Response of a packed-bed, fixed-film bioreactor to zinc toxicant

An anaerobic, upflow bioreactor was fed a zinc chloride and nutrient solution, and the response of the bioreactor was monitored over a two-week period. The main objectives of this project were to assess the biological performance of the bioreactor in response to zinc toxicant and to determine the capability of the column for zinc removal. A step-input of Zn/sup + +/ (100 mg/l) was added to a synthetic waste being fed to a bench-scale unit at a superficial velocity of 0.034 cm/min. This column, which had previously been operating at steady-state conditions, was operated simultaneously with an identical column to which Zn/sup + +/ had not been added. The test was conducted for 320 h, or five hydraulic residence times. More than 95% of the zinc entering the column was removed by the reactor. Inhibition of anaerobic processes, including gas production, was noted, but the bioreactor was apparently retuning to the expected performance level toward the end of the two-week testing period. Zinc accumulated mostly in lower regions of the bioreactor, with biological processes decreasing in that region but shifting to higher regions in the column after a delay period. The tolerance level of the column to zinc could notmore » be estimated during the relatively short testing period.« less