| dc.description.abstract | Wastewater treatment plants have always been pollutant collection points in cities and industrial areas, thus being the last line of defense before pollutants enter natural water bodies. Rigorous control of pollutant emissions is an important issue. Being one of the most toxic heavy metals, mercury (Hg) is considered the priority pollutant to be handled properly. To prevent the aggravation of Hg pollution, Taiwan has regulated total Hg (THg) and methylmercury (MeHg) in the discharge, of which total Hg is 5μg/L and MeHg is 0.2 ng/L. However, when comparing these standards with the regulations of other countries and with the reported values of effluents in literature, it is obvious that the ratio of MeHg to THg pertinent to the Taiwan regulations is much lower than those observed in the majority of natural and engineered systems. This may result in difficulties in treating and managing MeHg issues in treatment plants. In view of this, two wastewater treatment plants located in North Taiwan were selected to collect aqueous samples from each operating unit and analyze THg and MeHg concentrations in order to understand the concentration change and treatment efficiency among units. In the meantime, other important environmental factors were also analyzed to explore the Hg methylation potential of each unit. The goal was to investigate the potential correlation between THg and MeHg with key environmental factors. Results show that the treatment efficiency of THg and MeHg in the treatment plants is fairly good at present with 92% and 76% for total Hg, as well as 82% and 95% for MeHg, and the discharged effluent of the two plants meets the regulations. Through Spearman’s correlation coefficient analysis, it is found that there is an extremely significant positive correlation between THg, MeHg, and total suspended particulates, whereas the concentration of dissolved active mercury has a significant negative correlation with the methylation potential. In terms of seasonal differences, there is no difference in the distribution of THg and MeHg between the two treatment plants, indicating that the seasonal stability of the mercury treatment is good. According to the correlation with environmental factors, it is concluded that reducing the concentration of total suspended particulates in water and increasing the amount of dissolved oxygen in water would be the most effective and economical methods for controlling Hg and MeHg levels. Due to the large correlation between Hg and MeHg and the difference in toxic intensity, it may not be appropriate to regulate both THg and MeHg concurrently in the discharge. At the end of this study, it is more recommended to use TMDL to control MeHg, and to control the pollutants of Hg species with the strict THg standard only, which can make the treatment plant easier to implement and achieve the purpose of controlling pollutant emissions. | en_US |