In the water preservation sector, there is a continuing debate between rainwater harvesting supporters and those who for the possibility of water recycling to meet domestic purposes. Says MN Thippeswamy, Retired Chief Engineer-Super Time, Bangalore Water Supply and Sewerage Board (BWSSB): “Wastewater recycling can meet more than 20 per cent of the city’s daily requirements.'' Besides, it produces optimistic effects such as cleansed lakes, rivers and groundwater. (The pie-chart on ‘Strategy for Sustainable Water Supply to Bangalore’ evaluated the effectiveness of wastewater recycling at 10 per cent and rainwater harvesting at 20 per cent.)
Out of 1,600 million liters of day (MLD) of sewage that the city produces (about 80 per cent of water consumed is wastage, as a general rule), only about 600 MLD is conducted by about 25 plants established by the BWSSB and apartment complexes, the total installed capacity being about 1,500 MLD. Of this 600 MLD, no more than a tenth is reused. For instance, the Yelahanka tertiary treatment plant supplies water for other uses apart from drinking to the Kempegowda International Airport and a few other institutions. Most purification plants use a wastewater recycling system to treat water till the secondary stage, making it suitable for releasing it into the lakes or for definite industrial utilization such as cooling.
Anant S Kodavasal notices, Director, Ecotech, a company that builds up sewage recycling plants and manages O&M for apartment complexes and industrial plants in Bangalore and other places: “There are at least 2,500 STPs in apartment complexes in Bangalore which can efficiently treat 350 MLD of sewage. This works out to 20 per cent of total sewage produced. However, 80 per cent of these plants as well as the ones managed by BWSSB are no longer in use.”
Strikingly, Bangalore, according to State government sources, is planning to process sewage for drinking purposes using a wastewater recycling system. A project that is likely to get Central funds will clean sewage of the Vrishabhavathi river flowing in the south-western side till the third stage and put that water into the Arkavathi river in the south-eastern side which, in turn, will be treated for drinking.
“This is like the Singapore model, where water is reprocessed and in a roundabout manner sent back to households, so that preconceptions are also considered,” Tippeswamy explains.
In Delhi, the condition is better on paper. A consumption of 3,420 MLD leads to waste water of over 2,600 MLD, of which 1,600 MLD is treated and 338 MLD is reused. However, that does not clearly describe the reason behind Yamuna becoming a dirty river. The Delhi government admits that the slow flow of sewage in STPs, and trunk and outer sewer lines still to be joined to them has obstructed the performance of water purification.
The waste water treatment situation is much inferior in Mumbai. According to officials in the Municipal Corporation of Greater Mumbai (MCGM), out of 3,750 MLD supplies, 2,300-2,400 MLD flows into the sea, almost contaminated. MCGM officials assert that its seven STPs are working. Tenders have been put down for six sewage treatment plants, which will purify 2,600-2,700 MLD. Construction is expected to begin in October.
The treated water will be used for other purposes such as toilets and washing of trains. An investment of ₹6,000 crore will be required to transform grey water into clean drinking water, officials say.