SRT duality in densified activated sludge systems: Measurement methods, metrics and perspectives

Area of Science:

• Environmental Engineering
• Wastewater Treatment Technologies
• Microbial Ecology

Background:

• Densified activated sludge (DAS) systems enhance settling and nutrient removal through biomass densification.
• Accurate sludge age characterization is challenging in DAS due to coexisting flocs and granules with distinct sludge retention times (SRTs).

Purpose of the Study:

• To develop and validate a granular-weighted SRT (gwSRT_DAS) metric for precise sludge age determination in DAS systems.
• To assess the operational implications of gwSRT_DAS for optimizing wastewater treatment and energy recovery.

Main Methods:

• Implementation of a dynamic monitoring framework on a full-scale hydrocyclone-based DAS system.
• Analysis of five years of operational data to compare gwSRT_DAS with conventional bulk SRT.
• Correlation analysis between gwSRT and biochemical methane potential.

Main Results:

• Granule SRT was found to be up to 3.5 times higher than bulk SRT, while floc SRT remained lower.
• The gwSRT_DAS metric effectively captured the differences in SRT among sludge components.
• A strong linear correlation (R² = 0.98) was observed between gwSRT and biochemical methane potential.

Conclusions:

• The gwSRT_DAS metric provides a more representative measure of sludge age in DAS systems than conventional bulk SRT.
• This metric offers practical insights for optimizing DAS operation, particularly under nutrient limits and seasonal variations.
• Potential for improved sludge biodegradability and energy recovery by managing bulk and granular SRTs strategically.