Algae Control:

Algae tend to float and are not easy to remove by means of settling basins. The best way to kill algae is by pre-chlorination before reaching the basins with a dose of 1 mg/l. Where organisms are more, a heavier dose of copper sulphate (2 mg/l) or chlorine (3-5 mg/l) may be necessary and again this high dose has to be removed before water is allowed to use. Strainers are widely used to remove algae either in the form of rapid sand filters running without coagulants or as micro-strainers. Micro-strainers are also effective if water is silt free and have been found to reduce the algae problems to the extent of 80% to 90%.

Pre-settlement Basins

They are included in the treatment system to reduce the silt load on basins. The pre-settlement basins are required in case water has suspended solids concentration more than 1000 mg/l by dry weight. Although 3 hours detention period is more than sufficient, pre-settlement basins with 1 hour detention period have been found to be effective.