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%.