This problem pertains to the class Environmental Engineering. Please provide all details to help with understanding. Thanks in advance. Problem $4($category: disinfection$)$ An old treatment plant uses a slow sand filtration. Currently the plant uses chlorine dioxide as a disinfectant. However, the on$-$site equipment that produces the chlorine dioxide is old and needs to be replaced. There have also been some close calls in regards to the safety of operators.

Consequently, the plant is considering switching to free chlorine. The plant would like to keep the chlorine dose to a maximum of $1\mathrm{.}8$ mg$/$L for cost in storage reasons.

The average water temperature is $5\backslash$deg C in the winter and $20\backslash$deg C in the summer. The average water pH is $7\mathrm{.}5$ in the winter and $7$ in the summer.

The hydraulic residence time of the chlorine contact chamber is $45$ minutes and the chamber has a baffled inlet with some intra$-$basin baffles.

Advise the plant as to whether the switch will pass EPA requirements for Giardia and virus log$-$inactivation. If not, we can be changed $($with minimal expense$)$ so the requirements are met.