Seambiotic & Israel Electric Company (IEC) - Algae-based CO2 Capture

Seambiotic Ltd.( www.seambiotic.com)   was founded in 2003 with an objective to grow and process marine micro algae using a revolutionizing ecologically based environmental system.

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Seambiotic Open Pond Site, Israel

Image Courtesy: Seambiotic

Seambiotic's Pilot Plant Ė The Process

Seambiotic's pilot plant was established in 2006 and is located within the campus of the Rutenberg power plant, close to the city of Ashkelon, where land  has been leased from the Israel Electric Corporation (IEC), approximately 100Ė150 m from the  smokestack,  thereby obviating issues of transport of the flue gases from the stack to the plant. The algae are cultivated in open ponds using flue gas from the  power station, which provides intensive CO2 enrichment.


The process of Seambiotic's microalgae's process has been illustrated in the diagram below:


Image Courtesy: Seambiotic Ltd..

Seambiotic's Cultivation System:

The company uses open pond cultivation system. The total area of the Seambiotic pilot plant is 1,600 m2 containing open ponds with a total  surface area of about 1,000 m2.


Water Mixing

Efficient water mixing is an important issue when cultivating microalgae. The goal is to provide  each cell with the necessary conditions to absorb sufficient sunlight to optimize the  photosynthetic process. Mixing is necessary, even in shallow ponds of less than 0.5 m depth.

In Seambioticís ponds, the algae water medium is mixed by traditional paddle wheels driven by  a geared electric motor. The paddle wheels are constructed using a stainless steel axis and fiberglass blades. Seambiotic is performing  proprietary  research and development to test alternative methods to the traditional paddle wheels that might materially increase productivity and reduce power consumption.

The paddle wheels generate unsteady water motion, including flow in the horizontal direction  at 20 cm/sec and oscillations of the free surface in the vertical cross section. Therefore, the water  particles have both vertical and horizontal velocities.

The available vertical velocity component is the element principally responsible for mixing the  medium in the vertical plane which is crucial for raising particles from the pond floor towards the surface where they receive sufficient sunlight to participate in photosynthesis. The amount of vertical velocity depends on the paddle wheelís rotation velocity, which Seambiotic has optimized after researching and adapting to each algal species.

One main approximately 200 m long PE pipe with a diameter of 160 mm supplies the gas effluent from the blower to the algae ponds. A 160 mm manifold redistributes the gas among  the ponds through 63 mm pipes to ensure even gas flow. Gas is dispersed in the pond water by  underwater bubble aerators or diffusers. Large ponds are serviced by two pipes, smaller ponds  by one. A compound saddle is situated on the 63mm pipe with an exit to a  flexible pipe of 20 mm diameter. The diffusers are connected to the end of each 20 mm pipe.  The flue gas approaching the ponds is at ambient temperature with approximately 12% CO2 content. The amount and consistency of unabsorbed flue gas content is not checked.

Seawater Supply System

Seawater is supplied from the turbine condenser cooling water system of  the power stationís discharge channel. A submerged pump with 20m3/h capacity installed in the power stationís discharge channel fills the ponds when necessary. 

Algae Harvesting, Drying, and Storage

Algae are harvested from the ponds when the cultures reach a cell density of at least 100 million  cells/mL, equivalent to 0.5 g/L.  Algae from smaller ponds are then moved up to the larger  ponds. For harvesting, Seambiotic uses a centrifuge,  which increases the concentration of the algae from an initial 0.1% to approximately 15Ė18% solids. Although the use of a centrifuge is highly effective in separating and concentrating the harvested algae into paste form, both the capital and operating costs of a centrifuge are significant and would not be suitable for any end  product other than high-grade food supplements and similar products.

Harvested paste is kept frozen and stored for downstream processes. Algae paste can then later be dried to form a powder using a Spray Dryer. Dried algae can  be stored without cooling.

Spray dryers involve a material capital and operational cost that makes this technology unattractive for mass markets such as biofuel.  As with centrifuge technologies for initial dewatering, alternatives to the spray dryer are being studied.

Seambioticís final product is dry algae powder. This product is food grade and can be used in fish, animal and human food markets. Further downstream processes can take the powder and separate the algae into its constituent parts: lipids, carbohydrates, and proteins.


 CO2 Uptake 

Diffusing flue gas usually dissolves CO2 in the liquid medium to the somewhat acidic pH level of 5.2.  Carbonic acid is then added  to control the pH of the culture at approximately 7 while maintaining the total dissolved carbon (TDC) at 2Ė5 mM, thus avoiding acidity-related issues.

The rate of algae growth using FGD gases from the  IEC  Rutenberg plant was found to be about 50% higher than  when using  pure food-grade CO2 and fossil oil.

Further analysis of the solid particles in the FGD gases showed the presence of a range of heavy metals essential for algal growth, such as vanadium, strontium, mercury, and zinc, in ppb concentrations, implying there was no further need to supply trace metals in the growth medium. In addition to the nutrients in the flue gas, nitrates and phosphates are also added to the growth medium at approximately 3 mM and 0.5 mM, respectively, to assist in the growth of the algae at optimal rates.  

Another major impact of the power plant configuration is the level of SO2 resulting from the presence of the FGD system, which should be below 120 ppm.

Seambiotic uses gas diffusers, which  are placed  in the liquid culture about 20 cm deep and  provide the flue gas by continuous pH-controlled diffusion. No fresh water is needed. After a few cycles of growth, the culture is harvested and restarted with fresh culture on new seawater. The typical growth cycle of the full process, from inoculation to scaleup dilution or to the harvest of the last pond, is 3 days at high season and 7 days at low season.

Algae at the Seambiotic pilot plant are harvested through liquid-solid separation by centrifugation. The concentration of the inlet material is approximately 0.5 g/L, and that at the outlet is approximately 150 g/L, for a concentration factor of about 300.

Flocculation with inorganic or organic flocculants can be used for successive biomass extraction for bioenergy, pigments, fatty acids, and so on as these products require a lower cost of  production. For even lower value products (for example, biofuels), other methods such as filtration and sedimentation must be used currently in order to be economically competitive. In July 2010, Seambiotic has entered into a collaboration with one such company, Rosetta Green (more)

Seambiotic research suggests that, under optimal conditions and prior to additional development that may further increase productivity, the company can reach yearly average production yields averaging approximately 20g biomass/m2/day.

Seambioticís pilot plant is operated as a research facility rather than for optimal algae growth at all times. As a result, there are frequent changes of algae species in the ponds and time elapses between trials and projects.

Despite this, the pilot project has cultivated several tons of algae per
year.The plant also has the capability of producing dry powder as an end product for its harvesting process. In this respect, Seambiotic has harvested several tons of dry weight for research projects and other markets for the product.  

Read More:http://www.seambiotic.com/uploads/Seambiotic%20Ltd.%20-%20Algae%20Pilot%20Plant%20white%20paper.pdf