| Summary: | 碩士 === 明志科技大學 === 生化工程研究所 === 95 === Since GaAs was served as the wafer material the treatment of wastewater containing arsenic gradually become a significant issue. The prevalent treatment method for arsenic wastewater is calcium sedimentation incorporated with coagulation/flocculation process, however, the quantity of arsenic in effluent is still hard to meet the standard of Scientific Industrial Park. Additionally, because the original sludge is too tiny to precipitation the calcium and coagulant were over-dosed to enhance the settling of sludge. The large quantity of sludge containing arsenic will increase the expense of sludge treatment. The objective of this study was to evaluate the capability of electrocoagulation for the treatment of wastewater containing arsenic. Also, the effluent standard of 0.5 ppm arsenic was the evaluating criteria.
The experiments in this study were mainly divided into two parts: one was designed to compare the influence of Al of Fe electrode on the treatment of wastewater containing arsenate or arsenite; the other one was designed to explore the optimum molar ratio of calcium to arsenic. The species transformation between arsenate and arsenite, the characteristics of sludge as well as the influence of other co-existing ions were also explored in this study.
In the systems with low arsenic concentration the optimum initial HCl concentration was 0.003M for Fe electrode/arsenate, 0.002M for Fe electrode/ arsenite, 0.002M for Al electrode/arsenate, 0.001M for Al electrode/arsenite, respectively. Also, in electrocoagulation processes there was no arsenic species transformation. In the high arsenic concentration system the Al electrode incorporated with [Ca]/[As] over 1.5 are the best treatment conditions. The results indicate that the suitable operating conditions can successfully removal the arsenic from industry wastewater and yield the near neutral pH effluent. The results of co-existing ions effect experiments display that the phosphate ion can significantly influence the arsenic removal by electrocoagulation.
Since the corrosion potential used in Tafel experiments is smaller than the voltage in the actual electrocoagulation experiment, the passive phenomenon will not occur in actual electrocoagulation. In A.C. impedance experiment, the resistance between the electrode plate surface and the solution decrease with the applied voltages increasing. This phenomenon can prove that elevating the applied voltage lead to the fierce reaction.
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