One hundred seventy-five million metric tons of urea, a simple organic compound, is produced every year. This molecule has a lot of impacts despite its small size. Half of the world's food supply is nitrogen enriched, which allows populations to grow beyond what Malthus or Keynes ever dreamed of.
It consumes half of the global ammonia output, weighing in as an economic powerhouse worth tens of billions of dollars a year. If the century-old reaction is replaced with a green solution, what will happen? With the looming threat of global warming, the amount of fossil fuels used to sustain the process are not negligible.
The reaction produces 2 tons of carbon dioxide for every ton of ammonia and consumes 30 and a half megajoules of energy for every kilogram of ammonia formed. Three quarters of the energy is attributed to hydrogen gas productio n, usually through steam-reformation of non-renewable natural gas, and the rest is spent in the compression steps needed for ammonia formation. This methodology is not un changeable.
Recent innovations in chemistry and green energy hold the potential to diminish the environmental impact of the reaction. A classic example of waste not want not is the synthesis of sustainable ammonia and urea using food waste and brown water as inputs. Motivated by rises in global population and subsequent increases in greenhouse gas emissions, the project highlights the technologies' potential to divert megatonnes of waste by comparing them to three non-treatment processes.
The energy intensity, greenhouse gas emissions, and environmental impacts of processes utilizing green technologies to synthesise ammonia and urea from waste were modelled to determine their respective efficiency compared to current production processes. The study includes dark fermentation bioreactors, anaerobic bioreactors, solid state ammonia solid oxide fuel electrolysis cells,MFI, and electrochemical separation. A sustainable ammonia and urea production process using food waste and brown water as feedstocks was found to be the most efficient way to reduce green house gas emissions.
A two-stage waste treatment system using a dark fermentation process coupled with a water electrolysis-based hydrogen source would produce ammonia with the lowest energy intensity, making it nearly seventy percent more efficient than traditional water electrolysis coupled Haber-Bosch processes, and nearly thirty-seven percent more. Plants utilized well-known systems. The engineering required for integration into waste treatment systems is the only obstacle to making these schemes reality.
The benefits of fertilizers are not taken lightly. It is imperative that new processes are sought out to replace the current ones because their dependence has become unsustainable. Rapid developments in solar-based ammonia and urea refineries have laid out the encouraging groundwork for these changes, but it remains to be seen whether waste and brown water can provide us with a similar promise.
Email: g.ozin@utoronto.ca, Website: www.solarfuels, University of Toronto Modeling and Simulation of a Novel Ammonia Production Process from Food Waste and Brown Water is a reference.
