期刊
ENVIRONMENTAL TECHNOLOGY
卷 42, 期 20, 页码 3122-3131出版社
TAYLOR & FRANCIS LTD
DOI: 10.1080/09593330.2020.1723710
关键词
Two-stage coagulant; micro-floc; final aggregate; velocity gradient; coagulation-flocculation
资金
- National Natural Science Foundation of China [51478010]
Two-stage addition of aluminium sulphate in coagulation process forms larger and easily removable flocs, resulting in 85.1% lower residual turbidity compared to single addition under 580 rpm and 120 s conditions.
In a coagulation-flocculation process, optimal separation of the resultant aggregates plays a decisive role on coagulation performance and provides a lower burden for subsequent treatment units. This separation highly depends on the stability of the micro-flocs formed during the initial, rapid stage of coagulation. In this work, a two-stage addition of aluminium sulphate (alum, Al-2(SO4)(3)) was employed by adding 0.04 and 0.08 mM Al-2(SO4)(3) at the beginning and the end of rapid mixing, respectively. The coagulation performance and floc characteristics were compared to conventional single addition with the same total coagulant dosage, and the effects of variable rapid-mixing speeds (160-850 rpm) and duration time (10-120 s) were investigated. The results showed that the residual turbidity of two-stage coagulant addition was 85.1% lower than single addition when applied at a mixing speed of 580 rpm and a duration time of 120 s. The underlying coagulation mechanism revealed that the two-step addition more effectively neutralized colloids and formed larger aggregates that settled better and could more easily be removed. Moreover, the aggregates were less firm, which was attributed to different interactions among the micro-flocs, the second addition of Al-2(SO4)(3) and destabilized colloids. The present work provides data to broaden the window of rapid-mixing environments for more effective coagulation.
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