Mineral nitrogen recovery from manure slurry through multi-layer sorption of NH3 and CO2 onto pyrolyzed biomass

View the project final report

Commodities

• Miscellaneous: Biomass-derived organic fertilizer

Practices

• Animal Production: manure management
• Crop Production: fertilizers, water management
• Education and Training: participatory research
• Energy: byproduct utilization
• Farm Business Management: new enterprise development
• Natural Resources/Environment: carbon sequestration
• Pest Management: compost extracts, sanitation
• Production Systems: integrated crop and livestock systems
• Soil Management: composting, nutrient mineralization, soil analysis, soil chemistry, soil quality/health
• Sustainable Communities: new business opportunities, sustainability measures

Nitrogen management is a major challenge in agricultural systems, its procurement and disposal costing farmers thousands of dollars annually. The shift toward sustainable farming highlights the need for tighter coupling between waste nutrients and nitrogen fertilizer. We propose a method by which nitrogen in dairy manure can be sustainably recovered through adsorption and precipitation reactions with biochar in the presence of carbon dioxide. Through column experiments, we will evaluate which nitrogen species in liquid manure, whether volatile ammonia, dissolved ammonia, or ionic ammonium, facilitates the greatest extent of ammonium bicarbonate precipitation. We will also evaluate the effect of biochar surface area and surface charge on nitrogen loading. The final product, biochar intercalated with crystalline ammonium bicarbonate, is expected to contain between 10-20% plant-available nitrogen per unit weight biochar, a proportion commensurate to commercial fertilizers such as diammonium phosphate (18% N) and ammonium bicarbonate (17.7%). The effectiveness of our mineral-organic combination fertilizer will be tested in a greenhouse trial with wheat, with the expectation of improved plant nitrogen use efficiency compared to synthetic N and liquid manure. For, even as ammonium bicarbonate dissolves upon incubation in soil, extended retention in soil will be facilitated through repeated sorption and desorption on biochar surfaces over time. Together with our collaborators from Cornell ProDairy, Innovation Center for US Dairy, and GreenTree Garden, we will develop a process by which liquid dairy manure can be re-purposed as dry, crystalline nitrogen fertilizer in a manner which neither compromises crop nutrient needs or environmental quality.

1. To determine the optimal nitrogen (N)-exposure method, whether ammonia (NH3) gas, soluble NH3, or soluble ammonium (NH4+), which facilitates ammonium bicarbonate (NH4HCO3) precipitation through multi-layer adsorption of NH3 and carbon dioxide (CO2). For this objective, we will pyrolyzed manure solids and expose them to ammoniacal N as either gaseous NH3, dissolved NH3, and NH4+ from the liquid fraction of separated manure.

H1: We hypothesize that N exposure via gaseous NH3 will facilitate greater N loading than exposure to dissolved NH3 and NH4+. NH3 forms hydrogen bonds with surface functional groups in a similar manner as water. Thus, hydration may inhibit chemisorption of NH3. Ionic NH4+ will electrostatically bond to negatively charged surface functional groups which have lower pKa values than the pH, 6, of the buffered solution. 

2. To determine the relative contribution of two signature properties of biochar: surface area and extent of oxidation, on N loading through multi-layer adsorption of NH3 and CO2. For this objective, we will create a set of pyrolyzed manures characterized by different surface properties and degrees of oxidation. 

H2: We expect oxidized biochar which contains a higher proportion of oxygenated functional groups to facilitate strong NH3 adsorption. NH3 adsorption will in turn increase the quantity of amine functional groups, enhancing CO2 adsorption. Without initial surface re-functionalization with NH3, subsequent layers of CO2 and NH3 are unlikely to develop. It follows that we expect the greatest N loading on biochar characterized by both high surface area and high extent of oxidation. 

3. To assess the plant- availability of N-loaded biochar when amended to PVC-packed columns full of sand.  

H3: We expect 75% of N retained on biochar to be precipitated as NH4HCO3 and to be plant-available. The remaining 25% is expected to be chemisorbed and available after extended incubation in soils. 

4. To test, in a greenhouse trial with wheat, whether N-loaded biochar improves plant nitrogen-use efficiency (NUE) compared to NUE resulting from synthetic N and liquid manure additions. 

H4: We expect the greatest plant NUE with N-loaded biochar due to reactive surface functional groups in biochar which are able to re-sorption and retain dissolved NH4 over a growing season.