Bioaugmentation Of Soil Research Articles

Toxicological Parameters of Albino Rats Fed with Amarantus hybridus Grown on Crude Oil Post-remediated Agricultural Soil

Hydrocarbon and heavy metal accumulation in Amarantus hybridus grown on crude oil post-remediated soil and its effect on the toxicological indices of Wistar albino rats was carried out. Eighteen square metre farmland was divided into three sites (A, B, C) of 4 m2 each and 2 m space was allowed in between the three sites. Two out of the 3 sites were polluted, bioremediated for 16 weeks and healthy seedling of Amarantus hybridus were planted on the three sites. The vegetables were grown for 28 days and their healthy leaves were harvested. The highest growth rate was observed in Amarantus hybridus grown on the bioaugmented soil for 4 weeks with values of 107.20 ± 12.25 cm, 61.69 ± 2.32 cm, 1.72 ± 0.31 g and 0.37 ± 0.02 g for height, leaf area, fresh weight and dry weight respectively. Amarantus hybridus leaves from natural attenuated soil had the highest aliphatic hydrocarbon, polycyclic aromatic hydrocarbon and heavy metal with values of 9.78 ± 0.04 mgkg-1, 7.43 ± 0.09 mgkg-1 and 0.08 ± 0.00 g/100g for C29, Benzo(α)pyrene and Lead respectively. Thirty six healthy Wistar albino rats divided into 4 groups of 9 rats each (adult male, adult female, wealing male and wealing female) and sub-grouped into 3 were acclimatized for one week and fed with formulated feed pellet of 50% dry weight of Amarantus hybridus, from each of the three lots for 28 days. Assay of the toxicological indices of the test animals showed elevated concentrations of urea, creatinine, alkaline phosphatase, alanine and aspartate aminotransferases, while a slight increase in amylase activity was observed in the animal. Packed Cell Volume (PCV) and haemoglobin concentration of the test animals decreased. These results were authenticated by the histological analysis of the liver, kidney and pancreas sections.

Simazine biodegradation and community structures of ammonia-oxidizing microorganisms in bioaugmented soil: impact of ammonia and nitrate nitrogen sources

The objective of the present study was to investigate the impact of ammonia and nitrate nitrogen sources on simazine biodegradation by Arthrobacter sp. strain SD1 and the community structures of ammonia-oxidizing archaea (AOA) and bacteria (AOB) in non-agricultural soil. Soil microcosms with different treatments were constructed for herbicide biodegradation test. The relative abundance of the strain SD1 and the structures of AOA and AOB communities were assessed using quantitative PCR (q-PCR) and terminal restriction fragment length polymorphism (TRFLP), respectively. The co-existence of two inorganic nitrogen sources (ammonia and nitrate) had certain impact on simazine dissipation by the strain SD1. Bioaugmentation could induce a shift in the community structures of both AOA and AOB, but AOA were more responsive. Nitrogen application had significant impacts on AOA and AOB communities in bioaugmented soils. Moreover, in non-bioaugmented soil, the community structure of AOA, instead of AOB, could be quickly recovered after herbicide application. This study could add some new insights towards the impacts of nitrogen sources on s-triazine bioremediation and ammonia-oxidizing microorganisms in soil ecosystem.

Diversity of The Chlorite Dismutase Gene in Low and High Organic Carbon Rhizosphere Soil Colonized by Perchlorate-Reducing Bacteria

Chlorite dismutase (cld) is an essential enzyme in the biodegradation of perchlorate. The objective of this study was to determine the change in sequence diversity of the cld gene, and universal bacterial 16S rRNA genes, in soil samples under varying conditions of organic carbon, bioaugmentation, and plant influence. The cld gene diversity was not different between high organic carbon (HOC) and low organic carbon (LOC) soil. Combining results from HOC and LOC soil, diversity of the cld gene was decreased in soil that had been bioaugmented or planted. However, with both bioaugmentation and planting the cld diversity was not decreased. These observations were repeated when focusing on LOC soil. However, in HOC soil the cld diversity was not affected by reactor treatment. General bacterial diversity as measured with 16S rRNA was significantly greater in HOC soil than in LOC soil, but no significant difference was observed between reference soil and planted or bioaugmented soil. Different sequences of the cld gene occur in different species of microorganisms. In LOC soil, combining bioaugmentation and planting results in a highly diverse population of perchlorate degraders. This diverse population will be more resilient and is desirable where perchlorate reduction is a critical remediation process. Supplemental materials are available for this article. Go to the publisher's online edition of International Journal of Phytoremediation to view the supplemental file.

PAH removal of high molecular weight by characterized bacterial strains from different organic sources

This study analyzes the capacity of native bacteria associated with humic acids (HA), sugar cane bagasse (SCB), vermicompost (VC) and the earthworm Eisenia andrei (EaW), to remove polycyclic aromatic hydrocarbons of high molecular weight (HMW-PAH). Bacteria isolation was carried out previous enrichment of the organic sources (OS) with mineral salts and kerosene. An average of 25 bacteria were isolated from each OS and their capacity to remove the PAH, per group (each added at 0.5 O.D), was tested according to a combinatory experimental design with two controls: enriched and non-enriched supernatants of the OS. The bacterial mixture provided by the HA and SCB (44) showed the best performance for degrading the selected PAH. Isolated bacteria associated to these materials were classified into 12 genera, three of which have been previously reported as highly efficient hydrocarbon degraders: Gordonia, Mycobacterium, and Rhodococcus. Regarding the other bacterial genera found, they possess interesting characteristics which include efficient surfactant production capacity, tolerance to high metal concentrations and capacity to reproduce in dry and nutrient-deficient conditions. Therefore, given the characteristics of the isolated hydrocarbonoclastic strains, they could be successfully applied to bioremediation by bioaugmentation of soil co-contaminated with hydrocarbons, metals and even pesticides.

Bioaugmentation of a polychlorobiphenyl contaminated soil with two aerobic bacterial strains

The consortium of aerobic bacterial strains Rhodococcus ruber P25 and Microbacterium sp. B51 was bioaugmented in natural and industrial soils, contaminated by commercial mixture of polychlorinated biphenyls (PCBs) Sovol. The results showed that the bioaugmentation of bacterial strains led to PCBs degradation in soil. Sovol at the initial concentration of about 100mgkg−1 was removed by 72.2% in the bioaugmented system with natural soil within 90 days, while the system with industrial soil removed 96.4% of this compound within the same period. The biodegradation kinetics of PCBs in the bioaugmented soil systems was not dependent on the presence of indigenous microflora. It was found that the growth dynamics of the strains R. ruber P25 and Microbacterium sp. B51 correlated with the specific degradation of Sovol. The strains R. ruber P25 and Microbacterium sp. B51 displayed high degradative activity to all congeners (ortho-, meta- and para-substituent) contained in Sovol. Removal percentage for each congeners amounted to 59–100% in the bioaugmented systems. This study suggests that augmentation of PCB-contaminated soils with strain R. ruber P25 and Microbacterium sp. B51 is promising in PCB bioremediation.

Simazine degradation in bioaugmented soil: urea impact and response of ammonia-oxidizing bacteria and other soil bacterial communities

The objective of this study was to investigate the impact of exogenous urea nitrogen on ammonia-oxidizing bacteria (AOB) and other soil bacterial communities in soil bioaugmented for simazine remediation. The previously isolated simazine-degrading Arthrobacter sp. strain SD1 was used to degrade the herbicide. The effect of urea on the simazine degradation capacity of the soil bioaugmented with Arthrobacter strain SD1 was assessed using quantitative PCR targeting the s-triazine-degrading trzN and atzC genes. Structures of bacterial and AOB communities were characterized using terminal restriction fragment length polymorphism. Urea fertilizer could affect simazine biodegradation and decreased the proportion of its trzN and atzC genes in soil augmented with Arthrobacter strain SD1. Bioaugmentation process could significantly alter the structures of both bacterial and AOB communities, which were strongly affected by urea amendment, depending on the dosage. This study could provide some new insights towards s-triazine bioremediation and microbial ecology in a bioaugmented system. However, further studies are necessary in order to elucidate the impact of different types and levels of nitrogen sources on s-triazine-degraders and bacterial and AOB communities in bioaugmented soil.

Enhancement of deltamethrin degradation by soil bioaugmentation with two different strains of Serratia marcescens

Deltamethrin is one of the most commonly used pyrethroid in agricultural practice in different geo- graphic regions of the world. It is detected in many envi- ronments, especially in soil and water, and can exhibit toxic effect to human and other organisms. In this study, we describe two bacterial strains DeI-1 and DeI-2, isolated from soil, and both identified as Serratia marcescens based on profile of the fatty acid methyl esters, biochemical test, and 16S RNA gene analysis, which were shown to effi- ciently degrade deltamethrin. Degradation of deltamethrin in mineral salt medium (50 mg l -1 ) proceeded by strains DeI-1 or DeI-2 reached the values of 88.3 or 82.8 % after 10 days, and DT50 was 2.8 or 4.0 days, respectively. Bioaugmentation of deltamethrin-contaminated non-sterile soils (100 mg kg -1 ) with strains DeI-1 or DeI-2 (3 9 10 6 cells g -1 of soil) enhanced the disappearance rate of pyrethroid, and its DT50 was reduced by 44.9, 33.1, 44.4, and 58.2 days or 39.1, 25.8, 35.6, and 46.0 days in sandy, sandy loam, silty loam, and silty soils, respectively, in comparison with non-sterile soils with only indigenous microflora. The three-way ANOVA indicated that DT50 of deltamethrin was significantly (P 0.01) affected by soil type, microflora presence, and inoculum, and the interaction between these factors. Generally, the lower content of clay and organic carbon in soil, the higher degradation rate of deltamethrin was observed. Obtained results show that both strains of S. marcescens may possess potential to be used in bioremediation of deltamethrin- contaminated soils.

The effect of soil bioaugmentation with strains of Pseudomonas on Cd, Zn and Cu uptake by Sinapis alba L.

The aim of this study was to assess the ability of selected metal resistant strains of the Pseudomonas genus to increase Zn, Cd and Cu uptake by the metalophyte Sinapis alba L. under laboratory conditions. Moreover, the mechanisms of the plant growth promotion in the tested strains and their impact on the shoots and roots of white mustard biomass were examined. Soil inoculation with the tested strains resulted in higher concentrations of Zn, Cd and Cu in the shoots and roots of the plants in comparison with those grown in non-inoculated soil. The highest phytoextraction enhancement was caused by Pseudomonas fluorescens MH15 which increased Zn, Cd and Cu accumulation in shoot tissue by 60%, 96% and 31%, respectively, in comparison with control plants. Moreover, all the tested strains also exhibited a significant increase of Cd translocation from roots to shoots of the white mustard. Three Pseudomonas putida (MH3, MH6, MH7) and two P. fluorescens biotype G and C (MH9 and MH15, respectively) strains had the ability to produce siderophore, 1-amino-cyclopropane-1-carboxylic acid deaminase, indole 3-acetic acid as well as hydrocyanic acid. Additionally, P. putida strains were also capable of solubilizing inorganic phosphate. The ability of the tested strains to increase the metal uptake in white mustard and their plant growth-promoting properties make them good candidates for supporting heavy metal phytoextraction as well as for plant growth promoting.

Biodegradation of alachlor in liquid and soil cultures under variable carbon and nitrogen sources by bacterial consortium isolated from corn field soil

Alachlor, an aniline herbicide widely used in corn production, is frequently detected in water resources. The main objectives of this research were focused on isolating bacterial consortium capable of alachlor biodegradation, assessing the effects of carbon and nitrogen sources on alachlor biodegradation and evaluating the feasibility of using bacterial consortium in soil culture. Kavar corn field soil with a long history of alachlor application in Fars province of Iran has been explored for their potential of alachlor biodegradation. The influence of different carbon compounds (glucose, sodium citrate, sucrose, starch and the combination of these compounds), the effect of nitrogen sources (ammonium nitrate and urea) and different pH (5.5-8.5) on alachlor removal efficiency by the bacterial consortium in liquid culture were investigated. After a multi-step enrichment program 100 days of acclimation, a culture with the high capability of alachlor degradation was obtained (63%). Glucose and sodium citrate had the highest alachlor reduction rate (85%). Alachlor reduction rate increased more rapidly by the addition of ammonium nitrate (94%) compare to urea. Based on the data obtained in the present study, pH of 7.5 is optimal for alachlor biodegradation. After 30 days of incubation, the percent of alachlor reduction were significantly enhanced in the inoculated soils (74%) as compared to uninoculated control soils (17.67%) at the soil moisture content of 25%. In conclusion, bioaugmentation of soil with bacterial consortium may enhance the rate of alachlor degradation in a polluted soil.

Study of the Bioremediation of Atrazine under Variable Carbon and Nitrogen Sources by Mixed Bacterial Consortium Isolated from Corn Field Soil in Fars Province of Iran

Atrazine herbicide that is widely used in corn production is frequently detected in water resources. The main objectives of this research were focused on assessing the effects of carbon and nitrogen sources on atrazine biodegradation by mixed bacterial consortium and by evaluating the feasibility of using mixed bacterial consortium in soil culture. Shiraz corn field soil with a long history of atrazine application has been explored for their potential of atrazine biodegradation. The influence of different carbon compounds and the effect of nitrogen sources and a different pH (5.5–8.5) on atrazine removal efficiency by mixed bacterial consortium in liquid culture were investigated. Sodium citrate and sucrose had the highest atrazine biodegradation rate (87.22%) among different carbon sources. Atrazine biodegradation rate decreased more quickly by the addition of urea (26.76%) compared to ammonium nitrate. Based on the data obtained in this study, pH of 7.0 is optimum for atrazine biodegradation. After 30 days of incubation, the percent of atrazine reduction rates were significantly enhanced in the inoculated soils (60.5%) as compared to uninoculated control soils (12%) at the soil moisture content of 25%. In conclusion, bioaugmentation of soil with mixed bacterial consortium may enhance the rate of atrazine degradation in a highly polluted soil.

Bacterial Degradation of the Saturate Fraction of Arabian Light Crude oil: Biosurfactant Production and the Effect of ZnO Nanoparticles

The aim of this research was to study the influence of nanoparticles and the initial oil amount on the biodegradation of crude oil. Production of biosurfactants was also assessed. Crude oil-utilizing bacteria were isolated from oilfields via enrichment in chemically defined medium with crude oil a sole carbon source. The isolates could be affiliated to the genera Bacillus, Pseudomonas, Achromobacter, and Microbacterium by 16S rDNA sequencing and phylogenetic analysis. GC/FID analysis revealed 52 to 98% degradation of the oil saturate fraction within one month. Nanoparticles of ZnO inhibited growth and crude oil biodegradation by one isolate. (NBHCO4). Two strains, NBHCO2 and NCEOW, emulsified and utilized water-in-oil emulsions (chocolate mousse). Two bacterial strains, I-19 and NBHCO2 grew with crude oil in cultures containing up to 20% oil. Degradation extent in the I-19 culture increased as the oil amount increased. On the contrary, the NBHCO2 culture exhibited a decrease in degradation extent as the oil amount increased. Biosurfactant production in only one crude oil culture (I-19) could be confirmed by the observed reduction in surface tension. Some isolates produced biosurfactants from water-soluble substrates such as glucose. The NBHCO2 strain produced a lipopeptide biosurfactant which reduced the surface tension of the growth medium from 72 to 27mN/m. A gene of catechol dioxygenase was detected in the I-19, NBHCO4, and NCEOW isolates. In conclusion, metal oxide nanoparticles can interfere with crude oil biodegradation. Biosurfactants are not necessarily a prerequisite for crude oil biodegradation. The initial oil amount is a significant determinant of oil biodegradability. The isolates can by applied for bioaugmentation of petroleum-polluted soil and biosurfactants production.

Significance of autochthonous Bacillus sp. KK1 on biomineralization of lead in mine tailings

The aim of the study was to isolate and characterize potential autochthonous bacteria for biomineralization of Pb in mine tailings. A total of four bacteria were isolated from the soil samples and assayed for tolerance to Pb and other heavy metals. Isolate KK1 exhibited maximum Pb resistance and was subsequently identified as Bacillus sp. based on the partial 16S rRNA gene sequences. The isolate KK1 reduced the Pb ions and did not harbor pbrT gene. Selective sequential extraction of bioaugmented soil revealed that the isolate significantly reduced (26%) the exchangeable fraction and increased (38%) the carbonate fraction of Pb. X-ray diffraction studies confirmed the role of bacterially induced calcite precipitation in the bioremediation of mine tailings. A significant increase in the urease (334%), DHO (dehydrogenase) (14%), and phosphatase (37%) activity was observed in the bioaugmented mine soil.

Rhizodegradation of petroleum hydrocarbons by Sesbania cannabina in bioaugmented soil with free and immobilized consortium

The present study reports the effect of bioaugmentation by free and immobilized bacterial culture on the rhizodegradation of petroleum-polluted soil using Sesbania cannabina plant. Total petroleum hydrocarbon (TPH), hydrocarbon-degrading bacterial counts, microbial activity and root morphology were assessed during 120 days of plant growth. TPH concentration analyzed by GC–MS showed that bioaugmentation did not improve the TPH degradation. TPH concentration decreased from 2541mgkg−1 to 673mgkg−1 and 867mgkg−1 in the rhizosphere of free (FR) and immobilized bacterial inoculated (IR) soil, respectively at the 120th day while in the rhizosphere of uninoculated soil (CR) concentration decreased to 679mgkg−1 only at the 90th day, showing higher and rapid rhizodegradation with indigenous bacteria than bioaugmented bacterial cultures. Various predominant bacterial groups responsible for higher TPH degradation in the rhizosphere of S. cannabina were identified by PCR–DGGE analysis. It is concluded that natural plant-microbe interaction in the rhizosphere of S. cannabina was efficient enough to degrade TPH and plant rhizosphere keeps bacterial community in its surrounding therefore immobilized culture had no obvious effect on petroleum degradation.

Bioaugmentation of polyethylene succinate-contaminated soil with Pseudomonas sp. AKS2 results in increased microbial activity and better polymer degradation

Pseudomonas sp. AKS2 isolated from soil degrades polyethylene succinate (PES) efficiently in the laboratory. However, this organism may not be able to degrade PES with similar efficiency in a natural habitat. Since in situ remediation is preferred for the effective removal of recalcitrant materials like plastic, in the current study, bioaugmentation potential of this organism was investigated. To investigate the potential of the AKS2 strain to bioaugment the PES-contaminated soil, a microcosm-based study was carried out wherein naturally attenuated, biostimulated, and AKS2-inoculated (bioaugmented) soil samples were examined for their ability to degrade PES. The results showed better degradation of PES by bioaugmented soil than other microcosms. Consistent with it, a higher number of PES-degrading organisms were found in the bioaugmented microcosm. The bioaugmented microcosm also exhibited a higher level of average well color development in BiOLOG ECO plate assay than the other two. The corresponding Shannon-Weaver index and Gini coefficient revealed a higher soil microbial diversity of bioaugmented microcosm than the others. This was further supported by community-level physiological profile of three different microcosms wherein we have observed better utilization of different carbon sources by bioaugmented microcosms. Collectively, these results demonstrate that bioaugmentation of PES-contaminated soil with AKS2 not only enhances polymer degradation but also increases microbial diversity. Bioaugmentation of soil with AKS2 enhances PES degradation without causing damage to soil ecology. Thus, Pseudomonas sp. AKS2 has the potential to be implemented as a useful tool for in situ bioremediation of PES.

Soil bioaugmentation with amphibian cutaneous bacteria protects amphibian hosts from infection by Batrachochytrium dendrobatidis

Amphibians worldwide are declining in part due to the disease chytridiomycosis caused by the cutaneous fungal pathogen Batrachochytrium dendrobatidis (Bd). While several experimental disease mitigation strategies are currently being tested, no proven implementable strategy exists to combat chytridiomycosis in the field. A plausible conservation strategy is the use of probiotic anti-Bd bacteria to combat chytridiomycosis (bioaugmentation). In this study, we examined the use of soil bioaugmentation in mitigation of chytridiomycosis in a laboratory experiment. Specifically, we sought to determine if the anti-Bd bacterial species Janthinobacterium lividum could be successfully introduced into natural soil, if the introduced bacteria could then be transmitted to the skin of the amphibian species Plethodon cinereus, and if the environmental transmission of J. lividum could reduce Bd infection on P. cinereus. We demonstrated that J. lividum can be successfully introduced into soil and can be environmentally transmitted to P. cinereus skin. We found that the environmental transmission of J. lividum inhibited colonization by Bd on the skin of P. cinereus five days post-Bd exposure. Soil bioaugmentation may be a feasible conservation strategy that could protect amphibians susceptible to chytridiomycosis from declines driven by the disease.

Bioremediation of endosulfan-contaminated soil by using bioaugmentation treatment of fungal inoculant Aspergillus niger

The persistence of endosulfan and intermediate metabolite endosulfan sulfate in the environment and their toxic effects on biota necessitate their removal. This study investigated the bioaugmentation of endosulfan-contaminated soil by fungal inoculant Aspergillus niger ARIFCC 1053. The influence of bioaugmentation by A. niger on endosulfan-contaminated soil was evaluated with the help of change in pH and released chloride, and by thin layer chromatography and gas chromatography analysis. Its effects on soil functionality were monitored by estimating dehydrogenase and arylsulfatase enzyme activities. The endosulfan degradation reached an undetectable level on day 15. The pH of the medium was nearly neutral (6.9) at the time of inoculation and it decreased to 3.6 on day 15. The amount of chloride released at particular intervals in the endosulfan degradation ranged from 28 \mug mL^{-1} to 104 \mug mL^{-1}. Change in pH and the increase in released chloride correlated with metabolic activities involved in the simultaneous degradation of endosulfan. Endosulfan sulfate, an intermediate metabolite, was detected and had disappeared on day 11 of the process. The increase in enzyme activities is an indicator of soil fertility and suggests possible involvement of these enzymes in endosulfan degradation. These results demonstrate that bioaugmentation by A. niger may be a viable tool for the remediation of soil contaminated with endosulfan.

Enhancement of phenol degradation by soil bioaugmentation with Pseudomonas sp. JS150

To test whether bioaugmentation with genetically modified Pseudomonas sp. JS150 strain could be used to enhance phenol degradation in contaminated soils. The efficiency of phenol removal, content of humic carbon, survival of inoculant, number of total culturable autochthonous bacteria and changes in fatty acid methyl esters (FAME) profiling obtained directly from soils were examined. Bioaugmentation significantly accelerated phenol biodegradation rate in tested soils. Phenol applied at the highest concentration (5.0 mg g(-1) soil) was completely degraded in clay soil (FC) within 65 days, whereas in sand soil (FS) within 72 days. In comparison, phenol biodegradation proceeded for 68 and 96 days in nonbioaugmented FC and FS soils, respectively. The content of humic carbon remained at the same level at the beginning and the end of incubation time in all soil treatments. The number of introduced bacteria (2.50 × 10(9) g(-1) soil) markedly decreased during the first 4 or 8 days depending on contamination level and type of soil; however, inoculant survived over the experimental period of time. Analysis of FAME patterns indicated that changes in the percentages of cyclopropane fatty acids 17:0 cy and 19:0 cyω10c and branched fatty acids might be useful markers for monitoring the progress of phenol removal from soil. It was confirmed that soil bioaugmentation with Pseudomonas sp. JS150 significantly enhanced soil activity towards phenol degradation. Cyclopropane and branched fatty acids were sensitive probes for degree of phenol utilization. In future, genetically modified Pseudomonas sp. JS150 strain could be of use in the bioaugmentation of phenol-contaminated areas.

Enriched Microbial Community in Bioaugmentation of Petroleum-Contaminated Soil in the Presence of Wheat Straw

The bioaugmentation of petroleum-contaminated soil using Enterobacter cloacae was profiled from the evolution of microbial community, soil dehydrogenase activity, to the degradation of petroleum contaminants. The seeding and proliferation of inoculant and the consequential microbial community were monitored by denaturing gradient gel electrophoresis analysis of the amplification of V3 zone of 16S rDNA. Degradation process kinetics was characterized by the degradation ratio of nC17 to nC18. The dehydrogenase activity was also determined during the degradation process. An abrupt change in the microbial community after inoculation was illustrated as well as successive changes in response to degradation of the petroleum contaminants. Seeding with E. cloacae stimulated the growth of other degrading stains such as Pseudomonas sp. and Rhodothermus sp. The application of wheat straw as a representative lignin waste, at 5% (w/w), induced an increase in the total dehydrogenase activity from 0.50 to 0.79, an increase in the microbial content of 130% for bacteria and 84% for fungi, and an increase of the overall degradation ratio from 44% to 56% after 56 days of treatment. The above mentioned results have provided a microbial ecological insight being essential for the design and implementation of bioaugmentation processes.

The Effect of Lignite and Comamonas testosteroni on Pentachlorophenol Biodegradation and Soil Ecotoxicity

Biodegradation of pentachlorophenol (PCP) in soil by autochthonous microflora and in soil bioaugmented by the bacterial strain Comamonas testosteroni CCM 7530 was studied. Subsequent addition of lignite, an abundant source of humic acids, has also been investigated as possible sorbent for PCP immobilization. Biodegradation of PCP and number of colony-forming units were determined in the three types of soil, haplic chernozem, haplic fluvisol, and haplic arenosol, freshly spiked with PCP and amended with tested sorbent. The enhancing effect of sorbent addition and bioaugmentation on PCP biodegradation depended mainly on the soil type and the initial PCP concentration. Microbial activity resulted in biotransformation of PCP into certain potentially toxic substances, probably lower chlorinated phenols that are more soluble than PCP, and therefore more toxic toward present biota. Therefore, it was necessary to monitor soil ecotoxicity during biodegradation. Addition of lignite resulted in a significant improvement of PCP biodegradation and led to a considerable decrease of soil toxicity especially in bioaugmented soils. The method could potentially serve as a promising technique in remediation technology for reducing high initial PCP content in contaminated soils.

Evaluation of Bioaugmentation with Entrapped Degrading Cells as a Soil Remediation Technology

Soil augmentation with microbial degraders immobilized on carriers is evaluated as a potential remediation technology using a mathematical model that includes degradation within spatially distributed carriers and diffusion or advection-dispersion as contaminant mass transfer mechanisms. The total volume of carriers is a critical parameter affecting biodegradation performance. In the absence of advection, 320 and 20 000 days are required to mineralize 90% of the herbicide linuron by Variovorax sp. SRS16 encapsulated in 2 mm beads with 5 and 20 mm spacings, respectively. Given that many pesticide degraders have low intrinsic degradation rates and that only limited carrier to soil volume ratios are practically feasible, bioaugmented soils are characterized by low effective degradation rates and can be considered fully mixed. A simple exponential model is then sufficient to predict biodegradation as verified by comparisons with published experimental data. By contrast, the full spatially distributed model is needed to adequately model the degradation of faster degrading contaminants such as naphthalene and benzene which can be mass-transfer limited. Dimensionless Damköhler numbers are proposed to determine whether the spatially distributed model is required. Results show that field scale applications of immobilized degraders will be limited by the amount of carriers required to reach acceptable degradation rates.