[Characteristics of Denitrification Inhibiting Sulfate Reducing Process]

Area of Science:

• Environmental microbiology
• Wastewater treatment
• Bioreactor technology

Background:

• Oil field gathering and transportation systems generate high-salt wastewater requiring effective treatment.
• Sulfate reduction by sulfate-reducing bacteria (SRB) leads to sulfide production, causing environmental and operational issues.
• Denitrification is a potential strategy to inhibit sulfate reduction.

Purpose of the Study:

• To investigate denitrification inhibiting sulfate reduction in high-salt wastewater using a two-stage UASB reactor.
• To characterize the granular sludge and microbial community under denitrification inhibition.
• To determine the optimal conditions for inhibiting sulfate reduction and sulfide production.

Main Methods:

• Utilized a two-stage Upflow Anaerobic Sludge Blanket (UASB) reactor.
• Introduced sodium nitrite (NaNO2) to promote denitrification.
• Analyzed microbial populations using colony counting and Polymerase Chain Reaction-Denaturing Gradient Gel Electrophoresis (PCR-DGGE).
• Measured granular sludge properties (particle size, sedimentation velocity) and sulfate reduction inhibition rates.

Main Results:

• Addition of NaNO2 significantly increased denitrifying bacteria (DNB) and decreased sulfate-reducing bacteria (SRB).
• Sulfate reduction was inhibited, with an overall inhibition rate stabilizing at 82%, and sulfide (S2-) inhibition reaching 92% at a specific microbial mass to nitrite ratio.
• Denitrification inhibition promoted the formation of larger, denser granular sludge with good settling velocity (47.6 m·h-1).
• Microbial diversity decreased, with a shift in dominant species from SRB to autotrophic denitrifying bacteria, notably uncultured *Sulfurimonas* sp.

Conclusions:

• Denitrification effectively inhibits sulfate reduction and sulfide production in high-salt wastewater.
• The process favors the growth of denitrifying bacteria over sulfate-reducing bacteria, leading to a shift in microbial community structure.
• The formation of robust denitrifying granular sludge with favorable settling properties is enhanced under these conditions.