Dynamic modeling and simulation of the impact of micro-aeration on anaerobic treatment of sulfate-rich wastewater

Abstract

This study investigates the application of micro-aeration to remove dissolved sulfide produced during the anaerobic treatment of wastewater containing sulfate. A completely mixed batch reactor was used to develop a dynamic model of batch anaerobic digestion with micro-aeration of the liquid phase using Bio Win (version 6.2) software to simulate the performance of sulfate reduction and sulfide oxidation in a single reactor unit. When calibrating the micro-aerated model, maximum specific growth rate for sulfur-reducing acetotrophic bacteria was set to 0.38 d’1, switching function of sulfur reducing pathway DO half saturation concentration was set to 0.0001 mgOifL and air was introduced to the system at two stages; for 12 hours at a rate of 0.018 m3/hr and another 12 hours at a rate of 0.015 m3/hr. When comparing the calibrated micro-aerated model and the strictly anaerobic model, rate of sulfate reduction reduced with micro-aeration, but complete removal could be expected. Although methane production improved over the first half of the time period in calibrated micro-aerated model, a negative impact of the presence of oxygen on methanogens could evident when the oxygen presents in the system beyond 13 hours. The calibrated micro-aerated model showed a significant decrease in dissolved sulfides when compared to the anaerobic model. Moreover, an average of 80% H2S removal could be achieved with micro-aeration. It indicates the possibility of adapting micro-aeration in liquid phase of anaerobic reactors to reduce formation of gaseous H2S by oxidizing dissolved sulfides to elemental sulfur, alongside the simultaneous removal of sulfate.