Assessment of Technologies for Screening, Floatable Control, and Screenings Handling
Screening and floatable controls are used at wastewater treatment, sanitary sewer overflow (SSO) and combined sewer overflow (CSO) locations. Screening is a preliminary treatment step and used to protect downstream equipment. Screening and floatable control is a means of removing visible inorganic and non-biodegradable organic material from further treatment processes or discharge. In CSO applications screening and floatable control avoids the discharge of visible objectionable material. Screening and screenings handling are among the unpopular processes to deal with due to aesthetic and health concerns, odor, and the historically questionable reliability of the equipment. The operation and maintenance can be costly and labor intensive. Existing and proposed environmental regulations require floatables control from CSO and sanitary sewer overflow (SSO) sites, often at locations that are unmanned. Screening was one of the first methods of removing large solids from wastewater. Coarse screens are used to protect equipment and remove larger objects from the wastewater. Fine screens will remove smaller material and some amount of organic material. Very fine screens or microscreens remove even smaller material and potentially replacing grit removal and primary treatment. The type of screening device used at a particular location depends on the screen opening required and the flow rate. Peripheral devices, such as screenings washing and compaction, are often required to meet final disposal requirements. Generally, the finer the screen, the smaller the material to be removed, and the larger the unit to reduce the head loss through the process. WERF identified the need to assess traditional and emerging screening technologies and provide a review of practices to ensure that new and upgraded facilities will be up-to-date, operator-friendly and reliable. This work reviews applications and issues associated with screening and their peripheral equipment and their use at various locations with a variety of treatment and handling goals.