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Surfactants as bubble surface modifiers in the flotation of algae: dissolved air flotation that utilizes a chemically
Rita K Henderson1, Simon A Parsons, Bruce Jefferson
1Centre for Water Science, Cranfield University, Cranfield, Bedfordshire MK43 0AL, United Kindgom.
Environmental Science & Technology
|August 6, 2008
Summary
Surfactant-modified bubbles in dissolved air flotation (DAF) enhance Microcystis aeruginosa removal. Cationic surfactants improved efficiency, with optimal performance linked to surfactant hydrophobicity and DAF recycle ratio.
Area of Science:
- Environmental Engineering
- Water Treatment Technologies
- Colloid and Surface Science
Background:
- Dissolved air flotation (DAF) is a key water treatment process.
- Bubble modification with surfactants can potentially enhance DAF efficiency.
- Microcystis aeruginosa poses challenges in water treatment due to its prevalence and potential toxicity.
Purpose of the Study:
- To investigate the impact of surfactant-modified bubbles on dissolved air flotation (DAF) efficiency.
- To determine the optimal surfactant characteristics and operational parameters for enhanced removal of Microcystis aeruginosa.
- To explore the relationship between particle size, surfactant properties, and removal efficiency in DAF.
Main Methods:
- Investigated bubble modification by dosing various surfactants into the DAF saturator.
- Assessed cell removal efficiency for Microcystis aeruginosa under different surfactant types and concentrations.
- Varied the recycle ratio in the DAF unit while maintaining a constant dose-to-saturator ratio.
- Evaluated bubble collection efficiency and its relationship with influent cell concentration and recycle ratio.
- Examined the effect of particle size on removal efficiency and required surfactant dose for different species.
Main Results:
- Cationic surfactants significantly improved Microcystis aeruginosa cell removal efficiency.
- Optimal removal was achieved with 0.0022-0.004 mequiv L(-1) cationic surfactant, dependent on hydrophobicity and adsorption.
- Maximum removal efficiency of 87% for M. aeruginosa was observed with increasing recycle ratio.
- Bubble collection efficiency remained constant at approximately two cells per bubble.
- Larger species showed increased removal efficiency and required lower surfactant doses, aligning with theoretical predictions.
Conclusions:
- Surfactant modification of bubbles, particularly with cationic surfactants, is an effective strategy to enhance DAF performance for Microcystis aeruginosa removal.
- Surfactant hydrophobicity and adsorption at the bubble interface are critical factors influencing removal efficiency.
- DAF operational parameters, such as recycle ratio, play a significant role in optimizing treatment efficacy.
- The findings support the potential for tailored surfactant application in DAF for improved removal of various aquatic species based on their size and surface properties.
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