Co-digestion of elephant grass (Penisetum purpuerum) and cow manure to produce biogas using semi-continuous fed anaerobic digester

Novelty: Biogas is a prospective source of renewable energy in the future, and therefore the development of new substrates is important. In this research, we prove that elephant grass is a potential substrate for the biogas process. In addition, we also found that the physical treatment and addition of urea combined with the loading rate and frequency of substrate feeding had an effect on the biogas production from a mixture of elephant grass and cow manure. Highlight: 1) Biogas production from mixture of elephant grass and com manure was assessed; 2) Physical pretreatment and urea addition enhanced the biogas and methane yield from anaerobic digestion of elephant grass; 3) Loading rate and feeding frequency influence biogas yield; 4) The highest biogas yield (average 4.608 L/d or 153.60 Ld-1m-3) with methane content 51.79% was observed from digester with feeding frequency of once in four days. Abstract— Elephant grass is promising substrate to produce biogas. This research aimed at investigating the effect of loading rate, physical pretreatments, urea addition, and feeding frequency on the biogas production from co-digestion of elephant grass and cow manure. Experiments were conducted using semi-continuous digesters separated into two steps. Experiment-1 used chopped grass with cow manure at a total solid (TS) content 10%, working volume 25 L, loading rate of 0.625 and 1.25 L/d, and urea addition 1.25 g/L. Experiment-2 used pulped grass with TS content 5%, loading rate 0.5 L/d and five different feeding frequency. Results showed that biogas yield was influenced by urea addition, loading rate, feeding frequency, and grass physical treatment. Biogas yield increase with decreasing loading rate and urea addition and achieved 3.09 L/d or 123.72 Ld-1m-3 at loading rate 0.625 L/d and urea addition 1.25 g/L. Biogas yield was affected strongly by grass physical treatment than urea addition. Biogas generated from pulped grass had significantly higher methane content than those of chopped grass. Feeding frequency of four days produced the highest biogas yield (average 4.608 L/d or 153.60 Ld-1m-3) with methane content of 51.79%.