Howden Extended Aeration/ Active Sludge System

This system offers a well-proven method of treating domestic waste water. The reactor/aeration zone is the heart of the process where oxidation of the sewage pollutants is achieved by mixing incoming sewage with recycled activated sludge. The mixed liquor is aerated and agitated to create and maintain an appropriate working level of micro-organisms or biomass. The reaction is a natural process which is sustained by maintaining a correct balance between oxygen input, micro-organisms and incoming sewage load.

Mixed liquor is displaced by incoming flow from the reactor to a stilling chamber/settling zone where clear liquor tends to rise to an upper level collection point whilst more dense sludge liquor settles in a hopper base. This settled activated sludge is then recycled back to the reactor by a recycle pump or alternatively a Howden design air lift. In the reactor it is mixed with incoming sewage. The clear liquor rises gently in the upper section of the settlement zone where it is collected and discharged for final sterilization. A chlorine tank with retention time of at least 30 minutes is provided to receive effluent for sterilization.

Key Stages For EA/AS System

• Pre-Treatment
• Aeration Zone / Reactor
• Settling Zone
• Wet Well
• Recycle Pumps / Air Lift
• Control System
• Chlorine Dosing

If desired, raw sewage can be routed to a septic tank for pre-treatment where floating matter, grease and fats are trapped at surface and heavier solids tend to settle at base.