Increasing biosolids phosphorus fertilizer value and decreasing biogas carbon dioxide content for municipal wastewater treatment processes with anaerobic digestion
Bibliographic record
Abstract
Municipal wastewater treatment by the City of Ottawa produces biosolids and biogas by-products from anaerobic digestion of sewage sludge. Some of these biosolids are distributed to selected farmlands. The biosolids contain a variety of low-solubility iron phosphate solids, which contribute to their low phosphorus (P) fertilizer value. Some of the biogas is used to produce electric power and heat at the plant. In this research, we investigated the potential to increase the biosolids P fertilizer value by using endogenous microbial activity and sulfur chemistry to dissolve iron phosphate, which can later be precipitated as higher-solubility calcium phosphate, and decrease the biogas carbon dioxide concentration by precipitating calcium carbonate. Precipitation of lower-solubility iron sulfide was examined for its potential to dissolve higher-solubility iron phosphate within biosolids and consequently increase the dissolved inorganic orthophosphate (o-Pi) concentration. Endogenous bacteria within the biosolids were hypothesized to generate sulfide from inexpensive elemental sulfur. Experiments were performed to test the effect of incubating 10 % biosolids with different molar ratios of elemental sulfur (S0) to total phosphorus (TP) (S/TP: 0 – 4) and times (24 h – 192 h) at different temperatures (22 °C, 32 °C, or 42 °C) on P dissolution. Experiments were conducted on five biosolids batches from different times of year. Dissolved TP concentration plateaued after an S/TP molar ratio of 0.5. For winter 2023 biosolids, higher dissolved TP was obtained for an incubation at 32 °C or 42 °C than at room temperature (22 °C). The maximum observed dissolved TP concentration was 7 % of the TP for winter 2023 biosolids incubated with 0.5 S/TP at 32 °C for 168 h. Summer 2024 biosolids yielded significantly lower TP concentrations at all temperatures than winter 2023 biosolids. The incubation temperature did not significantly affect the TP concentration. The different biosolids batch compositions were found to influence the P dissolution and the effect of temperature on P dissolution. Waste concrete fines and wollastonite (CaSiO3) were tested as potential inexpensive sources of soluble Ca and alkalinity for calcite precipitation of dissolved carbon dioxide in biogas. Both the waste concrete fines and wollastonite were leached with acetic acid. Experiments selected using design of experiments was used to assess the effect of percent solids, acetic acid concentration, and temperature on soluble calcium concentration in the leachates for both the waste concrete fines and wollastonite. The effect of percent solids and acetic acid concentration on the Ca extraction from the concrete fines and wollastonite was more significant than the effect of temperature. Calcium ion extraction was inversely proportional to pH for both wollastonite and calcined concrete. Leaching with 1.0 % solids and 100 mM acetic acid at 32 °C resulted in ~100 % calcium ion extraction for the concrete fines and ~20 % calcium ion extraction for wollastonite. The leachate for the concrete fines had a higher pH compared to that of the wollastonite. Endogenous microbial activity in biosolids can reduce elemental sulfur to sulfide, precipitate iron sulfide, and dissolve a fraction of the range of iron phosphate solids in biosolids. Waste concrete was found to dissolve more calcium ions and alkalinity than wollastonite by acetic acid leaching under mild conditions, for carbon capture from biogas. Combination of these two research findings presents an opportunity to reduce the carbon dioxide concentration in biogas, reduce carbon dioxide emissions, and increase the P-fertilizer value of biosolids produced by municipal wastewater treatment processes with anaerobic digestion, although the net energy cost remains to be ascertained
Fetched live from OpenAlex and de-inverted. Abstracts are not stored in this database: the inverted indexes are 8.6 GB of the frame’s 9.3 GB of text, and the host has 13 GB free.
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 | 0.001 | 0.000 |
| Meta-epidemiology (narrow) | 0.001 | 0.001 |
| Meta-epidemiology (broad) | 0.001 | 0.000 |
| Bibliometrics | 0.000 | 0.001 |
| Science and technology studies | 0.001 | 0.000 |
| Scholarly communication | 0.000 | 0.001 |
| 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 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".