EXPERIMENTAL PROTOCOLS FOR ESTIMATING THE DESIGN PARAMETERS OF PERMEABLE REACTIVE BARRIERS”; Classification VERY GOOD
Permeable Reactive Barriers (PRB’s) became recently a consistent technological option, economically attractive, for the removal and/or transformation of the contaminants transported by groundwater, being specially used for the deshalogenation of the chlorinated organic compounds and for the removal of heavy metals transported as anionic complexes. They consist in a relatively porous barrier, with permeability higher than that of the aquifer, being constructed in the subsoil in a direction normal to the groundwater flow. They are constituted by inert materials and by a reactive element added in a granular form, being the granular metallic iron the most common. When the contaminants flow across the barrier they are transformed into environmentally innocuous compounds, generally by oxidation and reduction reactions with the reactive material. It is also possible to construct biologically mediated barriers, being in this case the redox reactions caused by the biological activity of microorganisms.
It is aimed in this project to establish experimental protocols which will allow estimate the essential parameters for designing barriers which use zero valence granular iron, namely
- Kinetic rates of degradation (by redox reactions) of the halogenated organic compounds;
- Kinetic rates of transformation of the descents chemical compounds (for instance kinetic rate of transformation of TCE in DCE, of DCE in VC, and final transformation to ethene);
- Determination of the iron consumption in the main and in the secondary reactions, specially the iron oxidation by the oxygen dissolved in water);
- For the metallic anions the formation of solid solutions inside the barrier will be studied and the consequences of its occlusion will be quantified through the variations in the permeability;
- Effects of some initial physical parameters of the barrier, such as its initial permeability and the size distribution of the inert material, in the overall process efficiency and its reflex as parameters affecting the design.
An experimental device, constituted by several columns sectionalized by adjustable segments, allowing the simulation of different lengths for the barrier and also allowing intermediated sampling, will be built. The composition of water in the main contaminant and its chemical descendents will be analyzed, as well as the iron concentration.