Quantification of Greenhouse Gas Emissions from Windrow Composting of Garden Waste

Abstract

Microbial degradation of organic wastes entails the production of various gases such as carbon dioxide (CO₂), methane (CH₄), nitrous oxide (N₂O), and carbon monoxide (CO). Some of these gases are classified as greenhouse gases (GHGs), thus contributing to climate change. A study was performed to evaluate three methods for quantifying GHG emissions from central composting of garden waste. Two small-scale methods were used at a windrow composting facility: a static flux chamber method and a funnel method. Mass balance calculations based on measurements of the C content in the in- and out-going material showed that 91 to 94% of the C could not be accounted for using the small-scale methods, thereby indicating that these methods significantly underestimate GHG emissions. A dynamic plume method (total emission method) employing Fourier Transform Infra Red (FTIR) absorption spectroscopy was found to give a more accurate estimate of the GHG emissions, with CO₂ emissions measured to be 127 ± 15% of the degraded C. Additionally, with this method, 2.7 ± 0.6% and 0.34 ± 0.16% of the degraded C was determined to be emitted as CH₄ and CO. In this study, the dynamic plume method was a more effective tool for accounting for C losses and, therefore, we believe that the method is suitable for measuring GHG emissions from composting facilities. The total emissions were found to be 2.4 ± 0.5 kg CH₄–C Mg⁻¹ wet waste (ww) and 0.06 ± 0.03 kg N₂O-N Mg⁻¹ ww from a facility treating 15,540 Mg of garden waste yr⁻¹, or 111 ± 30 kg CO₂–equivalents Mg⁻¹ ww.