UBC Theses and Dissertations

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UBC Theses and Dissertations

An investigation of in-vessel composting process control strategies Fraser, Bud S.


Composting provides environmental benefits including an alternative method for organic waste disposal, as well as improving soil fertility. However poor compost quality and odour emission are often significant problems in the composting industry. Composting process control can potentially help reduce both of these problems. In spite of the recent development of a number of process control strategies, very few direct comparisons have been made between these, particularly in terms of compost quality and odour emission. To help address this need, a series of experiments was conducted to evaluate the effects of several in-vessel process control strategies on compost quality and odour emission. The strategies tested focussed on aeration control, which in turn affects temperature, oxygen, and moisture, the most important conditions for microbial activity. Fixed aeration (Beltsville method), temperature feedback (Rutgers method), oxygen feedback, and combined temperature/oxygen feedback were tested. A modified algorithm based on temperature, called linear temperature feedback, was also developed and tested. Results showed that while many quality parameters such as C:N ratio and organic matter loss were similar between process control methods, compost oxygen was maintained more consistently using oxygen feedback or linear temperature feedback methods; these methods may also provide greater nitrification and lower phytotoxicity. Linear temperature feedback is preferable to oxygen feedback in that it does not require oxygen sensors to operate. Odorous gas (including ammonia) mass emission rates were typically found to increase with higher aeration rates, such as those used to limit temperature, though the gas concentration was lower. For maximum retention of nitrogen, adequate supply of readily biodegradable carbon in the feedstock is vital.

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