Hygienic Implications of Small-Scale Composting in New York State

Abstract

Small-scale composting is an effective way to recycle organic wastes generated in the home and/or community. Little research has been done to determine potential human health risk of composts generated on a small scale. Bacteriologic testing of twenty composts from across New York State representing a wide variety of small-scale composting practices and situations was conducted. No statistical relationships were found between concentrations of total coliforms, fecal coliforms, enterococci, Escherichia coli, Salmonella spp., and Clostridium perfringens, indicating that none of these organisms could be considered a good indicator of general microbial presence. Compared with microbial standards for sewage sludge composts, these composts generally met those standards. Basic compost parameters were also analyzed. Water holding capacity ranged from50% to 246%, organic matter 9% to 80.5%, C to N ratio 10.4 to 29, Total Kjeldahl Nitrogen 0.185% to 2.419%, density 24 lb/ft3to 82 lb/ft3, solids 27.7% to 75.6%, moisture 24.4% to 72.3%, pH 6.54 to 8.65, and Solvita maturity from 3 to 7. No statistically significant relationships at the p=0.1 level were found between microbial concentrations and compost parameters. However, the relationship between pH and TKN was close to the statistical cut off, with higher pH and TKN associated with higher concentration of microbes. An unanticipated finding was that the two laboratories used for bacteriological testing employed different methodologies to look for the same bacteria which may account for some of the discrepancy in results between the labs. Researchers and composters alike need to ensure methods appropriate for compost are used. The results of this research led to a recommendation to follow good hygiene practices (such as washing hands) when working with composts. Similar practices are advisable when dealing with any soil material since these too may contain bacterial pathogens.