Biodiesel production by Cryptococcus curvatus using volatile fatty acids from lipid-extracted sewage sludge digestion

Abstract

In this study, the objective is first to create a system where lipid production can be performed using food waste and activated sludge and second the reutilization of the lipid extracted biomass coming from the first stage to produce more lipids. Food waste water was utilized as a substrate for the lipid enhancement in activated sludge controlling the C:N ratio. After lipid enhancement, the effluent obtained was centrifuged to concentrate the biomass. Consequently, the biomass was dried and undergone a particle size reduction to perform lipid extraction. The final lipid content after four days was in average 25.15% ± 3.7% in dry basis. Residual biomass was processed in a one-stage anaerobic digester to produce volatile fatty acids in continuous process. The reactor was feeding with different concentrations of lipid-extracted biomass (10 g · L-1, 20 g · L-1 and 30 g · L-1). In steady state, the concentrations of total volatile fatty acids were 5.98 ± 0.21 g · L-1, 10.56 ± 0.21 g · L-1 and 15.20 ± 0.20 g · L-1, respectively. The effluent with highest concentration was pretreated to reduce ammonium concentration by generation of struvite increasing the C:N ratio. After the pretreatment Cryptococcus curvatus was inoculated and lipid production performance was evaluated in a repeated fed-batch system. Final concentration of lipid after four batches was 2.25 ± 0.11 g · L-1 and 57.98% of lipid content. Produced lipids were transesterified and the fatty acids content was analyzed.