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.~ of < 100 mg/1 have been more typically treated (Canby, 1993; Altringer, et al, 1992). At initial wad cyartide levels of <50 mg/l, treated levels of <0.50 mg/I aze achievable, with treated levels of <0.20 mg/1 being reported. An initial growth and acclimation period of 10- 15 days is usually needed, along with a degradation period ranging from 10-15 days. For design purposes, a conservarive total retention time for growth, acclimation, and degradation on the order of 20-30 days is recommended for the configuration of the Biopass System. The cyanide would be utilized for energy production, as well as a source of carbon. In the case of the removal of monovalent and divalent metal cations through sorption and sulfide precipitation, an efficiency of 95 percent is reasonable based upon data gathered from bench, pilot, and full scale sulfate reduction systems. Removal efficiencies of up to 99 percent have been reported. A conservative removal efficiency of 50 percent is anticipated for selenium and sulfate, although higher removal efficiencies up to 75 percent have been reported. With an average air temperature in the fifties and an N-situ biochemical system, bacterial degradation and reduction should proceed without climate inhibition. The levels of sulfate, nitrate, metals, and cyanide present in the drainage would be within ranges that have been treated in bench, pilot, and full scale anaerobic systems. 4.0 LABORATORY EVALUATION OF THE BIOPASS SYSTEM In order to evaluate the performance of the Biopass System on a more quantitative basis, a long-term continuous flow laboratory study was conducted. The study involved a series of six columns, each filled with a different organic material and fed barren solution taken from a mining operation in Nevada. The analysis of the various barren solutions contained straw only and served as a con[rol. The second, third, and fourth columns contained a composed cow manure. The difference between these colurtuts -11- was based upon the hydraulic retention times used and whether or not the organic material had been microbially seeded prior to its placement in the column. The fifth and sixth columns contained much more expensive mushroom compost or peat mixed with manure. The organic material placed in colutrms 2 through 6 was mixed with 5% straw to provide additional surface for bacterial attachment and [o minimise COmpaCC10R. The clear Plexiglas columns were six inches in diameter and eigh[ feet in height. A positive displacement pump was used to feed the columns at such a rate to create a fifreen to thirty day empty bed retention period. The seeding of columns 1, 3, 4, 5, and 6 was accomplished by spraying the organic matter prior to its placement within [he column with a mix[ure of solutions collected from various process ponds and soils from around the mine site. The six colutnns were sealed to exclude air, with the effluent from each column reporting to a closed container adjacent to the top of each column [o aid in the removal of off- gases, such as hydrogen sulfide. The presence and/or absence of sulfate reducing, general anaerobic, and denitrification bacterial populations were monitored on a semi- quantita[ive basis with the use of Hach Chemical microbial growth kits. The results of the analyses indicated that large populations of all three of these bacterial types were present in the effluent from the columns. Once the cofutruu filled with barren solutions and effluent began appearing, solution samples were collected for analysis. The results of those analyses are presen[ed in Table 1. As shown in Table 1, the straw column was the least effective in removal of the constituents of interest. The remainder of the columns provided very high levels of treatment of cyanide, mos[ metals, and nitrate, with removal efficiencies exceeding 90% in many instances. The effluent concentra[ions of cyanide, copper, mercury, selenium and nitrate were reduced [o below drinking water standards. The removal