Chromium(VI) bioaccumulation capacities of adapted mixed cultures isolated from industrial saline wastewaters

Enrichment mixed cultures tolerating relatively high concentrations of chromium and salt ions were isolated and their bioaccumulation properties improved by adaptation. Mixed cultures were enriched in Nutrient Broth media containing 25–300 mg l−1 Cr(VI) and 0%, 2%, 4%, 6% (w/v) NaCl. Bioaccumulation of Cr(VI) was studied in a batch system as a function of initial pH (7, 8 and 9), Cr(VI) and NaCl concentrations. Increasing NaCl and Cr(VI) concentrations led to significant decreases in percentage uptake and dried weight of mixed cultures but increased maximum specific chromium uptake. The maximum specific chromium uptake value at pH 8 was 58.9 mg g−1 for 316.1 mg l−1 Cr(VI) in the absence of NaCl, while at pH 9 it was 130.1 mg g−1 in media including 194.5 mg l−1 Cr(VI) and 2% NaCl concentrations. At 4% NaCl, the maximum Cr(VI) uptake of 127.0 mg g−1 for 221.1 mg l−1 Cr(VI) occurred at pH 9, while at 6% NaCl the maximum Cr(VI) uptake of 114.9 mg g−1 for 278.1 mg l−1 Cr(VI) was found at pH 7.