Abstract: Waste sludges containing up to 35% weight percent hydrocarbon contaminants and up to 50% weight percent inorganic materials are treated to induce acclimation of indigenous microbes present therein, the acclimated indigenous microbes thereby releasing extra-cellular enzymes capable of catalyzing hydrolysis of at least the hydrocarbon contaminants in the waste sludges. This step is pursued until a substantial increase of biological activity takes place in the waste sludges. Biological activity is allowed to continue at an increased rate until the hydrocarbon contaminants are substantially biodegraded.