Characterization of aerobic granules by microbial density at different COD loading rates

Area of Science:

• Environmental Microbiology
• Wastewater Treatment Engineering
• Biotechnology

Background:

• Aerobic granulation is a key process in advanced wastewater treatment.
• Sequencing batch reactors (SBRs) are effective for granulation but require precise operational control.
• Existing methods for assessing granule health and growth can be limited.

Purpose of the Study:

• To develop a new, sensitive parameter for defining and monitoring aerobic granules.
• To optimize chemical oxygen demand (COD) loading rates for aerobic granulation in SBRs.
• To correlate the new parameter with established metrics like sludge volume index (SVI) and biomass concentration.

Main Methods:

• Cultivation of aerobic granules in a high aspect ratio SBR under alternating aerobic/anoxic conditions.
• Development of a 4,6-diamidino-2-phenylindole hydrochloride staining and fluorescence image processing protocol.
• Analysis using d(tm) parameter, sludge volume index (SVI), COD, nitrogen removal, and laser particle size analysis (LS-PSA).

Main Results:

• The d(tm) parameter was developed and validated as a sensitive indicator of aerobic granule formation.
• Increased COD loading rates beyond 2.52 kg/m(3)d did not promote further aerobic granule growth.
• d(tm) showed better correlation with COD/nitrogen removal and particle size distribution than SVI.
• The optimum COD loading rate for aerobic granulation in the SBR was determined to be 2.52 kg/m(3)d.

Conclusions:

• The d(tm) parameter offers a more accurate and sensitive method for classifying aerobic granules compared to SVI.
• d(tm) can be effectively used to optimize operational conditions for aerobic granulation processes.
• This advancement aids in improving the efficiency of wastewater treatment using aerobic granular sludge technology.