Which of the following is a physical means of disinfection?

Ultrasonic waves are effective as a physical means of disinfection because they use high-frequency sound waves to disrupt the cellular structures of microorganisms. This method can lead to the destruction or inactivation of various pathogens without the use of chemicals, providing a unique approach to disinfection. The process typically involves creating cavitation bubbles in a liquid medium; as these bubbles implode, they generate shockwaves that can impact and damage the microorganisms present.

While other methods listed, such as chemical treatment and chlorination, rely on chemical reactions to eliminate pathogens, filtration serves primarily to physically remove larger particles, rather than achieving disinfection through microbial destruction. The focus in this context is on the mechanical and physical nature of disinfection, making ultrasonic waves the suitable choice for the question asked.