(399d) Lipid Accumulation Kinetics and Microbial Community Analysis of Activated Sludge Microbiota

The prospect of utilizing the microbiota in sewage activated sludge for the production of lipids for biofuels application via fermentation of lignocellulose sugars was investigated as an alternative to plant-based lipid feedstocks. In addition to this, there are no known studies dealing with the relationship between lipid production and microbial composition of sludge systems in which lipid yields are enhanced by adjusting the carbon-nitrogen (C:N) ratio of the wastewater. In this study, the effect of changing the C:N ratio (10:1, 40:1, 70:1) and initial sugar loading (20, 40, 60 g/L) on activated sludge bioreactors dosed with glucose was examined for seven days. Biomass production, lipid accumulation (as fatty acid methyl esters), and glucose uptake kinetics were measured using conventional gravimetric and instrumental methods. Variations in the microbial composition of the activated sludge were determined using sequence analysis of 16S rRNA gene clone libraries. Results show that lipid production was higher in high C:N ratio bioreactors, although the total cell biomass and sugar utilization were lower. After 48 h, Firmicutes (Gram positive bacteria) represented two thirds of the bacteria in moderate and low C:N ratio reactors while Proteobacteria (Gram negative bacteria) represented 87 % of the bacteria in reactors exposed to high a C:N ratio. Proteobacteria membership also changed between 48 h, with gamma-Proteobacteria representing over 82 % of all bacteria, and 168 h with alpha-Proteobacteria representing over 86 % of all bacteria in high C:N ratio bioreactors. The results show that changes in microbial composition may be correlated to lipid production. These data will be used in future studies to identify and isolate potential lipid-accumulating bacteria in municipal wastewater activated sludge.