Photooxidation of a TM pulp and paper mill effluent with hydrogen peroxide

The photooxidation of a Thermo-Mechanical (TM) pulp and paper mill effluent with hydrogen peroxide $ rm(H sb2O sb2)$ was investigated at different experimental conditions by using a batch photochemical reactor operating at a dominant UV light wavelength of 253.7 nm. Photolysis of $ rm H sb2O sb2$ produces hydroxyl radicals ($ cdot$OH), which are very powerful oxidizing species. The effluent consisted of a "heat condensate" obtained from toxic vapors generated during various stages of the pulping process. Several operational parameters were varied and their effects on the process were observed and analyzed, in order to achieve its optimization. In addition, heterogeneous photocatalysts such as cupric oxide (CuO) were also investigated as a complement to the photooxidation process.The main parameter used to determine the quality of the wastewater before and after photooxidation was the Chemical Oxygen Demand (COD), using a closed reflux standard procedure. COD values of the treated solution were determined at subsequent time intervals and used to draw curves illustrating the rate of oxidation of the wastewater. Other parameters, such as Dissolved Organic Carbon (DOC) and dissolved lignin concentration, were investigated towards the end of the research in order to obtain a more complete characterization of the quality of the wastewater after treatment.The experimental data reveal that there is an optimal $ rm H sb2O sb2$ concentration that is best suited for the photooxidation of the effluent. Moreover, an increase in temperature accelerates the rate of elimination of COD. An increase in effluent concentration is detrimental to the speed of the process, since it causes an increase in its absorbance which can act as a barrier against UV light. The efficiency of the photooxidation process is not affected by variations in the initial pH of the wastewater. Cupric oxide (CuO), when exposed to UV light, efficiently catalyzes the production of OH radicals and is therefore very beneficial to the photooxidation process