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Campbell K.M.,U.S. Geological Survey | Davis J.A.,U.S. Geological Survey | Davis J.A.,Lawrence Berkeley National Laboratory | Bargar J.,Stanford University | And 14 more authors.
Applied Geochemistry | Year: 2011

Reductive biostimulation is currently being explored as a possible remediation strategy for U-contaminated groundwater, and is being investigated at a field site in Rifle, CO, USA. The long-term stability of the resulting U(IV) phases is a key component of the overall performance of the remediation approach and depends upon a variety of factors, including rate and mechanism of reduction, mineral associations in the subsurface, and propensity for oxidation. To address these factors, several approaches were used to evaluate the redox sensitivity of U: (1) measurement of the rate of oxidative dissolution of biogenic uraninite (UO 2(s)) deployed in groundwater at Rifle, (2) characterization of a zone of natural bioreduction exhibiting relevant reduced mineral phases, and (3) laboratory studies of the oxidative capacity of Fe(III) and reductive capacity of Fe(II) with regard to U(IV) and U(VI), respectively. © 2011.

Ronicke H.,Helmholtz Center for Environmental Research | Schultze M.,Helmholtz Center for Environmental Research | Neumann V.,BGD Boden und Grundwasserlabor GmbH Dresden | Nitsche C.,BGD Boden und Grundwasserlabor GmbH Dresden | Tittel J.,Helmholtz Center for Environmental Research
Limnologica | Year: 2010

Lake Bockwitz, a pit lake in a former lignite open-cast mine south of Leipzig (Germany), was neutralised (from pH 2.65 to pH 7.1) by addition of soda ash (14,620 t) from 2004 to 2007. The additions had to be continued due to ongoing inflows of acid ground and surface water. This paper reports on the changes in the plankton community accompanying the neutralisation. At the beginning, the community composition and biomass was comparable to other acidic pit lakes, i.e. the pigmented flagellates Chlamydomonas and Ochromonas dominated the autotrophs, and ciliates and rotifers were the top predators. The biomass was small (maximum 2 mg fresh weight per litre) and decreased until the end of 2008. With increasing pH, the autotrophic community became more diverse, whereby diatoms, chrysophyceans and blue greens contributed significantly to biomass. Although neutral pH conditions were achieved in autumn 2007, picocyanobacteria were not present until the end of 2008. In addition, crustaceans were under-represented in terms of biomass and diversity. Daphnids were not found. We attributed this to short-term changes of the ionic composition of the water and to the limited time available for non-acido-tolerant organisms to colonise the system. © 2009 Elsevier GmbH. All rights reserved.

Can iron hydroxide residues (EHR) from treated mine waters safely be embedded in excavated tertiary sands that liberate acidity due to sulfide oxidation? By a series of reactor experiments we tested the hypothesis that the intrinsic alkalinity in EHR can both buffer the acidity and thereby thwart its reductive dissolution. Simulated scenarios of groundwater recharge and groundwater ascent showed that in the presence of EHR the output of weathering products (protons, sulfate, Fe2+, heavy metal ions) was lower than in EHR-free control reactors. The best results were achieved when mixing EHR with the tertiary materials. The overall results neither indicate chemical dissolution of EHR nor favorite conditions for microbial iron reduction. © 2015, Technical University Freiberg. All rights reserved.

Gasch C.,TU Dresden | Hildebrandt I.,BGD Boden und Grundwasserlabor GmbH Dresden | Rebbe F.,GICON Grossmann Ingenieur Consult GmbH | Roske I.,TU Dresden
Energy, Sustainability and Society | Year: 2013

Background Biogas is one of the most promising regenerative energies. The simple fundamental principle underlying behind biomethanation is the conversion of biomass into biogas by microorganisms in four steps, whereby proper process regulation is crucial. Even today, the control of biogas plants is a challenging process which is based merely on physical and chemical parameters. A lack of meaningful microbiological control variables that can be quickly and easily determined locally makes it difficult for operators to react immediately if necessary. Methods In this study, different chemical parameters and several enzyme activities as well as their response to process disturbances were analyzed using two-phase anaerobic digestion systems with maize silage as substrate. The pH value, soluble chemical oxygen demand (COD), volatile fatty acids and total inorganic carbon (VFA/TIC) ratio, and biogas composition were examined using standardized cuvette or titration tests and online monitoring equipment. Hydrolase activities of esterase, amylase, protease, alanine-aminopeptidase, carboxymethyl cellulase, and xylanase were determined photometrically. Results: Hydrolases (esterase, amylase, protease, alanine-aminopeptidase, carboxymethyl cellulase, and xylanase) represent key enzymes in the first stage of biogas generation. In normal operation, the optimum values of the specific hydrolase activities varied over retention time. This allows for a visualization of the digestion progress. Furthermore, sudden strong activity attenuation has always indicated a disruption, even before any alterations in chemical parameters were affected. Beyond that, a direct correlation between esterase activity and COD discharge could also be identified. Moreover, in terms of the utilized substrate, specific microbial enzyme activities could be discovered as quality indicators. Thus, correlations to both the age of the silage and the effective cumulative COD yield could be determined. Conclusion: Based on our analyses, the significance of various microbial enzyme activities and their association with the biogas process was demonstrated. The photometric determination of these enzyme activities allowed a sophisticated control of biomethanation to be carried out, which requires very little effort and equipment. © 2013 Gasch et al.

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