What is the acceptable final effluent free chlorine residual range?

The acceptable final effluent free chlorine residual range is crucial for ensuring effective disinfection in wastewater treatment systems. A range of 0.2 to 1.5 mg/l is recommended because it provides sufficient chlorine to eliminate pathogens while minimizing the risk of harmful byproducts. When free chlorine levels are maintained within this range, it ensures that the treated effluent can safely be returned to the environment or used for other purposes, such as irrigation, without posing a risk to human health or ecosystems.

This range accounts for factors like varying chlorine demand and contact time, ensuring that disinfection is effective. Chlorine levels that are too low may not be sufficient to kill pathogens, while levels that are too high can lead to excessive formation of chlorinated byproducts which may be harmful. Thus, the chosen range strikes a balance between effective disinfection and environmental safety, adhering to regulatory standards. The other options fall outside this optimal range, making them unsuitable for effective and safe wastewater treatment practices.