Environmental Biotechnology - Theory and Application

114 Environmental Biotechnology

Table 6.1 Illustrative examples of typical effluent com-

ponents by industry 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

Table 6.2 Illustrative examples of typical

effluent BOD by industry sector

Industry sector Typical BOD

Abattoir 2600

Brewery 550

Distillery 7000

Landfill leachate 20 000

Paper pulping 25 000

Petroleum refinery 850

Sewage 350

Tannery 2300

All values in g/m^3.

removal of any co-existing toxic substances and the removal and/or destruction
of pathogens. It is beyond the scope of this book 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 screen-
ing, 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 solid loading is commonly achieved. At various
times, and in many parts of the world, discharge of primary effluent direct to the
sea has been permissible, but increasing environmental legislation means that this