Effects of process conditions on composting efficiency and nitrogen immobilization during composting of manure in a drum composting system

Effects of process conditions (i.e. change in the rotation and air flow speed and rhythm) were studied to determine their influence on process efficiency and on nitrogen balance in two separate drum composting experiments. Composting was carried out on a farm scale horizontal, continuously working drum composting system with controlled rotation and air flow, daily infeeding and outfeeding, and seven days in-vessel processing time. Experiments were conducted with processing cattle manure and straw or peat as bulking agent, and changes in temperature, hygienization, N-min, C/N ratio, C-tot and N-tot were determined. Along with changes in rotation speed, air flow and rotation rhythm, N immobilization and composting efficiency changed profoundly when manure was composted with straw. Composting efficiency was not markedly affected by process conditions when manure was composted with peat, however, loss of N decreased with reducing rotation speed, and decreased still more with lowering air flow. It was clearly demonstrated in the composting experiments reported in this paper, that it is possible to find process conditions for drum composting, which enable, at the same time, optimal composting, satisfactory hygiene and N immobilization.