Effect Of Polytetrafluoroethylene Nanoplastics On Combined Inhibition Of Bivalent Copper And Ciprofloxacin On Nitrogen Removal In Sequencing Batch Reactor

The pollution of nanoplastics（NPs）to aquatic ecosystem has attracted worldwide attention,but its occurrence and impact in wastewater treatment plants（WWTPs）are rarely reported.The activated sludge process can effectively remove pollutants in the wastewater treatment process.Removing nitrogen plays an important role in wastewater treatment,which requires the participation of many functional microorganisms.Due to the fact that WWTPs are important gathering areas for various pollutants,they may cause the coexistence of NPs,heavy metals,and antibiotics in wastewater.Due to NPs has large specific surface area,it can adsorb heavy metals and antibiotics.That may be more toxic to microorganisms when it was adsorbed by sludge.Therefore,it is urgent to understand the effects of NPs,heavy metals,and antibiotics on the removing nitrogen process of activated sludge systems,especially the related toxic effects.This article focuses on polytetrafluoroethylene nanoparticles/microplastics（PTFE-NPs/MPs）,divalent copper(Cu²⁺),and ciprofloxacin（CIP）as research objects.The effects of PTFE-NPs/MPs,Cu²⁺,and CIP on biological nitrogen removal efficiency were studied by using sequencing batch reactors（SBRs）.（1）In the long-term impact experiment of single PTFE-NPs on the nitrogen removal performance of SBR process,the average removal rates of COD and NH₄⁺-N decreased to 85.91%and 79.18%,respectively,under the pressure of PTFE-NPs.The average contents of NO₂^--N and NO₃^--N were 0.25 and 4.05 mg L^-1,respectively.Compared with seeding sludge,the average specific oxygen consumption rates（SOUR）,specific ammonia nitrogen oxidation rates（SAOR）,specific nitrate nitrogen oxidation rates（SNOR）,and specific nitrate nitrogen reduction rates（SNRR）were reduced by 65.26%,65.24%,41.77%,and 54.56%under the PTFE-NPs pressure,respectively.The impact of inhibition of PTFE-NPs on the activities of ammonia oxidizing bacteria（AOB）was stronger than those of nitrite oxidizing bacteria（NOB）.Compared with seeding sludge,the content of reactive oxygen species（ROS）and the release of lactate dehydrogenase（LDH）increased by 130%and 50%,respectively,under the pressure of PTFE-NPs.Under the action of PTFE-NPs,the protein（PN）contents were higher than those of sugar（PS）in loosely attached extracellular polymers（LB-EPS）and tightly attached extracellular polymers（TB-EPS）,indicating that extracellular polymers（EPS）mainly reduced the effect of PTFE-NPs on cells through PN.In addition,PN in LB-EPS was more sensitive to PTFE-NPs than that in TB-EPS.The amino,carbonyl,and nitrile groups in PN and the hydroxyl groups in PS played important roles in the interaction between EPS and PTFE-NPs.（2）In the long-term impact experiment of PTFE-NPs on the combined effects of Cu²⁺and CIP to suppress the nitrogen removal performance of SBR process,the combined inhibitory effect of Cu²⁺and CIP on COD and NH₄⁺-N removal were different from those without PTFE-NPs stress.Compared with seeding sludge,the addition of PTFE-NPs weakened the antagonism of mixed Cu²⁺and CIP on SOUR,SAOR,SNOR and SNRR.The adsorption kinetics experimental results showed that the maximum adsorption capacities of PTFE-NPs for Cu²⁺in the binary and binary systems were 0.85 and 0.89 mg g^-1,respectively,and the maximum adsorption capacities for CIP were 1.01 and 1.28 mg g^-1,respectively.The maximum adsorption capacities of PTFE-NPs for Cu²⁺and CIP in the binary system were always higher than those in the binary system.The experimental results of adsorption thermodynamics indicated that the adsorption processes of PTFE-NPs on Cu²⁺and/or CIP were non spontaneous,and the complexes of PTFE-NPs with Cu²⁺and/or CIP were unstable,and Cu²⁺and/or CIP could be resolved from the unstable complexes with PTFE-NPs,Cu²⁺and CIP.PTFE-NPs altered the sensitivities of AOB and NOB to CIP,but did not alter their sensitivities to Cu²⁺and mixed Cu²⁺/CIP.Cu²⁺and CIP had antagonism on denitrification bacteria whether PTFE-NPs were added or not.In the ternary and binary systems of Cu²⁺and CIP,whether PTFE-NPs were added or not,the protective effect of PN in LB-EPS on bacteria was more important than TB-EPS.In addition,PTFE-NPs reduced the binding of amino,hydroxyl,carbonyl,and nitrile groups with mixed Cu²⁺/CIP.（3）In the short-term impact of the combined effects of PTFE plastic particles,Cu²⁺and CIP on the nitrification process,the inhibitory effects of Cu²⁺,CIP,and PTFE-NPs/MPs（800 nm,3μm and 15μm）and its binary and ternary combination systems on sludge activity were concentration dependent.And its inhibitory effects gradually increased with the increase of concentrations.In the Cu²⁺+CIP mixed systems,CA models were more suitable for predicting the toxicity of the mixture than IA models.In the mixed systems of Cu²⁺+PTFE plastic particles with different particle sizes,the CA models were more suitable for predicting the toxicity of the mixture to AOB than the IA models.At the same time,with the increase of plastic particle sizes,the toxic effects of Cu²⁺and PTFE-NPs/MPs mainly changed from antagonism to synergistic effects.When the reaction time was 60 min,with the increase of the plastic particle sizes,the toxic effects of the mixture on NOB changed from antagonism to synergistic effects and finally to antagonism.In the CIP+PTFE plastic particle mixture systems with different particle sizes,some mixture combinations had antagonistic or synergistic effects on AOB.At the same time,as the plastic particle sizes increased,there were no significant changes in the toxicity of binary mixtures to NOB.In the ternary mixed systems of Cu²⁺,CIP and plastics with different particle sizes,the combined systems were either suitable for CA models or suitable for IA models to predict the toxicity trends of the mixture,and some of them show synergistic or antagonism effects.