Aerobes and Effluents - Environmental Biotechnology: Theory and Application - page 139

Figure6.8 Schematicmembranebioreactor
nitrobenzene, dichloroaniline and polyaromatic hydrocarbons (PAHs), for
example which represent a significant risk, both to the environment and human
health, due to their high toxicity. Removal efficiency for these substances can
approach 99%.
The membrane bioreactor has proved its suitability as an efficient system for
degradation of recalcitrant compounds and significantly higher biomass con-
centrations and utilisation rates are routinely achieved than in corresponding
alternative treatment systems. In common with most operational, rather than
experimental, biological detoxification processes, not all of the contaminants
present in the effluent are typically completely converted into carbon dioxide
and water, a certain percentage being turned into metabolic by-products instead,
though this can amount to less than 5% in a well managed bioreactor system.
Part of this involves the gradual and controlled introduction of novel wastewater
elements, to ensure that acclimatisation is maximised and any potential tendency
for 'shock loadings' avoided. This is a clear example of the value of permitting
optimised microbial adaptation to the individual application.
These systems are, of course, more expensive than the conventional activated
sludge or trickling filters, but produce a much smaller quantity of excess sludge
for subsequent disposal of treatment. In addition, they produce an elevated COD
removal and would seem particularly well suited to use in small scale plants
where the production of high quality final effluent is a priority. Never-the-less,
for most of the first decade of its commercial history, and despite this evident