What is screening and why is it done?

    Screening is the process of removing large material from the wastewater as it enters the beginning of the wastewater treatment process.  When wastewater arrives at the treatment plant, it contains a large amount of debris that gets washed off the streets and into catch basins during rainstorms.  The mechanical bar-screen at the treatment facility removes this material which usually consists of rags, sticks, litter, leaves and just about anything else that can find its way into a catch basin during a storm.  La Porte's screening system consists of two catenary bar-screens.  This allows one to be used as a backup bar-screen if there is trouble with the primary bar-screen.  As the wastewater flows through the screen, level meters monitor the level in front of the screen, and then the level behind the screen.  When the difference between the levels reaches a predefined setpoint, the screen automatically actuates.  This clears the accumulated debris from the screen and allows the level in front and behind the screen to even out again.  The material that is pulled out of the waste stream is then deposited into a holding container and sent off to a landfill for disposal.  Screening is an important part of the treatment process because the removal of large debris helps to reduce wear and blockages on the pumps and other equipment that follows the bar-screen in the treatment process.  After the wastewater is screened, it proceeds to Grit Removal.