ABSTRACT
78Biochemical energy recovery using digestion and co-digestion of faecal matter collected from urine diverting dehydrating toilet faeces (UDDT-FS) and mixed organic market waste (OMW) was studied under laboratory and pilot scale conditions. Laboratory scale biochemical methane potential (BMP) tests showed an increase in methane production with an increase in OMW fraction in the feed substrate. In subsequent pilot scale experiments, one-stage and two-stage plug flow digester were studied by, applying UDDT-FS:OMW ratios of 4:1 and 1:0, at about 10 and 12% Total Solids (TS) slurry concentrations. Comparable methane production was observed in one-stage (Ro-4:1, 12%) (314±15 mL CH4/g VS added) and two-stage (Ram-4:1, 12%) (325±12 mL CH4/g VS added) digesters, when applying 12% total solids (TS) slurry concentration. However, biogas production in Ram-4:1, 12% digester (571±25 mL CH4/g VS added) was about 12% higher than in Ro-4:1, 12%, significantly more than the slight difference in methane production, i.e. 3–4%. The former was attributed to enhanced waste solubilisation and increased CO2 dissolution, resulting from mixing the bicarbonate-rich methanogenic effluent for neutralisation purposes with the low pH (4.9) influent acquired from the pre-acidification stage. Moreover, higher process stability was observed in the first parts of the plug flow two-stage digester, characterised by lower VFA concentrations.
