Exhaust Gas Concentrations and Elemental Losses from a Composting Drum Treating Horse Manure

A farm scale composting drum was used to study exhaust gases from horse manure, and from horse manure mixed with tomato plant residues (TPR) with a lower C/N ratio. To study whether this addition increased gaseous losses of nitrogen (N) and sulphur (S), selected gas compounds of carbon (C) and N, and sulphur dioxide (SO2), were measured on three dates by Fourier Transform Infrared spectroscopy (FTIR). From the gas production in the drum (g per kg wet substrate), and the content of C, N and S in substrates, elemental losses of C, N and S were assessed. Temperatures in the substrate inside the drum reached 55–60 °C. The production of methane (CH4) increased when the mean retention time increased from about 2 to 6.3 days. Replacing 50% of the substrate weight by TPR slightly increased the production of NH3, but not of N2O, NO2 or SO2. We did not find increased losses of C, N or S after addition of TPR, but the production of NH3 and SO2 fluctuated much more. The mean production of nitrous oxide (N2O) and CH4 comprised 15 g CO2 equivalents per kg wet substrate, ranging from 8 to 27. Nitrous oxide comprised 80–90%. Over three gas measurements, drum treatment reduced the C content in wet substrate by 7–10%, the N content by about 2% and the S content by 0.2–1%.