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Nitrite reduction and methanogenesis in a single-stage UASB reactor
L I Borges1, C M López-Vazquez2, H García2
1Sanitary Engineering Chair Group, Department of Environmental Engineering and Water Technology, UNESCO-IHE Institute for Water Education, Westvest 7, 2611 AX Delft, The Netherlands; Grupo Biotecnología de Procesos para el Ambiente (BioProA), Instituto de Ingeniería Química, Facultad de Ingeniería, Universidad de la Republica, Herrera y Reissig 565, CP.11300, Montevideo, Uruguay
Summary
This study shows that combining nitrite reduction and methanogenesis in a single-stage upflow anaerobic sludge blanket (UASB) reactor is feasible for treating wastewater. Granular sludge protects against nitrite inhibition, enabling efficient combined COD and nitrogen removal.
Area of Science:
- Environmental Engineering
- Microbial Ecology
- Wastewater Treatment Technologies
Background:
- High-strength domestic wastewater treatment requires efficient removal of chemical oxygen demand (COD) and nitrogen.
- Simultaneous nitrogen removal and organic matter degradation in a single reactor is desirable for process intensification.
Purpose of the Study:
- To investigate the feasibility of simultaneous nitrite reduction and methanogenesis in a single-stage upflow anaerobic sludge blanket (UASB) reactor.
- To evaluate the long-term effects of high nitrite loading rates on reactor performance and microbial activity.
- To understand the role of sludge morphology in mitigating nitrite inhibition of methanogenesis.
Main Methods:
- Long-term operation of a single-stage UASB reactor with synthetic high-strength domestic wastewater under high nitrite loading.
- Short-term batch activity tests using anaerobic sludge samples at varying COD to nitrite ratios.
- Analysis of COD removal, denitrification efficiency, and methane production.
Main Results:
- Complete denitrification and stable COD removal efficiency were achieved in the long-term UASB reactor.
- Methane production decreased by only 13%, indicating successful co-existence of methanogenesis and denitrification.
- Batch tests revealed that granular sludge morphology offers protection to methanogens against nitrite inhibition, likely due to transport limitations.
Conclusions:
- Combined COD and nitrogen removal via nitrite in a single-stage UASB reactor is a viable technology for high-strength domestic wastewater.
- The spatial separation of microbial processes within the UASB reactor facilitates simultaneous denitrification and methanogenesis.
- Granular sludge structure plays a crucial role in protecting methanogens, enabling the successful implementation of this combined treatment process.
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