| With the increasingly strict sanitary standards of drinking water quality,ultrafiltration technology with high efficiency of pollution removal has a wide application prospect in drinking water treatment.However,under the background of frequent eutrophication of natural water bodies,membrane pollution caused by algae will seriously restrict the promotion of ultrafiltration membrane water purification process.Therefore,the influence of the growth and metabolism of algal cells on the polluted membrane of algal source membrane during ultrafiltration and the exploration of its mechanism are of great significance for the popularization and application of ultrafiltration technology in the field of water pollution treatment.In response to this problem,a laboratory scale pilot study was carried out,taking Microcystis aeruginosa as the representative species of natural algal water,using three chemical agents(sodium nitrate,glucose,copper sulfate)to change the growth environment of algal cells,to explore the change mechanism of algal cell layer on the surface of ultrafiltration membrane in the ultrafiltration process,and its impact on membrane pollution.Under the conditions of different concentrations of chemicals,the growth and metabolism of algal cells on the filter cake layer are different: Chapter III the growth and metabolism of algal cells in the medium group is faster,the growth of algal cells in the low nitrogen group is slower than that in the medium group,the growth of algal cells in the no nitrogen group and the high nitrogen group is stagnant,and a large number of algal cells in the no nitrogen group are apoptotic and chlorotic after 15 days.In Chapter 4,the addition of 10 mg/L glucose promoted the reproduction of algal cells on the filter cake layer,while the growth of algal cells was limited and chlorotic and yellow at glucose concentrations of 50 and 100 mg/L.In Chapter 5,the addition of copper sulfate significantly inhibited the activity of algal cells.The initial copper ion concentration of 0.05 mg/L reappeared part of the algal cell coverage on the membrane surface at 8 days,and the degree of inhibition was relatively light.The growth of algal cells with initial copper ion concentrations of 0.12 mg/L and 0.24 mg/L was severely inhibited,and withered within 3-4 days.The research results of the influence of sodium nitrate on the algae source membrane pollution pre covered with Microcystis aeruginosa layer are as follows: the four groups of membrane pollution are culture medium group > low nitrogen group > no nitrogen group > high nitrogen group.The main cause of membrane pollution is filter cake layer pollution.In low nitrogen group and medium group,a large number of algae cells and EOM(extracellular organic matter)attached to the surface of the membrane,causing the thickness of the filter cake layer to become thicker and the structure to be dense;The growth conditions of algal cells in the medium group were suitable,and the utilization of nutrients was more sufficient than that in the low nitrogen group.At the end of the experiment,the dry weight of algal cells and their metabolites in the filter cake layer was 1.86 times that in the low nitrogen group,and the degree of membrane pollution was more serious;In the nitrogen free group,a large number of algal cells gradually chlorosis and apoptosis under the condition of nitrogen starvation.In the middle and late stage of the experiment,algal cells in this group burst and release more IOM(intracellular organic matter),causing the blockage of ultrafiltration membrane pores and the compact structure of filter cake layer;The growth of algae cells in the high nitrogen group stagnated,EOM and IOM were less than those in the other three groups,the content of unsaturated organic matter was significantly lower,the structure of filter cake layer was slightly changed,and the degree of membrane pollution was less.The effects of glucose on the fouling of algal source membrane pre covered with Microcystis aeruginosa are as follows: 4 days before the experiment,the amount of glucose added is proportional to the membrane fouling resistance;At the end of the experiment,the membrane fouling was the most serious when the initial glucose concentration was 100 mg/l.The membrane fouling resistance value was close when the initial glucose concentration was 0,10 and 50 mg/L,but the causes were different.Within 4-8 days of the experiment,the nitrogen consumption of the standard group was 1/3 of that of the other three groups,while the phosphorus consumption was the highest,that is,the addition of glucose broke the symbiotic relationship between algae cells and bacteria,promoted the growth of bacteria,and the growth of bacteria and algae cells scrambled for survival resources.The growth of algae cells was indirectly inhibited,in which the growth of algae cells was always stagnant in the two groups of 50 and 100 mg/L glucose dosage,and the color of filter cake layer changed from green to yellow.Bacterial growth affects the initial structure of the filter cake layer within 0-4 days,causing initial differences in membrane fouling resistance.The structural changes of the filter cake layer caused by algal source membrane fouling caused by different growth conditions of algal cells are the main factors for the subsequent continuous increase of membrane fouling resistance on this basis.The research results of the influence of copper sulfate on the algae source membrane pollution pre covered with Microcystis aeruginosa layer are as follows: the addition of copper sulfate will increase the resistance of membrane pollution,and the initial addition of copper sulfate concentration of 0.12 mg/L will cause the most serious membrane pollution.The initial addition of copper sulfate of 0.5,1.2 and 2.4 mg/L will make the phosphorus consumption 0 within 8 days,that is,the growth of algal cells is inhibited.Copper ions affect the permeability of algal cell membrane,promote the release of IOM and combine with macromolecular substances in IOM,resulting in compact structure of filter cake layer and increased membrane fouling resistance.In this study,the growth of algal cells in the cake layer during ultrafiltration and the effects of different components of algal sources on membrane fouling were analyzed.To explore the mechanism of algal membrane pollution,and make specific exploration and Mechanism Analysis on the growth and metabolism of algal cells,the difference of membrane surface characteristics,the change of raw water quality and the structure change of filter cake layer in the process of ultrafiltration,is of great significance for correctly understanding the algal membrane pollution nature of filter cake layer and the promotion of ultrafiltration membrane treatment of algal water. |
