AIRLIFT CROSS-FLOW MEMBRANE FILTRATION - A FEASIBILITY STUDY WITH DEXTRAN ULTRAFILTRATION

In this paper, a novel membrane process - airlift crossflow filtration , is developed. It uses the airlift effect to drive liquid flow tangen tially across the membrane surface whilst simultaneously making use of the enhancing effect of gas bubbles on membrane performance. The comp ressed air also provides the transmembrane pressure for the filtration operation. The feasibility of this new concept was demonstrated by th e 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 flow rate, about a 30% increase in permeate flux was obtained with the airl ift crossflow operation without the need of a recirculation pump. Proc ess scale-up for tubular membrane systems was discussed, and a specifi c design comprising a tubular membrane module with internal circulatio n was presented. Evaluation of the process energy requirement indicate d that this would be a low energy cost process compared to conventiona l single phase crossflow operation, whilst also saving process capital cost due to the elimination of a recirculating pump. Hence, this proc ess is particularly attractive to cost-sensitive processes such as was te effluent treatment.