IT202100009617A1 - PROCEDURE FOR THE TREATMENT OF SLUDGE CONTAINING CHEMICAL POLLUTANT SUBSTANCES - Google Patents

Description

DESCRIPTION

Field of application

The present invention relates to the treatment of sludge, for example coming from waste water purification plants in the civil and/or industrial sector.

In particular, the present invention relates to a process for the treatment of sludge containing polluting chemical substances, for the recovery and thermal destruction of the latter, and to a plant for its execution.

Known art

The sludge coming from civil and/or industrial wastewater purification plants is commonly treated within sludge treatment lines, present in large-sized purification plants.

In contexts of this type, the sludge first of all undergoes a pre-thickening phase during which its dry matter content is increased; such an operation? commonly performed by decantation and elimination of waste water. The latter can be sent to the head of the purifier.

The sludge what? thickened can undergo possible passages of anaerobic digestion with possible production of biogas.

While the biogas cos? product can? be sent to a generator for the production of electricity or to a boiler, the digestate, i.e. the residual sludge from digestion, undergoes further treatments including a dehydration step until a dehydrated sludge is obtained.

Finally, the dehydrated mud can be recovered for agricultural use or pu? be subjected to a drying phase inside a dryer, obtaining dried sludge that can? be used as fuel, particularly in cement factories.

As known, in particular the sludge coming from some specific activities? industrial, waste water obtained by thickening of these, as well as? the liquids and condensates obtained from the above dehydration and drying operations have a high content of polluting chemical substances.

Among the polluting chemical substances often present in sludge from waste water purification plants in the civil and/or industrial sector there are certainly halogenated compounds and, in particular, perfluoroalkyl substances (PFAS).

With the term ?perfluoroalkyl substances? or PFAS a series of compounds is indicated having a perfluoroalkyl structure (linear or branched) with a length ranging from 4 to 14 carbon atoms and a terminal sulphonic or carboxyl functional group.

Developed since the late 1940s, fluorinated chemicals have found wide industrial applications and have been used for example as surfactants, carpet protectors, leather, textiles, flooring, food packaging, flame retardants, shampoos and toothpastes, photographic film and fire extinguishing foams.

The compounds more Known and studied are porfluorooctanesulphonic acid (PFOS) and perfluorooctanoic acid (PFOA):

Perfluoroalkyl substances have properties physicochemical details such as a contemporary hydro- and oleophobicity?, stability? chemical and biological and low surface tension.

These characteristics are attributable to the fluorine atoms of the alkyl chain which shield the carbon-carbon bonds from possible attacks.

The high energy of the carbon-fluorine bond makes these molecules particularly stable and inert both chemically and thermally: they are in fact resistant to hydrolysis, photolysis, oxidative processes and biodegradation and are not metabolised by living organisms. It follows that these compounds turn out to be extremely persistent substances as they are resistant to common degradative processes and the persistence? the greater the more long ? the chain of carbon atoms.

The health effects of these substances are under investigation: they are currently considered among the risk factors for a wide range of diseases. In particular, it is believed that PFAS intervene on the endocrine system, compromising growth and fertility, and that they are carcinogenic substances. It is also believed that a long exposure to these substances is related to the onset of tumors of the kidneys and testicles, the development of thyroid disease, pregnancy hypertension and ulcerative colitis. Some studies have hypothesized a relationship between fetal and gestational pathologies and contamination by these substances.

It is therefore particularly important to avoid incorrect disposal and in any case the release of these substances into the environment.

In fact, although the release of PFAS is also regulated in the context of waste water purification and sludge treatment plants in order to ensure that the concentration of these substances in the waste released into the environment is below risk values, the PFAS are however normally released into? the environment and cos? they easily penetrate groundwater, where they accumulate over time.

Therefore, through the water, in groundwater and surface water, they reach the fields and agricultural products, and therefore? Foods.

The European Union, with Directive 2006/122/EC, has introduced a series of restrictions on the marketing and use of PFAS in products and articles and with Directive 2013/39/EU, the European Union has included PFAS among the priority hazardous substances to be monitored in EU water bodies.

In 2006 the European project PERFORCE started? a survey to establish the presence of perfluoroderivatives in the waters and sediments of the major European rivers, from which it resulted? that the Po River had the highest concentrations of perfluorooctanoic acid (PFOA) among all European rivers.

A study conducted by IRSA-CNR] between May 2011 and February 2013 in the main Italian river basins shows? the presence of PFAS both in the surface waters of some rivers and in the drinking waters of certain aqueducts.

From the analysis of the results obtained, a worrying situation was highlighted, as regards drinking water, in some areas of the Brenta and Adige basins, particularly in the provinces of Padua, Vicenza and Verona.

Therefore, is the need particularly felt? to make available a process for the treatment of sludge, in which any solid, liquid or gaseous effluent is essentially free of polluting chemicals, so? to prevent their release into the environment and their subsequent accumulation in surface waters, groundwater and in general in all ecosystems.

In particular, it is required that this process can prevent the release of halogenated compounds and in particular of perfluoroalkyl substances (PFAS) into the environment.

Ultimately, in the light of the state of the art and of the drawbacks reported above, the problem at the basis of the present invention is that of making available a process for the treatment of sludge that is efficient from an energy and application point of view, effective in the destruction of the polluting chemical substances contained therein, as well as? a plant suitable for its execution.

Summary of the Invention

The aforementioned problem ? been resolved by making available a process for the treatment of sludge containing polluting chemical substances comprising the phases of:

a) drying sludge containing chemical polluting substances in a dryer at a temperature between 40°C and 300°C, obtaining a stream comprising dried sludge and vapours;

b) feeding the aforementioned flow to at least one cyclone, obtaining a solid precipitate comprising dried sludge containing polluting chemical substances and a vapor flow;

c) feeding the solid precipitate comprising dried sludge containing polluting chemical substances to a unit? of thermal valorisation and burning it at a temperature higher than or equal to 700?C, preferably higher than or equal to 850?C, obtaining ash and an exhaust gas, and at the same time,

feed the aforementioned flow of vapors to a wet scrubber, cos? to bring the vapor stream into contact with a washing liquid, obtaining a polluted washing liquid and a partially purified vapor stream;

d) feeding at least a part of this partially purified stream of vapors to a condensation column, obtaining a liquid condensate and a gaseous effluent stream.

According to the present invention, with the term ?sludge? does it mean a heterogeneous mixture in which the dispersing phase ? substantially water and the dispersed phase ? essentially constituted by solids, as well as? in general from organic and/or inorganic compounds insoluble in water.

The dispersing phase can also include a liquid oily component, possibly emulsified, as well as? air or, more? in general, gas.

Preferably, in accordance with the present invention, the sludge containing polluting chemical substances can come from waste water purification plants.

In particular, the sludge in question is residue deriving from wastewater purification processes, which may consist of domestic wastewater, i.e. wastewater from residential settlements and services and mainly deriving from human metabolism and human activities. domestic wastewater, industrial wastewater, i.e. any type of wastewater from buildings or installations where activities are carried out? commercial or for the production of goods, or urban wastewater deriving from the mixture of domestic wastewater, industrial wastewater and/or runoff rainwater conveyed into sewage networks.

Pi? in particular, the aforementioned muds in question may have preliminarily undergone pre-thickening, thickening, digestion and/or dehydration treatments plus? or less partial.

Preferably, the aforementioned muds in question can comprise a dry matter content of between 2% and 25%, plus? preferably between 15% and 20%, by weight on their total weight.

According to the present invention with the expression ?flow comprising dried sludge and vapours? it means a flow comprising dried sludge in powder form and vapours, in which these vapors are obtained by evaporation of the volatile component of the sludge in question during stage a) of drying.

The process according to the present invention therefore allows sludge containing chemical polluting substances to be dried, obtaining a flow comprising dried sludge and vapours; subsequently, the latter is fed into at least one cyclone, effectively breaking down the dried sludge and obtaining a solid precipitate comprising dried sludge containing chemical polluting substances which is finally thermally destroyed by combustion inside a unit? of thermal enhancement.

Furthermore, in an absolutely advantageous manner, from the combustion of this solid precipitate comprising dried sludge containing polluting chemical substances, ashes and exhaust gases are obtained, in which the ashes and the exhaust gas are suitably free from the polluting chemical substances originally contained in the sludge containing substances polluting chemicals fed to the dryer in the aforementioned phase a).

In fact, just the combustion at a temperature equal to or higher than 700?C allows the destruction of the pi? part of the polluting chemical substances originally present in the sludge in question, including particularly stable substances from a chemical point of view such as perfluoroalkyl substances (PFAS).

Advantageously, therefore, both the solid ashes obtained from combustion, essentially comprising the inorganic component mostly? of a metallic nature of the original sludge, both the exhaust gases cos? obtained are free from polluting chemical substances, are free from perfluoroalkyl substances (PFAS), such as perfluorooctanesulphonic acid (PFOS) and perfluorooctanoic acid (PFOA) or their derivatives.

Preferably, within the meaning of the present invention, such chemical pollutants may comprise halogenated compounds, wherein the halogenated compounds may more preferably be perfluoroalkyl substances (PFAS).

Furthermore, in a completely advantageous way, there is to say that the solid precipitate recovered during phase b) of cyclonic abatement allows to recover about 99% of the dry matter and most of the polluting chemical substances such as perfluoroalkyl substances (PFAS) contained in it.

Ultimately, the process according to the present invention not only particularly effective in the recovery of polluting chemical substances from sludge, but also provides for the destruction and thermal valorisation of these, allowing an advantage also from the point of view of consumption and sustainability? environment of the process itself.

Indeed, according to a modality? for carrying out the process of the present invention, the sole feeding of the aforementioned solid precipitate comprising dried sludge containing chemical polluting substances as fuel into the unit is sufficient. of thermal valorisation for the purpose of maintaining a temperature greater than or equal to 700?C and of the correct thermal destruction of the polluting chemical substances included therein.

For example, obtaining a solid precipitate comprising dried sludge having a calorific value of 3000 kcal/kg, feeding the solid precipitate alone? sufficient to guarantee, inside the unit? of thermal valorisation, its complete combustion and the thermal destruction of the polluting chemical substances included in it.

Preferably, the unit? of thermal valorisation pu? be in any case further fueled with fuel of mineral or vegetable origin, pi? preferably with biomass of vegetable origin, for example wood derivatives or wood chips.

Equally preferably, in step c) of the process according to the invention the solid precipitate comprising dried sludge containing chemical polluting substances can be burned at a temperature between 850?C and 1100?C.

According to a preferred embodiment of the process of the present invention, the aforementioned dryer is a turbo dryer.

Preferably, the turbo-dryer comprises a cylindrical tubular body having at least one inlet opening and at least one discharge opening, a heating jacket to bring the cylindrical tubular body to a predetermined temperature value, and a rotor, arranged in the tubular body cylindrical and comprising a shaft fitted with elements protruding radially from it, and passage a) of drying sludge containing chemical polluting substances comprises the following subpasses:

i) feeding a continuous flow of the aforementioned sludge into the turbo-dryer;

ii) centrifuge the sludge in question against the internal wall of the turbo-dryer, the rotor being set in rotation at a speed? greater than or equal to 100 rpm, preferably between 200 rpm and 1000 rpm, the sludge particles advancing in substantial contact with the internal wall of the turbo dryer towards the discharge opening, thus to form such a stream comprising dried sludge and vapors; And,

iii) discharge the flow comprising dried sludge and vapors from the discharge opening.

Advantageously, how will it come? more shown in detail in the detailed description, performing step a) inside a turbo dryer makes sludge drying more efficient. effective and fast, obtaining also? a stream comprising dried sludge and vapours, in which the solid particles of the dried sludge have an average size smaller than homogeneous.

Preferably, the drying step a) is carried out at atmospheric pressure.

In this way, the subsequent abatement step b) inside at least one cyclone can be in turn performed in a more? effective, allowing a substantially complete reduction of the solid particles of dried sludge included in the aforementioned flow fed to the cyclone.

Preferably, the cylindrical tubular body of the turbodryer is placed at a temperature between 40?C and 300?C, pi? preferably between 100?C and 280?C, by heating the inner wall through the heating jacket.

Quite preferably, inside the aforementioned dryer or turbo-dryer the flow of sludge containing polluting chemical substances so fed is placed in contact with a flow of air heated to a temperature between 40?C and 300?C, plus? preferably between 100?C and 280?C.

Quite preferably, this flow of heated air is fed to the turbo-dryer in co-current with the continuous flow of sludge containing polluting chemical substances.

Equally preferably, the heating jacket of the cylindrical tubular body of the turbo dryer is traveled by a heat exchange fluid, pi? preferably the heat exchange fluid ? made up of water vapor or diathermic oil.

More preferably, the average residence time of the aforementioned sludge inside the turbo-dryer is? between 30 seconds and 20 minutes, plus? preferably between 1 minute and 15 minutes, even more? preferably between 5 minutes and 15 minutes

As a function of the range, the speed? and of the average particle size in the aforementioned dried sludge stream so? product, during step a) of drying, the subsequent step b) of abatement can? be performed within two or more? cyclones in parallel with each other, of equal volume and hourly flow rate.

According to a preferred embodiment of the present process, at least a part of the partially purified vapor stream obtained in step c) is fed to the dryer or turbo dryer.

Preferably, such at least a part of the partially purified vapor stream is fed to the dryer or turbo dryer after heating to a temperature ranging from 40°C to 300°C, plus? preferably between 100?C and 280?C, and possible mixing with the aforementioned flow of heated air.

More preferably, the heating of this part of the partially purified vapor stream to be fed to the dryer or turbo dryer is carried out inside a heating unit. of heat exchange, for example comprising a heat exchanger with indirect heat exchange, as will be seen? more forward in relation to the system according to the present invention.

Advantageously, in accordance with this last embodiment, ? It is possible to recycle at least a part of the gaseous flow leaving the wet scrubber and, after appropriate heating, reuse these gaseous volumes as drying air inside the dryer or turbo-dryer.

In other words, ? what? It is possible not only to recover part of the heat possessed by this gaseous flow leaving the scrubber, whose heating will involve an energy expenditure certainly lower than that which would be necessary to heat freshly supplied cold air, but the volume of the partially purified vapor flow to be fed to the subsequent purification step d) is simultaneously reduced; there is therefore a considerable energy saving also from this last point of view, i.e. the volume of partially purified vapors to be treated before their eventual feeding to the unit decreases. of thermal valorisation or their eventual emission into the atmosphere in accordance with the law.

Consistently, the combination of the washing operations and the first condensation in a wet scrubber of the aforementioned vapor flow and the subsequent condensation almost complete in the condensing column allows for a gaseous effluent stream essentially free of water-soluble low-boiling chemicals.

The gaseous effluent flow cos? formed can? possibly have a residual content of low-boiling chemicals that are not soluble in water.

For this reason, as anticipated and in an entirely preferred way, the gaseous effluent obtained in phase d) can be fed to the aforementioned unit? of thermal valorisation as combustion gas.

Therefore, in a very advantageous way, the low-boiling chemical substances insoluble in water, possibly present in the gaseous effluent, are thermally destroyed by combustion inside the unit. of thermal valorisation, whose gaseous effluent gases - as mentioned - are completely devoid of the polluting chemical substances originally present in the sludge.

Furthermore, in this way, the process according to the present invention actually determines the arrangement of a closed circuit in which the gaseous effluents obtained in step c) of washing and of the subsequent step d) of purification are recycled and whose thermal potential, intended as transmissible heat by conduction or convection or as intrinsic calorific value of the organic molecules present in them, it is fully exploited.

This operation is performed in order to remove the polluting chemical substances contained therein from the liquid flows in question, such as possibly perfluoroalkyl substances (PFAS) not absorbed or adsorbed in the particles of the solid precipitate comprising dried sludge containing polluting chemical substances produced during the previous phase b ) of abatement.

Preferably, the process according to the present invention comprises the following further steps:

- subjecting the polluted washing liquid and the condensate liquid obtained in step c) and in step d), respectively, to an ultrafiltration operation, obtaining a first liquid filtrate and a concentrated suspension;

- subjecting this first liquid filtrate to a nanofiltration or reverse osmosis operation, obtaining a second liquid filtrate and a concentrated crude liquid, in which the second liquid filtrate is ? free from polluting chemicals;

- feeding the concentrated suspension and, at the same time, feeding the concentrated raw liquid to the aforementioned dryer or turbo dryer.

These operations are performed in order to remove the polluting chemical substances contained therein from the liquid flows in question, such as possibly perfluoroalkyl substances (PFAS) not absorbed or adsorbed in the particles of the solid precipitate comprising dried sludge, containing polluting chemical substances, produced during the previous phase b) abatement.

In essence, in an extremely advantageous manner, this last embodiment of the process according to the present invention determines on the one hand the production of a second liquid filtrate, which is completely free from polluting chemicals, such as perfluoroalkyl substances (PFAS), which can therefore be released into the environment without risk of damage to ecosystems or intended for other uses, for example a share of this can? be fed to the aforementioned wet scrubber.

The concentrated suspension obtained during the ultrafiltration operation, so? such as the concentrated raw liquid obtained from the nanofiltration or reverse osmosis operation, containing potentially harmful substances and residues, are suitably sent to the top of the dryer or turbo-dryer, in such a way as to avoid further specific treatments for this waste product.

Furthermore, the polluting chemical substances contained in the concentrated suspension and in the concentrated raw liquid can therefore advantageously be disposed of and destroyed by feeding the concentrated suspension and the raw liquid to the dryer or turbo dryer, to obtain a solid precipitate during the subsequent abatement step in the cyclone and, finally, for feeding the solid precipitate inside the unit? of thermal enhancement.

Finally, according to a particular embodiment of the present process, the exhaust gas produced during the aforementioned combustion step c) can be fed into an abatement scrubber, this abatement scrubber using a basic aqueous solution as the scrubbing liquid for the above-mentioned exhaust gas, so? to obtain an exhaust scrubbing liquid and a purified gaseous stream.

The exhaust gas produced during the combustion phase c) can? in fact possibly rich in halogen acids.

In particular, due to the possible significant content of halogenated compounds, such as perfluoroalkyl substances (PFAS), in the aforementioned sludge initially fed to the dryer in the aforementioned phase a), the thermal destruction of the solid precipitate comprising dried sludge containing chemical polluting substances thus? product and, therefore, the combustion of these halogenated compounds in excess of oxygen determines the formation of carbon dioxide, water and anhydrides.

The anhydrides then combine with hydrogen radicals present in the flame, resulting in the formation of halides and, therefore, of hydrogen halides, such as for example hydrofluoric acid and hydrochloric acid.

Inside the abatement scrubber, located downstream of the unit? of thermal valorisation, the anhydrides and halogen acids are eliminated and neutralized by reaction with this basic aqueous solution used as washing liquid.

In particular, the aqueous solution can be a sodium hydroxide solution.

Waste scrubber liquid includes neutralization salts so? trained; for example, the formation of sodium chloride occurs from the reaction of hydrochloric acid and caustic soda.

Preferably, the waste washing liquid can be then conveyed by the abatement scrubber to a? unit? of ultrafiltration for its treatment and purification.

In particular, non-polluting salts dissolved in water, such as sodium chloride, exceed the next unit? of reverse osmosis or nanofiltration, remaining in the filtrate and continuing towards the surface water body, being discharged into the environment, while the polluting chemical substances possibly contained in the concentrated raw liquid formed by the reverse osmosis or nanofiltration operation are recycled upstream of the dryer.

Conversely, the purified gas stream can be sent to a chimney for its release into the atmosphere, either directly or after treatment within a fume filtering system, for example through an activated carbon filter.

The aforementioned problem ? It has also been resolved by making available a plant for the treatment of sludge containing chemical pollutants comprising the following units:

- a dryer for producing a stream comprising dried sludge and vapours;

- at least one cyclone for the abatement of such dried sludge and the obtaining of a solid precipitate comprising dried sludge containing chemical polluting substances and a stream of vapors, in which such at least one cyclone ? upstream in fluid communication with the dryer;

- a?unit? of thermal valorisation for the combustion of this solid precipitate, in which the unit? of thermal valorisation ? upstream in fluid communication with such at least one cyclone;

- a wet scrubber for washing the aforementioned vapor flow and obtaining a polluted washing liquid and a partially purified vapor flow, in which the wet scrubber is ? upstream in fluid communication with the aforementioned at least one cyclone;

- a condensation column for the treatment of the partially purified vapor flow and the obtaining of a liquid condensate and a gaseous effluent, in which the condensation column is? upstream in fluid communication with the wet scrubber and, optionally, downstream in fluid communication with the unit? of thermal enhancement.

According to a preferred embodiment, the aforementioned dryer is a turbo dryer comprising a cylindrical tubular body having at least one inlet opening and at least one discharge opening, a heating jacket for bringing the cylindrical tubular body to a predetermined temperature value, and a rotor, arranged in the cylindrical tubular body and comprising a shaft equipped with elements radially protruding from it, more? preferably in which the? opening of the discharge ? in fluid communication with that at least cyclone.

Quite preferably, the plant for the treatment of sludge containing polluting chemical substances according to the present invention comprises a unit? for the generation of a forced flow of air; in which the aforementioned at least one? inlet opening of the turbo dryer ? in fluid communication with the unit? for the generation of a forced flow of air so as to allow it to be fed into the cylindrical tubular body of the turbo-dryer, subject to its possible heating inside the unit. of heat exchange, with reference to the following paragraphs, obtaining a flow of heated air.

Furthermore, in accordance with a preferred embodiment of the present plant, the aforementioned wet scrubber is downstream in fluid communication with the dryer or with such at least one inlet port of the turbo dryer.

Advantageously, as already? explained above with reference to the process according to the present invention, at least a part of the partially purified vapor flow leaving the wet scrubber can be recovered and sent to the dryer or turbo dryer, possibly after mixing it with this flow of heated air.

Preferably, in accordance with the latter embodiment, along a fluid path from the wet scrubber to the dryer or such at least one inlet port of the turbo dryer ? installed a?unit? of heat exchange.

This unit? of heat exchange? adapted to the heating of the flow of vapors partially purified that pu? sent from the wet scrubber to the dryer or turbo dryer.

Pi? preferably, this unit? exchange includes an indirect heat exchanger, which? traversed by a heat exchange fluid, wherein in a wholly preferred way this heat exchange fluid ? water vapor or diathermic oil.

Pi? preferably, the present sludge treatment plant comprises a unit? of ultra-filtration for the treatment of the aforementioned polluted washing liquid and the aforementioned condensate liquid, in which the unit? of ultra-filtration ? upstream in fluid communication with the wet scrubber and with the condensation column, respectively, comprises and such a plant further comprises a unit? additional filtration, suitable for carrying out nano-filtration or reverse osmosis operations.

Finally, according to a preferred embodiment of the sludge treatment plant according to the present invention, the unit? of thermal valorisation comprises at least one discharge opening and the plant itself comprises an abatement scrubber, in which the abatement scrubber is upstream in fluid communication with this at least one discharge opening of the unit? of thermal enhancement.

The advantages and typical characteristics of the present invention will emerge more clearly from the detailed description, given below as a non-limiting illustration of preferred embodiments of the present invention, with reference to the accompanying figure.

Brief description of the figures

Figure 1 shows a schematic view of a plant in which the process according to the present invention can be conducted according to a preferred embodiment thereof.

Detailed description of a preferred embodiment A preferred embodiment of a particular embodiment of the plant according to the present invention is described below, in which the method described above can be performed.

First, a turbo dryer 100 is shown, which comprises a cylindrical tubular body 101, closed at the ends opposite each other by bottoms 102 and 103, and coaxially equipped with an optional heating jacket 104 and intended to be crossed by a heat exchange fluid, for example water or diathermic oil, to keep the inner wall of the tubular cylindrical body 101 at a predefined temperature .

This heating jacket 104 has an inlet opening 104a and an outlet opening 104b, generally arranged for the inlet of the heat exchange fluid and for the outlet of the heat exchange fluid, respectively.

The direction of the arrows drawn at the openings 104a and 104b exemplify the direction of this incoming flow of the heat exchange fluid and the outgoing flow of the heat exchange fluid, respectively.

THE TUBULAR BODY 101 ? provided with inlet openings 106 and 105 for the sludge containing polluting substances to be treated and for a flow of heated air, respectively.

The tubular body 101 rotatably supports inside it a rotor comprising a shaft 108 equipped with radially protruding elements 109 in the form of blades, these blades 109 being helically oriented to mix, centrifuge and simultaneously convey the flow comprising sludge towards a discharge opening 107 dried and vapors that can? be obtained within it.

The direction of the arrows drawn at the openings 105, 106 and 107 exemplify the direction of these incoming flows and the outgoing flow comprising dried sludge and vapors, respectively.

The turbo dryer 100 ? therefore suitably prepared for the execution of phase a) of drying.

An engine not shown ? suitably provided for the operation of the rotor of the turbo dryer 100 at speed? variables, which can be equal to or greater than 100 rpm, preferably between 200 and 1000 rpm.

The discharge opening 107 results in fluid communication with a discharge conduit 112 into which a continuous flow is conveyed comprising dried sludge and vapors leaving the cylindrical tubular body 101.

Downstream from the 100 turbo dryer ? a cyclone 10 is arranged, equipped with an opening 15 for the inlet of the flow comprising dried sludge and vapors, suitable for carrying out the abatement step b).

Cyclone 10? otherwise? equipped with a first and a second discharge opening 17 and 18, adapted for the discharge of a solid precipitate comprising dried sludge containing polluting chemical substances and a stream of vapors, respectively. The solid fraction discharged from the bottom of the cyclone contains the polluting chemical substances, for example PFAS, which are then thermally destroyed in the unit? 20.

The discharge opening 17 ? in fluid communication with a? unit? of thermal valorisation 20; the?unloading opening 18 ? in fluid communication with the wet scrubber 30 for washing the flow of vapors leaving the cyclone 10. The plant 1 therefore comprises a wet scrubber 30 for washing the flow of vapors and allows to obtain a polluted washing liquid and a partially purified stream of vapors.

The wet scrubber 30 comprises a discharge outlet 37 in fluid communication with a discharge conduit 212 into which the polluted washing liquid is conveyed.

The wet scrubber 30 also includes? a discharge outlet 38 in fluid communication a condensation column 40 towards which at least a part of the partially purified vapor flow is conveyed.

L?unloading opening 38 ? otherwise? in fluid communication with the inlet opening 105 of the cylindrical tubular body 101 of the turbodryer 100 in order to allow the sending and feeding to the latter of at least a part of the partially purified vapor flow leaving the wet scrubber 30 .

In particular, along a fluid path from the discharge opening 38 of the wet scrubber 30 to the inlet opening 105 of the cylindrical tubular body 101 ? installed a? unit? exchanger 31, which comprises an indirect heat exchanger for heating this at least part of the partially purified vapor stream by means of a heat exchange fluid, for example diathermic oil.

Along this fluid path, pu? also be positioned a fan, not represented why? entirely conventional.

Furthermore, always along this fluid path, downstream from the unit? of heat exchange 31 this flow of partially purified vapors is mixed with a flow of heated air, in which also the latter can? be fed to the cylindrical tubular body 101 of the turbo dryer 100 through the inlet opening 105, as mentioned.

The present plant therefore also comprises the condensation column 40 for the treatment of the partially purified vapors and allows to obtain a liquid condensate and a gaseous effluent.

The condensation column 40 comprises a discharge outlet 47 in fluid communication with a discharge conduit 212 into which the condensate liquid is conveyed.

The condensation column 40 also comprises a discharge outlet 48 in fluid communication with the unit? of thermal valorisation 20 towards which the gaseous effluent is conveyed.

The discharge duct 212 puts the discharge outlet 37 of the unit in fluid communication. 30 for washing and condensation and the outlet 47 of the condensation column 40 with a unit? of ultrafiltration 51, contained in the filtration block 50 for the treatment of the polluted washing liquid and the condensate liquid.

The filtration block 50 comprises, in order from upstream to downstream along a fluid path, the unit? of ultrafiltration 51 and a?unit? additional filtration unit 52, suitable for carrying out nanofiltration operations.

According to an alternative embodiment not shown, the system 1 according to the present invention can understand a? unit? additional filtration suitable for the execution of a reverse osmosis operation.

The unit of ultrafiltration 51, as well as with the unit? additional filtration 52, ? downstream in fluid communication with the inlet opening 106 of the cylindrical tubular body 101 of the turbo-drier 100, so as to be able to feed the latter the concentrated suspension thus obtained from the ultrafiltration operation; a first liquid filtrate pu? instead be suitably sent to the? unit? additional filtration 52.

The unit filtration unit 52 has two fluid discharges: a concentrated raw liquid fluid discharge and a liquid second filtrate fluid discharge, so permeated.

The first discharge of concentrated raw liquid is sent towards the inlet opening 106 of the cylindrical tubular body 101 of the turbo-dryer 100 in such a way as to send the polluting chemical substances, such as for example the perfluoroalkyl substances (PFAS), at the beginning of the sludge drying process.

The second liquid filtrate, so? permeated and deprived of pollutants, pu? be discharged into the environment or reused for other treatment site processes, such as wet scrubber water make-up 30.

In the embodiment of the plant 1 represented in figure 1? otherwise? it is clear that the? unit? The heat recovery system 20 comprises a first discharge port 27 and a second discharge port 28 adapted for discharging inorganic ash and a flue gas stream, respectively.

Downstream with respect to the unit? of thermal enhancement 20 and in fluid communication with the second discharge port 28? installed an abatement scrubber 60, suitable for? Abatement and neutralization of the anhydrides and halogen acids contained in the exhaust gas leaving the combustion chamber of the unit? of thermal enhancement.

The abatement scrubber 60 comprises a first discharge outlet 67 for the aforementioned discharge washing liquid, comprising neutralization salts of anhydrides and halogen acids contained in the combustion fumes, as well as a second exhaust outlet 68 for a purified gas stream.

The first exhaust exit 67 ? in fluid communication with the unit? filtration system 51 via a pipeline not shown. The second exhaust outlet 68 ? instead in fluid communication with the external environment, for the release of the purified gaseous flow into the atmosphere, after treatment of the same inside a fume filtering system, for example an activated carbon filter, also not represented because? entirely conventional.

Is a mode shown below? execution of the process according to the invention, carried out by means of the aforementioned apparatus starting from a flow of sludge containing polluting chemical substances and coming from an urban waste water purification plant.

Example 1

A flow of sludge containing chemical pollutants with a dry matter equal to 18% by weight of the total weight of the sludge? been fed to the turbo-dryer 100 of the Vomm company through the inlet opening 106.

The sludge feed rate to the turbo-dryer was 5 tons/hour.

The engine of the turbo dryer 100 ? been placed at a speed? equal to about 800 rpm.

During the permanence of the sludge flow inside the dryer 100, in the heating jacket 104? was made to flow diathermic oil, cos? to maintain the temperature inside the cylindrical tubular body 101 of the turbo-dryer 100 at a value equal to approximately 250°C.

At the same time, inside the cylindrical tubular body 101 of the turbo-dryer 100 is was fed, through the inlet opening 105, a flow of pre-heated air (with a flow rate of about 30,000 m?/h) at a temperature of about 250?C and in equi-current with the flow of sludge advancing inside the cylindrical tubular body 101 itself.

The drying step? conducted at atmospheric pressure.

The sludge was kept inside the turbo-dryer 100 for a time of approximately 15 minutes.

? been so? obtained a flow comprising dried sludge and steam, which ? was then fed to the cyclone 10 to obtain a solid precipitate comprising dried sludge containing polluting chemical substances and a stream of vapours.

The solid precipitate comprising dried sludge containing polluting chemicals? been discharged from the cyclone 10 through the discharge opening 17 and then fed to the unit? 20.

The solid precipitate comprising dried sludge containing chemical polluting substances had a dry matter content of 80% by weight of its total weight and was ? been fed to? unit? of thermal valorisation 20 according to a flow rate of 1.125 tons/hour.

The solid precipitate comprising dried sludge containing polluting chemical substances had a calorific value PCI of about 3000 kcal/kg.

The combustion chamber of the unit? of thermal valorisation 20 ? been otherwise? fed with biomass of vegetable origin and of external origin from the sludge drying process, specifically wood chips with a PCI calorific value of approximately 3900 kcal/kg and fed with a flow rate of 150 kg/hour.

As explained in reference to the summary, the phase c) of combustion pu? in any case, be performed even without additional calorific input given that the temperature reached inside the combustion chamber of the unit? of thermal valorisation pu? be sufficiently high even with the sole combustion of the solid precipitate comprising dried sludge containing polluting chemical substances.

In the present example, the temperature cos? reached inside the combustion chamber was equal to 900?C.

Simultaneously, the flow of vapors coming from the exit 18 of the cyclone 10 ? been fed to a wet scrubber 30 in which ? mains water was sprayed as a cleaning and scrubbing liquid.

At the outlet of the wet scrubber 30, a part of the partially purified, but only partially cooled, vapor stream is been sent to the inlet opening 105 of the cylindrical tubular body 101 of the turbo-dryer 100 for its recycling, after heating it to a temperature of 250?C inside the unit? of heat exchange 31.

Outgoing from the wet scrubber 30, the remaining part of the partially purified vapor stream is been fed to the condensation column 40 in order to bring the water-soluble low-boiling pollutant chemical substances to complete condensation.

Outgoing from the condensation column 40, the gaseous effluent flow, completely free of water-soluble low-boiling polluting chemical substances, is been fed in the combustion chamber of the? unit? of thermal valorisation 20 as combustion gas.

Coming out of the wet scrubber 30 and the condensate column 40, the polluted scrubbing liquid and the condensate liquid so? products in these units? have been collected and sent, through the discharge duct 212, to the unit? of ultra-filtration 51.

The flow of fluid entering the unit? of ultrafiltration 51 had a flow rate equal to 6 m<3>/h and had an overall content of suspended solids (TSS) equal to 0.4% by weight, as well as? an NH3 concentration of 200 ppm and a chemical oxygen demand (COD) value of 10000 mg/L.

From the unit of ultrafiltration 51 the first liquid filtrate cos? obtained ? been fed to? unit? filtration unit 52 for carrying out the nanofiltration operation with the production of a concentrated raw liquid having a flow rate of 500 litres/h. The concentrated raw liquid, containing both ammonia and perfluoroalkyl substances (PFAS), is been finally recirculated to? unit? of drying 100.

At the same time, by crossing the filters of the unit? of nanofiltration ? A second liquid filtrate was produced which is completely free from perfluoroalkyl substances (PFAS) and, consequently, which can be discharged directly into the environment.

The concentrated suspension coming out of the unit? of ultrafiltration ? instead been sent to the turbodryer 100 after having been partially thickened through the aid of a belt press, not represented in figure 1 why? entirely conventional.

Finally, the exhaust gas leaving the combustion chamber of the unit? of thermal valorisation 20 ? been treated inside the abatement scrubber 60 with the production of a purified gaseous flow, completely free from polluting chemical substances, and of a waste washing liquid, comprising salts such as sodium fluoride, sodium sulphate and sodium chloride, below sent with a flow rate of 100 litres/hour to the unit? of ultrafiltration 51.

Claims (15)

1. Process for the treatment of sludge containing polluting chemical substances comprising the phases of: a) drying said sludge containing chemical polluting substances in a dryer (100) at a temperature comprised between 40°C and 300°C, obtaining a stream comprising dried sludge and vapours; b) feeding said flow to at least one cyclone (10), obtaining a solid precipitate comprising dried sludge containing polluting chemical substances and a vapor flow; c) feeding said solid precipitate comprising dried sludge containing polluting chemical substances to a unit? of thermal valorisation (20) and burning said solid precipitate at a temperature higher than or equal to 700°C, preferably higher than or equal to 850°C, obtaining ash and an exhaust gas; and, at the same time, feeding said stream of vapors to a wet scrubber (30), so? to bring said stream of vapors into contact with a washing liquid, obtaining a polluted washing liquid and a partially purified stream of steam; d) feeding at least a part of said partially purified vapor flow to a condensation column (40), obtaining a condensate liquid and a gaseous effluent flow. 2. Process for treating sludge according to claim 1, wherein said polluting chemical substances comprise halogenated compounds, preferably perfluoroalkyl substances (PFAS). 3. Process for treating sludge according to claim 1 or 2, wherein said sludge containing chemical polluting substances comes from waste water purification plants. 4. Process for treating sludge according to any one of claims 1 to 3, wherein said dryer (100) is a turbo dryer comprising a cylindrical tubular body (101) having at least one inlet port (105, 106) and at least one discharge port (107), a heating jacket (104) for carrying said cylindrical tubular body (101) at a predetermined temperature value, and a rotor, arranged in the cylindrical tubular body (101) and comprising a shaft (108) provided with elements (109) protruding radially from it, and in which said drying passage a) comprises the following sub-passages : i) feeding into the turbo-dryer (100) a continuous flow of said sludge containing polluting chemical substances; ii) centrifuging the sludge containing polluting chemical substances against the internal wall of the turbo-dryer (100), the rotor being set in rotation at a speed? greater than or equal to 100 rpm, preferably between 200 rpm and 1000 rpm, the particles of said sludge advancing in substantial contact with the internal wall of the turbo dryer (100) towards the discharge opening (107 ), what? to form said stream comprising dried sludge and vapors; And, iii) discharging from the discharge port (107) the flow comprising dried sludge and vapors. The process for treating sludge according to claim 4, wherein the cylindrical tubular body (101) of the turbo dryer (100) is placed at a temperature between 40?C and 300?C, preferably between 100?C and 280?C, by heating said inner wall by means of the heating jacket (104). 6. Process according to any one of the preceding claims, wherein inside said dryer or said turbo-dryer (100) the stream of sludge containing chemical polluting substances is brought into contact with a stream of heated air at a temperature ranging from 40 ?C and 300?C, preferably between 100?C and 280?C. 7. Process according to claim 6, wherein at least a part of said partially purified stream of vapors obtained in step c) is fed to said dryer or turbo-dryer (100), preferably after heating to a temperature ranging from 40°C and 300?C, more? preferably between 100°C and 280°C, and possible mixing with said stream of heated air. 8. Process for treating sludge according to any one of the preceding claims, wherein said gaseous effluent obtained in step d)? fed to said unit? of thermal valorisation (20) as combustion gas. 9. Process for treating sludge according to any one of the preceding claims, in which the following further steps are performed: - subjecting said polluted washing liquid and said condensate liquid obtained in step c) and in step d), respectively, to an ultrafiltration operation, obtaining a first liquid filtrate and a concentrated suspension; - subjecting said first liquid filtrate to a nano-filtration or reverse osmosis operation, obtaining a second liquid filtrate and a concentrated raw liquid, said second liquid filtrate being free from polluting chemical substances; - feeding said concentrated suspension and said concentrated raw liquid to said dryer or said turbo dryer (100). The sludge treatment process according to any one of the preceding claims, wherein said exhaust gas is fed into a scrubber (60), preferably being said exhaust gas rich in hydrogen halides, the scrubber (60) using a basic aqueous solution as the scrubbing liquid for said exhaust gas, obtaining an exhaust scrubbing liquid and purified gas stream. 11. Plant (1) for the treatment of sludge containing chemical pollutants comprising the following units: - a dryer (100) for producing a stream comprising dried sludge and vapours; - at least one cyclone (10) for breaking down said dried sludge and obtaining a solid precipitate comprising dried sludge containing polluting chemical substances and a stream of vapors, said at least one cyclone (10) being upstream in fluid communication with said dryer (100); - a?unit? of thermal valorisation (20) for the combustion of said solid precipitate, said unit? of thermal valorisation (20) being upstream in fluid communication with said at least one cyclone (10); - a wet scrubber (30) for scrubbing said vapor stream and obtaining a polluted washing liquid and a partially purified vapor stream, said wet scrubber (30) being in fluid communication upstream with said at least one cyclone (10); - a condensation column (40) for treating said partially purified vapor flow and obtaining a liquid condensate and a gaseous effluent, said condensation column (40) being in fluid communication upstream with said wet scrubber (30) and, optionally, downstream with said unit? of thermal valorisation (20). The sludge treatment plant (1) according to claim 11, wherein said dryer is a turbo dryer (100) comprising a cylindrical tubular body (101) having at least one inlet port (105, 106) and at least one discharge port (107), a heating jacket (104) for carrying said cylindrical tubular body (101) at a predetermined temperature value, and a rotor, arranged in the cylindrical tubular body (101) and comprising a shaft (108) provided with elements (109) protruding radially therefrom, said discharge opening (107) being in communication of fluid with said at least one cyclone (10). The sludge treatment plant (1) according to claim 11 or 12, wherein said wet scrubber (30) is? downstream in fluid communication with said dryer or with said at least one inlet port (105, 106) of the turbo dryer (100), preferably along a fluid path from said wet scrubber (30) to said dryer or said at least one inlet opening (105, 106) of the turbo dryer (100) being a unit? heat exchanger (31). 14. Plant (1) for treating sludge according to any one of claims 11 to 13, comprising a unit? of ultrafiltration (51) for the treatment of said polluted washing liquid and of said condensate liquid, said unit? ultrafiltration unit (51) being upstream in fluid communication with said wet scrubber (30) and with said condensation column (40), respectively, and further comprising a unit? filtration unit (52), suitable for carrying out nano-filtration or reverse osmosis operations. 15. Plant (1) for treating sludge according to any one of claims 11 to 14, wherein said unit? of thermal valorisation (20) comprises at least one discharge opening (27, 28) and comprising a reduction scrubber (60), said reduction scrubber (60) being upstream in fluid communication with said at least one discharge opening (27, 28) of the unit? of thermal valorisation (20).