WO2008140307A1

WO2008140307A1 - Method for concentrating microbiological organisms suspended in a flowing liquid

Info

Publication number: WO2008140307A1
Application number: PCT/NL2008/050277
Authority: WO
Inventors: Robert Schook
Original assignee: Schinfa Engineering
Priority date: 2007-05-15
Filing date: 2008-05-08
Publication date: 2008-11-20
Also published as: AU2008251119A1; EP2155352A1; NL2000649C2; BRPI0810264A2; MX2009012356A

Abstract

The invention relates to a method for concentrating from a flowing liquid microbiological organisms suspended in the liquid, comprising the processing steps of : A) feeding the liquid with microbiological organisms suspended therein to a stationary cyclone (20), B) rotating the liquid with microbiological organisms suspended therein in a stationary housing of the cyclone, and.C) discharging at least two different fractions from the stationary cyclone; a first fraction having an increased concentration of suspended microbiological organisms relative to the supplied liquid and a second fraction having a decreased concentration of suspended microbiological organisms relative to the supplied liquid. The liquid is rotated in the stationary housing of the cyclone as a result of the presence of at least one guide element (43).

Description

METHOD FOR CONCENTRATING MICROBIOLOGICAL ORGANISMS SUSPENDED IN A FLOWING LIQUID

The invention relates to a method for concentrating from a flowing liquid microbiological organisms suspended in the liquid.

In the search for organic material as raw material for for instance bio-fuel, and also other industrial applications, such as application as food supplements, biological raw material for construction materials and so on, algae have been found to have a number of advantageous properties. There are for instance types of algae whose mass consists of as much as 50% oil, while • depending on the intended application - other advantageous substances such as dyes and the omega fatty acid EPA are also present in the algae. Another advantage is that the production capacity (the photosynthesis) in the production of algae can be particularly high. The production of algae per unit area has been found in practice to be as much as 100 to 150 times more efficient than the cultivation of a number of agricultural crops such as for instance maize and soya. The algae can also be used to purify waste water, and CO2 from for instance flue gases or fermentation waste gases can here be bonded. See for this for instance the ECN report "Duurzame co- productie vanfljnchemicalien en energie uit micro-algen (Renewable co-production of fine chemicals and energy from microalgae) ", public final report E.E.T. project K99005/398510-1010 by J.H. Reith, April 2004.

A drawback of the production of algae is however that, as microbiological organisms, they are not easy to separate from the liquid in which they develop. Due to the generally very small dimensions of the microbiological organisms, the separation is difficult and expensive. Flotation, centrifugation, sand filtration and membrane technology are referred to as possible separating techniques. Chemical extraction is also recommended for the extraction of determined substances. All these separating techniques are only possible for high-quality application of the products to be separated. For relatively low- quality application of the microbiological organisms (more in particular as bio-fuel) these separating techniques are all too costly, and moreover do not even usually produce a positive (or even very slightly advantageous) energy balance. Centrifugation is thus for instance an energetically less favourable separating technique as centrifugation is an energy-intensive process. This is also the case for, among others, the method and device described in the international patent application WO 03/059821 for removing from a flowing liquid particles and organisms suspended in the liquid. The method comprises the steps of: feeding a low-pressure liquid flow tangentially to a stationary cyclone; rotating the liquid in the stationary housing of the cyclone; and discharging at least two different fractions from the stationary cyclone. The cyclone described in this document is provided with a filter element for the purpose of also separating from the liquid particles lighter than the specific mass of the liquid. This technique is not suitable either for the purpose of commercial concentration of suspended microbiological organisms from a flowing liquid for relatively low-quality application of the microbiological organisms (such as the above stated bio-fuel).

The present invention has for its object to provide a more efficient method of concentrating from a flowing liquid microbiological organisms suspended in the liquid.

The invention provides for this purpose a method for concentrating from a flowing liquid microbiological organisms suspended in the liquid as according to claim 1. As a result of the rotation of the liquid with suspended microbiological organisms therein in the stationary housing of the cyclone using at least one guide element present for this purpose, a lighter fraction will migrate to the inner side of the cyclone in at least substantially efficient manner, and a heavier fraction will migrate to the outer side of the cyclone. The heavier fraction and the lighter fraction are discharged from the cyclone at spaced-apart positions. By means of the present invention the efficiency of a cyclone can be increased relative to that of a tangential cyclone as proposed in the prior art. The feed of flowing liquid with suspended microbiological organisms can now also take place radially and/or axially as desired in very efficient manner, i.e. either radially or axially or a combination of radially and axially. Another reason why precisely the presence of at least one guide element now results in said efficient concentration is that, as a result of the at least one guide element, the flow pattern in the vortex is relatively stable compared to a prior art vortex in which such a guide element is absent.

A cyclone is a centrifugal separator in which a heavier fraction is flung to the outer side by the centrifugal force as a result of the greater mass. The different fractions usually leave the cyclone via different sides. One of the reasons why it is not self-evident according to the prior art to separate microbiological organisms from a liquid by means of a cyclone is that microbiological organisms do not coagulate, or hardly so. Coagulation is here understood to mean droplets coalescing into a larger drop. This property can be influenced by for instance the composition of a mixture, the pH value, the presence of additives and so on. This means that a determined degree of separation in the cyclone does not result in a stable separated situation as is for instance the case in an oil/water separation, a separating technique in which the use of cyclones is popular. The non-coagulation of the microbiological organisms, in particular algae, will therefore immediately result again in re-mixing in the case of any small disruption of an ideal cyclone. This problem is all the greater when the differences in mass density between the liquid and the microbiological organisms are small, as is the case in a water/algae mixture. The difference in mass density between the liquid and the microbiological organisms is here typically less than 200, 150, 100, 50 or even 30 kg/m3. The present invention now provides the insight that it is possible to concentrate microbiological organisms in a stationary cyclone in viable manner. Concentration not only refers to the complete separation but also to the pre-separation (increasing the concentration of microbiological organisms suspended in a liquid). A correct dimensioning of the vortex must first be chosen here, for instance a diameter smaller than 20 millimetres. This because the vortex must develop a sufficient centrifugal force to concentrate the small, non-coagulating microbiological organisms, and the flow pattern must moreover be such that re-mixing is prevented. On the other hand, there is the insight that a complete separation is not essential but that a substantial increase in the concentration of microbiological organisms in a first fraction of the liquid flow is already very advantageous. A doubling of the concentration of for instance a few hundred milligrams per litre already results in a considerable increase in the efficiency of the overall separating process since the subsequent separating steps can now after all be performed more efficiently.

Of great importance in the concentration of microbiological organisms suspended in the liquid is that the flow pattern in the vortex is very stable; this of course in order to prevent the very rapidly occurring re-mixing. In addition to using a suitable dimensioning, stabilization of the flow pattern can for instance also be obtained by applying guide elements and/or stabilizing elements in the vortex. It is important here to keep the local Reynolds number as low as possible everywhere, whereby preferably no (heavily) turbulent flow occurs in the vortex. For a further stabilization of the liquid flow in the cyclone it is also advantageous if the liquid is fed to the device from a plurality of sides. All these measures contribute toward the flow of the medium mixture to be fed to the cyclone having a substantially stable flow pattern during processing step A).

The separating space in the vortex usually has an elongate form which has an inner side of circular cross-section (i.e. in a cross-section perpendicularly of the longitudinal or lengthwise axis of the cyclone). The separating space can optionally be tapering and can be provided as desired with a core around which the mixture is set into rotation as a vortex. It is noted that the liquid in the stationary housing of the cyclone can also follow a fully helical flow path (the structure need not be tapering here, but can also be cylindrical). The rotating flow can be generated by a helical structure.

For economic and environmental reasons, among others, the liquid is preferably formed by water with microorganisms dispersed therein. Depending on the conditions, this can be fresh, brackish or salt water.

In yet another preferred variant (free and/or dissolved) gas is added to the flowing liquid such that gas bubbles are created in the liquid. These gas bubbles are preferably present in the liquid during rotation of the liquid in the stationary housing of the cyclone. The thus present (micro)bubbles adhere to the microbiological organisms, whereby the difference in mass density of the fractions for separating can be changed, as a result of which a simpler separation becomes possible. This effect can otherwise also be obtained (or be enhanced) by causing the liquid with microbiological organisms suspended therein to expand during the feed to the stationary housing of the cyclone. The expansion can take place during the feed or at any moment the liquid is already situated in the stationary housing. Advantageous results are further obtained when the liquid expands over the infeed openings during feed, for instance preferably such that microbubbles are created. This principle works particularly well if the medium mixture is oversaturated (supersaturated with gas) when entering the cyclone. With the described method it is difficult or even impossible to obtain a complete separation of liquid and microbiological organisms. This is not a drawback however. The concentration of suspended microbiological organisms of the first fraction discharged from the stationary cyclone according to processing step C) and already 5 having an increased concentration of suspended microbiological organisms relative to the supplied liquid, can be increased further in a plurality of subsequent steps. For instance by effecting a subsequent separating step after the pre-separation by means of one or more of the processes of: centrifugation, pressing, further concentration, decanting and/or drying. 0

In yet another variant of the method according to the present invention a flocculant for the microbiological organisms is added to the flowing liquid with suspended microbiological organisms. Such a flocculant results in the small microbiological organisms joining together into larger complexes (flocculent precipitates) which are S easier to concentrate (or can even be separated from the liquid). The flocculant can have a chemical composition, although it is preferably formed by a natural flocculant such as for instance Chitosan. It is otherwise noted here that microbiological organisms can also coalesce, bind or clot by means of other phenomena. 0 The present invention will be further elucidated on the basis of the non-limitative exemplary embodiments shown in the following figures. Herein: figure 1 shows a cut-away perspective view of a device for performing the method according to the invention, and figure 2 shows a cut-away perspective view of an alternative embodiment variant of a5 device for performing the method according to the invention.

Figure 1 shows a vortex 20 with a core 1 and a casing 2, between which guide fins 3 are positioned. The liquid with suspended microbiological organisms (for instance algae) is fed substantially axially as according to arrow Pl and obtains a rotating tangential0 component due to guide fins 3; see arrow P2 herefor. The method of feeding the liquid is of minor importance; the liquid can also have a radial component upstream of guide fins 3 (see for instance arrow Pl'). In order to stabilize the flow in vortex 20 still further, stabilizing fins 4 can additionally be arranged between guide fins 3. As a consequence of guide fins 3 and stabilizing fins 4 the local Reynolds number will be lower, with the result of a stable flow more quickly at that location. In the further description of this figure it will be assumed that the microbiological organisms have a greater density than the liquid, although if the opposite were to be the case, the following description must also be understood in reverse. The highly oleaginous Botryococcus braunii Botryococcus braunii has for instance a mass density lower than that of water, whereby it can be separated as the lighter fraction, and bio-fuel can thus for instance be produced in very efficient manner. Separation of the lighter fraction is generally more advantageous in a cyclone than separation of the heavier fraction.

Due to a strong rotating flow at the distal end of casing 2 the microbiological organisms (for instance algae) will move to the outer side of separating space 9 under the influence of the centrifugal action. Separating space 9 is bounded by core 1 and casing 2. In order to obtain a stable flow (and to prevent boundary-layer separation) the periphery of the distal end of core 1 decreases gradually by means of an end part 8 provided with a decreasing diameter. A tail section S is also provided in order to increase the retention time in vortex 20. This tail section S has an elongate form and is here shown in conical form, although it can for instance also take a cylindrical form. A critical value in practice relates to the distal side of tail section S which must preferably be smaller than 20 mm, more preferably even smaller than 15, 10 or 5 mm. The advantage of the presence of tail section S is that maintaining the momentum further increases the centrifugal force, and this results in an improved separation. The liquid with increased concentration of microbiological organisms will move in axial direction via a wall 10 of tail section 5 toward an outlet 6, where the first fraction of liquid with the increased concentration of microbiological organisms leaves vortex 20 as according to arrow P3. From the centre of tail section 5 the second fraction of the liquid with a decreased concentration of microbiological organisms will leave vortex 20 rearward as according to arrow P4 through an opening 7 arranged in the core. Because of the fractions exiting in different directions as according to arrows P3 and P4 the vortex 20 is also referred to as a counterflow device.

Figure 2 shows a vortex 30, the components of which corresponding with the components as shown in vortex 20 according to figure 1 are designated with the same reference numerals. Guide fins 3 are once again positioned between a core 1 and a casing 2, and the liquid with suspended microbiological organisms is fed substantially axially as according to arrow PI such that due to guide fins 3 it obtains a rotating tangential component as according to arrow P2. Stabilizing fins 4 can once again be arranged for further stabilization of the flow. It is once again assumed here by way of example that the microbiological organisms have a higher density than the liquid. Due to a strong rotating flow at the distal end of casing 2 the microbiological organisms (for instance algae) will move under the influence of the centrifugal action toward the outer side of the separating space 9 bounded by core 1 and casing 2. Core 1 is again provided with an end part 8 with gradually decreasing diameter, and a tail section S is also provided. The liquid with increased concentration of microbiological organisms will move in axial direction via a wall 10 of tail section S to an outlet 11, where the first fraction of liquid with the increased concentration of microbiological organisms leaves vortex 30 as according to arrow P5. The second fraction of the liquid with a decreased concentration of microbiological organisms will likewise leave vortex 30 on the distal side from the centre of tail section 5 through discharge element 12 as according to arrow P6. Because of the fractions exiting in different directions as according to arrows P5 and P6 the vortex 30 is also referred to as a vortex of the throughfiow type.

Claims

Claims 8

1. Method for concentrating from a flowing liquid microbiological organisms suspended in the liquid, comprising the processing steps of:

5 A) feeding the liquid with microbiological organisms suspended therein to a stationary cyclone,

B) rotating the liquid with microbiological organisms suspended therein in a stationary housing of the cyclone, and

C) discharging at least two different fractions from the stationary cyclone; a first 0 fraction having an increased concentration of suspended microbiological organisms relative to the supplied liquid and a second fraction having a decreased concentration of suspended microbiological organisms relative to the supplied liquid, characterized in that the liquid with suspended microbiological organisms therein is rotated in the stationary housing of the cyclone as a result of the presence of at least one S guide element.

2. Method as claimed in claim 1, characterized in that the microbiological organisms are substantially algae. 0

3. Method as claimed in any of the foregoing claims, characterized in that the difference in mass density between the liquid and the microbiological organisms is less than 200, 150, 100, 50 or 30 kg/m3.

4. Method as claimed in any of the foregoing claims, characterized in that the5 microbiological organisms do not coagulate.

5. Method as claimed in any of the foregoing claims, characterized in that the liquid is water. 0

6. Method as claimed in any of the foregoing claims, characterized in that gas is added to the flowing liquid such that gas bubbles are created in the liquid.

7. Method as claimed in claim 6, characterized in that the gas bubbles are present in the liquid during rotation of the liquid in the stationary housing of the cyclone.

8. Method as claimed in any of the foregoing claims, characterized in that the concentration of suspended microbiological organisms of the first fraction discharged from the stationary cyclone according to processing step C) and already having an increased concentration of suspended microbiological organisms relative to the supplied liquid is subsequently increased further.

9. Method as claimed in any of the foregoing claims, characterized in that the liquid with microbiological organisms suspended therein expands at the feed to the stationary housing of the cyclone.

10. Method as claimed in any of the foregoing claims, characterized in that a flocculant for the microbiological organisms is fed to the flowing liquid with suspended microbiological organisms.

11. Method as claimed in any of the foregoing claims, characterized in that the liquid follows a helical flow path in the stationary housing of the cyclone.

12. Method as claimed in any of the foregoing claims, characterized in that the flowing liquid consists substantially of water and the microbiological organisms are formed substantially by Botryococcus Braunii.

13. Method as claimed in any of the claims 1-11, characterized in that the flowing liquid consists substantially of water and the microbiological organisms are formed substantially by Chlorella.