Enhancement of Anaerobic Digestibility of Thickened Waste-Activated Sludge Using Combined Free Nitrous Acid Pre-Treatment (Combined FNA-Heat, and FNA-H2O2)
Bibliographic record
Abstract
The application of sludge pretreatment strategies to improve solids handling in wastewater treatment plants has gained increasing attention. Free nitrous acid (FNA) sludge pretreatment is a novel approach, as, unlike other chemicals, FNA is a waste-derived, and renewable chemical that can be produced directly from wastewater treatment plants as a by-product, and therefore, FNA-based pretreatment can be determined as an environmentally friendly and economically feasible strategy. The use of FNA as a chemical pretreatment for anaerobic digestion (AD) has indicated the potential to increase the hydrolysis rate by releasing the internal organic matter of thickened waste-activated sludge (TWAS) via its biocidal effects. Furthermore, the effects of combined FNA-based pretreatment on volatile fatty acids production through two-stage AD are unknown. Therefore, this study aimed to investigate the effect of combined FNA-based pretreatment on single- and two-stage AD of TWAS. In the first phase of the study, the influence of different FNA dosage, temperature, and pretreatment time combinations on the anaerobic degradation of TWAS was evaluated through biochemical methane potential tests, and in batch mode. Higher temperature, longer reaction time, and moderate FNA concentration (1.4 mg/L) were favorable for increased solubilization of organic matter and methane production from TWAS. The optimum operating conditions for maximum methane yield were determined to be 60°C, 21 hr, and 1.4 FNA mg HNO2-N /L. The effect of combined FNA-Heat and FNA-H2O2 was also studied on single- and two-stage anaerobic digestion of TWAS. Application of combined FNA-Heat and FNA-H2O2 pretreatment resulted in up to ~32-43 % total suspended solids reduction, respectively which was more than that of the sole acidogenic fermentation process (~16%). Among all tested scenarios, the implementation of the two-stage AD fed with FNA- H2O2 pretreated sludge (1.4 mg HNO2-N/L and 50 mg H2O2 /g TS) revealed the highest ultimate biomethane recovery of 224 mL/g TCODadded, which was 41% higher than that of the single-stage AD of raw TWAS (159 mL/g TCODadded). Given the findings of this research, the two-stage AD following combined FNA-based pretreatment can be suggested as an effective strategy for improved bioconversion of TWAS.
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 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 | 0.000 | 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".