Anaerobic co-digestion of landfill leachate and sewage sludge: Determination of the optimal ratio and improvement of digestion by pre-ozonation

Background: Anaerobic co-digestion (AcoD) of various wastes is a suitable method for the removal of contaminants and biogas production. The first aim of this study was to determine the optimal ratio of landfill leachate (LL) and sewage sludge (SS) for AcoD, and the second one was to evaluate the effect of pre-ozonation of the mixture on AcoD. Methods: The LL and SS samples were taken from landfill sites and municipal wastewater treatment plants (MWTPs), respectively. In the first step, five reactors were used and named R1 (100% SS), R2(100% LL), R3 (15% LL/85% SS), R4 (25% LL/75% SS), and R5 (45% LL/55% SS). Mesophilic anaerobic digestion (AD) was performed on the reactors and the optimal ratio was determined. In the second stage, the optimal mixtures were subjected to an ozonation process before AcoD. Results: The results of the first stage showed that the highest efficiency removal of the total solids (TS), volatile solids (VS), and chemical oxygen demand (COD), and the highest biogas production belonged to R3 digester, containing 15% LL and 85% SS. In the second stage, the results showed that the removal efficiency of COD and VS in the ozonated sample at the dosage of 7.6 gO3/h were 29.8% and 36.6% higher than the non-ozonated sample, respectively. Furthermore, in the ozonated sample, the biogas yield and the content of methane in the gas mixture were 27% and 9% higher respectively, compared to the non-ozonated sample. Conclusion: According to the results, the appropriate ratio of LL to SS and pre-ozonation of LL/SS mixture have a great impact on the performance of AcoD.