Impact of the plant rhizosphere and augmentation on remediation of polychlorinated biphenyl contaminated soil

Abstract

This study investigated the interactive effects of bioaugmentation, biostimulation, and the rhizosphere during remediation of Aroclor 1242-contaminated soil. Treatments were repeatedly augmented with polychlorinated bipheny (PCB)-degrading bacteria, inducers (carvone and salicylic acid), surfactant (sorbitan trioleate), minimal salts medium in a 20-cm high soil column, or a combination of these elements. Soils containing a single Brassica nigra plant achieved 61% PCB removal in the 0 to 2 and 2 to 6 cm depths after 9 weeks of bioaugmentation, whereas only 43 and 14% PCB removal, respectively, was achieved in unplanted controls. Gas diffusion coefficients of 13.0 and 5.0 x 10(-7) m2 s(-1) were calculated from a methane diffusion assay for planted and unplanted soils respectively, indicating the positive effect of plant roots on gas diffusion into the soil. A second, modified column study removed 87, 73, 63, and 45% of PCB after 12 weeks in the 0 to 5, 5 to 11, 11 to 26, and 26 to 35 cm depths, respectively, in planted-bioaugmented soils, whereas 65, 54, 53, and 47% of PCB was removed from the planted-minimal salts treatment, respectively. Shifts in the soil microbial community structure were demonstrated by denaturing gradient gel electrophoresis of bacterial 16S ribosomal DNA. Results support that Brassica nigra directly contributed to accelerated PCB removal by increased oxygen diffusion, amendment infiltration, and microbial enrichment.

Rhizosphere processes and management in plant-assisted bioremediation (phytoremediation) of soils

“…Similarly, studies using spiked soils that had been aged for at least several weeks before the experiment started were less successful than those using freshly spiked substrate in terms of the "plant effect" (i.e., the percentage of additional degradation in the presence of a plant relative to an unplanted control at termination of the experiment) on pollutant degradation (e.g. Singer et al 2003;Unterbrunner et al 2007). The highest additional effects of plant treatments were obtained with graminaceous species (Dams et al 2007;Chiapusio et al 2007;He et al 2005He et al , 2007 on spiked soil material.…”

“…Six (Dams et al 2007;Singer et al 2003;Van Dillewijn et al 2007;Johnson et al 2004;Mehmannavaz et al 2002;Child et al 2007) out of the twenty three studies compared the effect of plant inoculation on pollutant degradation. In four studies, biodegradation in the presence of inoculate was slightly (Singer et al 2003) to substantially (Dams et al 2007;Johnson et al 2004;Child et al 2007) enhanced.…”

New Approaches for Bioaugmentation as a Remediation Technology

“…6,86 The selection of specific microorganisms in the rhizosphere has potential advantages for bioaugmentation. 117,215 Specific rhizosphere-competent microorganisms that degrade a given contaminant can be added to soil along with a plant that supports the growth of these microorganisms. By using the plant-microorganism combination, the microorganism is added to soil along with a niche (the plant root) supporting its growth thus increasing the likelihood for the microorganisms' survival.…”

Evaluation of Plant–Microorganism Synergy for the Remediation of Diesel Fuel Contaminated Soil

“…At the same time, the plants exudates and sloughed tissue may enhance the degradation of the complex compounds due to increased bioavailability of the contaminants and the interaction among microbes, nutrients and contaminants (Tesar et al 2002;Banks et al 2003;Kaimi et al 2006). Root growth also opens deeper soil to better water infiltration and oxygen diffusion (Singer et al 2003), disrupts soil aggregates and enhances biodegradation of entrapped hydrophobic contaminants (Banks et al 2003). It also changes the conditions of the soil including carbon dioxide concentration, pH, osmotic potential, redox potential, oxygen concentration, and moisture content (Anderson et al 1993), all of which can help microorganism to achieve high biomass.…”