Methane oxidation in a biofilter (Part 1): Development of a mathematical model for designing and optimization

Impact of temperature on the performance of compost-based landfill biocovers

Methane (CH4) emissions from landfills are a major contributor to global greenhouse gas emissions. Compost-based biocovers offer a viable approach to reduce CH4 emissions from landfills; however, the effectiveness in climates with varying temperatures is not well understood. The methane removal performances of two compost-based biocover materials (food and yard waste compost) were examined under different temperature conditions using laboratory column experiments. A reactive transport model was used to simulate the experimental results to develop a better quantitative understanding of the effect of temperature on overall methane removal efficiency. As expected, experimental results indicated that the oxidation rate was influenced by temperature, as it was reduced when the temperature decreased from 22 °C to 8 °C. However, some oxidation was observed at a lower temperature, which was confirmed by CO2 concentrations above the initial level and the observed temperatures above the exposure temperature along the height of biocover column. Furthermore, results showed that when the compost-based materials were subjected to 8 °C and then increased to 22 °C, methane oxidation within the material recovered quickly and returned to similar oxidation rates as observed before the temperature was reduced, suggesting that compost-based biocovers may not be affected by cyclic temperature variations when used in colder climates. Methane oxidation capacity was limited by the maximum oxidation rate, the biocover porosity, and the gas saturation profile that affects residence time and overall methane oxidation in the columns. The model results show that the CH4 oxidation rate was reduced by one order of magnitude when the temperature decreased from 22 °C to 8 °C. Therefore, the calculated Q10 values were 4.19 and 5.18 for the food and yard waste compost, respectively. Overall, compost-based landfill biocovers, such as food and yard waste compost, are capable of mitigate CH4 emissions from old and small landfills under different temperature conditions.

Dynamic modeling of anaerobic methane oxidation coupled to sulfate reduction: role of elemental sulfur as intermediate

The process dynamics of anaerobic oxidation of methane (AOM) coupled to sulfate reduction (SR), and the potential role of elemental sulfur as intermediate are presented in this paper. Thermodynamic screening and experimental evidence from the literature conclude that a prominent model to describe AOM-SR is based on the concept that anaerobic methane oxidation proceeds through the production of the intermediate elemental sulfur. Two microbial groups are involved in the process: (a) anaerobic methanotrophs (ANME-2) and (b) Desulfosarcina/Desulfococcus sulfur reducers cluster (DSS). In this work, a dynamic model was developed to explore the interactions between biotic and abiotic processes to simulate the microbial activity, the chemical composition and speciation of the liquid phase, and the gas phase composition in the reactor headspace. The model includes the microbial kinetics for the symbiotic growth of ANME-2 and DSS, mass transfer phenomena between the gas and liquid phase for methane, hydrogen sulfide, and carbon dioxide and acid-base reactions for bicarbonate, sulfide, and ammonium. A data set from batch experiments, running for 250 days in artificial seawater inoculated with sediment from Marine Lake Grevelingen (The Netherlands) was used to calibrate the model. The inherent characteristics of AOM-SR make the identification of the kinetic parameters difficult due to the high correlation between them. However, by meaningfully selecting a set of kinetic parameters, the model simulates successfully the experimental data for sulfate reduction and sulfide production. The model can be considered as the basic structure for simulating continuous flow three-phase engineered systems based on AOM-SR.