Journal of Bioprocessing & Biotechniques

Microbial Lipid Accumulation Capability of Activated Sludge Feeding on Short Chain Fatty Acids as Carbon Sources through Fed-Batch Cultivation

Abstract

Dhan Lord Fortela, Rafael Hernandez*, Mark Zappi, Todd W French, Rakesh Bajpai, Andrei Chistoserdov, Emmanuel Revellame and William Holmes

The potential of activated sludge microbial lipid technology as a sustainable energy platform has been recognized in the past years, but it has been challenged by the cost of carbon sources. This study hypothesized that Short Chain Fatty Acids (SCFAs) that can be derived from organic wastes can be alternative carbon sources. Therefore, this work evaluated the capability of activated sludge microbial consortia to accumulate microbial lipid by fed-batch feeding of SCFAs acetic acid, propionic acid, and butyric acid that were fed every 12 h period in 5 liter bioreactors. Activated sludge microbial consortia can accumulate microbial lipid by feeding on acetic acid. Acetic acid at 1.5 g/L loading per feeding enhanced the lipid content of activated sludge up to around 20% (w/w) dry biomass. This is comparable to that of oleaginous microorganisms. The feeding of nitrogen source (ammonium) at molar C/N of 70 only at the start resulted in significant lipid accumulation as compared to that from feeding of nitrogen for every feeding of the carbon source (acid-substrates). Fatty Acid Methyl Esters (FAMEs) profiles of the extracted lipids changed during cultivation. A biodiesel volumetric yield increase of 325% (w/w) from initial culture was achieved. This microbial lipid enhancement was confirmed using fluorescence microscopy imaging of neutral lipids, which also showed that the neutral lipid-containing cells are in the size range of yeasts. This work proved the hypothesis that activated sludge microbial consortia can accumulate microbial lipid by feeding on SCFAs.