Membrane scaling problems can limit broad applications of electrodialysis (ED) for nutrients recovery from wastewater. In this study, we investigated the calcium- and magnesium-scale precipitation on ion-exchange membranes (IEMs) using a laboratory-scale ED reactor. Two high-strength wastewater streams, including municipal waste (MW) liquid digestate and food waste (FW) liquid digestate, were fed into the ED reactor. For the operation with MW liquid digestate, the cumulative Ca²⁺ loss increased with the increasing electric current, while the electric current conditions did not affect the cumulative Mg²⁺ loss. After 8-h operation, 60.1% of Ca²⁺ and 39.0% of Mg²⁺ in the MW liquid digestate were lost in the form of precipitates. Observed scalants on cation-exchange membranes were vaterite, amorphous calcium carbonate (ACC), and struvite, while ACC was not found on anion-exchange membranes. Observed scalants of calcium carbonate with MW liquid digestate (vaterite and ACC) were different from scalants (calcite) found with synthetic solutions. Among these scalants, struvite was formed as sharp (needle-shaped) crystals that can potentially damage the IEM. The gradual loss of Mg²⁺ was observed with FW liquid digestate because of high PO₄³⁻ concentration, indicating the formation of struvite. The membrane with high selectivity for divalent ions resulted in the rapid decrease in electric current, implying serious membrane scaling on IEMs. These findings demonstrated that the membrane scaling problems by calcium and magnesium precipitation are ubiquitous in ED for nutrients recovery from wastewater.

中文翻译：

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用高浓度废水供给的电渗析中的膜结垢

膜结垢问题会限制电渗析 (ED) 从废水中回收养分的广泛应用。在这项研究中，我们使用实验室规模的 ED 反应器研究了离子交换膜 (IEM) 上的钙和镁垢沉淀。两种高强度废水流，包括城市垃圾 (MW) 液体消化物和食物垃圾 (FW) 液体消化物，被送入 ED 反应器。对于MW液体消化液的操作，累积Ca ²⁺损失随着电流的增加而增加，而电流条件不影响累积Mg ²⁺损失。运行 8 小时后，Ca ^{2+ 为}60.1 %，Mg ^{2+ 为}39.0%MW 液体消化液中的 以沉淀物的形式丢失。在阳离子交换膜上观察到的结垢是球霰石、无定形碳酸钙 (ACC) 和鸟粪石，而在阴离子交换膜上没有发现 ACC。观察到的具有 MW 液体消化物（球霰石和 ACC）的碳酸钙结垢与合成溶液中发现的结垢（方解石）不同。在这些结垢物中，鸟粪石形成为可能损坏 IEM 的尖锐（针状）晶体。由于高 PO ₄ ³⁻，在 FW 液体消化物中观察到Mg ²⁺逐渐损失浓度，表明鸟粪石的形成。对二价离子具有高选择性的膜导致电流快速下降，这意味着 IEM 上的膜结垢严重。这些发现表明，钙和镁沉淀引起的膜结垢问题在 ED 中普遍存在，用于从废水中回收养分。