Survey of filamentous microorganisms from bulking and foaming activated-sludge plants in Italy

A survey of both biological bulking and foaming in activated-sludge plants in Italy was carried out from January 1996 to July 1998. Of 167 plants surv eyed, 84 had a foaming problem, 81 had a bulking problem, and 55 were affec ted by both during the sampling period. Bacterial identification revealed t hat Microthrix parvicella was the most common filamentous microorganism inv olved in bulking and foaming. Other filamentous microorganisms such as the Eikelboom types 0041, 021N, 0092, 0675, Thiothrix, and nocardioform actinom ycetes (GALOs), were also detected at lower frequencies. An increase in the size of the filamentous population resulted in a deterioration of the sett ling properties of the biomass with loss of sludge through the final efflue nt. Our survey indicates that the use of the contact zone technique or the addition of chemicals such as oxidants and coagulants are promising approac hes for solving bulking and foaming problems. (C) 2000 Elsevier Science Ltd . All rights reserved.