應用乳化液進行底泥中鄰苯二甲酸酯類去除及生物降解模場實驗

Abstract

河川底泥在生態系中扮演重要功能，因為人類活動，使得河川底泥遭受污染，污染物循食物鏈造成生態系之破壞，人體健康也因此受到危害。鄰苯二甲酸酯類化合物（phthalate esters, PAEs）為新興污染物中內分泌干擾物質的一種。在日常生活中使用之聚氯乙烯（poly vinyl chloride, PVC）材質之塑膠中即會有高量之PAEs。台灣室內空氣塵粒中之塑化劑濃度為全球最高，土壤與底泥中之鄰苯二甲酸二（2-乙基己基)酯（di(2-ethylhexyl)phthalate, DEHP )濃度與世界各國比較也偏高。PAEs因其為疏水性物質極易蓄積於底泥中，但目前PAEs整治技術大多針對廢水處理，其處理方式有物化處理及生物處理，無法適用於河川底泥整治，如添加藥劑可能使底泥環境遭受二次破壞，而生物處理則因為廢水處理使用之菌株，可因操作之條件不同而提高處理效果，但對於本研究主要處理目標為現地整治直接整治，並無法調整一適合菌株降解PAEs之所需環境。然而目前國際間廣泛使用之河川底泥整治方法，因台灣地勢陡峭且河流湍急，並不完全適用於台灣污染場址。 本研究以大豆油製成之不穩定乳化液，藉由乳化液之油相與土顆粒相對較高之比表面積，在高速有效碰撞下，將底泥中之PAEs重新分布至油相且總油水分層回收而去除，並且利用殘餘之乳化液加強其生物降解。本研究除了針對乳化液之除污處理成效外，亦同時探討自然回復、厭氧分解、好氧分解以及厭氧-好氧分解之不同處理方法進行模場測試PAEs整治復育之效果。其結果為乳化液添加量與底泥乾重比為1:0.84，破乳化之碳酸鈉最終濃度0.78M進行回收去除，最佳操作條件為使用每分鐘4 L之曝氣流量、曝氣時間30分鐘、靜置時間12小時進行乳化液回收試驗。依據模場試驗結果顯示乳化液去除之部分：針對額外新添加之PAEs之污染物去除率為60-70%，但對於底泥中風化之污染回收僅BBP去除率77%較佳外，其他三種去除率為3-25%；生物降解之部分，有添加乳化液之組別的確有增強生物降解之情況，結果顯示添加乳化液除了有去除污染效果，也有助於PAEs之降解。

River sediments play a vital role in an ecosystem, such as self-purification, habitats for benthic organisms and planktons, fish reproduction and feeding place, and feeding ground for wading birds. However, due to human activities, sediments are polluted. Thus, human health in turn is under threats. Phthalate esters (PAEs) are one of the endocrine disrupting compounds in the so-called emerging contaminants and are usually used as industrial plasticizers to increase the flexibility and softness of plastics. Commonly used poly vinyl chloride (PVC) plastics have high level of PAEs. The concentrations of PAEs on the dusts of indoor air in Taiwan are the highest in the world. The concentration of one type of PAEs, di(2-ethylhexyl)phthalate (DEHP) in soil and sediment Taiwan is also ranked at the front of all countries in the world. Due to their hydrophobicity, they tend to accumulate in sediments. However, most treatment methods for PAEs are aimed at wastewater treatment instead of sediment contamination. These methods include physicochemical and biological methods and cannot be directly applied to sediment remediation. Moreover, currently widely applied technologies on sediment remediation cannot be employed in Taiwan because the steep landscape of Taiwan resulting high flow velocity of river water in Taiwan. In this study, an instable soy bean oil emulsion is used to recover PAEs from contaminated sediment through frequent high speed collision between oil droplets and sediment granules resulting re-partitioning of PAEs between sediments and soybean oil. Afterwards, the emulsion is broken by increasing ionic strength and the extracted PAEs are removed with separated soybean oil. The residual soybean oil and surfactants elevated the biodegradation rates of PAEs. In this pilot study, both weathered and fresh PAEs in sediment were tested and several different biological treatment schemes were tested, i.e., natural attenuation, anaerobic remediation, aerobic remediation, and sequential aerobic-anaerobic remediation. The optimum emulsion removal parameters are as follows: the ratio of emulsion to sediment (dry weight) at 1:0.84, the final concentration of sodium carbonate as emulsion breaker at 0.78 M, aeration rate at 4.0 L/min, aeration time at 30 min, and left-undisturbed period at 12 hours. Emulsion removal of fresh PAEs ranged from 60% to 70% while that of weathered PAEs ranged from 3% to 25% with an exception of benzyl-butyl phthalate at 77%. For the biological treatment, emulsion did enhance the biodegradation of PAEs.