Anaerobic Wastewater Treatment
Biofilm plants
A COD mass balance for the wastewater looks as follows:
(9.5)
The reaction rate, rA,M can often be described with a zero order kinetics, both in the
biofilm itself and in the liquid (that is, the biofilm is fully utilized).
If the volume of the biofilm is Az• · Lz (Lz is the thickness), and the concentration of
biomass in the biofilm itself is Xs,f,2t we have
Where Xs,z is the volumetric concentration of biomass of an anaerobic tank.
Substituted in (9.5) we find
(9.6)
The concentration of biomass, Xs,£,2, can be high in the biofilm itself (10-50 kg
COD/m 3 ) which means that the concentration compared with the total tank
volume, Xz, can also be high.
9 .2. Plant types, anaerobic processes
Like for other biological processes, the plant types for anaerobic processes can be
divided into plants with suspended sludge and plants with biofilm. As anaerobic
treatment plants often treat concentrated wastewater, sometimes wjth high sludge
concentrations, it may be necessary to pretreat the wastewater. The pretreatment
may consist in a separation of suspended and dissolved solids.
9.2.1 Pretreatment of wastewater, anaerobic plants
The pretreatment may consist in a phase separation in the form of:
- fine screening
-settling
-flotation
- hyper-filtration
possibly in combination as for example settling and hyper-filtration can be combined. Fig 9.4 shows an example of a plant layout where the fixed and liquid phases
are separated, and subsequently, two separate anaerobic plants are used. The sludge
289
Biofilm plants
A COD mass balance for the wastewater looks as follows:
(9.5)
The reaction rate, rA,M can often be described with a zero order kinetics, both in the
biofilm itself and in the liquid (that is, the biofilm is fully utilized).
If the volume of the biofilm is Az• · Lz (Lz is the thickness), and the concentration of
biomass in the biofilm itself is Xs,f,2t we have
Where Xs,z is the volumetric concentration of biomass of an anaerobic tank.
Substituted in (9.5) we find
(9.6)
The concentration of biomass, Xs,£,2, can be high in the biofilm itself (10-50 kg
COD/m 3 ) which means that the concentration compared with the total tank
volume, Xz, can also be high.
9 .2. Plant types, anaerobic processes
Like for other biological processes, the plant types for anaerobic processes can be
divided into plants with suspended sludge and plants with biofilm. As anaerobic
treatment plants often treat concentrated wastewater, sometimes wjth high sludge
concentrations, it may be necessary to pretreat the wastewater. The pretreatment
may consist in a separation of suspended and dissolved solids.
9.2.1 Pretreatment of wastewater, anaerobic plants
The pretreatment may consist in a phase separation in the form of:
- fine screening
-settling
-flotation
- hyper-filtration
possibly in combination as for example settling and hyper-filtration can be combined. Fig 9.4 shows an example of a plant layout where the fixed and liquid phases
are separated, and subsequently, two separate anaerobic plants are used. The sludge
289