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Significant in situ sludge yield reduction in an acidic activated sludge system
Zheng Kong1, Zhiyao Wang1, Xi Lu1
1Australian Centre for Water and Environmental Biotechnology, The University of Queensland, St Lucia, QLD 4072, Australia.
Water Research
|July 10, 2024
Summary
This study introduces acidic activated sludge technology to reduce sludge yield by 58% in wastewater treatment. The novel process uses low pH and free nitrous acid (FNA) for cost-effective sludge management.
Area of Science:
- Environmental Science
- Microbiology
- Chemical Engineering
Background:
- Minimizing sludge generation is crucial for reducing operational costs in wastewater treatment plants (WWTPs).
- Small WWTPs often lack bioenergy recovery, making sludge reduction a key economic factor.
Purpose of the Study:
- To introduce and evaluate a novel acidic activated sludge technology for in situ sludge yield reduction.
- To compare the sludge yield and operational performance of the acidic system with a conventional neutral-pH system.
Main Methods:
- Long-term operation (400 days) of activated sludge systems at acidic pH (4.6-4.8) and controlled free nitrous acid (FNA) levels (1-3 mg/L).
- Calculation of observed sludge yield (Yobs) based on sludge generation and COD removal.
- Mechanism studies including endogenous respiration, sludge hydrolysis, microbial community analysis, and intracellular ATP content measurement.
Main Results:
- The acidic process achieved a significantly lower observed sludge yield (Yobs) of 0.106 gMLSS/gCOD, a 58% reduction compared to the neutral system (0.250 gMLSS/gCOD).
- Effective sludge settling and organic matter removal were maintained in the acidic system over long-term operation.
- Acidic sludge exhibited higher endogenous respiration and hydrolysis rates, enriched specific hydrolytic bacteria, and showed lower intracellular ATP content.
Conclusions:
- Acidic activated sludge technology effectively reduces sludge yield through enhanced sludge disintegration, hydrolysis, and cryptic growth.
- The technology offers a promising solution for cost- and space-effective wastewater management, particularly for small WWTPs.
- The findings suggest a potential decoupling of catabolism and anabolism under acidic conditions with FNA, contributing to reduced biomass production.
