Question

Two part question:

1) Design a chlorine contact basin (serpentine) to disinfect 1 MGD flow and meet 4- log virus removal with a free chlorine residual of 0.1 mg/L (pH=7, Temp = 25C). Use a length:width ratio of approximately 20:1 and a depth of 4 to 6 feet.

2) Alter the design to achieve 3-log removal of Giardia cysts using free chlorine (still must treat 1 MGD, pH=7, T = 25C). How would the design change if you used chlorine dioxide?

Answer 1

Chlorine treatment chamber or tanks (pre or post treatment) is open to atmosphere with dimensions of 220X11X1.83 metres. The volume is equal to 1MGD assuming US gallon of 4.5 liters.

The chlorine dixoide (gas) is harmful to working persons (ClO₂) and has to be contained in a chamber. The ClO₂ explosive and catches fire hence preserved in chilled water tanks at 5 degree celsius. This also acts as disinfectant but the design principles are different. The volume space is far less compared to conventional chlorination tanks and very effective as disinfectant. It also has no smell unlike chlorine.