Response surface optimization of anaerobic self-forming dynamic membrane (AnSFDM) formation: Dominant parameter, interaction relationship and experimental evidence

Anaerobic self-forming dynamic membrane (AnSFDM) bioreactors have attracted increasing attention owing to their cost-effectiveness and lower carbon footprint. AnSFDM formation is the initial process of their operation and of pivotal importance for determining the basic characteristics of AnSFDMs. Nevertheless, the effect of operational parameters on the AnSFDM formation process has not been studied in a systematical and quantitative manner. In this study, response surface methodology was for the first time, applied to elucidate the effect of mixed liquor suspended solids concentration, stirring speed and flux as well as their interactions on the characteristics of newly formed AnSFDMs, i.e., formation time, filtration resistance and fouling propensity. Response surface methodology analysis quantified the effect degree regarding different operational parameters and evaluated interaction effects. At higher flux and mixed liquor suspended solids concentration, the formation time of AnSFDMs shortened while their filtration resistance and fouling propensity increased. As stirring speed increased, the formation time of AnSFDMs increased while their filtration resistance and fouling propensity decreased first (200-250 rpm) and then increased (250-300 rpm). Experimental evidence showed that the operational parameters affecting AnSFDM formation primarily via modifying particle size and extracellular polymeric substances content. The optimal values of mixed liquor suspended solids concentration, stirring speed and flux turned out to be 4126 mg/L, 236 rpm and 154 L/(m²∙h), respectively, corresponding to the formation time, filtration resistance and fouling propensity values of 82.47 min, 1.50 × 10⁹ m^-1 and 1.48 × 10⁸ m^-1min^-1, respectively.