Page 255 - Industrial Wastewater Treatment, Recycling and Reuse

Novel Technologies for the Elimination of Pollutants 229

Figure 5.12 Tower Biology at Bayer Leverkusen site.

Primary clarification: Residence time 2.5 h.
Tower Biology (Figure 5.12): Four rubber-lined steel tanks
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( 26 30 m) in parallel; liquid height 26.5 m, tank volume 13,600 m , total
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volume 54,400 m . Aeration via 4 72 slot injectors. O 2 uptake 120 t/day,
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22,000 m /h air (standard conditions) being required for an O 2 utilization of
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up to 4% O 2 by volume in the off-gas. Volume load 1.8 kg/m d BOD 5 ,
sludge load 0.32 kg BOD 5 per kg dry mass per day, residence time 14.5 h.
Off-gas purification: The off-gas is preheated in a counter-current to
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about 580 C and mixed with approximately 160 m /h of natural gas.

“Non-flaming combustion” is induced by infrared radiation. This oxidation
takes place in a reaction chamber at 750 C. The flue gas is subsequently

cooled in a counter-current heat exchanger to 200 C, and the HCl result-

ing from the oxidation of chlorinated hydrocarbons is washed down by
caustic scrubber. The off-gas purified in this way is discharged into the atmo-

sphere through a short chimney at a temperature of about 180 C.
Intermediate clarification: Each tower has a “collar” of 16 sedimentation
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funnels of 9 m with a total volume of 16 420 m ¼6720 m per tower,
residence time 7 h, superficial velocity 0.95 m/h.
Basin biology (second stage in the biological treatment of Bayer effluent):
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Four basin cascade biology with total volumes of 34,000 m for C and N
elimination. Residence time 3.4+7.5 h, O 2 uptake 60 t/day.
Secondary clarification (sedimentation of biomass): Basin with scraper
(t¼3 h) and sedimentation funnels (t¼6.3 h)