Degradation Of Unsymmetrical Dimethylhydrazine By O₃/UV

The application of some advanced oxidation processes(AOPs) based on O3/UV for the treatment of unsymmetrical dimethylhydrazine(UDMH) wastewater was investigated. The enhancement of VUV lamp (emitting 185nm ultraviolet) and TiO2 film photocatalyst on the degradation of UDMH was assessed in the batch experiments. For the O3/VUV and O3/VUV/TiO2, the effects of pH, UDMH concentration, ozone feed rate and carbonate concentration on UDMH removal were studied. At last, continuous flow experiments were conducted to degrade UDMH by O3/VUV/TiO2 process, and the process was modified to improve efficiency.It was showed that the degradation of UDMH by O3/UV based processes were all in accordance with the first ordor kinetic. Replacement of UV with VUV significantly increased the rates of UDMH degradation and mineralization. The enhancement of TiO2 on O3/UV and O3/VUV depended on the ozone feed rate. The enhancement decreased with the increase of ozone feed rate. O3/VUV/TiO2 is more applicable for the wastewater containing low concentration UDMH.During the degradation of UDMH by O3/VUV and O3/VUV/TiO2, pH value decreased with time. When the pH value was close to 7, the removal rate of UDMH was highest and the formaldehyde concentration was lowest. Either basic pH or acidic pH led to a lower removal rate of UDMH and a higher concentration of formaldehyde. The reciprocal of reaction rate constant decreased linerly with the initial concentration of UDMH. The reaction rate constant increased linerly with the ozone feed rate. The carbonate in the range of 0~2mmol/L had little effect on UDMH degradation. UDMH was degraded faster in tap water than in deionized water.The efficiency of O3/VUV/TiO2 for the treatment of UDMH was much lower in continuous flow experiments than in the semibatch experiments. To meet the discharge limit of formaldehyde, the retention time and ozone dosage should be increased. Moreover, the concentration of residual ozone in the exhaust gas was high and wasted. Thus, the residual ozone was introduced into a stirred tank for pretreatment of UDMH. The concentrations of intermediate formaldehyde and TOC in the effluent were obviously lowered in the modified process, and the cost was correspondingly decreased.