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

[Image: see text] The amine-rich surfaces of pyrolyzed human solid waste (py-HSW) can be “primed” or “regenerated” with carbon dioxide (CO(2)) to enhance their adsorption of ammonia (NH(3)) for use as a soil amendment. To better understand the mechanism by which CO(2) exposure facilitates NH(3) adsorption to py-HSW, we artificially enriched a model sorbent, pyrolyzed, oxidized wood (py-ox wood) with amine functional groups through exposure to NH(3). We then exposed these N-enriched materials to CO(2) and then resorbed NH(3). The high heat of CO(2) adsorption (Q(st)) on py-HSW, 49 kJ mol(–1), at low surface coverage, 0.4 mmol CO(2) g(–1), showed that the naturally occurring N compounds in py-HSW have a high affinity for CO(2). The Q(st) of CO(2) on py-ox wood also increased after exposure to NH(3), reaching 50 kJ mol(–1) at 0.7 mmol CO(2) g(–1), demonstrating that the incorporation of N-rich functional groups by NH(3) adsorption is favorable for CO(2) uptake. Adsorption kinetics of py-ox wood revealed continued, albeit diminishing NH(3) uptake after each CO(2) treatment, averaging 5.9 mmol NH(3) g(–1) for the first NH(3) exposure event and 3.5 and 2.9 mmol NH(3) g(–1) for the second and third; the electrophilic character of CO(2) serves as a Lewis acid, enhancing surface affinity for NH(3) uptake. Furthermore, penetration of (15)NH(3) and (13)CO(2) measured by NanoSIMS reached over 7 μm deep into both materials, explaining the large NH(3) capture. We expected similar NH(3) uptake in py-HSW sorbed with CO(2) and py-ox wood because both materials, py-HSW and py-ox wood sorbed with NH(3), had similar N contents and similarly high CO(2) uptake. Yet NH(3) sorption in py-HSW was unexpectedly low, apparently from potassium (K) bicarbonate precipitation, reducing interactions between NH(3) and sorbed CO(2); 2-fold greater surface K in py-HSW was detected after exposure to CO(2) and NH(3) than before gas exposure. We show that amine-rich pyrolyzed waste materials have high CO(2) affinity, which facilitates NH(3) uptake. However, high ash contents as found in py-HSW hinder this mechanism.