Sulfate Reduction-Mediated Syntrophic Microbiomes Accelerated Waste-Activated Sludge Fermentation on the Basis of SO₄^•– Oxidation and Eliminated Superfluous Sulfate

Sulfate radical (SO₄^•–) based advanced oxidation (E° = 2.43 V_NHE), as a new research hotspot, has been proven to be effective for waste-activated sludge (WAS) disintegration prior to anaerobic fermentation; however, it is still limited by the generated superfluous sulfate in practice. This study explores a novel strategy, i.e., coupling persulfate (PDS) oxidation with sulfate reducing bacteria (SRB) mediated syntrophic microbiomes, to enhance WAS fermentation, especially for the acetogenesis step. Experimental results showed that coupling treatment clearly enhanced short-chain fatty acids (SCFAs) production (393.7 ± 28.0 mg of chemical oxygen demand (COD)/g of volatile suspended solids (VSS) with 63.2 ± 0.7% acetic acid (HAc)), which increased 43.0 mg of COD/g of VSS (24%) over the sole PDS group. PDS oxidation clearly enhanced WAS disintegration and sulfate radical (SO₄^•–) was the key radical that played important role by radical scavenging and electron paramagnetic resonance analysis. Thermodynamic analysis showed the introduction of SRB consortia was more beneficial for acetate conversion during the acetogenesis by having a much lower ΔG⁰. The mechanism of coupling treatment was supported as well by the distribution of functional microbiomes, with fermenters predominating (36.1%), followed by 2.4% of SRB and 1.3% of hydrogen-producing acetogen (HPA). The possible synergetic relationships among fermenters, homoacidogen, HPA, and SRB were revealed by molecular ecological network analysis. This study provides a scientific basis for the potentially practical technology for value-added biometabolite recovery from SO₄^•–-based mixed-culture WAS fermentation.