Patent Description:
The present invention relates to a system and method for harvesting aquatic plants and, more particularly, but not exclusively, to a system and method for harvesting duckweed from a body of water.

Some aquatic plants such as duckweed and aquatic algae are known for their high nutritional value as well as their rapid growth rate. Due to these qualities there is a growing interest in using such aquatic plants for various applications. Known applications include water remediation, bio-energy production, and more recently for food application. Duckweed is known to have a relatively high protein yield, e.g. as compared to soya beans, high green pigment content and as well as being a good vitamins and polyphenol source.

Wolffia also known as watermeal is one known genus of duckweed. Wolffia are gibbous and float unattached on fresh water surfaces. Wolffia globosa is an example species of Wolffia. Wolffia globosa is known to grow in mats on the surface of calm, freshwater bodies, such as ponds, lakes, and marshes. It is a very tiny, oval-shaped plant with no leaves, stems, or roots. Wolffia globosa has been described as the world's smallest flowering plant, at <NUM>-<NUM> in diameter. Like other Wolffia, the plant is edible and makes a nutritious food.

Although the potential for aquatic plants such as duckweed and aquatic algae may be vast, difficulties associated with harvesting is usually the largest deterrent to realizing the practical and economical cultivation of these aquatic plants.

<CIT> entitled "Cultivation, harvesting and processing of floating aquatic species with high growth rate" describes an apparatus for culturing a duckweed species outdoors. The apparatus includes a container configured to contain the duckweed species in culture medium. The container has a raceway configuration allowing the culture medium to flow in a continuous loop, a propulsion mechanism to cause the motion thereof and a sensor configured to monitor thickness of a floating mat of the duckweed species. A harvesting system includes a conveyer belt configured to be lowered into the culture medium below the floating mat of the duckweed species and a surface skimmer configured to skim a top surface of the culture medium. It is also described that the harvesting system includes a mechanism for recycling the culture medium to the container.

<CIT> entitled "Method and apparatus for harvesting aquatic plants," describes a recovering a duckweed slurry from the body of water by adjusting a feed head having a mixing chamber, the feed head being proximate the surface of the body of water so duckweed from the surface of the body of water, and water from the body of water flow into the feed head and the mixing chamber. Duckweed slurry comprising duckweed and water from the body of water is transported to a land-based dewatering station in which a majority of the water is removed. The water removed from the duckweed slurry is then returned to the body of water.

Japanese Patent Publication <CIT> discloses continuously performing dust removal without lowering filtration efficiency of wastewater by removing films or fibers from a filter medium. The filter medium is submerged in water to clean it and means are provided to subsequently clean the dirt from the filter.

<CIT> discloses cleaning of a micro-sieve medium such as a belt in a rotating belt sieve.

<CIT> discloses a removal apparatus for green algae floating in water. A screen unit pulls the algae from the water as it rotates, and the algae are cleaned off and collected using cleaning and collecting units.

The apparatus comprises first and second cleaning units arranged to spray air to so as to separate and remove green algae. A brush unit contacts with the outer surface of the screen unit.

<CIT> discloses a method and system for cultivating aquatic plants at the surface of a body of water. The plants are cultivated in a basin to which is supplied nutrient rich water at one location. Water is extracted at another location inducing movement of the aquatic plants to a collection region.

The present invention is directed to a system and method to continuously harvest aquatic plants in a culture medium while maintaining stable growing conditions in the culture. In some example embodiments, the harvesting is based on skimming a surface of a culture medium. According to some example embodiments, the harvesting (or skimming) is performed without disrupting a floating or immersed culture surface area of the aquatic plants, e.g. without breaking a continuum of a floating or immersed mat formed by the aquatic plants. Maintaining the floating (or immersed) culture surface area intact during harvesting is advantageous as it may significantly reduce a potential of algae contamination that may occur due to unintentional light penetration. According to some example embodiments, system and method also provides for harvesting the aquatic plant with little residual of liquid medium and with substantially no mechanical damage to the aquatic plant.

According to a first aspect of the present invention, there is provided a harvesting system for harvesting aquatic plants in or floating on a culture medium, the system comprising: a harvesting bed configured to be circulated in and out of the culture medium; an actuator configured to circulate the harvesting bed; a scraper positioned against the harvesting bed and configured to scrap the aquatic plants on the harvesting bed; a channel configured to transport the aquatic plants removed by the scraper; and a collection vat configured to receive the aquatic plants transported via the channel.

The harvesting bed is a plate and the actuator is configured to rotate the plate about an axis of rotation, wherein the axis of rotation is perpendicular to the harvesting bed.

Optionally, the plate is fixedly supported on an axle and wherein the actuator is configured to rotate the axle.

Optionally, the system includes a plurality of plates is fixedly supported on a single axle and wherein the actuator is configured to rotate the axle.

According to the first aspect of the invention, the plate is disc shaped.

Optionally, the plate has a thickness of <NUM>-<NUM>.

Optionally, the system includes a Z stage configured to position the plate at a desired height.

Optionally, the harvesting bed is a belt.

Optionally, the belt is an endless belt that is circulated with a conveyor system.

Optionally, the belt is configured to be immersed in the culture medium such that a surface of the belt is parallel to a direction of flow in a tank containing the culture medium.

Optionally, the harvesting bed is a roller.

Optionally, the scraper is stationary and circulation of the harvesting bed is configured to actuate scraping of the aquatic plants.

Optionally, the scraper is fixedly attached to a trough configured to collect the aquatic plants scrapped by the scraper.

Optionally, the trough is tilted toward the channel.

Optionally, the system includes a pair of the scrapers positioned against each of the two opposing flat surfaces of the harvesting bed.

According to the first aspect of the invention, the system includes a nozzle configured to spray fluid on a surface of the harvesting bed at a height above a position of the scraper; and a fluid source configured to supply the nozzle with fluid.

Optionally, the system includes a pair of the nozzles configured to spray fluid on each of two opposing surfaces of the harvesting bed.

Optionally, the system includes a controller configured to control a rate of the circulating.

According to a second aspect of the invention, there is provided a method for harvesting aquatic plants in or floating on a culture medium, the method comprising: partially immersing a harvesting bed in a culture medium, the culture medium comprising aquatic plants; circulating the harvesting bed in and out of the culture medium; scraping the aquatic plants adhering to the harvesting bed as the harvesting bed as it is being circulated; channeling the aquatic plants removed by the scraper toward a collection vat; and collecting the aquatic plants in the collection vat.

Optionally, the harvesting bed is a plate.

Optionally, the scraping is actuated based on the rotating of the plate.

According to the second aspect of the invention, the method includes spraying a portion of the plate above the scraper with a fluid.

Optionally, the method includes aligning an edge of the plate with a direction of flow of the culture medium.

Optionally, the method includes aligning a surface of the plate at an acute angle with respect to a direction of flow of the culture medium.

Optionally, the method includes partially immersing a plurality of plates in a culture medium wherein the plurality of plates displaced from each other by a defined distance and wherein the plurality of plates are rotated about a same axis of rotation.

Optionally, the harvesting bed is an endless belt that is circulated with a conveyor system.

Optionally, the method includes immersing the endless belt in the culture medium such that a surface of the belt is parallel to a direction of flow in a tank containing the culture medium.

Optionally, the method includes aligning a surface of the belt at an acute angle with respect to a direction of flow of the culture medium.

Optionally, the method includes positioning a longitudinal axis of the roller perpendicular to a flow direction of the culture medium.

Some embodiments of the invention are herein described, by way of example only, with reference to the accompanying drawings (including images).

A invention relates harvesting system includes a harvesting bed that is circulated in and out of the culture medium. The harvesting bed is at least one rotating plate, e.g. disc that is configured to be partially submerged in the culture medium so that it cuts into the surface of the medium as it rotates about its axis. As the disc is rotated, the aquatic plants floating on or near the surface of the culture medium may adhere to surfaces of the disc. Optionally, the aquatic plants that adhere to the disc may grow fully immersed in the culture medium. Adhesion to the surfaces of the disc may be due to adhesive properties of the aquatic plant and may also be due to surface tension between the plant and the surface of the disc. According to some example embodiments, the disc is mounted on an axle or a shaft rotated with a motor. Optionally, more than one disc may be mounted on a shaft. In some example embodiments, more than one shaft each with one or more discs may be extended into the tank with the culture medium. In some example embodiments, the tank includes flow in a defined direction and the disks are oriented in a direction of the flow so surfaces of the discs are substantially parallel to a direction of flow. As such, the discs do not disturb the flow through the tank and a mat that may be formed by the aquatic plants is left intact.

The harvesting system additionally includes a scraper that engages the disc above a surface of the culture medium and scraps off the aquatic plants from surfaces of the disc. The scraping may be actuated by rotation of the disc. The aquatic plants removed from surfaces of the disc are then be pipelined through a collection channel positioned below the scraper and into a collection tank. The harvesting system additionally includes a spray nozzle that directs a water flow on the surfaces of the rotating disc above the scraper. The water flow may assist in detaching the aquatic plant from the surface of the disc and may also provide flow for channeling the collected aquatic plants through the collection channel in to the collection tank.

According to some example embodiments of the method, the harvesting bed is a belt. In some example embodiments, the belt is part of a conveyor system that is partially immersed in the culture medium. As portions of the belt are immersed in the culture medium the aquatic plants adhere to surfaces of the belt. Scrapers positioned along the belt above the culture medium may scrap a surface of the belt as the belt is advanced between rotating drums of the system. The system includes one or more nozzles that direct a water flow on the surfaces of the belt to aid in releasing the plants from the surface of the belt. Optionally, the belt is oriented so that its surface is parallel with a direction of flow of the culture medium in the tank. In this orientation, movement of the belt does not significantly break up the mat formed by the aquatic plants.

According to embodiments of the present invention, the harvesting system provides continuous harvesting of the floating material in a fully automated operation. Optionally, a rate at which the aquatic plant is harvested may be controlled based on one or more of controlling a depth at which the disc is submerged in the culture medium, controlling rotation speed of the discs and number of discs being used for harvesting. Optionally, harvesting may also be controlled based selectively altering a material of the disc. In some example embodiments, an angle of the rotating disc may be altered to actuate a mixing of the culture medium. Optionally, the harvesting system may be positioned on a bend in the flow direction of the culture medium so that an angle (an acute angle) is formed between a direction of flow and a surface of the disc. Optionally, the angle may be between <NUM>-<NUM> degrees. Optionally, the harvesting system is positioned at a rounded end of a raceway tank. For example, the discs, which are rotating perpendicular to the water surface, may be placed in parallel to the flow direction, causing no disturbance to the water flow or in a minimal angle to the laminar flow, causing slight disturbance to the water motion and generating desired mixing effect. Optionally, the angle at which the disc is positioned with respect to the direction of flow may be periodically altered to further perturb the medium. Optionally, mixing may assist in dispersion of the nutrients in the medium.

According to some example embodiments, the harvesting system is configured to be a self-regulated system. The amount of plants able to adhere to a rotating disc may be in direct proportion to density of the aquatic plant in the pool. Optionally, the harvesting system may include a sensor configured to sense density of material adhered to the rotating disc. Optionally, the sensor includes a camera that is configured to capture images of the surface of the disc as it immerges from the culture medium.

Reference is now made to <FIG> showing a simplified schematic drawing of an example harvesting system in accordance with some example embodiments. A harvesting system <NUM> includes a disc <NUM> providing two opposing surfaces on which aquatic plants <NUM> may adhere when disc <NUM> is dipped into a tank <NUM> in which aquatic plants <NUM> are cultivated in culture medium <NUM>. Disc <NUM> may be supported by an axle or shaft <NUM> fixedly engaged to a center of disc <NUM> and rotated about its longitudinal axis with motor <NUM>. Disc <NUM> may be partially immersed in tank <NUM> at a substantially vertical orientation so that an edge of disc <NUM> cuts into the body of water as disc <NUM> is rotated without substantially disrupting a continuum of a floating or immersed mat formed by aquatic plants <NUM>. In some example embodiments, tank <NUM> may include induced flow in a defined raceway and disc <NUM> may be oriented in tank <NUM> so that it surface is parallel to a direction of the flow. Alternatively, disc <NUM> may be oriented in tank <NUM> so that its surface is angled with respect to a direction of the flow. Optionally, angling disc <NUM> with a direction of the flow induces mixing of the culture medium.

A scraper <NUM> is positioned to engage each of surfaces 150A and 150B of disc <NUM> at a height above the surface of the culture medium <NUM> in tank <NUM> and scrapes off plants <NUM> collected on disc <NUM>. As disc <NUM> continues to rotate, a section of disc <NUM> that has been scraped with scraper <NUM> is immersed again in the culture medium and provides a clean area on which additional plants <NUM> may adhere. Plants <NUM> scraped off the disc <NUM> may be collected in a trough <NUM> and channeled through a channel <NUM> to a collecting vat <NUM>.

The harvesting system <NUM> additionally includes a nozzle <NUM> connected to a water source <NUM> that sprays fluid <NUM>, e.g. water on a surface of disc <NUM> above scraper <NUM>. Nozzle <NUM> may be installed for each of the two surfaces of disc <NUM>. Fluid <NUM> may help detach plants <NUM> from disc <NUM> in a gentle manner to prevent mechanical damage to plants <NUM>. Optionally, detachment is based on fluid <NUM> being sprayed on disc <NUM> and scraper <NUM> provides a surface that directs plants <NUM> detached with fluid142 toward trough <NUM>. The spray nozzle may spray a thin layer of water or other fluid that may aid in detaching the plant parts from the disc without creating a spill flow. In this manner, the plants may be harvested with little extra fluid.

According to some example embodiments, operation of harvesting system <NUM> is automated and the automated operation is controlled by a controller <NUM>. Controller <NUM> may include a user interface from which a user may selectively alter operation parameters for operating harvesting <NUM>. Optionally, operational parameters of system <NUM> may be controlled based on one or more sensors <NUM>. In some example embodiments, sensor <NUM> may include an imaging system and a processor and sensor <NUM> may sense density of plants on disc <NUM>. Density may be detected based on output from the imaging system. In some example embodiments, a harvesting rate may be controlled by controller <NUM> based on controlling a rotational speed of shaft <NUM>, based on controlling a depth at which disc <NUM> is immersed in culture medium <NUM> with plants <NUM> and may also be controlled based on controlling flow rate of culture medium <NUM> in tank <NUM>. In some example embodiments axle <NUM> and motor <NUM> may be supported on a stand <NUM> that may be height adjusted, e.g. with a Z axis stage to alter depth of immersion of disc <NUM>.

In some example embodiments, disc <NUM> may be <NUM>-<NUM> in diameter, e.g. <NUM> and may be submerged at a depth of <NUM>-<NUM> or <NUM>-<NUM>. Disc <NUM> may be selected to be thin enough to avoid creating openings through a mat formed with plants <NUM> while maintaining mechanical stability. Optionally, thickness of disc <NUM> may be <NUM>-<NUM>, e.g. <NUM>-<NUM> or <NUM>. Disc <NUM> may be formed from stainless steel, e.g. stainless steel <NUM>, a polymer, e.g. polyethylene or polyvinylidene difluoride or other material that may provide adequate surface tension for accumulating plant <NUM>.

In some example embodiments harvesting system <NUM> may include a plurality of stations around tank <NUM>. Each station may include disc <NUM> including scrapers <NUM> and nozzles <NUM> supported by shaft <NUM> and rotated by a motor <NUM>. Each station may also include dedicated troughs <NUM>, channels <NUM> and a dedicated collection vat <NUM>. Alternatively, plants <NUM> collected from a plurality of different stations may be channeled to a common collecting vat <NUM>.

Reference is now made to <FIG> showing a simplified schematic drawing of an example disc with scraper and nozzle in accordance with some example embodiments. According to some example embodiments, disc <NUM> is partially submerged in a culture medium <NUM> including a layer of plants <NUM>. Plants <NUM> may be for example a floating (or immersed) mat of aquatic plants. As disc <NUM> is rotated about its axis <NUM>, plants <NUM> in culture medium <NUM> adhere to surfaces of disc <NUM>, e.g. surface 150A and forms a ring of biomass. A width W of the ring is defined by a depth D at which disc <NUM> is immersed in culture medium <NUM>.

According to some example embodiments, a scraper <NUM> is positioned against surface 150A and collects plants <NUM> accumulated on surface 150A as disc <NUM> rotates. In some example embodiments, nozzle <NUM> sprays water on surface 150A just above scraper <NUM> to gently release plants <NUM> from surface 150A. Optionally nozzle <NUM> sprays fluid <NUM> at a height of about <NUM>-<NUM> above scraper <NUM>. Optionally, fluid <NUM> sprayed by nozzle <NUM> is water or a water based solution that may help release plants <NUM> from surface 150A. Fluid supplied by nozzle <NUM> may additionally provide flow for transporting plants <NUM> from trough <NUM> through channel <NUM>. As disk <NUM> rotates, a portion <NUM> of surface 150A that is cleaned with scraper <NUM> is immersed again in culture medium <NUM> and collects more plants <NUM>. A similar process may be performed on a surface opposite surface 150A.

Scraper <NUM> is shown to be positioned at angle with respect to a radial direction on surface 150A but may alternately be aligned with the radial direction. Optionally, scraper <NUM> is sized to extend over a substantial portion a radius of disc <NUM> and including width W.

Reference is now made to <FIG> showing a side view of an example harvesting system and to <FIG> showing a top view of the example harvesting system both in accordance with some example embodiments. According to some example embodiments, a harvesting system <NUM> may include a plurality of discs <NUM> that are optionally supported and rotated by a common shaft <NUM>. A pair of scrapers <NUM> and collecting channels <NUM> may be installed on each of discs <NUM>. In some example embodiments, plants <NUM> collected in each of baths <NUM> is directed toward a channel <NUM> that continues to transport harvested plants to a collection vat. Optionally, discs <NUM> may be positioned on shaft <NUM> with a gap of <NUM>-<NUM>, e.g. <NUM> between them. Distance between discs <NUM> may be selected based on size of the tank in which they are immersed, a desired rate for harvesting and based on growing characteristics of the layer <NUM> of aquatic plants.

Reference is now made to <FIG> showing an image of an example pair of discs immersed in a culture medium and to <FIG> showing an image of an example channeling unit for directing the plants to a collection vat both in accordance with some example embodiments. According to some example embodiments, harvesting system <NUM> includes two discs <NUM> supported on a common shaft <NUM>. Each disc <NUM> is installed with a pair of scrapers <NUM> and a pair of nozzles <NUM>, one on each surface of disc <NUM>. Each of scrapers <NUM> and nozzles <NUM> may be fixed to a trough <NUM> that collects plants <NUM>. Optionally, trough <NUM> is angled so that the collected plants may spill toward a channel <NUM> based on gravitation force. Optionally, directed water flow, a conveyer belt, or other mechanical means may urge the collected plants toward channel <NUM>. In some example embodiments, troughs <NUM> may be attached and supported by channel <NUM> that may extend generally parallel to shaft <NUM> toward an edge of tank <NUM> and a collection vat <NUM>. Channel <NUM> may be supported with frame <NUM> positioned adjacent tank <NUM>. Optionally frame <NUM> may include structure extending over tank <NUM> to further support channel <NUM> as well as other elements of the harvesting system. Channel <NUM> and trough <NUM> may be formed from aluminum or other light weight material. Optionally, columns may be positioned in tank <NUM> to support elements of the harvesting system <NUM>. In some example embodiments, frame <NUM> is mounted on a Z-axis (vertical) stage with which shaft <NUM> may be selectively lifted or lowered to position discs <NUM> at a desired depth of immersion.

Reference is now made to <FIG> showing an image of example scraper with watering nozzle in accordance with some example embodiments. In some example embodiments, scraper <NUM> may include a blade <NUM>. Optionally, scraper <NUM> with blade <NUM> is formed from stainless steel or aluminum. In other example embodiments, blade <NUM> may be formed from an elastic material. Scraper <NUM> is installed so that blade <NUM> touches the surface of disc <NUM> without substantially interfering with rotation of disc <NUM>. Blade <NUM> may be fixed to trough <NUM> so that plants120 scraped off disc <NUM> with scraper <NUM> may be collected and channeled to common channel <NUM> that may run generally parallel to shaft <NUM> but at an angle to provide flow of plants <NUM> with gravitation force. In some example embodiments, nozzle head <NUM> is fixedly attached to trough <NUM>, e.g. with a bracket and positioned at an orientation in which nozzle <NUM> sprays fluid <NUM>-<NUM> above scraper <NUM> and generally normal to surface 150A. Optionally, spraying with nozzle <NUM> loosen the plants <NUM> from surface 150A so that plants may drop into trough <NUM>.

Reference is now made to <FIG> showing a simplified flow chart of an example method for harvesting in accordance with some example embodiments. According to some example embodiments, a disc that is supported on an axle is partially immersed in a culture medium in which aquatic plants are being cultured (block <NUM>). In some example embodiments, the disc is immersed in a generally vertical orientation, e.g. with surfaces of discs being normal or substantially normal to surface of the body of water and with surfaces of the disc being generally parallel to a direction of flow of the body of water in the tank.

According to some example embodiments, the disc or discs are rotated with an axle which they are supported (block <NUM>). Optionally, rotation is in a direction that corresponds with a direction of flow in the tank. As the disc rotates, plants may be collected on surfaces of the disc.

According to some example embodiments, the plants collected on the disc may be released by spraying water on a portion of the disc above surface of the culture medium (block <NUM>). A scraper position against disc <NUM> may scrap a surface of disc <NUM> to collect the plants (block <NUM>). The plants collected may then be channeled with flow based on gravitation motion to a collection vat (block <NUM>).

Reference is now made to <FIG> showing a simplified schematic drawing of another example harvesting system in accordance with some example embodiments. According to some example embodiments, a harvesting system <NUM> is a conveyor type system and includes an endless belt <NUM> and an electric motor and drive unit <NUM>. Belt <NUM> may be suspended from a pulley <NUM>, with the lower portion immersed in culture medium <NUM> including aquatic plants <NUM>. As belt <NUM> descends into medium <NUM>, aquatic plants <NUM> adheres to one or both sides of the belt. One or more scrapers <NUM> mounted along belt <NUM>. The harvested aquatic plants (the biomass) may be collected into a trough <NUM> and channeled via channel <NUM> to a collection vat.

According to some example embodiments, belt <NUM> may be partially immersed in culture medium <NUM> so that its surface is substantially parallel to a direction of flow <NUM>, e.g. a width W extends along direction of flow <NUM> in tank <NUM>. In this manner, the conveyor motion does not significantly disrupt a surface of growing aquatic plants <NUM> in medium <NUM>.

In some example embodiments, only one surface of the belt is formed from material on which the aquatic plants may adhere and the second surface is not configured to accumulate the plants. In this manner, the aquatic plants are not pressed between belt <NUM> and pulley <NUM>. In other example embodiments, harvesting system <NUM> may include a dedicated scraper <NUM> that removes the aquatic plants on one side of the belt prior to the aquatic plants reaching the upper pulley <NUM>.

Reference is now made to <FIG> showing a simplified flow chart of another example method for harvesting in accordance with some example embodiments. According to some example embodiments, a conveyor belt system is partially immersed in a culture medium in which aquatic plants are being cultured (block <NUM>). In some example embodiments, the conveyer belt system is partially immersed, e.g. with surfaces of the belt positioned generally parallel to a direction of flow in the tank.

According to some example embodiments, the belt is advanced in and out of the culture medium based on rotating drums of the conveyor system (block <NUM>). As the belts advances, plants may be collected on surfaces of the belt.

According to some example embodiments, the plants collected on the disc may be released by spraying water on a portion of the belt above surface of the culture medium (block <NUM>). A scraper position against the belt may scrap a surface of belt to collect the plants (block <NUM>). The plants collected may then be channeled based on gravitation motion to a collection vat (block <NUM>).

Reference is now made to <FIG> showing a simplified schematic side and front drawing of yet another example harvesting system in accordance with some example embodiments. According to some example embodiments, a harvesting system <NUM> is a roller type system and includes a roller <NUM> and an electric motor and drive unit <NUM>. Roller <NUM> may be rotatably supported on an axle <NUM>. Axle <NUM> may be engaged with electric motor and drive unit <NUM>. A scraper <NUM> may extend along length of roller <NUM> and a trough <NUM> may collect plants <NUM> that is scraped. A channel <NUM> may direct collected plants to a collection vat <NUM>. A shaft <NUM> may support the trough <NUM> and scraper <NUM>. One or more water drip or spraying nozzles <NUM> may spray water on the roller to aid in releasing plants <NUM> from roller prior to scraping. The water nozzles may also be supported on shaft <NUM>.

According to some example embodiments, roller <NUM> may be partially immersed in culture medium <NUM> so that its longitudinal axis is substantially perpendicular to a direction of flow <NUM>, e.g. a length of roller <NUM> is perpendicular to a direction of flow <NUM> in tank <NUM>. In this manner, the conveyor motion does not significantly disrupt a surface of growing aquatic plants <NUM> in medium <NUM>. In other example embodiments, roller <NUM> may be aligned with a direction of flow <NUM>.

Reference is now made to the following examples, which together with the above descriptions illustrate some embodiments of the invention in a non-limiting fashion.

A harvesting system prototype shown in <FIG> was made with three discs, <NUM> in diameter all supported on a common shaft <NUM>. Each of the discs was made from different material:.

The three discs were partially submerged at a depth of <NUM>-<NUM> in a tank including wolffia culture as shown in <FIG>. The wolffia culture was at a density of <NUM>-<NUM> gm/m<NUM>, which enabled substantially full coverage of the water surface area. The discs were rotated at a rotating speed of <NUM>-<NUM> rpm. The adhesion ability of the plant, e.g. the fronds to each of the discs material under different depth and speed condition was studied. Harvesting was achieved on each of the three discs. The highest harvesting capacity of the wolffia culture was achieved with the stainless-steel disc <NUM> in all various conditions tested.

A harvesting system as shown in <FIG> including two spinning stainless steel <NUM> discs <NUM> with a diameter of <NUM> was constructed and installed in a tank <NUM> including a wolffia globosa culture with an approximate surface density of <NUM> gm/m<NUM>. The tank includes a raceway curve. The harvesting system was positioned at the beginning of the raceway curve of tank <NUM>. The spinning discs <NUM> were inserted into the culture a depth of <NUM>-<NUM> and rotated at a rotation speed of <NUM> RPM. The rotation was controlled by variable frequency converter. A scraper <NUM> made from PVDF were installed to scrap the plants off of surface of discs <NUM>.

Removal of the plants was further facilitated with a small spray of water from nozzles <NUM>. A harvest rate of <NUM> gm/min was achieved. After <NUM> minutes of operation, <NUM> of material were harvested. The rotational speed of discs <NUM> was then increased to <NUM> and <NUM> RPM. This increase had a negative effect on the adhesion ability on discs <NUM> and on the harvesting efficiency. Apparently, the reduction in adhesion was due to culture medium being carried up due to surface tension with disc <NUM>. The excess liquid may have prevented adhesion of the aquatic plants to the disc.

Claim 1:
A harvesting system (<NUM>) for harvesting aquatic plants (<NUM>) in or floating on a culture medium (<NUM>), the system comprising:
a harvesting bed configured to be circulated in and out of the culture medium (<NUM>);
an actuator (<NUM>) configured to circulate the harvesting bed;
a scraper (<NUM>) positioned against a surface of the harvesting bed and configured to scrape the aquatic plants (<NUM>) on the harvesting bed;
a nozzle (<NUM>) configured to spray fluid (<NUM>) on a surface of the harvesting bed at a height above a position of the scraper (<NUM>);
a fluid source (<NUM>) configured to supply the nozzle (<NUM>) with fluid;
a channel (<NUM>) configured to transport the aquatic plants (<NUM>) removed by the scraper (<NUM>); and
a collection vat (<NUM>) configured to receive the aquatic plants (<NUM>) transported via the channel (<NUM>), wherein
the harvesting bed is a plate (<NUM>), in that the actuator is configured to rotate the plate (<NUM>) about an axis of rotation, in that the axis of rotation is perpendicular to the harvesting bed, and in that the plate (<NUM>) is disc shaped.