Sequential Ammonia and Carbon Dioxide Adsorption on Pyrolyzed Biomass to Recover Waste Stream Nutrients

Abstract

The amine-rich surfaces of pyrolyzed human solid waste (py-HSW) can be “primed” or “regenerated” with carbon dioxide (CO2) to enhance their adsorption of ammonia (NH3) for use as a soil amendment. To better understand the mechanism by which CO2 exposure facilitates NH3 adsorption to py-HSW, we artificially enriched a model sorbent, pyrolyzed, oxidized wood (py-ox wood) with amine functional groups through exposure to NH3. We then exposed these N-enriched materials to CO2 and then resorbed NH3. The high heat of CO2 adsorption (Q st) on py-HSW, 49 kJ mol–1, at low surface coverage, 0.4 mmol CO2 g–1, showed that the naturally occurring N compounds in py-HSW have a high affinity for CO2. The Q st of CO2 on py-ox wood also increased after exposure to NH3, reaching 50 kJ mol–1 at 0.7 mmol CO2 g–1, demonstrating that the incorporation of N-rich functional groups by NH3 adsorption is favorable for CO2 uptake. Adsorption kinetics of py-ox wood revealed continued, albeit diminishing NH3 uptake after each CO2 treatment, averaging 5.9 mmol NH3 g–1 for the first NH3 exposure event and 3.5 and 2.9 mmol NH3 g–1 for the second and third; the electrophilic character of CO2 serves as a Lewis acid, enhancing surface affinity for NH3 uptake. Furthermore, penetration of 15NH3 and 13CO2 measured by NanoSIMS reached over 7 μm deep into both materials, explaining the large NH3 capture. We expected similar NH3 uptake in py-HSW sorbed with CO2 and py-ox wood because both materials, py-HSW and py-ox wood sorbed with NH3, had similar N contents and similarly high CO2 uptake. Yet NH3 sorption in py-HSW was unexpectedly low, apparently from potassium (K) bicarbonate precipitation, reducing interactions between NH3 and sorbed CO2; 2-fold greater surface K in py-HSW was detected after exposure to CO2 and NH3 than before gas exposure. We show that amine-rich pyrolyzed waste materials have high CO2 affinity, which facilitates NH3 uptake. However, high ash contents as found in py-HSW hinder this mechanism.

Enhancing plant N uptake with biochar-based fertilizers: limitation of sorption and prospects

“…Adsorption of NH 3 gas on biochar surfaces appears to reach high values when biochar is activated with acids or oxidants, as detailed in a previous section. Values of 40 to 90 mg NH 3 -N per g biochar (Hestrin et al 2019;Krounbi et al 2020;Ro et al 2015) are well with the future sorbent category presented at Fig. 6.…”

“…While untreated biochar displays only limited sorption for NH 3 gas, i.e. in the range of m 0.15 to 5.09 mg•N g-1 (Ro et al 2015), most promising results have been obtained in experiments using biochar treated with oxidants or acids (Hestrin et al 2019;Krounbi et al 2020;Ro et al 2015). Under pure NH 3 atmosphere, oxidized biochar has been reported to fix between 40.6 and 90.3 mg N g −1 (Hestrin et al 2019; Krounbi et al 2020).…”

“…in the range of m 0.15 to 5.09 mg•N g-1 (Ro et al 2015), most promising results have been obtained in experiments using biochar treated with oxidants or acids (Hestrin et al 2019;Krounbi et al 2020;Ro et al 2015). Under pure NH 3 atmosphere, oxidized biochar has been reported to fix between 40.6 and 90.3 mg N g −1 (Hestrin et al 2019; Krounbi et al 2020). Ro et al (2015) were able to fix up to 52 mg NH 3 -N per g of biochar activated with phosphoric acid in a continuous-flow experiment with 103 ppm NH 3 gas.…”

“…Also, initial research suggests that high P content (e.g. Ro et al 2015) and low K content (Krounbi et al 2020) would facilitate binding of N, suggesting that the resulting product will need blending with other materials to produce a balanced NPK BCF.…”

Plant uptake of nitrogen adsorbed to biochars made from dairy manure

“…They also have the ability to adsorb residual ammonium (NH 4 ) 27 and volatile ammonia gas (NH 3 ) 29 and can enhance plant N-use efficiency 40 . The ability to sorb NH 3 increases after pre-exposure to carbon dioxide (CO 2 ) 41 . Since CO 2 is a by-product of the pyrolysis process 42 , biochars made from the solid portion of dairy manure can be treated with CO 2 before using them to sorb volatile NH 3 from slurry lagoons.…”