Mathematical Modeling of SMP Production in Membrane Bioreactors: Choosing an Appropriate Model Structure

The ability to predict the soluble microbial product (SMP) concentration, a key MBR foulant, with mathematical models provides the opportunity to use foulant production as an MBR design and optimization parameter. This study examined the assumptions of two widely-applied model structures regarding the mechanisms of SMP production. The production mechanisms evaluated are (1) the erosion or hydrolysis of floc-associated extracellular polymeric substance (EPS) and (2) biomass decay. The models were compared based on their ability to predict SMP concentrations observed in an MBR system during a period of increased SMP and flocassociated EPS production due to increased predation. Predation was an important contributor to overall biomass decay. Both erosion of floc-associated EPS and biomass decay were shown to be important mechanisms of SMP production. Therefore, both mechanisms should be included in the mathematical model used to predict SMP concentrations because the dominant mechanisms of SMP production changes with key process parameters, most notably the solids retention time.