Aerobes and Effluents - Environmental Biotechnology: Theory and Application - page 116

Table6.1 Illustrativeexamplesof typicaleffluentcomponentsbyindustry
sector
Industry sector

Typical effluent component

Chemical industry High COD, toxic compounds

Distillery High BOD

Engineering Oils, metals

Food processing Fats, starches, high BOD

Paper pulping Very high BOD, bleaches

Tanning High BOD, chromium

Textile manufacture High BOD, surfactants, pesticides, dyestuff

Timber Preservatives, fungicides

Table6.2 Illustrativeexamplesof typical
effluentBODbyindustrysector
Industry sector

Typical BOD

Abattoir 2 600

Brewery 550

Distillery 7 000

Landfill leachate 20 000

Paper pulping 25 000

Petroleum refinery 850

Sewage 350

Tannery 2 300

All values in g/m 3 .

Sewage Treatment

Looking at sewage works in the strictly literal term, the aims of treatment can
be summarised as the reduction of the total biodegradable material present, the
removal of any co-existing toxic substances and the removal and/or destruction
of pathogens. It is beyond the scope of this topic to examine the general, non-
biological processes of sewage treatment in great detail, but for the sake of
establishing the broader context in which the relevant biotechnology functions, a
short description of the main key events follows. It is not, nor is it intended to be,
a comprehensive examination of the physical processes involved and the reader
is urged to consult relevant texts if this information is authoritatively required.
The typical sewage treatment sequence normally begins with preliminary
screening, with mechanical grids to exclude large material which has been
carried along with the flow. Paper, rags and the like are shredded by a series
of rotating blades known as comminutors and any grit is removed to protect
the pumps and ensure free movement of the water through the plant. Primary
treatment involves the removal of fine solids by means of settlement and
sedimentation, the aim being to remove as much of the suspended organic
solid content as possible from the water itself and up to a 50% reduction in