In situ directional enzymatic hydrolysis couple with two-stage fermentation process for enhancing microbial lipids production from food waste and waste activated sludge

Low microbial lipids (MLs) yield and high feedstock-associated cost are the main challenges in current large-scale MLs-based biodiesel production. This work developed an innovative approach for enhancing MLs production from low-cost food waste (FW) and waste activated sludge (WAS) by in situ directional enzymatic hydrolysis coupled with a two-stage fermentation process. Two directional multiple enzymes (DMEs) were developed by Aspergillus oryzae using FW and WAS as substrates, respectively, and directly used for subsequent hydrolysis of FW and WAS. Under the optimal operation parameters, the highest activities of amylase and protease in FW-DME could reach 2287.5 U/g and 36.5 U/g, while those in WAS-DME reached 401.28 U/g and 39.88 U/g. It was found that DMEs pretreatment could strengthen solid disintegration and organic matter dissolution, leading to the soluble chemical oxygen demand (SCOD) and total nitrogen (TN) concentrations of FW hydrolysate (FWH) reach 83,500 mg L⁻¹ and 820 mg L⁻¹, while 4860 mg L⁻¹ and 360 mg L⁻¹ for WAS hydrolysate (WASH). Based on the different ratios of C/N obtained from the directional FWH (38) and WASH (5.06), a two-stage process was developed for enhancing MLs production in consideration of the different C/N requirements for cell proliferation and MLs synthesis. Ultimately, the biomass concentration, MLs concentration and MLs content were respectively increased by 23.39 %, 47.62 % and 19.65 % compared with one-stage process, which presents the excellent synergistic effect of co-fermentation of FW and WAS for MLs production. The engineering analysis evidently suggests that the proposed approach is economically and technically viable, while the limitations and directions forward are also outlined accordingly.