Humans are now recognizing the water crisis that is gripping the world and looking for initiatives that can help in one way or the other. While large-scale initiatives like developing Sponge City are a huge task, there are many other small and everyday efforts that can be taken. There is an old adage which says “A stitch in time saves nine”. Simply put in this context, a small step in saving water every day can help us in fighting the big crisis. Grey water recycling fits this bill.
Understanding Grey water
Every household uses and then drains out two types of water, potable and non-potable. While potable water is the drinking water, the non-potable water is the one being used in other areas like cleaning, washing etc. This waste water from generated in homes or offices without faecal contamination i.e. wastewater from toilets is the Grey water. This water is much easier to handle in terms of recycling, treatment and reuse as there is no contact with human or animal (pet) waste. When put to use properly, the recycling can save on a lot of water thus saving, precious resource, money and replenishing the groundwater table.
Treating Grey water
Treated Grey water can never be used for drinking, but can be used for many other purposes. Grey water too contains a trace amount of pathogens due to dead skin cells from bath or clothes that have been washed so a little pre-treatment is required. Grey water from kitchen sinks is loaded with organic matter, fats, oils and grease so it too requires some treatment before being stored into a grey water storage tank for further processing.
The first step in processing the grey water starts with the correct plumbing. If possible, the grey water should be separately collected through proper plumbing. If the plumbing is already in place, an expert should be called in as to how best the water can be separated out by using direct methods or installing new pipes without disturbing the plumbing in place.
The next step involves assessing the usage of greywater. It can be either used immediately or stored for further use. If being used immediately, not much processing is required. Say the plumbing opens up in a garden and a trough pathway takes it all through the connected gardens, then the water is being utilized immediately. This needs no processing on water other than taking care of the fact that water doesn’t stall. In case one needs to store the water for further use, say providing water for flush systems, it needs storage treatment.
The treatment process used for filtration, storage and further use of grey water will depend on the scale of use. Two kinds of systems can be established for processing – Biological System and Mechanical System.
Biological system, as the name suggests uses nature and natural products as a filter for cleaning the grey water. This process has a number of methods:
- Creating a wetland is one method in which a marked area is filled with the grey water and suitable plants are planted on it. The vegetation, with its roots and stem system, provides a natural breakdown layer where microorganisms grow to breakdown the organic impurities in the grey water. The water thus filtered is naturally collected through percolation in a deep pit and can be syphoned out for use.
- Sand filter method has the grey water first filtered through sand which removes large particles. The water then goes through a simple soil-box consisting of four layers of material – 2 feet deep layer of humus-rich topsoil, followed by a bed of very fine building sand, which sits on a layer of course sand and the final layer of pea-shingle at the bottom to achieve filtration and excellent drainage.
- Grey water laden with food waste needs to be pre-treated in a septic tank which can then be treated using either of the above-mentioned methods.
Mechanical Systems use pumps, chemicals and treatment methods like UV etc. to treat the water and then pump it to a storage tank. Thereafter, the water can be sent into existing or specially designed plumbing system to fill in the flush tanks etc.
Benefits and Usage
Although not fit for human consumption, recycled grey water finds its usage in several other areas of life. It can be safely used to water plants, flushing systems, washing cars and more. Other benefits include:
- Reduced pressure on freshwater extraction and provisioning
- Reduced pollution due to treatment
- Recharge of groundwater
- Reclamation of soil nutrients
Grey water Recycling, when done with proper process and precautions can be the proverbial drop in the ocean that fills it up. Every drop of water saved today matters for a better tomorrow.
– Sneha Sinha
