Comparative Study On Removal Efficiency Of Microplastics By Different Wastewater Treatment Processes

Microplastics(MPs)cannot be completely removed in the treatment process of urban wastewater treatment plants.It is discharged into the water environment with the wastewater treatment plant and finally into the ocean.Therefore,urban wastewater treatment plant is one of the main sources of MPs pollution in the water environment.By comparing the different effects of different treatment processes in different existing sewage plants on MPs removal efficiency,we can select the wastewater treatment process with the highest MPs removal rate,so as to guide the selection of treatment processes in future wastewater treatment plants and achieve the purpose of optimizing the overall control of sewage quality in the city.At the same time,we can expand the impact on human activities in the water ecological environment and promote the indepth study of MPs traceability in the water environment.In this study,four wastewater treatment plants with different processes in Kunming were selected for sampling research,including AAO-V Filter,BIOCOS-D Filter,AAO-MBR Filter and AAO-D Filter.The purpose is to compare the MPs removal efficiency of different wastewater treatment processes and recommend the best wastewater treatment process for MPs removal.The main conclusions are as follows:(1)The concentration of MPs in the incoming water of the wastewater treatment plant varies greatly,ranging from 31 to 118/L;The effluent concentration is between 0.05-9.3/L,and the total removal rate is between 88.6-92.1%.(2)The removal rate of primary treatment is 13.6%-28.2%,that of secondary treatment is 44.7%-83.3%,and that of tertiary treatment is 76.2%-99.25%.(3)Among the four sets of sewage treatment processes,the removal efficiency of MPs is ranked as follows:AAO-MBR Filter>BIOCOS-D Filter>AAO-D Filter>AAO-V Filter.The removal efficiency of MPs in the four wastewater treatment plants is 99.9%,96.1%,92.1%and 88.6%respectively.Therefore,AAO-MBR wastewater treatment plant has the best removal effect of MPs.It is suggested that the removal rate of MPs should be properly considered on the basis of considering the removal rate of nitrogen and phosphorus in the new wastewater treatment plant in the future,and the process should be preferred as much as possible.(4)Pollution characteristics of MPs in urban wastewater:in terms of shape,five shapes of MPs were detected in four sewage plants:fiber,film,fragment,particle and small ball,of which the most content was fibrous MPs(54.3%-73.2%)and the least was small spherical MPs(1%-1.8%).In terms of color,seven colors of MPs were detected in the four WWTPs:transparent,blue,yellow,red,green,black and white,of which transparent MPs accounted for the most(33.7%-56.7%).In terms of particle size,MPs particle size is divided into three categories:≤0.5 mm(22.1%-33.1%),0.5-1 mm(35.8%-41.7%)and 1-5 mm(25.2%-42.1%),with little difference in overall distribution.In terms of types,eight kinds of polypropylene(PP,33.8%-53.4%),polyethylene(PE,19.3%-42.7%),polyethylene terephthalate(PET,2.4%-10.9%),polystyrene(PS,2.2%-9.2%),polyethersulfone(PES,0.8%-8.8%),polyamide(PA,2.5%-5.6%),polyolefin(PO,1.1%-6.6%),polyacrylonitrile(Pan,0.5%-7.5%)and others(1.4%-5.4%)were detected,among which PP and PE were the most.