Co-digestion performance of organic fraction of municipal solid waste with leachate: Preliminary studies

The main aim of the study was to evaluate the co-digestion performance of OFMSW with different wastes. Leachate, reverse osmosis (RO) concentrate collected from a leachate treatment facility and dewatered sewage sludge taken from a wastewater treatment plant (WWTP) were used for co-digestion in this paper. An extra effort was made to observe the effect of leachate inclusion in the co-digestion. In the study, the mono-digestion of OFMSW, leachate, RO concentrate and sewage sludge as well as digestion of 7 different waste mixtures were carried out for this objective. The experiments were carried out for approximately 50 days under mesophilic conditions. The highest methane yield was 785 L CH₄/kg VS_added in the reactor, which had only OFMSW. While the methane yield derived from OFMSW was found higher than previous studies, methane yield of leachate was found to be 110 L CH₄/kg VS_added, which was lower than findings in the literature. The mono-substrate of OFMSW was followed by the reactor of having waste mixture of leachate + sewage sludge + OFMSW + water (C7) with 391 L CH₄/kg VS_added, which was the only combination included water. In order to understand the effect of leachate and water inclusions on co-digestion, two separate waste combinations; leachate + sewage sludge + OFMSW + water (C7) and leachate + sewage sludge + OFMSW (C1) were prepared that had different amounts of leachate but same amounts of other wastes. The methane yield of leachate + sewage sludge + OFMSW + water (C7) indicated that addition of some water instead of leachate could stimulate biogas production. Methane yield of this reactor was found to be 71% higher than the waste combination of leachate + sewage sludge + OFMSW (C1). It could be thought that the high amount of non-biodegradable matters in leachate could be responsible for lower methane yield in leachate + sewage sludge + OFMSW (C1) reactor. Methane yields of the reactors showed that co-digestion of OFMSW and leachate could be a solution not only for treatment of leachate and but also increasing the biogas potential of leachate. Leachate addition could also adjust optimum total solids (TS) content in anaerobic digestion. It was also understood that RO concentrate did not affect the methane yield in a negative way. The similar characterization of leachate and RO concentrate in this study could offer the utilization of RO concentrate instead of leachate. The findings showed that volatile solids (VS) removals were changed from 32% to 61% in the reactors. While the reactor of leachate + RO concentrate + OFMSW (C6) had the highest VS removal, the reactor of the sole substrate leachate had the lowest VS removal.