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The power of recycled water
Large volumes of water are piped into cities every day. This water reaches thousands of homes, is used for various purposes and then is released to flow in sewage pipes and stormwater drains, polluting water bodies and ground water on its journey out from the city. Approximately 80 per cent of the water entering a house leaves it as waste water. However, as the singer says, ‘the times they are a changing.’ It is now commonly accepted that this flow is a huge re
source and that this water can be recycled and put to productive use.
China, for example, is in the process of putting up 1,000 waste water recycling plants for many of its cities and towns. From Sydney to Singapore and from Windhoek to Wellington recycling systems are being put in place.
Treatment
Waste water treatment has evolved over the years, and with improved understanding has come better technologies. A wide array of systems covering small volumes to huge volumes has emerged. The division of treatment in simple terms has been primary, secondary and tertiary.
In primary treatment, waste water is screened and solid particles are removed. It is also allowed to settle and the sludge separated from the liquids.
In the secondary part, oxygen is pumped into the liquid. This enables the ‘good’ bacteria to grow and consume all the organic waste. Nature still remains the only ‘treatment’ process for our wastes. The pumping of oxygen enables the bacteria to grow and eat its food and clean the water in the process.
In the tertiary treatment part, the water is filtered through membranes and treated with chlorine, ozone or ultra-violet rays to remove pathogens.
Tertiary treated water has been used for many purposes. At its best in Singapore after micro filtration, reverse osmosis and ultra- violet treatment process, it is bottled and sold as ‘NEWater’. In Windhoek, Namibia, tertiary treated waste water is put back into the catchment and reused in the piped water supply. In many places it has been shown that technology can treat recycled water to meet the most stringent quality requirements including WHO guidelines for drinking water. The barriers are essentially psychological.
In general, however, treated waste water is easier put to such uses as gardening, agriculture, pavement washing, toilet flushing, car washing, filling water bodies and for industrial process use.
Since most consumption use of water is for non-potable purpose, recycled water can replace this use, freeing good quality water for higher end use.
A good recycling system will need to be reliable, occupy little space, be easy for operations, have a low capital and maintenance cost and deliver high quality output all the time.
Technological developments have been rapid along these lines as more and more companies see the future of waste water treatment as an economically profitable venture.
Examples
The city of Bhuj, Gujarat, is a typical example. The city has a massive lake in the centre, historically the provider of water to the entire town. Over time, the stream linking the catchment in the hills to the lake became an open sewage drain spoiling the water quality in the lake itself. NGOs and the city municipality came together and set up a decentralised waste water treatment system in the main drain of the town.
This system cleaned up the sewage which was released back into the stream. A dialogue with neighbouring residents saw the elimination of garbage being thrown into the stream. Appropriate landscaping and a walking trail converted a derelict and polluting waste water channel into a beautiful and usable urban space.
In Bangalore, Cubbon Park was suffering from water shortage. The Bangalore Development Authority turned to the firm Degremont for a solution. A tertiary treatment plant with a capacity to handle 1.50 million litres per day using membrane filtration technology was set up. The plant delivers excellent recycled water from raw sewage picked up from adjacent mainlines.
The treated water is estimated to cost Rs. 5 to Rs. 8 a kilo-litre. Compare this to a stated production cost of Rs. 18 a kilo-litre for fresh water from the Cauvery and the advantages are clear.
There are many such examples, the recycling unit set up by the Chennai Petroleum Corporation Ltd and Madras Fertilizer Ltd at Manali in Chennai being a recent one.
The way ahead
With water becoming a scarce resource, waste water recycling has emerged as a cost competitive, always available and reliable alternative. It is the permanently broke water supply agencies which are unable to seize the initiative to take it forward. By adopting a decentralised approach to waste water management and linking demand to supply, the impact of water pollution can be eliminated, ground water sources protected and water shortage situations overcome.
Since there is virtually little politics in waste water treatment it is likely that the private sector will enter this sector more easily and bring its R & D capabilities to improve the efficiency of treatment and reduce cost.
As the scale of the solutions come down, the day is not far when we will have household water recycling plants. Water shortages and stinking sewage flows in drains may then become a thing of the past.
www.rainwaterclub.org
www.arghyam.org
email:zenrainman@gmail.com
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