Harvesting technique could make algae a viable biofuel
Share
Algae may become an economically viable biofuel thanks to the development of a harvesting technique from Sheffield University.
Algae produce an oil that can be used to create a useful biofuel. Biofuels made from plant material are considered an important alternative to fossil fuels and algae, in particular, has the potential to be a very efficient biofuel producer.
Until now, however, there has been no cost-effective method of harvesting algae and removing water from it so that it can be processed effectively.
The technique from Sheffield University builds on previous research in which microbubbles were used to make algae blooms denser and consequently easier to harvest. However, removing the water so the algae could be harvested remained problematic.
Now, a team led by Mark Zimmerman in the Department of Chemical and Process Engineering at Sheffield University believes it has solved the problem.
Zimmerman told The Engineer: ‘What we’ve found is that we can separate the microalgae from the water or harvest it using microbubbles that are created by a fluidic oscillator.
‘A fluidic oscillator switches flows rapidly from one outlet to another, using feedback to do so with no moving parts. It is like an opening and closing mechanical valve that results in pulsing flow.’
Zimmerman explained that the process is much cheaper than attempting to make microbubbles through an industrial process known as dissolved air flotation, which generates bubbles that are too turbulent to harvest algae.
The fluidic oscillating system developed by Zimmerman’s team uses up to 1,000 times less energy to produce the microbubbles and, in addition, the cost of installing the Sheffield University microbubble system is predicted to be much less than existing flotation systems.
‘Our bubbles are made under laminar flow and we use practically no more energy than is required to make the interface of the bubble,’ said Zimmerman.
As a result of the low energy input, the bubbles rise very slowly, which is crucial as it means the algae particles can attach themselves to the bubbles more easily.
Two chemicals added to the liquid in the process — a flocculant and a coaggulant — help the algae bond to the rising microbubbles.
‘The idea is to create a surface on the algae particles that is hydrophobic so the microbubbles are attracted to it,’ said Zimmerman.
When the bubbles and the particles reach the surface, the flocculant and the coaggulant keep the algae in a fixed layer.
The blanket of algae can then be skimmed off the surface with something such as a belt skimmer, said Zimmerman. ‘In the lab, we use a knife,’ he added.
At the moment, the technique has only been demonstrated on a laboratory scale, but Zimmerman believes it can be scaled up relatively easily.
The technology is likely to have applications in lakes that have suffered from eutrophication. This occurs when a build-up of nutrients causes algal blooms to form and is often attributed to farming fertilisers entering water bodies.
The team has been in talks with Ken Shu, a scientific adviser to the Chinese government, to set up pilot-scale trials on remediating algal blooms in eutrophied lakes in China.
‘China has demographic drinking-water problems,’ said Zimmerman. ‘They’re running out because the lakes that used to be used for drinking water are all eutrophied with algal blooms.’
Readers' comments (7)
Durwood Dugger | 26 Jan 2012 2:13 am
Flotation harvesting of alga is certainly nothing new (as stated) - nor does it represent a major reduction of the over all cost in the process of growing algae to useable fuel currently in excess of 10x+ above petroleum production costs - with which all alternative fuels have to compete. It fails additionally to change algae biofuels lack of sustainability due to its dependence on NPK fertilizer - which which all at at scale biofuels - including algae are dependent upon.
As well it would seem to be a little premature to make an announcement of economic benefits of any kind - if the new technique has only been demonstrated using a "knife" to "harvest" floated algae in the lab. Call us when there are some decent energy budget based financial audits available.
Unsuitable or offensive? Report this comment
James Stewart | 26 Jan 2012 3:19 pm
Do you sir mean to imply that none of the nutrients can possibly be recycled back to process? This means of harvesting is at least a 5-10 fold increase in efficiency compared to the old screening methods that were tried early on, I suspect. Let's try not to be entirely so pessimistic, the key issue will ultimately be placement of algal acreage where there is enough water resource (saline underground water) to pump to provide makeup water to the system, and where sunlight is abundant. American Southwest, and desert regions where little or no production now exists might be excellent choices.
Unsuitable or offensive? Report this comment
Will Zimmerman | 26 Jan 2012 6:56 pm
Thanks, Mr Dugger for your advice.
Microflotation is a different means of achieving flotation separation, using very little energy to create the bubbles compared with dissolved air flotation.
We are scaling up to pilot scale and industrial scale in other applications, but I have no illusions that algal biofuels will become profitable overnight. It usually takes 5-10 years for the uptake of large tonnage process technology. But there are already profitable processes where the technology should be able to slot in.
Unsuitable or offensive? Report this comment
Rich Arnold | 27 Jan 2012 3:56 pm
I have been seeking a method of harvesting algae from ponds and would like to offer my aquaculture operation free for expanding your method to the next level. It will be easier than attacking large lakes and prototype equipment could be built and tested with easy access. My motive is attempting to control aquatic plant growth in ponds where I raise prawns. I also manage 60 acres of shallow water for crawfish production, thus lots of algae. Maybe far fetched, but if I could find a use for the algae and a method for harvesting without chemicals.... well??? Why not? Even if the production ultimately was marginally profitable, it could be self sustaining and elminate my problem aquatic plants.
I hope some likeminded person reads this and communicates with me.
Rich Arnold
Ida, Louisiana
318-470-4806
Unsuitable or offensive? Report this comment
Christian Lohrey | 28 Jan 2012 12:46 pm
Would this technology work without the use flocculant and/or coaggulant? Recycling the harvested water back to the algae ponds is critical in terms of water management for biofuel applications, so I think that is one aspect that must be addressed.
I agree with Durwood that the announcement of this promising new technology was entirely premature. We'd like to see numbers like harvesting efficiency, actual energy consumption, and flowrates that this could be scaled to. I will keep my eyes open and be looking in literature for some results with this new technology.
Unsuitable or offensive? Report this comment
Mario D. Castillo | 28 Jan 2012 6:07 pm
Hi Mark Z.,
I like your innovative & cost-effective concept. Coupled with other cost-effective harvest, dewatering and oil extraction unit operations, perhaps we could tie them all up to get an end-to-end biofuel production process that is competitive.
Mario D. Castillo
Fairfiled, California 94534
707-421-9332
Hi Rich Arnold,
I'll call you. We have a common interest in algae harvest technology.
Mario D. Castillo
Fairfield, California 94534
707-421-9332
Unsuitable or offensive? Report this comment
Anonymous | 30 Jan 2012 1:31 pm
Considering the vast amounts of money poured into fatuous high profile systems such as hydrogen fuel cells and electric cars in general (which may be relvant once unlimited low carbon energy and in the latter case a battery that isn't merely laughable become available), surely we should welcome anything that shows promise.
Unsuitable or offensive? Report this comment