Abstract: Nutritious materials, including proteins, are separated from acidic waste-activated sludge in a process which comprises:(A) converting by physical means active bacteria in said sludge to an inactive form;(B) subjecting the acidic sludge to an adsorbent material which is capable of adsorbing said proteinaceous material in an uncharged state from said sludge;(C) extracting said proteinaceous material from said adsorbent material by contacting it with an alkaline material having a cationic species to form a mixture of said separated proteinaceous material and said alkaline material; and(D) separating said proteinaceous material from said cationic species and other cations by contacting said mixture with a cation exchange resin.