Kinetics of Acidic Macrocapsules in Controlling the pH of Groundwater

Abstract

The effectiveness of novel acidic macroencapsulated buffers in controlling pH was evaluated in batch experiments and through detailed mathematical modeling. When exposed to a high pH solution, the macrocapsules decreased the pH to 7.5. A batch model accounting for detailed chemical equilibria was developed and used to extract the macrocapsule release kinetics within a simulated annealing algorithm. The model predicted the change in pH of the batch solutions well. The batch model was incorporated within a two-dimensional mathematical model coupling transport (convection/dispersion) and fate (including chemical reactions) of chemical species and chemical equilibrium to study the potential use of the macrocapsules in controlling pH of the groundwater in a horizontal field domain. The model was used to simulate three scenarios (reaction throughout a domain with subsequent release of base equivalents, reaction within a reactive layer with a constant release of base equivalents, and a combination of the first two scenarios), with macrocapsules added through point sources and line source. Macrocapsules are more effectively deployed as a line source as shown by the improved removal efficiency of a target contaminant. Effective life of the macrocapsule was 6 to 10 months under the conditions of the simulations.