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A stochastic model of an ozonation reactor
1Swiss Federal Institute for Environmental Science and Technology (EAWAG) and Swiss Federal Institute of Technology (ETH), Duebendorf, Switzerland. gujer@eawag.ch
Water Research
|February 26, 2003
Summary
This study presents a stochastic model for microorganism disinfection in continuous flow reactors, improving predictions for systems with poor performance. Bacillus subtilis spores are not reliable surrogates for Cryptosporidium parvum oocysts in real-world disinfection assessments.
Area of Science:
- Environmental microbiology
- Water treatment engineering
- Mathematical modeling
Background:
- Disinfection lag-phase is challenging to model in continuous flow reactors.
- Deterministic models are insufficient for systems with poor disinfection performance.
Purpose of the Study:
- Introduce a stochastic disinfection model for continuous flow reactors.
- Evaluate the statistical predictability of microorganism inactivation.
- Assess the suitability of Bacillus subtilis spores as surrogates for Cryptosporidium parvum oocysts.
Main Methods:
- Developed a stochastic model tracking individual microorganisms through reactors.
- Combined exponentially distributed transport processes with delayed exponential disinfection kinetics.
- Simulated large populations (up to 10,000 individuals) for statistical evaluation.
Main Results:
- Deterministic models accurately predict disinfection for high-performance systems (>2 log reduction).
- Stochastic models are necessary for reactors with poor disinfection efficacy.
- Bacillus subtilis spores showed significant differences from Cryptosporidium parvum oocysts in real reactors, especially those deviating from plug-flow behavior.
Conclusions:
- Stochastic modeling is crucial for accurately predicting disinfection in underperforming continuous flow reactors.
- Bacillus subtilis spores are unreliable surrogates for Cryptosporidium parvum oocysts in dynamic reactor environments.
- Reactor hydrodynamics significantly influence the efficacy of disinfection and the validity of surrogate microorganisms.
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