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Sewage sludge minimisation by OSA-MBR: A pilot plant experiment
Alida Cosenza1, Daniele Di Trapani1, Paulo Marcelo Bosco Mofatto1
1Engineering Department, Palermo University, Viale delle Scienze, Ed. 8, 90128, Palermo, Italy.
Chemosphere
|November 17, 2023
Summary
The Oxic Settling Anaerobic (OSA) process combined with Membrane Bioreactors (MBR) significantly reduces excess sludge. However, optimizing hydraulic retention time (HRT) is crucial to balance sludge minimization with greenhouse gas emissions.
Area of Science:
- Environmental Engineering
- Wastewater Treatment Technologies
- Bioreactor Systems
Background:
- Membrane Bioreactors (MBR) are effective for wastewater treatment but generate significant excess sludge.
- Sludge minimization is a critical challenge in MBR systems to reduce operational costs and environmental impact.
- Greenhouse gas (GHG) emissions from wastewater treatment are often overlooked but are an important consideration.
Purpose of the Study:
- To evaluate the effectiveness of the Oxic Settling Anaerobic (OSA) process in minimizing excess sludge in an MBR system.
- To assess the impact of different hydraulic retention times (HRT) in the OSA process on sludge production, nutrient removal, and membrane fouling.
- To monitor and analyze greenhouse gas emissions associated with the combined MBR-OSA system.
Main Methods:
- A pilot-scale MBR system was operated with and without the integrated OSA process.
- The OSA process was tested at two different HRTs (4 and 6 hours) using real wastewater.
- Key parameters monitored included sludge production, carbonaceous and nitrogenous pollutant removal, membrane fouling, biokinetic behavior, and GHG emissions (N2O-N).
Main Results:
- The MBR-OSA system achieved significant excess sludge reduction: 59.7% at 4h HRT and 89.7% at 6h HRT compared to MBR alone.
- The 6h HRT in the OSA process showed superior PO4-P removal but poorer performance for COD, NH4, and Total Nitrogen removal.
- No significant changes in membrane fouling were observed across the experimental periods, while increased HRT in the anaerobic stage led to higher N2O-N emissions.
Conclusions:
- Combining MBR with OSA process is a viable strategy for substantial excess sludge minimization in wastewater treatment.
- An increase in HRT within the OSA process requires careful consideration due to its impact on nutrient removal and potential for increased greenhouse gas emissions.
- A trade-off exists between achieving maximum sludge reduction and controlling nutrient removal efficiency and GHG emissions, necessitating optimized operational strategies.
