Abstract
This paper is a progress report on studies whose objectives are to determine methods of analysis that will rate metal sorption and sulfate reduction activity of organic materials for use in passive treatment systems (PTS). Substrates tested include agricultural residues (alfalfa pellets, sugar beat pulp pellets, brewery waste, corncobs, and walnut hulls), inoculums (dairy manure and wetland inoculum), and a variety woods (maple, oak, pine, poplar, and walnut). Characteristics targeted include moisture, organic and nutrient content; water, ethanol and acid soluble and insoluble fractions and metal sorption capacity. The short-term and long-term effects of organic substrate characteristics on metal removal and sulfate reduction rate are being evaluated in batch and column experiments receiving mine water. These data are not presented in this paper but will be included in the oral presentation. Measured values of moisture and organic content ranged from 5.5 to 65% and 7.4 to 95% relative to raw sample weights, respectively. The water-soluble fractions and protein content ranged from 0 to 32% and 2 to 23% relative to dried samples, respectively. Low concentration zinc sorption studies were described well by Freundlich isotherms. Using a wider range of concentrations, manganese sorption to substrates was more closely modeled by Langmuir isotherms. The highest manganese sorption was observed for manure, corncobs, walnut hulls and wetland inoculum (8-13 mg Mn / gram substrate at an equilibrium concentration (Ce) = 50 mg/L Mn). Corncobs and walnut hulls can be included in substrate specifications to target manganese removal. Moisture and organic content are important parameters in the specification of organic substrates as a significant portion of the raw organic substrate weight can be inorganic. A high soluble fraction should correlate with a rapid startup of SRB activity and thus is an important element in substrate specification. All substrates have some capacity for metal sorption and their quantification is essential for use in PTS.
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