A New Method to Estimate the Effects of Ambient Wind on the Open Chamber Measurement of Biofiltered Compost Pile Emissions

Commercial composting has become increasing popular as a method to produce fertilizer while diverting organic waste from landfills. Composting produces various emissions, including those of greenhouse gases, so there has been an interest in reducing those emissions using biofiltration. One form of biofiltration used in commercial facilities involves pumping compost emissions through a exposed pile of coarse woody debris. Measurement of the effectiveness of this biofiltration is challenging, and may be accomplished with open chambers and flow measurements. Similar chambers with portals open to the atmosphere are used for flux measurements from soils and other compost pile types, instead of closed chambers, to reduce measurement errors caused by artificial modification of the closed chamber microclimate. We establish a methodology to estimate biofiltration efficiency and emissions, including a new technique to account for infiltration of the ambient wind into the biofilter and the open chambers themselves. Results from a pilot study at an active commercial facility show that biofiltration significantly reduces greenhouse gas emissions of methane and nitrous oxide. These results also show that not accounting for ambient wind leakage into chambers yields potentially large errors in the estimation of the biofiltration efficiency and greenhouse gas emissions. Our work implies that chambers with open portals, to be used for soil flux measurements for carbon dioxide and other trace gases, could suffer from wind leakage problems that must be accounted for. The methodology described here, which includes the use of a relatively inert, ambient trace gas, could allow development of correction factors for wind leakage for such chambers.