Biofilm Stress Effects And Blocking Mechanisms Of Trace Amounts Of Sulfadiazine/2,4-D In Drinking Water

Micropollutants exist widely with concentration levels ranging fromμg/L to ng/L exist widely in drinking water sources,drinking water treatment processes cannot completely remove these micropollutants currently.Microorganisms stress response under prolonged exposure to micropollutants such as antibiotic and pesticide may pose a hazard to drinking water,such as the increase of disinfection byproducts（DBPs）precursors and proliferation of antibiotic resistance genes（ARGs）.Biological activated carbon（BAC）as a core advanced treatment process of drinking water treatment utilizes its adsorption capacity and biodegradation to remove micropollutants,addressing the microorganisms stress response is essential to controlling the increase of DBPs precursors and ARGs.The paper studied the removal mechanism of DBPs precursors and ARGs in drinking water by BAC and its improved process,aiming at the stress effect of sulfadiazine（SDZ）and 2,4-Dichlorophenoxyacetic acid（2,4-D）on microorganisms.The main research contents and conclusions are as follows:（1）The drinking water biofiltration process was constructed with coconut shell activated carbon（CAC）as filler.Study effects of biofilm stress response on N-DBPs precursors and ARGs during BAC treatment.The results showed that under complex SDZ and 2,4-D,the total formation potential of N-DBPs was 751.47 ng/L,which was much higher than the control group（440.67 ng/L）,the relative abundance of ARGs（17.27%）was more than twice that in the control group in BAC effluent.Complex SDZ and 2,4-D induced overexpression of functional genes for microbial protein synthesis,leading to secretion of extracellular polymeric substance secretion（EPS）.Meanwhile,the dominant microorganisms of the complex SDZ and 2,4-D contributed to the production of precursors of N-DBPs and enhanced the horizontal transfer of ARGs.（2）The drinking water biofiltration process was constructed with coconut shell activated carbon loaded with Fe（CAC-Fe）as filler.It was found that the CAC-Fe filter could efficiently diminishing the stress effects of complex SDZ and 2,4-D on biofilm controlling the production of precursors of N-DBPs and the propagation of ARGs.Reducing the metabolic demand of exogenous carbon by microorganisms in a synergistic interaction between microorganisms and Fe²⁺/Fe³⁺,thereby weakening its stress effect on microorganisms.This resulted in the down-regulation of the expression of microbial oxidative stress response related enzyme genes and reduced microbial EPS secretion,inhibiting the generation of N-DBPs precursors and the horizontal transfer of ARGs.（3）Biofiltration reactor was constructed with g-C₃N₄/Cu-Al₂O₃/Al₂O₃（HCLL-S8-M）as filter.The results showed that HCLL-S8-M efficiency removed N-DBPs precursors and ARGs was much higher than that of CAC filter.Microorganisms gained electrons from the electron-rich area while the organic matter adsorbed in the electron-poor area was cleaved,under the collaboration between microorganisms and a dual electron-rich/poor reaction center on the surface of HCLL-S8-M,which diminished the stress effects of the complex SDZ and 2,4-D on microorganisms.Furthermore,the expression of microbial oxidative stress response and amino acid biosynthesis functional genes were down-regulated,and the secretion of microbial EPS in filter was reduced,which further controlled the increase of N-DBPs precursors and the propagation of ARGs.