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Performance evaluation of hybrid and conventional sequencing batch reactor and continuous processes
H L S Tam1, D T W Tang, W Y Leung
1Drainage Service Department, Revenue Tower, Wanchai, Hong Kong. hlstam@dsd.gov.hk
Summary
Hybrid activated sludge systems, using biofilm carriers, significantly improve nitrogen removal in wastewater treatment. These compact systems achieve high nitrification-denitrification even with shorter sludge ages, offering efficient upgrades for municipal facilities.
Area of Science:
- Environmental Engineering
- Microbiology
- Water Treatment
Background:
- Conventional activated sludge processes face challenges in achieving efficient nitrification-denitrification.
- Optimizing sludge age and mixed liquor suspended solids (MLSS) concentration is crucial for nitrogen removal.
- Hybrid systems incorporating biofilm carriers offer potential for enhanced biological wastewater treatment.
Purpose of the Study:
- To evaluate the nitrification-denitrification performance of hybrid activated sludge systems compared to conventional configurations.
- To assess the impact of hybrid biofilm carriers on sludge age, MLSS concentration, and sludge settleability.
- To determine the suitability of hybrid systems for upgrading existing wastewater treatment plants (WWTPs) in Hong Kong.
Main Methods:
- Bench-scale testing of continuous clarifier modified Ludzack Ettinger (MLE) and sequencing batch reactor (SBR) configurations.
- Comparison of systems with and without hybrid suspended biofilm carriers.
- Analysis of effluent nitrogen concentrations (NH4-N, NO3-N), hydraulic retention time, sludge age, MLSS, and sludge volume index (SVI).
Main Results:
- Hybrid SBR and MLE systems achieved near-complete nitrification and substantial nitrogen removal within a short hydraulic retention time (7.5 hours) and low sludge age (5.2 days).
- Hybrid systems retained nitrifying bacteria on biofilm carriers, enabling operation below the critical sludge age for nitrification.
- Conventional MLE required significantly longer sludge ages (1.5-2.5 times critical) for complete nitrification.
Conclusions:
- Hybrid MLE is a viable option for upgrading existing wastewater treatment works for nitrogen removal and increasing hydraulic capacity without major civil modifications.
- Hybrid SBR demonstrates stable nitrogen removal performance, potentially suitable for new WWTP designs due to its equalization capacity.
- Further full-scale trials are recommended to optimize hybrid systems for higher hydraulic capacity and nitrogen removal efficiency.