Abbau von nitroaromatischen Xenobiotika durch Ozonisierung und biologische Nachbehandlung
Degradation of nitroaromatic xenobiotics by ozonization and subsequent biological treatment
. Ozonization of 2,4-dinitrotoluene (DNT) and 4-nitroaniline (NA) was conducted in completely mixed reactors by semi-batch tests. At pH 7 both direkt and radical reactions contribute to the oxidation of the nitroaromatic compounds. In a partially mass transfer- limited reaction a specific ozone absorption of A* = 3.0 ... 3.5 g g-' was measured for a 398 % elimination of the target compounds. About 80 ... 90 % of the input ozone were absorbed and 10 ... 20 % left the system unreacted. At pH 7 the degree of DOC reduction increased linearly with the specific ozone absorption to final values of 35 % (NA) and 44 % (DNT) respectively. Subsequent biodegradation of the oxidation products by non-acclimated bacteria increased the degree of mineralization to 75 %. Compared to ozonization alone 35 and 50 % of ozone were thus saved by the sequential chemical-biological process. Batch tests with a real wastewater from the alkaline hydrolysis of a mixture of 2,4,6- Trinitrotoluene (TNT) and 1,3-Dinit rotoluene (DNB) confirmed the approach. No reduction in the required ozone dosage was achieved in a completely mixed continuous system of ozonization followed by biodegradation even when compared to batch ozonization alone. Therefore, the reduction of longitudinal mixing in continuous ozonization systems is of fundamental importance.