Showing papers by "Swiss Federal Institute of Aquatic Science and Technology published in 1986"

A multispecies biofilm model

Abstract: Using a continuum approach and observing conservation principles, an analytical mathematical model of microbial interaction in biofilms was developed. The model predicts changes in biofilm thickness and describes the dynamics and spatial distribution of microbial species and substrates in the film. It allows for biomass detachment due to shear stress and sloughing, external mass transfer limitations, as well as variations in substrate concentrations in the bulk liquid. A computer implementation of the model is provided using an example of heterotrophicautotrophic competition to illustrate how the observed phenomena can be numerically reproduced and indicating how they might affect overall biofilm performance.

Primary and diagenetic carbonates in the anoxic sediments of Lake Bosumtwi, Ghana

Abstract: Cores of organic-rich muds from the tropical meteorite crater Lake Bosumtwi, Ghana, contain laminae of authigenic calcite polyhedra and aragonite needles, as well as scattered diagenetic calcite, Mg-calcite spherulites, and aggregates of dolomite crystals. Their respective origins are traced by analyses of oxygen and carbon stable isotopes. Anoxic dolomite and Mg-calcite formed in pore waters reflecting highest degrees of evaporative concentration and high rates of methanogenesis. Carbon dioxide reduction must have been the dominant methanogenic pathway, producing diagenetic carbonates with ..delta../sup 13/C values up to + 27% PDB. This example shows the inherent problems of interpreting bulk samples with progressive mineralogical sequences of calcite to Mg-calcite to aragonite to dolomite merely in terms of Mg/sup 2 +//Ca/sup 2 +/ in lake waters. It provides a model for the interpretation of ancient lacustrine carbonates from organic-rich environments.

Rapid microbial mineralization of toluene and 1,3-dimethylbenzene in the absence of molecular oxygen.

Abstract: Up to 0.4 mM 1,3-dimethylbenzene (m-xylene) was rapidly mineralized in a laboratory aquifer column operated in the absence of molecular oxygen with nitrate as an electron acceptor. Under continuous flow conditions, the degradation rate constant (pseudo-first order) was >0.45 h/sup -1/. Based on a carbon mass balance with (ring-/sup 14/C)m-xylene and a calculation of the electron balance, m-xylene was shown to be quantitatively (80%) oxidized to CO/sub 2/ with a concomitant reduction of nitrate. The mineralization of m-xylene in the column also took place after reducing the redox potential, E', of the inflowing medium with sulfide to <-0.11 V. Microorganisms adapted to growth on m-xylene were also able to degrade toluene under denitrifying conditions. These results suggest that aromatic hydrocarbons present in anoxic environments such as lake sediments, sludge digestors, and ground water infiltration zones from landfills and polluted rivers are not necessarily persistent but may be mineralized in the absence of molecular oxygen.

Thermische Energieflüsse an der Wasseroberfläche: Beispiel Sempachersee

Abstract: Data collected every 20 minutes for 18 months by a meteorological buoy moored on Lake Sempach in Switzerland (maximum depth 86 m, surface area 14.1 km2) are used to calculate different processes contributing to the net heat flux between water and atmosphere. The processes considered are shortwave and longwave radiation, evaporation/condensation and sensible heat transfer. The temporal resolution of the measurements allows the evaluation of the processes occurring on three different time scales: diurnal variations, weather events of a few days and yearly cycles. The heat content of the lake is calculated from quasi-continuous measurements of water temperature at different depths. The yearly amplitude of the heat content is 1100·106 J/m2. Short-time variations of the heat flux determined from water temperature analysis agree well with the flux variations modeled using meteorological data. However, the latter generally underestimates the measured net heat flux in the long term. Wind measurements, together with the net heat flux, are used to calculate the Flux Richardson Number and the Monin-Obukov Length. Examples are given to show the predominant influence of the wind on the stratification of the upper water column and thus on the surface water temperature.

Factors governing the growth rate of roachRutilus rutilus (L.) in pre-alpine Lake Sarnen

Abstract: Most of the mesotrophic to eutrophic lakes in central Europe have been showing signs of oligotrophication during recent years. The question as to how the fish populations would react to this new situation was investigated looking at the growth rate of roachRutilus rutilus (L.) of Lake Sarnen, central Switzerland. The water temperature sum as day-degrees over 12 to 13°C for the months of June to October was found to be the predominant factor governing the marked year-to-year fluctuations of the growth rate. Contrary to expectation, the decreasing trophic state of the lake has not yet manifested itself noticeably in the growth rate.

Behaviour of Nonionic Surfactants in Biological Waste Water Treatment

Abstract: Effluents and sludges from municipal sewage treatment plants in Switzerland were analyzed for nonylphenol polyethoxylates (NPnEO, n=3–20), nonylphenol mono- and diethoxylate (NP1EC, NP2EC), corresponding nonylphenoxy carboxylic acids (NP1EC, NP2EC) and nonylphenol (NP). These chemicals derive from nonionic surfactants of the alkylphenol polyethoxylate type and contribute significantly to the organic loading in sewage effluents (2–13% of the total dissolved organic carbon in primary effluents). Specific analytical methods were used to study their behaviour during mechanical-biological sewage treatment and subsequent sewage sludge treatment. The parent NPnEO surfactants (n=3–20) with concentrations in raw and mechanically treated sewage from 400 to 2′200 mg/m3 were efficiently removed by the activated sludge treatment (usually more than 90%). However, this resulted in the formation of several metabolic products, and the refractory nature of NP1/2E0, NP1/2EC and NP was recognized. The abundance of the different metabolites varied depending on the treatment conditions. Both biotransformations and physicochemical processes determine the behaviour and fate of the nonylphenolic substances in sewage treatment.

Sorption behavior of neutral and ionizable hydrophobic organic compounds

Abstract: Factors influencing the equilibrium distribution of neutral and ionizable hydrophobic organic pollutants between water and natural solid phases are discussed. For neutral hydrophobic compounds, the sorption process can be viewed as a simple partitioning of the organic solute between the water and the natural organic matter present in a given solid phase, if the organic matter exceeds ~ 0.1%. The degree of sorption can be expressed by a partition coefficient, which may be estimated from the octanol/water partition constant of the compound and the organic carbon content of the sorbent. For ionizable (anionic) hydrophobic compounds (represented by polychlorinated phenols), the distribution ratio depends on both the pH and on the major ion composition of the aqueous phase, in contrast to the partitioning model for neutral compounds in which the chemical composition of the aqueous phase is relatively unimportant.

Microbial Degradation of Nitrilotriacetate (NTA) in Groundwater: Laboratory Studies under Aerobic and Anaerobic Conditions

Abstract: Plexiglas columns filled with aquifer material where continously fed with a mineral salt medium supplemented with NTA. Different parameters (electron acceptor, temperature, concentration of NTA) were tested for their influence on the microbial degradation of NTA. Under aerobic conditions, more than 90% of NTA was removed during the column passage starting from initial concentrations of 105, 160 and 600 μg/1. At a smaller concentration (11 μg/l) the degradation rate decreased. A change from aerobic to denitrifying conditions resulted in a partial breakthrough of NTA at the column effluent. After 5 days of adaption, however, again more than 90% of NTA was degraded. The degradation of NTA was determined over the temperature range of 5 to 20 °C. The NTA concentration in the column effluent increased temporarily when the temperature was decreased, but after adaption times of 4–20 days, high degradation rates were again obtained. [14C] NTA was mineralized to 14C02 under aerobic (≥ 68%) and denitrifying conditions (≥ 85%).

Mathematical Modelling of the Behaviour of Organic Micropollutants in the Aquatic Environment

Abstract: Modelling of the behaviour of micropollutants in the aquatic environment serves to generalize to other systems the knowledge gained from measurements in a specific situation, provided that certain rules are obeyed In order to use a model as a tool for predicting concentrations in natural systems, calibration of the model is necessary The model should be as simple as possible and only contain quantities which can be actually measured The proper choice of model dimensionality, a key factor of model complexity, can be made by comparing reaction and mixing rates

Biotransformation of Nitroaromatic Compounds

Abstract: Nitroaromatic compounds are used as dyes, pesticides, explosives and solvents. They are ubiquitous pollutants in the environment. Their microbial mineralization is generally slow and proceeds through: (i) an initial reduction to an aminoaromatic compound (aniline), followed by an oxidative removal of the amino-substituent as ammonium, or (ii) an initial oxidative liberation of the nitro-substituent as nitrite. Both pathways eventually lead to catechol, which is a central metabolite in the aerobic degradation of most aromatic compounds and rapidly degradable.

Résultats préliminaires d'études sur des méthodes de détermination de l'âge individuel par l'histologie chez quelques Téléostéens

Abstract: The study discusses the potential of various histological methods for enhancing the readability of the lines of arrested growth (LAC, annuli) in different bony elements, particularly fin rays, of some freshwater fish species.