Interaction between sorption and biodegradation processes in the contaminant transport

The main goal of this work is to examine in detail the equilibrium and non-equilibrium sorption in a multiple species contaminant transport system undergoing multiplicative Monod biodegradation kinetics, which characterizes a scenario of subsurface contamination by organic contaminants. Mathematically, the problem is given by a nonlinear advection-diffusion-reaction partial differential system coupled by the reaction terms, associated with the biodegradation process. A new operator splitting approach is proposed for treating in a sequential fashion the convective-diffusive and reactive terms. A predictor-multicorrector algorithm with Newton–Raphson and stabilized finite element (streamline-upwind Petrov-Galerkin, SUPG) methods is used in the time and spatial discretizations, respectively. Numerical results illustrate the good applicability of the present approach, corroborating the well-known observation nonlinear physical and biological processes should be inserted in the model that to better predict the contamination scenarios.     

Total phosphorus accident pollution and emergency response study based on geographic information system in Three Gorges Reservoir area

• A new algorithm of two-dimensional water quantity and the quality model was built. • The migration and diffusion of TP was simulated. • The emergency measures for sudden water pollution accidents was proposed. In recent years, sudden water pollution accidents in China’s rivers have become more frequent, resulting in considerable effects on environmental safety. Therefore, it is necessary to simulate and predict pollution accidents. Simulation and prediction provide strong support for emergency disposal and disaster reduction. This paper describes a new two-dimensional water quantity and the quality model that incorporates a digital elevation model into the geographic information system. The model is used to simulate sudden water pollution accidents in the main stream of the Yangtze River and Jialing River in the Chongqing section of the Three Gorges Reservoir area. The sectional velocity distribution and concentration change of total phosphorus are then analyzed under four hydrological situations. The results show that the proposed model accurately simulates and predicts the concentration change and migration process of total phosphorus under sudden water pollution accidents. The speed of migration and diffusion of pollutants is found to be greatest in the flood season, followed by the water storage period, drawdown season, and dry season, in that order. The selection of an appropriate water scheduling scheme can reduce the peak concentration of river pollutants. This study enables the impact of pollutants on the ecological environment of river water to be alleviated, and provides a scientific basis for the emergency response to sudden water pollution accidents in the Three Gorges Reservoir area.     

多无人机协作监测污染气团的研究现状

分析了多无人机协作监测污染气团的研究意义,以及涉及到的4个主要技术问题——未知环境的搜索方法、环境地图建模、任务分配和路径规划的研究现状,指出多无人机协作监测研究的仿真平台、三维空间的监测技术及精确的模型是开展该项工作的重要研究方向。     

硝酸钙投加频次对污泥生物调理效果的影响

在接种了反硝化菌的剩余污泥中投加硝酸钙药剂,利用反硝化菌消耗NO3-进行反硝化作用去除污泥中易生物降解的有机物,利用Ca2＋的中和、架桥作用,改善污泥的脱水性能.固定NO;总投加浓度为100 mg?g-1 TS,在6d的时间内,按1次、2次、3次、6次的投加频次向污泥中投加硝酸钙.结果表明,1次投加对污泥脱水性能的提升...     

The hydrogeology of a tailings impoundment formed by central discharge of thickened tailings: implications for tailings management

The Kidd Creek Cu–Zn sulfide mine is located near Timmins, Ontario. Mill tailings are thickened and deposited as a slurry in a circular impoundment with an area of approximately 1200 ha. Deposition of tailings as a thickened slurry from a central discharge ramp results in a conical-shaped tailings deposit with low perimeter dykes, a uniform grain-size distribution, uniform and low hydraulic conductivity, and a tension-saturated zone above the water table up to 5 to 6 m thick. These characteristics provide benefits over conventionally disposed tailings with respect to tailings management. The thick tension-saturated zone within the tailings limits the thickness of unsaturated tailings that are susceptible to rapid sulfide oxidation. The conical shape of the deposit results in the formation of a recharge area near the centre of the impoundment and discharge in the peripheral areas. In contrast, the elevated nature of many conventional, unthickened tailings impoundments results in recharge over most of the surface of the impoundment, with discharge occurring outside the impoundment through large containment dykes. Three-dimensional pore water flow modelling suggests that approximately 90% of the total discharge from the thickened tailings occurs within the tailings impoundment. When discharge is confined within the impoundment, there is improved control over low-quality effluent, and an opportunity to design passive control measures to reduce treatment costs and minimize environmental impacts.     

Factors affecting nitrate distribution in shallow groundwater under a beef farm in South Eastern Ireland

Groundwater contamination was characterised using a methodology which combines shallow groundwater geochemistry data from 17 piezometers over a 2 yr period in a statistical framework and hydrogeological techniques. Nitrate–N (NO₃-N) contaminant mass flux was calculated across three control planes (rows of piezometers) in six isolated plots. Results showed natural attenuation occurs on site although the method does not directly differentiate between dilution and denitrification. It was further investigated whether NO₃-N concentration in shallow groundwater (<5 m below ground level) generated from an agricultural point source on a 4.2 ha site on a beef farm in SE Ireland could be predicted from saturated hydraulic conductivity (K_sat) measurements, ground elevation (m Above Ordnance Datum), elevation of groundwater sampling (screen opening interval) (m AOD) and distance from a dirty water point pollution source. Tobit regression, using a background concentration threshold of 2.6 mg NO₃-N L⁻¹ showed, when assessed individually in a step wise procedure, K_sat was significantly related to groundwater NO₃-N concentration. Distance of the point dirty water pollution source becomes significant when included with K_sat in the model. The model relationships show areas with higher K_sat values have less time for denitrification to occur, whereas lower K_sat values allow denitrification to occur. Areas with higher permeability transport greater NO₃-N fluxes to ground and surface waters. When the distribution of Cl⁻ was examined by the model, K_sat and ground elevation had the most explanatory power but K_sat was not significant pointing to dilution having an effect. Areas with low NO₃ concentration and unaffected Cl⁻ concentration points to denitrification, low NO₃ concentration and low Cl⁻ chloride concentration points to dilution and combining these findings allows areas of denitrification and dilution to be inferred. The effect of denitrification is further supported as mean groundwater NO₃-N was significantly (P < 0.05) related to groundwater N₂/Ar ratio, redox potential (Eh), dissolved O₂ and N₂ and was close to being significant with N₂O (P = 0.08). Calculating contaminant mass flux across more than one control plane is a useful tool to monitor natural attenuation. This tool allows the identification of hot spot areas where intervention other than natural attenuation may be needed to protect receptors.     

A flow-through passive dosing system for continuously supplying aqueous solutions of hydrophobic chemicals to bioconcentration and aquatic toxicity tests

A continuous supply of water with defined stable concentrations of hydrophobic chemicals is a requirement in a range of laboratory tests such as the OECD 305 protocol for determining the bioconcentration factor in fish. Satisfying this requirement continues to be a challenge, particularly for hydrophobic chemicals. Here we present a novel solution based on equilibrium passive dosing. It employs a commercially available unit consisting of ∼16 000 polydimethylsiloxane (PDMS) tubes connected to two manifolds. The chemicals are loaded into the unit by repeatedly perfusing it with a methanol solution of the substances that is progressively diluted with water. Thereafter the unit is perfused with water and the chemicals partition from the unit into the water. The system was tested with nine chemicals with log K_OW ranging from 4.1 to 6.3. The aqueous concentrations generated were shown to be largely independent of the water flow rate, and the unit to unit reproducibility was within a factor of ∼2. In continuous flow experiments the aqueous concentrations of most of the study chemicals remained constant over 8 d. A model was assembled that allows prediction of the operating characteristics of the system from the log K_OW or PDMS/water partition coefficient of the chemical. The system is a simple, safe, predictable and flexible tool that generates stable aqueous concentrations of hydrophobic chemicals.     

Non-intrusive characterization of the redox potential of landfill leachate plumes from self-potential data

Contaminant plumes (e.g., associated with leakages from municipal landfills) provide a source of natural electrical potentials (or "self-potentials") recordable at the Earth's surface. One contribution to these self-potentials is associated with pore water flow (i.e., the "streaming potential"), and the other is related to redox conditions. A contaminant plume can be regarded as a "geobattery": the source current potentially results from the degradation of the organic matter by micro-organisms, which produces electrons. These electrons are then carried by nanowires that connect bacteria and thorough metallic particles that precipitate in areas of strong redox potential gradient. In the case of the Entressen landfill (South of France), reported here, the hydraulic head differences measured in piezometers outside the contaminant plume is strongly linked to the surface self-potential signals, with a correlation coefficient of -0.94. We used a Bayesian method that combines hydraulic head and self-potential data collected outside the contaminated area to estimate the streaming potential component of the collected self-potential data. Once the streaming potential contribution was removed from the measured self-potentials, the correlation coefficient between the residual self-potentials and the measured redox potentials in the aquifer was 0.92. The slope of this regression curve was close to 0.5, which was fairly consistent with both finite element modelling and the proposed geobattery model.     

Multiple batch extraction test to estimate contaminant release parameters using a Bayesian approach

Industrial activities produce vast amounts of weakly contaminated materials which are commonly reused as filling materials on natural ground. There is a strong demand to define guidelines for the application of these materials, to estimate the leaching potential of contaminants from the materials, and to assess the potential hazard for groundwater pollution. We present a multiple batch experiment, where measurements of liquid-phase concentrations at varying liquid/solid ratios are used to estimate the total mass of contaminant that can be extracted from a contaminated material with a mild extractant like water. Furthermore, the experiment yields estimates of the isotherm describing the partitioning of the contaminant between the solid and liquid phases, and a concentration that might be expected under soil hydraulic conditions representative for the field situation. Model parameters are estimated from liquid-phase concentrations within a Bayesian framework by applying the Shuffled Complex Evolution Metropolis Algorithm (SCEM-UA), an efficient Markov Chain Monte Carlo sampler. A sensitivity analysis and inversions of synthetically generated data corrupted with noise show the general suitability of the proposed method. An uncertainty analysis for model parameters and model predictions shows the expected accuracy of the estimates. An application to concentration measurements obtained from a multiple batch extraction test illustrates the applicability of the approach for a real situation.     

Ecological degradation and hydraulic dispersion of contaminant in wetland

For the typical case of a pulsed contaminant emission into a free surface wetland flow, a theoretical analysis is presented in this paper for the decay of the depth-averaged concentration under the combined action of ecological degradation and hydraulic dispersion. Based on a first-order reaction model extensively employed in related ecological risk assessment and environmental hydraulic design, the effect of ecological degradation is separated from the hydraulic effect via an exponential transformation for the general formulation for contaminant transport. The speed profile of a fully developed steady flow through the wetland is obtained. A hydraulic dispersion model for the depth-averaged concentration is devised as an extension of Taylor’s classical analysis on dispersion, and corresponding hydraulic dispersivity is obtained by Aris’s method of moments. Analytical solution of depth-averaged concentration is rigorously derived and characterized. For typical pollutant constituents in wastewater emission, the evolution of contaminant cloud in the wetland flow is illustrated by critical length and duration of influenced region with contaminant concentration beyond given environmental standard level, with essential implications for ecological risk assessment and environmental management.