The enhancement of microbial oil in municipal sewage activated sludge by cultivation on short chain fatty acids (SCFAs) as carbon sources was investigated. Previous works showed that activated sludge microbial consortia can accumulate lipidic oil when cultivated on high carbon-to-nitrogen ratio using sugars as carbon sources. The commercialization of this sugar-based technology, however, is challenged by the high cost of the sugar substrates. This study proposes to use as alternative carbon sources the SCFAs that are inherent stream constituents in wastewater treatment. The model SCFAs used in this study are acetic acid, propionic acid, and butyric acid. Unlike sugars, these SCFAs are toxic to many microorganisms even at relatively moderate concentrations. Therefore, this study implemented and examined several techniques that reduce toxicity and enhance utilization of SCFAs for lipid accumulation. First, the extent of inhibition and utilization of the short chain fatty acids as functions of mass fractions and loading of the SCFAs were evaluated using respirometric method and flask cultivation experiments. Then, the biomass growth and oil accumulation of activated sludge at various loading of SCFAs, loading of nitrogen source, and pH levels were evaluated by fed-batch cultivation in bioreactors. Afterwards, the stabilization of lipid-derived fatty acid methyl esters (FAMEs) profiles and the selection of microbial community of activated sludge were tested. Finally, the techno-economic potential of an integrated anaerobic digestion and oil accumulation of municipal wastewater sewage sludges was evaluated via order-of-magnitude simulations. Results show that the effects of pH, SCFAs mass fractions, and SCFAs loading were significant factors in the inhibition of activated sludge. The SCFAs were utilized in the following order: acetic acid > butyric acid > propionic acid. Activated sludge could accumulate up to 20% (w/w) lipids under acetic acid fed-batch cultivation. Fluorescence microscopy images of neutral lipids show that the microbial cells accumulating lipids were in the size range of yeasts. This observation is complemented by the finding that budding yeasts proliferated and dominated during lipid accumulation on acetic acid. Further improvements are needed on activated sludge lipid accumulation from SCFAs to achieve economical integration with anaerobic digestion.
|Commitee:||Bajpai, Rakesh, Chistoserdov, Andrei, Gang, Daniel, Zappi, Mark|
|School:||University of Louisiana at Lafayette|
|School Location:||United States -- Louisiana|
|Source:||DAI-B 78/04(E), Dissertation Abstracts International|
|Subjects:||Chemical engineering, Sustainability|
|Keywords:||Bioreactors, DNA analysis, Fluorescence microscopy, Inhibition, Microbial selection, Techno-economic analysis|
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