Sulfate-reducing ammonium oxidation (SRAO) is an emerging anaerobic autotrophic nitrogen removal process that combines ammonium oxidation with sulfate reduction. However, it faces some challenges, such as the slow growth of autotrophic microorganisms, weak synergistic interaction between different microorganisms, and poor substrate transfer capability. Herein, graphene oxide (GO) was added to a lab-scale bioreactor to promote SRAO reaction, and its effect on nitrogen removal was systematically investigated. The results demonstrated that GO served not only microbial carriers but also electron shuttles, which were conducive to microbial spatial distribution and better electron transfer, improving the sulfur cycle-driven multi-pathway nitrogen removal performance. The addition of 50 mg/L GO not only enhanced the SRAO activity and increased the ammonium removal efficiency by 24.7%, but also reduced the effluent nitrite concentration and promoted nitrogen production. After reaction, the main functional groups on the surface of GO had been changed, and the composite aggregates of microorganisms were formed. Mass balance analysis revealed that SRAO was the dominant pathway, while Anammox and sulfur-autotrophic denitrification (SADN) played complementary roles. Moreover, after adding GO, the relative abundances of Desulfosarcinaceae and Bacillus, which were functional microorganisms in the SRAO reaction, were increased by 35.7% and 58.5%, respectively. This study will provide an in-depth understanding of the mechanisms for nitrogen removal in the SRAO bioreactor.
Yao et al. (Mon,) studied this question.