Microbial population dynamics during aerobic sludge granulation at different organic loading rates

Area of Science:

• Environmental microbiology
• Biotechnology
• Wastewater treatment

Background:

• Aerobic granulation is a key process in advanced wastewater treatment.
• Understanding bacterial community dynamics is crucial for optimizing granulation.
• Filamentous bacteria are often associated with sludge bulking, but their role in granulation is debated.

Purpose of the Study:

• To investigate bacterial community evolution during aerobic sludge granulation.
• To determine the effect of different chemical oxygen demand (COD) loading rates on granule formation and characteristics.
• To identify key bacterial species involved in aerobic granule formation and stability.

Main Methods:

• Laboratory experiments using three sequencing batch reactors (SBRs) with varying COD loading rates (1.5, 3.0, 4.5 kg/m³d).
• Monitoring bacterial diversity using polymerase chain reaction (PCR) and denaturing gradient gel electrophoresis (DGGE).
• Analysis of 16S rDNA sequences to identify dominant bacterial species.

Main Results:

• Aerobic granules formed successfully on glucose-based wastewater without significant filamentous bacteria.
• Higher COD loading rates resulted in faster formation of larger, looser granules.
• Lower COD loading rates led to slower formation of smaller, denser granules with higher bacterial diversity.
• Bacterial diversity was inversely related to the COD loading rate.
• Dominant species included beta- and gamma-Proteobacteria and Flavobacterium, with common species identified as crucial for granule structure.

Conclusions:

• Aerobic sludge granulation is achievable with glucose-based synthetic wastewater, independent of significant filamentous bacterial presence.
• Sludge granulation is influenced by substrate loading rates, affecting granule morphology, structure, and bacterial community composition.
• Specific bacterial consortia, particularly certain Proteobacteria and Flavobacterium species, are vital for the formation, growth, and structural integrity of aerobic granules.