Long-term analysis of a full-scale activated sludge wastewater treatment system exhibiting seasonal biological foaming.

The seasonal accumulation of biological foam on the activated sludge system of the Urbana-Champaign Sanitary District Northeast (UCSD-NE) wastewater treatment plant was investigated over an 8-year period by statistical analyses including path analysis, multivariate regression, and principal component analysis. Results of these analyses suggested that variation in the activated sludge reactor temperature and the use of a stream bypassing the primary clarifier were the two main factors determining the observed temporal foam profile. Characterization of the primary clarifier influent and effluent suggested the involvement of high lipid loading rates from the bypass stream in foam accumulation. In light of these results, it is hypothesized that increasing temperatures and lipid loading rates are responsible for foam formation through the same mechanism: the foam-forming microbial population is specialized in consuming lipids, substrates classified as slowly degradable. When the temperature increases, the rate of lipid hydrolysis becomes sufficiently high for this population to become abundant, accumulate on the surfaces of the aeration basins, and cause biological foaming.