Final answer:
Most treatment plants use chlorine to treat effluent and reduce biological contamination. Ozone is also an effective disinfectant that leaves no harmful residue. Filtration is a method that physically removes microbes from samples without killing them.
Step-by-step explanation:
To further reduce biological contamination, most treatment plants treat the effluent primarily with chlorine. This chemical is effective in killing harmful bacteria and other pathogens in wastewater. While chlorine is commonly used owing to its efficiency, it must be managed carefully to avoid negative impacts on the environment and living organisms. For example, excessive chlorine can be harmful to marine life and humans, hence, sometimes it must be neutralized with other chemicals after it has done its job in disinfecting.
Another method of disinfection is ozone or ozonation, which is a powerful oxidizing agent capable of inactivating various waterborne organisms, including harmful protozoa and pathogens. Ozone disinfection is popular in Europe and has been adopted by some municipalities in North America. It is made on-site and added to water through a process that doesn't leave harmful residues.
It's important to consider that other methods of microbial control are also pertinent. For instance, filtration physically removes microbes from water samples, and it is a technique that does not kill microbes but rather separates them from the water.