Gray Water Treatment for Reuse

Dinesh Sh / Bishal K. *

Water level at Nambul river at the Keishampat bridge in 2012 :: Pix - TSE

Why is there need for water conservation?

Existence of human life like other living species is impossible without water. It is rightly said that water is elixir to life. Although 75% of the earth is covered in water only 2.5% of it is fresh water. Out of this fresh water only about 0.007% of the fresh water is accessible to the people. So it is very important for us to conserve water for our own survival on earth. Even with the advancement of science and technology, inhabitation on any other planet having abundant water is far from reality.

International Water Management Institute (IWMI) states that at least 1 out of every 3 person in the world will face acute water shortage by 2025. The United Nations (UN) said that nearly 1.1 billion people around the world do not have access to safe drinking water. In our country/state a problem of water shortage is still going on. There has also been a report of seasonal droughts. The people have been facing acute shortage of potable water. Due to the climate change, pond water dries up.

Again due to population explosion more houses are to be built at the locations where ponds were found. It is the right time that we should think of alternate ways to conserve water. So as to conserve fresh water we may use the treatment of waste water as an alternative method.

Waste water is divided into two categories i.e. gray water and black water. Gray water refers to the waste water that is discharged from the bathrooms, wash basins, washing machines, etc. Black water refers to the waste water that is discharged from the toilet and kitchen sinks.

Black water has higher amount of bacterial coliform as compared to gray water. So treatment of black water requires a more complex process. Gray water also accounts for 60% of the total waste water. So treatment of gray water is necessary so as to prevent pollution of soil and fresh water. This initiative can also be taken up in our houses.

Water scarcity in India:

Residents in 22 major cities have been hit by water scarcity recently in India. In Kanpur, Dhanbad, Meerut, Hyderabad, etc. only 30% of the demand of water could be supplied. 80% of the water needs of India has been exploited from the ground water. This has led to the depletion of water table. An initiative for supply of water to drought prone area has been taken up by villagers of Palve Budruk with support from UNICEF and government.

Water scarcity has become a big problem in our state, Manipur. Many big institutes, hotel, hospitals store large quantities of water from the water tankers. Almost all of the household buy water from the water tankers. People cannot get water through pipelines as no proper system is built. People cannot get the benefit of water from the pipelines. So they are forced to buy water from the tanker or to fetch water from the local pond.

Why do we need to treat gray water?

Gray water contain a lot of dust, dirt, soap, detergent, grease, toothpaste etc. If this type of water is allowed to flow down the drain then it may become septic due to the contamination by the germs, bacteria, virus, etc. Gray water can also pollute the soil and the water system and it may affect the environment. In order to save the environment from potential damage by the gray water it will be wise to treat gray water for re use.

Locations where gray water treatment plant has been installed

Four treatment plants for gray water have been set up in Bangalore. The four gray water treatment plants in Bangalore are located at V. Valley, Yelahanka, Cubbon Park and Lal Bagh. They have supplied treated gray water to various parts of Bangalore at the rate of Rs15/Kl at the plant site and at Rs25/Kl through pipelines.

National Environmental Engineering Research Institute (NEERI) Nagpur and UNICEF Bhopal had collaborated to build gray water treatment system in rural schools in Madhya Pradesh. Waste water treatment plant is commonly found in US, Europe, Jordan and many other developed countries.

Process of treating gray water for household purpose:

Collect the gray water in the gray water collection tank using appropriate outlet pipes. Let it settle in a sedimentation tank for 1-2 hrs. The floating materials like hair, plastic and grease must be removed. Add chalk powder to the gray water. The chalk powder must be the blackboard chalk powders which mainly consist of calcium sulphate (CaSO4). We can add half teaspoon of chalk powder to 1Litre of water. A precipitate will be seen floating above the surface of the water.

The precipitate contains soap salt. Water is pumped to the first filter tank containing sand and gravel. (The sand and gravel must be rinsed properly so that water passing through it will be clean). When water is allowed to pass through the filter tank the precipitate is trapped in the sand and gravel layer. Aeration is done such that bacterial growth increases.

The bacteria will consume the organic materials. In the second process a type of charcoal known as activated charcoal is used. This helps to remove odor from gray water. The activated charcoal can also filter grease and oil particles. The treated water is again allowed to pass through a filter tank containing sand so as to purify the water. At last the treated water is collected in the collection tank where the water is chlorinated to kill the germs and harmful bacteria. The chlorinated water must be kept for 24 hours so that chlorine can be evaporated from water.

Benefits of gray water treatment:

Reuse of treated gray water will reduce the demand of fresh water and water bills. It will also help in maintaining the water table. The treated gray water can be used for irrigation, flushing of toilets, bathing, cloth washing, etc. The sludge contain nitrogen and phosphorous which can be used as a nutrient for the plants. Treatment of gray water reduces the demand for fresh water and water bills. Gray water re use also reduce the extent of water pollution. The treatment of gray water will decrease the pollution levels of rivers.

Precautions to be taken:

Untreated gray water must not be stored for more than 24 hours, otherwise it will turn septic. Untreated gray water must not be allowed direct contact with the parts of the plants that are to be eaten raw. The pipes used for this process must be labeled properly. We must make sure that animals and human beings do not make contact with the gray water. The untreated gray water must not be allowed to have contact with fresh water. The recycled gray water is not potable. It cannot be used for drinking purposes.

Ways to reduce water usage:

Check if there is any leakage in faucets, taps, pipes, etc. Collect the water used for rinsing vegetables and fruits. Use it for watering plants and trees. Do no keep the tap running while washing utensils. Use drip irrigation for watering plants and trees. Turn off the tap and faucets tightly. One drop of water leak per second can add up to 19 liters per day.

*** The writer has presented a model on this topic in the State Level Science Exhibition, 2013