Experimental Study On The Treatment Of Antibiotic Wastewater By Catalytic Wet Oxidation

The COD concentration of antibiotic wastewater is high,and the biological toxicity is strong,it is difficult to be degraded by microorganisms,and its in the environment poses certain risks to the ecological environment and seriously threatens human health.The traditional sewage treatment method degrades slowly and is inefficient.Catalytic Wet Air Oxidation(CWAO)is a technology for the effective treatment of highly concentrated organic wastewater,which has attracted wide attention due to its high efficiency and non-selectivity.At present,the research on the treatment of antibiotic wastewater by catalytic wet oxidation mainly stays in the laboratory exploration stage,and the degradation and transformation mechanism,degradation pathway,kinetic parameters and degradation efficiency of organic matter and nitrogen in antibiotic wastewater are not clear.Therefore,it is of theoretical significance and practical application value to study the efficacy of catalytic wet oxidation in treating antibiotic wastewater and explore the degradation mechanism of organic matter and nitrogen for determining process parameters and promoting practical engineering application.This paper takes cephalexin simulated wastewater(COD_cr value is about5500mg/L)as the treatment object,and carries out experimental research on the treatment of antibiotic wastewater by catalytic wet oxidation.The main research contents and conclusions are as follows:(1)Preparation and characterization of catalystScanning electron microscopy(SEM),Fourier transform infrared(FI-TR),X-ray diffraction(XRD)and BET analysis were used to investigate the effects of catalyst types and preparation methods on the catalytic performance.The results show that the Cu SO₄-AC catalyst has the highest activity and can effectively reduce the concentration of COD_cr and TN under the condition that coconut shell activated carbon is selected as catalyst carrier,the concentration of impregnation solution is 0.1mol/L and the condition of no calcination.The structure of Cu SO₄-AC was characterized by FT-IR.The results showed that the main oxygen-containing functional groups on the activated carbon carrier included hydroxyl and carbonyl groups.The catalysts were characterized by SEM,XRD and FT-IR,and it was found that the main active substances supported on the catalyst were cupric sulfate trihydrate and cupric sulfate pentahydrate.BET detection and analysis showed that Cu SO₄-AC catalyst had a large specific surface area and pore size was mainly concentrated in micropores.(2)Influence factors of catalytic wet oxidation on the treatment of cephalexin wastewaterThe influence factors of reaction temperature,p H value,reaction time,catalyst type and concentration were tested.The results showed that under the same reaction conditions,the treatment effect of C and N in simulated wastewater of cephalexin gradually improved with the increase of catalyst dosage,and the treatment rates of C and N reached the peak when the dosage was 50g/L.When the reaction temperature was lower(less than 180?),the degradation effect of C and N increased rapidly with the increase of temperature,while when the temperature was higher than 180?,the enhancement effect of the treatment effect decreases.Prolonged reaction time can improve the treatment effect of C and N,but when the reaction time exceeds 15min,the improvement effect slows down.The degradation effect of C gradually decreases with the increase of p H value,and the treatment effect of N is better when p H value is close to neutral.Considering the effects of various factors,it is considered that the best treatment effect of C and N elements is achieved under the conditions of catalyst dosage of 50g/L,reaction temperature of 180?,reaction time of 30min and initial p H value of5.0.The removal rate of CODcr and TN reaches about 95%and 80%respectively.(3)Catalytic and organic conversion mechanism of Cu SO₄-ACCatalysis and complexation.The surface groups of activated carbon before and after the reaction were detected and analyzed.It was found that the characteristic peaks representing carboxylic anhydride and carbonyl group almost disappeared after the reaction,while the characteristic peak-to-peak values representing hydroxyl group increased.The change of functional groups on the surface of activated carbon indicated that it participated in the chain reaction and played a certain catalytic role.HPLC-MS analysis showed that copper ions complexed with primary amine group at branch chain C₁₁ and tertiary amine group on?-lactam ring,which was helpful to initiate the chain reaction.Conversion mechanism of organic matter and nitrogen.In the reaction process,various free radicals are formed with the participation of molecular oxygen,and cephalexin molecules are attacked by free radicals,leading to a series of chain reactions,and finally to the formation of carbon dioxide and water and other mineralized substances.In the degradation process of cephalexin,the primary amine on the branch chain is complexed off and exists in the form of ammonia nitrogen.Subsequently,through a series of reactions such as chain breaking,the tertiary amine on the ?-lactam ring is gradually converted to ammonia nitrogen,and the ammonia nitrogen generated by the above reactions is eventually generated through ammonia oxidation and disproportionation reaction N₂.(4)Analysis of catalytic wet oxidation products and degradation pathway of cephalexinThe reaction products were analyzed by HPLC-MS,and it was concluded that the degradation pathways of cephalexin mainly included free radical attack,protonation reaction,ring cleavage reaction and final mineralization.Hydroxyl radicals first attack sulfur ether at S₁,C=C at C₃-C₄ and carboxyl group at C₄,and convert them into unstable macromolecules.Under the complexation action of Cu²⁺,corresponding protic compounds are generated,and then the macromolecules are gradually degraded into small molecules.Then,the benzene ring and hydrothiazine ring are decomposed into propionic acid,oxalic acid,maleic acid and small molecule amides through the ring cleavage reaction.Finally,small molecule acids are oxidized into CO₂,H₂O and N₂,etc.(5)Kinetics of catalytic wet oxidation of cephalexinThe first-order,second-order and lumped kinetics of the catalytic wet oxidation process of cephalexin at different temperatures(80?,100?,120?,150?and 180?)were fitted.The results showed that the reaction process could be divided into two stages,which was more consistent with the lumped kinetics characteristics of the two-stage first-order kinetics.The R~2 values of the first order kinetic fitting of the two stages reached 0.9426-0.9941 and 0.9139-0.9821 respectively,and the cut-off points of the fast and slow stages were all about 15min after the reaction started at various temperatures.