Plasma Treatment of Organic Waste

  • Plasma Treatment of Organic Waste
The project is to establish the scientific foundations of a novel plasma-catalysis technique to greatly increase worldwide nutrient utilization efficiency of reactive nitrogen for fertilizer.This technology will capture and recycle reactive nitrogen now being wasted (generally lost to the environment) so that less synthetic fertilizer will be needed per unit of food grown. Ammonia released from bacterially degraded, N-containing organic waste such as animal manure, if not trapped, will escape to the environment, triggering a series of damaging reactions. And the organic fertilizer loses N, thus diminishing its effectiveness. Waste acidification has been known for centuries to be effective in trapping otherwise volatile ammonia created in organic waste as an involatile ammonium salt. If nitric acid is used to acidify the waste, the resulting ammonium nitrate has double the nitrogen content compared to ammonium salts made from other acids such as sulfuric acid. This project explores air-based plasma coupled with heterogeneous catalysis in order to efficiently create nitric acid that can in turn be used to acidify organic, nitrogen-rich animal, human and food-based waste.

This method of fixing nitrogen from air requires only electricity, air, water and a source of organic waste containing nitrogen. Large ammonia plants are currently located mostly where inexpensive natural gas is available. This technology would replace some of this natural gas use with distributed, renewable sources of energy such as solar photovoltaic and wind turbines. Electricity needed for the plasma process would be generated where the NH3 is created from bacterially degraded, N-containing organic waste, thus reducing long supply chains from remote fertilizer plants. 

  • Nitrogen Fixation by Air Plasma
Air plasmas have been proposed for nitrogen fixation through production of NOx from air which can be readily converted to nitric acid. However, a major challenge remains in reducing the energy cost of NOx production in air plasmas to make the technology economically competitive. Different types of discharges such as arcs, sparks, dielectric barrier discharges have been investigated for NOx production but they are challenging to compare due to differences in their structure, geometry and excitation modes etc. Different discharges also utilize potentially different chemical reaction pathways to produce NOx. As of yet, there are no general evaluation criteria to determine the qualities of an appropriate discharge configuration for energy-efficient NOx production. 

We found the two key parameters controlling NOx production efficiency to be the average electric field E and average gas temperature T . Using these parameters, we define the dimensionless parameter χ , the normalized product of E and T. Surprisingly, this quantity appears to effectively correlate specific energy cost of NOx production for the discharges we studied as well as results from the literature.