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Title: Catalytic ozonation for textile dyeing wastewater treatment and reuse
Authors: Hu, Enling
Degree: Ph.D.
Issue Date: 2016
Abstract: Wastewater treatment is a crucial issue in the textile industry, which generates plenty of polluting effluents containing significant residual dyes and dyeing auxiliaries. If the effluent is discharged without appropriate treatments, adverse influences would be given not only to the environment but also human health. As a consequence, degradation of dyes, as well as other organic contaminants, in textile dyeing effluents has been rated as one of the most important tasks in the sustainable production of textile products. However, significant challenges still exist to tackle this issue. Conventional treatment such as biological method is ineffective to degrade dyes satisfactorily and is extremely time-consuming. Therefore, some other approaches which employ chemical oxidation to remove contaminants have been developed. Among them, ozonation technology has been thought to be a promising approach due to merits of ozone, such as high oxidation capacity, no byproducts from self-decomposition and easy application without additional thermal or light energy. The current research concentrates on the application of carbon aerogel (CA) materials in catalytic ozonation for wastewater treatment and reuse. The catalysts are expected to strengthen degradation of organic dyes through ozonation, in order to improve efficiency of dyeing wastewater treatment and regenerate waste dyeing effluents for successive reuse. The catalytic performance of the catalysts was evaluated by degradation of typical anthraquinone (C.I. Reactive Blue 19) and azo (C.I. Reactive Black 5) dyes in simulated dyeing wastewater, in different operational conditions. The results have shown that the catalysts could greatly enhance dye degradation, in terms of decolorization and Chemical Oxygen Demand (COD) removal, during catalytic ozonation which followed chemical oxidation principle rather than physical absorption. In addition, the systematical parameter study has indicated that improve temperature, pH, ozone dosage or catalyst dosage during the treatment would effectively enhance dye degradation efficiency. In addition, a primary industrial trial was also carried out in a dyeing wastewater treatment plant to validate the effectiveness and efficiency of ozonation technology in the treatment of real textile wastewater. An integrated treatment system (capacity: 20 L/h) was installed in the plant for in-site treatment. The results have shown that in the specific conditions the treatment system which based on ozonation technology could greatly shorten the treatment time by over 50% to obtain the equivalent treatment outcome. In the aid of post reverse osmosis treatment, the water quality of centrally filtrated effluents was in compliance with suggested standards for textile wastewater reuse in China.
What's more, considering the recent topic in wastewater treatment has been extended to utilize advanced treatment of effluents for direct reuse, catalytic ozonation with CA materials was performed for regeneration of the waste effluents from the first dyeing bath in reactive dyeing for reuse. It has indicated that the waste effluents could be successfully regenerated by catalytic ozonation. The regenerated effluents could be additionally reused in successive dyeing without sacrificing color quality of the fabrics. Color difference of the fabric dyed with the regenerated effluent was within the acceptable tolerance (ΔEcmc(2:1) < 1.0), meanwhile excellent color levelness and equivalent colorfastness have also been achieved. Apart from the above, catalytic ozonation of oxalic acid, which is the common refractory compound from catalytic oxidation by ozone, was evaluated to investigate the removal efficiency and mechanisms occurred. The observations have indicated that, in catalytic ozonation of oxalic acid with CA, removal efficiency was rapidly improved in compliance with different principles. The radical reaction in bulk solution was much pronounced when the catalyst dosage was low, by contrast, ozone-molecule reaction over the catalyst surface was however dominated the entire degradation when catalyst dosage was high. The acidic condition, in which the degradation was mainly attributed to molecular ozone oxidation occurred on the catalyst surface, was more preferred for the efficient removal. To the best of the author's knowledge, this is probably the first study using CA materials as ozonation catalysts in textile dyeing wastewater treatment and reuse. With the efficient catalysts, it could be concluded that catalytic ozonation is a promising technology for the rapid treatment of textile wastewater to shorten the entire treatment time and in-situ regeneration of waste dyeing effluents in textile dyeing plant rather than remote treatment in wastewater treatment plant. The research may help to develop a new alternative approach for both cleaner production of textile dyeing and sustainable development of textile industry, which is beneficial to the whole industries and environmental protection.
Subjects: Hong Kong Polytechnic University -- Dissertations
Sewage -- Purification -- Oxidation
Dyes and dyeing -- Environmental aspects
Pages: xxvii, 251 pages : color illustrations
Appears in Collections:Thesis

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