Development of a Bench Scale Biodigester for the Production of Bio-fertilizer using Cow Dung and Watermelon Peels

In order to reduce environmental pollution arising from watermelon waste and cow dung, conversion of these wastes into bio-fertilizer is an effective mechanism of waste management.  As a result a study was carried out for the development of a bench scale batch anaerobic bio-digester (23 L) for the production of bio-fertilizer. Five kilograms (5 kg) each of cow dung and pre-treated watermelon peels were mixed with water in a ratio of 1:1 w/v to obtained 18 L of slurry. The slurry was then charged into the developed bio-digester and allowed for 35 days at a temperature of 26-31˚C. Bio-fertilizer yield of 83% and biogas yield of 17% were obtained. Plants macronutrients (i.e. NPK) content were substantially increased in the digestates by 79%, 89% and 85% respectively. The presence of Clostridium (a nitrogen fixer bio-fertilizer), Bacillus and Pseudomonas (phosphate solubilizing bio-fertilizers) in the digestate indicated its suitability as bio-fertilizer. Keywords: Bio-fertilizer; Biodigester, Anaerobic digestion; Retention time; Cow dung; Watermelon peels