Co-pyrolysis of Eppawala Rock Phosphate and Potassium Feldspar with Fish Waste and Rice Husk as Base Feedstock for Enhancing Nutrient Availability in Biochar

Abstract

The demand for biochar as a soil amendment is increasing due to its ability to enhance soil properties and sequester carbon. While conventional biochar is known to improve soil quality, it is not commonly recognized as a source of nutrients because the thermochemical conversion process often results in the loss or leaching of the nutrients in the biochar feedstock biomass. This research aimed at developing a novel method for manufacturing nutrient enhanced biochar by pyrolyzing organic matter with inorganic matter. Here, a combination of rice husk (RH) and fish waste (FW) were utilized as organic feedstocks, while Eppawala Rock Phosphate (ERP) and Potassium Feldspar (PF) were employed as inorganic additives, for the pyrolysis process by keeping the mixture in a small, closed tubular reactor in the muffle furnace. Seven different RH: FW: ERP: PF ratios were used; 70:20:5:5, 55:30:7.5:7.5, 40:40:10:10, 75:20:5:0, 75:20:0:5, 50:40:10:0, 50:40:0:10, respectively. Totally, twenty one different combinations were utilized at 30 minutes retention time at temperature of 550 ◦C. The produced biochar was evaluated for its physicochemical properties following the biochar quality standard test protocol. Biochar generally had a basic pH, while electrical conductivity and total dissolved solids showed no correlation with mixing ratios. Potassium availability varied with mixing ratios, increasing with higher PF. Phosphorus availability also varied with mixing ratios, increasing with higher ERP ratios. The study reported the highest phosphorus content as 1816.6 mg/L and the highest potassium content as 7986 mg/L. In conclusion, copyrolysis of organic and inorganic matter seems promising method to manufacturing biochar with high nutrient content.