Causes and control practices of filamentous foaming in wastewater treatment plants

Three large Wastewater Treatment Plants (WWTP) in Greece with occasional severe foaming were selected in order to evaluate the influence of the recycle of foaming filamentous bacteria from the solids handling processes to their foaming problems. According to the results, a range of 3–39% of the total quantity of viable foaming filamentous bacteria present in biological wastewater treatment stage of the WWTPs was found to be recycled through the underflows of thickening and dewatering processes. In parallel, the feasibility of alternative nonspecific foam control methods was assessed. Within the context of this study two foam control practices were evaluated: (a) the addition of polyaluminium chloride (PAX) to the mixed liquor and (b) the selective wasting of foam from the activated sludge system followed by dewatering. The economic feasibility of each method was assessed by evaluating and comparing the total cost (capital cost and operation and maintenance costs) of each alternative for Psyttalia Sewage Treatment Works, which is the largest WWTP in Greece serving the Greater Athens Area with a treatment capacity of approximately 3.5 million people. The estimated total costs of the two foam control methods were 0.009 and 0.002 €/m3 of wastewater for PAX addition and selective wasting of foam, respectively.

Characterization of filamentous foaming in activated sludge systems using oligonucleotide hybridization probes and antibody probes

A quantitative method was developed for estimating Gordona mass in activated sludge foam and mixed liquor samples. The technique involves in situ hybridization with a genus-specific fluorescently labeled oligonucleotide probe calibrated on pure cultures of Gordona. The immunofluorescent technique of Hernandez et al. was modified to allow staining with fluorescently labeled antibody and hybridization probes. The results of this technique were compared to those from membrane hybridization studies using radioactively-labeled oligonucleotide probes. Quantitative membrane hybridizations, in situ hybridizations, and antibody staining resulted in significantly different levels of Gordona in activated sludge foam, activated sludge mixed liquor, return activated sludge, and anaerobic digester sludge. Simultaneous staining with labeled antibodies and oligonucleotide probes provide a definitive identification for Gordona, and represents a new approach for in situ studies of this organism's role in foaming.

A survey of filamentous foaming in activated sludge plants in Hong Kong

Of five major secondary sewage treatment works surveyed during 1993 in Hong Kong, two had frequent foaming in the activated sludge plants which resulted in unmanageable operational problems. In this study, branched-filamentous Nocardia amarae was identified as the main causative bacteria in foaming sludges. In vitro studies showed that fatty acids that are commonly found in municipal sewage could be utilized by N. amarae as the sole carbon source, and presence of these fatty acids in sewage could stimulate growth.