The Pollution Characteristics Of Microplastics In Songhua River And Its Removal Efficiency By Coagulation-adsorption

Microplastics(MPs)is a kind of emerging contaminants,has been proved to widely exist in all kinds of waters such as marine,river and lake,which is extensive source,difficult to be degraded and easy to migrate.Traditional drinking water treatment plant(DWTP)is difficult to remove MPs effectively,the drinking water has become the main way for MPs to enter human body.Songhua River located in the north of northeast China and is one of the seven major rivers in China.Songhua River is also the main drinking water source of the cities along the river.Therefore,the characteristics of MPs in Songhua River,and the efficient MPs treatment technology is an important way to improve the quality of drinking water for the residents.Coagulation-adsorption is the commonly used water treatment technology in DWTP,which has shown great removal efficiency on most kinds of contaminants,and has great application potential for the removal of MPs,with both high efficiency and practicability.So,this study focused on the MPs,analyzed the removal efficiency and main mechanism of MPs by traditional coagulant and new coagulant,on basis of the characteristics of MPs in water according to the research,and the adsorption properties of biochar for MPs,investigated the application of coagulation-adsorption technology,in order to improve the removal efficiency of MPs in DWTP.The study showed that MPs was widespread in Songhua River,and the average abundance of MPs was 5.72 ± 4.02 n/L,MPs with size < 100 μm which was the most common MPs and easier to migrate was the typical MPs in the water.The removal of MPs with size < 100 μm should be paid more attention.According to the results of one-ANOVA and two-ANOVA,the size of MPs was the main factor of the coagulation.MPs could be divided into size < 6.5 μm,[6.5,13)μm,[13,25)μm,[25,48)μm and [48,106)μm.Poly Aluminum Chloride(PAC)and Polyacrylamide(PAM)are the most widely used traditional coagulants,when MPs was removed by PAC + PAM,the removal efficiency of MPs with size ≥ 13 μm could reach to more than 70%.Combined with interparticle force analysis and coagulation dynamics simulation,electric neutralization was the main mechanism,adsorption bridging and net sweep would play an auxiliary role in the removal of MPs.Then starch based coagulant(modified starch)which is a kind of eco-friendly coagulant with higher charge and larger molecular was selected to remove MPs collaborated with PAC.When modified starch /(PAC + PAM)was used as the coagulant,the dosage of coagulant was reduced,the removal efficiency of MPs with size < 13 μm was greatly improved,and the average removal efficiency of MPs could reach to more than 80%.The results of interparticle force analysis and coagulation dynamics simulation showed that electric neutralization,adsorption bridging and net sweep would all be effectively played,when modified starch /(PAC + PAM)was used collaboratively.Therefore,the use of modified starch could make the coagulation of MPs both efficient and economical.The removal efficiency of MPs by biochar was more than 90%,which was significantly higher than the removal efficiency of MPs by traditional sand filter,with great recycling performance at the same time.Therefore,the removal efficiency of MPs would be further improved by biochar.In the successive operation of MPs removal with the actual water,the average removal efficiency of MPs was more than97%,and it had strong adaptability to raw water quality,showing a good application prospect.In summary,the coagulation-adsorption technology could effectively improve the removal efficiency of MPs in water,and would be helpful to the removal of MPs in DWTP.This research could provide technical reference for enhancing the quality of DWTP effluent and ensuring the safety of drinking water.