Aerobic degradation processes in active landfill cells

Abstract

II | P a g e ABSTRACTA landfill is built up in cells with each cell filled in layers. Layers are covered with soil, typically 200 to 300mm thick as a temporary measure to maintain sanitary conditions. A thicker cover, typical 500mm, would be placed over a completed cell. Previous researchers have measured O 2 concentrations at shallow depth beneath soil covers as well as high concentrations of CO 2 relative to CH 4 from the surface of soil layers.Despite evidence of the ingress of O 2 through soil covers, the extent that the uppermost waste beneath soil covers is degraded aerobically has not been quantified. A major challenge in the quantification of aerobic processes in beds of soil covered waste is that CH 4 oxidation, composting and anaerobic digestion could occur simultaneously in different zones close to the surface of the bed.The objectives of this study were: To develop and verify a mass balance model for a waste bed exposed to atmosphere at the upper surface to determine the rate of CH 4 oxidation (r ox ), composting (r com ) and anaerobic digestion (r AD ) based on surface fluxes of gas components and concentrations of the same components at the base of the bed; and  To apply and validate the model on packed beds of fresh waste with a surface exposed to atmosphere in order to determine the contribution of aerobic processes to waste degradation. The mass balance model that was developed is a steady state mass balance of the gaseous components CH 4 , CO 2 , O 2 and the stable isotope III | P a g e  Reactor 1 was fed with CH 4 at the base of bed. Reactor 2 was flushed with 2-Bromoethanesulfonate to partially suppress CH 4 generation and therefore CH 4 oxidation. Reactor 3 contained a bed covered by a 10-15cm layer of soil to limit O 2 intrusion. Reactor 4 was the control reactor, containing the same amount of waste and operated in the same manner as the other reactors.The consumption rate of O 2 and the production rates of CH 4 and CO 2 were measured on-line while the production of 13 C-CO 2 was measured by manual sampling and analysing at 10-15 day intervals.The mass balance model was used to estimate r at each 13 C-CO 2 sampling event over the course of experiment (26 weeks). The result of this experiment showed that anaerobic digestion, CH 4 oxidation and composting occurred simultaneously in both the covered and uncovered beds.The emitted biogas in the uncovered beds implied that they were fully aerobic. The results of mass balance model, however, revealed that both r AD and r OX were significant and based on an integration of r AD , 49% of the beds COD was degraded anaerobically. The generated CH 4 was subsequently oxidized leading to a minimal CH 4 emissions from the uncovered beds. Similarly, approximately 35% of the total emitted C from the soil covered bed was CH 4 , superficially implying this was the only bed supporting anaerobic activity. However, the mass balance model showed r AD was only marginally enhanced by the presence of soil layer with 68% of the solids (COD basis) degradedanaero...

Aerobic processes in landfill: an Australian field trial

“…The first phase of the overall project was developed by R.Rafiee (Rafiee, 2016) with a mass balance method on four components of O2, CO2, CH4, δ 13 C-CO2 applied to a series of pilot reactors simulating semiaerobic landfill conditions. The initial proposal for this thesis was originally designed as a mass balance on six components including: O2, CO2, CH4, δ 13 C-CO2, δ 13 C-CH4 and δ 2 H-CH4 for application to a fresh waste lift at an operational landfill.…”

“…This can be expressed in terms of a mass balance with isotope values, assuming all of the low molecular weight organic carbon substrate (CLMW) is produced and subsequently converted to CO2 or CH4: The δ 13 C-CLMW used for this study was adopted from previous classification of waste from the same facility and stage as -24.1‰ (Rafiee, 2016, Rafiee et al, 2017.…”

“…The described rates (rAD, rOX and rCOM) have been previously estimated in laboratory reactors that contained packed beds of waste overlain with soil sourced from the same landfill batter (Rafiee, 2016). These rates were determined from the measurement of the net fluxes of CH4, CO2, O2 and 13 C-CO2 with mass balances for each of these four components.…”

“…With ranging from 0.7 -0.8 expressed on a molar basis as reported from a variety of experimental studies (Perera et al, 2002, Lei et al, 2014, Rafiee, 2016.…”