Removal of flocculated TiO₂ nanoparticles by settling or dissolved air flotation

Area of Science:

• Environmental Science
• Water Treatment Technologies
• Nanomaterial Engineering

Background:

• Engineered nanoparticles of titanium dioxide (TiO2-NPs) are widely used in industry.
• These nanoparticles are released into aquatic environments, posing a contamination risk to water supplies.
• Effective removal methods are needed to mitigate TiO2-NP pollution in watercourses.

Purpose of the Study:

• To investigate the removal of TiO2-NPs from water using flocculation-based methods.
• To compare the efficiency of settling and dissolved air flotation (DAF) for TiO2-NP removal.
• To analyze the mechanisms and practical aspects of the removal processes.

Main Methods:

• Bench-scale experiments were conducted to remove TiO2-NPs (450 nm mean volumetric diameter).
• Heterocoagulation was induced using iron hydroxide (30-40 mg/L Fe3+) and gelatinized corn starch (10-20 mg/L) as a flocculant at pH 7.
• Removal efficiencies were assessed over time, along with particle size, zeta potential, and floc characteristics.

Main Results:

• Both settling and DAF achieved high removal efficiencies (95-100%) of TiO2-NPs within 5 minutes.
• Treated water exhibited low turbidity (< 3 NTU) and TiO2-NP concentrations (< 1 mg/L).
• DAF produced sludge with higher solids content (1.9% w/w) compared to settling (0.7% w/w), aiding dewatering, but DAF was less efficient at high TiO2-NP concentrations (>100 mg/L).

Conclusions:

• Heterocoagulation with iron hydroxide and starch is a highly effective method for removing TiO2-NPs from water.
• Both settling and DAF are viable and sustainable removal techniques, with DAF offering sludge handling advantages.
• Settling performance improved with higher dosages, indicating its robustness for varying contamination levels.