In-vessel composting system for converting food and green wastes into pathogen free soil amendment for sustainable agriculture

Abstract

To derive new methods for converting food and green wastes into soil amendment, this study researched on a in-vessel composting system. The performance of an in-vessel composting system was evaluated during food and green wastes digestion. A series of experiments was conducted using both pilot-scale and bench-scale in-vessel systems. During the digestion process, external heat and continuous mixing were provided for achieving the typical composting temperature of 60 °C. The feedstock included food waste, horse manure, palm-tree waste, and green waste. The digestate was tested for understanding the inactivation of pathogens (Escherichia coli (E. coli) and Salmonella enterica serovar Typhimurium LT2 (Salmonella)). Subsequently, pathogen inactivation models were developed to determine the quantitative time-dependent relationships between digestion time and potential pathogen cells in digestate. The digestate was also analyzed for evaluating the changes in pH, moisture level, variations in carbon content, and carbon to nitrogen ratio during the digestion process. Further, the effects of additives on the digestion process and digestate were evaluated by comparing the digestate quality under additive and without additives conditions. Results showed that the proposed method produced a pathogen-free soil amendment from the food and green wastes. The pH and moisture content of the digestate of pilot-scale experiment varied from 3.8 to 4 and 60.6–67.9%, respectively. The observations showed that E. coli survived greater than 10 h, while Salmonella counts were not detectable beyond 40 min of digestion. The results of predictive models showed that Salmonella could survive till 80 min during in-vessel composting at 60 °C, while the elimination of E. coli may take 16–25 h. The authors anticipate that the in-vessel digestion system, which is proposed here, will help in accelerating the conversion of organic waste into pathogen-free soil amendment, thereby, enhancing sustainable agriculture.