I have been working on algae. I have a problem that is harvesting micro algae chlorella about 50lt. Are there any ways to harvest without centrifugation?
I worked approximately 5lt and it was not a problem, but now takes too much time.
Question
Is there any way to harvest microalgae without centrifugation or 20 micron filter membrane?
All Answers (23)
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Algae Harvesting - Flocculation
Alum and ferric chloride are chemical flocculants used to harvest algae.
The main disadvantage of this separation method is the additional chemicals are difficult to remove from the separated algae, probably making it inefficient uneconomic for commercial use, though it may be practical for personal use. The cost to remove these chemicals may be too expensive to be commercially viable.
Below link may be useful for algal harvesing
http://www.nrel.gov/docs/legosti/old/2396.pdf -
Thank you your answer. I will try this procedur. Thank you again -
The Center for Borefining at the University of Minnesota recently developed a flocculation process for Chlorella using starch. Some algae witl settle out without the use of flocculants or other technologies like centrifugation. -
And what is the working mechanism that i can not imagining :)
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Changing the polarity of the algal membranes causes them to aggregate and settle to the bottom (flocculate). Various chemical additives can cause this to occur. Also, gravity plays a role.
You should also look at the new machine developed by Origin Oil. Their One Step process involves
pulsed electrostatic charges that can cause the algae to flocculate. At higher intensity it can also cause the algae cells to rupture to release their lipid content. The lipid floats while the rest of the algal biomass sinks. Their web site has a U tube video of this process. The new machines are presently being delivered to Australia. -
We are using natural gravitational method for harvesting large culture volume of 2000 L for every 15 days. practically it si working in our lab. -
Google "Electrolytic Foam Flotation Harvesting". I found this discussion on Yahoo last year, tried it and it works a treat. It works like DAF (Dissolved Air Flotation). If you look through the discussion at Yahoo you will see some pictures of experiments with electrolytic foam flotation harvesting. I have used 2 stainless steel perforated plates with either 20 volts or 50 volts DC connected. The DC was from a bench top power supply I have used it with containers up to 160 litres. The only downside is the algae cake on the water surface is very frothy, however the initial cost is quite small and it doesn't use much electricity on small scale setups.
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Dear Trevor Honeychurch,
Filter paper/cloth of small pores can't be used for large culture volume. it will block the pores. you can follow the below steps.
50 lit culture can be easily harvested by gravitational settling. Please use narrow bottom container and add your culture night and allow it without distraction. Next day morning you will fine clear supernatant and settled biomass down. Carefully remove the supernatant and left with maX 1-2 lit of thick biomass (50 lit culture volume now reduced to 1-2 lit, now you can go for drying or further down streaming process).
If you find working/not working please do let me know. -
Dear Arumugam,
The system I have mentioned does not need filter paper. The algae floats to the surface where you simply scrape it off. I grow Scenedesmus and as you say it will sink if left overnight, however if I'm in a hurry then electrolytic foam flotation harvesting is much faster. I can clear a litre of thick microalgae in 5 minutes.
P.S. I'm off for a holiday, so I won't be able to add any more comments for a week or so. -
I have been trying to carry out a Life Cycle Assessment of the cultivation, harvesting/drying, lipid oil extraction and lipid conversion through transesterification process into biodiesel. I am in need of inputs/outputs data for each of the processes. Could anyone with useful data help me out with such please? Regards. -
Well, trick is, how can one harvest tonnes of algae biomass from over 1 billion cubic meters of medium? Centrifugal sedimentation of these highly buoyant microorganisms is highly energy-intensive as it requires massive g-forces, hence rotor velocities. Is it really the algae one should be after? Or would one rather opt to isolate algal lipids - or starch - only? For a recent overview: http://pubs.acs.org/doi/abs/10.1021/ef3004569 -
Any chance you can send me a reprint so I don't have to buy the paper?
As far as your question is concerned, I favor culturing the algae using carbon dioxide and nutrients from the biodigester and then converting all of the algae (not just lipids) to biofuel using pyrolysis.
Peter Rubec, Ph.D. -
I would prefer HTC (aka wet pyrolysis) over pyrolysis: doi:10.1016/j.algal.2012.02.002. I do not see the added value of using both anaerobic digestion as well as pyrolysis. The downside may be: HTC generates coal... (known in the US as "clean coal", an oxymoron)
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I assume that by HTC you mean Hydrothermal Liquifaction? Are there any commercial sized units available for this?
Peter -
HTC stands for HydroThermal Carbonization, a process that produces biochar. As the process is exothermic, there is a significant loss in energy density in the obtained end-product (~25 vs. 50 MJ/kg for coal and methane, respectively). In case you have a lot of coal power plants installed, this energy loss is irrelevant but HTC simply wastes too much energy to regard it as sustainable solution. In my opinion.
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Centrifuges are suited to the separation of the particle sizes and concentrations found in microalgal suspensions and have been widely used to separate microalgal for non-fuel uses, but may have too high an energy consumption to be suitable for the production of algal biofuel. The energy to harvest micro-algal by disc stack centrifuges I have briefly discussed in an open access journal article: Milledge, J.J. & Heaven, S. (2011). Disc Stack Centrifugation Separation and Cell Disruption of Microalgae: A Technical Note. Environment and Natural Resources Research, 1, (1), 17-24. http://www.ccsenet.org/journal/index.php/enrr/article/view/12590.
The most energy efficient method of harvesting may not be part of the most overall energy efficient micro-algal biofuel production process. The most energy efficient micro-algal biofuel process could consist; of a growth system that does not give the maximum yield, but results in a more easily harvested micro-algae and an energy extraction process that requires the minimum concentration by the micro-algal harvesting method. If efficient harvesting is, as many researchers consider, the major challenge of commercialising micro-algal biofuel it will have a considerable influence on the design and operation of both upstream and downstream processes in an overall micro-algal biofuel production process.
Hydrothermal treatments that produce syngas, bio-oil or char have the advantage of using wet material, but the energy to raise the wet material to the required temperatures and pressures can be considerable. Lack of production of char is generally considered to be an advantage of hydrothermal treatment as bio-oil can have a greater commercial potential than both char and syngas and the application of hydrothermal carbonisation for biofuel production may therefore be more limited than hydrothermal liquefaction.
Biogas from the anaerobic digestion of micro-algae also has the advantages that wet biomass can be used and the potential to exploit the entire organic biomass for energy production and use lower temperature than encountered with hydrothermal treatments Some of the earliest studies on extracting bioenergy from micro-algae examined anaerobic digestion. Unfortunately current biogas yields from the anaerobic digestion of micro-algae are considerable below theoretical maximum, but if we can improve practical AD yields it could be part of the solution to producing biofuel from micro-algae. -
@John: have you ever correlated microalgae lipid content with algae density? Apparently, some miocroalgae species tend to accumulate lipids during nitrogen starvation, I guess this will affect algae buoyancy but I've never seen actual numbers and/or studies. In the recent meta-study that I published on a microalgae to biogas scenario, it soon became evident that microalgae AD is far from established technology - it is yet to resolve important issues such as sodium and ammonium accumulation or algae degradation. The downside of any microalgae to biofuel process is still the high catalytic content of these algae, i.e. proteins and their "precursors" RNA/DNA. Algae obviously need these enzymes to thrive but it also dictates high nutrient demand and their accumulation during down-stream processing. From an ecological foodweb point of view: microalgae are eaten by shrimps, not by fish. As primary consumer it is apparently impossible to harvest enough microlagae for a fish to live on. This obvious problem of biomass dilution in water is not encountered on land, such as grass.
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The density of micro-algae is close to the density of salt water and therefore there is little density difference driving micro-algal settlement, flotation or centrifugation The cytoplasm of marine micro-algae has a density between 1030 and 1100 kgm-3(Smayda 1970). The average density of carbohydrate is 1500 kgm-3, protein 1300 kgm-3 and lipid 860 kgm-3 (Reynolds 1984) and micro-algae with a high lipid content may settle less readily due to the lower density.
Reynolds CS (1984) The ecology of freshwater phytoplankton. Cambridge University Press, Cambridge
Smayda TJ (1970) The suspension and sinking of phytoplankton in the sea. In: Barnes H (ed) Oceanography and marine biology annual review, vol 8. George Allen & Unwin, London, pp 353-414 -
The Pacific Northwest Laboratory of Dept of Energy developed a process called Hydrothermal Gasification. It uses catalysts to convert wet biomass (such as plant material or algae) to methane with about 98% efficiency. Genifuels presently owns the marketing rights to this process, which they claim is ideal for the conversion of algae to methane.
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Conventional biomass gasification processes require a dry feedstock (Guan et al. 2012a), but supercritical water gasification (SCWG) is an alternative gasification technology for the conversion of high moisture biomass and it is suggested it can be net energy positive in a well-engineered systems (Guan et al. 2012b). The enthalpy change needed to take ambient liquid water to a low-density supercritical state (400C and 250 bar) is similar to that required to vaporise liquid water at ambient temperature, but the advantage of the SCWG process is that much of the energy invested in reaching the supercritical state can be captured and used again with the hot effluent from the gasification reactor being used to preheat the wet biomass feed stream (Guan et al. 2012a).
Experimental studies on supercritical water gasification at 550°C of Nannochloropsis found the energy conversion of biomass to syngas of up to 60 % (Guan et al. 2012a). Unfortunately a recent review has concluded that there is little data available on the gasification of micro-algae and in particular the energy balance and the need for drying of micro-algae prior to gasification (Brennan and Owende 2010).
Brennan L, Owende P (2010) Biofuels from microalgae--A review of technologies for production, processing, and extractions of biofuels and co-products. Renewable and Sustainable Energy Reviews 14 (2):557-577. doi:DOI: 10.1016/j.rser.2009.10.009
Guan QQ, Savage PE, Wei CH (2012a) Gasification of alga Nannochloropsis sp in supercritical water. J Supercrit Fluids 61:139-145. doi:10.1016/j.supflu.2011.09.007
Guan QQ, Wei CH, Savage PE (2012b) Kinetic model for supercritical water gasification of algae. Phys Chem Chem Phys 14 (9):3140-3147. doi:10.1039/c2cp23792j -
Dear Aydin,
If you want to harvest algae for research purposes, a lab centrifuge is obviously too small for 50 L of culture broth. We use a centrifuge used for de-fatting milk. They sell these small centrifuges for small goat farms for a decent price (about 500 euro) and they work well.
Alternatively, you could first concentrate Chlorella by flocculation and sedimentation. Chitosan would work well, but you could also try by increasing pH to about 11. All cells should be at the bottom of your container half an hour later.
regards,Koenraad -
Genifuel Inc (not Genifuels) uses the process called Catalytic Hydrothermal Gasification (CHG). There are papers published on this by Dr. Elliot of DOE Pacific Northwest Laboratory. This process can convert wet algae (about 15 % moisture) to methane and carbon dioxide (about 60 to 40 ratio).
I am not sure what you mean by supercritical water gasification.? Does this work with wet algae or dried algae? -
There is a great clip on supercritical fluids on youtube
http://www.youtube.com/watch?v=yBRdBrnIlTQ
