(619az) What If We Make Fuel Oil from Our Sanitary Sewage?
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 were acetic acid, propionic acid, and butyric acid. Unlike sugars, these SCFAs are toxic to many microorganisms even at relatively moderate concentrations. 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 biodiesel (as fatty acid methyl esters or FAMEs) profiles and the speciation of microbial community of activated sludge were tested. Results show that the effects of pH, SCFAs mass fractions, and SCFAs loading are significant factors in the inhibition of activated sludge. The SCFAs are utilized in the following order: acetic acid > butyric acid > propionic acid. Activated sludge can 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 are in the size range of yeasts.