Design and Fabrication of Small-scale Bio-digester for Bio-fertilizer Production from Locally Sourced Construction and Organic Materials

Abstract

Applying chemical fertilizers causes environmental pollution, but bio-fertilizers produced from bio-digesters provide an environmentally friendly alternative. This study designed and fabricated a bio-digester having 22 kg size, 42 cm height and 32 cm inner diameter. Galvanized steel,fiber glass and stainless steel were used for fabrication. Holes were provided for organic materials (poultry dung, cattle dung, cooked jollof rice and beans), stirring shaft and control panel. Organic materials were sourced in Ota before microbial characterization, grinding and mixing were conducted. Retention time was 28 days and digestate samples were obtained at 7 days interval for analyses. Bacillus, Pseudomonas and Escherichia coli species were commonest bacteria isolated. Digestate analyses on 28th day in mg/l were; pH (7.2); Temperature (32 °C); Nitrogen (18251); Phosphorus (6215); Carbon (98236); Potassium (1379.3); Electrical conductivity (15.00); Calcium (71.8);Magnesium (60.0); Manganese (73.5); Iron (19.5); Zinc (31.6); Aluminium (2.4); Biological oxygen demand (226.1); Chemical oxygen demand (99.3); Total solids (8.85%); Moisture (0.55); and Escherichia coli (8.1 * 105MPN/G). Organic materials were fit for bio-fertilizer production since digestate results met United States Environmental Protection Agency standards, but further studies can vary mixes in separate digesters for optimized results.