For a university project, I need to use the following equations, but I am having difficulty with the units of the term of the left-hand side (ΔXh). As far as I understand it, the units of this term should be µgCOD/(litre*hour), but I cannot see how that is the case. Perhaps I just have the units of one of the right-hand side terms incorrect?

ΔXh = Yh*(1 - kuap - keps)*Ubom*Xh


Yh [µgCOD/µgCOD]

kuap [µgCOD/µgCOD]

keps [µgCOD/µgCOD]

Ubom [µgCOD/(litre*hour)]

Xh [µgCOD/litre]

where µgCOD = micograms of chemical oxygen demand (a mass unit)

Thanks in advance for any help!


1 Answer 1


Isn't this your equation?: $\frac{\operatorname{d} X_h}{\operatorname{d} t} = Y_h\cdot (1 - k_{UAP} - k_{EPS})\cdot U_{BOM}\cdot X_h$


$X_h [\mu gCOD]$ concentration of biomass (heterotroph)

$Y_h [\mu gCOD/\mu gCOD_x]$ true yield coefficient (heterotroph)

$k_{UAP} [\mu gCOD/\mu gCOD_x]$ UAP formation rate constant

$k_{EPS} [\mu gCOD/\mu gCOD_x]$ EPS formation rate constant

$U_{BOM} [\mu gCOD/(\mu gCOD_x\cdot L\cdot Hr)]$ utilisation rate of biological organic matter

  • $\begingroup$ Thanks very much for your clarification of the equation. It made everything clear to me. $\endgroup$
    – user142224
    Aug 7, 2014 at 14:07

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