Enhanced biological phosphorus removal by granular sludge: from macro- to micro-scale

Area of Science:

• Environmental Microbiology
• Wastewater Treatment Engineering
• Biotechnology

Background:

• Biological phosphorus removal (BPR) is crucial for mitigating eutrophication.
• Microbial granulation offers enhanced settling and volumetric efficiency in wastewater treatment.
• Sequencing batch reactors (SBRs) are versatile systems for BPR.

Purpose of the Study:

• To cultivate phosphorus accumulating microbial granules in an SBR.
• To evaluate the efficiency and stability of BPR using these granules.
• To investigate the granulation mechanism and granule characteristics.

Main Methods:

• Cultivation of microbial granules in a sequencing batch reactor (SBR) with synthetic wastewater.
• Monitoring of phosphorus removal efficiency and effluent phosphorus levels over 300 days.
• Analysis of granule diameter, particle charge, micro-pore structure, and spatial phosphorus distribution.

Main Results:

• Successfully cultivated microbial granules with an average diameter of 0.74 mm.
• Achieved high BPR efficiency (>94.3%) with effluent phosphorus <0.50 mg/L.
• Identified positively charged particles formed during anaerobic phosphorus release as granulation cores.
• Observed a micro-pore structure (291.5–446.5 nm pore width) and decreasing spatial phosphorus content towards granule centers.
• Found smaller granules exhibited higher specific area, pore width, and phosphorus removal activity.

Conclusions:

• Phosphorus accumulating microbial granules are effective for high-efficiency BPR in SBRs.
• The granulation process is initiated by positively charged particles formed during anaerobic phosphorus release.
• Granule microstructure and size influence phosphorus removal performance, with smaller granules being more active.