Seasonal Variation Of CVMSs Concentration And Estimation Of Discharge In Dalian Wastewater Treatment Plants

Cyclic volatile methyl siloxanes(cVMSs)are a kind of chemicals with an increasing range of applications and widespread distribution in the environment,and they have hjigh volatility and high lipophilicity,and are considered as potential environmental pollutant.In this paper,the concentrations of three cyclic volatile methyl siloxanes(D4,D5,D6)were investigated using liquid-liquid microextraction method in influents and effluents from eight wastewater treatment plants(WWTPs)in Dalian,Liaoning Province,China.For a period of one year,the seasonal variation of cVMSs concentration influents and effluents was investigated.The concentration of cVMSs in the air around different the aeration tank style of eight WWTPs was analyzed with time and space variation,source analysis and estimation of discharge.The annual average concentrations of siloxanes in influents and effluents were 830.2 and 234.8 ng/L in WWTPs,respectively.The average concentrations of D4,D5 and D6 in influents of the eight WWTPs were 471.9,1.565×103 and 453.6 ng/L,respectively.The average concentrations of D4,D5 and D6 in effluents were 249.3,244.1 and 210.9 ng/L,respectively.In general,cVMSs removal efficiency range was 47.2-84.4%.Concentrations of D4,D5 and D6 in influents were higher than those found in effluents.The percentage ratio of D5 is 62.2%.The concentration of cVMSs in influents and effluents of WWTPs had obvious seasonal variations,with higher concentration in winter and lower in spring and autumn.The annual average concentration of cVMSs influents is 1.57 times in winter that of spring,21.26 times that of autumn,1.95 times that of spring in effluents and 4.24 times that of autumn.Compared to biological aerated filter(BAF)and cyclic activated sludge technology(CAST)processes,constant water level sequencing batch reactor(CWSBR)had higher removal rate for cVMSs.The cVMSs concentrations in the air above the eight aeration tanks varied between 5.0×10-5 and 37.94 ?g/m3(3.14 ?g/m3)with decamethylcyclopentasiloxane(D5)as the dominant compound(63.8%of the cVMSs).The total cVMSs concentrations varied between 5.0×10-5 and 37.94 ?g/m3 in ambient air of "close" and between 5.0×10-5 and 16.19?g/m3 in the "open".The average concentration of cVMSs in the air from "close" WWTPs were higher than that in the "open" WWTPs(P<0.01).For both style aeration tanks,the concentration of ?cVMSs was the highest in summer,and the lowest in winter.The cVMSs average concentrations in air measured were significantly positively correlated with the monthly mean temperature as plot of regression line(P<0.01).The cVMSs in the air from"open" WWTPs were negatively correlated with average wind speed(P<0.01).Simplified Gaussian dispersion model and single chamber model were introduced to estimate emissions rates(kg/yr).The estimated ?cVMSs yearly emissions for five "open" and three "close"WWTPs ranged from 86.90 to 165.1 kg/yr and from 202.9 to 278.2 kg/yr,respectively.A new method of Tenax-TA-PAS was used to collect and analyze cVMSs in the air.The sampling time was long and continuous.The results showed apparent seasonal variations of cVMSs concentrations.