Biogas Production from Waste By-products of Ethanol Production: 3. Modeling of Gas Yield with Time

The modeling of gas yield with time for the biogas production from waste by-products of ethanol production process was studied. The wastes from the processing of four 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). The wastes 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) giving ET-CD, ET-SD, ET-FG and ET-FG-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 conditions. The modeling and simulation of biogas yield with time was carried out using NLREG version 6.3 software. The results of the study showed that ET-SD had the highest co-efficient of multiple determinations (Ra2) of 80% followed by the ET-A with Ra2 of 70% and ET-CD, 51.5% while, ETP-FG-GL had the least Ra2 value of 1.43%, ETP-A had 8.68%, and ETP-FG, 12.63%. General results showed that gas yield with time for these waste types can only be predicted for ET-A and its combinations (ET-SD and ET-CD).