Rotating Belt Screens: An Attractive Alternative for Primary Treatment of Municipal Wastewater

Properly designed and operated primary sedimentation tanks or clarifiers should remove 50 to 70 percent of the total suspended solids and 25 to 40 percent of the 5-day carbonaceous biochemical oxygen demand from the wastewater feed (i.e., primary treatment performance criteria). The recent development of better screening materials and equipment has allowed the use of fine screen systems typically with a mesh size in the range from 100 to 500 microns, to be used as a replacement for primary sedimentation. The use of fine mesh screen systems may be particularly attractive as the primary treatment step in flowsheets involving innovative biological treatment systems such as the membrane biological reactor and the biological aerated filter where fine screening is required to protect respectively, the membrane component and the influent distribution component. The results from Norwegian and North American pilot and small full scale technology assessment studies imply fine mesh, rotating belt screen (RBS) systems with certain mechanical design and operational features, are a particularly attractive alternative for meeting the primary treatment performance criteria. The study results indicate to maximize the treatment performance of fine mesh RBS systems such as the Salsnes Filter, design and operating parameters of importance include the screen surface hydraulic loading rate, the area of the screen submerged in the wastewater feed, whether a significant mat on the filter surface is maintained and selection of an appropriate screen mesh size.