Modeling nitrogen removal in membrane aerated biofilm reactors: the role of nitritation, denitritation, and anammox nitrogen removal
Bibliographic record
Abstract
This study develops a two-dimensional, multi-species biofilm model to investigate the influence of environmental factors, specifically temperature and concentrations of oxygen, acetate, and ammonium on nitrogen removal in membrane aerated biofilm reactors (MABRs). The resulting model is a highly nonlinear reaction-diffusion system, explored through computer simulations, and captures microbial interactions, substrate transport, and nitrogen transformations within a biofilm, incorporating the counter-diffusion mechanism. Three nitrogen removal pathways have been examined in this study: nitritation-denitritation (ND), partial nitrification-anammox (PN/A), and conventional nitrification-denitrification (CND). The simulation results show that temperature and concentrations of oxygen and acetate significantly affect nitrogen removal rates and contributions of each pathway. ND dominates under most conditions, while PN/A prevails in oxygen-limited scenarios ($ O_{\infty} = 0.25-0.5\; gm^{-3} $) and co-dominates with ND at moderate oxygen levels ($ O_{\infty} = 0.5-1\; gm^{-3} $). CND is significant only at higher oxygen concentrations ($ O_{\infty} = 5\; gm^{-3} $) with low ammonium ($ N_{1\infty} = 5-15\; gm^{-3} $) and acetate levels ($ A_{\infty} = 6\; gm^{-3} $). Moreover, it has been shown that temperature enhances nitrogen removal primarily by increasing the contribution of anammox. Effective removal rates ($ > 0.1\; g/m^2/d $) occur at $ O_{\infty}\geq 1\; gm^{-3} $ with low to moderate acetate levels ($ A_{\infty} = 6\; gm^{-3} $ to $ < 100\; gm^{-3} $). The simulations further indicate that MABRs can achieve a stable ND nitrogen removal efficiency with biofilm thickness exceeding approximately $ 0.8\; mm $. In this scenario, ammonium-oxidizing bacteria (AOB) and ND denitrifiers outcompete aerobic heterotrophs and nitrite-oxidizing bacteria, resulting in a biofilm structure predominantly composed of AOB and ND denitrifiers. The findings of this study provide valuable insights for optimizing MABR design and operation to achieve energy efficient nitrogen removal.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.001 |
| Meta-epidemiology (narrow) | 0.001 | 0.000 |
| Meta-epidemiology (broad) | 0.001 | 0.001 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.001 | 0.001 |
| Open science | 0.001 | 0.000 |
| Research integrity | 0.002 | 0.001 |
| Insufficient payload (model declined to judge) | 0.000 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".