Investigating the effect of crude glycerol from biodiesel industry on the anaerobic co-digestion of sewage sludge and food waste in ternary mixtures

This work evaluated the production of biogas and methane (CH4) through the anaerobic co-digestion (AcoD) of primary sludge (PS) from sewage treatment, food waste (FW), and crude glycerol (GL). To address the effect of the latter on AcoD stability and performance, biochemical methane potential (BMP) tests were carried out at different GL concentrations (1 and 3% v/v). Control experiments with PS or PS + FW were also performed. A modified Gompertz model was used to describe biogas/methane production behaviour. The results demonstrated that small increases in the organic load resulting from glycerol addition led to significant increments in biogas and methane production. Although methanogenesis was transiently inhibited in the BMP trials with the highest GL concentration, implying a longer adaptation period for methanogenic archaea, methane production was restored and even maximized under these conditions. The biogas yield amounted to 432.4 and 692.6 mL/gVS (removed) at 1% and 3% GL, respectively, while the methane yield corresponded to 343.3 (1% GL) and 525.7 mLCH4/gVS (3% GL). The latter represent increases of 45.4% and 122.7% compared to those achieved with PS + FW. Finally, the energy potential from the AcoD of the ternary mixture was estimated to evaluate its contribution to electricity supply in Brazil. •Effect of crude glycerol on co-digestion of WWTP sludge and food waste was assessed.•Addition of crude glycerol led to significant increases in biogas and methane yield.•CH4 yield reached 343.3 and 525.7 mLCH4/gVS at 1% and 3% glycerol, respectively.•Glycerol dosage must be carefully selected to avoid system overload and instability.•Overall energy potential from ternary mixture anaerobic co-digestion was estimated.