Anaerobic Digestion of Organic Waste for the Production of Biogas in Calabar, Cross River State, Nigeria

The quest for environment friendly means the waste management has prompted studies on technologies for treatment of municipal organic wastes. Among these, there is anaerobic digestion. This research was thus conducted to assess the potential of fruit wastes; Watermelon (Citrus lanatus) peel (W), Pawpaw (Carica papaya) peel (P), Banana (Musa acuminata Cv. AAA group) peel (B) and Cow dung (C) for the production of biogas through anaerobic digestion processes. The production of biogas was carried out in single, double, and multiple substrates combinations at 13 kg, 6.5 kg, and 3.25 kg, respectively, per substrate. The substrates were digested anaerobically in 60-liter digesters for 45 days. The treatment comprised 11 substrates and water as a control. The results indicated that the moisture content ranged from 82.0 to 93.0%, and the pH of wastes ranged from 4.9-8.3, with a majority of the substrates falling between 6.0-7.1. Treatment W+C+P+B produced the highest amount of biogas (49.4 mL) at 45 days of digestion. This was followed by the treatments W+C and W+B, which resulted in 24 and 23.4 mL, respectively. Treatments B and C+B had the lowest methane yield of 2.2 and 7.6 mL, respectively. The combination of W+C+P+B (8.4) and C+B (6.7%) had the highest values of nitrogen content, while W+C (11%) and C+P (1.4%) had the lowest values. The mineral contents of N, P, K, Ca, and Mg in the most cases were higher than those obtained before digestion. Hence, Fruit waste (W+C+P+B) was the most suitable substrate for producing biogas and bio-fertilizer. Moreover, the values of nitrogen, phosphorus, and potassium in the digestate indicate that it will be a good source of fertilizer for crop production.