Smoldering Combustion (STAR) for the Treatment of Contaminated Soils: Examining Limitations and Defining Success

Abstract

Smoldering combustion, commercially available as the Self‐sustaining Treatment for Active Remediation (STAR) technology, is an innovative technique that has shown promise for the remediation of contaminant source zones. Smoldering combustion is an exothermic reaction (net energy producing) converting carbon compounds and an oxidant (e.g., oxygen in air) to carbon dioxide, water, and energy. Thus, following ignition, the smoldering combustion reaction can continue in a self‐sustaining manner (i.e., no external energy or added fuel input following ignition) as the heat generated by the reacting contaminants is used to preheat and initiate combustion of contaminants in adjacent areas, propagating a combustion front through the contaminated zone provided a sufficient flux of air is supplied. The STAR technology has applicability across a wide‐range of hydrocarbons in a variety of hydrogeologic settings; however, there are limitations to its use. Impacted soils must be permeable enough to allow a sufficient flux of air to the combustion front and there exists a minimum required concentration of contaminants such that the soils contain sufficient fuel for the reaction to proceed in a self‐sustaining manner. Further limitations, as well as lessons learned and methods to mitigate these limitations, are presented through a series of case studies. In summary, the successful implementation of STAR will result in >99 percent reduction in contaminant concentrations in treated areas, limited residual contaminant mass, reduced groundwater contaminant mass flux which can be addressed through monitored natural attenuation; and an enhanced site exit strategy, reduced lifecycle costs, and reduced risk. ©2016 Wiley Periodicals, Inc.

Processes defining smouldering combustion: Integrated review and synthesis

“…Smouldering has been applied commercially for in situ (i.e., on site, below ground) remediation of industrially polluted soil [47][48][49][50][51][52][53][54]. Commercial smouldering systems have been developed to treat waste industrial liquids, such as crude oil tank bottoms, in above ground systems [55].…”

Organic liquid mobility induced by smoldering remediation

“…This concept was recently introduced as a promising remediation approach for contaminated soil [4,5]. Smoldering for the destruction of organic liquid wastes is possible but requires the liquids to be mixed intentionally with an inert porous matrix, such as sand [6].…”

In Situ Thermal Remediation for Source Areas: Technology Advances and a Review of the Market From 1988–2020

“…Additionally, 85% of the STAR projects identified on Figure 3 were performed as pilot tests. As a newer technology that utilizes air injection to control the combustion front, pilot testing will likely continue for STAR designs to establish site‐specific radius of influence, rates of combustion front propagation, mass destruction, and volatile mass loading to the ex situ treatment system (e.g., Grant et al 2016; Savron 2018).…”