analysis of a pilot-scale anaerobic baffled reactor treating domestic ...

where D is the electron equivalence of SBCOD with characteristic stoichiometric representation of
CXHYOZNA:
D = 4X
+ Y − 2Z
− 3A
CXHYOZNA has a COD of
And a molar mass
215
Eq. A6- 12
Eq. A6- 13
Eq. A6- 14
Then if νj is the stoichiometric coefficient of component j in Eq. A6- 11, then for all components
except VFA and CH4 the amount of component j produced in the steady-state model is calculated as
and the amount of CH4 produced (SM) is calculated from Eq. A6- 10.
The outflow concentration of each component j is determined as
1.4 Weak acid-base chemistry
Eq. A6- 15
Eq. A6- 16
The digester pH value in a methanogenic reactor rate-limited by hydrolytic processes is dominated by
the partial pressure of CO2 in the headspace, PCO2, the bicarbonate concentration and the ionic strength
in solution. The partial pressure of CO2 is calculated from the ratio of the production of CO2 and CH4.
The dependence of pH on PCO2 and [HCO3 - ] is expressed in Eq. A6- 17 (Sötemann et al., 2005)
where
- ( e eq./mol)
[ Y + 2⋅
( 2⋅
X − Z ) − 3 ] ( gCOD/ l)
COD = 8⋅ ⋅ A
MM = 12⋅ X + Y + 16⋅
Z + 14⋅
A
j
j
( S S )
∆S = ν ⋅ −
S = S ⋅ ∆S
P
je
ji
=
10
bPi
j
bPe
( gVSS/mol)
' /
−
pKC1
− pH pH − pKC
2
[ HCO3
] ⋅ ( 1+
10 + 10 )
'
pK
/ / /
HCO
2
pH − pKC1
pH − pKC1
− pKC
2
⋅ ( 1+
10 + 10 )
CO2
−
2
Eq. A6- 17
[HCO3 - ] = bicarbonate concentration (which is approximately equal to total alkalinity)
[mol/ℓ]
PCO2 = partial pressure of CO2 in the gas phase [atm or mol fraction]
pK’HCO2 = -log10 of apparent Henry’s law constant for CO2
pK’C1, pK’C2 = -log10 of apparent dissociation constants for carbonate system corrected for
ionic strength