| Mercury（Hg）pollution is one of the significant global environmental problems.Hg concentration in water near amalgamation gold mines and mercury mines far exceeds the normal value of the natural water.There is a certain amount of Hg pollution even in the urban road runoff.Constructed wetland（CW）is a common water treatment technology,which can effectively remove many nutrients and heavy metals.Constructed wetlands have been widely used in non-point source pollution control and water ecological restoration.It is of great practical significance to study the restoration of Hg contaminated water systems by using CWs.In the current study,synthetic water with a total Hg（THg）concentration of81.23±42.96μg/L and a partition coefficient of 5.13±0.23 was prepared to simulate the urban road runoff and the gold mines surrounding water.The migration of THg,particulate mercury（PHg）and dissolved mercury（DHg）along the horizontal subsurface flow constructed wetlands（HSSF-CWs）were investigated.Current study was aimed to analyze the effect of operating conditions on the removal of different Hg species;establish a kinetic model for the transformation of different valence states of mercury;and investigate the correlation between Hg and other water quality parameters.The findings of the current work are as follows:（1）The removal effeciency of THg,PHg and DHg in HSSF CWs were 94.7%,95.0%and 92.7%,respectively.The THg and PHg were mainly removed in the first quarter of the CWs,accounting for 88.6%and 97.8%of the total removal,respectively.The concentration of DHg was reduced at a constant rate of 0.18μg·L-1·cm-1.（2）The removal of Hg was mainly affected by HRT,plants and temperature significantly.Findings reveal that no significant relationship was found between HRT and PHg removal,but affected the removal of DHg.Results reveal that when the HRT was less than 1 day,the removal rate of DHg was positively correlated with HRT.The removal rate of DHg was stable at above 90%when HRT was higher than 1 day.Results also reveal that plants have no role in PHg removal,whereas the removal rate of DHg in planted wetland was 20%higher than that in unplanted wetland.Current study also aimed to investigate the removal of THg and Hg2+in different temperatures（5oC,10oC,22oC,28oC）.The removal rate of THg and Hg2+increased with temperature,between81.495.9%and 75.791.7%,respectively.（3）The transformation of different valence states of Hg in CWs were found different.The removal rate of Hg2+and Hg0 were 97.8%and 68.9%,respectively.Results reveal that the first order reaction kinetic constants of THg,Hg2+and Hg0 in the unplanted CWs were 0.468,0.534,and 0.129 h-1,respectively.While the first order reaction kinetic constants of three Hg species in the planted CWs were 0.467,0.461,and 0.406 h-1,respectively.It shows that plants have no effect on the removal of THg and Hg2+,but have a noticiable effect on the removal of Hg0.（4）Finding reveal that there is no significant correlation between different Hg species with TSS,but significant linear correlation with sulfate(SO42-)and pH.The pearson correlation coefficients between SO42-and three Hg species were 0.854,0.807and 0.960,respectively.The pearson correlation coefficients between pH and three Hg species were-0.909,-0.996 and-0.900,respectively.If required,it is possible to indirectly replace the Hg concentration in the CWs using the easy measure indicators such as SO42-and pH.The current study provided an alternative for the ecological restoration of Hg contaminated water. |
