Organic matter
The biodegradable part of the COD may in certain cases be further subdivided. The
dissolved, easily degradable fraction can be divided into two fractions: Very easily
degradable organic matter, SHAc, and easily degradable organic matter, Ss. Very
easily degradable organic matter can be removed directly by the micro-organisms,
and it may diffuse into floes and biofilm. Probably easily degradable organic matter,
Ss, is to be hydrolyzed before it is diffusable and can be absorbed by the organisms.
Very easily degradable materials may be of importance in connection with biological phosphorus removal where this fraction is decisive for the functioning of the
process. Likewise, the very easily degradable fraction is also essential for the oxygen
demand in very highly loaded biological processes.
The suspended, easily degradable organic matter can be divided into micro-organisms, Xs, and other suspended materials, Xs. The micro-organisms in wastewater
may influence the composition of the biomass in biological treatment plants, and
hence influence the removal rate and the efficiency of the treatment.
Below it is briefly outlined how the individual COD-fractions can be determined.
- Inert dissolved organic matter, SI, is determined as dissolved COD after 20-30
days' oxidation of the wastewater mixed with activated sludge. Parallel
blind tests, solely with activated sludge, should be carried out.
44
- Easily degradable organic matter, Ss, is determined on the basis of a respiration test /18/. An example of such a test is shown in Fig 2.6. Knowing the
yield constant, Y& Ss can be determined by means of an oxygen mass balance
rv,oz· V = Q · Ss· (1- YH)
Ss = rv,oz· 9/(1- YH)
(2.5)
as (1 - YH) is the part of the easily degradable organic matter which is
oxidized whereas YH is the part which is transformed into biomass. 9 is the
hydraulic retention time. A BOD-curve as shown in Fig 2.7 may also be used
for an estimate on Ss as the first "quick" part of the curve may be assumed
to represent Ss.
- Very easily degradable dissolved organic matter, SHAc, is a part of the easily
degradable matter. Methods for its determination have not yet been firmly
established. A considerable constituent is acetic acid which may be determined specifically by gas chromatography, ion chromatography etc. The
concentration of materials of a molar weight less than 800- 1000 constitutes
the major part of this fraction (however, there is a small concentration of
dissolved inert matter with a low molecular weight).
- Suspended inert organic matter is determined on the basis of the sludge
production rate by tests with varying sludge ages. XI can be estimated by
means of curve adaptation with a mathematical model /17 I. XI may also be
estimated on the basis of a long-term aerobic sludge stabilization.
The biodegradable part of the COD may in certain cases be further subdivided. The
dissolved, easily degradable fraction can be divided into two fractions: Very easily
degradable organic matter, SHAc, and easily degradable organic matter, Ss. Very
easily degradable organic matter can be removed directly by the micro-organisms,
and it may diffuse into floes and biofilm. Probably easily degradable organic matter,
Ss, is to be hydrolyzed before it is diffusable and can be absorbed by the organisms.
Very easily degradable materials may be of importance in connection with biological phosphorus removal where this fraction is decisive for the functioning of the
process. Likewise, the very easily degradable fraction is also essential for the oxygen
demand in very highly loaded biological processes.
The suspended, easily degradable organic matter can be divided into micro-organisms, Xs, and other suspended materials, Xs. The micro-organisms in wastewater
may influence the composition of the biomass in biological treatment plants, and
hence influence the removal rate and the efficiency of the treatment.
Below it is briefly outlined how the individual COD-fractions can be determined.
- Inert dissolved organic matter, SI, is determined as dissolved COD after 20-30
days' oxidation of the wastewater mixed with activated sludge. Parallel
blind tests, solely with activated sludge, should be carried out.
44
- Easily degradable organic matter, Ss, is determined on the basis of a respiration test /18/. An example of such a test is shown in Fig 2.6. Knowing the
yield constant, Y& Ss can be determined by means of an oxygen mass balance
rv,oz· V = Q · Ss· (1- YH)
Ss = rv,oz· 9/(1- YH)
(2.5)
as (1 - YH) is the part of the easily degradable organic matter which is
oxidized whereas YH is the part which is transformed into biomass. 9 is the
hydraulic retention time. A BOD-curve as shown in Fig 2.7 may also be used
for an estimate on Ss as the first "quick" part of the curve may be assumed
to represent Ss.
- Very easily degradable dissolved organic matter, SHAc, is a part of the easily
degradable matter. Methods for its determination have not yet been firmly
established. A considerable constituent is acetic acid which may be determined specifically by gas chromatography, ion chromatography etc. The
concentration of materials of a molar weight less than 800- 1000 constitutes
the major part of this fraction (however, there is a small concentration of
dissolved inert matter with a low molecular weight).
- Suspended inert organic matter is determined on the basis of the sludge
production rate by tests with varying sludge ages. XI can be estimated by
means of curve adaptation with a mathematical model /17 I. XI may also be
estimated on the basis of a long-term aerobic sludge stabilization.