Treatment of Wastewater Containing 4NP or 24DNT

Laboratory-scale experiments were successfully carried out with an activated sludge reactor at an influent concentration of 400 mg L-1 4-NP by Jakobezyk et al. (1984). If very low effluent concentrations (pg L-1 range) are required, bioreactors must be used (e.g. fixed-bed reactors) which have activated carbon as a support material for bacteria (Speitel et al. 1989). For the treatment of highly loaded synthetic wastewater (630-2500 mg L-1 4-NP), Heitkamp et al. (1990) used a fixed-bed reactor with an immobilized culture of Pseudomonas sp. At a mean retention time of only 2.3 h, they obtained a mineralization efficiency of 93%. These experiments show that high reaction rates are possible after some time if slow-growing bacteria are immobilized. An effluent from a 2,4-DNT production plant of BASF Schwarzheide GmbH has been treated since 1995 by a two-step anoxic/aerobic activated sludge plant. In the first step, 2,4-DNT is most likely reduced to amino-nitroto-luene and 2,4-diaminotoluene, which are mineralized in the second step (Socher 1997).

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