Improved biogas production from food waste by co-digestion with de-oiled grease trap waste

• A single-stage and two two-stage anaerobic systems were synchronously operated.
• Co-digestion with de-oiled grease trap waste increased the biogas yield up to 19%.
• Two-stage process with recycling achieved a hydrogen yield of 1 mol/mol hexose.
• More alkalinity was consumed in the co-digestion than the mono-digestion.
• Single-stage process favored the conversion of lipid and long-chain fatty acids.

The objective of this study was to assess the feasibility of co-digesting food waste (FW) and de-oiled grease trap waste (GTW) to improve the biogas production. A lab-scale mesophilic digester (MD), a temperature-phased anaerobic digester (TPAD) and a TPAD with recycling (TPAD-R) were synchronously operated under mono-digestion (FW) and co-digestion (FW + de-oiled GTW). Co-digestion increased the biogas yield by 19% in the MD and TPAD-R, with a biogas yield of 0.60 L/g VS added. Specific methanogenic activity in the TPAD-R was much higher than that in the MD. In addition to methane, hydrogen at a yield of approximately 1 mol/mol hexose was produced in the TPAD-R. Alkalinity was consumed more in the co-digestion than in mono-digestion. Co-digestion resulted in more lipid accumulation in each digester. The MD favored the degradation of lipid and conversion of long-chain fatty acids more than the TPAD and TPAD-R.