Synthesis Of Bacteriostatic Forward Osmosismembrane And Its Properties Of Algae-Water Separation

Microalgae has been widely used in sewage treatment,biodiesel,nutrition and other fields.Currently,the bottleneck of large-scale application of microalgae is mainly due to the problems about high energy consumption and high cost of algae-water separation process.As a new membrane separation technology,the forward osmosis technology with the advantages of low energy consumption,little pollution and no external pressure as the driving force,has great merits and application potential in algae-water separation.In this thesis,we mainly investigated the properties of the osmotic pressure-driven forward osmosis membrane which was used in the algae-water separation,and the antibacterial positive permeable membrane material was synthesized to improve the antibacterial property of the forward osmosis membrane.This paper first studied the performance of algae-water separation with ultrafiltration technology driven by water pressure and forward osmosis technology with osmotic pressure as the driving force.The research found that the initial flux of the forward osmosiswas lower than that of the ultrafiltration technology.However,the forward osmosis technology had better application potential because of a low degree of membrane fouling and a strong ability to retain pollutants in water quality.The presence of irreversible membrane fouling is mainly due to adsorption of microorganisms such as bacteria.Based on the above research,theforward osmosis membrane was prepared by using cellulose triacetate(CTA),and the membrane was modified by hyperbranched amine as bacteriostatic agent to reduce the microbial contamination.The performance of theforward osmosis membrane before and after the antibacterial modification which was used in the algae-water separation was investigated.To investigate the effects of the content of CTA,the content of lactic acid and the time of evaporation on the properties of the membrane,the optimum parameters weredetermined as following:the content of CTA was 12wt%,the mesh size of polyester mesh was 250 mesh,the evaporation time was 30s,the relative humidity was 70%,the heat treatment temperature was 60oC,and the heat treatment time was 20min.Under this condition,the pure water flux of the membrane was about 15.0L/(m~2·h)and the rejection was about 95%.The results of SEM showed that the prepared membrane was composed of dense cortex and porous finger structure,and had a typical asymmetric structure.On the forward osmosis basement membrane,the interface polymerization was carried out with hyperbranched amine and trimesoyl chloride on the surface of the membrane,and amino groups with antibacterial property were introduced onto the surface of the prepared membrane to achieve the antibacterial modification.The results showed that the optimum experimental parameters of hyperbranched amine modified forward osmosis membrane were as following:the content of hyperbranched amine was2.5%and the content of trimesoyl chloride was 0.4%.The water flux of membrane was maintained at 14-15 L/(m~2·h),and the rejection rate of salt was about 97%.Using the prepared antibacterial forward osmosis membrane to carry out algae-water separation experiment,the results proved that the water flux downward trend of the modified forward osmosis membrane was slow.And the retention ability of the pollutants in the microalgae solution was enhanced.The rejection rates of COD,ammonia nitrogen and total phosphorus were 94.81%,93.79%and 96.95%,respectively.And themembrane biological pollution was significantly slowed down with little bacterial adsorption of the membrane surface.