Impacts of orthophosphate addition on chloramine decay and biofilm development in a model drinking water distribution system
Bibliographic record
Abstract
• Orthophosphate increased biofilm growth and chloramine decay in a phosphorus-limited water. • Biofilm growth rose substantially between 1 and 2 mg PO43-/L. orthophosphate dosages. • Higher orthophosphate dosages enhanced biofilm metabolic activity, formation potential, and chloramine decay. • Biofilm activity correlated strongly with chloramine decay due to microbial demand. • Results support optimizing orthophosphate dosing for corrosion and microbial control. Orthophosphate is commonly added as a corrosion inhibitor in drinking water distribution systems (DWDSs). However, there is limited understanding of the interrelationships between its addition, monochloramine decay, and biofilm growth. Further research is needed to evaluate its potential to accelerate monochloramine decay and promote biofilm development. This study examines the impact of orthophosphate doses (0 to 4 mg PO 4 3- /L) on monochloramine decay and biofilm growth using model distribution systems (MDSs) at a 10-day residence time, fed with phosphorus-limited water. Findings showed that, in addition to expected enhanced microbial growth, biofilm formation potential, and metabolic activity (i.e., carbon utilization), orthophosphate addition also increased monochloramine decay. For instance, biofilm growth increased from 2.9 to 3.2 to 5.3–6.3 log CFU/cm 2 between 1 and 4 mg PO 4 3- /L, with the most substantial increase observed between 1 and 2 mg PO 4 3- /L (an increase of >2 log units). Around day 52, changes in metabolic activity, biofilm formation potential, and biofilm growth in MDSs with added orthophosphate suggested a shift in the microbial community from early colonizers to bacteria thriving in biofilms. A correlation between biofilm profiles and monochloramine decay was apparent, with significant positive correlations between total chlorine decay and (i) biofilm HPC (R 2 = 0.86, p < 0.001), (ii) biofilm formation potential (R 2 = 0.73, p < 0.01), and (iii) metabolic activity (R 2 = 0.81, p < 0.001). Higher orthophosphate concentrations (2–4 mg PO 4 3- /L) were linked to greater biofilm growth and monochloramine demand, while 1 mg PO 4 3- /L had minimal impact. Total chlorine decay coefficients ranged from 0.0034-0.004 h -1 (control) to 0.0050-0.0072 h -1 (4 PO 4 3- /L) in the phase of further biofilm development. These findings emphasize that orthophosphate usage in DWDSs needs to balance corrosion control aspects with effects on water quality (e.g., biofilm growth and monochloramine stability).
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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 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 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 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 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".