An integrated strategy for sequential nitrite removal and methane recovery: Sludge fermentation driven by nitrite...

Area of Science:

• Environmental microbiology
• Biotechnology
• Anaerobic digestion

Background:

• Sludge treatment with free nitrous acid recovers short-chain fatty acids.
• Sequential nitrite reduction and methane recovery without acidic pH adjustment is understudied.

Purpose of the Study:

• Investigate the effect of varying nitrite levels on nitrite reduction and methane production.
• Determine the feasibility of nitrite reduction for enhanced methane recovery from sludge.

Main Methods:

• Anaerobic digestion of sludge with different initial nitrite concentrations (100–800 mg/L).
• Monitoring of nitrite reduction rates and methane production volumes.
• 16S rRNA gene sequencing to analyze microbial community changes.
• Model-based analysis to assess methane yield and production rates.

Main Results:

• Complete nitrite reduction occurred within 1–4 days depending on initial concentration.
• Nitrite reduction stimulated sludge fermentation and hydrolysis, increasing organic matter availability.
• Methane production increased by 83.2% at 100 mg/L nitrite compared to controls.
• High nitrite concentrations (200–800 mg/L) inhibited methane production due to toxicity and competition for carbon sources.
• 16S rRNA analysis revealed increased abundance of hydrolytic bacteria.

Conclusions:

• Nitrite reduction is a viable strategy for enhancing methane production from sludge under non-acidic conditions.
• Optimizing nitrite concentration is crucial to maximize methane yield and avoid inhibition.
• This method offers an environmentally and economically attractive approach to sludge treatment and biogas production.