Removal of heavy metals from industrial wastewater by a microcell electro-coagulation process

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Removal of heavy metals from industrial wastewater by a microcell electro-coagulation process


Author: Wong, Siu-wai Kenny
Title: Removal of heavy metals from industrial wastewater by a microcell electro-coagulation process
Degree: M.Sc.
Year: 1999
Subject: Sewage -- Purification -- Heavy metals removal
Hong Kong Polytechnic University -- Dissertations
Department: Multi-disciplinary Studies
Dept. of Civil and Structural Engineering
Pages: xiii, 148, [11] leaves : ill. (some col.) ; 30 cm
Language: English
InnoPac Record:
Abstract: Heavy metal bearing wastewater always causes adverse effects to the environment. Proper pre-treatment is required prior to the discharge of those wastewater into the public sewer. Although there are a number of existing technologies available for treating heavy metal bearing wastewater, they have the common disadvantages of high capital cost, high operating cost, large space requirement, complicated operations, etc. These constraints affect their application to Hong Kong's Industries. Therefore, a rather new treatment concept, microcell electro-coagulation process, was investigated in this study. The study was conducted in two stages. In the first stage, the feasibility of the microcell electro-coagulation process for the removal of heavy metals from the industrial wastewater was assessed. A series of bench-scale jar tests were conducted to evaluate the ability of heavy metal removal by the process, especially to several common heavy metals presented in industrial wastewater, such as copper, chromium, zinc, lead, nickel, etc. The effectiveness of heavy metals removal under different operation conditions was determined in the bench-scale experiments. Also some tests were conducted at a bench-scale for assessing whether the application of electricity would accelerate the reaction rate of the microcell electro-coagulation process. The results obtained from those tests were used as basic design parameters for the development of a laboratory-scale continuous treatment reactor. In the second stage, several laboratory-scale reactors were designed and fabricated. These reactors were operated with a continuous flow mode so as to simulate the real operation of a packaged industrial wastewater treatment system. In the continuous flow tests, heavy metals bearing wastewater samples were collected from real industrial operations for conducting the experiments. The concentrations of the heavy metals in the wastewater before and after the treatment were analyzed. In order to achieve the best operating conditions, the various operating parameters to affect the treatment performance were evaluated individually, which were the variation of pH value, the ratio of iron wool to activated carbon, influent concentration, hydraulic retention time, consumption rate of iron wool and activated carbon and selectivity of this process to different heavy metal ions. The results obtained from the bench mode and continuous mode showed that the microcell electro-coagulation process performed satisfactorily with various sources of copper bearing wastewater. The removal efficiency of copper ion presented in the wastewater was as high as 99.5%. Through a series of batchwise bench-scale tests and continuous treatment experiments, the preferable operating parameters of the microcell electro-coagulation process were obtained. It was found that the best operating pH value was between 4.5-6.5; the minimum hydraulic retention time in the laboratory-scale reactor was 0.2 hour; the operating cost of this process was only 35% of the cost required for conventional chemical precipitation process; and the heavy metals with higher electrode potential can be removed more efficiently by the process.

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