Environmental Engineering Reference
In-Depth Information
was determined. For other food wastewater sources, energy production per ton of
the product was calculated.
Equation (5.1) gives the current production potential per ton of product,
I
MFC,
i
(Ampere-hours/ton or A h /ton).
1
3600
∗
COD
i
M
COD
∗
n
e
n
COD
∗
I
MFC,
i
=
Q
i
b
i
∗
F
η
c
(5.1)
This can then be used to determine the electricity production potential per ton of
product,
E
MFC,
i
(Watt h /ton or W h/ton), as per Eq. (5.2).
E
MFC,
i
=
I
MFC,
i
V
(5.2)
Where,
COD Chemical oxygen demand for wastewater stream
i
,g/L
M
COD
Molecular weight of oxygen (COD)
32 g/mole
Q
i
Wastewater flow rate per ton of product
i
, L/ton
b
i
biodegradability of organic carbon in wastewater type
i
n
e/
n
COD
Electrons released per mole of COD during anodic degradation of
organic carbon in MFC
=
=
4
F
Faraday constant
=
96485.3 C/mole. One Ampere is equivalent to
one C/s.
η
c
Coulombic efficiency of the MFC
V
Voltage generated in MFC, Volts
The anodic and cathodic half reactions for the degradation of carbohydrate, as an
example of organic carbon present in wastewater, can be given as:
4H
+
+
4e
−
+
→
CO
2
+
Anode: CH
2
O
H
2
O
(5.3)
Cathode: 4H
+
+
4e
−
+
O
2
→
2H
2
O
(5.4)
The following assumptions were made based on the justification given below:
Biodegradability of organic carbon (COD) in wastewater
=
0.8 [4],
Voltage generated in MFC
=
0.4 volts,
Coulombic efficiency (CE)
=
50%.
The voltage generated in an MFC is a function of the external electrical load. An
MFC will typically be operated close to its maximum power density, which in turn
decides the voltage output. The voltage at maximum power density in MFCs can
range from 0.2 to 0.5 V depending on the design of the MFC and its performance.
In this analysis, a voltage output of 0.4 V is used, which is reasonable consider-
ing that better MFC designs will emerge which can provide a steady voltage output
ranging up to 0.5 V during a continuous MFC operation. The coulombic efficien-
cies (CE) reported in literature range from 5 to 59% for wastewaters containing
