Life cycle environmental performance of photocatalytic removal process for chromium wastewater by Cu/TiO2
Date Issued
2016
Date
2016
Author(s)
Huang, Chiao-Cheng
Abstract
Chromium is commonly used in electroplating and metal surface treatment process and mainly exists in the environment in the form of trivalent chromium and hexavalent chromium. Traditional treatment for chromium containing industrial wastewater is chemical coagulation, which is a low-cost method in operation. However, chromium containing sludge created in this process may cause significant chromium pollution through leaching from landfill to soil and groundwater if it was not properly disposed of. A potential alternative is the use of heterogeneous photocatalysis with TiO2, which has been widely applied for organic pollution degradation and heavy metal removal in recent years due to its chemical and thermal stability, low toxicity and low cost. This study aimed to remove chromium metal from synthetic wastewater with Cu/TiO2 prepared by photodeposition method. The results show that the 0.5 wt% Cu/TiO2 has a much better chromium removal efficiency than TiO2 under neutral condition. BET, XRD and Zeta Potential Analyzer were used to measure catalyst surface property. XANES was used to measure the surface structure and the oxidation state of chromium adsorbed inside the catalyst pore. The results clearly prove that a trace amount of Cr(VI) was adsorbed by catalyst during dark adsorption period. During photocatalysis, Copper deposit on the surface mainly in the form of CuO with trace amount of Cu2O and Cr(III) form codeposition with copper on catalyst surface mainly in the form of Cr2O3. Life cycle assessment of this study used TRACI 2.1 impact assessment model to quantify and compare the environmental impact of chemical coagulation, electrochemical coagulation, copper-iron bimetallic and photocatalysis process which was conducted previously. The results show that copper-iron bimetallic and photocatalysis process have a higher impact than chemical coagulation and electrochemical coagulation. The single point results show that the impact hotspot was mainly attributed to the electricity consumption of catalyst production process. The results of sensitivity analysis show doubling catalyst yield leads 47% variation to the total impact of photocatalysis process, which shows increasing catalyst yield could effectively reduce the total impact of photocatalysis process. This investigation was conducted based on the principles of green chemistry, summarizing the mechanism of photocatalytic process for chromium removal from wastewater. LCA results provide suggestions for future application to full-scale plant.
Subjects
Chromium
Copper loading TiO2
Heterogeneous photocatalysis
Life cycle assessment (LCA)；X-ray adsorption near edge structure (XANES)
Type
thesis
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