Design of Kinetics and Constants

1. BASIC ASSUMPTION AND DEFINITION

  • No microorganism in influent
  • Waste stabilization by microorganism occurs only in the reactor units
  • Only volume of the reactor unit used for calculating the mean cell-resident time qc,
  • Definition of qc:

    • qc = XVR /(QW XW + QE XE)
    X ¾ MLVSS in aeration tank, mg/l
    V ¾ volume of aeration tank, ft3
    Qw  ¾ sludge wastage rate, gal/day
    Xw ¾ wastage sludge conc., mg/l
    XE ¾ MLVSS in effluent, mg/l

2. MICROORGANISM IN SYSTEM AND EFFLUENT QUALITY

    qc = {Y(So-SE)/(q X)} - kd
    X = qcY(So - S)/[q (1+kdqc)]
    S = KS(1+kdqc)/[qc(YK-kd)-1]
    Y ¾ maximum yield coefficient, mg VSS/mg BOD5
    q ¾ V/Q, hydraulic detention time
    K ¾ maximum substrate utilization rate, mg BOD5/mg VSS× time, K=mmax /Y
    kd ¾ endogenous decay coefficient, 1/time
    Ks ¾ half-velocity constant, substrate concentration at one-half the maximum growth rate, mg BOD5/l
    S ¾ effluent BOD5, mg/l

3. PROCESS DESIGN AND CONTROL RELATIONSHIP

    Removal efficiency: E = (So-S)/So

    Food-microorganism ratio: F/M = QSo/(VX)

    Specific utilization rate: U = Q(So-S)/(VX) 1/time

    Relationship between U and qc: 1/qc= YU - kd = Y(F/M)E - kd

    Process control: qc= VX/(Qw XW)

Operation phase: Most activated sludge treatment systems operate in the range between the declining growth phase and the endogenous phase of microorganisms. In this range, the metabolism of organic is nearly complete and sludge exhibited well settling characteristics:

Use qc to control the growth rate of microorganisms and hence their degree of waste stabilization, qc = 5 ~ 15 days.

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