Chemical Treatment to Reduce Turbidity in Pumped Construction Site Water

Many construction projects need to pump turbid water from borrow pits or other excavations into stilling basins or sediment filter bags prior to discharge. This study evaluated the effectiveness of these devices with polyacrylamide (PAM) injection to reduce effluent turbidity. Results from laboratory jar tests using two coastal plain sediments of North Carolina suggested that a cationic PAM was the most effective in reducing turbidity, followed by a nonionic PAM. Anionic PAM was effective in whole-soil jar tests but not when turbid supernatant was tested. A stilling basin was not effective in reducing the turbidity of the pumped water without PAM. Cationic and nonionic PAMs injected to the pumped turbid water reduced effluent turbidity from the basin by 98% and 90%, respectively. Pumping the turbid water through a sediment filter bag was also not effective for turbidity reduction unless PAM was injected into the pumping system. Our results suggested that the relatively nontoxic, nonionic PAM may be an alternative where anionic PAM is not effective in reducing turbidity in borrow pit operations.