Page 248 - Industrial Wastewater Treatment, Recycling and Reuse

222 Industrial Wastewater Treatment, Recycling, and Reuse

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Figure 5.8 Two-step LOPROX plant for the pretreatment of 20 m /h of effluent from the
production of dyestuff at Bayer's Leverkusen factory.

Figure 5.8 shows a two-step LOPROX plant for the pretreatment of
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20 m /h (88 gpm) of effluent from the production of dyestuffs at Bayer’s
Leverkusen factory.
The first step primarily involves the oxidation of inorganic reducing sul-
fur compounds in an alkaline medium at a temperature of 120 C (250 F)

and a pressure of 6 bar (85 psi). The pH of the wastewater is then adjusted to
between 1 and 2 by the addition of sulfuric acid.
After addition of the catalyst, the organic substances in the wastewater are

oxidized at 140 C (284 F). The second step takes place in a one-piece,

glass-lined steel column, which was the first in the world to be manufactured
with dimensions of 10.5 m (34.4 ft) in height and 1.8 m (6 ft) in diameter.
The off-gas generated by the reaction is released into the central off-gas
treatment unit via a pressure-maintaining valve. The pretreated wastewater
is transferred to the central treatment plant for final purification.
Before this plant was commissioned, it was tested for about 2 years in the
form of a pilot plant. The capital expenditure for this totalled approximately
$3 million, while annual operating costs ran at around $0.9 million.
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A further LOPROX plant for treating 6 m /h (36 gpm) of effluent from
the production of anthraquinone dyes was planned and built in 1999. Test
results show that one-step operation in an acid medium at a temperature of