Study On Processes And Mechanism Of Dmso Production Wastewater Treatment Enhanced By Microwave

Dimethyl sulphoxide (DMSO) is an organic solvent or intermediate, which has been widely used in the manufacture of products such as acridine, electronics, chemical industry and etc.. However, the residual DMSO in wastewaster of DMSO production will produce volatile and noxious compounds in natural water body, such as (CH3)2S or hydrogen sulfide (H2S). Furthermore the biological treatment of wastewater containing DMSO is known to be difficult. On the other hand, the effluents of oxidation section in DMSO production process contain high-concentration nitrite, which can't be effectively removed by biological and physicochemical processes. To resolve the above technical problems with the treatment of wastewater in DMSO production process, catatlytic wet oxidation process, Fenton process and chemical reduction process were employed to combine with microwave technology. Based on the advantage of high efficiency and quickness under microwave irradiation, three efficient microwave enhanced process on wastewater treatment were established to treat with DMSO and nitrite. As a result, optimal removals were achieved after the treatment of the above microwave enhanced processes.In the first part of the paper, CuOx-CeOy/GAC catalyst was prepared by using impregnation-deposition method, in which GAC activated by HNO3 was used as carrier, Cu was used as activated composition and Ce was used as assistant composition. According to the results of structure analysis, Cu element existed in the form of Cu (elementary substance) and Cu2O and Ce element existed in the form of CeO2, Ce2O3 and CeO on the surface of CuOx-CeOy/GAC catalyst. It is believed transition metal with different valent states could adsorb more microwave energy, that would facilitate the catatlytic wet oxidation process. By the addition of Ce, the loading percentage of Cu increased both on the surface and in the catalyst. The loading percentage of Cu was 10.81% of the catalyst while Ce was 0.56%. In light of the assistant composition Ce, better dispersity and smaller size of Cu and Cu2O crystals could be achieved, that intensified the interaction between actived composition and carrier, increased the activated sites and enhanced the stability and useful life of catalyst. Microwave enhanced catatlytic wet oxidation process was established with the prepared CuOx-CeOy/GAC catalyst. Under the optimal process conditions, 100mL synthetic wastewater containing 1000mg/L DMSO was treated in the process and over 85% of DMSO and 24.4% of total organic carbon (TOC) had be successfully removed within 3min and pH range 3~9.The oxidation mechanism of microwave enhanced catatlytic wet oxidation process was also studied in the paper. The fluorescence technology was employed to measure the generation of hydroxyl radicals (·OH) in different processes and the compared results demonstrated the use of CuOx-CeOy/GAC catalyst played a key role in the the generation of hydroxyl radicals. The generation of·OH in microwave enhanced catatlytic wet oxidation process was much more than in other processes, which indicated synergistic effect existed among microwave irradiation, catalyst and H2O2. As a result, the removal efficiency of DMSO was obviously enhanced.Microwave enhanced Fenton process for DMSO treatment was also established in this paper. Under optimal conditions of [H2O2]0=450mg/L, H2O2/Fe2+ molar ratio=2, microwave power=100W, irradiation time=5min and pH=2~7, 100mL synthetic wastewater containing 1000mg/L DMSO was treated when over 95% of DMSO and 46.3% of TOC had be successfully removed. Based on the results of batch experiments, dynamic system for practical utility was devised, which realized the efficient treatment of DMSO-containing wastewater under continuous flow. The optimized operating parameters for dynamic system were [H2O2]0=400mg/L, system temperature=60℃, circulating finished time=10min and air flow rate=20L/h, which had achieved DMSO removal of 99.1%Obvious kinetic experiments were conducted to study the differences between microwave enhanced Fenton process and conventional heating assisted Fenton process. Compared with heating assisted Fenton process at equal temperature, enhanced DMSO removal in microwave enhanced Fenton process might be ascribed to the non-thermal effect under microwave irradiation. According to results of major degradation intermediates variation and TOC removal, microwave enhanced Fenton process couldn't only shorten the degradation time for DMSO but also achieve much more removal of major degradation intermediates and TOC compared with Fenton process stirring at ambient temperature.In the final part of the paper, using sulfaminic acid as reductive chemical, microwave enhanced chemical reduction process was established to treat the practical nitrite-containing wastewater of high-concentration in DMSO production process. Based on the results of batch experiments, microwave enhanced chemical reduction continuous-flow process for practical utility was devised and achieved over 90% nitrite removal under optimal operating conditions. Compared with chemical reduction continuous-flow process without microwave irradiation, microwave enhanced chemical reduction continuous-flow process could save 25% sulfaminic acid, shorten the hydraulic retention time (HRT) from 3h to 0.5h, and save 45% cost for the treatment of every 1m3 wastewater. After treatment by microwave enhanced chemical reduction continuous-flow process, most nitrite in wastewater was converted into nitrogen gas and other reaction products were some innocuous inorganic compound. The concentration of nitrite was falling to a low level, which made it much less nocuous and suitable for further biological denitrification.In this paper, catatlytic wet oxidation process, Fenton process and chemical reduction process were combined with microwave technology to enhance the treating efficiency, and thus three new microwave enhanced processes were established for the treatment of DMSO or nitrite wastewater. The microwave enhanced processes for wastewater treatment take advantages in high treating efficiency, wide operational pH, quick reaction rate and proper effluent temperature. Furthermore the microwave enhanced processes need less occupation of land, operate easily, and is in favor of industrial popularity. The research results in this paper could not only provide a valid solution for DMSO and nitrite wastewater treatment in DMSO production process but extend series of new promising processes for the treatment of refractory and high-concentration nitrite wastewater in wide fields.