Model-based analyses of chromate, selenate and sulfate reduction in a methane-based membrane biofilm reactor: Fid-Bau Portal

Model-based analyses of chromate, selenate and sulfate reduction in a methane-based membrane biofilm reactor

Wang, Zhen / Chen, Xueming / Zhao, He-Ping

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Abstract Selenate (SeO4 ²⁻) and sulfate (SO4 ²⁻) are frequently present together with chromate (CrO4 ²⁻) in certain industrial wastewaters. SeO4 ²⁻ and CrO4 ²⁻ are required to be reduced while SO4 ²⁻ reduction should be minimized to avoid the production of toxic sulfide. In this study, a modified biofilm model was employed to investigate the interactions between CrO4 ²⁻, SeO4 ²⁻ and SO4 ²⁻ bioreduction in a methane (CH4)-based membrane biofilm reactor (MBfR). The model was calibrated using steady-state experimental data of two reported CH4-based MBfRs reducing these oxyanions. The modeling results suggested that the majority of methanotrophs (>80%) were located in the outer layer of the biofilm, while the oxyanions-reducing bacteria preferred to grow close to the membrane. The introduction of SeO4 ²⁻ or SO4 ²⁻ enriched selenate/sulfate-reducing bacteria (SeRB/SRB) but decreased the abundance of chromate-reducing bacteria (CRB). A biofilm thickness of >300 μm, an HRT of higher than 4 h and an influent dissolved oxygen concentration of 0.3 mg /L were favorable for simultaneous high-level CrO4 ²⁻ and SeO4 ²⁻ removal. A two-stage MBfR system with optimized operational conditions showed promise in retaining high-purity (>98%) selenium nanoparticles when treating both CrO4 ²⁻ and SeO4 ²⁻ impacted wastewaters. Moreover, the model indicated that efficient CrO4 ²⁻ removal (>90%) along with minor SO4 ²⁻ reduction (<10%) could be realized via maintaining appropriate biofilm thickness (200-250 μm) and influent dissolved oxygen (0.7–0.8 mg /L) in a single MBfR. These findings offer insights for the design and operation of CH4-based technology for remediating CrO4 ²⁻ contaminated industrial wastewaters.