Role of sulfate in regulating performance and metabolic mechanisms of bioelectrochemical up-flow anaerobic sludge blanket fed with methanolic wastewater

To investigate the impact of sulfate (SO₄²⁻) on the performance of bioelectrochemical up-flow anaerobic sludge blanket (BE-UASB), the COD/SO₄²⁻ ratio of sulfate-containing methanolic wastewater was gradually decreased from 20 to 3. The results showed that BE-UASB maintained higher COD and SO₄²⁻ removal (i.e., 91% and 70%, respectively) with methane production rate of 278.7 mL/L_reactor/d at COD/SO₄²⁻ ratio from 10 to 5, ensuring efficient energy recovery. Sulfidogenesis enabled the sludge re-granulation while bioelectrocatalysis further contributed to the growth/proliferation of biomass with interwoven filaments, rods, and spherical microorganisms. 16 S rRNA gene analysis demonstrated that bioelectrocatalysis promoted the diversity of methane-producing archaea (MPA), including Methanomethylovorans, Methanosaeta, Candidatus_Methanofastidiosum, and Methanobacterium. Sulfate-reducing bacteria (SRB), mainly comprising G_norank_f_Syntrophobacteraceae, Desulfomonile, and Syntrophobacter, tended to be enriched on bioelectrodes, which not only eased the competition with MPA but also achieved simultaneous removal of COD and SO₄²⁻ in synergy with MPA.