Identifier: TDX:306
Authors: Paradowska, Magdalena
Abstract:
The identification of more and more toxic organic compounds in wastewater, especially from industry, has challenged the conventional wastewater treatment methods. That is why there is a need to look for a new emerging technologies that can treat highly concentrated or non-biodegradable organic water pollutants. As it is impossible to use one universal method to destroy all the organic compounds, we have tested Catalytic Wet Air Oxidation (CWAO), hydrogen peroxide promoted CWAO, Wet Peroxide Oxidation and Fenton's Oxidation to remove aromatic organics belonging to different groups. For this purpose high temperature and high pressure continuous reactor system was designed and constructed. This equipment can be used either for catalytic or noncatalytic process. An activated carbon, that is low cost material, was used as a heterogeneous catalyst (CWAO), while iron sulphate was employed as a homogeneous catalyst (Fenton's Oxidation). Phenol, p-nitrophenol, aniline, nitrobenzene and sulfolane were studied, because these compounds are toxic, mostly non-biodegradable and at the same time, they are commonly found in industrial effluents. Also two samples of real industrial effluents coming from phenolic resins production were tested. Hydrogen peroxide was used as an oxidant, except in CWAO, where it was used as a promoter. This is because hydrogen peroxide is an excellent source of highly oxidative hydroxyl radicals. Firstly, each process was tested for phenol in order to find the influence of operational variables on the process efficiency. The aim was not only to destroy the original compound, but also to convert it to gas carbon dioxide and water, or at least in much more innocuous compounds easily biodegradable. Than the method performance with other compounds was examined. Finally, there can be achieved the complete conversion for every compound except nitrobenzene with highest conversion of about 80% during WPO experiments. However, for some compounds certain methods exhibited drawbacks such as corrosion problems with sulfolane, and plugging in the reactor during CWAO of aniline over activated carbon. In spite of this for every compound a removal technique among the methods studied can be proposed. Hydrogen peroxide resulted to be efficient oxidant, as 100% of stoichiometric quantity of H2O2 was sufficient to mineralise completely all the compounds, except nitrobenzene. Also, hydrogen peroxide is efficient as promoter of CWAO, enhancing greatly process efficacy. It is also interesting that all the methods could be performed in the same equipment after slight modification of the system. And Fenton's oxidation in continuous system in temperature about 200ºC permits similar removal of nitrobenzene (70%) using iron sulphate (II), that during noncatalytic WPO when employing 550ºC (80%). Also for real effluents it was observed that the oxidation techniques studied permitted to obtain complete phenol conversion and COD reduction over 50%. Even if it does not allow a complete mineralisation of organic compounds more refractory that phenol present in the wastewater it can probably increase the biodegradability.
Repositori URV