Biological processes of nitrogen removal and modeling oxygen diffusion in flocculent sludge and in granular sequencing batch reactors

BACKGROUND Simultaneous nitrification‐denitrification (SND) in biological wastewater treatment occurs under aerobic conditions in flocs and granules, exhibiting aerobic and internal anoxic zones; SND depends on dissolved oxygen concentration. Aerobic denitrification (AD) is an advantageous process b...

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Published in:Journal of chemical technology and biotechnology (1986) 2023-02, Vol.98 (2), p.404-418
Main Authors: Bucci, Paula, Marin, Juan C. Alzate, Zaritzky, Noemí, Caravelli, Alejandro
Format: Article
Language:English
Subjects:
Activated sludge
Aeration
Aerobic conditions
aerobic denitrification
Aggregates
Batch reactors
Biological activity
Biological wastewater treatment
Bioreactors
Carbon sequestration
Denitrification
Diffusion
Dissolved oxygen
flocculent sludge
Genomic analysis
Granular materials
granules
Metabolic pathways
Microbalances
Microorganisms
Nitrification
Nitrogen
Nitrogen removal
Oxygen
oxygen diffusion model
Reactors
Sequencing batch reactor
simultaneous nitrification‐denitrification
Wastewater treatment
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Summary:BACKGROUND Simultaneous nitrification‐denitrification (SND) in biological wastewater treatment occurs under aerobic conditions in flocs and granules, exhibiting aerobic and internal anoxic zones; SND depends on dissolved oxygen concentration. Aerobic denitrification (AD) is an advantageous process because control of aeration is not required. In the present study, the effects of anoxic/aerobic conditions and size of microbial aggregates on the AD process were evaluated using sequencing batch reactors (SBR) with activated sludge (anoxic/aerobic SBRAS) or aerobic granules (SBRAG). RESULTS Nitrogen mass balances were used to estimate nitrogen assimilation, nitrification and denitrification. An oxygen diffusion model was proposed to evaluate oxygen profiles in the microbial aggregates determining the contribution of AD on nitrogen removal. At COD:N ratio = 100:10, fully aerobic biomass was predicted for all flocs in SBRAS and for 82% of the granules in SBRAG. In SBRAS, intracellular carbon storage was favored in the anoxic phase; nitrification was followed by AD, achieving 67% inorganic nitrogen (Ni) removal. In SBRAG, SND was 55% and Ni removal 51%. For SBRAG, genomic analysis described microbial community and nitrogen metabolic pathways were proposed. Heterotrophic nitrification‐aerobic denitrification (HNAD) was proposed as the main nitrogen removal process. At COD:N = 100:15, 80% of the granules developed internal anoxic zones; anoxic denitrification predominated, allowing treatment of a higher nitrogen load with similar Ni removal. CONCLUSIONS Biological processes without oxygen control are simpler to operate. For anoxic/aerobic SBR, high Ni removal efficiency was achieved even with 3.5–5.4 mg O2 L−1 at the center of the flocs, as predicted by the diffusion model. In aerobic granular systems, SND carried out by HNAD bacteria constitutes a promising approach for nitrogen removal. © 2022 Society of Chemical Industry (SCI).
ISSN:0268-2575
1097-4660
DOI:10.1002/jctb.7253