Studies On ·OH Rapid Inactivation Of Typical Cyanobacteria And Red-tide Dinoflagellates

With the rapid development of China's industry and agriculture,industrial and agricultural sewage as well as domestic wastewater continue to flow into lakes,reservoirs and oceanic basins.Serious eutrophication in freshwater and marine waters lead to frequent outbreaks of harmful algal blooms,which result in water pollution and destroy the balance of freshwater and marine ecological system as well as cause potential threats to human health.Therefore,how to inactivate the harmful algal blooms quickly,efficiently and safely is one of the biggest challenges in handling freshwater blooms and red tides problems.In this paper,a ·OH treatment system based on a strong ionization discharge was established and high concentration of ·OH was produced to inactivate the typical cyanobacteria Microcystis aeruginosa,red-tide dinoflagellates Scrippsiella trochoidea,and Prorocentrum donghaiense.The effect of ·OH inactivation varying with different TRO dosages on the algae and morphological analysis were studied.Besides,this paper compared the effect of ·OH and three typical algaecides on algae.Here are the main research contents and conclusions:(1)The dose-effect and time-effect of ·OH were determined by using the experimental system with ·OH generation equipment as the core to inactivate the three kinds of algae.CT threshold relationships of ·OH were also studied,and the results are as follows.For algae M.aeruginosa with concentration of 1.02×106 cells/mL,the inactivation TRO dosage and contact time are 1.37 mg/L and 3 s repectively,with a corresponding CT threshold value of 0.07 mg-min/L;For algae S.trochoidea with concentration of 1.08 × 1 04 cells/mL,the inactivation TRO dosage and contact time are 0.79 mg/L and 6 s repectively,with a corresponding CT threshold value of 0.08 mg·min/L;For algae P.donghaiense with concentration of 1.05×104 cells/mL,the inactivation TRO dosage and contact time are 0.51 mg/L and 6 s repectively,with a corresponding CT threshold value of 0.05 mg-min/L.At these inactivation TRO dosages,the algal cells totally lost their photosynthetic activity.The chlorophyll-a decomposition rates of algae M.aeruginosa,S.trochoidea,and P.donghaiense reached 32.4%,68.0%and 75.0%,respectively at their different inactivation thresholds.(2)The results of morphological observation using SEM showed that the wholecelluar structure of M.aeruginosa and the two kinds of marine dinoflagellate remained intact at ·OH inactivation TRO dosages,and no obvious deformation or rupture of algal cells was observed.At these TRO dosages,the dissolved organic matter(DOC)contents in the treated water sample had no significant change.However,when the TRO value was 2 times as the inactivation TRO dosage,it was observed that the algal cells were deformed seriously,and some of the algal cells were ruptured.At these TRO dosages,the DOC contents increased obviously,indicating that the intracellular contents were overflowed.(3)Comparison of ·OH and the three algaecides(ClO2,CuSO4 and H2O2)at the same dosage on the inactivation of algae were investigated.For inactivation of M.aeruginosa,the CT threshold values of ClO2 and CuSO4 inactivation were 13.70 and 1972.8 mg·min/L respectively,which were 196 and 28184 times of ·OH inactivation values respectively;the inactivation rate reached 75.8%when the CT value of H2O2 was 3945.6 mg-min/L,indicating that H2O2 cannot totally inactivate M.aeruginosa.For the inactivation of P.donghaiense,the CT threshold value of ClO2 inactivation was 7.65 mg·min/L,which was 153 times of ·OH inactivation values;the inactivation rates reached 81.7%and 25.4%respectively when the CT values of H2O2 and CuSO4 were both 3945.6 mg·min/L,indicating that H2O2 and CuSO4 cannot totally inactivate P.donghaiense.(4)The drinking source water field test results of ·OH pretreatment in Xiangan water plant indicated that when the TRO dosage was 1.0 mg/L and the contact time in the pipeline was 20 s,the total living algae density decreased from 1.79×105 cells/mL to 280 cells/mL,which met the requirement of water intake in water plant.With NaClO pretreatment for 2 h at the same TRO dosage,the living algae density was decreased to 1.46×105 cells/mL.These alive algae would enter the pipe network and increased the difficulty of subsequent processing.After ·OH pretreatment,algal cells of M.aeruginosa colonies remained intact through SEM analysis;the four kinds of bacteria indexes reached the national standard of drinking water and other water quality values were obviously reduced,which were beneficial to the further treatment of the subsequent process in water plant.In conclusion,·OH generated by atmospheric pressure ionization discharge could inactivate harmful algal blooms quickly,efficiently and safely,which provides a new method for preventing and controlling the outbreak of freshwater bloom and red tide problems.