does chlorine oxidize NO2 thereby changing it into NO3 during WW disinfection
Indeed, free chlorine oxidizes nitrite (NO2) ions to nitrate (NO3) ions but you have to consider potential side effect such as:
-chlorine residual even at low dosage is toxic to aquatic life so to prevent any damage you would have to do a dechlorination
-you will potentially form THM (trihalomethane)
Removal of NO2 can be done by biological processes.