Recycling grey water
Every drop counts. This does not apply only to oil but to water as well. Harvesting and conserving water has become crucial as never before. After water harvesting in residences, it is time to look at recycling domestic grey water.
Grey water, also known as sullage, can be described as wastewater generated from domestic processes such as bathing, laundry and dish washing. Grey water comprises almost 50-80 per cent of residential waste water. It gets its name from its clouded and hazy appearance. Also, from its status as being neither fresh water (groundwater or potable water) nor heavily polluted (black water).
If channelled independently with a separate plumbing system, domestic grey water can be recycled directly within home to be used either immediately or processed and stored. However, water recycled in this manner is never clean enough to drink. A number of stages of filtration and microbial digestion can be used to make it fit for washing or flushing in toilets.
The simplest grey water recycling techniques are the ones which require little hassle and can be easily implemented in homes. These grey water diversion systems can be both designed to suit new homes, or retrofitted to many existing dwellings. For instance, they can be as basic as diverting water from kitchens and washing machines by connecting an outlet hose pipe to the outdoor garden.
Grey water from the shower or bath is considered good quality water for the garden. The diluted soap levels function as a wetting agent and are ideal for plants to grow. However, when laundry grey water is diverted to the garden care must be taken to ensure that the laundry products have low phosphate and salt levels and the pH balance is neutral.
Grey water may contain nutrients (from food particles, fertilizers, insecticides and so on) and pathogens (from the skin or other chemicals) and is often discharged warm which makes it crucial not to store it before using it for irrigation purposes, unless it is subjected to prior a treatment process.
Purification and filtration systems involve various “soft” processes to treat sewage and convert it into almost potable water. These are based on natural biological principles such as sand filtration and UV-radiation incorporated in plant systems such as treatment ponds.
Compact systems such as activated sludge systems, bio-rotors, aerobic and anaerobic bio-filters, submerged aerated filters and bio-rolls find wide application in today’s context. In a typical plant, depending on the amount of raw sewage received at the inlet, it is subjected to a series of processes — from oil skimming that traps the floating particles, oil, grease, debris to bubble aeration that generates bio mass, followed by chlorination and filtration.
“Excess biomass is removed at periodic intervals, dried in sludge drying beds and then disposed as manure. The filtrate from the sludge drying beds is directed back to the collection chamber averting any possibility of contamination. The treated water from a carbon filter is made to flow by gravity for irrigating the garden”, he elaborates. The cost varies with the capacity and volume of sewage inflow estimated. For an apartment complex of say, 100 dwelling units, assuming a plant capacity of 40-50 m3, the cost range could be between Rs. 5-6 lakh. For smaller recycling plants in individual houses, the investment can be as little as Rs. 2,500 – Rs.3,500.
DEEPTI ADLAKHA
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