Biofilters
Molecules with a molecular weight of less than 10 3 can be absorbed through the cell
membrane on the bacteria. It is not known where the diffusion limit into the biofilm
lies. 40-80 per cent of COD in municipal wastewater are particles bigger than 0.1Jlm
/18/. Very little material in the size fraction 0.01- 0.1Jlm has been found. However,
there is a significant fraction in the range 0.1-1 Jlm which is not included in
suspended solids, but in the" dissolved" fraction which certainly cannot diffuse into
the biofilm.
Fig 5.21 shows concentrations of organic matter in municipal wastewater from
Lyngby (Denmark) which are a result of different methods of analysis.
It is a condition for the removal of a non-diffusible material that it is degraded
extracellularly in a diffusible form in order to subsequently diffuse into the biofilm
where it is mineralized while consuming oxygen. The collective name for the
extracellular degradation is hydrolysis (see Chapter 3, Section 3.2.2.).
There are two different theories of the mechanism for hydrolysis in biofilm reactors:
Particle adsorption. According to this thesis the particles will be adsorbed to the
surface of the biofilm. This can be done by diffusion from the bulk water to the
surface, by settling and by entrapment on a rough (or filamentous) biofilm surface
/20/. Only qualitative determinations are available. We have no verification nor
any operational formulation of kinetic expressions.
External hydrolysis. From the biofilm extracellular enzymes are released to the bulk
water in which the hydrolysis takes place. The hydrolyzates should subsequently
diffuse into the biofilm and be degraded there. This mechanism is experimentally
Total COD
I r---~~--~-----+-----r----~1 500 g/m 3
GF/A
220
GF/C
210
0,2211
200
MW<10.000
120
MW<1.000
110
Gel filtration
110
VFA f----i 40
Carbohydrate H 15
Protein 1-----1 60
Total BOD
230
directly
easily
slowly
useable
hydrohydrolyzable
inert
inert ~ 1 c-sourrce 1 lyzable 1
10 100
100
200
90
Fig 5.21 Characterization of the COD content in raw wastewater. All units in COD!m 3 . /19/
183
Molecules with a molecular weight of less than 10 3 can be absorbed through the cell
membrane on the bacteria. It is not known where the diffusion limit into the biofilm
lies. 40-80 per cent of COD in municipal wastewater are particles bigger than 0.1Jlm
/18/. Very little material in the size fraction 0.01- 0.1Jlm has been found. However,
there is a significant fraction in the range 0.1-1 Jlm which is not included in
suspended solids, but in the" dissolved" fraction which certainly cannot diffuse into
the biofilm.
Fig 5.21 shows concentrations of organic matter in municipal wastewater from
Lyngby (Denmark) which are a result of different methods of analysis.
It is a condition for the removal of a non-diffusible material that it is degraded
extracellularly in a diffusible form in order to subsequently diffuse into the biofilm
where it is mineralized while consuming oxygen. The collective name for the
extracellular degradation is hydrolysis (see Chapter 3, Section 3.2.2.).
There are two different theories of the mechanism for hydrolysis in biofilm reactors:
Particle adsorption. According to this thesis the particles will be adsorbed to the
surface of the biofilm. This can be done by diffusion from the bulk water to the
surface, by settling and by entrapment on a rough (or filamentous) biofilm surface
/20/. Only qualitative determinations are available. We have no verification nor
any operational formulation of kinetic expressions.
External hydrolysis. From the biofilm extracellular enzymes are released to the bulk
water in which the hydrolysis takes place. The hydrolyzates should subsequently
diffuse into the biofilm and be degraded there. This mechanism is experimentally
Total COD
I r---~~--~-----+-----r----~1 500 g/m 3
GF/A
220
GF/C
210
0,2211
200
MW<10.000
120
MW<1.000
110
Gel filtration
110
VFA f----i 40
Carbohydrate H 15
Protein 1-----1 60
Total BOD
230
directly
easily
slowly
useable
hydrohydrolyzable
inert
inert ~ 1 c-sourrce 1 lyzable 1
10 100
100
200
90
Fig 5.21 Characterization of the COD content in raw wastewater. All units in COD!m 3 . /19/
183