Model-based assessment of chromate reduction and nitrate effect in a methane-based membrane biofilm reactor

Abstract

Chromate contamination can pose a high risk to both the environment and public health. Previous studies have shown that CH₄-based membrane biofilm reactor (MBfR) is a promising method for chromate removal. In this study, we developed a multispecies biofilm model to study chromate reduction and its interaction with nitrate reduction in a CH₄-based MBfR. The model-simulated results were consistent with the experimental data reported in the literature. The model showed that the presence of nitrate in the influent promoted the growth of heterotrophs, while suppressing methanotrophs and chromate reducers. Moreover, it indicated that a biofilm thickness of 150 μm and an influent dissolved oxygen concentration of 0.5 mg O₂/L could improve the reactor performance by increasing the chromate removal efficiency under the simulated conditions.

Keywords: Aerobic methane oxidation; Chromate reduction; Membrane biofilm reactor; Model analysis; Nitrate effect.

Graphical abstract

Fig. 1

The electron flow in microbial processes considered in this model.

Fig. 2

The concentrations and fluxes of chromate and nitrate from experiments and the model.

Fig. 3

Biomass concentration distribution and composition of solid species in the steady-state biofilm for stage 4 (A&D, without nitrate), stage 5 (B&E, 24 mg/L·d of nitrate loading), and stage 6 (C&F, 7.3 mg/L·d of nitrate loading).

Fig. 4

Effluent nitrate and Cr(VI) concentrations under different biofilm thicknesses (A), and biomass distribution under two sample biofilm thicknesses (B: 100 μm; C: 500 μm).

Fig. 5

Effluent nitrate and Cr(VI) concentrations under various influent DO concentrations (A), and biomass distribution under two sample influent DO concentrations (B:0.5 mg-O₂/L; C:1 mg-O₂/L).

Fig. 6

Reactor performance under various combinations of chromate and nitrate loading rates (A: chromate removal efficiency, B: nitrate removal efficiency).