B

Surface aerators

/ยก\ /l\

Raw waste water

To further treatment or to stream

Figure 2.4 Oxidation pond and aerated lagoon with simultaneous primary and secondary treatment

Several experiments have been made to combine the suspended and attached growth systems as listed in Table 2.2.

The main reasons for the combined cultivation are as follows:

- increase in reactor capacity

- increase in the biomass content in the system without an additional loading of the unit process

- achievement of better and more stable nitrification.

Table 2.3 shows a comparison of the amount of suspended solids produced and the yield coefficient in different nitrifying and denitrifying unit processes. Data for the organic compounds are added to the list for comparison. Nitrifiers, both in suspended and attached growth systems have a low yield coefficient and a low sludge production. Denitrifers have a low sludge production, but much higher yield coefficient. The nitrification process would, therefore, appear to be very difficult to initiate, compared with the denitrification process. As a comparison the heterotrophic bacteria have a high yield coefficient and ten times greater sludge production than the nitrifier.

Table 2.2 Examples of combination of suspended and attached growth processes for the nitrifying units described in the literature.

Example

References

Plastic foam particles freely dispersed in the suspended culture of activated sludge.

Hegemann (1983) Rogella and Payraudeau (1987) Rogella and Jarosz (1987)

Blocks of Trickling Filter packing materials submerged in activated sludge tanks.

Lang (1981)

Rogella and Jarosz (1987) Rogella etat. (1988) Schlegel (1988)

Rotating Biological Contactor (RBC) partly submerged into activated sludge

(SURFACT process). Guarino etal. (1980)

Packed-Cage RBC

Wanner etal. (1990)

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