Nitrate consumption by the oxidation of sulfides during an enhanced natural attenuation project at a contaminated site in Berlin, Germany

Abstract

Background Organic pollutants at contaminated sites are often eliminated naturally by biological degradation. The redox processes responsible can be enhanced by infiltrating electron acceptors such as nitrate or sulfate into the aquifer. However, the addition of oxidative agents can lead to undesired side-effects in the saturated soil zone such as the consumption of nitrate by the oxidation of sulfides contained in the aquifer. Laboratory-scale 1D column experiments in up flow mode were performed to evaluate the potential consumption of nitrate and the related kinetics by the oxidation of sulfides during an enhanced natural attenuation project at a site contaminated with monoaromatic compounds and trimethylbenzene. Water containing nitrate was infiltrated into aquifer soil material containing sulfides. To study side reactions, experiments were conducted with low levels of organic hazardous compounds. Results The results indicate that sulfide was oxidized with the simultaneous formation of sulfate by nitrate-consuming processes. The degradation rate of sulfide was calculated to be 1.26 mg kg−1 per exchanged pore volume, corresponding to nitrate consumption of 8.5 mg kg−1 in the case of incomplete denitrification and 3.4 mg kg−1 in the case of complete denitrification. Conclusion The presence of sulfides contained in the soil leads to a nitrate-consuming redox reaction following a linear function in case of sufficient availability of nitrate. This information is helpful for planning ENA projects at contaminated sites to reduce the risk of under- or overdosing the electron acceptor nitrate, which may lead to a lack of nitrate needed to enhance the biodegradation of contaminants in the aquifer or to the deterioration of groundwater quality.

One-Pot Synthesis and Characterization of CuCrS2/ZnS Core/Shell Quantum Dots as New Blue-Emitting Sources

“…Interestingly, as shown in Figure 4 c, some undesirable peaks appeared at 162.97 and 167.85 eV, indicating a S–S bond [ 23 ] and sulfate salt (SO 4 2− ) state [ 24 ], in S 2p of the CuCrS 2 core, respectively. The SO 4 2− salt peaks might be attributed to the oxidizing activity of nitrate salts in Cr(NO 3 ) 3 with DDT, as a sulfur source, which probably results in the formation of SO 4 2− in the CuCrS 2 core level [ 25 ]. As proof, when the ZnS shell was coated, undesired peaks did not appear in the S 2p survey, which indicated that no other states were formed when nitrate salt was not present in the ZnS shell coating.…”