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Published on: July 13, 2012
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Integrated approach for waste activated sludge stabilization under ultra-short solids retention time
Xi Lu1, Xiaotong Cen2, Zhiqiang Zuo3
1Australian Centre for Water and Environmental Biotechnology, The University of Queensland, St Lucia, QLD 4072, Australia.
Bioresource Technology
|June 18, 2025
Summary
This study stabilizes waste activated sludge (WAS) using an integrated approach with ultra-short solids retention time (SRT). Adding acid to promote free nitrous acid (FNA) formation achieved Class A standards cost-effectively.
Area of Science:
- Environmental Engineering
- Wastewater Treatment
- Microbial Ecology
Background:
- Sludge stabilization is crucial for safe disposal of waste activated sludge (WAS).
- Conventional methods often require long solids retention times (SRT).
- Ultra-short SRT offers potential for more efficient stabilization.
Purpose of the Study:
- To investigate an integrated approach for stabilizing unthickened WAS under ultra-short SRT.
- To evaluate the effectiveness of free nitrous acid (FNA) formation in sludge stabilization.
- To assess the economic viability of the proposed method.
Main Methods:
- Operated two aerobic digesters: a control (15-day SRT) and an experimental (1.5-day SRT).
- Reduced SRT to 2.5 days, observing pH drop and insufficient FNA.
- Supplemented with chemical acid to lower pH to 4.3 for enhanced FNA production.
Main Results:
- Achieved Class A sludge stabilization standards.
- Specific oxygen uptake rate was 0.2 ± 0.1 mg O2/g VS/h.
- Pathogen levels reached 2.3 ± 0.1 log MPN/g total solids.
Conclusions:
- The integrated approach effectively stabilizes WAS under ultra-short SRT.
- Microbial ammonia oxidation and controlled acidification are key to FNA generation.
- The method is cost-effective, minimizing chemical acid usage.
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