Removal Of Sulfonamides From Synthetic Urine By Advanced Oxidation Process Based On Biochar

Antibiotics contamination has attracted more and more attention for their possible adverse effects on natural ecosystem and human health.Urine contains high nutrients（such as P and N）and lots of pharmaceuticals,if discharged into the sewage system directly,would increase the burden of wastewater treatment process obviously.Source-separated urine would not only favor for the removal of pollutants,but also achieve the recycle and reuse of nutrient elements.Herein,five typical sulfa antibiotics（including sulfamethoxazole,SMX;sulfadiazine,SDZ;sulfadimethoxine,SDM;sulfamethazine,SMT;and N₄-acetyl-sulfamethoxazole,NSMX）were selected as target compounds to investigated the removal efficiency,influence factors and mechanisms in buffered solution and synthetic urine matrix by biochar and coupling technologies（biochar/H₂O₂and biochar/PDS）.Biochar used in this research was derived from cotton straw biochar under 350℃with the absence of oxygen.The adsorption of five sulfa antibiotics（SAs）on biochar with different dosage was first studied.Results shown that the adsorption of SAs was inhibited in urine compared with that in buffered solution.Langmuir isotherm model well described the adsorption process in both buffer and urine matrices.Adsorption and desorption rates were estimated by a kinetic model,which well fitted the removal of SAs in aqueous phase at various biochar doses.The adsorption of SAs on biochar was due to multiple forces,in which van der Waals forces and hydrophobicity played major roles in distinguishing their sorption behavior of different SAs.CO₃^·-was the dominant reactive species in biochar/H₂O₂ system.Considering that urine matrix could affect the removal efficiency of antibiotics in biochar system,the effect of three main urine components（NH₄⁺,Cl^-and HCO₃^-）on the adsorption and degradation of SAs was tested in this study.Results indicated that HCO₃^-was the most important factor affecting the antibiotic adsorption process,and it inhibited the adsorption of antibiotics by competing for binding sites on biochar.In biochar/PDS system,NH₄⁺and HCO₃^-inhibited the degradation process of SMX and NSMX slightly in batch experiments.However,the results in column experiments showed that urine component favored for PDS decomposition and enhanced the removal of antibiotics.Finally,electron paramagnetic resonance spectroscopy（EPR）and radical-quenching experiments indicated that·OH radical,singlet oxygen（¹O₂）and surface-bound radicals were produced in biochar/PDS system and dominant the oxidation of antibiotics synergistically.Toxicity test showed that the products of SMX after biochar/PDS treatment retained no obvious antimicrobial property.This study may help to improve the understanding of the catalytic role of biochar,and provide cost-effective treatment options for urine.