Redox-zones in the biomass
Due to the low solubility in water, an accumulation of methane may occur in the
internal zone of the biofilm to such an extent that the solubility is exceeded. This
may lead to bubble formation which may result in sloughing off of the biofilm from
the support material.
All these processes are acidity or alkalinity producing and will to some extent
influence the pH in the biofilm which is again important to the redox conditions. In
this way the processes interact in a complicated way, determined by the diffusion
conditions, the resulting redox conditions, the resulting pH conditions, the growth
and degradation rates in each zone, etc. The history of the growth of the biofilm and
the mechanical influence of hydrodynamic conditions are important factors for the
sloughing off and new growth.
Relatively little is known about these conditions and their importance to the engineering application of the biofilters in wastewater treatment. All these processes
fulfil an important role in the old-fashioned, low-rate trickling filters. In these filters
there was sufficient space for local clogging. The biofilm was degraded anaerobically and finally sloughed off to give room for new growth. These filters were problematic due to these conditions and today they are not competitive.
In trickling filters, submerged filters and rotating discs with normal load without
nitrification, it is not known to what extent anaerobic conditions play a role for the
net removal.
If the load is sufficiently low to allow nitrification, there are three zones: the aerobic,
the anoxic and the anaerobic zones. Denitrification occurs in such filters, as already
described. The importance of the anaerobic zones is practically unknown.
It is difficult to examine the processes in the interior of such complicated biofilms,
solely based on the bulk reaction in the filter. Recently, methods have been developed for the detailed analysis of these processes by measuring inside the biofilms
with microsensors /12/. It is today possible to measure the following substances by
means of microsensors:
pH, s 2 -, Oz, N02, N03, glucose.
The interaction between the processes in the different redox- zones can be simulated
with models for diffusion and for the processes. The problem is to know enough
about the processes to be able to describe the combination of redox-zones. The
research on biofilms has been intensified. A much better understanding of the
microbiological aspects ofbiofilms, the structure ofbiofilms and the redox-zones in
biofilms will emerge within the foreseeable future.
270
Due to the low solubility in water, an accumulation of methane may occur in the
internal zone of the biofilm to such an extent that the solubility is exceeded. This
may lead to bubble formation which may result in sloughing off of the biofilm from
the support material.
All these processes are acidity or alkalinity producing and will to some extent
influence the pH in the biofilm which is again important to the redox conditions. In
this way the processes interact in a complicated way, determined by the diffusion
conditions, the resulting redox conditions, the resulting pH conditions, the growth
and degradation rates in each zone, etc. The history of the growth of the biofilm and
the mechanical influence of hydrodynamic conditions are important factors for the
sloughing off and new growth.
Relatively little is known about these conditions and their importance to the engineering application of the biofilters in wastewater treatment. All these processes
fulfil an important role in the old-fashioned, low-rate trickling filters. In these filters
there was sufficient space for local clogging. The biofilm was degraded anaerobically and finally sloughed off to give room for new growth. These filters were problematic due to these conditions and today they are not competitive.
In trickling filters, submerged filters and rotating discs with normal load without
nitrification, it is not known to what extent anaerobic conditions play a role for the
net removal.
If the load is sufficiently low to allow nitrification, there are three zones: the aerobic,
the anoxic and the anaerobic zones. Denitrification occurs in such filters, as already
described. The importance of the anaerobic zones is practically unknown.
It is difficult to examine the processes in the interior of such complicated biofilms,
solely based on the bulk reaction in the filter. Recently, methods have been developed for the detailed analysis of these processes by measuring inside the biofilms
with microsensors /12/. It is today possible to measure the following substances by
means of microsensors:
pH, s 2 -, Oz, N02, N03, glucose.
The interaction between the processes in the different redox- zones can be simulated
with models for diffusion and for the processes. The problem is to know enough
about the processes to be able to describe the combination of redox-zones. The
research on biofilms has been intensified. A much better understanding of the
microbiological aspects ofbiofilms, the structure ofbiofilms and the redox-zones in
biofilms will emerge within the foreseeable future.
270