Bioreactors were developed for the treatment of industrial and mining leachates contaminating surface water  with hexavalent chromium at various locations in  South Africa; this talk will present the performance of the column studies and pilot-scale bioreactors designed and implemented for two of these sites.  The reactors are designed to immobilize the soluble hexavalent chromium via microbial reduction to insoluble trivalent chromium.  The treatment approach involves stimulating the indigenous biome to create anoxic conditions and enhancing bioreduction with the stoichiometrically-balanced addition of electron donor.  At a dolomite stone mine in the Northern Province, the surface water contained up to 8 mg/L hexavalent chromium, while the site in Mpumalanga had ~5.5 mg/L.  Due to the intermittent electrical service in these areas, a key component of the design was to use the water pressure produced by gravity feeding the influent water to run the fixed-film bioreactor filled with porous media, as well as sun panels for power. The contaminated water from each site was characterized geochemically and column studies were conducted to establish the efficacy of the indigenous bacteria,  the choice of matrix to support microbial biofilm formation, as well as the choice of electron donor and its optimal  stoichiometric balance for the reduction.  Three reactor designs were tested: a fixed-film flatbed (PV 23,500 L), a deeper more compact bioreactor (PV 11,500 L) and four upflow-tank bioreactors (PV 9,600 L).  Locally sourced citric acid was used as the electron donor and hydraulic retention time, reactor level, electron donor concentration, ORP, temperature and other chemical parameters were remotely controlled.  In addition to the complete Cr<sup>6+ </sup>removal, the bioreactors could also reduce nitrate concentrations to below the SANS drinking water standard.  The technology at the Mpumalanga site was extended to include a second stage barium carbonate reactor to remove high sulfate concentrations (&gt;2,000 mg/L) from the fly ash leachate, where 90% of this contaminant could be removed with concomitant decreases in EC (15%), TDS (20%), calcium (88%), magnesium (25%) and total hardness (72%) observed.  The successful up-scaling of the laboratory column studies to use fixed film reactors to treat industrial and mining leachates will be discussed.         <br/>

Bioreactors for the treatment of hexavalent chromium at remote locations in South Africa

253rd National Meeting (2017)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.