Apparatus for preventing impurities in a washing fluid from clogging an underdrain and methods for preventing clogging of the underdrain and/or monitoring the apparatus

A treatment unit for treating water or wastewater, said treatment unit including:

• (a) a filter bed having one or more layers of filter media;
• (b) an underdrain disposed below said filter bed;
• (c) a compartment for housing said filter bed and said underdrain;
• (d) a washing fluid delivery system for directing a washing fluid upwardly through the underdrain and said filter bed;
• and,
• (e) an underdrain anti-clogging device operably associated with the washing fluid delivery system, said underdrain anti-clogging device being configured to allow the washing fluid to pass through said underdrain anti-clogging device and into the underdrain while trapping impurities in the washing fluid to prevent the impurities in the washing fluid from entering the underdrain.

A method of monitoring, during a washing cycle, fluid pressure of a washing fluid prior to entering an underdrain of an existing or new treatment unit having an underdrain and a filter bed for treating water or wastewater, said method comprising the steps of:

• (a) providing a pressure sensor in a flume or space below the underdrain to monitor a fluid pressure of a washing fluid during a washing cycle in which a washing fluid flows through the flume or space below the underdrain and into and through the underdrain;
• (b) operably associating the pressure sensor with a controller that controls the flow of the washing fluid to the flume or space below the underdrain;
• and,
• (c) discontinuing the flow of the washing fluid to the flume or space below the underdrain when the pressure sensed by the pressure sensor exceeds a predetermined value to prevent damaging the underdrain.