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    • 专利摘要:
    A method for recovering sludge iron from sewage treatment plant obtained after precipitation with iron salts, characterized in that it comprises a single step of re-dissolving the iron of said sludge by biological means, followed by a step of separating the iron from the liquid fraction obtained at the end of the biological step of iron dissolution. The biological step comprises a single step of fermentation of said sludge in the presence of substrates rich in readily biodegradable carbon, at a content greater than or equal to 0.3 g of COD / MV, leading to the release of the iron from said sludge and its setting in solution. Use of the process for the recycling of at least a portion of the iron salts, such as those used in sewage treatment plants, for example implementing a step of precipitation with ferric chloride.
    公开号:FR3062124A1
    申请号:FR1750608
    申请日:2017-01-25
    公开日:2018-07-27
    发明作者:Marie-Line DAUMER；Etienne BRAAK
    申请人:Institut National de Recherche en Sciences et Technologies Pour Lenvironnement et lAgriculture IRSTEA；
    IPC主号:
    专利说明:

    Agent (s): trusted.
    IPSILON Simplified joint-stock company © PROCESS FOR THE RECOVERY OF IRON FROM SLUDGE FROM A WASTEWATER TREATMENT PLANT AND ITS USE FOR RECYCLING, IN PARTICULAR OF FERRIC CHLORIDE.
    FR 3 062 124 - A1 (57) Method for recovering iron from sludge from wastewater treatment plants obtained after precipitation with iron salts, characterized in that it comprises a single step of re-dissolving iron said sludge biologically, followed by a step of separating iron from the liquid fraction obtained at the end of the biological step of dissolving iron. The biological stage comprises a single stage of fermentation of said sludge in the presence of easily rich biodegradable carbon-rich substrates, with a content greater than or equal to 0.3 g of COD / MV, leading to the release of iron from said sludge in solution.
    Use of the process for recycling at least part of the iron salts, such as those used in wastewater treatment plants, for example using a precipitation step with ferric chloride.
    Fertilizer
    Liquid flow ”·“ Φ- Sludge
    i
    FIELD OF THE INVENTION
    The present invention relates to the field of waste water treatment and more particularly to a process for recovering iron from sludge from waste water treatment plants obtained after precipitation with iron salts, such as ferric chloride.
    The present invention also relates to the use of such a process for recycling at least part of the iron salts, such as ferric chloride in wastewater treatment plants.
    PRIOR ART
    The invention is situated in the general context of the reduction of phosphorus discharges into the environment, identified as the main responsible for the eutrophication phenomena of lakes and rivers.
    To this end, urban or industrial wastewater treatment plants use phosphate precipitation operations by chemical precipitation, such as flocculation-coagulation, using aluminum or iron salts, either primarily or complement of biological phosphate removal steps, which allow the phosphorus to be precipitated and concentrated in sludge. Ferric chloride is one of the most commonly used agents for this physico-chemical treatment, due to its ability to combine in particular with phosphate ions to form a precipitate of iron phosphate FePO4.
    The sludge from these treatment plants (STEP) is therefore both loaded with phosphorus and iron. The iron present in these sludges fixes the phosphorus which is therefore less available to plants, when these sludges are spread on the ground.
    Studies have been carried out recently to try to extract phosphorus from said sludge and recover it, in particular in the form of struvite (double ammonium and magnesium phosphate) which can be used as fertilizer. The presence of iron inhibits the crystallization of struvite and therefore also hinders these phosphorus recovery operations.
    A first object of the present invention is therefore to eliminate the iron in order to recycle the phosphorus.
    During research carried out by the inventors, it was discovered that, surprisingly, this iron could be redissolved in a biological way.
    SUMMARY OF THE INVENTION
    The present invention therefore provides a method for recovering iron from sludge from a wastewater treatment plant obtained after precipitation with iron salts, such as ferric chloride, characterized in that it comprises a single step of recovering dissolution of the iron in said sludge by biological means, followed by a step of separating iron from the liquid fraction obtained at the end of the biological step of dissolving iron.
    More particularly, the step of dissolving iron by biological means advantageously comprises a single step of fermentation of said sludge in the presence of substrates rich in carbon which are easily biodegradable, at a content greater than or equal to 0.3 g of COD / MV, preferably greater or equal to 0.5 g of COD / MV, leading to the release of iron from said sludge and to its dissolution.
    (COD: Chemical Oxygen Demand) (MV: Volatile Matter)
    By substrates rich in easily biodegradable carbon, we mean compounds which are easily and rapidly assimilated by the microorganisms present in these sludges from treatment plants.
    Preferably the substrates are compounds containing carbohydrates, or derivatives of carbohydrates, leading to the production of volatile organic acids and to an acidification of the medium, up to a pH value less than or equal to 5, preferably a value with a pH close to 4.
    These substrates can advantageously be chosen from sucrose or glucose and their derivatives, organic agricultural, industrial or urban waste, or plants or crop residues or fractions extracted from these products.
    Preferably, the fermentation step is an anaerobic or anoxic fermentation, carried out at a temperature between 20 ° C and 60 ° C, preferably between 25 ° C and 50 ° C, more preferably between 30 ° C and 40 ° C.
    This fermentation step in an oxygen-poor environment and without the addition of a specific inoculum, allows acidification and release in the liquid fraction, in particular of ferrous and / or ferric ions as well as phosphate ions.
    This single fermentation step is followed by a liquid / solid separation step, such as filtration or centrifugation of said acidified sludge. The liquid fraction recovered at the end of said separation is then brought into contact with a material capable of fixing the iron ions or of separating it from the phosphate ions, such as a cation exchange resin or an adsorbent material, retaining the iron ions of the liquid fraction and providing an iron-depleted or substantially iron-free solution.
    In order to recover the iron, the cation exchange resin or the adsorbent material can then be regenerated using a solution eluting the iron ions in the form of a solution which can be reused in a wastewater treatment plant. For example, the cation exchange resin or the adsorbent material can be regenerated using a hydrochloric acid solution, the eluate then containing ferric chloride in solution.
    The present invention also relates to the use of the process described above for the recycling of at least part of the iron salts, such as those used in wastewater treatment plants implementing a step of precipitation of the salts of iron. iron, especially in urban or industrial wastewater treatment plants implementing a flocculation-coagulation and / or phosphate removal step with ferric chloride.
    This results in a significant saving of ferric chloride, a reactive whose cost represents a significant part of the operation of these treatment plants.
    In addition, the fermentation as described above, which leads to solubilization of the iron simultaneously makes it possible to re-dissolve the phosphate ions. The process according to the present invention can thus also be used for the simultaneous recovery of phosphorus from treatment plant sludge, by precipitation of phosphorus, in the form of struvite, from said solution depleted or substantially free of iron.
    Thus the dissolution of the iron and its trapping make it possible to increase the recycling yield of phosphorus, without harming the quality of the product (struvite) obtained.
    BRIEF DESCRIPTION OF THE DRAWINGS
    The invention will be clearly understood on reading the following description of exemplary embodiments, with reference to the appended drawings in which:
    FIG. 1 is a schematic diagram of the different stages of treatment carried out in the treatment plant (STEP) including the method according to the invention (the dotted arrows schematize the circuit relating to the sludge);
    FIG. 2 is a diagram showing the qualities of dissolved iron after biological acidification according to the invention of sludges from different treatment plants (the abbreviations refer to the operations carried out in these stations: EBPR = Biological phosphate removal - FeCh = ferric chloride phosphate removal );
    Figure 3 shows schematically the ion concentration of the liquid fraction separated from the acidified sludge after trapping on different quantities of a strong cation exchange resin.
    EXAMPLES
    The overall diagram of the iron recycling process according to the invention with trapping by ion exchange resin, is presented in FIG. 1, including biological dissolution followed by recovery of the iron on an ion exchange column.
    Sludge tested
    Five sludges from different wastewater treatment plants (WWTPs), whether or not practicing biological phosphate removal, were collected and stored at 4 ° C in the laboratory. Tests have shown that a storage period between 24 and 240 hours does not disturb the dissolution mechanism, leaving a certain flexibility for the implementation of the process. STEP S1 has a controlled biological phosphating process, STEP S2 and queue 1 of STEP S4 have nitrogen and carbon treatment configurations inducing a more or less significant development of dephosphating bacteria (anaerobiosis instead anoxia upstream of the aerobic biological treatment basin for wastewater), STEP S3 and line 2 of station S4 have a predominantly ferric chloride dephosphatation. The Fe to tai / Ptotai molar ratios in the sludge are between 0.4 and 1.2.
    Measurements
    The dissolved or total forms of the elements: PO -, Fe 2+ , Ca 2+ , NH were assayed by UV-visible spectrophotometry (Gallery - Thermo Fisher). The monochromator is composed of a filter assembly ranging from 340 to 800 nm.
    The iron is assayed using a reagent composed of guanidine, ascorbic acid in acetate buffer and a second reagent composed of ferene S in acetate buffer. Ascorbic acid reduces Fe 3+ to Fe 2+ and ferene allows the formation of a blue complex with Fe 2+ with an absorbance peak at 593 nm.
    Phosphorus is measured in the form of orthophosphate which is soluble in water, according to the method of Riley and Murphy. Ammonium molybdate and antimony potassium tartrate under acidic conditions react with orthophosphates to form a 12-molybdophosphoric acid complex. This complex is reduced with ascorbic acid to form a blue heteropoly compound whose absorbance is measured by spectrophotometry at 880 nm and is proportional to the phosphate concentration.
    The COD concentration measurements were carried out according to the NFT 90-101 standard and the volatile matter (MV) according to the EN 15935 standard, on all of the sludges and co-substrates studied.
    The total forms of phosphorus and iron were determined from ash obtained after calcination at 550 ° C for 4 hours, followed by dissolution by adding a mixture of sulfuric and nitric acid (75/25) at pressure 1 bar , at 120 ° C for one hour.
    Biological dissolution:
    A co-substrate rich in easily degradable carbon (sucrose) is added to the sludge at a content of 0.5 gDCO / gMV. The fermentation reactors are inerted with nitrogen to be strictly anerobic and placed at 35 ° C with gentle stirring for 48 hours. In stations equipped with a digester, this step could be considered as a hydrolysis step prior to anaerobic digestion and could thus advantageously increase the yield of methane production.
    In the laboratory, inerting is essential to maintain anaerobic conditions because the reactors are small in volume and the dissolved agitation of oxygen which inhibits the biological dissolution of iron and phosphorus. In the industrial process the volume of the reactor makes it possible to maintain the anaerobic condition without inerting.
    Figure 2 shows the results obtained during the laboratory test on the five sludge samples. The fraction of dissolved iron by biological route varies from 33% for one of the stations practicing the phosphating only with ferric chloride up to 92% on the sludges of the station S1 with a controlled biological phosphating. It should be noted that these results are obtained without adding an incoculum.
    Compared to comparative tests of acidification by chemical means at lower pH, carried out on sludges from station S1 which did not make it possible to dissolve more than 20% of the iron in the sludges, biological acidification shows performances very interesting.
    Liquid / solid separation:
    The acidified sludge is separated from the liquid fraction in which the iron and phosphorus have been dissolved by centrifugation.
    Iron trapping:
    An iron trapping test on a strong cation exchange resin was carried out on the liquid fraction obtained after separation of the acidified biological sludge from station S4-1. The resin is a DOWEX type Marathon C resin.
    The initial pH of the liquid was 4.81 at the time of the tests. Increasing amounts of resin (5, 20 and 50 g.L ' 1 ) were added to the medium and the mixture was then stirred at room temperature for 1 hour. A witness without resin was added to the series. An amount between 5 and 20 g of resin per liter of liquid fraction resulting from the biological dissolution of iron makes it possible to trap most of the iron. The results are shown in the figure
    3. It is noted that the concentration of dissolved P is not modified.
    Alternatively, the iron can be fixed by passing the liquid fraction over columns of cationic exchange resin.
    Resin regeneration:
    The regeneration of the resin is carried out with an eluent comprising a 4% HCl solution. The iron is thus eluted in the form of ferric chloride which can be recycled in the treatment plant.
    The results of the above phosphorus tests show that:
    - The dissolution of P biologically for recycling in the form of struvite was possible on all the sludge tested.
    - These operations can be carried out without affecting the storage period between 2 and 10 days after collection.
    - The best P dissolution results (over 70%) are obtained with the sludge from a mainly biological treatment system supplemented with ferric chloride. In the sludge resulting from a mainly physico-chemical treatment, approximately 30% of the total P could be dissolved. The efficiency of the P recycling process will be greater at stations practicing biological phosphate removal.
    权利要求:
    Claims (11)
    [1" id="c-fr-0001]
    1. A method for recovering iron from sludge from wastewater treatment plants obtained after precipitation with iron salts, such as ferric chloride, characterized in that it comprises a single step of re-dissolving the iron of said iron. biological sludge, followed by a step of separating iron from the liquid fraction obtained at the end of the biological step of dissolving iron.
    [2" id="c-fr-0002]
    2. Method according to claim 1, characterized in that the step of dissolving iron biologically comprises a single step of fermentation of said sludge in the presence of substrates rich in easily (bio) degradable carbon, at a content greater than or equal to 0.3 g of COD / MV, preferably greater than or equal to 0.5 g of COD / MV, leading to the release of iron from said sludge and to its dissolution.
    [3" id="c-fr-0003]
    3. Method according to claim 2, characterized in that the substrates are compounds containing carbohydrates, or derivatives of carbohydrates, leading to the production of volatile organic acids and to an acidification of the medium, up to a pH value less than or equal to 5, preferably a pH value close to 4.
    [4" id="c-fr-0004]
    4. Method according to any one of claims 2 or 3, characterized in that said substrates are chosen from sucrose or glucose and their derivatives, organic agricultural, industrial or urban waste, or plants or crop residues or fractions extracted from these products.
    [5" id="c-fr-0005]
    5. Method according to any one of claims 2 to 4, characterized in that the fermentation step is an anaerobic or anoxic fermentation, carried out at a temperature between 20 ° C and 60 ° C, ίο preferably between 25 ° C and 50 ° C, more preferably between 30 ° C and 40 ° C.
    [6" id="c-fr-0006]
    6. Method according to any one of claims 2 to 5, characterized in that the fermentation step is followed by a liquid / solid separation step, such as filtration or centrifugation, the liquid fraction recovered at l after said separation is then brought into contact with a material capable of fixing iron ions or separating them from phosphate ions, such as a cationic exchange resin or an adsorbent material, retaining the iron ions from the liquid fraction and providing a solution depleted in iron or substantially free of iron.
    [7" id="c-fr-0007]
    7. Method according to claim 6, characterized in that the cation exchange resin or the adsorbent material is then regenerated by means of a solution eluting the iron ions in the form of a solution which can be reused in a treatment station. wastewater.
    [8" id="c-fr-0008]
    8. Method according to one of claims 6 or 7, characterized in that the cation exchange resin or the adsorbent material is then regenerated by means of a hydrochloric acid solution, the eluate containing ferric chloride in solution.
    [9" id="c-fr-0009]
    9. Use of the method according to one of the preceding claims for the recycling of at least part of the iron salts, such as those used in wastewater treatment plants using a salt precipitation step of iron.
    [10" id="c-fr-0010]
    10. Use according to claim 9 in urban or industrial wastewater treatment plants using a flocculation-coagulation and / or phosphate removal step with ferric chloride.
    [11" id="c-fr-0011]
    11. Use according to any one of claims 9 or 10, depending on claim 6 for the simultaneous recovery of phosphorus from sewage treatment plant sludge, by precipitation of phosphorus in the form of struvite from said solution depleted in iron or substantially 5 free of iron.
    FeCL, ±
    STEP
    Treated water
    Sludge
    B *
    Co-substrates _I
    C ^ ubstr8ts | w
    separation
    Btgesten
    Recycling
    Separation by biological solution of the soaking by ion exchange resin
    Sludge recovery / treatment
    Fertilizer
    Liquid flow m “Φ” Sludge
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    同族专利:
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    引用文献:
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    EP0755730A1|1995-07-26|1997-01-29|Commissariat A L'energie Atomique|Method for decontaminating soils and waste containing iron oxides and heavy metals|
    US20130058846A1|2010-05-19|2013-03-07|Jx Nippon Mining & Metals Corporation|Method for processing acidic solution that contains iodide ions and iron ions|
    CN109160630A|2018-09-04|2019-01-08|南京师范大学|It is a kind of to precipitate the phosphorus in waste water recovery process for combining alkaline anaerobic fermentation based on chemical strengthening level-one|
    EP3626684A1|2018-09-20|2020-03-25|SUEZ Groupe|Method for phosphorus recovery and ammonium abatement from wastewater|
    CN109336352A|2018-11-05|2019-02-15|李舒馨|A kind of method for sludge treatment|
    CN109354335A|2018-12-14|2019-02-19|谢绍舜|The optimum organization technique of town domestic sewage processing|
    CN109704530A|2019-03-05|2019-05-03|龚典局|A kind of alumina comprehensive utilization of mud method|
    CN110961076A|2019-08-12|2020-04-07|安徽国祯环卫科技有限公司|Novel method for adsorbing phosphorus in sludge anaerobic digestion biogas slurry by low-temperature pyrolysis residues|
    法律状态:
    2018-01-19| PLFP| Fee payment|Year of fee payment: 2 |
    2018-07-27| EXTE| Extension to a french territory|Extension state: PF |
    2018-07-27| PLSC| Publication of the preliminary search report|Effective date: 20180727 |
    2020-01-21| PLFP| Fee payment|Year of fee payment: 4 |
    2020-05-15| TP| Transmission of property|Owner name: INSTITUT NATIONAL DE RECHERCHE POUR L'AGRICULT, FR Effective date: 20200407 |
    2021-01-26| PLFP| Fee payment|Year of fee payment: 5 |
    2022-01-28| PLFP| Fee payment|Year of fee payment: 6 |
    优先权:
    申请号 | 申请日 | 专利标题
    FR1750608|2017-01-25|
    FR1750608A|FR3062124B1|2017-01-25|2017-01-25|PROCESS FOR RECOVERING IRON FROM SLUDGE FROM A WASTEWATER TREATMENT STATION AND ITS USE FOR RECYCLING IN PARTICULAR FERRIC CHLORIDE|FR1750608A| FR3062124B1|2017-01-25|2017-01-25|PROCESS FOR RECOVERING IRON FROM SLUDGE FROM A WASTEWATER TREATMENT STATION AND ITS USE FOR RECYCLING IN PARTICULAR FERRIC CHLORIDE|
    US15/499,324| US10597310B2|2017-01-25|2017-04-27|Method of recovering iron and/or phosphorus from sludge of waste water treatment plants|
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