Sleeve-fracturing limitations for measuring in situ stress in an anisotropic stress environment

In order to determine the far-field in situ stress using the sleeve-fracturing technique, two and three discrete fractures must be produced for the double-fracture and single-fracture method, respectively. Numerical modelling of the sleeve-fracturing process, using the fracture mechanics code FRANC2D/L, showed that the initiation and propagation of discrete fractures, using the single or double sleeve-fracture method, was controlled by the far-field in-plane stress ratio. The numerical modelling also provided the characteristic shapes of the pressure–displacement curves for sleeve fracturing under various boundary conditions and highlighted the difficulty of detecting the inflection points in the pressure–displacement curves for the sleeve-fracture method, a key to the successful interpretation of the in situ stress data.     

A simple, inexpensive in situ method for assessing acute toxicity of effluents to fish

Test chambers for conducting in situ fish bioassays were constructed from 81. polyethylene bottles. Yearling fathead minnows (Pimephales promelas) and young-of-the-year bluegill (Lepomis macrochirus) demonstrated greater than 50% survival in the chambers after 65 days of exposure in a reservoir, river and creek. Fathead minnow survival was substantially greater than that of bluegils. The chambers provide a simple, inexpensive, sensitive technique to screen effluents for toxicity.     

The comparison of two heavy fuel oils in composition and weathering pattern, based on IR, GC-FID and GC-MS analyses: Application to the Prestige wreackage

This paper compares the weathering patterns of two similar fuel oils: a fuel oil spilled after a ship accident (Prestige-Nassau, off the Galician coast -NW Spain-) and a fuel designed to cope with the numerous quests for samples to carry out scientific studies (IFO). Comparative studies were made to evaluate the capability of common fingerprinting analytical techniques to differentiate the fuels, as well as their capabilities to monitor their weathering. The two products were spilled under controlled conditions during ca. four months to assess how they evolved on time. Mid-IR spectrometry and gas chromatography (flame ionization and mass spectrometry detectors) were used. IR indexes related to total aromaticity, type of substituents (branched or linear chains) and degree of aromatic substitution reflected well the differences between the fuels during weathering. Regarding the chromatographic measurements, the n-alkanes became highly reduced for both fuel oils and it was found that the PAHs of the synthetic fuel (IFO) were more resistant to weathering. Regarding biomarkers, the different profiles of the steranes, diasteranes and triaromatic steroids allowed for a simple differentiation amongst the two products. The %D2/P2 ratio differentiated both products whereas the %N3/P2 one ordered the samples according to the extent of their weathering.     

Concentration-dependent response of estrone-degrading bacterial community in activated sludge analyzed by microautoradiography-fluorescence in situ hybridization

Inefficient removal of estrone (E1) in wastewater treatment plants (WWTPs) causes feminizing effects in male aquatic creatures. As E1 is mainly removed by biodegradation, investigation of E1 degradation is important to determine better removal strategies. Using microautoradiography-fluorescence in situ hybridization (MAR-FISH), we demonstrated that the structures of [³H]E1-incorporating bacterial communities were different at different E1 concentrations applied to activated sludge. At 200 μg/L E1, almost all [³H]E1-incorporating cells were associated with either Betaproteobacteria or Gammaproteobacteria (60% and 40% of MAR (+) cells, respectively). The proportion of Betaproteobacteria and Gammaproteobacteria in the total number of [³H]E1-incorporating cells decreased as the concentration of E1 decreased. In contrast, the proportion of Alphaproteobacteria in the total number of [³H]E1-incorporating cells increased as the concentrations of E1 decreased. At the lowest applied concentration (540 ng/L), almost all the [³H]E1-incorporating cells were Alphaproteobacteria (96%). The results of MAR-FISH applied to sludge samples collected from various plant locations and activated sludge processes, and during different seasons also demonstrated the high contribution of Alphaproteobacteria to the entire E1-degrading bacterial community (50.4 ± 11% of the total number of [³H]E1-incorporating cells) at 1 μg/L E1. Since the E1 concentration in domestic wastewater is at sub-μg/L levels, the key E1 degraders in activated sludge of domestic WWTPs are probably be Alphaproteobacteria. All [³H]E1-incorporating Alphaproteobacteria were hybridized with probe ALF968. Few MAR (+) cells were Sphingomonadales. An E1-degrading bacterial community at low E1 concentration appeared to consist of diverse bacterial groups of Alphaproteobacteria. This study suggested that substrate concentration is an essential factor for revealing E1-degrading bacteria in complex communities.     

In situ persistence of indicator bacteria in streams polluted with acid mine drainage

Persistence of indicator organisms (total coliforms, fecal coliforms, and fecal streptococci) associated with natural samples of raw sewage was studied following in situ exposure to five aquatic environments. Three of these streams contained significant amounts of acid mine water (AMW) while the other two were relatively uncontaminated. Indicator organisms were rapidly killed upon exposure to the acid mine systems, whereas little reduction in numbers was observed in the uncontaminated streams. Seasonal changes affected survival of indicators as reflected by prolonged persistence at colder in situ water temperatures. The fecal coliform group was most susceptible to the AMW stress, while the fecal streptococci were most persistent. An enrichment technique resulted in substantially enhanced recovery of certain species of sublethally injured survivors of acid stress. Enrichment was particularly beneficial for recovery of AMW-injured fecal coliforms. Relatively little improvement in recovery of fecal streptococci was afforded by the enrichment technique.     

Trace nutrient deficiency in Daphnia magna cultured in standard medium for toxicity testing. Effects of the optimization of culture conditions on life history parameters of D. magna

The suitability of various synthetic media for the culture of Daphnia magna was tested. Daphnids cultured in a standard medium for toxicity testing proposed by ISO showed low reproduction, reduced growth, high numbers of undeveloped parthenogenetic eggs and high mortality of neonates and adults. As a feature, animals cultured in the ISO medium lost parts of their second antennae. It could be shown that this was caused by selenium deficiency. The addition of selenium to the ISO medium clearly improved the quality of this medium. However, results of several tests were more variable than when a medium with a complex trace element composition (medium M4) was used. Medium M4 has allowed continuous culture of daphnids for three years up to now without any signs of reduced viability or reproduction. A mean reproduction rate of about 140 progeny/parent daphnid was calculated from 19 non simultaneous experiments. Neither a fourfold increase nor a reduction to one tenth of the trace element concentration of M4 had any effect on reproduction, growth or survival of daphnids. It was shown in this study that ion-exchanger cartridges can leach detrimental substances into the matrix water. Therefore, only ultrapure matrix waters should be used for the preparation of culture media.     

The influence of substrate, pH, diet and temperature upon cadmium accumulation in the asiatic clam (Corbicula fluminea) in laboratory artificial streams

The influence of substrate, pH, diet and temperature upon the accumulation of cadmium (0.05 mg l⁻¹ dose < 0.001 mg l⁻¹ control) in the visceral mass of the Asiatic clam Corbicula fluminea was studied in laboratory artificial stream systems at intervals of 0, 3, 5, 7, 10 and 14-day exposures. Four substrate conditions, sand; sand, silt and clay (SSC); sand, clay and organic matter (SCO); and no substrate (NoS), were considered. The greatest tissue accumulation of cadmium in C. fluminea occurred at 0.05 mg l⁻¹ Cd in NoS and the lowest in clams occupying SCO. Complexation of available metals, lower clam filtering rates and physical protection by the substrate were attributed to the depressed cadmium accumulation of clams exposed in the SCO substrate. Lower pH exposures (5.0 vs 7.8) significantly (P 0.05 level) reduced cadmium uptake at 21°C but had little effect at 9°C. Uptake was higher in clams fed with cadmium-exposed Chlamydomonas reinhardt at 21°C but not at 9°C. In temperature exposures alone at 0.05 mg l⁻¹ Cd, accumulation was significantly higher in C. fluminea exposed at 21°C than at 9°C. The results are discussed relative to the importance of standardized laboratory protocol and the use of C. fluminea as a bioindicator of heavy metal stress.     

Estimation of viable biomass in wastewater and activated sludge by determination of ATP, oxygen utilization rate and FDA hydrolysis

ATP content, oxygen utilization rate (OUR) and fluorescein diacetate (FDA) hydrolysis were tested for the ability to express the amount of viable biomass in wastewater and activated sludge.The relationship between biomass and these activity parameters was established in growth cultures made by inoculating a nutrient medium with either wastewater or activated sludge. Biomass was then determined directly by measurement of dry weight of growth culture (dw), and compared to data obtained by using the previously mentioned methods. In the exponential growth phase, ATP content showed the best correlation with biomass, while FDA hydrolysis in the sludge failed to show any such correlation. Conversion factors of 3 mg ATP/g dw, 300 mg O₂/h g dw and 0.4 A/h (mg dw/ml) for ATP, OUR and FDA methods, respectively, were calculated.When the methods were applied for in situ determinations in four different wastewater plants, it was found that ATP content and respiration rate estimated viable biomass to range from 81 to 293 mg dw/g SS for raw wastewater and from 67 to 187 mg dw/g SS for activated sludge with a rather weak correlation between ATP and respiration measurements. The FDA hydrolysis estimated viable biomass to be higher than suspended solids, for which reason this parameter could not be recommended for determination of viable biomass in wastewater and activated sludge.     

Removal of arsenic from water: Effect of calcium ions on As(III) removal in the KMnO4–Fe(II) process

A novel KMnO₄–Fe(II) process was developed in this study for As(III) removal. The optimum As(III) removal was achieved at a permanganate dosage of 18.6 μM. At the optimum dosage of permanganate, the KMnO₄–Fe(II) process was much more efficient than the KMnO₄–Fe(III) process for As(III) removal by 15–38% at pH 5–9. The great difference in As(III) removal in these two processes was not ascribed to the uptake of arsenic by the MnO₂ formed in situ but to the different properties of conventional Fe(III) and the Fe(III) formed in situ. It was found that the presence of Ca²⁺ had limited effects on As(III) removal under acidic conditions but resulted in a significant increase in As(III) removal under neutral and alkaline conditions in the KMnO₄–Fe(II) process. Moreover, the effects of Ca²⁺ on As(III) removal in the KMnO₄–Fe(II) process were greater at lower permanganate dosage when Fe(II) was not completely oxidized by permanganate. This study revealed that the improvement of As(III) removal at pH 7–9 in the KMnO₄–Fe(II) process by Ca²⁺ was associated with three reasons: (1) the specific adsorption of Ca²⁺ increased the surface charge; (2) the formation of amorphous calcium carbonate and calcite precipitate that could co-precipitate arsenate; (3) the introduction of calcium resulted in more precipitated ferrous hydroxide or ferric hydroxide. On the other hand, the enhancement of arsenic removal by Ca²⁺ under acidic conditions was ascribed to the increase of Fe retained in the precipitate. FTIR tests demonstrated that As(III) was removed as arsenate by forming monodentate complex with Fe(III) formed in situ in the KMnO₄–Fe(II) process when KMnO₄ was applied at 18.6 μM. The strength of the “non-surface complexed” As–O bonds of the precipitated arsenate species was enhanced by the presence of Ca²⁺ and the complexation reactions of arsenate with Fe(III) formed in situ in the presence or absence of Ca²⁺ were proposed.