WO1995021140A1

WO1995021140A1 - Method for processing semi-liquid manure and the device to be used

Info

Publication number: WO1995021140A1
Application number: PCT/BE1995/000011
Authority: WO
Inventors: Cesar Achiel Maurice De Vos; Leon Georges Petrus Blanckaert
Original assignee: G.C.M. Geodetics Construction Maintenance
Priority date: 1994-02-04
Filing date: 1995-02-06
Publication date: 1995-08-10
Also published as: AU1571995A; BE1008005A6

Abstract

A method for processing semi-liquid manure wherein this semi-liquid manure is separated by sieving into a liquid and a solid fraction, the liquid fraction is subjected to a biochemical decomposition process and to a flotation/sedimentation step. The thus obtained aqueous phase is in particular subsequently subjected to an ultrafiltration step, an ion exchange step and to a reverse osmosis in order to produce purified water and a concentrate. The ion exchanger is cleaned by means of lime milk, which thus also produces a usable fertilizer. The invention also relates to a device for applying this method.

Description

"Method for processing semi-licruid manure and the device to be used"

This invention relates to a method for processing semi-liquid manure, wherein this semi-liquid manure is separated in a liquid and a solid fraction.

Such a method is for example already disclosed in British Patent No. 1 576 423. In this known method, the semi-liquid manure is subjected to a vacuum filtration step, the obtained solid fraction being further squeezed under pressure to a moisture content of about 57%. In this way, a marketable solid product is obtained, possibly after mixing with peat, sand or soil.

A drawback of this known method is however that no solution is offered for the processing of the strongly polluted liquid fraction.

The invention has therefore as object to provide a method, which does not only produce a usable solid product, but which also offers a reusable liquid.

To this end, the method is characterized by the succession of process steps as pointed out in claim 1.

As a result of the biochemical decomposition process, a large portion of the organic matter can be removed via the supernatant and the sedimented phase, without requiring thereto flocculants such as polyelectrolytes. Such polyelectrolytes raise in fact the cost price of the purification process and constitute furthermore an additional pollution. The membrane separation is further clearly hampered by the presence of polyelectrolytes, because these poly- electrolytes tend to accumulate on the membranes, this in contrast to the used micro-organisms.

Said membrane separation is preferably done by application of the reverse osmosis technique. It was found that, compared to nanofiltration for example, this technique offers better results. The membranes have further a longer life span.

In an effective embodiment anions are removed out of said aqueous phase through ion exchange prior to said membrane separation. Through the ion exchange, anions such as nitrate are removed. Most of the cations of the aqueous phase arrive into the concentrate of the membrane separation, while in addition to this purified water is obtained. This water can be reused for example to clean stables, installations and the like, or it can also be used as drinking-water. In this latter case, minerals should be added, due to the low content of minerals.

In an effective embodiment of the method according to the invention, said separation of the semi- liquid manure in said liquid and solid fraction is carried out by sieving, more particularly on a shaking and/or vibrating sieve.

It was found that in this way the major part of the phosphor ends in the solid fraction, as a result of which the anion exchanger is clearly less loaded. Also the major part of the calcium ends thus in the solid fraction. Compared to the known filtration and squeezing technique, a larger part of the nutrient elements is valorized and the purification of the liquid fraction is considerably simplified.

Preferably, said aqueous phase is subjected prior to said membrane separation, in particular prior to said ion exchange, to an ultrafiltration step. Through this ultrafiltration chain molecules, such as proteins and the like, are removed, as a result of which these can no longer disturb the subsequent finer membrane separation and possibly also the ion exchange step.

An important advantage of the method according to the invention is that it can work as a closed system. With this is meant that only reusable products are produced. Both the above described supernatant phase and the sedimented phase can indeed be added again to the solid fraction and thus also serve as fertilizer. The concentrate of the membrane separation and the optional rest stream or concentrate of the ultrafiltration, on the contrary, can be added to the liquid fraction.

In a preferred embodiment, said ion exchange is carried out further in an ion exchanger, which is rinsed with lime milk at predetermined points in time.

The thus obtained lime milk enriched with the anions from the ion exchanger, in particular with nitrate, is a valuable fertilizer, which may possibly be added to the solid fraction after evaporation of the water. In this way, only a solid fertilizer and purified water are obtained.

The invention further also relates to a device for processing semi-liquid manure by applying the method according to the invention. The characterising properties of this device are pointed out in claim 10.

Further advantages and particularities of the invention will appear from the following description of a particular embodiment of the method and of the device according to the invention. This description is only given by way of example and is clearly not intended to limit the scope of the invention. The used reference numerals relate to the annexed drawings wherein the only figure shows a schematic representation of a possible embodiment of the device according to the invention. In the method according to the invention use is made as starting material of semi-liquid manure, for example semi-liquid pig manure, semi-liquid cattle manure or possibly analogous waste products. The semi- liquid manure has for example a composition as shown in the following table for semi-liquid pig manure :

Table 1 : Composition of semi-liguid pig manure in kg/m³

Water 940

Dry matter 80

Ashes 25

Organic matter 55

N-Kj eldahl 6 . 8

N-NH₄ 4 . 4

P ( as P₂0₅) 4 . 5

K ( as K,0) 6 . 5

Ca (as CaO) 4 . 5

Cl 1 . 5

S0₄ 2 . 0

In a first phase, the semi-liquid manure is mechanically separated in a solid and a liquid fraction.

This is preferably done by sieving. It was found that in this way the major part of the phosphor which is present and also of the calcium remains in the solid fraction. To sieve the semi-liquid manure, semi-liquid manure is pumped in the shown device, from a manure pit

1 via a pump 2 onto a shaking or vibrating sieve 3.

This sieve 3 retains in particular particles with a size up to 150 μ. The pump 2 is for example a three-way pump by means of which a portion of the semi-liquid manure can simultaneously be pumped again in the manure pit 1 so as to obtain in this way a homogeneous mixture. On the shaking sieve 3 a solidified fertilizer can be obtained which is conveyed by means of an Archimedean screw 4 to a reservoir 5, wherein the solid fertilizer can dry further. Any liquid which may possibly be set free by leaching, is guided again to the manure pit 1. The application of such a natural drying process results in an important increase in efficiency of the system.

In the liquid fraction, which is collected in a storage tank 6, a preparation on the basis of enzymes and/or bacteria is administered automatically by means of a dosing device 7. These enzymes and/or bacteria provide a decomposition of colloidally suspended particles or agglomerates which are present in the liquid fraction and this through a biochemical decomposition process. Preferably, these enzymes and/or bacteria have at least a polypeptidase effect, more particularly an α and 0-polypeptidase effect. The decomposition process continues at least until said agglomerates, which contain i.a. fats, sugars (starch) and proteins, are disintegrated into smaller components.

The liquid fraction is pumped over by means of pump 2 into a processing tank 8, wherein the biochemical decomposition process can continue. This tank 8 has for example a volume that is substantially equal to the total amount of semi-liquid manure to' be processed daily.

In the tank 8 the liquid fraction is subjected to a first flotation/sedimentation step. Due to the partial decomposition of the colloidal particles, this colloidal system is indeed disturbed in such a manner that a portion of the solid matter which is present will start to float, while another portion will settle down. Both the supernatant and the sedimented fraction are again applied onto the sieve 3, and this via an overflow 9 and a valve 10, respectively. Preferably, a portion of the solid fraction of the semi-liquid manure is still present on the sieve 3 , which contributes in preventing the supernatant and the εedimented fraction to arrive again into the reservoir 6. In the processing tank 8 a partition wall is preferably provided. The supply of liquid fraction in this tank 8 is controlled in particular in such a manner, that only a minimal disturbance of the liquid occurs. Next to the processing tank 8 is provided an analogous buffer tank 11, wherein the aqueous phase of the processing tank 8 is transferred through a valve 12. In this buffer tank 11, the enzymes and/or bacteria can do their work further and a separation of supernatant and sedimented phase is carried out again, via overflow 13 and valve 14, respectively.

On top of the tanks 8 and 11 a fan 15 is provided for exhausting gasses which are released from the liquid fraction, such as for example C0₂, produced by the aerobic bacteria. Furthermore a filter 16 is provided for purifying these gasses.

The aqueous phase removed from the buffer tank 11, is preferably first passed through an ultrafiltration system 17 or through an analogous filter system such as for example so called "cartridge filters" by means of which also bacteria and larger chain molecules can be removed. An important advantage of the method according to the invention is that the colloidal system or the emulsion can be broken in the tanks 8 and 11 by enzymes and/or aerobic bacteria, which will not accumulate or only to a small extent on the membranes of the ultrafiltration system. If, on the other hand, polyelectrolytes are used, it was found that the ultrafiltration membranes were quickly clogged up. Also a hard mass was obtained in the tanks 8 and 11 which was difficult to be processed further. The concentrate of the ultrafiltration system 17 can possibly be passed again to the storage tank 6, while the permeate is subjected to a further membrane separation in a membrane separator 19. In order to avoid disturbance of the sedimentation in the tanks 8 and 11 due to too high flow rates, an additional buffer tank 27 of for example 6000 1, wherein the concentrate of the ultrafiltration system is pumped in again over a valve 18, is provided in the shown embodiment between these tanks and the ultrafiltration system 17. The flow rate of this concentrate is indeed normally 70 times higher than the flow rate of the permeate. If the concentration in this additional buffer tank becomes too high, a portion thereof is fed again via a duct 28 to the shaking sieve, either on the semi-liquid manure, but preferably on compost or another organic material, which is thus enriched with plant nutrition elements. On top of the additional buffer tank 27, an overflow is provided which leads via a duct 29 also to the shaking sieve. By using the additional buffer tank, the flow rate through the tanks 8 and 11 can be kept smaller and constant. This tank enables also to control the temperature of the liquid fed via the duct 30 to the ultrafiltration system, in particular preferably between 30 and 35°C, to permit the ultrafiltration to be carried out under optimal circumstances.

The concentrate of this latter membrane separator 19 is again fed over a valve 20 to the storage tank 6. In this way no unusable rest streams are thus produced. The purified water arrives in a reservoir 21.

As membrane separator 19 use can possibly be made of a nanofiltration system. Furthermore, use could be made of an electrodialysis system, which is however relatively expensive. In the preferred embodiment as shown in the figure, better results are obtained, compared to a nanofiltration system, in a less expensive way by using a membrane separator 19 on the basis of the reverse osmosis technique. Before this membrane separator 19, an ion exchanger 22 is provided for removing anions out of the permeate of the ultrafiltration system 17. The major part of these anions is formed by nitrates, because most of the phosphates remained already in the solid fraction.

For removing the anions out of the ion exchanger 22, the exchanger is rinsed at predetermined points in time with a liquid from reservoir 23. As liquid, use is preferably made of lime milk. As a matter of fact, when this lime milk is substantially saturated with ions, it forms a valuable fertilizer. The saturated lime milk is then dried in a drying-device 24 to a solid calcium and nitrogen rich product. Preference is given to a so called "belt drying-device" wherein the evaporation can be speeded up further by blowing in hot air from the stable. The dried product can be used as such or can be admixed to the solid fraction. In this solid fraction, the plant nutrition elements are bound better to the solids than in the original semi-liquid manure, so that they penetrate more slowly into the soil and can be taken up better by the plants.

With regard to the purified water as it leaves the membrane separator, it has experimentally been established to be relatively alkaline. Any remaining ammonia can thus easily be removed by so-called "stripping", involving a fine atomization of the water. If desired, the pH can be adjusted by an automatic pH- adjuster 27. Furthermore the water in the basin 21 can be enriched with oxygen by aeration.

The water from the basin 21 can be used as such to clean the stables for example, or can, after addition of minerals, even be used as drinking-water. A part of the purified water is fed through a pipe 25 to a rinsing tank 26. With this water, the ultrafiltration system 17 and the membrane separator 19 can be rinsed at predetermined points in time. The rinsing-pipes required thereto have for clarity's sake not been shown in the figure. If harmless rinsing- liquids are used, the rinsing-water can after use be dosed in the storage tank 6, and this preferable extended in time. It will be clear from the above given description of a possible embodiment of a method and a device according to the invention that all kind of modifications can be applied hereto, without leaving the scope of this patent application. In this way, an additional ion exchanger could be provided after the valve 20, in order to remove cations out of the concentrate of the membrane separator 19. Further, means for controlling the temperature of the liquid in the tanks 8 and 11 can of course also be provided, and at the same time all sorts of control devices and automatic steering mechanisms. This device can thus function autonomously and continuously, which has a positive effect on the life span of the different membranes.

Claims

1. A method for processing semi-liquid manure, wherein this manure is separated into a liquid and a solid fraction, characterized in that said liquid fraction, containing colloidally suspended particles, is subjected to a biochemical decomposition process for decomposing said particles, the liquid fraction is subjected to a flotation/sedimentation step to produce a supernatant, a sedimented phase and an aqueous phase therebetween, and this aqueous phase is subjected to a membrane separation to produce purified water and a concentrate.

2. A method according to claim 1, characterized in that said membrane separation is done by application of the reverse osmosis technique.

3. A method according to claim 2 , characterized in that anions are removed out of said aqueous phase through ion exchange prior to said membrane separation by reverse osmosis.

4. A method according to claim 3, characterized in that said ion exchange is done in an ion exchanger, which ion exchanger is rinsed with lime milk at predetermined points in time.

5. A method according to claim 4, characterized in that said lime milk is evaporated, as soon as a predetermined amount of ions is present therein, more particularly as soon as this lime milk is substantially saturated with ions.

6. A method according to any one of the claims 1 to 5, characterized in that said separation of the semi-liquid manure in said liquid and solid fractions is carried out by sieving, more particularly on a shaking and/or vibrating sieve.

7. A method according to claim 6, characterized in that said supernatant and/or said sedimented phase are also put onto said shaking and/or vibrating sieve, more particularly on a portion of said solid fraction which is still present on the sieve.

8. A method according to any one of the claims 1 to 7, characterized in that said concentrate is again added to said liquid fraction at the beginning of the cycle.

9. A method according to any one of the claims 1 to 8, characterized in that said aqueous phase is subjected to an ultrafiltration step prior to said membrane separation, in particular prior to said ion exchange.

10. A device for processing semi-liquid manure by applying a method according to any one of the claims 1 to 9, characterized in that it comprises a separator (3) for separating the semi-liquid manure into a liquid and a solid fraction, means (7) for dosing enzymes and/or bacteria in said liquid fraction for decomposing organic compounds, at least one flotation/sedimentation tank (8, 11) for separating a supernatant, a sedimented phase and an aqueous phase situated therebetween, and a membrane separator (19) for separating said aqueous phase in purified water and in a concentrate.

11. A device according to claim 10, characterized in that it comprises a shaking and/or vibrating sieve (3) for separating the semi-liquid manure in said liquid and said solid phase.

12. A device according to claim 10 or 11, characterized in that it comprises an ultrafiltration system (17) for filtering said aqueous phase, before feeding this phase to said membrane separator (19) .

13. A device according to any one of the claims 10 to 12, characterized in that said membrane separator (19) is based on the reverse osmosis technique.

14. A device according to claim 13, characterized in that it comprises an ion exchanger (22) before said membrane separator (19) for removing anions out of said aqueous phase.