| In recent years, with the development of the industry, the water eutrophication hasbecome even more serious, and then brought the blue-green algae bloom, threatening watersafety. How to control algae bloom has become an important global environmental problem.This paper mainly discussed the inhibition and inactivation effect of AtmosphericPressure Plasma Jet (APPJ) on Microcystis aeruginosa (M. aeruginosa), which is thedominant species in algal bloom, and analyzed the discharge characteristics, meanwhileinvestigated the effects of discharge parameters, gas flow rate, and treatment time on theinhibition and inactivation of M. aeruginosa, finally the mechanism of algal inactivation wasdiscussed by the comparison of the changes of cell structure, enzyme activities andphysicochemical properties of the solution before and after discharges, and thephysicochemical actions on algae inactivation. The mian research results are as follows:(1) Jet length was related with applied voltage, gas flow. It increased with the increase ofdischarge voltage, and it increased firstly and then decreased with the increase of gas flow. Itwas found that there existed high frequency pulse spikes in the voltage curve, and the peaksof oxygen active species and nitrogen active species presented the discharge by the analysis ofthe optical emission spectroscopy spectrum.(2) The optimal process parameters through the experiments were determined. Theresearch results showed that the optimal process parameters were the discharge time at30min,voltage at7kV, flow rate at4L/min, the initial conductivity at1000μs/cm, respectively, andin this case the inactivation rate of algae could reach over99%.(3) The inhibition and inactivation of M. aeruginosa was studied from physiologicalparameters through the change of algae cell morphology by SEM observation, and theanalysises of superoxide dismutase (SOD) and malondialdehyde (MDA). It was found thatalgal cells appeared deformed and uneven on the surfaces after discharge treatment, and allalgal cells atrophied after cultivated for2days. SOD activity and MDA content increasedfirstly and then decreased, and SOD activity and MDA content reached the highest values atthe incubation for two days, which were increased from29.79U/mgprot and14.19nmol/mgprot to232.35U/mgprot and116.20nmol/mgprot respectively.(4) Physicochemical properties of the solution changed which was treated by APPJ. Theresearch results showed that the conductivity of the solution increased correspondingly withthe increase of discharge time and discharge voltage; pH of the solution decreased withincreasing of discharge time and discharge voltage. After discharge treatment, there generateda large amount of nitrate ions and nitrite ions in the solution, which is the main reason of pHdecrease; meantime there produed a large amount of oxygen active substances (·OH, H2O2, O3, etc.) in the solution, and OH, H2O2and O3concentrations were0.95μmol/L,10.64mg/Land0.53mg/L, respectively. Under the optimal process conditions, the conductivity of thesolution increased from1000μs/cm to1207μs/cm, and pH value decreased from the10.23to4.23. Nitrate and nitrite ion concentrations were obtained at49.99mg/L and36.69mg/L,respectively.(5) Effects of single and combined factors on algal inactivation were investigated todiscusse the main action factors on algae inactivation by APPJ. The research results illustratedthat UV radiation during the discharge had no obvious effect on algal inactivation. By onlypH adjustment (pH value at4.2) algal inactivation rate was48.34%. By adding hydrogenperoxide (10.64mg/L), algal inactivation rate was obtained at58.98%. Under the conditionwith ozone addition (0.25mg/L), algal inactivation rate reached51.35%. However, under thecondition with pH adjustment and simultaneously adding hydrogen peroxide (10.64mg/L)and ozone (0.25mg/L), algal inactivation rate could reach94.30%. It indicated that theinactivation of M. aeruginosa by APPJ was not the result of a single factor, but the result ofphysical and chemical combined actions. |
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