Electrokinetic remediation of soil polluted with insoluble organics using biological permeable reactive barriers: Effect of periodic polarity reversal and voltage gradient

Abstract

This study investigated the remediation of clay soil polluted with low-solubility organics (diesel hydrocarbons) using a combined electrochemical-biological technology. Electrokinetic soil flushing was used, coupled with a biological permeable reactive barrier, which was placed into soil away from electrodes to prevent the negative effects of the acidic and basic fronts on the viability of microorganisms. Three two-week long batch experiments were performed in a lab-scale installation specifically designed to evaluate the remediation of polluted soil. The primary variable under study was the electric field applied to the soil (0.5, 1.0 and 1.5 V•cm-1), and the experimental procedure included daily polarity reversal of the electrodes and the addition of anionic surfactant in the electrode wells. The polarity reversal was observed to be a key strategy, which allowed adequate experimental conditions to be maintained in the soil (especially temperature and pH) for the success of the organic biodegradation process. The surfactant was evenly distributed across the soil, which helped the pollutant be transported. The biological activity was not limited to the barrier area but extended to the entire soil portion due to the microbial transport and growth far from the central barrier position. The voltage gradient did not have a strong influence on the measured experimental conditions (soil temperature, pH and moisture) but affected the electroosmotic flow. A higher diesel removal efficiency (36%) was observed when using the higher voltage gradient (1.5 V•cm-1) after two weeks, which demonstrates a promising performance of the studied technology for a future real in-situ application.

[Preprint] An overview of electrokinetic soil flushing and its effect on bioremediation of hydrocarbon contaminated soil

“…However, oxyfluorfen transport is gravitatively/vertically more difficult when compared to dichlorophenoxyacetic acid/2,4-D (Risco et al, 2016). Temperature rises occurring on a laboratory scale (Mena et al, 2016c) is not high enough (even often ignored) when compared with pilot-scale studies (Mena et al, 2016b) where the temperature can rise from 20°C to maximum of 35°C in 1 V/cm of electric field. Maintaining evaporation is very important for electrokinetics and bioremediation (Mena et al, 2015).…”

“…Nutrients and electron acceptors are transferred through soil pores by electrokinetic processes so that increasing bioavailability of contaminants. If the environmental conditions do not support microorganisms growth, electrokinetic can transmit a number of nutrients, electron acceptors, complexing agents, and also surfactant to microorganisms so biodegradation limitation in soil can be reduced (Annamalai et al, 2017;Da Rocha et al, 2009;Guo et al, 2014;Li et al, 2012b;Luo et al, 2006;Mena et al, 2016c). Several researches also suggest that microorganisms can be flushed into soil to improve removal efficiency because indigenous microorganisms can not treat hydrocarbon contaminants effectively (Asgari et al, 2013;Kim et al, 2005;Mao et al, 2012).…”

“…Alkanes have non-polar properties and are difficult to migrate under weak electric field, whereas resins and asphaltenes are polar but have long carbon chains, very strong bonds with soil particles and very difficult to migrate under electric field (Li et al, 2010). Electrokinetic bioremediation has been proven to be used to treat a wide variety of hydrocarbon contaminants, including: polycyclic aromatic hydrocarbons (Lin et al, 2016;Mokhtarani et al, 2016;Wang et al, 2016;Xu et al, 2010), diesel oil Mena et al, 2016c), total petroleum hydrocarbon (Dong et al, 2013;Fan et al, 2015), pyrene , oxyfluorfen (Barba et al, 2017;Risco et al, 2016), and many more. In contrast to other hydrocarbon compounds, BTEX and TCE have large water solubility so they will be easily dissolved in pore fluid (Giannis et al, 2012;Park et al, 2007;Wu et al, 2012).…”

“…This technique is suitable to be applied both in-situ and ex-situ of hydrocarbon contaminated soil. The electrolyte solution is not only consisted of surfactant and deionized water, but also some enhancing agents such as salts, oxidant, and chelants to cover surfactant limitation (Hahladakis et al, 2014;Mena et al, 2016c;.…”

“…In electrokinetic system, surfactants may be added in the electrolyte chambers and flushed to soil pores through electrokinetic mechanism (some researchers often call it electrokinetic soil flushing/EKSF) and mixed it directly into the reactor (Reddy and Cameselle, 2010; Vieira dos Santos et al, 2016). This combined technology has been successfully remove hydrocarbon contaminant from soil (Mena et al, 2016c;. Table 1 describes different performance of EKSF-Bio as standalone technology in treating hydrocarbon contaminated soil.…”