Successful sulphide-driven partial denitrification: Efficiency, stability and resilience in SRT-controlled conditions

Area of Science:

• Environmental biotechnology
• Wastewater treatment
• Biogeochemical cycles

Background:

• Partial denitrification is crucial for supplying nitrite to Anammox systems.
• Sulfide-driven Partial Autotrophic Denitrification (PAD) integrates autotrophic nitrogen and sulfur removal.
• Optimizing PAD requires understanding the interplay of electron donor supply and operational parameters.

Purpose of the Study:

• To maximize nitrate (NO3-) reduction to nitrite (NO2-) coupled with complete sulfide (HS-) oxidation.
• To investigate the synergistic effects of influent S/N ratio and sludge retention time (SRT) on PAD performance.
• To characterize the microbial community and assess N2O emission potential.

Main Methods:

• Operation of a 2.5-L chemostat for 115 days under varying SRT (40, 23, 13 h) and S/N ratios (0.5-1 gS/gN).
• Respirometric tests to evaluate nitrate and nitrite uptake rates.
• Metabarcoding analysis to determine microbial community composition.

Main Results:

• Achieved high average NO2- conversion efficiencies of 77±17%, with a maximum of 99% at a S/N ratio of 0.58 gS/gN and SRT of 23 h.
• Stable NO3- uptake rates (90±10 mgN/gVSS/h) were observed, while NO2- uptake was sensitive to conditions.
• Microbial community was dominated by Sulfur Oxidizing Bacteria (>80%), with Thiobacillus favored under S-limiting conditions.

Conclusions:

• Sulfide-driven PAD is effective for nitrite production in Anammox systems.
• Optimized S/N ratio and SRT are critical for maximizing NO2- accumulation and efficiency.
• The study provides insights into microbial community dynamics and N2O emission potential in enhanced wastewater treatment processes.