By Neil Nooreyezdan
The idea of processing plant material to create liquid fuel is neither old nor unique. There are dozens of examples of crops (such as sugarcane, wheat, corn and molasses among others) being used to create bioethanol (Sarkar et al, 2012). Harder and Von Witsch, in 1942, were the first to propose the possibility of growing microalgae at a large scale for food or fuel (Harder & Von Witsch, 1942). This idea seemed to have a lot of promise for some obvious reasons.
Most other sources of biomass to produce biofuel were crops that needed to be grown on fertile land. This created competition with food crops, which means there would always be a limit to how much they could be grown. Some of them also have primary value as food and feed (Sarkar et al, 2012). Algae, meanwhile, grow on non-arable land and hence they could avoid competition for space with vital food crops (Dismukes et al, 2008). Moreover, algae are very genetically diverse (Deschamps & Moreira, 2009), a relatively high percentage of their biomass is composed of lipids (Kojima & Zhang, 1999), and are not especially picky with their water source. Wastewater contaminated with fertilisers could also be used as the primary source of water and nutrients (Douskova et al, 2009). Furthermore, algae can produce biomass extremely quickly – with some species having a doubling time of as little as 6 hours (Sheehan et al, 1998).
In the mid 2000s governments around the world placed subsidies on bioethanol and biodiesel in an attempt to increase consumption of alternate fuel sources. Due to their versatility, biofuels made from microalgae seemed like the perfect alternative. Companies all over the world diverted their attention towards producing algal biofuels, making bold claims about their potential. A company called Algenol planned to make 375 million litres of ethanol annually in the Sonoran desert by the end of 2009, and 3.75 billion litres by the end of 2012 (Gardner, 2008). Another company named PetroSun planned to develop an algae farm containing 1,100 acres of saltwater ponds, which would in theory produce 4.4 million gallons of algal oil per year (Babstock, 2008). Dozens of other companies made similar claims.
Billions of dollars in venture capital funding were raised by companies pursuing commercial algal fuels in this period, with millions more being invested in the form of grants from the American Department of Energy (Duan, 2019). People had proclaimed algae to be the future of fuel. In fact, Jim Lane of Biofuels Digest projected that algal biofuel capacity would reach 1 billion gallons by 2014.
Today, we are not even close to producing 1 million gallons of algal biofuel per year, rendering the projections of 1 billion gallons nothing but a pipe-dream. Many of the companies pursuing this goal have collapsed, and those that still stand have pivoted to using algae to produce higher value nutraceuticals, food products, colouring agents, cosmetics, etc. How did this seemingly promising tech go so wrong? To understand that, we need to look at the process of obtaining fuel from algae.
Phototrophic microalgae require some inorganic elements (including Nitrogen, Phosphorous, Iron and Sulfur), Carbon dioxide, fresh water and light to grow (Grobbelar, 2009). The algae are left to grow for a specific amount of time, under optimal conditions, and are then harvested. There are many different culture systems available, though the two most prevalent ones are open raceway ponds and closed photobioreactors. The algae are usually harvested through flocculation and dissolved air flotation followed by centrifugation (National Research Council, 2013). It was on these aspects of algal growth that researchers focussed their efforts on, working on optimising the culture systems and attempting to genetically modify strains of microalgae to increase their lipid content.
The biggest roadblock to achieving energy balance in the process (i.e. the fuel producing more energy than was used to produce it) is the fact that prior to extracting the lipids, the algal biomass needs to be separated from the water and dried. The downstream processes required are very energy-intensive, a factor that was not accounted for when researchers made their tall claims based on small-scale lab findings. Furthermore, a simulation of a microalgal biofuel production showed that to provide at least 10% of the EUs current transport fuel requirements would require an area 3 times the size of Belgium, and fertiliser equivalent to roughly 50% of the EUs current annual needs for crop plants (Teirstein, 2018). Along with this high operational cost, there was also a high capital cost, due to the infrastructure needed to produce this fuel at scale.
Nowadays, the algal biofuel bubble of the 2000s is seen as a case study in overoptimistic modelling based on pilot experiments conducted in laboratory environments. That being said, recent breakthroughs have stirred some interest in the field once again. One such breakthrough came in 2017, by a company called Synthetic Genomics – one of the few companies founded in the ‘gold rush period’ that still focuses on fuel production – in partnership with Exxon Mobil. Researchers created a genetically engineered new strain of Nannochloropsis gaditana that contains double the lipid content as a percentage of the biomass, compared to the wild strain (Ajjawi et al, 2017). Though this exciting development could have significant implications for the energy yield of the algal biomass, there are still concerns regarding the possibility of these genetically modified algae escaping to the environment and becoming harmful algal blooms (Flynn et al, 2013).
Improvements have also been made in the efficiency of downstream processing once the algae have been harvested. A team of researchers from the University of Utah attempted to address the energy balance issue by providing an alternative for the most energy-intensive part of the processing. Post-harvesting, the biomass needs to be dried to leave a powder or a slurry, to which a solvent can be added which remove the lipids from the residual biomass (Hannon et al, 2010). The researchers from their chemical engineering department devised a mixing reactor in which jets of the solvent are run against jets of the algae, creating a localised turbulence that allows separation of the lipids (Tseng et al, 2019). This process eliminates the need to dry the algae and is therefore much more energy efficient.
While these developments are encouraging, experts believe it will still take billions of dollars more of investment over decades for this technology to ever be commercially viable at scale. So for now, a world run on algae seems a distant dream.
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