Biogas production from waste by-products of ethanol production: 1. digestion of pure wastes

Biogas production from the pure wastes emanating from ethanol production process 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 as ET-A and ETP-A. 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. Physicochemical characterization was carried on the wastes, while microbial analysis was carried out on the waste slurries. Data analysis was carried out using one way analysis of variance (ANOVA). The results of the biogas production showed that the ET-A had a significantly higher cumulative biogas yield of 2,355.49 ml/kg slurry and average gas yield of 52.34±24.23 ml/kg slurry than the ETP–A with a lower cumulative biogas yield of 677.70 ml/kg slurry and average biogas yield of 15.0602± 6.7644 ml/kg slurry (p≤ 0.05). The onset of gas flammability for the ET-A was on the 9th day (lag period of 8 days), whereas ETP–A did not combust throughout the retention period. By the 45th day, both waste variants had minimal gas production. General results for the biogas indicate that the wastes from the processing of starch are better than those from fermentation wort. Their use is expected to provide effective waste management.