A Study On The Degradation Of MC-LR By Ultrasonic Electrochemical Technology

Microcystins–LR(MC–LR)is the most popular and strongest algae toxin variants,its physical and chemical properties are very stable.Methods commonly used in the degradation of MC-LR include physical method,chemical oxidation and biological degradation,and the traditional water treatment technology is not only difficult to completely remove the MC-LR from water,but also have the risk of secondary pollution.Electrochemistry(EC)technology is the use of an applied electric field to remove organic pollutants from wastewater through a series of chemical reactions,electrochemical or physical processes.Boron doped diamond(BDD)as a new type of electrode electrode material,which possess excellent electrochemical properties,such as wide electrochemical potential window,low background current,good physical and chemical stability and low adsorption characteristics,but it will still appear electrode polarization and passivation because of the lack of mass transfer ability.Ultrasound(US)refers to sound waves that are more than 20KHz or above,which can not be heard by human ears.Currently,there has been some progress in the management of organic pollutants in water.However,the efficiency of ultrasound alone in degradation of pollutants is low and energy consumption is relatively high.Ultrasonic sonoelectrochemistry(US-EC)used in combination can make use of the physical effect of ultrasound to improve the problems of electrode polarization and passivation phenomenon,and also accelerate the reaction rate,make some chemical reactions to be realized through the electrochemical oxidation of cavitation effect.Therefore,BDD electrode was chosen as the anode for electrochemical reaction,and the electrochemical and low-frequency power ultrasound were used in combination with the experimental condition to reduce the MC-LR simulation wastewater and optimize the parameters of US-EC degradation process.The biotoxicity test of MC-LR water samples before and after treatment of US-EC was conducted to investigate whether US-EC can reduce or eliminate the biotoxicity of MC-LR.On the basis of the research on the optimization of the laboratory process parameters,we used US-EC to treat the feild sewage of taihu yangwan algae removal station,and analyzed the effect of MC-LR degradation and water quality improvement before and after treatment.1.The experimental study of MC-LR degradation by ultrasonic sonoelectrochemistry.The ultrasonic-electrochemical water treatment device was constructed autonomously.Under the condition of laboratory study,the influence of current density(1,2,3,4,5mA/cm~2),ultrasonic power(15,20,25,30W),initial concentration(10,50,100?g/L)and treatment time(1,5,10,20,40min)on the degradation effect of MC-LR was discussed,and the degradation process of US-EC was optimized.US,EC and US-EC are also compared.The 10?g/L MC-LR simulated wastewater was treated by US-EC for 20min,MC-LR was not detected in the sample.While both the US and EC group treated after 20 min,the reation into the plateau,with the treated time prolong to 40 min,the sample could still remain in a certain amount of MC-LR,where US processing group with each parameter treated 40 min,final concentration of MC-LR in the sample were 3.0 to 5.4?g/L,and final concentration of MC-LR in the sample of EC processing group with each parameter were 0.54to 1.1?g/L.The results show that the degradation effect of US-EC was significantly better than that of US and EC group;within a certain range,the relationship between current density and removal rate is positive correlation,but when the current density reaches to a certain level,with the current density increased continuously,the increase of MC-LR removal rate is not obvious;When the process time was relatively short,the MC-LR removal rate increased with the increase of ultrasound,but when the current density was equal or greater than 3mA/cm~2,and the treatment reached 20min,the MC-LR removal rate of each the combined group was no difference(both lower than the detection limit).As the initial concentration of MC-LR increases,the time required to completely remove MC-LR is increased.With the extension of action time,removal rate of MC-LR increased.Above all,the current density of 3mA/cm~2,the ultrasonic power of 15W,and the working time of20min were found the optimal parameter for US-EC degradation of MC-LR,while the processing time should be adjusted according to the different concentration.2.Biotoxicity test of water samples containing MC-LR before and after ultrasonic sonoelectrochemistry treatment.C.elegans expose to a series of concentration of MC-LR(1,10,50,100?g/L)to investigate whether the environment concentrations of MC-LR can cause apoptosis and inhibition of PP2A activity of the c.elegans,and then select the appropriate indicators to build biological toxicity evaluation method of MC-LR.The toxicity of samples that before and after treated by 10?g/L was evaluated to reveal that whether the toxophore of MC-LR could be destroyed.The results shows that the 1?g/L dose group of MC-LR could induce apoptosis,which indicate that apoptosis could as a sensitive indicator to detect the biotoxicity of MC-LR at ambient concentrations.However,the activity sensitivity of PP2A was poor sensitive,compared with the control group,the difference was only significant in 100?g/L dose group.C.elegans expose to the MC-LR samples before and after US-EC treatment and cell apoptosis was used as indicator to evaluate the biological toxicity,the results shows that the apoptosis rate of samples after treatment was declined obviously than before,which shows that US-EC can eliminate biological toxicity of MC-LR in the process of degradation.3.Degradating effects of effluent from Taihu yangwan algae water separation station by ultrasonic sonoelectrochemistry.Field water samples was take from Taihu Yangwan algae removal station.Investigate the effect of US-EC on the degradation of MC-LR in field water,and the water quality index(including chemical oxygen demand(COD),total nitrogen(TN)and total phosphorus(TP))changes was analyzed at each time point in the course of processing.The results showed that MC-LR was completely by US-EC removed after 20min;The concentration of the TN decreased from 2mg/L to0.74mg/L;TP decreased from 0.14mg/L to 0.02mg/L;The COD decreased from 8.17mg/L to7.07mg/L.After dealing with 40 min:concentration of TN was 0.68mg/L;TP was 0.01 mg/L;COD was 6.97 mg/L.According to the change of COD,TN and TP,US-EC can improve water quality.Conclusion(1)US-EC can effectively degrade MC-LR in water,and its degradation effect is significantly better than that of single US and single EC.(2)US-EC can reduce or eliminate the toxic effect of MC-LR,which is a safe and feasible water treatment technology.(3)US-EC can effectively degrade MC-LR in the field water and reduce the level of TN,TP and COD in water to improve the water quality.