Evaluating the Ecological Footprint of Landfills: A Framework and Case Study of Fargo, North Dakota.

There is growing interest in better understanding the environmental impacts of landfills and optimizing their operation. Accordingly, we developed a holistic framework to calculate a landfill's Ecological Footprint (EF) and applied that to the Fargo, North Dakota, landfill. Parallelly, the carbon footprint and biocapacity of the landfill were calculated. We calculated the EF for six scenarios (i.e., cropland, grazing land, marine land, inland fishing ground, forest land, and built land as land types) and six operational strategies typical for landfills. Operational strategies were selected based on the variations of landfill equipment, the gas collection system, efficiency, the occurrence of fugitive emissions, and flaring. The annual EF values range from 124 to 213,717 global hectares depending on land type and operational strategy. Carbon footprints constituted 28.01-99.98% of total EF, mainly driven by fugitive emissions and landfill equipment. For example, each percent increase in Fargo landfill's fugitive emissions caused the carbon footprint to rise by 2130 global hectares (4460 tons CO2e). While the landfill has biocapacity as grazing grass in open spaces, it remains unused/inaccessible. By leveraging the EF framework for landfills, operators can identify the primary elements contributing to a landfill's environmental impact, thereby minimizing it.

Stabilization of phosphogypsum using class C fly ash and lime: assessment of the potential for marine applications.

Phosphogypsum (PG, CaSO(4).H(2)O), a solid byproduct of phosphoric acid manufacturing, contains low levels of radium ((266)Ra), resulting in stackpiling as the only currently allowable disposal/storage method. PG can be stabilized with class C fly ash and lime for potential use in marine environments. An augmented simplex centroid design with pseudo-components was used to select 10 PG:class C fly ash:lime compositions. The 43cm(3) blocks were fabricated and subjected to a field submergence test and 28 days saltwater dynamic leaching study. The dynamic leaching study yielded effective calcium diffusion coefficients (D(e)) ranging from 1.15 x 10(-13) to 3.14 x 10(-13)m(2)s(-1) and effective diffusion depths (X(c)) ranging from 14.7 to 4.3mm for 30 years life. The control composites exhibited diametrical expansions ranging from 2.3 to 17.1%, providing evidence of the extent of the rupture development due to ettringite formation. Scanning electron microscopy (SEM), microprobe analysis showed that the formation of a CaCO(3) on the composite surface could not protect the composites from saltwater intrusion because the ruptures developed throughout the composites were too great. When the PG:class C fly ash:lime composites were submerged, saltwater was able to intrude throughout the entire composite and dissolve the PG. The dissolution of the PG increased the concentration of sulfate ions that could react with calcium aluminum oxides in class C fly ash forming additional ettringite that accelerated rupture development. Effective diffusion coefficients and effective diffusion depths alone are not necessarily good indicators of the long-term survivability of PG:class C fly ash:lime composites. Development of the ruptures in the composites must be considered when the composites are used for aquatic applications.