Optimal backwashing in dead-end bacterial microfiltration with irreversible attachment mediated by extracellular polymeric substances production

Abstract

Microfiltration and ultrafiltration are methods of removing colloidal impurities from water and wastewater. One of the major issues when dealing with the practical implementation of membranes is the reduction of water productivity as the foulants accumulate on the membrane surface or within the pores. Membrane regeneration by periodic backwashing is an effective method of reducing fouling; however, to date the timing and duration of the backwashing for effective fouling control is largely only empirically determined. In this manuscript, we present an optimal control formulation to determine the timing and duration for membrane regeneration by backwashing. In this formulation, we use the direction of the flow as the control variable and make predictions regarding the optimal protocol. We explicitly include irreversible attachment due to bacterial deposition and biofilm formation on the membrane and demonstrate that irreversible attachment of bacteria has important ramifications for the effective timing of hydraulic backwashes as well as the efficiency in producing clean water. In particular, we find that irreversible attachment and additional fouling due to exo-polymeric substance (EPS) production and biofilm formation decreases the maximum filtration volume. Additionally, as the effectiveness of membrane regeneration declines, the timing of the cycling is also altered. In general, including the role of EPS in biofouling substantially changes predictions of backwashing timing and implies important considerations for practical predictions.

Removal of Bacterial Contamination from Bioethanol Fermentation System Using Membrane Bioreactor

“…Apparently, quick formation of a cake layer hindered effective removal of bacteria, because only 49% reduction in the reactors initial bacterial population was observed ( Figure 4a). As there are minimal changes in the turbidity of the permeate (Figure 4a), the reported decrease in bacteria concentration in the main reactor must probably be attributed to the attachment/deposition of bacterial cake on the membrane surface [33,34].…”

“…The surface condition of an immersed membrane directly affects its filtration capability [25]. In order to keep the membrane surface clean and prevent fouling, backwashing is an effective physical cleaning remedy [34]. Hence, 2 different backwashing regimes were applied: 3.5 min forward flow, and 0.5 min backwash (4 min cycle) at a dilution rate 0.5 1/h (109 L/h·m 2 ), and a more frequent backwash of 2.5 min forward flow plus 0.5 min backwash (3 min cycle) at a higher dilution rate of 0.66 1/h (144 L/h·m 2 ).…”

Influence of Solute Size on Membrane Fouling during Polysaccharide Enrichment Using Dense Polymeric UF Membrane: Measurements and Mechanisms

“…Assuming that R c is formed at the same pressure, when comparing the mass of foulants accumulated on the membrane surface, R c can be determined by Equation (3) [17][18][19], where α is the specific cake resistance, C b is the mass of dry cake solids per volume of filtrate, V is the cumulative permeate quantity, and A is the effective membrane surface area.…”

A review on anaerobic membrane bioreactors (AnMBRs) focused on modelling and control aspects

“…An application on a case study showed that the optimal strategy allows for significant gains in operating time and consumption of thinner in comparison with a conventional strategy of operation. Cogan et al (2016) applied the Pontryagin Maximum principle to predict the optimal times of switching between periods of filtration and backwashing that maximize the net production of water over a running time given a membrane filtration process. The authors adopted a specific model published in the literature describing the dynamics of the ultrafiltration/microfiltration reaching promising results.…”