Hydrodynamics and microbial physiology affecting performance of a new MBR, membrane-coupled high-performance compact reactor

In this study, hydrodynamics and physiology of microorganisms were investigated in a new type membrane bioreactor, MHCR, which is a membrane coupled HCR (High performance Compact Reactor) having very high COD removal efficiency. The degree of interference caused by inserting a submerged membrane was evaluated quantitatively by measuring the air suction rate and overall oxygen transfer coefficient (kL,,a). Despite such interference, MHCR showed greater oxygen transfer efficiency than HCR under particular hydrodynamic conditions. Higher recirculation rate generally resulted in a higher turbulence and thus alleviated membrane fouling. When the recirculation rate was too high however, the microbial flocs were broken by fluid shear and membrane permeability was decreased rapidly. All these results were elucidated through not only physicochemical but also microbiological factors.

HCR was combined with a submerged membrane to make an efficient membrane bioreactor, e.g., MHCR. Changes of HCR characteristics through coupling with a membrane were investigated in terms of microbial physiology and hydrodynamic behavior of fluid and the following conclusions can be drawn: a) Although air suction rate in MHCR was decreased regardless of recirculation rate of mixed liquor, MHCR maintained the same overall oxygen transfer coefficient as HCR and thus showed higher oxygen transfer efficiency than HCR at particular recirculation rate. b) Higher recirculation rate resulted in a higher turbulence and oxygen concentration in the reactor and alleviated membrane fouling. However, when the recirculation rate was too high, a rapid loss in membrane permeability was observed. It is not only because the size of colloidal particles are reduced approaching the size of the membrane pore, but also because the concentrations of colloidal particles as well as the soluble EPS are augmented.