甲基汞於廢水處理單元的流佈與制定其放流水標準的合理性;The distribution of methylmercury in the wastewater treatment process and the rationality of establishing its discharge regulation

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题名:	甲基汞於廢水處理單元的流佈與制定其放流水標準的合理性;The distribution of methylmercury in the wastewater treatment process and the rationality of establishing its discharge regulation
作者:	余萬俊;YU, WAN-JYUN
贡献者:	環境工程研究所
关键词:	總汞與甲基汞;廢水處理流程;放流水標準;總最大日負荷;Total Hg and methyl Hg;wastewater treatment processes;discharge regulations;TMDL
日期:	2020-01-17
上传时间:	2020-06-05 17:47:41 (UTC+8)
出版者:	國立中央大學
摘要:	污水處理廠一直以來都是城市及工業區之污染物匯集點，也是污染物進入自然水體前的最後一道防線，因此謹慎的管控污染物的排放濃度是一項重要的課題，而汞(Hg)身為全球最具毒性的重金屬一員，理所當然的該被視為重點控制目標。台灣為了防止汞污染的加劇，於最新的放流水標準裡規範了總汞及甲基汞，其中總汞為5μg/L、甲基汞為0.2 ng/L，但若比對國外之法規標準以及相關研究文獻的數據可知，在台灣法規所列的標準裡，甲基汞占總汞的比例遠低於一般自然界中尋常的比例，這會導致處理廠在處理甲基汞時出現難以管控的現象，且此規範發布後，本實驗室陸續收到廠商的詢問，表示常遇到其放流水的甲基汞超過管制標準的情況，儘管其原物料中沒有使用汞或甲基汞。有鑑於此，為了暸解污水處理單元中甲基汞生成及放流水甲基汞超標之問題，本研究藉由分析處理廠A及處理廠B之各個處理單元間的總汞及甲基汞，來了解兩者於各單元間的濃度變化及處理效率，更透過分析其他環境因子以探討各處理單元之汞甲基化潛勢高低，並藉由總汞及甲基汞與環境因子的相關性尋找控制方法。調查結果顯示兩污水處理廠對總汞及甲基汞的處理效率良好：總汞為92%、76%，甲基汞為82%、95%，且兩廠皆符合放流水標準；通過Spearman’s相關係數分析得知總汞、甲基汞及總懸浮微粒間存在著極度顯著的正相關，而溶解態活性汞的濃度與甲基化潛勢呈現顯著負相關；在季節差異上，兩處理廠的總汞及甲基汞流佈走勢沒有發現差異性，表示其處理汞之季節穩定性良好；藉由與環境因子的相關性得出，降低水中總懸浮微粒濃度及增加水中溶氧量是控制汞及甲基汞最有效且經濟之作法。最後，由於汞及甲基汞之間的相關性以及毒性強度差異大，於法規中同時規範兩者的排放限值似乎不甚恰當，本研究最後較建議可從TMDL的角度進行甲基汞控制，搭配放流水之總汞標準的調整來對汞物種進行污染物控制，既可使處理廠較容易實施，又可達到控制污染物排放之目的。;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.
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