including wudu (cleansing prior to prayer). A survey conducted among the students of SQU found that 44.5% opposed vegetable irrigation, 55% opposed irrigation of fruit trees, 67% would not eat a product irrigated with treated wastewater and 68% would not use treated wastewater at home. The perception about greywater seems to be better: 62.5% supported separating greywater from blackwater,

7 58.5% would use treated greywater for some use at home and 43% would pay extra to change existing plumbing to facilitate greywater use. When asked for the main reason for not accepting unlimited use of treated wastewater, 40% identified health as the prime concern and 37% ranked religious reasons as the main concern. Existing regulations on wastewater reuse Unrealistic laws have poor participation rates. Ludwig [15] cites the California greywater law which is being emulated world-wide as an example in this regard. At present the Omani wastewater reuse standards do not distinguish between greywater and blackwater. Under existing laws, it will be necessary to install treatment (at a basic level) facilities even for relatively clean Mosque greywater. Economics of greywater reuse Jeppesen [17] concluded that: where reticulated water is readily available, the payback period for the simplest of greywater system is not less than 10 years. Ludwig [15] stated that a typical residential greywater system in the USA would save $5-$20 worth of freshwater a month, at best. As such if the greywater system costs more than a few hundred dollars, the owner would have been better off just paying for the extra water. However, Faruqui and Al-Jayyousi [18] found 4 household irrigation projects in Jordan using greywater to have benefit-cost ratios from 2.8 to 9.4. Other constraints Health concerns related to greywater should not be taken lightly especially when human contact is likely. NSW Health [19] suggests steps to ensure that the potential to transmit disease has been minimized. Some of these steps are: minimizing human contact with untreated greywater; disinfection to an even higher standard for utilization in toilet and urinal flushing or laundry use; not irrigating raw or treated greywater on edible plants which are consumed raw; and preventing surface ponding or surface runoff of greywater and confining greywater within disposal area. Some concerns of greywater reuse on environment are: overloading the land application system; raising the water table which may affect foundations of houses and causes the soil to become permanently boggy; causing odors; alter soil salinity, permeability, ph, sodicity, cation exchange capacity, phosphorus sorption capacity [19]. CONCLUSION In arid countries greywater may be a potential source of water for selected uses. Experiences have shown that greywater can be a cost effective alternative source of water; and it can be used to further sustainable development and resource conservation without compromising public health and environmental quality. The challenge is to generate interest in public and government organizations, so that greywater reuse becomes a reality in arid countries. 7

8 8 ACKNOWLEDGEMENTS The financial support of Sultan Qaboos University (SQU Research Projects: IG/AGR/SOIL/02/01 and SR/AGR/BIOR/03/01) is gratefully acknowledged. REFERENCES [1] FAO, Irrigation in the Near East Region in figures, Water Report 9, Rome, (1997). [2] Al-Obaidani S.B.S., and Atta T.H.A., Water Resources Management in Oman, Country paper presented at Ministerial Conference on the Occasion of the 3 rd World Water Forum, Kyoto, Japan, March, (2003). [3] DWI/BSRIA, Greywater and Rainwater System, Final Report 13034/2, U.K., (1998). [4] Surendran S., and Wheatley A.D., Greywater Reclamation For Non-Potable Reuse, J. CIWEM, (1998), pp [5] Hodges D., Safe Use Of Household Greywater. Water & Environment Manager, November, (1998), pp [6] Shouler M.C., and Griggs J.C., Water Conservation, Internal publication of building research establishment ltd., BRE, U.K., (1998). [7] Hill M., Greywater Recycling for Three Self build Dwellings in Leeds, CIBSE/ASHRAE, Joint National Conference, U.K., (1996), pp [8] Griggs J.C., Shouler J.C., and Hall J., Water Conservation and the Built Environment, In Research Publication (21AD/WATER) from Oxford Brookes University, U.K., (1998). [9] Mustow S., Water Standards for Greywater Systems, In Research Publication (21AD/WATER) from Oxford Brookes University, U.K., (1998). [10] Nolde E., Greywater reuse systems for toilet flushing in multi-storey buildings over ten years experience in Berlin, Urban Water, 1(4) (1999), pp [11] Dixon A., Butler D., Fewkes A., and Robinson M., Measurement and Modeling of quality changes in stored untreated greywater, Urban Water, 1(4) (1999), pp [12] Goda T., General review and new concepts regarding the development of human waste water treatment in Japan, Water Science Technology, 18(7/8) (1986), pp [13] Jefferson B., Laine A., Stephenson T., and Judd S.J., Advanced biological unit processes for domestic water recycling, Int. Symp. On Waste Water Recycling and Reuse, Paris, (2000), pp [14] Abdel Rahman H.A., and Abdel-Majid I.S., Water Conservation in Oman, Water International, 18, (1993), pp [15] Ludwig, A., Create an Oasis with Greywate, Oasis Design, CA, USA, (2002). [16] Faruqui N.I., Biswas A.K., and Bino M.J., Water Management in Islam, IDRC and U.N. University Press, Ottawa, Canada, (2001).

9 [17] Jeppesen B., Domestic greywater re-use: Australia s challenges for the future, Desalination (106), (1996), pp [18] Faruqui N., and Al-Jayyousi O., Greywater reuse in urban agriculture for poverty alleviation: A case study in Jordan, Water International, Vol 27, No 3, (2002), pp [19] NSW Health, Greywater Reuse In Sewered Single Domestic Premises, Sydney, Australia, (2000). 9