US Patent 7381336 Automated water treatment system and method of use

An automated method for controlling a solids inventory in a continuous backwashing upflow sand filter system treating a liquid inflow having impurities therein, includes the steps of: monitoring an influent inflow pressure and controlling the air pressure in an air lift pump to maintain a target ratio range between the size of a solids inventory of the system and the size of the sand bed of the system.