Arguably, the only major challenge left for the activated sludge industry is to learn to engineer the microbial communities so that process efficiency is maximized while cost is minimized. In order to accomplish this task, Raskin and her research group believe that it is necessary to understand the ecophysiological principles that are necessary to manipulate microbial communities.

The operation of the activated sludge process hinges on effective separation of solids in the secondary clarifier. Thus, the ability of microorganisms to form settleable flocs is vital to the production of a clear effluent. Activated sludge foaming, which is often described as the formation of a stable, viscous foam layer on the surfaces of aeration basins and secondary settlers, is a common, worldwide problem that prevents the formation of a clear effluent. While some problems caused by filamentous bacteria, such as low dissolved oxygen bulking, are well understood, the problem of biological foaming seems much more complex. No general mechanism has satisfactorily explained all foaming events. Raskin’s proposed research is aimed at the heart of this problem.

Raskin and her students have studied biological foaming in activated sludge plants for the past eight years. They initiated this research by developing molecular tools, based on comparative sequence analysis of nucleic acids, to allow detection and monitoring of bacterial populations responsible for biological foaming. The use of these tools indicated a correspondence between high levels of Gordonia biomass and seasonal foaming episodes at several full-scale activated sludge plants. Detailed statistical analyses of data collected for one of these plants established a strong correlation between two parameters, temperature and mixed liquor suspended solids levels, and foaming. To explain this correlation, Raskin’s research team hypothesized that the Gordonia population is specialized in consuming certain lipids present in the influent wastewater. Based on this hypothesis, they developed a mathematical model, which so far has explained their experimental data better than any other competing hypothesis. Based on this knowledge, they decided to investigate the mechanisms of lipid degradation further. Their latest results suggest that the fatty acid signatures of lipids found in wastewater exert a strong selection on the microbial communities of activated sludge systems. Raskin’s proposed research will evaluate this hypothesis in detail.

What are the expected benefits of this research? If successful, the research results will make it possible to anticipate biological foaming during the design stage of a new wastewater treatment plant. Both the lipid content and the fatty acid signature of the lipids in the influent wastewater may be important in determining the foaming potential. By determining these factors, foaming as a potential problem will be recognized during the design stage. As a result, corrective measurements can be introduced in the design of a new plant, which should substantially reduce lifetime operational expenditures. In addition to the benefits for plant design, the proposed research will also help treatment plants that are already in operation. The molecular tools developed by Raskin’s research team can be used to rapidly evaluate the effect of corrective operational measures. The research team is developing solution-based hybridization methods integrated in hand-held, microfluidic devices to accommodate rapid analyses in the field. Use of these tools will allow plants to maximize efficiency.