ABSTRACT
Screening is normally the first unit operation used at wastewater treatment plants. The general purpose of screens is to remove large objects such as rags, paper, plastics, metals, and the like. The applications range from removal of settleable solids such as grit and primary sludge to polishing of effluent from final clarifiers. This chapter presents different types of screening devices and the design criteria for bar racks. It discusses step-by-step design procedure, operation and maintenance, and equipment specifications for bar racks in the design example. Screening devices can be broadly classified as coarse or fine. Screens may be manually or mechanically cleaned. The screen channel is designed to prevent the accumulation of grit and other heavy materials into the channel. The mechanically cleaned bar screens shall be operated by an independent, motor-driven time clock adjustable to give cycles ranging from 0 to 150 min. The control panel shall be enclosed and shall contain starters, circuit breaker, control relays, and transformers.
