Which of the following is used to disinfect wastewater?

All of the above

The correct answer is option 4. All of the above

All of the above options (ozone, chlorine, and UV light) are used to disinfect wastewater.

Here's a brief explanation of each method:

Chlorine: This is a widely used and effective disinfectant for wastewater treatment. It is relatively inexpensive and kills a broad spectrum of bacteria, viruses, and other pathogens. However, chlorine can also react with organic matter in the water to form disinfection byproducts (DBPs) that are potentially harmful.

Ozone: This is a powerful oxidant that can effectively disinfect wastewater and is more selective than chlorine in its reactions, meaning it forms fewer DBPs. However, ozone is more expensive to generate and can be less stable in water compared to chlorine.

UV light: This method uses ultraviolet radiation to disrupt the DNA of microorganisms, rendering them inactive. UV light is effective against a wide range of pathogens and has minimal environmental impact. However, it requires specialized equipment and may not be as effective in highly turbid (cloudy) wastewater.

The choice of which disinfection method to use depends on several factors, including the desired level of disinfection, cost-effectiveness, regulatory requirements, and the specific characteristics of the wastewater. In many cases, a combination of these methods may be used to achieve optimal disinfection results.