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.