Estimation of VOC emission factors for manure compost using continuous measurements by PTR-MS

Abstract:

The composting process is known to emit volatile organic compounds (VOCs), ammonia (NH₃), and green-house gases (GHG) such as CH₄ and N₂O. VOCs can cause odor and act as precursors for photochemical ozone and PM_2.5. Estimation of correct VOC and GG emission factors (EFs) allow air quality managers to implement applicable regulations and evaluate appropriate emission control technology. In this study, emissions monitoring was conducted using a 100-gallon tank filled with ~ 400 lbs of compost feedstock consisting primarily of solid manure waste from a diary. Tanks were positively aerated. Four experiments were conducted where GHG and VOC emissions were continuously measured. VOCs were measured using proton transfer mass spectrometry (PTR-MS). Discrete canister sampling was also done, and VOCs analyzed by GC-MS. Continuous measurements clarified that compounds such as alcohols and monoterpenes have largest emission rates during first days of composting. Monoterpenes, acetone, 2-butanone, methanol, dimethyl sulfide, and dimethyl disulfide were identified as the most abundant VOCs emitted. Total VOC emission factors (EF) were ~ 0.01 lbs/wet ton compost for three tanks and 0.19 lbs/wet ton for one tank with higher moisture level. These rates are significantly lower than emission factors of ~ 3.5 lbs VOC/ wet ton reported from green waste composting. Estimated EF for CH₄ was about 0.0005 MT CO₂e / wet ton. EFs for N₂O varied in the range of 0.002 to 0.02 MT CO₂e / wet ton. Emission rates of GGs are much lower than those reported by IPCC; 0.091 MT CO₂e/ton for CH₄ and 0.081 MT CO₂e/ton for N₂O likely due to the role of aeration.