Filtration characteristics of hollow fiber microfiltration membranes used in membrane bioreactor for domestic wastewater treatment

Cross-flow microfiltration using submerged membrane with air bubbling can provide a continuous solid-liquid separation system by simple equipment, such as a low-rate suction pump, an air blower and a vessel. In this system, the size of the separation module could be reduced by using hollow fiber membranes packed in high density. In order to apply this beneficial process to a wastewater treatment bioreactor, we constructed filtration models to design the membrane system. Higher transmembrane pressure and lower fluidity of feed operations (e.g. transmembrane pressure of over 40 kPa and air-liquid two phase flow velocity, u*, of under 0.5 m • s−1) caused the rapid crowding of hollow-fiber membrane elements and reduced the effective membrane surface area. Under the conditions that do not cause the rapid crowding, the steady-state filtration flux, Jss, is expressed as Jss = VL = Kʹ • ф • u*1.0 • MLSS−0.5, where, VL, K′ and ф were lift velocity, filtration constant and the geometric hindrance coefficient of membrane module, respectively. The Jss values of hollow fiber membranes corresponded to that of rigid tubular ceramic membranes packed in low density. In this study, we defined the conditions that the hollow fiber membrane module packed in high density could be applied for solid-liquid separation. The flexibility and movability of hollow fiber membrane elements could not improve the flux.