Erprobung und Erfolgskontrolle eines Phytoremediationsverfahrens zur Sanierung Sprengstoff-kontaminierter Böden

The final article of a series of three evaluates the in situ-remediation of TNT(trinitrotoluene)-contaminated soil from ‘Werk Tanne’. The multidisciplinary approach allows a differentiated assessment. Grading with large-scale machinery leads to a depletion of TNT for almost 90% within the first 6 months, while ADNT(amino-dinitrotoluene)-content decreases more or less steadily over 1,5 years. Grading reduces the heterogenous distribution of the contamination only slightly. Results from field-monitoring and biotest-battery indicate residual toxicities of ecotoxicological relevance and a reduced capacity for biological regeneration, in comparison with the uncontamined site. Mycorrhized plants safe-guard the site and improve the soilecological conditions. Their role in reducing lower level residual toxicity requires further investigation. There is need for future research (1) on the dynamics and mechanisms of the initial decrease of TNT followed by stagnation, (2) on the fate of the primary metabolites, (3) on long-term effects of the phytoremediation, and (4) on the establishment of the complex monitoring for routine work.     

Metal mobility during in situ chemical oxidation of TCE by KMnO4

The potential for trace-metal contamination of aquifers as a side effect of In Situ Chemical Oxidation (ISCO) of chlorinated solvent contamination by KMnO(4) is investigated with column experiments. The experiments investigate metal mobility during in situ chemical oxidation of TCE by KMnO(4) under conditions where pH, flow rate, KMnO(4), TCE, and trace-metal concentrations were controlled. During ISCO, the injection of MnO(4) creates oxidizing conditions, and acidity released by the reactions causes a tendency toward low pH in aquifers. In order to evaluate the role of pH buffering on metal mobility, duplicate columns were constructed, one packed with pure silica sand, and one with a mixture of silica sand and calcite. Aqueous solutions of TCE and KMnO(4) (with 1 mg/L Cu, Pb, Zn, Mo, Ni, and Cr(VI)) were allowed to mix at the inlet to the columns. After the completion of the experiments, samples of Mn oxide were removed from the columns and analyzed by analytical scanning and transmission electron microscopy. In order to relate the results of the laboratory experiments to field settings, the analyses of Mn-oxide samples from the lab experiments were compared to samples of Mn oxide collected from a field-scale chemical-oxidation experiment that were also analyzed by analytical electron microscopy as well as time-of-flight secondary-ion mass spectroscopy. The pH ranged from 2.40 in the silica sand column to 6.25 in the calcite-containing column. The data indicate that aqueous Mo, Pb, Cu and Ni concentrations are attenuated almost completely within the columns. In contrast, Zn concentrations are not significantly attenuated and Cr(VI) is transported conservatively. The results indicate that within the range 2.40 to 6.25, metal mobility is not affected by pH. Comparison of analyses of Mn-oxide from the lab and field demonstrate that a variety of metals are sequestered from solution by Mn oxide.     

Assessment of chemical process hazards in early design stages

A new method called SREST-layer-assessment method with automated software tool is presented that in a hierarchical approach reveals the degree of non-ideality of chemical processes with regard to SHE (safety, health and environment) aspects at different layers: the properties of the chemical substances involved (substance assessment layer (SAL)), possible interactions between the substances (reactivity assessment layer (RAL)), possible hazard scenarios resulting from the combination of substances and operating conditions in the various equipments involved (equipment assessment layer (EAL)), and the safety technologies that are required to run a process safely and in accordance with legal regulations (safety-technology assessment layer (STAL)). In RAL, EAL and STAL the main focus is put on process safety. A case study is used to show the principles of the method. It is demonstrated how the method can be used as a systematic tool to support chemical engineers and chemists in evaluating chemical process safety in early process development stages.     

A simulation model for organic phosphorus transformation in a forest soil ecosystem

A numerical model which simulates the decomposition of litter and mineralization and immobilization of P in the humus layer of a temperate forest (beech site of Solling) is described. The model takes into account the effect of moisture, temperature and C/N ratio. The simulated concentration of P in the effluent of the humus layer agrees well with the measured values. The model predicts an increase in the C/P ratio of the unde-composed litter with time and that there is no direct mineralization of P from litter without passing through a microbial body. The net rate of mineralization is, however, always positive with its highest peak in July. Maximum immobilization of P from solution occurs in June and the minimum in January.The model is stable against changes in the litter input, its C/P ratio and other initial conditions, but it is very sensitive to changes in the efficiency factor which represents the fraction of decomposed C incorporated into microbial tissue. This is a site-specific model but can be used for grassland or agricultural systems with changes in certain parameters.