Soto-Salcido Luis A, Pihlajamäki Arto, Mänttäri Mika
Department of Separation Science, LUT School of Engineering Science, LUT University, P.O. Box 20, 53851 Lappeenranta, Finland.
Department of Separation Science, LUT School of Engineering Science, LUT University, P.O. Box 20, 53851 Lappeenranta, Finland.
Waste Manag. 2023 Aug 30;171:124-133. doi: 10.1016/j.wasman.2023.08.025.
End-of-life (EoL) thin-film composite (TFC) reverse osmosis membranes were converted into ultrafiltration-like (UF) membranes in an accelerated degradation process of the polyamide (PA) using an oxidant (NaOCl) in the presence of either MgCl or CaCl. The PA degradation was evaluated by measuring pure water permeability (PWP), MgSO passage and molecular weight cut-off; the more PWP increased, and the less MgSO was retained after treatment, the more the PA was degraded. By adding 10 mM of metal ions, PWP increased 2.1 (MgCl) and 3.1 (CaCl) times compared to the increase achieved with hypochlorite alone (2560 ppm∙h of free chlorine). Changes in the membranes after treatment were analyzed by Fourier transform infrared spectroscopy (FTIR), field emission scanning electron microscopy (FE-SEM), and by measuring their surface charge and contact angle. FTIR and FE-SEM confirmed the PA layer degradation. FE-SEM micrographs showed that full removal of the PA layer can be achieved by using an oxidation dose of 12,700 ppm∙h when Ca is used but doses as high as 300,000 ppm*h are needed without catalyst. The results proved that by controlling the oxidation process it was possible to control the cut-off (MWCO) value of the membrane from 16,100 g∙mol to 27,100 g∙mol. Before treatment, EoL membranes showed a MWCO of approximately 1200 g∙mol, meaning that molecules with that size could be retained in a 90%. In summary, the presented method enables reducing waste by the conversion EoL membranes into tailored UF-like membranes and by decreasing the amount of oxidant used in the conversion process.
在聚酰胺（PA）的加速降解过程中，通过在MgCl或CaCl存在下使用氧化剂（NaOCl），将寿命终止（EoL）的薄膜复合（TFC）反渗透膜转化为类似超滤（UF）的膜。通过测量纯水渗透率（PWP）、MgSO4截留率和截留分子量来评估PA的降解情况；PWP增加得越多，处理后MgSO4的截留量越少，PA降解得就越厉害。与单独使用次氯酸盐（2560 ppm∙h游离氯）相比，添加10 mM金属离子后，PWP分别增加了2.1倍（MgCl）和3.1倍（CaCl）。通过傅里叶变换红外光谱（FTIR）、场发射扫描电子显微镜（FE-SEM）以及测量其表面电荷和接触角，分析了处理后膜的变化。FTIR和FE-SEM证实了PA层的降解。FE-SEM显微照片显示，当使用Ca时，氧化剂量为12,700 ppm∙h可实现PA层的完全去除，但在无催化剂的情况下需要高达300,000 ppm∙h的剂量。结果证明，通过控制氧化过程，可以将膜的截留分子量（MWCO）值从16,100 g∙mol控制到27,100 g∙mol。处理前，EoL膜的MWCO约为1200 g∙mol，这意味着该尺寸的分子有90%能够被截留。总之，所提出的方法能够通过将EoL膜转化为定制的类似超滤膜以及减少转化过程中所用氧化剂的量来减少废物。
