Field-scale evaluation of the chemical–biological stabilization process for the remediation of hydrocarbon-contaminated soil

Abstract

Developing countries face the challenge of growing their economy while reducing the negative environmental impacts of industry, thus requiring treatment technologies that are economical and effective. One recent technology developed in the tropical part of Mexico for the remediation of petroleum-contaminated soil was tested in this scale-up project at an industrial level, whereas previously it had only been tested at laboratory scale; 150 m 3 of bentonitic mud, contaminated with weathered hydrocarbons (3.4°API) at *50,000 ppm, was treated with 4 % Ca(OH) 2 , 4 % organic amendment, and a fine-root tropical grass. Hydrocarbons in soil and in leachates, as well as pH, and acute toxicity (Microtox) were monitored for 28.8 months. At the end of the study, basal respiration, root density, and earthworm toxicity were also measured. The hydrocarbon concentration in soil was reduced to 45 %, and toxicity was eliminated. Hydrocarbons in leachates were reduced to *1 mg/l, safe for human consumption. The pH adjustment depended on low soil moisture and was stabilized at 7.1. Intense revegetation resulted in good root density, within 90 % of nearby uncontaminated soil under pasture. Basal respiration was increased to levels comparable to uncontaminated tropical soils with agricultural use, pasture and gallery forest. At an industrial scale, strict moisture control was necessary for good pH stabilization. By controlling these conditions and applying this novel treatment process, it was possible to transform a heavily contaminated geological material into a non-toxic, fertile, soil-like substrate capable of maintaining a complete vegetative cover and microbial activity comparable to similar soils in a tropical environment.

Mitigation of water repellency in the treatment of contaminated muds using the chemical–biological stabilization process

“…This is the first study to the authors' knowledge of the demonstration of complete soil restoration in a remediation process. In addition to the elimination of toxicity and hydrocarbon concentrations in soil leachates, as well as the restoration of soil microbial activity, root density, and pH (demonstrated previously in Adams et al 2013), this method also restores the normal soil-water relationship, increasing FC, and reducing water repellency to levels which permit a vigorous plant growth (present study). Additionally, this study is the first of its kind that identifies and measures the soil water repellency in a remediation project in the context of in situ soil moisture content with respect to critical soil moisture content-a useful metric to evaluate the success in overcoming soil water repellency caused by petroleum contamination in soil.…”

“…Subsequently, this technology was evaluated at field scale (Adams et al 2013). In this study, a reduction in hydrocarbon concentration of nearly one-half and the complete reduction in toxicity were observed.…”

“…The hydrocarbons in the material were extremely weathered (1.05 g/cm 3 , 31 % asphaltenes). A treatment cell with dimensions of 15 m 9 20 m was built with a typical land-farm design, including earthen berms *1.2 m high, a 1 % grade, 30 mil high-density polyethylene liner (thermally sealed), a sandy leachate collection layer (*10 cm deep), and flow to a leachate recollection pit (see Adams et al 2013). Contaminated material from the mining unit was placed in the cell to a depth of *60 cm and treated by the chemical-biological stabilization process (Adams 2004, see Fig.…”

“…It was considered adequate to monitor for this time period, as more than two complete annual cycles were observed and an excellent vegetative cover was established, with complete reduction in toxicity and recovery of microbial activity to levels similar to other healthy soils in tropical conditions (Adams et al 2013). It is likely that the high temperatures and humidity in this tropical monsoon climate were important factors in this relatively rapid soil restoration (Adams et al 2013).…”

Electrokinetic remediation of perchloroethylene-contaminated soil

“…The contamination of soil with perchloroethylene (PCE) and trichloroethylene (TCE) is widespread (Arjoon et al 2013;Adams et al 2013). PCE is a halogenated aliphatic organic compound which, due to its unique properties and solvent effects, has been widely used in industrial degreasing agent and also used as a solvent in dry cleaning and an ingredient in paints, inks, and disinfectants.…”