Direct Cr (VI) bio-reduction with organics as electron donor by anaerobic sludge

• Highest direct Cr(VI) bio-reduction activity is achieved at pH 8.0.
• Direct Cr(VI) bio-reduction activity decreased with increased Cr(VI) concentration.
• Direct Cr(VI) bio-reduction rate is slower than the indirect one.
• Direct Cr(VI) bio-reduction at 1.0 mg Cr (VI)/L/h is demonstrated in UASB reactor.
• Desulfovibrio, Ochrobactrum and Anaerovorax cause direct Cr(VI) bio-reduction.