Study Of Algae Removal With High Voltage Pulse Discharge In Liquid

Research and development a security cost-effective ship ballast water treatment and biological species intrusion prevention technology is the difficult problem in world. Pulsed high voltage discharge directly in water was proposed to treat the analogue ship ballast water in this project.Two electrodes were immersed in liquid and high pulse voltage was supplied at both ends of the electrodes,and then the discharge will be formed in water directly.The plate-pole-plate reactor was used to avoid energy losses in high electric conductivity liquid.It could produce strong electric field,active species including radicals,ultraviolet and shock waves at the same time.The superpositions of these effects could treat the ballast water effectively.In this investigation,the algae including Chlorella,Platymonas spp,Dicrateria sp and Nitzschia closterium were treated using pulsed high voltage discharge technology that have been studied.The effects of pulse parameters and residence time of solution on the growth of different algae were studied;the mechanism of killing algae was researched by measurement of chlorophyll a in solutions and observation structure of algae cells before and after treatment.The results showed:(1)By increasing of pulsed peak voltage,pulsed frequency and treatment time,the killing rate of algae increased.The killing rate could reach 100%at the appropriate pulsed parameters.(2)The killing rate also have affected by the species and volume of algae.In selected species chlorophyta(Chlorella and Platymonas spp) is the most difficult to treat,the diatom(Nitzschia closterium) the second,and chrysophyte(Dicrateria sp) is the easiest. Platymonas spp is more difficult to treat than Chlorella.(3)With the lengthening of retention time,the treatment effects on algae became better.It could be shorten the retention time when the killing rate was 100%via increasing pulsed peak voltage and frequency.(4) The concentration of chlorophyll a deceased sharply after discharge treatment.By measurement the concentration of chlorophyll a in the solutions before and after treatment with the changes of pulsed voltage and cultured time,it showed that as the voltage increased,the concentration of chlorophyll a in the treated solution decreased; and after cultured a period of time,the concentration of chlorophyll a in the solution that the killing rate on algae didn't reach 100%,had to increased and otherwise didn't detect.(5)Pulsed discharge treatment was worked a change on the algae cell construction. The treated cell structure of Platymonas spp occurred various changes that were found out when we used microscope to observe the algae cell structure before and after treatment.This was further evidence that the discharge process damaged to the algal cells and achieved the purpose of inactiving algae.