Utilization of digestate from anaerobic co-digestion of water hyacinth and poultry waste as a sustainable source of organic fertilizer

Urbanization and population boom have resulted in increased crop production. However, the arable lands are not fertile enough to produce the required yield as a result of leaching and other anthropogenic activities, thus forcing farmers to resort to the use of inorganic (synthetic) fertilizers. These inorganic fertilizers though improve crop yield, have serious adverse effects on human health, the environment and soil fertility. Therefore, the need to look for traditional organic fertilizers cannot be emphasized enough. Water hyacinth (Eichornia Crassipes) is one of the world's most destructive, difficult to eradicate and noxious weed that has prolific growth rate of 17.5 metric tons of wet water hyacinth per hectare per day. However, it has high organic content which makes it a potential source for biogas and organic manure production. Also, poultry wastes which when disposed off on land pollutes groundwater and the environment, are also a very good source of organic manure and biogas.  These poultry wastes contain high amounts of uric acid, which can damage burners or gasifiers, so mixing the waste with other biomass fuel is a necessity. This study was carried out by co-digesting water hyacinth and poultry droppings for biogas and organic fertilizer production was carried out in a digester. The digester was fed with 70% ground water hyacinth paste (3.5 kg) and 10% poultry droppings (0.5 kg). The digester was stirred gently to facilitate better aeration and porosity. Moisture content, pH, carbon content, nitrogen, phosphorus and potassium were analyzed for every 15 days. After 45 days the product had 30% moisture, 9.67% Carbon with pH 7.26 while the slurry nutrient value measured as nitrogen, phosphorus and potassium (NPK) values were 1.2%, 0.74% and 0.60% respectively. The NPK values are good forms of soil conditioners, but since different crops require varying concentrations of NPK, the specific requirements for each crop should be determined and the corresponding supplement values added. In this study the deficit of the NPK nutrients required for maize cultivation by a 25kg digestate was determined. The digestate was supplemented with 23kg poultry droppings for N, 23.77kg bone meal for P and 24kg wood ash.