Effects of compost characteristics on nutrient retention and simultaneous pollutant immobilization and degradation during co-composting process

•A volume model technique was developed for controlled liquid manure addition.•Swine effluent and small bulking material sizes enhanced organic matter degradation.•Liquid manure types influenced nutrients and heavy metals retention potentials.•Reduced leachate generation was achieved via optimized co-composting condition. This study was conducted to examine the effects of controlled addition of liquid (LM) to solid (SM) manure compost using a volume-model technique on the co-composting of SM and LM, and further to investigate the major effects of bulking material sizes and LM types on the co-composting process and final compost characteristics. Results indicated that this volume-model technique played a critical role in reducing leachate generation and improving the overall efficiency of the co-composting process. Specifically, the developed model enhanced the evaporation rates of windrows during the co-composting process. For improved final compost properties, small bulking materials and swine-effluent-based LM were found to be more efficient for organic matter degradation, LM consumption, hazardous metals immobilization, and essential nutrients retention than large bulking materials and biogas-based LM. Thus, process parameter optimizations represent major research options for successful co-composting applications for the future.