Department of Chemical and Petroleum Engineering , University of Pittsburgh , Pittsburgh , Pennsylvania 15261 , United States.
Department of Civil and Environmental Engineering , University of Pittsburgh , Pittsburgh , Pennsylvania 15261 , United States.
Environ Sci Technol. 2019 Sep 3;53(17):10166-10176. doi: 10.1021/acs.est.9b02738. Epub 2019 Aug 19.
The impact of membrane cleaning with NaOH and HCl on the characteristics and associated changes in ion rejection was investigated in this study. NaOH affected the zeta potential of membranes with a greater concentration of carboxylic groups so that it was negative across the entire pH range investigated. Exposure to NaOH led to swelling of the active layer after each cleaning, especially for poly(piperazineamide) membranes. A 23% increase in the effective pore radii for these membranes after NaOH cleaning for 18 h led to 25, 36, 53 and 62% decrease in the rejection of magnesium, calcium, sodium, and chloride ions, respectively. Sulfate rejection decreased only slightly even for poly(piperazineamide) membranes (i.e., 7%) despite an appreciable increase in pore radii, which can be explained by the impact of charge exclusion on ion rejection that was enhanced by the 16% reduction in zeta potential. On the other hand, cleaning with HCl had a negligible impact on the zeta potential and performance of all membranes evaluated in this study. The increase in permeability after chemical cleaning was in agreement with the decrease in rejection of inorganic ions and correlated well with the effective pore radii measured using the membrane potential technique. The importance of charge exclusion in the rejection of inorganic ions was highlighted by the observed differences in rejection and permeability values when testing membranes after NaOH cleaning.
本研究考察了用 NaOH 和 HCl 清洗膜对特性和相关离子排斥变化的影响。NaOH 影响带有更多羧酸基团的膜的 ζ 电位，使其在整个研究的 pH 范围内均为负值。NaOH 暴露后，活性层在每次清洗后都会发生溶胀，尤其是对聚（哌嗪酰胺）膜而言。NaOH 清洗 18 小时后，这些膜的有效孔径增大了 23%，导致镁、钙、钠和氯离子的截留率分别下降了 25%、36%、53%和 62%。尽管孔径显著增大，但硫酸盐截留率仅略有下降（即 7%），这可以用电荷排除对离子截留的影响来解释，这种影响因 ζ 电位降低 16%而得到增强。另一方面，HCl 清洗对本研究评估的所有膜的 ζ 电位和性能的影响可以忽略不计。化学清洗后渗透率的增加与无机离子截留率的降低一致，与使用膜电位技术测量的有效孔径很好地相关。NaOH 清洗后测试膜时观察到截留率和渗透率值的差异，突出了电荷排除对无机离子截留的重要性。
