A METHOD OF AND AN APPARATUS FOR SEPARATING LIQUID MANURE INTO A THICK SLURRY PHASE WITH HIGH DRY MATTER CONTENT AND AN AQUEOUS PHASE WITH DESIRED - HIGH, MODERATE OR LOW - N-CONTENT

Abstract: Liquid manure is separated into a thick slurry phase and an aqueous phase by a method wherein the manure in a first treatment stepis sedimented into a thick slurry phase containing the coarse solid matter components of the liquid manure and a primary aqueous phase, which is filtrated and discharged as aqueous phase with high N-content, when desired, or, passed to a second treatment step where it is mixed with a flocculant, and flocculated and sedimented into a secondary thick slurry phase, which is united with the thick slurry phase formed in the first treatment step, and a secondary aqueous phase, which is discharged as aqueous phase with moderate N-content, when desired, or passed to a third treatment step where it is subjected to ion exchange with a cation exchanger and discharged as aqueous phase with low N-content. The thick slurry phase is discharged from the first sedimentation step.

Description: A method of and an apparatus for separating liquid manure into a thick slurry phase with high dry matter content and an aqueous phase with desired - high, moderate or low - N- content The present invention relates to a method of and an appa¬ ratus for separating liquid manure into a thick slurry phase with high dry matter content and an aqueous phase with desired - high, moderate or low - N-content. The disposal of liquid manure constitutes a considerable problem in agriculture. A steadily increasing portion of the livestock manure is handled in the form of liquid manure, and in Denmark approx. half the produced livestock manure is removed from the stable as liquid manure. This mode of handling offers quite some advantages work-wise in the stable, but on the other hand it gives rise to problems outside the stable. In the present context "liquid manure" is defined as a mixture of water, faeces, urine, straw and fudder residues obtained by washing and cleaning stables for livestock such as pigs, hens, cows and horses; and "N-content" is defined as total nitrogen content in whatever chemical form it may occur. Liquid manure is traditionally disposed of by spreading over the fields whereby the fertilizing value of the nutrients contained therein is poorly utilized. However, the concentration of nutrients in liquid manure is relatively low. This means that the volume which must be distributed onto the agricultural fields is large compared with its fertilizing value. Even though, as mentioned, the concentration of nutrients, i.a. nitrogen, is relatively low in liquid manure this does not mean that it is at all times possible to spread out the liquid manure directly in nature without causing i.a. serious environmental problems. A too high N-content and a too high content of dry matter may thus cause scorching of plants, and if the vegetation in the area of spreading is unable to bind the nitrogen which is essentially in the form of ammonia and ammonium ions, it will either be washed down into the soil and converted by bacteria into nitrite and nitrate or be transferred directly to groundwater or other recipients as surface run-off, which in both cases will cause unacceptable contamination of recipients and/or groundwater. The volume problems have traditionally been solved without considering the environmental problems by storing the liquid manure up until such time when it is desirable to spread the collected liquid manure onto the fields, with resulting considerable demands on liquid manure storage capacity in agriculture. Typically, the environmental problems have been solved by increasing the storage capacity for liquid manure so that the liquid manure may be spread out at such times of the year when the risk of surface run-off and subsoil wash-out of nutrients is minimized. A variety of methods of treating liquid manure and other waste waters is known by which a concentrated or improved plant nutrient product may be formed. Thus, DE OS 21 61 131 describes a method of purifying and clarifying waste water involving treatment thereof with a precipitation agent e.g. Bentonite, whereafter the precipitated material is separated from the aqueous phase which is subsequently treated first with a cation exchanger and then with an anion exchanger. The precipitated material may be used as a plant nutrient. Further, EP patent application No. 0 201 722 describes a method of converting liquid manure into a solid plant nutrient product which is unharmful to groundwater, according to which the liquid manure is taken from a liquid manure tank and after aeration added with a clay mineral, preferably belonging to the Montmorillonite or Vermiculite family, in an amount being sufficient for binding the total amount of ammonium contained in the liquid manure, i.e. typically about 200-400 kg Montmorillonite per 1 t liquid manure. Finally, DK patent application No. 7149/88 describes a method of treating liquid manure, which comprises clarification by flocculation and subsequent ion exchange. By this method liquid manure is first subjected to a mechanical separation step, whereafter the mechanically separated liquid manure is mixed with an aqueous suspension of one or more flocculating clay minerals, e.g. Bentonite, the resulting mixture subsequently being introduced into a sedimentation tank for flocculation and sedimentation, whereafter clarified liquid and flocculated slurry are taken out separately from the sedimentation tank. The clarified liquid is then mixed with one or more ion exchange minerals, the resulting mixture subsequently being introduced into a sedimentation tank from which ion exchanged liquid and a slurry of spent ion exchanger are taken out separately. These slurries may be used as plant nutrients. It is, however, desired to provide a method of treating liquid manure by which the following is achieved: reduction of necessary storage capacity; time-wise flexible spreading; simple spreading by conventional equipment; improved exploitation of the content of nutrients; and - reduction of environmental problems, most importantly reduced N-pollution through wash-out, surface run-off and evaporation, and reduced odour nuisances. It is further desired to provide a method of treating liquid manure which results in an aqueous phase having properties (low content of nutrients) allowing it to be distributed without restrictions on agricultural soil all the year round, or directly to recipients without environmental damage; and further in - a phase in the form of thick slurry with high dry matter content, which is subject to the same possible regulations that may apply to storage of liquid manure, and which can be handled by conventional liquid manure spreading equipment. As, however, the acceptable content of nutrients in such an aqueous phase varies widely from season to season, it is desirable to provide a method which offers the possibility of varying the content of nutrients, in particular the N-content, in the aqueous phase. It is the object of the present invention to provide such a method of and an apparatus for separating liquid manure which meet the above demands. According to the invention the object is achieved by a method of separating liquid manure into a thick slurry phase with high dry matter content and an aqueous phase with desired - high, moderate or low - N-content, which is characterized in that in a first treatment step liquid manure is subjected to sedimentation in a sedimentation tank with formation of a thick slurry phase having high dry matter content containing the coarse solid matter components of the liquid manure and a primary aqueous phase freed of the coarse solid matter content of the liquid manure, the latter phase after filtration being discharged as aqueous phase with high N-content, when this is desired, or, if not, passed to a second treatment step where the primary aqueous phase is mixed with an aqueous solution or suspension of a flocculant, preferably with an aqueous suspension of one or more flocculating smectitic clays in a mixing ratio of 0.3-10, preferably 1-3 kg smectite/t liquid phase, whereafter the mixture is subjected to flocculation and sedimentation with formation of a secondary thick slurry phase with high dry matter content containing sedimented flocculated material which is returned to the first treatment step and united with the thick slurry phase formed therein, and a secondary aqueous phase freed of the suspended solid matter content in the primary aqueous phase, the said secondary phase being discharged as aqueous phase with moderate N-content, when this is desired, or - if it is desired to take out an aqueous phase with low N-content - passed to a third treatment step where the secondary aqueous phase is subjected to ion exchange with a cation exchanger, preferably an inorganic cation exchanger, in particular selected from clays and/or zeolites with a high specific ion exchange capacity for ammonium, whereafter the thus treated secondary aqueous phase is discharged as aqueous phase with low N-content, and that the thick slurry phase is discharged from the sedimentation tank as thick slurry phase with high dry matter content. When carrying out the method according to the invention the stored amount of water in the liquid manure can constantly be kept at a desired low value, as it is possible to remove a liquid phase which can be discharged directly to farm land and recipients without risk of environmental contamination, its N-content always being adjustable at a desired, safe value, without performing more process steps than strictly necessary. Hereby a particularly economic and environmentally acceptable treatment method is provided by which both initial and operational costs are kept at a minimum. In the present context high, moderate or low N-content in the aqueous phase mean a N-content of 8-3 kg N/m 3 , 4-2 kg N/m 3 , and 1-0 kg N/m 3 , respectively. When the liquid manure has a dry matter content between 2 and 5 weight-% and a total N-content of 3-6 kg N/m 3 , the discharged thick slurry may typically have a N-content within the range 7-15 kg N/m 3 , and a dry matter content within the range 6-12 weight-%. An advantageous property of the thick slurry consists in its thixotropic nature which partly impedes the diffusion velocity of ammonium from the thick phase to the supernatant water phase in the tank - and partly ensures that it can easily be brought on and kept in a homogeneous, stable and pumpable form, which facilitates the removal from the tank and the subsequent spreading onto the field. According to a special embodiment the second treatment step is repeated at least once. According to another preferred embodiment the third treatment step is repeated at least once. As well the second as the third treatment step may be performed continuously or batch-wise. The ammonium loaded ion exchanger may be discharged from the third treatment step and either stored as a separate product or transferred to the first treatment step and united with the thick slurry phase formed therein. The ammonium loaded ion exchanger may also be discharged from the third treatment step and passed to a regeneration step to be subjected to a treatment with an aqueous solution of a regeneration agent, preferably in the form of an aqueous solution of CaCl-,, providing a fresh regenerated cation exchanger and an aqueous ammonium ion containing eluate, which is either stored as a separate product or united with the secondary thick slurry phase withdrawn from the second treatment step and transferred to the first treatment step with the secondary thick slurry. The regeneration of the ion exchanger may also be performed "in situ", i.e. without transfer of the ion exchanger to a separate regeneration unit. In this case the introduction of the secondary aqueous phase is cut off when about 66% of the capacity of the ion exchanger has been utilized and an aqueous solution of a regeneration agent, preferably an aqueous solution of CaCl-, is introduced continuously in an amount corresponding to at least 66% of the capacity of the ion exchanger. Thereafter the introduction of the secondary aqueous phase is immediately resumed. The introduced solution of the regeneration agent will move through a fixed ion exchange bed as a plug having a front end and a rear end. The arrival of the front end and rear end, respectively, at the exit end of the ion exchange unit is detected by a monitor, e.g. a conductivity sensor, controlling a valve at the exit end of the ion exchange unit having two positions, a first position corresponding to withdrawal of aqueous phase with low N-content as described above, and a second position corresponding to separate withdrawal of exhausted regeneration liquid. According to a third preferred embodiment the cation exchanger is added and discharged continuously in the third treatment step in counter-current to the secondary aqueous phase, and the cation regeneration step is also carried out continously and in counter-current. According to a fourth preferred embodiment the liquid manure contains at least 25 weight-% pig manure, calculated on the basis of solid material. When an aqueous suspension of smectitic clay is used as flocculant it is necessary to age the suspension for up to 3 days before use. If no continuous stirring is applied, a stable suspension can be obtained at a solids content of approx. 10 weight-%. The liquid used to make up the stock suspension is conveniently taken from the supernatant of already flocculated aqueous phase so that further addition of water to the system is avoided. The invention also relates to an apparatus for separating liquid manure into a thick slurry phase with high dry matter content and an aqueous phase with desired - high, moderate or low - N-content, which is characterized in that it comprises a sedimentation tank having an inlet for liquid manure, an outlet for thick slurry and an outlet for a primary aqueous phase which is connected with a filtration apparatus provided with an outlet for filtered liquid, which via a change-over valve is connected with an outlet for aqueous phase with high N-content and a transfer pipe communicating with an inlet pipe of a flocculation and sedimentation tank; a tank for an aqueous solution or suspension of flocculating agent, which via a pipe and said inlet pipe is connected with the flocculation and sedimentation tank having an outlet for thick slurry phase, which via a pipe is connected with the lower part of the sedimentation tank, and an outlet for secondary aqueous phase, which via a change-over valve communicates with an outlet for aqueous phase with moderate N-content and a transfer pipe being connected with a liquid inlet in an ion exchanger tank having an outlet for treated liquid phase being connected with an outlet for an aqueous phase with low N-content and optionally an inlet for fresh ion exchanger and an outlet for spent ion exchanger. An apparatus according to the invention suited for continuous operation of the second treatment step further comprises a buffer tank for primary aqueous phase arranged between the outlet for filtered liquid and the inlet pipe of the flocculation and sedimentation tank and a mixing unit arranged between the transfer pipes and said inlet pipe. An apparatus according to the invention suited for batch- wise operation of the second treatment step further comprises a buffer tank for the secondary aqueous phase arranged between the outlet for secondary aqueous phase and the transfer pipe connected with the liquid inlet in the ion exchanger tank. Use of the method and apparatus according to the invention i.a. makes it possible to work with an optimum N-spreading strategy, so that optimum exploitation of the storage capacity is ensured at all times. In the following the invention is described in more detail by way of examples, reference being made to the drawing, wherein Fig. 1 shows a continuously operating plant for carrying out the present method; Fig. 2 shows a corresponding plant in which the flocculation and sedimentation step is performed batch-wise; Fig. 3 shows the volumes of total material, aqueous phase and thick sludge stored in the sedimentation tank plotted as a function of time; Fig. 4 shows percentage dry matter, kg N/m 3 , respectively of the material stored in the sedimentation tank plotted as a function of time; and Fig. 5 shows accumulated values of kg N from stable, in tank and irrigated, respectively, as a function of time. Fig. 1 shows a continuously operating plant for carrying out the present method comprising a sedimentation tank 3 having an inlet for liquid manure 2 coming from a stable 1, an outlet for thick slurry 28 and an outlet 7 for aqueous phase, which outlet is connected with a filtration apparatus 8 having an outlet 9 for filtered liquid which is connected with a buffer tank 10 with an outlet 11 which via a not shown change-over valve is connected with an outlet 11' ' for aqueous phase with high N-content and a transfer pipe 11' being connected with a mixing unit 115. The apparatus further comprises a tank 13 for an aqueous suspension of flocculating smectite containing clay which via pipes 12 and 12' communicates with the mixing unit 115 and which via pipes 12 and 12' ' communicates with a second mixing unit 115'. The mixing unit 115 is via a pipe 14 connected with a flocculation and sedimentation tank 15 having an outlet 40 for thick slurry phase which via a pipe 16 communicates with the lower part of the sedimentation tank 3. Further, the tank 15 has an outlet 17 for liquid phase which is connected with the mixing unit 115' which via a pipe 14' is connected with a second flocculation and sedimentation tank 15' having an outlet 40' for thick slurry phase, which via a pipe 16' and the pipe 16 is connected with the lower part of the sedimentation tank 3. The tank 15' is further provided with an outlet for liquid phase 17' which via a change-over valve is connected with an outlet 17' ' for aqueous phase with moderate N-content and a transfer pipe 18, which is connected with a liquid inlet in an ion exchanger tank 19 having an inlet 20 for fresh ion exchanger, an outlet 22 for spent ion exchanger and an outlet 21 for treated liquid phase for taking out an aqueous phase with low N-content. The apparatus furthermore comprises a tank 23 for regeneration of spent ion exchanger being introduced via the pipe 22. The apparatus also comprises a tank 29 for aqueous regeneration liquid which is connected with the tank 23 via a pipe 24. The tank has further outlets 26 and 27 for regenerated ion exchanger and a concentrated aqueous ammonium salt solution, respectively. The outlet 27 for the concentrated ammonium salt solution is connected with the sedimentation tank 3 via the pipes 16' and 16. Fig. 2 shows a plant for carrying out the present method in which the flocculation and sedimentation step is performed batch-wise. This plant comprises a sedimenta¬ tion tank 3 having an inlet for liquid manure 2 coming from a stable 1, an outlet for thick slurry 28 and an outlet 7 for aqueous phase, which outlet is connected with a filtration apparatus 8 having an outlet for filtered liquid 9 which via a not shown change-over valve is connected with an outlet 11'' for aqueous phase with high N-content and a transfer pipe 11 being connected with a combined mixing and sedimentation tank 15. The apparatus further comprises a tank 13 for an aqueous suspension of flocculating smectite containing clay mineral which via pipes 12, 12' and 14 communicates with the combined mixing and sedimentation tank 15 and which via pipes 12, 12'' and 14' communicates with a second combined mixing and sedimentation tank 15'. The tank 15 has an outlet 40 for thick slurry phase which via a pipe 16 communicates with the lower part of the sedimentation tank 3. Further, the tank 15 has an outlet 17 for liquid phase which is connected with the pipe 14' which is connected with a second flocculation and sedimentation tank 15' having an outlet 40' for thick slurry phase, which via a pipe 16' and the pipe 16 is connected with the lower part of the sedimentation tank 3. The tank 15' is further provided with an outlet 17' for liquid phase which via a change-over valve is connected with an outlet 17'' for aqueous phase with moderate N- content and a transfer pipe 30, which is connected to a buffer tank 31 with an outlet 32 which via a transfer pipe 18, which is connected with a liquid inlet in an ion exchanger tank 19 having an inlet 20 for fresh ion exchanger, an outlet 22 for spent ion exchanger and an outlet 21 for treated liquid phase for taking out an aqueous phase with low N-content. The apparatus shown furthermore comprises a tank 23 for regeneration of spent ion exchanger being introduced via the pipe 22. The apparatus comprises also a tank 29 for aqueous regeneration liquid which is connected with the tank 23 via a pipe 24. The tank has further outlets 26 and 27 for regenerated ion exchanger and a concentrated aqueous ammonium salt solution, respectively. The outlet 27 for the concentrated ammonium salt solution is connected with the sedimentation tank 3 via the pipes 16' and 16. In operation of the plant shown in fig. 1 the manure is separated into three layers in the sedimentation tank 3: Uppermost: a float layer 6, then: a primary aqueous phase 5 and lowermost: "a sediment" 4 in the form of a thick slurry phase having a high dry matter content containing the coarse solid matter components of the liquid manure. The sedimentation tank 3 is provided with a not shown pump positioned on a raft floating on the surface of the liquid manure. The pump is provided with an adjustable suction pibe extending down into the thin phase from where it sucks up liquid phase which via the filter 8 is transferred into the buffer tank 10. This liquid, referred to above as the primary aqueous phase, is easily pumpable and may be irrigated using standard agricultural irrigation equipment when such irrigation is acceptable. In such case the liquid is withdrawn via the outlet 11' ' for aqueous phase with high N-content. This aqueous phase is a colloidal solution of mainly faeces particles of colloidal dimensions in an aqueous solution of mainly salts of ammonia. In case irrigation with this liquid is not acceptable the liquid is subjected to further treatment. First, a flocculant is added and it has been found that the clay type Bentonite is not only suited but also the best out of a number of substances investigated. The Bentonite is added as an aqueous suspension of Bentonite having a Bentonite concentration about 10 weight-%. The amount of added Bentonite is about 0.2 weight-%, corresponding to about 2 kg Bentonite per 1 t of liquid phase per treatment. By this process colloidal faeces particles and clay particles gather in lumps (flocks) and sink to the bottom in the sedimentation and flocculation tanks 15 and 15' . These lumps will only sink very slowly, as the sedimentation velocity is approx. 1 cm per min. Therefore, the liquid phase admixed with Bentonite must be passed to the tanks 15 and 15' at a velocity which ensures that the upward movement in the tanks is less than 1 cm per min. If the velocity is higher the flocculated material will be entrained in the upwardly moving flow and discharged via the outlet pipes 17 and 17'. By these two treatments with Bentonite, the second treatment being performed essentially for security reasons, it is possible to remove the organic dry matter from the liquid. This ends the ammonium production, but there are still ammonium and inorganic salts dissolved in the liquid referred to above as the secondary aqueous phase. If irrigation with this liquid is acceptable the liquid is withdrawn via the outlet 17'' for aqueous phase with moderate N-content and irrigated. In case irrigation with the secondary aqueous phase is not acceptable the liquid is subjected to further treatment in the next step in which ammonium is removed by ion exchange, preferably exchanged with calcium ions. The ion exchanger is regenerated continuously with calcium and is reused. Hereby ammonium is liberated in a concentrated form as compared with the form it previously had in the liquid manure and withdrawn as the abovementioned concentrated aqueous ammonium salt solution. This solution is combined with the thick slurry of flocculated material withdrawn from the sedimentation tanks 15 and 15' and returned to the lower part of the sedimentation tank 3. It has been found that this thick slurry of flocculated material has a remarkable ammonium binding ability manifesting itself in the sedimentation tank 3: even though a considerable dewatering of the thick slurry of the flocculated material takes place in the sedimentation tank 3 this is not accompanied by any noticeable transfer of ammonium to the liquid phase 5, in other words the ammonium recovered in the ion exchange step is effectively transferred to and retained in the thick slurry phase in the sedimentation tank. It should be noted that according to other embodiments the ammonia exchanged ion exchanger may be withdrawn and either be stored as a by-product or introduced into the sedimentation tank 3. When the ion exchanger is regenerated, preferably with an aqueous CaCl^-solution, the ammonium salt containing eluate may also be collected and stored as a by-product. In operation of the plant shown in fig. 2 the liquid phase is withdrawn batch-wise from the sedimentation tank 3, filtrated in the filtration apparatus 8 and transferred directly to the sedimentation and flocculation tank 15 with addition of about 0.2 weight-% Bentonite as an aqueous Bentonite suspension corresponding to that mentioned above. The two suspensions are homogenized in the tank 15 for a few minutes, e.g. by repumping, and then flocculation and sedimentation are allowed to take place. Then the thick slurry of flocculated precipitated solid material is transferred to the sedimentation tank 3, and the aqueous phase is transferred to the second flocculation and sedimentation tank 15' with addition of a corresponding amount of aqueous Bentonite slurry. The flocculation and sedimentation process in the tank 15' is carried out as described above for the process in the tank 15. The thick slurry precipitated in the sedimentation tank 15' is transferred to the sedimentation tank 3 and the aqueous phase is transferred to the buffer tank 31 which functions as a reservoir for aqueous phase which may be subjected to continuous ion exchange as described above. By using the present method the farmer obtains improved possibility of managing his livestock manure, as well as improved possibility of exploiting the fertilizing value. This means that a larger plant production and/or a smaller fertilizer consumption can be obtained. At certain times of the year the primary aqueous phase may be irrigated directly as aqueous phase with high N- content. When the ammonium content of the primary aqueous phase is unacceptably high, the secondary or at least the ion exchanged secondary aqueous phase with moderate and low N-content, respectively, may be irrigated without causing environmental or other problems. This concept of irrigation with aqueous phases having desired N-contents at various times during the year is further illustrated in example 1 and 2 and with reference to fig. 3 in which the volumes of total material, aqueous phase and thick sludge stored in sedimentation tank 3 are plotted as a function of time, fig. 4 which shows percentage dry matter, kg N/m 3 , respectively of the material stored in the sedimentation tank plotted as a function of time, and fig. 5 which shows accumulated values of kg N from stable, in tank and irrigated, respectively, as a function of time. EXAMPLE 1 The batch-wise embodiment of the present method illustrated in fig. 2 was carried out in a pig farm with a liquid manure production of 10 m 3 /24 h. The liquid manure exhibited a dry matter content of 2.5 weight-%. The storage capacity of the sedimentation tank 3 was 900 m 3 . In the second treatment step the primary aqueous phase was mixed with an aqueous suspension of Bentonite having a Bentonite concentration of 10 weight-%. The mineral Glauconite with a modal content of 90% was used as cation exchanger. The plant was operating in the following way: In the summer season, i.e. from April 1 to October 1, the liquid manure was continuously introduced into the tank which was substantially empty on April 1. In the period from mid May to the beginning of June the fields were irrigated with primary aqueous phase, i.e. liquid with high N-concentration. After further build-up irrigation with secondary aqueous phase, i.e. liquid with moderate N- concentration, started in mid June and ended in mid July. After a third build-up period the fields were irrigated with primary aqueous phase in the period from mid August to the end of September, and at the end of September the thick slurry accumulated in the sedimentation tank 3 was removed from this tank and distributed on the fields as a high N-plant nutrient. In the winter season, i.e. from October 1 to April 1, only irrigation with an aqueous phase with a low N-content was acceptable and in order to reduce the amount of stored manure irrigation with ion exchanged secondary aqueous phase took place in the period from September 1 to the end of February. At the end of March the tank 3 was emptied completely and the content was safely distributed on the fields. A number of operational data for the plant appear from figs. 3-5 and table 1 below. max. N-concentration sum max. N-concentration win total N from stable total N irrigated N irrigated, winter irrigated during the year distributed during the ye annual production of manure max. dry matter, tank winter max. dry matter, tank summer irrigated area, winter EXAMPLE 2 The continuous embodiment of the present method illustrated in fig. 1 was carried out on a pig farm with a liquid manure production of 10 m 3 /24 h. The liquid manure exhibited a dry matter content of 4 weight-%. The storage capacity of the sedimentation- tank 3 was 900 m 3 . In the second treatment step the primary aqueous phase was mixed with an aqueous suspension of Bentonite having a Bentonite concentration of 10 weight-%. The mineral Glauconite with a modal content of 90% was used as cation exchanger. The flows and material concentrations at a number of crucial positions in the plant are presented in table 2: theoretical value, calculated as ammonium chloride ** theoretically 1-5% d.m., dependent upon regeneration concentration *** max. values **** min. values "A": primary aqueous phase "B": secondary aqueous phase ion exchanged secondary aqueous phase

Claims: C l a i m s 1. A method of separating liquid manure into a thick slurry phase with high dry matter content and an aqueous phase with desired - high, moderate or low - N-content, c h a r a c t e r i z e d in that in a first treatment step liquid manure is subjected to sedimentation in a sedimentation tank with formation of a thick slurry phase having high dry matter content containing the coarse solid matter components of the liquid manure and a primary aqueous phase freed of the coarse solid matter content of the liquid manure, the latter phase after filtration being discharged as aqueous phase with high N-content, when this is desired, or, if not, passed to a second treatment step where the primary aqueous phase is mixed with an aqueous solution or suspension of a flocculant, preferably with an aqueous suspension of one or more flocculating smectitic clays in a mixing ratio of 0.3-10, preferably 1-3 kg smectite/t liquid phase, whereafter the mixture is subjected to flocculation and sedimentation with formation of a secondary thick slurry phase with high dry matter content containing sedimented flocculated material which is returned to the first treatment step and united with the thick slurry phase formed therein, and a secondary aqueous phase freed of the suspended solid matter content in the primary aqueous phase, the said secondary phase being discharged as aqueous phase with moderate N-content, when this is desired, or - if it is desired to take out an aqueous phase with low N-content - passed to a third treatment step where the secondary aqueous phase is subjected to ion exchange with a cation exchanger, preferably an inorganic cation exchanger, in particular selected from clays and/or zeolites with a high specific ion exchange capacity for ammonium, whereafter the thus treated secondary aqueous phase is discharged as aqueous phase with low N-content, and that the the thick slurry phase is discharged from the sedimentation tank as thick slurry phase with high dry matter content. 2. A method according to claim 1, c h a r a c t e r ¬ i z e d in that the second treatment step is repeated at least once. 3. A method according to claims 1-2, c h a r a c t e r - i z e d in that the third treatment step is repeated at least once. 4. A method according to claims 1-3, c h a r a c t e r ¬ i z e in that the ammonium loaded ion exchanger is discharged from the third treatment step and either stored as a separate product or transferred to the first treatment step and united with the thick slurry phase formed therein. 5. A method according to claims 1-3, c h a r a c t e r ¬ i z e d in that the ammonium loaded ion exchanger is discharged from the third treatment step and passed to a regeneration step to be subjected to a treatment with an aqueous solution of a regeneration agent, preferably in the form of an aqueous solution of CaCl 2 , providing a fresh regenerated cation exchanger and an aqueous ammonium ion containing eluate, which is either stored as a separate product or united with the secondary thick slurry phase withdrawn from the second treatment step and transferred to the first treatment step with the secondary thick slurry. 6. A method according to claims 1-5, c h a r a c t e r ¬ i z e d in that cation exchanger is added and discharged continuously in the third treatment step in counter- current to the secondary aqueous phase, and that the cation regeneration step is carried out continously and in counter-current. 7. A method according to claims 1-6, c h a r a c t e r - i z e d in that the liquid manure contains at least 25 weight-% pig manure, calculated on the basis of solid material. 8. Apparatus for separating liquid manure into a thick slurry phase with high dry matter content and an aqueous phase with desired - high, moderate or low - N-content, c h a r a c t e r i z e d in that it comprises a sedimentation tank (3) having an inlet for liquid manure (2), an outlet for thick slurry (28) and an outlet (7) for a primary aqueous phase which is connected with a filtration apparatus (8) provided with an outlet (9) for filtered liquid, which via a change¬ over valve is connected with an outlet (11'') for aqueous phase with high N-content and a transfer pipe (11, 11') communicating with an inlet pipe (14) of a flocculation and sedimentation tank (15); a tank (13) for an aqueous solution or suspension of flocculating agent, which via a pipe (12) and the inlet pipe (14) is connected with the flocculation and sedimentation tank (15) having an outlet (40) for thick slurry phase, which via a pipe (16) is connected with the lower part of the sedimentation tank (3), and an outlet (17) for secondary aqueous phase, which via a change-over valve communicates with an outlet (17'') for aqueous phase with moderate N-content and a transfer pipe (18) being connected with a liquid inlet in an ion exchanger tank (19) having an outlet for treated liquid phase being connected with an outlet (21) for an aqueous phase with low N-content and optionally an inlet (20) for f esh ion exchanger and an outlet for spent ion exchanger (22) . 9. Apparatus according to claim 8, c h a r a c t e r - i z e d in that it has a buffer tank (10) for primary aqueous phase arranged between the outlet (9 ) for filtered liquid and the inlet pipe (14) and a mixing unit (115) arranged between the transfer pipes (11, 12) and the inlet pipe (14). 10. Apparatus according to claim 9, c h a r a c t e r ¬ i z e d in that it has a buffer tank (31) for the secondary aqueous phase arranged between the outlet (17) for secondary aqueous phase and the transfer pipe (18) connected with the liquid inlet in the ion exchanger tank.

Inventors: FREDERIKSEN JENS, HENRIKSEN KARSTEN, FREDERIKSEN, JENS, HENRIKSEN, KARSTEN
Applicants: FLOCCO TEC APS, FLOCCO-TEC APS
Application year: 1992
Main classification: A01C3
IPC codes: A01C3, C02F1, C02F9, C05F3