STARx (Ex Situ) HottpadTM Pilot Test for the Treatment of Oil-Impacted Soil (OIS)

Active Oil Field, South East Asia

The subject Site is an active oil field in South East Asia. A STARx HottpadTM pilot test (IMAGE 1) was conducted to assess the range of soils that could be treated via smoldering combustion. Soil stockpiles were characterized as having high clay and silt content (>70-80%), moderate to high moisture content (15-40%) and variable, non-uniformly distributed oil content (1.0-4.5%) (IMAGE 2). The system consisted of two pilot scale HottpadTM units equipped with the heating elements for ignition and an air distribution system to support the smoldering combustion reaction. Each unit had the capacity to treat approximately 1.0 cubic meter (m3) of soil at a time. Ancillary equipment associated with the HottpadTM system included blowers for air delivery, a vapor collection system, and a control system for heater operation and air flow control (IMAGE 1).

Image 1: Dual HottpadTM pilot system showing injection and extraction blowers and associated piping.
Image 2: High clay-content OIS showing non-uniform distribution of oil within the soil matrix


System Operation and Results

A total of twelve (12) tests were conducted to assess the operational envelope of STARx treatment for soils with varying oil, moisture and clay content while developing information to support full-scale system design. All test soils were successfully treated (IMAGE 3 and 4). Soil mixing to improve oil distribution prior to treatment led to more predictable propagation throughout the soil pile, but the process was shown to be robust and does not require soil homogeneity. Lower injection air flow facilitates more uniform oxygen delivery to the combustion reaction within fine grained matrices.

Image 3: Photographs of OIS before (a) and after (b) treatment.

Image 4: STARx-treated OIS showing oil-free cap (used to reduce vapor temperatures) overlying treated soils.

Post-treatment soils were used in a rehabilitation study and were shown to support vigorous plant growth with only minor NPK fertilizer amendment just 6 weeks after treatment (IMAGE 5).

Image 5: Plants grown from seed in STARx-treated OIS 6 weeks after treatment.


The STARx technology is a rapid, safe, and low-cost treatment option for OIS in South East Asia. The HottpadTM system pilot test:

  • Demonstrated self-sustaining smoldering combustion (i.e., no energy input into the system following ignition);
  • Effectively treated a wide range of soils with high clay content, high moisture content, and variable oil content;
  • Testing supported the decision to select STARx as the full scale remedy for the treatment of 200,000 to 600,000 m3 of OIS; and,
  • Resulted in the collection of data required to support the design of large scale mobile and centralized HottpadTM facilities for the treatment of OIS at the site.

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