Enhanced lipid and biodiesel production from glucose‐fed activated sludge: Kinetics and microbial community analysis

Abstract

An innovative approach to increase biofuel feedstock lipid yields from municipal sewage sludge via manipulation of carbon-to-nitrogen (C:N) ratio and glucose loading in activated sludge bioreactors was investigated. Sludge lipid and fatty acid methyl ester (biodiesel) yields (% cell dry weight, CDW) were enhanced via cultivation in activated sludge bioreactors operated at high initial C:N ratio (!40:1) and glucose loading (!40 g L À1 ). Under C:N 70, 60 g L À1 glucose loading, a maximum of 17.5 AE 3.9 and 10.2 AE 2.0% CDW lipid and biodiesel yields, respectively, were achieved after 7 d of cultivation. The cultured sludge lipids contained mostly C 16 AC 18 fatty acids, with oleic acid consistently accounting for 40-50% of the total fatty acids. Microbial composition in activated sludge exposed to C:N 70 shifted toward specific gammaproteobacteria, suggesting their relevance in lipid production in wastewater microbiota and potential value in biofuel synthesis applications.

Enhanced microbial oil production by activated sludge microorganisms via co‐fermentation of glucose and xylose

“…These reductions that occurred while xylose consumption appeared to stall in the first 24 h could be attributed to the acclimation of the activated sludge microorganisms to xylose by synthesis of enzymes for xylose utilization or by the shifting of the microbial population, in which a fraction of the microorganisms more acclimated for xylose utilization proliferated and dominated while others declined similar to the results of our previous investigation. 24 Growth and lipid accumulation then commenced to reach average maximum levels of 14 and 3.2 g/L of non-lipid biomass and lipid, respectively. Over the course of these experiments, an average maximum lipid content of 21.5 6 3.6% CDW of the enhanced sludge was achieved, which is more than twice as much the initial lipid content of raw activated sludge and higher than those achieved when using glucose as sole carbon source.…”

“…Sludge biomass with increased lipid content and biodiesel yield of around 17.5 6 3.9 wt % and 10.2 6 2.0 wt %, respectively were generated-significantly higher than those obtained from raw sewage activated sludge. 24 Additionally, molecular analysis established that the increased oil content of the sludge could be attributed to a population shift in the activated sludge microbial community toward microorganisms that could potentially exhibit oleaginous behavior but are yet to be identified. 24 This process could pose the following cost advantages: Using mixed cultures such as activated sludge could eliminate the need for media sterilization and assist in the implementation of continuous cultures with minimal risk of contamination.…”

“…24 Additionally, molecular analysis established that the increased oil content of the sludge could be attributed to a population shift in the activated sludge microbial community toward microorganisms that could potentially exhibit oleaginous behavior but are yet to be identified. 24 This process could pose the following cost advantages: Using mixed cultures such as activated sludge could eliminate the need for media sterilization and assist in the implementation of continuous cultures with minimal risk of contamination. Furthermore, there a potential for scaling-up the process using available municipal wastewater treatment plant infrastructures and utilizing the existing supply chain transporting nutrient and carbon-rich municipal and industrial wastewaters which can be used as growth media and agroforestry lignocellulosic residues and industrial and municipal solid wastes as carbon sources into the wastewater treatment/ fermentation plant.…”

Effect of acetic acid on lipid accumulation by glucose‐fed activated sludge cultures

“…Biodiesel yield and fatty acid profile of the lipid extracts were estimated by a transesterification and gas chromatography-flame ionization detection (GC-FID) analysis method described in an earlier paper. 20 Residual acetic acid concentrations in the culture were measured using solvent extraction and subsequent analysis of the extracts by GC-FID based on a method described elsewhere. 27 Fermentation broth supernatant samples (0.5 mL) were transferred into microcentrifuge tubes and acidified by the addition of 0.5 mL of 50% (v/v) H 2 SO 4 in order to shift the acetic acid dissociation equilibrium towards the formation of the protonated acid which is more hydrophobic.…”

“…In a previous study, our group has demonstrated the novel application of activated sludge microbial cultures obtained from municipal sewage treatment plants to produce biofuel feedstock lipids. 20 The cost advantages of using mixed cultures such as activated sludge include eliminating the need for media sterilization and the implementation of continuous cultures with minimal risk of contamination. 21 Therefore, the objective of this study was to determine the effect of acetic acid on growth and lipid accumulation by activated sludge microbial communities using glucose as the primary carbon source.…”