Performance of a Compost Aeration and Heat Recovery System at a Commercial Composting Facility

Abstract

Composting of agricultural and forestry residuals can support regional nutrient management and environmental goals but faces various operational challenges. This case study evaluated nutrient status and financial and energy cost for a pair of commercial compost windrows with and without forced aeration at full scale in a normal production setting. Compost treated with a forced aeration and heat capture system was deemed suitable for market in approximately 25% less time than a conventional, straddle-turned windrow. Analysis of nitrogen (N) dynamics throughout the study suggested that forced aeration promoted N retention. From a mass balance analysis, force-aerated compost retained ~23% more of its initial total N (TN) by mass as compared to conventionally treated compost, which we hypothesize was due to greater rates of N losses to the atmosphere in conventional treatment. Consistently lower water-extractable phosphorus (WEP) suggested a lower risk for phosphorus (P) loss through leaching from force-aerated composting. During the active composting process, operation of force-aerated composting was 2.1 times more expensive and 5.5 times more energy-intensive than a conventional compost per m 3 . However, the energy and infrastructure cost offsets provided by the aeration and heat capture system as operated by this commercial compost facility could provide a net savings of $1.51 per m 3 finished compost when analyzed over the lifetime of the system's construction, operation, and use. This case study illustrates that forced aeration and heat capture systems have potential to provide time and energy savings benefits to compost producers, while maintaining or enhancing nutrient retention and compost quality.