The purpose of this project is to develop a granular, nitrogen (N) fertilizer from agricultural waste products: pyrolyzed biomass, the liquid fraction of separated liquid fraction (LF) of manure, and carbon dioxide (CO2). In repurposing waste nutrients as crop fertilizers, we aim to prolong the sustainability of the dairy industry as well as field-crop production in New York through improved resource stewardship, reduced environmental degradation, and lower overhead costs. We propose a method for adsorbing ammonia (NH3) and ammonium (NH4+) from LF onto pyrolyzed biomass, or biochar, relying on CO2 to enhance NH3 and NH4+ retention. Preliminary results suggest up to 10% N enrichment per unit weight biochar through mono-layer adsorption (1). Multi-layer adsorption may double results to 20%, or 200 kg/ton, equaling the amount of N removed from 45 m3 of LF (2,3) through exposure to one ton biochar. The hypothesized N-biochar physio-chemical sorption mechanisms will prolong N availability in soils, improving plant N use efficiency (NUE) beyond that of synthetic N to values commensurate to slow release fertilizers (4). Our project is a collaborative effort between the Innovation Center for US Dairy, Cornell University ProDairy extension services, and the GreenTree Garden Center in Ithaca, New York (NY) with an end goal of developing an alternative N fertilizer from LF, CO2, and biochar, which can be scaled to on-farm manure lagoons and industrial manure separation.
The 92200 tons of N excreted annually from NY dairy cows is sufficient to fertilize the state’s corn production (5,6). Obviating the ‘Haber Bosch’ process for NH4+ production can significantly lower fertilizer costs and the carbon footprint of agricultural production. N fertilizer comprises 30% of crop production costs (7), while industrial N fixation from atmospheric N2 via the Haber Bosch process emits 2% of all fossil-fuel-based anthropogenic CO2 worldwide (8). Another concern with synthetic N is its low use-efficiency. Rarely is more than 50% of applied mineral N (NH4+, NO3–) assimilated into crops (9), and leaching of NH4+ and nitrate (NO3–), as well as volatilization of NH3 and nitrous oxide (N2O), are common loss pathways. Nevertheless, utilizing manure N for crops is not a straightforward task, and proximity to the site of excretion rather than an actual need determines where nutrients are deposited. Farms with excess manure repeatedly inject slurry rather than trucking it to nutrient deficient farms due to prohibitive transportation costs (5,6). Such practices cause eutrophication of surface waters, groundwater contamination, and volatilization of greenhouse gases (10).
Technologies such as solid-liquid separation of manure are a first step in efficient re-use of waste nutrients (11). However, while manure separation and storage are efficient for offsetting nutrient runoff in early spring, exacerbated methane (CH4) and N2O emissions from stored slurry and LF have been reported (12,13). A technology is needed for removing N from LF and converting it into a granular fertilizer. Physio-chemical methods have proved effective for N removal from waste streams. High NH4+ and NH3 sorption has been observed on zeolites (14,15). However, zeolites must be replaced or regenerated to sustain the N-stripping process (3). Other more readily-available sorbents such as paper (16) and straw (17) have been proposed, yet sorption is limited by low surface area and charge of both materials. Another option which combines the high adsorption potential of zeolites with the resource availability of straw and paper is pyrolyzed biomass, or biochar. Pyrolysis transforms ordinary feedstocks such as straw, woody shrubs, and manure solids into highly porous, surface-functionalized adsorbents (18).
Biochar has proven effective in adsorbing both NH4+ and NH3 through acid-base reactions with carboxylic functional groups (19). However, N-loading can be enhanced beyond mono-layer surface adsorption to multi-layered sorption with CO2, resulting in the precipitation of ammonium bicarbonate (NH4HCO3) (21). Recent work has demonstrated that exposure of biochar to NH3 re-functionalizes surfaces with amine groups (1) in a manner which enhances CO2 adsorption (21,22,23). The incorporation of CO2 molecules may further enhance NH3 retention through the formation of ammonium bicarbonate. Our research will probe the bonding mechanisms and extent of N loading onto biochar through sequential adsorption of NH3 and CO2. Our end goal is to develop an NH4HCO3 -intercalated biochar fertilizer which promotes greater crop NUE than synthetic N (24).
A present-day scenario in NY state is one in which a farmer growing 200-acres of corn spends 28,000$/year for fertilizer (26), while a dairy farmer with 550 cows spends 27,000$/year for manure storage (6). In the removal of N from LF, our project aims to reduce whole farm costs pertaining to crop production and waste management, while mitigating nutrient loading and gaseous emissions into the environment. We will work closely with our collaborators to develop N-removal protocols which are scalable to farm-level manure lagoons as well as county-level treatment facilities.
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.
Preliminary lab experiments have been conducted since September 2017 to determine ammonia (NH3) adsorption on biochars made from manure waste. We have used gravimetry, by which the weight change with NH3 uptake is measured on a microbalance, and the change in carbon (C) and nitrogen (N) stoichiometry to determine the extent of N enrichment following exposure to NH3. As manure biochars contain relatively high N, it is necessary to ‘prime’ their surfaces with a material which enhances affinity to NH3. Carbon dioxide (CO2) as one such material, readily binding to nitrogenous compounds in manure.
Within a thermogravimetric analyzer (TA Q50, TA instruments), we expose small biochars samples to CO2 followed by NH3. We have used oxidized wood and manure waste char, and have used various lengths and sequences of gas exposure. We have also used isotopically-labeled gases, 13CO2 and 15NH3. During the experiment, gases are flushed for one hour through the instrument at low flux rates. The change in weight with adsorption of each gas is monitored every 0.15 seconds automatically by the instrument.
Following the experiment, samples are milled to < 50 microns, and analyzed for changes in total C/N content and with FTIR. We have also sent samples for isotopic probing at the Pacific Northwest National Lab (PNNL) in Washington state.
We have detected that CO2 treatments enhance NH3 uptake, proving that NH3 uptake on high N animal manures is possible if surfaces are altered toward a more acidic manner. Infrared spectroscopy reveal that surface functional groups of oxidized wood and manure biochars develop new nitrogen peaks after exposure to NH3, compared to the spectra of control biochars Samples_PNNL_FTIR122917_004. Our next step is to test isotopic stochiometry to determine uptake of 13C and 15N, as well as the availability of N in NH3-enriched biochar to plants and soil microbes.
Preliminary laboratory data on the nitrogen (N)-enrichment of manure biochar with ammonia reveal that N forms generated are not immediately plant-available, but require months of incubation in soil to degrade. Our material behaves as a long-term fertilizer, and we are working to enhance the availability of bound N for quicker release.