Generation, fate and transport of volatile chlorine compounds following hypochlorite discharges to municipal sewers
Bibliographic record
Abstract
The presence of volatile chlorine compounds in the headspaces of sewers receiving hypochlorite discharges is of concern because of their potential to cause corrosion of infrastructure and risks associated with human exposures. In the current study their presence was investigated using a commercial gas phase Cl 2 sensor. NCl 3 was identified as the most likely gas phase species when ammonia is present and it was found that the Cl 2 sensor was cross-sensitive to this species. The Cl/N ratio substantially impacted gaseous NCl 3 concentrations with maximum values observed at a Cl:N ratio of 12:1. Gaseous NCl 3 concentrations decreased as pH increased (6.5–7.5) and temperature decreased (20–15 o C). A model that included liquid-gas mass transfer (K L a) and first order decay in liquid (k dl ) and gas (k dg ) phases was calibrated. The value of k dl decreased as the Cl/N ratio increased (10:1–14:1) but increased as pH and temperature increased. Values of k dl and K L a were lower in real wastewater than in synthetic wastewater. Simulations with a sewer model revealed that with a fixed hypochlorite loading, peak headspace NCl 3 concentrations decreased as wastewater flow increased due to changes in Cl/N ratio. Increased air flow reduced headspace NCl 3 concentrations immediately downstream of the discharge due to dilution but had little effect further downstream. Wastewater pH impacted headspace NCl 3 concentrations by controlling the concentration of NCl 3 in the wastewater. Temperature influenced peak headspace concentrations through its impact on mass transfer and gas phase decay rates. This study provides insights that can be employed to develop sewer use bylaws that regulate hypochlorite discharges. • Discharge of hypochlorite into sewers can result in headspace NCl 3 . • NCl 3 is cross-detected by commercial Cl 2 sensors. • NCl 3 levels in headspaces affected by Cl/N ratio, pH, temperature. • Liquid and gas decay and mass transfer impact headspace levels. • Sewer use bylaws on hypochlorite should consider NCl 3 exposures.
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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) | 0.000 | 0.000 |
| 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) | 0.000 | 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".