MXPA00006710A - Dewatering of sludges deriving from paper industry - Google Patents

Abstract

A sludge, preferably derived at least in part from a paper mill, pulp mill or deinking plant, and which contains at least secondary sludge or primary sludge comprising deinking waste, recycled paper waste or mechanical pulping waste, is flocculated by being mixed with a phenolic material and a polyalkylene oxide and is then subjected to dewatering.

Description

SLUDGE DEHYDRATION BACKGROUND OF THE INVENTION This invention relates to the promotion of sludge dehydration by the addition of a flocculating sludge system prior to dehydration.It is a standard floccular practice to suspend a suspension of suspended solids by adding a polymeric flocculating agent to the suspension. The different suspensions, and the different dehydration processes, require different flocculating agents to obtain optimum results.In addition, the optimal results vary according to the nature of the suspension being treated, for example, when the suspension has a content of relatively low solids, typically below 1% and usually below 0.5% and often below 0.2%, optimal results are generally indicated by the achievement of the highest possible clarity of the supernatant or filtrate. It is a fluid cellulose paste to make paper, the result Optimal adhesions are generally indicated by the optimal formation of the paper sheet, generally accompanied by the optimal retention of suspended solids in the sheet. When the slurry is a residual sludge, the optimum results are generally indicated by a good combination of dehydration speed, clarity and solids content of the dehydrated product. For example, it may be unacceptable to obtain a cake with a high quantity of solids in a rapid dehydration process if the clarity of the resulting supernatant or filtrate is poor, but it can be uneconomical to obtain a cake with a high amount of solids and a high clarity if the dehydration speed is too slow. Solids in suspension in a low solids liquor to be clarified are usually different from those in a sludge. For example, a destillation liquor may contain inks, fillers or fillers and chemical release compounds, and these are separated during clarification. A primary sludge incorporating those separated solids is much more complex and also contains large amounts of different materials that have very different properties, such as rejects from screening, cleaning, flotation and other paper milling processes. A polymer that can be useful when dehydrated by a process, may not be useful when it is for another. For example, different polymers may be required in processes where cutting or pressure is applied to the flocculated material (for example in a filter press or centrifuge) of the polymer where such a cut or pressure is applied (for example in sedimentation processes). Different polymers are also required according to the differences in the suspended solids and in the dissolved phase. For example suspended suspensions of inorganic solids are often better treated using anionic polymers while suspensions of suspended organic solids are often better treated using cationic polymers. The molecular weight of the polymer also influences the performance and although optimal flocculation in some processes requires the highest possible molecular weight, in other processes a lower molecular weight gives better results. Even within any particular type of suspension, for example a fluid cellulosic pulp for making paper, the different types of fluid pastes require different types of polymers for optimum results. Therefore, there is a wide range of polymeric flocculants available to be considered for use in dehydration processes. They are selected from nonionic polymers, anionic polymers and a wide range of cationic polymers. Many are substantially water soluble polymers formed from ethylenically unsaturated acrylic monomer or other monomers or monomer mixtures in various portions and made at a low, medium, high or very high molecular weight. Among other polymers used to promote dehydration are polyamines, polyalkylene oxides, polyethylene imines, phenolic resins and diacrylamide polymers. There are numerous examples of processes in which water-soluble acrylic polymers are used for flocculation, for example EP-A-641,293 for paper-making wastewater pastes and EP-A-235,893 for papermaking. Examples of processes using phenol formaldehyde and polyethylene oxide include U.S. 5,354,479 and the CA 1,004,782 to treat waste paper manufacturing, and the 095/21296 to manufacture paper. An example of a process where it is proposed to use any of a substantially non-ionic acrylic polymer or PEO for papermaking is EP-A-017353. The polymers usually used to promote sludge dehydration are, generally, of relatively high molecular weight, water soluble, cationic polymers such as polymers of 20 to 95% by weight of acriiamide and 5 to 80% by weight of polymers. an acid or quaternary addition salt of a dialkylaminoalkyl (meth) acrylate or acrylamide. These polymeric acrylic flocculants give good results in many sludge dewatering processes. However, there are some particularly difficult muds where it is necessary to use unacceptably large amounts of these acrylic polymers to obtain satisfactory results, or where economically satisfactory results can not be obtained using such polymers. The difficult sludges that teens from this disadvantage tend to be those that include secondary sludge (especially when some or all of the sludge is derived from waste associated with papermaking) and the sludge that includes significant amounts of waste destiny, recycling waste. and residues of mechanical reduction to paste. Primary sludges are sludge obtained by the clarification and sedimentation of an aqueous liquor which can be, for example, municipal sewage or effluent from a paper mill, pulp mill or destiny plant. The separation of the primary sludge from the initial liquor results in the formation of a supernatant or filtrate and this is then usually subjected to biological treatment to form what is usually referred to as a secondary sludge. It is usually much more difficult to dewater the secondary sludge than the primary sludge and thus it is common practice to mix the primary and secondary sludge and then dehydrate the mixed sludge. This is true for the treatment of municipal wastewater and also for the treatment of industrial waste, in particular the treatment of effluent from paper mills, pulp mills and destination plants. As an indication of the greater difficulty of dewatering the secondary sludge, it can be mentioned that a typical primary sludge usually requires 0.1 to 1.5 kg of an optimal acrylic polymer flocculant per ton of dry mud solids while a primary sludge from an Designation, recycling or mechanical reduction to pulp requires 2 to 4 kg of optimal acrylic polymer flocculant per ton of dry sludge solids, and a secondary sludge usually requires 5 to 10 kg of optimal acrylic polymer flocculant per ton of solids. dry mud. Mud sludge containing secondary sludge, especially effluents from papermaking, pulping and destinization, often contain a higher proportion of organic waste which tend to interfere with the mechanisms of flocculation and dehydration. As a result, the rate of dehydration and / or clarity of the filtrate or supernatant and / or the dryness of the cake solids tends to be unsatisfactory when relatively large amounts of polymeric flocculant are used on the slurry. Polymers that have been accepted as being usually the most efficient for such sludges are usually molecular cationic acrylic polymers, sometimes in combination with low molecular weight cationic polymers such as polydimethyl diallyl ammonium chloride. It would be desirable to be able to improve the dewatering of difficult muds to obtain an improved dehydration rate combination and / or clarity of the filtrate or supernatant and / or solids of the cake, especially when the sludge originates (at least in part) in a paper mill, pulp mill or destiny plant.

Brief Description of the Invention According to the invention, a difficult mud is dehydrated by a process comprising flocculating the mud by mixing a flocculating system in the mud and separating the water from the flocculated mud, where the flocculating system comprises a phenolic material and a flocculant of polyalkylene oxide. Consequently, contrary to the conventional it is believed that the best results are obtained with a cationic acrylic polymer, in the invention a combination of a nonionic polymer (polyalkylene oxide flocculant) and a nonionic or anionic material (the phenolic material). The polyalkylene oxide is usually polyethylene oxide and the phenolic material can be a residue, such as a lignin-containing papermaking residue, or a phenolic resin. As a result of the invention it is possible to obtain an improved performance and, especially, it is possible to achieve an improved effectiveness of the dose. In this way not only can a better combination of the dehydration rate and / or clarity and / or solids of the cake be obtained frequently, but these and other good results can often be obtained using a lower dose of polymer than that which is requires when using the cationic acrylic polymer that was previously considered optimal.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The invention can be applied to sludges which are entirely municipal in origin, but the invention is of particular value when applied to sludge derived from industrial effluents. In particular, some or all of the mixed sludge is preferably derived from effluents from a paper mill, pulp mill and / or destination plant. For example, at least 10% and often at least 20 or 30% dry weight, and often 50 to 100% dry weight, preferably sludge is derived from a mill or plant. The sludge to be dehydrated can be a difficult primary sludge, in which case at least 10% by weight of the primary sludge is generally selected from destination waste, recycled paper waste and pulp mechanical reduction waste. In this way at least 10% of the dry weight of the solids in the sludge can be provided by the waste of a destiny plant and / or of a pulp reduction plant of recycled paper and / or of - a reduction plant Pulp mechanics, that is to say a plant where the reduction to pulp is conducted by mechanical or semimechanical means. Sludge from waste plant waste, recycled paper mills and mechanical pulp reduction plants are all considered as dirty sludge which is difficult to dehydrate.The sludge often contains at least 25% dry weight and frequently less 50% of such waste The advantages of the invention are particularly evident when the sludge is a mixed sludge containing primary and secondary sludge.The secondary sludge may be present in a small amount (for example at least 2%) when mix primary hard sludge with this, but usually the amount of secondary sludge is at least 5 or 10% by weight of the mixed sludge (ie 5 or 10% based on dry solids). in the invention it is technically possible but in a usual manner it is commercially desirable to include primary sludge with the secondary sludge and there is usually at least 5% of the primary sludge in the sludge Usually, the dry weight ratio of primary sludge: secondary sludge is not greater than about 50: 1, and usually not greater than 20: 1, preferably not greater than about 10: 1 or in many processes, not greater than 5: 1 It is usually not less than about 0.1: 1, preferably not less than about 0.2: 1 and generally not less than about 0.5: 1. Quantities in the range of approximately 5: 1 to 1: 1 are often adequate. The invention is of particular value when applied to mixed sludge in which at least 10% and preferably at least 20 or 30% by weight of the dry solids are derived from debris., waste of recycled paper and waste of mechanical reduction to pulp. The primary mud fiber content seems to contribute in a particularly beneficial way to the process and it is thus desirable that a significant portion, for example of at least 10 or 20% by weight and often 50 to 100% by weight, of Primary sludge is derived from a paper mill and / or pulp mill and / or destiny plant. Accordingly, the invention is of particular applicability when driving in a paper mill and / or pulp mill and / or complete destiny plant or mainly for the treatment of sludge generated in that mill or plant. The dehydration process that is promoted in the invention can be a thickening process, for example when the mixed slurry has a relatively low solid content, typically from 0.5 to 2% by dry weight. The thickening can be by filtration or sedimentation. Dehydration can be by flotation. Preferably the process results in the formation of a cake, for example as a result of subjecting the flocculated material to any of the conventional cake-forming dehydration processes such as strip processing, centrifugal dehydration or pressure filtration, for example with a screw press or filter press. The resulting cake preferably has a dry matter content of at least 20% by weight and usually at least 25% and preferably at least 28 or 30%, for example up to 35 or 40%. The sludge to be dehydrated to provide the cake may have a solids content as low as 1 or 2% but the solids content is usually at least 3% by weight, for example up to 15% or 20% by weight. %. The flocculation system is mixed in mud to effect flocculation. Although both components can be added simultaneously, they are preferably added sequentially. Usually, better results are obtained by mixing the phenolic material in the mud followed by the mixing of polyalkylene oxide in the mud.

It is necessary that both materials are in solution to cause them the desired flocculation effect and it is generally better to introduce the materials in the mud as preformed aqueous solutions. They are usually supplied at the optimum dilution before being mixed with the sludge, but if either or both of them are desired they can be introduced into the sludge in a more concentrated form, together with dilution water to facilitate distribution through the sludge. . When the phenolic material is first added, it is often convenient to observe the character of the mud after mixing the phenolic material in it. If the mud appears to be more viscous at this stage, it may be an indication that the amount of secondary mud in the mixture is greater than is appropriate for good results with that phenolic material. Under these circumstances it is desirable to modify the mixed sludge by reducing the proportion of the secondary sludge, or to test the effect of different phenolic materials to find one that does not have this viscous character. For example, changing the phenolic material to a resin that does not have a higher molecular weight can solve the problem without having to change the proportions of primary and secondary sludge. It seems desirable that the phenolic material react with the components of, especially, the secondary sludge, before the addition of the polyalkylene oxide. In particular, it appears that the phenolic material reacts with the proteinase material in the slurry and that the polyalkylene oxide causes flocculation by interaction with this complex or reaction product. Regardless of whether or not this mechanism is correct, we find that it is possible to obtain good results using phenolic residual materials, that is, materials which are by-products of an industrial process and have a phenolic content. This phenolic content can be monomeric or polymeric. When referring to "phenolic" we intend to refer not only to phenol itself, but also to phenols and substituted naphthols, whether in monomeric, oligomeric or polymeric form. Preferred residual liquors that can be added to the sludge to introduce the phenolic material into the sludge include residual liquor containing phenolics that were recovered from a paper mill, pulp mill or destiny plant. In this way a residual liquor with a relatively low solids content of such a mill or plant can be used to supply the required phenolic material. Such residual liquors are preferably byproducts of wood extraction processes, such as Kraft's Black Liquor, Neutral Sulfite Semi-Chemical Liquor and other sulfite liquors, as well as washing liquors obtained from washing the pulp after cooking. , or filtrate obtained through the extraction process conducted in the wood crushing, mechanical quimioterm pulp, thermomechanical pulp, bleached mechanical quimioterm pulp, unbleached pulp or in fact, any flow or current of a pulp mill or paper containing lignins , wood resins and similar phenolic components in a useful concentration. Other residual liquors containing lignin and other phenolic components and which can be used in the invention include residual liquors from sawmills and residual liquors from coal processing facilities, for example coal scrubbers. The preferred residual products are residual liquors of the pulp reduction, especially Kraft Black Liquor and Neutral Sulfite Semi-Chemical liquors and other sulfite liquors. Instead of relying solely on the residual phenolic material, it is often preferred to use phenolic resin, in particular deliberately synthesized or extracted phenolic resin, i.e., material which is commercially distributed as phenolic resin. The best results, especially from a cost point of view, are often obtained by using a combination of residual phenolic liquor and phenolic queen extracted or synthesized.

The phenolic resin can be any phenolic resin substantially soluble in water and is usually a formaldehyde phenolic resin. This may contain sulfone and / or sulfonic acid groups. Thus, while conventional soluble phenol formaldehyde resins can be used, it is particularly preferred to use phenolic resins containing sulfone and sulfonic acid groups, in particular the resins described in our application 095/21296 and US 5,538,596 to Satterfield et al, both of which are incorporated here as a reference. The polyalkylene oxide may be any polyalkylene oxide that has the potential to produce a useful flocculation. The alkylene groups can be propylene but are usually ethylene and the best results are obtained generally when the polyalkylene oxide is polyethylene oxide. The molecular weight is usually greater than 1 million but less than 25 million, for example from 3 to 10 million. Optimal amounts of phenolic material and polyalkylene oxides will be best found by routine experimentation on the particular slurry mixture to be treated. Usually the dry weight ratio of phenolic material: polyalkylene oxide is in the range of about 25: 1 or 1:10, preferably about 10: 1 or 1: 3 and often in the range of about 5: 1. or 1: 2. The dry weight of polyalkylene oxide that is added to the slurry is generally in the range of about 0.05 to 10 kg / t, often about 0.1 to 3 kg / t and usually about 0.2 to 1.5 kg / t. In particular, the amount of polyalkylene oxide is usually lower (and often less than two thirds or less than half) than the amount of conventional cationic polymer that would normally be used for optimum results with that particular slurry. For example, if that particular mud mixture was normally flocculated using 3 kg / t of cationic acrylic polymer, in the invention we find that the amount of polyethylene oxide "would normally be less than 1.5 and usually less than 1 kg / t. The combined weight of the polyalkylene oxide and phenolic material is generally less than the amount of conventional cationic polymer that is optimal, Typically the amount of phenolic material (dry weight) is 0.3 to 5 kg / t, often 0.5 to 3 kg With many sludges, quantities in the range of 0.5 to 1.5 kg / t of phenolic resin (or equivalent amounts of residual liquor containing phenolic material) are often adequate.The pH of the sludge may, if required, be adjusted beforehand. of the addition of the flocculant system, to optimize the effect of the flocculating system, if necessary, the temperature of the mud or of the solution or aqueous solutions of phenolic and flocculant material Polyalkylene oxide can be adjusted to give optimum results. Any of the mud or flocculating system may be above room temperature. Heating may be applied to achieve this or phenolic material containing hot liquor, for example pulp reduction liquor, may be used without deliberate cooling. Although the preferred processes of the invention depend on the flocculating system of phenolic material and polyalkylene oxide flocculant as the essential components, and in fact generally the only flocculating components used in the process, it is possible to add other synthetic polymers to promote flocculation. For example, the effect of the polyalkylene oxide flocculant can be increased or supplemented by the addition of nonionic polyacrylamide, with before or after the polyalkylene oxide, or some other synthetic polymeric flocculant (nonionic, anionic or cationic) can be added. Such materials to be added with, just before or after the polyalkylene oxide are usually of high molecular weight, for example with a intrinsic viscosity greater than 4dl / g or a molecular weight greater than 2 million. The intrinsic viscosity is measured by a suspended level viscometer in IN sodium chloride solution buffered at pH 7 at 20 ° C. It may be desirable to add an organic or inorganic cationic material to the slurry before adding the phenolic material and the polyalkylene oxide flocculant. This organic or inorganic cationic material can be a multivalent metal coagulant such as a ferric or aluminum coagulant but is preferably a water soluble cationic polymeric coagulant. This may be a natural cationic polymer but is generally a synthetic cationic polymer having an intrinsic viscosity less than 3dl / g. Usually this has a relatively high charge density, for example, of at least 4meq / g, thus indicating that, generally, at least 50%, and usually at least 70%, by weight of the monomeric material used to form the polymer is cationic. The IV of the cationic coagulant polymer is usually less than 2dL / g, the molecular weight is typically from 20,000 to 2 million, usually from 100,000 to 500,000 or sometimes up to 1 million. Suitable coagulating polymers include polyacrylamide and formaldehyde polymers, diallyl dimethyl ammonium chloride homopolymers and copolymers (generally with acrylamide) or dialkylaminoalkyl (meth) acrylate or acrylamide polymers (usually as an acid or quaternary ammonium addition salt) ), dimethylamino epichlorohydrin polymers and other polyamines or polyethylene imine. Instead of using a polymer with a high charge density and low molecular weight, it may sometimes be useful to include a higher molecular weight cationic acrylic polymer either before the defined flocculation system of phenolic material and polyalkylene oxide or with this , or more usually, after this. These higher molecular weight cationic polymers can conventionally be acrylamide copolymers with dialkylaminoalkyl (meth) acrylate or acrylamide (usually as methyl chloride or dimethyl sulfate or other quaternary salts) or diallyl dimethyl ammonium chloride. Typically they have an intrinsic viscosity of 4 to 20, often 6 12dl / g. The molecular weight is typically in the range of 500,000 to 15 million, often around 2 to 10 million. The following examples are examples of the invention.

Example 1 Waste effluent liquors from a paper mill were collected and subjected to sedimentation to form a primary slurry having a solids content of 2.5%. Those and other liquors in the mill were collected and subjected to biological digestion and therefore a secondary sludge with a solids content of 1.0% was produced. Two parts by dry weight of the primary slurry were mixed with one part by dry weight of the secondary sludge. The resulting mixed sludge was subjected to laboratory tests with several doses. of flocculating systems and free drainage values were determined to record the drained volume of 500 ml of the mud sample and 100 ml of drinking water (used to dilute the chemical additives) at 30 seconds and 60 seconds (simulating free drainage) initial) and under pressure at 120 seconds (simulating the ability to provide a dry cake). In each case, the highest value indicates a better performance. The angular quality values of the filtrate were determined, and again the highest value indicates the best filtering (the lightest). The following table shows the results for various doses of a single flocculant consisting of a copolymer of 90% by weight * of acrylamide and 10% by weight of quaternized dimethylaminoethyl methacrylate methyl chloride, an IV of 14dl / g (polymer I ) and results are also given for various combinations of polyethylene oxide, with a molecular weight of 7,000,000 (PEO) and phenol sulfone-formaldehyde resin (PSR). The reasons for adding the component were used per ton of dry sludge, that is, an addition of 0.1% is equal to 1 kg of component / ton of dry sludge.

TABLE I ) J From the foregoing, it can be seen that the results of the free draining and draining pressing improved considerably, and the clarity is considerably better, with the mixture of polyethylene oxide and phenolsulfone-folmaldehyde of the invention than with the conventional acrylic polymer, although the dose Total polyalkylene oxide and phenolsulfone-formaldehyde polymer was considerably lower than the optimal dose for the acrylic polymer.

EXAMPLE 2 The process extensively described in Example 1 was repeated except that pulp mill sludge mixed at a ratio of one part by dry weight of primary sludge to ten parts of secondary sludge was used. The resulting mixed sludge was subjected to laboratory tests with various flocculating systems to determine the drainage and clarity of the filtrate. The following table shows the results of several doses of flocculants consisting of a copolymer of 90% by weight of acrylamide and 10% by weight of quaternized dimethylaminoethyl methacrylate methyl chloride, with an IV of 14 dl / g (Polymer I) and also results are given for various combinations of polyethylene oxide, phenolsulfone-formaldehyde resin (PEO) with a molecular weight of 7,000,000, and phenol-formaldehyde resin (PFR). The reasons for addition of the component were based on dry mud ton, that is, the addition of 0.1% is equal to 1 kg of component / ton of dry mud.

TABLE 2 From the above it can be seen that the free draining and draining press were considered good, and the clarity was considerably better, with the phenolic mixture of polyethylene oxide of the invention than with the conventional acrylic polymer, even when the total dose of the The phenolic mixture of polyalkylene oxide was considerably lower than the optimum dose for the acrylic polymer.

EXAMPLE 3 The process widely described in Example 1 was repeated except that mixed paper mill sludges were used at a ratio of one tenth dry weight of primary sludge to one part dry weight of secondary sludge. The resulting mixed sludge was subjected to laboratory tests with various flocculating systems to determine the drainage and clarity of the filtrate. The phenolic material varied in these tests and, as shown in the table below, includes a phenolsulfone resin (PSR) containing sulphonic acid groups such as W095 / 21296 and a black Kraft liquor (KBL) from the reduction process. wood pulp as a source of part or all of the phenolic material. The ratios of the components were based on dry mud ton, is to say that an addition of 0.1% is equal to 1 kg of component / ton of dry mud.

TABLE 3 From the foregoing, "it can be seen that the results of free draining and draining pressing improved considerably, and clarity is considerably better, with the phenolic mixture of polyethylene oxide of the invention." Kraft's black liquor (KBL) could be used. as the cofactor of PEO itself or in combination with the phenol resin, sulfone-formaldehyde (PSR).

Example 4 The process described extensively in the Example 1 except that mixed paper mill sludge was used at a ratio of two parts by dry weight of primary sludge to 7 parts of primary destiny sludge from a paper recycling operation. It was determined that the resulting mixed slurry contained 1.3% solids and was subjected to laboratory tests with different flocculating systems to determine the drainage and clarity of the filtrate using a turbidimeter instead of the clarity wedge. The following table shows the results for the different doses of flocculants which consisted of a copolymer of 60% by weight of acrylamide and 40% by weight of methyl chloride of quaternized dimethylaminoethyl methacrylate, with an IV of 9 dl / g (Polymer II ) and the results are also given for various combinations of polyethylene oxide, phenolsulfone-formaldehyde resin (PSR) and a molecular weight of 7,000,000 (PEO). The component addition ratios were based on dry sludge ton, that is, the addition of 0.1% is equal to 1 kg of component / ton of dry sludge.

TABLE 4 ? or From the above, it can be seen that the free draining results improved considerably, and the clarity was considerably better with the mixture of polyethylene oxide and the phenolsulfone-formaldehyde resin of the invention than with the conventional acrylic polymer in mixed mud, the sludge primary, secondary and destiny. It is noted that in relation to this date, the best method known to the applicant to carry out the aforementioned invention, is that which is clear from the present description of the invention.

Claims (17)

CLAIMS Having described the invention as above, the content of the following claims is claimed as property:

1. A process for dehydrating sludge from which at least 10% is selected from secondary sludges and primary sludges derived from destiny waste, recycled paper waste and pulp mechanical reduction waste, characterized in that it comprises flocculating the sludge by mixing a flocculating system in the sludge and separating the water from the flocculated mud, where the flocculating system comprises a phenolic material and a polyalkylene oxide flocculant.

2. The process in accordance with the claim 1, characterized in that it comprises clarifying and sedimenting the effluent from a paper mill, pulp mill or destiny plant to form a primary sludge, mixing the flocculant system in the primary sludge optionally after mixing the secondary sludge in the primary sludge, and then dehydrating the slurry to provide a cake having a solids content of at least 20% by dry weight.

3. The process according to claim 2, characterized in that the sludge has a solids content of at least 3% by weight.

4. The process according to claim 2, characterized in that the dehydration is by means of a process selected from the band pressing, centrifugal dehydration and filter press.

5. The process according to claim 2, characterized in that the dehydration is by means of a filter press.

6. The process according to claim 1, characterized in that the sludge is a mixed primary and secondary sludge in which the dry weight ratio of the primary sludge to secondary sludge is 50: 1 to 1:10.

The process according to claim 1, characterized in that at least 50% by weight of the sludge is derived from a paper mill, pulp mill or destiny plant.

8. The process according to claim 1, characterized in that the flocculating system is mixed in the mud by mixing the phenolic material in the mud and then mixing the polyalkylene oxide in the mud.

The process according to claim 1, characterized in that the phenolic material is added to the sludge as a recovered phenolic waste liquor and a paper mill or a pulp mill or a destinization plant or a coal washing plant.

10. The process according to claim 1, characterized in that the phenolic material is added to the sludge as a residual liquor containing lignin.

11. The process according to claim 10, characterized in that the phenolic resin synthesized or extracted is added with the residual liquor.

12. The process according to claim 1, characterized in that the phenolic material comprises phenolic resin synthesized or extracted. The process according to claim 1, characterized in that the phenolic material is a phenolic resin selected from phenolic formaldehyde resins, phenolic sulfone resins and phenolic resins containing sulphonic acid groups. 14. The process according to claim 1, characterized in that the polyalkylene oxide is polyethylene oxide. 15. The process according to claim 1, characterized in that the dry weight ratio of phenolic material: polyalkylene oxide is from 15: 1 to 1: 3. The process according to claim 1, characterized in that the amount of polyalkylene oxide flocculant that is mixed in the suspension is 0.05 to 10 Kg / t dry weight, preferably 0.2 to 1.5 Kg / t dry weight. The process according to claim 1, characterized in that the cationic coagulant is mixed with the sludge before the phenolic material and the polyalkylene oxide flocculant, where the cationic coagulant is selected from multivalent metal compounds and soluble synthetic cationic polymers. in water having an intrinsic viscosity less than 3dl / g and a cationic charge density of at least 4meq / g.