Effects of Adsorption Phenomenon on Reduction of Compounds of Emerging Concerns by Nano-filtration Process
Date Issued
2016
Date
2016
Author(s)
Liu, Tse-Jung
Abstract
Adsorption is one of the main mechanisms of compounds of emerging concerns (CECs) rejection by a membrane process. CECs could be adsorbed not only by membrane but also by suspended solid during membrane filtration, i.e. NOM. Besides, CECs could not be removed by a conventional water treatment or a single advanced process, even a single activated carbon column or a commercial NF membrane. In this study, the NF270 membrane was coupled with granular activated carbon in fixed-bed column system (GACC) to investigate the performance on CECs removal. The role of Humic acid (HA) in Nano-filtration (NF) processes and adsorption processes was also examined as well. The NF270 membranes were modified further by monomer grafting method to improve the rejection of the selected CECs. Ten CECs, Erythromycin-H2O, Chlorpyrifos, Trimethoprim, Iopromide, Carbamazepine, Sulfamethoxazole, Caffeine, Acetaminophen, Bisphenol A and Estrone, which are commonly found in the aquatic environment, were chosen as model pollutants and grouped in this study. CECs are an important group of organic environmental contaminants that have the potential to cause health risks for humans as well as biota. Concentrations of CECs were analyzed by LC-MS-MS to ng/L level. The results indicated that the eight grouped CECs had different rejections in the range of 4% to 99% by a NF270 membrane both in raw or simulated natural water samples. The adsorption experiments revealed that the hydrophobic CECs can be adsorbed onto granular activated carbons (GAC) easily than the hydrophilic ones, and GACC generally had better removal efficiencies of CECs than membrane process. Adequate existence of HA showed helpful for CECs removal which means CECs can be adsorbed onto HA became a larger molecular then removed by a NF270 membrane easier. Characterization of the modified NF270 membrane using SEM, ellipsometry and ATR-FTIR analysis revealed that NF270 membranes grafting by SPM monomer increased its hydrophilic and thickness of surface layer, and the grafting extent was proportional to the system pressure, monomer concentration and duration time, especially system pressure. Both of the combination system of NF/GACC and the modified membrane studies can remove the targeted CECs to above 90%; For the engineering application, however, the modification method was limited by the quality control that the combination system was better for applying in water treatment in engineering consideration. The contrast of the sequence of NF/GACC or GACC/NF for CECs removal was not obvious in this study, and GACC had better rejections than a raw NF270. The above results suggest that the existence of HA can increase the rejection of CEC, and the modified membrane also work for CECs rejection. The performance on cost-benefit analysis of GACC, the combination system and the modified membrane showed good feasibility on a real scale application.
Subjects
compounds of emerging concerns (CECs)
nano-filtration
granular activated carbon
adsorption
membrane modification
cost-benefit analysis
SDGs
Type
thesis
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