Operation of a 27‐m3 biopile for the treatment of petroleum‐contaminated soil

Soil and groundwater contamination due to petroleum hydrocarbon spills is a frequent problem worldwide. In Mexico, even when programs oriented to the diminution of these undesirable events exist, in 2000, a total of 1,518 petroleum spills were reported. Exploration zones, refineries, and oil distribution and storage stations frequently are contaminated with total petroleum hydrocarbons (TPH); diesel fraction; gasoline fraction; benzene, toluene, ethyl benzene, and xylenes (BTEX); and polycyclic aromatic hydrocarbons (PAHs). Among the many methodologies available for the treatment of this kind of contaminated soil, bioremediation is the most favorable, because it is an efficient/low‐cost option that is environmentally friendly. This article discusses the capability of using a biopile to treat soils contaminated with about 40,000 mg/kg of TPH. Design and operation of a 27‐m³ biopile is described in this work, including microbiological and respirometric aspects. Parameters such as TPH, diesel fraction, BTEX, and PAHs considered by the U.S. Environmental Protection Agency were measured in biopile samples at 0, 2, 4, 6, 8, 10, and 22 weeks. A final average TPH concentration of 7,300 mg/kg was achieved in 22 weeks, a removal efficiency of 80 percent. © 2007 Wiley Periodicals, Inc.     

The Hidden Potential of Mass‐based Treatment: A Method for Preventing Rebound

A major challenge for in situ treatment is rebound. Rebound is the return of contaminant concentrations to near original levels following treatment, and frequently occurs because much of the residual nonaqueous phase liquid (NAPL) trapped within the soil capillaries or rock fractures remains unreachable by conventional in situ treatment. Fine‐textured strata have an especially strong capacity to absorb and retain contaminants. Through matrix diffusion, the contaminants dissolve back into groundwater and return with concentrations that can approach pretreatment levels. The residual NAPL then serves as a continuing source of contamination that may persist for decades or longer. A 0.73‐acre (0.3‐hectare) site in New York City housed a manufacturer of roofing materials for approximately 60 years. Coal tar served as waterproofing material in the manufacturing process and releases left behind residual NAPL in soils. An estimated 47,000 pounds (21,360 kg) of residual coal tar NAPL contaminated soils and groundwater. The soils contained strata composed of sands, silty sands, and silty clay. A single treatment using the RemMetrik^® process and Pressure Pulse Technology^® (PPT) targeted the contaminant mass and delivered alkaline‐activated sodium persulfate to the NAPL at the pore‐scale level via in situ treatment. Posttreatment soil sampling demonstrated contaminant mass reductions over 90 percent. Reductions in posttreatment median groundwater concentrations ranged from 49 percent for toluene to 92 percent for xylenes. Benzene decreased by 87 percent, ethylbenzene by 90 percent, naphthalene by 80 percent, and total BTEX by 91 percent. Mass flux analysis three years following treatment shows sustained reductions in BTEX and naphthalene, and no rebound. ©2015 Wiley Periodicals, Inc.     

Evaluation of a soil‐amendment process demonstration for reducing the bioavailability of lead

The U.S. Environmental Protection Agency (EPA) evaluated an in‐situ application of a soil‐amendment process at a residential site that was contaminated with lead. The goal of the evaluation was to determine if the soil‐amendment process resulted in lower concentrations of bioavailable lead in the contaminated soils. The relative bioavailability of lead (bioaccessible lead) was measured by an in vitro test procedure that uses a highly acidic extraction procedure to simulate human digestive processes. The soil‐amendment demonstration showed that the 11.2 percent mean reduction in bioavailable lead concentration between untreated and treated soils was not statistically different. © 2002 Wiley Periodicals, Inc.     

Lysinibacillus sphaericus and Geobacillus sp Biodegradation of Petroleum Hydrocarbons and Biosurfactant Production

Petroleum oil is a major driver of worldwide economic activity, but it has also created contamination problems during the storage and refining process. Also, unconventional resources are natural resources, which require greater than industry‐standard levels of technology or investment to exploit. In the case of unconventional hydrocarbon resources, additional technology, energy, and capital have to be applied to extract the gas or oil. Bioremediation of petroleum spill is considered of great importance due to the contaminating effects on human health and the environment. For this reason, it is important to reduce total petroleum hydrocarbons (TPH) in contaminated soil. In addition, biosurfactant production is a desirable property of hydrocarbon‐degrading microorganisms. Seven strains belonging to Lysinibacillus sphaericus and Geobacillus sp were selected to evaluate their ability to biodegrade TPH in the presence of toxic metals, their potential to produce biosurfactants, and their ability to improve the biodegradation rate. The seven bacterial strains examined in this study were able to utilize crude petroleum‐oil hydrocarbons as the sole source of carbon and energy. In addition, their ability to degrade crude oil was not affected by the presence of toxic metals such as chromium and arsenic. At the same time, the strains were able to reduce toxic metals concentration through biosorption processes. Biosurfactant production was determined using the drop‐collapsed method for all strains, and they were characterized as both anionic and cationic biosurfactants. Biosurfactants showed an increase in biodegradation efficiency both in liquid minimal salt medium and landfarming treatments. The final results in field tests showed an efficiency of 93 percent reduction in crude oil concentration by the selected consortium compared to soil without consortium. The authors propose L. sphaericus and Geobacillus sp consortium as an optimum treatment for contaminated soils. In addition, production of biosurfactants could have an application in the extraction of crude oil from unconventional hydrocarbon resources. © 2014 Wiley Periodicals, Inc.     

Polymer Mineralization in Soils: Effects of Cold Storage on Microbial Populations and Biodegradation Potential

Soil retrieval, processing and storage procedures can have a profound effect on soil microorganisms. In particular, changes in soil microbial populations may adversely affect the biological activity of a soil and drastically alter the soil's potential to mineralize added substrates. The effects of cold storage on the biodegradation of a series of test polymers was investigated using two soils—a synthetic soil mix (SM-L8) and a field soil (Bridgehampton silt loam) from Rhode Island (RI-1). Biodegradation tests were conducted using freshly prepared/collected soil and again following storage at 4°C for 3 to 8 months. Prior to each biodegradation test, the soils were incubated at 60% water-holding capacity (WHC) and 25°C to rejuvenate the microbial populations; the soils were incubated for periods of 48 h (freshly collected soil) or 25 days (soils stored at 4°C). Soil microbial populations were assessed by enumerating different segments of the population on agar plates containing different selective media. Mineralization of the test polymers (cellulose, poly-3-hydroxybutyrate, and starch acetate, d.s. 1.5) was monitored using standard respirometric techniques. Our results demonstrated that cold storage had a generally negative effect on the soil microbial populations themselves but that its effect on the capacity of the soil microorganisms to degrade the test polymers varied between soils and polymer type. Whereas cold storage resulted in dramatic shifts in the community structure of the soil microbial populations, substantial restoration of these populations was possible by first conditioning the soils at 60% WHC and ambient temperatures for 25 days. Likewise, although the effects of cold storage on polymer mineralization varied with the test polymer and soil, these effects could be largely offset by including an initial 25-day stabilization period in the test.     

An In Situ Bioreactor for the Treatment of Petroleum Hydrocarbons in Groundwater

Two pilot tests of an aerobic in situ bioreactor (ISBR) have been conducted at field sites contaminated with petroleum hydrocarbons. The two sites differed with respect to hydrocarbon concentrations. At one site, concentrations were low but persistent, and at the other site concentrations were high enough to be inhibitory to biodegradation. The ISBR unit is designed to enhance biodegradation of hydrocarbons by stimulating indigenous microorganisms. This approach builds on existing Bio‐Sep^® bead technology, which provides a matrix that can be rapidly colonized by the active members of the microbial community and serves to concentrate indigenous degraders. Oxygen and nutrients are delivered to the bioreactor to maintain conditions favorable for growth and reproduction, and contaminated groundwater is treated as it is circulated through the bed of Bio‐Sep^® beads. Groundwater moving through the system also transports degraders released from Bio‐Sep^® beads away from the bioreactor, potentially increasing biodegradation rates throughout the aquifer. Groundwater sampling, Bio‐Traps, and molecular biological tools were used to assess ISBR performance during the two pilot tests. Groundwater monitoring indicated that contaminant concentrations decreased at both sites, and the microbial data suggested that these decreases were due to degradation by indigenous microorganisms rather than dilution or dispersion mechanisms. Taken together, these lines of evidence showed that the ISBR system effectively increased the number and activity of indigenous microbial degraders and enhanced bioremediation at the test sites. © 2013 Wiley Periodicals, Inc.     

Perfluoroalkyl and polyfluoroalkyl substances thermal desorption evaluation

Per‐ and polyfluoroalkyl substances (PFAS) are highly resistant to biotic and abiotic degradation and can withstand very high temperatures before breaking down. The storage of PFAS‐impacted water and sediments in a holding pond or stockpiled investigation or remedial action‐derived waste is occurring on an increasing number of sites. The most common PFAS water treatment options include granular‐activated carbon and resins and the most common soil treatment options have been primarily limited to excavation, offsite incineration, and, in some cases, soil stabilization. An increasing number of states across the United States are establishing part per trillion PFAS guidance levels for drinking water. Removing PFAS from soils removes PFAS source impacts to groundwater. In this study, volatilization of PFAS from soil treated using in situ thermal heating is evaluated as a treatment method to achieve a high degree of PFAS removal from soils. The evaluation of temperatures needed to achieve removal is described. To minimize vapor treatment required for PFAS thermal remediation, a scrubber was incorporated into the treatment train to transfer PFAS to the liquid phase in a concentrated, low‐volume solution. Vapor‐liquid equilibrium behavior and the extent of PFAS volatilization from impacted soil over a range of temperatures were evaluated. Results showed that heating soil to 350°C and 400°C reduces PFAS soil concentrations by 99.91% and 99.998%, respectively. It was also confirmed that sulfonate‐based PFAS generally required higher temperatures for volatilization to occur than carboxylate‐based PFAS.     

Aerobic Biodegradation of Hydrocarbons in High Temperature and Saline Groundwater

A series of laboratory microcosm experiments and a field pilot test were performed to evaluate the potential for aerobic biodegradation of aromatic hydrocarbons and methyl tert‐butyl ether (MtBE; a common oxygenate additive in gasoline) in saline, high temperature (>30° C) groundwater. Aquifer, sediment, and groundwater samples from two sites, one in Canada and another in Saudi Arabia, were incubated for 106 days to evaluate the changes in select hydrocarbon and MtBE concentrations and microbial community structure. Almost complete biodegradation of the aromatic hydrocarbons was found in the Saudi Arabian microcosm samples whereas the Canadian microcosm samples showed no significant biodegradation during the laboratory testing. MtBE degradation was not observed in either set of microcosms. Denaturing gradient gel electrophoresis analyses showed that, while the Canadian microorganisms were the most diverse, they showed little response during incubation. The microbial communities for the Saudi Arabian sample contained significant numbers of microorganisms capable of hydrocarbon degradation which increased during incubation. Based on the laboratory results, pilot‐scale testing at the Saudi Arabian field site was carried out to evaluate the effectiveness of enhanced aerobic biodegradation on a high temperature, saline petroleum hydrocarbon plume. Dissolved oxygen was delivered to the subsurface using a series of oxygen diffusion emitters installed perpendicular to groundwater flow, which created a reactive zone. Results obtained from the seven‐month field trial indicated that all the target compounds decreased with removal percentages varying between 33 percent for the trimethylbenzenes to greater than 80 percent for the BTEX compounds. MtBE decreased 40 percent on average whereas naphthalene was reduced 85 percent on average. Examination of the microbial population upgradient and downgradient of the emitter reactive zone suggested that the bacteria population went from an anaerobic, sulfate‐reducing dominated population to one dominated by a heterotrophic aerobic bacteria dominant population. These studies illustrate that field aerobic biodegradation may exceed expectations derived from simple laboratory microcosm experiments. Also, high salinity and elevated groundwater temperature do not appear to inhibit in situ aerobic biorestoration. © 2014 Wiley Periodicals, Inc.     

Demonstrating the In Situ Biodegradation Potential of Phenol Using Bio‐Sep® Bio‐Traps® and Stable Isotope Probing

The effect of phenol concentration on phenol biodegradation at an industrial site in the south of Wales, United Kingdom, was investigated using standard Bio‐Sep^® Bio‐Traps^® and Bio‐Traps^® coupled with stable isotope probing (SIP). Unlike many ¹³C‐amendments used in SIP studies (such as hydrocarbons) that physically and reversibly adsorb to the activated carbon component of the Bio‐Sep^® beads, phenol is known to irreversibly chemisorb to activated carbon. Bio‐Traps^® were deployed for 32 days in nine site groundwater monitoring wells representing a wide range of phenol concentrations. Bio‐Traps^® amended with ¹³C‐phenol were deployed together with non‐amended Bio‐Traps® in three wells. Quantitative polymerase chain reaction (qPCR) analysis of Bio‐Traps^® post‐deployment indicated an inhibitory effect of increasing phenol concentration on both total eubacteria and aerobic phenol‐utilizing bacteria as represented by the concentration of phenol hydroxylase gene. Despite the chemisorption of phenol to the Bio‐Sep^® beads, activated carbon stable isotope analysis showed incorporation of ¹³C into biomass and dissolved inorganic carbon (DIC) in each SIP Bio‐Trap^® indicating that chemisorbed amendments are bioavailable. However, there was a clear effect of phenol concentration on ¹³C incorporation in both biomass and DIC confirming phenol inhibition. These results suggest that physical reductions of the phenol concentrations in some areas of the plume will be required before biodegradation of phenol can proceed at a reasonable rate. © 2013 Wiley Periodicals, Inc.     

Evaluation of white‐rot fungi for the remediation of creosote‐contaminated soil

Application of fungal‐based bioaugmentation was evaluated for the remediation of creosote‐contaminated soil at a wood‐preserving site in West Virginia. Soil at the site contained creosote‐range polycyclic aromatic hydrocarbons (PAHs) at concentrations in some areas that exceed industrial risk‐based levels. Two white‐rot fungi (Pleurotus ostreatus and Irpex lacteus) were evaluated for remediation effectiveness in a two‐month bench‐scale treatability test. Both fungi produced similar results, with up to 67.3 percent degradation of total PAHs in 56 days. Pilot‐scale testing was performed at the site using Pleurotus ostreatus grown on two local substrate mixtures. During the 276‐day field trial, total PAHs were degraded by up to 93.2 percent, with all individual PAHs except one achieving industrial risk‐based concentrations. It was recommended that fungal‐based remediation be applied to all contaminated soil at the site. © 2002 Wiley Periodicals, Inc.     

Alternative method of groundwater sparging for petroleum hydrocarbon remediation

An alternative method of in-situ groundwater sparging, termed density-driven convection (patent pending), is presented. This method has been successfully used to remediate eight underground storage tank releases involving a wide distillation range of petroleum hydrocarbons (gasoline to waste oil) and in a variety of site soils (clay to sandy gravel). Application of the density-driven convection method is detailed in a case study. The system, installed to remediate a gasoline and diesel release from an underground storage tank, was operated and monitored for a period of one year. Monitoring data indicate reductions in total petroleum hydrocarbon concentrations in groundwater and in soil. Concentrations of aromatic hydrocarbons (benzene, toluene, ethylbenzene, xylenes, and naphthalene) also decreased in both media. Stimulation of natural biodegradation, the primary mechanism of removal, occurred rapidly. Natural biological activity gradually declined over the subsequent 150 days. After one year of operation, the sparging system has achieved or is rapidly approaching the regulatory cleanup goals for both soil and groundwater, including reduction of dissolved concentrations below maximum contaminant levels established under the Safe Drinking Water Act.     

A comparison of mesophilic composting and unamended land treatment for the bioremediation of aged tar residues in soil

A field study was conducted to compare the effectiveness of land treatment and mesophilic composting in removing aged polycyclic aromatic hydrocarbons (PAH) from soil. The soil composting treatment, which had 20 percent (w/w) fresh organic matter incorporated into the soil, reached mesophilic temperatures of 45 to 50°C at week 3–4 and was effective in reducing PAH from 2240 mg/kg to 120 mg/kg after 224 days of treatment. Conventional land treatment with and without added cow manure (5 percent w/w) was less effective in removing the PAH from the soil than was the mesophilic soil composting treatment. In a parallel laboratory trial, PAH concentrations were reduced below 500 mg/kg (the target cleanup concentration for the site) when the contaminated soil was amended with 20 to 30 percent (w/w) fresh organic matter after 186 days of treatment. PAH degradation was lower in the laboratory trial compared with the field trial and no self-heating of soil was demonstrated in the laboratory. Based on the relatively high total heterotrophic and naphthalene-degrading microbial populations in the nonsterile treatments, it was apparent that the absence of microorganisms was unlikely to have limited the biodegradation of PAH in the current study. Fresh organic matter amendments of green tree waste and cow manure, regular mixing of the compost, and maintenance of moisture by regular watering were critical factors in achieving the target PAH concentrations.     

Evaluation of in situ steam‐injection processes for reduction of petroleum compounds within an abandoned canal

A conceptual approach of a novel application of in‐situ thermal processes that would either use a steam injection process or a steam/surfactant injection process was considered to remediate petroleum contaminated sediment residing in an abandoned canal. Laboratory tests were conducted in an attempt to volatilize or mobilize contaminants of concern (selected polycyclic aromatic hydrocarbons [PAHs]) from the contaminated sediment into a phase that could be physically removed. The processes were operated above ambient temperature and pressure in an attempt to increase the removal of the contaminants of concern from the sediment. The ability of both the steam injection process and the steam/surfactant process to remove PAHs from the sediment was considered ineffective; as only two of the seventeen selected PAHs (naphthalene and C1 naphthalene) were associated with a percentage mass reduction greater than 34% for both treatments (four trials). The steam/surfactant injection process generally resulted in higher reductions than the steam injection process, but had larger variances within the two trials using the treatment type. This preliminary evaluation suggests that steam‐based injection processes for removing petroleum contamination from this canal sediment, using the surfactants selected, equipment set‐up, and operating conditions studied, would be considered ineffective. © 2010 Wiley Periodicals, Inc. *

1 This article is a U.S. Government work and, as such, is in the public domain of the United States of America.

     

Bioventing of No. 2 Fuel Oil: Effects of Air Flowrate,Temperature, Nutrient Amendment,and Acclimation

A 14‐month pilot‐scale bioventing study, sponsored by the New Hampshire Department of Environmental Services, was conducted by the University of New Hampshire to determine the effects of the time between the contamination event and the onset of bioventing, as well as air flowrate, temperature, and nutrient amendments. Freshly contaminated soil was not readily amenable to bioventing. Bioventing was effective (82–92.5 percent removal) for acclimated soil amended with nutrients at 10 °C and 20 °C for the 275 cm³/min and 140 cm³/min air flowrates, respectively. First order degradation rates after nutrient addition were ?6.11 ± 0.83 (×10^?3)/day and ?6.57 ± 1.71 (×10^?3)/day, respectively. The results indicate that bioventing will be best applied when the contamination has occurred at least two years before the onset of treatment. © 2014 Wiley Periodicals, Inc.     

Petroleum biodegradation in soil: The effect of direct application of surfactants

The direct application of surfactants to petroleum-contaminated soil has been proposed as a mechanism to increase the bioavailability of insoluble compounds. Solubilization of hydrophobic compounds into the aqueous phase appears to be a significant rate limiting factor in petroleum biodegradation in soil. Nonionic surfactants have been developed to solubilize a variety of compounds, thus increasing the desorption of contaminants from the soil. In this study, laboratory scale land treatment scenarios were used to monitor the bioremediation of petroleum contaminated soils. In efforts to achieve the lowest levels of residual petroleum hydrocarbons in the soil following biotreatment, 0.5 and 1.0% (volume/weight) surfactant was blended into soils under treatment. Two soil types were studied, a high clay content soil and a sandy, silty soil. In both cases, the addition of surfactant (Adsee 799®, a blend of ethoxylated fatty acids, Witco Corporation) stimulated biological activity as indicated by increased heterotropbic colony forming units per gram of soil. However, the increased activity was not correlated with removal of petroleum hydrocarbons. The results suggest that the application of surfactants directly to the soil for the purpose of solubilizing hydropbobic compounds was not successful in achieving greater levels of petroleum hydrocarbon removal.     

Petroleum Hydrocarbons Rhizodegradation by Sebastiania commersoniana (Baill.) L. B. SM. & Downs

Petroliferous activities in Brazil have an accelerated development in the last years. As a consequence, the incidence of environmental accidents such as oil spills and contamination of soils has increased significantly. Therefore, it is extremely necessary to develop remediation techniques with lower costs, decontamination efficiency and impact minimisation. The aim of this work was to evaluate Sebastiania commersoniana phytoremediation potential in soil contaminated by petroleum. This species, which is a native tree, was selected due to its proven capacity for surviving in areas contaminated by petroleum. Experiments were carried out with soils that were vegetated but non-contaminated, soils that were freshly contaminated (25, 50 and 75 g kg^?1) but non-vegetated, and soils that were vegetated and contaminated, samples were collected 60 and 424 days after contamination with the purpose of evaluating the percentage of petroleum degradation in relation to the time. The results obtained in the present study allow us to state that S. commersoniana proves to be tolerant to petroleum contamination with respect to plant’s growth. The degradation of petroleum hydrocarbons was evaluated by gas chromatography with a flame ionisation detector (GC-FID) equipped with a capillary column HP-5 (5% phenyl-methylpolysiloxane, 30 m; 0.25 mm; 0.25 μm). According to chromatographic analysis, samples in contact with S. commersoniana showed a significant area reduction of the hydrocarbon peaks. Analysis of the 60-day samples showed a reduction of petroleum hydrocarbons area higher than 60% and the 424-day samples showed a reduction higher than 94%, which demonstrates that a petroleum degradation process is occurring.     

Effective low-temperature thermal aeration of soils

Low-temperature thermal aeration (LTTA) is a remedial technology developed by Canonie Environmental Services Corp. (Canonie) for use on soils containing nonchlorinated hydrocarbons, chlorinated solvents, volatile organic compounds (VOCs), chlorinated pesticides, and low levels of polynuclear aromatic hydrocarbons (PAHs). The LTTA system separates these hazardous constituents from excavated soils and allows the treated soils to be redeposited on-site without restriction. This article describes the various components and operation of LTTA systems for the remediation of soils contaminated with chlorinated and nonchlorinated constituents. The article also details the results of projects completed to date, principally for soil impacted with chlorinated hydrocarbons, and discusses the general characteristics and results of systems used for soils contaminated with nonchlorinated hydrocarbons (gasoline, etc.).     

Effect of Humic Acids and Fungal Inoculations on Cesium and Lead Concentrations in Lettuce Plants Grown in Contaminated Soils

A study was carried out to evaluate the effect of humic acid additives, applied either individually or in combination with Fusarium oxysporum fungi, on uptake and translocation of cesium and lead in cultivated Lettuce (Lactuca sativa) grown on Mostorud (clayey) and El‐Gabal El‐Asfar (sandy loam soil) soils in a complete randomized block experimental design. The selected soils from contaminated areas (Mostorud soil was irrigated with contaminated industrial water for more than 30 years and El‐Gabal EL‐Asfar soil was irrigated with sewage effluent for more than 50 years). The results indicated that the cesium and lead content was reduced by all treatments of humic acid application individually or when combined with Fusarium oxysporum inoculations, especially at 200 mmol/kg compared to a control and other treatments. On the other hand, retention of cesium and lead occurred in roots more than shoots. ©2016 Wiley Periodicals, Inc.     

Chlorinated Hydrocarbon–Contaminated Site Investigation With Optimized 3D‐CSIA Approach

An optimized “Three‐Dimensional Compound Specific Isotope Analysis (3D‐CSIA)'' investigation was conducted at a chlorinated hydrocarbon–contaminated site in order to (1) determine if multiple onsite sources of groundwater contamination existed and (2) demonstrate the cost‐effectiveness of applying isotope fingerprinting at such a complex contaminated site. Previous groundwater investigations identified chlorinated hydrocarbons at levels that significantly exceed drinking‐water standards but failed to determine the source(s) of contamination due to the lack of vadose‐zone contamination and the absence of groundwater contaminants in shallow portions of the surficial aquifer. To better understand the contaminant source(s), groundwater samples were taken and tested for both the presence of chlorinated hydrocarbons and their isotopic signatures of ¹³C/¹²C, ³⁷Cl/³⁵Cl, and ²H/¹H. A site investigation with an optimized 3D‐CSIA approach revealed multiple chlorinated hydrocarbon releases from different sources, which was also cost‐effective considering the new lines of evidence of target contaminants obtained with the 3D‐CSIA approach instead of any traditional fingerprinting approaches. In addition, the 3D‐CSIA results inferred in situ bioremediation of chlorinated hydrocarbons would be feasible at the site. © 2013 Wiley Periodicals, Inc.     

Potential of Rhizobacteria for Improving Lead Phytoextraction in Ricinus communis

Heavy metal–resistant bacterial strains were isolated from heavy metal–contaminated soils and identified as Bacillus sp. and Leclercia adecarboxylata on the basis of their morphology and biochemical characters using the VITEK 2 Systems Version 05.02. The heavy metal and antibiotic resistance of the isolates were studied. A green house pot experiment was conducted to examine the bacterial ability to extract the lead in soils and for their effect on lead uptake by Ricinus communis in an artificially contaminated soil. Bacterial inoculated pots increased the biomass of the R. communis compared to the uninoculated control, and the root growth of the plant was also increased in the inoculated pot. The experimental data confirmed that lead‐resistant bacteria have a pronounced effect on heavy metal uptake in plants, which may provide a new bacterially assisted phytoremediation of metal‐contaminated soils. © 2013 Wiley Periodicals, Inc.