Life cycle assessment for wastewater disinfection using sodium hypochlorite, peracetic acid or performic acid
Bibliographic record
Abstract
As the need for safe water is increasing, engineers are working on finding more efficient and environment-friendly technologies for disinfection of wastewater in order to provide safe water for discharge into the environment. Chlorination, using sodium hypochlorite (NaOCl), is one of the most commonly used disinfection methods. In recent years, extensive research has been done on performic (PFA) and peracetic acid (PAA), as they have a high oxidation potential and therefore can reduce bacterial and other types of contamination in wastewater. Life Cycle Assessment (LCA) is a holistic method used in order to investigate the environmental footprint of a product or a service over its entire life cycle, i.e. from "cradle-to-grave". The objective of the thesis is to use LCA to demonstrate the advantages in using either NaOCl, PAA or PFA for wastewater disinfection, from an environmental and health perspective. USEtox and Impact 2002+ models were used in order to evaluate their impacts on freshwater toxicity, human toxicity, climate change, mineral resources and non-renewable energy depletion. Data for the study were provided by a treatment plant in Italy near Venice that has performed full-scale disinfection trials using NaOCl, PAA and PFA, and by the North West Langley treatment plant near Vancouver, which traditionally used NaOCl for chlorination and sodium bisulfite for dechlorination, but transitioned to PAA disinfection in 2014. The functional unit for the Venice treatment plant is the removal of 3 log of E. coli from the effluent at a flow of 27 MLD during two months. For the NW Langley treatment plant, the functional unit was the disinfection of the effluent to the limit of 200 MPN/100 ml fecal coliforms at the edge of the dilution zone, from April to October and at a flow of 11.5 MLD. The LCA includes chemical production, infrastructure directly related to disinfection at the treatment plant, ancillary equipment for disinfection, transportation of equipment and the disinfectants, electricity for disinfection process itself as well as the residuals from disinfection. Results from the Venice treatment plant indicate that PFA could be the best option for wastewater disinfection due to the low dose needed to achieve regulatory limits, which reduces the potential impact of chemical production as well as transport. While PFA is more toxic than PAA, the residual concentration is lower leading to similar potential impacts on toxicity. Results from the NW Langley WWTP indicate that dechlorination significantly reduces potential impacts of chlorine on freshwater toxicity, however impacts on human toxicity, climate change and resource consumption (mineral and non-renewable energy) are increased due to the added production and transport of sodium bisulfite. The best choice of disinfectant at NW Langley therefore depends on the environmental priorities of the decision makers and government regulations. For each disinfectant, production is the highest contributor to total potential impacts on climate change, human toxicity and resource depletion. The highest contributor to freshwater toxicity impacts is the chemical residual from disinfection. The choice of chemical disinfectant also depends on regulations, cost and technologies available. The DesinFix unit is only being used in Europe; at this time the US EPA and the Canadian government have not yet approved the use of PFA for wastewater disinfection. Nonetheless, with upcoming reviews in regulations, PFA could soon be available in more countries. Furthermore, a cost analysis would give more information on the economic benefits of using one disinfectant over another.
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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 | 0.001 | 0.001 |
| Meta-epidemiology (narrow) | 0.001 | 0.000 |
| Meta-epidemiology (broad) | 0.001 | 0.002 |
| Bibliometrics | 0.001 | 0.001 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.001 | 0.001 |
| Open science | 0.001 | 0.000 |
| Research integrity | 0.001 | 0.000 |
| Insufficient payload (model declined to judge) | 0.002 | 0.001 |
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".