Sewage Treatment Plants in Kalwa, Thane.

Where Kalwa's sewage runs through open nalas rather than a sewer line, a decentralised plant placed where a nala leaves the settlement can intercept the dry-weather flow, treat it, and release cleaner water towards the mangroves, while monsoon flow passes over the interceptor. Plants of this kind must be compact, able to cope with grit and plastic, and simple enough for a municipal contractor to run. We size to measured dry-season flow rather than a population estimate, and design for what the nala really carries.

Kalwa lies across the creek from central Thane, joined to it by the Kalwa bridges and the railway. It is one of TMC's ward committees, and it is densely lived in: older buildings near the station, chawls, and large settlements climbing the lower slopes of the Parsik hills, with newer buildings on flatter ground. The creek edge on its western side is lined with mangroves, and nalas from the hill run down through the settlements into it. Thane-Belapur Road begins at its southern end. Open ground is scarce, and much of what exists is unplanned.