Study Of Polyhexamethyleneguanidine Coagulation To Remove Microplastics From Water

MIicroplastics(MPs)are plastics with a diameter of less than 5 mm.Due to their widespread distribution in water,they pose long-term ecological and environmental impacts and health risks.Therefore,efficient and environmentally friendly removal technologies are urgently needed.Coagulation precipitation has been widely used to remove MPs from water due to its simple operation,low cost and mature process equipment.However,the conventional coagulation precipitation method has poor removal effect on MPs with low concentration and small particle size in water.In order to solve the problem that MPs with low concentration and small particle size are difficult to remove,this paper took MPs with particle size less than 10 μm as the treatment object,green and safe fungicide polyhexamethyleneguanidine(PHMG)as the coagulant,and polyacrylamide(PAM)as the coagulant,studied the best condition and coagulation removal mechanism of MPs by coagulation precipitation.The main research contents and results are as follows:(1)Taking PS fragments as an example,the effects of PAM of different types and molecular weights,coagulation conditions,drug dosage and environmental factors on coagulation of PHMG were studied.Box-Behnke response surface optimization test was used to explore the influencing factors and the magnitude of their interaction.The results showed that when the dosage of PHMG was 4.5 mg/L and the dosage of APAM was 4.2mg/L,the rapid stirring intensity was 500 r/min for 80 s,and then the slow stirring intensity was 150 r/min for 23 min.The best coagulation precipitation removal efficiency reached 83%.Moreover,80% removal efficiency was achieved in the broad spectrum p H range of 5 to 10.HA,salinity,and coexisting anions were the main factors inhibiting the coagulation of PHMG in the water environment,which provided theoretical support for the subsequent removal experiments of MPs from surface water.(2)The surface morphology,functional groups and chemical composition of the initial MPs and flocs were analyzed by scanning electron microscopy(SEM),Fourier transform infrared spectroscopy(FTIR)and X-ray photoelectron spectroscopy(XPS).Combined with Zeta potential,the surface charge of MPs in the supernatant before and after coagulation was monitored under different p H conditions.It is proved that the coagulation mechanism of PHMG system mainly includes charge neutralization,adsorption bridging and net capture sweeping,and there are different dominant mechanisms under different water quality conditions and different drug additions.(3)The PHMG coagulation system was investigated for the removal of MPs from actual surface water in different periods.The results showed that the removal efficiency of PS debris in the dry season was higher than that in the wet season,reaching 77%,and the main influencing factor was HA concentration.The PHMG coagulation system had a good removal efficiency for different types of MPs.The removal efficiency of microspherical polyvinyl chloride(PVC),fibrous polypropylene(PP),and mixed microplastics was 78%,82%,and 76%,respectively.In addition,the PHMG coagulation system had a good sterilization effect while removing MPs from actual surface water,and the sterilization rate of microorganisms in actual surface water in wet season could reach 99.6%,which could save the disinfection and sterilization cost of drinking water treatment to a certain extent.This study provides a low-cost and simple environmentally friendly solution for the removal of MPs with low concentrations and small particle sizes in real surface water.