Settling Tank - Dimension 1


1. Determine the area of settling tanks

    a). Solid Flux Loading (SFL) Criteria

    0.4 ~ 0.8 lb/ft2Ěh for average loading

    1.2 lb/ft2Ěh = 29 lb/ft2Ěd < 50 lb/ft2Ěh for peak loading

    b). Calculate area required

    MLSSr = 7,500 ~ 11,000 mg/l

    R = 0.28 ~ 0.48

    a). Calculate area at MLSSr = 11,000 mg/l, SFL = 0.4 lb/ft2Ěh, R = 0.28

    A = 14,000 ft2

    R Q(gal/day) MLSS(mg/l) SFL(lb/ft2Ěh)

    (ft2)

    b). Calculate SFL at different operation conditions

    Keep MLSS = 2,500 mg/l in aeration tank

    Table of SFL at different operation conditions

    Select AL = 14,000 ft2

    SFL, lb/ft2.h 0.4 0.41 0.43 0.45 0.46 Peak, 0.92 Satisfaction
    Q mgd 5 5 5 5 5 10 All SFL satisfy the criteria
    R 0.28 0.32 0.37 0.44 0.54 0.48
    MLSSr 11,000 10,000 9,000 8,000 7,000 7,500
    1+R 1.28 1.32 1.37 1.44 1.54 1.48
    AL, ft2 13,900


Q(mgd) MLSS(mg/l) A(ft2) q(hr) qc(day) R

SFL (lb/ft2Ěh)
Q (mgd)
R
MLSSr
1+R

     

    c). Check surface overflow rate (SOFR) corresponding to the area decided by SFL

    SOFR = (1+R)Q/A

    At average flow, SOFR = (1+0.54) 5 106/14,000 550 gal/ft2Ěd,

    < 800 gal/ft2Ěd, ok

    At peak flow, for R = 0.48, SORF = (1+ 0.48) 10 106/14,000 1,100 gal/ft2Ěd,

    < 1,200 gal/ft2Ěd, ok

    R Q(gal/day) Area(ft2)

    (ft
    2)

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