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RESPIROMETRY AS A TOOL TO DETERMINE METAL TOXICITY IN A SULFATE REDUCING BACTERIAL CULTURE
Citation:
Holder, E., M. J. Kupferei, H H. Tabak*, AND J R. Haines*. RESPIROMETRY AS A TOOL TO DETERMINE METAL TOXICITY IN A SULFATE REDUCING BACTERIAL CULTURE. Presented at Society for Environmental Toxicology and Chemistry, Salt Lake City, UT, 11/16-20/2002.
Description:
A novel method under development for treatment of acid mine drainage waste uses biologically- generated hydrogen sulfide (H2S) to precipitate the metals in acid mine drainage (principally zinc, copper, aluminum, nickel, cadmium, arsenic, manganese, iron, and cobalt). The insoluble sulfides are sequentially removed via settling. The resulting effluent is fed to a biological reactor containing sulfate reducing bacteria (SRB) to effect removal of the sulfate acidity and to generate the needed H2S. The functioning of this biological reactor can be affected by metal toxicity so determining those toxic levels alone and in the waste matrix is important.
An enrichment culture of sulfate reducing bacteria was developed from sediment. This culture utilizes bicarbonate as the carbon source and hydrogen gas (H2) as the electron donor for the conversion of sulfate to H2S. Respirometers (NCON Systems Inc.) were adapted to measure hydrogen uptake instead of oxygen. Instrument tubing was replaced with FEP-lined Tygon to minimize loss of H2 in the system. Hydrogen uptake by SRBs is similar to the uptake of oxygen in aerobic cultures in that equimolar quantities of another gas are produced, H2S in the former case and carbon dioxide (CO2) in the latter. Produced H2S is removed with a zinc acetate trap, analogous to an alkaline trap in classical respirometry, but allowing for the retention of CO2 in the headspace.
Suppression of H2 uptake or increased lag time relative to a control without the target metal is considered an indication of metal toxicity. A major problem with toxicity determinations is that most bacteriological media contain components which can form metal complexes reducing its bioavailability and as a result, its toxicity. The culture media formulated by Sani et al. (Advances in Environmental Research 5 (2001) 269-276) was modified for use with this culture. Metal complexation was reduced by replacing orthophosphate with tryptone to provide necessary phosphorus and PIPES, an organic buffer, for pH control.
Quadruplicate respirometer bottles at six metal concentrations are being used to test zinc and copper toxicity. Respirometry data, metal, sulfate, and sulfide concentrations, headspace gas determinations for CO2 and H2S, and most probable number (MPN) of SRB will be presented.