The influence of aeration intensity on predation and EPS production in membrane bioreactors

Shear is used to control fouling MBRs. However, shear also affects the physical and physiological properties of MBR biomass. The current study examines the relationship between the level of shear and EPS production in MBRs. Two 20 L MBRs were operated identically except for aeration intensity. Changes in floc size and floc-associated and soluble EPS concentration were characterized for both reactors. Floc-associated EPS was extracted and quantified as COD. Soluble EPS was characterized as soluble COD in the mixed liquor. Focused beam reflectance measurements were used to measure changes in floc-size and microscopic images were used to monitor the population of Aeolosoma hemprichi. Vigorous aeration did not change floc-associated or soluble EPS production in the current study. However, increased shear had an indirect effect on EPS production by controlling the growth of predatory organisms in the high shear reactor. Predation by Aeolosoma hemprichi in the low shear reactor increased both floc-associated and soluble EPS production in that reactor.