Water Falling Film Dielectric Barrier Discharge Induced Degradation Of Sulfadiazine Antibiotics In Aqueous Solution

Sulfadiazine (SDZ,4-amino-N-(2-pyrimidinyl) benzene sulfonamide), is a potent antibacterial agent belonging to the sulfonamide class of antibiotics and is widely used as veterinary and human medicine. After administration to livestock, about 50% of SDZ is excreted through manure as is, and 30% is excreted as an acetyl conjugate. The major route through which SDZ antibiotics enter the environment is the excretion of faeces and urine from animals medicated in livestock and poultry farming, and the subsequent application of contaminated manure as fertilizer into agricultural land. So it may enter the food chain by plant uptake, may leach into groundwater, or may occur in surface water via runoff, and finally result in antibiotic resistance and toxicity effects. Thus, the search for new technology to prevent water contamination by antibiotic residues is necessary because of the risks that they pose for the environment and for human health.In this research SDZ was selected as the target contaminant, and a new water falling film dielectric barrier discharge was applied to the degradation of SDZ in the aqueous solution. The results indicated that the water falling film dielectric barrier discharge was very effective in the degradation of SDZ; the inner concentrations of 10 mg/L SDZ can be all removed within 30 min. The parameters that affect the degradation of SDZ such as output power intensity, solution flow rate, pH value, inner concentration and inner conduction were all strongly affected the SDZ degradation efficiency. Secondly, it was investigated the effectives additive Fe2+、Cu2+、TiO2 and carbonate salt on the removal efficiency of SDZ. The results indicated that the existence of Fe2+、Cu2+ and TiO2 in the liquid phase can promote the degradation of SDZ, but the high concentrations of Fe2+ would inhibit the degradation. The removal efficiency of SDZ declined when the carbonate salt was added into the reaction system, because the ·OH was captured and then the amount of ·OH that reacted with SDZ would reduce.In this research, the effects of the radical scavengers during the degradation process of SDZ were also invested. The degradation of SDZ was enhanced by the addition of hydrogen radical scavengers, and was inhibited by adding hydroxyl radical scavengers, although both additives can increase the concentrations of H2O2 in aqueous solution. But for the scavengers of hydrogen radical and hydroxyl radical, the mechanisms for increasing the H2O2 are different. The results obtained for the change of TOC indicated that the intermediates were quite refractory to further mineralization, leading to ineffective mineralization. The existence of Fe2+ and CCl4 in the liquid phase can promote the degradation and mineralization of SDZ. It was found that the degradation of SDZ was enhanced by CCl4 was mainly because of the increase of · OH due to the reaction of CC14 with*H that reduce the chances of their recombination with ·OH. The eight intermediates identified by LC-MS analysis revealed that the water falling film dielectric barrier discharge induced degradation of SDZ was mainly controlled by the oxidation of ·OH radicals. Most of these intermediates were almost completely removed after 30 min treatment time. However, traces of intermediates containing recalcitrant molecular structure can still be detected after treatment.