Process optimization for sustainable bio-fertilizer quality of digestate improvement from anaerobic co-digestion of organic wastes

Digestates, the byproduct of biogas production, produced by biogas facilities must be appropriately processed for further application. This study investigates the optimization of operating parameters for bio-fertilizer quality derived from biogas digestate through anaerobic co-digestion of biomasses. Since the Nitrogen (N), Phosphorus (P), and Potassium (K) content in mono-digestion is relatively low, co-digestion of cow dung (CD) with banana peel (BP), food waste (FW), and poultry manure (PM) under ambient conditions were explored. Response-Surface-Methodology (RSM) is used to optimize the bio-fertilizing value of biogas digestate. 75CD:25BP, 50CD:50FW, and 75CD:25PM were obtained highest biogas production coded as A, B, and C respectively. Design-Expert V13 was used to evaluate and model the optimization experiment data, and significance was recognized at a 0.05 level of probability ( P < 0.05). Experimental data yielded highly statistically significant regression model equations from the Central-Composite-Design (CCD) approach, with R 2 = 0.9887, 0.9819, and 0.9914 for P, N, and K, respectively. At the optimum temperature of 35 °C and retention time of 22.5 days the optimum value of K, N, and P have 1.28%, 1.65%, and 0.88% for substrate A, B, and C respectively. The study found that the improvement of biofertilizer quality through balancing of nutrients from biomass wastes.