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theses

Atmospheric ammonia gas (NH3(g)) forms particulate matter, negatively impacting human and environmental health. Agriculture is the largest source of NH3(g), primarily emitted from nitrogen (N) fertilizers and livestock waste. Sustainable sorbents for managing N-volatilization from agriculture is urgently needed to promote N-conservation. Sorbents reclaimed from agricultural wastes may be viable substrates. Struvite (MgNH4PO4∙6H2O), reclamation in nutrient-rich wastewaters encourages recycling of N and phosphorus (P) from wastes. Thermal analysis (TA) indicated struvite thermally decomposes, undergoing phase transitions at various temperatures, releasing partial to complete water vapor (H2O(g)), and N as NH3(g). Volatilizing ammonium (NH4+(s)) from struvite at low temperatures may enhance struvite’s potential for capture of NH3(g).

Comparing struvite-based sorbents, with conventional biochar and MOF sorbents, for NH3(g) sequestration, a simultaneous thermal analysis-pulse thermal analysis-Fourier transform infrared spectroscopy (STA-PTA-FTIR) technique was used. Sorbents were obtained by heating commercial struvite (HTS) from 55-300 °C, and struvite-bearing solids recovered from swine (S, 95-98% struvite) and dairy (D, 28-33% struvite) effluents to 150 and 300 °C. For HTS sorbents, HTS-150 resulted in highest uptake (23.5 mg NH3(g) g-1 sorbent). For S sorbents, heating to 150 °C (S-150) enhanced sorption capacity (47.2-49.9 mg NH3(g) g-1 sorbent) compared to unheated solids (9.9-11.2 mg NH3(g) g-1 sorbent). Heating D solids caused marginal increases in NH3(g) sorption, and was therefore not as effective, likely due to high calcite content. Biochar (BC) uptake (50.8 mg NH3(g) g-1 sorbent) was similar to S-150; and MOF was significantly higher (289.7 mg NH3(g) g-1 sorbent). After desorption, HTS-150 (38%) and BC (41%) were found to retain similar percentages of NH3(g). Sorption-desorption enthalpies indicated sorption mechanisms were physisorption and chemisorption to solid-state FTIR binding sites. For HTS sorption, speciation of reactive sites was more important than surface area. Sorption-desorption kinetic parameters were calculated from TA curves by model-dependent kinetics. Model-independent kinetics described sorption-desorption as fast, with simultaneous and rate-limiting steps.

The STA and kinetic modeling confirm high-struvite content solids from livestock wastes are promising non-traditional sorbents for NH3(g) sequestration. This work demonstrated STA-PTA-FTIR is an ideal technique for evaluation of gas sorption-desorption phenomena, providing fundamental data comparing common and novel, sustainably-sourced sorbents for NH3(g) sequestration.

ETD_10884

doi:10.7282/t3-6hxr-w929

Ph.D.

Includes bibliographical references

ETD doctoral

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