AWWA ACE95095

Granular activated carbon (GAC) filters have been used for 20 years to remove dissolved organic matter by adsorption. More recently, it has been shown that, in addition to adsorption of organic matter, GAC is also a good material for the development of attached bacterial films. In practice, GAC filtration is introduced between the ozonation and final chlorination steps. The success of GAC biological filtration requires that the biomass level be carefully controlled and maintained during a maturation period and during backwashing. Since biological GAC filters accumulate both biological and non-biological particles on the filter bed, the difference in the detachment of these groups of particles during backwashing will be an important aspect of operation of these filters. The removal of these particles during backwashing will have a bearing on optimization of backwash strategies for biological filters especially air scour and bed expansion, and assist in controlling bacterial detachment to improve effluent quality in the following filter run. Among mechanisms controlling biofilm reactor performance, biofilm detachment is one of the aspects of the process that is least understood and studied. Understanding the detachment mechanisms of biofilms would also have significance in wastewater treatment and in microorganism transport in groundwater. This study presents the results of an analysis of the detachment of biological and non-biological particles from biological filters during backwashing in terms of a microscopic force model and the evaluation of this model with results from operation of a pilot filter.