Experimental Study For Treating Cephalexin Contaminated Wastewater

Cephalosporin are widely used antibiotics in recent years.More than 60 cephalosporin antibiotics are available,and most of them show relative high stability and broad antibacterial spectrum.The antibiotics are widely used clinically to treat the infection caused by Gram-negative bacteria.In recent years,the antibiotic residues have been widely detected in surface water,groundwater,and soil.Nowadays,the residual antibiotic pollution in the environment has aroused great attention.Residual antibiotics will lead to an increase in drug-resistant bacteria,increasing spending on disease treatment.The enrichment of antibiotics through the food chain will also threaten human health.Aiming at efficient removal of cephalexin from wastewater.This research investigated the photocatalytic degradation and high-efficiency biological treatment of cephalexin contaminaed wastewater.The research results can provide a technical reference for the removal of antibiotics from wastewater.An efficient photocatalyst TWC3 was synthesized by a simple hydrothermal method and high-temperature calcination.The optimal synthesis mass ratios of WO3 and Carbon quantum dots(CQDs)were 2%and 3%,respectively.According to the first-order rate constant k fitted by the photocatalytic degradation kinetics of cephalexin,the catalytic activity of TWC3 is 3.1 times and 46.6 times that of pure TiO2 and pure WO3,respectively.A series of material characterization methods such as XRD,XPS,TEM,and BET have proved that TiO2,WO3,and CQDs are well combined.UV-DRS,PL,EIS,and visible light experiments were used to explore the photocatalytic mechanism.The results show that WO3 can form a heterojunction with TiO2,thereby improving the separation of electrons and holes,and expanding the visible light absorption spectrum.On the other hand,by using CQDs as photo-generated electron channels,the transfer rate of photo-generated electrons is faster,and the visible spectrum is further broadened,which significantly improves the photocatalytic activity.Free radical quenching experiments reveal that the reactive species such as holes,·OH,1O2,and·O2-are presented in the photocatalytic reactions,and their ability to contribute to oxidizing organics is in the order of:holes<1O2<·OH<·O2-.LC-MS was used to detect the photocatalytic degradation products of cephalexin.Based on quantitative structure-activity relationship(QSAR)predictions,the toxicity of cephalexin and its degradation intermediates was calculated using toxicity estimation software(T.E.S.T.).The results showed that some intermediates have higher biotoxicity than cephalexin.However,the biological potential of cephalexin wastewater can be significantly reduced because the mineralization efficiency of cephalexin can reach 92.4%after 4 h of photocatalytic experiments.A strain CQ2 capable of efficiently degrading cephalexin was isolated from the domestic sewage sludge.The 16S rDNA gene sequence identification reveal that the strain is Ochrobactrum sp.The strain cannot directly use cephalexin as the sole carbon source,but can use other organic substances such as glucose to degrade cephalexin under co-metabolism.The effects of temperature,pH,mixing strength and inoculum on the growth of CQ2 bacteria and the degradation efficiency of cephalexin were investigated.The results showed that the optimal culture conditions were 30?,pH 7.0,150 rpm,and 5%inoculation.After 28 h of culture under these conditions,the degradation rate of cephalexin at an initial concentration of 10 mg·L-1 can reach to undetected.Under optimal conditions,the 36-hour removal efficiencys of CQ2 bacteria for amoxicillin(penicillins),oxytetracycline(tetracyclines),sulfadiazine(sulfamin),and pefloxacin(quinolone)antibiotics were undetected level,62.34%,50.29%,5.12%,respectively,indicating that CQ2 also has a good removal effect on amoxicillin,but has poor resistance to pefloxacin.LC-MS/MS was used to determine the degradation intermediates of cephalexin,and two possible degradation pathways was proposed for degradation of cephalexin.The high-efficiency degradation bacteria for cephalexin(CQ2)and sulfadiazine(JSD2)were applied to actual wastewater.The antibiotics in pig farm wastewater were removed through batch and pilot tests.Compared with the cotrol test,the ability to remove antibiotics was slightly improved but the enhancement is not significant.Traditional activated sludge can also efficiently remove antibiotics from water in the SBR device after short-term domestication,and the overall removal efficiency is about 90%.Due to the low concentration of antibiotics(in the[?g·L-1 and ng·L-1 levels)in the pig farm wastewater used in the experiment,large detection inaccuracy appeared(detection error is 10%-20%).The removal efficiency of antibiotics without bacteria reaches 90%,which greatly increases the difficulty in evaluating the performance of high-efficiency degradation bacteria in degrading antibiotics in real wastewater.Therefore,an additional 10 mg·L-1 antibiotic was added to the actual water for subsequent testing.The optimal dosages of CQ2 bacteria and JSD2 bacteria for treating real water were 10%and 15%,respectively.In the pilot test,it was found that the addition of JSD2 bacteria slightly improved the removal of sulfadiazine.The sulfadiazine removal efficiency was increased by 1.91 times compared to the blank experiment,but the overall removal efficiency was less than 1/3 of the small test result.This resuts can be due to the low temperature at the pilot site,and the continuous inflow of wastewater with high antibiotic concentration.However,in the pilot test of CQ2 bacteria,the effect of CQ2 on the antibiotics removal in the pilot test cannot be verified because cephalexin cannot be detected in real water.