Hygiene Quality of Recycled Organic Matter Composts Available for Commercial Farming.

Recycled organic matter (ROM) composts are increasingly available for commercial farming with food chain implications. Compost is prepared from ingredients such leaf and yard debris and may include food scraps and manures. The emergence of new bacterial pathogens in the food chain has increased public perception of potential risks. Compost quality standards exist for certified organic farming. However, non-sludge composts not regulated under federal EPA rules are also widely used and 47% of states do not specify hygiene tests. We examine bacterial content of 94 market-ready composts in three states (WA, OR, CA) where exceptional recycling occurs but regulations on composting vary. We observed a statistically significant relationship of fecal coliform and E. coli bacteria (r²= 0.85, p<0.0001) suggesting validity of the fecal coliform test as a pathogen indicator. There was no correlation of fecal to Salmonella found in only 1 facility at low levels. Presence/absence of allowed manure in green composting also had no statistical relationship to fecal coliform levels, suggesting that manure alone is not the only source of fecal bacteria. Three composts were positive for E. coli-O157:H7 and were situated in commercial vegetable regions. Compost facility factors that had a significant impact on apparent hygiene were throughput size, turning technology and maturity. Of facilities handling less than 45,000 mt/a, only 7% did not meet the EPA fecal coliform standard whereas 31% of samples from large facilities (>45,000 mt/a) did not. Samples that were more mature significantly differed from compost not tested mature with regard to E. coli content. Since many composts in this study were found to be essentially pathogen free, improved hygiene standards are clearly achievable. More effort is needed to classify management practices in relation to attaining compost maturity and reducing hygiene risks for commercial farming.