Biogas production from waste by-products of ethanol production: 2. effect of batch co-digestion with some animal and plant wastes on biogas production

The effect of batch co-digestion of the wastes emanating from ethanol production process with some animal and plant wastes on the biogas yield was studied. The wastes from the processing of some starch feedstock and from their fermentation wort were utilized for the biogas production studies. The wastes constituted: (i) process wastes from starch extraction (ET) and (ii) fermentation wort (ETP). They were studied alone (ET-A) and (ETP-A) and in combination with some animal wastes (cow dung (CD) and swine dung (SD) and plant wastes (field grass (FG) and glycerol (GL). The biogas production capabilities of the wastes were in terms of (i) biogas yields (ii) onset of gas flammability and (iii) effective retention time. This was carried out for a retention period of 45 days under ambient mesophilic temperature range of 23oC – 38oC and slurry temperature of 38oC to 48oC using 1 liter micro-digesters under anaerobic digestion. Data analysis was carried out using one way analysis of variance (ANOVA). The results of the biogas production showed that the ET-SD had the highest cumulative biogas yield of 3,800.01 ml/kg slurry and average gas yield of 84.4447± 58.6707 ml/kg slurry while the ETP–A had the least cumulative biogas yield of 677.70 ml/kg slurry and average biogas yield of 15.0602± 6.7644 ml/kg slurry. The onset of gas flammability for the ET-SD and ET-CD were on the 6th day (lag period of 5 days), ETP–FG-GL (13 days) while the ETP–A and ETP-FG did not combust throughout the retention period. By the 45th day, all the other variants were still producing gas whereas the ETP-A and ETP–FG had minimal gas production. General results for the biogas indicate that the processing wastes from the bioethanol are better utilized in combination with animal wastes and with glycerol. These are expected to provide effective waste management system.