Development of a jar testing protocol for chemical phosphorus removal in activated sludge using statistical experimental design

Jar testing is an important tool for the determination of the best chemical dosing regime for a wastewater treatment process. A consistent methodology has been developed for physico-chemico processes such as sedimentation and coagulation. These techniques however, may not be applicable for precipitation processes in a biological system. A jar testing methodology was developed for the chemical removal of phosphorus from activated sludge mixed liquor. In these studies, the optimum conditions for 5 precipitants in activated sludge were determined to compare their relative effectiveness. The precipitants studied were aluminium sulphate, ferrous sulphate, ferric chloride and two aluminium-based polyelectrolyte compounds. Optimisation of this process by a conventional method requires many tests and is time consuming. A 7 factorial design experiment was used firstly to identify the most important variables, followed by a statistical “hill climbing technique” to determine the optimum conditions for a specific chemical precipitant. Using only 20 tests per chemical (not including repeats), good phosphorus removal efficiencies (ranging from 87.8–96.6%) were produced for all of the precipitants.