An electrolyte from used lead-acid car batteries was treated using a consortium of sulfate-reducing bacteria taken from a municipal wastewater treatment plant. The process was carried out in a pilot plant consisting of 7 reactors. Atter initial alkalization with NaOH or Na2CO3 and sepn. of the ppt., a biol. sulfate redn. process was carried out in the presence of a bacterial inoculum at 30-37 degrees C and pH 6.25. During the process, metals pptd. in the form of sparingly soluble sulfides, which could be used as a source of metals.