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Effect of pre-coagulation using different aluminium species on crystallization of cake layer and membrane fouling
npj Clean Water ( IF 11.4 ) Pub Date : 2019-08-14 , DOI: 10.1038/s41545-019-0040-3
Wenzheng Yu , Mengjie Liu , Xuejia Zhang , Nigel Graham , Jiuhui Qu

Pre-coagulation could mitigate the membrane fouling, and thus we used different Al coagulants as a pre-treatment for ultrafiltration to explore their effects on the morphology of the membrane cake layer and fouling. Parallel bench-scale tests, using three different species of Al (AlCl3, PACl15, and PACl25), with and without humic acid, were operated continuously for a long period to investigate the effects of floc aging (~13 days). Specifically, the presence of humic acid affects the cake layer by influencing the rate and extent of floc crystallization, as greater crystallization leads to greater fouling (bio-fouling was excluded in this study). The fouling rate (indicated by the trans-membrane pressure at constant flux) varied with Al species and was found to increase as follows: PACl15 < PACl25 < AlCl3. The presence of humic acid also intensify membrane flouling. The results showed that three species of Al induced different sizes of primary nanoparticles and fractal dimensions of flocs, and therefore produced cake layers with different thickness/structure. Analysis of flocs with different ages indicated a crystallization process in the cake layer. Crystallization exacerbate membrane fouling by decreasing the porosity of the cake layer, and the situation became severe in the presence of humic acid.



中文翻译:

不同铝种的预凝对饼层结晶和膜污染的影响

预凝结可以减轻膜的结垢,因此我们使用了不同的铝凝结剂作为超滤的预处理剂,以研究它们对膜滤饼层形态和结垢的影响。使用三种不同种类的Al(AlCl 3,PACl 15和PACl 25)(有或没有腐殖酸的情况下)长时间连续运行以研究絮凝物老化的影响(约13天)。具体而言,腐殖酸的存在通过影响絮凝物的结晶速率和程度来影响滤饼层,因为更大的结晶度会导致更大的结垢(本研究中不包括生物结垢)。结垢率(以恒定通量的跨膜压力表示)随Al种类而变化,并发现增加如下:PACl 15  <PACl 25  <AlCl 3。腐殖酸的存在也加剧了膜的絮凝。结果表明,三种Al引起不同程度的原生纳米颗粒和絮体的分形维数,因此产生了具有不同厚度/结构的饼层。对不同年龄的絮凝物的分析表明,在滤饼层中存在结晶过程。结晶通过降低滤饼层的孔隙率而加剧了膜的结垢,并且在存在腐殖酸的情况下情况变得更加严重。

更新日期:2019-08-14
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