METHOD AND SYSTEM FOR GROWING MICROALGAE IN EXPANDING SLOPED PONDS

Abstract

A system for growing an algal culture to create a biomass includes a plurality of linearly interconnected, sloped-gradient, gravity-driven, raceway ponds. Surface areas of the ponds are sequentially increased in accordance with a multiplier, with the pond surface area of the last raceway pond in the sequence being as large as fifty acres. For the present invention, a fluid transfer system connects each raceway pond with every other raceway pond in the system. Control over each individual raceway pond is provided to monitor and evaluate algal culture in the pond. Based on this evaluation, the fluid transfer system is activated to provide water, nutrients and other additives to maintain predetermined growth parameters for algae in each of the raceway ponds.

Claims

1. A system for growing algae which comprises: an open-pond, preparation system for growing an initial volume of an algal culture; a bio-production system for receiving algal culture from the preparation system, the bio-production system including a plurality of discrete raceway ponds, wherein each raceway pond holds a respective volume of algal culture to simultaneously cultivate an algal biomass from the culture at a constant growth rate, to maintain a same constant concentration density for a same controlled residence time within each raceway pond, wherein each raceway pond is U-shaped to establish contiguous parallel channels, wherein each raceway pond has an upstream end and a downstream end with a predetermined sloped gradient therebetween, and wherein each raceway pond has a unique predetermined surface area; a plurality of sumps, wherein each sump is connected to a respective raceway pond and is partitioned to have a lower sump in fluid communication with the downstream end of the raceway pond, and an upper sump in fluid communication with the upstream end of the raceway pond, and wherein the sump includes a pump for transferring algal culture from the lower sump to the upper sump for recirculation of the algal culture through the raceway; a plurality of sensors, wherein each sensor is submerged in algal culture in the upper sump of a respective raceway pond to collect algal growth parameter data from algal culture in the raceway pond; and a pond control system electronically connected with the plurality of submerged sensors in the respective raceway pond to monitor and evaluate the algal growth parameter data therein, in order to implement corrective actions necessary to maintain constant growth rates and constant algal culture concentration densities in the raceway pond of the bio-production system.

2. The system recited in claim 1 further comprising a fluid transfer network interconnecting each raceway pond in fluid communication with at least one other raceway pond.

3. The system recited in claim 2 wherein the fluid transfer network further comprises: a water source containing necessary nutrients for maintaining a predetermined level of salinity, depth and cell density for algal culture in each individual raceway pond; a media source for instigating oil production in the algal culture in each individual raceway pond; and a fertilizer source for supporting a growth of algal culture in each individual raceway pond.

4. The system recited in claim 3 wherein the growth parameters include temperature, pH, conductivity, CO.sub.2, turbidity, sump level, change in sump level, and algal cell concentration.

5. The system recited in claim 4 wherein a target for the concentration density of algal cells is a range between 0.5 and 1 gram per liter.

6. The system recited in claim 1, wherein the plurality of raceway ponds is sequentially organized according to an increase in the respective predetermined surface area of each pond in the plurality, and wherein the sequential increase is established in accordance with a multiplier, wherein the multiplier accounts for algae growth factors identified for the system, and wherein the multiplier relates the predetermined surface area of each pond in the sequence to a predetermined surface area of an immediately adjacent pond in the sequence.

7. The system recited in claim 6 wherein the predetermined surface area of the largest raceway pond in the sequence is fifty acres.

8. The system recited in claim 1 wherein the sloped gradient of each raceway pond generates a linear fluid velocity for the algal culture in a range between one and two feet per second and wherein algal culture is harvested from the raceway pond having the largest surface area.

9. The system recited in claim 1 further comprising a control module connected to each pond control system to determine an overall operational capability of the bio-production system.

10. The system recited in claim 1 wherein the preparation system comprises: a plurality of open ponds, wherein the open ponds are arranged in sequential order according to size, with an exponentially increasing surface area in one direction; a means individually provided for each pond in the sequence for stirring the algal culture in the respective open pond; and a pump for transferring algal culture from the preparation system to the plurality of open raceway ponds.

11. The system recited in claim 10 wherein the algal culture is transferred from a last open pond in the sequential order, and the last open pond has a surface area in a range between 400 and 4,000 m.sup.2.

12. A method for using a bio-production system for growing algae which comprises the steps of: providing a preparation system comprising an open pond reactor for growing an initial volume of an algal culture, a plurality of discrete raceway ponds in the bio-production system for sequentially receiving a respective volume of algal culture from the preparation system to simultaneously cultivate an algal biomass from the culture at a constant growth rate, to maintain a same constant concentration density for a same controlled residence time within each raceway pond, wherein each raceway pond is U-shaped to establish contiguous parallel channels, wherein each raceway pond has an upstream end and a downstream end with a predetermined sloped gradient therebetween, and wherein each raceway pond has a unique predetermined surface area, a sensor submerged in the algal culture in each raceway pond to collect algal growth parameter data, a pond control system to monitor and evaluate the algal growth parameter data, and a fluid transfer network interconnecting each raceway pond in fluid communication with at least one other raceway pond; connecting a water source, a media source, and a fertilizer source into respective fluid communication with the fluid transfer network of the bio-production system; implementing corrective actions to maintain constant growth rates and constant algal concentration densities in each raceway pond; and configuring the fluid transfer network to achieve a predetermined fluid flow pattern within the bio-production system required for the implementing step.

13. The method recited in claim 12 wherein the growth parameters include temperature, pH, conductivity, CO.sub.2, turbidity, sump level, change in sump level, and algal cell concentration.

14. The method recited in claim 12 wherein the implementing step is accomplished by moving water from the water source containing necessary nutrients to maintain a predetermined level of salinity, depth and cell density for algal culture in each individual raceway pond.

15. The method recited in claim 12 wherein the implementing step is accomplished by moving media from the media source to instigate oil production in the algal culture of each individual raceway pond.

16. The method recited in claim 12 wherein the implementing step is accomplished by moving fertilizer from the fertilizer source to support a growth of algal culture in each individual raceway pond.

17. The method recited in claim 12 further comprising the step of moving algal culture through the fluid transfer network from a pond having a relatively small surface area to a pond having a relatively larger surface area to empty the small pond for a predetermined purpose.

18. The method recited in claim 17 wherein the moving step is accomplished to reduce the system-wide surface area to minimize an impact from adverse weather conditions.

19. The method recited in claim 17 wherein the moving step is accomplished to allow for a re-inoculation of the empty pond.

20. The method recited in claim 17 further comprising the step of redistributing algal culture in the plurality of raceway ponds when the predetermined purpose is completed.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0029] The novel features of this invention, as well as the invention itself, both as to its structure and its operation, will be best understood from the accompanying drawings, taken in conjunction with the accompanying description, in which similar reference characters refer to similar parts, and in which:

[0030] FIG. 1 is a schematic view of the system of the present invention, illustrating the flow of algae from the closed reactor, through the expanding plug flow reactor, and to the standard plug flow reactor in accordance with the present invention;

[0031] FIG. 2 is an overhead view, riot to scale, of the expanding plug flow reactor shown in FIG. 1;

[0032] FIG. 3 is a longitudinal cross-sectional view of the expanding plug flow reactor of FIG. 2, showing the depth of the medium in the conduit;

[0033] FIG. 4 is a schematic view for an alternate embodiment of a system in accordance with the present invention;

[0034] FIG. 5 is a schematic representation of the present invention showing a mechanized algal culture preparation system in combination with a gravity-driven bio-production system in accordance with the present invention;

[0035] FIG. 6 is a top plan view of a representative raceway pond in the bio-production system;

[0036] FIG. 7 is a cross-section view of a channel for the raceway pond shown in FIG. 6 as would be seen along the line 7-7 in FIG. 6; and

[0037] FIG. 8 is a schematic representation of a bio-production system for the present invention showing a plurality of gravity-driven raceway ponds in combination with an interconnecting fluid transfer network and control capabilities.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0038] Referring initially to FIG. 1, a system for growing selected algae cells is shown, and is generally designated 10. As shown in FIG. 1, the system 10 includes a closed reactor 12, such as a continuous flow photobioreactor. As shown in FIG. 1, the closed reactor 12 is fed with an inoculum medium 14 and continuously grows an inoculum of algae 16. As the inoculum of algae 16 reaches the end 18 of the closed reactor 12, it is at full concentration. Then, the inoculum of algae 16 passes out of the closed reactor 12 in an effluence (arrow 20).

[0039] As shown in FIG. 1, the effluence 20 containing the inoculum of algae 16 passes from the closed reactor 12 to an open system 22, such as an open raceway. In FIG. 1, it can be seen that the open system 22 comprises an expanding plug flow reactor (EPFR) 24 and a standard plug flow reactor (SPFR) 26. Structurally, the EPFR 24 includes a conduit 28 with a first end 30 for receiving the effluence 20 and a second end 32. Further, the open system 22 includes a pump 34. As the effluence 20 enters the EPFR 24, the pump 34 adds a growth medium (arrow 36) to the EPFR 24 to dilute the concentration of algae 38 within the EPFR 24 to about 0.5 grams per liter of fluid. Further, the growth medium 36 includes the nutrients necessary to support the desired growth of the algae 38. As shown in FIG. 1, the open system 22 may include a plurality of pumps 34 for feeding the growth medium 36 at locations 40 along the length of the EPFR 24.

[0040] Referring now. to FIG. 2, the structure and operation of the EPFR 24 may be understood. As shown, the first end 30 of the EPFR 24 has a width W.sub.1 and the second end 32 of the EPFR 24 has a width W.sub.2 that is substantially greater than W.sub.1. In FIG. 2, the EPFR 24 is not drawn to scale. In certain embodiments, W.sub.1 will equal ten feet, while W.sub.2 will equal 300 feet. Further, the EPFR 24 can be seen to include a plurality of sections 42. Further each section 42 expands in width from its proximal end 44 to its distal end 46. As shown, the width of each section 42 doubles from its proximal end 44 to its distal end 46. As a result, the EPFR 24 has a substantially logarithmic increase in width. While FIG. 2 illustrates an increase in width for each successive section, it is envisioned that sections 42 having a constant width could be interspersed among the widening sections 42.

[0041] Importantly, the fluid growth medium 36 and algae 38 flow through the EPFR 24 under the influence of gravity. For purposes of the present invention, this gravity flow is accomplished using a structured gradient. A preferred embodiment of a structured gradient for use with the EPFR 24 is shown in FIG. 3. There it will be seen that the floor 48 of the conduit 28 is formed with a plurality of steps 50. In detail, the steps 50 are defined by a height h of approximately 3 centimeters, with a distance s between the steps 50 being preferably on the order of approximately 100 meters. Typically, the EPFR 24 may be over 1000 meters long and the algae 38 may have a residence time of about thirty days in the EPFR 24.

[0042] An important aspect of the EPFR 24 for the present invention will be appreciated with reference to FIG. 3. This aspect is that the depth d of the fluid growth medium 36 in the conduit 28 needs to be rather shallow (i.e. less than about 15 cm, and preferably around 7.5 cm). To maintain this depth d, however, it is necessary to add the fluid growth medium 36 along the length of the EPFR 24 as the EPFR 24 widens, Importantly, the increase in width among EPFR sections 42 allows for logarithmic growth of the algae 38 while the concentration of the algae 38 is maintained at the high concentration of at least 0.5 grams per liter.

[0043] In cross-reference to FIGS. 1 and 2, as the growth medium 36 and algae 38 reach the second end 32 of the EPFR 24, they are transferred to the SPFR 26. At this stage, the algae 38 stops growing and, instead, begins to produce oils to store energy. In order to instigate oil production in the algae 38, a pump 52 may introduce a trigger medium 64 into the SPFR 26. Specifically, the trigger medium 54 may lack a desired nutrient, such as nitrogen or phosphorus, which causes the algae 38 to produce oil. Alternatively, the SPFR 26 may receive only the algae 38 from the EPFR 24, without any additional trigger medium 54. In either case, oil production in the algae 38 is triggered by the lack of nutrients to support growth.

[0044] In FIG. 4, an alternate embodiment for the present invention is shown and is generally designated 60. As shown, the system 60 includes an n number of open ponds 62 with the smallest open pond 62.sub.(1) being designated as the first upstream pond, and the largest open pond 62.sub.(n) being designated as the last downstream pond. Intermediate open ponds 62 are arranged in order, according to size, with an exponentially increasing surface area in a downstream direction. In this case, the downstream direction extends from the first upstream pond 62.sub.(1) to the last downstream pond 62.sub.(n). For the system 60, the ratio between adjacent surface areas of respective open ponds 62 is established by a fixed multiplier. Importantly, this fixed multiplier is determined by the growth rate of the particular algae 38 that are to be cultivated in the system 60.

[0045] For the present invention, it is to be appreciated that all of the open ponds 62 in the system 60 are substantially similar to each other. The exception here is only in the size of their respective surface areas. Accordingly, each pond 62 will have a fluid circulating device 64 that is provided for moving (stirring) algae 38 around in the pond 62. Functionally, this is done to promote the growth of algae 38 while there is a culture of the algae 38 in the particular open pond 62. Examples for a suitable fluid circulating device 64 would be a standard circulation pump or a paddle wheel. Both of these types of devices are well known in the pertinent art.

[0046] It will also be seen in FIG. 4 that each open pond 62 has a medium addition conduit (represented by arrow 66) which is provided to add medium into the respective open pond 62, as needed. Further, the open ponds 62 are connected via respective transfer conduits for selective communication with each other. For example, the upstream open pond 62.sub.(n-1) is connected in fluid communication via a transfer conduit with its adjacent downstream open pond 62.sub.(n). Preferably, the transfer conduits are transfer pumps 68. As shown in FIG. 4, the transfer conduit between open pond 62.sub.(n-1) and open pond 62.sub.(n) is a transfer pump 68.sub.(n-1). As implied above, however, this particular structure is only exemplary. As an alternative to using transfer pumps 68, the open ponds 62 in system 60 can be terraced to provide for a gravity flow of liquid between the various pairs of upstream and downstream open ponds 62.

[0047] In addition to the specific structural components of the system 60 described above, inoculum algae 16 in an inoculum medium 14 can be fed into the first upstream open pond 62.sub.(1) via a first transfer conduit (represented by the arrow 70). At the downstream end of the system 60, after traversing the system 60, the now fully grown algae 38 can be removed from the last downstream open pond 62.sub.(n) via a last transfer conduit (e.g. transfer pump 68.sub.(n).

[0048] In the operation of the system 60, algae 38 are progressively grown as they are selectively passed from one open pond 62 to another. The actual time spent by the algae 38 in each open pond 62 in the series will be substantially the same, and will depend on the type of algae 38 that is being cultivated. As a practical matter, the time spent by algae 38 in a particular open pond 62 can be as much as several (e.g. 3) days. In the event, the transfer of algae 38 through the system 60 is done methodically. And preferably, the transfer will be accomplished at nighttime when the growth of algae 38 is delayed due to a lack of sun light.

[0049] A transfer sequence for moving algae 38 through the system 60 begins by first emptying the last downstream pond 62.sub.(n). To do this, the fully grown algae 38 therein are transferred through a transfer conduit (e.g. transfer pump 68.sub.(n)) to an oil formation pond (i.e. SPFR 26). Next, the contents of the adjacent upstream open pond 62.sub.(n-1) are then emptied into the now-empty last downstream open pond 62.sub.(n). At this time, additional medium can be added to the last downstream open pond 62.sub.(n) via the medium addition conduit 66.sub.(n). Specifically, this is done to establish proper conditions for further growth of algae 38 in the open pond 62.sub.(n). In turn, the contents of open pond 62.sub.(n-2) (not shown) are emptied into open pond 62.sub.(n-1), and an appropriate amount of medium is added. This continues, in sequence, with the contents of each upstream open pond (e.g. pond 62.sub.(2)) being transferred into the just-emptied adjacent downstream open pond (e.g. pond 62.sub.(3)). The transfer sequence finally ends when the contents of the first upstream open pond 62.sub.(1) have been emptied into open pond 62.sub.(2) and the now-empty upstream open pond 62.sub.(1) has been refilled with inoculum of algae 16. The system 60 then continues to grow algae 38 in respective open ponds 62 until another transfer sequence is initiated.

[0050] The raceways depicted in FIG. 4 are not sloped and therefore require paddle wheels or similar motive force for mixing. Once a pond size reaches a wetted area of a maximum of approximately 1 acre, paddle wheels are no longer practical. A further increase in pond size necessitates transfer to a sloped pond system where all mixing is due to gravity-induced flow.

[0051] Referring now to FIG. 5, a system in accordance with the present invention is shown and is generally designated 100. As shown, the system 100 includes both a preparation system 102 and a bio-production system 104. There are several important differences, however, between the preparation system 102 and the bio-production system 104 when they are used as components of the system 100.

[0052] With reference to the preparation system 102, it is to be appreciated that the system 102 includes a plurality of similarly constructed open pond(s) 106. Essentially, the preparation system 102 is as disclosed above for the system 60 with reference to FIG. 4. In detail, each open pond 106 includes a mechanized stirring device, such as the paddle wheel 108 which is shown with the open pond designated 106 in FIG. 5. Structurally, all ponds 106 of the preparation system 102 are similar, with the exception of the size of their respective surface area. With this in mind, the ponds 106 are sequentially arranged in an order of increasingly larger exposed surface area. As disclosed above, the relationship between the ponds 106 in this sequence is established by a predetermined multiplier.

[0053] Operationally, the preparation system 102 is connected into fluid communication with the bio-production system 104 via a pumping means, such as the pump 68.sub.(n) disclosed above. FIG. 5 also shows that the bio-production system 104 includes a plurality of raceway ponds 110. Structurally, with the exception of the size of their respective surface area, all ponds 110 of the bio-production system 104 are similar. Like the ponds 106 of the preparation system 102 disclosed above, the raceway ponds 110 of the bio-production system 104 are sequentially arranged in an order of increasingly larger exposed surface area. Again, the relationship between the raceway ponds 110 in this sequence is established by the same predetermined multiplier that is used for the preparation system 102.

[0054] Still referring to FIG. 5, it is shown that each raceway pond 110 in the bio-production system 104 includes a fluid flow channel 112 and a fluid flow channel 114. In combination, the channels 112 and 114 are interconnected by a turn-around 116. As shown, the channels 112 and 114 are parallel to each other, they are contiguous, and they provide for a continuous fluid flow from the upstream end 118 of the raceway pond 110 to its downstream end 120. Further, FIG. 5 shows that raceway pond 110 includes a sump 122. In detail, the sump 122 has a lower sump 124 that is in fluid communication with the downstream end 120 of the raceway pond 110. It also has an upper sump 126 that is in fluid communication with the upstream end 118 of the raceway pond 110. Also included in the sump 122 is a pump 128 for transferring fluid (i.e. algal culture) from the lower sump 124 to the upper sump 126 for recirculation of the fluid (algal culture) through the raceway pond 110.

[0055] With cross reference to FIG. 6 and FIG. 7, it will be appreciated that fluid flow through the raceway pond 110 over the bottom 130 of the channels 112 and 114 will be in directions respectively indicated by the arrows 132 and 134. As specifically indicated in FIG. 7, the velocity of fluid flow through the channels 112 and 114 will be determined by a sloped gradient 136. For purposes of the present invention, the sloped gradient 136 is established to move the fluid (algal culture) at a linear fluid velocity through the raceway pond 110 that is in a range between one and two feet per second.

[0056] Referring now to FIG. 6, it will be seen that a pond control 138 is provided for the particular raceway pond 110. Recall, all raceway ponds 110 are essentially the same, structurally and functionally. With this in mind, the pond control 138 is electronically connected with a submersible sensor array 140 via a line 142. Further, the sensor array 140 is submerged in the upper sump 126 for collecting growth parameters of the algal culture in the pond 110. In particular, these growth parameters include: temperature, pH, conductivity, CO.sub.2, turbidity, sump level, change in sump level and algal cell concentration. As they are being collected in real time, these growth parameters are transferred via the connecting line 142 to the pond control 138. FIG. 6 also shows that the pond control 138 receives input regarding weather conditions 144 as well as offline analytics 146, which can include a grab sample 148 that is taken from the lower sump 124. Together, all of this collected data is electronically transferred via line 150 from the pond control 138 to a set of flow controls 152.

[0057] As shown in Both FIG. 6 and FIG. 8, the flow controls 152 are separately connected with an algal source (i.e. preparation system 102), a water source 154, a media source 156 and a fertilizer source 158. Importantly, the flow controls 152 are connected with a fluid transfer network 160. As presented in FIG. 8, the flow controls have effective operational control over the fluid transfer network 160. With this control, the preparation system 102 can be selectively connected in fluid communication with any raceway pond 110 in the bio-production system 104. Further, the water source 154, the media source 156, and the fertilizer source 158 can be selectively and individually connected in fluid communication with any raceway pond 110 in the bio-production system 104.

[0058] As intended for the present invention, via the fluid transfer network 160, the water source 154 can be used to supply water for maintaining a predetermined level of salinity, depth and cell density for algal culture in each individual raceway pond 110. Also, the media source 156 can provide a carbon source for instigating oil production in the algal culture in each individual raceway pond 110. And, the fertilizer source 158, can be activated to provide a supply of liquid fertilizer which will support the growth of algal culture in each of the individual raceway ponds 110. Moreover, via the fluid transfer network 160, individual raceway ponds 110 can be connected in fluid communication with each other.

[0059] As an added feature of the present invention, along with individual control over raceway ponds 110, the present invention envisions providing for an overall operational control of the entire system 100. In particular, as shown in FIG. 8, the dashed lines 162 show that a control module 164 can be incorporated to collect data directly from each of the individual raceway ponds 110. An analysis of this collected data can then be used by the control module 164 to activate the flow controls 152.

[0060] In addition to the normal routine testing and evaluation of algal culture in the individual raceway ponds 110, the fluid transfer network 160 also provides other operational capabilities. For instance, it may be necessary or desirable to empty a raceway pond 110, or a group of raceway ponds 110, for a particular purpose. If so, in accordance with the present invention, algal culture can be moved through the fluid transfer network 160 from a selected raceway pond(s) 110 having a relatively small surface area to another raceway pond 110 having a relatively larger surface area. The result in this example is that, by emptying the smaller raceway pond 110 into larger and temporarily deeper ponds, the system-wide surface area for the bio production system 104 is reduced to thereby minimize an impact from unexpected or undesirable events such as excessive rainfall. Transfers can also be made to allow for a re-inoculation of an empty raceway pond 110 or for redistributing algal culture in the plurality of raceway ponds 110 when a predetermined purpose has been completed.

[0061] While the particular Method and System for Growing Microalgae in Expanding Sloped Ponds as herein shown and disclosed in detail is fully capable of obtaining the objects and providing the advantages herein before stated, it is to be understood that it is merely illustrative of the presently preferred embodiments of the invention and that no limitations are intended to the details of construction or design herein shown other than as described in the appended claims.