Ammonium-driven nitrification and methane-driven denitrification achieve simultaneous nitrogen and metal removal in...

Area of Science:

• Environmental Science
• Microbiology
• Chemical Engineering

Background:

• Wastewater sludge accumulates heavy metals, posing environmental and health risks.
• Conventional sludge treatments rely on chemical additives, increasing costs and environmental impact.

Purpose of the Study:

• To develop a fully biological, chemical-free strategy for managing heavy metals and nitrogen in wastewater sludge.
• To leverage nitrification and denitrification processes for metal solubilization and nitrogen removal.

Main Methods:

• Nitrification stage: Acid-tolerant ammonia-oxidizing bacteria (AOB) reduced sludge pH to ~2.0, solubilizing metals.
• Denitrification stage: A methane-based membrane biofilm reactor (MBfR) with n-DAMO microorganisms removed nitrogen and increased pH to ~8.0.
• Metal precipitation: Elevated pH in the MBfR facilitated >95.0% precipitation of solubilized metals.

Main Results:

• Efficient solubilization of metals: Cu (85.6%), Zn (95.2%), Mn (85.2%), Al (73.5%).
• High nitrogen removal efficiency: >98.0% total nitrogen removal at a rate of 753.3 ± 31.1 mg N/(L d).
• Effective metal precipitation: >95.0% of solubilized metals precipitated at pH ~8.0.

Conclusions:

• A novel, sustainable pathway for integrated nitrogen and metal management in wastewater sludge is demonstrated.
• The biological approach avoids chemical additives, reducing environmental impact and operational costs.
• Utilizes nitrogen-cycling microorganisms and inherent sludge nitrogen for resource recovery.