Abstract: Sulfate reducing passive bioreactors are increasingly being used to remove metals and raise the pH of acidic waste streams from abandoned mines. These systems commonly use a variety of organic substrates (i.e. manure, wood chips) for sulfate reduction. The effectiveness of these systems decreases as easily accessible reducing equivalents are consumed in the substrate through microbial activity. Using column studies at room temperature (23-26 degrees C), we investigated the addition of lactate and methanol to a depleted manure substrate as a method to reactivate a bioreactor that had lost >95% of sulfate reduction activity. A preliminary experiment compared sulfate removal in gravity fed, flow through bioreactors in which similar masses of each substrate were added to the influent solution. Addition of 148 mg/l lactate resulted in a 69% reduction in sulfate concentration from 300 to 92 mg/l, while addition of 144 mg/l methanol resulted in an 88% reduction in sulfate concentration from 300 to 36 mg/l. Because methanol was found to be an effective sulfate reducing substrate, it was chosen for further experiments due to its inherent physical properties (cost, low freezing point and low viscosity liquid) that make it a superior substrate for remote, high elevation sites where freezing temperatures would hamper the use of aqueous solutions. In these column studies, water containing sulfate and ferrous iron was gravity-fed through the bioreactor columns, along with predetermined methanol concentrations containing reducing equivalents to remove 54% of the sulfate. Following an acclimation period for the columns, sulfate concentrations were reduced from of 900 mg/l in the influent to 454 mg/l in the effluent, that reflects a 93% efficiency of electrons from the donor to the terminal electron acceptor. Iron concentrations were reduced from 100 to 2 mg/l and the pH increased nearly 2 units. (C) 1999 Elsevier Science Ltd.

Abstract: The aim was to assess over 2 years the treatment efficiencies of vertical-flow wetland filters containing macrophytes and granular media of different. adsorption capacities. Different concentrations of lead and copper sulfate (constant for 1 year each) were added to urban beck inflow water in order to simulate pretreated (pH adjustment assumed) mine wastewater. After 1 year of operation, the inflow concentrations for lead and copper were increased from 1.30 to 2.98 and from 0.98 to 1.93 mg/L, respectively. However, the metal mass load rates (mg/m(2)/d) were increased by a factor of approximately 4.9 for lead and 4.3 for copper. No breakthrough of metals was recorded. Lead and copper accumulated in the biomass of the litter zone and rhizomes of the macrophytes. Furthermore, microbiological activity decreased during the second year of operation. Bioindicators such as ciliated protozoa and zooplankton decreased sharply in numbers but diatoms increased. In conclusion, the use of macrophytes and, adsorption media did not significantly enhance the filtration of lead and copper. Particulate lead is removed by filtration processes including straining. Furthermore, some expensive and time-consuming water quality variables can be predicted with less expensive ones such as temperature in order to reduce sampling costs.