Floc size distribution FSD was measured by Mastersizer 2000 Malvern Panalytical

Floc size distribution fsd was measured by

This preview shows page 3 - 5 out of 8 pages.

every 10 minutes. Floc size distribution (FSD) was measured by Mastersizer 2000 (Malvern Panalytical, Malvern, UK) and each sample was measured three times to obtain the average results. During the slow mixing period in the third flocculation basin, zeta potential was measured by zetasizer Nano ZS (Malvern Panalytical, Malvern, UK). The images of flocs from the rapid mixer, third flocculation basin, and sedimentation tank were captured by IX71 digital photomicrography (Olympus, Tokyo, Japan). 3. Results and Discussion 3.1. Coagulation Behaviors under Different Rapid Mixing Speed 3.1.1. Floc Size Distribution in Three Processes Continuous experiments were performed under 250 mg/L magnesium ion with 30 L/h to investigate the effects of rapid mixing conditions on coagulation performance and floc size distribution. According to FSD, average floc size decreased when rapid mixing speed increased in the rapid mixer and sedimentation tank. In the flocculation basin, floc size tended to be stable or slightly broken with the increase of rapid mixing speed to 300rpm. This is consistent with the findings that repulsive forces tend to stabilize the suspension and prevent particle agglomeration [ 13 , 18 ]. As shown in Table 3 , the average floc sizes 8.39, 8.06 and 8.04 μ m were obtained with rapid mixing speeds of 250, 300 and 350 rpm in a rapid mixer, respectively. Small floc had the same trend to aggregate relatively large flocs. Average floc size was 8.06 and 7.89 μ m in the rapid mixer and flocculation basin when the mixing speed was 300 rpm. In general, the flocs will grow in the flocculation basin, but it seems that floc size decreased in the flocculation process. In fact, during the flocculation process, particles larger than 11.25 μ m accounted for 4.54% and 4.9% in the rapid mixer and flocculation basin, respectively. Particles smaller than 1 μ m also decreased in the slow mixing period. As can be seen also in Figure 2 (sedimentation tank), particles smaller than 1 μ m account for 6.2%, 10.0% and 12.6% with mixing speeds of 250, 300 and 350 rpm respectively. It was observed that the percentage of smaller particles increased with the increase of mixing speed. This indicates that the high mixing speed will break the flocs, and only part of the flocs will aggregate again after the flocs are broken. The general shape of the curves was broadly similar in different units. The average floc size decreased to a steady state; there was a dynamic balance between floc growth and breakage. When the stirring speed was increased from 250 rpm to 350 rpm, small average floc size could be observed in these three units. Following the breakage and aggregation period, there was only a partial flocs re-growth, showing that the broken flocs can only re-grow to a very limited extent.
Image of page 3

Subscribe to view the full document.

Appl. Sci. 2019 , 9 , 973 4 of 8 Table 3. Average floc size in different process units. Rapid Mixing (rpm) Average Floc Size ( μ m) Rapid Mixer Flocculation Basin Sedimentation Tank 250 8.39 7.96 14.41 300 8.06 7.89 11.21 350 8.04 7.95 10.58 ( a ) ( b ) ( c ) 0.01 0.1 1 10 100 1000 0 1 2 3 4 5 Size(μm) Volume(%) 250rpm 300rpm 350rpm Rapid mixer 0.01 0.1 1 10 100 1000 0 1 2 3 4 5 6 Size(μm) Volume(%) 250rpm 300rpm 350rpm Flocculation basin 0.01 0.1 1 10 100 1000 0 1 2 3 4 5 6 Size(μm) Volume(%) 250rpm 300rpm 350rpm
Image of page 4
Image of page 5
  • Fall '19

What students are saying

  • Left Quote Icon

    As a current student on this bumpy collegiate pathway, I stumbled upon Course Hero, where I can find study resources for nearly all my courses, get online help from tutors 24/7, and even share my old projects, papers, and lecture notes with other students.

    Student Picture

    Kiran Temple University Fox School of Business ‘17, Course Hero Intern

  • Left Quote Icon

    I cannot even describe how much Course Hero helped me this summer. It’s truly become something I can always rely on and help me. In the end, I was not only able to survive summer classes, but I was able to thrive thanks to Course Hero.

    Student Picture

    Dana University of Pennsylvania ‘17, Course Hero Intern

  • Left Quote Icon

    The ability to access any university’s resources through Course Hero proved invaluable in my case. I was behind on Tulane coursework and actually used UCLA’s materials to help me move forward and get everything together on time.

    Student Picture

    Jill Tulane University ‘16, Course Hero Intern

Ask Expert Tutors You can ask You can ask ( soon) You can ask (will expire )
Answers in as fast as 15 minutes