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This paper presents continuous flow two stage activated sludge treatability studies for the treatment of pet food wastewaters characterized by oil & grease concentration of 50,000-66,000 mg l(-1), total COD & BOD concentrations of 100,000 mg l(-1) and 80,000 mg l(-1), respectively. A pre-treatment system, dissolved air flotation (DAF) achieved 97-99% reduction in oil and grease down to about 400-800 mg l(-1). The pilot experimental results showed that for the DAF pretreated effluent, 97% soluble COD removal efficiency can be achieved by using two stage conventional activated sludge system at a 6-7 days HRT and applied initial soluble COD to biomass ratio of 1.17 mg COD mg VSS. Meanwhile, the system achieved 99.9% soluble BOD removal. Analysis of system kinetics indicated that this particular wastewater is very difficult to biodegrade, with an extremely high half velocity constant "Ks" of 5800 mg l(-1). The research showed the potential applications of activated sludge systems for the treatment of high oil and grease wastewater.