How long does it take for sewage to enter the treatment plant, treat it, and discharge into rivers and seas?

The average stay time of normal sewage treatment (standard activated sludge method) in Yokohama City varies depending on the amount of inflow sewage, but it is generally treated in about 11 to 14 hours after flowing into the treatment plant. , Released to rivers and the sea.

The general retention time for each processing step is as follows.

• Sediment basin and pump equipment 2 to 5 minutes
• About 1.5 hours at first, sedimentation pond
• Reaction tank 6 to 8 hours
• sedimentation pond 3 to 4 hours
• Disinfection equipment (contact tank) 15 to 30 minutes