New insight into waste activated sludge acetogenesis triggered by coupling sulfite/ferrate oxidation with sulfate reduction-mediated syntrophic consortia

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Abstract

Acetate (HAc) production via acetogenesis is a promising biorefinery approach
for waste activated sludge (WAS); however, it is hampered by the thermodynamic
constraints of the bioconversion of 3-5 carbon atom short-chain fatty acids (SCFAs). Sulfate radical (SO4∙‾)-based advanced oxidation is regarded as an appropriate
candidate for accelerating WAS fermentation. In this study, we enriched an
incomplete-oxidative sulfate reducing bacteria (io-SRB), combined with SO4∙‾
oxidation (generated by potassium ferrate (PF) and sodium sulfite (Na2SO3)), to boost WAS acetogenesis. Generated sulfate during SO4∙‾ oxidation served as the necessary substrates for io-SRB metabolism. A proof-of-concept based on experimental data for the whole process is presented. Results confirmed that the PF+Na2SO3+SRB test achieved the maximum SCFAs generation (4261 ± 210 mg COD/L with 60.9 ± 0.5% HAc) over the PF+Na2SO3 test without io-SRB mediation (2521 ± 109 mg COD/L with 50.6 ± 0.3% HAc). Particle size analysis and fluorescence spectroscopy indicated that PF+Na2SO3 oxidation had positive effects on accelerating soluble organics release. SO4∙‾ was the key radical, playing the most important role, as indicated by electron paramagnetic resonance and radical scavenging analysis. X-ray photoelectron spectroscopy revealed that io-SRB mediation further promoted the transformation of polysaccharides and proteins into carboxylic acids, based on SO4∙‾ oxidation. Moreover, 79% Fe(VI) was reduced to Fe(III), and most S(IV) was converted to SO4
2-, approximately 40% of which was metabolized by io-SRB consortium. Clearly, SO4∙‾ oxidation and io-SRB stimulation significantly altered the composition of the key microbiome, with fermentative acidogenic bacteria predominating. The possible synergistic relationships among io-SRB, hydrolyzing bacteria and acidogens were revealed by molecular ecological network analysis. This study provides new insights 3 into the improvement of value-added bio-metabolite recovery from SO4∙−-based WAS fermentation.
Original languageEnglish
Article number125885
JournalChemical Engineering Journal
Volume400
ISSN1385-8947
DOIs
Publication statusPublished - 15 Jun 2020

Keywords

  • Acetogenesis
  • Microbial interaction
  • Sulfate radical
  • Sulfate reducing bacteria
  • Waste activated sludge

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