Environmental Engineering Reference
In-Depth Information
that are routinely conducted on organic substrates (Kleerebezem and Van Loos-
drecht, 2006):
kg
−1
), corresponding to the amount of
oxygen equivalents required to oxidize all organic carbon to carbon dioxide.
Chemical oxygen demand (COD, g
O
2
kg
−1
), typically corresponding to 50
Organic dry matter content (ODM, g
ODM
−
kg
−1
). The difference between the
TDM and the ODM values is the inorganic ash concentration.
90 wt% of the total dry matter (TDM, g
TDM
kg
−1
), typically estimated from the total con-
centration of reduced nitrogen compounds (so-called
Kjeldahl
nitrogen) minus
the concentration of ammonium (NH
4
+1
).
Organic nitrogen content (N
org
,g
N
Three basic equations can be established that allow for identification of the elemental
composition of the organic feedstock. First of all, the COD value of organic matter can
be identified using the combustion equation, which in general terms can be expressed as
C
c
H
h
O
o
N
n
+
x
O
2
!
y
H
2
O+
z
CO
2
+
w
NH
3
ð
RX
:
14
:
2
Þ
By solving the elemental balances for C, H, O, and N, we can identify the stoichio-
metric coefficients
x
,
y
,
z
, and
w
. The stoichiometric coefficient
x
=(4+
h
3
n
)/4
represents the number of oxygen molecules required to combust one mole of organic
carbon (
c
= 1). Using the molar weights or the various compounds (e.g., 32 g.mol
−1
for O
2
) consequently, the COD/ODM ratio (g
O
2
−
2
o
−
g
−1
ODM
) can be defined as
ODM
=
32 4 +
h
COD
4
12 +
h
+16
o
+14
n
ð
−
2
o
−
3
n
Þ
=
ð
Eq
:
14
:
1
Þ
ð
Þ
From the organic nitrogen measurement, an equation can be derived for the stoichi-
ometric coefficient
n
:
n
=
N
org
12 +
h
+16
o
+14
n
ð
Þ
ð
Eq
:
14
:
2
Þ
14ODM
The third equation is based on the fact that carbon is always tetravalent, and the total
number of its bonds will be 4. Assuming C
-
H, C = O, and C
-
NH
2
as carbon bonds,
the following equation can be derived:
4=
h
+2
o
−
n
ð
Eq
:
14
:
3
Þ
These three equations can be solved to obtain the elemental composition of the
organic carbon compound (with
c
= 1):
308COD + 704N
org
49COD
h
=
ð
Eq
:
14
:
4
Þ
−
64N
org
+ 112ODM
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