Circular municipal waste management: Assessing pathogen deactivation, nutrient recovery, and quality assurance of co-compost produced from dewatered sewage sludge and organic green waste

Wastewater treatment plants generate substantial amounts of sewage sludge, which poses significant environmental and public health risks if not properly managed. Therefore, this study investigated the effect of thermophilic temperatures on pathogen deactivation when producing co-compost using dewatered sewage sludge (DSS) and organic green waste (OGW). The co-composting windrows were made using the following mixing ratios: 0%DSS:100%OGW, 15%DSS:85%OGW, and 25%DSS:75%OGW which were approximately 13 m 3 each (volume basis). The temperatures observed in the co-compost windrows differed significantly (p < 0.001) between treatments. Thermophilic temperatures equal to or greater than (≥) 55 °C, necessary for pathogen deactivation, were attained for 35 days in the 0%DSS:100%OGW; 17 days in the 15%DSS:85%OGW, and 15 days in the 25%DSS:75%OGW. Moreover, the highest temperature of 72 °C > 69 °C > 64 °C was obtained in the 25%DSS:75%OGW, 0%DSS:100%OGW, and 15%DSS:85%OGW, respectively. The bacterium Escherichia coli (E. coli) concentration was 0 MPN g −1 for all co-compost piles at the end of the co-composting process. Moreover, viable eggs of the parasitic worms Ascaris and Trichuris were deactivated to undetectable limits of 0 eggs g −1 of total solids (TS). Nitrogen content was 1.19 ± 0.00%, 1.38 ± 0.00%, and 1.48 ± 0.00% in the 0%DSS:100%OGW; 15%DSS:85%OGW and 25%DSS:75%OGW, respectively. All treatments had a germination index greater than 80%, indicating that the co-compost was phytotoxic-free. Taken together, our findings highlight the potential of municipal-scale windrow co-composting to produce a hygienic, pathogen-free, and phytotoxic-free co-compost.