Experimental Assessment of Using Soluble Humic Substances for Remediation of Heavy Metal Polluted Soils

Since heavy metals are nondegradable and strongly bonded in soils, remediation of heavy metal polluted soils by extraction is difficult and current extraction techniques require harsh chemicals such as ethylenediaminetetraacetic acid (EDTA). However, use of EDTA is environmentally problematic because of costs, persistence, toxicity and deterioration of soil structure. Therefore, the potential of soluble natural humic substances (HS) to extract heavy metals from contaminated soils is tested as an environmentally friendly substitute for EDTA. A strongly polluted, calcareous urban soil (CRC soil) and a moderately polluted agricultural soil (CUP soil) were extracted at neutral pH in batch mode by three HS solutions from beech and Norway spruce litter (Beech-HS and Spruce-HS) and processed cow slurry (Bio-HS), all containing 25 mM dissolved organic carbon (DOC). After 10 extractions with a solution to soil ratio of 5:1 (L/kg), 8% to 39% of the total Cd, Cu, Ni and Pb soil contents, lowest for Ni and highest for Cu/Pb, were extracted. Natural and processed HS samples had comparable capacities to extract the heavy metals. A comparison of 100 mM DOC of Bio-HS and EDTA as extractants for Cu from the CRC soil showed extraction of 67% by EDTA and 41% by Bio-HS, indicating somewhat higher efficiency of EDTA than of HS. Sequential extraction of the CRC soil after Bio-HS and EDTA extraction showed removal of exchangeable, carbonate- and metal oxide-bound Cu but also of some residual Cu. It is therefore concluded that HS appears to be an attractive and promising alternative to EDTA as remediation agent for heavy metal polluted soils provided cheap HS of good quality is easily available.     

Current views on EDDS use for ex situ washing of potentially toxic metal contaminated soils

The paper presents a mini-review on EDDS use for ex situ chemical washing of potentially toxic metal contaminated soil. The attention is focused, initially, on studies aimed at verifying the biodegradability and the toxicity of free EDDS and metal-EDDS complexes. Free EDDS is found to be highly biodegradable. Metal-EDDS complexes, instead, are indicated as having variable biodegradability, but their toxicity is found to be always very low. The results obtained during soil washing treatments are successively reviewed. Removal percentages as high as 80–90 % are indicated as maximum obtained values. The extraction process is initially very fast, and then tends to slow down reaching the final equilibrium in about 1 week or even more. Generally acidic conditions are favourable to enhance the process. The influence of organic matter on process efficiency and the interactions between EDDS and soil minerals are also considered, revealing variable effects of the organic matter presence depending on its characteristics, and highlighting the possibility of iron and aluminium washing off during the remediation treatment.     

Effects of organic amendments on Cd, Zn and Cu bioavailability in soil with repeated phytoremediation by Sedum plumbizincicola

Organic materials with different functional groups can be used to enhance metal bioavailability. Traditional organic materials (rice straw and clover) and ethylenediamine disuccinic acid (EDDS) were applied to enhance metal uptake from polluted soil by Sedum plumbizincicola after repeated phytoextraction. Changes in pH, dissolved organic carbon (DOC) and metal concentrations were determined in the soil solution after EDDS application. Amendment of the soil with ground rice straw or ground clove resulted in higher concentrations of Cd only (by factors of 1.92 and 1.71 respectively) in S. plumbizincicola compared to control soil. Treatment with 3 mmol kg(-1) EDDS increased all the metals studied by factors of 60.4, 1.67, and 0.27 for Cu, Cd, and Zn, respectively. EDDS significantly increased soil solution DOC and pH and increased soil plant-available metals above the amounts that the plants could take up, resulting in high soil concentrations of soluble metals and high risk of ground water contamination. After repeated phytoremediation of metal contaminated soils the efficiency of metal removal declines as the concentrations of bioavailable metal fractions decline. Traditional organic materials can therefore be much more effective and environmentally friendly amendments than EDDS in enhancing phytoremediation efficiency of Cd contaminated soil     

Remediation of Copper from Copper Mine Wastes and Contaminated Soils Using (S,S)-Ethylenediaminedisuccinic Acid and Acidophilic Bacteria

The biodegradable chelating agent (S,S)-Ehylenediaminedisuccinic acid (EDDS), autochthonous acidophilic bacteria, and a combination of the two means were investigated for the removal of pseudo-total and ethylenediaminetetraacetic acid (EDTA)-available content of Cu from surface layers of three soil categories in the Bor copper mining area. Their efficiencies were compared at mine overburden, flotation tailings, and agricultural land sites in order to determine the potential role of these approaches in the soil remediation process. The most effective removal of Cu was achieved on flotation tailings, where combined treatment showed significant reduction of pseudo-total and EDTA-available concentrations of Cu (40.5?±?27.3% and 99.6?±?0.2%, respectively). Acidophilic bacteria treatment showed high efficiency on flotation tailings, removing 94.1?±?1.2% of EDTA-available Cu. EDDS treatment showed discernible results in the removal of EDTA-available Cu from agricultural land soil (44.4?±?13.9%). In the case of overburden soil material, selected agents did not have statistically significant results in the removal of pseudo-total or EDTA-available fraction of Cu. Chosen remediation approaches showed diverse efficiency for soil categories on investigated sites. Combined approach showed synergistic results in the case of EDTA-available Cu removal from flotation tailings soils, suggesting that this combination deserves further attention as a potentially promising environmentally friendly remediation option.     

A field lysimeter study of heavy metal movement down the profile of soils with multiple metal pollution during chelate-enhanced phytoremediation

The agricultural soils near a copper smelter in southeast China were found to be highly contaminated with Cu, Pb, Zn, and Cd. Metal migration from the soil to groundwater presents an environmental risk that depends on the physicochemical properties of the contaminated soils. Soil solution samples were obtained using lysimeters from a loam soil with multiple metal pollutions over a period of about 1 yr. A field lysimeter study was also conducted to examine the potential use of (S, S')-ethylenediamine-N, N'-disuccinic acid trisodium salt (EDDSNa3) in chelate-enhanced phytoremedation and to evaluate the leaching of heavy metals. The average heavy metal concentrations in the soil solution (without the addition of EDDS) were high (e.g., 0.15 mg Pb L(-1) at a 50-cm depth) compared to the upper limit for protection of groundwater in China, but varied during the sampling period. Cu concentrations were not correlated with pH or dissolved organic carbon (DOC), but Zn and Cd concentrations were related to soil solution pH. EDDS enhanced metal solubility in the soil, but plant metal uptake by Elsholtzia splendens Nakai did not increase accordingly. There may be an increasing risk of groundwater pollution by Cu and the EDDS enhanced phytoremediation technique needs to be carefully applied to minimize this side effect.     

Enhanced phytoextraction: I. Effect of EDTA and citric acid on heavy metal mobility in a calcareous soil

Phytoextraction, the use of plants to extract heavy metals from contaminated soils, could be an interesting alternative to conventional remediation technologies. However, calcareous soils with relatively high total metal contents are difficult to phytoremediate due to low soluble metal concentrations. Soil amendments such as ethylene diaminetetraacetate (EDTA) have been suggested to increase heavy metal bioavailability and uptake in aboveground plant parts. Strong persistence of EDTA and risks of leaching of potentially toxic metals and essential nutrients have led to research on easily biodegradable soil amendments such as citric acid. In our research, EDTA is regarded as a scientific benchmark with which degradable alternatives are compared for enhanced phytoextraction purposes. The effects of increasing doses of EDTA (0.1,1,10 mmol kg(-1) dry soil) and citric acid (0.01, 0.05, 0.25, 0.442, 0.5 mol kg(-1) dry soil) on bioavailable fractions of Cu, Zn, Cd, and Pb were assessed in one part of our study and results are presented in this article. The evolution of labile soil fractions of heavy metals over time was evaluated using water paste saturation extraction (approximately soluble fraction), extraction with 1 M NH4OAc at pH 7 (approximately exchangeable fraction), and extraction with 0.5 M NH4OAc + 05 M HOAc + 0.02 M EDTA at pH 4.65 (approximately potentially bioavailable fraction). Both citric acid and EDTA produced a rapid initial increase in labile heavy metal fractions. Metal mobilization remained constant in time for soils treated with EDTA, but a strong exponential decrease of labile metal fractions was noted for soils treated with citric acid. The half life of heavy metal mobilization by citric acid varied between 1.5 and 5.7 d. In the following article, the effect of heavy metal mobilization on uptake by Helianthus annuus will be presented.     

Simultaneous and Repetitious Removal of 2,4-Dichlorophenol and Copper from Soils Using an Aqueous Solution of Ethyl-Lactate-Amended EDDS

Heavy metals and the transformation products of herbicides, such as 2,4-dichlorophenol (2,4-DCP), are toxic soil pollutants. We assessed the ability of an aqueous solution of the “green solvent” ethyl lactate alone and combined with [S,S]-ethylenediaminedisuccinic acid (EDDS) to remove 2,4-DCP and copper simultaneously from soils. Ethyl lactate extracted 2,4-DCP from contaminated soil comparable to Triton X-100. Ethyl lactate/EDDS extracted more 2,4-DCP and Cu from contaminated soils than ethyl lactate alone. The enhanced extraction of Cu increased slightly with an increase in the EDDS/Cu molar ratio; the maximum Cu extraction efficiency was about 32.3% at an EDDS/Cu ratio of 5. An increase in the ionic strength (NaCl) of the ethyl lactate/EDDS solution decreased the amount of 2,4-DCP extracted by maximally 12% but increased the amount of Cu extracted by >500%. We tested the recycling of the ethyl lactate/EDDS solution with the cation-exchange resin 001×7 and the hyper-cross-linked polymer resin NDA-150. Fresh ethyl lactate/EDDS solution and two sequentially recycled solutions removed 31.4, 28.3, and 26.7% of the Cu in Cu-contaminated soil and 77.7, 62.9, and 56.8% of the 2,4-DCP in 2,4-DCP-contaminated soils, respectively. The ethyl lactate/EDDS solution removed 31.8% of the Cu and 73.0% of the 2,4-DCP in Cu- and 2,4-DCP-contaminated soils, and the solution remained effective even after two recyclings. The aqueous solution of ethyl lactate/EDDS can be used to effectively remove Cu and 2,4-DCP from complex contaminated soils and can be reactivated.     

Assessment of a heavy metals‐contaminated site using sequential extraction,TCLP, and risk assessment techniques

The mobility of selected heavy metals in contaminated soil at a previous industrial site in Brisbane, Australia, was assessed using a sequential extraction technique. Copper, Pb, Zn, Cr, Fe, and Mn were extracted from the soil solution/exchangeable, carbonate, Fe and Mn oxides, and organic matter fractions. The amounts of metals adsorbed by these fractions were used as an indicator of each metal's mobility in the soil. Copper and Pb were largely adsorbed by the organic and oxide fractions, while a significant amount of Zn was extracted from the carbonate fraction. The potential mobility and biological availability of the metals in these soils is Zn > Cr = Cu ≈ Pb. Soils were also analyzed using the toxicity characteristic leaching procedure (TCLP) to determine whether the contaminated soil could be disposed of by landfilling. The leachability of all metals from the soils was very low, with metal concentrations below the allowable limits. The TCLP also showed that Zn was the most mobile metal in these soils. An environmental and health risk assessment was undertaken, and it was concluded that the site did not represent a risk despite the “total”; concentrations of some metals being up to 40 times the investigation threshold value adopted in Australia.     

Remediation of Arsenic-Contaminated Soil Using Alkaline Extractable Organic Carbon Solution Prepared from Wine-Processing Waste Sludge

Past studies have shown that dissolved organic carbon (DOC) washing can effectively remove heavy metals from contaminated soil. In this study, we used alkaline DOC solutions for remediation of arsenic (As)-contaminated soil (with an initial As concentration in the topsoil of 390 mg kg^?1). The removal of As and the change in soil nutrients during DOC washing were studied for 60 min at pH 10 with a 60:1 liquid/soil ratio (v/m). Approximately 88% of As was removed by washing the soil twice using a 3000 mg L^?1 DOC solution at 25°C. Following this treatment, the pH of the soil had increased from 5.6 to 9.2; organic carbon content had increased from 3.5% to 4.1%; cation exchange capacity, ammonium-N, and available phosphorus had increased to 2.3, 1.4, and 6.6 times their original levels, respectively; and exchangeable K, Na, Ca, and Mg had increased to 91, 6.1, 4.2, and 2.2 times their original levels, respectively. A sequential extraction investigation revealed that residual As and easily exchangeable As in the fraction were initially 10.2% and 9.2%, respectively, but that the former became the maximum remainder (64%) after the ultimate DOC washing.     

Phytotoxicity and metal leaching in EDDS‐assisted phytoextraction from pyrite wastes with Ethiopian mustard and fodder radish

Abstract

This study examines the influence of a low‐persistent chelator, [S,S]‐EDDS (ethylene diamine disuccinic acid), on the growth of Ethiopian mustard (Brassica carinata A. Braun) and fodder radish (Raphanus sativus L. var. oleiformis) and on metal leaching (ML) in As–Co–Cu–Pb–Zn‐contaminated pyrite wastes. Plants were grown in pots for 75 days with test doses of 2.5 and 5 mmol EDDS per kg of soil applied through irrigation one week before harvest, and 1 mmol EDDS per kg of soil repeated five times at 5‐ and 10‐day intervals, in comparison with untreated controls. Fodder radish treated with 1 mmol at the five‐day interval was also irrigated with 1 mg IBA (indole‐3‐butyric acid) per kg of soil every 10 days. Shoot biomass, leaf area and root growth were generally reduced by EDDS in both species, particularly in repeated applications and in radish, regardless of IBA supply, with root biomass being more affected than length and electrical capacitance (EC). EDDS generally improved shoot concentrations of Cu, Co, Zn and Pb, but repeated treatments caused significant ML (mainly of Cu), explained by a multivariate relationship (R ² = 0.52) including the integral over time of both leaf area (R ² = 0.43) and root EC (R ² = 0.09). We conclude that roots play a secondary role in preventing ML, because of the prevailing effect of leaf transpiration in controlling percolation. The best metal phytoextraction was achieved with EDDS applied at harvest – a safe ML strategy, especially at the low dose of 2.5 mmol per kg of soil.

Abbreviations: DTPA, diethylene triamine pentaacetic acid; EC, electrical capacitance; EDDS, ethylene diamine disuccinic acid; EDTA, ethylene diamine tetraacetic acid; HM, heavy metals; IAA, indoleacetic acid; IBA, indolebutyric acid; ICP‐OES, inductively coupled plasma optical emission spectroscopy; LA, leaf area; ML, metal leaching     

杨桃对土壤重金属元素的吸收与富集

通过对廉江市杨桃（Averrhoa carambola）绿色食品基地不同土质、不同树龄的土壤样品及果实样品重金属元素Cd、Hg、Cu、Pb、As、Cr含量的检测,分析杨桃果实对土壤重金属元素的吸收与富集作用。结果表明：①果园土壤pH≤5．50,为酸性土壤,杨桃果园土壤和鲜果中的重金属含量均符合我国水果绿色食品生产的质量要求;②杨桃对土壤重金属的吸收因土壤质地和重金属元素的种类不同而异;③杨桃对重金属元素的富集,以Cd元素为最强,富集系数高达0．947,各种重金属的富集系数按大小排序为：Cd（0．947）〉Hg（0．098）〉Cu（0．023）〉Pb（0．003）〉As（0．001）：Cr（0．001）。     

Extraction,Recovery, and Biostability of EDTA for Remediation of Heavy Metal-Contaminated Soil

Chelation removal of heavy metals from contaminated soil is seen as a viable remediation technique. A useful chelating agent should be strong, reusable, and biostable during metal extraction and recovery operations. This work tested the extraction, recovery, and biostability of EDTA as a potential remediating agent. Parameters, including EDTA concentration, soil type, soil content, washing cycle, precipitant concentration and type, and pH, were varied and tested during metal extraction and recovery operations. Factors, including EDTA concentration, aqueous and 5% soil slurry, presence of Pb, acclimated and unacclimated activated sludges, along with abiotic control, were varied and studied in the biodegradation of EDTA. The results showed that EDTA was able to extract lead completely from the tested soils, amenable to recovery by addition of cationic and anionic precipitants in the alkaline pH range, relatively biostable even under conditions very favorable toward biodegradation. Thus, EDTA is a strong, recoverable, and relatively biostable chelating agent that has potential for soil remediation application.     

Influence of [S, S]-EDDS on phytoextraction of copper and zinc by Elsholtzia splendens from metal-contaminated soil

Two pot experiments were conducted to investigate the time course effects of the (S, S)-N, N'-ethylenediamine disuccinic acid (EDDS) addition to contaminated soil on the uptake of Cu and Zn by the Cu accumulator Elsholtzia splendens and on plant Cu and Zn concentrations at different growth stages. EDDS increased the amounts of Cu and Zn soluble in the soil, taken up by plants, concentrated in the xylem sap, and translocated from roots to stems and leaves. The increase in soil-soluble metals, especially Cu, resulted in a corresponding increase in metal concentrations in the xylem sap and leaves. The addition of EDDS to the soil increased plant Cu and Zn concentrations, especially in the leaves, and changed the proportions of Cu and Zn taken up by different plant parts. The proportions of Cu and Zn taken up by the roots were higher than by the leaves of control plants, but EDDS-treated plants showed the opposite trend. EDDS exerted greater effects at the end of the vegetative growth stage than at the start of the flowering or reproductive stages.     

The Removal of Pb and Cd from Heavily Contaminated Soil in Kayseri,Turkey by a Combined Process of Soil Washing and Electrodeposition

In this study, a combined system of soil washing and electrodeposition was designed to remove Pb (16381±643 mg/kg) and Cd (34347±1310 mg/kg) from contaminated soil. 0.05 M Na₂EDTA was used as a chelating agent for the remediation of soil, taken from the nearby city Kayseri, Turkey. As a result of the batch extraction tests, maximum removals were determined as; at the 20:1 liquid: soil ratio for Pb is 60.7%, for Cd at the 30:1 liquid: soil ratio is 67.4%. An electrochemical treatment was applied to the waste washing solution which appeared to be the second pollutant after the Na₂EDTA extraction from the soil. With extraction tests of Pb and Cd, being transformed from the solid phase to the liquid phase. The electrochemical treatment (electrodeposition), performed in three different potential (6 V, 8 V and 10 V) and maximum removal efficiencies, were found 99.7% and 80.3% at 10 V for Pb and Cd, respectively.

Speciation tests (BCR) were carried out, both before and after the soil washing process, to evaluate the redistribution of metal fraction in the soil. The fraction, associated with the organic substance, was found as 10.67% for Pb and 1.81% for Cd. The metal bioavailability factor increased after soil washing, which indicates that EDTA could enhance the mobility of Pb and Cd.     

Extraction of Arsenic and Heavy Metals from Contaminated Mine Tailings by Soil Washing

In this study, the soil washing technique has been used to treat mine tailings contaminated heavily with arsenic and heavy metals at Jingok mine, which is one of the abandoned mines in Korea. The results showed that phosphoric acid, citric acid, oxalic acid, and sodium metabisulfite were highly effective in extracting arsenic and heavy metals. Among them, oxalic acid was the most effective (especially for Pb, Cu, and Zn), as even a residual fraction of arsenic was partly extracted. The optimum concentration of washing reagent and the ratio between the mine tailings and washing reagent were found to be 0.5 M and 1:20, respectively. In addition, the extraction kinetics of arsenic and heavy metals was fast, in which the reaction time of 30 minutes was deemed to be a sufficient contact time. From the results, it may be concluded that the low pH of washing solution and the amount of dissolved Fe may be considered as the most important factors in the extraction of arsenic and heavy metals.     

Effect of carbide sludge (lime) on bioavailability and leachability of heavy metals during rotary drum composting of water hyacinth

Abstract

The bioavailability and leachability of heavy metals play a major role in the toxicity of heavy metals in the compost applied for soil conditioning. A rotary drum composter was used for the study of heavy metal bioavailability and leachability during water hyacinth composting with a mixture of cattle manure, sawdust and lime. Lime was added in 1, 2 and 3% to the mixture of water hyacinth, cattle manure and sawdust at a ratio of 6:3:1 respectively. Influences of physico-chemical parameters on heavy metal bioavailability and leachability were studied during the process. The bioavailability of heavy metals solubility and diethylene triamine penta-acetic acid extractability was examined. The toxicity characteristics leaching procedure (TCLP) test was performed for assessing the hazardous properties of compost. The nutrients and the total concentration of heavy metals were increased during the composting process. The lime was very effective in reducing water solubility, plant availability and leachability of the selected heavy metals (Zn, Cu, Mn, Fe, Ni, Pb, Cd and Cr) during the process. The addition of lime provided a buffer against the decrease in pH and a sufficient amount of Ca that would improve the metabolic activity during composting. The addition of an excess amount of lime slowed the metabolic activity of the microbes due to its high alkalinity. The TCLP test confirms that the heavy metals concentrations in the control and in the lime-amended compost were below the threshold limits.     

Sawdust and natural zeolite as a bulking agent for improving quality of a composting product from anaerobically stabilized sewage sludge

This study has dealt with the production of compost from dewatered anaerobically stabilized primary sewage sludge (DASPSS) and sawdust (SWD). SWD is added in order to increase the humic substances in the final product. The DASPSS is mixed with clinoptilolite (Cli), which is used as a bulking agent at 20% w/w, and the mixture is amended with sawdust at 10%, 30% and 40% (w/w). The final results have indicated that by increasing the sawdust concentration in the initial mixture, the humic substances in the final product increase too. The natural zeolite that was added in the initial mixture takes up a significant amount of heavy metals. In order to observe the maturity of the final product, the germination index is used in oat cultivation. The results indicate that the substrate appears to be non-phytotoxic after 75 d of maturity. Also, in order to estimate the metal leachability of the final compost product, the generalized acid neutralization capacity procedure is applied, and it is found that by increasing the pH values, the heavy metal concentrations decrease.     

Solid-Phase Chemical Fractionation of Selected Trace Metals in Some Northern Kentucky Soils

The fractionation and distribution with depth of Cd, Cr, Cu, Ni, Pb, and Zn in 26 soils of Northern Kentucky were determined through a sequential extraction procedure in response to environmental concerns about increasing anthropogenic inputs in a fast-paced, urbanizing area. The selected sites have not received any biosolid- or industrial-waste applications. Average total concentrations per metal in soil profiles derived from alluvial, glacial till, and residual materials ranged from 0.43 to 56.00 mg kg^?1 in the sequence Zn > Ni > Pb > Cr > Cu > Cd, suggesting relatively small anthropogenic inputs. The distribution of Cu, Cr, Ni, and Zn increased with soil depth, whereas Cd and Pb remained stable, indicating a strong geological or pedogenic influence. Residual forms were most important for the retention of Cu, Zn, and Ni. Cadmium and Pb exhibited a strong affinity for the Fe-Mn oxide fraction, while Cr showed the strongest association with the organic fraction. In terms of metal mobility and toxicity potential inferred from metal concentrations in labile fractions, Cd posed the greatest risk, followed by Cr ～ Pb > Ni > Zn > Cu. Soil pH, OM, and clay content were the most important parameters explaining the partitioning of metals in labile and residual fractions, emphasizing the importance of metal fractionation in soil management decisions. Alluvial soils generally contained the highest total and labile metal concentrations, suggesting potential metal enrichment through anthropogenic additions and depositional processes. These environments exhibit the highest risk for metal mobilization due to drastic changes in redox conditions, which can destabilize existing metal retention pools.     

Chelator-assisted phytoextraction of arsenic,cadmium and lead by Pteris vittata L. and soil microbial community structure response

Abstract

Using biodegradable chelators to assist in phytoextraction may be an effective approach to enhance the heavy-metal remediation efficiencies of plants. A pot experiment was conducted to investigate the effects of ethylenediamine disuccinic acid (EDDS), citric acid (CA), and oxalic acid (OA) on the growth of the arsenic (As) hyperaccumulator Pteris vittata L., its arsenic (As), cadmium (Cd), and lead (Pb) uptake and accumulation, and soil microbial responses in multi-metal(loid)-contaminated soil. The addition of 2.5-mmol kg^?1 OA (OA-2.5) produced 26.7 and 14.9% more rhizoid and shoot biomass, respectively compared with the control, while EDDS and CA treatments significantly inhibited plant growth. The As accumulation in plants after the OA-2.5 treatment increased by 44.2% and the Cd and Pb accumulation in plants after a 1-mmol kg^?1 EDDS treatment increased by 24.5 and 19.6%, respectively. Soil urease enzyme activities in OA-2.5 treatment were significantly greater than those in the control and other chelator treatments (p?<?0.05). A PCR–denatured gradient gel electrophoresis analysis revealed that with the addition of EDDS, CA and OA enhanced soil microbial diversity. It was concluded that the addition of OA-2.5 was suitable for facilitating phytoremediation of soil As and did not have negative effects on the microbial community.     

Bioproduction of ethylenediamine-N,N'-disuccinic acid using immobilized fumarase-free EDDS lyase

Ethylenediamine-N,N'-disuccinic acid (EDDS) is a promising chelating agent for the remediation of heavy metal-contaminated soil. In general, EDDS is produced through a chemical method. In this study, we report an efficient biotechnological approach for EDDS production using an immobilized enzyme. We expressed the EDDS lyase in E. coli and obtained 19.8 g/L of EDDS through a reaction catalyzed by crude enzymes, containing EDDS lyase and fumarase. After performing metal affinity chromatography-mediated purification, we thoroughly eliminated the fumarase activity, which could result in the unnecessary formation of malate. Then, the purified EDDS lyase was immobilized on a glutaraldehyde-activated amino carrier, and the immobilized enzyme was used in 11 batches (864.5 h). After optimization, 209.3 g/L EDDS was obtained in a 100 mL reaction system, resulting in 20.2 g of EDDS product with a purity of 99.8 % after isolation. The yields of reaction and isolation were 94.0 % and 91.8 %, respectively. In conclusion, this study describes a promising bioproduction process for industrial-level EDDS production.