Low-sludge partial nitrification enabled by carbon-nitrogen decoupling and encapsulated biofillers

Area of Science:

• Environmental Engineering
• Microbiology
• Wastewater Treatment

Background:

• Excessive sludge production and nitrite-oxidizing bacteria (NOB) instability hinder sustainable partial nitrification (PN) in activated sludge systems.
• Achieving stable nitritation with reduced sludge output is crucial for efficient domestic wastewater treatment.

Purpose of the Study:

• To demonstrate a mainstream PN reactor strategy using encapsulated biofillers and carbon-nitrogen decoupling.
• To achieve stable nitritation with minimal sludge production for low C/N domestic wastewater.

Main Methods:

• Utilized a hydrolysis-acidification and denitrification (HA-DN) module for carbon management, creating a carbon-limited influent (C/N ≈ 0.8-1.2).
• Employed encapsulated biofillers in the PN reactor to create a high-density, long-SRT autotrophic niche.
• Operated under high dissolved oxygen (DO) and carbon-starved conditions to selectively enrich ammonia-oxidizing bacteria (AOB) and wash out NOB.

Main Results:

• Achieved stable nitritation with a nitrite accumulation rate >98%, even under increased ammonium loading.
• Significantly reduced sludge yield to 0.013 kgMLSS/kgCOD, a >93% decrease compared to conventional activated sludge (CAS).
• Successfully confined heterotrophic bacteria (HB) to a low-abundance, maintenance-oriented guild, shifting them toward endogenous respiration.

Conclusions:

• Carbon-nitrogen decoupling via encapsulated, carbon-starved PN niches offers a generalizable strategy for stable mainstream partial nitrification.
• This approach significantly minimizes sludge production in low C/N domestic wastewater treatment.
• The method effectively suppresses NOB and enhances AOB activity, leading to efficient nitritation.