Several lakes in Bengaluru such as Hulimavu and Puttenahalli lakes near J.P. Nagar, Subramanyapura lake in Uttarahalli and Arakere on Bannerghatta Road are under threat on account of overgrowth of water hyacinth. Bangalore Water Supply and Sewerage Board (BWSSB) has proposed to upgrade the existing 20 sewage treatment plants (STP) to include modifications required for removal of biological nutrients that spur their growth.
According to experts, one of the reasons for the overgrowth is the presence of phosphorus, potassium, and nitrates, known as biological nutrients, in abundance. This is attributed to the flow of sewage into the water bodies that not only compromises water quality, but also promotes the growth of microphytes and macrophytes such as algae and water hyacinth.
One way to control their growth is to prevent sewage from entering water bodies and removing biological nutrients through a separate process. B.C. Gangadhar, BWSSB Chief Engineer (Wastewater Management), said the board is upgrading a 248 MLD (million litres a day) STP at the Koramangala-Challaghatta Valley.
Mr. Gangadhar said that of the 33 STPs of the BWSSB, as many as 13 have been constructed over the past three years and have the necessary modifications for removal of biological nutrients. “We have proposed to upgrade the other 20 STPs. BWSSB had asked the Indian Institute of Science (IISc.) to prepare a report on modifications required to fulfil requirements as per norms of the Central Pollution Control Board and the National Green Tribunal. We are expecting the report in a couple of months,” he said.
The board has submitted to the State government a ₹716 crore proposal, including capital cost of ₹448 crore and operation and maintenance charges for seven years amounting to ₹268 crore, for modification of these STPs.
BWSSB is also undertaking a survey to identify drainage lines that are letting out sewage into the stormwater drain network. These lines, he said, would be connected to big lines connecting the STPs. This is likely to be completed by the end of December.
Experts, however, questioned whether upgrading the existing STPs would be enough to protect the water bodies.
Nagesh Aras, core member of Friends of Lakes, pointed out that the STPs with separate processes for removal of biological nutrients should ideally be set up in the valley systems. “Water hyacinth doubles in body mass in 10 days. No amount of removal will help,” he said.
V. Ramaprasad, also from Friends of Lakes, pointed to the lack of coordination between BWSSB, Bruhat Bengaluru Mahanagara Palike (BBMP), Karnataka State Pollution Control Board and Karnataka Tank Conservation and Development Board in maintaining water quality and protecting ecology and environment of water bodies. “Unless these agencies coordinate and come up with an action plan, measures taken individually will just mean water down the drain,” he added.
BBMP Chief Engineer (Lakes) B.T. Mohankrishna said that the civic body handles 204 lakes, of which 80 have been developed. “In these developed lakes, we have taken steps to prevent inflow of sewage by creating diversion channels. However, when it rains, sewage may enter the lakes,” he said and added that the civic body had constructed 14 STPs of smaller capacity. Five more are likely to be commissioned in four months.
