Airlift crossflow membrane filtration — a feasibility study with dextran ultrafiltration

Abstract

In this paper, a novel membrane process — airlift crossflow filtration, is developed. It uses the airlift effect to drive liquid flow tangentially across the membrane surface whilst simultaneously making use of the enhancing effect of gas bubbles on membrane performance. The compressed air also provides the transmembrane pressure for the filtration operation. The feasibility of this new concept was demonstrated by the ultrafiltration of a dextran solution, proving that higher permeate fluxes can be achieved with a very low gas injection rate. Compared to conventional single phase crossflow operation at the same liquid flowrate, about a 30% increase in permeate flux was obtained with the airlift crossflow operation without the need of a recirculation pump. Process scale-up for tubular membrane systems was discussed, and a specific design comprising a tubular membrane module with internal circulation was presented. Evaluation of the process energy requirement indicated that this would be a low energy cost process compared to conventional single phase crossflow operation, whilst also saving process capital cost due to the elimination of a recirculating pump. Hence, this process is particularly attractive to cost-sensitive processes such as waste effluent treatment.