Addition of allochthonous fungi to a historically contaminated soil affects both remediation efficiency and bacterial diversity

Botryosphaeria rhodina DABAC P82 and Pleurotus pulmonarius CBS 664.97 were tested for their ability to grow and to degrade aromatic hydrocarbons in an aged contaminated soil. To evaluate the impact of indigenous microflora on the overall process, incubations were performed on both fumigated and nonfumigated soils. Fungal colonization by B. rhodina was unexpectedly lower in the fumigated than in the nonfumigated soil while the growth of P. pulmonarius showed an opposite response. Degradation performances and detoxification by both fungi in the nonfumigated soil were markedly higher than those observed in the fumigated one. Heterotrophic bacterial counts in nonfumigated soil augmented with either B. rhodina or P. pulmonarius were significantly higher than those of the corresponding incubation control (6.7 ± 0.3 × 10⁸ and 8.35 ± 0.6 × 10⁸, respectively, vs 9.2 ± 0.3 × 10⁷). Bacterial communities of both incubation controls and fungal-augmented soil were compared by numerical analysis of denaturing gradient gel electrophoresis profiles of polymerase chain reaction (PCR)-amplified 16S ribosomal RNA (rRNA) genes and cloning and sequencing of PCR-amplified 16S rRNA genes. Besides increasing overall diversity, fungal augmentation led to considerable qualitative differences with respect to the pristine soil.     

Role of Autochthonous Filamentous Fungi in Bioremediation of a Soil Historically Contaminated with Aromatic Hydrocarbons

Nine fungal strains isolated from an aged and heavily contaminated soil were identified and screened to assess their degradative potential. Among them, Allescheriella sp. strain DABAC 1, Stachybotrys sp. strain DABAC 3, and Phlebia sp. strain DABAC 9 were selected for remediation trials on the basis of Poly R-478 decolorization associated with lignin-modifying enzyme (LME) production. These autochthonous fungi were tested for the abilities to grow under nonsterile conditions and to degrade various aromatic hydrocarbons in the same contaminated soil. After 30 days, fungal colonization was clearly visible and was confirmed by ergosterol determination. In spite of subalkaline pH conditions and the presence of heavy metals, the autochthonous fungi produced laccase and Mn and lignin peroxidases. No LME activities were detected in control microcosms. All of the isolates led to a marked removal of naphthalene, dichloroaniline isomers, o-hydroxybiphenyl, and 1,1′-binaphthalene. Stachybotrys sp. strain DABAC 3 was the most effective isolate due to its ability to partially deplete the predominant contaminants 9,10-anthracenedione and 7H-benz[DE]anthracen-7-one. A release of chloride ions was observed in soil treated with either Allescheriella sp. strain DABAC 1 or Stachybotrys sp. strain DABAC 3, suggesting the occurrence of oxidative dehalogenation. The autochthonous fungi led to a significant decrease in soil toxicity, as assessed by both the Lepidium sativum L. germination test and the Collembola mortality test.     

Role of autochthonous filamentous fungi in bioremediation of a soil historically contaminated with aromatic hydrocarbons

Nine fungal strains isolated from an aged and heavily contaminated soil were identified and screened to assess their degradative potential. Among them, Allescheriella sp. strain DABAC 1, Stachybotrys sp. strain DABAC 3, and Phlebia sp. strain DABAC 9 were selected for remediation trials on the basis of Poly R-478 decolorization associated with lignin-modifying enzyme (LME) production. These autochthonous fungi were tested for the abilities to grow under nonsterile conditions and to degrade various aromatic hydrocarbons in the same contaminated soil. After 30 days, fungal colonization was clearly visible and was confirmed by ergosterol determination. In spite of subalkaline pH conditions and the presence of heavy metals, the autochthonous fungi produced laccase and Mn and lignin peroxidases. No LME activities were detected in control microcosms. All of the isolates led to a marked removal of naphthalene, dichloroaniline isomers, o-hydroxybiphenyl, and 1,1'-binaphthalene. Stachybotrys sp. strain DABAC 3 was the most effective isolate due to its ability to partially deplete the predominant contaminants 9,10-anthracenedione and 7H-benz[DE]anthracen-7-one. A release of chloride ions was observed in soil treated with either Allescheriella sp. strain DABAC 1 or Stachybotrys sp. strain DABAC 3, suggesting the occurrence of oxidative dehalogenation. The autochthonous fungi led to a significant decrease in soil toxicity, as assessed by both the Lepidium sativum L. germination test and the Collembola mortality test.     

Simultaneous phenanthrene and cadmium removal from contaminated soil by a ligand/biosurfactant solution

Surfactants and inorganic ligands are pointed as efficient to simultaneous removal of heavy metals and hydrophobic organic pollutants from soil. However, the biosurfactants are potentially less toxic to soil organisms than other chemical agents. Thus, in this study the efficiency of combinations of iodide (I⁻) ligand and surfactants produced by different bacterial species in the simultaneous removal of cadmium (Cd²⁺) and phenanthrene in a Haplustox soil sample was investigated. Four microbial surfactants and the synthetic surfactant Triton X-100 were tested with different concentrations of ligand. Soil samples contaminated with Cd²⁺ and phenanthrene underwent consecutive washings with a surfactant/ligand solution. The removal of Cd²⁺ increased with increased ligand concentration, particularly in solutions containing biosurfactants produced by the bacterial strains Bacillus subtilis LBBMA155 (lipopeptide) and Flavobacterium sp. LBBMA168 (mixture of flavolipids) and Triton X-100. Maximum Cd²⁺ removal efficiency was 99.2% for biosurfactant produced by Arthrobacter oxydans LBBMA 201 (lipopeptide) and 99.2% for biosurfactant produced by Bacillus sp. LBBMA111A (mixed lipopeptide) in the presence of 0.336 mol iodide l⁻¹, while the maximum efficiency of Triton X-100 removal was 65.0%. The biosurfactant solutions removed from 80 to 88.0% of phenanthrene in soil, and the removal was not influenced by the presence of the ligand. Triton X-100 removed from 73 to 88% of the phenanthrene and, differently from the biosurfactants, iodide influenced the removal efficiency. The results indicate that the use of a single washing agent, called surfactant-ligand, affords simultaneous removal of organic contaminants and heavy metals.     

Soil and entomopathogenic fungi with potential for biodegradation of insecticides: degradation of flubendiamide in vivo by fungi and in vitro by laccase

Purpose

Flubendiamide is a highly toxic and persistent insecticide that causes loss of insect muscle functions leading to paralysis and death. The objective was to screen for filamentous fungi in soils where insecticides had been applied, to isolate entomopathogenic fungi from insect larva (Anticarsia gemmatalis) that infest soybean crops, and to use these in biodegradation of insecticides.

Method

Filamentous fungi were isolated from soils, and growth inhibition was evaluated on solid medium containing commercial insecticides, Belt® (flubendiamide) and Actara® (thiamethoxam). A total of 133 fungi were isolated from soil and 80 entomopathogenic fungi from insect larva. Based on growth inhibition tests, ten soil fungi, 2 entomopathogenic fungi, and Botryosphaeria rhodina MAMB-05 (reference standard) were selected for growth on commercial insecticides in solid media. Fungi were grown in submerged fermentation on media containing commercial insecticides and assayed for laccase activity.

Result

Isolates JUSOLCL039 (soil), JUANT070 (insect), and MAMB-05 performed best, and were respectively inhibited by 48.41%, 75.97%, and 79.23% when cultivated on 35 g/L Actara®, and 0.0, 5.42%, and 43.39% on 39.04 g/L Belt®. JUSOLCL039 and JUANT070 were molecularly identified as Trichoderma koningiopsis and Neurospora sp., respectively. The three fungal isolates produced laccase constitutively, albeit at low activities. Fungal growth on pure flubendiamide and thiamethoxam resulted in only thiamethoxam inducing high laccase titers (10.16 U/mL) by JUANT070. Neurospora sp. and B. rhodina degraded flubendiamide by 27.4% and 9.5% in vivo, while a crude laccase from B. rhodina degraded flubendiamide by 20.2% in vitro.

Conclusion

This is the first report of fungi capable of degrading flubendiamide, which have applications in bioremediation.

     

Simultaneous bioremediation of Cr(VI) and lindane in soil by actinobacteria

Environments co-contaminated with metals and organic compounds are difficult to remediate. Actinobacteria is an important group of microorganisms found in soils, with high metabolic versatility and potential for bioremediation. In this paper, actinobacteria were used to remediate soil co-contaminated with Cr(VI) and lindane. Five actinobacteria, tolerant to Cr(VI) and lindane mixture were selected: Streptomyces spp. A5, A11, M7, and MC1, and Amycolatopsis tucumanensis DSM 45259. Sterilized soil samples were inoculated with actinobacteria strains, either individually or as a consortium, and contaminated with Cr(VI) and lindane, either immediately or after 7 days of growth, and incubated at 30 °C during 14 days. All actinobacteria were able to grow and remove both contaminants, the consortium formed by Streptomyces spp. A5, M7, MC1, and A. tucumanensis showed the highest Cr(VI) removal, while Streptomyces sp. M7 produced the maximum lindane removal. In non-sterile soil samples, Streptomyces sp. M7 and the consortium removed more than 40% of the lindane, while Streptomyces sp. M7 demonstrated the greatest Cr(VI) removal. The most appropriate strategy for bioremediation of Cr(VI) and lindane co-contaminated soils would be the inoculation with Streptomyces sp. M7.     

Pilot Scale Bioremediation of Creosote-Contaminated Soil—Efficacy of Enhanced Natural Attenuation and Bioaugmentation Strategies

In this study, the efficacy of bioremediation strategies (enhanced natural attenuation with nitrate and phosphate addition [ENA] and bioaugmentation) for the remediation of creosote-contaminated soil (7767 ± 1286 mg kg^?1 of the 16 EPA priority PAHs) was investigated at pilot scale. Bioaugmentation of creosote-contaminated soil with freshly grown or freeze dried Mycobacterium sp. strain 1B (a PAH degrading microorganism) was applied following bench scale studies that indicated that the indigenous soil microflora had a limited PAH metabolic activity. After 182 days, the total PAH concentration in creosote-contaminated soil was reduced from 7767 ± 1286 mg kg^?1 to 5579 ± 321 mg kg^?1, 2250 ± 71 mg kg^?1, 2050 ± 354 mg kg^?1 and 1950 ± 70 mg kg^?1 in natural attenuation (no additions) and ENA biopiles and biopiles augmented with freshly grown or freeze dried Mycobacterium sp. strain 1B respectively. In ENA and bioaugmentation biopiles, between 82% and 99% of three-ring compounds (acenaphthene, anthracene, fluorene, phenanthrene) were removed while four-ring PAH removal ranged from 33 to 81%. However, the extent of PAH degradation did not vary significantly between the ENA treatment and biopiles augmented with Mycobacterium sp. strain 1B. Four-ring PAH removal followed the order fluoranthene > pyrene > benz[a]anthracene > chrysene. The high residual concentration of some four-ring PAHs may be attributable to bioavailability issues rather than a lack of microbial catabolic activity. Comparable results between ENA and bioaugmentation at pilot scale were surprising given the limited degradative capacity of the microbial consortia enriched from the creosote-contaminated soil.     

Degradation of endosulfan during substrate preparation and cultivation of Pleurotus pulmonarius

Summary Endosulfan is an insecticide used on many vegetable crops. In mushroom cultivation, vegetable materials used as a growth substrate may contain residues of endosulfan that may accumulate in the final mushroom biomass. After preparing the substrate, it is subjected to pasteurization and/or composting and then inoculated with the desired fungus. The purpose of this research was to determine the rate and extent of endosulfan reduction from a grass substrate that was either composted or sterilized by autoclaving. In addition, the rate and extent of removal of endosulfan from substrate colonized with Pleurotus pulmonarius was determined. The degradation of 65 mg/kg endosulfan was analyzed on both, the substrate preparation and the culture of P. pulmonarius on the grass Digitaria decumbens. During composting in presence of Ca(OH)₂ for 120 h, the concentrations of α and β endosulfan were reduced by 61.4 and 49.5% respectively, significantly higher compared with the control (without Ca(OH)_2,) in which the reduction was 38.5%. After sterilization the concentration of α and β endosulfan was reduced by 84.8 and 87.5% respectively. After the colonization of substrate by P. pulmonarius (15 days after spawning) α and β endosulfan were reduced by 96% and at the end of cultivation (35 days after spawning) were reduced by 99%. When carpophores were analyzed, residues of α and β endosulfan were observed between 0.019–0.084 mg/kg. The results showed that α and β endosulfan were partially removed during the preparation of substrate and entirely eliminated during fungal colonization on the substrate.     

Selection of functional consortium for crude oil-contaminated soil remediation

Microorganisms with high oil-degrading performance are essential for bioremediation of soil contaminated with crude oil. A positive end dilution method was employed for the selection of crude oil-degrading functional consortium from contaminated soil. The selected consortium was consisted of Rhizobiales sp., Pseudomonas sp., Brucella sp., Bacillus sp., Rhodococcus sp., Microbacterium sp. and Roseomonas sp. and removed nearly 52.1% of crude oil at initial concentration of 10,000 mg l⁻¹ at 30 °C within 7 days, with removal of aliphatic hydrocarbons by 71.4% and aromatic hydrocarbons by 36.0%, respectively. The effectiveness of the consortium for bioaugmentation was confirmed with microcosm test by contaminated soil (1.0 kg) from Karemary Oilfield, China. The removal efficiency of crude oil was enhanced to >50% in microcosms with the consortium compared with 8-13% or lower in controls over a 60 day period. The crude oil removal reaction was probably first order reaction and the rate was greatly enhanced by bioaugmentation. Supplementation of nitrogen and phosphate sources had limited effect on the oil removal in the tested soil.     

Differential mobilization and metal uptake versus leaching in multimetal soil columns using EDTA and three metal bioaccumulators

Tannery waste is a major environmental concern that needs proper management. Tannery solid waste (TSW) can be added to the soil as an organic amendment but needs metal removal. Chelant-assisted phytoremediation hastens the process of metal removal but also poses risk of leaching at the same time. This research evaluates Ethylenediaminetetraacetic acid (EDTA)-assisted phytoextraction and associated leaching hazard using metal-tolerant plants. Greenhouse trials were carried out with sunflower, spinach, and marigold using columns of uniform diameter packed with field soil and multimetal contamination of TSW (5% and 10%) with four EDTA doses. The amounts of metal absorbed or leached conformed to amounts in the soil amendment and the dose of EDTA. The mobilization of metals by EDTA was however metal-specific. The metals that were extracted in greater amounts by the plants were leached less compared to Cr and Cu. A significant amount of other metals was leached down and thus less amount was phytoextracted by the plants e.g. Cd and Ni. A high correlation was observed between the amount of metal absorbed by the plant and the amount in leachate except for Cr in all the plants. Antioxidant activities like SOD and catalase were also found to be high in sunflower and spinach.     

Performance and bacterial community shifts during bioremediation of acid mine drainage from two Portuguese mines

The performance of two up-flow anaerobic packed bed systems (UAPB) to treat acid mine drainage (AMD) from the Portuguese mines São Domingos and Tinoca was investigated. The response of bacterial populations to influent characteristics was also analysed by temperature gradient gel electrophoresis (TGGE). Effective neutralisation (pH raised from 2.8 to 6.5) and removal of metals (>99%) and sulphate (>72%) were observed independently of the AMD source. TGGE fingerprinting and phylogenetic analysis of 16S rRNA gene revealed that the structure of the bacterial consortia developed in each bioreactor was different. The main bacterial groups involved in the treatment of AMD from Tinoca mine were Desulfovibrio sp., Clostridium sp., Desulfitobacterium sp. and members of Bacteroidales order. These bacterial groups were also present in the community developed in the UAPB fed with AMD from São Domingos mine but an unidentified bacterium and bacteria affiliated to Citrobacter and Cronobacter genera were detected only in this last system. The results of present study showed that the AMD source fed to the system was determinant for the establishment of different bacterial populations. Furthermore, the potential of the bioremediation systems for the production of water for irrigation purposes was demonstrated.     

Optimization and/or acclimatization of activated sludge process under heavy metals stress

The present study aimed to overcome the toxicity of the heavy metals load, discharged with the industrial effluents into Alexandria sewerage network, on the activated sludge treatment system through effective acclimation for organic matter and heavy metals removal. Optimization and/or acclimatization of the activated sludge process in the presence of Cu, Cd, Co and Cr contaminating mixed domestic-industrial wastewater was investigated. Acclimatization process was performed through abrupt and stepwise addition of tested metals using sequencing batch reactors treatment approach and evaluated as microbial oxygen uptake rate (OUR), dehydrogenase activity (DHA), organic matter (COD) and heavy metals removal. Abrupt addition of metals adversely affected sludge bioactivity leading to decline in the removal efficiency of the targeted contaminants and loss of floc structure. Metals IC₅₀ confirmed that copper possessed the highest toxicity towards the OUR, DHA activity and COD removal with orders Cu > Cd > Cr > Co; Cu > Cd > Co = Cr and Cu > Cd > Cr > Co, respectively. The highest metal removal was recorded for Cd followed by Co, Cu and finally Cr, most of which was retained in the dissolved influent. However, controlled stepwise application of the tested metals exhibited high sensitivity of DHA and OUR activities only at the highest metal concentrations although enhanced at the lowest concentrations while COD removal was not significantly affected. In conclusion, this approach resulted in adaptation of the system where sludge microbes acquired and developed natural resistance to such metals leading to remarkable enhancement of both organic matter and heavy metals removal.     

Interaction of Heavy Metals in Multimetal Biosorption by Galerina vittiformis from Soil

ABSTRACT Soil heavy metal contamination, a major threat due to industrialization, can be tackled by an efficient and economical process called bioremediation. Mushrooms are employed to accumulate heavy metals from soil due to their high metal accumulation potential and better adaptability. The bioaccumulation potential of Galerina vittiformis was already reported for individual metals. At natural conditions, since soil consists of more than one polluting metal, more focus has to be given to multimetal systems. In this study, multimetal accumulation potential was analyzed using central composite design, and the responses obtained were analyzed using response surface methodology. Heavy metals such as Cu(II), Cd(II), Cr(VI), Pb(II), and Zn(II) were subjected to biosorption at 10–250 mg/kg concentrations along with pH 5–8. The results showed that the preference of the organism for the five metals under study was in the order Pb(II) > Zn(II) > Cd(II) > Cu(II) > Cr(VI) at pH 6.5 under multimetal condition. The study also indicates that the metal interaction pattern in multimetal interaction is a property of their ionic radii. The response surface methodology clearly explains the effect of interaction of heavy metals on the accumulation potential of the organism using three-dimensional response plots. The present work suggests that the fungus Galerina vittiformis could be employed as a low-cost metal removal agent from heavy metal–polluted soil.     

The chelating effect of citric acid,oxalic acid,amino acids and Pseudomonas fluorescens bacteria on phytoremediation of Cu,Zn, and Cr from soil using Suaeda vera

Phytoextraction is a green technique for the removal of soil contaminants by plants uptake with the subsequent elimination of the generated biomass. The halophytic plant Suaeda vera Forssk. ex J.F.Gmel. is an native Mediterranean species able to tolerate and accumulate salts and heavy metals in their tissues. The objective of this study was to explore the potential use of S. vera for soil metal phytoextraction and to assess the impact of different chelating agents such as natural organic acids (oxalic acid [OA], citric acid [CA]), amino acids (AA) and Pseudomonas fluorescens bacteria (PFB) on the metal uptake and translocation. After 12 months, the highest accumulation of Cu was observed in the root/stem of PFB plots (17.62/8.19 mg/kg), in the root/stem of CA plots for Zn (31.16/23.52 mg/kg) and in the root of OA plots for Cr (10.53 mg/kg). The highest accumulation of metals occurred in the roots (27.33–50.76 mg/kg). Zn was the metal that accumulated at the highest rates in most cases. The phytoextraction percentages were higher for Cu and Zn (～2%) with respect to Cr (～1%). The percentages of metal removal from soil indicate the need to monitor soil properties, to recognize the influence of each treatment and to increase the concentration of bioavailable metals by the use of agricultural management practices aimed at promoting plant growth.     

Effects of metal stress on biochemical response of some aquatic macrophytes growing along an industrial waste discharge channel

Abstract

The present research work focused on the metal translocation in the soil-plant system and subsequent metal stress on biochemical response of aquatic macrophytes growing along an industrial waste discharge channel. The bottom sediment of the effluent channel is highly contaminated with metals. High transfer factor (TF) for most of the metals indicated higher metal uptake by aquatic macrophytes of which Typha sp. was found to be the most suitable. Average TF was in the order of Fe (4.82) > Mn (3.91) > Cu (3.59) > Cd (2.29) > Zn (2.22) > Cr (1.83) > Pb (1.80). Hyper accumulation of metals within plants resulted in significant reductions in total chlorophyll, soluble sugar with an increase in protein and proline content. The investigation also demonstrated that exposure to high concentrations on metals resulted in enhanced activity of catalase (61.82–90.91%) and peroxidase (37.08–70.23%) in all examined macrophytes with a reduced (27.58–43.4%) or unchanged ascorbate peroxidase activity depending on plant species.     

A novel strategy using biodegradable EDDS for the chemically enhanced phytoextraction of soils contaminated with heavy metals

For the sake of cost and potential environmental risk, it is necessary to minimize the amount of chelants used in chemically enhanced phytoextraction. In the present study, a biodegradable chelating agent, EDDS was added in a hot solution at 90°C to the soil in which garland chrysanthemum (Chrysanthemum coronarium L.) and beans (Phaseolus vulgaris L., white bean) were growing. The application of hot chelant solutions was much more efficient than the application of normal chelant solutions (25°C) in improving the uptake of heavy metals by plants. When 1 mmol kg⁻¹ of EDDS as a hot solution was applied to soil, the concentrations of Cu, Zn and Cd and the total phytoextraction by the shoots of the two plant species exceeded or approximated those in the shoots of plants treated with 5 mmol kg⁻¹ of normal EDTA solution. The concentrations of metals in the shoots of beans were significantly correlated with the relative electrolyte leakage rate of root cells, indicating that the root damage resulting from the hot solution might play an important role in the process of chelant-enhanced metal uptake. The soil leaching study demonstrated that decreasing the dosage of chelant resulted in decreased concentrations of soluble metals in soils. On the 28th day following the application of chelant, the concentrations of soluble metals in the EDDS treated soil were not significantly different from the concentrations in the control soil to which chelants had not been applied. The application of biodegradable EDDS in hot solutions to soil may be an efficient alternative in chemically-enhanced phytoextraction to increase metal removal and to reduce possible leaching.Section Editor: J. Barcelo     

Bioremediation of multi-metal contaminated soil using biosurfactant — a novel approach

An unconventional nutrient medium, distillery spent wash (1:3) diluted) was used to produce di-rhamnolipid biosurfactant by Pseudomonas aeruginosa strain BS2. This research further assessed the potential of the biosurfactant as a washing agent for metal removal from multimetal contaminated soil (Cr-940 ppm; Pb-900 ppm; Cd-430 ppm; Ni-880 ppm; Cu-480 ppm). Out of the treatments of contaminated soil with tap water and rhamnolipid biosurfactant, the latter was found to be potent in mobilization of metal and decontamination of contaminated soil. Within 36 hours of leaching study, di-rhamnolipid as compared to tap water facilitated 13 folds higher removal of Cr from the heavy metal spiked soil whereas removal of Pb and Cu was 9–10 and 14 folds higher respectively. Leaching of Cd and Ni was 25 folds higher from the spiked soil. This shows that leaching behavior of biosurfactant was different for different metals. The use of wastewater for production of biosurfactant and its efficient use in metal removal make it a strong applicant for bioremediation.     

乌鲁木齐市道路林带土壤抗重金属细菌的筛选及重金属去除能力

【背景】道路重金属污染问题日益严峻,寻找高效的微生物资源用于环境修复已迫在眉睫。【目的】从乌鲁木齐市道路林带土壤中筛选抗重金属菌株,并对其重金属去除能力进行探究。【方法】使用含5种重金属离子(铅、镉、锌、铜、镍)的4种培养基进行抗性菌株筛选,通过形态学特征和16S rRNA基因序列进行鉴定,采用电感耦合等离子体发射光谱仪(inductively coupled plasma optical emission spectrometer,ICP-OES)检测分离株对重金属离子的去除情况。【结果】4种分离培养基中,TSA是抗重金属菌株筛选的最适培养基,共筛选出16株抗重金属菌,其中4株抗Pb菌、4株抗Cd菌、4株抗Zn菌、3株抗Cu菌和1株抗Ni菌,其抗性分别高达3 000、800、600、300和400mg/L,16株菌中以芽孢杆菌属(Bacillus)数量最多。在初始浓度为700mg/L Pb²⁺下,菌株Pb6的去除率高达92.48%,菌株Pb11、Pb3和Pb9的去除率分别为27.70%、40.37%和58.88%;在200mg/L Cd²⁺...     

Counter-Current Metal Leaching and Precipitation for Soil Remediation

Chemical acid leaching is an effective technique for extracting toxic metals from the finest fractions of polluted soils. Nevertheless, the use of large quantities of reagents and process water results in prohibitive operating costs. The purpose of this study was to evaluate the technical and economic advantages of recirculating water in a counter-current leaching process (CCLP). Five 1-h sulfuric acid extraction steps (at pH = 1.5) followed by three 5-min water-washing steps were applied to the fine particle fraction (<0.125 mm) of an industrial soil polluted by Cd (13.2 mg·kg^?1), Cu (3 100 mg·kg^?1), Mn (685 mg kg^?1), Pb (550 mg·kg^?1), and Zn (2 840 mg·kg^?1). The leaching experiments were carried out at ambient temperature using a 10% soil suspension and in 1-L working volume stirred tank reactors. This paper presents results of conventional and counter-current leaching process (CCLP) tests and shows that the CCLP yields removal results for Cu (85%), Zn (86%), Mn (75%), and Cd (90%) that are similar to those obtained using the conventional leaching process. Moreover, the CCLP uses half of the quantity of acid and one-eighth of the amount of water that the conventional process uses. Metal precipitation with NaOH and Ca(OH)₂ was applied to treat the acidic leachates, and good metal removal yields were achieved with both reagents. However, the large consumption of chemicals implies high operating costs. In addition, the precipitation causes considerable sludge production, particularly when using Ca(OH)₂. Overall, the CCLP coupled to metal precipitation using NaOH and water recycling appears to be the most attractive option for the removal of toxic metals from this industrial soil.     

Evaluation of Different Amendments to Stabilize Cadmium,Zinc, and Copper in a Contaminated Soil: Influence on Metal Leaching and Phytoavailability

The contamination of soils with heavy metals is a global disaster that is related to human activities. Phytostabilization basically refers to the use of metal-tolerant plants and inexpensive mineral or organic soil amendments to reduce the concentrations or toxic effects of contaminants in the environment. Here, we tested the effects of four cost-effective amendments (CaCO₃, phosphate rock, activated carbon, and exhausted olive cake ash) on Cd, Zn, and Cu leaching and uptake by ryegrass (Lolium perenne L.). The results showed that all amendments reduced Cd, Zn, and Cu leaching, mainly due to the alkalinity increase. Among all amendments tested, CaCO₃ was the most effective treatment in decreasing both the heavy-metal leaching and concentrations in ryegrass shoots. Results obtained suggest the efficacy of several amendments, but further work is needed to gain insight into their possible synergetic effects.