This is also consistent with the findings of a previous study 14 Appl Sci 2019

This is also consistent with the findings of a

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m. This is also consistent with the findings of a previous study [ 14 ]. Appl. Sci. 2019 , 9 , x 6 of 8 0.01 0.1 1 10 100 1000 0 1 2 3 4 5 6 Size(μm) Volume(%) a Flow: 30L/h Rapid mixer Flocculation basin Sedimentation tank 0.01 0.1 1 10 100 1000 0 1 2 3 4 5 6 7 Size(μm) Volume(%) b Flow: 60L/h Rapid mixer Flocculation basin Sedimentation tank ( a ) ( b ) Figure 4. Floc size distribution with different flows for three stages. (a) 30 L/h; (b) 60 L/h. 3.3. Images analysis The floc size distribution can tell us the percentages of different floc sizes (shown in Figure 4), and the removal efficiency is commonly used to estimate the coagulation performance. In order to gain further insight into the floc and sediment properties, image analysis was used to predict floc characteristics by IX71 digital photomicrography. In Figure 5, the average size of flocs in different reactors is clearly indicated. The floc formation and growth processes were carried out in the rapid mixer and no more aggregation occurred due to the strong repulsion between positively charged particles of magnesium hydroxide in the flocculation basin. In the sedimentation tank, flocs aggregated to form relatively large particles. This is consistent with the findings of FSD value which are shown in Figure 4. As for Figure 5a and 5d, they clearly show that increasing flow caused a decrease of the average size in the rapid mixer. The average floc size of magnesium hydroxide- reactive orange is 8.06 and 7.25 μ m. This is also consistent with the findings of a previous study [14]. Figure 5. Floc image analysis ( a ) rapid mixer for 30 L/h; ( b ) flocculation basin for 30 L/h; ( c )sedimentation tank for 30 L/h; ( d ) rapid mixer for 60 L/h. 4. Conclusions Figure 5. Floc image analysis ( a ) rapid mixer for 30 L/h; ( b ) flocculation basin for 30 L/h; ( c ) sedimentation tank for 30 L/h; ( d ) rapid mixer for 60 L/h. 4. Conclusions In this research, the effects of mixing conditions on magnesium hydroxide continuous coagulation performance and floc properties were investigated. Rapid mixing speed plays a significant role in floc
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Appl. Sci. 2019 , 9 , 973 7 of 8 formation and growth. The function of the rapid mixer is to provide a place for the rapid nucleation and precipitation of magnesium hydroxide. In this stage, coagulant and reactive orange formed flocs. In the flocculation basin, small flocs will form more dense flocs, but average floc size remains stable. After the sedimentation process, flocs aggregate to form relatively large flocs. Therefore, appropriate rapid stirring is conducive to the formation of flocculation and the removal of pollutants. Increasing the flow will cause a short retention time; the average floc size decreases from 11.21 to 10.47 μ m when flow increases from 30 to 60 L/h. The coagulation behavior indicates that magnesium hydroxide is an effective coagulant for reactive orange removal with an efficiency of 89%.
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