Biochemical Characteristics And DBPs Generation Characteristics Of Algae Cells By Ultrasound Irradiation

Toxins from algal blooms is a major water quality issue in source waters anddrinking water supplies.Algae as DBP precursors pose difficulties for drinking water treatment facilities running under normal operating conditions.Ultrasonic radiation is an effective method to improve the removal efficiency of algae cells,which can produce a variety of physical and chemical effects,inhibit the cell activity of algae and destroy the cell structure of algae.However,when algae cells are inactivated and broken,the selective permeability function of cell membrane is destroyed,and a large amount of intracellular organic matter is released into the water,which changes the characteristics of organic matter in water and interferes with the algae removal efficiency of water treatment processes such as coagulation.When the algal cells were inactivated,the physiological activity of the algae cells was inhibited,but the cell structure was basically intact,and the release of organic matter in the cells was less.Therefore,this paper studies the ultrasonic conditions for the inactivation of algae,taking typical algae(Microcystis and Anabaena)in the Three Gorges reservoir area as the object.The removal efficiency of algae cells by ultrasonic parameters,the physical and chemical characteristics,physiological characteristics and disinfection by-products were systematically studied.The main research contents include: the effect of ultrasonic radiation on the physical and chemical characteristics of algae cells;the characteristics and mechanism of inactivation of algal cells and the release of algae organic matter;the effect of ultrasonic radiation on the physiological characteristics of algae cells;the generation characteristics of disinfection by-products of inactivated algae cells.(1)The direct removal rate of algae cells by different ultrasonic parameters was studied to explore the breakage of algae cells by ultrasound,including ultrasonic power,ultrasonic frequency,ultrasonic time,ultrasonic amplitude,and intermittent sinusoidal ultrasonic signal Burst ultrasonic radiation.The results showed that the greater the power,the longer the ultrasound time,and the greater the direct removal rate of algae cells.Different amplitudes have little effect on the removal of algal cells.(2)The physicochemical properties of Microcystis aeruginosa were characterized,including growth inhibition,particle size,antioxidant system,and changes in morphological structure.The results show that ultrasound radiation can damage the phycobiliproteins related to cell photosynthesis,then affect the normal function of photosynthetic system and inhibit the growth of algae cells.The antioxidant enzymes(SOD,CAT)of algal cells can eliminate the damage of hydroxyl radicals produced by ultrasonic chemical effect on cells.When the ultrasonic dose exceeds the tolerance limit of algae cells,hydroxyl radicals react with membrane lipid to produce MDA.After ultrasonic irradiation,the surface of algal cells appeared folds and a small amount of broken fragments,which had obvious damage,and some cell structures were destroyed.(3)The differential expression of genes related to the physiological changes of algae cells,such as cell growth,photosynthesis,energy metabolism,and cell membrane damage,was studied to determine the stress response of algae cells after ultrasonic radiation.The results showed that the expression of down regulated genes was significantly different,and the damage of some genes in algae cells was more obvious,while the adaptive changes of algae cells under ultrasonic radiation were relatively slow.Energy metabolism,cofactor and vitamin metabolism,carbohydrate metabolism,terpenoid and polyketide metabolism,amino acid metabolism and signal transduction related genes were all downregulated,and such biological functions of algae cells have been inhibited to a certain extent.(4)The release characteristics of algae cells under ultrasonic radiation were studied,including the changes of TOC,EEMs,UV-Vis absorption spectra,FTIR,amino acids,polysaccharides,proteins and microcystins.High frequency ultrasound radiation damages algae cells more intensely,and the increase of intracellular organic matter is more obvious.After ultrasound irradiation,the fluorescence intensity of phycocyanin,tryptophan and humus like compounds were enhanced,and the corresponding intracellular substances were released into the water,especially phycocyanin.Ultrasonic radiation will increase the release of algae toxins in the microcystis aeruginosa cells,but a shorter time of ultrasonic radiation will release less algae toxins.(5)The total amount of DBPs generated by the chlorination reaction of Microcystis aeruginosa and Anabaena sp.increased with the increase of chlorination time,chlorine dosage,reaction temperature and pH.The results showed that the main precursors of DBPs produced by extracellular organic matter less than 30 k Da were humus like substance,algal cell metabolites,protein like,amino acids,etc.,while the main precursors of DBPs produced by extracellular organic matter larger than 30 k Da also included phycocyanin and chlorophyllin a.