Simultaneous COD, nitrogen, and phosphate removal by aerobic granular sludge

Area of Science:

• Environmental Science
• Microbiology
• Chemical Engineering

Background:

• Aerobic granular sludge technology enables compact wastewater treatment plants.
• Simultaneous removal of chemical oxygen demand (COD), nitrogen, and phosphate is achievable in a single sequencing batch reactor.
• Aerobic granules cultivated with pulse-feeding are unstable at low dissolved oxygen (DO) concentrations.

Purpose of the Study:

• To investigate the stability of aerobic granules at low DO concentrations.
• To enhance granule stability by selecting for phosphate-accumulating organisms (PAOs).
• To achieve simultaneous nutrient removal (COD, N, P) in a sequencing batch reactor.

Main Methods:

• Cultivating aerobic granules with a focus on selecting for PAOs.
• Operating sequencing batch reactors at low DO saturation (20%).
• Monitoring removal efficiencies for COD, nitrogen, and phosphate over an extended period.

Main Results:

• High removal efficiencies were achieved: 100% COD, 94% phosphate (P-), and 94% total nitrogen (N-) (including 100% ammonium removal).
• PAO selection improved granule stability at low DO concentrations.
• Nitrogen removal efficiency was found to be dependent on granule diameter.
• Evidence suggests P-removal occurs partly via biologically induced precipitation.

Conclusions:

• Aerobic granular sludge technology, particularly with PAO selection, offers a stable and efficient method for simultaneous nutrient removal in compact wastewater treatment plants.
• Optimizing granule diameter is crucial for maximizing nitrogen removal efficiency.
• The process is economically feasible for full-scale applications due to long feeding periods and high removal rates.