Waste valorization

Crop residue Crop residue, such as corncob, and other residues from the food processing industry, such as residues from biorefineries, have high potential for use in further processes, such as producing biofuel, bioplastics, and other biomaterials for industrial processes. Food waste One of the more fruitful fields of work is food waste—when deposited in landfills, food waste produces the greenhouse gas methane and other toxic compounds that can be dangerous to humans and local ecosystems. Human excreta == Mine wastes ==

Mine tailings and other mining residues can be very large in volume and cause significant environmental issues even when stored correctly (such as tailings dam failures and acid mine drainage). Additionally, demand for the rare minerals found in tailings is increasing. Red mud is a byproduct of the Bayer process which is the main process employed to generate alumina from bauxite. Numerous uses of the highly alkaline substance have been proposed, among them mitigating acid mine drainage. The largest waste by volume - especially in open pit mining - is usually overburden which is either used to fill the mine back in when mining ceases or can be used for various construction purposes, as aggregate or to create infill. However, depending on the composition of the material, this may come with risks and hazards if pollutants like heavy metals contaminate the material. In mining operations that remove significant amounts of material even after filling the overburden back in, the resulting land is often below the natural water table. In Germany the former lignite pits were thus turned into the Lusatian Lake District, the Central German Lake District and other similar areas. ==Nuclear waste==

While low and intermediate level waste are usually not the subject of much public attention, they make up the bulk (by volume and mass) of nuclear waste. However, spent fuel is responsible for the vast majority of the radioactivity produced by nuclear power plants. There are active industrial scale applications of waste valorization using spent nuclear fuel - primarily nuclear reprocessing using the PUREX process which yields reactor grade plutonium for use in MOX-fuel as well as reprocessed uranium. In addition to that process, there are numerous proposals and small scale applications of recovering various substances for use. While over 90% of spent fuel is uranium, the rest (namely fission products, minor actinides and plutonium) has also attracted considerable attention. High value products contained in spent fuel have both radioactive applications such as Americium-241 for use in smoke detectors, Tritium, Neptunium-237 for use as a precursor to Plutonium-238 or various industrial radionuclides like Krypton-85, Caesium-137 or Strontium-90, as well as nonradioactive applications as some fission products decay quickly to stable or essentially stable nuclides. Elements in the latter category include xenon, ruthenium or rhodium. There are also proposals to use the decay heat of spent fuel, which is currently "wasted" in the spent fuel pool, to generate power and/or district heating. Strontium-90 is suitable as a fuel for a radioisotope thermoelectric generator and has been extracted from spent nuclear fuel for this purpose in the past. However, the need to process the highly reactive metal into the inert perovskite form Strontium titanate reduces the power density to "only" about 0.46 watts per gram. Caesium-137 can also be used for food irradiation. ==See also==