Rapid start-up sulfur-driven autotrophic denitrification granular process: Extracellular electron transfer pathways...

Area of Science:

• Environmental microbiology
• Wastewater treatment technologies
• Biogeochemical cycles

Background:

• Sulfur-driven autotrophic denitrification (SAD) is effective for low-carbon wastewater but suffers from slow sulfur-oxidizing bacteria (SOB) growth, leading to long start-up times.
• Optimizing SOB enrichment is crucial for accelerating SAD processes and improving efficiency.

Purpose of the Study:

• To investigate a strategy for rapid in-situ enrichment of SOB in granular sludge.
• To evaluate the feasibility of switching electron donors from thiosulfate to elemental sulfur in autotrophic denitrification.
• To analyze the impact of this strategy on granule structure, extracellular electron transfer (EET), and microbial community composition.

Main Methods:

• Initiation of thiosulfate-driven autotrophic denitrification (TAD) using anaerobic granular sludge inoculation.
• Gradual transition of electron donor from thiosulfate to elemental sulfur under a high nitrogen loading rate (176.2 g N m⁻³ d⁻¹).
• Analysis of granule structure (protein secondary structure), extracellular electron transfer pathways, and microbial community composition (dominant genera).

Main Results:

• Successful initiation of TAD within 7 days and transition to elemental sulfur by Day 32.
• Stable, compact granule structures were maintained with specific protein secondary structure ratios.
• Shift in EET pathway from indirect to direct upon switching to elemental sulfur, with thiosulfate enhancing EET enzyme activity.
• Identification of dominant bacteria: Thiobacillus and Sulfurimonas in TAD, and Longilinea enriched during elemental sulfur-driven autotrophic denitrification.

Conclusions:

• The proposed strategy effectively enriches SOB in situ, significantly shortening the start-up duration for sulfur-driven autotrophic denitrification.
• The successful switch to elemental sulfur demonstrates a cost-effective approach for wastewater treatment.
• Understanding EET mechanisms and microbial dynamics provides insights for optimizing granular sludge processes.