SE532532C2 - Drainage of sludge - Google Patents

Description

532 532 components. A common problem with state-of-the-art technology, where the water is not sufficiently purified, is that the recycled non-digestible components will take up more and more space in relation to the degradable biomass and therefore the efficiency and profitability of the process will be lower.

In particular, impurities in undissolved form can lead to problems in biological purification, as microparticles containing organic carbon tend not to be separated by conventional technology, and therefore lead to a large increase in COD content in the treated effluent. Likewise, recirculation of additive water can result in a concentration of other substances such as chloride and anneuria, which can interfere with the decomposition process if it occurs at too high a concentration.

In other equivalent processes, the water is separated from the sludge and then discharged into the sewage system without being recycled.

With conventional technology e.g. the above-mentioned, water which is separated in order to be recirculated or to be discharged into the sewage system will become heavily polluted and require subsequent purification.

Purification with traditional technology can in this way also cause problems, since traditional technology in special cases is deficient in terms of avoiding the non-digested matter being recycled and concentrated in the digestion process.

In the rotten sludge that has been separated during conventional dewatering, there are also pathogenic bacteria and viruses. These pathogens can cause disease or damage to living organisms, such as when sludge is used as fertilizer. In some environments, this is remedied by cleaning the sludge before digestion, but conventional methods may not be sufficient to completely eradicate all pathogens. These pathogens can then multiply in the digestion, which is normally carried out at a temperature of 40 to 60 ° C. The thermal treatment carried out according to all the rules of art is expensive, both from an investment and use point of view. Treatment of chemical sludge, eg sludge containing iron or aluminum hydroxide, with ultra- or micro-filtration at a high temperature is described in WO 03/099728 .

However, this document only takes into account the predominant recovery of iron or aluminum from sludge by initial acidification of sludge and does not address the improvement of biogas production from biological sludge. In fact, initial acidification makes this method unsuitable for sludge digestion as the low pH prevents the digestion process.

Of this, an improved treatment of sludge from sludge chambers would be advantageous and in particular a method for dewatering sludge which improves the sludge's properties in relation to recovery and / or discharge the sewage system of water from biogas production, improved biogas and a more efficient and cheaper sludge treatment. 532 EEE ”FJ; Summary of the Invention.

Thus, the present invention preferably seeks to reduce, alleviate or eliminate one or more of the above-identified shortcomings and disadvantages alone or in any combination and at least solves the above-mentioned problems by providing a method of treating sludge which includes height. temperature of the sludge; and filtering the sludge in one or more ultra-filter (UF) and / or micro-filter (MF) plants, thereby obtaining a concentrate and permeate, said concentrate contains substantially all of said suspended biological matter and said permeate contains substantially no suspended biological matter. .

The advantageous features of the invention are determined by the dependent claims.

Brief Description of the Drawings These and other aspects, features and advantages which the invention is capable of will be appreciable and illustrated by the following descriptions of embodiments of the present invention, with reference to the accompanying drawings in which Figure 1 is a process diagram according to an embodiment of the invention. invention Figure 2 is a process diagram according to another embodiment of the invention Figure 3 is a process diagram according to yet another embodiment of the invention; and Figure 4 is a section on the process according to yet another embodiment of the present invention.

Figure 5 is a process diagram according to yet another embodiment of the invention.

Figure 6 is a process diagram according to yet another embodiment of the invention.

Description of embodiments.

The following descriptions focus on the modalities of the present invention applicable to the treatment of sludge and in particular for the treatment of sludge where sludge dewatering is carried out by ultra-filtration (UF) and / or micro-filtration plants or UF plants combined with micro-filtration plant plants. However, ultra-filtration, which is used on its own, is preferred.

The ultra-alter systems can be set in series and / or in parallel. 532 532 H Usually, for example according to previous methods, UF is used at temperatures well below 100 ° C, such as from 20 to 50 ° C. In this temperature range, the sludge is sluggish and its content of cells, protein, fat and other macromolecular substances makes the fate low and the risk of foulíng is high. This means that the process must be run with low load and frequent washing of the equipment and replacement of diaphragms to avoid problems. Traditional UF technology also requires open channels to be able to function, which gives the process low efficiency. The high temperature at which the UFzen is run according to the current invention leads to sludges with low viscosity and good filtration properties, which gives a high flow and a low risk of fouling even if the concentration of biological matter in the incoming sludge is high. The high temperature this year eel walls to crack, protein to coagulate and macromolecules to break down.

The heat created in the UF step or step according to the embodiment of the current invention can also be disastrous when heat exchanging with incoming sludge.

The technology with UF can thus provide noticeable energy savings, even when you make sure that ultrafiltration in many cases is in itself an energy-intensive process. About 80 to 90% of the dried energy can be recovered. The increased heat energy contributes partly to increasing the fl fate and TS content, and partly to sterilization and coagulation of proteins. In embodiments of the invention, the temperature of the slurry for ultrafiltration may be in the range of 100 to 250 ° C, and most preferably in the range of 100 to 200 ° C, in particular in the range of 120 to 170 ° C.

The method of filtering the sludge at a high temperature also has an advantage over the current method by making it possible to concentrate the sludge with a high capacity and high purity without problems with downtime and high costs for maintenance and cleaning.

At high temperatures, it is also possible to use a smaller diameter of the membrane duct, thereby obtaining a higher efficiency of the plant compared to traditional UF technology.

Thanks to the properties gained through the high temperature, a high TS content can be achieved. The TS content of the concentrate is the same as the content achieved with the current technological level but without the use of added auxiliary coagulants.

Ultra- or micro-filtration of sludge separates all undissolved substances, which is not the case with the current technological level where the water has a high quantity of undissolved substances. UF also separates larger organic molecules.

A separation of all undissolved substances can give a larger amount of organic carbon in the water, which in turn results in lower costs for treatment and a simpler purification process if the separated water there needs to be purified. 532 532 new) In addition, if the water is recirculated, no undigested suspended material ends up in the digester. This can provide a higher process efficiency. In addition, parts of the undigested material in the slurry will be able to be digested by hydrolysis at the high temperature used in filtration, and thus, since small compounds will pass UF and be returned as digested material by rewatering, the efficiency of the digestion process can be improved. Compared with the sister according to prior art, this can give a noticeable increase in capacity in existing plants where recycled water that is not sufficiently purified is used.

Hydrolysis of digestate can also improve efficiency when water is separated from sludge and recycled.

If the digestate is not hydrolyzed before the digester, large increases in process efficiency can be achieved via hydrolysis during dewatering and recirculation of additive water consisting of the degraded, degradable biological substance. This efficiency can not be achieved through state-of-the-art technology.

The process heat can also be used in the hygienization of sludge which is preferably carried out when sludge is used as fertilizer. Since the sieve is heated to over 100 ° C during filtration, a complete sterilization of the dewatered sludge is achieved. This can significantly reduce hygiene compared with the state-of-the-art methods. Alternatively, the energy in the process can be reused in the purification even before the digestion, which saves energy.

According to one of the embodiments, a system for treating digested sludge is described in which the sludge is ultra- or micro-filtered at high temperatures, which gives a permeate free from suspended solids and a concentrate from bacteria and viruses.

Water that is separated during dewatering can be recycled in the digestion process or purified for subsequent discharges or a combination of recirculation and discharges. If the content of DS is above about 3-7%, depending on the composition of the digestive tract, it may be economically advantageous to use a conventional dewatering step. Reject water from dry drainage, which can normally have a TS content of about 2-5%, can then be used in the process according to some of the embodiments of the invention. However, a disadvantage of this system is that not all sludge is sterilized.

Since neither ultra- nor micro-filtration of biologically digested sludge results in a total separation of dissolved organic substances, further purification of the permeate is usually necessary. An alternative to further biological purification is to treat UF or MF filtration with Nano-filtration (NF) or reverse osmosis (RO). Nanoaltration separates all organic molecules larger than about 200-400 Daltons and most of the polyvalent ions, while monovalent ions such as armnoniak and chlorine pass through the membranes. RO separates 532 532 ö.-. essentially all organic molecules and 90 to 95% of the dissolved salts. The most common and inexpensive NF and RO filters are spirally wound membranes. A necessary condition for being able to use this type of membrane is that the treated liquid is free fi than suspended substances. A liquid that is UF- or MF-filtered meets this requirement in the same way as reject water from a conventional plant.

However, the permeate from UF and lviF will still include dissolved proteins if the filtration has taken place at conventional low temperatures. These proteins cause contamination on the NF and RO membranes. This means that the membranes need to be cleaned often and also that the membranes are difficult to clean. Finishing UF or MF permeate with RO or NF is therefore difficult and uneconomical. When UF or MF of biological sludge is performed at high temperatures according to some embodiments, the protein coagulates in the sludge and is separated. The permeate is free of protein and this makes post-treatment with NF and RO possible.

Finishing of UF and MF permeate with NF or RO offers new possibilities for separating salts, eg ammonia free from the organic phase. By purification with RO, ammonia and salts can be separated from the UF permeate and a concentration of impurities in the recycled additive water is avoided. By purification with NF, ammonia and chlorides are separated from the other organic substances. The organic substances, largely digested by UF hydrolysis, can be partially or completely recycled in the digestion process and the NF perneat can be purified from ammonia by e.g. stripping. Purification from ammonia can be performed efficiently thanks to the fact that most of the buffering organic substances have been neutralized.

In cases where discharges into drains are desirable, a treatment step with NF / RO means that subsequent treatment can be carried out cheaper and more efficiently.

According to one of the first embodiments of the invention, a sludge, which comprises wholly or partly comprising biologically suspended material, is treated according to the fl destined diagram in Figure 1.

Slarnmet has a neutral or alkaline pH. A pump 11 pumps the incoming flow of sludge 110 into the system and increases the pressure so that, in all parts of the system, it exceeds the pressure of the boiling point of water at the specific operating temperature. Pump III can also be replaced by pumps so that the pressure can be adjusted separately if the incoming flow of sludge 10 is subdivided into several substreams. The electrical energy added to the circulation pump (s) is mainly converted into heat and can be used to heat the sludge and to the thermal hydrolysis. The pressurized flow of sludge can thus be distributed over a first heat exchanger 112 and a second heat exchanger 113. In the first heat exchanger 112 the sludge is subjected to heat exchange with a hot stream UP permeate 122, output from a first 115, second 116 and a third 117 UF unit , separately. In the second heat exchanger 113, 532 532 the sludge is subjected to heat exchange by the hot flow of concentrated UF, output from the first, second and third UF units 115, 116 and 117.

Of course, the first, second and third UF units 115, 116 and 117 may be replaced by a single UF unit, or other combinations of UF units and / or microelteration units, such as UF units connected in parallel and / or series connected as described below.

To reuse the maximum amount of heat, the incoming fl fate of sludge can be distributed, for example, proportionally to fl the fate of permeate and concentrate, each moving. After heat exchange, heat energy 114, pipes to compensate for possible heat loss in the system can be added. This heat energy 114 can, for example, be an addition of hot steam. Thereafter, the heated sludge is treated with ultrafiltration (UF) and / or milco filtration. In this example, the first, second and third UF units 115 116 and 117 are connected in series. A first 118, second 119 and third 120 UF pumps pump sludge through the first, second and third UF units 115, 116, 117, respectively.

To drive the UF units, the sludge is placed under increased pressure in one or more of your pressure pumps, the effect of which will be described in more detail below. The pressure should preferably exceed the pressure for boiling water in each part of the UF unit. In order to avoid contamination of the membrane surfaces as much as possible, the speed of fate through the membrane channel should preferably be high.

The thirstiest, second and third UF pump, 118 119 and 120 may have significantly higher capacity compared to pump 111. From each UF unit there is an outflow of a stream of permeate whereby the concentration of the suspended material as biological suspended material in the sludge is increased in the concentration. The flow of concentrate can be partially recirculated across the membranes and partially transferred to the next membrane step, as illustrated in Fig. 1. Thus, in one embodiment of the recovery, the concentrated sludge flow can be reused under pressure in each UF step.

The hydrolysis of the sludge depends partly on the residence time of the sludge and partly on the working temperature. The hydrolysis of the sludge can start already in the UF stage, ie. The UF units depending on the heat generated therein, and the added heat. In another embodiment of the invention according to fi g. Placing a tank 121 in one of the special UF stages further enhances the hydrolysis. The concentrated fl fate fi of the last UF stage then leads to tank 121. In tank 121, the hot concentrated sludge can have a residence time sufficient to achieve optimal hydrolysis. Meanwhile, the slurry can be purged at a higher temperature in tank 121, also to achieve optimal hydrolysis. Such a residence time and temperature preferably takes place in a range of 15 to 60 minutes and at a temperature in a range of 100 to 250 ° C 532 532 and preferably in a range of 100 to 200 ° C such as a range of 140 to 165 ° C.

A UF permeate desolation 124, desolation in the UF unit or the first heat exchanger 1 12, can then, for example, be used directly as additive water with a coal source or further treated for bottling and a concentrated UF desolation 125, effluent in the UF units, tank 121, or the second heat exchanger 113, can be used as fertilizer.

Thus, a method of formulations for treating sludge from a plant for the production of biogas, where the sludge contains at least partially suspended biological material, has been described. In this method, the temperature of the sludge is elevated, after which the sludge is filtered in one or more ultratiltration units and / or micro-filtration units, whereby a concentrated and a permeate are obtained, which mainly comprises said suspended biological substances and said permeate comprises substantially no suspended biological substances.

Factors that can be used to characterize the UFzn are the layout of the filter / filter, the working pressure, the working temperature, the membrane material, membrane properties, transmembrane pressure and the feed rate.

As stated above, in an embodiment according to the invention, the method can be performed in one or more UF units and / or zero filtration units, such as ultra-filtration membranes.

More specifically, in an embodiment according to the invention, the UF membranes are connected in series. In another form of drying of the invention, the UF membranes are connected in parallel. In yet another embodiment of the invention, the UF membranes are connected both in series and in parallel. In further embodiments of the invention, one or more of the UF membranes in the above-mentioned embodiments may be replaced by one or more of the microfiltration membranes.

To drive the UF units, place the sludge under elevated pressure in one or more of your pressure pumps until a pressure is reached. The division of the pressure increase on your pumps, such as a pump before each UF unit, can be advantageous in view of the stress on the pumps.

Also, if one pump does not work, the other pumps can compensate for the decrease in pump capacity, which emits sufficient pressure on at least some UF units and / or micro-filtration units to achieve the on-demand filtration power. In an embodiment of the invention, the pressure exceeds or is the same as the boiling point of water in each part of the UF unit. In order to prevent fouling on membranous surfaces as far as possible, the flow through the membrane channels should preferably be high, e.g. 6m / s. In one embodiment of the invention, the flow through the membrane channels is at a speed of 5 m / s. This flow is due in part to the transmembrane pressure. A high pressure, above 5 bar gives only a moderate increase in the fl fate while the risk of particles penetrating the active part of the membrane increases.

Thus, the transmembrane pressure is preferably in the range between 2 and 5 bar. In one embodiment of the invention, the average pressure on the transmembranes is approximately 3 bar. 532 532 (, As already stated above, according to an embodiment of the invention, the slurry is heated by heat exchange with eg hot UF permeate and concentrate, respectively, which are emitted from the UF surface (s). This is done to achieve the desired working temperature.

The heat exchange means that most of the heat that passes through the UF can be reused. To compensate for the systematic heat loss, energy can be added to the sludge. In one embodiment of the invention, this energy supply is made by injecting friend energy 114, such as hot steam. When the sludge has reached the desired operating temperature for the subsequent ultrafiltration rig, the sludge can be led to one or more UF stages.

The membranes used in the UF units and / or the micro-filtration units must be able to withstand the heat and pressure produced. Suitable membranes that meet these requirements are ceramic membranes.

In each filtration step, perineate is produced, which means that the sludge (concentrate) has an increasing content of dry matter content after passing each filtration step. In one embodiment, the membrane surface area in each UF stage and the number of UF stages at a given fate may be suitable partly for the amount of sludge to be treated and partly for the dry content desired after the final UF stage. With the high tea temperature in the UF, the same content of dry matter can be achieved as in a conventional dewatering equipment, ie. 10 to 20%. Suspended substances and molecules in the slurry, larger than the cut-off of the membrane, cannot pass through the membranes.

This makes the separation of impurities when using UF and / or micro-filtration superior to the use of only one centrifuge. Cut-off not only constitutes a clear limit for separation based on molecular weight, but also the shape of the molecular substances. The organic molecules that pass through the membranes and are found in the permeate are molecules with a relatively low molecular weight compared to those in the concentrate. Thanks to this, the permeate will contain organic substances that are easily biodegradable. The permeate can therefore be used as a source of carbon in treatment plants where nitrogen reduction is part of the purification process or as a carbon source in recycled additive water. Since no suspended material or larger molecules can pass through the mernbrans, the penetrate will be cleaner than the reject water fi- than conventional dewatering equipment. In one embodiment of the invention, the cut-off of the mernbran should preferably be 5 to 500 kD. According to an embodiment of the invention, set forth above, the hot concentrated UF feed 123 is passed to a reactor tank after concentration with UF where it is retained for a period of time. The total retention time of the slar (including the retention time in the UFzen) depends on the temperature and can vary from 15 to 60 minutes. In one embodiment of the invention, a retention time of 30 minutes at 165 ° C provides good heat hydrolysis. During the retention time in the reactor tank, the hydrolysed sludge can be subjected to heat exchange with a part fl of 532 532 lb the incoming sludge before it can be led to a buffer tank for storage. The stored sludge can then be used for eg fertilizer. '"In another embodiment of the present invention, according to fi g. 2, it is shown how phosphorus can be recycled from the permeate coming from the UF units. Phosphorus can be recovered from the sludge according to the following formula: Meroq.) + An * - + Mä * +31? + P02 'Where Me is an optional metal ion.

In this embodiment, sulfuric acid can be added to make the sludge acidic. Other acids can also be used within the scope of the present invention. Acidification can take place before the first UF stage. In this case, all the sludge and permeate will be acidic. The pH value is preferably reduced in the range between 1 and 2. If the sludge is heavily buffered, the amount of sulfuric acid will be needed, the pH value will increase.

Therefore, in another embodiment of the invention, the sludge is acidified before one of the UF units is deposited after the first UF unit and not before the first UF unit, if the UF units are connected in series. The amount of sludge that is acidified then decreases and so does the amount of sulfuric acid. Also, the acid-free permeate can in turn contribute to an increased pH if it is mixed with acidic permeate. This in turn can contribute to a reduction in the amount of base needed to later increase the pH of the permeate.

To increase the residence time and ensure a satisfactory solution of the metal phosphates in the sludge and / or increase the hydrolysis of the sludge according to one of the embodiments of the invention, tank 121 is part of the last UF stage instead of after the last UF stage, illustrated in Fig. 3. After the last sludge has passed the UF and reactor tank, and has been subjected to heat exchange of the incoming sludge, the outgoing concentrated sludge can be neutralized with a suitable base. Such a suitable base may, for example, be selected from a group comprising lye / caustic soda, lime, soda, magnesium oxide / magnesia. The choice of base is preferably made to optimize the sludge composition subsequent use as a fertilizer. The pH of the acidified permeate is increased to about 3 by the addition of the appropriate base. Such a suitable base may be, for example, NaOH (sodium hydroxide), but another suitable base may also be used without departing from the scope of the present invention. Before this, the permeate is cooled by a heat exchange process with incoming cold sludge (ie the sludge transported through the UF unit / units). After or before the pH of the acidified permeate is increased, a chemical coagulant is added. 532 532 A suitable chemical coagulant is trivalent iron. At pH around 3 a precipitate of sparingly soluble iron phosphate will occur. The precipitate of iron phosphate is separated by, for example, sedimentation, filtration or centrifugation. Thus, the iron phosphate precipitate from the permeate will contain less amount of heavy metals per kg of phosphate than untreated sludge because the refilling of heavy metals does not take place at pH3.

According to yet another embodiment of the invention, the hot UF fate 123 is led to an expansion insert 1210, i.e. according to Fig. 4. The expansion vessel 410 can be provided with an overpressure. The overpressure can for example be 0.1 to 0.5 bar, ie. if the pressure in the expansion vessel 410 is 1.1 to 1.5 bar. Consequently, water vapor 411 is released when the hot concentrated UF flow 123 enters the expansion vessel 410, since the pressure in the hot concentrated UF flow 123 is more than above 1.1 to 1.5 bar, such as 3 to 8 bar. In expansion vessel 410, the level of sludge can be kept largely constant, so that a concentrated sludge from the expansion vessel 412 can be taken from the bottom of expansion vessel 410 while the water vapor 411 of an expansion vessel can be taken from the top of expansion vessel 410. The concentrated sludge 412 can be led to buffer taric for storage. The stored concentrated slurry can be used for eg fertilizer. The water vapor flow 411 from the expansion vessel can be led to, and thus mixed with, the incoming sludge flow 110. In one of the excretory forms according to fig. 4, pump 11 is replaced by two pumps 111 and 11 lb, which are set in each part of the incoming sludge stream 10. Mixing of the water vapor flow from the expansion vessel 411 with the incoming sludge 110 can be performed on the suction side of pump 111b. According to another embodiment, however, said mixing can also be carried out in an arrangement where pump 111 simply replaces the second heat exchanger 113. All incoming sludge desolate 110 can be led to the first heat exchanger 112 and subjected to heat exchange by the hot UF permeate desolate 122, or only one part of the incoming sludge 110 is exposed for heat exchange to the first heat exchanger 112. The water vapor discharge 41 1 can thus heat the incoming sludge discharge 110 or a part of the incoming sludge discharge 110. In one of the discharge forms according to ñg. an example of the arrangement shown where in the water vapor flow 41 l heats parts of the incoming sludge flow 110 and parts of the incoming sludge flow 110 are subjected to heat exchange in the first heat exchanger 112.

In a discharge mold according to Fig. 5, incoming sludge 500 is led to a digester 511.

Digested sludge 511 is filtered 512. The filtration 512 can be done according to any of the previous forms. The filtered concentrate 513 is discarded and can be used as, for example, fertilizer.

The filtered permeate can be recycled 514 or passed to post-treatment 515.

Finishing 515 may be NF or RO, or a combination of NF and RO. The untreated permeate 516 can be further treated and / or discarded. It can also be 532 532 1 .... i. Recirculated 517. The pretreatment permeate can be discarded / further treated 518 or recirculated 519. Recycled filtered permeate 514, recirculated post-treated concentrate 517 and / or recirculated recreated permeate 519 are fed to an additive S20. From there, it is added 521 to the incoming sludge 500. In one embodiment, where the final treatment 515 is NF, the further processing process is ammonia removal. 1 an embodiment according to fi g. 6, no recirculation of permeate / filtration is performed. All other treated permeate is discarded 518 in, for example, the drain or tank.

The above-mentioned embodiments will now be exemplified in the following non-limiting examples: Example 1.

In an embodiment of the invention according to Fig. 1, an arrangement for dewatering and hydrolysis of sludge according to the invention is described.

Pump 111 pumps the incoming fl fate of sludge 110, with a pH of between 5 to about 9, into the system and increases the pressure so that, in all parts of the system, it exceeds the pressure of evaporation of water at the specific operating temperature. The compressed air-filled incoming flow of sludge 110 is spread over a first heat exchanger 112 and a second heat exchanger 113. In the first heat exchanger the sludge is subjected to heat exchange by the outgoing, hot flow of UF permeate 112 and in the second heat exchanger it is exposed to sludge exchanger 113. outgoing hot fl fate of UF concentrate 123. To reuse the maximum amount of heat, the incoming fl fate of sludge can be distributed Lex. proportional to the flow of permeate or concentrate, respectively. After the heat exchange, heat energy is added 14 14 to compensate for the heat loss in the system e.g. by adding hot steam. The heated sludge is then treated with ultra filtration (UF). In this example, three UF stages 115, 116 and 17 are connected in series. The UF pumps 118, 119 and 120 pump sludge through a UF separately. The UF pump pairs 118, 119 and 120 have significantly more capacity compared to pump 111. From each UF stage there is an outflow of permeate, whereby the concentration of sludge is increased in the concentrate which is partly recirculated through the membranes and partly taken to the next membrane stage. The outgoing cold fl fate of UF permeate 124 can then be used as additive water with carbon source or further treated. For dewatering, the outgoing cold concentrate stream 125 can be used as fertilizer.

Example 2. 532 532 Further embodiments of the invention illustrated in FIG. 2 and 3, the embodiments of which describe another arrangement, receive drainage and hydrolysis of sludge according to the invention, including recovery of phosphorus.

The basic set-up is the same as in Example 1. Before the first 1 15, second 116 and / or third 1 17 UF step, sulfuric acid can be added to the slurry to lower the pH. Consequently, bound phosphates (PO43 ') fi are released from the sludge concentrate.

The phosphates that have been released pass through the UF membranes 115, 116, 117 and will be recovered in the desiccant of the UF penneate 122. After the flow of UF permeate 122 has cooled in the thirsty heat exchanger 1 12, a chemical coagulant is added. An example of such a chemical coagulant is Fe ", such as ferric chloride. Before or after the addition of such a chemical coagulant, the pH can be adjusted by adding a base, eg lye. Addition of the chemical coagulant and / or base 214. Alternatively, the chemical coagulant and / or base may be added before said second tank 214 in the tube leading the fate of the UF permeate to the second tank 214. Preferably, said second tank 214 is provided with a stirrer. The precipitate is separated in, for example, a settling tank 125 where a clear water phase 216 is separated from an iron phosphate filter 217.

The clear water phase 216 from the sedimentation tank 215 can be further neutralized or used as additive water with a carbon source.

The outgoing cold stream of UF concentrate 218 is neutralized after cooling in the second heat exchanger 13 and decompressed. To ensure that a maximum of the precipitated phosphates is transferred to the iron form, tank 121 can be integrated into the last UF strut, thereby increasing the residence time for the production of the permeate. Tank 121 is then placed inside the closed circuit of the third UF 117 shown in fi g. 3.

Example 3.

In an embodiment according to Fig. 5, incoming sludge 500 is led to a digester, where it can be digested to eg biogas. Digested sludge 511 is filtered 512. The filtration 512 can be carried out according to any of the previous examples. The filtration concentrate 513 is separated and can be used as, for example, fertilizer. The filtration permeate can be recycled 514 or passed to post-treatment 515. After treatment 515 can be either NF or RO, or a combination of NF and RO. The treatment concentrate 516 can be further processed and / or discarded. In case the aftertreatment 515 is NF, the aftertreatment concentrate 516 is polyvalent salts and organic matter. In case the finishing 515 is RO, the finishing concentrate 516 is ammonia, salts and organic matter. The post-treatment concentrate can also be recycled 517. The post-treatment permeate can be discarded / further treated 518 or 532 532 re-recycled 519. Recycled filtration permeate 514, recycled post-treated concentrate 517 and / or recycled treatment permeate until the further 519 is added. In a formulation in which the final treatment 515 is NF, the further treatment 518 is the removal of ammonia e.g. by stripping or gas contact membranes, techniques well known to one skilled in the art.

Although the present invention has been described above with reference to specific embodiments, it is not intended to be limited to any particular form described herein. The invention is instead limited only by the accompanying claims and embodiments other than those specified above are equally possible within the scope of these appended claims, eg different layouts of the equipment than those described above. 1 the requirements do not exclude the term “covered / include” the existence of other elements or steps. In addition, although individual elements may be included in different claims, these may possibly be advantageously combined and the implication in different claims does not mean that a combination of elements is not possible and / or beneficial. In addition, references to the singular do not exclude plurals. The terms "one", "one", "first" second "etc. do not exclude speech.

References in the claims are provided for illustrative purposes only and should not be construed as limiting the scope of the claims in any way.

Claims (12)

5322 532 'REQUIREMENTS A method for treating sludge from biogas producing plants, wherein said sludge comprises at least partially suspended biological material, characterizes! by raising the temperature of the sludge to a temperature in the range between 100 to 250 ° C; and filtering the sludge in one or more ultra-filtration and / or micro-filtration units, a concentrate and permeate being obtained, said concentrates comprising substantially all of the aforementioned suspended biological material and wherein said permeate comprises substantially no suspended biological material. The method of claim 1, further comprising arranging at least two ultra-filtration and / or non-filtration units in series and / or in parallel. The method of claim 1 or 2, further comprising recovering the sludge over the ultrafiltration and / or mileage filtration unit or units. The method of claim 1 or 2, further comprising post-treating the perneat with nano-filtration and / or reverse osnos. The method of claim 4 further comprising purifying ammonia from the nano-filtered permeate. The method according to claim 1 or 2, wherein the ultrafiltration and / or microfiltration membrane is a ceramic membrane. The method according to claim 1 or 2, further comprising adding energy to said sludge before altering the sludge in one or more ultra-altering and / or micro-altering units. The method of claim 1 or 2 further comprising heat exchanging said permeate with said sludge before or after raising the pressure of said slurry. The method of claim 1 or 2 further comprising heating the concentrate to increase the hydrolysis. The method according to claim 9, wherein said heating takes place for a time period of 10 to 120 minutes. 532 532 The method of claim 1, 2, 7, 8 or 10 further comprising exchanging said concentrate with said sludge before or after raising the pressure of said sludge. The method of claim 1 wherein said concentrate is subjected to a pressure reduction, wherein water vapor is released from said concentrate.