Ammonium oxidation via nitrite accumulation under limited oxygen concentration in sequencing batch reactors
Sukru Aslan1, Lindsey Miller, Mohamed Dahab
1Cumhuriyet University, Department of Environmental Engineering, 58140 Sivas, Turkey. saslan@cumhuriyet.edu.tr
Bioresource Technology
|September 2, 2008
Summary
Optimizing sludge retention time (SRT) in nitritation reactors is key for efficient ammonia-nitrogen (NH4-N) removal. Lowering SRT increases reaction time but can lead to nitrite accumulation, impacting wastewater treatment processes.
Area of Science:
- Environmental Engineering
- Wastewater Treatment
- Microbial Ecology
Background:
- Nitritation reactors are crucial for nitrogen removal in wastewater treatment.
- Sludge retention time (SRT) significantly influences the efficiency of nitrification and nitrogenous compound accumulation.
- Understanding the impact of SRT on ammonia-oxidation and nitrite accumulation is vital for process optimization.
Purpose of the Study:
- To investigate the effects of varying sludge retention times (SRT) on ammonium-nitrogen (NH4-N) oxidation.
- To analyze the accumulation of nitrogen oxides (NOx-N), specifically nitrite-nitrogen (NO2-N), in nitritation reactors.
- To determine the optimal SRT for efficient NH4-N removal and controlled NO2-N accumulation.
Main Methods:
- Experimental study using nitritation reactors with controlled sludge retention times (SRT).
- Monitoring of NH4-N removal efficiency and reaction times at different SRTs (40, 30, 25, 20 days).
- Analysis of nitrite-nitrogen (NO2-N) and nitrate-nitrogen (NO3-N) concentrations and ratios (NO2-N/NOx-N).
Main Results:
- Decreasing SRT from 40 days to 20 days significantly increased the reaction time required for 99% NH4-N removal.
- At an SRT of 40 days, high NO2-N accumulation (177 mg/l) and a high NO2-N/NOx-N ratio (0.9) were observed.
- Lowering SRT below 40 days resulted in a slight increase in NO3-N and a drop in the NO2-N/NOx-N ratio to 0.8.
- Free ammonia (NH3-N) concentrations remained below inhibitory levels for nitrite-oxidizing bacteria (NOB) during the cycles.
Conclusions:
- Sludge retention time critically affects NH4-N oxidation rates and NO2-N accumulation in nitritation reactors.
- An SRT of 40 days favored high NO2-N accumulation, potentially due to combined dissolved oxygen limitation and NH3-N inhibition of NOB.
- Process control strategies should consider SRT to manage nitrogen species transformation and optimize wastewater treatment performance.
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