FR2867182A1 - Process of treatment of a water charged of nitrates, useful denitrification of water, comprises denitration of water carried out on ion exchange resin and biological treatment with bacteria to reduce the nitrates in gaseous nitrogen - Google Patents

Abstract

Process of treatment of water charged of nitrates, comprising a denitration of water carried out on ion exchange resin at the time of their regeneration by passage of a brine solution to give nitrate charged eluate, which is recuperated and subjected to a biological treatment with bacteria to reduce the nitrates in gaseous nitrogen and further operations of treatment, then recycled to provide the regeneration of ion exchange resin, is new. Process of treatment of a water charged of nitrates, comprising a denitration of water which is carried out on ion exchange resin at the time of their regeneration by passage of a brine solution to give nitrate charged eluate, which is recuperated and subjected to a biological treatment with suitable bacteria to reduce the nitrates in gaseous nitrogen, and further operations of treatment, recycled to provide the regeneration of ion exchange resin (where the concentration of eluate in salt after the biological treatment is compatible with the treatment by resins). An independent claim is also included for installation equipment for treating nitrate charged water, comprising: (a) a unit for water denitration by ion exchange resin; (b) means of recovery of eluate or regeneration of resin; (c) a biological treatment unit with suitable bacteria to reduce the nitrates in gaseous nitrogen for at least one part of the eluate; and (d) means to recycle the treated eluate to provide the regeneration of ion exchange resin.

Description

2867182 1

  METHOD AND INSTALLATION FOR TREATING WATER CHARGED WITH NITRATE.

  The invention relates to a method for treating a water charged with nitrates, according to which water denitration is carried out on ion exchange resins giving, during their regeneration by passage of a brine, charged eluates. of nitrates.

  Omnipresent in the environment, nitrates are non-toxic substances. However, when ingested, their transformation into nitrites during the digestive process has negative effects on health, especially on infants and other sensitive individuals.

  In recent years, many small and medium-sized rural communities have been facing significant and rapid degradation of their water resources. In the absence of an alternative solution, it is recommended to treat water for nitrate removal for waters with nitrate concentrations consistently exceeding the value of 50 mg / l.

  For example, for France, mainly in the west, in a number of localities the nitrate content of more than half of the raw water is greater than 40 mg / l. Such pollution may lead to the gradual abandonment of entire groundwater.

  The water treatment process on ion exchange resins is a simple and economical solution and provides a water whose nitrate content is significantly reduced and acceptable. During the regeneration of the resins by passage of a brine, the nitrate pollution of the water is transferred to a more concentrated phase called regeneration eluate. The volume of the eluates represents about 1.5% of the volume of water treated.

  A treatment implemented on a site in France (site of Ormes under Voulzies) consists of a partial denitration of a water of drilling on resins exchange of ions. The raw water contains about 60 mg / 1 of nitrates and the treated water 1 mg / 1. A 40% cut of the treated water is made with the raw water so that the mixed water contains 25 mg / 1 of nitrates. The flow rate of the water tower downstream is 20 m3 / h. Regeneration is triggered every time 700 m3 of water is passed over the ion exchange resins. The total volume of the eluates produced by such a station is 8.6 m3 by regeneration, that is to say about 1.2% of the volume of treated water. The characteristics of the elms of Ormes sous Voulzies are as follows: Calcium content Sodium content Chloride Sulfate Nitrate Conductivity at 20 C: These eluates are not currently treated and are diluted in the sewerage network. They constitute a liquid saline waste and pose a problem of final elimination.

  In general, currently eluates are: - or discharged directly into the natural environment (which is not acceptable for the environment) when there is no sanitation network nearby, - or well directed to the local sanitation network rarely equipped to handle such discharges, - or transported to a facility (STEP) capable of treating this type of effluent.

  The aim of the invention is, above all, to definitively eliminate nitrate pollution. The purpose of the invention is, above all, to permanently eliminate nitrate pollution. eluates generated by the denitration method on ion exchange resins, and to make the process more economical especially with regard to products used for the regeneration of resins.

  According to the invention, the process for treating a nitrate-laden water as defined above is characterized in that the eluates are recovered and subjected to a biological treatment with bacteria suitable for reducing the nitrates to gaseous nitrogen, and in that that the eluates, after further processing operations, are recycled to serve for the regeneration of the ion exchange resins, the conditions being chosen so that the salt concentration of the eluates after the biological treatment is compatible with the treatment with resins.

  Preferably, the biological treatment is an autotrophic denitrification treatment. More particularly, the autotrophic denitrification treatment is carried out on grains of sulfur, in particular sulfur beads, seeded with thiobacteria. Advantageously, Thiobacillus denitrificans are used as thiobacteria.

  Bacteria grow very quickly on the sulfur substrate and reduce nitrates to nitrogen gas, while sulfur is oxidized as sulfate.

  Sulfur serves both as a food (or, in other words, electron acceptor) to bacteria and as a colonization support since it is not soluble in water. An interest of the process is that the bacteria always have a source of energy in situ (total autonomy once the process started).

  After biological treatment, the eluates pass through a column of marine limestone (neutralite) or other type of limestone to precipitate the sulphates in the form of calcium sulfate Ca SO4, or other.

  Alternatively, simple sulphate precipitation can be effected by adding a solution of barium chloride, to be mixed with the eluates before the denitrification treatment.

  Generally the eluates are then filtered and disinfected, without this being necessary in all cases.

  The eluates are recycled in the denitration process on ion exchange resins, which reduces the consumption of regenerating salt.

  The conditions are designed so that, at the end of the treatment, the concentration of the eluates in sodium chloride NaCl is between 40 g / l and 100 g / l, preferably about 60 g / l for the biological treatment, in particular the autotrophic treatment on sulfur, and the denitration process on ion exchange resins are compatible with each other. The salt content of the treated eluates must be strong enough to allow efficient regeneration of the ion exchange resins, but low enough not to weaken the thiobacteria.

  The treatment of the eluates is carried out between two regeneration phases of the ion exchange resins (batch treatment, that is to say in batches).

  The invention also relates to an installation for implementing the method. Such an installation comprises a unit for denitratation of water by ion exchange resins and is characterized in that it comprises means for recovering the regeneration eluates of the resins, a biological treatment unit with bacteria suitable for reducing nitrates. nitrogen gas for at least a portion of the eluates, and means for recycling the treated eluates to be used for the regeneration of ion exchange resins. Generally, the installation comprises means of filtration and disinfection after biological treatment.

  Preferably, the biological treatment unit is capable of providing an autotrophic denitrification treatment. More particularly, the unit comprises grains of sulfur, in particular sulfur beads, seeded with thiobacteria, advantageously Thiobacillus denitrificans.

  The invention consists, apart from the arrangements set out above, in a certain number of other arrangements which will be more explicitly discussed below with reference to an example embodiment described with reference to the appended drawing, but which is in no way limiting.

  In this drawing, the single FIGURE is a schematic diagram of the method according to the invention.

  Referring to the figure of the drawing can be seen, symbolized by a rectangle 1, a raw water supply, loaded with nitrates. The raw water is directed to a unit 2 of ion exchange resins, comprising anion exchange resins for capturing the NO3 ions. The unit 2 delivers at the outlet 3 a water whose nitrate content has been lowered to a value acceptable.

  Generally, the nitrate content of the water at the outlet 3 is much lower than the acceptable limit. The water from the outlet 3 is cut with raw water by a bypass 4 bypassing the unit 2 and joining the water pipe downstream of the outlet 3. This gives the water mixed at 5. .

  The regeneration of the resins of the unit 2 is obtained by temporarily stopping the treatment of the raw water and by circulating on the ion exchange resins a brine, that is to say a solution of regenerating salts, usually sodium chloride, from a silo symbolized by the rectangle 6.

  The regeneration solution, after passing through the exchange resins, is discharged through an outlet R and constitutes an effluent or regeneration eluate 7, symbolized by a rectangle. The volume of the regeneration eluates represents approximately 1.5% of the volume of treated water passing through the outlet 3. The eluates 7 generally have a first fraction 7a with a low nitrate content (less than 40 mg / l) followed by a fraction 7b whose nitrate content is much higher than that of raw water because the nitrate pollution of water has been transferred to this phase.

  According to the invention, at least the concentrated fraction 7b of the eluates 7 is subjected to a biological denitrification treatment at 8. Despite the relatively low percolation rate of the biological treatment, for example of the order of 1 mh -1, it is possible to to make compatible treatment speeds on ion exchange resins and biological treatment without resulting too large and too expensive installations, because the volume of eluates to be treated is relatively small compared to that of the treated water .

  Preferably, the treatment carried out at 8 is an autotrophic denitrification treatment with sulfur, with thiobacteria, advantageously Thiobacillus denitrificans.

  Thiobacillus denitrificans is an autotrophic, facultative, gram-negative, facultative anaerobic bacterium that does not produce forms of resistance. This microorganism oxidizes a wide variety of sulfur compounds (S2, S, S2032) to sulphates and is thus able to reduce nitrates to free nitrogen.

  The eluate processing unit 8 comprises a column containing sulfur beads seeded with the thiobacterium thiobacillus denitrificans. The diameter of the balls is advantageously between 1 and 10 mm, preferably between 2 and 4 mm.

  On the sulfur substrate, these bacteria grow very rapidly and will reduce nitrates to nitrogen gas, while sulfur is oxidized in the sulphate form. The equation of the reaction is as follows: S + 50 NO 3 - + 2 0 CO 2 + 4 NH 4 + + 38 H2O 10 4 C 5 H 7 NO 2 + 25 N 2 + 5042 + 64 H + Sulfur serves both as a feed for bacteria (It is an acceptor of electrons, which makes it possible to reduce the nitrates in nitrogen) and of support of colonization since it is not soluble in the water An advantage of this process is that the bacteria have permanently of a source of energy in situ, which gives total autonomy once the system is started.

  The rate of biological treatment is of the order of 1 m / h (in fact 1 m 3 / m 2 / h).

  At the outlet of the biological treatment unit 8 and, more precisely, at the outlet of the sulfur column in the example under consideration, the treated eluates pass through a column 9 of marine limestone (neutralite) or of another compound calcium to precipitate sulphates produced as CaSO4 or mixed sulphates.

  Alternatively, a simple precipitation of the sulfates can be carried out by adding a solution of barium chloride, to be mixed with the eluates before denitrification treatment.

  The eluates are, in general, filtered and disinfected in step 10, but this is not always necessary.

  At least a fraction 11 of the eluates is recycled to serve during the regeneration phase in the ion exchange resin denitration process.

  This fraction is added to the regenerating salt solution from 6 and reduces the consumption of regenerating salt.

  The conditions are determined so that the salt content of the eluates after denitrification treatment is strong enough to allow effective regeneration of the ion exchange resins, but low enough not to weaken the thiobacteria.

  An optimum concentration of the eluates of sodium chloride (NaCl) is between 40 g / l and 100 g / l, preferably about 60 g / l, for the sulfur autotrophic process and the denitrification process to be compatible with each other. .

  The treatment of the eluates is carried out between two regeneration phases of the ion exchange resins (batch or batch treatment).

  In step 10, an addition of water 12 may be provided to obtain the desired concentration of NaCl, for example 60 g / l, for the recycling of the eluates.

  The surplus of eluates, without nitrates, can be rejected in 13 in the natural medium 14 as well as the fraction 7a of eluates of step 7 with a low nitrate concentration, lower than the authorized limit.

  Examples of treatment are given below. 25

EXAMPLE 1

  Or a plant with a production capacity of 50m3 / h, operating 15h / day, treating a drilling water with a nitrate concentration of about 55 mg / 1.

  The plant is equipped with an ion exchange resin unit with a volume of 900 1. The cutting rate is about 67%. The resin is regenerated with NaCl every 750 m3 of water passed on the resin, every 1.4 days.

  The plant generates about 10 m3 of eluates by regeneration. Only the concentrated portion 7b of the eluates 2867182 (salinity: 60 g / l) is sent to the biological denitrification process on sulfur. The other part 7a with low nitrate content can be sent to the natural environment. The sulfur column is fed with eluates at 1.7 m3 / day. It is dimensioned to a mass load of 2 kgNO3 / m3soufre.jour. It therefore contains a volume of 5.5 m3 of sulfur (height of the column: 2.5 m, diameter: 1.7 m). The sulfur column is followed by a column 9 with neutrality of the same dimensions, to readjust the alkalinity of the water. The effluent is recycled as a regenerant on the resin, with a supplement in new brine.

  Thanks to recycling, the consumption of NaCl is halved.

  The supply of nutrients on the sulfur column is not necessary. It must be sown (introduction of a quarter of seeded grains of sulfur to start the biological reaction).

EXAMPLE 2

  A second example is given below. The letters used have the following meaning: Q is the flow rate in m3 / h, C is the nitrate concentration and V is the volume. The ion exchange resins are designated by the abbreviation REI.

  In the drawing, the letters Q, C, V with indices 1 to 6 have been plotted on the lines corresponding to the indications given for this example.

  Underground resource Production rate: 50 m3 / h, Daily production volume: 750 m3 / day Nitrates at the inlet: 55 mg / 1 Output nitrates: 40 mg / 1 Ion exchange Resin treatment rate: 33% (16.5 m3 / h) Volume treated per day 248 m3 / day Volume of resins used: 900 liters Regeneration cycle: all treated 339 m3 of water Regeneration Regeneration rate used: 110 g / liter of resin Regeneration phase (to countercurrent) Fluid used: brine 90 g / 1 (from a brine of 300 g / 1) Duration 20 minutes Weight of salt: 99 kg / regeneration Volume brine: 1.1 m3 (0.14 m3 to 300 g / 1 + 0.96 m3 to 60 g / 1) Slow rinse phase (countercurrent). Fluid used: brine dilution water at 60 g / 1 (recycling of eluates) + water (complement to have 2 volumes of resins) Volume: 1.8 m3 (2 times the volume of resins) Rapid rinse phase (co-current ): Fluid used: water Volume: 7.2 m3 (8 times the volume of resins) Volume and concentration of the eluates (see diagram of the single figure): volume of water in the unit 8: 900 liters Regeneration phase (duration 20 minutes) What goes into unit 8 REI: From silo 6 to salt Q1 = 1 m3 / h Cl = 300 g / 1 V1 = 0.14 m3 Dilution water in 11 Q6 = 2.3 m3 / h (eluates treated) C6 = 60 g / 1 V6 = 0.96 m3 Regeneration brine Q2 = 3. 3 m3 / h C2 = 90 g / 1 V2 = 1.1 m3 What comes out of unit 8 REI Start: Q3 = 3. 3 m3 / h C3 = water (stuffing) --E 7a, discharge to natural environment 15 V3 = 0.9 m3 Medium and end: Q3 = 3.3 m3 / h C3 = 90 g / 1 -. to 7b treatment eluates V3 = 0.2 m3 Slow rinsing phase What goes into unit 8 REI: Start: Dilution water at 11 Q6 = 2.3 m3 / h (treated eluates) C6 = 60 g / 1 V6 = 0.76 m3 Medium and end (water) Q2 = 2.3 m3 / h C2 = 0 g / 1 V2 = 1 m3 What comes out of unit 8 REI Start: Q3 = 2.3 m3 / h C3 = 90 g / 1 -. to 7b eluate treatment V3 = 0.9 m3 Medium: Q3 = 2.3 m3 / h C3 = 60 g / 1 to eluate treatment 35 V3 = 0.76 m3 10 2867182 12 End: Q3 = 2.3 m3 / h C3 = 0 g / 1 to treatment eluates V3 = 0.14 m3 Rapid rinsing phase What goes into unit 8 REI Treated water 16.7 m3 / h 7. 2 m3 What comes out of unit 8 REI Treated water 16.7 m3 / h 0.4 m3 --É towards 7b treatment eluates 6.8 m3 7a natural environment discharge Recovered volume of eluates: 0.4 m3 (Og / l) + 0.14 m3 (0 g / 1) + 0.76 m3 (60 g / 1) + 0.9 m3 (90 g / 1) + 0. 2 m3 (90 g / 1) Total volume = 2.4 m3 (144.6 kg of salt) Concentration = 60 g / 1 Volume of recycled eluates in regeneration: 0.76 m3 + 0.96 m3 = 1.72 m3 (103.2 kg of salt) Quantity of nitrates in the eluates to be treated: Entry: 55 mg / 1 Output: 40 mg / 1 Production rate: 50 m3 / h Volume produced: 750 m3 / day (operating time: 15 hours) Volume treated with resins: 247.5 m3 / day Regeneration: all 339 m3 -. Quantity of nitrates: 11 kg / day Treatment of eluates (removal of nitrates). 35 Volume to be treated: 2.4 m3 every 1.4 days 10 2867182 13 Daily volume to be treated: 1.7 m3 / day Concentration: 60 g / 1 Amount of nitrates: 11 kg / day Treatment rate: 2kgNO3 / m3sour.day Sulfur quantity: 5.5 m3 of sulfur Sulfur column: H = 2.5 m, = 1.7 m Neutralite column (or other) Salt consumption: Without treatment or recycling of eluates 99 kg of salt / regeneration With treatment and recycling of eluates 15 42 kg of salt / regeneration According to the invention, the salt consumption is divided by 99/42, ie more than 2.

  The examples provided show the results produced by the invention.

Claims (2)

  1. A method for treating a nitrate-laden water, according to which a denitration of water is carried out on ion-exchange resins which, during their regeneration by passage of a brine, elutes charged with nitrates, characterized in that the eluates are recovered and subjected to a biological treatment (8) with bacteria suitable for reducing nitrates to nitrogen gas, and in that the eluates, after further processing operations, are recycled (11) to be used for the regeneration ion exchange resins, the conditions being chosen so that the salt concentration of the eluates after the biological treatment is compatible with the resin treatment.   2. Method according to claim 1, characterized in that the biological treatment is an autotrophic denitrification treatment.   3. Method according to claim 2, characterized in that the autotrophic denitrification treatment is carried out on grains of sulfur seeded with thiobacteria.   4. Process according to claim 3, characterized in that Thiobacillus denitrificans is used as thiobacteria.   5. Process according to claim 3 or 4, characterized in that the grains of sulfur are formed by sulfur beads.   6. Method according to one of the preceding claims, characterized in that after biological treatment, the eluates pass through a column (9) of marine limestone 2867182 (neutralite) or other type of limestone to precipitate sulphates.   7. Method according to one of claims 1 to 5,   characterized in that a simple precipitation of the sulphates is carried out by addition of a solution of barium chloride, to be mixed with the eluates before denitrification treatment.   8. Method according to claim 6 or 7, characterized in that the eluates are then filtered and disinfected (10) and are recycled (11) in the denitration process on ion exchange resins.   9. Method according to one of the preceding claims, characterized in that, at the end of treatment, the concentration of the eluates (11) sodium chloride NaCl is between 40g / 1 and 100 g / 1, preferably about 60 g / 1.   10. Installation for treating a water charged with nitrates, comprising a unit (2) for denitrating water by ion exchange resins, characterized in that it comprises means (7) for recovering the regeneration eluates. resins, a biological treatment unit (8) with bacteria suitable for reducing nitrates to nitrogen gas for at least a portion of the eluates, and means (11) for recycling the treated eluates to be used for the regeneration of the exchange resins. ions.   11. Installation according to claim 9, characterized in that the biological treatment unit (8) is adapted to provide an autotrophic denitrification treatment.   12. Plant according to claim 10 or 11, characterized in that the biological treatment unit (8) comprises sulfur beads, seeded with thiobacteria.   13. Installation according to claim 12, characterized in that the diameter of the sulfur balls is between 1 and 10 mm, preferably between 2 and 4 mm.   14. Installation according to claim 12 or 13, characterized in that the thiobacteria are Thiobacillus denitrificans.