In mid-2015, discussions in the Lok Sabha pointed towards water scarcity that India would face by 2025 as demands for water exceed supply from all sources (PTI, 2015). Almost as if presaging the forthcoming crisis, this summer, the city of Shimla faced a water shortage that forced the state government to call for a shutdown of schools in the city (Indian Express, 2018) while tourists were asked to avoid the town for as long as the crisis remained (Safi, 2018). The case of Shimla is but one in a series of crises that cities over the world – Cape Town, Moscow and more – have faced in the recent past or are likely to face with recurring regularity in the future (BBC, 2018).
Climate change, population growth and increasing water demand necessitate that we look beyond using water from natural sources, restrict use of freshwater in activities that do not require high levels of water quality and recycle and reuse the wastewater that is generated in both commercial and non-commercial activities. For this, greywater recycling and reuse has emerged as a viable alternative and can be used for irrigation and agriculture, in bathrooms and kitchens. It is therefore pertinent to examine what constitutes greywater, the methods of treating greywater and the ways in which countries across the world have adopted greywater reuse and recycling for efficient water management.
Composition of Grey water
Based on the levels of cleanliness in waste water, it can be categorised as—
■ greywater, which is specifically wash water– wastewater being discharged from a house including water from showers, bathtubs, sinks, kitchen, dishwashers and washing machines; and,
■ blackwater, which is heavily polluted by biological contaminants such as faecal waste and chemicals (Oron et al, 2014).
While substantially less harmful than black water, there are still hazardous chemical and biological particles in greywater. However, owing to its composition, which excludes the faecal matter and urine found in blackwater, greywater carries a decreased load of pathogens and about a tenth of nitrogen. The organic content of greywater, therefore, decomposes more rapidly than black water and is much easier to treat. These features make it usable as source for a number of activities such as agriculture and irrigation, if it meets the quality criteria (ibid).
The composition of greywater varies depending on the activity it has resulted from. It also depends on cultural habits, living standards, household demography and type of household chemical use. Because of the varying activities that contribute to its generation, not all greywater can have uniform composition. For example, kitchen sink water laden with food solids and laundry water that has been used to wash diapers is more contaminated than greywater from showers and bathroom sinks. Greywater from bathtubs, showers and hand wash basins is considered to be the least polluted source (FBR, 2012).
Kitchen grey water contributes to about 10 per cent of total grey water volume accruing from households (Pachkor and Parbat, 2017). It is contaminated with food particles, oil fats and chemical pollutants such as detergents and cleaning agents which are alkaline in nature and contain various chemicals supporting the growth of microorganisms. Since water from kitchen use is rich in organic and inorganic waste and is conducive to the growth of pathogens, it is difficult to reuse kitchen water in all kinds of grey water systems. Water from cloth washing contributes to 25 to 35 per cent of grey water, its quality depending on whether it is used for wash water, first rinse or second rinse. On the other hand, water used in bathrooms generates about 50 to 60 per cent of total grey water while being the least contaminated type of grey water (ibid). Common contaminants include soap, shampoo, and toothpaste (Lambe and Chougule, 2009). Thus, a major portion of grey water generated in households, about 60 per cent, can be recycled and reused.
Policies on Grey water – India and others
So far, India does not have a focused policy framework for management and usage of grey water in urban and rural areas. However, some guidelines for treatment of wastewater do exist. For example, The Central Public Health and Environmental Engineering Organisation (CPHEEO) has specified permitted discharge standards for treated water; use of treated wastewater in agriculture and horticulture (MoHUA, 2012). The Central Ground Water Board (CGWB, 2000) directs that treated wastewater can be used as a source of artificial ground water recharge once it meets standards and is compatible with existing groundwater. Further, India has been using treated sewage for farm forestry, horticulture, toilet flushing, industrial use and fish culture (ibid). However, drainage systems in traditional Indian villages lack a lateral line as result of which, only half of the population uses it efficiently. Black water goes into septic tanks of individual houses while greywater is discharged directly in to the open. The discharged water runs in to lakes and rivers resulting in pollution.
It is important that policy coupled with technological interventions are adopted in India so that the existing usage and generation of greywater can be regulated, recycled and reused. Since greywater is conducive to the growth of pathogens, it is imperative that safe disposal are mandated through law. Comparisons with countries that have already taken a step forward can be helpful.
In the United States of America (USA), the use of greywater is dependent on the standards set by environmental agencies of various states. For example, in the state of Arizona, it is recommended by the authorities that human contact with greywater be avoided. Thus, the usage of greywater for irrigation is restricted to subsurface drip irrigation using buried drip tubes. To encourage installation of greywater reuse systems in residential units, governments in arid and semi-arid regions in Arizona, California and Texas have been providing financial incentives (Oron et al, 2014). In Tokyo, Japan, it is mandatory for buildings with an area of over 30,000 sq m with a potential to reuse 100 cu m of greywater per day to install management systems (ibid).
So far, India has not mandated the installation of grey water systems in buildings that are generating high amounts of grey water. Taking a cue from the policy in Tokyo, we can implement a system wherein grey water generation from various commercial and apartment buildings can be checked and accordingly a regulation mandating installation of a grey water reuse system can be implemented. However, since grey water systems are not widely used in Indian households in both rural and urban areas, installation cannot be done in individual housing units, as it will require expensive retrofitting. For example, in the United Kingdom (UK), grey water systems for an individual house can cost as much as GBP 6,000 (INR 5,41,139) and installation can cost GBP 1,000 (INR 90,189) as per June, 2018 conversion rate (Ferguson, 2014). In rural areas, better drainage systems that prevent grey water from flowing into roads and river bodies and instead direct them to treatment units are a primary requirement.
The Need to Recycle and Reuse
It is important that grey water is put through an adequate treatment process and not discharged straight in to the environment since both organic and inorganic constituents in the greywater can often cause irreparable damage causing depletion of natural oxygen and development of septic conditions. The inorganic constituents – mainly phosphorus and nitrogen, when discharged into the aquatic environment, can lead to the growth of excessive aquatic life, deplete the dissolved oxygen content in water and cause the death of organisms vital to maintaining an ecological balance in water bodies (Schneider, 2009). Through the recycling of greywater, it is possible to both prevent potential harm to the environment and reduce the demand for freshwater by substituting it with recycled greywater where high quality is not required. Unlike rainwater harvesting, greywater is not dependent on unpredictable cycles of monsoon and variability of rainfall and is therefore a reliable water resource. Further, the high nitrogen and phosphorus content that is harmful to aquatic life, when used in irrigation can make a good nutrient or fertiliser source (FBR, 2012). It can also be used for toilet flushing and even bathing when adequately treated (Pachkor and Parbat, 2017).
Reusing Grey water: the methods
Reuse and recycling can engage low cost methods such as manual bucketing of grey water from outlets to structured treatment methods that screen oils, greases and solids before using it for irrigation (Lambe and Chougule, 2009). The choice of structured methods will depend on a number of factors such as planned site, available space, user needs and investment costs. (FBR, 2012).
Most systems for grey water treatment utilise seven major steps—screening; oil and grease traps; equalisation and sedimentation tank; junction chamber; horizontal roughing filter; slow sand filter; and, disinfection of water. The bar screen prevents entry of solid particles (such as plastic cups, polythene bags) above a certain size. The oil and grease traps are used to arrest oils and fats accruing from kitchen water. The equalisation and sedimentation tanks removes suspended particles while the horizontal roughing filter removes turbidity. The slow sand filter removes colour, bacteria and suspended solids. A final disinfection is undertaken to remove bacteria and odour (Lambe and Chougule, 2009).
In the rural area of Mohjri, Taluk Tivsa in Amravati district, Maharashtra, a laboratory scale grey water treatment was setup using five stages of physical operations—a raw grey water treatment unit with a capacity of 10 litres; sedimentation unit; first stage filtration unit and second stage dual filtration unit of 5 litre capacity (made of granular activated carbon and zea mays fodder) (Shegokar, Ramteke and Meshram, 2015). It was found that the sedimentation and filtration units were able to reduce a large number of total suspended solids (TSS) and significantly reduce the turbidity levels. About 87 per cent of TSS and 77 per cent of turbidity were removed in the sedimentation unit alone. The study found that the laboratory scale grey water system could readily applied and required little maintenance (ibid.). Natural and easily available low cost materials could be used for the treatment process and the unit would be economically viable as the system worked on the natural flow of water from the first stage to the last.
Lesser complex methods for household use can also be utilised—a screen trap for removing soap and froth from grey water followed by passing it through a sand filter can help in removing waste. The water can then be used for flushing and gardening (ibid). Further, these methods are not restricted to mechanical means alone. Germany, for example, has made ample use of constructed wetlands where physical, chemical, and biological processes combine to remove contaminants from wastewater (FBR, 2012).
In the present global scenario, the demand-supply ratio of fresh water and potable water often tends to be skewed. It is imperative that we look at alternatives and adopt methods for reuse and recycling so that unnecessary wastage of fresh water can be curtailed. Although India attempts to keep a check on the ways in which sewage is disposed and treated water is used, it is a far cry from what needs to be done. For efficient waste management a policy framework that specifically deals with grey water needs to be put in place.
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