RESUMEN
Radionuclides released in water systems--as well as heavy metals and organic toxicants--sorb to both the suspended solid particles and the bed sediments. Sorption is usually represented mathematically by the distribution coefficient. This approach implies equilibrium between phases and instantaneous fixation (release) of the pollutant onto (from) the surface of the soil particle. However, empirical evidence suggests that for some radionuclides the fixation is not achieved instantaneously and that the reversibility of the process can be slow. Here the adsorption/desorption kinetics of (60)Co and (137)Cs in fresh water environments were simulated experimentally and later on modelled mathematically, while the influence of the most relevant factors affecting the sorption were taken into account. The experimental results suggest that for adsorption and the desorption more than 24 h are needed to reach equilibrium, moreover, It was observed that the desorption rate constants for (60)Co and (137)Cs lie within ranges which are of two to three orders of magnitude lower than the adsorption rate constants.
Asunto(s)
Radioisótopos de Cesio/análisis , Radioisótopos de Cobalto/análisis , Agua Dulce/química , Ríos/química , Adsorción , Bélgica , Sedimentos Geológicos/química , Concentración de Iones de Hidrógeno , Cinética , Modelos TeóricosRESUMEN
This paper studies the effects of the implementation of wastewater treatment (WWT) on the water quality of small urban river systems by considering as an extreme case study (volumetric contribution of wastewaters >50%) the evolution of the Zenne River waters (Belgium) over the last 40 years. In urban rivers, organic matter (OM), oxygen, and nutrients are primarily controlled by wastewater releases which depend on the population and the WWT capacity in the river basin, the latter being dependent on environmental policy decisions. We introduce a novel basin-scale evaluation method that considers the evolution of annual pollutant loads at the outlet of the river basin directly as a function of WWT capacity. Based on this approach, we could prove that the load reductions observed after the implementation of WWT in the river basin was a good indicator of the global treatment efficiency of the WWT plants. We also show that high self-purification processes within the river basin may lead to reach minimum levels of OM before the completion of WWT. In addition, the effects of wet weather conditions did also change as a function of the WWT capacity going from positive effects at low capacity to negative effects at high capacity. Finally, the full implementation of WWT in urban river basins does not necessarily guarantee a good status for water quality, mostly because of the high volumetric proportion of treated wastewaters, which do not have the quality standards of river waters.
Asunto(s)
Ríos/química , Aguas Residuales/química , Contaminantes Químicos del Agua/análisis , Purificación del Agua/métodos , Calidad del Agua , Bélgica , Política Ambiental , UrbanizaciónRESUMEN
Environmental models are often over-parameterized. A sensitivity analysis can identify influential model parameters for, e.g. the parameter estimation process, model development, research prioritization and so on. This paper presents the results of an extensive study of the Latin-Hypercube-One-factor-At-a-Time (LH-OAT) procedure applied to the Soil and Water Assessment Tool (SWAT). The LH-OAT is a sensitivity analysis method that can be categorized as a screening method. The results of the sensitivity analyses for all output variables indicate that the SWAT model of the river Kleine Nete is mainly sensitive to flow related parameters. Rarely, water quality parameters get a high priority ranking. It is observed that the number of intervals used for the Latin-Hypercube sampling should be sufficiently high to achieve converged parameter rankings. Additionally, it is noted that the LH-OAT method can enhance the understanding of the model, e.g. on the use of water quality input data.