MAY RETENTION BASINS HAVE AN OVERALL NEGATIVE EFFECT?
Mathematical models for sewer networks and for waste water treatment plants are combined to simulate six summer months of actual rainfall in the Oslo area. The sewer network is a combined sewer system. The simulations showed that a retention volume installed at the storm overflow could cause more pollution to escape from the treatment plant on a yearly basis than it could prevent discharging in the storm overflow provided that the following conditions are fulfilled: -The surface load on the secondary clarifier is bigger than ca. 0.7 m3/m2h at dry weather flow. – The average amount of BOD7 in storm runoff (included flushed-out pipe deposits) is less than ca. 50 mg/1.