Study On Toxicity Variation Of Water Quality During The Electrocatalytic Oxidation Of Alage And MCLR

The pollution of algae and its secondary metabolites microcystins (MCs) are serious threats to drinking water security. As a new technology of killing algae and degrading microcystins, electrocatalytic oxidation catches great attention because of its simple manipulation and advantages of environmental compatibility. But few scholars are concerned about the security of treatment process.The experimental conditions of the luminescent bacteria acute toxicity test, dehydrogenase toxicity assay, Vicia faba root tip micronucleus method and single-cell gel electrophoresis assay were determined in this thesis. Based on acute toxicity and genotoxicity of the water samples, studies on the toxicity variation during the process of electrocatalytic oxidation killing algae and degrading microcystins were carried out. By combining analysis of intermediate products with water sample testing, the security of the method was discussed. In addition, the proposed method to control water quality toxicity during the process was offered. Furthermore the impact on water quality toxicity caused by intracellular material and oxidation by-product generated in the treatment was discussed.The results showed that for dehydrogenase activity method, using natural surface water as bacterial species sources and switch cultivating one time could make the activity of bacterial relatively good; the best ratio of sample fluid and bacteria was 6:1; before the testing, mixture was required to keep in a 37℃incubator for more than 50min to activating the bacterial. The best Vicia faba root dissociation time is 50-60min. The cell staining time should be more than 30min. During single-cell gel electrophoresis experiments, following 180 min cell lysis and 30min unwinding, electrophoresis for 55min in the electrical condition of 28V,300 mA can get good test results.Electrocatalytic oxidation can effectively remove microcystins in water samples. For water samples with a initial Microcystin-LR (MCLR) concentration of 102μg/L, the MCLR removal rate can reach 100% after 30min treatment. In addition, pigments and other intracellular organic matter can also be effectively degraded. Electrocatalytic oxidation can also effectively inactivate algal cells. During the treatment, microcystins and a variety of other intracellular substances were gradually released in the algal cell death process. As a result, there was a trace of MCLR in the water samples, persistently.During the process of electrocatalytic oxidation killing algae and degrading microcystins, some substances with acute toxicity were generated in water samples, causing the luminous bacteria and dehydrogenase toxicity of the solution to increase slightly. But along with the treatment, these substances were oxidized and degraded. As a result, the water samples ultimately showed little acute toxicity. The micronucleus rate of 45μg/L untreated crude MCLR was 6‰～7‰, while the rate of the same concentration of pure microcystins was more than 8‰. Over 66ug/Lμf crude MCLR can induce mouse cell DNA damage. As the treatment progressing, cells'DNA damage decreased, the genotoxicity of water samples showed a significantly decline (P<0.05).Studies on intermediate product of degrading microcystins showed that small molecule organic acids were the main intermediate reaction products and can be completely removed along with the processing time expending. During the water treatment process, appropriate extending treatment time can improve the security of this method after MCLR are completely degraded.