Method of treatment for separation of oil from oil-containing slurry waste

In the treatment of an oil-containing waste slurry containing sewage sludge, human or animal excrement, household waste, or industrial organic effluents from food processing or wool scouring plants, or mixtures of these materials, a method for separating an oil component from said oil-containing waste slurry comprising the steps of:

• adding a saponifying agent to the waste slurry to saponify part of the oil or fat contained therein;
• stirring the waste slurry containing the thus-formed soap to effect foaming of the waste slurry, whereby the remaining oil component adheres to the foam and rises to the surface of the waste slurry due to buoyancy;
• and
• separating the foam to which the oil component adheres from said waste slurry so that said waste slurry is converted to a slurry with a low oil content, wherein said separated foam to which the oil component adheres is in the form of a water-containing oil component, wherein said saponifying agent is selected from the group consisting of potassium hydroxide and sodium hydroxide in an amount of 1/100 to 1/30 parts by weight based on the amount of the organic substances present in the waste slurry.