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Photochemical Processes for the Treatment of Colored Wastewater: Influence of Operating Parameters, Modeling of Degradation Kinetic and Comparison of Eco- and Cost-Efficiency

Synthetic dyes are present in most spheres of our daily life and their application is continuously growing. They represent a sizable fraction in a vast array of contaminants of anthropogenic origin which inevitably reach our water supplies. Colored wastestreams from azo dye production processes and utilization industries present a major threat to the surrounding ecosystems due to the documented health hazards caused by toxicity and a potentially carcinogenic nature of such organic pollutants. Therefore, such wastewaters have to be treated in order to remove or at least to minimize the toxic organic content. Advanced oxidation processes (AOPs) represent an alternative when common wastewater treatment technologies are insufficiently effective. Among various types and combinations of AOPs, photochemical processes based on usage of various oxidants and UV irradiation shown potential as destructive and low- or non-waste generating technologies. The aim of the study was to compare three photooxidation processes (UV/H2O2, UV/S2O82- and UV/O3) for the degradation of an azo dye model pollutant. The influence of process parameters such as initial pH, the concentrations of oxidant in the reactor inlet stream and the type of oxidant was investigated using design of experiments approach. In order to investigate the influence of cross-factor effects of process parameters, the full factorial design was applied with three factors (two numeric and one categorical) at three levels combined with response surface modeling. The ANOVA results (R2, F, p) showed high accuracy of developed quadratic model for the zero-order mineralization rate constants of model dye wastewater. Among process parameters studied, the type of oxidant and the concentration of oxidant were shown to be the most influential parameters of studied photooxidation processes. In order to predict the detailed system behavior of studied photooxidation processes, a mathematical model simulating the influence of investigated process parameters was developed. According to the obtained results, the developed model can be characterized as interpretable, transparent, flexible and accurate. Besides that, processes effectiveness was compared from both eco- and cost-efficiency point of view. The highest rate of mineralization of model dye wastewater was obtained for UV/O3 process. Aside from the 78.3 % mineralization achieved after 60 minutes of treatment, the complete decolorization and degradation of naphthalene structures were obtained within 10 and 60 minutes of treatment, respectively. Originally non-biodegradable model dye wastewater was suitable for biotreatment after 60 minutes of treatment by UV/O3 process (BOD5/COD=0.59), and it was five times less toxic to vibrio fischeri than that before the treatment. However, when comparing the operating costs for each process studied, it was evident that UV/H2O2 process is 1.6 times less expensive than UV/O3 process considering the mineralization of organic content of model dye wastewater.

wastewater treatment; photochemical processes; UV irrad

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