Treatment of Wastewater Phosphate by Reductive Dissolution of Iron: Use of Ferric Oxyhydroxide Media
Bibliographic record
Abstract
In smaller wastewater treatment systems such as septic systems, there is an interest in the development of passive phosphorus (P) removal methods. This study tested fixed-bed filters containing ferric oxyhydroxide media for wastewater P removal in a laboratory column test and in a full-scale domestic septic system. In the column test, during 30 mo of dosing with domestic wastewater, reductive iron dissolution reactions delivered consistent moderate concentrations of Fe into solution (2.9 ± 1.6 mg L), and influent PO-P of 3.7 ± 1.0 mg L was attenuated to 0.09 + 0.04 mg L in the column effluent (98% removal). Phosphorus breakthrough at successive locations along the column indicated that in addition to sorption, mineral precipitation reactions probably also played an important role in the observed P attenuation. This was supported by electron microprobe analyses, which showed the presence of thick (20 μm) secondary Fe-rich coatings containing P on the primary ferric media grains. Assays of NaHCO-leachable and acid-extractable P on the column solids showed accumulation of up to 5.4 mg g acid-extractable P near the column inlet, but <5% of this amount was easily desorbable, further indicating P attenuation from processes other than sorption. Over 19 mo of operation, the domestic septic system also showed generally consistent increased Fe in the filter effluent (2.6 ± 1.7 mg L) and achieved 99% P removal to 0.03 ± 0.02 mg L when the effluent was subsequently oxidized in a sand filter. Ferric iron filters could be attractive options for P removal in smaller wastewater systems because of their passive nature.
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| 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 | 0.001 |
| Scholarly communication | 0.000 | 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 teacher head, 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".