Valuable material recovery from solid waste residues

Nearly half of the 281 million tons per year (T/yr) of municipal solid waste (MSW) that is produced in the U.S. is sent to landfills. Waste-to-Energy (WtE) facilities are the only viable alternative to this that matches the scale of waste produced, producing electricity and reducing the waste volume. The declining cost of electricity due to increased natural gas and renewable electricity generation means the WtE facilities need to go beyond energy generation. MSW contains valuable materials that must be recovered and incorporated back into the economy.

This project focuses on the treatment of waste to energy ash with other waste streams like gypsum wallboard and spent Fluidized Catalytic Cracking catalyst (FCC) that can change the oxidation state of metals and convert them into more extractible forms. The testing involves the addition of non-MSW waste streams such as wallboard diverted from the construction and demolition streams and spent clay-based FCC catalyst wastes. Currently spent FCC catalysts are classified as non-hazardous and amount to nearly 400,000 tons annually which are currently sent to landfills. Gypsum waste is estimated at 13 million tons annually of waste produced annually with only 2% recycled.  Therefore, if these materials can be profitably combined with the nearly 30 million tons of MSW annually processed in WtE facilities, a new avenue would open to increase the value of thermal processing facilities and recover the materials that currently are going directly to landfills.  

 Therefore, the aim is to combine these waste streams with the MSW generated in the WtE plants and treat it thermally process it to recover valuable materials which are landfilled right now. The type of reaction that takes place is solid-solid between the ash and the additives at high temperatures forming metal oxides and different metal complexes. This leads to changes in the oxidation states of the metals and depending on the oxidation state, metal can be easy or difficult to extract. Hence, it is important to study the chemical reactions taking place between the MSW ash when mixed with additives like waste gypsum which is a part of the non-MSW waste stream at elevated temperatures in oxidative environments.

WtE facilities can be viewed as a thermal digester that homogenizes the highly variable incoming MSW into the lowest thermodynamic products of CO2, H2O, heat, and power. These products also have the least value. In the future, the homogenization process can be tuned to allow for the extraction of valuable and useful products and intermediates at higher thermodynamic states. The addition of gypsum into MSW ash has been shown to improve ash behaviour by converting metals like Al, Mn, Mg, and Fe into more extractible phases.

WtE with co-feeds yielding value-added products (syngas and improved solid residues)

Related publications: 

  1. Weckhuysen B. M., & Yu J., “Recent advances in zeolite chemistry and catalysis”, Chemical Society Reviews, 2015, 44(20), pp. 7022–7024.
  2. Li Z., Qiu Z., Yang J., Ma B., Lu S., & Qin C. (2018). “Investigation of phosphate adsorption from an aqueous solution using spent fluid catalytic cracking catalyst containing lanthanum”, Frontiers of Environmental Science and Engineering, 2018, 12(6), pp. 1-11.
  3. Guetteche M. N., Zergua A., & Hannachi S. “Investigating the Local Granulated Blast Furnace Slag”, Open Journal of Civil Engineering, 2012, 02(01), pp. 10–15.
  4. Castaldi M., “Impact of Additives to MSW for Pre-Combustion Enhancement of Syngas and Solid Residue Improvement”, DE-F Tech FOA-0001953 Technical Volume.
  5. Raj Goud Burra, K., Fernández, I., Castaldi, M. J., Goff, S., & Gupta, A. K.,” Effect of Gypsum Waste Inclusion on Gasification of Municipal Solid Waste”, J. Energy Resour. Technol. Feb 2023, 145(2): 021701.