Occurrence of perfluorinated compounds in aqueous environments and the treatment by electrofiltration

• Main Authors: Yu-Ting Tsai, 蔡宇庭
• Other Authors: Kung-Cheh Li
• Format: Others
• Language: zh-TW
• Published: 2011
• Online Access: http://ndltd.ncl.edu.tw/handle/76556883924073414901

博士 === 國立臺灣大學 === 環境工程學研究所 === 99 === We investigated the occurrence of perfluorinated compounds (PFCs) in the effluents of an industrial wastewater treatment plant (IWWTP) and its receiving rivers. Ten target PFCs including three perfluoroalkyl sulfonates (PFASs)：perfluorobutane sulfonate (PFBS (C4)), perfluorohexane sulfonate (PFHxS (C6)), and perfluorooctane sulfonate (PFOS (C8)) and seven perfluoroalkyl carboxylates (PFCAs)：perfluorohexanoic acid (PFHxA (C6)), perfluoroheptanoic acid (PFHpA (C7)), perfluorooctanoic acid (PFOA (C8)), perfluorononanoic acid (PFNA (C9)), perfluorodecanoic acid (PFDA (C10)), perfluoroundecanoic acid (PFUnA (C11)), and perfluorododecanoic acid (PFDoA (C12)) were detected in the effluents of IWWTP; PFOS (6930 ng/L) and PFHxS (2662 ng/L) were the major constituents of PFASs; PFOA (3298 ng/L) was the major constituent of PFCAs. IWWTP effluent and its receiving rivers demonstrated to have similar PFCs distribution and concentrations, indicating that the IWWTP wastewater is the major source of PFCs to its receiving rivers. Compared to the reported Avian Wildlife Value (AWV), PFBS (392 ng/L) and PFOS (7165 ng/L) level detected showed to exceed the AWV 23 and 152 times, respectively, which may potentially result in adverse effects to birds and other wildlife. In addition, PFOS concentration found (7165 ng/L) at the receiving rivers was higher than the reported Criteria Continuous Concentration (CCC), indicating the potential chronic toxicity to aquatic organisms. In sediment samples, five PFCAs (PFHxA, PFOA, PFDA, PFUA and PFDoA) and two PFASs (PFHxS and PFOS) were detected. PFOS (1.5-78 ng/g), PFOA (0.5-5.6 ng/g), and PFDoA (nd-5.4 ng/g) were present at relatively higher concentration. Log (Csediment / Cwater) increases with an increasing carbon chain length of PFCAs; the Log (Csediment / Cwater) values for PFOA, PFDA, PFUA, and PFDoA were 0.2-0.3, 2.2-2.5, 2.5-2.7, and 3.2-3.3, respectively and therefore, PFCs with higher carbon numbers (PFDA, PFUA and PFDoA) are easier adsorbed onto sediments. In biological tissue, PFOS was presented at higher concentration among the target PFCs and was the predominant PFCs (PFOS % in total PFCs in muscle tissue：76-84% in Keya River；55-64% in Keelung River and in liver tissue：94-95% in Keya River；44-51% in Keelung River). The PFCs concentration in the liver tissue was higher than those found in the muscle tissue (e.g. in A1-mouthbeeder biological tissue, PFOS concentration was 28933 ng/g in liver tissue; 1386 ng/g in muscle tissue). Log (Cbiological tissue / Cwater) increases with an increasing carbon chain length of PFASs or PFCAs. In liver tissue, the Log (Cliver / Cwater) values for PFBS, PFHxS, and PFOS were 1.0-1.5, 2.2-2.3, and 3.5-3.7, respectively；the Log (Cliver / Cwater) values for PFOA, PFNA, PFDA, PFUA, and PFDoA were 1.7-1.8, 3.8-4.2, 3.7-4.0, 4.3-4.4, and 5.3-5.4, respectively. The results indicated that PFCs with higher carbon numbers are easier accumulated in biological tissues. In addition, PFC concentrations in biological tissues in Keya River were 1-197 times greater than levels found in Keelung River. These water, sediment and biota data together imply that the receiving aquatic environments were impacted by the industrial discharges. Therefore in order to reduce, and better yet, to eliminate PFCs discharge into aqueous environments, advanced treatment technologies appear viable for their removal. PFCs are negatively charged and have low pKa values in water; therefore, a laboratory-scale electro-microfiltration (EMF) unit that applies a direct-current (DC) electrical field across its membrane can greatly enhance their removal from aqueous systems. We examined the effects of electrical field strength (0, 29, 43.5 and 58 V/cm), an aqueous inorganic matrix (pH: 4, 7 or 10; ionic strength: 0.4-4.8 mM; ionic composition: Na2SO4, NaCl, NH4Cl or CaCl2) and an organic matrix such as dissolved organic matter (DOM) on the ability of EMF to remove PFOA and PFOS. In the absence of an electrical field, PFOA and PFOS removal efficiencies were low; however, the application of a DC electrical field through the membrane greatly enhanced PFOA and PFOS removal. PFC rejections increased from <3% (0 V/cm) to >84% (58 V/cm) at pH=10 solution. Decreases in PFOA and PFOS removal were observed as the increase of proton concentration and ionic strength, suggesting decreased membrane zeta potential, in turn reducing the electrostatic repulsion force between the membrane and PFOA and PFOS. At 29 V/cm, the electrical field was less than the critical electrical field strength (Ecritical, HA), conditions under which humic acid (HA) could be transported toward the membrane; thus, its adsorption would decrease the membrane zeta potential. HA adsorption would decrease the PFOA and PFOS rejection efficiency during EMF with an electrical field strength lower than its critical value. Therefore, we hypothesize that these matrices affect PFOA and PFOS rejection by altering membrane zeta potential during filtration in the presence of an electrical field. EMF was found to remove coexisting PFCs including PFOA, PFOS and three other PFCs (PFDA, PFHxS and PFHxA) effectively; at 58 V/cm, their removal efficiencies were 70-76% and 81-86% at pH=7 and pH=10, respectively. In addition, EMF was also able to remove effectively 70% PFOA and PFOS and 80% DOM from real industrial wastewaters at 58 V/cm.