Algal and bacterial filamentous bulking of activated sludge

During late summer, Southerly Wastewater Treatment Plant in Columbus, Ohio, suffers from filamentous bulking caused by the blue-green alga Schizothrix calcicola. The treatment plant is a plug-flow, tapered-aeration facility; 6% of its flow and 45% of its organic load comes from a brewery. Algal bulking occurs when dissolved oxygen levels at the aeration tank inlet are low and when the influent condition alleviates the bulking. Although wastewater will support filamentous bulking by Sphaerotilus spp. and Beggiatoa spp. under certain conditions, these organisms are not the cause of bulking at Southerly. A theoretical kinetic model suggests that bulking occurs when the algae are limited by acetate and the zoogloeae by oxygen.