Besides solar fuels that can replace fossil fuels in various applications, concentrated solar energy may also be used directly to satisfy thermal or power needs of various processes. For instance, solar energy could be incorporated in the sector of waste treatment that comprises another modern-day management problem that deals with hazardous compounds. After basic processing, such products are usually disposed of in sites with limited storage capacity. Due to this space limitation, technologies that recycle hazardous materials and convert them into valuable products have been developed. The recycling technologies used require thermal processes with high energy demand and thus use huge amounts of fossil fuels. Incorporation of solar energy in such processes would play a significant role both economically and from an environmental point of view (Steinfeld and Meier, 2004).
An attractive way to treat toxic chemical wastes (including large varieties of industrial products, pharmaceuticals, and everyday chemicals) and avoid the production of toxic products during their combustion (Tributsch, 1989), would be to first pyrolyze them in closed reactors and then treat them under suitable conditions (temperature and pressure) with hydrogen. The final products of this process would be similar to upgraded products retrieved from natural gas and mineral oil (Tributsch, 1989). This process would have even higher worth if the hydrogen used were derived from solar energy and water. A similar process, that requires high temperatures and solar hydrogen as a reducing agent, could be applied for the recycling of oxidized metals (e. g., Fe2O3, Al2O3, CuO or PbO).
By-products that may derive from these processes, such as soot and amorphous carbon, could be used in other applications, for example the tire and color industries. Besides the significant environmental benefits, such applications also have high economic benefits that are more considerable for industries, since they produce valuable by-products and eliminate the high cost of the disposal of their chemical wastes (Tributsch, 1989).