Foodwaste as a co-substrate in a fed-batch anaerobic biowaste digester for constant biogas supply

The use of foodwaste as a supplementary substrate for an anaerobic municipal biowaste digester during night times and as the sole substrate during weeks ends, when no biowaste suspension was available was studied in order to equilibrate biogas production. Assays were performed in semi-continuously fed laboratory reactors with real substrates, simulating practical feed conditions. Biogasproduction of biowaste or foodwaste reached 0.39 or 0.52m3-kg~1 CODatjded. with an average methane content of 62-66 percent, respectively. By foodwaste co-digestion during the night in a semi-continuously fed bioreactor, the total biogas production of the reactor increased by 21-37 percent compared to biogas production during biowaste-only-fed periods during the day and no feeding during the night. After three weeks of supplemenary foodwaste digestion during the nights and during week ends, the COD elimination efficiency of the reactor reached the same level as in biowaste-only-fed periods (51-65 percent). During co-digestion of foodwaste with biowaste, the volatile solids elimination efficiency was between 62-65 percent, which was insignificantly less compared to the volatile solids elimination during biowaste-only-fedperiods (63-68 percent).