title: A mass balance model to estimate the rate of composting, methane oxidation and anaerobic digestion in soil covers and shallow waste layers.
abstract: Although CH4oxidation in landfill soil covers is widely studied, the extent of composting and CH4oxidation in underlying waste layers has been speculated but not measured. The objective of this study was to develop and validate a mass balance model to estimate the simultaneous rates of anaerobic digestion (rAD), CH4oxidation (rOX) and composting (rCOM) in environments where O2penetration is variable and zones of aerobic and anaerobic activity are intermingled. The modelled domain could include, as an example, a soil cover and the underlying shallow waste to a nominated depth. The proposed model was demonstrated on a blend of biogas from three separate known sources of gas representing the three reaction processes: (i) a bottle of laboratory grade 50:50% CH4:CO2gas representing anaerobic digestion biogas; (ii) an aerated 250mL bottle containing food waste that represented composting activity; and (iii) an aerated 250mL bottle containing non-degradable graphite granules inoculated with methanotrophs and incubated with CH4and O2to represent methanotrophic activity. CO2, CH4, O2and the stable isotope13C-CO2were chosen as the components for the mass balance model. The three reaction rates, r (=rAD, rOX, rCOM) were calculated as fitting parameters to the overdetermined set of 4mass balance equations with the net flux of these components from the bottles q (= [Formula: see text] , [Formula: see text] , [Formula: see text] and [Formula: see text] ) as inputs to the model. The coefficient of determination (r2) for observed versus modelled values of r were 1.00, 0.97, 0.98 when the stoichiometry of each reaction was based on gas yields measured in the individual bottles and q was calculated by summing yields from the three bottles. r2deteriorated to 0.95, 0.96, 0.87 when using an average stoichiometry from 11 incubations of each of the composting and methane oxidation processes. The significant deterioration in the estimation of rCOMshowed that this output is highly sensitive to the evaluated stoichiometry coefficients for the reactions. r2deteriorated further to 0.86, 0.77, 0.74 when using the average stoichiometry and experimental measurement of the composition and volume of the blended biogas to determine q. This was primarily attributed to average errors of 8%, 7%, 11% and 14% in the measurement of [Formula: see text] , [Formula: see text] , [Formula: see text] and [Formula: see text] relative to the measurement of the same quantities from the individual bottles.
authors.affiliation: Centre for Solid Waste Bioprocessing, Schools of Civil and Chemical Engineering, The University of Queensland, Brisbane 4072, Australia.
authors.forename: Reza
authors.initials: R
authors.lastname: Rafiee
authors.affiliation: Centre for Solid Waste Bioprocessing, Schools of Civil and Chemical Engineering, The University of Queensland, Brisbane 4072, Australia.
authors.forename: Lizanne
authors.initials: L
authors.lastname: Obersky
authors.affiliation: Centre for Solid Waste Bioprocessing, Schools of Civil and Chemical Engineering, The University of Queensland, Brisbane 4072, Australia.
authors.forename: Sihuang
authors.initials: S
authors.lastname: Xie
authors.affiliation: Centre for Solid Waste Bioprocessing, Schools of Civil and Chemical Engineering, The University of Queensland, Brisbane 4072, Australia. Electronic address: william.clarke@uq.edu.au.
authors.forename: William P
authors.initials: WP
authors.lastname: Clarke
mesh_terms: D000393:Air Pollutants / Q000032:analysis*; D008697:Methane / Q000032:analysis*; D008956:Models, Chemical; D010084:Oxidation-Reduction; D012037:Refuse Disposal / Q000379:methods* / Q000706:statistics & numerical data; D012987:Soil; D012988:Soil Microbiology; D064091:Waste Disposal Facilities / Q000706:statistics & numerical data*
chemical_list: D000393:Air Pollutants; D012987:Soil; D008697:Methane
keywords: Aerobic processes; Carbon isotopes; Composting; Landfill; Mass balance