Due to the increasing climate change concerns, biofuels have attracted more attention in the energy field as potential alternative energy sources. Particularly, microalgal biofuel has stood out because of its higher fuel yield potential and lower water and land demand than terrestrial biomass. Because of its outstanding photosynthetic efficiency, the microalgal technology is also investigated by researchers around the world as a potential biological solution for carbon capturing in the industrial sector. To explore the prospects of microalgal technology in a local context, this research lays it focus on investigating the potentiality of microalgal biofuel in the cement industry on Gotland, which is the largest emitter of greenhouse gases on the island. For this purpose, the thesis implements a series of estimations based on the emission data of Cementa AB, Slite, a picture of the potential production of algal biomass and biofuel was created, followed by comparisons to the energy situation on Gotland.
While practical data of the selected microalgae species are presented, the results indicate a high potential of microalgae in the production of algal biofuel and the possibility for algal biofuel to power the industrial sector of Gotland, or even the island entirely. Although the estimations are made based on an assumption where all controlling parameters are assumed to be perfectly manipulated, the results still indicate the significance of microalgal technologies in the near-future bioeconomy and global energy system.
This thesis becomes a reality with the kind support and help of many individuals in my life. I would like to extend my sincere thanks to all of them.
First of all, I would like to thank my program director, course lecturers and friends for making my time at Uppsala University Campus Gotland an exceptional and unforgettable experience in the past three years.
Thanks also go to my supervisor, Dr. Simon Davidsson Kurland, for imparting his knowledge and expertise in this study, without whom, this project could not have been possible. And my thesis group peers, for providing guidance and support throughout the course of this research.
Personally, I would like to thank my parents for their constant source of encouragement and understanding, and their accompany through every step of this incredible journey.
Last but not least, thanks go to Johnny the cat, for accompanying me through the most frustrating times and filling my life with happiness and goofiness.
CO2 Carbon Dioxide
CCS Carbon Capture and Storage
GHG Green House Gas
HCI Hydrochloric Acid
LCA Life Cycle Assessment
NOx Nitrogen Oxide
SOx Sulfur Oxide
Climate change has remained a heatedly debated subject for decades. Scientists’ warnings on climate change has now been proved farsighted and the current warming trend is of particular significance. The discussion on global warming can be dated back to 1988, when James Hansen, the climate scientist of the National Aeronautics and Space Administration with three other senior researchers suggested that the accumulation of carbon dioxide and other greenhouse gases produced from human activities was causing the warming trend in Earth’s temperature (Butler, 2018). The heat-trapping nature of carbon dioxide and other greenhouse gases is affecting the transfer of infrared energy through the atmosphere and causing global warming (NASA, 2021). The threats from climate change are not a bitter pill only for human society to swallow, the ecosystems are also under huge pressure. The role of fossil fuels is undeniably significant in the phenomenon of global warming: human societies have been heavily relying on the burning of fossil fuels over the past century. Even today, fossil fuels including oil, coal, and gas still contribute to 84 percent of the world’s energy needs (BP, 2020).
The enormous toll on the environment and humanity urges all governments and individuals to seek more sustainable alternatives and approaches to mitigate and adapt to global warming. As one of the renewable fuel alternatives, biofuel is considered an environmentally friendly benign alternative to fossil fuels(Rodionova et al, 2017). The development of biofuel is mainly driven by the depletion of fossil fuels and the mitigation of climate change. Being a green substitute to petroleum resources, the production of biofuel aims to generate energy fuel through biological processes or derive from biomass to ensure energy security and minimize the impact on the environment (Rodionova et al, 2017). Biomass products are famous for their ability to create energy dense, liquid-storage fuels that are compatible with petroleum-based energy infrastructure (Sayre, 2010). This type of energy source is expected to contribute to the welfare and sustainability of the energy system through its environmental, economic, and energy security effects (Lundgren and Marklund, 2013).
However, recent research has raised doubts about the carbon neutrality of traditional biofuel. Criticism towards biofuels mainly lies in the production of first and second generation biofuel, where fuels are derived from food-grade agricultural products and other non-food biomass like wood, plant, and animal material (Itskos et al, 2016). The debate around greenhouse gas emission (GHG) from biofuel intensifies as the agricultural areas continue to expand to boost biofuel production. Meanwhile, given that water is consumed at all stages throughout biofuel production, the large consumption of water for irrigation and cooling becomes a threat to the ecological environment and local communities (Bergtokl et al, 2017). The limitations from available arable land, the demand for food and water quality lead to the development of third and fourth generation biofuel, known as the algal biofuel.
As an attempt to promote the development of biofuel and minimize its environmental impact, algae was introduced as an alternative feedstock for biofuel generation. The process of photosynthesis has been proven to be one of the most important links in the global carbon cycle. Meanwhile, the nature of microalgae made it a unique and fastest growing photosynthetic organism, which distinguishes it from other energy feedstock (Chisti, 2007). Statistically, microalgae species (58,700 to 136,900 L/ha) have shown much higher production of oil per yield if compared to terrestrial energy feedstock like corn (172 L/ha), soybean (446 L/ha), and canola (1190 L/ha). Thanks to its outstanding photosynthetic efficiency, microalgae species have much higher efficiency in the conversion of water, light and CO! into biomass and oxygen (Chisti, 2007).
According to researcher Rodionova et al (2017), algae contains approximately 50 percent of lipids for the production of biodiesel, and the remaining components like sugar and proteins can be used for bioethanol production. Besides its ability to produce several bio-oils, the advantages of microalgae-based biofuel can be seen in its greater production yields, available land area, and its ability to capture CO! through its biofixation process. In comparison to land plants, algae have higher photosynthetic efficiency, and up to 50 percent of algae’s weight is composed of oil (Sayre, 2010). A variety of industrial sources CO! are utilized in the cultivation of microalgae, including industrial wastewater and flue gas. Additionally, the injection of industrial flue gases into algae ponds are proven to be effective in elevating algal biomass yields (Sayre, 2010).
Meanwhile, the potentiality of microalgae biofuel has become a popular research topic in the academic world. Researches on microalgae biofuel commonly focus on technological outbreaks and their outstanding lipid content. Researches Ghasemi et al (2011) point out the attractive characteristics of microalgae biofuel: algal biodiesel has been proven to be
a non-toxic and sulfur-free energy source, which is highly biodegradable and has way less environmental impact than conventional fuels (Ghasemi et al, 2011).
The application of microalgae technology and its feasibility have been investigated by many researchers. Medeiros et al (2014) conducted research to get an insight into the application of the technology through previously done life cycle assessment (LCA) microalgae studies. The research compares microalgae biofuel with fossil fuel options and the integration of algae biofuel in a local electricity grid. The result shows the high efficiency of microalgae as an energy feedstock and its huge potential in reducing the dependence on fossil fuels (Medeiros et al, 2014). The carbon fixation ability of microalgae is another attractive topic in the field of biotechnology. The research done by Yahya et al (2020) is an example: the research looks into the use of native algal species for carbon fixation at coal-fired power plants. Eduardo et al (2019) also wrote a chapter in the literature “Biofuels from Algae”, dedicated to the use of microalgae as both energy feedstock and biological carbon capture solution.
In Öland Cementa, researchers Olofsson et al (2015) looked into the transformation of cement flue gas into valuable biomass in the cement factory, where industrial flue gas was used as CO! sources for microalgal cultivation. Olofsson et al (2015) examined the impact of cement flue gas toxicity on algal biomass production, the compositions such as lipids, proteins, and carbohydrates are examined to assess the feasibility of using cement flue gas in algal biomass production. The algae cultivated with cement flue gas was compared to the natural microalgal community and the results show that high quality and high production of microalgal biomass can be achieved with the integration of industrial flue gas. The research results concluded that microalgae cultivation is a feasible biological solution to convert industrial waste into renewable energy sources (Olofsson et al, 2015). The research is particularly referential for other Cementa power plants that hope to explore more alternatives in their sustainable development program.
To explore the potentiality of microalgae technology in a local context, an investigation is made in this research to examine the potential of microalgae biofuel as a climate mitigation strategy in the cement industry on Gotland.
As a pilot area for sustainable development, Gotland has a long record in successful local initiatives and coping with international climate goals. In 2019, the Swedish Energy Agency (Länsstyrelserna) published a Sankey diagram that shows the energy flow of Gotland. The result indicates that 62 percent of used energy came from the industrial sector on Gotland (Länsstyrelserna, 2017). This large consumer of energy is supplied primarily by non-renewable waste and fossil fuels, making it a huge challenge for Gotland to reach 100 percent renewable or even move further in its sustainable development. The Cement industry in Slite is the dominant contributor, 45 percent of its energy consumption came from fossil fuels in 2018 (Ahlvin et al, 2018). As the major contributor to Gotland’s energy consumption, Slite Cementa faces pressure from both local and national environmental policies. The industry is one of the biggest obstacles in the move towards a carbon-neutral energy system on Gotland.
The biological nature of microalgae makes it a win-win solution for Slite Cementa. While microalgae are produced in the power plant as a renewable energy source, the cement flue gas is decarbonized during microalgae cultivation. The potential of microalgae biofuel in Slite Cementa is investigated through several calculations. The research begins with simplified estimations to show the amount of algal biofuel that can be produced with the current carbon emission at the cement production site. The estimations further allow the exploration into the efficiency of different algal species and the heat production of the produced algal biofuel. The estimations are expected to start a discussion around the opportunities and challenges of the algal biofuel technology in a local energy system. With the purpose in mind, a research question is formed:
How much microalgal biofuel can be produced therotically with the carbon emission from Slite Cementa and what is its potential in the sustainable development of Slite Cementa?
The Swedish cement industry is dominated by Cementa AB, which owns three cement plants across Sweden. The cement industry in Sweden contributes to 19 percent of total industry emissions, posing a challenge for the decarbonisation of Swedish industries. Although energy efficiency strategies and fuel switching has contributed to a lower emission level in Sweden, the reduction of carbon emission per ton of cement remains concerningly high: the current CO! emission is around 722 to 701 kg CO! -eq/ton cement, while the historical cement emission is approximately 1 tonne CO! -eq/ton cement. The main reason for this improvement is the increased share of biofuels (21 percent) in the system as a more sustainable energy alternative (Klugman et al, 2019).
According to Cementa, approximately 60 percent of carbon emission comes from the calcining process during the cement production, while 40 percent of emissions are released during the combustion of fuels used to provide heating during the production process (Cementa, n.d). To cope with the global responsibility to keep the rise of worldwide temperature below 2 degree celsius, the Cementa group has set out objectives to reduce its CO! emission per tonne of cement by 30 percent compared with the 1990 level by the end of 2030 (HeidlbergCement, 2019).
The Heidelberg group has successfully achieved approximately 22 percent reduction of carbon emission across all its production site by the end of 2019, and the group continued to work on intensifying the use of alternative raw materials (HeidelbergCement, 2019). Specifically, Slite Cementa has adopted the carbon capture and storage (CCS) technology as an approach to separate carbon dioxide from flue gases to enable further storage and recycling (Cementa, n.d). Although algae cultivation has not been adopted in Slite Cementa, the technology has been investigated by the group in a demonstration project in the Safi cement plant in Morocco. The project investigates the possibility to use CO! from the cement kiln to cultivate microalgae and examine the efficiency of different algae species (HeidlbergCement, 2019).
Being an important sector for climate change mitigation, the cement industry contributes to 5% of global carbon dioxide emissions. The CO! emission in the cement industry is created in multiple processes, including the calcination of limestone, combustion of fuel, and power generation (Worrell et al, 2001). As an important part of the Cementa’s group, Cementa Slite serves as a strong cornerstone for sustainable community building in Sweden. Due to the requirement for high temperature during limestone burning, the production of cement has high energy demand and thus a large amount of combustion related CO! emission. The CO! emitted from the production is mainly concentrated in the cement flue gas, which requires additional emission and pollution control (HeidlbergCement, 2019).
Cement kilns typically compose of NOx, SOx, CO!, HCI, and dust. According to the World Business Council for Sustainable Development the range of emissions from European cement kilns contains 71-995 ppm NOx, 0-1,693 oom SOx, and 0.3-227 mg Nm-3 of dust (WBCSD, 2012). A higher concentration of water and carbon dioxide can be observed in cement flue gas, while a reduction of the levels of oxygen and HCI is shown. The carbon dioxide rate in flue gas varied based on the type of raw material, combustion process, cleaning techniques, and fuel in the industry. Typically, the burning of coal contributes to 10 to 15 percent of the carbon emission during the combustion process, while the use of natural gas takes a share of 5 to 6% (Naggapan et al, 2019)
The components of cement flue gas include carbon dioxide, nitrogen, and sulfur oxides, which can be used as nutrients for microalgae cultivation. Microalgae can also sequestrate heavy metals contained in cement kiln dust, which adds benefits to the pollution reduction of the cement industry. Thus, the inclusion of microalgae biofuel production in the cement industry has drawn more and more attention (Naggapan et al, 2019).
The initial studies about microalgae cultivation took place in the 40’s, where microalgae was investigated for its potential as a source of food. Researches Sydney et al (2019) suggested that the interest in the use of microalgae in wastewater treatment grew with the increase of awareness on climate change in the 60s and eventually moved its focus to renewable fuel production in the 70s. The popularity of microalgal biofuel grew with the increasing price of oils in the 00’s, attracting the attention of the industrial sector and its investors (Sydney et al, 2019).
Microalgae is a group that covers both prokaryotes and eukaryotes. While a cyanobacteria (blue-green algae) facilitates the process of photosynthesis through the photosynthetic membranes in its internal organization, the eukaryotic autotrophic microorganism rely on their light-harvesting photosynthetic pigments to generate energy for its growth (Sydney et al, 2019). The photosynthetic microorganisms convert carbon dioxide into organic compounds and release molecular oxygen with the help of solar energy.
The reaction shown above describes the photosynthesis process of microalgae: algae transform light, carbon dioxide and water into biomass and oxygen through the catabolic process and the storage of energy in organic form (Eloka-Eboka and Lnambao, 2017). In other words, the cultivation of microalgae achieves the decarbonisation of CO! in air and the production of energy feedstock at the same time.
Researcher Li et al (2013) in the literature of Bioresource Technology indicated the carbon content of microalgae is approximately 50 percent. This means that roughly 1.83 ton of CO! is needed to produce 1 ton of microalgae. The research result from Li et al (2013) is endorsed by Yahya et al (2020): as seen in equation 2, the balanced photosynthesis formula on the ratio between carbon dioxide moles and molecular formula of biomass indicates that approximately 1.8 gram of CO! can be fixed by every gram of microalgae produced.
While microalgae has been successfully used for fixation of atmospheric CO!, it is important to consider the difference of CO! concentration between atmospheric air (0.038 percent) and industrial flue gas (4-14 percent). The endurance of flue gas components varied between different microalgae species, therefore it should be considered while implementing a microalgal biofuel project. As seen in table 1, the species Chlorella sp shows that the CO! fixation performance and biomass productivity change with the temperature CO! concentration of NOx/SOx concentration (Zhang, 2015). The CO! fixation rate can be stabilized at 50 percent while the nutrient, temperature, light and CO! concentration are controlled in a reasonable manner. Thus, the average proportion of carbohydrates in microalgal biomass can be estimated as 55.5 percent as suggested by Yahya et al (2020) and Li et al (2013).
Table 1. Growth characteristics of Chlorella sp. Under different CO2 concentration, temperature and NOx/SOx contents. Adapted from (Zhang, 2015).
While carbon capture by microalgae has been considered an attractive mitigation strategy in the cement industry, researchers still remain doubtful about the influence of NOx and SOx components on microalgae. The research done by Lara-Gil et al (2014) investigates the toxicity of cement flue gas in microalgae CO! mitigation systems, and the growth of certain algae species in a controlled environment with tested concentration of NOx and SOx components. The typical flue gas conditions in modern cement plants contain high concentration of CO!, ranging from 14 to 33 percent v/v. The exhaust gas also contains significant amounts of nitrogen oxides (NOx), sulfur oxides (SOx) and dust. These components have been proven to have an impact on microalgae growth at different levels in the several researches (Kurano et al, 1995).
The toxicity of cement flue gas is further investigated in other microalgae biofuel projects, where the growth of microalgae is observed under the increase of NOx and SOx components. In the research by Yoshihara et al (1996), the elimination of nitric oxide and carbon dioxide was reported in the cultivation of marine microalgae, strain NOA-113. In a long tubular photobioreactor, about 40 mg of nitric oxide and 3.5 g of carbon dioxide were eliminated per day in a controlled reactor column. Researchers Yang et al (2004) demonstrated that high SO4 2− and HSO3 − concentration do not have a negative impact on the growth of Botryococcus. However, an opposite result was achieved by Lar-Gil et al, where the species D.abundans experienced a drastic decline in its growth under a high SO4 2− concentration (Lara-Gil, 2014). This result indicates that the NOx and SOx tolerance of microalgae largely depend on the species .
Based on a calculated demand for algal biofuel, the lipid content of microalgae species is investigated to select a suitable microalgae species for the algal biofuel production. Researchers Sun et al (2018) in the literature of Biotechnol Biofuels indicated the benefits of microalgae as a promising sustainable source of lipids and carotenoids. The lipid and carotenoids content of microalgae is determined not only by its species, but also the stress conditions such as nutrient limitation, exposure to physical factors and temperature. Sun et al suggests that the oil levels of 20 to 50 percent are common among the normal microalgae species, oil content by weight of dry algae can reached up to 80 percent by some outstanding species. In most cases, microalgae with high oil productivity are desired for the production of microalgae biofuel (Sun et al, 2018).
To determine the influence of microalgae species in the production of algae biofuel in Gotland’s context, the research result by Chisti (2007) in the literature Biotechnology Advances is adopted. As seen in table 2, six species are selected among the 14 species
that were investigated and compared in Chisti’s publication. The selected six species are some of the most common microalgae species used in algal biomass production (Chisti, 2007).
The open pond production system has been used for microalgae cultivation since the 1950s. Covering different sizes and shapes of open systems, both natural waters (lagoons, lakes, ponds) and artificial ponds or containers like tanks and circular ponds can be utilized in an open pond production system (figure 2). Compared to a closed system, open pond systems require smaller investment and less maintenance. However, the productivity of an open pond system is highly dependent on the location and weather. At the same time, temperature, natural competitors and predators can make a significant impact on the growth of microalgae (Zhang, 2015). In the context of Slite Cementa, surrounding natural waters are not available. Yet, there are possibilities to construct safer and cost efficient open systems like tanks and raceway ponds.
In comparison to an open pond system, a closed system allows higher biomass productivity because of a higher mass gas transfer rate. The design of photobioreactors (PBR) block the cultivation system from the outside environment by obstructing any direct exchange of gases and contaminants and turn the system into a greenhouse. The technology allows axenic algal cultivations of monocultures, better control over the controlling factors like water pH, temperature, light and CO! concentration and prevent water evaporation. The loss of gas is typically much lower in a closed system than in an open pond system. Yet, the high equipment and maintenance cost are unignorable drawbacks to be considered while using a closed system method (Zhang, 2015).
As explained in 3.1, microalgal technology uses solar energy to facilitate photosynthesis for its growth. The cultivation of microalgae can take place in both closed photobioreactor and open pond systems. Thus, the selection of the system can be made based on the geographical and financial situation of the industrial site. Typically, the system operator regulates the controlled nutrients, conditions (light, temperature) and the selection of species to achieve a desired CO! fixation performance and fuel production. As can be shown in figure 3, the cultivation stage of microalgae biofuel involves the insert of cement flue gas in the system as a nutrient source. The contribution of CO! in algal cultivation is significant, which takes approximately 60 percent of nutrient cost.
The cultivation stage further involves the growth of microalgae, where nutrients, light intensity, water condition and temperature will be scientifically manipulated to favor outputs. Maximization and optimization of strategies like thermochemical processes can be employed to improve performance. The harvesting stage requires extra attention in reducing the water content of algae suspension. This step involves the separation of microalgae from bulk suspension (bulk harvesting) and the concentration of slurry through centrifugation, filtration and ultrasonic aggregation. The thickening step typically has a higher energy consumption than the bulk harvesting (Zhang, 2015)). The
drying step is grouped into the cultivation stage by Culaba et al (2020), where the drying process is considered the last preparation stage before further processing. This definition is not endorsed by Zhang, he describes drying as the most costly processing stage, which can constitute 70 to 75 percent of the processing cost. Zhang suggests that drying
methods such as drum drying, spray drying, solar drying can be considered based on the condition of the production site. (Zhang, 2015).
The drying process typically involves the conversion of dry algal biomass into powder or a compressed form. As explained in 3.3, approximately 20 to 50 percent of the dry algal biomass can be converted into liquid depending on the lipid content of microalgae species. While the solvent extraction is typically used for extracting oil from dry microalgae biomass, the supercritical fluid extraction can be used to process wet paste microalgae biomass (Zhang, 2015).
In the processing stage, the oil extraction step leads to the production of different types of sustainable energy carriers, including biodiesel, bioethanol, biogas (methane) and biohydrogen (Zhang, 2015). At the same time, the surplus unextracted product can be used as fertilizer or animal feed for agricultural activities, which can make extra profits for the cement company. The production of biodiesel is specifically investigated in this research as a renewable alternative to the fossil fuels used in the energy system of Slite Cementa.
Based on the scope and aim illustrated in 1.4, methodologies are selected to create a feasible research design with the highest accuracy possible. The research design consists of a series of calculations that are made based on research results and formulas sourced in various publication regarding microalgae cultivation and microalgal biofuel. In Section 3.1, the chemical reaction occurred in the biological process of microalgae cultivation lays out the theoritical fundation for this research: the amount of algal biofuel that can be produced can be estimated based on the current carbon emission from fuel combustion at Slite Cementa. The results were expected to help start a discussion around the selection of microalgae species and the heat production with algal biofuel in chapter 6.
The emission data from Slite Cementa plays an important role in the research, which again highlights the need for decarbonsiation in the cement industry. The carbon emission of Cementa AB, Slitefabriken in 2020 is published through Naturvårdsverket, showing the emission from the production of cement, clinker or lime. Following the environmental management system ISO 14001, the data is provided under the supervision of the county Administrative Board of Gotland County (Naturvårdsverket, 2020). As seen in figure 4, the total CO! emission and the emission from the burning of fossil fuel and biomass at Cementa AB, Slite in 2020 are provided. Due to the lack of information regarding the share of cement flue gas in the total emission, the carbon emission to air from fossil fuel combustion is used in the thesis as the estimated amount of CO! in cement flue gas at Cementa AB, Slite in 2020.
As indicated in 2.7, the open pond system has been a popular and cost efficient method in microalgae cultivation, while photobioreactors are experiencing lower popularity due to its high investment cost. The context-based comparison between the open pond and closed pond methods seems to be understudied in the academic world. Researchers tend to focus on the differences theoretically, rather than on a particular location or site. Therefore, this research adviced from several researches that use the open pond method to avoid too idealistic and unfeasible results that require high investment in tehcnological innovation. Considering the nature of this research, the contribution from the ongoing CCS project is excluded from the estimation to allow investigation into the maximum potentiality of microalgae biofuel technology. The environmental impact of microalage technology is not investigated in this research, yet the discussion around the environmental concern and possible solutions for the integration of microalgae technology is included in Section 6.3.
Previously mentioned in 3.3, approximately 1.8 gram of carbon dioxide is consumed to produce 1 gram of microalgal biomass (dry weight) (Li et al, 2004). With this in mind, a simplified equation is formed:
The Biomass from the given equation above refers to the dry weight of algal biomass that can be produced with the given amount of carbon dioxide. WCO2 refers to the amount of CO2 used as the carbon source of algae cultivation. In the context of Slite Cementa, WCO2 is the amount of carbon emission to air through fossil fuel combustion.
The production of algal biofuel through the cultivated dry algal biomass is calculated based on the lipid content illustrated in table 1. Based on the range of lipid content of different species from figure 1, a simplified equation is generated:
The equation 4 calculates the amount of biofuel (Wbiofuel) that can be produced with the given amount of biomass (kg). L refers to the lipid content of a microalgae species, which can be found in figure 1 in 3.3. The result further allows the comparison of microalgae species and the discussion around the relevant controlling factors that contribute to the efficiency of biofuel production.
While the energy content of biodiesel can vary depending on its energy feedstock, the average calorific value of biodiesel is estimated as 37.27 MJ/kg (Matthews and Mortimer, 2003). Using the equation shown below, the energy value of the produced biofuel was calculated:
The energy production was calculated to show the amount of energy can be produced with the selected microalgae species cultivated in Slite Cementa. The results enable discussion around the potential in reducing the share of fossil fuels at Slite Cementa and the possibility to influence the sustainable development of Gotland. The comparsion with the energy demand of Slite Gotland and the energy consumption on Gotland are made based on the Sankey diagram published by Länsstyrelserna in 2017.
This chapter presents the results of the calculations from Section 4. The estimations are adjusted into commonly used units to enable easier discussions and comparisons in the following chapter.
Calculated from the current carbon dioxide emission of Slite Cementa, table 1 from Section 3.1 shows that the carbon dioxide emission in Cementa Slite primarily comes from the combustion of fossil fuels. Result from eq 3 in Section 4.1 indicates that approximately 2,628,171 tonne of dried algal biomass can be produced at Slite cementa with its CO! emission to air from fossil fuel combustion.
As illustrated in 3.3, the biofuel production largely depends on the lipid content of microalgae species. The oil content of a species can be maximized if an ideal growing environment is provided, and further achieve an increase in biofuel production.
Figure 4 shows the estimtation of minimum and maximum biofuel production with the selected six species. Schizochytrium sp as the most efficient algal energy feedstock, has shown up to 77 percent of lipid content of its dried weight. This means that if the growing environment is controlled in an responsible way, 2024 kilotons of biofuel can be produced in Cementa (figure 5). The lipid content of Schizochytrium sp (50 to 77 percent) indicates a possibility of the species to be an exceptional energy feedstock. However, international researchers typically lay their focus on the potentiality of replacing fish oil with Schizochytrium sp in fish farming. Thus, further investigation is required if the species is applied in energy production.
Botryococcus braunii appears to have the second highest lipid content, reaching up to 75 percent of oil content. The species has been previsouly investigated as an energy feedstock to produce transport fuels (Hillen et al, 2004). While showing the possibility of producing 1971 kilotons of biofuel for Slite Cementa, the species also show high vulnerability to a poorly controlled environment: the oil content of botryococcus braunii can drop to 25 percent under undesired growing conditions.
Nannochloropsis sp as the third most efficient microalgae species in figure 2, show relatively higher stability than botryococcus. The lowest lipid content in the species is 35 percent, which allows a minimum of 815 kilotons of biofuel produced in Slite Cementa.
Neochloris oleoabundans as the fourth most efficient species in the selection of six, shows a lipid content of 35 to 54 percent. This means that the species is less vulnerable to changing conditions compared to other selected microalgae species. Approximately 920 to 1419 kilotons of algal biofuel can be produced with Neochloris oleoabundans under different controlled environments.
Chlorella sp and Dunaliella primolecta have the lowest lipid content compared to the others, providing the opportunity of producing 604 to 841 kilotons of biofuel. Chlorella sp has shown to be the least vulnerable species to changing conditions among the list: only small changes of lipid content is observed compared to other listed species. Meanwhile, information about the changes in the lipid content of Dunaliella primolecta remains understudied.
The energy outcome estimations from section 4.2 were made under the assumption where only one species was adopted at once from the selection of six microalgae species (Section 3.3), in other word, the mixing of microalgae species in a project is not considered. The results in figure 5 presents the potential energy outcome in the scenario where the biofuel is not mixed with other types of non-renewable fuels and be controlled under an environment where the relevant parameters (eg. light, temperature and gas concentration) were controlled reasonably.
As figure 6 shows, the energy potential of microalgal biofuel in Slite Cementa ranges from 6253 to 20954 GWh depends on the weight of biodiesel produced. Dunaliella primolecta provides the lowest biodiesel production (604 kilotons), indicating an energy outcome of 6253 GWh. Meanwhile, Schizochytrium sp gives the highest energy outcome under outstanding growign environment (20954 GWh).
The following analysis considers the feasibility of microalgae technology at Cementa AB, Slite, and the impacts of the technology on the sustainable development of the company. The analysis discusses the efficiency of microalgae as a bio-fixation tool and its potential as clean energy supply to the company and Gotland’s energy system. Although desirable results were obtained in the estimations above (Section 5.1 and 5.2), parameters such as the control of nutrients, growing environment, production methods and financial situation can affect the final results of a microalgae project. Thus, an analysis is made in this section to underline the major challenges to be considered if to integrate microalgae technology in Slite Cementa.
The fast-growing characteristic and carbon capture ability of microalgae species provide a sustainable mitigation method for the removal of CO! at energy intensive industry like the Cementa factory at Slite. Table 3 in Section 4 shows that CO! emission at Cementa AB, Slite is primarily released through cement flue gas to air, proving its suitability in providing CO!-rich waste gas for microalgal cultivation. As mentioned in Section 3.2, the components of average cement flue gas are satisfactory for the growth of most microalgae species and have no stress effect on the productivity of microalgal communities. This is endorsed by the results reported in figure 2 and 3: the lowest lipid content indicates the productivity of microalgal cultivation in non-ideal growing environment and the lowest expected fuel production shows a desirable energy outcome in Table 4.
As previously discussed in Section 3.1, the growth of microalgae communities is highly dependent on the conditioning of the raw cement flue gas and the input of solar energy. Being the sunniest place across Sweden, Gotland provides an advantageous growing environment with approximately 1900 sunshine hours per year (WACI, 2021). This indicates a possibility for open pond methods, where the solar energy can be directly input into the container.
As another important limiting factor for microalgae cultivation, temperature control plays an important role in stimulating the photosynthetic ability of microalgae species. The IEA report by Zhang indicates an optimum temperature value of 15 to 26℃ for most common microalgae species, while most species can easily tolerance 15℃ lower than its optimal growing temperature (Zhang, 2015). Considering the high temperature of the conditioned cement flue gas (150 to 200 ℃), cooling methods are required to prepare the cement flue gas for microalgae cultivation (Olofsson, 2015). In the context of Cementa AB, Slite, it is important to consider the seasonal weather changes and provide countermeasures for extreme weather.
Olofsson suggests that locally adapted species can have relatively higher performance in outdoor biomass cultivation, due to its ability to cope with the local environmental conditions. Depends on the seasonal adaptability of different algae species, it is possible to integrate more than one microalgal species in the system to maximize the annual biomass production (Olofsson et al, 2015). Previous studies have shown the success in using multispecies to recreate an optimal growing environment in outdoor mass cultivation of microalgae. The diversity of microalgal species have been proven to have complementary effect to the productivity of algae species. In other words, a highly productive monoclonal culture can be created to recreate a seasonal algal bloom in controlled environment. The diverse microalgae communities can create a more stable and resilient production system and decrease its vulnerability to changing factors like weather and other controlling parameters (Olofsson et al, 2015). Additionally, the geographical location of Gotland provides easy access to the Baltic Sea, giving the opportunity to investigate the monoclonal culture in local environment.
As demonstrated in figure 1, the lipid content of microalgae species varied, and it is heavily influenced by the growing conditions. While the results have shown high productivity of biofuel with the selected microalgae species, the application of specific algae species should consider although Schizochytrium sp has shown to be the most productive species among all, its application in fuel production is understudied. On the other hand, Botryococcus braunii has the history of being investigated as an alternative feedstock to produce transport fuel, which makes it more reliable than the other poorly studied species in the energy field (Watanabe et al, 2014). However, considering the complexity of controlling parameters, the achieved estimation cannot be considered as a proxy for the final biomass production. As a result, the selection of algae species for algal biomass production at Cementa AB, Slite should be made based on the activity of algae species in surrounding marine environment and the weather dependency of specific species. More importantly, the avoidance of invaded species should be taken into consideration to avoid damage to the local environment.
Microalgae has been studied as an alternative feedstock for bioenergy production and its ability of producing multiple fuel types has been proven. Figure 7 gives a summary of the energy supply and consumption on Gotland: in 2019, according to the County Adminsitration Boards of Sweden (Länsstyrelserna), the energy consumption on Gotland was approximately 4114 GWh in 2017, and the industrial sector had contributed to 62 percent of the energy consumption (2546 GWh). Taking a closer look into the current supply of biofuels on Gotland, the supplied solid biofuel, bio-oils and biofuels contributed to 448 GWh in 2017, while non-renewable oil took a larger share (607 GWh) (Länsstyrelserna, 2017). This means that the results from Section 5.2 indicates a high potential of microalgal biofuel: if the efficiency in growing environment and processing technologies have been maximized, microalgae biofuel can produce up to 6253 to 20954 GWh (figure 8), making enormous contribution to the decarbonization of Gotland’s energy system. By boosting the share of renewable fuel in Gotland’s energy system, the integration of microalgae biofuel can help phase out non-renewable fuels on Gotland.
While the result seems to be outstanding and game-changing, it is also overly optimistic: the estimations were made based on a flawless hypothesis where the growing environment is assumed to be optimal for every selected species. The changes in weather can require pauses in algal cultivation and modification of the cultivation environment during certain seasons. As the efficiency of the transfer of cement flue gas remains unknown, the energy and nutrient loss was unable to be included. Meanwhile, the dependency of biomass productivity on harvesting, drying and extraction technologies should also be taken into account.
As mentioned in 3.5, multiple fuel types can be produced with microalgal biomass via thermochemical and biochemical conversions like direct combustion and gasification (Zhang, 2015). This highlights the possibility to produce not only biodiesel, but also bio hydrogen, biogass, bioehanol, bio-char and jet fuel to better adapt to the energy demand of Cementa AB, energy system’s of Gotland. However, the compaitability of algal biomass in different sector should be further investigated.
While the CCS technology has the ability to prevent the release of large quantities of carbon dioxide to the atmosphere (HM Government, 2018), the biological nature of algal biofuel brings along with unavoidable GHG emission throughout the production process (Culuba et al, 2020). Considering the carbon emission alone, it is undeniable that carbon dioxide emitted throughout the cultivation of algae biomass and biofuel production will add on to the current emission of Cementa AB, Slite. Table 5 shows the main co-products produced in microalgae biomass production: both the biochemical conversion occurs in the fermentation process and biodiesel combustion make contribution to CO! emission. However, the emitted CO! can be collected and reused in microalgae cultivation as CO! feedstock for microalgae cultivation. The transestertification process typically produce co-products like glycerol and methanol, both co-products can be used in the production of commercialied products (Culuba et al, 2020).
Meanwhile, the consideration of ecosystem conservation should also be included during the integration of microalgae biofuel. While the algae species with higher lipid content will be likelier to be adopted in a microalgae project, it is important to remain critical about the impact of an imported species on the local ecosystems. Statistically speaking, the invasive alien phytoplankton species was recorded in the Baltic Sea, while over 51 phytoplankton species are indicated as alien species in European coastal waters. The introduction of marine alien species in aquatic ecosystems often cause a decline in ecological quality due to changes in physical, chemical and biological properties (Olenina et al, 2010).
The mass production of microalgae has been extensively exploited for its application in food production, aquaculture and biodiesel production. Research by Wen et al (2016) suggests that fossil fuel is still the dominent energy source on the global and its competitive price pose a challenge for renewable fuel alternatives like microalgal biofuel. The commercial feasibility of large-scale biofuel production remains questionable due to its low yield of storage lipid in outdoor microalgae mass cultivation. Statistics shows that the algal biomass cultivation in large-scale raceway reported a low solar-to-biomass conversion efficiency (3 percent) and an undesirable production rate (20 to 40 g dry weight per square meter a day). This is caused by the low concentration of carbon dioxide in the air and the inefficient transfer of solar energy through natural sunlight (Wen et al, 2016). Although further research has been implemented on the isolation, screening, genetic modification and outdoor cultivation of microalgae strain, the lipid productivity of algae in large-scale cultivation remain unstable (Wen et al, 2016). The complex nature of microalgae studies pose a challenge to local research, as the local environment, weather, carbon concentration and cultivation method all more or less affect the production result.
The complexitiy of microalgae project indicates a need for further and more context based investigation into the technology. Table 3 has divided the pre-study of a microalgae project into three main parts, the future project developers are encouraged to implement further invesigation on the suggested areas to enable more feasible project implementation. The consideration of Cementa AB, Slite as the targeted research site is included in the table.
The optimization of microalgae cultivation requires the inclusion of a wider range of parameters such as flow, gas transfer and cultivation culture. The optimization of harvesting, drying and extraction technologies can improve the production performance by reducing energy loss. It is also important to remember that the selection of algae species determines its photosynthesis efficiency and carbon capture ability. All in all, the interactions between algal species, controlling parameters and cultivation technologies can be complicated and highly context based, which requires time-consuming pre-study before actual implementation.
Microalgae has made itself an outstanding candidate for biofuel production because of its rapid growth rate and high lipid content. Due to its nature of being a biological solution, the microalgae technolgoy has shown to be more sustainable and environmental friendly in comparsion to current chemical or physical CO! removal processes. The microalage technolgy can be considered a win-win solution for an energy intensive company like Cementa AB: microalgae can also enable the production of commercially valuable products can provide new opportunities for the company to promote profitable by-product or sell the surplus biofuels. The combination of carbon capture approach, biomass production can also be combined with wastewater treatment on site, to further maximize the benefits of the technology and promote sustanable development at Cementa AB, Slite.
Theoretically, the microalgae technology has the ability to decarbonize cement flue gas through bio-fixation and convert the CO! emission to microalgal biomass. This result is reflected from the estimation on the energy outcome of algal biofuel can be produced from Cementa: approxiamtely 604 to 2024 kiloton of algal biofuel can be produced from the selected site, with the possbility of generating 6253 to 20954 GWh and decarbonize 1460095 tonnes of CO!. The estimations indicates a role of algal biofuel as a high potential biological solution and climate mitigation strategy. The technology has the ability to facilitate simontaneous decarbonisation process and clean energy production, making it an unique addition to the energy system. The integration of the algal technology can also promote the sustainable development of Gotland in the given aspects: algal cultivation benefits the agriculture sector by contributing to an efficient and low-carbon food production. The production of bio-energy can be expected to increase with the contribution from algal biomass, achieving an increase in the share of renewable energy in the system. Most importantly, the pressure from the cultivation of terrestrial biomass on the local ecosystems will be eased, and contribution to land and forest conservation will be made.
The result of this study is limited to the estimation of the scenarios proposed and investigated, and the results indicate a clear advantage of microalgae technology as a candidate for Carbon Capture and clean energy production at Cementa AB, Slite. Therefore, the technology can be viewed as a mitigation strategy or an addition to the existing sustainable development as a complementary component. It is highly recommended to make further investigation into the production environment and energy demand at Cementa AB, Slite.
Bergtold, J.S., Sant’Anna, A.C., Miller, N., Ramsey, S., Fewell, J.E., 2017. Chapter 2.2.1 – Water Scarcity and Conservation Along the Biofuel Supply Chain in the United States: From Farm to Refinery, in: Ziolkowska, J.R., Peterson, J.M. (Eds.), Competition for Water Resources. Elsevier, pp. 124–143. https://doi.org/10.1016/B978-0-12-803237- 4.00007-0
Bp Statistical Review of World Energy 2020, 2020. 68.
Butler, C.D., 2018. Climate Change, Health and Existential Risks to Civilization: A Comprehensive Review (1989–2013). Int J Environ Res Public Health 15. https://doi.org/10.3390/ijerph15102266
Cementa, n.d. Slite i världsklass för hållbart samhällsbyggande [WWW Document]. URL https://www.cementa.se/sv/slite-i-varldsklass-for-hallbart-samhallsbyggande (accessed 5.3.21).
Chisti, Y., 2007. Biodiesel from microalgae. Biotechnology Advances 25, 294–306. https://doi.org/10.1016/j.biotechadv.2007.02.001
Climate Change Evidence: How Do We Know? [WWW Document], n.d. . Climate Change: Vital Signs of the Planet. URL https://climate.nasa.gov/evidence (accessed 5.2.21). Culaba, A.B., Ubando, A.T., Ching, P.M.L., Chen, W.-H., Chang, J.-S., 2020. Biofuel from Microalgae: Sustainable Pathways. Sustainability 12, 8009.
Elamzon, J., n.d. Energistatistik – För 18 län med tillhörande kommuner för år 2017 40. Eloka-Eboka, A.C., Inambao, F.L., 2017. Effects of CO2 sequestration on lipid and biomass productivity in microalgal biomass production. Applied Energy 195, 1100–1111. https://doi.org/10.1016/j.apenergy.2017.03.071
Fibropol Fiberglass Aquaculture – Cam Takviyeli Plastik, FRP, Fiberglass, Polyester, GRP, Fiberglass Reinforced Plastics, n.d. URL https://fibropol.com/ (accessed 5.19.21). Ghasemi, Y., Rasoul-Amini, S., Naseri, A.T., Montazeri-Najafabady, N., Mobasher, M.A.,
Dabbagh, F., 2012. Microalgae biofuel potentials (Review). Appl Biochem Microbiol 48, 126–144. https://doi.org/10.1134/S0003683812020068
Heidelbergcment. 2019. Sustainability Report 2019. (accessed 5.19.21). Hillen, L.W., Pollard, G., Wake, L.V., White, N., 2004. Hydrocracking of the oils of Botryococcus braunii to transport fuels … [WWW Document]. archive.ph. URL DOI: 10.1002/bit.260240116 (accessed 5.18.21).
HM Government, n.d. The UK Carbon Capture Usage and Storage deployment pathway: an action plan 76.
Itskos, G., Nikolopoulos, N., Kourkoumpas, D.-S., Koutsianos, A., Violidakis, I., Drosatos, P., Grammelis, P., 2016. Chapter 6 – Energy and the Environment, in: Poulopoulos, S.G., Inglezakis, V.J. (Eds.), Environment and Development. Elsevier, Amsterdam, pp. 363– 452. https://doi.org/10.1016/B978-0-444-62733-9.00006-X
Klugman, S., Stripple, H., Lönnqvist, T., n.d. A climate neutral Swedish industry – An inventory of technologies 53.
Lara-Gil, J.A., Álvarez, M.M., Pacheco, A., 2014. Toxicity of flue gas components from cement plants in microalgae CO2 mitigation systems. J Appl Phycol 26, 357–368. https://doi.org/10.1007/s10811-013-0136-y
Li, S., Luo, S., Guo, R., 2013. Efficiency of CO2 fixation by microalgae in a closed raceway pond. Bioresource Technology 136, 267–272.
Lundgren, T., Marklund, P.-O., 2013. Economics of Biofuels: An Overview*, in: Shogren, J.F. (Ed.), Encyclopedia of Energy, Natural Resource, and Environmental Economics. Elsevier, Waltham, pp. 184–187. https://doi.org/10.1016/B978-0-12-375067-9.00096-6
Martin Ahlvin, Arriaga, Y., Baumann, E., Berglund, H., Magnusson, C., Wiklund, S., 2018. Energiomställning Gotland: Alternativ för att nå ett förnybart energisystem. Medeiros, D.L., Sales, E.A., Kiperstok, A., 2015. Energy production from microalgae biomass: carbon footprint and energy balance. Journal of Cleaner Production, Integrating Cleaner Production into Sustainability Strategies 96, 493–500.
Nagappan, S., Tsai, P.-C., Devendran, S., Alagarsamy, V., Ponnusamy, V.K., 2020. Enhancement of biofuel production by microalgae using cement flue gas as substrate. Environ Sci Pollut Res Int 27, 17571–17586. https://doi.org/10.1007/s11356-019-06425- y
Olenina, I., Wasmund, N., Hajdu, S., Jurgensone, I., Gromisz, S., Kownacka, J., Toming, K., Vaiciūtė, D., Olenin, S., 2010. Assessing impacts of invasive phytoplankton: The Baltic Sea case. Marine Pollution Bulletin 60, 1691–1700.
Olofsson, 2015. Baltic Sea microalgae transform cement flue gas into valuable biomass. Algal Research 11, 227–233. https://doi.org/10.1016/j.algal.2015.07.001 Rodionova, M.V., Poudyal, R.S., Tiwari, I., Voloshin, R.A., Zharmukhamedov, S.K., Nam, H.G., Zayadan, B.K., Bruce, B.D., Hou, H.J.M., Allakhverdiev, S.I., 2017. Biofuel production: Challenges and opportunities. International Journal of Hydrogen Energy 42, 8450–8461. https://doi.org/10.1016/j.ijhydene.2016.11.125
Sayre, R., 2010. Microalgae: The Potential for Carbon Capture. BioScience 60, 722–727. https://doi.org/10.1525/bio.2010.60.9.9
Sun, X.-M., Ren, L.-J., Zhao, Q.-Y., Ji, X.-J., Huang, H., 2018. Microalgae for the production of lipid and carotenoids: a review with focus on stress regulation and adaptation. Biotechnology for Biofuels 11, 272. https://doi.org/10.1186/s13068-018-1275-9
Sydney, E.B., Sydney, A.C.N., de Carvalho, J.C., Soccol, C.R., 2019. Chapter 4 – Potential carbon fixation of industrially important microalgae, in: Pandey, A., Chang, J.-S., Soccol, C.R., Lee, D.-J., Chisti, Y. (Eds.), Biofuels from Algae (Second Edition),
Biomass, Biofuels, Biochemicals. Elsevier, pp. 67–88. https://doi.org/10.1016/B978-0- 444-64192-2.00004-4
Utsläpp i siffror – Cementa AB, Slitefabriken [WWW Document], n.d. URL https://utslappisiffror.naturvardsverket.se/Sok/Anlaggningssida/?pid=834 (accessed 5.25.21).
WACI, n.d. Average monthly hours of sunshine in Visby (Gotland), Sweden [WWW Document]. World Weather & Climate Information. URL https://weather-and climate.com:80/average-monthly-hours-Sunshine,visby,Sweden (accessed 5.25.21).
Watanabe, H., Li, D., Nakagawa, Y., Tomishige, K., Kaya, K., Watanabe, M.M., 2014. Characterization of oil-extracted residue biomass of Botryococcus braunii as a biofuel feedstock and its pyrolytic behavior. Applied Energy 132, 475–484.
Yahya, L., Harun, R., Abdullah, L.C., 2020. Screening of native microalgae species for carbon fixation at the vicinity of Malaysian coal-fired power plant. Scientific Reports 10, 22355. https://doi.org/10.1038/s41598-020-79316-9
Yang, S., Wang, J., Cong, W., Cai, Z., Ouyang, F., 2004. Effects of bisulfite and sulfite on the microalga Botryococcus braunii. Enzyme and Microbial Technology 35, 46–50. https://doi.org/10.1016/j.enzmictec.2004.03.014
Zhang, X., n.d. Microalgae removal of CO2 from flue gas 95.