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Showing papers by "Stefan B. Haderlein published in 2019"


Journal ArticleDOI
TL;DR: It is demonstrated that even in the absence of electron exchange with the sorbent, adsorption to polar mineral surfaces considerably affects the redox properties of NOM.
Abstract: Natural organic matter (NOM) is an important redox-active component of natural porous media and predominantly occurs in the sorbed state. Nevertheless, the effects of NOM sorption at minerals on it...

21 citations


Journal ArticleDOI
TL;DR: In this article, an erfolgreiche biologische In-situ-Sanierung von PCE-kontaminierten Grundwasserleitern erfordert hinreichend reduzierende Bedingungen sowie die Anwesenheit von molekularem Wasserstoff, der dehalogenierenden Bakterien al as Elektronendonor dient.
Abstract: Eine erfolgreiche biologische In-situ-Sanierung von PCE-kontaminierten Grundwasserleitern erfordert hinreichend reduzierende Bedingungen sowie die Anwesenheit von molekularem Wasserstoff, der dehalogenierenden Bakterien als Elektronendonor dient. Durch Injektion eines biologisch gut abbaubaren Hilfsstoffs (Auxiliarsubstrat) konnen diese Faktoren gesteuert werden. Die vorliegende Fallstudie beschreibt die Verfahrensschritte fur eine erfolgreiche Stimulierung des biologischen PCE-Abbaus in einem ursprunglich sauerstoffhaltigen Grundwasserleiter. Laboruntersuchungen in Mikrokosmen (Stufe I) verifizierten das standorteigene bakterielle Abbaupotenzial sowie die Eignung des Auxiliarsubstrats (hier: Melasse). Basierend auf hydrogeologischen und geochemischen Felddaten wurde die erforderliche Melassemenge abgeschatzt sowie deren Wirkungsbereich im Aquifer modelliert (Stufe II). Im Feldversuch erfolgten periodische Injektionen des Auxiliarsubstrats (hier: 170 Tage) begleitet von geochemischen und molekularbiologischen Analysen (Stufe III). Durch die Melasseinjektion konnten im PCE-kontaminiertem Bereich des Aquifers methanogene Bedingungen sowie eine massive Zunahme von Schlusselbakterien der Gattung Dehalococcoides induziert werden. Der erfolgreiche In-situ-Bioabbau von PCE zu Ethen wurde durch substanzspezifische Kohlenstoff-Isotopenanalysen bestatigt.

1 citations


Posted ContentDOI
TL;DR: In this paper, the effects of extraction conditions on the redox and electron shuttling properties of soil organic matter (SOM), including humic substances (HS), were investigated.
Abstract: . Soil organic matter (SOM), including humic substances (HS), is redox-active, can be microbially reduced, and transfers electrons in an abiotic reaction to Fe(III) minerals thus serving as electron shuttle. The standard procedure to extract HS from soil and separate them into humic acids (HA) and fulvic acids (FA) involves alkaline and acidic solutions potentially leading to unwanted changes in SOM chemical and redox properties. To determine the effects of extraction conditions on the redox and electron shuttling properties of SOM extracts, we prepared HS and SOM extracts from a forest soil applying either a combination of 0.1 M NaOH and 6 M HCl, or water (pH 7). Both chemical extractions (NaOH / HCl) and water extractions were done in separate setups under either oxic or anoxic conditions. Furthermore, we applied the NaOH / HCl treatment to a subsample of the water-extracted-SOM. We found that soil extraction with NaOH lead to ca. 100 times more extracted C and the extracted HS had 2–3 times higher electron exchange capacities (EEC) than SOM extracted by water. For water-extracted SOM, anoxic extraction conditions lead to about 7 times more extracted C and 1.5 times higher EEC than under oxic extraction conditions. This difference was probably due to the occurrence of microbial reduction and dissolution of Fe(III) minerals in the soil during the water extraction at neutral pH and the concomitant release of Fe(III) mineral-bound organic matter. NaOH / HCl treatment of the water-extracted SOM lead to 2 times higher EEC values in the HA isolated from the SOM compared to the water-extracted SOM itself, suggesting the chemical treatment with NaOH and HCl caused changes of redox-active functional groups of the extracted organic compounds. Higher EEC of extracts in turn resulted in a higher stimulation of microbial Fe(III) mineral reduction by electron shuttling, i.e. faster initial Fe(III) reduction rates, and in most cases also in higher reduction extents. Our findings suggest that SOM extracted with water at neutral pH should be used to better reflect environmental SOM redox processes in lab experiments and that potential artefacts of the chemical extraction method and anoxic extraction condition need to be considered when evaluating and comparing abiotic and microbial SOM redox processes.

1 citations