Integrated windrow-based co-composting of domestic wastewater treatment plant sludge and solid waste for high-quality compost fertilizer production

Background: This study aimed to explore the feasibility of producing compost fertilizer through co-composting solid waste materials and dewatered sludge from the domestic wastewater treatment plant (WWTP) at Gole-Gohar Mining and Industrial Company, employing the windrow method with various treatments. Methods: In this experimental study, three windrow piles were established, each with a volume of 0.3 m3 and weight ratios of 1:2 (food waste:dewatered sludge) and 1:4 (garden waste:dewatered sludge), along with a control group without sewage sludge (SS) modification. The parameters influencing the compost production process, including temperature, moisture content, volatile solids, pH, electrical conductivity (EC), organic carbon, organic matter, C/N ratio, heavy metals, density, alkalinity, phosphorus content, microbial load, cations and anions were examined. Results: The results showed that the concentrations of heavy metals and pH levels in all three compost piles fell within acceptable ranges. EC values fluctuated between 2 and 6 mS/cm across all piles. The C/N ratio decreased, with the pile containing sewage treatment plant sludge and food waste achieving the optimal range of 15-25. The germination index (GI) for lettuce, cress, and mung bean seeds was higher than the standard in all three piles. The produced compost was classified as Class A in terms of microbial load. Conclusion: Overall, the physicochemical parameters of the produced composts met standard limits. According to the results, compost-containing food waste emerged as the most suitable for agricultural use.