The finer the screens, the more screenings and organics are removed from wastewater. Typical solids content of raw screenings ranges from 10 to 15 % DS. Fecal matter in the screenings is odorous, attracts pathogen vectors and contains much water. Fecal matter should be washed out of the screenings. Well washed screenings can be better compacted and their transportation and disposal costs are lower. Fine screens remove some BOD but hardly any nitrogen from the inflow. The finer the screens, the more they reduce the BOD/N ratio, which can impair the denitrification capacity during secondary treatment. BOD return from screenings washing reduces this effect.
This paper shares Huber’s findings of 30 years with the readers of this paper. It consists of our practical experience in design, manufacture, installation, service and operation with a variety of screenings washers.