RU2793787C2 - Method for removing pollutants from wastewater from industrial production and a system for implementing such method - Google Patents

Abstract

FIELD: removal of contaminants from wastewater.
SUBSTANCE: claim is related to a method of removal of contaminants from wastewater from the industrial production of fertilizers, in particular wastewater from the production of nitrophosphate or other mineral or organomineral fertilizers. The method includes the steps of concentrating the pollutants in the wastewater, chemically converting the pollutants in the wastewater by means of electrolysis, recycling the electrolyzed wastewater into industrial production. As a result of electrolysis, pollutants form a gas. The wastewater concentration step is carried out using a direct osmosis module or a pressurized osmosis module comprising a first compartment and a second compartment separated by a membrane. The step of concentrating the waste water includes the step of directing the waste water to the first compartment of the osmosis module. The recycling step includes directing the electrolyzed waste water to the second compartment of the osmosis module and recycling the waste water from the second compartment of the osmosis module to fertilizer production.

EFFECT: increased efficiency of pollutant removal, increased current utilization factor.

11 cl, 4 dwg, 6 ex

Description

TECHNICAL FIELD OF THE INVENTION

The present application relates to a new system and method for the treatment using electrolysis of concentrated waste water from the industrial production of fertilizers, in particular waste water from the production of nitrophosphate or other mineral or organo-mineral fertilizers.

State of the art of the present invention

Industrial wastewater is one of the important sources of water pollution. During the last century, vast quantities of industrial wastewater have been released into rivers, lakes and coastal areas. This has led to serious water pollution problems and caused adverse impacts on the ecological system.

There are numerous types of industrial wastewater depending on different industries and pollutants; each sector produces its own particular combination of pollutants. Based on the varied characteristics of industrial wastewater, industrial wastewater treatment must be tailored specifically to the specific type of emissions produced.

In many industrial systems, the goal is to reduce the amount of wastewater released to the environment by recycling the discharged wastewater back to the appropriate industrial system. Within the industrial production of fertilizers, the nature of the wastewater may vary depending on the types of fertilizers produced and the particular processes involved.

Mineral fertilizers contain one or more primary (basic) nutrients, which are nitrogen (N), phosphorus (P) and potassium (K) in inorganic form or in the form of urea or cyanamide. Essential nutrients (N, P and K) are required by plants in large or moderate amounts. Depending on the composition, mineral fertilizers also contain other nutrients required by plants to a lesser extent, such as Ca, Mg and S. Trace elements required in small quantities are B, Cl, Cu, Fe, Mn, Mo, Zn. Fertilizers are classified according to their content of essential nutrients: simple fertilizers usually contain only one primary or primary nutrient (N, P or K), while complex fertilizers contain two or more primary nutrients (NP, PK or NPK and more specifically NP or NPK).

There are two general methods for producing complex fertilizers, namely the mixed acid method and the nitrophosphate method. In particular, in the nitrophosphate process, the phosphate rock is first dissolved in an excess of nitric acid, and Ca(NO ₃ ) ₂ ⋅4H ₂ O is removed after pulping from the original phosphate solution by cooling and filtering. Then, by neutralizing the resulting filtrate, a solution containing mainly ammonium nitrate and double ammonium and calcium phosphates is obtained. By evaporating a solution containing ammonium nitrate, monoammonium phosphate and dicalcium phosphate (AN-MAP-DCP), a molten suspension is obtained, to which potassium chloride and potassium sulfate salts can be added. Using these initial components and the described method, it is possible to obtain a wide variety of fertilizer compositions as a result of the subsequent formation of particles from a solution of complex fertilizers.

The main components of wastewater from the production of NP or NPK fertilizers are ammonia, nitrates, fluorides and phosphates, and the wastewater may also contain heavy metals from the phosphate rock such as Cd, Hg and Zn.

In 2002, the Austrian Environmental Protection Agency issued a report entitled "State of the Art of Fertilizer Production in Relation to the Integrated Pollution Prevention and Control (IPPC) Directive", monograph volume 105, M-105 (see http://www.umweltbundesamt .at/fileadmin/site/publikationen/M105.pdf, see also Best Available Techniques for the Prevention and Control of Contamination in the European Fertilizer Industry, Booklet #7 of 8, Nitrophosphate NPK Fertilizer Production, European Fertilizer Association, 2000 .). The Austrian report discusses specific ways to reduce wastewater emissions and makes the following seven recommendations regarding the state of the art of the nitrophosphate process, in particular:

1. elimination of antifoam agents from phosphate rock treatment;

2. returning the scrubbing liquid resulting from the treatment of off-gases from the processing of phosphate rock to the production process;

3. return of washing water for sand washing to the production process;

4. elimination of direct cooling/extinguishing, for example, condensation of exhaust vapors;

5. return of the scrubbing liquid resulting from the purification of the ammonization off-gases to the production process;

6. combined cleaning of exhaust gases of neutralization/evaporation and granulation/drying units; And

7. the use of buffer tanks to compensate for fluctuations in the volume and content of waste water.

Recommendation 2 is in line with the aforementioned objective of reducing the amount of wastewater released into the environment by recycling the discharged wastewater back into an appropriate industrial system. It is beneficial to recycle nitrogen, phosphorus and potassium containing wastewater to NPK fertilizer production as it reduces the environmental impact and optimizes the amounts of raw materials and water that enter the production process.

Chlorides are commonly regarded as important contaminants in wastewater from fertilizer production. This may be due to the relatively low levels of chlorides that are present in wastewater from fertilizer production and may be only about 1000 ppm. As a comparison, drinking water has a maximum chloride content of 250 ppm, while salt water contains 35,000 ppm sodium chloride, with a corresponding chloride fraction of approximately 21,400 ppm. For this reason, the content of chlorides present in waste water from fertilizer production is not usually considered as an environmental problem.

However, safety limits must be observed when recycling wastewater from fertilizer production back into the solution used for fertilizer production. As such, at high temperatures in the granulation or evaporation step for subsequent granulation, strict chlorine restrictions must be observed in order to prevent the decomposition of ammonium nitrate and the associated fire and explosion hazards. Therefore, the level of waste water recirculation must be controlled with respect to the chlorine content, which must remain below the safety limit in the fertilizer solution before the granulation step.

Alternatively, treating the wastewater to remove chlorine will provide additional flexibility with respect to the volume of wastewater returned to the process and/or the chlorine content of the phosphate rock that enters the first stage of the process.

The treatment of nitrogen-containing wastewater to remove nitrogen compounds is disclosed in US 6,132,627. Electrolysis converts chloride ions into hypochlorite ions, and the reaction of these hypochlorite ions with nitrogen compounds produces pure nitrogen gas, CO ₂ and chloride ions. The chloride ions can be converted to hypochlorite ions by recycling the waste water back to the cell.

JPS 5113007 discloses a two-stage treatment of wastewater from chemical fertilizer production. In the first step, CaF ₂ is removed in the first electrochemical cell by adsorption on diatomaceous earth activated by pre-electrolysis. In the second stage, in the second electrolyser, amines are converted to chloramines by reaction with chlorine and hypochlorite. Chlorine and hypochlorite are obtained separately by the electrolysis of sea water, and the resulting electrolyzed water is added to a second electrolyser for treating waste water from fertilizer production. In this second electrolytic cell, electrolysis and adsorption by electrolytically active diatomaceous earth ensure the stability of the chloramines. In this case, phosphates and SiO ₂ are removed in two processing steps.

Applications WO 2017/103041 and WO 2017/103042 present methods for treating industrial waste water, in particular waste water from the production of nitrophosphate fertilizers or waste water from the production of other mineral and organo-mineral fertilizers. Both applications disclose the removal of chlorides in the form of chlorine gas by electrolysis of waste water. In addition, WO2017/103042 solves the problem of deposit formation in the cathode chamber by recirculating the acid anolyte into the cathode chamber, whereby the deposit is dissolved. The applications disclose low chloride concentrations of 250 ppm after their removal by electrochemical treatment. WO 2017/103042 discloses a Faraday current utilization factor of 8.6%.

Accordingly, more efficient systems and methods for removing contaminants from wastewater from industrial production, in particular from wastewater from fertilizer production, are required.

Brief summary of the present invention

This paper describes a new concept for the removal of contaminants from wastewater from industrial production, in particular from the production of fertilizers. It has been found that the efficiency of the process can be greatly increased by concentrating contaminants in the wastewater prior to the electrolysis step.

According to an aspect of the present application, a method is disclosed for removing contaminants from industrial wastewater. This method includes the following steps:

a) concentration of contaminants in wastewater;

b) chemical transformation of pollutants in waste water by means of electrolysis, whereby, in particular, the pollutants form a gas as a result of electrolysis; And

c) recycling electrolyzed wastewater to industrial production. It has been found that by means of the concentration step, the method provides an increased efficiency of the electrolysis step.

In an exemplary process according to the present application, the contaminants are chlorides and the concentration of chlorides in the wastewater after the concentration step is between 1250 and 2250 ppm, in particular between 1500 and 2250 ppm and more particularly between 1750 up to 2250 ppm

In an exemplary method according to the present application, the wastewater concentration step is carried out using a direct osmosis module or a pressurized osmosis module comprising a first compartment and a second compartment separated by a membrane.

In an exemplary method according to the present application, the method includes the additional step of directing wastewater to the first compartment of the osmosis module, and the recycling step includes the steps of directing electrolyzed wastewater to the second compartment of the osmosis module and recycling wastewater from the second compartment of the osmosis module to fertilizer production.

Within the framework of the possible method according to the present application, the flow of waste water in the first compartment of the osmosis module is opposite to the flow in the second compartment of the osmosis module.

In an exemplary method according to the present application, the method includes the additional step of adding a brine solution to the second compartment of the osmosis module or upstream.

In an exemplary process according to the present application, the brine added to the second compartment of the osmosis module or upstream contains one or more salts of ammonium nitrate, double ammonium and calcium phosphates, and calcium nitrate.

Within the scope of the possible method according to the present application, industrial production is the production of fertilizers, in particular the production of nitrophosphate or other mineral or organo-mineral fertilizers, and more specifically the industrial production of compositions containing ammonium nitrate.

In an exemplary process according to the present application, the contaminants are chlorides and the concentration of chlorides in the electrolyzed waste water is less than 350 ppm.

According to a further aspect of the present application, a system is disclosed for removing industrial wastewater from contaminants present in wastewater. The system may include a concentration unit for fluid transfer connection to industrial waste water and an electrochemical treatment unit for contaminant removal and fluid transfer downstream of the concentration unit. The electrochemical treatment unit may comprise an electrolytic unit and may be designed to be fluidly coupled to the recycling of treated wastewater to industrial production. The concentration unit may be a direct osmosis module or a pressurized osmosis module, and the osmosis module may comprise a first compartment and a second compartment separated by a membrane. Wastewater from industrial production to be treated may be fluidly connected to the first compartment. The first compartment may be fluidly connected to the inlet of the electrochemical processing unit. The outlet of the electrochemical treatment unit may be fluidly connected to the second compartment, and the second compartment may be designed to be fluidly connected to industrial production, in particular configured such that the wastewater treated in the electrochemical treatment unit, can flow through the second compartment and be recycled to industrial production. Optionally, a brine source is fluidly connected to the second compartment.

In an exemplary system according to the present application, the system comprises a concentrating unit operably coupled to transfer fluid to wastewater from fertilizer production and an electrochemical treatment unit to remove contaminants coupled to circulate fluid downstream of the concentration unit and movably coupled fluid to recycle treated wastewater into fertilizer production.

In an exemplary system according to the present application, the concentration unit is a direct osmosis module, a pressurized osmosis module, a reverse osmosis module, or an electrodialysis module.

In an exemplary system according to the present application, the concentration unit is a direct osmosis module or a pressurized osmosis module comprising a first compartment and a second compartment separated by a membrane. Industrial wastewater to be treated is fluidly connected to the first compartment, the first compartment is fluidly connected to the electrochemical treatment unit, and the treated wastewater is fluidly connected to the second compartment and flows through the second compartment for recycling to industrial production. Optionally, a brine source is fluidly connected to the second compartment.

In an exemplary system according to the present application, the concentration unit comprises several osmosis modules, in particular two or three osmosis modules connected in series.

In an exemplary system according to the present application, the flow of waste water in the first compartment of the osmosis module flows in the opposite direction with respect to the flow of water in the second compartment of the osmosis module.

According to a further aspect of the present application, the use of the system according to the second aspect of the present application in the production of fertilizers, in particular in the production of nitrophosphate fertilizers, or in the production of other mineral or organomineral fertilizers, more specifically in the production of fertilizers that are compositions containing ammonium nitrate, is disclosed.

Brief description of the figures

In FIG. 1 schematically illustrates a process for the concentration, electrolysis and recycling of wastewater from fertilizer production.

In FIG. 2A and 2B schematically illustrate a concentration process involving osmosis, electrolysis, and recirculation of wastewater from fertilizer production.

In FIG. 3 schematically illustrates a multi-stage osmosis module for concentrating wastewater from fertilizer production before electrochemical treatment and for recycling wastewater after electrochemical treatment.

Detailed disclosure of the present invention

Throughout the description and claims of the present invention, the words "include" and the corresponding grammatical forms mean "including but not limited to", and they are not intended to exclude, and do not exclude other fragments, additives, components, integers or steps. Throughout the text of the description and claims of the present invention, the singular covers the plural, unless otherwise required according to the context. In particular, if singular grammatical forms are used in the description of the present invention, it should be understood that both the singular and the plural are possible unless otherwise required by the context.

Features, integers, characteristics, compounds, chemical moieties, or groups described in connection with a particular aspect, embodiment, or example of this application should be considered applicable to any other aspect, embodiment, or example described herein, unless there is incompatibility. . All features set forth in the description of the present invention (including any features in the accompanying claims, abstract and figures) and/or all steps of any method or process so described may be combined in any combination, except for combinations in which at least some of such features and/or steps are mutually exclusive. The present application is not limited to the details of any of the above embodiments. This application extends to any new feature or to any new combination of features presented in the description of the present invention (including any features in the accompanying claims, abstract and figures), or to any new step or to any new combination of steps of any method or process described Thus.

The representation of numerical values by numerical ranges includes all integer and fractional values in the specified ranges, as well as the endpoints represented.

The term "approximately" when used to represent a measurable value such as a parameter, amount, period of time, and so on, is intended to represent deviations of +/-10% or less, preferably +/-5% or less, preferably +/- 1% or less, and even more preferably +/-0.1% or less of the specified value, and thus, these deviations apply in the application described herein. It should be understood that the very meaning to which the term "approximately" refers is also considered to be described.

The term "from ... to" when used in relation to a range of a measurable value, such as a parameter, quantity, period of time, and so on, is also intended to represent limit values relating to a range that is described in this way.

All documents cited in this specification are hereby incorporated by reference in their entirety.

When reading this document, attention should be paid to all materials and documents that are filed at the time of or prior to the filing of the description of the present invention in conjunction with this application, and which are open for public review along with the description of the present invention, and the content of all such materials and documents is included to this document by reference.

The present invention will now be described in detail in relation to the removal of chlorides from wastewater from fertilizer production by generating and removing chlorine gas from wastewater. However, the present application can be applied to remove from any industrial waste water any pollutants that can be subjected to chemical transformation through electrolysis, in order to recycle the waste water back into industrial production. Such contaminants are present, for example, in streams, including, without limitation, salt solutions, which are present in the production of uranium and in the electrolysis of sodium sulfate. Examples 3 and 4 describe such applications for non-fertilizer wastewater or recirculation streams, and Example 6 also describes the improvement in Faraday current efficiency due to preconcentration. In particular, contaminants form gases and are removed in the gas phase during the electrolysis step.

As defined herein, the Faraday current utilization factor is the percentage of current passing through the cell that is used to convert contaminants.

As used herein, the term "electrochemical processing unit" means a unit in which an electrochemical reaction can take place, the electrochemical reaction being preferably electrolysis.

As used herein, the term "electrolytic block" means a block containing an electrolytic cell in which electrolysis can take place.

Chlorides may be present in wastewater from the production of fertilizers, in particular in wastewater from the production of nitrophosphate, organic or organomineral fertilizers. Without being limited by theory, the source of chlorides may be phosphate rock depending on where the phosphate rock is mined. These impurities may be present only in small concentrations of approximately 1000 ppm. If the waste water is simply released into the environment, this chloride content cannot pose any environmental or compliance issues. However, if the wastewater is then recycled back to the fertilizer industry, then the chlorides, even if present in small amounts, can destabilize the ammonium nitrate, which can become explosive and pose significant safety concerns. More specifically, during the manufacturing process of, for example, NPK pellets, water evaporates and the concentration of any chloride present may increase significantly. Since ammonium nitrate is also present, the combination can then become explosive.

The use of electrolysis to remove chlorides from wastewater from fertilizer production has been described in WO 2017/103041 and WO 2017/103042. After the waste water is electrolyzed and the chloride concentration is reduced to suitable levels, the electrolyzed waste water is recycled to the fertilizer industry.

Electrolysis is a well known technology, and the following discussion of electrode reactions and the nature of possible electrodes and electrolytes is not intended to limit the generality of the technology to those skilled in the art.

As mentioned above, low chloride wastewater streams can have particular advantages in relation to the production of nitrophosphate, other mineral or organomineral fertilizers, and also, in particular, when the wastewater is recycled back to the production of fertilizers, as described in this application.

Electrolysis of concentrated waste water can be used to bring the chloride concentration to levels of less than 500 ppm and in particular less than 350 ppm, even more specifically less than 250 ppm. In all cases presented in this application, the chloride content was measured according to ASTM D512-12 by potentiometric titration with silver nitrate using an ion selective electrode.

The electrolysis can be carried out at elevated temperatures. The anolyte and/or catholyte may have a temperature above 20°C. In particular, the anolyte and/or catholyte may have a temperature above 30°C. In particular, the anolyte and/or catholyte may have a temperature above 40°C. In particular, the anolyte and catholyte may have a temperature in the range from 30 to 80°C. Temperatures above the boiling point of the solution at atmospheric pressure can be used if the process is carried out at elevated pressure. Operation at an elevated temperature can facilitate the removal of chlorine from a solution in which chlorine is formed during electrolysis. Operation at elevated pressures can result in downsizing of any gas handling equipment.

Treatment of concentrated waste water from the production of nitrophosphate, other mineral or organic fertilizers in an electrochemical cell ensures the removal of chlorides. At the anode, the chlorides are oxidized to form chlorine, which is released as chlorine gas. The oxidation of chlorides to form chlorine competes with the oxidation of water to form oxygen. The relative rate of oxidation of chloride to form chlorine compared to the rate of oxidation of water increases with increasing chloride concentration. For this reason, preconcentration can contribute to the economic efficiency of the process. After being released in the cell, chlorine gas can be separated from the cell effluent and then removed using an off-gas scrubber before any remaining harmless gases are vented to the atmosphere along with the resulting oxygen. Alternatively, after the scrubber, the gas, which may contain components such as hydrogen, can be used as feed gas for combustion devices. In addition, if the gas is used to supplement the air in the combustion equipment, and if this combustion equipment is suitably equipped with an acid gas absorption device, the gases can be directed directly to the combustion equipment.

A suitable off-gas treatment system that can be used to absorb liberated chlorine may contain, for example, NaOH as a scrubbing agent. In this case, NaCl is formed, as well as NaClO, which can be reused as a decontamination agent or released to the sea after converting NaClO to NaCl using, for example, sodium thiosulfate or sodium bisulfite. In addition, solid state scrubbers may be used, or a mixture of Cl ₂ , O ₂ and H ₂ gases may be combusted in a controlled manner as described above.

While oxygen and chlorine are released at the anode, hydrogen gas is typically released during the cathodic reaction. Usually it is favorable to separate the anodic and cathodic reactions, for which a porous separator (diaphragm) or an ion-selective membrane (porous or ion-selective) is used. This can produce many beneficial results, including the following:

1. prevention of parasitic redox pairs (eg, Fe ²⁺ /Fe ³⁺ and NO ₃ ^- /NO ₂ ^- ), which reduce the Faraday current utilization factor;

2. keeping metal ions away from the cathode in order to minimize the risk of electrodeposition;

3. separating the gas streams (which are chlorine/oxygen released at the anode and hydrogen released at the cathode) for safety reasons and for subsequent post-treatment purposes, since the mixing of gas streams can lead to the formation of an explosive mixture or hazardous components (this applies to mixtures of hydrogen and oxygen, as well as mixtures of hydrogen and chlorine); And

4. prevention of mutual reactions of products with each other.

5. Although in a typical cell, the anolyte and catholyte compartments are separated by a microporous separator or membrane, an undivided cell can also be used for the purpose of this application. This alternative approach provides the advantage of simplifying the design of an electrolyser containing only one fluid circuit and, of course, eliminates the need for a separator. However, it does not have the advantages presented above.

For the removal of chloride, in the context of wastewater treatment, in particular from the production of nitrophosphate, other mineral or organic fertilizers, anolyte is wastewater. Wastewater can be concentrated in a concentration step before entering the electrolyzer where it is converted to anolyte. The catholyte may also be waste water or a concentrated salt solution after treatment at the anode side of the electrolytic cell, an acid solution such as nitric acid, an aqueous solution, or another appropriate solution selected by a person skilled in the art.

The anode material of the cell must be stable in the electrolyte. In addition, this material must be suitable to withstand the release of oxygen and chlorine, showing low wear rates for both reactions, and also have a low overvoltage for the release of chlorine. Typical materials suitable for use as anode materials are boron-doped diamond containing a coating of titanium coated with metal oxides such as, for example, iridium oxide, mixed oxide of iridium and ruthenium, and tin oxide), carbon (graphite) and bulk platinum. Typically, known electrodes for commercial chlor-alkali production, such as the DSA™ electrode from Permascand, can be used to release chlorine.

The materials chosen as cathode materials should exhibit stability in the electrolyte and, ideally, low overvoltage to produce hydrogen. Stability is often not a problem when the material is cathodic protected, also during operation, but the material must also be stable when the operation is stopped. In this context, stainless steel may be a suitable and reasonably inexpensive material, but it does not in any way limit the range of materials available, and there is a wide variety of other materials that are quite obvious to one skilled in the art and can also be used for this purpose. .

Typical separators or diaphragms are polymeric in nature and can be any of a number of commercially available alternatives that are obvious to those skilled in the art. Separators can be diaphragms that provide physical separation but do not selectively carry anions or cations, or ion exchange membranes. Common examples of diaphragm materials are asbestos or microporous polypropylene. A suitable separator may also be a PMX® diaphragm from De Nora. An exemplary ion exchange membrane separator is Nafion® (a copolymer based on a sulfonated tetrafluoroethylene fluoropolymer), which constitutes a cation selective membrane. In particular, separators designed for industrial production of chlorine and alkali can be advantageously used. The membranes used in the industrial production of chlorine and alkali are usually made of perforated polymers and are resistant to chlorine oxidation. The membranes may contain one or more layers, but usually they consist of two layers for use in the production of chlorine and alkali. One of these layers consists of a perforated polymer containing carboxyl groups as a substituent and is adjacent to the cathode side. The other layer consists of a perforated polymer containing sulfonic groups as substituents and is adjacent to the anode side. To give the membrane mechanical strength, the membrane can be reinforced with polytetrafluoroethylene fibers.

In the case of dechlorination, the reaction at the anode can be divided into several discrete steps:

1. transfer of chloride by diffusion, migration or convection from the volume of the solution to the surface of the electrode (mass transfer);

2. desolvation of the solvated chloride;

3. oxidation of chloride ions on the anode surface (charge transfer);

4. release of chlorine gas.

In the electrolysis of chlorides from waste water from the industrial production of fertilizers, and more particularly from the production of nitrophosphate, other mineral or organic fertilizers, the first step, namely mass transfer, may be the limiting step. This is due to the relatively low concentrations of chlorides present, which are typically only about 1000 ppm. As noted above, mass transfer limitation can be reduced by increasing the concentration of particles to be transferred, in this case chloride ions.

For safety reasons, when wastewater is recycled back to the production of nitrophosphate fertilizers, it is advantageous to reduce the limit levels of dissolved chlorine in elemental or ionic form. However, for most practical purposes, a level of less than 500 ppm, more specifically, less than 350 ppm, is generally considered acceptable. Even lower levels may be obtained, such as levels below 250 ppm, below 200 ppm, or below 150 ppm. These levels can be achieved more economically by removing water from the feedstock, electrochemically treating the more concentrated feedstock, and then recombining the water and treated feedstock.

It has been found that the additional step of concentrating the waste water prior to the electrochemical treatment leads to an increase in the Faraday current utilization of the electrochemical treatment by reducing the limitations of mass transfer and kinetics. In some embodiments, the electrochemical processing unit comprises an electrolytic unit. This discovery can be exploited by operating a smaller, lower capital cost cell at higher current density, or by operating a larger, lower current density cell with higher Coulomb efficiency and voltage output. For the case of chloride oxidation, the current required to convert chloride ions to chlorine gas can be reduced by feeding the electrolytic cell with chlorides at a higher input concentration. This reduction of the electrode surface in electrochemical cells represents the main advantages of simultaneously reducing the costs associated with the electrodes and the impact of the electrochemical cell on the environment. In addition, operating costs are reduced.

Any concentration technology known to those skilled in the art and suitable for concentrating the fertilizer solution can be advantageously used to concentrate the system prior to the electrochemical treatment process. Evaporation, electrodialysis, reverse osmosis and direct osmosis are examples of such concentration technologies.

According to a specific embodiment of the present application, the osmosis module is a direct osmosis module or a pressure osmosis module. In a chemical process or waste water treatment process where there are different salt concentrations in the incoming and outgoing streams, by virtue of the process itself or the intention of adding a reagent, there are possibilities for water transfer between the inlet and outlet streams using the osmotic pressure difference between two streams. This can be used to advantage in order to concentrate the starting material for the process and provide process intensification. This occurs in particular when the process is carried out more efficiently by increasing the concentration of the starting material. If the product stream is in principle more concentrated due to the process, then direct osmosis can be used to concentrate the feedstock by introducing water into the product. The direct osmosis process does not change the total amount of water leaving the process. If the wastewater treatment is carried out by means of electrolysis, direct osmosis eliminates the requirement that all water be contained in the electrochemical cell. Even if the process effluent does not differ significantly in concentration from the feed, there are still significant benefits of water exchange between the inlet and the feed, for example if the product is used as a "clean up stream" on what is traditionally the permeate reverse osmosis system. Water can be transferred from the feed to the cleaning side at a much lower pressure than would be required to overcome the full osmotic pressure and produce pure water as permeate. This is called pressurized osmosis. Compared to other concentration processes such as evaporation or electrodialysis, osmosis-based processes, including reverse osmosis, direct osmosis, and high pressure osmosis, can achieve lower capital and operating costs.

In particular, in the production of nitrophosphate fertilizers and for introducing waste water into an electrochemical cell in order to remove chlorides from this waste water, the total concentration of dissolved salts is from 40 g/l to 100 g/l. In some embodiments, the electrochemical cell is an electrolytic cell. The chloride concentration is from 1250 ppm to 15000 ppm, or from 1500 ppm to 10,000 ppm, or from 1750 ppm to 2500 ppm. It has been found that the efficiency of the pollutant removal process can be increased by concentrating the wastewater stream to a higher degree. After electrochemical treatment of this stream, the total concentration of dissolved salts increases only slightly in the range from 41 g/l to 105 g/l, this increase due to electrolysis and evaporation losses, and the chloride concentration decreases to below 350 ppm, or below 250 ppm or below 200 ppm or below 150 ppm The treated solution exiting the cell is then reintroduced back into the process. In particular, components such as calcium nitrate, which are required for the downstream process, are added to the treated solution. This stream is suitable for use as a direct osmosis carrier stream to remove water from the feed stream to the electrolytic cell. Likewise, it can be used for high pressure osmosis in order to reduce the required pressure compared to conventional reverse osmosis if it is not suitable enough, i.e. requiring excessively high energy, for direct osmosis. In any case, it is possible to provide energy efficient preconcentration before the electrochemical cell using osmosis embodiments.

According to a specific embodiment, in the concentration step, the contaminants in the wastewater are concentrated prior to electrolysis, in particular to a level of greater than 10%, more specifically greater than 20%, more particularly greater than 25%, more particularly greater than 50 %, more specifically higher than 75%, more specifically higher than 100%, more specifically higher than 125% or more specifically higher than 150%.

Various exemplary aspects of the system and method described herein are detailed below with reference to the figures.

In FIG. 1 is a general flow diagram in which wastewater from fertilizer production 100 is first concentrated in concentrator 200. Chlorides from wastewater are then removed in electrochemical treatment unit 300 before the wastewater is recycled to fertilizer production 100. In a more specific embodiment, as illustrated in FIG. 2A, concentrator 200 is a direct osmosis module 210. Direct osmosis module 210 includes a first compartment 400 and a second compartment 500 separated by a membrane 450. and thus less energy is required to remove water from stream 400 for a direct osmosis process compared to a reverse osmosis process. For example, a direct osmosis module may be an INSIDE™ osmosis module from Aquaporin.

It has been found that due to the removal of water by electrolysis and the evaporation of water into the gas phase during the electrolysis step, the waste water leaving the electrochemical treatment unit 300 is naturally more concentrated than the water leaving the electrolyzer. Therefore, in a direct osmosis process, water will naturally flow from the first compartment 400 to the second compartment 500. This driving force can be low because the amount of water removed by electrolysis and evaporation is small compared to the total amount of water flowing through the system. . However, this may contribute to an osmotic imbalance between the two sides 400 and 500 of the cell.

The concentration step described herein will not specifically concentrate the chloride ions in the wastewater, but will concentrate all the ions present in the wastewater. This concentration step should not be interpreted as a purification step from chlorides only. In addition, the concentrations of other ions present in the wastewater may not have a significant impact on the chloride removal efficiency of the electrochemical treatment unit 300.

According to the embodiment shown in FIG. 2A, the waste water is concentrated by directing the waste water to the first compartment 400 of the direct osmosis module 210, and the electrolyzed water is sent to the second compartment 500 of the direct osmosis module 210. The waste water is then recycled from the second compartment 500 of the direct osmosis module 210 to the fertilizer production 100.

Let's consider a demonstration plant for the treatment of 250 l/h of waste water, which can be directed to the first compartment of the osmosis module. The flow is preferably carried out at a temperature of from 25 to 60°C, which is determined by the temperature limitations of the osmotic system. In particular, the flow of saturated water into the second compartment when returning from the electrolytic cell is between 250 and 100 l/h, which represents a 2.5-fold osmotic concentration and a decrease in the volume of water compared to the source material. Pumps (not illustrated) may be used as needed to ensure proper flow of waste water through the system.

According to the embodiment illustrated in FIG. 2A, the flow of wastewater in the first compartment 400 is opposite to that in the second compartment 500. The concentration gradients in each compartment will be more favorable in the concentration step when such an opposite flow profile is used. However, direct osmosis can also be used in case of co-directional flows. In typical designs, chlorides can be concentrated from about 1000 ppm to 2500 ppm, or in other words, the concentration factor can be 2.5. This value should not be considered as a theoretical limit on the degree of concentration that can be realized. It will depend on the solution to be concentrated, the contacting mode (co-directional or opposite), the specific features of the contacting equipment, and the tendency of the solution to clog osmotic membranes through the formation of deposits. Generally, the process will be favored by concentrating the solution to the maximum practical extent at which the solubility limit is reached.

In particular, the production of fertilizers 100 is the production of fertilizers, which are compositions containing ammonium nitrate. In the production of such compositions, the removal of chlorides is necessary in order to provide safe and acceptably low levels of chlorine for recycling to fertilizer production 100. In particular, the concentration of chlorides in the electrolyzed water that is recycled to fertilizer production 100 through the second compartment 500 is less than 350 ppm

The concentration step is further enhanced by adding brine to the second compartment 500 of the osmosis module 210 from the brine tank 600, as shown in FIG. 2A. Adding such a saline solution to the second compartment 500 will increase the osmotic pressure and as a result will further facilitate the flow of water molecules from the first compartment 400 to the second compartment 500. Without being limited by theory, any saline solution can be used to increase the osmotic pressure. In turn, as the osmotic pressure increases, the space required for the concentration step will decrease. In a specific embodiment, the brine from the brine tank 600 is a fertilizer solution that is substantially free of chlorides. As defined herein, the virtual absence of chlorides means that their content is less than 500 ppm, more specifically, less than 350 ppm, and even more specifically, their content is even at a lower level, constituting, for example less than 250 ppm, less than 200 ppm, or less than 150 ppm Such low levels of chloride ions will prevent any safety hazards in the downstream fertilizer production process.

More specifically, in each case, the fertilizer plant 100 to which the electrolyzed water is recycled is an ammonium nitrate plant, and the brine from the brine tank 600 is a brine containing ammonium nitrate. More specifically, the fertilizer plant 100 to which the electrolyzed water is recycled is a nitrophosphate or other organomineral fertilizer plant, and the brine from the brine tank 600 is a fertilizer solution containing mainly ammonium nitrate, double ammonium and calcium phosphate or calcium nitrate, or a combination thereof. Thus, a portion of the existing process feedstock can be used as the saturated solution feedstock entering the second compartment 500 of the osmosis module 210. However, any saline solution can be used to increase the osmotic pressure across the membrane 450. The only real limitation in selection of the corresponding salt solution is that in any salt there should be practically no chlorides. In this context, the practical absence means that the content of chlorides in the salt solution is less than the content of chlorides present in the waste water after the electrolysis step. In other words, the brine should not be an additional source of chlorides going back into the wastewater. Accordingly, in some embodiments, the chloride content of the brine from the brine tank 600 is less than 500 ppm, more specifically less than 350 ppm, less than 250 ppm, less than 200 ppm, or even less than 150 ppm

According to another embodiment shown in FIG. 2B, instead of the direct osmosis module shown in FIG. 2A, a pressurized osmosis module is present. This requires a pump 700 and check valve 800, but uses the product flow in compartment 500 as the driving force to significantly reduce the pressure required for osmosis. using reverse osmosis, by reducing the pressure required to pass the fluid through the membrane.

In a specific embodiment, the concentration unit 200 may include a plurality of direct osmosis modules 210 connected in series, such as two or three direct osmosis modules. In FIG. 3 is an illustration of such an embodiment in which there are three direct osmosis modules 210 connected in series, each containing a first compartment 400 and a second compartment 500 separated by a membrane 450. The wastewater is then treated in an electrochemical treatment unit 300. As discussed above, the flow of waste water in the first compartments 400 may be opposite to the flow in the second compartments 450, as shown in FIG. 3, or the flows may be co-directional.

Examples

It should be noted that, as mentioned in the detailed description, in all cases, the chloride content indicated in the following examples was measured according to ASTM D512-12 by potentiometric titration with silver nitrate using an ion selective electrode.

Example 1 Comparative example without direct osmosis

The separated cell contained an anode which was a dimensionally stable anode from Permascand and a cathode which was made of SS 316 stainless steel. The membrane separator was Nafion 324. experiment. The structural material of the cell was polyvinyl chloride.

Waste water from the Norwegian municipality of Porsgrunn containing 1100 hours/million chlorides and 5.1 wt. % dissolved solids, which is mainly ammonium nitrate, was introduced into the anode compartment of the cell, and the pH was reduced to 2.0 by adding nitric acid. A catholyte solution was prepared using sodium sulfate and the pH was lowered to 0.5 by adding nitric acid such that the solution had the same ionic strength as the waste water to minimize the osmotic transfer of water in the cell. This solution was then introduced into the cathode compartment of the cell.

The cell was operated at an electric current density of 860 A⋅m ^-2 in batch mode. The experiment was carried out at room temperature. Calculations show that the Faraday current utilization factor was approximately 8% to remove chlorides up to 200 ppm within 115 minutes.

Example 2 Implementation of direct osmosis without the addition of calcium nitrate

The separated cell contained an anode which was a dimensionally stable anode from Permascand and a cathode which was made of SS 316 stainless steel. The membrane separator was Nafion 324. experiment. The structural material of the cell was polyvinyl chloride.

The wastewater flow according to Example 1 was first directed at a flow rate of 1.1 l/min to an inlet on the tubular side of the Aquaporin module, which contained a shell and tube compartment with pipes made of a permeable membrane. This Aquaporin INSIDE™ module was a direct osmosis shell and tube module with a 2.3 m ² membrane. The concentration of chlorides in the waste water leaving the pipe side was 1470 ppm and the weight percentage of solids in this outgoing solution at the outlet of the first compartment was 7.4%. This discharged waste water was collected at a rate of 0.8 l/min. The carrier stream entering the housing of the Aquaporin module was a "simulative" concentrated solution, which is returned from the electrolyser after removal of chlorides. This "dummy" waste water had a weight percentage of solid ammonium nitrate of 14% and contained 0 ppm chlorides. She entered the casing at a flow rate of 0.9 l/min. The shroud effluent had a weight percent solids content of 10.3% and contained 26 ppm chlorides; it was collected at a flow rate of 1.2 l/min.

Concentrated waste water was introduced into the anode compartment of the cell and the pH was lowered to 2.0 by adding nitric acid. A catholyte solution was prepared using sodium sulfate and the pH was lowered to 0.5 by adding nitric acid such that the solution had the same ionic strength as the waste water to minimize the osmotic transfer of water in the cell. This solution was then introduced into the cathode compartment of the cell.

The cell was operated at an electric current density of 860 A⋅m ^-2 in batch mode. The experiment was carried out at room temperature. By interpolating the experimental results, a Faraday current utilization factor of approximately 25% was obtained to reduce the chloride content from 1470 ppm to 400 ppm within 120 minutes. If this solution was then diluted in a direct osmosis module as a carrier stream (as illustrated in FIG. 2A) to a solids content of 5.1% from example 1, the chloride content was below 200 ppm, which is equivalent to the result from example 1, in which the concentration step was not performed before the electrolysis step.

This experiment demonstrated the feasibility of a single stage in a reverse flow direct osmosis cascade system using typical effluent from 1100 to 2000 ppm chloride to operate an electrolytic cell with increased Faraday current utilization. After removal of chlorides in the electrolyser, the stream can be reused as a carrier stream for a direct osmosis system because it will be slightly concentrated due to evaporation and loss of water during the electrolysis process.

Example 3 Implementation of direct osmosis with the addition of calcium nitrate

The separated cell contained an anode which was a dimensionally stable anode from Permascand and a cathode which was made of SS 316 stainless steel. The membrane separator was Nafion 324. experiment. The structural material of the cell was polyvinyl chloride.

To demonstrate that the concentrated wastewater stream used in the study described above can be obtained using a direct osmosis system, wastewater at 25°C from the municipality of Porsgrunn with a chloride content of 1100 ppm and a mass percentage of solids of 5, 1% was directed at a flow rate of 1.1 l/min to the inlet on the tubular side of the Aquaporin module, which contained a shell and tube compartment with pipes made of a permeable membrane. This Aquaporin INSIDE™ module was a direct osmosis shell and tube module with a 2.3 m ² membrane. The concentration of chlorides in the waste water leaving the pipe side was 1470 ppm and the weight percentage of solids in this outgoing solution at the outlet of the first compartment was 7.4%. This discharged waste water was collected at a rate of 0.8 l/min. The carrier stream entering the housing of the Aquaporin module was a "simulative" concentrated solution, which is returned from the electrolyser after removal of chlorides. This "dummy" wastewater had a weight percent solid ammonium nitrate of 14% and contained 0 ppm chlorides. She entered the casing at a flow rate of 0.9 l/min. The shroud effluent had a weight percent solids content of 10.3% and contained 26 ppm chlorides; it was collected at a flow rate of 1.2 l/min.

Concentrated waste water was introduced into the anode compartment of the cell and the pH was lowered to 2.0 by adding nitric acid. A catholyte solution was prepared using sodium sulfate and the pH was lowered to 0.5 by adding nitric acid such that the solution had the same ionic strength as the waste water to minimize the osmotic transfer of water in the cell. This solution was then introduced into the cathode compartment of the cell.

The cell was operated at an electric current density of 860 A⋅m ² in batch mode. The experiment was carried out at room temperature. Calculations show that the Faraday current utilization factor was approximately 25% to remove chlorides up to 400 ppm within 120 minutes. If this solution was then diluted in a direct osmosis module as a carrier stream (as illustrated in FIG. 2A) to a solids content of 5.1% from example 1, the chloride content was below 200 ppm, which is equivalent to the result from example 1, in which practically the stage of concentration before the stage of electrolysis.

This experiment demonstrated the feasibility of a single stage in a reverse flow direct osmosis cascade system using typical effluent from 1100 to 2000 ppm chloride to operate an electrolytic cell with increased Faraday current utilization. After the chlorides are removed in the electrolytic cell, calcium nitrate (a salt that is used downstream in a typical nitrophosphate fertilizer production) can be added to the stream before being used as a carrier stream for a direct osmosis system. This stream now has a significantly higher ionic strength than the feed stream and the direct osmosis system requires a smaller membrane area.

Note regarding examples 4-6:

While not limited to the specific treatment of chloride-containing wastewater from nitrogen fertilizer production, the present inventors propose other applications for the concepts implemented in this patent that are outside of this particular area. These applications are described below in examples 4, 5 and 6.

Example 4. Electroreduction of iron(III) to iron(II) for the extraction of uranium from phosphoric acid

US 8,703,077 B2 describes a process for extracting uranium from phosphoric acid. This process uses iron exchange or solvent extraction to remove uranium from the phosphoric acid stream, which is then recycled to the process. Iron in the Fe(III) state, which is present in the acid along with uranium, competes with uranium for sites in the ion exchange resin or in solvent extraction. Electroreduction of iron(III) to iron(II) that does not compete with uranium in the ion exchange/solvent extraction process is one option for improving the performance of the uranium extraction process. The Faraday current utilization factor for this electroreduction process will be limited by the competition of the reduction of iron(III) to iron(II) with the release of hydrogen due to the low concentration of iron in the acidic solution. Osmotic concentration of the cell feed solution in a direct osmosis or pressurized osmosis process using a treated stream as the carrier stream will benefit the process by increasing the iron(III) concentration in the feed and increasing the Faraday current utilization.

Example 5 Electrochemical Decomposition of Salts in Salt Solutions Produced from Oil and Gas Fields

In the oil and gas sector, there is a problem with the proper disposal of the so-called "produced water". It is a brine stream that is produced along with hydrocarbons. It contains mainly sodium chloride, and the salt concentration can be up to about 5 wt. %. More specifically, this concentration is close to the concentration of NaCl in sea water, in which it is approximately 3.5 wt. %.

One approach to the disposal of produced water and to the benefit is the electrochemical decomposition of the salt in the brine to produce sodium hydroxide and hydrochloric acid. Both of these chemicals may be required in numerous oil and gas fields. Salt extraction desalinates the water and makes it easier to reuse. Electrolysis or a bipolar membrane electrodialysis cell can be used to decompose the salt.

The process of electrochemical decomposition of salt becomes more efficient when using a salt solution of the highest available concentration. In addition, the addition of water is required for the anolyte and catholyte compartments of the cell in order to maintain the concentration of the respective products. Direct osmosis between product and feed solutions, as discussed in detail in this patent, is found to be suitable for reducing the energy consumption of the entire process by economically concentrating the feed stream while maintaining anolyte and catholyte concentrations by dilution using water extracted from the feed.

Example 6. Preconcentration of acid in the process of salt decomposition in a three-chamber electrolyzer

Sodium sulfate can be subjected to electrochemical decomposition in a three-chamber electrolyzer. The sodium sulfate solution flows into the central compartment, from which sodium ions pass through the cation exchange membrane into the catholyte compartment, and sulfate ions pass through the anion exchange membrane into the anolyte compartment. Due to the membrane transfer mechanism, there is a significant transfer of water (approximately 12 to 15 mol H ₂ O per 1 mol Na ₂ SO ₄ ) from the central compartment to the anolyte and catholyte compartments. In order to minimize voltage losses in the central compartment, this stream does not reach complete depletion, but is recycled back to the solids dissolution process stage. Additional is required to compensate for the loss of water on the membranes.

Concentration of sulfuric acid in the anolyte compartment cannot be carried out economically above about 2.0 mol/l without loss of Faraday current utilization due to back migration through the membrane. The acid stream is then subjected to concentration in various stages, for example, up to 98 wt. %. Because the center compartment (containing sodium sulfate) can be operated near the solubility limit (approximately 2.6 mol/l), there is an ionic gradient between the two streams that can be used in a direct osmosis system to remove water from the acid production stream and to recycle the sulfate stream sodium to dissolve fresh solid sodium sulfate. This approach is an energy efficient process for initially concentrating the produced sulfuric acid and can further increase Faraday current utilization by operating at a lower acid concentration in the anolyte compartment.

Claims (26)

1. A method for removing pollutants from wastewater from fertilizer production, comprising the following steps: a) concentration of contaminants in wastewater; b) chemical transformation of pollutants in waste water by means of electrolysis, whereby, in particular, the pollutants form a gas as a result of electrolysis; And c) recycling electrolyzed waste water into industrial production; wherein the step of concentrating the wastewater is carried out using a direct osmosis module or a pressurized osmosis module comprising a first compartment and a second compartment separated by a membrane; wherein the stage of waste water concentration includes the stage of directing waste water to the first compartment of the osmosis module, and the recirculation stage includes the following stages: i) directing the electrolyzed waste water to the second compartment of the osmosis module; And ii) recycling of waste water from the second compartment of the osmosis module to fertilizer production. 2. The method according to claim 1, wherein the contaminants are chlorides, wherein the concentration of chlorides in the waste water after the concentration step is, in particular, from 1250 to 2250 ppm, more specifically from 1500 to 2250 ppm and even more specifically, from 1750 to 2250 ppm. 3. The method according to claim 1 or 2, wherein the flow of waste water in the first compartment is opposite to the flow in the second compartment. 4. The method according to any one of paragraphs. 1-3 further comprising the step of adding the brine to the second compartment of the osmosis module or upstream. 5. The method of claim 4 wherein the brine contains one or more of ammonium nitrate, double ammonium and calcium phosphates, and calcium nitrate. 6. The method according to any one of paragraphs. 1-5, in which the production of fertilizers is the production of nitrophosphate fertilizers or the production of other mineral or organomineral fertilizers, in particular, the production of fertilizers, which are compositions containing ammonium nitrate. 7. The method according to any one of paragraphs. 1-6, in which the concentration of chlorides in the electrolyzed waste water is less than 350 ppm. 8. A system for removing pollutants from wastewater present in wastewater from industrial production, comprising: a) a concentration unit designed to be connected with the possibility of transferring fluid to waste water from industrial production, b) an electrochemical treatment unit for the removal of contaminants, fluidly coupled downstream of the concentration unit and designed to be fluidly coupled to the recycling of treated waste water into industrial production, wherein the concentration unit is a direct osmosis module or a pressurized osmosis module, the osmosis module comprises a first compartment and a second compartment separated by a membrane, wherein: i) industrial wastewater to be treated is fluidly connected to the first compartment; ii) the first compartment is fluidly connected to an inlet of the electrochemical processing unit; iii) the outlet of the electrochemical treatment unit is fluidly connected to the second compartment, and the second compartment is designed to be fluidly connected to the industrial production and is preferably configured such that the wastewater treated in the electrochemical treatment unit can flow through the second compartment and recycle to industrial production; and optional iv) a brine source is fluidly connected to the second compartment; and wherein the electrochemical processing unit comprises an electrolytic unit. 9. The system according to claim 8, wherein the concentration unit comprises several osmosis modules connected in series, in particular two or three osmosis modules connected in series. 10. The system according to any one of paragraphs. 8 or 9, in which the flow of waste water in the first compartment flows in the opposite direction with respect to the flow of water in the second compartment. 11. The use of the system according to any one of paragraphs. 8-10 in the production of fertilizers, in particular in the production of nitrophosphate fertilizers or in the production of other mineral or organomineral fertilizers, more specifically in the production of fertilizers which are compositions containing ammonium nitrate.

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