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The next “black gold” could be green

In a few days, a glass of nutrient-rich water from a pond will turn a vibrant green. The green color is caused by microalgae, which are microscopic single-celled organisms that float freely in water. These organisms multiply rapidly when given sunlight, carbon dioxide, and water that is rich in organic waste or fertilizer washed from fields. Algae don’t store their energy in starch, as plants do, but are instead full of vegetable oil – making them the equivalent of “green gold.”

In recent decades, there have been several cycles of interest to be able to exploit these organisms. Researchers have studied the use of alga for removing nutrient-rich wastewater from coastal seas or industrial chimneys. They also examined its potential to absorb carbon dioxide directly from the air or industrial chimneys. Why has microalgae been used in this way, given its undeniable virtues?

The concept of this idea is simple, but its execution is not. According to some media reports, you might expect algae farms to spring up all over the place. Microalgae is still not being cultivated at a large scale despite the billions invested by government, industry, and venture capital funds. In a 2010 article published in the Royal Society Interface Journal, I and some colleagues examined the technical hurdles that are associated with microalgae-based biofuel production.

To convert microalgae oils into biodiesel, the first step is to separate them from the water. The amount of algae in water is around 0.1%. Therefore, 1 kg microalgae can be produced from a tonne of water (1m 3). Evidently, that means 999Kg must be removed. This is a difficult operation, as it takes a lot of time to process enough algae. It is difficult to separate the algae by centrifuge or conventional filtration because they are so small and have the same density as water. The chemical method of flocculation uses highly charged metals or polymers to attract algae together and sink. This method is effective, but it adds complexity and expense.

The 1 kg weight is wet, but microalgae contain 30-40% oil by dry weight. Dry, 1 kg microalgae could weigh 100g and yield 30-40g oil. Oils can be extracted by pressing or solvents and then converted into biodiesel. The chemistry involved in this process means that not all of the oil can converted. This further reduces the yield.

A tubular photobioreactor in which algae can grow and be harvested almost continuously. Varicon Aqua Solutions Ltd

The genetic modification of algae can be used to improve different characteristics such as the ease of harvesting, the cell wall rupture, or oil yield. The impact of accidentally releasing GM algae into the wild is something that needs to be carefully considered.

Microalgae have the advantage of being able to be grown on marginal coastal land, which isn’t used for food crops. They can also use seawater instead of fresh water. It also reduces the ethical criticisms of biofuels that they negatively affect food production. Building fascia panel has been used to grow microalgae grown on wastewater and carbon dioxide emissions.

Processing is still a challenge. However, advances in microfiltration methods and physical flocculation have made significant improvements. There have been other methods of converting microalgae oil to biodiesel. Hydrothermal liquefication, whereby wet, entire microalgae is heated under pressure, and Pyrolysis, whereby whole microalgae are heated quickly in an oxygen-free atmosphere, are two methods that don’t require the oil to be removed before conversion to biodiesel.

The initial stages of the development of microalgae-based fuels were marked by intense hype. The hype has now passed, and the challenges have been well-understood. The future of biodiesel production requires significant improvements in economics. Microalgae can be integrated into carbon dioxide reduction and wastewater treatment programs. The fuel produced is an added benefit. A model that creates a high-value product, such as health supplements with biofuel oil as a secondary revenue source, may be more successful.

While large-scale cultivation remains possible, finding low-cost methods to remove the water is still a challenge. Microalgae will make a huge leap forward if they can match algae with high cell density and rapid growth with water removal methods that are low-cost. As always, the technology is only part of the problem. A societal, legislative, and political framework must also be in place.

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Jane S. King

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