A-Stage process - Challenges and drawbacks from lab to full scale studies: A review

Area of Science:

• Environmental Engineering
• Biotechnology
• Resource Recovery

Background:

• Growing global resource scarcity necessitates viewing wastewater as a resource, not waste.
• Conventional wastewater treatment plants (WWTPs) oxidize organic matter, hindering recovery for biomaterials or biogas.
• The A-Stage process offers a solution by concentrating organic matter for valorisation, suitable for retrofitting existing WWTPs.

Purpose of the Study:

• To summarize peer-reviewed research on the A-Stage process under real conditions.
• To highlight key operational parameters for maximizing resource recovery.
• To critically review modeling efforts and identify areas for future research.

Main Methods:

• Review of pilot-scale and full-scale studies of the A-Stage process.
• Analysis of key operational parameters such as sludge retention time (SRT), hydraulic residence time (HRT), and dissolved oxygen (DO).
• Evaluation of nutrient removal efficiencies and discussion of settling efficiencies and modeling.

Main Results:

• Optimal SRT of 0.3 days maximizes influent COD redirection (up to 50%) to sludge flux while limiting mineralization (<25%).
• Optimal HRT of 30 minutes and DO levels of 0.5 mg/L are identified.
• Observed nutrient removal efficiencies: 15-27% for total nitrogen and 13-38% for total phosphorus.

Conclusions:

• The A-Stage process effectively recovers organic matter from wastewater.
• Sludge retention time is a critical parameter for optimizing resource recovery.
• Further research is needed on mixing, wet weather flow, temperature impacts, and settling processes for improved A-Stage process understanding and modeling.