Enhancing microplastic removal from natural water using coagulant aids

Area of Science:

• Environmental Science
• Water Treatment Engineering
• Polymer Science

Background:

• Microplastic (MP) pollution is a growing environmental concern, necessitating effective water purification strategies.
• Conventional water treatment methods require optimization for microplastic removal.

Purpose of the Study:

• To evaluate the efficacy of coagulation, flocculation, and sedimentation for removing various types of microbeads from water.
• To identify optimal treatment conditions and key factors influencing microplastic removal efficiency.

Main Methods:

• Investigated the performance of polyaluminium chloride (PAC) and polyacrylamide (PAM) as coagulants and flocculants.
• Optimized parameters including coagulant dosage, flocculant dosage, pH, stirring speed, and sedimentation time.
• Tested removal efficiency across different microplastic types, sizes, and densities in natural water samples.

Main Results:

• Polyaluminium chloride (PAC) demonstrated superior microplastic aggregation with flocs, achieving over 95% removal under optimal conditions (0.4 mmol/L PAC, 3 mg/L PAM, pH 8, specific stirring and sedimentation times).
• Polyacrylamide (PAM) significantly enhanced microplastic removal across various coagulants and microbead types, with peak efficiency at concentrations ≥3 mg/L.
• Removal efficiency was size-dependent, with larger microbeads (>250 μm) removed more effectively (95%) than smaller ones (<250 μm, 49% removal). Denser microplastics settled more efficiently than lighter ones.

Conclusions:

• Coagulation, flocculation, and sedimentation, particularly with PAC and PAM, offer a highly effective method for removing a significant portion of microplastics from water.
• Treatment efficiency is influenced by microplastic size and density, with smaller and lighter particles posing a greater challenge.
• Further research into advanced technologies is needed to address the removal of smaller, less dense microplastics.