Leveraging calcium-NOM complexation phenomenon as RO fouling mitigation strategy during treatment of lake water

Advanced Membranes Pub Date : 2024-01-01 DOI:10.1016/j.advmem.2024.100105

Oranso T. Mahlangu, Samkeliso S. Ndzimandze, Mxolisi M. Motsa, Bhekie B. Mamba

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Abstract

Organic fouling during reverse osmosis (RO) is exacerbated by the presence of calcium up to a limit where extremely high calcium concentration results in lesser fouling due to formation of large organic-calcium aggregates with lower cake resistance. Therefore, this work leveraged on this phenomenon and used calcium chloride as coagulant (at varying concentration) to reduce membrane fouling while enhancing NOM removal. Membrane cleaning efficiency through calcium-EDTA chelation which disintegrates the fouling layers was explored. RO fouling was performed with sodium alginate solutions and lake water. The fouled membranes were soaked in 0.1 mM EDTA (1 h) and backwashed with water to remove the fouling layer. Alginate fouling was worsened (45–85 %) by increase in calcium concentration up to 5 mM but lessened at > 5 mM calcium concentration (35–15 %). Similar observations were made when filtering lake water, except that lesser fouling was observed at calcium concentrations greater than 15 mM. Membrane soaking in EDTA enhanced cleaning efficiency leading to over 90 % flux recovery for both alginate and late water. However, prolonged membrane exposure to 10 mM calcium resulted in slight decline in membrane salt rejection (<2 % change) and tensile stress (1.3–1.1 N/mm²), while the membrane flux increased (<3 % change). Finally, NOM removal improved with calcium addition (up to 90 %) – key in reducing potential formation of disinfection by-products due to addition of disinfection agents. The proposed use of calcium as a common coagulant/chelating agent for fouling mitigation/remediation during advanced membrane filtration has a potential for wider application and commercialization.

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在湖泊水处理过程中，利用钙-NOM 复合现象作为反渗透污垢缓解策略

反渗透（RO）过程中的有机污垢会因钙的存在而加剧，在一定限度内，极高浓度的钙会形成大的有机钙聚集体，降低滤饼阻力，从而减少污垢。因此，本研究利用这一现象，使用氯化钙作为混凝剂（浓度不同）来减少膜污垢，同时提高 NOM 的去除率。研究还探讨了通过钙-EDTA 螯合作用分解污垢层的膜清洁效率。使用海藻酸钠溶液和湖水进行反渗透膜污垢处理。将堵塞的膜浸泡在 0.1 mM EDTA 中（1 小时），然后用水反冲洗以去除堵塞层。钙浓度增加到 5 mM 时，藻酸盐污垢会加重（45-85%），但当钙浓度达到 > 5 mM 时，污垢会减轻（35-15%）。在过滤湖水时也观察到了类似的情况，只是当钙浓度超过 15 mM 时，污垢程度较轻。将膜浸泡在乙二胺四乙酸（EDTA）中可提高清洁效率，使藻酸水和晚期水的通量恢复率超过 90%。然而，将膜长时间暴露在 10 mM 的钙中会导致膜盐排斥（变化 2%）和拉伸应力（1.3-1.1 N/mm2）的轻微下降，而膜通量则会增加（变化 3%）。最后，钙的添加提高了对 NOM 的去除率（高达 90%）--这是减少因添加消毒剂而可能形成的消毒副产物的关键。在高级膜过滤过程中，建议使用钙作为普通混凝剂/螯合剂，以减少/修复污垢，这具有更广泛的应用和商业化潜力。

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来源期刊

Advanced Membranes

CiteScore

8.50

自引率

0.00%

发文量