Gas-lift Anaerobic Membrane Bioreactor (Gl-AnMBR): Preliminary Results From a Filterability Assessment

The membrane bioreactor (MBR) is generally known for its high quality effluent and small footprint. Compared to its aerobic counterparts, the anaerobic MBR (AnMBR) has the additional potential of energy generation (e.g. biogas), fertilizer recovery (e.g. nutrients), and low sludge generation. Under optimal operational conditions, an AnMBR can be used not only for on-site wastewater treatment, but generation of reusable water for agricultural applications. Additionally, biogas produced in the anaerobic process could potentially more than satisfy energy requirements of the system (Liao, 2006). Better understanding, however, is needed regarding maximization of the overall energy balance (energy footprint) in AnMBR. Recent studies have demonstrated improved energy efficiency of membrane technology by enhancing shear over membrane surface in vacuum-driven modules using air scouring (e.g. reducing cake layer deposition in submerged membranes). Sidestream membrane configurations in aerobic airlift supported modules, which has successfully been deployed for municipal wastewater treatment, have shown great potential in reducing energy consumption. However, little is known about the application of this configuration in anaerobic mode by using biogas for gas-lift. In this in study, an up-flow anaerobic sludge blanket (UASB) bioreactor has been coupled with gas-lift tubular ultrafiltration membrane to create a novel Gl-AnMBR configuration. Analogous to the air-lift MBR, this system uses biogas to provide two phase flow through the lumen of vertically placed tubular membranes. By introducing biogas bubbles into the membrane feed, the potential of membrane fouling is decreased through increased shear and turbulence over the membrane surface. Additionally, recirculation through the membrane module is assisted by the gas-lift and less crossflow velocity is necessary to drive filtration. Pumping requirements for recirculation and filtration are minimized, allowing less energy consumption. For the filterability assessment of this new MBR, anaerobic sludge at a MLSS concentration of 8 g/L was used. Previous studies have shown average fluxes of 6 LMH when filtering anaerobic sludge at a solids concentration of 10 g MLSS/L using UASB flat sheet microfiltration membranes (Do and Yeh, 2009). The current prototype Gl-AnMBR with a sustainable flux of at least 20 LMH, with potential for further optimization towards the typical flux (45 LMH) exhibited by its aerobic commercial counterparts. The energy consumption for the membrane system of the Gl-AnMBR was also evaluated.