Abstract Membrane scaling by silica is a major challenge in desalination, particularly for inland desalination of brackish groundwater or geothermal water, which often contain high concentrations of silica and dissolved solids. Adjustment of feed pH may reduce silica scaling risk, which is important for inland facilities that operate at high water recoveries to reduce brine disposal costs. However, water recovery of reverse osmosis is also limited due to increased osmotic pressure with feed water concentration. Membrane distillation (MD) is a thermally driven membrane desalination technique that is not limited by increased osmotic pressure of the feed. In this investigation, pH adjustment was tested as a strategy to reduce silica scaling risk in the MD process. With feed water pH less than 5 or higher than 10, scaling impacts were negligible at silica concentrations up to 600 mg/L. Scaling rates were highest at neutral pH between 6 and 8. Cleaning strategies were also explored to remove silica scale from membranes. Cleaning using NaOH solutions at pH higher than 11 to induce dissolution of silica scale was effective at temporarily restoring performance; however, some silica remained on membrane surfaces and scaling upon re-exposure to supersaturated silica concentrations occurred faster than with new membranes.

中文翻译：

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使用 pH 调节预防和管理膜蒸馏中的二氧化硅结垢

摘要 二氧化硅引起的膜结垢是海水淡化中的一个主要挑战，特别是对于微咸地下水或地热水的内陆脱盐，其中通常含有高浓度的二氧化硅和溶解固体。调整进料 pH 值可以降低二氧化硅结垢风险，这对于以高水回收率运行以降低盐水处理成本的内陆设施很重要。然而，由于渗透压随着进水浓度的增加而增加，反渗透的水回收也受到限制。膜蒸馏 (MD) 是一种热驱动的膜脱盐技术，不受进料渗透压增加的限制。在这项研究中，测试了 pH 调节作为降低 MD 过程中二氧化硅结垢风险的策略。给水 pH 值小于 5 或​​大于 10，在二氧化硅浓度高达 600 mg/L 时，结垢影响可以忽略不计。在 6 到 8 之间的中性 pH 值下，结垢率最高。还探索了清洁策略以去除膜上的二氧化硅垢。使用 pH 值高于 11 的 NaOH 溶液进行清洁以诱导二氧化硅垢的溶解可有效暂时恢复性能；然而，一些二氧化硅保留在膜表面，并且在再次暴露于过饱和二氧化硅浓度时结垢的速度比新膜更快。