Department of Civil and Environmental Engineering, The George Washington University, 641 Academic Center, 801 22nd Street, NW, Washington, D.C. 20052, USA.
Environ Sci Technol. 2010 Mar 15;44(6):2022-8. doi: 10.1021/es903623r.
This study investigates gypsum scaling and cleaning behavior in forward osmosis (FO). The results show that gypsum scaling in FO is almost fully reversible, with more than 96% recovery of permeate water flux following a water rinse without addition of chemical cleaning reagents. Parallel comparisons of fouling and cleaning were made between FO (without hydraulic pressure) and RO (under high hydraulic pressure) modes. The shape of the water flux decline curves during gypsum scaling is similar in the two modes, but the flux recovery in FO mode is higher than that in RO mode by about 10%. This behavior suggests that operating in FO mode may reduce the need for chemical cleaning. The role of membrane materials in controlling gypsum scaling and cleaning was investigated using cellulose acetate (CA) and polyamide (PA) membranes. Gypsum scaling of PA membranes causes more severe flux decline and is harder to clean than that of CA membranes. AFM force measurements were performed between a gypsum particle probe and the membrane surfaces to elucidate gypsum scaling mechanisms. Analysis of adhesion force data indicates that gypsum scaling of the PA membrane is dominated by heterogeneous/surface crystallization, while gypsum scaling of the CA membrane is dominated by bulk crystallization and subsequent particle deposition.This finding implies that membrane surface modification and new material development can be an effective strategy to mitigate membrane scaling.
本研究考察了正向渗透（FO）过程中的石膏结垢和清洗行为。结果表明，FO 过程中的石膏结垢几乎是完全可逆的，仅用水冲洗即可回收超过 96%的渗透水通量，无需添加化学清洗试剂。FO（无液压）和 RO（高压）两种模式下的结垢和清洗进行了平行比较。两种模式下石膏结垢过程中的水通量下降曲线形状相似，但 FO 模式下的通量恢复比 RO 模式高约 10%。这一行为表明，在 FO 模式下操作可能减少对化学清洗的需求。通过使用醋酸纤维素（CA）和聚酰胺（PA）膜研究了膜材料在控制石膏结垢和清洗方面的作用。PA 膜的石膏结垢会导致更严重的通量下降，且比 CA 膜更难清洗。在石膏颗粒探针和膜表面之间进行了原子力显微镜（AFM）力测量，以阐明石膏结垢机制。对粘附力数据的分析表明，PA 膜的石膏结垢主要由非均相/表面结晶引起，而 CA 膜的石膏结垢主要由体相结晶和随后的颗粒沉积引起。这一发现表明，膜表面改性和新材料开发可以是减轻膜结垢的有效策略。
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