TRACKING ORGANIC SUBSTRATE ALTERATIONS IN PASSIVE REACTIVE ZONES FOR PLANNING AND MONITORING

摘要

Microorganisms within passive reactive zones (e.g. wetlands, SR bioreactors, PRB's, etc.) utilize organic substrates, such as wood, in the process of reducing sulfate and immobilizing the metals from mine drainage. The rate and extent of substrate utilization controls the performance and longevity of the passive treatment system. This paper evaluates alterations in substrate composition for four reactive mixtures, over time. The alterations are determined using a method adapted from a sequential extraction technique used to determine carbohydrate and lignin composition in agricultural products. Tracking substrate alterations in this way can be used as a tool for substrate selection as well as evaluation of substrate performance over time. The data collected by tracking organic substrate alterations from pre-operational to post-operational conditions for the four bioreactors can be tied with performance data to better understand the function of the bioreactors. Analysis of the data shows that using total carbon to predict the longevity of passive treatment systems is not enough because the carbon must be in a form that is bioavailable to the microbial community. Analysis also shows that using cellulose to lignin ratios may be useful in the substrate selection process. Tracking substrate alterations over time also allow for the estimation and prediction of substrate utilization that can be correlated with sulfate reduction rates. Applicability of tracking substrate alterations over time is not limited to lab scale bioreactors. It can be used to analyze both spatial and temporal samples for within any passive treatment system to provide valuable insight for the planning and monitoring of passive reactive treatment zones. It can show if the proposed reactive mixture contains carbon in the forms that can be used by the microorganisms. It can also show why a system may be reducing sulfate at a lower than expected rate. Finally, it can help manage the sustainability of the passive treatment system by showing when and if the reactive mixture needs to be refreshed.