The application of nitrogen (N)–based fertilizers and agricultural techniques, such as composting, contribute significant amounts of ammonia gas (NH3(g)) to the atmosphere. Production of NH3(g) from volatilization of solid and aqueous ammonium (NH4+) causes various environmental hazards and exacerbates nutrient loss from soils to the environment. Adsorption technology for capturing NH3(g) has been studied for typical sorbents including zeolites and biochars. Struvite, (MgNH4PO4●6H2O), is readily precipitated in wastewater treatment plants which facilitates phosphorus (P) and N removal from wastewater. Intentional precipitation of struvite and subsequent application as fertilizer thus promotes wastewater valorization. Due to the availability of struvite recovered from wastewaters, other uses of the mineral should be explored. The aim of this work was to study the adsorption of NH3(g) onto struvite , and its heat-treated decomposition products (HTS). To obtain HTS substrates, struvite was heated in the range 55-300 °C in a muffle furnace. For comparison with typical sorbents, NH3(g) adsorption to two commercially obtained Biochars A and B, was also evaluated (BC-A, BC-B). Adsorption experiments were conducted at 25°C. Samples were placed in a simultaneous thermal analyzer (STA) coupled to a Fourier transform infrared spectrometer (FTIR) for evolved gas analysis (EGA), with NH3(g) added at different concentrations by a pulse thermal analyzer (PTA). The order of total adsorbed mass of NH3(g) was BC-B &gt;BC-A&gt; HTS-150 &gt; HTS-200 &gt;HTS- 250 &gt;HTS-300 &gt;HTS-100 &gt;S-55 &gt; struvite. The adsorption capacities for struvite and HTS solids were in the range 4.1 to 23.5 mg NH3 /g sorbent. Exothermic adsorption enthalpies ranged from -4.6 to -118 J/g. Upon desorption, 100 to 59.2 % of total adsorbate was found to be reversibly bound. Enthalpies of desorption ranged from 1.3- 67.6 J/g. These results showed struvite and heat-treated struvite products could be useful substrates for mitigating NH3(g) emissions.

Quantification of ammonia gas uptake by heat-treated struvite decomposition products using simultaneous thermal analysis – pulse thermal analysis

254th National Meeting (2017)

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