The Effects Of Dom And Heavy Metals Of Biogas Slurry On The Photochemical Behavior Of Sulfamethazine

Antibiotics have been increasingly detected in environmental media as emerging environmental pollutants and their transportation, conversion, environmental fate and health risk have attracked rising attention. Because of the widespread use of antibiotics for humans and veterinary purposes, the biogas slurry produced by livestock industry becomes potential repository of antibiotics and antibiotic resistance genes. The photochemical behavior of antibiotics and the removal of resistance genes in biogas slurry have gained acute concern. Therefore, the present study selected sulfamethazine (SM2) as the representative sulfonamides antibiotics, investigated its photodegradation kinetics in different water bodies and the effects of UV-irradiation on resistance genes in the biogas slurry.Firstly, the effects of light sources, initial concentrations, pH and reactive oxygen species (ROS), H2O2 on photochemical degradation of SM2 in aqueous solution were investigated. The experimental results indicated that:1) The photolysis of SM2 follows pseudo-first-order kinetics equation, and the photolytic rate constants of SM2 under different light sources were significantly different, k (300 W ML)> k (1000 W XL). Under the same photolysis conditions, its photolytic rate constants decreased with increasing initial SM2 concentrations. The pH values of solution significantly influenced the photolysis rates of SM2; 2) Reactive oxygen species (ROS) scavenging experiments indicates that the photolysis of SM2 involves direct photolysis and self-sensitized photodegradation via singlet oxygen (1O2); 3) Under UV-vis irradiation, adding appropriate amount of H2O2 can generated·OH which promotes the photolysis of SM2. However, excessive H2O2 becomes·OH quencher that inhibits the photolysis of SM2.The photodegradation experiments of SM2 were performed under irradiation of ultraviolet (UV-vis) to study the effects of dissolved organic matter(DOM), heavy metal ions and their complexes.The experimental results indicated that:1) Humic acid (SRHA) and Fulvic acid (SRFA) could inhibit the photolysis of SM2, and the inhibitory effects increase with increasing concentrations of SRHA or SRFA. The main reason is the masking effect of light; 2) The coexistence of SRHA and Cu(II) or Zn(II) in solution promotes the photolysis of SM2 due to the formation of metal ions-SRHA complex; 3) Experiments were carried out to clarify the effects of different DOM on SM2 photodegradation. When DOM from different sources were added into SM2 solutions, the biogas slurry DOM promotes the photodegradation of SM2 and the other DOM restrain the photodegradation of SM2. This is mainly because the different sources of DOM have different compositions and photochemical properties, resulting in the different effects on the photolysis of SM2; 4) Adding biogas slurry into SM2 can promote the photolysis of SM2, and the photolysis rate first increases then decreases with increasing volumes of biogas slurry.35.8mL addition of biogas slurry leads to the highest photolysis rate.Since biogas slurry contains a large number of resistance genes, we also investigated the effects of UV light on resistance genes.The results show that:1)The concentrations of resistance genes decreased with prolonging UV irradiation, indicating that UV light can effectively eliminate resistance genes of the biogas; 2) Under UV irradiation,different resistant genes have different degradation trends,which comes from the different tolerance of resistance genes to UV light; 3)Under irradiation of 300 W and 500 W mercury lamp, the degradation patterns of resistance gene aresimilar. However, they have different degradation rates, the degradation rates of ARGs is faster under irradiation of 500 W than 300 W mercury lamp, may be the different light intensity of the two sources.In conclusion, this study revealed the photochemical behavior of sulfamethazine in pure water and simulated biogas slurry, and the effects of UV light on resistance genes.The results can help us to better understand the environmental fate and ecological effects of sulfamides, andprovide theoretical and scientific basis for pollution control and ecological risk assessment of these antibioticsand biogas slurry.