Green scum and great expectations

Compared with existing crops grown for biofuels, marine microalgae appear to offer many advantages. They do not require fresh water. Nor do they require farmland - a huge mark in their favour, given the controversies about biofuels using food-growing land and driving deforestation through displacement (ENDS Report 399, pp 30-33 ). Microscopic algae could also gobble up flue-gas carbon dioxide from power plants, steelworks or cement factories.

In October 2006, US company Valcent announced results from its Texas algae test facility which, if they could be scaled up, would achieve astonishing biodiesel yields of up to 1.4 million litres per hectare per year. Soya grown for biodiesel in US fields yields just 470 litres/ha/year.

So where are the tankers of algal biofuel?

Ami Ben-Amotz, chief adviser at Israeli algal biofuels firm Seambiotic, has been involved in alga farming for more than 20 years. "We have many thousands of years of agricultural experience growing and harvesting plants, whereas with algae we have at most 100," Dr Ben-Amotz says. "This knowledge is not sufficient for successful large-scale cultivation."

Like any other plant, algae need food, sunlight and CO₂. As they grow they lay down lipids as energy reserves, which in some species make up more than 50% of their weight. Like other crops they must be harvested and processed before the lipids are extracted and converted into useful biofuels by chemical processing. The residual algal biomass could in the future be sold as animal feed, fish meal or even for human use.

There are two main ways to cultivate algae. The simplest is to grow them in large, shallow and continually stirred saltwater ponds known as raceways. Add to the mix nutrients such as nitrogen and phosphorus, and pump in copious quantities of CO₂.

Get the conditions just right, and your chosen algal species will thrive above others, much as farmers must control weeds to grow a single crop in their fields. Get it wrong and the ponds can be taken over by unwanted algal invaders or decimated by rotifer pests - microscopic grazers which dine out on algae. This is a major problem for open-air algae farms.

Dr Ben-Amotz points out that farmers confronted with pests or weeds can visit their local agrichemicals representative. In contrast an algae farmer must empty ponds, clean them out and start again with a fresh injection of the right algae.

To avoid such problems algae can be grown in sealed vessels known as photobioreactors, which are usually plastic tubes or bags. The system is sealed, so infestations are easier to avoid and conditions can be more tightly tuned.

Cost of control
But the added control comes at a cost. The investment required to set up an open-pond algae ‘farm’ is already up to ten times higher than for a conventional farm. Land must be flattened and ponds built and lined before the infrastructure needed for harvesting and processing the crop is even considered. Photobioreactors are another ten times more expensive.

Commercial algae production today totals less than 10,000 tonnes per year worldwide, almost all of it in raceway ponds. The market is for high-value food supplements, with the cheapest algal biomass being produced for about $5 per kilogram.

Assuming algal species with reasonably high lipid content could be produced at similar cost, algal biofuel would cost upwards of $20 per litre. Nowhere in the world is algal biofuel in commercial production, but dozens of start-up firms are using venture capital and public sector support in a race to reach the forecourt with oil produced consistently at competitive cost.

Some of the oil giants are interested. Shell has invested in an algal biofuel joint venture to explore the feasibility of the idea. The company, Cellana, is working on a pilot facility in Hawaii.

ENDS spoke to a selection of the players in the field. Among all the claims about high yields and technical advances that will revolutionise the industry, ENDS found a reluctance to discuss the details. One company even refused to provide an aerial photo of its pilot facility for fear of revealing its new process.

Dutch firm AlgaeLink which designs and makes photobioreactors says it has sold 32 demonstration units worldwide to companies investigating the use of algae to soak up CO₂ or produce dietary supplements as well as for biofuel production.

At just 42 square metres, these units are intended to be test plants to establish feasibility at customers’ sites. AlgaeLink is also working on five commercial-scale plants, but most will be for CO₂ sequestration rather than biofuels. A spokeswoman said the system was not economically viable for oil production without co-product sales or biodiesel subsidies.

US-based algal biofuels company Algenol also uses photobioreactors, but rather than going through the energy-intensive process of harvesting algal biomass and extracting lipids for biodiesel, Algenol grows an ethanol-producing species of algae.

The ethanol and water evaporates into the reactor’s headspace and is piped off for separation. Because Algenol does not have to continuously stir or harvest its algae, the process is cheaper than its rivals’, says chief executive Paul Woods. Unlike most other algal biofuel companies, Algenol does not rely on selling co-products.

It has been operating a pilot facility in Florida for about two years, and plans to start building on two more sites in Florida and Texas later this year. The largest will cover 130ha.

Mr Woods claims a recent life-cycle analysis showed an 81% reduction in greenhouse gas emissions compared with fossil fuels, although the company has yet to publish the basis of that estimate. The largest part of the energy requirement is for separating the ethanol-water vapour mix. The company claims its process yields 56,000 litres per hectare per year of ethanol, but expects to boost this to 94,000 litres/ha/year by the end of 2009.

But Aurora Biofuels chief executive Bob Walsh says he is sceptical about photobioreactors. Aurora, another US firm, was founded in 2006 and has over $23m in venture funding. He says open pond algae cultivation is "the only way it’ll be economic".

For Aurora, it’s not just about the lipids for conversion to biodiesel; the co-products sell for almost as much as the fuel itself. The cost of production is tightly linked to the total yield of biofuel per unit area.

Unlike Valcent, or indeed Algenol, Aurora stands at the more conservative end of this range. "We think up to 12,000 litres/ha/year might be possible [in the longer term], but at the moment we are at 9,000 litres/ha/year in the lab," says Mr Walsh. "Now we’ve got to take it to the field."

Aurora is working on an 8ha demonstration plant at its site in coastal Florida which should be completed this year. The company hopes it will be competitive with oil at $80 per barrel, but won’t know for sure until the plant is in operation. It is cautious about the transition to commercial-scale production.

"I don’t think anyone’s commercially ready until they’ve proved they can grow algae outside month after month, without crashing it," says Mr Walsh, referring to population crashes caused by invasion, infection or grazers.

Energy-saving innovations
Aurora has introduced a number of cultivation and harvesting innovations. It uses the CO₂ being pumped into the ponds to drive circulation instead of a paddle wheel, saving about four fifths of the energy normally required.

It also uses a novel harvesting method. Instead of gathering the algae from water in an energy-hungry centrifuge, Aurora’s adds chemical flocculent to make the algae clump together. Clumps float to the surface and can be skimmed off, yielding sludge with a yoghurt-like consistency. Lipids are extracted from the ‘yoghurt’, avoiding the need for energy-intensive drying.

US firm Sapphire Energy avoids the need to dry its biomass by extracting lipids and other useful products from the algal slurry. Based in San Diego and one of the biggest players in the field, last year it announced it had raised more than $100m with investors including the Wellcome Trust, Bill Gates’ Cascade Investment and Rockefeller family investment vehicle Venrock.

Sapphire extracts what it calls ‘green crude’ from algal biomass grown in open ponds. This is made up of oil and carbohydrates, while the algal protein will be removed and sold for animal feed.

Green crude can be put through a standard oil refinery to produce gasoline, diesel or even jet fuel which is a big advantage over biodiesel or bioethanol, says Tim Zenk, Sapphire’s vice president of corporate affairs.

The company has a 9ha open-pond research and development facility in New Mexico and has acquired another 1,200ha for development. In April Sapphire set out its scale-up timeline: it plans to produce 3.8 million litres of fuel during 2011, rising to at least 380 million litres by 2018 and up to 3.8 billion litres by 2025.

The 2011 target is based on 120ha yielding 31,000 litres/ha/year, described as a conservative estimate by Mr Zenk. "There’s no need to hype the numbers, and when you have backers like the Wellcome Trust you just can’t make statements you can’t back up."

Mr Zenk admits that producing algal biofuel today is expensive. But once production reaches the billion-litre scale "we’ll easily be in the $60-80/barrel range".

Sapphire is the only company ENDS contacted to have publicly available figures for a life-cycle analysis of its carbon emissions. On a ‘well-to-wheels’ basis, its ‘green diesel’ emits 35 grams of CO₂ per megajoule of fuel used, comparing favourably to US corn ethanol or European biodiesel. Fossil diesel emits 86g/CO₂ /MJ so Sapphire’s green diesel gives a 60% saving.

In recent testimony to the US Senate, Sapphire Energy pleaded for a carbon cap-and-trade scheme to give CO₂ emitters the right incentives to make their CO₂ problem algal biofuel companies’ feedstock solution.

The issue highlights the importance of locating alga cultivation near a suitable CO₂ source. The gas is an essential ingredient for high-yield production, along with cheap, flat land, plentiful sunlight and saline water - although the latter could come from brackish groundwater sources instead of being piped from the sea.

Deserts, often touted as an alga grower’s paradise may not always fit the bill because of cold night-time temperatures and a lack of access to salt water. They may also lack nearby CO₂ producing industry.

Florida-based PetroAlgae claims to be commercially viable already, without subsidies. It says it uses a computer-controlled light-management system to maximise productivity. Its business model is to sell the design for 5,000ha PetroAlgae ‘units’, along with expertise and teams of technicians, to other companies.

Each PetroAlgae unit is made up of 5,000 1ha modules and will produce a projected 284 million litres of green diesel per year, equivalent to 57,000 litres/ha/yr. This figure is based on a pilot facility in Fellsmere, Florida, which has two full-scale 1ha modules.

"We will be commercialising this year," says company chairman John Scott. In March, PetroAlgae signed its first license agreement with a company in China, where construction will start later this year. Dr Scott anticipates the first batch of oil will be produced in the first half of 2010.

Extravagant claims
But some companies are struggling. In May, the doors closed at GreenFuels Technologies which had operations at an Arizona power plant and the Massachusetts Institute of Technology. Previously one of the most prominent algal biofuel players, it had raised over $70m in venture capital funding.

It too, had made extravagant claims regarding the potential yields of its patented photobioreactor alga growth system, known as "the matrix".

A September 2007 company report described field testing over 19 days that summer, with average productivity of 98g/m²/day. Its patent applications also received considerable scrutiny. In heated exchanges played out over the internet, GreenFuels was accused of violating the first law of thermodynamics, with more fuel energy supposedly being produced than the energy available from photosynthesis under normal sunlight.

Claims such as those made by Valcent and GreenFuels "go far beyond exaggeration into the realms of science fantasy", writes David Walker, professor emeritus of photosynthesis at the University of Sheffield in a recent paper.¹

Alga expert John Benemann is even more dismissive. "Whatever any such company says has no value. You might as well have listened to General Motors when it said it wouldn’t go bankrupt." Dr Benemann is a veteran of the US Aquatic Species Program, an 18-year research project funded by the US Department of Energy’s National Renewable Energy Laboratory which ended in 1996.

In his paper, Professor Walker sets out the physical limits on photosynthesis, leading to an unequivocal maximum theoretical yield of about 140g/m²/day.

But it is not possible for algae to usefully convert all of the sunlight they receive. According to Professor Walker’s calculations, the theoretical maximum yield is thus reduced to a more likely maximum achievable yield of 54g/m²/day. This does not account for factors such as disease, invasion, pestilence and nutrient limitations and could never be achieved in practice, he argues.

The paper concludes "there is in fact no credible evidence to support the contention that algae produce much more biomass per unit area per unit time than any other green organism".

Professor Walker’s argument is well supported by facts. The widely referenced Aquatic Species Program achieved average algal biomass productivity in a 12-month field trial of about 10g/m²/day, with 50g/m²/day on a good day.

Over a year, 10g/m²/day equates to 36.5t/ha/year, similar to the biomass yield of conventional biofuel crops (see table).

Good but not exceptional
Professor Mario Tredici at the University of Florence, is president of the newly launched European Algae Biomass Association (EABA) which promotes links between scientists and industry to realise algae’s potential. He told ENDS: "Algae are good producers, but not exceptional. They are maybe similar to sugarcane. You cannot expect much more than 80-90t/ha/year. In the future we can aim for perhaps 150t."

The key difference, says Professor Tredici, is in the output of biofuel per unit of biomass. The most productive conventional crops such as sugarcane or sugar beet yield only relatively small amounts of biofuel per tonne.

In contrast, some algal species can contain more than 50% lipids by weight. This means that a hectare of algae might yield 20,000 litres of oil in a year, whereas Indonesian oil palm yields less than 4,000. The spread of oil palm plantations has been roundly condemned for the associated destruction of tropical rainforest.

There is no doubt, then, that biofuels from algae have a huge potential to cut CO₂ emissions compared with today’s biofuel crops. But the UK government’s Renewable Fuels Agency, which administers the Renewable Transport Fuel Obligation (RTFO), says it will not conduct a ‘new fuel chain’ analysis to calculate a default greenhouse gas saving for algal biofuel until at least one million litres is supplied to the UK market. Currently there is none.

Biofuels are set to be rewarded under the RTFO according to how much carbon they save from April 2010, a move that is likely to benefit algal biofuels - assuming they reach the marketplace (ENDS Report 390, pp 40-41 )

But the path to industrial-scale production will take ten or even 15 years from now, according to EABA’s executive director Raffaelo Garofolo.

Several of the companies ENDS spoke to felt governments should support basic research and development while the alga industry finds its feet. Biofuel subsidies or carbon emissions trading are insufficient to bring the technology to market, they say.

Taking just such an approach, the UK government-backed Carbon Trust launched its Algae Biofuel Challenge in October 2008 to help develop commercial-scale open-pond alga cultivation for biofuels by 2020 (ENDS Report 408, p 30 ).

"When you hear claims for 50,000 litres/ha/year in the near term it is tending towards the absurd," says Ben Graziano, who is coordinating the project. "This is a ten-year race, despite the hype from some companies. We need to bring down the costs by a factor of at least ten."

Although algae will be grown in bulk in warmer, sunnier climes than Britain, Dr Graziano says it is still worth investing UK public funds in the technology "because of the skills base and scientific expertise we have". Furthermore, investment in algae is still relatively limited when compared with other advanced biofuels such as lignocellulosic ethanol. So, he argues, the Carbon Trust’s investment could have a real impact on the development of algal biofuels while helping UK firms and researchers to take a stake.

The challenge’s first phase, worth £3-6m, will fund research and development in areas such as strain selection for productivity, maximising solar conversion efficiency, sustained open-pond cultivation techniques and engineering of cost-effective mass culture systems. It has ruled out photobioreactors because, says Dr Graziano, "we have not seen any evidence to suggest [they]… could ever be viable and cost effective."

There is usually an inverse relationship between lipid content and biomass productivity in algae, while the harvesting method may be different for each species. Sustained cultivation will require robust strains that can outcompete rivals and resist attack from viruses or algae grazers.

For quickly selecting and improving algal strains, their short generation time is at least one real advantage compared with conventional crops, where new strains can take 20 years to develop.

The Carbon Trust’s target yield is 20,000 litres of biofuel/ha/year, equating to 60t of biomass/ha/year with 30% oil content.

Phase two, the construction and operation of a 10ha demonstration plant for algal biofuel will start in 2010 with £7-10m from the Carbon Trust over five years. Site selection, probably in a sunny tropical climate, will be based on a range of sustainability criteria.

There is great potential for marine algae to produce low carbon transport fuel while avoiding the damage to humans and biodiversity threatened by more conventional biofuel crops. But it will be many years before that tanker of algal biofuel pulls onto your local forecourt.