Anaerobic co-digestion of the OFMSW in mixture with the sludge from septic tanks for CH4 production

Semi-dry thermophilic anaerobic co-digestion of the OFMSW (90% w.w.b.) in mixture with the sludge from septic tanks (10% w.w.b.) for CH4 production was carried out at lab-scale. Three one-stage completely mixed batch reactors (R1, R2 and R3) with a working volume of 3 L were loaded with the aim to assess the influence of type and concentration of the inoculum sludge on process performance: R1 was inoculated with a sludge coming from a wet mesophilic full-scale facility; R2 was inoculated with the same mesophilic inoculum sludge which was subjected to a centrifugation treatment in order to increase the biomass content inside the reaction chamber and for the R3 reactor a sludge coming from a wet thermophilic plant was used. As regards process stability, all the experimental trials showed good results, no significant differences were detected between the R1 and R2 reactors and the R3 reactor showed the best performance as regards cumulative biogas and CH4 production (68.08 and 22.08 NL, respectively), average biogas and CH4 production rate (1.24 and 0.40 NL/d, respectively, respectively) specific biogas and CH4 production (407.80 and 132.24 NL/kgVSremoved, respectively), VS removal efficiency (31.13%) and CH4 content in biogas (65% vol.).