How do ultraviolet rays kill bacteria in wastewater treatment?

Ultraviolet (UV) rays kill bacteria primarily by destroying their cellular genetic material, specifically DNA. When microorganisms are exposed to UV light, the energy from the UV radiation causes the formation of thymine dimers, which are abnormal covalent bonds between adjacent thymine bases in the DNA strand. This disruption prevents the bacteria from replicating and synthesizing proteins essential for their survival, ultimately leading to cell death.

This method of disinfection is effective because it targets the core mechanism of cellular functions, thereby making it highly efficient against a wide range of pathogens without introducing harmful chemicals into the environment. Other methods of disinfection, such as chemical agents, apply substances that can pose hazards or lead to residual contaminants, while heating typically requires high temperatures, which may not be feasible or efficient for larger volumes of water. Increased air exposure does not directly address microbial death and instead relates more to aerobic processes in treatment systems.