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Focus on Algae - Part II: Energy

In the last focus section, we discussed how algae can be used to treat waste waters and mitigate CO2 in the process. Today's post will explore how algae can be used for energy generation. As already mentioned in the last time, biofuels have become very visible as of late due to environmental, economical and geopolitcal reasons. If at the heart of traditional biofuel generation lies in the creation and decomposition of biomass, then it would be easy to substitute corn or other less controversial land-based plants with algae. Although a lot of attention is paid to the use of algae in biofuel generation, and this article also mainly focusses on this aspect, it should be noted that algae can also be used to generate electricity by direct combustion of the biomass. Plans for these kinds of schemes are already on the way in Venice and a few other European locations [1].

Algae and Biofuels

What happens to the biomass after it has been created depends on the type of biofuel that is desired.

Figure 1. Modes of Algal Biomass Conversion adapted from Bet Wang et. al. (2008).

Using biochemical techniques or microorganisms, the algal biomass can either be fermented or anaerobically digested. The first can yield ethanol, acetone and butanol while the latter would produce methane and hydrogen [2].

There are several ways of thermochemically converting the biomass into usable fuels. Pyrolysis, the process of chemical breakdown at high temperatures (~ 500°C) in the absence of oxygen, can produce some oil and coal also known as bio-oil, and biochar to better distinguish their origins from the traditional fossil fuels. Gasifiers take the biomass or biochar and convert them into a combustible gas mixture (sometimes called syngas) under even higher temperatures (~800-900°C) but limited oxygen conditions. Liquefaction on the other hand, uses uses high pressure, but rather lower temperatures (~ 200°C) to convert the biomass or biochar into bio-oil. And lastly, purely chemical processes take advantages of the abundance of lipds in the cell membrane of the algae. Additionally, many algal species are known to accumulate various amounts of oils inside the cells. These amounts can vary anywhere from ~ 30-70% of the dry biomass [1].Using transesterification reactions, biodiesels can be produced [3]. It should be noted that many of these processes have occured naturally in the environment under geological conditions. This is what produced the fossil fuels. We are just enhancing the processes in controlled and optimized conditions using current biomass instead of biomass from the past.

Advantages of Using Algae for Biofuel Production

The advantages of using algae for biomass generation are plentiful. For one, algae have the advantage of not competing with valuable arable land and water needed to cultivate food crops. Depending on the type of algae used, fresh water may not even be needed. More importantly, although there are significant differences between different algal species, the generation time, that is the time it takes for an algae cell to divide, is much faster than for any other land-based plant. This can be as little as one hour! As a result, biomass can be generated much quicker than achievable with any land-based plant.

Figure 2. Integrated uses of Algal Biomass adapted from Yusuf Chisti (2008)

The methods mentioned above are not mutually exclusive. Rather, there is great potential to combine several processes into an integrated a pipeline which is where the greatest benefits of using algae for biofuel generation lie. One possible pipeline could start with waste water streams that are used to grow algal biomass while cleaning up the water and removing carbon dioxide in the process. Some of the biomass generated could be refed to the system while the majority is used for bio-oil, or biodiesel production through various extraction methods such as transesterification. The remainder after biomass extraction can still be used further downstream. The remainder of the biomass is still rich in nitrogen, phosphorous and protein sources which is ideal for animal feed (potentially posing some public concerns that need to be addressed) or fertilizer material. Alternatively, the biomass could be pyrolysed or anaerobically digested to produce biochar or biogas usable for cogenerating electricity and heat that the surrounding communities could use [3].

Challenges to Algal Biofuels

Despite the promises of algal biofuels, the current fraction of biofuels generated from different sources of algae is rather small as costs associated with the challenges and research to overcome them are still high.

The major challenges in algal biofuels come from dealing with sources of contamination that could out-compete the algae to be cultivated, and high energy costs associated with potential circulation of the system as well as biomass recovery. To bring down the cost, test sites need to be scalable which in itself can represent difficulties with some approaches. Research on all these fronts costs money a lot of money.

All these factors contribute to current cost of biofuel generation from algae. For only biodiesel production, the estimated current cost is estimated to be about $ 33 a gallon. However, the cost significantly comes down to about $ 5.50 when integrative approaches are used such as cogeneration of electricity and heat. A further cost reduction to about $ 3.50 can be achieved from selling algal byproducts such as animal feed, fertilizer materials, or other high-value products on the near-term [4]. Although much more manageable, this is still slightly higher than the current cost of diesel. But research to enhance efficiencies are being researched to lead us to price competitiveness.

Innovations in Algal Biofuels

Despite the challenges, many companies across the world are pushing forwards with their efforts to bring algal-based biofuels to the market supported by an increased effort of academic research, government subsidies, and changes in the regulatory-framework.

Current research is focused on finding more suitable algal species through bioprospecting. Genetic engineering can improve biomass generation, increase the oil content, or improve the sturdiness of algal species for a given condition. Up to now, the extraction process also killed the algae. But, as discussed on NPR's Science Friday show (3 July 2009), the possibility to develop technologies for "milking" the algae without killing is being researched.

On the industrial side, many companies are putting their ideas to the test by bringing their innovative approaches to the growing but challenging biofuels market. While Solazyme has adapted the approach of growing algae in completely dark vats and feeding them sugar [5], other companies such as Solix have worked on bringing improved bioreactors to large-scale [6]. Other companies, such as Sapphire Energy have focussed on directly extracting 'green crude oil' from algae [7]. There are also a couple of companies working on converting sewage water into biodiesel. A New Zealand company named, Aquaflow claims to have been the first company to successfully do so all the way back in 2006 [8].

By no means is this supposed to be an expansive list of current innovations in the field. But one thing is clear: Despite the 20 year history of research into algal biofuels, it only seems that now conditions and research have come far enough to seriously consider algae for biofuels. Which of these companies will eventually become successful is unknown at this time. Many hurdles remain. But the examples, hopefully, provide a glimpse to the bright future of algal biofuels and explain why there is so much excitement in the field.

Quoted Sources:

[1] Venice Seaport Eyes Algae for Energy Needs. Visited: 2009-08-21. www.reuters.com
[2] Bet Wang et. al. (2008) CO2 bio-mitigation using microalgae. Appl Microbiol Biotechnol 79:707–718
[3] Yusuf Chisti (2008) Biodiesel from microalgae beats bioethanol. Trends in Biotechnology Vol.26 No.3
[4] Algae Biodiesel: It's $33 a Gallon. Visited: 2009-08-22. www.greentechmedia.com.
[5] Solazyme Produces World’s First Algal-Based Jet Fuel . Visited: 2009-08-22. www.solazyme.com
[6] Solix Biofuels Begins Large-Scale Production of Algae-Based Biofuels at Coyote Gulch Demonstration Facility. Visited: 2009-08-22. www.solixbiofuels.com
[7] Sapphire Energy turns algae to 'green crude'. Visited: 2009-07-20. www.sapphireenergy.com
[8] NZ company makes bio-diesel from sewage world first. Visited: 2009-07-21. www.nzherald.co.nz
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