Study On The Transformation Mechanism Of Silver Nanoparticles In A~2O Treatment Process For Urban Sewage

The increasing production and use of silver nanoparticles?AgNPs?have attracted attention due to environmental and human health risks.The vast majority of AgNPs entering the environment will eventually enter the urban sewage system.But the removal mechanism of AgNPs in the urban sewage treatment system is not clear.Therefore,the overall objective of this study were:?1?to optimize the parameters of cloud point extraction?CPE?and inductively coupled plasma mass spectrometry?ICP-MS?combination process,which aimed to determinate AgNPs in municipal wastewater,by utilizing the single factor experiment and response surface methodology?RSM?;?2?to investigate the adsorption mechanism and characteristics of AgNPs on activated sludge;?3?to study the aggregation of AgNPs in aqueous solution.The single factor experiments and response surface methodology?RSM?were used to optimize the determination of silver nanoparticles in municipal wastewater by cloud point extraction?CPE?and inductively coupled plasma mass spectrometry?ICP-MS?combination process.Experimental results demonstrated that the optimized conditions for the extraction efficiency should be pH=3,40 min of water bath time,at the extraction temperature of 40°C for the centrifugal time of 10 min.And,the concentration of the silver nanoparticles in the urban sewage treatment can be quantified and identified to reach the optimized condition.It was found that the AgNPs removal rate of the inlet and outlet of the sewage treatment plant about 72%.In the adsorption experiments,the maximum adsorption capacity ranged in 12–32mg·g^-1 at temperatures of 10–30?.Thermodynamic experiments showed that the adsorption of AgNPs by activated sludge was a spontaneous and endothermic reaction.The factor results indicated that the adsorption of AgNPs onto activated sludge was influenced by electrostatic repulsion,agglomeration,and the process of oxidation and sulfurization.Activated sludge adsorbed the AgNPs with primary amino?R-NH₂?radical groups.The fixed AgNPs had an oxidation state of+1.Variation in environmental pH played a significant role in determining AgNPs behavior.The probability of aggregation got higher as the pH approaches the iso-electric point pH(pH_PZC)of AgNPs.Several ions showed different adsorption propensity on AgNPs surfaces,in the order:?1?positive ions:Ca²⁺>NH₄⁺>K⁺>Na⁺;?2?negative ions:Cl^->SO₄^2->NO₃^-.The effects of ionic strength on different coating AgNPs aggregation were different.The electrosterically stabilized?PEI-AgNPs?was similar to uncoated AgNPs,and it was easy to aggregate under acidic and high ionic strength conditions.While sterically stabilized?PVP-AgNPs?had good stability under different pH values,different electrolyte types and different ionic strengths.As IS increased,electrostatic stabilization of AgNPs would drop greatly due to compressing electric double layer and charge screening.In addition,NOM had been highly entangled to form more NOM/Ca²⁺bridging under chemical bonding,which would enhance AgNPs'aggregation.