Grey water recycling

Water quality is an important issue touching on all aspects of human well being and ecosystems. Water quality is defined by its desired end-use. Broadly speaking water quality is defined as the ‘physical, chemical and biological characteristics of water necessary to sustain the desired end-use. After its use, water usually returns back to the hydrological system and if left untreated can severely affect the environment. Water quality is affected by organic loading, agricultural runoffs, heavy metals, oil pollution, synthetic and persistent engineered chemicals such as plastics and pesticides, hospital residue, radioactive and thermal pollution. Apart from quality, the quantity of water is even bigger an issue. Water use has more than tripled globally since 1950 and one out of every six persons does not have regular access to safe drinking water. To have more equitable distribution of one of the most essential resources, there is an urgent need to improve efficiency of water consumption. Moreover the existing sources of water need to be augmented with more sustainable alternatives. Wastewater reuse is one important option for both environmental and economic reasons. Wastewater reuse has several benefits. Recycled wastewater is more dependable water source. Moreover it contains useful substances for some applications. Quantity and quality of wastewater may be more consistent compared to freshwater as climate conditions tend to have less pronounced effect on wastewater generation. Wastewater can be used in agriculture, recharging of ground water, industry and household. Raw wastewater reuse is an important practice in several countries especially for agriculture. Some wastewater streams contain useful material such as organic carbon, nitrogen and phosphorus. The use of nutrient rich water for agriculture and landscaping may lead to a reduction or elimination of fertilizers. With adequate treatment wastewater can meet specific need and purposes such as pavement and car washing, landscaping, recreational use, fire protection, boiler feed water, toilets, laundry, construction wash –down water, constructed wetlands etc. Wastewater could be gray or black. Grey water is wastewater generated from domestic activities such as laundry, dishwashing and bathing which can be recycled on-site for uses such as landscape irrigation, cleaning of premises and toilets.  Grey water differs from water from the toilets which is designated sewage or black water to indicate it contains human waste. Several low cost decentralized technologies for wastewater treatment are now available. Waste water treatment processes can be categorized into Physical Process, Chemical Process and Biological process. Removal of impurity by sedimentation, filtration, flotation, absorption, adsorption and centrifugation etc. come under physical process.  Impurities are removed chemically through coagulation, absorption, oxidation reduction, disinfection and ion exchange. Biological process could be aerobic, anaerobic and photosynthetic. Conventional wastewater treatment consists of the preliminary, primary, secondary and disinfection.  Most municipal wastewater treatment facilities use combination of physical, biological and chemical treatment technologies. Preliminary and primary treatments are usually physical processes such as screening for the removal of debris and large solids and sedimentation. A secondary treatment may utilize biological processes such as stabilization ponds, trickling filter, oxidation ditch and activated sludge. Tertiary and advanced level treatment is done for removal of specific pollutants such as nitrogen and phosphorus.

Decentralised Wastewater Treatment Systems (DEWATS) provides treatment for wastewater flows from 1 - 500 cubic meters per day, from both domestic and industrial sources. DEWATS is based on four treatment systems: Sedimentation and primary treatment in sedimentation ponds or septic tanks; Secondary anaerobic treatment in fixed bed filters or baffled septic tanks; Secondary and tertiary aerobic/ anaerobic treatment in constructed wetlands and Secondary and tertiary aerobic / anaerobic treatment in ponds. DEWATS technology is scalable meaning it can be used at household, Institutional, housing society or township level.

If you are scared by the technicality of DEWATS then try to follow the simple best practices of water conservation and grey water reuse at household level. Plan at least for dual plumbing at the supply end – One fresh water supply line and one treated waste water supply line. This means two overhead tanks – one for fresh water and another for treated grey water.  Of course this is in addition to the hot water supply line which is essential in Kashmir. One can plan for dual wastewater plumbing to separate grey water and black water. One can use high efficiency dual flush systems, one for solid waste and the other for liquid waste in case one is using fresh water for flushing. One can connect washbasin exhaust pipe to cistern of flush. However use simple part flush systems when grey water reuse is being done. This is the single most important fixture that can save a lot of water. If possible, try and treat grey water separately onsite through a system such as DEWATS and store the treated grey water to be used for flushing. Make arrangements to pump this treated grey water to the overhead tank for treated grey water. This line should be connected to the flushes. Design a back up source of water for flushes. Try and treat black water also through a DEWATS system. If a sanitation connection is available, both the grey-water and wastewater lines should be connected to the sanitation connection as a backup. This connection can be controlled through a valve system. Use the excess treated waste-water for landscaping requirements. One can plan for a sump to capture rainwater run-off from the rooftop. Install rainwater down-take pipes so that it can easily be led to the sump.

If one is really interested in this field one can attend short term course on ‘Domestic waste water treatment and reuse’ from Centre for Science and Environment, New Delhi. Alternate Hydro Energy Centre (AHEC), Indian Institute of Technology (IIT), Roorkee is offering a two year M.Tech. Programme on 'Conservation of Rivers & Lakes' sponsored by the ministry of environment and forest . Admission in this programme is open for in-service/sponsored candidates from State and Central agencies as well as GATE qualified fresh candidates.