K and C valley STP demystified

K and C valley STP demystified

Fourteen Sewage Treatment Plants (STPs) and a range of Intermediate Sewage Pumping Stations (ISPS) are at the forefront of BWSSB’s battle against the city’s rising waste water volumes.

This raging battle couldn’t get more fierce than at the two STPs in Belur Nagasandra village behind the HAL Airport. Treating combined volumes of about 190 MLD (estimated daily actual average), spread over 85 acres, this Plant is the Water Board’s biggest and caters to almost a third of the city’s population.

Set up in the 1970s to treat the sewage generated in Koramangala and Chellaghatta valleys (K and C valley) the plant was upgraded as a secondary treatment plant in the 1990s with a capacity of 218 MLD. A second plant with 30 MLD capacity was commissioned in 2005. Bellandur lake, also the city’s largest water body, is the chief beneficiary of the plant.

The adjoining military farmland and the Karnataka Golf Association take a marginal volume of three MLD. Functioning 24/7, the plant uses 1,500 kV of power every month.
Here’s briefly how the treatment adopted at this plant, the advanced sludge process, works: The first stage is Screening, where larger floating solids and organic solids in the sewage are cleared.

The next stage is Grit removal, where heavier inorganic matter such as grit, sand, egg shells and gravel are taken off the sewage through sedimentation of the particles. The desilted water then enters Primary clarifiers, a tank where inorganic matter settles in 2 to 2.5 hours and are taken out as primary sludge.

The primary clarified water then enters the aeration tanks where atmospheric air is induced for oxygen to react with the organic matter in the wastewater consisting proteins and carbohydrates. This produces CO2, H2O and NH3. The grown microorganisms will absorb the organic matter in the wastewater and multiply. They are then removed in the secondary clarifiers and recycled continuously.

After going through a secondary clarifier for 1.5 to 2 hours, the organic matter settles, the secondary sludge goes for sludge thickening, digested and drying. Through these processes, the Biochemical Oxygen Demand (BOD) of the water is reduced to 10mg / Litre at the K & C Treatment Plant, and the Chemical Oxygen Demand (COD) to 450 to 500 mg/L.


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