Pressure signal analysis of combined water and air backwash of rapid gravity filters

Many problems encountered in water filtration are associated with the effectiveness of backwashing. Combined air and water backwashing especially using flow rate combinations resulting in “collapse-pulsing” provide the most effective cleaning. This study examines a technique of analysing pressure signal fluctuations in order to determine the onset of “collapse-pulsing”. The technique provides a non-subjective and practical method of “collapse-pulsing” determination. The resultant pressure fluctuation traces are examined in combination with headloss versus water velocity profiles at particular set air flow rates. The occurrence of significant fluctuation patterns at the position where headloss becomes constant implies that “collapse-pulsing” determined by this technique is the onset of three phase fluidisation.