Abstract
The generation of renewable energy from the digestion of biodegradable waste is one of the favoured waste management options as it also mitigates climate change by reducing greenhouse gas emissions. The energy produced can be enhanced through co-digestion of different types of wastes. The study was aimed at quantifying methane production from the digestion of different livestock manure and their co-digestion with waste water from palm oil production. The substrates constituted equal masses of FM+OW (Poultry manure and Oil mill waste water), PM+OW (Pig Manure and Oil mill waste water), CM+OW (Cow manure and Oil mill waste water), FM+CW (Poultry manure + Clean water), PM+CW (Pig Manure + Clean water) and CM+CW (Cow Manure + Clean water). 650 ml of each mixture was subsampled into a 1 L plastic teflon bottle with a replicate (6x2=12 digesters). 50 mL of inoculum was added in each of the bottles. The bottles were incubated in a water bath at 37±2 o C for 2 months. A portion of each mixture was subsampled for pH, dry matter and volatile solid contents determination before and after incubation. During the incubation process, the volume of biogas produced and the concentration of CH4 were measured using frequently. The pH of the slurries in the digesters before digestion was in the range 5.76 - 7.12, and after digestion the pH was in the range 5.78 - 7.95. The moisture content increased while the dry matter content decreased after digestion. There was also a drop in the volatile solid contents in all the feedstock after digestion. There was a significant difference in CH4 production between the different feedstocks and mixtures. Further analyses revealed that cow manure produced the highest volume of CH4 (0.024 m3 CH4 /kg VS), followed by pig manure CH4 (0.034 x 10-1 m3 CH4 /kg VS). Cow manure and pig manure when mixed separately with palm oil waste water showed no significant difference in CH4 production, as was with pig manure. The least CH4 production was observed from the mixture of fowl manure and palm oil waste water (0.024 x 10-2 m3 CH4 /kg VS). It is recommended that the co-digestion of oil mill waste water with livestock manure at different proportions should be further investigated.
Key words: Anaerobic digestion, biomethane potential, biogas, co-digestion, livestock manure, methane.