Basic Biological Processes
3.2.3 Decay
Living bacteria have a certain death rate which is essential to the conversions of
substances in biological treatment plants. The fact that the organism dies does not
change the amounts of the substances, but it means that slowly degradable material
is added to the system. This material is hydrolyzed and subsequently causes new
growth and for instance oxygen consumption or nitrate consumption. See Fig 3.3.
Normally decay is described as a first order process as regards the biomass, XB
rv;xB= b · XB
(3.5)
where b is the constant for decay (dimension T -I, unit for example d- 1 ).
In connection with decay, some biologically non-degradable (or very slowly degradable) material is released. It is, at any rate, non-degradable (inert) at the
retention times we find in biological treatment plants.
3.3. Aerobic heterotrophic conversion of
organic matter
3.3.1 Reactions, aerobic conversions
Organic matter which is fed to an aerobic biological treatment plant may be exposed to:
a.
oxidation to carbon dioxide and different nutrients (specifically in the form of
N, P and S-compounds),
b.
assimilation in biomass (sludge),
c.
unchanged passage, which means that the matter is biologically nondegradable
=inert (at least in the plant concerned),
d.
conversion into other organic matter.
Normally it is the total amount of organic matter to be removed which is interesting.
Only in special cases, for example in respect of toxic waste such as cyanide, phenols
and chlorinated hydrocarbons, it is the specific substances which are interesting to
observe. Details of biological conversions in wastewater can for example be found
in /36/.
Organic matter in wastewater has the following approximate chemical composition: Cu~H1g()9N /7/. If the matter is oxidized by micro-organisms to carbondioxide, it may result in the following two expressions:
C1sH1909N + 17.5 Oz + H+ ---.18 COz + 8 HzO + NH!
(without nitrification)
(3.6)
65
3.2.3 Decay
Living bacteria have a certain death rate which is essential to the conversions of
substances in biological treatment plants. The fact that the organism dies does not
change the amounts of the substances, but it means that slowly degradable material
is added to the system. This material is hydrolyzed and subsequently causes new
growth and for instance oxygen consumption or nitrate consumption. See Fig 3.3.
Normally decay is described as a first order process as regards the biomass, XB
rv;xB= b · XB
(3.5)
where b is the constant for decay (dimension T -I, unit for example d- 1 ).
In connection with decay, some biologically non-degradable (or very slowly degradable) material is released. It is, at any rate, non-degradable (inert) at the
retention times we find in biological treatment plants.
3.3. Aerobic heterotrophic conversion of
organic matter
3.3.1 Reactions, aerobic conversions
Organic matter which is fed to an aerobic biological treatment plant may be exposed to:
a.
oxidation to carbon dioxide and different nutrients (specifically in the form of
N, P and S-compounds),
b.
assimilation in biomass (sludge),
c.
unchanged passage, which means that the matter is biologically nondegradable
=inert (at least in the plant concerned),
d.
conversion into other organic matter.
Normally it is the total amount of organic matter to be removed which is interesting.
Only in special cases, for example in respect of toxic waste such as cyanide, phenols
and chlorinated hydrocarbons, it is the specific substances which are interesting to
observe. Details of biological conversions in wastewater can for example be found
in /36/.
Organic matter in wastewater has the following approximate chemical composition: Cu~H1g()9N /7/. If the matter is oxidized by micro-organisms to carbondioxide, it may result in the following two expressions:
C1sH1909N + 17.5 Oz + H+ ---.18 COz + 8 HzO + NH!
(without nitrification)
(3.6)
65