Studies On Photographic Wastewater Treatment By Catalytic Wet Air Oxidation

As a representative high concentration hazardous effluent, Photographic wastewater contains many undegradable and bio-toxic substances, which were listed in the National Catalogue of Hazardous Wastes. Discharged into water body without treatment, it will increase environment load dramaticly and cause serious problems. As an efficient technology for industrial wastewaters, catalytic wet air oxidation (CWAO) process was tentatively applied in the photographic wastewater treatment in this study.Ru/TiO2 catalyst, Fe-Al pillared clay catalyst and spinel type catalyst were tested in the CWAO of hospital photographic wastewater. Having high catalytic activity, Ru/TiO2 was thus selected and used in the CWAO process. Samples of waste fixer, waste developer and methyl-p-aminophenol sulfate solution were treated separatedly by WAO or CWAO process.Yielded from previous study, wet air oxidation (WAO) and catalytic wet air oxidation (CWAO) were connected in series to treat fixing wastewater. The influence of reaction time, temperature, oxygen partial pressure and pH on the performance of WAO was mainly studied and the effluent of WAO was tentatively treated by CWAO to remove its ammonia nitrogen. Preferable conditions for WAO were found to be: T=160℃, Po2=1.0MPa, t=2h, pH=4.8, with a CODCr removal rate of 79.0% and an effluent pH value of 1.4. The WAO effluent was further treated by CWAO under the conditions of pH=12.9, T=250℃,Po2=3.0MPa, t=2h, with overall CODCr removal rate of 99.8% , ammonia nitrogen removal rate of97.8% and effluent pH value of 5.6. The WAO-CWAO combined technology was shown to be effective in fixing wastewater treatment.Feasibility of pretreatment technology on hospital developing wastewater by catalytic wet air oxidation (CWAO) was studied. The optimum reaction conditions were resulted that the dosage of catalyst was at 2.0g/L, the temperature was at 220℃, the pressure was at 1.5MPa and the pH was at 8.9 by researching the effects of these factors on CODCr removal rate. The CODCr removal rate was 62.5%, the chroma removal rate was 98.0% and the ratio of BOD5/CODCr was improved from 0.07 to 0.45 under the optimum conditions. As a conclusion, it is feasible that CWAO is used to treat hospital developing wastewater as a pretreatment method for the improvement of decomposability and the benefit of bio-treatment.As the main substance of black-white developer, methyl-p-aminophenol sulfate was treated by WAO in this study. Finally, hospital photographic wastewater was further treated in the CWAO device using continuingly bubbling mode to characterize the activity and stability of the Ru/TiO2 catalyst. This paper provided some theoretical supports for the real practice of photographic wastewater treatment.