Carbon Footprint of Biosolids Disposal to Landfills and Land Farms in the United States

Biosolids offer the opportunity for carbon sequestration or emission retardation. Proper landfill burial allows the long-term sequestration of a large portion of the biosolids carbon. Land application is associated with the retarded return of biosolids carbon to the environment. The emissions due to biosolids transportation to points of disposal may counter the carbon sequestration or retardation potential of biosolids, depending on the transportation mode and on the landfill distance. Furthermore, environmental and health concerns associated with transportation add more reasons to reduce emissions (therefore, carbon emissions) from biosolids transportation.This paper compares the carbon footprints of biosolids disposal using trucks and trains. A carbon footprint model for biosolids disposal using semi-trailer trucks and trains was developed. The specific carbon footprint (i.e., the carbon dioxide equivalent emission per unit mass transported per unit distance covered) and the relative carbon footprint (i.e., the ratio of carbon emissions to carbon potentially sequestrable) are the model outputs. We also calculated ideal turning-point distances, where the diesel emissions for transportation equal the maximum potentially sequestrable carbon in the train or truck load. For example, biosolids trucking from a wastewater treatment plant with 5% of carbon that would exert CO2 (therefore, potentially sequestrable) have an ideal turning-point distance of approximately 500 km (˜310 miles). Since semi-trailer trucks have a specific carbon footprint approximately 10 times that of trains, the “turning-point” for trains is approximately 10 fold.The diminished footprint of train shipments may offer opportunities for carbon-emission offset by switching transportation mode, when possible. In any case, emissions are severely reduced when shipping to nearer disposal sites (when available). Biosolids transportation contributes to global warming, therefore it should be analyzed during evaluation of new strategies for improved biosolids management inclusive of reductions in carbon footprint.