Impacts of reduced sulfur components on active and resting ammonia oxidizers
Bibliographic record
Abstract
While there has been significant research on the nature and extent of the impact of inhibitory reduced sulfur with respect to anaerobic (e.g., methanogenic and sulfidogenic) microbial systems, only limited study has yet been conducted on the comparable effects of soluble sulfides which might occur within aerobic wastewater treatment systems. Admittedly, aerobic reactors would not normally be considered conducive to the presence of reduced sulfur constituents, but there do appear to be a number of processing scenarios under which related impacts could develop, particularly for sensitive reactions like nitrification. Indeed, the following scenarios might well involve elevated levels of reduced sulfur within an aerobic reactor environment: (1) mixed liquor recycle back through sulfide-generating anaerobic zones (e.g., in conjunction with biological nutrient removal processes, etc.), (2) high-level side-stream sulfide recycle via sludge digestion, etc., back to aerobic reactors, and (3) high-level influent sulfide inputs to wastewater treatment facilities via specific industrial, septage, etc., streams. The objective of this study was, therefore, to determine the subsequent metabolic impact of soluble sulfide under aerated and unaerated conditions, focusing in particular on ammonia-oxidizing bacteria due to their critical first-step role with nitrification. The obtained results indicated that, under catabolically active conditions, cultures of ammonia oxidizers were extremely sensitive to the presence of sulfide. At total soluble sulfide concentrations of 0.25 mg l(-1) S, active ammonia oxidation was completely inhibited. However, immediately following the removal of this soluble sulfide presence, ammonia oxidation started to recover; and it continued to improve over the next 24 h. Similar sulfide impact tests conducted with inactive ammonia oxidizers exposed during anaerobic conditions, albeit at higher dosage levels, also revealed that their subsequent aerobic activity would correspondingly be retarded. These results indicated that, after sulfide exposure under unaerated conditions, subsequent aerobic oxidative activity rates rapidly decreased as the soluble sulfide exposure was increased from 0.5 gm l(-1) S to 5 mg l(-1) S and that further reductions in this activity progressively developed as the concentration was increased to 200 mg l(-1) S. The recovery following unaerated exposure to sulfide was significantly higher at pH 7, as compared with pH 8, and although the specific nature of this variation was not established, a hypothetical explanation appeared warranted.
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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 | 0.001 | 0.001 |
| 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".