Modeling the anaerobic treatment of sulfate-rich urban wastewater: Application to AnMBR technology

Abstract

Although anaerobic membrane bioreactors (AnMBR) are a core technology in the transition of urban wastewater (UWW) treatment towards a circular economy, the transition is being held back by a number of bottlenecks. The dissolved methane released from the effluent, the need to remove nutrients (ideally by recovery), or the energy lost by the competition between methanogenic and sulfate-reducing bacteria (SRB) for the biodegradable COD have been identified as the main issues to be addressed before AnMBR becomes widespread. Mathematical modeling of this technology can be used to obtain further insights into these bottlenecks plus other valuable information for design, simulation and control purposes. This paper therefore proposes an AnMBR anaerobic digestion model to simulate the crucial SRB-related process since these bacteria degrade more than 40% of the organic matter. The proposed model, which is included in the BNRM2 collection model, has a reduced but all-inclusive structure, including hydrolysis, acidogenesis, acetogenesis, methanogenesis and other SRB-related processes. It was calibrated and validated using data from an AnMBR pilot plant treating sulfate-rich UWW, including parameter values obtained in off-line experiments and optimization methods. Despite the complex operating dynamics and influent composition, it was able to reproduce the process performance. In fact, it was able to simulate the AD of sulfate-rich UWW considering only two groups of SRB: heterotrophic SRB growing on both VFA (propionate) and acetate, and autotrophic SRB growing on hydrogen. Besides the above-mentioned constraints, the model reproduced the dynamics of the mixed liquor solids concentration, which helped to integrate biochemical and filtration models. It also reproduced the alkalinity and pH dynamics in the mixed liquor required for assessing the effect of chemical precipitation on membrane scaling.