Chlorination for Filament Control: A Revised Approach

Well regarded literature (Jenkins, Richard, and Daigger, 2004) continues to offer the same guidance offered in 1986 ( Jenkins, Richard, and Daigger, 1986) regarding chlorination practices to control filamentous bulking in activated sludge plants. This guidance has been widely accepted and embraced by the field during the last 23 years. It states that the chlorination should be applied to the aeration basin biomass inventory at a frequency of at least 3 times/day and at doses of 5 to 12 kg Cl2/1000 kg Mixed Liquor Suspended Solids, MLSS, in both aeration basins and clarifiers/day depending upon the severity of bulking. Typically this dose is applied to the return activated sludge (RAS) line unless greater frequency of exposure requires application directly in the aeration basin. This dose is continued until the desired filament damage is achieved (greater than 60 percent) or the desired improvement in sludge settleability is achieved. At this point, a maintenance dose of 2 to 3 kg Cl2/ 1000 kg MLSS/day may be applied to keep filamentous growth abated.Both authors followed this guidance for years successfully until there were 6 repetitive failures to achieve desired filament damages or sludge settleability improvement for two different industries. This prompted both authors to heavily question the historical approach and to question one of the most noted authorities, Michael Richard in 2004. A new approach was developed and applied successfully at two industries (one where two prior failures had been experienced using the “conventional approach”). This new approach then failed at an industry in 2008 to provide the desired filament damage and sludge settleability control. A “unique approach” was developed that was proven successful at the industry in 2008 where the “new approach” failed. This unique approach is fundamentally sound and should provide a successful future in this practice of chlorination activated sludge for filamentous bulking control.This paper provides case histories using all three approaches (conventional, new, and unique) and concludes with recommendations that should allow practitioners to experience greater success and lower costs in future applications of chlorination to control activated sludge bulking.