Microalgae, The Key To Replacing Fossil Fuels

Algae are an incredible species, and one that is severely underestimated a lot of the time. Because of the exceptional capabilities and properties these photosynthetic organisms possess, they are being looked into for usage in a variety of fields, one notably being biofuels. Algae, quite literally, have the potential to change the game of where we get our energy altogether. There are just a few barriers to get past first.

Introduction to Algal Biofuels

Down to the basics — what are biofuels, and what are algae?

Today’s Biofuels

When you hear the word biofuels, the segment bio likely makes you think of synonymous words, like green, eco friendly, and sustainable. Biofuels are the opposite and better alternative to fossil fuels — right?

The truth is, today’s biofuels don’t really fit this narrative. Biofuels are fuels extracted from biomass, and biomass is any plant or animal waste. These fuels are generally blended with petroleum fuels such as gasoline (however this can vary). The vast majority of biofuels are produced from agricultural crops, breaking off into two primary types: ethanol, the number one liquid biofuel usually made from fermenting corn and sugarcane, and biodiesel, made from the fruit of palm trees, canola, and soybeans.

While it may be true that biofuels generate less pollution and emissions than regular fossil fuels, there’s still a lot of environmental concerns, as well as those related to the economy. For one, there’s the land impact, seeing as removal of arable regions would take away from food production. Biofuels made from crops destroy forests and push people off their land, while directly skyrocketing the price of and diminishing food supply. Additionally, the excessive use of fertilizers will drastically increase nitrogen pollution, contributing to already growing problems like eutrophication.

Many critics argue that the way we are approaching biofuels isn’t helping our fossil fuel problem — in fact, it’s adding to it. This is where algae comes in.

Macroalgae vs Microalgae

There are two classifications for algae: macroalgae and microalgae. They have their similarities, such as being able to grow in both marine and freshwater habitats, but they also differ in many aspects.

Macroalgae, as their name may give away, are of a much larger size than microalgae. They can grow tens of meters, are easily visible to the human eye, and are often called seaweed. Macroalgae are multicellular and the three main groups within this classification include red algae (Rhodophyta, as shown in the image below), green algae (Chlorophyta), and brown algae (Phaeophyta). Thus, macroalgae can differ greatly since these subgroups are not very closely related, despite having some of the same physical attributes like their stem-like and root-like structures.

Microalgae, on the other hand, are much smaller photosynthetic organisms that are measured on the micrometer scale and can only be observed under a microscope. Often called phytoplankton, microalgae are unicellular and can be brown, orange, yellow, or even blue-green in colour. They can live in many areas from rivers to ponds to lakes to the sea, and sometimes form ‘colonies’ through cell grouping.

Microalgae branch off into diatoms and dinoflagellates. Diatoms are eukaryotic organisms that have cell walls made of transparent and opaline silica, which are almost glass-like. Diatoms are crucial to the aquatic food web, making up of 20% of carbon fixation worldwide. Dinoflagellates have a biflagellated structure, its cell wall being composed of cellulose. They behave like both plants and animals as they can produce their own food and also move themselves through water using flagella along their bodies. Certain species of dinoflagellates, Gonyaulax and Gymnodinium, are the cause of the red tide.

Why and How Microalgae Works

Why is microalgae a good option for biofuels and how are they actually converted into such substances?

Advantages of Microalgae For Biofuel

Microalgae and macroalgae can both be used for biofuels, but microalgae in particular serve many benefits. They can tolerate a huge range of conditions, including temperature, salinities, light, and pH, making them able to grow pretty much anywhere. They are also higher in productivity, have a higher energy density, and allow much more efficient usage of land. Microalgae can grow incredibly quickly, with the capacity to double in size in as little as three hours!

On top of this, microalgae are a rich source of carbon compounds, producing bioproducts like pigments, proteins, vitamins, antioxidants, lipids, and polysaccharides. They can play a role in mitigating CO2 emissions through sequestration. All of these advantages add up to high potential for biomass derived from microalgae.

Microalgae for Bioethanol

As mentioned previously, ethanol is the #1 liquid biofuel used today, namely for the transportation industry. As also mentioned, this is not good for the environment. Instead, some researchers are turning to bioethanol as an alternative. Bioethanol produces much less greenhouse gas emissions, and is the only biofuel that can be used in automobiles without the need for any modification. America and Brazil are world leaders in bioethanol production, mainly extracted from corn grain, sugar cane, and wheat, but again, this is unsustainable for many reasons.

Why is this significant? Well…guess what can also yield bioethanol? Microalgae (big surprise)! Their high algal sugar profiles are fantastic for this purpose. However, the carbohydrates in the biomass of algae are primarily in polymeric form and need conversion to monomers to be fermented by microorganisms so that they can produce bioethanol.

To understand what this really means, let’s understand the physical structure of microalgae on a bit of a deeper level. Lignocellulosic biomass is plant biomass containing polymers of cellulose, hemicellulose, and lignin. Going a little more technical and exploring what that really means in 3, 2, 1 ⬇️

Lignin is an important organic polymer found in the outer cell wall, serving biological functions like water transport. We want to reduce the accumulation of lignin in energy plants because it can reduce production efficiency of biofuels. Right in the lignin shell, there’s the cellulose. Cellulose comprises hydrogen, oxygen, and carbon atoms, and is the primary substance in plant cells, responsible for making it remain upright and found in the leaves, stem, and other fibrous parts. Cellulose is super important for biofuels and when used instead of grain can be very advantageous. Lastly, there’s the hemicellulose. Hemicellulose is found between cellulose and lignin and is made up of several polymers as opposed to glucose monomers like cellulose.

We need to separate the cellulose from the hemicellulose and lignin which is done in the pre-treatment stage, also sometimes called pre-hydrolysis. The hemicellulose is broken down into xylose and other sugars, and the lignin is burned as the energy exceeds processing requirements.

Next, hydrolysis of the cellulose takes place to obtain fermentable sugars, and the final step is fermentation. The process of fermentation, meaning the fermenting of the microorganisms, converts sugars to bioethanol. Fermentable sugars like glucose can be used as microorganism substrates, changing them into ethanol and CO2. The fermentation process used directly correlates to the quality and yield of the bioethanol. Reacting ethylene with steam through chemical processes can also be performed instead of fermentation but is less common. Once fermentation is complete, distillation to separate and purify the bioethanol occurs.

Barriers

For microalgae to become a plausible bioethanol feedstock, there are limitations we have to get past. Maximizing algal biomass and carbohydrate productivity while also reducing the costs is a must-have combination. The entire production process is currently quite expensive, as well as the culturing of the algae and harvesting. Economic feasibility is microalgae’s downfall as of right now.

Microalgal Cultivation

Open pond (raceway) and closed systems (photobioreactors) are the two major types of cultivation systems being used for microalgae production. How do they work and is one better than the other?

Open Pond Cultivation

Open pond systems are the simplest way to cultivate microalgae. They have a similar shape to racetracks, hence their alternative name being raceways. In this method, necessary nutrients and CO2 are pumped in a cycle outdoors, and algae get light from the sun. The problem is that due to the open ponds’ depth, there is reduced light supply and efficiency is limited. Moreover, large amounts of water with low concentration having to be processed consumes a lot of energy. Since raceways are open to the atmosphere, evaporation can occur, meaning there can be high losses of water, and microalgae are quite difficult to monitor. The price varies from area to area as those with a dense population may be more costly in terms of getting access to open land.

Besides race tracks, open pond microalgae cultivation systems can be circular ponds, unmixed open ponds, and thin layer inclined ponds. In general, because of the minimal equipment needed (a trench or shallow depth pond), this is much cheaper than closed system cultivation, discussed in more detail in the next section. Lower cost has allowed open ponds to be the most commonly used approach for growing microalgae, however certain species cannot be grown in this system because of their sensitivity to contamination. The designs of open systems are beginning to be modified, like high rate open ponds where complex geometries are taken advantage of to make it so that algae remain in the illuminated part of the loop.

Closed System Cultivation

Closed system cultivation systems are generally photobioreactors (PBRs), which are transparent tube-like containers. PBRs work with essentially every microalgae strand because of lower susceptibility to contamination. They are cheaper in terms of harvesting the algae, while also having higher productivity, reduced CO2 and water costs, and easier regulation.

Despite these factors, there are also some downsides. The upfront cost is more expensive than open pond systems, and on top of that there’s the issue with industrial scale performance. PBRs have to balance a thin layer of culture suspension, low energy, cost, ratio of the height column (which needs to be high), and optimized light, amongst other contributors. Light attenuation and increased CO2 both come into play when scaling and have to be considered because these limit productivity. PBR systems can cost up to 30 times more than open ponds and so if we want them to be widespread, a lot of work needs to be done.

Conclusion

All in all, microalgae is a pretty mind-blowing organism that could be the key to better biofuels in the future. Let’s do an overview of what we learned!

• Today’s biofuels are unsustainable because they take up vast amounts of land, energy, food sources, and water
• Algae can be used to create biofuels; algae can be microalgae, or macroalgae, where microalgae are unicellular and much smaller, and macroalgae are multicellular and much larger
• Microalgae are rich in compounds, can grow in a variety of climates and conditions, and can double in size in very short amounts of time
• Microalgae can yield bioethanol but to do this, pre-treatment, hydrolysis, and fermentation need to take place which can be expensive
• Microalgae can be cultivated in open ponds, which is much cheaper but low in efficiency for numerous reasons
• They can alternatively be cultivated in closed systems, which is more efficient but also more costly and faces issues on an industrial scale

Thank you so much for reading this! I’m a 15-year-old passionate about sustainability, and am the author of “Chronicles of Illusions: The Blue Wild”. If you want to see more of my work, connect with me on LinkedIn, Twitter, or subscribe to my monthly newsletter!