Optimization of windrow food waste composting to inactivate pathogenic microorganisms

Composting is a popular means of treating organic wastes. Properly controlled composting can destroy the pathogenic microorganisms present in wastes for environmentally friendly end product. Optimization of windrow composting of food waste, manure, and bulking agents was evaluated for maximum pathogen inactivation (Salmonella and E. coli O157:H7). Seasonal effects on reductions of Salmonella and E. coli O157:H7 related to the compost temperatures were studied (90-150 days). Fecal conforms and fecal streptococcus were also monitored during composting. The results of this study indicated that seasonal differences caused significant effects on the peak temperatures and the duration of high thermophilic temperatures (≥5°C) of windrows. Winter conditions resulted in inconsistent inactivation of pathogenic microorganisms including regrowth to high values during several time intervals. The reduction levels of Salmonella spp. and E. coli O157:H7 ranged from initial ranges of 377-483 MPN/g to final ranges of 6-150 MPN/g in winter, and to ≤ 0.3 MPN/g in summer. It was also observed that summer composting resulted in a better correlation (r²>0.90) between number of fecal conforms and the pathogenic microorganisms (Salmonella spp and E. coli O157:H7). Fecal streptococcus was slightly reduced in most trials from 377-483 to 221-514 MPN/g in winter and from 365-460 MPN/g to a range of 11-265 MPN/g in summer. Extreme Vertices Mixture Design (EVMD) analysis suggested an optimum mixture as: 43.3% food waste, 28.3% manure, and 28.3% bulking agents. The performance of the optimum mixture has been validated, achieving a high level of inactivation of pathogens similar to previous trials, good correlations of fecal coliforms to the pathogens of interest, and high resistance of fecal streptococcus. Therefore, it was concluded that the EVMD design was successful in optimizing windrow composting for maximum pathogen reduction.