WO2013139959A1 - Method for treating sludge by adding an organic polymer, as well as granules obtained from said method - Google Patents

Description

METHOD FOR THE TREATMENT OF SLUDGE SLUDGE BY ADDITION OF ORGANIC POLYMER AND GRANULES OBTAINED FROM THE PROCESS

The invention is directed to a process for the treatment of sewage sludge, in which the water-containing, possibly mitteis a dehydration and / or drying process partially dewatered sewage sludge with a material containing or consisting of a water-absorbing organic polymer material is mixed, and thereby the moisture of the sewage sludge is partially absorbed by the polymer material, wherein the water-absorbing organic polymer material is water-insoluble and swellable at room temperature and normal pressure and at least 4 times, preferably at least 10 times, more preferably at least 30 times, its own weight Can absorb water. The water-containing sewage sludge is converted into a granulate.

The water absorption capacity of the organic polymer materials is to be regarded as a material property of these pure materials; In contrast, in the real sludge-containing compositions of the invention, the actual water uptake of the water-absorbing organic polymer materials may be much lower (for example, because there is not enough water).

The granules thus obtained may be further treated in a process for drying by contact with a gaseous medium or by supplying thermal energy.

Furthermore, the invention is directed to granules which are obtainable by the described method, and their use.

Hydrous materials such as suspensions, sludges, filter cakes, pastes and wet solids, especially those from wastewater treatment, are often difficult to handle. The poor storage and transport properties of wet materials are a particular problem. Especially with very finely divided materials or with materials derived from microbiological treatment processes, dehumidification succeeds often only with difficulty. Due to the moisture and the partially thixotropic behavior of such materials, caking or sticking is often formed during transport, storage or processing.

Sewage sludge usually accumulates in sewage treatment as liquid sludge or after mechanical dewatering as a moist solid. Sewage sludge contains organic matter in the form of living or dead microorganisms; In addition, sewage sludge may contain mineral substances as well as inorganic or organic compounds which may be dissolved or undissolved. Residues from the cleaning of household waste water or industrial wastewater may contain, in addition to organic material in the form of living or dead microorganisms, numerous other compounds in different proportions, depending on the source of the wastewater.

Sewage sludge in this application refers to all materials originating from processes involving a step for the biological treatment of domestic or industrial wastewaters, or from processes involving a biological process step, for example using microorganisms, for example fermentation residues from biogas plants, residues from the production of foodstuffs such as cloudy substances from beer, must, wine or juices, residues from agriculture or residues from the cleaning of household wastewater or industrial wastewater.

Residues from the paper industry, which in addition to mineral fillers and pigments also contain fibers and organic compounds, constitute sewage sludge in the context of the invention.

The mechanical dewatering of sewage sludge and / or residues from the purification of domestic wastewater or industrial wastewater is usually first by filter presses, centrifuges, belt presses or screw presses after the liquid sludge flocculants, such as organic polymeric compounds were added. A particular problem is the poor handling, storage and transport properties of sewage sludge. Due to the high humidity and partly thixotropic behavior, caking is often formed.

WO 2005 095 291 describes a process in which first a sewage sludge suspension is thickened with the aid of a flocculant in the form of an organic polymer material and then a second flocculant based on an organic polymer material is added to the thickened suspension and finally a mechanical dewatering process follows ,

After mechanical dehydration, the dry matter content increases to about 15 to 40%. For economically viable recycling, for example as a fuel, however, significantly higher dry matter contents are required. These higher Trockenstoffgehaite can be achieved by drying. In addition to conventional drying methods, drying by means of solar energy has also been proposed. A disadvantage of the drying process is either the energy requirement or the area and the time required, in the case of solar drying is still the dependence of the sunlight added.

EP 2 228 347 describes a method and an apparatus for dewatering mechanically dewatered sewage sludge. The sewage sludge is conveyed by means of a screw located in a closed housing along the longitudinal axis of the screw conveyor in a conveying direction, being blown for further dewatering of sewage sludge air substantially perpendicular to the conveying direction in the closed housing and the sewage sludge is acted upon with the air. This has a high expenditure on equipment and energy costs result.

Disadvantages of the prior art.

- Mechanical dewatering leads to dry matter contents of typically only 15 to 30 wt .-%, with elaborate high-pressure filter presses a maximum of 40 to 50 wt .-%. - Sludges are not easy to handle, especially disadvantageous is the tendency to caking during storage and transport and the tendency to thixotropy

 - Conventional thermal drying processes are complex and expensive and require appropriate equipment; a special problem is the so-called "glue phase" during the drying of sewage sludge

- Drying with air requires expensive devices, especially for the dedusting of the resulting during drying gas streams

 - Solar drying processes require large area, solar radiation and long residence time and often mechanical devices to improve the contact with the gas atmosphere

It was therefore an object to provide a method which makes it possible to improve the storage and / or transport properties of sewage sludge and to dry the sewage sludge, in whole or in part, in a particularly simple and energy-saving manner.

Furthermore, it was an object to provide granules of sewage sludge, which have good storage and transport properties and preferably a low residual moisture.

The object is achieved by a method for treating sewage sludge, in which the water-containing sewage sludge is mixed with a material containing or consisting of a water-absorbing organic polymer material and the moisture of the sewage sludge is at least partially absorbed by the polymer material, wherein the Water-absorbing, organic polymer material is water-insoluble and swellable at room temperature and atmospheric pressure and can absorb at least 4 times, preferably at least 10 times, more preferably at least 30 times its own weight of water. The water-containing sewage sludge is converted into a granulate.

The water absorption capacity of the organic polymer materials is to be regarded as a material property of these pure materials; in the real world The sludge-containing compositions according to the invention can be the actual water absorption of the water-absorbing organic

On the other hand, polymeric materials should be much smaller (for example because not enough water is available).

Preferably, the water-absorbing organic polymer material contains or consists of a superabsorbent and / or a hydrogel.

In addition to the water-absorbing organic polymeric materials, finely divided materials may additionally be added as additives. Additives which are combustible are of particular interest in an intentional combustion of sewage sludge.

Advantageously, the sewage sludge mixed with the polymer material is converted into a granular form, which consists of a large number of, in particular, flowable and / or free-flowing as well as particulate granules.

Granules are understood as meaning a flowable and pourable, particulate material. The appearance is often grainy to powdery. However, the appearance thereof may vary as long as the material is flowable and free-flowing. A material is defined as free-flowing and free-flowing if, in a glass cylinder filled with 500 ml volume and 48 mm diameter filled with it, a maximum of 10% by weight of the material adhere when turned over.

The process is preferably characterized in that the granules have a sieve passage of more than 80% by weight on a 5 mm sieve, preferably on a 4 mm sieve, more preferably on a 2.5 mm sieve.

The method is furthermore preferably characterized in that the dry matter content of the granules preferably obtained by application of a granulation method is 10 to 50% by weight, preferably 15 to 45% by weight, particularly preferably 20 to 35% by weight. This information refers to the state immediately after the preparation, when the granules leave the granulation, as the granules can quickly release moisture in air. The resulting granules form a transportable, in particular pneumatically conveyable and not to caking prone bulk material. The granules do not stick permanently to each other or to the wall of containers. With small dosing of the water-absorbing, organic polymer material, the individual granules may adhere to each other; However, this liability is not permanent and the granules dissolve easily again from each other. In the meantime, compact structures ("snowballs") forming pressure during storage decompose back into the starting granules even when subjected to low shear forces.

The morphology and particle size of the granules is dependent on the type and amount of water-absorbing, organic polymer material and the type and intensity of the mixture or of the mixing unit. The composition of the sewage sludge and the particle size of the water-absorbing, organic polymer material (superabsorber) can also have an influence. Preferably, a suitable granule size is adjusted by suitable selection and dosage amount of the water-absorbing, organic polymer material. These relationships can be determined for the respective clarifier composition and quality by simple routine mixing experiments. The following applies: the higher the dosage, the finer the granules are obtained.

The finely divided materials according to claim 9 can be used in an amount of from 3 to 50% by mass, preferably from 5 to 30% by mass, particularly preferably from 10 to 20% by mass, based on the weight of aqueous, moist sewage sludge to which they are added. be added to optimize the granule properties.

In a further embodiment of the invention, the finely divided, preferably pulverulent, materials have a BET surface area of more than 50 m ² / g, preferably more than 100 m ² / g, particularly preferably more than 200 m ² / g.

As finely divided, preferably powdery, materials, zeolites, silicon compounds, preferably pyrogenic or precipitated silicas or Water-absorbing phyllosilicates, in particular bentonite, find use or those substances which contain the materials mentioned.

If subsequent drying and combustion of the sewage sludge is intended, it is advantageous if the finely divided, pulverulent materials at least 80%, preferably at least 90%, more preferably at least 95% of the adsorbed or absorbed moisture at temperatures of less than 50 ° C, preferred less than 40 ° C, more preferably less than 30 ° C, again can deliver. The release of moisture takes place by contact with a gas, preferably air, at room temperature.

With regard to an energetic utilization of the sewage sludge, it is particularly advantageous if the finely divided materials are combustible. For example, coal, wood flour or other combustible materials are suitable or substances containing the materials mentioned.

The finely divided materials may also be added in an amount of 50 to 1000% by mass, preferably 100 to 300% by mass, particularly preferably 100 to 200% by mass, based on the mass of hydrous, moist sewage sludge to which they are added , if thereby the further, in particular thermal, recovery is favored.

It is also possible that the sewage sludge moist, combustible materials, preferably finely divided moist combustible materials are mixed. In this way, a common drying instead of two separate drying processes take place.

It is also possible that in order to increase the stability of the granules additionally from 0.1 to 20% by mass, preferably from 0.1 to 5% by mass, particularly preferably from 0.1 to 3% by mass, of materials which contain water or moisture may be added chemically, preferably cement, in particular cement with a setting time of less than 1 hour, quicklime, fly ash, anhydride or salts, which are able to move into a crystal water-rich form. In this way, the resulting granules are mechanically stabilized and improved in terms of their storage and transport properties and can also be used in the construction sector.

Particularly advantageous may be the addition of CaO, as this facilitates the use of the wet and dried granules, e.g. in agriculture.

Preferably, the addition of the materials which can bind water or moisture chemically, following the addition of the other additives and formation of the granules, since in this way a setting and curing of the entire mass is avoided during mixing.

The term "water-absorbing organic polymeric materials" primarily includes so-called "superabsorbents." The term "superabsorbents" includes in particular those polymers which are capable of absorbing by swelling a multiple of their own weight in water or other liquids and to retain the absorbed amount of liquid even under a certain pressure. Superabsorbents can be of natural or synthetic origin. From DE 202011002784, potato starch or polysaccharides of a general type are known as examples of natural superabsorbents.

Chemically, a superabsorbent is on the rise! a so-called base polymer, in particular a consisting of acrylic acid (propenoic acid, C ₃ H ₄ 0 ₂ ) and sodium acrylate (sodium salt of acrylic acid, a0 ₂ C ₃ H3) existing copolymer, wherein the ratio of the two monomers to each other may vary. In addition, a so-called core crosslinker is added to the monomer solution, which connects the long-chain polymer molecules formed in places with each other by chemical bridges (crosslinked). These bridges make the polymer water insoluble. The insolubility in water caused by the three-dimensional crosslinking is an essential feature of the superabsorbents or hydrogels used according to the invention. This water insolubility distinguishes this polymer material substantially from chemically very similar flocculants or flocculation aids, which are not three-dimensionally crosslinked. When liquid or moisture penetrates into a polymer particle, it swells and tightens At the molecular level this network so that the liquid or moisture is bound.

The water-absorbing, organic polymer materials or superabsorbents are i.d.R. Small, powdery particles with diameters ranging from the nanometer range to several hundred micrometers, but can also have a size in the millimeter range. In general, synthetic superabsorbents are prepared by polymerizing partially neutralized acrylic acids in aqueous solution in the presence of polyfunctional crosslinkers by free-radical reaction to give a gel which is dried, ground and classified into the desired particle size.

Superabsorbents are also known which are formed in the reaction of natural compounds with synthetic materials or monomers. Furthermore, superabsorbent substances are known which form a mixture of polymeric superabsorbers and ground mineral additives.

In superabsorber technology, a distinction is still made between superabsorbents and hydrogels. While superabsorbents are understood to mean the almost dry, water-pulling substances, hydrogels are already wholly or partially swollen superabsorbers. Thus, SAP particles can be particles of superabsorbent polymer in the dry state, especially particles that contain either no water at all or up to about 10% by weight of water, as disclosed in DE 602004002202. The terms superabsorbent gel, superabsorbent hydrogel, then refer to a superabsorbent polymer having a water content of at least about 10% by weight, typically particles that have absorbed at least their own weight and typically many times their own weight in water. The use of pre-swollen superabsorbent gels or hydrogels or superabsorbent hydrogels, all terms describing the same state, may be advantageous because hydrogels that are not yet saturated with liquid, in some cases absorb more fluid more quickly. The present invention thus also encompasses the use of hydrogels for (ver) mixing with sewage sludge. The "European Disposables and Nonwovens Association", Avenue Eugene Plasky, 157-1030 Brussels, Belgium (EDNA), has published a typeface "EDNA Recommended Test Methods" (ERT for short) from the year 2002, which describes, among other things, three procedures that characterize the source behavior. These are:

- Free Swell Capacity (FSC) ERT 440.2-02

 - Centrifuge Retention Capacity, (CRC) ERT 441.2-02

 - Absorption under Pressure, (AUP) ERT 442.2-02.

All the materials listed above represent a water-absorbing organic polymeric material in the context of the present invention. In particular, a water-absorbing organic polymeric material is understood to mean all superabsorbents or superabsorbent compositions containing superabsorbents or hydrogels, which are characterized in that they are in accordance with EDNA ERT 440.2-02 or ISO 17190-5: 2001-12 have a swelling capacity (FSC value) of at least 4 g / g, preferably 10 g / g and particularly preferably more than 30 g / g.

Preferably, the water-absorbing organic polymeric materials include or are comprised of polymers of acrylic acid, preferably a copolymer of sodium acrylate and acrylamide. The presently specified superabsorbents or hydrogels or substances or materials containing them are thus part of the subject of the invention. It is particularly advantageous with the superabsorbers or hydrogels that only a small amount is required due to their high water binding potential. In this way, the total mass of sewage sludge is increased only slightly and the cost of mixing, packaging, storage and transport is limited.

It has been found that the superabsorbents only have to absorb a small part of the water present in order to achieve a considerable change in the consistency of the sewage sludge (suspension, sludge, filter cake or paste is introduced into the sludge) Granules converted). Due to the small amount of superabsorber added, the residual moisture content of the resulting granules is generally scarcely changed in comparison to the residual moisture of the sewage sludge before the addition of the superabsorbent. With the help of superabsorbents or hydrogels, therefore, it is possible to obtain stable and easy-to-handle granules despite a generally very high water content.

The addition amount of the water-absorbing organic polymeric materials may be from 0.01 to 10% by weight, preferably from 0.05 to 3% by weight, more preferably from 0.3 to 2% by weight, based on the total mass of the (wet) Sewage sludge, amount.

For example, Luquasorb 1 161 from BASF or Favor from Evonik can be used. With the same dosage or processing, slightly finer granules can be obtained with Luquasorb 1161.

It is also possible to use so-called "off-spec" products as superabsorbents or hydrogels, ie materials which have been produced or treated incorrectly, because of the high quality requirements for substances which may come into contact with the human body Although superabsorbents or hydrogels are (no longer) suitable for hygiene applications, for example because of microbiological contaminants, but are easily usable for sewage sludge treatment, the method according to the invention can represent a practicable and economically attractive utilization possibility for such defective batches. Use superabsorbent or hydrogels, which have already been used for another application, but still have a part of their absorption capacity.

Furthermore, the granules are characterized in that they have a bulk density of less than 1, 6 g / cm ³ , preferably less than 1, 2 g / cm ³ , more preferably less than 1, 0 g / cm ³ , and / or a tamped density (1000 strokes in the tamping volume according to DIN 53 94) of less than 1.7 g / cm ³ , preferably less than 1.5 g / cm ³ , more preferably less than 1.4 g / cm ³ .

In contrast to the organic polymeric materials used as superabsorbents, which are insoluble (but swellable) in water, have the Flocculants for sewage sludge used organic polymers

Materials have a similar basic chemical structure, but no crosslinking of the polymer chains and are water-soluble.

The purpose of the flocculants is to combine solid particles or microflakes into larger structures, while the purpose of the superabsorbents is to bind or absorb water.

Superabsorbents or hydrogels in the sense of this invention are therefore only those compounds which have a swelling capacity or a water absorption capacity of at least 4 g / g, but not such compounds which are water-soluble and act as flocculating agents (and occasionally also erroneously referred to as superabsorbents).

Furthermore, in addition to the water-absorbing, organic polymer material, additives for reducing the development of odors, for example iron sulfate, may additionally be added.

Particularly preferred is the use of a combination of a superabsorbent and a finely divided material as additives for sewage sludge. In particular, if the finely divided material is combustible, favorable synergistic properties result: The required amount of superabsorbent for the formation of suitable granules is less, and the finely divided material has in addition to its promoting the granulation function additionally the positive effect of an energy carrier in a subsequent combustion of granules.

Very particularly advantageous is a combination of a superabsorbent and a finely divided, combustible material as additives for sewage sludge, when the finely divided, combustible, material is in a moist state and for the intended use as an energy source to undergo a drying step, such as wet coal, especially lignite. In this case, joint processing and drying is possible, resulting in significant cost savings. Preferably, the sewage sludge is mechanically dewatered, or partially dewatered, prior to the addition of the water-absorbing, organic polymer material, for example by means of a filter press or a centrifuge. In this case, preferably a dry matter content of 10 to 50 wt .-%, preferably 15 to 45 wt .-%, particularly preferably 20 to 35 wt .-%, can be achieved. After mechanical dehydration, the sewage sludge is preferably in particulate or pasty form, but not as a suspension, and is then mixed with the water-absorbing organic polymer material and transferred to granules. The mixing can be continuous or discontinuous. Continuous mixing can better prevent initial caking of the sewage sludge, especially if a partial stream of dried sewage sludge is recycled to the mixing process. In this way, the metered amount of the water-absorbing organic polymer material can be reduced.

It is also possible to add coal or mineral additives as filtration aids to the not yet mechanically dewatered sewage sludge. As a result, the mechanical drainage can be favorably influenced.

The mechanical dehydration is advantageous because in this way only comparatively small amounts of water-absorbing, organic polymer material are required to form the granules according to the invention.

As a mixing unit, all mixers, stirrers, kneaders or other devices can be used, which allow a sufficiently large homogeneity of the mix in a reasonable time. Advantageously, devices with high-speed mixing tools. But even kneaders may be suitable. Typical mixing times for the formation of the granules according to the invention in devices with high-speed mixing tools are about one to three minutes. In this case, all components can be added either one after the other or together in the mixing device. It may be advantageous to first add the superabsorbent and / or a finely divided and / or powdery additive and only then the sewage sludge into the mixing unit. Too long mixing time can lead to clumping and sticking; that's why it's the mixing process abort as soon as the resulting granules have sufficiently good flow properties.

The granules obtained according to the invention have good storage and transport properties and can be filled as bulk material in containers and removed from them again. In particular, the granules are characterized in that they are pneumatically conveyed.

In a preferred embodiment of the invention, after the granulation, the moisture content of the resulting granules is reduced by contact with a gaseous medium, preferably by fluidized bed or fluidized bed drying, and / or by supplying thermal energy.

The granules can be dried by adding a gaseous medium, e.g. Air is passed through the granules or past the granules. Due to the significantly larger compared to the liquid, pasty or lumpy starting material surface of the granules drying takes place very quickly.

Compared to a lumpy material with an assumed average diameter of 20 cm (a not untypical value for filter cake from a filter press), the geometric surface of granules with a diameter of 10 mm becomes larger by a factor of 20, with a diameter of 1 mm the factor the surface enlargement 200, with a diameter of 0.1 mm, the factor of the surface enlargement 2000.

In addition, the time it takes water to get from the inside of a particle to its surface is considerably smaller for smaller particles than for large ones. With good gas exchange at the surface of the particles, this may be the rate-determining step for drying.

Therefore, the granules in thin layers at room temperature within a few hours a large part of their moisture (more than 60%, sometimes more than 85%), lose without the need for large gas flows! As gaseous medium, air, preferably heated air having a temperature of less than 70 ° C, particularly preferably having a temperature of 40 to 60 ° C, can be used. It is particularly advantageous to dry the moisture content of the granules obtained in the mixture with a gas which contains waste heat which is otherwise not usable. Thus, the waste heat of an industrial combustion process can be used, which can no longer be used to generate electricity or steam. For example, waste heat from sewage sludge incineration can be used to dry fresh sewage sludge granules.

Due to the large geometric surface of the granules but can also with air at a temperature of less than 50 ° C, preferably less than 40 ° C, more preferably less than 30 ° C, dried. This has the advantage that either little or no energy costs for drying are required.

Due to the good storage and transportability of the granules, which are obtained when mixing sewage sludge with the water-absorbing, organic polymer material, the sewage sludge can be easily moved to a place where such waste heat is obtained.

Also, a storage in silos or a transport in silo vehicles is made possible, so that odors are avoided. Furthermore, it is possible to carry out the drying of the granules in the silo vehicle by passing air through the silo.

It is also possible to use for drying a gas containing dust particles. In this way, in addition to the drying effect at the same time allows dedusting of the gas.

In one embodiment of the invention, the resulting granules are in the form of a bed in a bulk material container, preferably a silo, which is flowed through by a gas, is particularly preferably flows through from bottom to top. The gas velocity is preferably chosen so that the obtained granules in the form of a fixed bed and have no macroscopic movement.

Alternatively, the granules obtained may be in the form of a flat bed, wherein the height of the bed is less than 0.5 m, preferably less than 0.3 m, more preferably less than 0.1 m. In this way, due to the large geometric surface of the granules an effective drying is achieved without complex mechanical methods for turning the granulate are required. The drying effect can be additionally accelerated by the granules are swept by a gas stream, which is preferably produced by fans. Also contact of the granules with an absorbent pad can cause or support a moisture reduction.

Even when thermal energy is supplied, the granular form can promote drying, especially in devices which mechanically treat the material to be dried in such a way that fresh surface is produced. For example, drying units which operate on the principle of contact drying, such as drum, tumble, plate, screw or paddle dryer.

The formation of granules according to the invention is particularly advantageous because it significantly reduces the negative effects of the so-called "glue phase" during the drying of sewage sludge.When sewage sludge is dried, between 40 and 60% of dry matter, a sticky phase occurs due to the mechanical stress "Glue phase" on. This causes, for example, in thin-film dryers significant problems (for example, blockages, damage to the drives). In contrast, the granules can be dried without any problem, as they undergo mostly rolling motions and do not have to be cut mechanically to create a fresh surface.

It is also possible that granulation and drying are carried out together in one process step. In this case, no finished granules are fed to the dryer, but the granules produced in the dryer by the water-absorbing organic polymeric materials, in particular Superabsorbent and / or hydrogels, are mixed together with the substance to be dried in the drying unit by mechanical action. It is possible to introduce the components either together or spatially and / or temporally separated into the drying unit.

Particularly advantageous is the formation of granules in the drying unit by adding a superabsorbent or hydrogel, when the material to be dried tends to form caking or shows thixotropic behavior.

The process according to the invention is particularly advantageous in the case of materials to be dried having a high degree of abrasiveness, for example sewage sludge with a high proportion of mineral compounds. The formation of granules, the abrasive effect of such materials can be significantly reduced. This is made possible, for example, by the granules in a drum dryer performing predominantly no grinding but rolling movements. Particularly advantageous in abrasive materials is the use of a drum dryer. Due to the favorable surface-to-volume ratio of a drum dryer, the proportion of granule particles that touches the dryer wall is relatively low.

Due to the good rheological properties of the granules, an increased throughput during drying or combustion can be achieved, since the good rheological properties of the granules ensure that all granules from all sides have an optimal contact with the gas phase or the drying gas.

The moisture content of the granules obtained and subsequently dried during the mixing may preferably be less than 30% by weight, preferably from 5 to 25% by weight, particularly preferably from 10 to 20% by weight.

The moisture content or the moisture or the residual moisture (all these terms are used synonymously here) corresponds to the weight loss, which occurs at 105 ° C in a drying oven until the mass constancy is reached. Mass constancy is considered reached when the mass change between 30-minute weighing intervals less than 0.1% absolute. The dry matter content (or solids content) in% corresponds to 100% minus residual moisture content (in%).

The invention also granules, which are obtainable by one of the claimed methods.

The invention preferably comprises granules comprising water-containing or moist, in particular partially dewatered, sewage sludge and also 0.01 to 10 wt.%, Preferably 0.05 to 3 wt.%, Particularly preferably 0.3 to 2 wt organic polymeric materials based on the mass of the aqueous or moist sewage sludge, preferably superabsorbent and / or hydrogel (s). The dry matter content of the resulting granules is 10 to 50 wt .-%, preferably 15 to 45 wt .-%, particularly preferably 20 to 35 wt .-%.

In each case a superabsorbent or a hydrogel, but also mixtures of one or more superabsorbents and / or one or more hydrogels can be used.

Furthermore, the granules may contain further additives in the form of finely divided materials. The finely divided additives may be either dry and / or powdery or moist. The advantage with dry and / or powdered additives is the lower requirement for water-absorbing organic polymeric materials. The advantage of wet additives is the synergy in a common drying process. More preferably, combustible materials are used as finely divided additives, e.g. moist or dry coal, in particular coal dust, wherein the proportion of the combustible or additives based on the dry mass of sewage sludge preferably 5 to 200 wt .-%, particularly preferably 20 to 50 wt .-%, is.

Other finely divided additives may be: sand, CaO, pyrogenic SiO2, dusts from metal processing, filter dusts or mineral wastes.

Preferably, the volume fraction of the cavities in a granulate bed formed from the granules is 2 to 35 wt .-%, preferably 5 to 25 wt .-%, more preferably 10 to 20%. The determination of the volume fraction of the cavities can be determined by adding a water-immiscible solvent in a granular bed and the required amount is determined up to the upper edge of the granular bed.

A further advantage is that storage in silos or transport in silo vehicles is made possible by the conditioning of the sewage sludge according to the invention, so that odor nuisance is avoided.

The treatment of sewage sludge according to the invention can be carried out jointly for the mineral fraction (primary sludge), the activated sludge fraction (also biological fraction) or both.

The optimum granule size results from the intended uses.

If the granules obtained are to be dried, it is advantageous to provide granules which, on the one hand, have the largest possible geometric surface area, but on the other hand are not blown away by the gas stream used for drying. Preference is therefore given to preparing granules having an average diameter (volume average) of 0.1 to 20 mm, preferably 0.5 to 10 mm, particularly preferably 1 to 5 mm. The determination of the granule size and the mass fraction is carried out by (light microscopic) counting assuming a constant density and a spherical shape of the individual particles.

The higher the metered amount of the water-absorbing, organic polymer material is selected, the finer are usually the granules particles. If sufficient time and space are available for drying, the granules may also have an average diameter of more than 3 mm, but if the drying process is to be very efficient, smaller granules are desirable. Accordingly, the cost of the fine granule process is higher due to the cost of the water-absorbent organic polymeric material. The granules preferably have a sieve passage of more than 80% by weight on a 5 mm sieve, preferably on a 4 mm sieve, more preferably on a 2.5 mm sieve.

In any case, it is advantageous to strive for a bed of granules which has the largest possible void volume and the lowest possible flow resistance for the gas used for drying. This is preferably achieved by not using too fine granules and a largely uniform granule size.

Preferably, the bulk density of the (not dried) sewage sludge granules is at least 0%, more preferably more than 20% less than the density of the sewage sludge prior to the addition of the water-absorbing, organic polymer material.

If dust formation during drying should be kept as low as possible, larger granules should be aimed for. Particularly preferred is the production of granules having a mean size of 0.5 to 10 mm, in particular 1 to 5 mm, with a subsequent drying, in which only a small mechanical stress of the granules. In this way, dedusting during drying can be completely dispensed with, or else a simple and cost-effective method for dedusting can be selected (for example cyclone or wet scrubber).

Particularly advantageous is a fluidized bed drying, since in this case good mixing of the granules and, on the other hand, low dust formation is achieved by the interaction of gas flow and mechanical action (for example vibration).

An advantageous embodiment of the invention is the return of a partial flow of dried material in the mixing and granulation process. In particular, a partial fraction of the dried granules can be separated by sieving and the coarse and too fine granules can be recirculated to the mixing and granulation process.

In this way, the mechanical and conveying properties of the material to be dried are improved, so that a smaller amount of superabsorbent is required for granulation.

In summary, the invention shows the advantages that sewage sludge can be converted by simple addition of a water-absorbing organic polymer material in a granulate and thus in a manageable form, so that storage or transport as bulk material or pneumatic conveying is much easier. In addition, the granule structure allows a much easier evaporation or evaporation of moisture and thus efficient drying of the sewage sludge, which was possible in the prior art only by means of complex mechanical support or with the aid of considerable amounts of thermal energy.

Claims

claims: A process for treating sewage sludge to improve handling, storage and / or transport properties, comprising mixing the hydrous sewage sludge with a material containing or consisting of a water-absorbing organic polymeric material while partially saturating the moisture of the sewage sludge from the polymer material is absorbed, the water-absorbing, organic Polymermateria! is water-insoluble and swellable at room temperature and normal pressure and can absorb at least 4 times, preferably at least 10 times, more preferably at least 30 times, its own weight of water according to ISO 17190-5: 2001-12. A method according to claim 1, characterized in that the water-absorbing, organic polymer material contains or consists of a superabsorbent and / or a hydrogel. A method according to claim 1 or 2, characterized in that the water-absorbing, organic polymer material contains polymers of acrylic acid, preferably a copolymer of sodium acrylate and acrylamide, or is composed of and is three-dimensionally crosslinked. Method according to one or more of the preceding claims, characterized in that the sewage sludge is converted into a granulate. Method according to one of the preceding claims, in which sewage sludge is dewatered mechanically, preferably by means of a filter press, belt press, screw press or centrifuge, before the addition of the water-absorbing, organic polymer material, and after the mechanical dehydration has a solids content of 10 to 50% by weight. , preferably 15 to 45 wt .-%, particularly preferably 20 to 35 wt .-%, and further characterized in that the sewage sludge before the addition of the water-absorbing organic polymer material in particulate or pasty form, but not in the form of a suspension. 6. The method according to one or more of the preceding claims, characterized in that the dry matter content of the resulting granules 10 to 50 wt .-%, preferably 15 to 45 wt .-%, particularly preferably 20 to 35 wt .-%, is. 7. The method according to one or more of the preceding claims, characterized in that the addition amount of the water-absorbing, organic Polymermateriais 0.01 to 10 wt .-%, preferably 0.05 to 3% by weight, particularly preferably 0.3 to 2 wt .-%, based on the mass of the water-containing (wet) sewage sludge. 8. The method according to one or more of the preceding claims, characterized in that the granules a sieve passage of over 80 wt .-% on a 5 mm sieve, preferably on a 4 mm sieve, particularly preferably on a 2.5 mm Sieve, exhibit. 9. The method according to one or more of the preceding claims, characterized in that the sewage sludge in addition to the water-absorbing organic polymer material additionally finely divided materials are added as additives. 10. The method according to claim 9, characterized in that the finely divided materials are added in an amount of 3 to 50% by mass, preferably 5 to 30% by mass, particularly preferably 10 to 20% by mass, based on the mass of sewage sludge , 1 1. A method according to any one of claims 9 or 10, characterized in that the finely divided materials are zeolites, finely divided silicon compounds, preferably fumed or precipitated silicic acids or moisture-absorbing phyllosilicates, in particular bentonite or these. 12. The method according to any one of claims 9 to 1 1, characterized in that the finely divided materials in an amount of 50 to 1000 mass%, preferably 100 to 300 mass%, particularly preferably 100 to 200 mass%, based on the Mass be added to sewage sludge. 13. The method according to any one of claims 9 to 12, characterized in that the finely divided materials are combustible and are preferably coal or wood flour or other combustible materials or containing them. 14. The method according to one or more of the preceding claims, characterized in that the sewage sludge further materials are mixed, preferably moist, combustible materials, particularly preferably finely divided, moist, combustible materials. 15. The method according to one or more of the preceding claims, characterized in that the components to be mixed are introduced spatially and / or temporally separated in a mixing unit and / or granulating. 16. The method according to one or more of the preceding claims, characterized in that the, in particular obtained after a mixing operation and / or granulation, granules are pneumatically conveyed. 17. The method according to one or more of the preceding claims, characterized in that the moisture content of the granules obtained in the mixture by contact with a gaseous medium, preferably by means of fluidized bed or fluidized bed drying, is reduced. 18. The method according to one or more of the preceding claims, characterized in that the moisture content of the granules obtained in the mixture is reduced by supplying thermal energy, wherein drying units are used, which operate on the principle of contact drying, preferably drum, tumble , Plate, screw or paddle dryer. 19. The method according to claim 17, characterized in that the gaseous medium, preferably air, a temperature of less than 70 ° C, preferably less than 50 ° C, more preferably less than 40 ° C, wherein the gaseous medium is particularly preferably heated by solar energy. 20. The method according to one or more of the preceding claims, characterized in that the granules obtained are in the form of a flat-spread bed, wherein the height of the bed is less than 0.5 m, preferably less than 0.3 m, more preferably less than 0.1 m, and wherein the granules are in contact with a gas, which is preferably produced by fans. 21. The method according to one or more of the preceding claims, characterized in that granulation and drying are carried out together in one process step. 22. The method according to one or more of the preceding claims, characterized in that the granules have a sieve passage of over 80 wt .-% on a 5 mm sieve, preferably on a 4 mm sieve, and these granules are subjected to a subsequent drying , where after the drying either no dedusting takes place or dedusting mitteis a cyclone or a wet scrubber takes place. 23. The method according to one or more of the preceding claims, characterized in that the moisture content of the dried granules less than 30 wt .-%, preferably 5 to 25 wt .-%, particularly preferably 10 to 20 wt .-%, is. 24. Granules obtainable according to one of the preceding claims. 25. granules containing sewage sludge and based on the weight of the sewage sludge from 0.01 to 10 wt .-%, preferably 0.05 to 5 wt .-%, particularly preferably 0.3 to 2 wt .-%, of a water-absorbing, organic Polymer material, in particular superabsorbent and / or hydrogel (s), which is water-insoluble at room temperature and atmospheric pressure and can absorb at least 4 times, preferably at least 10 times, more preferably at least 30 times its own weight of water. 26. Granules according to claim 24 or 25, characterized in that the dry matter content is 10 to 50 wt .-%, preferably 15 to 45 wt .-%, particularly preferably 20 to 35 wt .-%, is. 27. Granules according to one or more of the preceding claims, characterized in that the volume fraction of the cavities in a granular charge formed from the granules 2 to 35 vol .-%, preferably 5 to 25 vol .-%, particularly preferably 10 to 20 vol. -%, is. 28. Granules according to one or more of the preceding claims, characterized in that the moisture content of the dried granules less than 30 wt .-%, preferably 5 to 25 wt .-%, particularly preferably 10 to 20 wt .-%, is. 29. Granules according to one or more of the preceding claims, characterized in that they contain at least one further combustible additive, preferably coal, wherein the proportion of the combustible or additives based on the dry mass of sewage sludge preferably 5 to 200 wt .-%, particularly preferably 20 to 50 wt .-%, is.