Soil remediation using an electrokinetic method

Abstract Remediation of soils contaminated by heavy metals can be accomplished by subjecting the soil to an electric DC field. The heavy metals that are dissolved will move to either the cathode (mostly) or the anode, depending on their charges. The electrical field also induces electro-osmotic flow that can carry uncharged species. Precipitated and sorbed species will dissolve as the solution is depleted. The acid that is generated at the anode can considerably enhance the dissolution. The acid moves toward the cathode and generates a region with high concentration and mobility of the cationic metals. We present the theoretical basis of the method, the results of some remediation experiments, and the results of some numerical simulations that were used to interpret the experimental results. The remediation experiments are supple mented by determinations of the acid neutralization capacity as well as the sorption capacity and sorption distribution constants for the metal ions. These are essential data for the modelling and can be used to assess whether remediation could be accomplished within a reasonable length of time

The role of biofilms in subsurface transport processes

Landfill and radioactive waste disposal risk assessments focus on contaminant transport and are principally concerned with understanding the movement of gas, water and solutes through engineered barriers and natural groundwater systems. However, microbiological activity can affect transport processes, changing the chemical and physical characteristics of the subsurface environment. Such effects are generally caused by biofilms attached to rock surfaces. Currently most existing transport models have to introduce additional assumptions about the relationships between the microbial growth and changes to the porosity and permeability. These relationships are particularly poorly understood. This paper reviews recent experimental work directed at the development of biofilms and their influence on subsurface flow and the transport of contaminants in intergranular and fracture porosity flow systems. The results are then discussed in terms of a more complex conceptual model

The climatic response of thermally integrated photovoltaic–electrolysis water splitting using Si and CIGS combined with acidic and alkaline electrolysis

The Horizon 2020 project PECSYS aims to build a large area demonstrator for hydrogen production from solar energy via integrated photovoltaic (PV) and electrolysis systems of different types. In this study, Si- and CIGS-based photovoltaics are developed together with three different electrolyzer systems for use in the corresponding integrated devices. The systems are experimentally evaluated and a general model is developed to investigate the hydrogen yield under real climatic conditions for various thin film and silicon PV technologies and electrolyser combinations. PV characteristics using a Si heterojunction (SHJ), thin film CuInxGa1−xSe2, crystalline Si with passivated emitter rear totally diffused and thin film Si are used together with temperature dependent catalyst load curves from both acidic and alkaline approaches. Electrolysis data were collected from (i) a Pt–IrO2-based acidic electrolysis system, and (ii) NiMoW–NiO-based and (iii) Pt–Ni foam-based alkaline electrolysis systems. The calculations were performed for mid-European climate data from Jülich, Germany, which will be the installation site. The best systems show an electricity-to-hydrogen conversion efficiency of 74% and over 12% solar-to-hydrogen (STH) efficiencies using both acidic and alkaline approaches and are validated with a smaller lab scale prototype. The results show that the lower power delivered by all the PV technologies under low irradiation is balanced by the lower demand for overpotentials for all the electrolysis approaches at these currents, with more or less retained STH efficiency over the full year if the catalyst area is the same as the PV area for the alkaline approach. The total yield of hydrogen, however, follows the irradiance, where a yearly hydrogen production of over 35 kg can be achieved for a 10 m2 integrated PV–electrolysis system for several of the PV and electrolyser combinations that also allow a significant (100-fold) reduction in necessary electrolyser area for the acidic approach. Measuring the catalyst systems under intermittent and ramping conditions with different temperatures, a 5% lowering of the yearly hydrogen yield is extracted for some of the catalyst systems while the Pt–Ni foam-based alkaline system showed unaffected or even slightly increased yearly yield under the same conditions