ITMI20081490A1 - EXTRACTION PROCESS OF AMMONIACAL NITROGEN FROM LIQUID WASTE - Google Patents

Description

Title: "Process of ammonia nitrogen extraction from liquid waste."

The present invention refers to a process for the extraction of ammonia nitrogen from liquid wastewater.

The present invention is part of the technical sector of the treatment of nitrogen-containing wastewater, in particular of zootechnical waste containing animal waste deriving from pig, bovine, poultry and other animal breeding, of civil and industrial wastewater, and of landfill leachate.

Over time, national and international environmental regulations have imposed and impose ever more restrictive limits on the quantity of nitrogen that can be distributed in the environment by spreading animal waste on agricultural land. In particular, the limits imposed on the spreading of manure in those agricultural areas in which the concentrations of nitrates in the soil have reached such high values as to qualify them as â € œneitrate vulnerable areasâ € are increasingly restrictive.

Without prejudice to the quantity of manure produced and their nitrogen content, the overall surface of the land available for spreading therefore becomes progressively insufficient to guarantee the disposal of manure unless the nitrogen content is reduced.

Similarly, the disposal of civil and industrial wastewater and landfill leachate also represents a major environmental problem due to the large quantities produced, but also to the onerous costs that they entail.

In the state of the art, various processes for treating liquid waste containing nitrogen are known and used, aimed at completely removing or at least reducing the nitrogen content thereof. In the case of livestock manure from pig farms, for example, nitrogen is present in concentrations ranging from 1000 to 6000 mg / l, according to the specific diet used at the farm and the dilution caused by washing more or less frequently carried out for cleaning the pigsty.

A medium-sized pig farm (3000-5000 head) produces a quantity of this effluent ranging from 30 to 50 m <3> / day.

Almost complete nitrogen removal (98-99%) can be obtained using biological wastewater treatment processes. These processes, which include at least a biological oxidation phase of the wastewater followed by a denitrification phase, are however very complex to manage, as well as requiring the construction of rather expensive plants.

Since the final destination of livestock manure remains mainly spreading on agricultural land, the removal of nitrogen does not necessarily have to be complete or, in any case, very high. In fact, a reduction of the nitrogen content of a wastewater equal to 50% by weight compared to the total nitrogen would be sufficient to allow the spreading of a double quantity of wastewater on the same agricultural surface (compared to the original wastewater). Equally important is also the cost-effectiveness of the treatment, ie the relationship between the cost of the treatment and its effectiveness.

From this point of view, a type of wastewater treatment process that allows the nitrogen content to be reduced to acceptable levels and, at the same time, at low costs compared to the processes known to the state of the art, is that based on extraction ( or stripping) of the nitrogen contained in the wastewater in the form of ammonia. This type of process, which is typically carried out in flat towers or rashling rings, involves the extraction of ammonia nitrogen by insufflation of an air current (stripping current) in countercurrent with respect to the fall of the liquid waste with consequent removal of gaseous ammonia. To favor the development of gaseous ammonia, the wastewater is generally heated and added with basifying agents, such as NaOH.

Usually the wastewater must also be screened or filtered, possibly after the addition of flocculating agents, since the presence of solids, even if small, can obstruct the holes in the dishes or dirty the rashling rings, causing the plants to stop . Furthermore, to allow acceptable extraction rates, the wastewater must be heated to a temperature above 80 ° C with a very high energy expenditure.

The stripping stream containing gaseous ammonia is generally treated in washing towers with acid solutions. Once the gaseous ammonia has been absorbed in the washing solution, the resulting ammonia-free gaseous stream is released into the atmosphere.

The stripping-based treatment, although sufficiently effective in removing the nitrogen contained in the wastewater, nevertheless involves rather high energy consumption and significant costs linked to the use of chemical additives. To carry out the process, in fact, large quantities of basifying and flocculating agents are required, as well as energy to move the air mass of the stripping stream and to heat the wastewater. All this makes the construction of treatment plants on farms, especially small ones, economically unattractive.

A type of wastewater treatment process that allows to overcome the aforementioned drawbacks and that is energetically and economically more convenient than the processes of the known art is that described in the Italian application MI2007A0002448.

This process involves the extraction of nitrogen by means of the generation of a gaseous flow which, passing over the free surface of the wastewater with the addition of a basifying agent, is able to drag a gaseous stream including ammonia out of the reactor.

It has now been found that by combining the aforementioned extraction process with the use of a special ionized air system, it is possible to obtain a further increase in the overall extraction efficiency, in the sense of both the extraction speed and the concentration limit. final ammonia in the treated wastewater.

The object of the present invention is therefore a process for the extraction of ammonia nitrogen from liquid wastewater, comprising the following operating steps:

a) bringing the wastewater into contact with a basifying agent in a reactor;

b) generating an ionized gaseous flow over the wastewater and in particular over the free surface of the wastewater and drawing a gaseous stream comprising ammonia out of the reactor;

c) recovering the ammonia from the gaseous stream leaving phase b) with the formation of a purified gaseous stream.

Preferably, the process is carried out using in step b) an ionized gaseous flow inlet formed by one or more gases and / or vapors selected from: air, nitrogen and argon.

The process according to the present invention is applied to wastewater from various types of farms, such as pigs, cattle, poultry, etc., and more generally to all wastewater containing nitrogen in ammonia form, for example those resulting after anaerobic digestion treatment (industrial and civil waste, landfill leachate).

The wastewater collected at the production sites in which it is generated (eg inside one or more farms, purification plants, landfills, etc.) are stored in a collection tank. They generally occur in a liquid or liquid-muddy state and can be moved by means of the pumping systems typically used in the sector. Sometimes, according to the nature of the wastewater, before being subjected to treatment, the wastewater can be mixed together and / or diluted with water until it reaches the most suitable fluidity for their handling with the aforementioned pumping systems.

The process according to the present invention is generally carried out in a single reactor if it is a question of the discontinuous mode, or in a special system comprising several reactors with preferentially vertical development, if it is a continuous mode. Inside this system, the wastewater is loaded by means of pumping systems. In a preferred embodiment of the invention, the loading of the wastewater takes place in a completely automated way.

Phase a) of the process according to the present invention consists in putting in contact the wastewater characterized by a neutral pH, which according to the chemical-physical conditions is subjected to the necessary preliminary treatments (e.g. filtration, flocculation), with a quantity of agent basifying agent capable of raising the pH value up to a value ranging from 7.2 to 13, preferably from 10.0 to 13.

If the pH is already with a value higher than 10.00, it is possible to proceed directly to the nitrogen extraction treatment.

The Applicant has observed that the basifying action is preferably performed by a solid basifying agent selected from CaO, MgO and / or their mixtures or chosen from aqueous solutions of Ca (OH) 2, Mg (OH) 2 and / or their mixtures . Preferably, the basifying agent is in granular solid form. Unlike the basifying agents used in the processes of the state of the art (eg NaOH), these additives have a much lower cost.

Preferred basifying agent is quicklime that is a CaO / MgO mixture. This is for what concerns the treatment of livestock manure, which after treatment must be distributed (spreading) on agricultural land; in the case of leachate from landfills, traditional basifying agents can also be used (eg soda or caustic potash).

The present invention can however be realized with the same advantages, albeit in limited form, also with other basifying agents such as Na2O, K2O, NaOH, KOH, Na2CO3, K2CO3 and / or their solid mixtures or with the respective aqueous solutions and / or their blends.

In general, the basifying agent can be added to the wastewater to be treated in solid form or as an aqueous solution. Typically, when the basifying agent is added in solid form, its dosage varies from 5 to 20 kg of agent per m3 of wastewater to be treated. When added in the form of an aqueous solution, typically at 30% by weight, the dosage varies from 30 to 50 liters / m3.

As a result of the increase in pH, the ammonia nitrogen contained in the wastewater, (in which it is mainly present in the form of NH4 ions), tends to separate from the wastewater in the form of gaseous NH3. The concentration of ammonia in the liquid wastewater increases until, under the specific operating conditions of temperature and pressure, it spontaneously tends to escape from the wastewater until an equilibrium condition is reached.

By generating a gaseous flow inside the reactor that removes the ammonia that evolves from the wastewater, this balance is altered and new ammonia is produced in the wastewater, which will tend to escape from it to restore balance.

It has been observed that this phenomenon is particularly accentuated if the gaseous flow is generated by the introduction of an ionized gaseous flow above the free surface of the wastewater, since in this way, in addition to promptly removing the outgoing ammonia, the extremely strong electrostatic attraction that the ionized gaseous flow exerts towards the polar ammonia molecule. The speed of ammonia release is thus enormously increased and the rapid evolution of new ammonia from the wastewater is favored.

The pressure of the gaseous flow generated to extract the ammonia varies from -100 mbar (reactor in depression - aspirated gaseous stream) to 100 mbar (injected gaseous stream), i.e. the gaseous flow which allows to extract the gaseous stream comprising ammonia can be generated either by introducing a gaseous current that flows over the wastewater head or by placing the reactor in depression. In a preferred embodiment, the pressure of the gaseous flow is chosen between -10 and 10 mbar.

In both operating modes, ie using a gas stream introduced or placing the reactor in depression, the gas flow generated is present above the surface of the wastewater without bubbling inside.

By not making huge masses of air bubble in the wastewater, as usually occurs in processes according to the state of the art, foam formation is avoided, with a consequent reduction in operating costs deriving from the use of antifoam products.

The gaseous flow drags the ammonia, which gradually separates from the wastewater, out of the reactor. The gaseous stream comprising ammonia is then sent to the next phase c) of the process.

It has been observed that the nitrogen reduction process proceeds more rapidly when the gaseous phase is removed by generating the gaseous flow by means of an injected gas stream instead of placing the reactor inside under vacuum.

It has also been observed that the extraction of ammonia from the wastewater is faster in reactors having a shape such as to create a large exchange surface between the wastewater and the gas stream.

Preferably, the reactors are made up of one or more rectangular tanks with a narrow and long shape, with the ionized air inlet from the long side.

The gaseous flow generated above the wastewater and in particular on the free surface of the wastewater inside the reactor, being produced by means of a gaseous stream introduced at low pressure or by placing the reactor in slight depression, involves a modest energy consumption. The energy consumption for the ionization of this flux is also modest.

The process object of the present invention, therefore, allows to obtain the removal of ammonia nitrogen from the wastewater under economically favorable conditions with respect to the processes known to the state of the art. Furthermore, to carry out the process according to the present invention, means for pumping gas and / or vapors of modest size and ionization systems that are easy to manufacture or readily available on the market at low costs are sufficient.

To facilitate the nitrogen extraction process from the wastewater and reduce the duration of the treatment, the wastewater can be heated and maintained at a temperature of about 50 ° C, for example, by means of special heating elements, such as coils immersed in the body of the wastewater. At this temperature, both the formation of foam, due to the decomposition of bicarbonates, and the precipitation of insoluble carbonates with consequent formation of limestone deposits on the reactor walls and on the heating coils are avoided. In the case of zootechnical waste, heating can be particularly useful in the winter period where the collected waste is at an average temperature of 15-20 ° C, while in the summer the temperature of 40-50 ° C of the waste is easily reachable. Furthermore, as a result of the addition of the basifying agent there is a temperature rise of 4-5 ° C due to the exothermicity of the dissolution reaction.

The process of extracting nitrogen from the wastewater according to the present invention proceeds at an acceptable speed even in the absence of agitation of the wastewater.

In order to further increase the extraction speed, it is however useful to carry out an intermittent stirring by insufflation of the gaseous flow used directly in the wastewater itself in order to allow a greater homogenization of the mass or, alternatively, by means of mechanical stirring, preferably of the paddle stirrers.

Agitation can also be obtained by applying ultrasound to the wastewater or by relaunching a part of the wastewater itself, taking it from the bottom of the reactor and re-introducing it into a second point of the reactor, located above the head of the wastewater, so as to create turbulence inside it.

Typically, the recirculation flow rate of the wastewater varies from 0.2 to 3.5 recirculations / hour, i.e. it is such as to recirculate the volume of waste subjected to treatment from 0.2 to 3.5 times an hour (for example if the volume of the wastewater to be treated is 5000 liters, 2 recirculations / hour correspond to a recirculated volume equal to 10,000 liters / hour).

In a further embodiment of the invention, in addition to the effect of the aforementioned recirculations, the wastewater can be kept agitated also by insufflation of air captured from the outside.

The agitation of the wastewater according to the methods described above allows to increase the efficiency of the process by increasing the ammonia extraction speed.

In order to reduce the overall energy consumption of the process and to limit the emissions into the atmosphere deriving from it, at least part of the gas stream leaving the reactor, once the ammonia in phase c) has been purified (even only partially), can be used as a gas stream introduced in phase b). Preferably, all the purified gas stream is recycled to step b) of the process so as to create a closed recovery cycle.

At the end of the process, the wastewater is discharged from the reactor and stored in tanks waiting to be destined for spreading on agricultural soils and / or is partially used to pre-basify the new wastewater to be treated. If the wastewater is spread over the land, it may be necessary to correct its pH in order to make its characteristics comply with the criteria established by the relevant environmental regulations.

In a preferred embodiment of the invention, the end of the treatment is determined automatically by means of a continuous analysis system which, by continuously determining the concentration of nitrogen still present in the wastewater (for example the ions ammonium) or that extracted in the gaseous phase (for example gaseous ammonia), is able to indicate the level of nitrogen reduction achieved by the process.

The process according to the present invention can be carried out in discontinuous mode, ie by treating predefined quantities of waste within a single reactor until the end of the process or in continuous mode. The discontinuous version is preferable for the treatment of livestock waste, while the continuous version is preferable for industrial, civil and leachate. In practice, the operating methods depend greatly on the concentration of ammonia in the wastewater and on the daily flow rate to be treated, as well as on the final concentration required.

In the discontinuous configuration (figure 1) the gaseous flow (air) is sent by a fan to the ionization system, generating an ionized gaseous flow, and from here it is made to pass with a horizontal flow on the free surface of the wastewater to be treated. Typically the flow rate of the ionized gaseous flow (air) sent varies from 1500 to 2000 Nm <3> / h for each m <3> / h of wastewater to be treated.

The ionization system is made up of commercially available devices, preferably a system consisting of charge generators with both negative and positive polarity is used, with adjustable voltage from 0Ã · 40 KV and 50mA (max) in direct current, produced by the Company Martignoni Elettrotecnica srl (Vanzaghello-MI).

The ionization system of the gaseous flow (air) is essentially constituted as follows: there is a generator of charges (which can be negative or positive) which is a high voltage direct current transformer. From the generator then comes the connection to a charging bar or ionizing bar, a bar that is made up of a series of metal tips one next to the other, embedded in an insulating resin with a special electronic regulation circuit that prevents it from firing. electric discharge (for example when the air flow becomes particularly conductive due to the increase in humidity); always at the output of the generator there is then the grounding which closes the circuit (in the case of the present invention it is connected to the liquid to be treated).

In conclusion, a negative or positive ionization is generated (depending on the generator used), while the bar is always the same, placed at about 15-20 cm from the surface of the liquid and at the entrance of where the input is introduced. ™ air or gaseous flow to be ionized, which (since the liquid is connected to the generator earth) is immediately ionized.

Preferably, bars of variable length are used depending on the size of the reactor, placed at about 15-20 cm on the free surface of the wastewater while the closure of the circuit has been carried out directly in the liquid itself; in this way, an ionization and extraction effect is obtained much higher than that obtained by using a metallic counter-electrode for closing the circuit (in practice it has been seen that such a metallic counter-electrode is effectively replaced by use of the same wastewater as â € œ against electrodeâ €).

The ionized gas flow is diffused inside the reactor by introducing the gas into an upper channel made by making a slot on the long side of the reactor. The loading bar is positioned in the upper part of the slot for the entire length of the tank (4m length bars can also be made). Just above the bar, the tank is closed by means of a plastic plate (given the high tension used, all parts of the reactor must be rigorously in plastic material) which thus determines the formation of a `` channel '' for the sliding of the € ™ air along the width of the tank; on the opposite side of the tank (always on the long side) there is an air outlet slot exactly the same as that of the inlet. The closure of the circuit (as previously mentioned) takes place directly on the liquid to be treated in order to have a degree of ionization as high as possible, located a few cm from the free surface itself.

The wastewater is fed to the reactor which preferentially consists of a rectangular tank with a narrow and long shape, with ionized air inlet from the long side, in order to reduce the distance between the inlet and outlet of the water as much as possible. air and thus maintain a high speed. Furthermore, at regular intervals, the wastewater is stirred for a certain time in order to maintain the uniformity of the ammonia concentration.

In the continuous configuration (figure 2) the process is carried out by connecting two or more reactors in series.

In this case, the ionization system can consist of the charging bars described previously placed a few centimeters from the free surface of the wastewater. The charging bar system is preferably adopted.

In practice, a charging bar is positioned on each tank along the side of the air inlet / inlet (or passage) with the closure of the circuit (also in this case) in the liquid itself.

The charging bar has proved to be more effective than the network and also has the advantage of allowing both extraction systems (continuous discontinuous) to regulate the real power required by means of an electronic system as a function of the ammonia extraction speed.

In the continuous process (figure 2), the wastewater is pumped into the upper part of a special reactor with overlapping rectangular tanks. The tanks containing the wastewater alternate with the ammonia absorption tanks containing water acidulated by acids of different nature (organic or inorganic).

The gaseous stream leaving a first tank, once the ammonia has been purified, is introduced into the next tank, increasing the speed of nitrogen removal from the wastewater compared to that of the process conducted in a single reactor (with the same quantity of treated wastewater) and at the same time decreasing the specific energy consumption of the process.

The number of tanks and their dimensions are chosen by the expert in the field in such a way as to obtain an optimal â € œevaporation surface / volume of wastewaterâ € ratio to maximize ammonia extraction efficiency and minimize energy costs and of chemical additives to be used, also depending on the specific chemical composition of the wastewater.

Figure 3 exemplifies a possible embodiment of a tank for the treatment of wastewater (sewage tank) and of a tank for ammonia absorption (ammonia absorption tank).

The reactors can be made of plastic or composite material, stainless steel, alloy steel with anti-corrosion treatment or waterproofed reinforced concrete.

The energy and material savings (chemical additives) allowed by the process according to the present invention is even more evident if we consider that the processes according to the state of the art provide for the insufflation of considerable masses of clean air into the wastewater, which they must necessarily be purified before they can be released into the atmosphere under the conditions envisaged by environmental regulations, with a decidedly high energy and material cost.

The recovery of the gaseous ammonia in phase c) of the process according to the present invention can be carried out with different techniques. For example, the gaseous stream coming from phase b) can be bubbled in an acid solution (neutralization). Alternatively, the gaseous stream is sent to a scrubber which uses a similar acid solution as a washing liquid.

In the discontinuous process, the washing system consists (diagram figure 1) of a tank divided by one or more sectors containing water acidified with acid and / or mixtures of acids (both organic and inorganic). The gaseous stream containing ammonia after having undergone a first washing in one compartment is sent to a second compartment for further washing. The division into sectors allows to obtain, according to the acid used in the different compartments, different types of ammonium salts as a final co-product.

The water that after the absorption of ammonia has a pH between 7.0 â € “7.5, is sent to a collection tank where the pH is brought to values between 6.0 â € “6.5 by adding acids and sent again to the washing tank.

In an embodiment of the invention, the gaseous stream (air) coming from phase b) of the discontinuous process, is introduced perpendicularly into the absorption liquid with a variable head of 1Ã · 3 cm, so as to allow intimate contact with the acid solution that captures the ammonia and neutralizes it, forming the corresponding ammonium salt, limiting the pressure drops as much as possible to avoid reducing the flow rate to too low values which would stop the process.

The diffusion of the gaseous flow (air) inside the absorption solution is obtained by distributing the flow along the entire width of the tank by means of tubes having a diameter ranging from 1 to 5 cm such as not to generate a reduction in the total section, compared to the initial inlet diameter (the total section of the main duct is equal to the sum of the individual sections of the inlet pipes on the liquid).

According to the needs (and therefore according to the length of the absorption tank) it is possible to carry out 2 or more washes of the gaseous stream.

In another embodiment of the invention which relates to the continuous extraction system, the ammonia absorption tanks which preferentially develop vertically, are interspersed with the tanks containing the wastewater to be treated. The basins, as shown in the diagram in figure 2, can be slightly inclined in the opposite way from one to the next. This allows any sediment to be discharged and obstructions in the connecting channels between one tank and another are avoided.

In this case the gaseous flow (air) is introduced from the bottom into the first tank of the wastewater passing on the free surface of the same, where it is ionized by the charging bar located about 15-20 cm on the air inlet; in the next absorption tank, the air coming out of the first wastewater tank is introduced on the long side parallel to the absorption liquid (the diffusion system is practically identical to the discontinuous case) and about 1Ã · 2 cm below the free surface, to then be collected from the opposite side of the tank and sent to the next wastewater tank, where it is introduced from below to then pass on the free surface of the same and finally be ionized by the charging bar, as previously described. The air flow from the wastewater tank can continue towards a further absorption tank until the extraction is complete.

The wastewater which, as mentioned, is introduced from the top of the reactor, flows downwards, also helped by gravity. It is conceivable that it is possible to create approximately a system with 5 extraction tanks containing the wastewater, each connected to a corresponding absorption tank.

The difference between the continuous system and the discontinuous system lies in the fact that by operating continuously, the efficiency of the ionization of the air is much greater, as it is generated directly on the wastewater and therefore is not affected by the length of the path during which exhausts the effect of ionization.

According to the present invention, for the absorption of ammonia it is preferable to use an aqueous solution of an inorganic acid selected from sulfuric acid (H2SO4), phosphoric (H3PO4), nitric (HNO3), carbonic (H2CO3), hydrochloric (HCl ) and / or their mixtures or of an organic acid such as citric, acetic, sulfamic acid.

The resulting solution at the end of the ammonia recovery operation (bubbled or saturated washing solution) is an aqueous solution containing one or more ammonium salts, depending on the mixture of acids used for neutralization (for example, using H2SO4 you will have (NH4) 2SO4, using HNO3 you will have NH4NO3, using H2CO3 you will obtain ammonium carbonate and / or bicarbonate). The solution of ammonium salts can be conveniently used as a fertilizer. Typically, the concentration of ammonium salt varies (depending on the type of acid used) from 150 to 350 g / l and the quantity of solution obtainable from 1500 to 2000 liters per day, for example carrying out the process according to the present invention in a farm of 10,000 pigs.

To recover the ammonia in phase c) it is also possible to make the gaseous stream exiting the reactor bubble into water and / or wash it in water washing towers. The product of this recovery is an ammonium hydroxide solution.

According to a further alternative, it is possible to condense ammonia through condensation systems (eg condensation towers) obtaining anhydrous ammonia.

It is also possible to foresee the combustion of the gas stream leaving the reactor and containing ammonia. The current can be used either as it is or mixed with other fuels.

Preferably, a fraction of this stream is sent for combustion and the remaining fraction is used as a reagent to neutralize the nitrogen oxides (NOx) produced by the combustion of the first fraction.

The ammonia recovered in phase c) is also possible to subject the gaseous stream leaving the reactor to a process of ammonia dissociation with the formation of H2 and N2, then storing the H2 in an appropriate way, for example by using suitable compounds solid state.

A further alternative for the recovery of ammonia extracted from the wastewater is that of liquefaction. By compressing the gaseous stream containing ammonia, after dehydration and using suitable conditions of temperature and pressure, it is in fact possible to obtain the separation of ammonia in liquid form.

To dehydrate the gas stream, CaO or MgO and / or their solid mixtures can be used. For example, by carrying out the process according to the present invention in a farm of 10,000 pigs, it is possible to obtain about 150 ÷ 200 Kg / day of liquid ammonia.

Unlike neutralization, the recovery of ammonia through its liquefaction makes it possible to obtain a product of high commercial value, decidedly higher than that of liquid fertilizer and / or ammonium hydroxide, as liquid ammonia it can be used as a raw material in other industrial processes.

The process according to the present invention has several advantages with respect to the processes for reducing the nitrogen content in zootechnical manure known to the state of the art.

It allows, first of all, to obtain a further increase in the overall efficiency of nitrogen extraction from wastewater. The obtainment of treated wastewater containing a smaller quantity of nitrogen makes it possible to spread a greater quantity of the same on agricultural land qualified as â € œzones vulnerable to nitratesâ €. Typically, ammonia nitrogen in a manure of porcine origin amounts to about 50% of the total nitrogen present.

Furthermore, the use of a low pressure ionized air flow over the free surface of the wastewater makes it possible to obtain higher wastewater treatment speeds in the face of low energy consumption required to generate this flow.

These advantages, together with the fact that the realization of the equipment for the implementation of the process involves modest costs and its operation can be completely automated, make the process according to the present invention particularly suitable for being industrially exploited in the field of breeding of pigs, cattle, poultry and other animals.

Possible embodiments of the process according to the present invention are shown in the diagrams of figures 1, 2 and 3, which respectively illustrate the discontinuous extraction process, the continuous extraction process and two examples of realization of the tanks for the treatment of wastewater and the Absorption of ammonia.

The following embodiments are provided for illustrative purposes only of the present invention and must not be construed as limiting the scope of protection defined by the attached claims.

Example 1

4000 liters of wastewater from pig farms and containing 4500 mg / l of nitrogen in ammonia form, (equal to 68% of the total nitrogen of the wastewater), corresponding to a total quantity of 18 kg of nitrogen in ammonia form, Ã It was treated for 1.5 hours in a single reactor plant. 40 kg of a mixture of CaO and MgO in granules were added to the wastewater until the pH was brought to a value of 11.2. The pressure of the gas stream introduced was equal to 5 mbar and the flow rate equal to 4000 Nm <3> / h.

The air introduced from the long side of the reactor was ionized by means of an electrostatic generator (mod. 50 mA- 40KV dc of the Martignoni Elettrotecnica srl company) and relative ionizing bar placed on the long side of the air inlet, and with closure of the circuit on the wastewater itself.

The flow rate of the wastewater recirculation has been set at 800 liters / hour. The gaseous stream containing ammonia exiting the reactor was passed through a two-stage washing system placed above the extraction tank itself, and more precisely, introduced 2Ã · 3 cm below the free surface of the acid solution (having volume of 500 liters) of H2SO4 at 9.14% by weight.

At the end of the treatment, the ammonium concentration in the wastewater was about 300 mg / l; this means that 4200 mg / l of ammonium were extracted from the wastewater, which gave rise to 500 liters of a solution of 12.5% by weight of ammonium sulphate.

Claims (17)

CLAIMS 1. Extraction process of ammonia nitrogen from liquid wastewater, including the following operational phases: a) bringing the wastewater into contact with a basifying agent in a reactor; b) generating an ionized gaseous flow over the wastewater and in particular over the free surface of the wastewater and drawing a gaseous stream comprising ammonia out of the reactor; c) recovering the ammonia from the gaseous stream leaving phase b) with the formation of a purified gaseous stream. 2. Process according to claim 1 wherein the gaseous flow in step b) is generated by means of an introduced gaseous stream, preferably constituted by one or more gases and / or vapors selected from the group comprising air, nitrogen and argon. Process according to any one of the preceding claims in which the gaseous flow introduced has a pressure ranging from -100 to 100 mbar, preferably ranging from -10 to 10 mbar. 4. Process according to any one of the preceding claims in which the basifying agent is added in such quantity as to bring the pH to a value ranging from 7.2 to 13, preferably ranging from 10.0 to 13. 5. Process according to any one of the preceding claims in which the basifying agent is selected from CaO, MgO and / or their mixtures or from aqueous solutions of Ca (OH) 2, Mg (OH) 2 and / or their mixtures, preferably It consists of a CaO / MgO mixture. Process according to any one of the preceding claims in which the purified gaseous stream leaving the reactor in step (c) is totally recirculated as a gaseous stream fed into step (b). 7. Process according to any one of the preceding claims in which the wastewater is kept agitated in the reactor by means of paddle stirrers, or by the application of ultrasounds, or by insufflation of the gaseous flow used directly in the body of the wastewater itself, or by means of insufflation of air captured from the outside, or by extracting a part of said wastewater from the bottom of the reactor and re-introducing it in a second point of the reactor above the wastewater head. Process according to any one of the preceding claims in which the ionized gaseous flow is generated by a fan which sends the flow to an ionization system. 9. Process according to any one of the preceding claims in which the flow rate of the ionized gaseous flow varies from 1500 to 2000 Nm <3> / h for each m <3> / h of wastewater to be treated. 10. Process according to claims 8 or 9 in which the ionization system consists of charge generators with both negative and positive polarity, with adjustable voltage from 0Ã · 40 KV and 50mA (max) in direct current, which transfer the voltage generated to the bars. 11. Process according to claim 10, in which the bars of the ionization system are placed at about 10-20 cm from the free surface of the wastewater while the closure of the circuit is carried out directly in the liquid itself. 12. Process according to any one of the preceding claims characterized by the fact that it is carried out simultaneously in two or more reactors or is carried out in continuous mode by connecting two or more reactors in series. 13. Process according to claim 12, wherein the purified gaseous stream leaving a first reactor is used as a gaseous stream fed into the process conducted in the subsequent reactor. 14. Process according to any one of the preceding claims in which the recovery of ammonia in phase c) is carried out by passing the gaseous stream coming from phase b) on the free surface of an acid solution or by passing the gaseous current coming from phase b) on a system consisting of a tank divided by one or more sectors containing water acidified with acid and / or mixtures of acids, or by introducing perpendicularly the gaseous stream coming from phase b) into the acidified water with a variable head of 1Ã 3 cm. 15. Process according to any one of the preceding claims in which two or more ammonia recovery processes are carried out. 16. Process according to any one of the preceding claims, in which the ammonia recovery in phase c) is carried out by bubbling the gaseous stream exiting from phase b) into water and / or washing it in water washing towers, or by condensation of the gaseous stream exiting from phase b), or by combustion of the gaseous stream exiting from phase b), or by liquefaction of the gaseous stream exiting from phase b, after dehydration. 17. Process according to any one of the preceding claims in which part of the treated wastewater is used to pre-basify the wastewater to be treated.