An exploratory study on the aqueous Cr(VI) removal by the sulfate reducing sludge-based biochar

Biological sulfate reduction has been demonstrated to be a promising biotechnology for the sulfate-laden wastewater treatment. However, the excessive waste sulfate reducing sludge needs further disposal and treatment. In this study, the sulfate reducing sludge was firstly utilized as the raw materials and pyrolyzed at 500celcius under oxygen-limited condition for biochar (marked as SBC-500) fabrication. And the application of SBC-500 for Cr(VI) removal was explored herein. Meanwhile, the normal anaerobic sludge derived from anaerobic digester in a sewage treatment plant was also employed to produce biochar as the control (marked as BC-500). Batch experiments for Cr(VI) removal were performed under different biochar dosages, pH and initial Cr(VI) concentrations. The results indicated that the SBC-500 was superior to BC-500 in terms of pore volume and specific surface area as well as the Cr(VI) removal performance. The Cr(VI) removal efficiency by SBC-500 could achieve 97.31% within 24 h (pH of 3.0, 0.5 g biochar dosage, 30 mg Cr(VI)/L). Langmuir isotherm model and pseudosecond-order kinetic model were determined to the Cr(VI) removal process. In the presence of SBC-500, the Cr (VI) in the aqueous phase was removed synergistically by the chemisorption with reduction of Cr(VI) to Cr(III). The SBC-500 still exhibited a satisfactory Cr(VI) removal with the efficiency of 91.98% after five cycles of adsorption-desorption. Thus, the results of this study may shed light on a new approach for simultaneous economical sulfate reducing sludge disposal and the sustainable remediation of the Cr(VI)-contaminated wastewater.

Automated summary

This study utilized sulfate reducing sludge to fabricate biochar for Cr(VI) removal, and found that SBC-500 outperformed BC-500 with a removal efficiency of 97.31%. The results suggest a new approach for cost-effective disposal of sulfate reducing sludge and sustainable remediation of Cr(VI)-contaminated wastewater.