How much energy can algae produce?

May 28, 2008

Some say algae can grow faster than any other crop growing on land. The numbers range up to 150 (300) tonnes algal biomass/ha.year, which is several times higher than the best known arable crop. Can algae really deliver this enormous amount of biomass? At the first congress on algae in The Netherlands, Eugène Roebroeck from Lgem made some interesting calculations.

There is only a limited amount of energy reaching the earth’s surface which plants can use to grow.

First, let’s look at the sun and the energy it provides. The sun provides a limited amount of energy per square meter. At the tropics the sunshine is very intense, in contrary to the poles where there is little solar energy. Clouds are also an important factor; regions with more clouds recieve less solar energy at ground level. The World Metereological Organisation has combined these two factors and calculated the annual solar energy available at any given location.

The annual average of solar energy for the Netherlands (and for Belgium) is 110 W/m². This is the maximum energy you can use. But since the spectrum of sunlight has a range from 250 to 2700 nm, containing next to visible light also ultraviolet radiation and infrared radiation, not all of this energy can be used. The figure underneath shows the distribution of energy over the wavelengths. The red area between the two vertical lines is approxymately the energy algae can use: only 43% of the total energy of the sun.

Figure: the total solar spectrum. The red area is the energy at ground level. The red area between the two vertical lines is the part algae can use.

When we know that algae can only use 43% of 110W/m², we see that algae can only use 48 W/m².

Then, we have the efficiency of the photosynthetic apparatus of plants. Research shows that we need about 8-10 photons per captured CO2 molecule. Researchs on trees show that trees can take up only 5-6% of the available photons. This means we have in practice 3 W/m² which the algae can effectively use. Extrapolated to biomass this means we have a potential of 40 tonnes biomass/ha.year.

Since algal growth can be improved to reach higher effeciencies than the data shown above, the maximum value for photosynthetic efficiency can be 10%, which means a maximum potential of 5 W/m² or 68 tonnes biomass/ha.year.

In literature, this theoretical 10% efficiency is applied to areas (for example, the Sahara area) with much higher solar power (350 W/m² instead of 110W/m²), which results in the theoretical production rates of ~150 tonnes biomass/ha.year. This is the maximum amount of energy algae can capture per surface area.

But what has been proven? The NREL reported production rates of 50 tonnes algal biomass/ha.year, so this value can be achieved.

Is this enough to compete with other energy crops? Literature (Van Sark et al., 2006) suggests 8-12 tonnes DRY weight/ha.year for current bioenergy crops. At the congress some people argued that sugar beets can reach productivities of 25 tonnes dry mass/ha.year.

GBEV – Workshop Second Generation Biodiesel

April 11, 2008

On the 10th of March 2008 there was a  seminar on the second generation biodiesel at Het Pand, Ghent. It was organised by the Ghent Bioenergy Vally, a consortium which wants to stimulate growth in bioenergy in the Ghent region.

The host was Prof. dr. ir. W. Soetaert, who emphasised that the first generation biofuels clears the way for the second generation. What this really ment became clear during the lectures. First generation biofuels compete with edible crops, and are often not sustainable, nor economically viable. Second generation biofuels include non edible crops such as Jatropha curcas or algae oil and therefore don’t compete with food production. The third generation of biofuels based on hydrogen should start at 2030.

This was the schedule for this evening:

• Wim De Greyt – Desmet-Ballestra:
New technologies for the conversion of alternative resources to sustainable ‘second generation’ biodiesel. –

A very interesting presentation on the general aspects of second generation biodiesel. He added some useful yield/hectare data.

  • Soybean: 0,4 tonnes oil/ha.year
  • Rapeseed: 0,8 tonnes oil/ha.year
  • Jathropha: 1-1,5 tonnes oil/ha.year
  • Palmoil: 4 tonnes oil/ha.year
  • Algae: an estimate of 10-25 tonnes oil/ha.year

• Frans Goudriaan – Biofuel NV:
HTU® Diesel from wet wastestreams –
(pdf) (dutch)

The presentator explained the HTU process his company was developping and implementing. When you heat organic material such as wood to 300-350°C at a pressure of 120-180 bar in the presence of water for 5-20 minutes, you’ll get a mixture of 45% biocrude (raw organic oil), 25% gas (90% CO2, 10% CO), 20% H2O and 10% dissolved organics (acetic acid, …). The biocrude has an energetic value of 30-35MJ/kg (compared to biomass: 18 MJ/kg, coal: 25 MJ/kg, and raw oil: 40-45 MJ/kg).

This process is pretty fascinating. In the picture below, you a see match in a tube. This tube is heated to 300°C and a photograph is taken every minute. You see the match is being desintegrated into a brown fluid within 5 minutes. During this you see the volume increase and the match shrink. The brown liquid formed in the process is biocrude.

• Prof. Wolter Prins – BTG- Universiteit Twente – UGent:
The possible use of fast pyrolysis in the production of biofuels –

Pyrolysis is the heating of dry organic material to a temperature of 500°C in anaerobic conditions. This generates a complex mixture of organic molecules which can be condensed into an energy rich liquid. He mentioned the advantages this system can have on a local scale.

• Henk Joos – D1 Oils Plant Science:
Jatropha curcas, an alternative source for biodiesel production –

Henk Joos is a geneticist currently researching Jatropha curcas L. (note the L. should not be in italics). Jatropha curcas is a bush which produces fruits containing 4-5 seeds of 2 cm. These seeds contain 40% oil, which is built of 60% mono unsaturated fatty acids. The plant can be grown around 30° North and 30° South.

His company researches which cultivars should be used in which regions. He was very realistic in his speech and emphasised that the expectations about Jatropha should be viewed critically. The ‘environmental elasticity’ (i.e. at which site and at which soil Jatropha grows well) is part of his research. Currently they cooperate with Shell to plant 70 millions Jatropha plants at the end of 2008.

• Prof. Chris Stevens & Prof. Roland Verhé – UGent:
Biodiesel production from non-edible oils and fats –

Part of the research was about the topic ‘which non edible oil can be converted to biodiesel’. They used used cooking oils (used at 190°C), animal fat from dead non-edible cows (rendac), and some other oil species. A technical outlie on the chemistry and production of biodiesel.


Algal research at MIT

April 7, 2008

Researchers at Massachusetts Institute of Technology used algae to capture carbon dioxide in flue gasses of electricity plants. A reactor has been built at the MIT to test this (see youtube video below). In most algae setups, the amount of carbon dioxide in the water is too low to provide maximum algal growth. In this setup, large amounts of carbon dioxide are blown through the water, thus providing high concentrations of CO2 which provides excellent conditions for exponential growth. Not only CO2 is removed by the algae, also harmful wastegas components are removed such as NOx. Additionally, the heat of the flue gasses can be used to set the growing tubes at ideal growing temperatures (20-35°C). A promising implementation, in this link you’ll find more detailed information.

AlgaeLink – How to make your own biodiesel course

April 6, 2008

Last week I visited the AlgaeLink facility in Roosendaal (Netherlands) where i attended the “How to make your own biodiesel” course. I was very interested in the potential of biodiesel production. Making biodiesel at lab scale turned out to be very easy. We only needed some pure vegetable sunflower oil, a few drops of NaOH, some methanol and a magnetic stirrer. After a few hours my first biodiesel was made.

The recipe for making biodiesel can be found in this link.

How to make your own biodiesel course - practical exercises

The industrial process of creating biodiesel is more complicated. Since the oil you buy is not entirely pure – it can contain too much FFA (free fatty acids) or phosphate – one needs to adjust the amount of reagents. Odour also is a problem. To remove these components you need to heat the oil at 80-120°C under vacuum.

After these practical exercises we got a tour in the factory. They showed their biodiesel production equipment and their photobioreactors, which were pretty shiny. They have full automated process control for different production parameters (pH, OD, temperature, …). To date, 27 of these reactors have been shipped for research purposes to a variety of countries.

€18.000 - AlgaeLink Roosendaal

In this reactor – demonstrated at the Roosendaal facility – they used a salt water Nannochloropsis strain.

Thanks to everyone for making it such an interesting day!

Algal Research at MIT >>

A small introduction on Bioenergy and Algae

April 6, 2008

High oil prices, global warming, and emphasis in renewable technology are attracting new interest in a potentially rich source of biofuels: algae. Currently, no alternative technology seems to be able to entirely replace our vast energy demands. Yet, we need new technologies to provide us the energy we need. One of these technologies which is recieving more and more attention is bioenergy derived from algae.

Microalgae can contain up to 40% oil, they can grow in wastewater and in live places where no agriculture is possible. They are able to grow very fast and they even capture large amounts carbon dioxide while doing so. These facts look very promising for use of algae in bioenergy, but can these algae really deliver?

Currently I am researching the integration of solar energy via algae into methane and electricity. The aim of the thesis is to research and develop the potential use of microalgal biomass for conversion into bioenergy.

So, how does this work? The algae are grown in salt water ponds in our laboratories. The algae convert carbon dioxide with energy from solar radiation into biomass, a process which is called photosynthesis. After they reach a certain density, an amount of water containing algae is put into an anaerobic digestor for 20 days. In this digestor, which is basically an airtight container with an microbial inoculum, the biomass of the algae is converted into biogas (65% methane, the rest is carbon dioxide). This digestor is built in a way that no air comes in, but the biogas is being captured for analysis. Theoretically, it should generate ~0,5 l biogas per gram dry algae.

Microbial Fuel CellWhen the algal fluid is digested, it is transferred into an Microbial Fuel Cell (as seen left), which is a sort of bio battery. The main goal of the microbial fuel cell is to generate electricity while further degrading the effluent of the digestor. It contains two 165 ml compartments seperated by a membrane. One compartment contains the digested fluid and an active microbial mat which converts the organic material, the other contains water with dissolved oxygen. Organic compounds are metabolised by bacteria in the first compartment, and the electrons are transferred via the electrode to the other compartment, where they are taken up by oxygen and form water. This current can be used as electricity.

Microbial fuels should generate a potential about 100 mV or more and some current. After the fluid has passed through the microbial fuel cell, it is poured into the ponds to the algae can grow again.

Microbial Fuel Cell

Figure: scheme of a microbial fuel cell. In the left compartment, substrate is oxidized. Electrons transfer to the other compartiment and react with oxygen.

Now you know something about the general principles of this research. This work is just a tiny addition in the rapidly growing algal to bioenergy field. Converting algae to biogas and electricity is not the only possible application for algae. Other projects on algae involve the use of algae in reducing carbon dioxide emissions from energy plants (MIT – USA). Some companies use algae to produce omega-3 (SBAE – Belgium) fatty acids or pharmaceuticals. Some grow algae strains with high oil contents in order to produce biodiesel (AlgaeLink – Netherlands, Shell/Cellana – Hawaii). Many other projects worldwide are currently researching algal production for bioenergy creation.

In the coming months I’ll regularly post updates on the progress of these potentially vital researchs.