Modeling Sulfate-reducing Permeable Reactive Barriers for Treatment of Acid Mine Drainage

The performance of sulfate-reducing permeable reactive barriers (PRB) used for the treatment of acid-mine drainage is critically affected by kinetics of cellulose decomposition and substrate production, as well as by kinetics of sulfate reduction and methanogenesis. When biofilm models are considered, the rate of substrate diffusion into the biofilm also affects performance. In this regard, results from an algorithm adapted to simulate the kinetics of the processes occurring in the PRB environment for the purpose of design and evaluation of PRBs are presented. The processes considered include solid organic-matter decomposition, glucose fermentation to acetate (the microbial substrate), sulfate reduction, precipitation of heavy metals as insoluble sulfides, and methanogenesis. Knowledge of the composition of the reactive mixture within the PRB is a prerequisite for modeling cellulose degradation, especially in terms of parameter estimation. Preliminary modeling results for batch (no-flow) conditions reveal issues of practical importance in the design of sulfate-reducing permeable reactive barriers, such as restrictions in PRB performance due to slow kinetics of cellulose decomposition, and due to competition between sulfate reducers and methanogens for acetate.