Low-Carbon Fertilizer Production from Tropical Biomass Gasification

The Russian invasion of Ukraine in February 2022 and subsequent 30% spike in fertilizer prices globally highlight the direct links between fossil natural gas and fertilizer production and U.S. national and economic security. Russia is the world’s largest exporter of fertilizer with 21% global market share in potash and 14% in nitrogen fertilizers. In addition, nitrogen fertilizer application produces the over 74.2% of U.S. agricultural GHG emissions, due to synthetic nitrogen offgassing from soil; and this does not even include the GHG emissions from the natural gas used to make the fertilizer. In our home market of Hawaii, over 99% of the food, energy, and fertilizer are imported; the municipal landfill in every county has less than 10 years of life left; and land and fresh water resources are very limited. Fertilizer costs are the highest operating expense for farmers in Hawaii after labor, and fertilizer in Hawaii typically costs 40 to 100% more than the U.S. national average. This price differential doubles again for organic farmers. On the positive side, diverting and re-using waste to displace imports and virgin materials are very popular and frequently requested by community members in municipal and state proceedings, environmental reviews, and unofficial forums. Recycling wood waste from construction and demolition debris (C&D) is also seen as a correction of a historical environmental injustice, as the sole C&D landfill in Hawaii is surrounded by the state’s largest Hawaiian Homeland area. How this problem is being addressed: We are developing an integrated gasification process to convert mixed urban wastes such as “dirty” wood from construction and demolition debris (C&D) into biopower and biofuels. Based upon community input on our proposed bioenergy plant over the past two years, we expanded our feedstock focus to also include “clean” biomass from green waste sourced across the island of Oahu. Enough of this mixed tropical green waste is generated on the island of Oahu alone to supply all of the feed for our commercial-scale gasification plant. Through this work, we discovered that the ash from this “clean” biomass creates an opportunity to re-use the ash and its nutrients as an organic and slow-release nitrogen and potash fertilizer. Our simple estimates of the carbon intensity showed a lifecycle GHG reduction over 97% below traditional fossil fuel fertilizer inputs. Over a third of the ash produced in gasification conditions consisted of mineralized carbon, providing additional GHG benefits through permanent carbon sequestration. Key process objectives we will test with the physical research include: 1. Economically viable collection and preparation for gasification of mixed tropical biomass 2. Physical gasification trial on real-world tropical greenwaste and urban wood waste from Honolulu 3. Physico-chemical analysis of the tropical biomass ash for plant and soil nutrition 4. Fertilizer formulation trials of the ash with other locally-sourced organic nutrient-rich wastes 5. Crop trial in on tropical vegetables and benchmarking against organic and conventional fertilizers 6. System Engineering for a commercial plant using community-informed bioenergy project design 7. Technoeconomic optimization for product quality, community benefit, and commercial viability 8. Workforce development and community benefits opportunity identification Our research partners for this effort include the Energy and Environment Research Center of North Dakota and the College of Tropical Agriculture of the University of Hawaii.