Nils Hoth

Predominance of Methanolobus spp. and Methanoculleus spp. in the Archaeal Communities of Saline Gas Field Formation Fluids

The microbial communities in sulfate-rich, saline formation fluids of a natural gas reservoir in Lower Saxony, Germany were investigated to enhance the knowledge about microbial communities in potential carbon dioxide sequestration sites. This investigation of the initial state of the deep subsurface microbiota is necessary to predict their influence on the long-term stability and storage capacity of such sites. While the bacterial 16S rDNA gene library was comprised of sequences affiliating with the Firmicutes, the Alphaproteobacteria, the Gammaproteobacteria and the Thermotogales, the archaeal 16S rDNA libraries were simply dominated by two phylotypes related to the genera Methanolobus and Methanoculleus. The monitoring of the archaeal communities in different formation fluid samples by T-RFLP and Real-Time-PCR indicated that these two methanogenic genera dominated at all, whereas the proportion of the two groups varied. Thus, methylotrophic and autotrophic methanogenesis seems to be of importance in the reservoir fluids, dependent on the provided reduction equivalents and substrates and it also may influence the fate of CO2 in the subsurface.

Predictive modelling of dump water impact on the surroundings of the lignite dump site Jänschwalde (Eastern Germany)

Abstract Open cast mining of lignite leads to dumps containing highly mineralised pore waters. To predict the impact of the dump waters on the undisturbed aquifers two steps are necessary. (1) The prediction of dump water quality at times when steady state flow conditions will be established. (2) The simulation of the dump ground water migration with a model that is able to handle the complexity of the homogeneous and heterogeneous interactions of the migration process. For the investigated site Janschwalde, which is still dewatered, a chemical mass balance was performed. The predicted alkalinity potentials exceed acidity potentials for the dump as a whole. The distribution of these parameters show high alkalinity potentials for the northern part. In order to model the migration process the transport code PCGEOFIM ® [Anwenderdokumentaion, IBGW Leipzig, (in German)] was coupled with the geochemical equilibrium code PHREEQC [USGS, Water-Resources Investigations Report]. This was done to simulate redox reactions, mineral dissolution and precipitation, and cation exchange in the ground water zone. The model is verified by a column flow test. The results of the simulations show a small effect of the migrating dump waters on the quartenary aquifer with respect to acidity changes. This results from calcite buffering and cation exchange. The impact on the quartenary aquifer by sulphate is much higher.

Relevance of Deep-Subsurface Microbiology for Underground Gas Storage and Geothermal Energy Production

This chapter gives the reader an introduction into the microbiology of deep geological systems with a special focus on potential geobiotechnological applications and respective risk assessments. It has been known for decades that microbial activity is responsible for the degradation or conversion of hydrocarbons in oil, gas, and coal reservoirs. These processes occur in the absence of oxygen, a typical characteristic of such deep ecosystems. The understanding of the responsible microbial processes and their environmental regulation is not only of great scientific interest. It also has substantial economic and social relevance, inasmuch as these processes directly or indirectly affect the quantity and quality of the stored oil or gas. As outlined in the following chapter, in addition to the conventional hydrocarbons, new interest in such deep subsurface systems is rising for different technological developments. These are introduced together with related geomicrobiological topics. The capture and long-termed storage of large amounts of carbon dioxide, carbon capture and storage (CCS), for example, in depleted oil and gas reservoirs, is considered to be an important options to mitigate greenhouse gas emissions and global warming. On the other hand, the increasing contribution of energy from natural and renewable sources, such as wind, solar, geothermal energy, or biogas production leads to an increasing interest in underground storage of renewable energies. Energy carriers, that is, biogas, methane, or hydrogen, are often produced in a nonconstant manner and renewable energy may be produced at some distance from the place where it is needed. Therefore, storing the energy after its conversion to methane or hydrogen in porous reservoirs or salt caverns is extensively discussed. All these developments create new research fields and challenges for microbiologists and geobiotechnologists. As a basis for respective future work, we introduce the three major topics, that is, CCS, underground storage of gases from renewable energy production, and the production of geothermal energy, and summarize the current stat of knowledge about related geomicrobiological and geobiotechnological aspects in this chapter. Finally, recommendations are made for future research.

Hydro-geochemical paths of multi-layer groundwater system in coal mining regions — Using multivariate statistics and geochemical modeling approaches

Groundwater is an important drinking water resource that requires protection in North China. Coal mining industry in the area may influence the water quality evolution. To provide primary characterization of the hydrogeochemical processes and paths that control the water quality evolution, a complex multi-layer groundwater system in a coal mining area is investigated. Multivariate statistical methods involving hierarchical cluster analysis (HCA) and principal component analysis (PCA) are applied, 6 zones and 3 new principal components are classified as major reaction zones and reaction factors. By integrating HCA and PCA with hydrogeochemical correlations analysis, potential phases, reactions and connections between various zones are presented. Carbonates minerals, gypsum, clay minerals as well as atmosphere gases - CO2, H2O and NH3 are recognized as major reactants. Mixtures, evaporation, dissolution/precipitation of minerals and cation exchange are potential reactions. Inverse modeling is finally used, and it verifies the detailed processes and diverse paths. Consequently, 4 major paths are found controlling the variations of groundwater chemical properties. Shallow and deep groundwater is connected primarily by the flow of deep groundwater up through fractures and faults into the shallow aquifers. Mining does not impact the underlying aquifers that represent the most critical groundwater resource. But controls should be taken to block the mixing processes from highly polluted mine water. The paper highlights the complex hydrogeochemical evolution of a multi-layer groundwater system under mining impact, which could be applied to further groundwater quality management in the study area, as well as most of the other coalfields in North China.

Stable isotope fractionation related to technically enhanced bacterial sulphate degradation in lignite mining sediments

A mine dump aquifer in the Lusatian lignite mining district, Germany, is contaminated with acid mine drainage (AMD). The only natural process that can counteract the effects of the contamination is bacterial sulphate reduction. The technical measures chosen to handle the contamination include the injection of glycerol into the aquifer to supply electron donors and to accelerate the growth and activity of sulphate-reducing bacteria. An initial assessment of the hydrochemical conditions in the aquifer showed that sulphate concentrations are subject to alteration due to flow-related processes. Consequently, the decision whether sulphate reduction is occurring in the investigated aquifer section was based on the stable isotopic composition of dissolved sulphate and sulphide, which were used in combination with sulphate concentrations. The significant enrichment of both heavy sulphur and heavy oxygen in the remaining sulphate pool and a characteristic isotope fractionation pattern are a clear evidence for the activity of sulphate-reducing bacteria utilising the injected glycerol as an electron donor. This activity seemed to intensify over the observation period. The spatial distribution of sulphate reduction activity, however, appeared to be highly inhomogeneous. Rather than occurring ubiquitously, sulphate reduction activity seemed to concentrate in a defined reaction zone. Regardless of the inhomogeneous distribution, the overall turnover of sulphate during the period of investigation proves the applicability of this enhanced natural attenuation method to handle the restoration of aquifers contaminated with AMD.

First Evidence of Active Sulphate Reduction in a Lignite Mine Dump Site at Low pH Values – the Plessa Site

It has been postulated that bacterial sulphate reduction is related to pH-values above 5.5 (e.g. [1]). First investigations for the 80-year old dump Plessa in the Lower Lusatian mining district (East Germany) show evidence for active sulphate reduction. Mining dump waters from the Plessa site have pH values of 2.4 to 4.9 and pe values between 2 and 6. Measured sulphide concentrations range from 50 to 1200 -g/L. The influence of bacterial sulphate reduction on the development of sulphate concentrations in the dump waters is supported by increasing δ34S and δ18O values with decreasing sulphate concentrations. These findings document that sulphate reduction under natural conditions is not exclusively related to neutral pH values and strongly reducing conditions. Furthermore the tertiary organic matter contained in the dump sediments is the main carbon source for sulphate reducing bacteria.

Numerische Simulation dichtebeeinflusster und reaktiver Stofftransportprozesse im Grundwasser

KurzfassungFür die Prognose der Gefährdung der Schutzgüter Grundwasser und Boden gewinnen numerische Programmsysteme zur Simulation von Strömungs- und Stofftransportprozessen immer mehr an Bedeutung. Im Mittelpunkt des Interesses stehen dabei komplexe geochemische Reaktionsvorgänge, dichtebeeinflusste Strömungs- und Stofftransportvorgänge, komplizierte hydraulische Gegebenheiten und die Parameterbelegung großer Modelle. Das hier beschriebene Programmsystem MODCALIF erlaubt die dreidimensionale Simulation der dichtebeeinflussten Strömung und des Stofftransportes. Die Verwendung neu integrierter Lösungalgorithmen ermöglicht eine grobe räumliche Diskretisierung und damit eine deutliche Verringerung des Rechenaufwandes. Die Berücksichtigung unterschiedlicher Ansätze zur Beschreibung der Wechselwirkungen zwischen gelöstem Stoff und Feststoff sowie die Kopplung mit dem geochemischen Gleichgewichtsprogramm PHREEQC erlauben die Simulation des Stofftransportes für vielfältige Problemstellungen. Aufbauend auf einer kurzen Darstellung der theoretischen Grundlagen des Programmsystems MODCALIF wird das Programm verifiziert und seine Anwendbarkeit an zwei ausgewählten Fallbeispielen praktisch demonstriert.AbstractNumerical program systems for simulations of flow and mass transport processes gain more and more importance for the prognosis of the endangering of the natural resources of groundwater and soil. Here, the focal points of interest are complex geochemical reactions, density-dependent flow and mass transport processes, complicated hydraulic conditions, and the determination of parameters of large models. The described code MODCALIF allows a three-dimensional simulation of density-dependent flow and mass transport processes. Applying new solution algorithms permits a rough three-dimensional discretization and thus an essential reduction in computing time. The simulation of mass transport within various problem ranges is made feasible by considering different approaches to descrobe the interactions between a dissolved component and the soil as well as by coupling to the geochemical equilibrium program PHREEQC. A brief description of the theoretical basis of the program system MODCALIF is taken as a starting point for the representation of verification calculations for standardized problems. Its applicability is then demonstrated on the base of two selected examples.

Investigation of Phenomena in Uranium Mine Waters using Hydrogeochemical Modeling – a case study

One of the main aspects in the remediation of closed uranium mine sites is the treatment of mine water. In order to understand speciation and processes in uranium mine waters, hydrogeochemical modeling is carried out. The importance of modeling in mine water treatment is shown by the example of two case studies. The first deals with precipitation processes in a stripping column. In the second case uranium speciation of different mine waters is characterized. By means of modeling results, treatment technologies can be adjusted and improved.

Challenges in Modern Lignite Mining – Mass Management to Protect the Environment and the Budget

The densely populated Central German region in the south of Berlin is rich in lignite. In addition to an energetic use of the lignite, the material use of lignite will become more important in the future. Due to the annual excavation of 1 billion m3 of sediments, valuable land will be lost. Therefore, it is important to use edited dumps for the generation of reclamation areas. These dumps should have good geotechnical as well as geochemical conditions, considering the surrounding waters and to protect the receiving waters. Unfortunately, the overburden above the coal includes pyrite, which causes problems such as groundwater acidification and the discharge of sulfate, iron and trace metals. As the groundwater level in the future tipping of the open pits will rerise, it is important to investigate the influence of weathering of pyrite depositions (acid mine drainage), buffering by glacial till and of the resulting solutes on the surrounding water body. By superposing geochemistry and geology it is possible to mark main problem areas, improve buffer potentials by changing the technology and implement suitable technological countermeasures. In the future, this will significantly reduce the impact to the surrounding waters by material loads from the dump bodies. The optimal use of the existing buffering potentials can save a large amount of money, that otherwise would be necessary for the subsequent rehabilitation. The public authorities annually pay millions of € on remediation. The private mining operators are now responsible for bearing the costs by their own. Hence it is beneficial to invest technological know-how for mining operation to obtain significantly lower cost in the aftercare. The client MIBRAG mbH wants to turn from unstructured to a structured dump bodies with existing equipment of excavators, spreaders and conveyor belt systems only by the change of technology.

Speciation analysis based design of mine water treatment technologies

The strong dependence of water treatment efficiency from pollutant speciation was demonstrated at the example of uranium removal from TMF seepage water by ion exchange. The pH dependence of carbonate equilibria was used to manipulate uranyl speciation in the investigated seepage water. Ion exchange experiments were carried out with TMF seepage feeds of the same origin but of different pH and thus of different uranyl speciation. Geochemical modeling and TRLFS measurements revealed calcium uranyl carbonate complexes to hamper sorption to ion exchange resins, whereas non-calcium uranyl carbonate complexes promote sorption. The manipulation of uranyl speciation by pH adjustment caused a rise in ion exchange efficiency from insignificant to technically feasible levels.