Dubhaltach MacLochlainn

An evaluation of the feasability of algal biofuel production

as a renewable alternative energy source in Ireland

Abstract

The production of oil from petroleum is expected to fall over the next century, as demand outstrips supply. One alternative source of fuel for the transport sector is algae. They can be divided into two categories, microalgae and macroalgae, which are morphologically quite different. Algae can be grown and then processed to produce biofuels, such as biodiesel, biogas and bioethanol, which will run in most conventional internal combustion engines. The culture of microalgae is land based and tends to require a significant capital investment. Macroalgae can be grown at sea, attached to longlines and later transported for processing to a biorefinery. Although no commercially viable operations depending solely on algal production for biofuel exist, operations in Israel and in Japan have proven that co-production of algae for use as biofuels, as well as other uses is feasible. The problems envisaged in setting up algal production in Ireland include the reduced solar radiation, and high cost of production. Further research is required to suitably adapt current technologies to Irish conditions. Companies such as Solazyme and Joule Unlimited are currently employing new techniques to produce algal biofuel, and merit some attention in future. Overall, this industry is in its infancy, and many gaps in production need to be covered through intensive R&D before it can be considered a feasible option for the future.

Introduction

It is estimated that the world’s production of petroleum, the primary energy source used today, peaked in 2004, at 74 million barrels of oil per day. It is therefore considered that a global decline, and subsequent crisis will begin around 2020, where the price will become prohibitive for most conventional uses.

Because of this, the Irish government, in keeping with international accords has put in place the Energy (Biofuel Obligation and Miscellaneous Provisions) act 2010. This is a biofuels obligation scheme, which aims to displace a proportion of fossil fuels used for transport, leading to biofuels making up 10% (on an energy basis) by 2020.[1]

This achievement will greatly depend on the improvement of production and availability of biofuels, which is why it is in the interests of the government to invest in research and development of a native, sustainable biofuel resource. One possible source, which has the added advantage of not taking up land, which could otherwise be used for food crop production, is the use of algae. Although research into this potential source of biofuels is still in its infancy, there is a great deal of interest, and investment in the area throughout the world.

My proposal is to investigate the feasability of culture and processing of marine algae, as a renewable source of biofuel. Ireland enjoys an extensive coastline (over 3000km) and large marine territory, which contain nutrient rich warm waters, ideal for the production of many algal species. A significant amount of research is currently under way into the use of both micro and macroalgae for the production of biofuels for use in the transport sector.

Ireland’s Marine Environment

Ireland’s marine territory consists of a large triangular area, extending to the west of the country. Most of this territory consists of two large masses of continental shelf, with maximum depths of 500m, divided by an abyssal trough to the northwest, which is up to 3000m deep. To the south west, lies an abyssal plain with depths of over 5000m. The total area is over 650,000sq km, which is 10 times greater than our landmass, and constitutes the biggest marine territory of any country in the European Union. [2]

fig 1. The real map of Ireland, courtesy of the Marine Institute. [3]

The Irish coastline is also of significant length, estimated by the ordinance survey to be 3171km [4]. Most of this length lies to the west, and consists of numerous islands, peninsulas, bays and inlets.

Ireland enjoys what is known as a temperate maritime climate, with typical daytime land temperature extremes of 8°C in January and 19°C in July. The moderate nature of the climate is due to the influence of the Atlantic ocean, as well as North Atlantic drift. This is a continuation of the gulf stream, a fast moving North westerly ocean current, originating in the gulf of Mexico, affecting the sea temperatures as far away as the north west coast of Europe. Sea temperatures vary from 7°C to 10°C in the winter to 13°C to 16°C in the summer.[5]

The amount of solar radiation falling on Ireland varies significantly throughout the year, due to it’s latitude, and the effect of cloud cover. In 2010, for example, a minimum and maximum of 622MJ/m² and 5724 MJ/m² were recorded in Dublin airport in January and June respectively. This is almost a ten fold difference, and accounts for a high level of seasonality in the growth of photo-synthesisers. [6]

Ocean currents, flowing from deeper waters onto the continental shelf brings nutrients, such as carbon and nitrogen up into the warmer waters of the continental shelf. These natural upwellings, lead to an abundance of planktonic growth, which in turn feeds the diverse marine ecosystems, which exist off the coast of Ireland. [7]

Algae types and biology

According to Biology-Online, the definition of algae is:

"A group of aquatic, photosynthetic, eukaryotic organisms ranging from unicellular to multicellular forms, and generally possess chlorophyll but lack true roots, stems and leaves characteristic of terrestrial plants." [8]

Although the term “algae” is commonly referred to as above, the group of organisms referred to in fact span two kingdoms (prokaryotes and eukaryotes), and are polyphyletic (having multiple origins). Their exact taxonomic classification is still somewhat disputed, and is constantly updated as new information arises as to their genetic and biological make-up. [9]

For the purposes of this report, we will deal with the group from a morphological, rather than a taxonomic perspective, and focus on types which are of interest to the biofuels sector.

The vast majority of algae are considered photoautotrophs, which means that they depend almost entirely on sunlight and CO₂ to fulfill their nutrient and energy requirements. This is carried out by a process called photosynthesis, where CO₂ is converted into carbohydrates and ATP by a chemical called chlorophyll. The most basic chemical reaction which occurs during the photosynthetic process can be summarised as follows.

light + 6CO₂ + 12H₂0 ===>Chlorophyll ===> C₆H₁₂O₆ + 6O₂ + 6H₂0

When light, in the form of photons in the wavelength of between 400 and 700nm (known as Photosynthetic Active Radiation) is absorbed by a molecule of chlorophyll, contained in micro-organelles, called chloroplasts, it's energy causes a charge separation, which is known as the redox potential of the molecule. This potential is used to perform electrochemical work within the chloroplast, by generating reduction and oxididation reactions. As shown in the equation above, a simplified version of this reaction would involve taking carbon in an oxidised state (carbon dioxide, or CO₂) and via reduction, converting it into carbohydrates (CH₂0), using light. The redox potential, generated in the chloroplast is also used to generate all the proteins, complex carbohydrates and other molecules, which are to become the constituents of the organism, but more importantly from a biofuel point of view, the increase in chemical potential energy may be utilised by conversion processes to generate the fuels which can then be utilised in the transport sector.

Algae are in fact very effective photosynthesisers, capable of making use of a much greater range of light wavelengths and intensities than the more modern terrestrial equivalents, plants. The by-product of the photosynthetic process is oxygen, which would have built up in the earth’s atmosphere over millions of years, and eventually reached levels which could support the evolution of air breathing animals, such as ourselves.

Morphologically, algae can be divided into two groups, micro and macro algae. Micro algae are microscopic single celled organisms, which mostly live in the part of the water column exposed to light (planktonic), whilst as macroalgae are large plant-like organisms, which may either be attached to a substrate (benthic), or free floating on the surface.

Micro Algae

fig 2. A variety of microalgae species, courtesy of Biofarms Hawaii LLC.[10]

This group consists of over 5,000 planktonic species, and constitute the primary food source at the base of most marine food chains. They are responsible for the production of approximately 50% of the oxygen in the earth’s atmosphere. They are usually unicellular organisms, although some form colonies of individual organisms, which can also survive independently. Although most species live in the earth’s oceans, there are also many freshwater varieties, and they can tolerate a wide variety of salinities and pH levels. Apart from being a source of biofuel, microalgae are also currently grown as food in aquaculture facilities for other marine organisms, such as filter feeding bivalve molluscs, and fish larvae. They are also grown commercially as a valuable source of Omega 3 and beta-carotine, which have become popular nutritional supplements in recent times.

Microalgae vary greatly in their biochemical make-up, but in this study we will primarily be concerned with those species which have significant levels of lipids, as they are the key component in the production of biofuels. As can be seen in the table below, the lipid quantities vary greatly, depending on the species. Certain stress conditions can, however induce microalgae to produce excess lipids, and will be detailed in the culture and harvesting section.

Table 1 Chemical Composition of Micro-Algae Expressed on A Dry Matter Basis (%))

Source: Becker, (1994) [11].

Detailed in table 1, above, are the biochemical composition of some of the lipid producing varieties of microalgae. The content is as high as 40% of the dry weight of the algae, which makes these algae an excellent source of lipids, that may then be converted to biodiesel through standard chemical processing techniques.

Macro Algae

This group is the more obvious of the two, existing on every coastline in the world, and commonly referred to as Seaweed. There are three types of seaweed, categorised by their pigmentation. They are red, green and brown. Red seaweeds tend to be prevalent closer to the tropics, although all three are commonly seen in Irish waters. Among the dominant species seen here are the brown seaweed, Laminaria, commonly known as kelp, the red seaweed, Palmaria palmata, known as dillisk, and the green seaweed Ulva, or sea lettuces. The most commercially important species currently, in Ireland is the brown seaweed, Ascophyllum nodosum, or the bladder wrack, which is harvested from the wild by Arramara Teoranta, in Connemara for the production of alginate, and other extracts.

Fig 3 Ascophylum nodosum (left), Laminaria digitata (centre) and Ulva lactaluca. [12]

Morphologically, there is great variation in the shape and size of the seaweeds, mainly depending on the environment they inhabit. In general, benthic species, which are found attached to rocks on the coast consist of a stem, known as a thallus, from which branch the fronds, the sites of nutrient absorption and photosynthesis, and a holdfast, consisting of hair like structures, which attach to the substrate. They may be intertidal or subtidal, and can tolerate a large amount of agitation and tidal exchange, as is common on the Atlantic coast of Ireland. The most common species of this type found in Ireland would be Laminaria, Palmaria and Ulva. There are also a great amount of free floating species, which float on the water surface with the aid of gas filled pods, known as bladders. They tend to be found washed up along the coastline, particularly in the summer, where they appear in great abundance. Wracks, such as Ascophyllum are particularly abundant in Ireland. There is a massive variation in size of seaweed, and species can be found from a few milimeters to tens of metres in length. The kelp, for example has been found up to 6m in length, whilst as the sea lettuce is rarely more than a few centimeters long.

The biochemical composition of a typical seaweed, such as Laminaria consists of over 85% water. Of the remainder, approximately 25% is ash, or mineral matter, and about 60% sugars (mostly alginates and laminarian) Only about 6% of dry weight consists of cellulose, which is the dominant form in land plants, and is commonly used in fermentation processes to produce biogas [13].

Biofuel production from algae

The processes used to produce biofuel from algae depend on the raw materials which are to be used. The type of fuel produced also varies, depending on the process. The main fuels and their production methods are outlined below:

Biodiesel

Fig 5. A proposed algal production facility (left) and biogas digester [17]

Consisting of methane, carbon dioxide, and small amounts of hydrogen sulfide, biogas is natural gas, derived from the anaerobic digestion of organic compounds. It's production has been extensively researched and developed in latter years, as a way of using waste products to produce energy. In order to use biogas in combustion engines for transport purposes, the gas must first be processed to remove the highly corrosive hydrogen sulfide from it.

Biogas is produced by placing the algal biomass in a sealed tank, containing methanogenic bacteria, which break down the organic molecules in the biomass into methane and CO₂. This process is known as anaerobic digestion and consists of the following four different stages:

• 1. Hydrolysis: This is a chemical reaction, which involves the breaking down of larger carbohydrate, fat and protein molecules into sugars, fatty acids and amino acids, which can then be readily accessed by bacteria in the digester. It is caused by the addition of hydroxyl groups to the mix.

  2. Acidogenesis: Fermenting bacteria in the mix further break down the products of hydrolysis into carbolic acids, alcohols, carbon dioxide, hydrogen and ammonia.

  3. Acetogenesis: Here, another set of bacteria further break down the products of acidogenesis into acetic acid and carbon dioxide.

  4. Methanogenesis: Finally, methanogenic bacteria take the acetic acid and byproducts from the previous processes and convert them to methane and CO₂. Any remaining undigested material is known as the digestate, which can also be extracted and used as fertiliser or compost in the agricultural sector.

The process of converting biogas into a useful fuel is called biogas upgrading and commonly consists of running water in contra-flow to the pressurised gas, causing the CO₂, and other trace elements to be absorbed by the water. This leads to the production of biomethane, which consists of up to 98% methane, and is comparable to natural, or petroleum derived gas in its efficiency.

Bioethanol

Fig 6. An E85 gasoline pump in the United States [18]

Although much less popular as a fuel derived from algae, it is worth mentioning, due to claims from several companies, regarding this fuel type. It is currently a popular method of using cellulosic waste material, such as byproducts from sugar cane and corn processing plants to produce biofuels. It can be used in standard petrol engines, although an adjustment of the compression ratio will greatly improve efficiency. It is currently used as a blend with standard petrol, known as E85 (85% petrol, 15% ethanol) in order to compensate for the effects of altitude on engine power. Ethanol blends may also, however increase the tendency for vapour lock to occur, which leads to stalling of an engine at high temperatures.

The common production of ethanol involves three steps:

• 1. Fermentation: This is the same process as that used to produce acoholic beverages. Sugars, such as cellulose and starch, the main constituents of many land plants are broken down by bacteria into ethanol. In algae, the readily accessible sugars include mannitol and laminarian, and approximately 26% of the composition of a typical seaweed is sugars. This makes them a good candidate for fermentation, although this has not been done on a large scale to date.

  2. Distillation: After all available sugars have been converted to ethanol, the ethanol must be removed from the medium. This is commonly done by a distillation process, where the medium by heating it and causing the ethanol to evaporate. This is a very energy intensive process, and in some cases takes almost as much energy as that produced in the resulting ethanol. The product of this process is known as hydrous ethanol, which still contains up to 5% water. Although this compound can be used as a fuel in this state, it is more commonly further refined, so that the ethanol can be mixed with gasoline.

  3. Dehydration: This step once involved the further distillation of the ethanol, using different compounds to remove the water. The current trend is to use molecular sieves, which contain beads that absorb the water into pores from the ethanol as it is forced through the bed. The beads must be regularly dehydrated to remove the accumulated water, and therefore the process usually contains two bead beds, one of which is in use at all times. The dehydration is usually done by applying a vacuum, or inert atmosphere. This process is much less energy intensive than distillation, and is therefore preferred by most producers.

Bioethanol production from algae is currently in its infancy, as conventional fermentation techniques do not work with the sugars found in algae, such as alginate. There are no economical means currently available to break these sugars down to a useable form either. Much research needs to be carried out to develop a process which can use algae, and their derivatives in the fermentation process.

Algae cultivation and harvesting

There are currently estimated to be up to 3 million wet tonnes of natural kelp beds along the Irish coast. This could be used as a source of biomass for the production of biofuel, although the harvesting would have to be carefully managed to prevent significant depletion and potential ecological consequences of over-harvesting. There are currently significant natural harvesting operations in both France and Norway, which are carried out with the use of trawlers, but the stocks are intensely monitored and highly regulated to ensure sustainable harvesting. The quantities of seaweed which would be required to produce biofuels would probably place an extremely high burden on the natural stocks in any country, and therefore it is considered less ecologically harmful, and more efficient to obtain a reliable source of biomass through the artificial culture of the desired crops in our coastal waters. Likewise, there is no efficient way of harvesting microalgae from the wild, and such harvesting could lead, not only to the reduction in basic nutrients from the vicinity, but also to the reduction in the amount of oxygen in the waters, which could lead to severe implications for other animals in the local ecosystem. For this reason, only cultivation methods are detailed in this report.

Microalgae cultivation

There is a long history of microalgae cultivation, even prior to its consideration as a source of biofuel. Several species have been cultivated as a foodstuff in the aquaculture industry. Due to the high value of the end product in these aquaculture ventures, the cultivation was usually carried out in a controlled environment, using artificial light. If grown for the purposes of biofuel production, a much larger scale operation, using natural light is the only economically viable method of cultivation.

Two systems are commonly used to grow microalgae as a fuel soruce, and in some cases, they are used in conjunction with each other, in order to make use of the benefits they each offer. Both are land based, and although microalgae exist in both fresh and saltwater, the latter is more commonly used, as there is a plentiful and cheap supply in any coastal location. A factor common to both is the ready availability of good natural light, which is something which must be considered in greater detail when evaluating Ireland as a site for microalgal cultivation.

Raceways

Fig 6 a series of raceway ponds in the United States (left) and a proposed raceway system (right) [19]

This is the less controlled of the two systems, and is also much cheaper to construct and maintain. It usually consists of a large shallow elliptical pond, with a barrier running along the middle, and a paddle wheel, which provides mechanical mixing, and flow of water around the pond. There are many variations in shape and size of the raceway, but the basic principle is the same. The pond is innoculated with the desired species of microalgae, the appropriate nutrients are added, and the paddle wheels ensure vertical and horizontal mixing of the water, to ensure the entire volume gets exposure to light for photosynthesis. Usually, CO₂ is added, as a source of nutrients for the microalgae, and some trace quantities of nitrogen and phosphorous are also applied. The latter two components can be cheaply supplied in the form of agricultural fertiliser, and ideally, a free source of CO₂ , such as a neighbouring power plant or production facility can be used.

Although the cost of construction and maintenance of this system is considerably less, it does have a much lower productivity yield, and is prone to contamination by foreign algae and bacterial species, which leads to competition and a further lowering of productivity.

Photobioreactors (PBRs)

Fig 7. a bank of photobioreactors in a greenhouse [20]

This is a closed system, in which the microalgae are also grown in suspension. It usually consists of glass, or plastic tubes, through which the suspension is pumped. The levels of nutrients and gas are closely monitored, and therefore adjusted to optimum levels. The PBR has the added advantage of using vertical, as well as horizontal space, and may even be structured in such a way that individual panels can be moved, much like solar panels, to track the sun. The amount of nutrients added can be precisely measured, and its enclosed nature means that any CO₂ added, remains within the system, until absorbed by the microalgae yields from a PBR are significantly higher than those from the raceway system, but the cost of construction and maintenance of PBRs has been prohibitive in the past. There are ongoing trials of PBR systems in many locations, and the most feasible justification for their use would be if the algae are also used to produce other more valuable components, such as nutraceuticals, or health supplements. As mentioned previously, they may also be used in conjunction with raceways, in order to artificially modify the environment that the algae are exposed to at some point in the growth cycle. One option is to use PBRs to produce the innoculum, with which the raceways are subsequently populated. The higher density of the initial biomass ensures that contamination with foreign species is less of an issue.

Harvesting of microalgae

After sufficient concentrations of microalgae have been attained, they need to be extracted from the water and concentrated for processing to form biofuel. Four main methods are used to obtain a concentration of 2 to 7% solid material. They are the following:

• 1. Sedimentation: In some species, there is a natural tendency for the organisms to form clots, or form sediments. The ceasing of mechanical agitation of the substrate may be sufficient to allow these species to settle to the bottom, and this technique is applied in some systems. The water due to be harvested is pumped into a series of large shallow settlement ponds and allowed to settle there for a period of time. The water is then pumped out again, leaving behind a sediment of concentrated microalgae. This can then be removed and sent for further processing. This is the most economical option, as it involves very little mechanical effort.

  2. Filtration: Where the algae are free floating, and do not drop out of the water column, it is possible to filter the seawater and therefore remove the algae from it. This can be achieved using a rotary filter, which consists of a rotating filter drum, through which the water is forced. As the algae accumulate on the drum, it rotates, and the algae are washed into a separate collection system, from where they can be collected for further processing. This system involves greater mechanical effort, and also requires regular maintenance.

  3. Flotation: If tiny enough air bubbles are passed through the water column, they tend to accumulate suspended particles on their surface. These bubbles then rise to the surface from where they can be skimmed and removed. The generation of oxygen by the algae, as well as the high concentration of oils also aid in the flotation of the algae. A deeper water column is more favourable for this type of harvesting.

  4. Centrifugation of the water is the most expensive method of harvest, but is extremely fast and efficient. It involves spinning the water in a large porous drum, which results in the accumulation of the microalgae within the centrifuge, whilst the water is flung out. It is able to attain much greater concentrations than the other three processes, but requires more elaborate equipment.

Further dewatering may be attained by the use of a press, or a centrifuge. Heating, in order to evaporate the water is also possible, but the cost is usually prohibitive. It can also lead to a degrading in the chemical quality of the algal compounds. For biodiesel, a concentration of 90% algae is required, which entails considerable further dewatering, which causes the cost of processing to mount significantly. This area requires significant further research, in order to make the production of biofuel more economical.

Macroalgae cultivation

Unlike microalgae, the best way to cultivate seaweeds is at sea. They require much less maintenance, and capital cost, but due to the higher biomass requirement, are much more labour intensive. Harvesting and maintaining the growing structures requires the usage of a boat, and transport of the vast amounts of biomass can lead to high levels of fuel consumption. The most common method of seaweed cultivation is the longline, which is also commonly used to grow mussels and other shellfish.

Longlines

These consist of two parallel lengths of rope, held together, and afloat by large plastic floats, which are attached at intervals of approximately 10m. Usually 200 litre plastic chemical barrels are used as floats, as they are widely available and inexpensive to purchase. Seaweed spores are usually produced in a land based facility, and spools of thread are immersed in the spore medium until the plantlets attach to the thread. The spool is then fed onto the parallel lengths of rope at sea, and pulled along its length. The thread wraps spirally along the rope, and the plantlets then grow, attaching themselves to the rope. This method has been tried and tested in Ireland with trials in the cultivation of Alaria esculenta run in Roaring Water Bay, achieving yields of up to 15kg per metre of rope over a 5 month period [21]. In order to make harvests of sufficient size to merit cultivation, a large area must be covered with longlines. Yields may be improved by locating longlines nearby other aquaculture facilities, in order to make use of nitrates and other nutrients released, and share the infrastructure needed to maintain and harvest algae from the longlines. The added advantage of this polyculture system is the oxygenation of the surrounding waters, which leads to greater growth rates for the finfish and shellfish.

Macroalgae Harvesting

Although the removal of the harvest from the longline, and subsequent transport to the coast is relatively straightforward, the further dewatering and breakdown of the plants involves significant effort and energy usage. Seaweeds are 85% water, and the removal of this water is necessary for most biofuel processes. The presence of salt also acts as an inhibitor to many reactions the algae need to undergo. The advantage of biogas production, however is that the digestion process is carried out in water, therefore allowing for less drying of the harvest. Some freshwater would need to be added to the biomass, however, in order to reduce its salinity. The algae are usually chopped finely, in order to increase the surface area available to the microbes for digestion. The main reason that drying is an advantage is due to the cost of transportation, it being more economical to transport the reduced bulk of a dry or semi-dry biomass.

Economic evaluation

The vast majority of algal biofuel projects are currently in the R & D phase, and have therefore not been successfully evaluated at a large enough scale to give a reliable economic perspective. The few commercially viable algal production facilities currently in operation are producing much higher value algae derived products, such as nutritional suplements and cosmetic components. The capital and maintenance costs of such operations, however may be used to give a preliminary assessment of the expected costs of set-up and running of a large scale biofuel production system. In order to apply the costs to an Irish setting, they must be assessed by researching the difference in costs between the original project and any potential Irish venture.

Microalgae

Fig 8. The seambiotic algal production facility in Israel. [22]

One such microalgae production facility called Seambiotic is currently in operation in Israel, and consists of approximately 1000m² of eliptical open pond raceways, which are being used to grow a variety of microalgae for R & D purposes. Particular emphasis has been placed on the culture of Nanochloropsis sp., as it has a high lipid and Poly Unsaturated Fatty Acid (PUFAs) content and is relatively easy to grow. The plant is located next to a power plant, which provides free CO₂ emissions from its flue gas, and using seawater. A self flocculation technique is used and harvests of up to 20g/m²/day dry weight have been obtained. The harvest is then further processed to extract Omega 3 and biodiesel. The estimated cost of production is $0.34/kg, and a conversion of 12% of the dry weight to biodiesel has been achieved. This puts the cost of diesel feedstock at over $2.80/kg, which will have to be further refined to produce a useable biofuel. This is much higher than the current market price, and the plant is only viable due to the production of high value co-products, such as Omega 3 and PUFAs. A precursor to seambiotic produced beta carotine capsules which were sold door to door in Japan at a retail price of $4000/kg [23]. Until the cost of production isn't reduced dramatically, sole production of biofuel is not considered a viable option for such a facility.

Potential problems

Despite the prevailing excitement and investment in algal biofuels, a great deal of challenges to the establishment of a feasible and practical system have arisen over the years. There are also a whole new set of problems, which would arise, when considering Ireland as a location for the development of such fuel sources. The main issues are summarised in the following section.

Environmental

Although Ireland would not be the most obvious choice as a location for the development of an algal culture and biofuels processing venture, it is worth analysing the advantages and disadvantages a bit further.

The most obvious disadvantage that Ireland has, regarding the culture of any organism, is the reduced levels of sunlight that penetrate our cloud covered skies. The average value of solar radiation in Ireland, for example was 2.5-3kWh/m² per day [24]. When compared to Hawaii, a location in which alot of research is carried out into algal cultivation, the value there is 6kWh/m² per day [25]. In other words, Ireland receives less than half the solar radiation of a more obvious algal culture location.

Despite this, photosynthesis is not a perfect process, and it is estimated that, at most, only 6% of the available solar radiation is in fact utilised in the photosynthetic process by algae [26]. As irradiance rises, the rate of photosynthesis increases, but saturation occurs at the point in which the rate of photon absorption exceeds the rate of electron transport from the H₂O molecules to the CO₂. The point at which the absorption rate equals the transport rate is called the saturating irradiance, E_k,and for algae is typically 10% of the full irradiance [27]. Any further light absorbtion is released as either heat or luminescence from the algae and is wasted. One common occurrence when higher solar radiation is present is a process called photoinhibition. This is where the greater light levels interfere with the photosynthetic process and can even lead to damage of the chloroplast machinery. This means that algae cultures need to be adequately protected in areas of greater solar irradiance, in order to prevent a drop in yields due to excessive light levels. In the case of microalgae, this may be achieved by varying the levels of mechanical mixing applied to the culture medium, the effects of which can be evaluated on a trial and error basis, in order to perfect the culture system in the long term. For seaweeds, the depth at which the longlines are immersed can be varied, in order to filter the amount of light reaching the plants. Trial and error would also be the best method of evaluation in this case. Different strains of algae are also affected in different ways, and it would be expected that varieties suited to conditions in Hawaii may not be the best option for Ireland. The possibility of equivalent yields in areas of high and low irradiance cannot be ruled out, unless trials to this effect are carried out, but should nevertheless be considered when designing and constructing a culture facility.

Despite the expected lower values for growth in the higher latitudes, the concentration of chlorophyll a has been mapped since the early 1970s via satellite, and has uncovered some interesting trends. It can be assumed that the abundance of chlorophyll (seen as a green colour in satellite images) is a useful indicator of the amount of photosynthetic activity in any particular location. As can be seen below, the greater concentrations of chlorophyll appear to be along coastlines in the north Atlantic, and of particular interest in this report, significant levels exist around the island of Ireland.

Fig 8 chlorophyll concentrations spread over the Fall to Spring season in 1978-79 in the Atlantic Ocean [28]

The reason for this unexpected distribution could be the availability of nutrients, but may also be due to the levels of light exposure. It may be surmised that the algae have the ability to adapt their levels of chlorophyll to suit the climate in which they are growing. This could indicate that the latitude, and therefore levels of solar radiation might not be as critical as expected to the yield of algae per square metre.

The temperature of Irish waters is also significantly lower than the lower latitude sites commonly evaluated. This could have a significant effect on the growth rates of the algae, but strain selection can also determine the best suited algae to the Irish climate.

Cost of Production

Perhaps the greatest hindrance to any development of an algal biofuel market, both in Ireland and globally is the cost of production. As of December 2011, the Irish market price of petrol and diesel, the primary transport fuels, lie at approximately 147.9c and 148.9c per litre respectively (including tax), and on the world markets, a barrel of oil lies at approximately $100. In order to make economic sense, the cost of production of biofuels should not exceed this price. This is a major stumbling block for all biofuel production, as the cost of production is currently significantly higher. There are no commercial production facilities in operation for algal biofuels to date, although a huge amount of research is going into the area. One estimate, in 2007, which evaluated the viability of photobioreactor cultivation of microalgae concluded that the price of a barrel of oil would have to exceed $800 for algal biofuel to become feasible [29]. Although technology has advanced significantly since then, the question still arises as to the cost effectiveness of any operation. The key to the production of a fuel capable of competing with petroleum derivatives is the scale of operations, and the co-production of other higher value compounds, such as nutritional supplements and substances which can be used by the cosmetics industry. Any biorefinery should also be designed carefully to maximise the efficiency of extraction.

Although current oil prices may not justify the production cost of algal biofuels, there will be an inevitable rise in the price, as demand outweighs supply, and eventually an alternative to petroleum will have to be sourced. Land crop based biofuels will only be able to supply a small portion of the expected demand in future, and therefore with sufficient technological advances, the price of production may well be justifiable in the not so distant future.

Recent Technological advancements

Solazyme

Based in California in the United States, Solazyme entered the market as a biofuel producer in 2003. Initially, all efforts were focused on production of microalgae, using both pond raceways and photobioreactors. It soon became clear, however that yields from either system wouldn't be a cost effective method of producing biofuels. Instead, Solazyme have developed a process which uses non photosynthesising microalgae, which digest sugars in large tanks to produce ethanol. They also produce a wide variety of health and nutritional products, which help to supplement the cost of fuel production. They have recently won a contract with the US navy to supply 450,000 gallons (1.7 million litres) of biofuel for use in both jets and maritime vessels. The estimated price paid was $7 per gallon, which is more than twice the current market price for gasoline in the U.S. Initial trials employed ethanol as a jet fuel, and there is an ongoing trial, which will use bioethanol in a supertanker, currently operating in the Pacific [30]. Solazyme have shown that there is more than one way to effectively use microalgae to produce biofuels, and have attracted sufficient funding to allow further development of their systems.

Joule Unlimited

Based in Cambridge, Massachusetts, in the United States, Joule have developed a genetically modified cyanobacteria (a microalgae, which is more closely related to bacteria), which after an initial growth period, switches its photosynthesis machinery to the production and secretion of a diesel like fuel directly into the water. This fuel then rises to the surface where it can be separated quite easily from water and sent for processing to a refinery. One of the advantages of this system is that the bacteria themselves do not need to be harvested and broken down to extract fuel [31]. Although their claims have yet to be verified independently, Joule claim that they will be able to produce oil at a price of $30 per barrel, using their new technology. They are currently building a test facility in New Mexico, which will cover an area of 850 acres and has been estimated to be able to produce 15,000 gallons (57,000 litres) per acre per year. As may be appreciated, this is a "game changing" technology, and if their claims are true, could revolutionise the biofuels market. Such claims have been made in the past, however, and any company which has did not last long after their claims were discredited. One famous example was a company called Greenfuel Technology, which attracted a huge amount of investment since its foundation in 2001. It subsequently upscaled its operations after successful pilot schemes, but went out of business in 2009, due to a shortfall in funding for the construction of its new flagship plant in Arizona. The cost of extracting fuel from the algae ended up being twice that estimated by the company [32].

Conclusions

Case study

References:

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30.Solazyme, Dynamic Fuels score big US Navy aviation fuel contracts, Lane, J., Biofuels Digest 2011

31. Joule Unlimited company profile, Technologyreview.com, 2011, http://www.technologyreview.com/tr50/jouleunlimited/

32. As Algae Bloom Fades, Photosynthesis Hopes Still Shine, Voosen, P., Greenwire 2011.

http://www.nytimes.com/gwire/2011/03/29/29greenwire-as-algae-bloom-fades-photosynthesis-hopes-stil-54180.html?pagewanted=all