| Abstract: | Degradation of Nitroaromatic Xenobiotics by Ozonization and Subsequent Biological Treatment Ozonization for 2,4-dinitrotoluene (DNT) and 4-nitroaniline (NA) was conducted in completely mixed reactors by semi-batch tests. At pH 7, both direct and radical reactions contribute to the oxidation of the nitroaromatic compounds. In the dominantly mass transfer-limited reaction, a specific ozone absorption of A* = 3.0…3.5 g g?1 was measured for a ?98% 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. A subsequent biological treatment 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-dinitrobenzene (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 regarded to be of fundamental importance. |
