| The dielectric barrier discharge (DBD) is a leading advanced oxidation water treatment technology that can produce large amounts of active substances which contain high energy electron, ion and plasma. The organic pollutants, biocide in water can be degraded and killed rapidly by the active substances, so DBD has the advantages of high treatment efficiency, time-energy saving and without secondary pollution. The gas-liquid mixture DBD can treat sewage derectly, but the gas DBD can not unless utilizing the gas-liquid mass transfer. In this paper, a new type gas-liquid mixture DBD reactor was designed, and a gas DBD reactor was also designed to contrasting the differences of the two discharge morphologies and mechanisms by changing experimental parameters, and to studying the discharge characteristics of gas-liquid mixture DBD. The production of ozone and hydrogen peroxide in discharge process were investigated. The inactivation of Chlorella spp. with DBD in gas-liquid mixture was studied experimentally. The results showed that:(1) Compared the photos and voltage-current waveforms of both gas-liquid mixture DBD and gas DBD discharge by changing the discharge peak voltage, repetition frequency and discharge gap.With the same power parameter conditions, when the solution conductivity was lower, the gas discharge intensity and uniformity were higher than the gas-liquid mixture discharge, when the solution conductivity became higher, the gas discharge intensity and uniformity between the two discharge modes had a few differences, even were similar to each other. The discharge intensity increased with raising discharge peak voltage, the number of plasma channels increased much more, the channels attached together gradually; The discharge intensity depended on repetition frequency, discharge intensity increased at first and then decreased with the addition of repetition frequency; The smaller discharge gap contributed to the increasing discharge intensity, more uniform discharge form, and lower starting voltage.(2) The impact of the solution conductivity on the gas-liquid mixture DBD was investigated. The increasing of the solution conductivity led to an easy discharge and the discharge intensity increasing; the solution conductivity increased with the addtion of the discharge peak voltage and time. (3) The impact of the solution pH on the gas-liquid mixture DBD was investigated. The changes in solution pH had little effect on the discharge intensity because that the conductivity was similar; pH decreased with the increase of the discharge peak voltage and time.(4) The production of ozone and hydrogen peroxide increased with the increase of the discharge peak voltage and discharge time. Under the same conditions, M1 was represented the yield of ozone by gas discharge, M2, M3 were represented the yield of ozone in the gas and liquid phase respectively by gas-liquid hybrid discharge, the result showed that Mi> M2> M3.(5) The inactivation of Chlorella spp. with gas-liquid mixture DBD was studied experimentally. The relation of peak voltage, treatment time, the initial content of Chlorella spp. and conductivity of solution to the inactivation rate of Chlorella spp. was investigated, and the inactivation mechanism of Chlorella spp. preliminarily was studied. The inactivation rate increased with increasing of peak voltage, treatment time and electric conductivity, and decreased with the addition of initial content of Chlorella spp.. It was found that the inactivation rate of Chlorella spp. arrived at 100% when the initial content was 4×106cells/mL, and the optimum operation condition required a peak voltage of 20kV, a treatment time of 10min and a frequency of 7kHz. |
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