Biomedical Engineering Reference
In-Depth Information
AD.
Fermentation
in this context relates to the wider application of the word
to encompass all microbial breakdown and not simply the anaerobic production
of alcohol and e
utrophic
refers to the nutrient-rich environment within which it
takes place.
The process arose as a result of research into the enhanced aerated remediation
of post AD liquor. The idea of introducing air into liquid or slurrified waste, as
was discussed in Chapter 6, is well established as a means of treatment. A
laboratory prototype treatment was developed for the specific effluent and was
successfully trailed at pilot scale, before subsequently being further developed
and extended to the treatment of biowaste.
EF involves rendering the waste into a fine slurry, which is then contained
within a bioreactor (Figure 8.4), aerated by means of bubble diffusers at the base
of the vessel, mixed and heated to around 35
◦
C. Within this environment, the
input waste breaks down to leave only about 10% of the original volume as
recoverable solids within 35 days. The process liquor itself is characteristically
less strong than for AD and typically contains only some 6-10% suspended
solids. Analysis of this liquid by the Agricultural Development Advisory Ser-
vice (ADAS) has indicated that it has some potential fertiliser use, based on key
performance indicators such as nitrogen, phosphorous and potassium levels, elec-
trical conductivity, generalised nutrient content and heavy metal residues. The
resultsareshowninfullinTables8.4and8.5.
With a 'satisfactory' pH of 6, a 'low' BOD of 2790mg/l, low ammoniacal
nitrogen and the likely slow release of much of the total nitrogen content over
several months, ADAS concluded that the liquor was a 'useful source of nitrogen
and potash for crop growth'.
Though this method proved itself remarkably efficient in laboratory and inter-
mediate trials, the company for which it was developed subsequently abandoned
further research into biological waste treatment and, consequently, EF has never
been taken to pilot scale. As a result, it is not possible to say how well it
might perform, though for such aerobic processes utilising a completely-mixed,
Figure8.4
EFbioreactor
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