D10: Impact of Contaminants - Hydromod

Integrated Water Resource Management for Important Deep European Lakes and their Catchment Areas
EUROLAKES
D10: Impact of Contaminants
The growth rate of bacteria is following the function of MONOD.
FP5_Contract No.: EVK1-CT1999-00004
Version: 4.0
Date: 25/07/01
File: D10-vers.4.0.doc
Figure 11-1 Monod function
Page 94 of 136
That means low substrate concentrations (effluent concentrations) can only be
achieved with low growth rates. Further the bacteria growth rate is approximately the inverse
of the sludge age and the sludge age again is a function of the sludge load, say
the pollution load per sludge (bacteria) unit. That means if a plant is operated with a low
sludge load (say high activated bacteria / sludge masse for the incoming waste load)
the sludge age is high and bacteria with low growth rates, specialised for the metabolisation
of compounds which are difficult to reduce, can accumulate in the system. According
to MONOD the effluent concentration is then not a function of the incoming inflow
concentration but a function of the growth rate, say sludge age. In plants designed
to meet the requirements of Council Directive 941/271/EEC the sludge load is low
enough to allow the growth of bacteria which are able to metabolise compounds which
are in very low concentrations and which are difficult to reduce. [KREUZINGER, 1998]
Processes with attached growth
Most micro-organisms are able to grow on the surface of solid when organic compound,
mineral salts and oxygen are available. They are anchored by means of an exopolymerbased
gelatinous material produced by the bacteria, inside, which the bacteria can, to
some extent, move about. The colonisation of the solid matters begins in selected areas,
whence the bio-film develops continuously until the entire surface of the support is
covered with a monocellular layer. From this moment on , growth is carried on by the
production of new cells covering the first layer.