Use of metal-reducing bacteria for bioremediation of soil contaminated with mixed organic and inorganic pollutants

Mixed contamination by organic and inorganic compounds in soil is a serious problem for remediation. Most laboratory studies and field-scale trials focused on individual contaminant in the past. For concurrent bioremediation by biodegradation and bioleaching processes, we tested metal-reducing microorganism, Geobacter metallireducens. In order to prove the feasibility of the coupled process, multiple-contaminated soil was prepared. Mineralogical analyses have shown the existence of labile forms of As(V) as amorphous and/or weakly sorbed phases in the secondary Fe oxides. In the biotic experiment using G. metallireducens, biodegradation of toluene and bioleaching of As by bacteria were observed simultaneously. Bacteria accelerated the degradation rate of toluene with reductive dissolution of Fe and co-dissolution of As. Although there have been many studies showing each individual process, we have shown here that the idea of concurrent microbial reaction is feasible. However, for the practical use as a remediation technology, more details and multilateral evaluations are required in future studies.

     

Use of metal-reducing bacteria for bioremediation of soil contaminated with mixed organic and inorganic pollutants

Mixed contamination by organic and inorganic compounds in soil is a serious problem for remediation. Most laboratory studies and field-scale trials focused on individual contaminant in the past. For concurrent bioremediation by biodegradation and bioleaching processes, we tested metal-reducing microorganism, Geobacter metallireducens. In order to prove the feasibility of the coupled process, multiple-contaminated soil was prepared. Mineralogical analyses have shown the existence of labile forms of As(V) as amorphous and/or weakly sorbed phases in the secondary Fe oxides. In the biotic experiment using G. metallireducens, biodegradation of toluene and bioleaching of As by bacteria were observed simultaneously. Bacteria accelerated the degradation rate of toluene with reductive dissolution of Fe and co-dissolution of As. Although there have been many studies showing each individual process, we have shown here that the idea of concurrent microbial reaction is feasible. However, for the practical use as a remediation technology, more details and multilateral evaluations are required in future studies.     

Preface

The combination of bioremediation and electrokinetics, termed bioelectrokinetics, has been studied constantly to enhance the removal of organic and inorganic contaminants from soil. The use of the bioleaching process originating from Fe- and/or S-oxidizing bacteria may be a feasible technology for the remediation of heavy metal–contaminated soils. In this study, the bioleaching process driven by injection of S-oxidizing bacteria, Acidithiobacillus thiooxidans, was evaluated as a pre-treatment step. The bioleaching process was sequentially integrated with the electrokinetic soil process, and the final removal efficiency of the combined process was compared with those of individual processes. Tailing soil, heavily contaminated with Cd, Cu, Pb, Zn, Co, and As, was collected from an abandoned mine area in Korea. The results of geochemical studies supported that this tailing soil contains the reduced forms of sulfur that can be an energy source for A. thiooxidans. From the result of the combined process, we could conclude that the bioleaching process might be a good pre-treatment step to mobilize heavy metals in tailing soil. Additionally, the electrokinetic process can be an effective technology for the removal of heavy metals from tailing soil. For the sake of generalizing the proposed bioelectrokinetic process, however, the site-specific differences in soil should be taken into account in future studies.     

A feasibility study on bioelectrokinetics for the removal of heavy metals from tailing soil

The combination of bioremediation and electrokinetics, termed bioelectrokinetics, has been studied constantly to enhance the removal of organic and inorganic contaminants from soil. The use of the bioleaching process originating from Fe- and/or S-oxidizing bacteria may be a feasible technology for the remediation of heavy metal-contaminated soils. In this study, the bioleaching process driven by injection of S-oxidizing bacteria, Acidithiobacillus thiooxidans, was evaluated as a pre-treatment step. The bioleaching process was sequentially integrated with the electrokinetic soil process, and the final removal efficiency of the combined process was compared with those of individual processes. Tailing soil, heavily contaminated with Cd, Cu, Pb, Zn, Co, and As, was collected from an abandoned mine area in Korea. The results of geochemical studies supported that this tailing soil contains the reduced forms of sulfur that can be an energy source for A. thiooxidans. From the result of the combined process, we could conclude that the bioleaching process might be a good pre-treatment step to mobilize heavy metals in tailing soil. Additionally, the electrokinetic process can be an effective technology for the removal of heavy metals from tailing soil. For the sake of generalizing the proposed bioelectrokinetic process, however, the site-specific differences in soil should be taken into account in future studies.     

The role of Acidithiobacillus ferrooxidans and Acidithiobacillus thiooxidans in arsenic bioleaching from soil

Bioleaching of As from the soil in an abandoned Ag–Au mine was carried out using Acidithiobacillus ferrooxidans and Acidithiobacillus thiooxidans. A. ferrooxidans is an iron oxidizer and A. thiooxidans is a sulfur oxidizer. These two microbes are acidophilic and chemoautotrophic microbes. Soil samples were collected from the Myoungbong and Songcheon mines. The main contaminant of the soil was As, with an average concentration of 4,624 mg/kg at Myoungbong and 5,590 mg/kg at Songcheon. A. ferrooxidans and A. thiooxidans generated lower pH conditions during their metabolism process. The bioleaching of As from soil has a higher removal efficiency than chemical leaching. A. ferrooxidans could remove 70 % of the As from the Myoungbong and Songcheon soils; however, A. thiooxidans extracted only 40 % of the As from the Myoungbong soil. This study shows that bioleaching is an effective process for As removal from soil.     

Natural and synthesised iron-rich amendments for As and Pb immobilisation in agricultural soil

The immobilisation of heavy metals in contaminated soils is a promising alternative to conventional remediation techniques. Very few studies have focused on the use of iron-rich nanomaterials and natural materials for the adsorption of toxic metals in soils. Synthesised iron-rich nanomaterials (Fe and Zr–Fe oxides) and natural iron-rich materials (natural red earth; NRE) were used to immobilise As and Pb in contaminated agricultural soil. Total concentrations of As and Pb in the initial soil (as control) were 170.76 and 1945.11 mg kg^?1, respectively. Amendments were applied into the soil at 1, 2.5 and 5% (w/w) in triplicate and incubated for 150 days. Except for the NRE-amended soil, soil pH decreased from 5.6 to 4.9 with increasing application rates of Fe and Zr–Fe oxides. With addition of Fe and Zr–Fe oxides at 5%, the ammonium acetate (NHO₄Ac)-extractable Pb was greatly decreased by 83 and 65% compared with NRE addition (43%). All subjected amendments also led to a decrease in NHO₄Ac-extractable As in the soils, indicating the high capacity of As immobilisation. Soil amended with NRE showed a lower ratio of cy19:0 to 18:1ω7c, indicating decreased microbial stress. The toxicity characteristic leaching procedure produced results similar to the NHO₄Ac extraction for As and Pb. The NRE addition is recommended for immobilising heavy metals and maintaining biological soil properties.     

Successful genetic bioaugmentation with Pseudomonas putida for toluene degradation in soil columns

There is a strong need for effective and sustainable treatment methods for remediating soils and waters contaminated by fossil fuel pollutants such as aromatic hydrocarbons. Remediation could be improved by genetic bioaugmentation that uses conjugation of catabolic plasmids between bacteria. Research on the conditions for success, effectiveness, and long-term impact of genetic bioaugmentation are therefore necessary. Here the effects of genetic bioaugmentation with Pseudomonas putida BBC 443 was studied in continuous-flow soil columns with or without glucose amendment. Results show that the highest transconjugant occurrence of 21.7 ± 2.1 %, and development of microbial communities with the highest overall toluene degradation potential of 0.0790 ± 0.0055 mg toluene/g soil/h, were achieved in soil columns that received a continuous addition of 1 g/L glucose. Plasmid transfer and toluene biodegradation did not depend on the survival of donor P. putida BBC443, suggesting that genetic bioaugmentation was successful. Furthermore, bacterial community structure analysis revealed that genetic bioaugmentation had limited long-term impact on the soil bacterial community structures, regardless of the specific treatment. Our findings show that genetic bioaugmentation was successful and resulted in limited long-term ecological impact, thus demonstrating that genetic bioaugmentation can provide an effective and sustainable method for in situ bioremediation.     

包气带不同深度土壤对甲苯和三氯乙烯的吸附研究

采用批实验研究了华北平原地下水中检出率较高的三氯乙烯和甲苯在沿污水河包气带不同深度土壤中的吸附情况。从3个地点分析结果来看,其中有机碳（OC）的质量分数均较低（最高为1.01%）。在河床和近河处土壤对甲苯和三氯乙烯的吸附总体上呈现出浅部土壤吸附性强的特点。在实验浓度范围内,土壤中无机矿物对有机污染物（特别是三氯乙烯）的表面吸附扮演了重要角色。土壤对甲苯的吸附表现出了强烈的非线性,而对三氯乙烯的吸附表现出了良好的线性关系。甲苯的吸附与土壤有机碳质量分数的关系要比三氯乙烯更密切,这说明了吸附作用过程与有机化合物的分子结构、疏水性等方面的性质也有关系。     

Sulphur-oxidising bacteria isolated from deep caves improve the removal of arsenic from contaminated harbour sediments

Acidophilic S-oxidising bacteria isolated from sulphur-rich deep caves (Frasassi, Italy), characterised by relatively low temperature, were tested for their ability to mobilise (semi-)metals from contaminated sediments. Sediment samples from two commercial Italian seaports were used to set up bioleaching experiments. The effect of different growth substrates was also investigated. Our experiments revealed that S-oxidising bacteria isolated from Frasassi caves have a high potential to remove As from contaminated marine sediments, as never reported before. Although As solubilisation efficiency was quite low (i.e. about 30%), only a small amount of As was associated with non-residual fractions of the sediment. On the contrary, the solubilisation efficiencies of Zn and Ni (20% and 10%, respectively) were lower than those previously obtained by the use of other acidophilic bacteria and mainly influenced by the experimental conditions rather than by the presence of the S-oxidising bacteria. Results presented here open new perspectives in bioleaching applications for the remediation of contaminated sediments. Indeed, microbial strains adapted to relatively low-temperature environments could improve sediment bioleaching at temperature regimes where mesophilic and thermophilic strains are not favoured. Such strains could be exploited for developing selective bioremediation procedures for sediments contaminated with As, to be applied in multistep biotreatment processes.     

Sustainability of agricultural and wild cereals to aerotechnogenic exposure

In recent decades, the problem of the constantly increasin level of anthropogenic load on the environment is becoming more and more acute. Some of the most dangerous pollutants entering the environment from industrial emissions are heavy metals. These pollutants are not susceptible to biodegradation over time, which leads to their accumulation in the environment in dangerous concentrations. The purpose of this work is to study the sustainability of cultivated and wild plants of the Poaceae family to aerotechnogenic pollution in the soil. The content of heavy metals in couch grass (Elytrigia repens (L.) Nevski), meadow bluegrass (Poa pratensis L.) and soft wheat (Triticum aestivum) plants grown in the impact zone of Novocherkassk Power Station has been analyzed. Contamination of cultivated and wild cereals with Pb, Zn, Ni and Cd has been established. It has been shown that the accumulation of heavy metals is individual for each plant species. An average and close correlation have been established between the total HM content and the content of their mobile forms in the soil and their content in plants. For the plants studied, the translocation factor (TF) and the distribution coefficient (DC) of HM have been calculated. The TF is formed by the ratio of the concentration of an element in the root plant dry weight to the content of its mobile compounds in the soil. The DC value makes it possible to estimate the capacity of the aboveground parts of plants to absorb and accumulate elements under soil pollution conditions and is determined as the ratio of the metal content in the aboveground biomass to its concentration in the roots. TF and DC values have shown a significant accumulation of elements by plants from the soil, as well as their translocation from the root system to the aboveground part. It has been revealed that even within the same Poaceae family, cultural species are more sensitive to man-made pollution than wild-growing ones.

     

Sequestration of heavy metals from soil with Fe–Mn concretions and nodules

In recent years, heavy metal contamination has become a major environmental issue in many parts of the world. Fe and Mn oxides, oxyhydroxides and hydroxides have long been recognized as scavengers playing an important role in controlling the location, mobility and bioavailability of metal contaminants in soils. Fe–Mn concretions and nodules are discrete bodies made of soil or sediment materials cemented together under the influence of Fe and Mn oxides. Here metals sorption by Fe–Mn concretions and nodules are surveyed and critical reviewed. Valuable available literature data demonstrate that the formation of Fe–Mn concretions and nodules is the most efficient and durable process for metal contaminants sequestration in the soils. The papers discussed in this review show that the application of Fe–Mn concretions and nodules, as geochemical scavengers for remediating metal contaminated soils, is strongly recommended.     

Löwenzahn Taraxacum officinale Web. als (städtischer) Bioindikator

Investigations of the dandelion, Taraxacum officinale Web. in Poland, Romania and Germany showed that the species concentrates various elements dependent on the intensity of the pollutants. In this study, we followed up the question of whether T. officinale enriches pollutants by the atmospheric deposition on the leaves or via the soil. Therefore, samples from at least 10 plants and a soil sample at 57 sample sites were collected from a grid of 500 m × 500 m. In addition to the analysis of the total soil sample, the (mobile) ion pool of the soil (DIN V 19739) was analysed. The elements Al, As, Ba, Ca, Cd, Ce, Co, Cr, Cu, Fe, Ga, K, Mg, Mn, Mo, Na, Ni, Rb, Sr, Ti, Tl, V, and Zn were determined through the use of spectrometry with inductive coupled plasma (ICP-MS and ICP-OES). The results are compared with the element concentrations of washed and unwashed leaf samples in T. officinale. We could only find two direct correlations (Ti and Zn) between the element content, of the entire soil samples, but 14 correlations (As, Ba, Cd, Cu, Ga, K, Mn, Mo, Na, Ni, Rb, Ti, Tl und Zn) between the ion pool of the soil and the washed samples. The grid point data interpolation by ArcInfo showed a similar distribution pattern for the unwashed leaf elements Al, Ce, Fe, Ti and V (r≥0.75). The elements Al, Ce, Fe, Ti, and V are washed out at the same ratio. Thus, although the concentration of these elements were significantly reduced by the washing procedure, the correlations were not influenced. The admissibility of the grid point data interpolation for a distribution map of the town area was investigated, as well. It is shown that the element content varies with the land use (meadow, field, rural areas), the sampling point and the local pollutants. However, none of the discussed elements, Al, Ce, Fe, Ti, and V, is significantly influenced by the land use. The data allows one to make the conclusion that the elements of Al, Ce, Fe, Ti and V are dependent on the dry and wet deposition on the leaves of T. officinale. These elements are taken up not only by the roots, but also by the surface of the leaves. This is evident because there is no correlation between one of these elements in the leaves and the ion pool of the soil.     

Assessing biodegradation benefits from dispersal networks

The performance of biodegradation of organic pollutants in soil often depends on abiotic conditions and the bioavailability of these pollutants to degrading bacteria. In this context, bacterial dispersal is an essential aspect. Recent studies on the potential promotion of bacterial dispersal by fungal hyphae raised the idea of specifically applying fungal networks to accelerate bacterial degradation processes in situ. Our objective is to investigate these processes and their performance via simulation modelling and address the following questions: (1) Under what abiotic conditions can dispersal networks significantly improve bacterial degradation? and (2) To what extent does the spatial configuration of the networks influence the degradation performance? To answer these questions, we developed a spatially explicit bacterial colony model, which is applied to controlled laboratory experiments with Pseudomonas putida G7 organisms as a case study. Using this model, we analyzed degradation performance in response to different environmental scenarios and showed that conditions of limited bacterial dispersal also limit degradation performance. Under such conditions, dispersal networks have the highest potential for improving the bioavailability of pollutants to bacteria. We also found that degradation performance significantly varies with the spatial configuration of the dispersal networks applied and the time horizon over which performance is assessed. Regarding future practical applications, our results suggest that (1) fungal networks may dramatically improve initially adverse conditions for biodegradation of pollutants in soil, and (2) the network's spatial structure and accessibility are decisive for the success of such tasks.     

Degradation of toluene and benzene by Trametes versicolor

In this study, biological degradation of non-polar monoaromatic compounds, benzene and toluene, by one of the white rot fungi, namely Trametes versicolor was analyzed and the biomass formed was determined. The studies were carried out in mediums which contain basic nutrients in certain amounts, toluene and benzene at concentrations of 50, 100, 200, 250 and 350 mg/l, pH at 5, temperature at 28 degrees C and rpm at 150. Within an incubation period of 48 hours, it was observed that, removal was completed in 4 hours when toluene concentration was 50 mg/l and was completed in 36 hours when concentration was 300 mg/l. Biodegradation was completed at the end of 4th hour at benzene concentration of 50 mg/l while it continued for 42 hours at the concentration of 300 mg/l. With the addition of veratryl alcohol (3,4-Dimethoxybenzyl alcohol) to the basic feed medium, the operation of the enzyme system gained speed and biodegradation completed in a shorter time period.     

Biogeographical distribution of acidophiles and their effects around the Zijinshan heap bioleaching plant

The Zijin heap bioleaching plant started operation by the end of 2005; due to the proximity of the Ting River, concerns rose about the migration of acidophiles outside of the heap. In this study, 53 soil samples and 51 liquid samples were collected, and the biogeographical distribution of acidophiles was investigated using clone libraries and real-time polymerase chain reaction (PCR), the physicochemical characteristics were analysed by Inductively Coupled Plasma Optical Emission Spectrometry (ICP). The results indicated the bioleaching system had some influence on the surrounding environment. Both microbial community and physiochemical index emerged correlation with distance of sampling sites from bioleaching system, mainly limited in the zone 30?m outside bioleaching system. Correlation analysis indicated the migration of different acidophiles was influenced by different factors. Leptospirillum had higher migration capability than the other acidophiles, and such migration capability was one of the important influence factors for its distribution. Environment factors and survival ability were the key influence factors for Acidithiobacillus, Sulfobacillus and Ferroplasma to survive in the surrounding environment.     

Bioremediation of 3,4-dichloroaniline and 2,4,6-trinitrotoluene in soil in the presence of natural adsorbents

The use of some adsorbents may decrease the toxicity of organic pollutants to microbes and plants during soil bioremediation. Experiments were conducted with 3,4-dichloroaniline (DCA) and 2,4,6-trinitrotoluene (TNT). Here we demonstrate that activated carbon can reduce the toxicity of readily available chemicals in soil by transferring them to a less available fraction. This process results in accelerated biodegradation of dichloroaniline by the inoculated Paracoccus denitrificans st. 3XA. In the case of TNT, activated carbon promotes strong binding through accelerated microbial reduction of its nitro-groups and catalytic chemical oxidation of the methyl-group and polymerisation or binding of the products formed.     

低质量浓度除草剂2，4滴丁酯处理对土壤动物群落结构的影响

土壤动物是土壤污染的敏感指示生物,对土壤环境变化表现出比较灵敏的反映,为了解低质量浓度除草剂对土壤生态系统的影响,进一步推动除草剂使用的安全性评价研究,采用除草剂2,4滴丁酯对土壤动物群落进行室内染毒模拟试验,参照农田施用常规参考质量浓度,设置4个质量浓度梯度和一个不喷施除草剂的对照质量浓度,质量浓度最高限于参考喷施质量浓度的3~4倍,一次染毒后分别于12、24、48和72 h后对土壤动物进行分离并对群落结构特征进行分析。试验共获得土壤动物18655个,隶属于2门,4纲,12目,群落结构分析结果表明低质量浓度2,4滴丁酯导致土壤动物个体数和类群数有所减少,但减少的程度并不大。个体数量变化与质量浓度增高之间呈现较明显负相关（r=-0.856,P〈0.05）,种类数变化与质量浓度之间不具有明显的相关性,土壤动物种类数的减少主要取决于稀有类群和极稀有类群,数量的变化则主要是优势类群和常见类群的增减。2,4滴丁酯的施加使得土壤动物群落多样性指数和优势度指数降低,均匀度指数增高。土壤动物个体数量和类群数量变化与染毒后经历的时间之间并未表现出明显的规律性,染毒后不同时间土壤动物优势度指数相差较大,而多样性指数和均匀度指数在不同历时时间段内相差不大。综合各分析结果能够看出,低质量浓度2,4滴丁酯处理会对土壤动物群落造成一定影响,但影响程度并不大。     

土壤中地乐酚降解的实验研究

利用一系列批实验来研究地乐酚在不同土壤样本中的非生物降解和生物降解，并对各土壤特性与降解参数的相关性作统计分析。结果表明地乐酚的降解主要是生物降解。地乐酚在土壤中降解缓慢，加上实验土壤对地乐酚的弱吸附，因此地乐酚对当地地下水资源存在较大的威胁。在本实验地区降解参数服从正态分布。在水平α=0．05下，地乐酚的降解与已知的几种土壤特性以及吸附的相关性不显著。     

The effects of <Emphasis Type="Italic">Acidithiobacillus ferrooxidans</Emphasis> on the leaching of cobalt and strontium adsorbed onto soil particles

Bioleaching from soil artificially contaminated with analogues of radionuclides, Co and Sr, was carried out using a Fe-oxidizing bacterium, Acidithiobacillus ferrooxidans. Due to bacterial metabolism, the pH and dissolved Fe³⁺ concentration in a biotic slurry decreased and increased respectively, over time, but the concentrations of Co and Sr extracted from the soil showed no significant enhancement compared with those under abiotic control. In both cases, Co and Sr were leached from the soil during the initial period of the experiment, due to the initially low solution pH of 2.0, and the dissolved concentrations remained almost constant for the duration of the experiment (300 h). Since oxidation of Fe²⁺ by A. ferrooxidans led to the production of Fe precipitates and colloidal suspensions, the Co and Sr extracted into solution were most likely re-adsorbed onto the Fe solids. Also, A. ferrooxidans, without an external supply of Fe²⁺, extracted almost equal or greater amounts of Co and Sr from the soil than when Fe²⁺ was supplied. Under the same leaching conditions, the extent of Sr removal was much lower than that of Co. On the contrary to the high efficiency of microbial metal leaching in biohydrometallurgy for low-graded sulfide ores, which has been widely documented, conventional bioleaching techniques with A. ferrooxidans supplied with enough Fe²⁺ showed low efficiency for the removal of radionuclides loosely bound onto soil particle surfaces.     

Bepflanzung einer Tankstelle mit Weiden

In Axelved, Denmark, an abandoned gas filling station serves as a test field for phytoremediation. Laboratory studies accompany the project. The toxicity of fresh and weathered gasoline and diesel to willow and poplar trees was studied by use of a tree transpiration toxicity test. The correlation between diesel content in soil and decrease in willow tree transpiration (Salix viminalis x schwerinii) was highly significant (r ²=0.81, n=19). the EC₅₀ (50% inhibition of transpiration) for the sum of hydrocarbons (HC) was determined to be 3910 mg/kg (95% confidence interval from 2900 to 5270 mg/kg). The EC₁₀ was 810 mg/kg (95% confidence interval 396 to 1660 mg/kg). The results were verified with artificially mixed diesel and gasolinecontaminated soils and two willow and one poplar species (S. viminalis, S. alba andPopulus nigra). The degradation of radiolabeledm-xylene was studied with and without willows. The compound was readily degraded. Willow trees accelerated the elimination, but mainly due to the volatilization ofm-xylene. Model studies provided the result that biodegradation in soil is the fastest elimination process at the site, but it is limited by the availability of electron acceptors. The pollutants are almost persistent in the groundwater, but in aerated soil, 10000 mg/kg hydrocarbons at 1 m depth are degraded within 13 years. The main effect of willows on the pollutants’ persistence is that willows transpire water, lower the groundwater level and aerate the soil, hereby speeding up biodegradation.