Biofertilizer production via composting of digestate obtained from anaerobic digestion of post biocoagulation sludge blended with saw dust: Physiochemical characterization and kinetic study

•Digestate blended with saw dust was subjected to composting.•Kinetics of the composting process was investigated.•Biofertilizer was produced from digestate blended with saw dust.•The kinetic results followed second order model.•Reaction rate increased with temperature within a limited range suitable for microorganism activity. A study on biofertilizer production via oxidation of heterogeneous mass and microbial decomposition of organic matter in the digestate obtained after anaerobic digestion of post biocoagulation sludge was undertaken. The digestate was characterized. Effect of process variables on composting was investigated. The kinetics of composting was studied. The characterization results show that digestate and saw dust contains macro (nitrogen-N, phosphorus-P, magnesium-Mg, sodium-Na, Calcium-Ca and potassium-K) and micro (manganese-Mn, zinc-Zn, Fe-iron and Cu-copper) nutrients that when composted can be used as biofertilizer/soil improver. Also, the final compost (biofertilizer) contains Zn, Cr, Cu, Cd and Pb that lay within the recommended limits for agricultural use. The kinetic data fitted very well to the second order model with R2 of 0.9675 and activation energy of 1442.15 kJmol. Composting kinetic analysis showed that temperature dependence of rates reaction clearly followed the Arrhenius equation. Also, the kinetics results revealed that the degradation of organic waste could be quantitatively predicted using the second order reaction model. It can be concluded that the composting of digestate with saw dust resulted in biofertilizer production; thus, converting waste to wealth.