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Partition Coefficients
Bioconcentration Factor BCF
The amount of a chemical to accumulate in aquatic
organisms.
BCF = Corg /C, where
Corg = equilibrium concentration in organism (mg/kg or
ppm), and
C = concentration in water (ppm).
Octanol-Water Partition Coefficient
The ratio of a chemical's concentration in the octanol phase
to its concentration in the aqueous phase of a two-phase
octanol-water system.
Kow = Co / Cw, where
Co = concentration of chemical in octanol phase (mg/L
or µg/L) and
Cw = concentration of chemical in aqueous phase (mg/L
or µg/L).
149
ENVIRONMENTAL ENGINEERING (continued)
Organic Carbon Partition Coefficient Koc
Koc = Csoil / Cwater, where
Csoil = concentration of chemical in organic carbon
component of soil (µg adsorbed/kg organic C, or
ppb), and
Cwater = concentration of chemical in water (ppb or µg/kg)
Retardation Factor R
R = 1 + (ρ/η)Kd, where
ρ = bulk density,
η = porosity, and
Kd = distribution coefficient.
Soil-Water Partition Coefficient Ksw = Kρ
Ksw = X/C, where
X = concentration of chemical in soil (ppb or µg/kg),
and
C = concentration of chemical in water (ppb or µg/kg).
Ksw = Koc foc, where
foc = fraction of organic carbon in the soil
(dimensionless).
♦ Steady-State Reactor Parameters
Comparison of Steady-state Mean Retention Times for Decay Reactions of Different Order a
Equations for Mean Retention Times (θ)
Reaction Order r Ideal Batch Ideal Plug Flow Ideal CMFR
Zero b –k
Co
k
( Co -Ct)
k
( Co-Ct) k
First –kC 1
k
In ( Co k
Ct)
( Co Ct) -1
k
Second –2kC 2
1
2kC o
( Co Ct) -1
2kC
( Co Ct) -1
2kC
a Co = initial concentration or influent concentration; Ct = final condition or effluent concentration.
b Expressions are valid for kθ ≤ Co;otherwise Ct = 0.
Comparison of Steady-State Performance for Decay Reactions of Different Order a
Equations for Ct
Reaction Order r Ideal Batch Ideal Plug Flow Ideal CMFR
Zero b t ≤ Co/k –k Co – kt Co – kθ Co – kθ
t > Co/k 0
First –kC Co[exp(–kt)] Co[exp(–kθ)] o C
1+kθ
Second –2kC 2
Co
1+ 2ktC o
Co
1+2kθC o
( )1 8kθC 2
o +1 -1
4kθ
a
Co = initial concentration or influent concentration; Ct = final condition or effluent concentration.
b
Time conditions are for ideal batch reactor only.
♦ Davis, M.L. and S.J. Masten, Principles of Environmental Engineering and Science, McGraw-Hill, 2004.
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