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 surveyed, 84 had a foaming problem, 81 had a bulking problem, and 55 were affected by both during the sampling period. Bacterial identification revealed that Microthrix parvicella was the most common filamentous microorganism involved in bulking and foaming. Other filamentous microorganisms such as the Eikelboom types 0041, 021N, 0092, 0675, Thiothrix, and nocardioform actinomycetes (GALOs), were also detected at lower frequencies. An increase in the size of the filamentous population resulted in a deterioration of the settling properties of the biomass with loss of sludge through the final effluent. Our survey indicates that the use of the contact zone technique or the addition of chemicals such as oxidants and coagulants are promising approaches for solving bulking and foaming problems.