Biomedical Engineering Reference
In-Depth Information
Continuously stirred tank reactor (CSTR)
Intended to treat slurries and liquid biowastes, this system is essentially the same
as the preceding Completely Mixed Contact Reactor (CMCR) design, but without
the need for the solids recycle.
Fluidized bed reactor (FBR)
Sometimes termed the Expanded Bed Reactor, this system relies on an internal
microbial growth medium which is fluidized by the waste liquid circulating within
it. Accordingly they are only suitable for liquid biowastes or very dilute slurries.
Multi-phasic processes (MPPs)
Physically separating the stages of AD into different reactors, these systems
are principally of use as experimental tools for increasing understanding of the
pathways and mechanisms of the AD process. They are featured here for com-
pleteness, but they do not generally have any commercial application.
Upflow anaerobic sludge blanket (UASB)
These systems hold relatively high numbers of active bacteria, which makes them
suitable for treating biowastes of low solids content and they are commonly used
to process high strength industrial waste liquids or light suspensions.
From all of this discussion, it should be obvious that, however proprietary AD
technologies are classified, no one type is universally ideal or superior, each hav-
ing certain characteristics which make it appropriate for particular wastes and less
suitable for others. This means, of course, that although comparisons of the vari-
ous approaches are of great interest to potential users, in practice they are difficult
to make in any meaningful way. Even certified data from an operating plant can
only be taken as broadly indicative of how a similar one might perform elsewhere,
especially in respect of breakdown efficiency and biogas generation or quality.
Process parameters
Efficient AD requires the development and maintenance of an optimised internal
environment to facilitate biological activity. This is of particular importance in
the commercial setting and a number of both physical and chemical factors must
be taken into account to achieve it, of which the most important are:
•
temperature;
•
retention period;
•
agitation;
•
wetness;
•
feedstock;
•
loading rate;
•
pH and VFAs.
Search WWH ::
Custom Search