| Biological foaming is characterized by the accumulation of biomass on the surfaces of activated sludge wastewater treatment systems. It is caused by the high abundance of mycolic acid containing actinomycetes, or mycolata, and is often referred to in the literature as Nocardia foam. The goal of this research was to elucidate the mechanism responsible for the seasonal variation in the abundance of mycolata leading to foam accumulation at the Urbana-Champaign Sanitary District Northeast (UCSD-NE) wastewater treatment plant. With a statistical analysis of the plant operation data and complementary laboratory experiments, it was shown that high temperatures and high lipid loading rates are the key parameters promoting foam accumulation at the UCSD-NE plant. This suggests that they are part of a single mechanism, namely that mycolata specialize in consuming lipids. Since lipids need to be hydrolyzed extracellularly before being taken up by bacteria, the mechanism suggests that the COD flux through the hydrolysis reaction determines the abundance of mycolata, and that this flux can be increased by raising temperature or lipid loading rates.; The validity of this mechanism was first tested by studying the relationship between lipase (lipid hydrolyzing enzyme) activity, temperature, and foam occurrences. Lipase activity was found to be higher in foaming plants and very sensitive to temperature, substantiating the role of temperature in seasonal biological foaming. The validity of the assumption that the mycolata specialize in consuming lipids, which are slowly degradable substrates, was also tested. To this end, a model capable the predicting the dynamics of the cellular rRNA pool was developed and validated. This model predicted that the diurnal rRNA profile of a population consuming slowly degradable substrates remains stable throughout the day. Conversely, the diurnal rRNA profile of a population consuming readily degradable substrates varies due to variations in COD loading rates. Thus, the modeling exercise linked the molecular identification of microbial populations and the determination of their ecological function. Diurnal rRNA profiles were then measured for bacterial populations found in full-scale activated sludge wastewater treatment plants, and the experiment support the assumption that mycolata specialize in consuming lipids. |
