A light weight medium for growing microorganisms includes a mass of polymeric foam, such as a polyurethane foam, having an outer region enclosing an inner region. A plurality of fragments of an inorganic material, such as sand, are at least partially embedded in the outer region. The light weight medium may be used to support growth of microorganisms in a wide variety of biological and/or biochemical processes, or may be used without microorganisms in chemically treating wastes.