Which of the following is not classified as a physical method of wastewater treatment?

Electrodialysis is characterized as a physical-chemical process rather than purely a physical method of wastewater treatment. It utilizes an electric field to drive the transport of ions through selective ion-exchange membranes. This process is designed to remove dissolved solids and can be affected by the chemical composition of the wastewater.

In contrast, filtration, settling, and activated sludge processes focus on the physical or biological manipulation of wastewater without reliance on electrical currents. Filtration physically separates solids from liquids, settling allows gravity to remove suspended particles, and activated sludge processes rely on biological processes to treat wastewater but include significant physical aspects such as aeration and sedimentation. Therefore, among the given options, electrodialysis stands out as a method that integrates electrical energy into the separation process, distinguishing it from the other purely physical methods of treatment.