The Combination Process Of Ozone Pre-oxidation And Coagulation For The Removal Of Arsenic In Drinking Water

Arsenic contamination has been a global problem. In present, many countries and regions in the world have the problem of arsenic contamination of drinking water. People drinking high level of arsenic in water would get serious damage to kidney, skin, nervous system and reproductive systems. Studies have shown that arsenic can cause teratogenic, carcinogenic and mutagenic. Arsenic existing in the water generally presents trivalent and pentavalent states of the form. And trivalent arsenic has stronger toxicity,more stability and more difficult to remove than pentavalent arsenic. Moreover, trivalent arsenic in the natural environment oxidized to pentavalent arsenic is a very slow process. Therefore, it is an effective way to oxidized trivalent arsenic to pentavalent arsenic when we remove arsenic in the water. In 2006 the State enacted a new living drinking water standard (GB 5749-2006) for the first time to reduce the arsenic concentration limits to 10μg / L. But the current method of removal of arsenic can hardly match it and the cost is higher. The arsenic removal process has become an urgent problem.In this study, high-arsenic ground water in rural areas is the research object. In first we turned trivalent arsenic to pentavalent arsenic by ozone oxidation. Then, the arsenic was removed by sedimentation or filtration technology. Studies examined the relationship between time and flow of the ozone oxidation and the removal rate of arsenic, the connection between temperature, turbidity, pH and arsenic removal by ozone, the connection between Iron and manganese ion concentration and arsenic removal by ozone. Studies also showed the relationship between sedimentation, filtration and pre-oxidation in the removal of arsenic.The studies showed the removal of arsenic reached to 50% ~ 60% in the supernatant fluid, when controlled the time of ozone aeration at 5 min and the time of precipitate at 15 min. These showed Arsenic removal efficiency and ozone flow become direct ratio. When it comed to the joint use of ozone aeration and filtration or the joint use of ozone aeration and coagulation, the removal of arsenic reached above 90 % , and fulfilled the national standard for drinking water. The arsenic levels in the supernatant fluid, which had been aeration by ozone, had some connection with the precipitation time of treated water. In the 30 min, the longer of precipitation time, the lower of arsenic levels. Ozone preoxidation could jump the arsenic effect of coagulants of the physico-chemical process, aluminum salt and polyblend classes. The order of the effect of flocculences to deal with the arsenic removal was: FeCl3> Al2(SO4)3> PAFC >PAC. With the process of ozone pre-oxidation, arsenic removal could be increased if Fe and Mn ions existed alone, in which there was better effect for Fe than Mn. When Fe and Mn were co-existed, the arsenic removal efficient by Fe would be inhibited by Mn. And arsenic removal efficiency could be stable when the change of temperature and turbidity was physico-chemical. According to the high level arsenic in the field, it contained 0.17mg/L arsenic concentration. coagulant was FeCl3, dosing quantity reached to 30 mg/L, it could ensure that the outlet arsenic levels fall to 0.01 mg/L. In the test, the arsenic removal were beween 50%~ 95%.