Parameters Governing Permeate Flux in an Anaerobic Membrane Bioreactor Treating Low‐Strength Municipal Wastewaters: A Literature Review

Abstract

The objective of this review was to conduct a comprehensive literature survey to identify the parameters that govern the permeate flux in an anaerobic membrane bioreactor (AnMBR) treating municipal wastewater. Based on the survey, research to date indicates that the optimal membrane system for an AnMBR consists of an organic, hydrophilic, and negatively charged membrane with a pore size of approximately 0.1 lm. The use of both external and submerged membrane configurations shows promise. The operating parameters that affect permeate flux in an external membrane system are transmembrane pressure (TMP) and cross-flow velocity. The operating parameters that affect permeate flux in a submerged membrane system are TMP, sparging intensity, and duration of the relaxation period. Both cross-flow velocity and sparging intensity impart a significant amount of shear force on the biomass in an AnMBR. High shear forces can reduce the microbial activity in an AnMBR. In addition, high shear forces can reduce the size of the biosolids in the mixed liquor and increase the release of soluble microbial products. In this respect, external and submerged membrane systems are expected to perform differently because the magnitude of the shear forces to which the biomass is exposed in an external membrane system is significantly greater than that in a submerged system. The size of the biosolid particles and concentration of soluble microbial products in the mixed liquor affect permeate flux. Higher concentrations of soluble microbial products may be present in the mixed liquor when an AnMBR is operated at relatively low operating temperatures. Aerobic polishing following anaerobic treatment can potentially significantly reduce the concentration of some components of the soluble microbial products in the mixed liquor. It is not possible to remove the foulant layer on an organic membrane with caustic cleaning alone. Acidic cleaning or acidic cleaning followed by caustic cleaning is required to remove the foulant layer. This suggests that both biological/organic and inorganic material contribute to membrane fouling. Water Environ. Res., 78, 887 (2006).

Anaerobic fluidized membrane bioreactor polishing of baffled reactor effluent during treatment of dilute wastewater

“…The fouling extent varies with wastewater characteristics and reactor operating conditions. At higher temperatures fouling is reduced as a result of the higher hydrolysis rate of particulate organics and by the reduced permeate viscosity . Accumulation of biological agents such as soluble microbial products (SMP), either through the growth process or subsequent cell decay and lysis, has been widely associated with membrane fouling …”

Anaerobic membrane bioreactors for treating waste activated sludge: Short term membrane fouling characterization and control tests

“…However membrane fouling typically increases with flux and hence membranes are typically operated below a critical flux region to minimize fouling [14]. Berube et al [15] conducted a comprehensive review to identify the parameters governing permeate flux in an anaerobic membrane bioreactors treating low strength municipal wastewaters. Their survey indicated that the optimal membrane system for an AnMBR treating low strength wastewater consisted of an organic, hydrophilic, and negatively charged membrane with a pore size of approximately 0.1 mm.…”

A pilot study of anaerobic membrane digesters for concurrent thickening and digestion of waste activated sludge (WAS)

“…In addition, high shear forces can reduce the size of the biosolids and increase the release of soluble microbial products which in turn affects the permeate flux negatively(Berube et al 2006).During the transient state operation of the neutral membrane, no significant long term decline in membrane flux was observed except when there were changes in the properties of the digester feed sludge (i.e. addition of polymers to thicken the WAS) (Figure 3a -c).…”