Utilization of Co-digestion of Local Brewery Wastes and Cattle Dung as a Potential Source of Biogas and Organic Fertilizer

Biogas production from co-digestion of local brewery waste (BW) and cow dung (CD) was studied for value added to this solid waste. The objective of this research was to find the optimum condition for maximum biogas production rate and also examining the effectiveness of the process residue (liquor from anaerobic digestion process) as a nitrogen source for the production of okro. The experiments were performed in a laboratory scale through which 1.5 litter plastic bottles were used as digesters operated in batch mode and mesophilic conditions [35°C±0.5]. The feedstock were tested in the CD:BW ratios of 90:10, 80:20. 70:30, 60:40, 50:50, 40:60, 30:70. 20:80, and 10:90. The maximum biogas yield was attained with mixtures in the proportions of 70:30 CD:BW. The addition of BW increased the biogas production rate from 0.40 to 0.92lt/lt.day. It was found that CD: BW ratio of 70:30 is the optimum ratio from batch process. The gradual reduction of the VFA concentration clearly indicated the stability of the process. A micro (pot) experiment was conducted to study the comparative effects of biogas process residues and NPK fertilizers on growth and yield using okro as the test crop. Twelve experimental soil filled pots in a complete randomized block design were used comprising of Control T1 (no NPK and no BR), T2 100% NPK fertilizer, T3 50% biogas process residues (BR) plus 50% NPK fertilizers and T4 biogas residues (BR 100), all in triplicates. The parameters studied showed that plant height, root length, number of fruits per plant and fruit weight were affected by the addition of BR. A maximum 20.2% plant height increase over control T1 was observed in T3, 100% NPK yielded 10% height increase while T4 has 8%. A maximum increase of 28.57% in number of fruits was recorded in treatment T2 and T3, while 14.29% increase was recorded in T4 compared with the control. The 50% BR applied in combination with 50% NPK (T3) resulted in 25.42% increase in fruit weight over control, T4 had 20.34% weight increase and 16.95% was observed in T2. Based on these results, it may be concluded that the application of approximately 50% of biogas process residue and 50% inorganic fertilizer improves the production of okro.