TESTING THE CONTROL OF FILAMENTOUS MICROORGANISMS RESPONSIBLE FOR FOAMING IN A FULL-SCALE ACTIVATED-SLUDGE PLANT RUNNING WITH INITIAL AEROBIC OR ANOXIC CONTACT ZONES

Effects of anoxic conditions on the growth of nocardioform actinomycet es and of aerobic conditions on growth of Microthrix parvicella in act ivated sludge were studied to prevent foaming caused by these filament ous microorganisms. The study was conducted on a full-scale plant cons isting of three parallel lines fed with the same settled wastewater an d subjected to severe foaming due to a massive growth of M. parvicella in winter and of nocardioform actinomycetes in summer The first line was rigged with an initial contact zone (selector) and the data were c ompared with those observed in one of the lines without a selector: A complete suppression of the growth of nocardioforms was obtained in ex periments where returned activated sludge was mixed with wastewater un der both anoxic conditions and high sludge loading (11.48 kg BOD5/kg M LSS day). Under moderate sludge loading (1.80 kg BOD5/kg MLSS day) con ditions, the selector suppressed the growth of nocardioforms but was n ot able to improve settlement of the sludge and prevent the growth of other filamentous microorganisms responsible for foaming, such as M. p arvicella Finally, a substantial suppression of the growth of M. parvi cella was obtained in experiments where returned activated sludge was mixed with wastewater under aerobic conditions and with a high sludge loading (24 kg BOD(5)kg MLSS day); as a consequence, the foaming produ ced by this filamentous microorganism was highly reduced. (C) 1997 Els evier Science Ltd.