The anaerobic exposure time (AET) as a novel process parameter in the anaerobic side-stream reactor (ASSR)-based process for excess sludge minimization.
Sara Mulone1, Santo Fabio Corsino1, Marco Capodici1
1Department of Engineering, University of Palermo, Viale delle Scienze, Building 8, 90128 Palermo, Italy.
Water Research
|February 27, 2024
View abstract on PubMed
Summary
Reducing excess sludge in wastewater treatment is key. A new parameter, anaerobic exposure time (AET), effectively minimizes sludge production (10-60%) by promoting hydrolysis and decay, outperforming traditional metrics.
Area of Science:
- Environmental Engineering
- Wastewater Treatment Technologies
- Microbial Ecology
Background:
- Minimizing excess sludge from wastewater treatment plants (WWTPs) is a critical environmental and economic challenge.
- Anaerobic side-stream reactor (ASSR) processes are widely used for sludge reduction, but their effectiveness is inconsistently linked to parameters like hydraulic retention time (HRT), anaerobic sludge loading rate (ASLR), and sludge interchange ratio (SIR).
- Existing literature lacks a clear, predictive relationship between operational parameters and sludge minimization yields in ASSR systems.
Purpose of the Study:
- To introduce and validate a novel parameter, anaerobic exposure time (AET), for quantifying and predicting excess sludge reduction in ASSR processes.
- To establish a robust correlation between AET and the reduction of the observed yield coefficient (Yobs).
- To elucidate the microbial mechanisms driving sludge reduction at different AET levels.
Main Methods:
- Implementation of a lab-scale ASSR plant to study sludge reduction.
- Definition and application of the anaerobic exposure time (AET) parameter.
- Correlation analysis (Pearson, R2) of AET, Yobs, ASLR, and ASSR-HRT using experimental data and a comprehensive literature review.
Main Results:
- A significant reduction in excess sludge production (10-60%) was achieved by increasing AET (7.9-13 h/d) while maintaining constant HRT and SIR (100%).
- A strong positive correlation (Pearson = 0.763) and linear relationship (R2 = 0.92) were identified between AET and Yobs reduction.
- Low AET (< 6 h) primarily involved maintenance and uncoupled metabolism, whereas high AET (>8 h) enhanced extracellular polymeric substances (EPS) hydrolysis and endogenous decay, leading to greater sludge reduction.
Conclusions:
- Anaerobic exposure time (AET) is a reliable and superior parameter for predicting and controlling excess sludge reduction in ASSR processes compared to HRT and ASLR.
- Optimizing AET can significantly improve the efficiency of sludge minimization strategies in wastewater treatment.
- The study provides a validated framework for utilizing AET in the design and operational control of ASSR-based wastewater treatment systems.
