Bangalore , where water is thicker than itself

Bangalore Water Supply and Sewerage Board (BWSSB) is planning to construct new water treatment plants (WTPs) in the city at an estimated cost of Rs148 crore. The move comes in the wake of treated water quality falling below acceptable levels owing to the overloading of existing WTPs in the city.

BWSSB has prepared a detailed project report (DPR) for the construction of new WTPs, which are expected to rehabilitate the existing WTPs at TK Halli, Malavalli taluk, Mandya district.

The existing WTPs of Cauvery water supply scheme stage I & II, each with a capacity to treat 135 million litres per day (MLD), were commissioned in the year 1974 and 1982 respectively. As these WTPs are being overloaded, the quality of treated water from these plants have dropped significantly, and clogging of the filters has become a regular feature.

In addition, the rate of filtration in both the treatment plants is not adequate to meet the increased requirement of filtered water to maintain desirable levels in the clear water tanks in Tataguni, the last pumping station.

The rate of filtration further dips when turbidity levels rise during monsoon (June to September). The turbidity levels go up to 8 to 10 Nephelometric Turbidity Units (NTUs) during monsoons, while the normal turbidity is in the range of 0 to 5 NTUs.

According to sources from the BWSSB, the existing WTPs have clariflocculators and rapid sand filters for treating water. They said that it is essential that these treatment plants are rehabilitated to meet the water quality standards as per Central Public Health and Environmental Engineering Organisation (CPHEEO) norms.

“We have prepared a detailed project report and it has been submitted to the government for its nod. We have also sought grants from Jawaharlal Nehru National Urban Renewal Mission,”’ said S Krishnappa, chief engineer, BWSSB.

Presently, the BWSSB pays Rs 32 crore to Rs 34 crore to the Bangalore Electricity Supply Company (Bescom) for supplying power for pumping water to the city.  “If the proposed WTPs become a reality, the BWSSB can save Rs 2 crore to Rs 3 crore per month with respect to the electricity bill per month,” said Krishnappa.

The sorry state of affairs
A study conducted on the existing WTPs at Cauvery water supply scheme state I & II made these observations:

The civil structure is 40-years-old and is not in a sound condition; mechanical equipments are inefficient

Online monitoring instruments do not exist

The velocity in the raw water channel is more than 1.8 m/s, and its hydraulic capacity is not inadequate, resulting in overflows

The removal efficiency of clariflocculators is in the range of 17-22 % against the design norms of 60-80%

Clarifier units are overloaded with respect to their design capacity, as a result of which there is hardly any free board/ free fall of water

The telescopic sludge discharge device to enable visual inspection of sludge is defunct; filters have a pumped backwash system only and no air scour system

Backwash pumps and air scour pumps have inadequate capacities

Instrumentation system in filters are defunct

The filtrate quality is poor and does not meet the quality requirements of CPHEEO. It is observed that, turbidity removal efficiencies are in the range of 29-39%, against the minimum of 90% as per design norms

Civil, mechanical and electrical units need complete replacement. The filter unit has served for more than 35 years.