Study On The Adsorption Performance And Transport Behavior Of Nanoplastics In Activated Carbon Filter Columns

With the mass production and use of plastic products,plastic waste inevitably enters the water environment.In recent years,there has been a lot of research on microplastics,but the research on nanoplastics is still in the primary stage.Compared to microplastics,nanoplastics are small in size,have a high specific surface area,are hydrophobic,have a high affinity for cells,and can interact with numerous contaminants.The nanoplastic can enter biological tissues,blood and cells,which is a threat to human health.The flow of nanoplastics discharged into the water environment with surface runoff has led to the contamination of many drinking water sources,and since both nanoplastics and antibiotics are commonly found in the water environment,nanoplastics have strong adsorption to antibiotics,which may alter the removal efficiency of antibiotics in the drinking water treatment process,thus posing a threat to drinking water safety.Activated carbon has a large pore structure,a huge specific surface area and good adsorption performance,and is widely used in the deep treatment of drinking water.The removal performance and mechanism of activated carbon on nanoplastics is still unclear,so it is very important to study the adsorption performance and transport behavior of nanoplastics in the activated carbon filter column,and the transport behavior of nanoplastics and antibiotics in the carbon filter column to ensure the safety of drinking water quality and how to control the pollution of nanoplastics.In this paper,we first investigated the adsorption performance of polystyrene nanoplastics（PSNPs）on carbon filtration columns,investigated the effects of column height,initial concentration and flow rate on the adsorption of PSNPs on carbon filtration columns,analyzed and predicted the penetration curves of PSNPs in carbon filtration columns by dynamic models,and explored the adsorption mechanism of PSNPs on the surface pore system of activated carbon in combination with scanning electron microscopy（SEM）;Secondly,the effect of surface interaction between nanoplastics and activated carbon,such as electrostatic force and van der Waals force,was considered,and then the effect of surface effect on the interaction between PSNPs and activated carbon was explained by the experiment of transport law of PSNPs in the carbon column and DLVO theory;Furthermore,in this paper,the static adsorption behavior of PSNPs on NOR was investigated using norfloxacin（NOR）as a typical antibiotic,and the interaction between the two in the charcoal column was explored.The main conclusions are as follows.:（1）Increasing the height of the carbon filter column and decreasing the initial concentration of PSNPs and water flow rate can prolong the penetration time of the carbon filter column.Both the Thomas model and the Yoon-Nelson model were able to fit the adsorption process of PSNPs on the carbon filter column under the conditions of the three influencing factors well.Among them,the Yoon-Nelson model can accurately predict the time required for 50%of PSNPs to penetrate the carbon filter column.There are four main mechanisms for the adsorption of PSNPs by activated carbon:PSNPs are intercepted in spaces smaller than those between activated carbon;PSNPs enter the pores on the surface of activated carbon;particles on the surface of activated carbon can"encapsulate"PSNPs;and PSNPs can collect and sink on the surface of activated carbon.（2）Decrease in ionic strength,increase in flow rate and p H can promote the transport of PSNPs in the carbon filter column.Ionic strength and p H mainly affect the stability of PSNPs in the system,high ionic strength and low p H reduce the stability of PSNPs in the system,making PSNPs less mobile.Compared with Na⁺,Ca²⁺has a stronger inhibitory effect on the transport of PSNPs in the carbon column.Humic acid（HA）could promote the transport of PSNPs in the carbon column,but when the HA concentration continued to increase,the transport of PSNPs did not change significantly.Changing the ionic strength of the solution can release the PSNPs deposited in the secondary potential well,and further reducing the ions of the solution can make the repulsion between the PSNPs and the activated carbon continue to increase,and the PSNPs can continue to be released from the system when the repulsion force is greater than that of the primary potential well.（3）The static adsorption experiments showed that the adsorption of PSNPs on NOR mainly occurred in the first 4 h and could reach the adsorption equilibrium at 16h.The kinetic adsorption process is in accordance with quasi-secondary kinetics,and the adsorption isotherm is in accordance with the Langmuir equation.The adsorption process is dominated by several mechanisms,such as microporous filling,electrostatic interaction,hydrogen bonding andπ-πinteraction.When PSNPs carry NOR in the charcoal column,PSNPs can facilitate NOR transport in the charcoal column because NOR can adsorb on the surface of PSNPs and penetrate the charcoal column with them.At the same time,the NOR adsorbed on PSNPs can"shield"the negative charge on the surface of PSNPs and reduce the repulsive barrier between the activated carbon and PSNPs,so the NOR can inhibit the transport of PSNPs in the carbon column.