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<strong>Membrane</strong> Systems Planning <strong>and</strong> Design 365<br />

Table 8.5<br />

Summary of VCF equations for various hydraulic configurations<br />

VCF equation<br />

Hydraulic configuration Typical membrane<br />

process(es)<br />

Equation<br />

No.<br />

Equation<br />

No. VCFmax<br />

VCFavg<br />

(20)<br />

(22)<br />

(24)<br />

h i<br />

tf (26)<br />

1 exp<br />

t<br />

(28)<br />

Deposition mode MCF 1 1<br />

MF/UF<br />

Small volume crossflow MF/UF<br />

tf<br />

(19) tf<br />

[(tb ?Qb) < Vf] (w/o feed tank) 2t<br />

t<br />

Large volume crossflow MF/UF<br />

tf Qf tf<br />

[(tb ?Qb) > Vf] (w/ feed tank)<br />

1<br />

tb Qb 2 t tf<br />

" #<br />

(21) tf Qf<br />

Qf<br />

tb Qb<br />

tb Qb<br />

CSTR w/o<br />

NF/RO (small-scale) 1<br />

(23) 1<br />

backwashing MF/UF (w/ bleed) 1 R<br />

1 R<br />

CSTR w/ backwashing MF/UF (w/ bleed) 1 t<br />

h i<br />

tf (25) 1<br />

1 1 exp<br />

1 R tf<br />

P<br />

t<br />

1 R<br />

PFR NF/RO<br />

VCFðxÞ QpðxÞ<br />

(27) 1<br />

Qp<br />

1 R<br />

Qb = backwash flow, gpm.<br />

Qf = feed flow, gpm.<br />

Qp = filtrate flow, gpd.<br />

Qp(X) = filtrate flow at position “X” within the membrane unit, gpd.<br />

R = membrane unit recovery, decimal percent.<br />

tb = backwash duration, min.<br />

tf = filtration cycle duration, min.<br />

t = solids retention time, min.<br />

VCFavg = average VCF, dimensionless.<br />

VCFmax = maximum VCF, dimensionless.<br />

VCF(X) = VCF at discrete position “X” within the membrane unit, dimensionless.<br />

Vf = volume of feed, gal.<br />

X = position in the membrane unit in the direction of tangential flow (i.e., X = 0 at the entrance to the first module), ft.

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