Abstract
The coagulation of combined sewer overflows (<TEX>$CSO_{s}$</TEX>) was investigated by jar-testing with several commercial coagulants. <TEX>$CSO_{s}$</TEX> sample showed different characteristics of coagulation from secondary wastewater with three common coagulants, aluminum sulfate, ferric chloride and polyaluminum chloride (PACl). Jar-tests showed that relatively wide range of optimal SS and T-P removal yielded with alum and ferric chloride compared with cationic polymers, though efficient SS and T-P removal can be achieved with all three coagulants. The decrease of pH was caused by the increase in dosage of aluminum sulfate, ferric chloride and PACl as coagulants. The pH was changed from 7.0 to 4.7 with the dosages of ferric chloride 25 mL/L. Aluminum sulfate revealed pH of 5.0 and PACl was highest pH of 5.4 after dosing of coagulants. The optimal pH to treat <TEX>$CSO_{s}$</TEX> with aluminum sulfate were 6-6.5; with PACl 6-7, and with ferric chloride higher than 7.
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