D I S C U S S I O N
J. Blok, Netherlands.
In systems with very low loadings only a part (30-40%) is directly oxidised. Another part serves as
reserves and is slowly degradable by endogenous respiration. As endogenous respiration and exogenous
respiration occur together it is a simplification to think in terms of degradable and non degradable
substances.
Reply
It is true that part of the cell material that is considered as non-biodegradable degrades at a slow
rate. It would even be possible to determine this rate and incorporate an average value of this rate in
the proposed mathematical model. However, the accuracy claimed for the model is not such that it
would make an appreciable difference for fast to moderate rate activated sludge systems such as those
considered as extended aeration systems. However, it could be said to have an appreciable effect on a
model for aerated lagoons or total oxidation systems. In this case the effect would be masked by the
variation in the effluent suspended solids.
387
J. Blok, Netherlands.
In systems with very low loadings only a part (30-40%) is directly oxidised. Another part serves as
reserves and is slowly degradable by endogenous respiration. As endogenous respiration and exogenous
respiration occur together it is a simplification to think in terms of degradable and non degradable
substances.
Reply
It is true that part of the cell material that is considered as non-biodegradable degrades at a slow
rate. It would even be possible to determine this rate and incorporate an average value of this rate in
the proposed mathematical model. However, the accuracy claimed for the model is not such that it
would make an appreciable difference for fast to moderate rate activated sludge systems such as those
considered as extended aeration systems. However, it could be said to have an appreciable effect on a
model for aerated lagoons or total oxidation systems. In this case the effect would be masked by the
variation in the effluent suspended solids.
387