Competing TCE and cis-DCE degradation kinetics by zero-valent iron-experimental results and numerical simulation

The successful dechlorination of mixtures of chlorinated hydrocarbons with zero-valent metals requires information concerning the kinetics of simultaneous degradation of different contaminants. This includes intraspecies competitive effects (loading of the reactive iron surface by a single contaminant) as well as interspecies competition of several contaminants for the reactive sites available. In columns packed with zero-valent iron, the degradation behaviour of trichloroethylene (TCE), cis-dichloroethylene (DCE) and mixtures of both was measured in order to investigate interspecies competition. Although a decreasing rate of dechlorination is to be expected, when several degradable substances compete for the reactive sites on the iron surface, TCE degradation is nearly unaffected by the presence of cis-DCE. In contrast, cis-DCE degradation rates decrease significantly when TCE is added. A new modelling approach is developed in order to identify and quantify the observed competitive effects. The numerical model TBC (Transport, Biochemistry and Chemistry, Sch?fer et al., 1998a) is used to describe adsorption, desorption and dechlorination in a mechanistic way. Adsorption and degradation of a contaminant based on a limited number of reactive sites leads to a combined zero- and first-order degradation kinetics for high and low concentrations, respectively. The adsorption of several contaminants with different sorption parameters to a limited reactive surface causes interspecies competition. The reaction scheme and the parameters required are successfully transferred from Arnold and Roberts (2000b) to the model TBC. The degradation behaviour of the mixed contamination observed in the column experiments can be related to the adsorption properties of TCE and cis-DCE. By predicting the degradation of the single substances TCE and cis-DCE as well as mixtures of both, the calibrated model is used to investigate the effects of interspecies competition on the design of permeable reactive iron barriers. Even if TCE is present in only small concentrations (>3% of molar cis-DCE concentration) it is the contaminant limiting the residence time and the required thickness of the iron barrier.     

Effects of solution conditions on the precipitation of phosphate for recovery. A thermodynamic evaluation

To understand the effects of solution conditions on the precipitation of calcium phosphates from wastewater for recovery, a computer programme PHREEQC was employed to calculate the speciation and saturation-index (SI) with respect to hydroxyapatite of a chemically defined precipitation system, which contains phosphate of 1–200 mg P/l, with Ca/P molar ratios of one to 10 times of the stoichiometric calcium to phosphorus molar ratio of hydroxyapatite, at a pH range of 7.0–11.0. The results show that the SI is respectively the logarithmic function of the phosphate concentration and the calcium concentration, increasing with the increase of either of them; the SI is a polynomial function of the solution pH value and increases with its increase, and the effect of solution pH value is due to its influence on base uptake of the precipitation reaction and the speciation of phosphate and calcium ions; the SI is also a logarithmic function of the solution ionic strength but decreases with its increase; at the temperature range of 5–30 °C the SI increases linearly with solution temperature and the effect of temperature is also due to its influence on the speciation of phosphate and calcium ions.     

Effects of elevated CO2, nitrogen supply and tropospheric ozone on spring wheat-II. Nutrients (N, P, K, S, Ca, Mg, Fe, Mn, Zn)

CO(2) enrichment is expected to alter leaf demand for nitrogen and phosphorus in plant species with C(3) carbon dioxide fixation pathway, thus possibly causing nutrient imbalances in the tissues and disturbance of distribution and redistribution patterns within the plants. To test the influence of CO(2) enrichment and elevated tropospheric ozone in combination with different nitrogen supply, spring wheat (Tritium aestivum L. cv. Minaret) was exposed to three levels of CO(2) (361, 523, and 639 microl litre(-1), 24 h mean from sowing to final harvest), two levels of ozone (28.4 and 51.3 nl litre(-1)) and two levels of nitrogen supply (150 and 270 kg ha(-1)) in a full-factorial design in open-top field chambers. Additional fertilization experiments (120, 210, and 330 kg N ha(-1)) were carried out at low and high CO(2) levels. Macronutrients (N, P, K, S, Ca, Mg) and three micronutrients (Mn, Fe, Zn) were analysed in samples obtained at three different developmental stages: beginning of shoot elongation, anthesis, and ripening. At each harvest, plant samples were separated into different organs (green and senescent leaves, stem sections, ears, grains). According to analyses of tissue concentrations at the beginning of shoot elongation, the plants were sufficiently equipped with nutrients. Elevated ozone levels neither affected tissue concentrations nor shoot uptake of the nutrients. CO(2) and nitrogen treatments affected nutrient uptake, distribution and redistribution in a complex manner. CO(2) enrichment increased nitrogen-use efficiency and caused a lower demand for nitrogen in green tissues which was reflected in a decrease of critical nitrogen concentrations, lower leaf nitrogen concentrations and lower nitrogen pools in the leaves. Since grain nitrogen uptake during grain filling depended completely on redistribution from vegetative pools in green tissues, grain nitrogen concentrations fell considerably with severe implications for grain quality. Ca, S, Mg and Zn in green tissues were influenced by CO(2) enrichment in a similar manner to nitrogen. Phosphorus concentrations in green tissues, on the other hand, were not, or only slightly, affected by elevated CO(2). In stems, 'dilution' of all nutrients except manganese was observed, caused by the huge accumulation of water soluble carbohydrates, mainly fructans, in these tissues under CO(2) enrichment. Whole shoot uptake was either remarkably increased (K, Mn, P, Mg), nearly unaffected (N, S, Fe, Zn) or decreased (Ca) under CO(2) enrichment. Thus, nutrient cycling in plant-soil systems is expected to be altered under CO(2) enrichment.     

Levels of dioxin-like compounds in sewage sludge determined with a bioassay based on EROD induction in chicken embryo liver cultures

A bioassay for the detection of dioxin-like compounds was used to estimate levels in sewage sludge from Swedish sewage treatment plants (STPs). The sludge extracts were HPLC-separated into three fractions containing a) monoaromatic/aliphatic, b) diaromatic (e.g. polychlorinated biphenyls [PCBs], polychlorinated dibenzodioxins and polychlorinated dibenzofurans [PCDDs/Fs]), and c) polyaromatic compounds (e.g. polycyclic aromatic hydrocarbons [PAHs]). The bioassay, which is based on EROD (7-ethoxyresorufin O-deethylase) induction in cultured chicken embryo livers detected dioxin-like activity in all unfractionated extracts and in the di- and polyaromatic fractions of all sludge extracts, but not in the monoaromatic/aliphatic fractions. The levels ranged between 6 and 109 pg bio-TEQ/g sludge (d.w.). In sediment samples from rural lakes in Sweden, levels of about 5 pg bio-TEQ/g (d.w.) have been found. The polyaromatic fractions of the sludge samples were potent in the bioassay, probably due to various PAHs and other polyaromatics in the sludge. The levels of six PAHs that are screened for in the sludge at Swedish STPs accounted for only 3-10% of the observed EROD-induction by the polyaromatic fractions. Consequently, many other polyaromatic EROD-inducing compounds were present in the sludge. Inclusion of a biological test like the chicken embryo liver bioassay in the screening of sludge would improve the ability to detect the presence of bioactive dioxin-like compounds. A theoretical estimation of bio-TEQ concentrations in farm-soil following long-term application of sludge with bio-TEQ concentrations similar to those observed in this investigation indicated that the bio-TEQ levels in soil would increase very slowly over time. The chicken embryo liver bioassay proved useful in assessing levels of dioxin-like compounds in sewage sludge and it gives valuable complementary information to chemical analysis data.     

Concentrations of cadmium and other metals in Fucus vesiculosus L. and Fontinalis dalecarlica Br. Eur. from the northern Baltic Sea and the southern Bothnian Sea

Concentrations of Cd and ten other metals (Al, Co, Cr, Cu, Fe, Mn, Ni, Pb, V and Zn) were determined in the brown seaweed Fucus vesiculosus L. and the aquatic moss, Fontinalis dalecarlica Br. Eur. from the northern Baltic Sea and the southern Bothnian Sea. Elevated concentrations of metals were found in samples taken close to densely populated areas, such as Stockholm and Nyn?shamn. Very high concentrations of especially Zn were found in both Fucus and Fontinalis samples taken from the area south of the Gulf of G?vle. The results indicate that mining and industrial activities along the river Dal?lven are the main sources of Zn and several other metals. Cd concentrations in Fucus plants reached maximum values (24.5 mg kg(-1)) at the northern site. The gradual increase of Cd concentrations in Fucus plants northward could not be totally explained by the salinity gradient in the Baltic Sea; reasons for this are discussed in this paper.     

Influence of the mode of matrix porosity determination on matrix diffusion calculations

The theoretical basis for matrix diffusion in fractured rocks and the methodology for the determination of diffusion coefficients in the laboratory are well established. One significant problem, however, remains in that it is difficult to quantify the degree of sample disturbance affecting the geometrical, geophysical and hydraulic properties of the rock matrix. A new technique, with in situ rock impregnation with resin, for examining the diffusion-accessible rock matrix has been developed and successfully adopted to the rock matrix behind a water-conducting fracture in host crystalline rocks at Nagra's Grimsel Test Site in Switzerland and JNC's Kamaishi In Situ Test Site in Japan. In line with the results of a large number of natural analogue and laboratory studies, the existence of an in situ interconnected pore network was substantiated. Matrix porosities determined on the laboratory samples from both the sites are 1.5-3 times higher than in situ values, irrespective of the technique applied. On the Grimsel granodiorite matrix, matrix porosity existing in situ and artefacts of stress release and physical disturbance, induced by sampling and sample preparation, were clearly distinguished, allowing in situ porosity to be quantified. Laboratory work with conventional techniques tends to overestimate the porosity of the rock matrix, hence leading to an overestimation of in situ matrix diffusion. The implications of these differences to a repository performance assessment are assessed with a couple of examples from existing assessments, and recommendations for future approaches to the examination of in situ matrix porosity are made.     

Comparing electron ionization high-resolution and electron capture low-resolution mass spectrometric determination of polybrominated diphenyl ethers in plasma, serum and milk

Gas chromatography coupled to low-resolution mass spectrometry with electron capture negative ionization as detection mode (GC-LRMS (ECNI)) has been compared to gas chromatography coupled to high-resolution mass spectrometry using electron ionization as detection mode (GC-HRMS (EI)) for determination of polybrominated diphenyl ethers (PBDEs) in biological samples. Extracts of 5.0 g plasma, serum and milk samples were analyzed using both methods. The GC-LRMS (ECNI) and GC-HRMS (EI) systems were found to be equally well suited for determination of PBDEs in the biological samples, as well as in standard solutions, with respect to response, detection limits and repeatability at the pg-level. The estimated limits of detection (LOD) in milk extracts ranged from 0.3-0.6 pg PBDE/g milk and 0.4-0.7 pg PBDE/g milk, for the GC-LRMS (ECNI) and GC-HRMS (EI) systems, respectively. The method repeatability including sample preparation was in the range 4.7-8.4% and 0.6-10% relative standard deviation (RSD) for the GC-LRMS (ECNI) and GC-HRMS (EI) systems, respectively.