Assessement of Bio-fertilizer Quality of Anaerobic Digestion of Watermelon Peels and Cow Dung

Abstract

A study was carried out for assessement of bio-fertilizerquality of anaerobic digestion of watermelon peels and cow dung as substrates. Five kilogram (5 kg) each of water melon peels and cow dung were collected, pre-treated and mixed with water in a ratio 1:1 w/v to prepared 18 L slurry that was charged into the batch bio-digester and digested for 35 days at mesophilic temperature of between 26.2-30.8℃. The physicochemical and microbiological analyses of the substrates were determined before and after the digestion process using standard methods. The analyses showed that biochemical oxygen demand, total solids, organic carbon, carbon/nitrogen ratio reduced by 99.84%, 6.22%, 59.32% and 77.25% respectively, while chemical oxygen demand, total suspended solids and pH increased by 67.16%, 86.01% and 24.14% respectively after digestion. Bio-fertilizer yield of 83.35% and biogas yield of 16.65% were obtained. Plants macronutrients (N,P,K) content were substantially increased in the digestates by 78.57%, 89.09% and 84.62%. The presence of Clostridium (nitrogen fixer bio-fertilizer), Bacillus and Pseudomonas (phosphate solubilizing bio-fertilizers) revealed that the digestate was bio-fertilizer. Moreover, the implication of salmonella in the digestate is a major health concern, it is therefore recommended that further study to check if an extended retention period would ensure the removal of Salmonella.