Sewage treatment, a saga of wasted energy

Consuming huge amounts of electricity, Bangalore’s 14 existing sewage treatment plants (STPs) produce only 484 MLD of treated water.

But the daily demand from the City’s industries is poor, and there are hardly any takers among the public.

The power problem could have been easily solved had the decades-old STPs smartly used the tonnes of sludge, the semi-solid material left behind from the treatment process. Instead of being given off free, or sold for a pittance, the sludge could have yielded methane gas. The gas could then generate enough electricity to power all the needs of each STP.

But this is theory. Here’s the reality: At the Koramangala and Chellaghatta Valley STP behind HAL Airport, for instance, about 25 tonnes of sludge are taken away by agriculturists, free of cost, every week.

Reason: The access to this facility is through winding high-traffic roads. Nobody would want that sludge if they had to pay for it. In the other STPs, the price of a truckload of the nutrients-rich sludge is barely Rs 450.

So, why is the sludge not being used to eventually generate electricity? The Digester Tanks that extract methane from the sludge in the final stages of the treatment process are in a bad shape and are prone to leakage at the K & C Valley, Vrishabhavathi Valley and Hebbal Valley treatment plants. A top BWSSB official himself admitted this to Deccan Herald. These three STPs have a combined capacity of 488 MLD, making up over 70 per cent of the total treatment in the entire City.

The State government had spent crores of rupees to rehabilitate these Digesters in the 1990s. But the problems remained due to disuse, although a delayed effort is now on to get a power-generation unit at the K & C Valley plant.

While this STP and the one in the Vrushabhavathi Valley have four Digesters each, the Hebbal Valley STP has two.
Self-reliance in energy is thus out of the window for these STPs.

Every month, the K & C Valley plant uses 1,500 kV of power from the Bangalore Electricity Supply Company at a monthly cost of Rs 10 lakh. The combined cost of power, pumpsets, operation and maintenance, labour and staff salaries tops Rs 32 lakh.

Most of the water treated at this STP is let out into the Bellandur Lake. But only one of the 18 inlets into the lake is treated. Untreated sewage enters from most other inlets, virtually negating the effects of the costly treatment process.

The demand for treated water is so low that STPs sell it at Rs 15 for 1,000 litres. Since the Karnataka Golf Association has invested in the pipeline link to its golf course near K & C Valley, the rate is 50 paise for 1,000 litres.

“Surmounting those psychological barriers, people should come forward to buy this treated water. They could use this water for gardening, construction, curing and other purposes,” a BWSSB official told this newspaper.

Thanks to a new regulation by the Karnataka State Pollution Control Board on mandatory use of treated water for construction projects, some builders have now started approaching the STPs.

Treated water is also used by the horticulture department in Cubbon Park and Lalbagh, besides Bengaluru International Airport, and a handful of fire-tenders.