Dynamic assessment of nutrient evolution in fecal sludge-based organic fertilizer during a 91-day composting process

This study examines changes in the physicochemical properties of fecal sludge-based organic fertilizer during a 91-day composting period. Ten samples were monitored for temperature, pH, electrical conductivity [EC], and key nutrients—nitrogen, phosphorus, potassium, calcium, and magnesium. The process followed mesophilic, thermophilic, and second mesophilic phases, with temperatures peaking at 67 °C–70.2 °C, ensuring rapid degradation and sanitization. pH initially rose due to ammonia formation and later declined to mildly acidic levels [6.13–6.19], indicating maturity. EC increased from 1.94 to 2.87 dS cm−1, reflecting mineralization without reaching phytotoxic levels. Nutrient concentrations increased consistently: nitrogen up to 1.6%, phosphorus 0.43%, and potassium 0.73%, due to organic matter breakdown and mass reduction. Calcium and magnesium stabilized at 1.43% and 0.21%, respectively. These trends were influenced by bulking agents, microbial activity, and environmental factors like moisture, temperature, and aeration. The results confirm that co-composting fecal sludge with suitable bulking agents yields nutrient-rich, mature, and stable organic fertilizer, supporting safe reuse of human waste in sustainable agriculture.