The fractionation of dextran polymer by ultrafiltration to yield clinical products

A review of ultrafiltration (UF) theory and equipment has been made. Dextran is fractionated industrially by ethanol precipitation, which is a high energy intensive process. The aims of this work were to investigate the fractionation of dextran using UF and to compare the efficiency and costs of UF fractionation with ethanol fractionation. This work is the continuation of research conducted at Aston, which was concerned with the fractionation of dextran using gel permeation chromatography (GPC) and hollow fibre UF membranes supplied by Amicon Ltd. Initial laboratory work centred on determining the most efficient make and configuration of membrane. UF membranes of the Millipore cassette configuration, and the DDS flat-sheet configuration, were examined for the fracationation of low molecular weight (MW) dextran. When compared to Amicon membranes, these membranes were found to be inferior. DDS membranes of 25 000 and 50 000 MW cut-offs were shown to be capable of fractionating high MW dextran with the same efficiency as GPC. The Amicon membranes had an efficiency comparable to that of ethanol fractionation. To increase this efficiency a theoretical UF membrane cascade was adopted to utilize favourable characteristics encountered in batch mode membrane experiments. The four stage cascade used recycled permeates in a counter- current direction to retentate flow, and was operated 24 hours per day controlled by a computer. Using 5 000 MW cut-off membranes the cascade improved the batch efficiency by at least 10% for a fractionation at 6 000 MW. Economic comparisons of ethanol fractionation, combined GPC and UF fractionation, and UF fractionation of dextran were undertaken. On an economic basis GPC was the best method for high MW dextran fractionation. When compared with a plant producing 100 tonnes pa of clinical dextran, by ethanol fractionation, a combined GPC and UF cascade fractionation could produce savings on operating costs and an increased dextran yield of 5%.

Performance evaluation of reverse osmosis (RO) pre-treatment technologies for in-land brackish water treatment

Integration of renewable energy with desalination technologies has emerged as an attractive solution to augment fresh water supply sustainably. Fouling and scaling are still considered as limiting factors in membrane desalination processes. For brackish water treatment, pre-treatment of reverse osmosis (RO) feed water is a key step in designing RO plants avoiding membrane fouling. This study aims to compare at pilot scale the rejection efficiency of RO membranes with multiple pre-treatment options at different water recoveries (30, 35, 40, 45 and 50%) and TDS concentrations (3500, 4000, and 4500mg/L). Synthetic brackish water was prepared and performance evaluation were carried out using brackish water reverse osmosis (BWRO) membranes (Filmtec LC-LE-4040 and Hydranautics CPA5-LD-4040) preceded by 5 and 1μm cartridge filters, 0.02μm ultra-filtration (UF) membrane, and forward osmosis (FO) membrane using 0.25M NaCl and MgCl2 as draw solutions (DS). It was revealed that FO membrane with 0.25M MgCl2 used as a draw solution (DS) and Ultra-filtration (UF) membrane followed by Filmtec membrane gave overall 98% rejection but UF facing high fouling potential due to high applied pressure. Use of 5 and 1μm cartridge filter prior to Filmtec membrane also showed effective results with 95% salt rejection.