Evaluation and kinetics of biogas yield from morning glory (Ipomoea aquatica) co-digested with water hyacinth (Eichhornia crassipes)

Abstract

Morning glory (MG, Ipomoea aquatica) with water hyacinth (WH, Eichhornia crassipes) were co-digested for 17 weeks at five different MG:WH ratios of 100:0, 70:30, 50:50, 30:70 and 0:100 (w:w dry basis). Fixed quantity of cow dung slurry was added to each treatment as inoculum to seed the digesters. Biodegradation and maximum biogas yield models based on first-order kinetics were fitted to the experimental biogas yields to describe the cumulative and predict maximum biogas yields, respectively from each treatment. From the results, it was observed that MG was viable and prolific for biogas production. Although co-digestion did not have significant (p>0.05) effect on biogas yield, MG:WH (50:50) recorded the highest yield (0.29dm3kg−1 vs fed day−1). However, co-digestion affected (p≤0.05) total bacterial count. The biodegradation model described the observed biogas yields satisfactorily as indicated by the high R2. Similarly, the high R2 values and percentages of predicted maximum yield/observed maximum yield showed that the maximum biogas yield model predicted the maximum yields satisfactorily. Biogas yield from MG:WH (100:0) was the best described and predicted by the biodegradation and maximum yield models, respectively.