Abstract:
Systems and methods for filtering and collecting algae from fluid including a piston and pressurized air system to scrape and clean algae from the filter.

Description:
[0001]    This application is a divisional of and claims priority to U.S. application Ser. No. 13/273,036 filed Oct. 13, 2011, and entitled “ALGAE HARVESTING DEVICES AND METHODS,” that is currently pending, and which is itself a continuation of and claims priority to U.S. application Ser. No. 13/149,524, filed May 31, 2011, which is a continuation of and claims priority to PCT Application No. PCT/US2011/028027, filed Mar. 11, 2011 and entitled “ALGAE FILTRATION SYSTEMS AND METHODS,” and U.S. Provisional Patent Application Ser. No. 61/315,602 filed Mar. 19, 2010 and entitled “ALGAE FILTRATION SYSTEMS AND METHODS”, both of which are incorporated herein by reference in their entirety. 
     
    
     BACKGROUND 
       [0002]    A. Field of the Invention 
         [0003]    Embodiments of the present invention relate generally to systems and methods for filtering algae from fluid. In particular, embodiments of the present invention concern the use of filtration systems and methods with a piston that can be used to scrape algae from the filter material. 
         [0004]    B. Description of Related Art 
         [0005]    Production of biofuel from algae is a very promising technology. Among alternative energy sources, algae represent a renewable biomass resource that is ready to be implemented on a large scale without any environmental or economic penalty. Due to CO 2  fixation by the algae, all the organic matter biodegraded is converted into biomass under photosynthetically oxygenated treatments. The photosynthetic efficiency of aquatic biomass is much higher (6-8%, on average) than that of terrestrial plants (1.8-2.2%, on average). Also, aquatic algae are readily adaptable to growing in different conditions, including fresh- or marine-waters. 
         [0006]    Algae can be harvested by coagulation, flocculation, flotation, centrifugation, screen or membrane filtration, and gravity sedimentation. Unfortunately, none of the common industrial approaches have been proven to be economical and suitable for large-scale microalgae separation or removal. Recovery of biomass can be a significant problem because of the small size (3-30 μm diameter) of the algal cells and the large volumes or water that must be processed to recover the algae. 
         [0007]    Screens or membrane filter are generally high efficient. However, the use of water jets to dislodge the algae from the screen or membrane can cause severe dilution of the harvested algae. Therefore, a cost-effective system and method of filtering algae from water and removing the algae from the screen or membrane filter is needed. 
       SUMMARY 
       [0008]    Embodiments of the present disclosure address issues related to systems and methods of filtering algae from water. In certain embodiments, the filtration system and method utilize a piston configured, water or pressurized air to scrape, scour and collect the filtered algae from the filter. 
         [0009]    Typical algae culture concentration at the end of growth cycle and product accumulation phases is between 1-10 g/L. It is therefore desirable to filter the algae from the fluid utilizing systems and methods as disclosed herein. 
         [0010]    Exemplary embodiments of the filtration systems disclosed herein can comprise a tubular metal mesh or a screen to support a filter. In certain embodiments, the metal is resistant to corrosion based on the components of the culture, and the filter cloth can be attached firmly to the metal. In exemplary embodiments, the pore size of the filter is in the range of micrometers and the material of the filter is smooth so that algae cake layer can be easily scraped or removed easily by the piston, water or air. 
         [0011]    Embodiments of the filtration system comprise two fluid pathways: the permeate path through the filter and the retentate path, which is a flow through path in the filter and has a valve at the end called the retentate valve. Initially, the retentate valve is closed to operate the system in a dead end filtration mode. Algae-containing water enters the apparatus and algae will be retained on the filter. During the filtration process, the flow and pressure before and after the filter can be monitored. The culture accumulates in the filter and algae is concentrated and forms a cake on the filter surface as the water and the nutrients flow through the permeate pathway due to an increase in the pressure. The permeate flux drops as the process continues. When the tubular filter is filled with algae or the algae cake resistance is too high to obtain reasonable flux, the feed valve can be closed and the collection program is initiated. 
         [0012]    Embodiments of exemplary filtration methods comprise: 1) draining the concentrated algae suspension inside the filter housing back to the algae container (2) using a piston to push the algae collected on the filter to an algae container; 3) backwashing the filter using water directed by pressurized air or pressurized air from the permeate side to dislodge remaining algae material from the filter; 4) backwashing the feed side of the membrane with air. 
         [0013]    Exemplary embodiments can comprise a piston valve connected to the top of the tubular filter during filtration. A collection or retentate valve at the bottom of the filter can be opened and the scraping device moved through the filter to push the algae cake though the filter. Upon complete collection of the concentrated algae, the scraping device can be pulled back and returned to its original position. 
         [0014]    After scraping, there may be algae particles remaining in the filter. These can be cleaned using a backwash. By increasing the pressure on the downstream of the permeate side of the system, the blocked particles on the surface of the filter are dislodged. In addition, air can be used to scour the algae particles off the filter surface into algae container. 
         [0015]    It is contemplated that any embodiment discussed in this specification can be implemented with respect to any method or system of the invention, and vice versa. Furthermore, systems of the invention can be used to achieve methods of the invention. 
         [0016]    The term “conduit” or any variation thereof, when used in the claims and/or specification, includes any structure through which a fluid may be conveyed. Non-limiting examples of conduit include pipes, tubing, channels, or other enclosed structures. 
         [0017]    The term “reservoir” or any variation thereof, when used in the claims and/or specification, includes any body structure capable of retaining fluid. Non-limiting examples of reservoirs include ponds, tanks, lakes, tubs, or other similar structures. 
         [0018]    The term “about” or “approximately” are defined as being close to as understood by one of ordinary skill in the art, and in one non-limiting embodiment the terms are defined to be within 10%, preferably within 5%, more preferably within 1%, and most preferably within 0.5%. 
         [0019]    The terms “inhibiting” or “reducing” or any variation of these terms, when used in the claims and/or the specification includes any measurable decrease or complete inhibition to achieve a desired result. 
         [0020]    The term “effective,” as that term is used in the specification and/or claims, means adequate to accomplish a desired, expected, or intended result. 
         [0021]    The use of the word “a” or “an” when used in conjunction with the term “comprising” in the claims and/or the specification may mean “one,” but it is also consistent with the meaning of “one or more,” “at least one,” and “one or more than one.” 
         [0022]    The use of the term “or” in the claims is used to mean “and/or” unless explicitly indicated to refer to alternatives only or the alternatives are mutually exclusive, although the disclosure supports a definition that refers to only alternatives and “and/or.” 
         [0023]    As used in this specification and claim(s), the words “comprising” (and any form of comprising, such as “comprise” and “comprises”), “having” (and any form of having, such as “have” and “has”), “including” (and any form of including, such as “includes” and “include”), or “containing” (and any form of containing, such as “contains” and “contain”) are inclusive or open-ended and do not exclude additional, unrecited elements or method steps. 
         [0024]    Other objects, features and advantages of the present invention will become apparent from the following detailed description. It should be understood, however, that the detailed description and the examples, while indicating specific embodiments of the invention, are given by way of illustration only. Additionally, it is contemplated that changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description. 
     
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         [0025]      FIG. 1  is a schematic side view of an exemplary embodiment of filtration system according to the present disclosure. 
           [0026]      FIG. 2  is a schematic top view of components of the exemplary embodiment of  FIG. 91 . 
       
    
    
     DESCRIPTION OF EXEMPLARY EMBODIMENTS 
       [0027]      FIG. 1  is a schematic view of an exemplary embodiment of a filtration system  100  comprising a filter housing  110 , a filter support  120  and a filter material  130 . In this embodiment, filter housing  110  is constructed from stainless steel or polyvinylchloride (PVC) and is approximately 0.45 meters in diameter. In the exemplary embodiment shown, filter support  120  comprises a stainless steel or PVC tubular meshes or screen approximately 0.2 meters in diameter, with a nominal pore size of 50 microns. In this embodiment, filter material  130  comprises a stainless screen, cellulose acetate (CA), polysulfone (PS), polyethylene (PE), polyethersulfone (PES), polyvinylidene difluoride (PVDF) or PVC membrane with a nominal pore size of less than 1 microns. In addition, filtration system  100  comprises a piston  140  extending into one end of filter material  130 . As explained in more detail below, piston  140  may be used to remove filtered material from filter material  130 . 
         [0028]    Filtration system  100  further comprises a backflow system  150  configured to direct air or permeate across filter material  130  in a direction that is reverse to the direction of flow across filter material  130  during normal operation. Backflow system  150  comprises conduit  152  (e.g., tubing or piping) configured to direct air into filter housing  110 . 
         [0029]    Filtration system  100  comprises an inlet conduit  160  configured to allow algae-containing fluid to enter an inner volume  121  of filter support  120  and filter material  130  during operation. Inlet conduit  160  can also comprise a pressure indicator (e.g., a gauge)  162  that monitors the fluid pressure prior to the fluid entering inner volume  121 . 
         [0030]    As shown in the top schematic view of  FIG. 2 , piston  140  comprises apertures  142  configured to allow the algae-containing fluid to pass through the central portion of piston  140 . During operation, the fluid passes from inner volume  121  through filter material  130  and filter support  120  and into an outer volume  111  between filter support  120  and filter housing  110 . As the fluid passes through filter material  130 , algae  122  is separated from the fluid and remains in inner volume  121 . 
         [0031]    The fluid can exit filter housing  110  via an outlet conduit  170  and be sent for further processing or recycling. Outlet conduit  170  can also comprise a pressure indicator (e.g., a gauge)  172  that monitors the fluid pressure downstream of filter housing  110 . 
         [0032]    During operation, the pressure at pressure indicators  162  and  172  can be monitored to determine the pressure across filter material  130 . When the differential pressure reaches a predetermined value (e.g., 15 psig), the user may cease flow of the fluid through filter material  130  by closing an inlet valve  163  and outlet valve  173 . In other embodiments, the flow of fluid may be stopped at predetermined time intervals, even if the differential pressure remains below the pre-determined value. A drain valve  174  can then be opened to drain water back to a supply tank. 
         [0033]    A collection conduit  180  (comprising a collection valve  183  and a pressure indicator (e.g., a gauge)  182  can then be opened to collect the harvested algae. During harvesting, piston  140  is pushed downward from the position shown in  FIG. 1  towards collection conduit  180 . As piston  140  is pushed downward, it scrapes algae  122  from filter material  130 . Algae  122  can then be forced out through collection conduit  180 . 
         [0034]    After algae  122  has been collected or harvested, filter material  130  can be cleaned by backflow system  150 . In this embodiment, backflow system  150  comprises valves  154  and nozzles  153 . During the cleaning process, valves  154  can be opened to allow higher pressure air (or other suitable cleaning fluid) to enter outer volume  111  between filter housing  110  and filter support  120 . The introduction of higher pressure air into outer volume  111  can create a pressure differential across filter material  130  and dislodge algae  122  from filter material  130 . The dislodged algae  122  can then be pushed down to the bottom of filter housing  110  by pressurized air via valve  156  and be collected via collection conduit  180 . With collection valve  183  open, algae  122  can be directed to a collection vessel. After algae  122  is collected, collection valve  183  can be closed and the system prepared for additional filtration. For example, piston  140  can be returned to the position shown in  FIG. 1 , drain valve  174  can be closed, and outlet valve  173  and inlet valve  163  can be opened to allow water to pass through filtration system  100  as previously described. 
         [0035]    In certain exemplary embodiments, the clearance between piston  140  and filter material  130  is between 0.1 and 1.0 mm. In specific embodiments, piston  140  may be constructed from rubber and be coupled to a stainless steel support rod  141 . 
         [0036]    In certain embodiments, piston  140  may comprise a retractable scraper constructed from polypropylene or stainless steel that can be adjusted to increase or decrease the outer diameter of piston  140 . Such a configuration can allow for variation in the diameter of filter material  130 . 
         [0037]    In still other embodiments, piston  140  may comprise a nylon brush that engages filter material  130 . Such a configuration may be useful when the algae layer on filter material  130  is thinner than the clearance between rubber portion of piston  140  and the inner diameter of filter material  130 . 
       REFERENCES 
       [0038]    The following references are herein incorporated by reference in their entirety.
   U.S. Pat. No. 3,951,805   U.S. Pat. No. 3,983,036   U.S. Pat. No. 4,255,261   U.S. Pat. No. 4,465,600   U.S. Pat. No. 4,869,823   U.S. Pat. No. 4,554,390   U.S. Pat. No. 5,562,251   U.S. Pat. No. 5,254,250   U.S. Pat. No. 6,063,298   Borowitzka, M. A. ( 1999 ). Commercial production of microalgae: ponds, tanks, tubes, and fermenters.  J Biotechnol  70, 313-321.   Chisti, Y. (2007). Biodiesel from microalgae.  Biotechnol Adv  25, 294-306.   Daigger, G. T., B. E. Rittmann, S. S. Adham, and G. Andreottola (2005). Are membrane bioreactors ready for widespread application?  Environ. Sci. Technol.  39: 399A-406A.   Rittmann, B. E. (2008). Opportunities for renewable bioenergy using microorganisms.  Biotechnol. Bioengr.  100: 203-212.   Rittmann, B. E. and P. L. McCarty (2001).  Environmental Biotechnology: Principles and Applications.  McGraw-Hill Book Co., New York.