STAR/STARx ranks highly with respect to sustainability due to the net positive energy generated by the process.
This means the energy generated by smoldering exceeds the sum of the heat sinks and losses: igniting the reaction, heating the contaminated materials up to smoldering temperatures, boiling off water and some volatiles, and radial heat losses.
The net energy surplus increases with increasing scale of the STAR/STARx application. In other words, full field applications are more energy efficient than laboratory experiments and small pilot tests. This occurs for two main reasons. First, larger systems result in a larger thickness of contaminated materials along the treatment path, which generates more energy. Second, larger systems have a larger distance perpendicular to the smoldering travel path, which reduces heat losses.
As a result of this energy efficiency, STAR/STARx has a small carbon footprint relative to other active remediation techniques:
- STARx is applied on-site; this means no off-site transport of materials for landfilling or incineration, with the associated carbon footprint and hazards of transport.
- STARx destroys contaminants close to the source (i.e., in situ or on-site ex situ), reducing the handling, storage, and off-site destruction or disposal with the associated risks and costs.
- Since the reaction is self-sustaining, the contaminant-destroying smoldering reaction will continue for days without external energy input. This contrasts with incineration or endothermic thermal techniques (e.g., thermal desorption, electrical resistive heating, etc.), which requires continuous and copious fuel addition (such as diesel for incinerators) or energy use.
- STAR continuously generates net gains in energy and stores it in the soil, meaning that the taller and wider the scale of the system, the more excess energy that is available for recovery and reuse.
- The only amendment required for STARx is air, which is inexpensive and innocuous.