Studies On Photo-degradation Of Trace Sulfonamides In Wastewater By TiO₂

Sulfonamides are synthetic antimicrobial agents, which are used in aquaculture, animal husbandry and human medicines commonly. With the agriculture development in our country, the usage amount of sulfonamides as veterinary and fisher drugs increase every day. Some researches showed that self-decomposition of sulfonamides was slow and a considerable amount of its still remained for a long time in environment. TiO2 is considered to be the most suitable for widespread environmental photocatalytic applications due to its considerable photocatalytic activity, high stability, non-environmental impact and low cost.The degradation of trace sulfadiazine and sulfamethoxazole in water by TiO2 and TiO2 /EP was investigated. The effects of various parameters on the performance of degradation rates were studied too. It is provided some basic data for treating trace sulfadiazine and sulfamethoxazole in water. Results are showed that:(1) The photodegradation of trace SDZ in wastewater by using UV/TiO2 can get a good result at the optimal conditions. The degradation efficiency of SDZ reached 99% under the conditions of initial concentration of SDZ of 5.0 mg/L, TiO2 dose of 0.08g/L, solution pH of neutral, radiation intensity of 1000 uw/cm2 and reaction time of 50 min.(2) The photodegradation of trace SDZ (SMX) in wastewater by using UV-TiO2/EP can get a good result at the optimal conditions. The degradation efficiency of SDZ (SMX) reached 94%(96%) under the conditions of initial concentration of 5.0 mg/L, TiO2 loading of 20 wt%, solution pH of 6.7, radiation intensity of 1000μw/cm2 and reaction time of 45 (30)min.(3) The degradation efficiency of SDZ and SMX were enhanced at low concentration and was not remarkable at high concentration by HCO3-. The degradation efficiency of SDZ and SMX were slightly inhibited by SO42- and Cl-, and it was strongerly inhibited by HA, the inhibition was stronger as the concentration higher.(4) The mechanism of SDZ may involved in high oxidation ability of active hydroxyl radicals (·OH) which are strongly enough to break the S-N, C-S and S-C bond of SDZ. Froming the intermediate product:sulfanilicacid,4-(2-iminopyrimidine-1(2H)-vl)aniline, 4-(2-iminopyri-midine-1(2H)-vl) aniline salfacid. And then·OH again attacks benzene ring, C-N and C-S bond of the intermediate product, finally, SDZ is broken into SO42-, NO3-, NH4+, CO2 ect. Thus, we can concluded that the degradation of SDZ may have three pathway.