In many current photobioreactor systems, chosen, desirable strains of algae can be difficult to maintain in a photobioreactor that is not scrupulously sterilized and maintained in a condition that is sealed from the external environment. The reason for this is that the algal strains being used in such photobioreactors are not well adapted or optimized for the conditions of use, and other, endemic algal strains in the atmosphere are more suitably conditioned for the local environment, such that if they have the ability to contaminate the photobioreactor they will tend to predominate and eventually displace the desired algae species.
Use of such protocols and algae strains produced by such protocols may not only increase productivity and longevity of algal cultures in real photobioreactor systems, thereby reducing capital and operating costs, but also may reduce operating costs by reducing or eliminating the need to sterilize and environmentally isolate the photobioreactor system prior to and during operation, respectively. Many power plants include ponds or other bodies of water to which waste heat is discharged. In some embodiments, especially in colder climates, a photobioreactor may be positioned on top of a wastewater pond to achieve one or more possible advantages.
By floating or otherwise positioning a bioreactor on a body of water, the photobioreactor system may take advantage of the inherent flatness of the surface of a body of water over an expansive area. Further, by using an already existing pond, limited additional geographic area is required for the photobioreactor system. One embodiment of a photobioreactor unit adapted for positioning on a body of water is shown in FIG. Photobioreactor unit is supported by two pontoon floats that extend longitudinally along the length of the photobioreactor unit.
Of course, other structures may be used to float or support one or more photobioreactor units on a body of water. In one embodiment of a drainage system, a drainage hole is provided periodically along a collection channel positioned between two photobioreactor units of the photobioreactor system.
The drainage hole empties into a drainage conduit that transversely spans each of the photobioreactor units that are positioned side-by-side. The drainage conduit leads to a drainage trench to lead water away from the photobioreactor system.
In some embodiments, the drainage trench may be wide enough to accommodate various vehicles e. For example, as illustrated in FIG. Liquid effluent from quench zone may be disposed of, or in some embodiments, returned to photobioreactor units dashed line.
Using liquid medium to quench the flue gas heats the medium and may reduce the pH of the medium. One or both of these effects may help kill adventitious biological species, such as rotofers, cilitates, bacteria, and viruses that may impair the growth of the desired algae. If the quench effluent stream is returned to the system upstream of the dewatering step, it may improve the dewatering operation.
For example, reducing the pH of the dewatering feed may improve the effectiveness of polycationic coagulants and alum-based flocculants. Additionally, thermally heating the algae-containing media may induce necrosis and autoflocculation, which simplifies the dewatering process and may reduce or eliminate the need for chemical additives. In an alternative embodiment illustrated in FIG. The liquid effluent from quench zone may then be sent to dewatering system to enrich the algae. As with some other embodiments described herein, algae-free medium from dewatering system may optionally be returned to photobioreactor units In a further embodiment of a photobioreactor system including quenching, illustrated in FIG.
Using dewatered algae in quench zone may help to stabilize the algae against decomposition, preheat the algae to aid in downstream processing, and allow some components to react with the acid gases, which may promote downstream processes such as fermentation.
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Further description of such an integrated system, which can be used in conjunction with embodiments of photobioreactor systems disclosed herein, may be found in commonly-owned PCT Publication No. Patent Application Publication Nos. One embodiment of a configuration for quench zone is illustrated in FIG. In this embodiment, spray elements extend perpendicularly to a liquid supply conduit and are configured spray liquid into a gas headspace Liquid effluent is collected from the bottom of a trench and either disposed of or recycled back into the photobioreactor system.
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A perspective view of one embodiment of quench zone in FIG. In some embodiments of the invention, waste heat in the form of heated water may be used to heat liquid media in a photobioreactor system. One embodiment of tubes submerged in liquid medium is shown in FIG.
Tubes in FIG. In some embodiments, jets may be used to increase the flow rate of liquid medium past tubes to increase the rate of heat transfer. In this example, a laboratory test of an embodiment of a photobioreactor of the present disclosure is compared to a model of the same.
Algae species Nannochloris sp. The test results are shown in FIG. Chemical Engineering Science , In: Laskin, I. CRC Handbook of Microbiology. Cleveland CRC Press, pp , The model productivities matched the measured productivities well, as shown in Table 1. The results are shown in FIG. Recycled media from dewatering is used to enhance the CO 2 gas-liquid exchange. The test results illustrate the increase in CO 2 transfer rates which can be obtained by properly re-injecting the dewatering fluid into the reactor. These higher CO 2 transfer rates can reduce the bioreactor area requirements in situations where the algal productivity is limited by gas mass transfer.
Alternatively these higher CO 2 transfer rates can be used to increase the total biomass production rates from a bioreactor of fixed size. A covered bioreactor is modeled using the algal growth model discussed above and the mass transfer rates from the gas-liquid tests. The bioreactor is sufficiently long that the flow is essentially plug flow; i. The liquid phase comprises Media 1 maintained at pH 7. The reactor productivity, CO 2 conversion, power requirements for the flue gas handling and water consumption are listed in Table 2 for three levels of solar insolence.
Table 2 also shows. This example illustrates the advantage of embodiments of photobioreactors disclosed herein compared to a conventional raceway pond. The reactor productivity, CO 2 conversion, power requirements for the flue gas handling, and water consumption are listed in Table 3 for the highest level of solar insolence using the same operating conditions of Example 1, based on published values for CO 2 conversion and evaporation rates. Flue gas is sparged into a 2-meter deep well in the raceway via a blower that compresses flue gas to 8 psig.
The results show that the hybrid bioreactor achieves comparable growth rates, while attaining greater CO 2 conversion and using substantially less power. The raceway pond power consumption is significantly higher due to its lower CO 2 capture efficiency, requiring higher flue gas flows per unit of algae produced, and its higher pressure drop.
Water consumption for both reactors is comparable because both use evaporative cooling to maintain reactor temperature. The system of Examples 1 and 2 is operated at identical conditions, with the exception that none of the recycled media of Example 1 is directed towards the cooling zone, and low-level heat from the power plant condenser cooling loop is used to maintain the bioreactor temperature. The results show that this reactor has significant advantages over an open raceway pond.
This example illustrates options for integrating the dewatering operation with the bioreactor. Nannochloris sp. The biomass concentration ranges from 0. The algae is dewatered using the techniques known in the art as Dissolved Air Flotation. Essentially algae-free filtrate is recycled to the reactor, allowing unreacted nutrients to be returned to the system.
Recycling this stream reduces total water and nutrient requirements. Optionally a portion or all of the dewatering feed stream can be contacted with flue gas in the quench zone prior to dewatering. For flue gases containing acid gases such as SO 2 , NO x , and HCl, absorption of the acid gases reduces pH from approximately range to a more preferred range of 6.
In this pH range, the quantity of aluminum sulfate required to dewater the algae is reduced. This example illustrates the use of Tangential Flow Filtration for dewatering the algae. The algae of Example 5 is run in a system using tangential flow filtration instead of dissolved air floatation.
The filtration process uses a sterile-grade membrane and operates at low trans-membrane pressure and low shear rates to increase the algae concentration by a factor of Cellular debris and bacterial contaminants are concentrated with the algae-rich stream. The sterilized permeate stream is recycled to the reactor, conserving water and nutrients while reducing risk due to recycle of deleterious species such as bacteria and cell lysates. This example illustrates the use of different operating conditions upstream and downstream of the algae recycle point s to affect changes in the algae growth rates and algae composition.
Recycled media is used to add nitrate such that the concentration in the feed end is 0. In the zone downstream of the algae recycle stream split, the recycled media contains nutrients such as phosphate, but no nitrate. The algae in the first zone experience growth rates of 1. More generally, those skilled in the art would readily appreciate that all parameters, dimensions, materials, and configurations described herein are meant to be exemplary and that actual parameters, dimensions, materials, and configurations will depend upon specific applications for which the teachings of the present invention are used.
Those skilled in the art will recognize, or be able to ascertain using no more than routine experimentation, many equivalents to the specific embodiments of the invention described herein. It is, therefore, to be understood that the foregoing embodiments are presented by way of example only and that, within the scope of the appended claims and equivalents thereto, the invention may be practiced otherwise than as specifically described. Effective date : Year of fee payment : 4. Certain embodiments and aspects of the present invention relate to a photobioreactor including covered photobioreactor units through which a liquid medium stream and a gas stream flow.
The liquid medium comprises at least one species of phototrophic organism therein. In certain embodiments, a portion of the liquid medium is diverted from a photobioreactor unit and reintroduced upstream of the diversion position. The photobioreactor system also comprises a liquid inlet to provide liquid medium to the photobioreactor section, a liquid outlet from which to remove liquid medium comprising phototrophic organisms therein from the photobioreactor section, a gas inlet to provide gas containing an elevated concentration of carbon dioxide into the gas headspace, a gas outlet from which to remove gas containing carbon dioxide at a concentration less than at the gas inlet, and a blower fluidically connected to the gas outlet able to create a flow of gas through the gas headspace from the gas inlet to the gas outlet.
In the drawings: FIG. Example 5 This example illustrates the use of Tangential Flow Filtration for dewatering the algae. Example 6 This example illustrates the use of different operating conditions upstream and downstream of the algae recycle point s to affect changes in the algae growth rates and algae composition. A photobioreactor system comprising: a plurality of interconnectable photobioreactor sections which, when connected together, form at least one longitudinally-oriented photobioreactor unit of the photobioreactor system, the photobioreactor sections each comprising a liquid flow channel, and.
A system as in claim 1 , wherein a first subset of the plurality of interconnectable photobioreactor sections comprises a different functionality than a second subset of the plurality of interconnectable photobioreactor sections. A system as in claim 1 , wherein the photobioreactor system comprises a plurality of photobioreactor units.
A system as in claim 3 , wherein the plurality of photobioreactor units are arranged in parallel. A system as in claim 4 , wherein the plurality of photobioreactor units each include the same number of sections. A system as in claim 1 , wherein the liquid flow channel contain a liquid medium comprising phototrophic organisms. A system as in claim 6 , wherein the phototrophic organisms comprise algae. A system as in claim 1 , further comprising a gas inlet in fluid communication with the gas headspace, wherein the gas inlet is connected to a source of waste gas having an elevated concentration of CO 2.
A system as in claim 8 , wherein the waste gas comprises a flue gas. A system as in claim 1 , further comprising a dewatering system in fluid communication with an output of the at least one longitudinally-oriented photobioreactor unit. A system as in claim 1 , further comprising a mister disposed within a photobioreactor section of the plurality of photobioreactor sections and configured to spray a liquid within the gas headspace. A system as in claim 11 , wherein the mister is configured to spray the liquid downwardly towards the liquid flow channel.
A system as in claim 1 , wherein the cover is supported by ribs attached to the base. A system as in claim 1 further comprising two pontoon floats that extend longitudinally along a length of the photobioreactor unit and configured to support the photobioreactor unit on a body of water. Photobioreactor systems and methods for treating CO2-enriched gas and producing biomass. USB2 en. Closed photobioreactor system for continued daily In Situ production of ethanol from genetically enhanced photosynthetic organisms with means for separation and removal of ethanol.
Methods and systems for controlling growth rates of autotrophic microbial cultures. Systems and methods for cultivating and harvesting blue water bioalgae and aquaculture. Photobioreactor cell culture systems, methods for preconditioning photosynthetic organisms, and cultures of photosynthetic organisms produced thereby.
JPA en. How to convert directly the carbon dioxide into hydrocarbons by using a metabolic engineered photosynthetic microorganisms. EPA4 en.
USA1 en. CNB en. WOA1 en. Container, method and system for cultivating microorganisms, and method to cultivate free oxygen during cultivation of microorganisms. Solar biofactory, photobioreactors, passive thermal regulation systems and methods for producing products. Process for the generation of algal oil and electricity from human and animal waste, and other hydrocarbon sources. GBB en.
CNA en. AUA1 en. Photobioreactor system and method for the growth of algae for biofuels and related products. FRB1 en. USB1 en. Method of removing algae adhered inside a bioreactor through combined backwashing and lowering of pH level. BEA3 en. Biomass production process using aqueous sprays containing photosynthetic microorganisms. Process for growing biomass by modulating inputs to reaction zone based on changes to exhaust supply. Method for reducing carbon dioxide emission and fossil fuel consumption in fossil fuel power plant.
Method and apparatus using an active ionic liquid for algae biofuel harvest and extraction. Alkalizers marine wastewater treatment plants with recovery and consumption of co2 and production of solar electricity. WOA2 en. AUB2 en. Diffusion-based method for obtaining volatile hydrocarbons produced by photosynthetic microorganisms in two-phase bioreactors.
Upgrading of biogas to marketable purified methane exploiting microalgae farming. Reaction jacket for a photosynthetic reactor and reactor combines photosynthetic. Method to optimize the utilization of captured carbon dioxide through the cultivation and processing of microalgae. Process and system for re-using carbon dioxide transformed by photosynthesis into oxygen and hydrocarbons used in an integrated manner to increase the thermal efficiency of combustion systems.
Method for the capture of carbon dioxide through cryogenically processing gaseous emissions from fossil-fuel power generation. CAA1 en. USA en. GBA en. JPSA en. Process and apparatus for commercial farming of marine and freshwater hydrophytes. Optical apparatus and method for measuring the characteristics of materials by their fluorescence. Process for the biotechnological preparation of poly-d- - hydroxybutyric acid. FRA1 en. EPA1 en. Continuous process for manufacture of lactide polymers with controlled optical purity.
Process for obtaining a polyhydroxyalkanoate from the cell material of a microogranism. JPHA en. Apparatus for the automatic, continuous cleaning of the pipe of the solar receptor of a photobioreactor. Continuous process for the manufacture of a purified lactide from esters of lactic acid.
Photoconversion of gasified organic materials into biologically-degradable plastics. Process for the selective production of polyunsaturated fatty acids from a culture of microalgae of the porphyridium cruentum. System using tubular photobioreactors for the industrial culture of photosynthetic microorganisms. DEC1 en. Process and equipment for the cultivation and fermentation of microorganisms or cells in liquid media. DEA1 en. Method and system for water bioremediation utilizing a conical attached algal culture system. Photobioreactors and closed ecological life support systems and artifificial lungs containing the same.
Rotating solar photobioreactor for use in the production of algal biomass from gases, in particular co2-containing gases. JPB2 en. Bioconversion of a fermentable carbon source to 1,3-propanediol by a single microorganism. Impact modified melt-stable lactide polymer compositions and processes for manufacture thereof.
Process of outdoor thin-layer cultivation of microalgae and blue-green algae and bioreactor for performing the process. Optical chemical sensor based on multilayer self-assembled thin film sensors for aquaculture process control. Production of lactate using crabtree negative organisms in varying culture conditions. Photobioreactor with improved supply of light by surface enlargement, wavelength shifter bars or light transport.
Method of culturing algae capable of producing phototrophic pigments, highly unsaturated fatty acids, or polysaccharides at high concentration. System for small particle and CO2 removal from flue gas using an improved chimney or stack. Photobioreactor and process for biomass production and mitigation of pollutants in flue gases. Biofilm carrier, method of manufacture thereof and waste water treatment system employing biofilm carrier. Method, apparatus and biomass support element for biolocical waste water treatment. Method of cooling high-temperature exhaust gas, apparatus therefor and combustion treatment equipment.
Method and means for recovering hydrocarbons from oil sands by underground mining. Hydrogen production with photosynthetic organisms and from biomass derived therefrom. Synthetic and biologically-derived products produced using biomass produced by photobioreactors configured for mitigation of pollutants in flue gases. WOA3 en. Integrated photobioreactor-based pollution mitigation and oil extraction processes and systems.
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JPSY2 en. PTE en. ITB en. JPSB2 en. The ability of the algal biomass industry to access federal programs that support the agricultural phase is imperative for future growth. This report analyzes the place of algae in the current agricultural policy and funding landscape, and the opportunities and pitfalls that exist for algae within this policy framework. Algae projects in the U. Algal biomass projects exist in almost every state in the U. Blue pins denote a research institution, green denote a private project or company. These programs, however, focus on research and development of algae for fuels at smaller scales.
The program provides either one-time establishment payments, annual payments, or matching payments to help with harvest, storage, and transportation of biomass. Since the passage of the original Agricultural Adjustment Act of , each subsequent farm bill has evolved to address rising relevant issues in agriculture. This frequently involves drafting new programs or expanding existing programs to the new developing technologies. Shaded circles signify all feedstocks within that crop group are eligible for a particular service, empty circles signify no feedstocks within that crop group are eligible, and half-shaded circles signify only certain feedstocks within that crop group are eligible.
For example, farm service programs are only available for algal biomass feedstocks that are used to produce food or feed commodities. The current farm bill, primarily through the arm of the USDA and associated agencies, funds a large number of assistance programs for agriculture and aquaculture Agricultural Act of , Additional programs, such as the Feedstock Flexibility Program for sugar, also instill price control while simultaneously attempting to bridge the gap with biofuel producers looking to meet RFS standards.
These programs ensure that market prices for program crops never fall below a certain limit and provide direct income support or revenue assistance. Farmers of specialty crops, such as fruits and vegetables, aquaculture crops, horticulture crops, and livestock are eligible for a range of support programs outside of the safety net.
These programs provide extension services, loans, crop insurance, and incentives for improving environmental quality of farms Mercier Some of the most important benefits allotted to agriculture and aquaculture in the U. Extension services are some of the oldest programs in U. The purpose of the programs has always been to 1 develop applications for agricultural research and 2 provide instruction on agricultural technologies to farmers. Today, the Cooperative Extension Service program of the USDA provides funding through the National Institute of Food and Agriculture to support programs that connect scientific agricultural research with local farmers.
Extension services are administered through regional offices that bring expertise from land-grant universities to local levels to instruct farmers in emerging technologies that can increase productivity. Extension services are essential for disseminating information about innovative research and technologies throughout the agricultural industry. They also play an extremely important role in providing more immediate assistance to issues faced by local farmers and in developing plans that address regional problems. The additional support programs available for all farmers are important for the continuing success of non-program crops.
These programs provide assistance for the development, commercialization, and continuation of farms and provide incentives for environmentally sound farming practices. The largest of these programs, in which all farmers including those of aquaculture and livestock can participate, is the crop insurance program. The original crop insurance program began in and only covered major crops Agricultural Adjustment Act of , , but the passing of the Federal Crop Insurance Act of expanded the program to be universal Federal Crop Insurance Act of , Over crops are currently eligible for the Federal Crop Insurance FCI program, in which farmers pay a subsidized premium for insurance delivered by private companies.
While program crops are eligible for revenue-based loss insurance, specialty crops typically only participate in physical crop-loss insurance. Sea grass, a similar crop to algae that requires a blend of agriculture and aquaculture, is eligible for Non-Insured Crop Disasters Assistance FSA Additional insurance support is available for all farmers to cover losses from natural disasters under the Supplemental Revenue Assurance Program. This program provides additional assistance beyond crop insurance to farmers who experience a decrease in revenue due to natural disasters and is only available for crops that are enrolled in one of the crop insurance programs.
The expansion of crop insurance programs to specialty crops, aquaculture, and livestock was important for the development and protection of these industries. Farms of these commodities are all affected by the same environmental factors as those of program crops, such as lower-than-expected production due to droughts, natural disasters, soil quality, water availability, etc. The farming of algae is equally susceptible to different but similar factors that affect biomass and crop yields.
Farm loans are essential in successful agriculture as up-front capital is needed to make purchases of inputs such as fertilizer, equipment, land, etc. Most farm loans are authorized by the Consolidated Farm and Rural Development Act and can be in the form of direct loans, guaranteed loans or emergency loans. Direct loans cover input purchases and farmland purchases, require farmers to complete financial training courses and are given preferentially to beginning farmers. Guaranteed loans are available in coordination with banks and emergency loans can help cover natural disasters.
Agriculture, aquaculture, and livestock farms have traditionally been eligible for a number of federal programs that incentive environmentally friendly practices and resource conservation. Most notable, the Environmental Quality Incentives Program EQIP , introduced in the farm bill, provides technical and financial assistance to farmers to increase the environmental quality of their farmland. EQIP funds are distributed by states in competitive programs that focus either on innovation of novel conservation practices or water enhancement, including enhancing water quality and conservation.
EQIP also works in partnership with farms to aid in farm design that promotes environmental quality and resource conservation. The Conservation Stewardship Program CSP awards funds to farmers that have adopted uncompensated practices across their entire operation for overall conservation.
To be eligible for CSP funds, farmers must be sustaining conservation of a certain resource and must demonstrate improvement and maintenance of conservation practices. The final environmental program, the Agricultural Management Assistance AMA Program was established in the Agricultural Risk Protection Act of to address the fact that crop insurance is heavily concentrated among program crops in only a few states. The AMA provides assistance for conservation practices in a select 16 states.
The algae industry, which has most recently been associated with renewable energy production with the added constraints of reducing greenhouse gas emissions and being cost-competitive with fossil fuels, has already made substantial technological advances in freshwater conservation and nutrient recycling for commercial-scale production.
Additionally, to increase economic feasibility, algae can be grown on non-potable saline or wastewater and nutrients can be recycled, drastically mitigating freshwater use and fertilizer inputs. The company BioProcess Algae, for example, has successfully utilized waste outputs of water, heat, and CO 2 from corn ethanol fermentation to cultivate algal biomass for various end products. Coupling algae cultivation with waste outputs from other industrial processes provides cost-effective and sustainable solutions to cultivation barriers. Agricultural products are frequently subjected to market analyses by the USDA such as economic and census reports.
As the commercialization of algae progresses, market analyses will be advantageous to assess the strengths and weaknesses of the industry, the interplay between the agricultural and energy aspects of algae, and the outlook of the industry. To successfully break into the agricultural market, algae would benefit from the marketing services available from the USDA. Defining the commercial cultivation of algae as agriculture provides opportunities at the state level as well. Beyond financial assistance, states can control laws associated with agricultural property and zoning.
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For example, the Ohio state legislatures recently defined algaculture as agriculture to allow use value assessments of algae cultivation land for tax purposes, thus lowering property taxes for land used for commercial algaculture OH-H. The law additionally limits the authority of zoning laws to restrict algae cultivation on lands. Although decisions on specific investments in algae development are made at the regional and local levels, a federal initiative is still imperative to establish and influence direction and focus for the industry, as well as to develop guidance for new algae programs.
Opportunities currently exist for algae cultivation to expand commercialization within agriculture if it were defined as such. The most notable is the potential to fill a large void in agriculture of the use of non-arable land to produce renewable hydrocarbons and high value protein. Unlike terrestrial crops, algae do not require fertile soil or arable land for growth, thus expanding the areas of the country in which algae can be cultivated.
Algae do require other inputs such as salt or freshwater, nutrients, and consistent year-round sunlight. These sites exclude any cropland, urban land, protected lands, wetlands, wilderness, or significantly sloping landscapes Wigmosta et al. The USDA currently asserts jurisdiction of algae as an agricultural crop, and can potentially offer agricultural safety net programs to algal biomass companies.
Despite the role of the USDA in overseeing agricultural programs for algae, barriers still exist to the application of these programs. Many of these barriers exist at the federal and state levels, and stem from lack of an overall national plan for the development of algaculture, from the overlapping jurisdictions of other federal agencies over different aspects of algae cultivation, Fig. Federal agency jurisdiction over algae versus terrestrial crops. Four different federal departments hold jurisdiction over various aspects of algae cultivation, research, and products.
The DOE has been involved in algae biofuel research since the onset of the year long ASP in and has done extensive research on both algal biology and large-scale cultivation under its Biomass Program Sheehan et al. DOE It has currently entered contracts for developing commercial-scale production.
While the USDA is responsible for regulatory oversight and approval, biotechnology and environmental regulation of genetically modified crops, the EPA has asserted jurisdiction for the permitting of genetically engineered algae varieties under its Toxic Substance Control Act, further supporting the notion of uncoordinated and overlapping federal support and regulation of the algae industry. Existing law, although not defined well and left open to individual programs for interpretation, may have the ability to support algae when used to produce a feed or food; the same standard, however, is not applied to algae if the end product is used to produce energy.
None of these inconsistencies exist for the program crops e. The USDA asserts responsibilities for agricultural policies pertaining to algae, but the end-use of algae as an energy source has created uncertainty in the applicability of these policies to algae cultivation. While a clear case can be made for expanding these programs for algal biomass used for food and nutraceutical purposes, there are still holes in the existing framework to accommodate algal biomass grown for bioenergy purposes. Because algae are such unique crops in their diversity of end product potential, no precedent exists to determine if a particular algae cultivation facility is eligible for agricultural programs or not.
The USDA currently has no clear methodology for evaluating algal biomass producers within the agricultural landscape. Extension services, such as those provided under the Smith-Lever Act, would be appropriate to link regional USDA centers with local institutions and algae cultivators to develop methodology for evaluating algal biomass production under the agricultural framework. Since then, a number of reports have been published agreeing that commercialization of algae, particularly for biofuels, is feasible given certain improvements in the production process NRC ; ANL et al.
Furthermore, since these reports, many of these improvements have been made and technologies have been developed that successfully demonstrate the ability to sustainably cultivate and harvest algae on large scales. The overlapping jurisdiction of algae, lack of a national plan, and specifically the assumption of major responsibility by the DOE, has caused the focus of algal policies to primarily revolve around its downstream use for energy, and to overlook expansion of policies that would support its most basic properties as a crop.
Consistent, long-term federal policies are essential for scaling up biomass production of algae for energy, carbohydrates, protein and many other products U. The farming of algae requires biology, cultivation, harvest, and biomass processing practices, modeled after agricultural systems, which require independent and unique support networks for commercialization from those required for the downstream conversion of biomass into fuel such as extraction, conversion, and biorefining processes.
Schematic of fast pyrolysis process principles Apparatus used for hydrogenation within an autoclave Fermentation process of microalgae They are aquatic plants that carry out the same process and mechanism of photosynthesis as higher plants in converting sunlight, water and carbon dioxide into biomass, lipids and oxygen. They can grow on land that will not compete with food production, as do traditional crops like corn.
Some of the main characteristics that sets it apart from other biomass resources are that algae: possess a high biomass yield per unit of light and area; can have a high oil or starch content; do not require agricultural land; fresh water is not essential and nutrients can be supplied by wastewater and CO2 by combustion gas .
Microalgae and macroalgae describe two different species of algae. Mic roalgae have many different species with varying characterizations and they often exist as single cell colonies. This factor and the lack of specialization make their cultivation easier and more controllable, while their small size makes subsequent harvesting more complicated . Macroalgae on the other hand are less versatile, there are far fewer options of species to cultivate, and there is only one main viable technology for producing renewable energy: anaerobic digestion to produce biogas .
Both groups are identified in the dissertation, but as there is more research, practical experience, culture and more fuel options from microalgae, these will be considered in depth. Varying levels of success have been achieved by companies and research in the genetic modification of algal species for efficient sunlight utilization ; and production of specific hydrocarbon chains for direct processing into gasoline  , diesel , and jet fuel [,]. Nevertheless, the exploitation of microalgae for biofuels is not a near-term commercial prospect.
ADAGHA biomass with a high content of vegetable oils or other biofuel precursors, required by the high capital and operating costs of algae production , presents the critical challenge. In order to play a dominant run in the energy mix of the future algal production systems must have low capital and operating costs to compete with other crops and alternative energy sources.
However, the commercial viability of algae-based biofuels production is largely a factor that will be decided by the economies of scale. Regardless of whatever advances might come in terms of technology and biology, the fact remains that the commercial marketplace will not have an appetite for funding capital intensive energy projects unless the risk-return ratio is acceptable to debt and equity financiers . A number of researchers, companies and government organizations have previously assessed different cost effective production designs for algae systems.
These efforts are justified by the potential to produce biofuels that do not compete with food crops . The most popular of designs previously analyzed include open ponds, open raceways, and closed photo-bioreactors. Generally, these assessments have concentrated largely on the capital, operations, and maintenance costs.
The capital costs are usually broken down into costs associated with algal biomass growth, harvesting, dewatering 1, and algal oil extraction systems . In addition, there are more traditional project costs such as engineering, infrastructure preparation, and balance of plant, installation and integration, and contractor fees. However, while due consideration will be given to these factors, a number of key issues which are fundamental to the commercial viability of algae biofuels need to be addressed. Furthermore, an attempt is made to understand the long-term planning considerations and other issues relative to the commercial scale deployment of algae biofuels, based on current data, accurate and objective assessments.
It attempts to define and recommend the best practical processes that can be developed for a commercially viable algae fuel production based on present knowledge. Thus, an attempt will be made to explo re the various aspects, promises and limitations of algae as a bio energy resource. The comparative approach incorporated the use of case studies and addresses the research issue from a different perspective than has been the norm.
Instead of forecasting the likely costs and yield for a given production procedure, the goal is to assess what a project would require in order to make it commercial ly viable. Dumitresc u  posited that a significant portion of the petroleum that is extracted from the ground today was deposited betwee n and million years ago during the Early Cretaceous epoch. Organic material thrived in the volcanic and carbon-rich environment, which was then deposited on the seafloor to be compressed and stored for millions of years. Thus, the petroleum we extract from the ground today is the result of millions of years of high temperatures and pressures from geologic forces transforming the organic matter.
By growing algae in ponds or reactors, the same procedure is simulated, whilst avoiding the millions of years of processing . The practical use of microalgae cultures was, apparently, first given serious consideration in Germany when Von Witsch  proposed them as a source of vegetable oils.
That proposal was based on the discovery that under conditions of nitrogen deficiency some microalgae would accumulate large amounts of lipids, mostly unsaturated triglycerides . This holds true of some species of algae; principally the green algae and diatoms, but not of blue green algae or red algae, nor of the seaweeds. Another factor which focused attention on microalgae was their extensive use during the 's and 's in basic research on photosynthesis.
Warburg , in particular, used Chlorella cultures in experiments which led him to believe in a ''four quantum'' CO2 fixation reaction. This was a highly controversial theory2, and not strictly applicable to microalgae alone. On the basis of the background research, microalgae became a subject of interest in the United States and Europe, specifically its implications on food production . A small scale production system for microalgae 2 Almost all researchers now believe that at least eight quanta are required for photosynthesis.
Little Company in the early 's, under sponsorship of the Carnegie Institute of Washington, which brought together early studies of microalgae productions in a classic book: Algae Culture: From Laboratory to Pilot Plant . Almost all the issues of importance and concern for microalgae production were first discussed in this publication: the need for low cost harvesting techniques such as spontaneous flocculation leading to settling or floatation; the need for mixing the culture; the attenuation of light by the culture 3; the flashing light effect; the need to recycle all of the water used in growing a crop of algae; the problem of maintaining a pure, unialgal culture; the problem of preventing grazers and maintaining a stable culture; the trade -offs of density, productivity, and retention time; temperature controls; the supply of CO2; among others.
A variety of small systems for algae production were described, from vertical tubular transparent reactors, to open circular and trough-like reactors, to the large plastic bag - about foot long - used by the A. Little project. The use of algae for fuel production was proposed by Meiers 4  at the first meeting of the Solar Energy Society in Tucson, where he presented a scheme for the conversion o f algae biomass to methane.
This concept was later demonstrated in the laboratory by Golueke and Oswald 5, who showed that they could operate chemostat for conversion algae biomass to methane gas . The nutrients were recycled, thus only CO2, makeup water and nutrients needed to be supplied in addition to sunlight.
Subsequently, Oswald and Golueke, developed a conceptual process  based on shallow, open, mixed ponds, called "high rate ponds". In this procedure, carbon is recycled by converting methane to electricity. Makeup water and nutrients were to be supplied by local sewage flows. The authors concluded that even using very favourable assumptions, microalgae derived electricity would not compete with projected nuclear power costs .
The concept of the "high rate" pond was applied at a small waste treatment plant in St. Helena, California [17, 18]. In Dortmund, Germany, a process for microalgae protein production was developed using open, high rate ponds mixed with paddlewheels . This led to the establishment of over a dozen small production facilities . The initial biological and engineering challenges were overcome without regard for cost, as the demand for Chlorella tablets were on the rise. Microalgae were again actively considered as an energy source in the early 's, with the start of the energy crisis.
The US National Science Foundation USF and a number of European bodies organized a collaborative research partnership to investigate the algae to methane , the production of methane and hydrogen by microalgae was proposed with W. Oswald and C. Golueke as principal investigators. They carried out experiments on digestion of microalgae biomass to methane . Benemann et a1  carried out a subcontract dealing with the economics of microalgae production.
None of these economic analyses by the groups involved contained detailed supporting information on designs or costs. In recent years, the production of oils and hydrocarbons from algae as a possible route to fuels has witnessed considerable activity in terms of research and literature. Thus, this project has carried out a more in-depth analysis of the realistic routes to commercial algae production. National Renewable Laboratory between and The double benefit from success of this program would be the development of a viable renewable fuel along with a viable technology for reducing great quantities of CO 2 emissions.
During the nearly two decades of this program significant advances were made in the science of manipulating the metabolism of algae and the production engineering of microalgae systems. The programme, despite its accomplishments, was terminated in largely due to plummeting oil prices. Nevertheless, various researchers have made far-reaching contributions to the science of algae biofuels in the intervening years. And the crux of this work is based on these contributions in terms of research and analytical perspectives.
Rosenberg et al  identified green microalgae of the class Chlorophyceae among the eukaryotic widely utilized for current commercial applications belong to the genera Chlamydomonas, Chlorella, Haematococcus, and Dunaliella. The study of these freshwater and marine algae has generated a wealth of information concerning their physiology, biochemistry, and cultivation [30— 33].
In regard to genetic engineering, these species are amenable to nuclear transformation, necessary for metabolic control, and secondly, to chloroplastic transformation, for high levels of protein expression, and thirdly, more straightforward approaches to genetic modification compared to higher plants . Diatoms, a group of silicon-rich microalgae, and prokaryotic cyanobacteria also offer substantial opportunities for metabolic engineering and biotechnology, but will not be examined extensively in this review [34, 35]. Source: NREL.
Adapted from  For algae to grow, a few relatively simple conditions have to be met: light, carbon source, water, nutrients and a suitably controlled temperature . Many different culture systems that meet these requirements have been developed over the years; nevertheless, meeting these conditions for scaled systems is difficult.
Algae are widely regarded as the aquatic relatives of terrestrial plants, and they thrive in aerated, liquid cultures where the cells have sufficient access to light, carbon dioxide, and other nutrients . They are primarily grown photoautotrophically; yet some species are able to survive heterotrophically by degrading organic substances like sugars .
Additionally, because algae consume carbon dioxide, large-scale cultivation can be used to remediate the combustion exhaust of power plants . Culture systems are very different between macroalgae and microalgae. ADAGHA One important prerequisite to grow algae commercially for energy production is the need for large scale systems6 which can range from very simple to open air systems which expose the algae to the environment. The photosynthesis process is a light-driven reaction which splits water and assimilates carbon into the biomass .
Energy in the form of photons is absorbed by the algae cells, which convert the inorganic compounds of CO 2 and H2O into sugars and oxygen. The sugars are processed and converted to carbohydrates, proteins and lipids inside the cell walls. Wogan et al  documented a series of procedures in order to extract the valuable lipids from within the algae cells a series of steps must be undertaken to isolate the algae cells and oil: the traditional process begins by when the algae biomass is separated during the dewatering stage using either centrifuges, filtration or flocculation techniques.
Man-made production of algae tends to mimic the natural environments to achieve optimal growth conditions. According to literature put forward by various authors  — , —, among others: growth depends on many factors and can be optimized for temperature, sunlight utilization, artificial light, PH control, fluid mechanics and more.
Algae production systems can be organized into two distinct categories: open ponds and closed photo-bioreactors. Open ponds are defined by large tracts of water pumped into the ground with some mechanism to deliver CO 2 and nutrients to circulate the algae culture . Both systems have their peculiar traits and are briefly discussed in the next two sub-sections. Pond reactors are usually unsophisticated contraptions that consist of little more than depressions in the ground, sometimes lined with plastic, and usually designed in a raceway pattern .
Experimental examples of open pond reactor are illustrated below in Figure 4: Figure 4. Examples of experim ental, open outdoor systems for cult ivation of mic roalgae, whic h can be scaled up to large production facilit ies 10 1. Adapted from . ADAGHA According Wogan et al , most ponds are open to the atmosphere, which allows unwanted or competing strains of algae with undesirable properties to enter the pond. These competing algae strains can potentially take over the pond thus rendering the harvest useless. CO 2 is usually delivered to the ponds through natural mass transfer from the atmosphere to the water.
Since CO 2 only composes 0. CO2 can be bubbled through the water to increase the level of dissolved gas, although recent researches  — , indicate that unused CO2 still escape into the atmosphere. Open ponds are however not without drawbacks. The simplicity of the systems leads to problems with controlling the growth environment and operating conditions delivering less than ideal algae yields .
While ponds are more productive per acre of land than terrestrial crops, a significant amount of land must be used to grow algae in ponds . Other growth conditions such as temperature and PH are also difficult to manipulate. Temperature is difficult to maintain because heat is continuously transferred to the environment.
Also, nutrient and oxygen production affect the PH levels in the water. In most open systems, growth rates are generally lower for open ponds because sunlight energy is diminished below the water surface leaving algae cells at the bottom of the pond with little energy for growth . Mixing can be implemented to allow algae cells adequate exposure to photons, but mixing is not classified as a definite solution. They offer continuous operation, a high level of controllability and elevated biomass concentrations, which results in lower space requirements and lower harvesting costs per tonne of algae .
It consists of a photostage loop, heat exchanger, degasser, circulation pump, CO2 supply, and sensors e. Created by PalSek. The water loss results from the elevated water levels in the algae biomass solution. This allows for the cultivation of algae also in arid areas7 where classical terrestrial agriculture is not possible.
A summary of some closed systems are briefly annotated in following sub sections: 2. Aadapted from ,  Scalability of this system is limited since, when putting several systems close together, they will cast a shadow on each other. See fig. The Field of bubble columns induce linear shading [ 51]. Fig Tubular reactor system  However, this has its own scaling problem: algae will consume nutrients and CO 2 while producing O28 causing further deterioration along the tube.
The complicated flow regime inside the reactor and scalability are the major challenges associated with this reactor, although the latter has been greatly improved by a design called the green wall panel . There are many variations and innovations on the previously described closed systems. Many different designs of photo bioreactors have been developed, but most are relatively expensive compared to open ponds. Nevertheless, photo bioreactors appear to satisfactorily meet the conditions for producing algal biomass on a large scale.
Closed, controlled, indoor algal photo bioreactors driven by artificial light are already economical for special high-value products such as pharmaceuticals, which can be combined with production of biofuel to reduce the cost. ADAGHA depth Oxygen concentration Usually low enough Build-up in closed system because of continuous requires gas exchange spontaneous outgassing devices O2 must be removed to prevent inhibition of photosynthesis and photo oxidative damage Temperature Highly variable, some Cooling often required by control possible by pond spraying water on PBR or depth immersing tubes in cooling baths Shear Usually low gentle mixing Usually high fast and turbulent flows required for good mixing, pumping through gas exchange devices Cleaning No issue Required wall-growth and dirt reduce light intensity , but causes abrasion, limiting PBR life- time Contamination risk High limiting the number Low Medium to Low of species that can be grown Biomass quality Variable Reproducible Biomass concentration Low, between 0.
According to -, factors such as temperature, irradiance and, most markedly, nutrient availability have been shown to affect both lipid composition and lipid content in many algae. ADAGHA stimulate TAGs accumulation while under low irradiances; mainly polar lipids structurally and functionally associated with cell membranes are synthesized. However, large variability exists in the response to nitrogen deficiency. Generally, diatoms, which have relatively high log-phase lipid content, do not respond to nitrogen starvation by increasing their lipid content , .
Green microalgae show a variety of responses, from several fold increases from log-phase values to no change or even a slight reduction . Within the same genus some strains were found to accumulate starch under nitrogen starvation, whereas others accumulated prevalently neutral lipids . When nitrogen deprivation is imposed upon a culture exposed to suitable irradiances, photosynthesis continues, albeit at a reduced rate, and the flow of fixed carbon is diverted from protein to either lipid or carbohydrate synthesis . Microalgae concentrations always remain very low while growing, typically 0.
The average length of most algae species are measured in micrometers. These two aspects make the harvesting and further concentration of algae difficult and therefore expensive. Harvesting has been claimed to contribute 20—30 percent to the total cost of producing the biomass . In order to reduce the cost of production, concentrating the algal biomass to a water content that is low 10 This means 1 tonne dry biomass has to be recovered from m3 to m3 water.
Thus, it is necessary to maintain an effective interaction between the development of harvesting technologies and the selection of algal species for mass culture . A short review of the main harvesting methods for microalgae is presented in the subsequent section: 2. Once a day the settling pond is filled with a fully grown algae culture and drained at the end of that day, leaving a concentrated biomass volume at the bottom, which is stored for further processing . Thus, about 85 percent and up to 95 percent of the algal biomass was found to be concentrated in the bottom of the pond at 3 percent dry matter , although this will depend on the species used.
Settling pond require significant additional space. See figure It is usually carried out commonly on membranes of modified Cellulose with the aid of a suction pump. Several options have been described by researchers, including different materials, vacuum, pressured and rotating filtering. Some acceptable results have been obtained for colonial microalgae, but not for unicellular species , . One involves the use of a reverse-flow vacuum in which the pressure operates from above, making the process easier whilst avoiding the packing of cells .
This method itself has been adapted to allow concentration of high water volumes in relatively short time A second process uses a direct vacuum but involves a stirring blade in the flask above the filter which prevents the particles from settling at all during the concentration process . Filtration is considered as advantageous because it can be employed as a concentrating device and is able to collect microalgae or cells of very low density. However, concentration by filtration is limited to small volumes and leads to the eventual clogging of the filter by the packed cells when vacuum is applied .
It is often used for the concentration of high-value algae, and generally considered expensive and electricity consuming; although subsequent advancements in technology may prove it to be useful on a commercial and industrial scale , .
Betting on Algal Biofuels
The procedure involves the concentration of high-density, small unicellular algal cultures in a centrifuge . Products such as aluminium sulphate and ferric chloride cause cells to coagulate and precipitate to the bottom or float to the surface. The algal biomass is recovered by removing the uppermost part of the cells from the surface. Continuous-flow centrifugation with the classical Foerst rotor is a widely employed. ADAGHA method is essentially unselective ; all particles with a sedimentation rate above some limiting value will be collected, although the integrity of the recovery rate emerge as questionable.
Adapted from ,  The Aquatic Species Programme estimated the costs for centrifugation at 40 percent of production cost and 50 percent of investment cost . However, applying centrifugation as a secondary harvest method, to concentrate from percent dry matter to percent would reduce centrifugation costs at least 50 times .
Levin et al  developed a highly efficient froth flotation procedure for harvesting algae from dilute suspensions. The method is not dependent on the addition o f flotants. Rather, harvesting is done in a long column containing the feed solution which is aerated from below. A stable column of algae foam is generated and harvested from a side arm near the top of the column. According to Levin et al, the cell concentration of the harvest as a function of PH, aeration rate, aerator porosity, feed concentration, and height of foam in the harvesting column. The economic aspects of this process seem favourable for mass harvesting of algae for food or other purposes.
Gotaas and Golueke further emphasized the notion in an experiment they carried out in : the froth flotation harvesting process concentrates the product to a point necessary for economical drying. Thus, the froth flotation process is highly rated as a commercially viable method and has been applied to large volumes of fluid processing procedures. Flocculants are described as chemical agents that cause colloids and other suspended particles in liquids to form aggregates.
Alum and ferric chloride are chemical flocculants used to harvest algae . This procedure has some limitations, chief among which is the difficultly in separating the algae from the added chemicals. Also, interrupting the flow of CO 2 to the system can cause algae to flocculate on its own without control. As a result, the procedure can hardly be classified as economically viable. Other determining criteria are usually water content and chemical composition of the biomass .
Energy requirements and efficiency are determined by separation processes and conditioning steps of the products. ADAGHA Fig Biomass for fuel applications—ranges of moisture content  First indication for conversion efficiency12 is given by the enthalpy of reaction in table 2.
Posten , posits that biotechnological conversion processes generally have higher efficiencies than chemical conversion processes. Thus, a combination of biomass growth yield and conversion efficiency leads to overall yields of upgraded fuels per unit ground area. Table 2: Idealiz ed formulation of photo biological and chemic al reactions for fuel generation and related enthalpy changes. Based on empiric al correlation for heat of combustion Eq.
Adapted from . ADAGHA The energy conversion reaction of biomass can be classified into biochemical, thermochem ical and direct combustion . Biochemical conversion can be further subdivided into fermentation, anaerobic digestion, bio-electrochemical fuel cells and other fuel producing processes utilizing the metabolism of organisms.
Thermochemical conversion processes are further classified as gasification, pyrolysis and liquefaction . Biomass can also be converted into three main products: two of them related to energy and one as a chemical fe edstock . Energy conversion processes from microalgae. Adapted from ,  2. These are discussed in detail in the subsequent sections: 2.
ADAGHA A flow diagram of an algae fuel production system by low temperature gasification of biomass, as proposed by Tsukahara et al  , is presented in Fig. Elliot  developed a low temperature catalytic gasification of biomass with high moisture content. In this process, algae biomass with high moisture is gasified directly to methane rich fuel gas without drying. In a study conducted by Patil et al , and  — , direct hydrothermal liquefaction in sub-critical water conditions is a technology that can be employed to convert wet biomass material to liquid fuel. Adapted from ,  — .
The liquefaction is performed in an aqueous solution of alkali or alkaline earth salt at about C and 10 MPa in the absence of a reducing gas such as hydrogen or carbon monoxide. Dichloromethane is used to separate the oil fraction from the algae biomass. The dichloromethane extract was filtered from the reaction mixture, following which the residual dichloromethane is filtered and evaporated at 35 degrees under reduced pressure . Earlier studies adopted the slow pyrolysis system and the conversion was done at a low heating rate and a longer residence time.
A schematic of a fluidized bed, fast pyrolysis system is shown in Fig. Schematic of fast pyrolysis process principles. Adapt ed from . Since algae usually have high moisture content, a drying process requires much heating energy . Microalgae are subjected to pyrolysis in the fluid bed reactor . The products are then separated into char, biofuel and gas.