The world has known for years that extracting biofuel from algae is technologically feasible. Now the quest is under way to prove that it can be sound business. Researchers around the world are pursuing the same goal,¹ yet the paths they are taking are very different.

It involves collaborations across science and industry. A five-year project based in Spain to create energy from algae grown using waste water has attracted €7 million of EU funding. Co-ordinated by global water management company Aqualia, it involves partners from Germany, Austria and the Netherlands, and is driven by scientific research fromthe University of Southampton in the UK.

Various approaches   

In the US, research teams are ploughing their own furrows. Scientists at Iowa University's Center for Sustainable Environmental Technologies (CSET) have pursued catalytic pyrolysis – a thermochemical conversion process - of microalgae as their way forward. They see it as a less energy-intensive and more economical method of producing petrochemicals and ammonia.

Meanwhile, in a programme that began in 2007 at Scripps Institution of Oceanography, UC San Diego, Dr Mark Hildebrand’s team of marine biology researchers have manipulated algae genetically to improve the yield of key components for biofuel production. Hildebrand’s project was recently rated the best of its kind in the country by the U.S. Department of Energy, citing “outstanding research, technical progress, project relevance and potential commercial applications.”  

Most scientists have been working with green algae found in freshwater systems such as lakes and ponds. But the Scripps team believes that diatoms — among the most prevalent oceanic algae — are “uniquely suited” to biofuel production. That they can be grown in sea water is a big bonus in drought-prone areas such as California, for it relieves pressure on fresh water supplies.

Their key discovery is the possibility of “turning off” an enzyme in diatoms that breaks down lipids for energy. This enables algae to accumulate more lipids without slowing their growth.  Hildebrand believes his team has conquered a major obstacle to algae biofuel production.

Three varied approaches, but so far proven only on a small scale. The big question: how will they work when taken out of the lab? Everyone’s trying to find out, but no one thinks it will be easy. Hildebrand says the certainty of his team’s enzyme discovery became clear about two years ago. However, what works in the lab doesn’t necessarily work in the outside.

“There’s never going to be one strain of alga that fulfils all the criteria for energy production,” he noted. The next step is to create an outdoors cultivation area (about an acre). “In a couple of years’ time we should be able to do this.” (Crop rotation will be applied to see which alga works best at any particular time.)  

Other factors are involved apart from science. “This is a genetically modified organism, so there are a lot of regulations to deal with,” Hildebrand explained. “However, I think these will be less rigorous [than for crops] – we won’t be using them as a food source.”  

Hildebrand says it’s hard to predict overall where the process will go. “Our plan is to continue the work in real world conditions — we want to keep pushing the science forward,” he stated. “It’s very clear that improving the lipid content is a key factor in reducing the cost of [fuel] production.”

The major effort — in terms of cultivating the algae — is being done by Sapphire Energy, with which Scripps is said to be interacting informally. Hildebrand is also working closely with Global Algae Innovations. “There have been donors to this project through the company,” he said, adding that the gains are very substantial. “We wanted to demonstrate that this approach is viable.”  

Robert C Brown, CSET Director at Iowa University, agrees with him about the scope for gain. Brown’s path to exploring the biofuel potential of algae follows on from CSET’s experimental catalytic pyrolysis of lignocellulosic biomass, such as wood and grasses, to produce aromatic hydrocarbons.

“We thought it interesting to evaluate microalgae as a feedstock for pyrolysis because it’s so different,” Brown stated. “Microalgae also contain significant levels of lipids and proteins, which occur in only low concentrations of lignocellulose.”  

Brown’s research team was able to pyrolyze the microalgae, but the nitrogen from the protein ended up as undesirable compounds in the bio-oil, he explained. That’s when the decided to investigate catalytic pyrolysis. “We found it produced hydrocarbons that were both oxygen- and nitrogen-free, which is very attractive from the standpoint of production of fuels.”

But why, unlike some other research teams, has Brown’s team chosen to work with Chlorella vulgaris, a green microalga low in lipids? As it turns out, catalytic pyrolysis provides the answer. “When we discovered that it could convert virtually all microalgae components (including the protein) into hydrocarbons, we realized that what was important was overall yield — not simply lipid yield,” Brown explained. “It turns out that overall biomass yield goes down as lipid content goes up, so the best choice of feedstock is often lipid-lean microalgae.”  

Brown determined that a variety of microalgae could be employed. This has also encouraged his research team to look at other lipid and protein-rich feedstocks, including distillers’ dried grains and solubles (DDGS), the co-product from grain ethanol production. “It opens up interesting possibilities of blending,” he explained.   

So, what of the business possibilities? Brown admits that there’s a long way to go. So far CSET has carried out a technoeconomic analysis which includes computer simulation of a commercial-scale biofuels facility to identify the most promising feedstocks and process improvements needed. 

“Microalgae are still relatively expensive, so we’ve been focusing on feedstocks with similar composition but lower cost, as well as residues from industrial fermentations and waste water treatment,” Brown said. “But at this time, we’ve not moved the process out of the laboratory.”

Echoes here of the EU-backed waste water project already underway in Spain. A year has already passed since the first crop of algae biomass was grown at Aqualia’s site in Chiclana. Things started up in 2011 and, so far, are on a relatively small scale (the prototype cultivated area covering just 1000 square metres).  But by the end of 2015, there are plans to increase this ten-fold — and tenfold again, across 10 hectares, in 2016.

“This current prototype confirms all the results we’ve had in the preliminary phases on the pilot ponds,” said Frank Rogalla, who serves and research co-ordinator and director of innovation and technology at Aqualia. “Now the whole chain will be integrated and [ready to power] the first car by the end of the year.”

After anaerobic pre-treatment to maximize biogas production, wastewater is further purified by the growth of algal biomass, a process that uses energy from sunlight.  Harvested algae will be treated for extraction of oils and other by-products, while the remaining algal biomass is turned into biomethane, CO₂ and minerals, together with residual biomass from waste water and/or agriculture.

Rogalla expects that each cultivated hectare will be able to fuel three cars “of average size” with algae biomethane, assuming each travels 15 000 kilometers a year. “We’re also producing biogás from raw sewage before the algae treatment, which should roughly double the methane production,” he added.  

“After the end of the project, we hope that the client, the municipality of Chiclana, will continue to operate the facility, as it will be a self-sustainable system. This biofuel could also be transformed into electricity with a CHP (combined heat and power) engine.”

Aqualia operates about 300 wastewater treatment plants, mostly in small towns. It plans to build similar facilities, mostly in southern Spain, but also in the Middle East. “The main limitation is space - for 10,000 people, three hectares would be required,” he says. “The treatment depends on climate and temperature but so does conventional treatment — about 10? C difference means a doubling in reactor volume, so in more northern locations the space needed will be higher.”

Aqualia claims that removing nitrogen and phosphorous from waste water will minimise pollution and conform to stringent discharge requirements. There will be the potential to make fertilizer and biochemicals without depleting other natural resources.

“We see a great potential for smaller cities with lots of space to convert energy —consuming and expensive wastewater treatment into something beneficial — running local vehicles,” Rogalla stated. “From a net electricity consumer, the towns would transform into a biofuel producer. “To treat sewage conventionally costs the municipality about €11 000 each year in energy alone. Instead of costing more than €11k a year, wastewater would produce an equivalent income.”

The road ahead

So, three cases where research is well advanced and which would appear to show commercial promise. Yet it may be this is a story that has only just begun unfolding. For scientists are very aware of the several thousand algae about which almost nothing is known – and which could also have great potential if their secrets become unlocked.

REFERENCES

1. The annual European Algae Biomass Conference, which brings together senior executives from industry and academia, has been running since 2011. There, technical developments, challenges and research breakthroughs are chewed over in detail. Beyond the technical research aspects, there’s also a strong emphasis on current and future commercial markets.  

Also, be sure to read Andrew Mourant’s blog on additional research pointing to prospects for creating renewable energy fuel from microalgae.