GB2497285A

GB2497285A - Shallow dam and fall arrangement for photobioreactor

Info

Publication number: GB2497285A
Application number: GB1120796.6A
Authority: GB
Inventors: Prakashkumar Narasimhamurthy
Original assignee: Individual
Current assignee: Individual
Priority date: 2011-12-04
Filing date: 2011-12-04
Publication date: 2013-06-12
Also published as: GB201120796D0; WO2013083942A1

Abstract

A photobioreactor, its construction and a method for its use are disclosed. The photobioreactor comprises a shallow sloping (1:20) gas-tight first tank having a dam or weir 15 connecting it with a second gas-tight tank having an opaque sloping base and transparent roof and a second dam at the bottom of the slope. In use, media overflows from the dam of the first tank and down the sloping surface of the second tank as a thin film. The dams may be arranged adjacent plate 14 to form a narrow channel or opening 16. Preferably the second tank comprises barriers 24 (figure 3) to agitate the flowing thin film. The device further comprises filter/drier 29 (figure 4) which contains a mesh filter to separate biomass from culture medium (which is recycled) and a hot air drier to dry the biomass for subsequent biofuel extraction.

Description

Description:

Background

The invention is a cost effective process to grow, filter and dry a dense micro algae culture which reduces the carbon and water footprint when used in conjunction with greenhouses growing protected crops installed with Co generators (CHP) or boilers as well as when used in conjunction with industries and power stations emitting C02 and waste heat. It addresses all important parameters regulating micro algae growth and provides ideal conditions for photosynthesis resulting from enhanced reflection of available sunlight, optimum absorption of induced C02, energy efficient retention of heat or cold transferred to the culture, uniform temperature and pH control throughout the culture, natural agitation and the highly effective removal of dissolved oxygen from the culture in a continuous cycle. It also provides cost effective method to filter and dry biomass.

Current major problems facing the dense micro algae culture are: * The process of dense micro algae culture in Runway ponds and Photo bioreactors and thereafter drying the biomass for the purpose of extracting oil are not found to be cost effective enough for the production of Bio-oil or Biodiesel.

* The quality and quantity of micro algae yield cultured for the purpose of its use in Nutraceuticals, human & animal nutrition and functional food market is thought to have scope for further improvement.

Several researches and trials are done around the world to improve the efficiency of Runway ponds and Photo bioreactors in order to increase the quantity and quality of the micro algae yield as well as to reduce the capital and the process costs.

The challenges that face dense micro algae culture which need solution are: * Providing a condition where all the growing micro algae in especially dense flowing culture receive sufficient sunlight uniformly throughout its growing cycle and the effective use of available sunlight for photosynthesis.

* Uniform and controlled C02 distribution to all the growing micro algae in especially dense flowing culture throughout the growing cycle.

* Energy efficient means to retain heat or cold transferred to the flowing culture from external sources.

* Maintaining optimum and uniform temperature as well as pH control throughout the flowing culture.

* Effective and cost efficient removal of dissolved 02 from the dense micro algae culture.

* A method to provide a respite to growing micro algae in a continuous process to regenerate and allow them to freely breathe in C02 without being choked by dissolved 02 throughout its growing cycle.

* A process to naturally agitate the flowing culture without the need for energy to remove dissolved 02 continuously from the micro algae culture.

* Recovery of residual heat and C02 from the process of growing micro algae and using it to grow protected crops in greenhouses.

* A process and the design of photo bioreactor which will allow effective utilization of the space.

* A process and the design of the photo bioreactor which allows easy cleaning and maintenance and maintains consistency in quality and quantity of the micro algae yield in every repeated growing cycle.

* A batch process requiring less or no energy to filter and dry biomass which fits into the continuous process of dense micro algae culture.

* A process that can be made very cost effective when used in conjunction with greenhouses growing protected crops installed with Co generators (CHP) or boilers as well as industry and power stations emitting C02 and waste heat.

The preferred embodiment Shallow Dam & Fall (SDF) The preferred embodiment is a process of growing micro algae in a shallow culture flowing inside a semi transparent continuous photo bioreactor which comprises an air tight Shallow Dam (C02 receiving chamber) and an air tight Fall (Dissolved 02 removing chamber).

Construction of the semi transparent photo bioreactor: The Shallow Dam: This is a horizontally laid shallow tank in 1:20 slope at an elevated height above the ground level supported by scaffolding or permanent structures from underneath. The base of the tank and walls are made from an opaque material, for example, Expanded Polystyrene which is light in weight, has a good insulation property and is naturally white in colour. The material is shipped to site as square edged, dove and tail or tongue and grooved tiles for base and as a made to measure square edged or tongue and grooved solid blocks for the walls. The tiles for base are assembled together to make a tank base of desired dimension and the made to measure solid blocks are glued on to the perimeter of the tank base leaving its front perimeter side open. The side of the walls will be supported by scaffolding or a permanent structure to provide structural stability especially when it contains flowing solution. A transparent non permeabie materiai sheet, for example, polythene sheet is roiled to cover the inner wall and the base of the entire tank. Number of pipes (preferably white in colour) with fabricated holes facing downwards are hung and horizontally suspended just above the inner base of the tank leaving a gap between the pipe and base to allow free flow of growing algae culture without any obstruction. Similarly white coloured radiator pipes (without holes) are hung and horizontally suspended parallel to the pipes with holes. A gate (as in a dam) is placed on the front edge of the tank. The gate will comprise a fabricated plate and a block with a narrow parallel gap between them. The height of the block determines the depth of the flowing culture. The entire tank is covered from above by a transparent material, for example, two layered foam bubble packed poly sheets to keep the shallow dam air tight, allow the sunlight to pass through as well as provide insulation against heat or cold loss. All pipes are suspended in air are securely held by hooks and hangers hanging from the ceiling structures supporting the span of two layered foam bubble packed poly sheet cover. Fall:

The construction method for the shallow dam is repeated for the fall. However, this is placed sloping towards the ground from the front edge of the dam and is connected to the dam which creates fall when the culture flows down the slope. Scaffolding or a permanent structure will provide the required structural support from underneath and sides. The polythene sheet spread to cover the inner base and wall of the shallow dam is extended to cover the base and wall of the fall so that the entire shallow dam and fall are covered with one single spread sheet. A fabricated structure with barriers combined with a gate (similar to the gate in the front edge of the shallow dam) located at the bottom end of the fabricated structure is allowed to rest on the inner base of the fall. The fall is also covered from above with two layered foam bubble packed Poly sheets and is made air tight similar to the shallow dam. The bottom of the fall is placed in a receiving tank which is connected to a pump. The receiving tank is covered from the top to protect the contents from outside atmosphere.

The light weight material used in the assembly construction of the shallow dam and fall holding shallow depth of flowing solution makes it possible to support the shallow dam and fall from underneath with economically spaced out scaffolding or permanent structures.

The process and benefits: Photosynthesis in micro algae during day light The culture with desired micro algae strain is pumped into the shallow dam which will slowly flow towards its front until the flow is obstructed by the block in the front edge of the dam and starts to till the height of the shallow dam to the height of the block. The depth of the shallow flowing culture in the dam is determined by the height of the block. The culture overflowing the block is interrupted by the tall plate attached to the block. The passage between the block and the plate is kept narrow to deliberately close the air gaps on the surface of the culture and to thin down the stream before it flows down the steeper slope inside the fall. The gate in the shallow dam is used as a means to prevent the residual free gas in the shallow dam (CO2 receiving chamber) escaping to the fall (Dissolved 02 removing chamber).

The thin stream will gain velocity as it flows down the slope like a fall and naturally agitate when it comes across the barriers on the slope. The gate at the bottom end of the falls acts similar to the gate in the shallow dam preventing the gas in the fall (Dissolved 02 removing chamber) escaping into the following receiving tank.

Hot or cold water to a preset temperature is continuously circulated in the radiator pipes and a pre-determined flow rate of C02 is injected into the pipe with holes. The hot or cold radiator pipes maintain a uniform temperature in the flowing solution throughout the shallow dam. The insulation provided by the opaque expanded polystyrene material used in the assembly and construction of base, walls and the transparent two layered foam bubble pack material covering the top reduce unnecessary heat or cold loss from the respective air tight chambers and make the process of dense micro algae culture energy efficient.

Micro algae receive adequate C02 via pipes with holes and breathe out 02 after absorbing required C02 as the C02 bubbles throughout the shallow flowing culture in the shallow dam. Unused C02 and some 02 escape the surface of the flowing culture which is helped by natural agitation due to the bubbling C02. The freed unused C02 and 02 escaping the flowing culture is trapped within the air tight shallow dam which is removed via an extractor. This can be diverted for recirculation or put to good use for another application, for example growing protected crops in a greenhouse. However some quantity of the dissolved 02 and C02 may be retained in the flowing culture which flows into the fall (02 removing chamber).

Enhanced reflection of sunlight within the shallow dam due to natural white colour background and shallow flowing culture combined with controlled optimum temperature and flow of adequate C02 throughout the flowing culture will provide best conditions for photosynthesis in a dense micro algae culture in both hot and cold climatic conditions.

The fall (02 removing chamber) is air tight and is neither injected with fresh C02 nor exposed to open atmosphere. Hence the thinner stream of micro algae growing culture flowing down the slope will temporarily get a respite from C02 which would allow them sufficient time to regenerate in a continuous process. During this respite the micro algae will continue to breathe in available dissolved C02 and breathe out 02 in the thin stream of fall. More importantly, the natural agitation created when the fall come across barriers will help remove much of the dissolved 02 in the thin stream as the 02 molecular weight is lighter than the molecular weight of C02. The agitation may also remove some of the dissolved C02 in the culture which is received from the shallow dam. The fall is not exposed to the open atmosphere and is in 02 free air tight zone hence the thin stream of solution cannot gain 02 from the atmosphere during agitation. The combination of all these factors makes the removal of dissolved 02 from the dense algae culture highly efficient and cost effective continuous process.

The unused C02 and 02 escaping the thin stream of agitating culture is trapped within the air tight falls which is removed via an extractor. This can be diverted for recirculation or put to good use for growing protected crops in a greenhouse.

The shallow dam and fall is a semi transparent photo bioreactor because its base and sides are covered by an opaque material (expanded polystyrene) and the top is covered by a transparent material (two layered foam bubble packed Polythene sheets) Respiration of micro algae during night under darkness Micro algae breathe in 02 and breathe out C02 during night under darkness. The breathing rate of 02 during the night under darkness by micro algae is found to be less compared to the breathing rate of C02 during photosynthesis in the day light. Injecting air into the growing culture and maintaining a preset temperature uniformly throughout the culture during night under darkness is found to support micro algae growth.

During the night under darkness air can replace C02 via pipes with holes to support respiration. The escaping C02 from the shallow dam as well as fall can be diverted and held in the greenhouse during the night so that the plant leaves would absorb them when they receive the early morning sunlight.

Free space for other production activities The process and the semi transparent photo bioreactor will provide a free space underneath the shallow dam almost equal to the area of the shallow dam. The large space (minus the supporting structures) can be put to good use for any other production activities for example, filtering and drying of biomass, extraction of oil from biomass, production of biodiesel and potential co-products, fish culture, prawn culture, mushroom culture, chicken farming etc. combined with location of office, stores or warehouse, CHP or boiler room and storage tanks under a covered opaque roof.

The highly insulated roof and one side of the wall will provide natural energy efficient covered space for such activities in hot or cold climates.

Cost effective, sustainable, energy and water efficient cycle to reduce carbon & water footprint: Co generators (CHP) OR Boilers + Wasted water & nutrient from greenhouse, growing, drying, extracting oil from micro algae-ø cost effective production of biodiesel & co-products + Growing protected crops with residual heat, C02 & nutrient rich water from fish culture waste 4 Free food and space for fish culture + reduced carbon & water footprint -0 Cheaper biodiesel for Co generators (CUP) OR Boilers + The preferred embodiment when used in conjunction with the greenhouse growing protected crops installed with Co generators (CHP) or boiler makes the entire process of growing and drying micro algae, growing protected crops and for example fish culture under the covered roof very cost effective, energy and water efficient and will significantly reduce the carbon and water foot print.

* CHP or boiler would run on the economical biodiesel produced from the micro algae culture in the preferred embodiment and produce cheaper electricity (only in case of CHP) at a high efficiency rate and low C02 emissions.

* Waste C02, heat from CHP, boiler and the wasted nutrient, water from the greenhouse growing protected crops is used to grow micro algae. The free space available underneath the shallow dam is used to filter, dry and extract oil from bioniass. The space can also be used for additional production activities for example production of biodiesel and co-products, fish culture. The algae crust after oil extraction provides free food for fish culture.

The entire process from growing to oil extraction of micro algae combined with fish culture becomes very cost effective and significantly reduces the carbon and water foot print.

* The residual C02 and the heat from the micro algae culture is diverted into greenhouse growing protected crops which results in effective absorption of remaining CO2 while it continues to benefit from the residual heat. The nutrient and water subject to waste in the greenhouse can be inter-changed with nutrient rich waste from the fish culture to make the process more sustainable and water efficient.

* Some amount of cheaper electricity generated from CHP is needed for extracting oil from dried micro algae and any other further oil refining production activities. Also the energy is needed to light up the covered area and aerate the water in fish tank. The residual heat from the greenhouse growing protected crops and the insulated roof is put to good use to maintain required temperature in the fish tank especially in cold climates.

Economical filtering and drying of biomass: The filter cum drier is built as two layers of containers which are fully insulated to prevent any heat loss.

Construction of the filter cum drier: The filter cum drier comprises an upper container to receive concentrated solution of micro algae solution from the receiving tank. This container is fabricated with holes in its base and will have inlets for the concentrated micro algae culture as well as incoming hot gas and an outlet for the returning hot gas. A lower container under the upper container would receive the filtered solution and is fabricated with a hole to return the filtered solution back to the shallow dam. A removable lid which is fully insulated provides cover from above.

Batch process of filtering cum drying: A removable membrane filter is placed to cover the entire inner base and walls of the container receiving concentrated algae culture from the receiving tank. The lid is closed and concentrated culture is let into the container. Hot gas is sent into the container and intermittently pressurized within the upper container. The intermittent pressure pushes the excess water through the filter membrane and holes in the base of upper container while the constant heat from the gas dries the micro algae simultaneously in a fully insulted and enclosed environment. The filtered solution from the concentrated culture is recycled back to the shallow dam. The residual gas and heat is diverted for another use or application, for example greenhouse growing protected crops.

The flow of the concentrated solution, temperature of the gas and duration for drying is preset and controlled automatically. After the drying process is complete, the lid is open and the filter membrane containing dried biomass is removed from the container and the membrane is cleaned of all the dried biomass before reuse.

Description of drawing: Fig 1

The Shallow Dam (1) OR C02 receiving chamber: This is a horizontally laid shallow tank in 1:20 slope at elevated height (2) using scaffolding or permanent pillar structures (3, figi, figs) to support it from underneath. The base of the tank (4, figi, figs) and walls (5, figi, figs) are made from an opaque material for example Expanded Polystyrene which is light in weight, has a good insulation property and is naturally white in colour. The material is shipped to site as plain, dove and tail or tongue and grooved slab tiles (7, fig6, fig7) for base (4) and as made to measure solid blocks (5) or tongue and grooved solid blocks (fig 8) for the walls. The base slab tiles are assembled together to make a tank base of desired dimension (fig 6, fig 7) and the made to measure solid blocks are glued on to the perimeter of the base leaving its front side (8) open. The side of the walls will be supported by scaffolding or a permanent structure (9, figl, figs) to provide structural stability especially when it contains flowing solution (9 A). Fig 2

A transparent polythene sheet (10, fig 2, fig5) is rolled to cover the inner wall and the base of the entire shallow dam (1). Number of pipes (preferably white in colour) with fabricated holes facing downwards (11) are horizontally suspended just above the inner base of the tank leaving a gap between the pipe and base (12) to allow free flow of growing algae solution without any obstruction.

Similarly white coloured radiator pipes without holes (13) are horizontally suspended parallel to the pipes with holes (11). A gate (as in a dam) is placed on the front edge of the tank. The gate will comprise a fabricated plate (14) and a block (15) with a narrow parallel spacing between them (16).

The entire shallow dam is covered from the top with a two layered foam bubble packed poly sheets (17, fig2, figs) to keep the shallow dam air tight, allow the sunlight to pass through as well as provide insulation against heat or cold loss. Any gas present in the shallow dam is removed via (1 A) with the help of an extractor (not shown in the drawing). All pipes are suspended in air are securely held by hooks and hangers (18, fig 5) hanging from the ceiling structures (19, fig 5) which also support the span of two layered foam bubble packed poly sheet cover (17).

Fig 3: Fall (20) OR 02 removing chamber: The construction method for the shallow dam is repeated for the fall. However, this is placed sloping towards the ground (21) from the front edge of the shallow dam and is connected to the shallow dam which creates fall (22) when the solution flows down the slope. Scaffolding or a permanent structure (23) will provide the required structural support from underneath and sides. The transparent polythene sheet (10) spread to covering the inner base and wall of the shallow dam is extended to cover the base and wall of the falls so that the entire shallow dam and fall are covered with one single sheet. A fabricated structure with barriers (24) combined with a gate (25) which is similar to the gate in the front edge of the dani is located at the bottom end of the fabricated structure (24)and the entire fabricated structure (24) is allowed to rest on the inner base of the fall on top of the polythene sheet ( 10). The fall is also covered on the top with two layered foam bubble packed Poly sheets (26) and is made air tight similar to the shallow dam. Any gas present in the shallow dam is removed via (20 A) with the help of an extractor (not shown in the drawing). The bottom of the slope is placed in a receiving tank (27) which is connected to a pump (28 A). The receiving tank (27) is covered on the top (28) to protect the contents from outside atmosphere. The fresh nutrient mixing and storing tank (28 B) will top up the feed in shallow dam and fall when required. A set of solenoid valves (28 C) connected to timer and sensors will automate the entire process of growing and drying of micro algae.

Fig 4: Filter cum drier (29) The filter cum drier is built as two layers of containers which are fully insulated (30) to prevent any heat loss.

Construction of the filter cum drier: The filter cum drier comprises a upper container to receive concentrated micro algae culture (31) from the receiving tank (27). The upper container is fabricated with holes in its base (31) arid will have inlets for the concentrated algae solution (32) as well as incoming hot gas (33) and an outlet for the returning hot gas (34). The upper container is fitted above a lower container which would receive the filtered solution (35) and is fabricated with a hole to return the filtered solution (36) back to the shallow dam. A removable lid which is fully insulated (37) provides cover from above.

A removable membrane filter (38) is placed to cover the entire inner base and walls of the container receiving concentrated algae solution from the receiving tank (27). The lid (37) is closed and concentrated solution is let into the upper container (30). A valve (38) located on (34) is intermittently closed to build intermittent pressure inside the upper container (31) to force the concentrated algae solution through the removable membrane filter (38) while the hot gas dries the filtered algae sediment (39) to produce dry biomass. The filtered solution received in the lower container (35) is pumped back to the shallow dam (1).

Fig: 5 Is the front view of the shallow dam. Alternatively to (1 A), the escaping residual gas from the air tight zone is continuously removed from the zone via passage (40) with the help of an extractor fan (not shown in the drawing). The C02 injecting pipes as well as hot and cold water circulating radiator pipes are suspended from the ceiling structures (19) with the help of hangers and hooks (18). All pipes can be disconnected for maintenance and cleaning at (41). A large space is available between the ground and the base of the shallow dam (42) to carry out any other secondary production activities. The base of the shallow dam will provide a highly insulated building roof for such activities.

Fig 6: Moulding of Expanded Polystyrene slab tiles for base (7): Each slab tile (7) is flat edged on all sides (43) and is glued together like a butt joint on site to achieve a desired dimension for the base of the shallow dam and falls.

For speedier installation on site, the slab tiles (7) can be moulded to have tongue (44) and groove (45) and when laid together the base (46) as seen from the top.

Fig 7: Alternatively the slab tiles (7) can be moulded to have dove (47) and tail (48) and when laid together the base (49) as seen from the top.

Fig: 8 Moulding of Expanded Polystyrene blocks for wall(s): The solid blocks for wall (5) can have a flat edge on all sides. Alternatively can be moulded to have tongue (50) and groove (51) and when lined together the wall (52) as seen from the side.