Digested sewage sludge resulting from sewage plant treatment of municipal sewage is disposed of and used in an ecologically acceptable manner by the incorporation of such sludge in hardenable compositions further including, for example, lime, fly ash and, in some cases, alkaline earth metal sulfates and/or soil or other inert or complimentary additives. These hardenable compositions may be emplaced in an area open to the atmosphere and permitted to cure over a period of time to act as land fill or as road base materials.