Basic Biological Processes
Example 3.1
The wastewater from an industry contains glutamic acid, C5H904N. The concentration
is 1.5 kg/m 3 , the volume of wastewater 300 m 3 /d.
What is the COD-concentration in the wastewater?
How much oxygen should be added per day to a biological treatment plant which is assumed to oxidize 70 per cent of the organic matter in the wastewater? The plant does
not nitrify.
The COD-value is found by an equation of reaction
C5H904N + 4.5 02 + H+ ---> 5 C02 + 3 H20 + NH;\
(as the organically bound nitrogen is not oxidized in connection with the COD-analysis). It is found from the equation that 1 mole of glutamic acid (molar weight 5 · 12 + 9 ·
1 + 4 · 16 + 1 · 14 = 147 g/mol) consumes 4.5 moles of oxygen (weight 4.5 · 16 · 2 =
144 g/mol). Hence the oxygen consumption is 144 g 0 2/147 g glutamic acid= 0.98 g
oxygen/g glutamic acid and subsequently the COD-concentration is: 1.5 kg glutamic
acid/m 3 · 0.98 kg oxygen/kg glutamic acid = 1.47 kg 0 2/m 3 ).
The daily oxygen consumption from the wastewater is
1.47 kg 0 2/m 3 · 300 m 3 /d · 0.70 = 309 kg 0 2/d.
3.3.2 Yield constant, aerobic heterotrophic
conversions
If the organic matter is integrated in biomass, it is, in other words, used for growth,
it will only be possible to find part of it again in the biomass. In connection with
aerobic growth, micro-organisms have an energy efficiency,~' of 55-60 per cent /8 I.
The yield constant, measured in energy units, is therefore also 0.55-0.60. This is the
maximum yield constant, Ymax·
In a microbial system, the observed yield constant, YobSr may vary from negative
values and up to Y max· The size of the observed yield constant depends on the
design of the system and the amount of food available.
If the yield constant is known, an equation of reaction can be written for aerobic
growth, the ratio between produced amount of biomass (composition CsH7N02)
and removed amount of substrate (composition CtsHlg()gN) being exactly the yield
constant.
where
b· MWbiom
----=Yobs
a· MWorg
(3.11)
(3.12)
67
Example 3.1
The wastewater from an industry contains glutamic acid, C5H904N. The concentration
is 1.5 kg/m 3 , the volume of wastewater 300 m 3 /d.
What is the COD-concentration in the wastewater?
How much oxygen should be added per day to a biological treatment plant which is assumed to oxidize 70 per cent of the organic matter in the wastewater? The plant does
not nitrify.
The COD-value is found by an equation of reaction
C5H904N + 4.5 02 + H+ ---> 5 C02 + 3 H20 + NH;\
(as the organically bound nitrogen is not oxidized in connection with the COD-analysis). It is found from the equation that 1 mole of glutamic acid (molar weight 5 · 12 + 9 ·
1 + 4 · 16 + 1 · 14 = 147 g/mol) consumes 4.5 moles of oxygen (weight 4.5 · 16 · 2 =
144 g/mol). Hence the oxygen consumption is 144 g 0 2/147 g glutamic acid= 0.98 g
oxygen/g glutamic acid and subsequently the COD-concentration is: 1.5 kg glutamic
acid/m 3 · 0.98 kg oxygen/kg glutamic acid = 1.47 kg 0 2/m 3 ).
The daily oxygen consumption from the wastewater is
1.47 kg 0 2/m 3 · 300 m 3 /d · 0.70 = 309 kg 0 2/d.
3.3.2 Yield constant, aerobic heterotrophic
conversions
If the organic matter is integrated in biomass, it is, in other words, used for growth,
it will only be possible to find part of it again in the biomass. In connection with
aerobic growth, micro-organisms have an energy efficiency,~' of 55-60 per cent /8 I.
The yield constant, measured in energy units, is therefore also 0.55-0.60. This is the
maximum yield constant, Ymax·
In a microbial system, the observed yield constant, YobSr may vary from negative
values and up to Y max· The size of the observed yield constant depends on the
design of the system and the amount of food available.
If the yield constant is known, an equation of reaction can be written for aerobic
growth, the ratio between produced amount of biomass (composition CsH7N02)
and removed amount of substrate (composition CtsHlg()gN) being exactly the yield
constant.
where
b· MWbiom
----=Yobs
a· MWorg
(3.11)
(3.12)
67