Citation:

Tabak*, H H. AND R. Govind. ADVANCES IN BIOTREATMENT OF ACID MINE DRAINAGE AND BIORECOVERY OF METALS: 2. MEMBRANE BIOREACTOR SYSTEM FOR SULFATE REDUCTION. B.E. Rittmann (ed.), BIODEGRADATION. Kluwer Academic Publishers, Hingham, MA, 14(6):437-452.

Description:

Acid-mine drainage (AMD) is a severe pollution problem attributed to past mining activities. AMD is an acidic, metal-bearing wastewater generated by the oxidation of metal sulfides to sulfates by Thiobacillus bacteria in both the active and abandoned mining operations. The wastewaters contain substantial quantities of dissolved solids with the particular pollutants (metal sulfates) dependent upon the mineralization occurring at the mined rock surfaces. The exposure of post-mining residuals to water and air results in a series of chemical and biological oxidation reactions that produce an effluent which is highly acidic and contains high concentrations of various metal sulfates. The metals (metal sulfates) usually encountered and considered of concern for human risk assessment are: arsenic, cadmium, iron, lead manganese, zinc, and copper. These metals as well as sulfate are considered serious pollutants of the acid mine drainage. The pollution generated by abandoned mining activities in the area of Butte, Montana has resulted in the designation of the Silver Bow Creek-Butte area known as Berkeley Pit, the largest superfund (National Protection List) site in the U.S. This paper reports on bench-scale studies conducted to develop a biotreatment method for acid mine water (AMW) using membrane bioreactor systems to maximize the biological sulfate conversion rate and thus enhance the bioremediation of acid mine water from Berkeley Pit as well as other acidic water pit lakes.
Several biotreatment techniques for the treatment of sulfate reducing bacteria (SRB) have been proposed in the past, however few of them have been practically applied to treat sulfate containing AMD. This research deals with the development of an innovative polypropylene hollow fiber membrane bioreactor system for the treatment of AMW from the Berkeley Pit lake using hydrogen consuming SRB biofilms. The advantages of using the membrane bioreactor over the conventional tall liquid phase, gas sparged bioreactor systems are: large microporous membrane surface to the liquid phase; formation of hydrogen sulfide outside the membrane thus preventing mixing with pressurized hydrogen gas inside the membrane; no requirement for gas recycle compressor for hydrogen; membrane surface is suitable for immobilization of active SRB, resulting in formation of biofilms, thus preventing washout problems associated with suspended culture reactors; and lower operating costs in membrane bioreactors, eliminating gas recompression and gas recycle costs. Information will be provided on sulfate reduction rate studies and on biokinetic tests with suspended SRB in anaerobic sludge and sediment source master culture reactors and with SRB biofilms in bench-scale SRB membrane bioreactors. Biokinetic parameters have been determined using biokinetic models for the master culture and membrane bioreactor systems. Data will be presented also on the effect of AMW sulfate loading at 25, 50, 75 and 100 ml/min in scale-up SRB membrane units, under varied temperatures (25, 35 and 40 degrees C), to determine and optimize sulfate conversion for an effective AMD biotreatment. Pilot-scale studies have generated data on the effect of flow rates of AMW (in MGD) and varied inlet sulfate concentrations in the influents on the resultant outlet sulfate concentration in the effluents and on the number of SRB membrane modules needed for the desired sulfate conversion rates. The pilot-scale data indicate that SRB membrane bioreactor systems can be applied toward field-scale biotreatment (sulfate conversion) of AMW from Berkeley Pit lake as well as from other acidic water pit lakes and for a recovery of high purity metals and a usable water from the AMW wastes.

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