Controlled, High Rate Composting of Mixtures of Food Residuals, Yard Trimmings and Chicken Manure

Abstract

Three mixtures of ground yard trimmings (50 percent by volume in each mix), chicken manure (50, 27 and 40 percent) and potato processing, gelatin and bakery wastes were composted in four pilot-scale, 208 liter, insulated vessels (the first mixture was replicated). The mixes were obtained from a commercial composter and were studied both to obtain kinetic parameters for materials of this type and to help solve a problem of inconsistent maturity of product at the commercial operation. A 65°C set point controlled a high/low fan aeration system for each vessel. Temperature (at several points), air flow, oxygen consumption, carbon dioxide evolution and ammonia production were monitored. The vessels were weighed and materials were remixed twice each week during a four week composting period. At each remix, water was added to maintain a 50 percent by weight moisture content, and samples were taken for moisture content, volatile solids, chemical composition (including C:N ratio), pH and compost stability determinations. Results showed that C:N ratios were reduced from the 13 to 20 range, initially, down to 11 to 12 for all three mixes. Dry matter loss was from 31.6 to 33.7 percent for the different mixes (50 to 54 percent reduction in organic matter). Loss rate peaked at six percent/day on day 2 for mixes 1 and 3 and at three percent/day on day 11 for mix 2. Additionally, in the early, active portion of the process and at the low fan rate used, it was found that the system could go completely anaerobic in about an hour.