Effect of two-stage coagulant addition on coagulation-ultrafiltration process for treatment of humic-rich water.
Effect of two-stage coagulant addition on coagulation-ultrafiltration process for treatment of humic-rich water.
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DOI：
10.1016/j.watres.2011.05.037
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发表时间：
2011-08
期刊：
影响因子：
12.8
通讯作者：
Ting Liu;Zhong-lin Chen;Wenling Yu;Ji-min Shen;J. Gregory
中科院分区：
文献类型：
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作者：
Ting Liu;Zhong-lin Chen;Wenling Yu;Ji-min Shen;J. Gregory
本研究研究了一种新型两阶段混凝剂添加策略，该策略应用于混凝超滤 (UF) 工艺，用于在中性 pH 值下处理富含腐殖酸的水。当快速混合阶段和絮凝阶段中途添加硫酸铝（明矾）剂量为3:1时，两级添加明矾的一体化工艺在总剂量相同的情况下，实现了与传统一级明矾添加几乎相同的有机物去除效果。而跨膜压力（TMP）发展所表现出的两阶段添加可以有效减轻膜污染。研究发现，TMP 的发展主要归因于膜表面的外部污垢，这与絮体特性密切相关。罐式试验结果表明，两段投料方式形成的絮体平均粒径比一级投料方式大约大一半，这对减少膜污染具有有益的效果。而且，两阶段明矾的添加导致絮体结构更加不规则，有效密度较低，导致膜表面絮体形成的滤饼层孔隙率较高。膜表面的显微镜观察表明，两阶段明矾的添加也可以显着限制膜孔中的内部污垢。由于形成了更活泼的基团或吸附了更不稳定的铝物质，新形成的氢氧化物沉淀物的表面特征可能与老化沉淀物不同。因此，絮凝物可以进一步连接和聚集，从而为混凝超滤过程的过滤性能提供更好的性能。作为一种简单有效的方法，两阶段混凝剂添加策略在混凝膜工艺中具有重要的实际意义。
A novel two-stage coagulant addition strategy applied in a coagulation-ultrafiltration (UF) process for treatment of humic-rich water at neutral pH was investigated in this study. When aluminum sulfate (alum) doses were set at a ratio of 3:1 added during rapid mix stage and half way through flocculation stage, the integrated process of two-stage alum addition achieved almost the same organic matter removal as that of conventional one-stage alum addition at the same overall dose. Whereas membrane fouling could be effectively mitigated by the two-stage addition exhibited by trans-membrane pressure (TMP) developments. The TMP developments were found to be primarily attributed to external fouling on membrane surface, which was closely associated with floc characteristics. The results of jar tests indicated that the average size of flocs formed in two-stage addition mode roughly reached one half larger than that in one-stage addition mode, which implied a beneficial effect on membrane fouling reduction. Moreover, the flocs with more irregular structure and lower effective density resulted from the two-stage alum addition, which caused higher porosity of cake layer formed by such flocs on membrane surface. Microscopic observations of membrane surface demonstrated that internal fouling in membrane pores could be also remarkably limited by two-stage alum addition. It is likely that the freshly formed hydroxide precipitates were distinct in surface characteristics from the aged precipitates due to formation of more active groups or adsorption of more labile aluminum species. Consequently, the flocs could further connect and aggregate to contribute to preferable properties for filtration performance of the coagulation-UF process. As a simple and efficient approach, two-stage coagulant addition strategy could have great practical significance in coagulation-membrane processes.