Short-sludge age EBPR process - Microbial and biochemical process characterisation during reactor start-up and...

Area of Science:

• Environmental Microbiology
• Environmental Biotechnology
• Wastewater Engineering

Background:

• Short solid retention times (SRT) are proposed for enhanced resource recovery in wastewater treatment.
• Understanding microbial communities and biogeochemical processes in short-SRT systems is crucial but limited.
• Enhanced biological phosphorus removal (EBPR) systems are key for nutrient management.

Purpose of the Study:

• To investigate the microbial community and performance of a short-SRT EBPR system.
• To identify factors affecting nitrification and phosphorus removal under short SRT conditions.
• To optimize operational parameters for effective EBPR and mitigate operational issues like filamentous bulking.

Main Methods:

• Operation of a sequencing batch reactor (SBR) for EBPR with municipal wastewater supplemented with propionate.
• Analysis of microbial community structure using 16S rRNA amplicon sequencing.
• Monitoring of phosphate removal, nitrification, sludge settling properties (SVI), and operational parameters (SRT, dissolved oxygen).

Main Results:

• High phosphate removal (>99%) and complete ammonia oxidation were achieved at an initial SRT of 8 days.
• Shifting to a 3.5-day SRT inhibited nitrification, led to filamentous bulking (Thiothrix proliferation, SVI up to 1100 mL/g), and reduced phosphorus removal.
• Reducing anaerobic SRT suppressed sulphate-reducing bacteria (SRB) and improved sludge settling (SVI ~200 mL/g).
• Effective phosphate removal and mitigated nitrification were achieved at a 3-day SRT with 2-3 mg/L dissolved oxygen.

Conclusions:

• Short SRT operation in EBPR systems presents challenges, including nitrification inhibition and filamentous bulking, potentially linked to SRB competition.
• Adjusting anaerobic SRT and maintaining optimal dissolved oxygen levels are critical for successful short-SRT EBPR.
• This study provides insights into microbial dynamics and operational strategies for optimizing short-SRT wastewater treatment systems for nutrient removal and resource recovery.