Influence Constructed Wetland With Different Substrates On Removal And Speciation Of Pb In Wastewater

Water is the source of life.With the rapid development of economy and the increase of population,water environment has become the key to restrict the development even survival of mankind.In recent years,the C hina's coal mining industry and transportation industry developed rapidly,and the heavy metal pollution has become the focus of domestic attention.In this study SSFGF,FSSGF,FSSFF,FSSFG and FSFGF five different types of wetland substrates,consisting of fly ash,sludge,soil,fine cinder,gravels and fine sand,was made to treat the Pb2+ wastewater with different concentrations(10,20,40,80,160 mg/L),hydraulic retention time was 0.25,0.5,1,2,4,8,12,24 and 48 h.The physicochemical indexes of 5 substrates were determined.The concentration of Pb in outlet water and the 5 forms(exchangeable state,carbonate bound state,organic bound state,Fe-Mn oxidation state and residual state)of Pb in substrates were determined.Through the analysis of variance,correlation and other statistical analysis methods comprehensively evaluated:The 5 kinds of wetland with different substrates had a certain extent removal effect on Pb2+ wastewater,and 12 h is the best hydraulic retention time.At this time the corresponding removal rate of SSFGF,FSSGF,FSSFF,FSSFG and FSFGF system is 75.41-81.91%,83.04-94.19%,81.34-92.78%,47.86-92.43% and 44.70-90.42%,the average removal rate respectively is 79.01,89.07,86.27,73.75 and 68.40%;Analysis of variance and multiple comparisons show that after the treatment of the same concentration of wastewater treatment at the same time,the removal rate of Pb in wastewater is different between different substrate wetlands;and there are differences among the 5 forms of Pb in different substrates;Under the same hydraulic retention time,there are some differences in the percentage of 5 forms of Pb in different substrates after the treatment with different concentration of wastewater,and the residual state Pb occupies the highest proportion between 30-45%.The proportion of exchangeable and carbonate bound states between 21-27%.When the HRT is 12 h,the removal efficiency is significantly correlated with the substrates' D10,D80,CEC,Water conductivity,exchangeable Ca,exchangeable Al and effective Fe,and the relationship is negative.When the HRT is 12 h,the concentration of exchangeable speciation and carbonate speciation Pb in substrates are significantly correlated with the substrates' D10,D80,K80,CEC,water conductivity,exchangeable Ca and effective Fe,and the relationship is positive,but significantly negative correlated with the substrates' effective Mn.That is to say,with the substrates' D10,D80,K80,C EC,water conductivity exchangeable Ca and effective Fe increases,the concentration of exchangeable speciation and carbonate speciation Pb in substrates increases;and with the substrates' effective Mn increases,the concentration decreases.The concentration of residual speciation Pb in substrates are significantly correlated with the substrates' D10,CEC and volumetric weight,and the relationship is positive,but significantly negative correlated with the substrates' effective Mn,bulk porosity,K80 and exchangeable Al.