Bioremediation of lanthanides and actinides wastes using microbial electrochemical cell

Abstract

The present disclosure provides a Microbial Electrochemical Cell (MECC) for bioremediation of lanthanides and actinides wastes, wherein the MECC comprises an anode, and a cathode connected by an electrical pathway, wherein the anode and the cathode are connected to an electrical source. A redox mediator is used as the anolyte, preferably the redox mediator is Potassium Ferrocyanide. Waste containing lanthanides and actinides metals or their oxides are leached with a conc. acid to form a leached metal salt precipitate, which was diluted with water and used as catholyte. One or more bacterial strain was added to the catholyte. A constant pulse current is applied to stimulate the bacterial strain to grow as an electrically conductive biofilm on the cathode. The biofilm via its NADP to NADPH pathway releases electron and recovers the lanthanide or actinide metals.

Description

[0001] TITLE

[0002] BIOREMEDIATION OF LANTHANIDES AND ACTINIDES WASTES USING MICROBIAL ELECTROCHEMICAL CELL

[0003] CROSS REFERENCE TO RELATED APPLICATIONS

[0004] The present application is based upon and claims priority to India complete patent application number 202441075528 filed on October 05, 2024 the entire contents of which is herein incorporated by reference.

[0005] FIELD

[0006] The present disclosure relates to treatment of lanthanides and actinides wastes by Microbial Electrochemical cell (MECC), more particularly the present disclosure relates to bioremediation of lanthanides and actinides wastes using MECC.

[0007] BACKGROUND

[0008] The use of heavy metals across the globe is rising for creation of energy and is expected to expand by 2024. About 4.1 million tonnes of wastes in India were generated by Uranium milling and mining operations alone. Heavy metal wastes are generally rich in variety of radionuclides, organic solvents and other toxic substances. The leaching of the heavy metals and other contaminants to other sites can damage the ecosystem. Heavy metals like other organic contaminants are not subject to degradation. Toxicity of metal contamination can only be reduced by making metals non-bioavailable which is done either by physical removal like adsorption or re-speciation into less toxic forms. A number of physico-chemical methods are used for the treatment of these wastes but bioremediation offers the cheap and eco-friendly method of treating these wastes. Moreover, bioremediation can remove metals present in very low concentrations, which are not removable by chemical methods.

[0009] Microbial Electrochemical cells (MECC) are known for production of renewable bioenergy and bioremediation, which are the devices that convert chemical energy into electrical energy. Microbial Electrochemical cells operate in a manner essentially similar to chemical fuel cells, and are bio-electrochemical systems wherein the expensive catalyst of chemical fuel cells is being replaced with microorganisms. Microbes by virtue of their respiratory activity oxidize organic substrates with anode acting as an electron acceptor. The protons so released permeate to the cathode which is separated from anode via proton exchange membrane (PEM) / salt bridge. The reduction reaction happens at cathode. The conventional MECCs employs microbes only at anode for oxidation of organic matter whereas cathode is essentially abiotic. The recent reports employ microbes even at cathode wherein they act as efficient electron acceptors. Both the designs prove to be useful for pollutant remediation.

[0010] Geobacter metallireducens has been reported for direct interspecies electron transfer (DIET) by several studies (Summeres et al., 2010; Rotaru et al., 2014). The use of conductive materials for DIET such as nanowire and conductive pili (Park et al., 2018) makes Geobacter metallireducens a suitable candidate to be used in MECCs for the mitigation of heavy metal wastes. The second most abundant species was found to be Lactobacillus secaliphilus (14%). This species was first isolated from the type II sourdough fermentation (Ehrmann et al., 2007). This is the first time this species has been reported for the U(VI) reduction. However, around 30% of the species found in this study belong to the Lactobacillus genus. In a previous study, Lactobacillus found to be the most abundant genera in Japanese Uranium mines. It was observed that Lactobacillus genera could remove around 2200 pM Uranium / gram dry weight of microbial cell within 1 hour (Tsuruta, 2006; Tsuruta, 2011). Prevotella sp. (11%) is a most common genera found in the gut of humans and farm animals. Prevotella sp. has been previously reported for the removal of Cd and Cr (Banach et al., 2020).

[0011] Heavy metal wastes may include radioactive materials and therefore the microorganism used needs to be radiation resistant. Deinococcus geothermalis (D. geothermalis) is an extremely radiation resistant microbe moderately thermophillic bacterium (capable of growing at 55°C). It is a gram positive radiophile closely related to Deinococcus radiodurans belonging to the family Deinococcaceae. It can withstand chronic radiation of 50 Gy / h, and at this radiation level it has been found to reduce Fe (III)-NTA, U (VI) and Cr (VI). It has also been genetically engineered to detoxify Hg (II). It is capable of forming biofilms and can anaerobically respire using nitrate reductase, which is desirable for it to be an exoelectrogenic candidate for MECC and for metal reduction.

[0012] The present inventors envisage, in the MECC, the renewable hemi-cellulosic biomass as an input chemical energy is converted to electrical energy, and concomitant detoxification of heavy metals via reduction can be achieved, where use of D. geothermalis as well as mixed culture bacterium for heavy metal removal, radionuclides removal with simultaneous renewable bioelectricity generation which would make the process self-sustainable. Apart from that other radionuclides after reduction Pu(V) to Pu(IV), Np(V) to Np(IV), Tc (VII) to Tc (IV) can be precipitated and thus removed by MECC technology.

[0013] An article titled “Geobacter metallireducens gen. nov. sp. nov., a microorganism capable of coupling the complete oxidation of organic compounds to the reduction of iron and other metals” (DOI: 10.1007 / BF00290916) by Lovley et al. (1993) discloses Geobacter metallireducens which is a gram-negative metal reducing bacteria and belongs to delta protocobacteria, for the reduction of Fe (III) to Fe (II).

[0014] In addition to Fe (III), Geobacter metallireducens is also reported for the reduction of Mn (IV), U (VI), and nitrate.

[0015] An article titled “Biological Reduction of Np(V) and Np(V) Citrate by Metal- Reducing Bacteria” (D01:10.1021 / es0618550) by Icopini et al., 2007 discloses the degradation of other radionuclei waste Np (V) using Geobacter metallireducens.

[0016] Even other articles have reported the degradation of Pu (IV) using Geobacter metallireducens.

[0017] The most common pathway for radionuclei reduction in microbes is enzymatic employing either hydrogen or any organic molecule as electron donor substrate. For example, An article titled “Biochemical and genomic facets on the dissimilatory reduction of radionuclides by microorganisms - A review” (DOI: 10.1016 / j.mineng.2010.03.004) by Mohapatra et al., 2010 discloses the microbial conversion of U (VI) to U (IV) is facilitated by an enzyme named as Uranium reductase.

[0018] Furthermore, an article titled “Direct exchange of electrons within aggregates of an evolved syntrophic coculture of anaerobic bacteria” (DOI: 10.1126 / science.1196526) by Summeres et al., 2010; and an article titled “Direct Interspecies Electron Transfer between Geobacter metallireducens and Methanosarcina barkeri” (DOI: 10.1128 / AEM.00895-14) by Rotaru et al., 2014, have reported Geobacter metallireducens for direct interspecies electron transfer (DIET).

[0019] The use of conductive materials for DIET such as nanowire and conductive pili (Park et al., 2018) makes Geobacter metallireducens a suitable candidate to be used in MECCs for the mitigation of nuclear wastes. The second most abundant species was found to be Lactobacillus secaliphilus (14%). This species was first isolated from the type II sourdough fermentation (Ehrmann et al., 2007). This is the first time this species has been reported for the U (VI) reduction. However, around 30% of the species found in this study belong to the Lactobacillus genus. In a previous study, Lactobacillus found to be the most abundant genera in Japanese Uranium mines. It was observed that Lactobacillus genera could remove around 2200 pM Uranium / gram dry weight of microbial cell within 1 hour (Tsuruta, 2006; Tsuruta, 2011). Prevotella sp. (11%) is a most common genera found in the gut of humans and farm animals. Prevotella sp. Has been previously reported for the removal of Cd and Cr (Banach et al., 2020).

[0020] India granted patent No. 381339 (India Patent Application No. 202041033271) discloses a microbial electrochemical cell for degrading waste materials into useful products. The microbial electrochemical cell comprises an anode disposed within an organic solvent containing mixed and unsorted waste such as plastic, organic and inorganic wastes, wherein one or more bacterial strains suspended within the organic solvent, wherein the one or more bacterial strain form a biofilm on the anode; wherein the cathode is disposed in a redox mediator and buffer mixture; and a salt bridge or a membrane is provided to selectively transfer the ions between the organic solvent containing the mixed and unsorted waste and the redox mediator and buffer mixture; wherein the waste material received within the anode chamber is transformed into an useful product.

[0021] SUMMARY

[0022] The present disclosure provides a Microbial Electrochemical Cell (MECC) for bioremediation of lanthanides and actinides wastes, wherein the MECC comprises an anode portion comprising at least one anode, a cathode portion comprising at least one cathode, wherein the anode and the cathode are connected to an electrical source. Potassium Ferrocyanide is used as the anolyte, which acts as the redox mediator, the anolyte is maintained at neutral pH. Waste containing lanthanides and actinides in pure state or their oxides are leached with a cone, acid to form a leached metal salt precipitate, which was diluted with water and used as catholyte. One or more bacterial strain was added to the catholyte. The cathode portion is completely sealed and made anaerobic. The cathode portion and the anode portion are connected by an electrical pathway. A constant pulse current is applied to stimulate the bacterial strain to grow as an electrically conductive biofilm on the cathode. The biofilm via its NADP to NADPH pathway releases electrons and recovers the lanthanide or actinide metals.

[0023] BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS

[0024] Fig. 1 illustrates working principle of MECC for bioremediation of lanthanides and actinides wastes, wherein the anodic portion and the cathodic portion are connected by an electrical pathway such as a salt bridge or a permeable membrane, the aerobic anodic reaction occurs in the anode half-cell of the MECC, and the anaerobic cathodic reaction occurs in the cathode half-cell of the MECC.

[0025] Fig. 2 illustrates Nyquist plot of MECC for reduction of the metals from lanthanides and actinides wastes through reduction process by the microbes, EIS recorded simultaneously as the CV analysis was carried out. Fig. 3 illustrates the Equivalent Circuit and parameters of the Nyquist plot for the reduction of lanthanides and actinides metal ions by the bacteria through the MECC of the present disclosure.

[0026] Fig. 4. depicts the SEM image of the lanthanides or actinides alloy formed on the graphite electrode.

[0027] Fig. 5 illustrates the Cyclic Voltammogram of MECC (Example 1) with Lanthanide and actinide waste composite leached metal salt catholyte (100 ppm), and Potassium Ferrocyanide anolyte at 5mV / s.

[0028] Fig. 6 illustrates the Cyclic Voltammogram of MECC (Example 2) with Lanthanide and actinide waste composite leached metal salt catholyte (lOOOppm), and Potassium Ferrocyanide anolyte at 5mV / s.

[0029] DETAILED DESCRIPTION

[0030] The subject matter of the present disclosure is described in detail with reference to the accompanying drawings. Unless otherwise specified, all the technical and scientific terms used herein have the same meaning as is generally understood by a person skilled in the art pertaining to the present disclosure. Headings are used solely for organizational purposes, and are not intended to limit the disclosure in any way.

[0031] The use of the singular includes the plural unless specifically stated otherwise. As used herein, the singular forms “a,” “an” and “the” are intended to include the plural forms as well. The use of “or” means “and / or” unless stated otherwise. Unless otherwise indicated, all numbers used herein to express quantities, dimensions, and so forth used should be understood as being modified in all instances by the term "about." It is to be understood that wherein a numerical range is recited, it includes all values within that range, and all narrower ranges within that range, whether specifically recited or not. As used herein, "including," "containing" and like terms are understood to be synonymous with "comprising" and are therefore open-ended and do not exclude the presence of additional undescribed or unrecited elements, materials, phases or method steps. In addition, it should be appreciated that any figures provided herewith are for explanation purposes to persons ordinarily skilled in the art and that the drawings of them are not necessarily drawn to scale.

[0032] Any method / process steps and / or operations and / or instructions used in this disclosure, are for illustrative purposes in a particular order and / or grouping. Other orders and / or grouping of the process steps or its portions and / or operations or its portions and / or instructions or its portions are possible and, one or more of the process steps and / or operations and / or instructions can be combined and / or deleted.

[0033] The present disclosure provides a Microbial Electrochemical Cell (MECC) for bioremediation of lanthanides and actinides wastes, wherein the MECC comprises an anode portion comprising at least one anode, a cathode portion comprising at least one cathode, wherein the anode and the cathode are connected to an electrical source.

[0034] Anode portion:

[0035] - Anolyte: A redox mediator solution.

[0036] - at least one anode is disposed within the redox mediator solution in the anode portion, wherein the redox mediator reduces the lanthanide and actinide from higher to lower oxidation state or to native state.

[0037] - The anode portion is left unsealed and a plastic passage is fixed to allow any gases such as CH4 and H2 generated during the electrochemical process to escape through.

[0038] - Anode portion is maintained at neutral pH using a buffer, The buffer solution can include, but is not limited to, mild acidic or basic or neutral buffer. A preferred buffer is a phosphate buffer such as potassium dihydrogen phosphate. Other suitable known buffers can also be used.

[0039] In an aspect, graphite rod is used as anode. In an aspect, the redox mediator is Potassium Ferrocyanide, preferably IM Potassium Ferrocyanide.

[0040] Cathode portion:

[0041] - Catholyte: Waste containing lanthanides and actinides metals or their oxides are leached with a cone, acid such as cone. HC1 or H2SO4 or HNO3 into individual salts. The stock solution is the leached metal salt (e.g. chloride, sulphate, nitrate) precipitate. The leached metal salts are diluted with water to prepare different concentrations, such as 2ppm (0.002M), 50ppm (0.05M), lOOppm (0.1M), 500ppm (0.5M), lOOOppm (IM) and 5000 ppm (5M) solutions. The diluted salt solutions were used as catholyte.

[0042] - Inoculum: One or more bacterial strain was added to the catholyte. In an aspect, a mixed bacterial culture with species of Geobacter metallireducens, Geobacter suphurreducens, Schwenella oneidenisis was added to the catholyte. Other suitable microorganisms can also be used.

[0043] - The cathode portion is completely sealed and made anaerobic as the inoculum is anaerobic in nature.

[0044] - pH is allowed to change during reduction of metal ions into metal in the MECC.

[0045] - Flooding of catholyte is avoided by maintaining higher concentration of protons in cathode portion.

[0046] - The one or more bacterial strain forms an electrically conductive biofilm on the cathode.

[0047] In an aspect, graphite rod is used as cathode.

[0048] Electrical pathway (between anode portion and cathode portion)

[0049] - The cathode portion and the anode portion are connected via an electrical pathway for proton transport from the cathode portion to the anode portion.

[0050] - In an aspect, the electrical pathway is established through a salt bridge. The ingredients of salt bridge can include, but is not limited to agar-agar solution and potassium chloride (KC1) solution, or agar-agar solution and Sodium chloride (NaCl) solution. Other suitable ingredients as salt bridge can also be used. However, a salt bridge of Agar-agar (KC1) or Agar-agar (NaCl) is preferred because the agar-agar medium is suitable for bacteria to grow.

[0051] - In another aspect, the electrical pathway between the anode portion and the cathode portion is a membrane.

[0052] Fig. 1 illustrates working principle of MECC for bioremediation of lanthanides and actinides wastes, wherein the anodic portion and the cathodic portion are connected by an electrical pathway such as a salt bridge or a permeable membrane.

[0053] As shown in Fig. 1, the aerobic anodic reaction occurs in the anode half-cell of the MECC, and the anaerobic cathodic reaction occurs in the cathode half-cell of the MECC.

[0054] Aerobic anodic reaction:

[0055] Oxidation reaction happens in the anode portion at Neutral pH.

[0056] The potassium ferrocyanide (redox mediator) anolyte in the anode portion is transformed to Potassium ferricyanide by losing an electron.

[0057] K4[Fe(CN)6] K3[Fe(CN)6] + e"

[0058] Anaerobic cathodic reaction:

[0059] U6++ 2e ^ U4+Eo = - 1.66 V TC7++ 3C ^ TC4+Eo = - 1.18 V Pu6++ 2e Pu4+Eo = - 0.28 V

[0060] Np5++ e Np4+Eo = - 0.26 V

[0061] Cs++ e Cs Eo = - 0.34 V

[0062] Sr++ e Sr Eo = - 0.40 V

[0063] The bacteria act on the lanthanides and actinides wastes via the following depicted process. Microorganisms feed on organic or inorganic waste and produce electron during the oxidation process. Oxidation of organic substrates generates electrons that are passed on to the electrodes and generate electricity in MECCs. The microbial development into the electrode surface without penetrating into the electrode results in transfer of electrons inside of the bacterial cell to the electrode surface either by transfer of reduced species or by hopping of electrons on redox enzymes in the cell membrane. When electrons get transferred from the cell it leads to formation of redox species which links the bacterial cell wall to electrode electronically. This redox species are called as the mediator. Shewanella oneidensis can transfer electrons via Fe3+ions. Geothrix ferementans and pseudomonas also have inherent electron mediators. As biosynthesizing of the electron mediator is thermodynamically unfavourable process, inherent electron shuttles are less efficient in MECCs. Numerous microbes possess self-ability to move electrons across bacterial cell wall to electrode. Shewanella putrefaciens, Geobacter sulferreducens, Geobacter metallireducens and Rhodoferax ferrireducens are such bacteria that can move electrons from inside of the cell to electrode surface via c-type cytochromes, biofilms and conducting pili nanowires. The coulombic efficiency (CE) of such MECCs is very high. The biofilm created by these bacteria can develop from the anolyte working as electron acceptors and transfer electrons directly to the anode leading to higher power production.

[0064] In MECC, biofilm formation begins with the attachment of microorganisms to the electrode surface via chemical and physical interactions (Van der Waals forces, electrostatic attraction, and chemical bonding between the functional moieties). The initial adhesion is supported by the surface roughness and chemical environment of the electrode material, which offers a site for microorganism adhesion. After the initial adhesion on the electrode surface, the extracellular polymeric substances (EPS; including polysaccharides, proteins, nucleic acids, lipids) produced by the microorganism enhances their adhesion and promotes the biofilm growth. Subsequently, the electron transfer and transport are being channelled through the biofilm to the electrode surface and stimulates the bio electricity production. Hence, the development of stable and viable biofilm formation potentially influences the performance of MECC and other bio electrochemical processes (bioremediation).

[0065] Different factors affect the performance of MECCs such as microbe, biomass and its concentration, ionic strength, pH, temperature, electrode materials, PEM or salt bridge and the operational conditions of electrodes. Upon oxidation of organic substrate by microbes, protons are generated in the anode leading to pH change in the system. To avoid this pH change, buffers are used in MECCs. pH change leads to undesirable side reactions such as hydrogen evolution reaction and oxygen reduction reaction at the electrodes causing non-performance of MECCs. By separating the anode and cathode chambers using membrane, protons generated in the anode can be transferred to cathode resulting in H2O formation in cathode thereby attaining equilibrium in the proton production rate at anode to oxygen reduction rate at cathode. The Open Circuit Voltage of the MECC stabilizes and when the OCV falls to zero or near zero the biofilm or bacterial action becomes complete.

[0066] At different dilutions (ca. 10, 100, 1000, 10000 times of the acid leached salts) of the electrolyte is utilised in the MECC, the Cyclic Voltammogram is recorded for all the dilutions. With increase in the dilution, the peak current increases, as the peak current is directly proportional to the concentration of the electroactive species in the electrolyte. The dilution at which the peak current shows no variation indicates the completion of the reduction of the metal ions in the electrolyte.

[0067] The present disclosure also provides a bio-electrochemical process for bioremediation of lanthanides and actinides wastes, wherein the process comprises the following steps.

[0068] - providing a microbial electrochemical cell having an anode portion with at least one anode and a cathode portion with at least one cathode, wherein the at least one anode and the at least one cathode are connected to an electrical source; - providing an electrical pathway between the anode portion and the cathode portion for proton transport from the cathode portion to the anode portion;

[0069] - adding a redox mediator solution to the anode portion;

[0070] - adding a leached metal salt of lanthanides wastes, actinides wastes, lanthanide oxides wastes, or actinide oxides wastes to the cathode portion;

[0071] - adding one or more bacterial strain within the leached metal salt; and

[0072] - applying a constant pulse current to stimulate the one or more bacterial strain to grow as an electrically conductive biofilm on the at least one cathode.

[0073] The redox mediator preferably is Potassium Ferrocyanide, preferably IM Potassium Ferrocyanide.

[0074] Recovery Efficiency of the MECC for recovery of lanthanides and actinides metal ions:

[0075] The recovery efficiency RE is calculated via the following expression.

[0076] Wherein, minput - weight of lanthanide and actinide waste such as weight of U waste, weight of Th waste, weight of Pu waste, moutput - weight of lanthanide and actinide metal such as U, Th, Pu, deposited on graphite substrate, mass % is the mass of a particular lanthanide or actinide material present in the total mass of materials taken into consideration.

[0077] The multistep electron transfer is very facile in the MECC of the present disclosure due to following reasons.

[0078] - External electrochemical perturbation increases the electron density on the graphite surface.

[0079] - Biofilm formed on the graphite surface reacts with the proton in the solution to facilitate NADP to NADPH reduction process and release electrons in the system. The biofilm via its NADP to NADPH pathway releasing electrons, wherein elemental lanthanide or actinide metal is reduced and deposited on the graphite surface.

[0080] - Thus, the surface electron density of the biofilm coated graphite surface is very high leading to fast transfer of electrons from the biofilm surface to the metal ions.

[0081] - Thus, the rate determining step in the MECC reduction of lanthanides and actinides waste metal ions in the absence of electrochemical perturbation is the biological process of NADP conversion to NADPH inside the bacteria and electron crossing the bacterial cell membrane to the catholyte solution. Hence, there is an activation polarisation occurring between the interfaces of (i) graphite and biofilm, (ii) biofilm and catholyte. This activation polarization is overcome by externally perturbing the biofilm via supply of electrons. At very slow scan rate of 5 mV / s, the activation polarization is compensated by the electrochemical perturbation and increase the rate of transfer to electrons and hence the reduction of metal ions occurs as can be seen from the Fig 1.

[0082] Examples:

[0083] The present disclosure will now be explained in further detail by the following examples. These examples are illustrative of certain embodiments of the disclosure without limiting the scope of the present disclosure.

[0084] Example 1

[0085] MECC includes:

[0086] - Graphite anode,

[0087] - Graphite cathode,

[0088] - Anolyte: 500 ml of IM Potassium Ferrocyanide is filled in the anode portion, phosphate buffer solution

[0089] - Catholyte: The collected lanthanides and actinides wastes were leached with cone. HC1. The resulting stock solution is the leached metal chloride salt precipitate. The leached metal chloride salts are diluted with water to prepare a lOOppm (O.1M) solution. This diluted salt solution was used as catholyte. 500 ml of catholyte was added in the cathode portion.

[0090] - 1 gm of anaerobic inoculum containing a mixed culture bacteria was added to the catholyte.

[0091] - The cathode portion was sealed to make it anaerobic as the inoculum is anaerobic in nature.

[0092] - Salt bridge: Agar-Agar powder mixed in aqueous IM KC1 and filled in PVC Pipes of 6cm long and 3mm diameter. The cathode portion and the anode portion were connected through the salt bridge.

[0093] Electrical current of 1A was supplied to the MECC.

[0094] - The electrolyte is subjected to the potential scan of -2 to 2 V

[0095] - the scan rate of the redox reaction is fixed at 5 mV / s

[0096] - the appropriate lanthanide or actinide element / metal is reduced and deposited on the graphite surface

[0097] Fig. 2 illustrates Nyquist plot of MECC for reduction of the metals from lanthanides and actinides wastes through reduction process by the microbes, EIS recorded simultaneously as the CV analysis was carried out.

[0098] The Electrochemical Impedance Spectroscopy (EIS) of the MECC during the reduction of metal ions by the bacteria is studied at an AC amplitude of lOmV in the frequency range of 1Hz to 1kHz. As observed from Fig. 2, the process is controlled by charge transfer and a complete semicircle is observed without tailing off (no diffusion).

[0099] This demonstrates that the rate determining step in the bio electrochemical process of reduction of lanthanides and actinides wastes to be charge transfer of:

[0100] (i) metal ions from bulk to biofilm surface,

[0101] (ii) electrons from inside of the cell of bacteria to the surface via cell membrane and (iii) electrons from graphite surface to the bacteria via cell membrane (bacteria acts as a conduit of electrons).

[0102] The x-intercept of the Nyquist plot is very low say 112.3 mQ. The x-intercept signifies the solution resistance of the system. The very low solution resistance indicates higher ionic conductivity of the solution thereby supporting the facile charge transfer from bulk to biofilm surface.

[0103] Fig. 3 illustrates the Equivalent Circuit and parameters of the Nyquist plot for the reduction of lanthanides and actinides metal ions by the bacteria through the MECC of the present disclosure.

[0104] As illustrated in Fig. 3, The circuit fitting for the Nyquist plot resulted in three components for the system

[0105] - Solution Resistance (Rs); 112.3 mQ.

[0106] - Charge Transfer Resistance (Rct); 25 Q.

[0107] - Constant Phase Elements (CPEs) for biofilm / catholyte, graphite / biofilm interfaces; 118.7 mF and 285.3 mF respectively.

[0108] The recovery efficiency of each metal is illustrated in Table 1.

[0109] Table 1

[0110] The Cyclic Voltammetry analysis of the processes occurring in MECC with the lanthanides and actinides waste material as catholyte revealed that even at infinite dilution of the catholyte in the system (i.e., 5ppm), the reduction peaks for the corresponding metal ions were noticed at appropriate voltage with respect to Standard Hydrogen Electrode (SHE). According to the Randle Sevick’s equation, which states that the intensity of the peak current is directly proportional to the concentration of the electroactive species in the system under consideration, the peaks appear with low intensity (due to infinite dilution of anolyte made of lanthanides and actinides waste materials). The following electrochemical reactions are expected in MECC during the reduction of lanthanides and actinides waste into metal alloy.

[0111] Eo = 0.34 V

[0112] Eo = - 0.26 V

[0113] Eo = - 0.28 V

[0114] Eo = - 1.13 V Eo = - 1.66 V

[0115] The deposited metal alloy on graphite electrode had been subjected to Scanning Electron Microscopy (SEM) and Energy Dispersive Spectroscopy (EDS) analysis to understand the morphology and chemical composition.

[0116] Fig. 4. depicts the SEM image of the lanthanides or actinides alloy formed on the graphite electrode.

[0117] Fig. 5 illustrates the Cyclic Voltammogram of MECC (Example 1) with:

[0118] - Lanthanide and actinide waste composite leached metal salt catholyte, wherein the Lanthanide and actinide waste composite leached metal salt catholyte includes the chloride salt (as HC1 is used) of lanthanides and actinides diluted by distilled water,

[0119] - Potassium Ferrocyanide anolyte in two electrode mode with symmetric graphite electrodes. As illustrated in Fig. 5, the broadened humps are due to low concentration of the catholyte and at scan rate of 5 mV / s with respect to SHE. Blank and background correction is not done as the electrolyte itself is the electroactive species.

[0120] Example 2

[0121] MECC includes:

[0122] - Graphite anode,

[0123] - Graphite cathode,

[0124] - Anolyte: 500 ml of IM Potassium Ferrocyanide is filled in the anode portion, phosphate buffer solution

[0125] - Catholyte: The collected lanthanides and actinides wastes were leached with cone. HC1. The resulting stock solution is the leached metal chloride salt precipitate. The leached metal chloride salts are diluted with water to prepare a lOOOppm (IM) solution. This diluted salt solution was used as catholyte. 500 ml of catholyte was added in the cathode portion.

[0126] - 1 gm of anaerobic inoculum containing a mixed culture bacteria was added to the catholyte.

[0127] - The cathode portion was sealed to make it anaerobic as the inoculum is anaerobic in nature.

[0128] - Salt bridge: Agar-Agar powder mixed in aqueous IM KC1 and filled in PVC Pipes of 6cm long and 3mm diameter. The cathode portion and the anode portion were connected through the salt bridge.

[0129] Electrical current of 1A was supplied to the MECC.

[0130] - The electrolyte is subjected to the potential scan of -2 to 2 V

[0131] - the scan rate of the redox reaction is fixed at 5 mV / s

[0132] - the appropriate lanthanide or actinide element / metal is reduced and deposited on the graphite surface

[0133] Fig. 6 illustrates the Cyclic Voltammogram of MECC (Example 2) with: - Lanthanide and actinide waste composite leached metal salt catholyte, wherein the lanthanide and actinide waste composite leached metal salt catholyte includes the chloride salt (as HC1 is used) of lanthanides and actinides diluted by distilled water,

[0134] - Potassium Ferrocyanide anolyte in two electrode mode with symmetric graphite electrodes.

[0135] As illustrated in Fig. 6, the broadened humps are due to low concentration of the catholyte and at scan rate of 5 mV / s with respect to SHE. Blank and background correction is not done as the electrolyte itself is the electroactive species.

[0136] Advantages:

[0137] The bioremediation of lanthanides and actinides wastes using MECC of the present disclosure has the following non-limiting advantages.

[0138] - Reduce health and environmental risks.

[0139] - Easy extraction of the Lanthanides and actinides in its native elemental state even at concentration of ppm or ppb.

[0140] Applications:

[0141] The bioremediation of lanthanides and actinides wastes using MECC of the present disclosure has the following non-limiting industrial applications.

[0142] - Recovery of lanthanides and actinides

[0143] - Bio-remediation of the waste with valuable metals or heavy metals thereby enhancing circular economy and reducing environmental pollution.

[0144] Although the present disclosure is described in terms one or more embodiments, it is to be understood that they have been presented by way of example, and are not limiting. Thus, the present disclosure should not be limited by any of the abovedescribed exemplary embodiments, but should be defined only in accordance with the following claims and their equivalents. Source And Geographical Origin of Biological Materials:

[0145] The source and geographical origin of biological materials used in the present disclosure are as mentioned below:

Claims

CLAIMS1. A microbial electrochemical cell (MECC) for bioremediation of lanthanides and actinides wastes comprising:- an anode portion comprising at least one anode disposed within a redox mediator solution;- a cathode portion comprising at least one cathode disposed within a catholyte, wherein the catholyte includes leached metal salt of lanthanides wastes or actinides wastes, or leached metal salt of lanthanide oxides wastes or actinide oxides wastes, and one or more bacterial strain suspended within the leached metal salt; and- an electrical pathway engaged between the anode portion and the cathode portion for proton transport from the cathode portion to the anode portion; wherein the anode and the cathode are connected to an electrical source, wherein the one or more bacterial strain forms an electrically conductive biofilm on the cathode, wherein, the biofilm via its NADP to NADPH pathway releases electrons, and reduces the diluted leached metal salt into elemental lanthanides and actinides metals, and deposited on the graphite surface.

2. The (MECC) for bioremediation of lanthanides and actinides wastes as claimed in claim 1 , wherein the leached metal salt is included in the cathode portion in a diluted form, wherein the leached metal salt is diluted with water, wherein the dilution is done to have a concentration selected from 2ppm (0.002M), 50ppm (0.05M), lOOppm (0.1M), 500ppm (0.5M), lOOOppm (IM) or 5000 ppm (5M) solutions.

3. The (MECC) for bioremediation of lanthanides and actinides wastes as claimed in claim 1, wherein the redox mediator is IM Potassium Ferrocyanide solution.

4. The (MECC) for bioremediation of lanthanides and actinides wastes as claimed in claim 1, wherein the leached metal salt is obtained by treating lanthanides or actinides wastes or lanthanide oxides wastes or actinide oxideswastes with a concentrated acid forming their salts, wherein the concentrated acid is selected from HC1 or H2SO4 or HNO3.

5. The (MECC) for bioremediation of lanthanides and actinides wastes as claimed in claim 1, wherein the one or more bacterial strain is an inoculum containing a mixed bacterial culture.

6. The (MECC) for bioremediation of lanthanides and actinides wastes as claimed in claim 1, wherein the one or more bacterial strain is a mixed bacterial culture with a mixture of species of Geobacter metallireducens, Geobacter suphurreducens, Schwenella oneidenisis.

7. The (MECC) for bioremediation of lanthanides and actinides wastes as claimed in claim 1 , wherein the anode is a graphite anode and the cathode is a graphite cathode.

8. A bio-electrochemical process for bioremediation of lanthanides and actinides wastes comprising:- providing a microbial electrochemical cell having an anode portion with at least one anode and a cathode portion with at least one cathode, wherein the at least one anode and the at least one cathode are connected to an electrical source;- providing an electrical pathway between the anode portion and the cathode portion for proton transport from the cathode portion to the anode portion;- adding a redox mediator solution to the anode portion;- adding a leached metal salt of lanthanides wastes, actinides wastes, lanthanide oxides wastes, or actinide oxides wastes to the cathode portion;- adding one or more bacterial strain within the leached metal salt; and- applying a constant pulse current to stimulate the one or more bacterial strain to grow as an electrically conductive biofilm on the at least one cathode,- the biofilm via its NADP to NADPH pathway releasing electrons, wherein elemental lanthanide or actinide metal is reduced and deposited on the graphite surface.

9. The bio-electrochemical process for bioremediation of lanthanides and actinides wastes as claimed in claim 8, wherein the leached metal salt is added to the cathode portion in a diluted form, wherein the leached metal salt is diluted with water, wherein the dilution is done to have a concentration selected from 2ppm (0.002M), 50ppm (0.05M), lOOppm (0.1M), 500ppm (0.5M), lOOOppm (IM) or 5000 ppm (5M) solutions.

10. The bio-electrochemical process for bioremediation of lanthanides and actinides wastes as claimed in claim 8, wherein the redox mediator is IM Potassium Ferrocyanide solution.

11. The bio-electrochemical process for bioremediation of lanthanides and actinides wastes as claimed in claim 8, wherein the leached metal salt is obtained by treating lanthanides or actinides wastes or lanthanide oxides wastes or actinide oxides wastes with a concentrated acid forming their salts, wherein the concentrated acid is selected from HC1 or H2SO4 or HNO3.

12. The bio-electrochemical process for bioremediation of lanthanides and actinides wastes as claimed in claim 8, wherein the anode is a graphite anode and the cathode is a graphite cathode.

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