Suchergebnisse

Increasing volumes of waste sludge, an intense environmental awareness and stringent legislation impose increasing demands upon conventional sludge dewatering equipment. In this study, the electrokinetic dewatering of waste slurries is studied. Full-scale electrokinetic facilities were developed that were based on a combination of a gravity-driven thickening belt and a belt press. The method was tested at a drinking water production site. By the use of the electrokinetic facility when drying `aluminum-coagulated' drinking water sludge (i.e. coagulated by the addition of Al-ions), the dry solids content increased by electro-osmosis from 17 to 24% m/m at an additional energy consumption level of 60 kWh per ton dry solids. Additionally, the filter belt fouling was reduced drastically and the loss of solid particles from the cake was almost completely suppressed due to electrophoresis. Corrosion of the anode was effectively suppressed by using Ir2O3-coated titanium plates. Supplementary laboratory experiments suggest that electrokinetic dewatering is also useful in dewatering `iron-coagulated' drinking water sludge, sewage treatment sludge and fresh water dredging sludge. Theoretical analyses indicate that electro-osmosis will contribute to dewatering significantly, at lower and especially at higher volume fractions of solids, provided the slurry particles are of the order of micrometers or smaller. Under such conditions the conventional dewatering is slow due to excessive hydrodynamic resistance.

The paper presents results of the research on the influence of electrokinetic characteristics of fluids on its flow in porous media. Experimental studies have shown the effect of fluid slippage in the channels of porous media due to the electrically charged boundary "liquid-porous medium". It is shown that the change of flow velocity profile and pressure gradient is caused by the display of electrokinetic effects in the filtration of polar liquids.The investigation has shown that the process of the electrolyte solutions filtration in a porous medium is accompanied by the change in the liquid flow rate and the electro-potential of the flow. The periodic nature of changes in flow characteristics is explained by continuous charge formation and charge interaction in the diffuse layer. Periodic charge accumulation and subsequent charge transfer across the channel cross section depending on the charge sign acquired, as well as compression of the diffuse layer with increasing NaCl electrolyte concentration in aqueous solution may be the cause of fluid flow variations. The observed effects may serve as a tool for controlling fluid flow in water-oil-saturated formations and, in particular, injectivity of injection wells by controlling electrical conductivity of water injected into the formation.

A mathematical model for reactive-transport processes in porous media is presented. The modeled system includes diffusion, electromigration and electroosmosis as the most relevant transport mechanism and water electrolysis at the electrodes, aqueous species complexation, precipitation and dissolution as the chemical reactions taken place during the treatment time. The model is based on the local chemical equilibrium for most of the reversible chemical reactions occurring in the process. As a novel enhancement of previous models, the local chemical equilibrium reactive-transport model is combined with the solution of the transient equations for the kinetics of those chemical reactions that have representative rates in the same order than the transport mechanisms. The model is validated by comparison of simulation and experimental results for an acid- enhanced electrokinetic treatment of a real Pb-contaminated calcareous soil. The kinetics of the main pH buffering process, the calcite dissolution, was defined by a simplified empirical kinetic law. Results show that the evaluation of kinetic rate entails a significant improvement of the model prediction capability. ; This work has received funding from the European Union's Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No. 778045. Part of this work was supported financially by the European Commission within the project LIFE12 ENV/IT/442 SEKRET "Sediment electrokinetic remediation technology for heavy metal pollution removal". Paz-Garcia acknowledges the financial support from the "Proyecto Puente - Plan Propio de Investigación y Transferencia de la Universidad de Málaga", code: PPIT.UMA.B5.2018/17. Villen-Guzman acknowledges the financial support from the University of Malaga through a postdoctoral contract.