Study on Wet Air Oxidation of Antibiotics
|School||East China University of Science and Technology|
|Keywords||wet air oxidation enrofloxacin sulfadazine oxytetracycline co-oxidation|
Every year, more than 5,000 tons of antibiotic wastewater is discharged in China, which is the largest antibiotic production and consumption country all over the world. The wastewater contains toxic and highly concentrated recalcitrant contaminants for which conventional biological treatment is not feasible. By using wet air oxidation (WAO), these organic pollutants are either partially oxidized into biodegradable intermediates or mineralized to carbon dioxide, water, and innocuous end products. In this thesis, enrofloxacin (ENR), sulfadiazine (SDA) and oxytetracycline (OTC) with extensive occurrence were chosen as model compounds for WAO treatment.A deep oxidation method for Catalytic Wet Air Oxidation (CWAO) of ENR with FeCl3 and NaNO2 as catalyst was developed. At 150℃,0.5MPa and 120 minutes of reaction condtions, ENR was almost completely eliminated, and removals of COD and TOC were 37% and 51%, respectively. The primary degradation products were detected by LC-MS, and the corresponding reaction pathways were proposed. End degradation products were identified by GC-MS and IC, indicating that biodegradable compounds are generated. In addition, the BOD5/COD ratio of reaction solution increased from 0.01 to 0.12, and the inhibition of bioluminescene decreased from 43% to 12%. With comparison of the well developed method of ozonation, CWAO of ENR shows higher mineralization degree and lower ecotoxicity.Simultaneous OTC and ENR wet air oxidation, a co-oxidation system, was investigated. In this system, OTC and ENR could be effectively degraded under optimal conditions. The degradation products detected by LC-MS, GC-MS and IC implied the generation of biodegradable compounds. The increase in BOD5/COD ratio and decrease in ecotoxicity demonstrated that this co-oxidation was an efficient pretreatment for antibiotic wastewater. Moreover, it was found that the presence of OTC in the system could promote the generation of H2O2, thus initializing the oxidation. After using LC-MS/MS with DMPO as trap agent, DMPO-OH was detected, indicating that hydroxyl radicals were generated during the process.CWAO of SDA with NaNO2 as catalyst was also investigated. Results demonstrated that removals of COD and TOC were low under optimal conditions. The high toxicity of aqueous solution after oxidation showed the formation of toxic and recalcitrant intermediates. Moreover, ozonation of SDA was studied and found to be effective for the treatment of SDA with high removal of TOC and COD and lower economic costs.