Removal Of Microcystis Aeruginosa By Fe²⁺/Persulfate And Its Ecological Risk

Currently,along with the rapid socio-economic development in China,environmental problems have become increasingly serious.One of the most serious problems is the frequent occurrence of cyanobacteria caused by eutrophication of fresh water resources is one of the.The structure of aquatic ecosystem was destroyed,the production of aquatic organisms such as fish and shrimp were sharply reduced,and there was also a risk of endangering human health.However,conventional treatment techniques have either poor treatment results,high treatment costs,or the risk of secondary pollution.Therefore,a method for controlling cyanobacteria outbreaks in current aquaculture was imperative in a safe,efficient and economical way.Microcystis aeruginosa,the dominant species of cyanobacteria,was applied to study the conditions and mechanism of Fe²⁺/Persulfate(Fe²⁺/PS)for efficient and moderate damage removal of M.aeruginosa and microcystins.The behavior of M.aeruginosa,extracellular organic matter,and microcystins during algal-laden storage period under natural aquaculture conditions were investigated to evaluate its risk.Simultaneously,the toxicological effects of Fe²⁺/PS on zebrafish were alsoinvestigated to further evaluate the safety of Fe²⁺/PS for the cyanobacterial outbreak's treatment.The main conclusions are as follows:?1?Fe²⁺/PS decomposed algal organic matters?AOMs?through pre-oxidation,which reduced the stability of M.aeruginosa,and the in-situ formed Fe???improved the coagulation efficiency.SO₄^·-and OH^·are the main function free radicals for the AOMs degradation.Dissolved microbial metabolites and protein-like substances are more susceptible to be oxidized.The optimum pre-oxidation and coagulation conditions are 0.1 mmol/L ferrous sulfate and 1:1 Na₂S₂O₈/Fe SO₄ mass ratio.The residual Fe was below the standard limit to avoid the danger of heavy metal.Only a small scale of algal cells damage was occurred,which not only avoided the ecological risk of numerous intracellular microcystins release,but also effectively removed extracellular microcystins.?2?After the cyanobacteria-laden water was treated with Fe²⁺/PS,extracellular MCs continued to decline and were significantly lower than those in the control group?P<0.05?.The presence of four peaks,representing protein-like substances,intermediate dissolved microbial metabolites,fulvic and humic-like compounds in EEM were significantly lower than those in the control group.However,due to the protective EPSs and the hydrolyzed polymer were decomposed and lacked sufficient nutrients,the M.aeruginosa cells were stimulated by the external environment from d-3,and the algal cells suffered slight damage but most of cells remained intact.Additionally,the viability of M.aeruginosa has decreased significantly compared with the control group?P<0.05?to reduce the risk of secondary of cyanobacteria relapse.?3?The mortality rate of zebrafish was highest in M.aeruginosa-laden water,but was decline after applying Fe²⁺/PS treatment.There was no significant effect on zebrafish growth ability under different treatment groups,however,the oxidative stress responses were induced.The most serious damage in zebrafish was in only M.aeruginosa treatment and caused excessive ROS.With the prolonged exposure time,the activity of Na⁺K⁺-ATPase was destroyed,and the activities of SOD and CAT were inhibited,which led to the accumulation of MDA and the increased consumption of GSH,in order to eliminate the toxic effects of ROS.However,applying the Fe²⁺/PS treatment on M.aeruginosa-containing water not only caused harmless to zebrafish,but also relieved the damage of cyanobacteria in zebrafish to a certain extent.Research indicated that Fe²⁺/PS integrated pre-oxidation and coagulation technology can be used to control cyanobacteria outbreaks,because it can effectively remove M.aeruginosa without serious secondary pollution risk during initial sludge storage period.and also alleviate the toxic effect of aquatic organisms.