The present invention regards a device for concentrating liquids, in particular for concentrating liquid wastes of various types and sources, including saline solutions deriving from industrial processes, such as for example from the fabric dying process, liquid manure coming from animal rearing farms and especially liquids seeping through from landfills.

Prior art

As known, municipal solid waste (MSW) is often gathered in landfills, which are substantially made up of a large basin, covered by a layer of waterproof material, on which the collected waste is heaped. The waste mass behaves like a biochemical reactor, in which anaerobic bacteria consume the organic components present in the waste essentially producing biogas (methane in particular) and water. The water generated by these fermentation chemical reactions accumulates at the bottom of the basin, alongside rainwater which seeps through the waste mass. This water mass is conventionally referred to as leachate and it contains highly pollutant substances deriving from the decomposition of the organic and non-organic parts of the waste. Basically, the formation of the leachate is the direct consequence of the decomposition phenomena of the storage substances in the landfill, associated to the filtration and leaching phenomena which occur in the waste mass. The hazard- ousness of the leachate arises not only from the high concentration of pollutant substances present therein, but above all from the non-homogeneity thereof. Thus, potential diffusion of the leachate into the soil could permanently harm the water tables.

In order to avert this risk, it is provided for that the leachate be removed and treated periodically. This treatment is not generally meant for eliminating the pollutant substances, which are however present in the landfill waste, but rather reducing water accumulation and thus the risk that the water carries the pollutant matter towards the water table. To this end, the leachate is thus collected using suitable wells obtained in the landfill and transported and transferred to plants for treating polluted water approved and authorised to receive this kind of pollutant.

In some cases, the leachate collected in the landfill is subjected to an evaporation process, so as to eliminate water alone and obtain a pollutant concentrate that can be recycled in the landfill once again or that can be transferred to waste water purification plants authorised to collect, but at lower volumes. Vacuum heat concentration, for example by means of multiflash evaporators, is one of the most common techniques for concentrating leachate, just like most of the liquid waste coming from industrial and animal farming plants. This technique essentially consists in artificially evaporating the water contained in the solution, by heating it using the heat energy generated by noble fuel and in vacuum tanks, so as to lower the water evaporation point. Though efficient, this technique reveals various economic and environmental challenges. From an economic point of view, these plants have a rather high installation cost, require constant monitoring by qualified personnel when running and, above all, they entail considerable expenditure when it comes to procurement of the fuel required for producing the heat energy. From an environmental point of view, the heating of water in these processes can reach temperature values that cause the evaporation of some of the pollutant substances present in the solution, the aforementioned pollutant substances being released into the atmosphere or requiring extra and expensive filtering devices. Furthermore, in the case of the leachate, the concentrate obtained using these processes could transform into an extremely harmful gel if recycled in the landfill.

A concentration technique that enables attaining the same object by exploiting the air enthalpy energy was proposed with the aim of overcoming these problems. This technique essentially consists in exposing the liquid to be concentrated to contact with large amounts of ambient air, so as to reduce water through the natural evaporation phenomenon. Natural evaporation is a process according to which, at constant enthalpy, the air unsaturated of humidity absorbs water and thus cools and moves towards the complete state of saturation. As a function of its enthalpy, the ambient air tends to spontaneously reach the saturation equilibrium, transforming the water with which it is at contact into water vapour. This causes an increase of the relative humidity of the air, which tends to saturate, and a reduction of the water content present in the solution, thus increasing the concentration thereof. The total amount of water that can evaporate obviously depends on the flow rate of the air, the temperature thereof and the relative humidity thereof.

Thus, in order to efficiently exploit this physical phenomenon there arises the need to increase air exchange and contact surface between the ambient air and the liquid to be concentrated as much as possible. Regarding this, the technique in question provides for spraying the liquid to be concentrated on special evaporation walls made up of polymeric mesh panels with honeycomb structure, through which a natural or mechanical air current is made to pass. On these evaporation walls, the liquid lies in form of many minute droplets globally defining a very large surface for contact with air. At the same time, the evaporation walls offer very low resistance to the air motion, thus efficiently enabling the continuous exchange thereof. Thanks to this solution, some of the water contained in the liquid sprayed on the evaporation walls is transferred to the air current in form of vapour, while the residual concentrate is collected in a small vat arranged at the base of the evaporation walls, so as to be sprayed thereon once again. These evaporation cycles are repeated several times, until in the vat there is collected a sufficiently concentrated liquid, which basically still contains all pollutants present in the initial leachate. With respect to the heat-concentration techniques, besides very low investment costs the natural evaporation technique outlined above has the advantage of requiring very low management costs, given that the evaporation plant needs little monitoring and very sporadic maintenance. In addition, the plant requires close to zero electrical energy to run in case of natural ventilation, and very low electrical energy even in case of mechanical ventilation. Another major advantage of the natural evaporation technique lies in that the evaporation is obtained at ambient temperature. Thus, besides reducing energy consumption, this normally does not allow the pollutant substances present in the liquids to be concentrated to move to the gaseous state. Other advantages lie in the fact that the operating of the plant is quite simplified in that it can be remote-operated and it does not require the presence of manpower. Conveyed to the plant directly, the leachate must not be transferred to the purification plants using trucks, which - besides producing atmospheric pollution through their emissions - can also be a source of risk related to pouring the leachate. Lastly, the operation of the plant is basically insensitive to variations as concerns the composition of the leachate.

However, even the natural evaporation technique reveals some drawbacks, which mainly arise when the temperature of the air which touches the evaporation walls is rather low. The capacity of the air to absorb humidity actually inversely proportionally depends on its temperature and on its relative humidity and thus the natural evaporation process may have low or no efficiency due to the relatively low temperatures. Furthermore, the natural evaporation of water always entails a simultaneous reduction of air temperature, which tends to move from the so-called dry-bulb temperature to the so-called wet- bulb temperature. Thus, if the initial air temperature is in the order of a few degrees (e.g. below 3°C), the further cooling caused by the evaporation process could bring it to below the water solidification temperature. In this context, the water present in liquid sprayed on the evaporation walls tends to freeze, thus completely jeopardising the operation of the plant which must thus be shut down.

As easily observable, the problems outlined above are even more sensitive during winter, which actually marks the period of the year with highest production of leachate, as observable in the chart of figure 1 . Thus, this concurrence of negative factors requires having evaporation plants provided with leachate collection vats with considerable capacity, thus entailing hefty resources both in terms of costs and space.

Another drawback of the evaporation plants described above lies in the fact that the concentrated liquid obtained at the outlet of the concentrator device is not always easy to dispose. In particular, where possible, such liquid can be recycled in the landfill, but in any other case it must be transferred to waste water purification plants authorised to collect it, with ensuing increase of processing costs as well as making the landfill dependent on third parties even after the closure thereof.

Summary of the invention

In light of the above, one of the objects of the present invention is to overcome the aforementioned drawbacks of the prior art through a solution that is simple, rational and inexpensive.

These objects are attained by the characteristics of the invention, which are outlined in the independent claims. The dependent claims outline preferred and/or particularly advantageous aspects of the invention.

In particular, an embodiment of the present invention provides a device for concentrating a liquid, in particular landfill leachate, which comprises:

- a vat for collecting the liquid to be concentrated,

- at least one evaporation wall made of a mesh with honeycomb structure exposed to air,

- a hydraulic circuit suitable to draw the liquid from the collecting vat and spray it against the evaporation wall, and

- at least one fan positioned so as to be suitable to generate an airflow that passes through the evaporation wall, and

- an adjustment apparatus for regulating the flow rate (e.g. volumetric flow rate) of the airflow which passes through the evaporation wall.

Thanks to this solution, varying the flow rate of the airflow that passes through the evaporation wall, the absolute amount of evaporated water (i.e. the evaporation capacity of the device) can be advantageously increased or reduced in a manner substantially independent from the air temperature and/or humidity conditions. In other words, if the capacity of the air to absorb humidity is low (e.g. low temperature and/or high relative humidity), it is advantageously possible to cause the evaporation of a considerable amount of water from the liquid to be concentrated by increasing the volumetric flow rate of the airflow that passes through the evaporation wall. Vice versa, if the capacity of the air to absorb humidity is high (e.g. high temperature and/or low relative humidity), it is advantageously possible to cause the evaporation of the same amount of water from the liquid to be concentrated even with a low volumetric flow rate of the airflow that passes through the evaporation wall. Thus, it is generally possible to maintain the performance of the concentrator device almost constant even in cases where the conditions of the air change over time.

Thus, this greater uniformity of performance of the concentrator device enables obtaining collecting vats with smaller dimensions with respect to the current ones with the ensuing saving in terms of costs related to installation, management and occupied spaces.

According to an aspect of the invention, the aforementioned apparatus for regulating the airflow rate can be configured to vary the rotation speed of the fan.

This aspect of the invention provides an extremely simple and rational solution for varying the flow rate of the airflow that passes through the evaporation wall.

According to another aspect of the invention, said adjustment apparatus can be configured to regulate the flow rate of the airflow that passes through the evaporation wall based on at least one operative parameter of the device. Thus, the regulation of the airflow rate may occur in a substantially automatic manner, without requiring the direct intervention of an operator and thus without requiring manpower.

In particular, an aspect of the invention provides for that said operating parameter can be the period of the year in which the device is running, for example the day, the week or month of the calendar.

Thus, the flow rate of the airflow that passes through the evaporation wall can for example be increased on winter days, weeks or months, when the capacity of the air to absorb humidity is generally rather low, thus guaranteeing suitable productivity of the concentrator device to meet needs arising from the higher production of leachate. Vice versa, the flow rate of the airflow that passes through the evaporation wall can for example be reduced on summer days, weeks or months, when the capacity of the air to absorb humidity is generally rather high, thus reducing energy consumption required to operate the concentrator device. Regarding this, it should be borne in mind that the electrical power absorbed by a fan is normally proportional to the cu- be of the generated flow rate.

Another aspect of the invention provides for that the indicative parameter, based on which the flow rate of the airflow that passes through the evaporation wall is regulated, can be the air temperature and/or relative humidity of the air.

Thus, it is advantageously possible to obtain an "accurate" regulation of the production capacity of the concentrator device, capable of promptly meeting needs arising from any variations of the air conditions that may occur in relatively short periods of time, for example in the course of the same day.

According to another aspect of the invention, the indicative parameter for the regulation of the flow rate of the airflow that passes through the evaporation wall can be the amount (for example the volume) of liquid to be concentrated which is contained in the collecting vat.

This enables obtaining a regulation of the airflow rate based on the amount of liquid to be concentrated not only produced, but also accumulated, thus implicitly taking all the factors outlined above into account. Basically, the flow rate of the air that passes through the evaporation wall can be increased every time the amount of liquid accumulated in the collecting vat is high, this generally occurring in winter and when the capacity of the air to absorb humidity is rather low, or whenever there arises the need to concentrate high amounts of leachate. Vice versa, the flow rate of the air that passes through the evaporation wall can be reduced every time the amount of liquid accumulated in the collecting vat is low, this generally occurring in summer and when the capacity of the air to absorb humidity is rather high, or whenever there is no need to concentrate large amounts of leachate.

In addition, another embodiment of the present invention provides a plant for concentrating a liquid, typically landfill leachate, which comprises:

- the concentrator device described previously,

- a concentration vat suitable to receive the concentrated liquid flowing out from the device,

- a covering arranged to surmount said concentration vat, and

- at least one fan suitable to generate a horizontal airflow in the space comprised between said covering and the free surface of the liquid contained in the concentration vat.

Thanks to this solution, the concentration vat, the covering and the fan define a final concentrator which, applying the same isenthalpic evaporation principle, is capable of treating the liquid previously concentrated by the evaporation walls up to turning it into a semi-solid substance (e.g. sludge) which, as such, is much easier to sell and store.

According to an aspect of the invention, the maximum depth of the concentration vat is not greater than 0.2 m.

Thanks to this solution, the concentrated liquid is arranged in the concentration vat as a wide and shallow liquid mass, so as to facilitate the evaporation process.

According to an aspect of the invention, the bottom of the concentration vat is inclined.

Thus, the solid obtained from the evaporation of the liquid to be concentrated accumulates in pre-established areas of the concentration vat, thus facilitating the subsequent removal thereof.

According to another aspect of the invention, the plant may comprise a plurality of vertical partitions extending from the covering of the collecting vat downwards and arranged in mutual succession along the direction of the airflow generated by the fan.

Thanks to this solution, the airflow generated by the fan is forced to follow a sinuous path above the free surface of the liquid contained in the concentration vat, facilitating the evaporation of the water.

Another aspect of the invention provides for that the plant may also comprise a heat exchanger suitable to heat the bottom of the concentration vat.

This advantageously facilitates the evaporation process of the water present in the liquid to be concentrated.

A further aspect of the invention provides for that the plant may comprise a scraper member that can be driven in motion to scrape the bottom of the concentration vat.

This solution enables facilitating the operations of removing the sludge ac- cumulated at the bottom of the vat.

According to an aspect of the invention, at least the concentration vat, the covering and the fan (i.e. the final concentrator) can be replicated and superimposed and installed on board a vehicle, for example on a transportable trailer.

Thanks to this solution, the last evaporation step is made extremely flexible. Another embodiment of the invention obviously also provides for a method for concentrating a liquid which, coherently with the device described previously, comprises the steps of:

- providing the liquid to be concentrated in a collecting vat,

- drawing the liquid to be concentrated from said collecting vat and spraying it on at least one evaporation wall made of a mesh with honeycomb structure exposed to air,

- generating an airflow which passes through the evaporation wall,

- regulating the flow rate of the airflow which passes through the evaporation wall,

This embodiment substantially obtains the same effects and advantages described previously, in particular that of increasing or reducing the absolute amount of water that is evaporated, in a manner substantially independent from the air temperature and/or humidity, thus meeting any needs arising from seasonal variations of the liquid to be concentrated.

Obviously, all aspects of the invention that have already been described regarding the device or regarding the plant are directly applicable to the method too.

In particular, an aspect of the method provides for that the regulation of the flow rate of the airflow can be carried out based on an operative parameter selected from among the group constituted by: the period of the year in which the device is operating, the air temperature, the air relative humidity and the amount of liquid to be concentrated contained in the collecting vat.

Another aspect provides for that the method may comprise the further steps of:

- transferring the concentrated liquid coming from the evaporation wall into a concentration vat,

- generating a horizontal airflow which touches the free surface of the liquid contained in the concentration vat.

Brief description of the drawings

Further characteristics and advantages of the invention will be apparent from reading the following description - provided by way of non-limiting example - with reference to the figures illustrated in the attached drawings.

Figure 1 is a chart illustrating the variation in the production of landfill leachate (curve P) and the evaporation capacity of an evaporator device of the prior art (curve Q) in the course of the months of the year.

Figure 2 is the diagram of a plant for treating leachate coming from landfills. Figure 3 is a plan view of a support base for a concentrator device suitable to be used in the plant of figure 2.

Figure 4 is section IV-IV of figure 3.

Figure 5 is the plan view of the concentrator device suitable to be mounted on the support base of figure 3, in which some elements have been concealed for a better view of the underlying evaporation walls.

Figure 6 is section VI-VI of figure 5, in which the previously concealed parts are also shown.

Figure 7 is a chart illustrating the variation in the production of landfill leachate (curve P) and the evaporation capacity of an evaporator device according to the invention (curve L) in the course of the months of the year.

Figure 8 is a simplified diagram of a final concentrator which can be added to the plant of figure 2.

Detailed description

The aforementioned figures show a plant 100 for treating liquids, in particular for treating landfill leachate. The plant 100 may comprise, as shown in figure 2, a first collecting vat 105, which is used for progressively accumulating the leachate as it is removed from the landfill. Basically, it serves as an accumulation reservoir which enables supplying the subsequent devices of the plant 100 in a controlled and most constant possible fashion.

In the collecting vat 105 there may be installed a pump system 1 10, for ex- ample one or more submerged pumps, which are suitable to lift the leachate and supply it in a subsequent reception vat 1 15. This pump system 1 10 may be controlled by special level switches (not shown), for example level switches of the floating bulb type, which can be arranged in the collecting vat 105 and/or in the reception vat 1 15.

A further pump system 120, for example one or more volumetric pumps, which are suitable to lift the leachate and supply it to an oxidation vat 125 is associated to the collecting vat 1 15. This pump system 120 may also be controlled by special level switches (not shown), for example level switches of the floating bulb type, which can be arranged in the reception vat 1 15 and/or in the oxidation vat 125.

Submerged diffusers 130, which are connected to a suitable pneumatic system (not shown), for example to a plurality of pneumatic blowers for directly insufflating air into the leachate which is contained in the oxidation vat 125, are generally installed in the oxidation vat 125.

Thus, an aerobic digestion phenomenon with production of active sludge occurs in the oxidation vat 125.

The aerobic digestion mechanism may be summarised in a simplified manner as a phase in which the organic substances present in the leachate are metabolised by particular aerobic bacteria strains, i.e. bacteria which live in presence of dissolved oxygen, generating additional simpler biomass (commonly referred to as active sludge), carbon dioxide and water, according to the following simplified diagram:

OrganicMatter + 0 ₂ — ^{aerohlchactena ■} > NewBiomass + C0 ₂ + H ₂ 0 .

Actually, the information summarised in the diagram above is the combination of several concurrent processes, including adsorption, stripping, biodeg- radation and oxidation of non-stable compounds, which - together -contribute to the removal of the organic products present in the leachate.

In order to accelerate the implementation of the biological regime and optimise performance, in the oxidation vat 125 there may be inoculated a bacteria mixture, at an initial amount of 30÷50 g/m ³ (wherein m ³ refers to the volume of the vat) for activating the bacteria flora, and then settling - if neces- sary - at an amount of 5÷10 g/m ³ (wherein m ³ in this case refers to the volume of the inflowing liquid waste).

The dosage of this bacteria mixture can be carried out by means of a dosage pump (not shown), which can be controlled by a floating bulb level switch and whose dosage capacity can be set by an operator by acting on a control panel.

Given that the oxygenation of the leachate by insufflating air can cause the creation of considerable amounts of foam, the oxidation vat 125 can be provided with a further dosage pump (not shown), which is suitable to supply a special anti-foam product into the leachate. Also this dosage pump can be controlled by a floating bulb level switch and its dosage capacity can be set by an operator by acting on a control panel.

Inside the oxidation vat 125 there also occurs an important process for the deodorisation of the leachate, substantially consisting in inhibiting the volatilisation of the main odour releasing components contained in the leachate, in particular ammonia and sulphur-based compounds.

For example, ammoniacal nitrogen, which did not get into the biomass production cycle, must be nitrified, i.e. oxidised, as nitrogen salts, in form of nitrates (NO3), according to the following simplified reaction:

y^- + bacteria ^ ~ bacteria ^ ~

In order to obtain this step for the deodorisation of the leachate, it is generally required that the insufflation of air occurs under constant monitoring of the pH values and redox potential of the treated leachate, as well as under periodic monitoring of the present bacteria columns, for example through microscopic analysis.

In particular, the pH of the treated leachate must preferably be maintained basic. At the same time, the redox potential, which indicates the degree of oxidation (if positive) or reduction (if negative), must be maintained at positive values.

In order to control the redox potential, the operation of the blowers of the submerged diffusers 130 must be managed by an electronic unit 135, for example by a PLC, which is connected with at least one redox meter 140 hav- ing the measurement probe thereof submerged in the leachate contained in the oxidation vat 125. Thus, the electronic unit 135 may be programmed to receive the redox potential value provided by the redox meter 140 and for regulating the amount of air insufflated by the submerged diffusers 130, so as to maintain the redox potential of the leachate in a pre-set range of values, for example the ones mentioned above.

In order to control the pH value, the oxidation vat 125 can be further provided with a dosage pump 145 to add dosed amounts of acid solution, for example a sulphuric acid solution, to the leachate, and with a dosage pump 150 for adding dosed amount of basic substance, for example soda, to the leachate. The operation of these pumps 145 and 150 can also be managed by the electronic unit 135, by connecting with at least one pH meter 155 having the measurement probe thereof submerged in the leachate contained in the oxidation vat 125.

To this end, the electronic unit 135 can be programmed to receive the pH value provided by the pH meter 155 and for comparison thereof with the preset threshold values, for example the ones mentioned above. Should the pH value drop below the lower threshold value, the electronic unit 135 can activate the pump 150 to introduce a dosed amount of basic substance into the leachate. Vice versa, should the pH value exceed the higher threshold value, the electronic unit 135 can activate the pump 145 to introduce a dosed amount of acid solution into the leachate. In both cases, the dosage is carried out to compensate pH variation and bring it back to within the pre-set values. Thus, the aerated and deodorised leachate flowing out from the oxidation vat 125 passes by gravity, for example through an overflow pipe, to an oxidative sedimenter 160, in which the new biomass produced by means of the active sludge process is separated from the liquid (water).

In particular, the water/sludge mixture flows into the sedimenter 160 through a stilling cylinder and it is forced to traverse the cylinder in the reverse direction with respect to the outflow direction. This enables the sludge, whose specific weight is greater than that of water, to sediment. Furthermore, the sludge descending towards the bottom, simultaneously creates a biological filter, which - combined with the hydrodynamic action of water which tends to rise - contributes towards blocking and adsorbing the suspended particles. This enables obtaining a clear separation of the liquid part from the solid part and, as final result, the sludge accumulates at the bottom of the sedimenter 160 while the clarified supernatant is concentrated on the surface.

A pump system 165, for example one or more centrifuge pumps, which are suitable to discharge and move the sedimented biomass (sludge) away, can be associated to the sedimenter 160. This biomass can be partly returned and recycled in the oxidation vat 125, so as to maintain - therein - a desired concentration of volatile suspended solids (VSS), while the surplus amount of biomass is eliminated from the cycle and directly transferred to a vat 167 for collecting the concentrates.

This pump system 165 can be controlled by a PLC (not shown) which regulates the sedimentation stage, as a function of the actual operative parameters which can be set by an operator by acting on a special panel or the electric control panel. In particular, this PLC can regulate the sedimentation stage by varying the operating times of the pumps 165 as well as controlling one or more valves (not shown) which are designated to divert the biomass towards the collecting vat 167 or towards the oxidation vat 125,

The clarified liquid obtained by the sedimenter 160 is instead transferred to a recirculation vat 170, which is provided with a pump system 175, for example one or more centrifuge pumps of the submerged type, which can be controlled by floating bulb level switches and they are suitable to transfer the clarified liquid to a second collecting vat 180.

The collecting vat 180 can be made of concrete and it is provided with a further pump system 185, for example one or more pumps of the submerged type mounted on a floating structure, which can be controlled by a PLC (not illustrated) for transferring the clarified liquid to a service vat 250 of a concentrator device 200.

The collecting vat 180 substantially serves as an accumulation reservoir and it should have a volume such to enable to meet the needs arising during periods in which, due to climate reasons, the concentrator device 200 cannot operate or cannot evaporate an amount of water equivalent to the flow rate of the clarified waste water flowing out from the sedimenter 160.

As illustrated in figure 3, the concentrator device 200 may comprise a support base 205, which can be made of concrete. The support base 205 may be shaped to form a relatively slim body with rectangular-shaped base, which is provided with two juxtaposed and parallel longitudinal edges 210 and 215 and with two juxtaposed and parallel transversal edges 220 and 225.

As observable in figure 4, the support base 205 also has a lower face, which is substantially defined by a single flat surface 230 suitable to lie horizontally against the ground, and an opposite upper face comprising two flat surfaces, respectively 235 and 240, both being slightly inclined with respect to the lower surface 230. In particular, each of the upper surfaces 235 and 240 is inclined from the top towards the bottom, starting from a respective longitudinal edge 210 and 215 towards the centreline of the support base 205. Thus, the upper surfaces 235 and 240 are both slanted towards a channel 245, which is attained at the centre of the support base 205 and develops parallel to the longitudinal edges 210 and 215.

This central channel 245 is in turn inclined from the top towards the bottom starting from the transversal edge 220 towards the transversal edge 225, so as to terminate in the service vat 250 for the clarified liquid to be evaporated, which can be obtained as a single body with the support base 205 and can be buried at least partly.

As illustrated in figure 6, above the support base 205 there are mounted suitable support structures, for example made of metal material, which support two evaporation walls 255 and 260.

These evaporation walls 255 and 260 are oriented in a manner substantially parallel to the longitudinal edges 210 and 215 and they extend substantially over the entire length of the support base 205.

In particular, the evaporation walls 255 and 260 are positioned juxtaposed with respect to each other, each resting against a respective longitudinal edge 210 and 215 of the support base 205.

Thus, between the evaporation walls 255 and 260 there is internally defined a central corridor 265, which is closed at the bottom by the upper surfaces 235 and 240 of the support base 205.

Each of the evaporation walls 255 and 260 is also inclined from the top towards the bottom starting from the respective longitudinal edge 210 and 215 towards the centre of the support base 205, so that the aforementioned central corridor 265 has a tapered cross-section, substantially frusto-conical in this case, narrowing from the support base 205 towards the top part.

In particular, the inclination of the evaporation walls 255 and 260 is basically the same, so that they are arranged in a substantially mirror-like fashion with respect to a vertical plane passing through the centreline of the support base 205 and parallel to the longitudinal edges 210 and 215.

Each evaporation wall 255 and 260 can be obtained by a plurality of single evaporation panels, which for example can have an overall height of about 4 m, a width of about 50 cm and a thickness of about 30 cm. These evaporation panels are arranged adjacent and against each other in the direction of their width, up to obtaining an evaporation wall of the desired length.

The evaporation panels can be obtained using a mesh made of polymeric material, for example such as HDPE, whose pattern has dimensions such to be able to withhold the drops of a liquid with which it is to be sprayed. Said mesh is conveniently folded on itself, so as to confer the evaporation panels a honeycomb structure having a plurality of cells, for example with triangular cross-section, each of which defines an open duct which traverses the thickness of the evaporation panel. In other words, each evaporation panel has two flat and juxtaposed surfaces which respectively define an outer face A and an inner face B of the relative evaporation wall 255 and 260, and the honeycomb structure is such that the relative cells define open ducts which place the outer face A in communication with the inner face B, thus enabling the air to flow through between the external and the internal of the central corridor 265.

The top part of the central corridor 265 may be closed by an upper covering 267, on which there can be mounted one or more fans 270, three in this case (see figure 5). These fans 270 are arranged aligned with respect to each oth- er in the direction of the length of the central corridor 265 and they have rotors 275 suitable to rotate around vertical axis, so as to create a vacuum in the central corridor 265. This depression generates two mechanical air currents which, coming from opposite sides, pass through the two evaporation walls 255 and 260, converge into the central corridor 265 and are lastly discharged outside in vertical direction.

To each evaporation wall 255 and 260 there is associated a respective group of dispensing nozzles 280 and 285, which are connected by respective hydraulic circuits to a pump 295 (schematically represented in figure 2) suitable to draw the clarified liquid contained in the service vat 250. The pump 295 can for example be a centrifuge pump of the submerged type which is directly installed in the service vat 250. The dispensing nozzles 280 and 285 are arranged outside the central corridor 265 and distributed over the entire length of the concentrator device 200, so as to spray the liquid supplied by the pump 295 directly on the outer face A of the respective evaporation wall 255 and 260.

To each evaporation wall 255 and 260 there can also be associated a respective heat exchanger 300 and 305, which is suitable to be touched by the air current before the latter passes through the relative evaporation wall 255 and 260 to reach the central corridor 265. Each of these heat exchangers 300 and 305 can for example be made up of a substantially flat extension tube bundle, which is arranged parallel and adjacent to the outer face A of the respective evaporation wall 255 and 260, so as to define - therewith - an interspace in which the dispensing nozzles 280 and 285 are respectively received. In order to increase the heat/air exchange surface, said tube bundle may comprise a plurality of finned tubes.

Each heat exchanger 300 and 305 may be connected to a circuit in which there flows a carrier fluid (typically water) whose temperature is higher than the ambient air temperature and which, flowing through tubes of the tube bundle, is thus suitable to heat the air current before the latter passes through the evaporation wall 255 and 260.

This carrier fluid can be heated using the recovery heat produced by other apparatus or devices that can be associated to the plant 100, so that such heating does not considerably affect the energy consumption of the concentrator device 200.

Should the concentrator device 200 be installed in a landfill, the carrier fluid can be heated using part of the heat that is introduced by the torches that are commonly used to burn the biogas generated by the fermentation chemical reactions of the biological components of the waste.

Alternatively, the heat exchangers 300 and 305 can be directly connected to the system for cooling biogas-fuelled internal combustion engines which are at times installed at the landfill to generate electrical power, so that the coolant of these engines also serves as a carrier fluid and transfers part of the combustion heat to the air which passes through the heat exchangers 300 and 305.

In other embodiments, the carrier fluid circulating in the heat exchangers 300 and 305 could be heated using other heat sources, such as for example solar panels or any other source of renewable or non-renewable energy.

The concentrator device 200 may lastly comprise a demister 310, i.e. a permeable membrane made up of a more or less closely-knit wire mesh which is positioned in a manner such to intercept the air currents flowing downstream of the evaporation walls 255 and 260, or from inside the central corridor 265 towards the external, so as to facilitate the separation of the liquid drops possibly dragged by the gaseous current.

The demister 310 may for example be made of the same honeycomb- structured polymeric mesh also used for obtaining the evaporation walls 255 and 260.

In the illustrated example, the concentrator device 200 in particular comprises a plurality of demisters 310, each of which is directly inserted into the cylindrical casing of a relative fan 270 upstream of the rotor 275. In other embodiments, the demister 310 can be obtained in form of a single mesh, for example made of polymeric material which is directly positioned in the central corridor 265, for example fixed to the upper covering 267 and maintained stretched by means of a counterweight. The concentrator device 200 may possibly also comprise a tank 315 for containing an acid solution, for example a sulphuric acid solution, and a hydraulic circuit 320 suitable to draw said solution from the tank 315 and spray the aforementioned demister/s 310 therewith. Thus, the demister/s 310 also become suitable for reducing the odours that may possibly be released by the liquid during evaporation.

Said hydraulic circuit 320 may comprise a pump (not shown) suitable to supply a plurality of dispensing nozzles 325 which directly spray the acid solution on the demister/s 310. In other embodiments, the hydraulic circuit 320 could more simply comprise perforated gutters which are positioned above the demister/s 310 and which are supplied with the acid solution, so that the latter drips on the underlying demister/s 310 by gravity.

When the concentrator device 200 is running, the fans 270 are actuated, so as to generate the air currents that pass through the evaporation walls 255 and 260.

The clarified liquid present in the service vat 250 is supplied by the pump 295 to the dispensing nozzles 280 and 285, which spray it against the evaporation walls 255 e 260. Preferably, the spraying of the evaporation walls 255 and 260 occurs sequentially, i.e. only a given number of evaporation panels are sprayed at a time.

Following the spraying, the clarified liquid is withheld by the evaporation walls 255 and 260 in form of droplets, which thus have a large surface for contact with the ambient air. This large contact surface and the continuous air exchange, due to the currents that pass through the evaporation walls 255 and 260, enable the clarified liquid to undergo a natural evaporation process. In other words, the ambient air tends to spontaneously reach the saturation equilibrium, transforming the water with which it is at contact into water vapour. This causes an increase of the relative humidity of the air, which tends to saturate, and a reduction of the water content present in the clarified liquid, thus increasing the concentration thereof.

In order to facilitate this natural evaporation, especially in winter, the heat exchangers 300 and 305 may be actuated, so that the air currents can be heat- ed by a few degrees before passing through the evaporation walls 255 and 260.

Thus, the relative humidity of the air drops, thus simultaneously increasing its capacity to absorb humidity from the liquid sprayed on the evaporation walls 255 and 260. In addition, raising the initial temperature enables compensating the cooling to which the air is subjected during the evaporation of the water, thus hindering the formation of ice on the evaporation walls 255 and 260. The non-evaporated clarified liquid that remains on the evaporation walls 255 and 260, or that is withheld by the demister/s 310 upstream of the fans 270, then drips onto the support base 205 and slides on the inclined surfaces 235 and 240 towards the central channel 245, from which it once again converges into the service vat 250.

This cycle is repeated severally so that, as the water evaporates progressively, the liquid returning to the service vat 250 is increasingly more concentrated and thus its level in the service vat 250 drops progressively.

When the level of the liquid in the service vat 250 reaches a pre-set value, that can be measured by means of a level sensor, this means that such liquid has reached a desired concentration value.

At this point, the concentrated liquid left in the service vat 250 can be conveyed, for example by means of a pump 295 and a pneumatic control divert- er valve, to the collecting vat 167 and/or directly to a final concentrator described in detail hereinafter.

Thus, the entire liquid dripping from the evaporation walls 255 and 260 can be advantageously collected, maintaining a very compact and small structure.

It should be observed that the concentrator device 200 described above is substantially a modular structure that can be easily combined with other modular structures of the same type, so as to vary the potential of the entire plant 100 over time, thus attaining the variation of the amount of leachate to be treated (which may generally vary over the years) over time.

In addition, it should be pointed out that the collecting vats 105, 167 and 180 could be obtained arranged close to each other, one adjacent to the other, and that the structure/s with evaporation panels of the concentrator device/s 200 could be efficiently installed above said collecting vats 105, 167 and 180, so that the latter are closed (like it is often required by certifying bodies) thus simultaneously reducing the overall space occupied by the plant 100.

In order to enhance the operating efficiency of the concentrator device 200 it is provided for that the latter may comprise an adjustment apparatus, indicated in its entirety with 330 in figure 6, which is configured for regulating the flow rate (for example the volumetric flow rate) of the airflow that passes through the evaporation walls 255 and 260.

Thus, the adjustment apparatus 330 is capable of varying the evaporation capacity of the concentrator device 200, i.e. the amount (e.g. the mass) of water that the concentrator device 200 is capable of evaporating within the time unit, in a manner substantially independent from the inherent capacity of the air to absorb humidity.

In order to attain this object, the adjustment apparatus 330 can be configured to regulate the rotation speed of the fans 270. For example, the adjustment apparatus 330 may comprise an electronic control unit 335, for example a PLC, connected to one or more motors 340 (for example electric motors) suitable to actuate the fans 270 and configured to regulate the rotation speed of the aforementioned motors 335, thus also regulating the rotation speed of the fans 270.

In particular, the adjustment apparatus 330 (e.g. the electronic unit 335) may be configured to regulate the speed of the fan/s 270, and thus the flow rate of the airflow that passes through the evaporation walls 255 and 260, based on at least one characteristic operating parameter of the concentrator device 200.

For example, this characteristic parameter can be the amount (e.g. the volume or level) of the clarified leachate that is present in the collecting vat 180, which can be measured by means of a level sensor 345 associated to the collecting vat 180 and connected with the adjustment apparatus 330 (e.g. with the electronic unit 335).

In this context, the adjustment apparatus 330 (e.g. the electronic unit 335) can be configured to increase or reduce the rotation speed of the fans 270, and thus the flow rate of the airflow that passes through the evaporation walls 255 and 260, respectively following an increase or reduction of the amount of clarified leachate present in the collecting vat 180.

Thus, the flow rate of the airflow is automatically regulated as a function of the amount of leachate not just produced but also accumulated. Thus, it is implicitly also a function of the evaporation capacity of the air, thus its temperature and relative humidity.

In particular, the airflow rate that passes through the evaporation walls 255 and 260 is automatically increased each time the amount of liquid accumulated in the storage basin 180 is high, for example in winter when the capacity of the air to absorb humidity is rather low. Vice versa, the airflow rate that passes through the evaporation walls 255 and 260 is automatically reduced each time the amount of liquid accumulated in the storage basin 180 is low, for example in summer and when the capacity of the air to absorb humidity is rather high.

As illustrated in the chart of figure 7, this type of regulation of the flow rate of the airflow enables further enhancement of the homogeneity of the evaporation capacity of the concentrator device 200 over the entire year. Comparing the chart of figure 7 with that of figure 1 , it is actually observable that the surplus evaporation obtained in the hot months of the year, i.e. in summer, is considerably lower and counter-balanced by an increase of the evaporation capacity of the concentrator device 200 in the cold months, i.e. in winter. Another advantage of the possibility to regulate the flow rate of the airflow lies in the fact that, in the hot months, the low rotation speed of the fans 270 entails a reduction of the absorbed electrical power (the absorbed power varies proportionally to the cube of the flow rate), thus enabling further considerable saving in terms of management costs.

In spite of the example described above providing for regulating the flow rate of the airflow as a function of the amount of leachate present in the collecting vat 180, it cannot be ruled out that, in other embodiments, the control apparatus 330 (e.g. the electronic unit 335) can be configured to carry out such regulation directly based on the period of the year in which the device is running, for example based on the date, week or month of the calendar, which can be established by means of a time counter (e.g. a clock or calendar) implemented in the electronic unit 335.

Alternatively or additionally, the control apparatus 330 (e.g. the electronic unit 335) could be configured to regulate the flow rate of the airflow that passes through the evaporation walls 255 and 260 directly as a function of the air temperature and/or relative humidity of air, which can be measured using special sensors associated to the concentrator device 200 and connected with the electronic unit 335.

Regardless of the mode of regulation of the flow rate of the airflow, the liquid flowing out from the concentrator device 200 can be subsequently conveyed to a final concentrator 350 like the one schematically illustrated in figure 8. This final concentrator 350 may comprise a concentration vat 355 suitable to receive the concentrated liquid flowing out from the concentrator device 200, for example from the collecting vat 167 or directly from the service vat 250. The concentration vat 355 is generally dimensioned so that the depth thereof is lower than the base dimensions thereof, i.e. the length and width thereof. For example, the maximum depth of the concentration vat may be equal to or smaller than 0.2 m. Thus, the concentrated liquid coming from the concentrator device 200 lies in the concentration vat 355 as a large and shallow liquid mass, i.e. with a surface area of the free surface exposed to air that is much larger than the depth.

Furthermore, the concentration vat 355 may have an inclined bottom surface 360 with respect to the horizontal, for example by an angle comprised between 8 and 15 degrees so that the depth of the liquid mass accumulated therein varies gradually.

The final concentrator 350 further comprises a covering 365, which can for example be obtained as a horizontally-lying flat roof. The covering 365 is arranged in a manner such to surmount the concentration vat 355, so that, between the free surface of the liquid arranged in the concentration vat 355 and the covering 365, it defines an interspace 370 in which the ambient air can circulate.

In order to guarantee such circulation, the final concentrator 350 may comprise one or more fans 375, which are configured to generate an air current which flows horizontally, in the interspace 370, so as to touch the free surface of the liquid contained in the concentration vat 355, preferably starting from the shallower area towards the deeper area.

The final concentrator 350 may also comprise a plurality of partitions 380, which depart from the covering 365 and extend into the interspace 370 in a substantially vertical direction, up to moving the lower end thereof near the free surface of the liquid contained in the concentration vat 355, but without coming into contact therewith. In particular, the partitions 380 can be arranged parallel to each other and mutually spaced along the direction of flow of the airflow generated by the fan/s 375, so that said airflow is forced to follow the sinuous path above the liquid contained in the concentration vat 355. Obviously, the number of partitions 380, just like the dimensioning of the fan/s 375 that generate the airflow, may be contingently defined according to the specific treatment need.

Thus, applying the same isenthalpic evaporation principle, the final concentrator 350 is capable of treating the previously concentrated liquid of the concentrator device 200 up to turning it into a semi-solid matter (e.g. sludge). In order to improve and optimise this evaporation process, the final concentrator 350 may also comprise a heat exchanger 385, for example a tube bundle heat exchanger, which is arranged at the bottom surface 360 of the concentration vat 355 and it is suitable to heat the liquid contained therein.

To this end, the heat exchanger 385 may be connected to a circuit in which there circulates a carrier fluid (typically water) whose temperature is higher than that of the liquid contained in the concentration vat 355. This carrier fluid can be heated using the recovery heat generated by other apparatus or devices that can be associated to the plant 100. For example, the carrier fluid can be heated using part of the heat that is generated by the torches that are commonly used for burning the biogas generated by the fermentation chemical reactions and the biological components of the landfill waste, or the heat exchanger 380 can be directly connected to the cooling system of the biogas- fuelled internal combustion engines that are at times installed at the landfill to generate electrical power. In other embodiments, the carrier fluid circulating in the heat exchanger 300 could be heated using other heat sources, such as for example solar panels or any other source of renewable or non-renewable energy.

In any case, the semi-solid matter collected at the bottom of the concentration vat 355 at the end of the evaporation process, can be removed and once again stored in the landfill, without having to be transferred to other disposal plants.

In order to facilitate the removal of the obtained solid, the final concentrator 350 can further comprise a scraper member 390, which can be actuated using suitable driving means (not illustrated) so as to move at the bottom of the concentration vat 355.

In order to make the final evaporation step more flexible, the final concentrator 350 may be entirely installed on board a vehicle (not illustrated), for example on a transportable trailer.

Obviously, the treatment plant described above, may be subjected - by a man skilled in the art - to numerous technical/application modifications, without departing from the scope of protection of the invention as claimed below.