Minimising odour formation in composting of biowaste

In Finland biowaste treatment is mainly based on composting. Composting plants are considered as one of the most common reasons for odour complaints. Odours can be managed by treating the gases that leave the system and by manipulating the composting process to prevent their formation and/or emission. Manipulation of the process which has generally been regarded as a black box, presumes an understanding of odour formation and removal mechanisms. The main objective of this study was to gain knowledge on odour formation in composting processes and apply new methods to optimise industrial composting processes and to reduce odour problems. Special focus was put on examining possibilities for on-line process monitoring based on gas analysis. Pilot-scale tests for process enhancement were performed with different bulking material and composting accelerators. Gas samples were drawn from compost processes both from inside the compost bulk and the process emission. Chemical composition and components were analysed on-line with a combination of FT-IR and three dimensional gas chromatography. Off-gas samples were analysed with olfactometry. There was no consistent indicator for high odour emission. Odour data was correlated with microbiological, chemical and physical parameters of the composting bulk. These analyses gave neither a clear indication of any single parameter relating to off-gas odour concentration. Gas analysis and physico-chemical measurements of the compost mass indicated that hardwood chips provided the best conditions for aerobic degradation and gave the lowest odour level. Studies of odour formation of drum process after the addition of compost accelerating agents showed that compost accelerators do not necessarily diminish the waste gas odour concentration. It could be shown that the choice of bulking material can be an economical way to diminish the total odour load.