Tracing sources and transformations of ammonium during river bank filtration by means of column experiments.

Ammonium is an undesirable substance in the abstracted water of riverbank filtration (RBF) schemes, due mainly to the complications it causes during post-treatment (e. g. during chlorination). During RBF, ammonium can be formed in the riverbed by mineralization of organic nitrogen. Column experiments with riverbed sediments and river water from the Elbe were performed to evaluate the controls on ammonium concentrations during riverbed infiltration. Concentrations of ammonium went from <0.1 mgN/l in the feed water up to 1 mgN/l in the columns effluent. Higher temperatures and lower infiltration rates led to increased ammonium concentrations in the effluent. This shows higher susceptibility to ammonium increases of RBF settings in warmer climates and points to potential threats of climate change to water quality at RBF sites. In the later phases of the experiments, after the columns have been flushed their pore volumes several times, ammonium concentrations continually decreased. This behavior was attributed to the partial consumption of easily degradable organic material in the sediments, leading to lesser reducing conditions and lower mineralization rates. Based on operation with varied nitrate concentrations (0-11 mgN/l) and 15N isotopic measurements, dissimilatory nitrate reduction to ammonium (DNRA) was not shown to be relevant in the formation of ammonium. Anaerobic ammonium oxidation (anammox), however, was hypothesized to be an important sink of ammonium inside the columns, which indicates that rivers with high nitrate concentrations, such as the Elbe, may have a buffer of protection against ammonium formation during RBF.

Further optimisation of the denitrifier method for the rapid 15 N and 18 O analysis of nitrate in natural water samples.

RATIONALE: This study aims to develop a simplified denitrifier method for the δ15 N and δ18 O analysis of nitrate (NO3 - ) in natural water samples combining the method of Zhu et al (Sci Total Environ. 2018; 633: 1370-1378) and the original denitrifier method of Sigman et al (Anal Chem. 2001; 73: 4145-4153). Unlike in the aforementioned methods, the aerobic cultivation was performed without the addition or removal of nitrate in the liquid medium. We remove the nitrate contained in the nutrient medium as N2 O in the gas phase by an additional purging step after incubation overnight before the water sample is injected. This eliminates the need for another preparation step, thus saving working time. METHODS: The δ15 N and δ18 O values of dissolved NO3 - were determined using a Delta V Plus isotope ratio mass spectrometer coupled to a GasBench II sample preparation device that included a denitrification kit. RESULTS: After optimising the influencing factors (i.e., purging gas, purging time, and type of crimp seals), the method yielded high accuracy and precision (standard deviations were generally ≤0.7‰ for δ18 O values and ≤0.3‰ for δ15 N values), confirming the suitability of this procedure. Finally, the potential applicability of the method was demonstrated by measuring the isotopic composition of NO3 - in natural water samples. CONCLUSIONS: The denitrifier method for converting NO3 - into N2 O for isotope analysis was optimised. This allowed the sample preparation time to be further reduced. The complete working time for sample preparation, including all steps, takes 10 min per vial if 60 vials are prepared in one run. The water samples are ready for isotope analysis on the fourth day after preparation has started. Isotope measurements can be performed up to 14 days after preparation.

Collected Rain Water as Cost-Efficient Source for Aquifer Tracer Testing.

Locally collected precipitation water can be actively used as a groundwater tracer solution based on four inherent tracer signals: electrical conductivity, stable isotopic signatures of deuterium [δ2 H], oxygen-18 [δ18 O], and heat, which all may strongly differ from the corresponding background values in the tested groundwater. In hydrogeological practice, a tracer test is one of the most important methods for determining subsurface connections or field parameters, such as porosity, dispersivity, diffusion coefficient, groundwater flow velocity, or flow direction. A common problem is the choice of tracer and the corresponding permission by the appropriate authorities. This problem intensifies where tracer tests are conducted in vulnerable conservation or water protection areas (e.g., around drinking water wells). The use of (if required treated) precipitation as an elemental groundwater tracer is a practical solution for this problem, as it does not introduce foreign matters into the aquifer system, which may contribute positively to the permission delivery. Before tracer application, the natural variations of the participating end members' tracer signals have to be evaluated locally. To obtain a sufficient volume of tracer solution, precipitation can be collected as rain using a detached, large-scale rain collector, which will be independent from possibly existing surfaces like roofs or drained areas. The collected precipitation is then stored prior to a tracer experiment.

δ15 N analysis of ammonium in freeze-dried natural groundwater samples by precipitation with sodium tetraphenylborate.

RATIONALE: To perform the δ15 N isotopic analysis of ammonium (NH4 + ) with an elemental analyzer (EA) coupled to an isotope-ratio mass spectrometer, it is necessary to isolate the NH4 + prior to the analysis. Existing methods are work-intensive and time-consuming. For broader applicability in the environmental sciences, it is desirable to simplify the sample preparation process. The method used here is based on the insolubility of ammonium tetraphenylborate ((C6 H5 )4 BNH4 ) in water. Its suitability for the stable isotope measurement of δ15 N values for NH4 + has already been proven (Howa et al. Rapid Commun Mass Spectrom. 2014;28:1530-1534). However, there are no studies on the usability of the method for the analysis of ammonium-containing water samples. In this study, the method was tested for its applicability to natural groundwater samples. METHODS: To achieve the necessary high NH4 + concentrations for complete (C6 H5 )4 BNH4 precipitation, the water samples were first freeze-dried and then prepared for the analysis. To precipitate the NH4 + , sodium tetraphenylborate ((C6 H5 )4 BNa) was added to the samples. The precipitate was then separated from the water by filtration using a membrane filter and analyzed using an EA interfaced with an isotope ratio mass spectrometer to determine the nitrogen isotope ratio. RESULTS: A consistent 15 N enrichment of +0.65‰ was found in the measured isotope ratios. No significant effect due to other ions in the water samples could be identified. There was no significant difference between the isotope ratios of the natural groundwater samples determined from the tetraphenylborate (TPB) method and those determined from the diffusion method (DM). This indicates that the TPB method can easily be used for natural groundwater samples. CONCLUSIONS: The TPB method in combination with freeze-drying is an efficient technique for the precise δ15 N measurement of NH4 + in natural groundwater samples. The laboratory effort required for sample preparation is very low, and the repeatability of the measurements is very high.

Investigation of factors influencing biogas production in a large-scale thermophilic municipal biogas plant.

A continuously operated, thermophilic, municipal biogas plant was observed over 26 months (sampling twice per month) in regard to a number of physicochemical parameters and the biogas production. Biogas yields were put in correlation to parameters such as the volatile fatty acid concentration, the pH and the ammonium concentration. When the residing microbiota was classified via analysis of the 16S rRNA genes, most bacterial sequences matched with unidentified or uncultured bacteria from similar habitats. Of the archaeal sequences, 78.4% were identified as belonging to the genus Methanoculleus, which has not previously been reported for biogas plants, but is known to efficiently use H(2) and CO(2) produced by the degradation of fatty acids by syntrophic microorganisms. In order to further investigate the influence of varied amounts of ammonia (2-8 g/L) and volatile fatty acids on biogas production and composition (methane/CO(2)), laboratory scale satellite experiments were performed in parallel to the technical plant. Finally, ammonia stripping of the process water of the technical plant was accomplished, a measure through which the ammonia entering the biogas reactor via the mash could be nearly halved, which increased the energy output of the biogas plant by almost 20%.