| Abstrakt: |
Effects of composting on odorous chemicals in dairy manure were investigated in replicated pilot-scale studies. Three 16-day composting trials were conducted, using 205 L vessels containing 83 kg mass. Fresh or 12-day-aged manure, from lactating cows, was mixed with sawdust (3man:1saw w/w). Vessels were either aerated continuously with high (2.3 kg/hr)/low (0.8 kg/hr) air flow controlled by thermostats or intermittently on a 5 min high air flow/55 min off clock controlled cycle. Six vessel replicates were conducted on each manure/air flow treatment combination. Temperatures, air flow, O2consumption, and CO2production were recorded every 10 minutes. Trapped NH3emissions were determined daily. Exhaust air was passed through water-cooled condensers to analyze emitted volatiles, and condensate volume, pH, and volatile fatty acids (VFAs) were quantified at 12 or 24 hour intervals. Solids were collected from each vessel initially, at remix at the end of day 7, and at the end of each trial (day 16) for analysis of moisture, pH, ash, C/N, and odorants. Phenolics and indolics were extracted with ethyl ether. VFAs were recovered with pH 2.0 water. Analysis was by flame or mass selective detection gas chromatography. Temperature increased most rapidly in continuously aerated vessels yet maintained a lower mean temperature (49 vs 58°C) than intermittent aeration. Both returned to near ambient temperature by day 16. Continuous aeration nearly doubled (11 vs 18 L) the amount of condensate released over 16 days. Fresh manure/sawdust mixes contained 6553, 795, 77, 51, 19, and 17μg/g of acetate, propionate, isobutyrate, isovalerate, phenol, and p-cresol. Aged manure mixes contained 9350, 3397, 2810, 445, 285, 441, 34, 176, and 18 μg/g acetate, propionate, butyrate, valerate, isobutyrate, isovalerate, phenol, p-cresol, and skatole, as well as a number of C11to C17fatty acids. Both aeration methods maintained conditions that resulted in the destruction of most of the odorous chemicals studied in the composting mass in 7 days with only small quantities of acetate, isobutyrate, and skatole present by the end of day 16. Continuous aeration, as opposed to intermittent, more than doubled (115 vs 55 g) the emissions of NH3-N and increased the emissions of VFAs in condensate four-fold. Whereas, limited aeration did not destroy the odorants as rapidly, they remained in the compost until destruction. |
