Study On Catalytic Degradation Of Antibiotics By Chloroperoxidase

According to the report abuse of antibiotics has become one of the great difficulties in China at present. The consequences of the abuse of antibiotics in addition to the medical treatment cost growth, resistance to enhance, the potential threat to the environment pollution also not allow to ignore. Most of antibiotics are found in environment after ingest in human body as they are usually not metabolized. In recent years, antibiotics were frequently detected in surface water, ground water, rivers and soil at concentrations ranging from ng·L-1 to μg·L-1. The general physical treatment methods of antibiotics could do nothing due to the smaller residual, structure stability and not easy to be destroyed in environmental water. Various chemical methods such as Fenton oxidation exist methods complex and secondary pollution and so on all kinds of problems. Aiming at the bottleneck of antibiotic wastewater treatment technology, a rapid and efficient enzymatic degradation by chloroperoxidase (CPO)-H2O2-Cl- was presented in this work. Sulfamethoxazole, sulfadimethoxine, sulfamerazine, sulfamethazine, sulfacetamide, lincomycin and norfloxacin of seven organic compounds were selected as substrates to research the degradation conditions, degradation products, degradation mechanism of CPO and substrates, COD detection and toxicological evaluation of products. Based on the experimental results, the following conclusions are drawn:(1) Optimization of enzymatic degradation process:This work mainly investigates the influence of the pH of buffer solution, reaction time, concentrations of H2O2 and CPO on the degradation efficiency. Overall, the degradation of this system need to be in the acidic environment, pH should be maintained at 3-5; H2O2 concentration was in mM level (0.1 mmol·L-～0.12 mmol·L-1); While the most advantage of this system is that the amount of enzyme required was very few in nM level (0.6 nmol·L-～15 nmol·L-1). Under optimum conditions, the degradation efficiency can almost reach 100% in the 10 min～20 min, and show a tempting application prospect.(2) Analysis of the degradation products and mechanism:The HPLC-MS technology was employed to determine the degradation products, and the degradation pathway was speculated accordingly. The results showed that the four drug molecules were broken into smaller pieces effectively after CPO-H2O2-CI- process. Combined with activated sludge, the removal rate of COD is ideal. It shows that the biodegradability of the degraded fragments was increased. So this enzymatic oxidation by CPO and activated sludge can be taken as a very efficient treatment to decontaminate pollutants completely.(3) Catalytic cycle of CPO:CPO has a variety of catalytic properties due to its unique active center. The chlorination activity of CPO was the most unique catalytic activity was used in this study. Firstly, CPO was oxidized by H2O2 to generate a compound I intermediate. Compound I could be best described as an oxyferryl π-cation radical ([(Fe4+=O)’+]). Compound I oxidized Cl" of solution quickly to generate Cl2 or HClO, which was small active molecular and could oxidize substance. The catalytic oxidative reaction was carried out in fact in bulk solution instead of in active site of enzyme, thus achieve the CPO catalytic oxidation degradation of the substrate, which would get rid of the restriction of the size of substrate required by the channel access to substrate pocket in enzymatic active site.(4) Performance and safety evalution of CPO-H2O2-Cl- process:The results showed that the COD value of four substrates was decreased when the drugs treated by enzymatic degradation process. Especially combined with the activated sludge treatment, the removal rate of COD was achieved 42.61%～65.31%. Toxicity test was carried out using green algae Chlorella Pyrenoidosa as ecological indicators. Drug concentration required to cause 50% reduction in growth (EC50 value) was calculated under different degradation efficiency. The results showed that the EC50 value increased rapidly as degradation efficiency was increased. These results demonstrated that the degraded products of antibiotic had lower toxicity compared with the parent compounds.