Disinfection | Activated Sludge Process | Wastewater Treatment Plant

 Disinfection

Purpose

• Kill or inactivate harmful organisms in the treated effluent before releasing it into the receiving stream.

Process Descriptions

Chlorination

• Chlorine solution can be made by combining chlorine gas and treated effluent, or it can be purchased commercially as sodium hypochlorite solution.
• The clarified effluent from secondary clarifiers is treated with a chlorine solution.
• The initial mixing of the chlorine solution and clarifier effluent is critical to process efficiency.
• Following the addition of a chlorine solution, the effluent is routed through a "chlorine contact tank." The tank provides the necessary detention time to ensure that the disinfectant comes into contact with the organisms.
• At the design annual average daily flow, contact tanks must be sized to provide a minimum of 30 minutes of hydraulic detention time.

Detention time is the time it takes to fill a tank at a given flow rate, or the theoretical time it takes for a certain amount of wastewater to pass through a tank.

Ultraviolet Light Radiation

• Effluent is routed through banks of UV bulbs, where UV radiation kills microorganisms.
• There is no need for a contact tank with a 30-minute detention time.
• To maintain adequate UV radiation, bulbs must be replaced on a regular basis and cleaned.
• It has no residual disinfecting properties.