introduce me a good subject

2 Answers

1. 

   donmichael 4 months ago #

   You have four basic tenants of the overall system. I will list the currently considered methodologies for each.
   
   Waste (nutrient) Capture System:
   
   There is little need for research in this area but the separation of certain compounds in flu gasses and waste water may be good for future applications.
   
   Growth Systems:
   
   1) Pond Systems -
   
   Good because of low construction cost and holds more water in less space, but there is a problem with light exposure so the culture has to be continuously churned and this is energy intensive. There is also a problem with culture densities where the denser the culture the less penetration of light therefor slower growth rates.
   
   However, a mixotrophic species may store more oil when faced with this condition. In denser cultures where light is limited the alga will increase lipid production in order to float to the top to reach sunlight. This also facilitates the floatation of a whole biofilm of lipid ripe algae.
   
   Another problem with pond systems is contamination of invasive airborn species of competitive algae and temperature control. Both of these can be adressed in a couple of ways. One is to cap the pond with a greenhouse or geodesic dome.
   
   Another is to grow a community of bacteria and algae species that share a symbiotic relationship. Both of these should be combined. Find a species of algae that you want that survives warm conditions and a desired beneficiary that survives best in cold conditions. The same goes for dark/light (phototrophic/mixotrophic/heterotrophic) species and also for better consumption of certain nutrients as well as protection from invasive species. The study of algae/bacteria communities is a fairly new one and least considered but probably the most promising for the growing aspect of the algae industry because most companies are trying to grow pure cultures and this is showing to be problematic.
   
   
   2) Closed Photobioreactors -
   
   Growing algae in clear tubes is currently the most widely used method. More expensive than ponds but still failry cheap.
   
   The closed tubes protect against contamination and help with temperature regulation. The algae still need to be mixed and suspended in the culture to reach maximun light exposure therefore the water must be continuously pumped.
   
   Tempured glass tubing is better for insulation and light exposure than plastic tubing but is more expensive. The differenses between these types of tubing material would be a good research project. The glass is more expensive but since it insulates better the cost of temperature regulation is lower. It would be good to know the differences in pricing over the long term.
   
   Since the bioreactor is closed, nutrient rich air must also be pumped through the water. Typically co2 laden air is pumped into the bottom areas of the reactor so the air bubbles will float to the top through the water, giving the algae more time to sufficiently absorb it. The best thing about this system is the free source of energy from the sun. The continuous circulation of algae water allows all the alga cells to reach the sun. However there is still an issue of culture density. Currently it takes about 100 gallons or more of water to harvest one gallon of vegitable oil.
   
   
   3) Heterotrphic Fermentation (dark growth)
   
   Some algae can grow in the dark and some algae can grow in both light and dark and there are some algae that grow in the light only, but will increase lipid content when sunlight is not available while also being fed sugar as the subsitute for light. Growing algae in the dark while force feeding them sugar causes a rapid increase in lipid production in all kinds however. In this condition sunlight is not needed for oil production or growth and therefor the densities of the culture can be significantly increased. This means more oil in less water and there has been reports from the field claiming production rates of 1000 times higher per unit of water.
   
   The problem with denser cultures is slower growth rates. This doesn't correlate with lipid production however. This means that while the algae grow slower they are in fact using more nutrients and space for oil production rather than biomass growth and reproduction.
   
   There is a dance between growth, reproduction, and oil production rates that need to be addressed in the industry still. So I am working on a system that combines both phototrophic and heterotrophic growth methods. A problem with dark growth tanks are the need for large supply of sugars to feed the algae in the dark but algae also produce sugar from the sun, so I am looking for ways to harvest sugar from an algae species grown in the sun so I can provide the same species of algae (grown in the dark) with an endless supply of sugar from the sun.
   
   Another key point about algae grown in dark conditions is that when algae switch from light growth to dark growth they also switch from oxygen release to hydrogen release which can then be harvested for electricity. Depriving algae of sulfur also acts to increase hydrogen production. The dynamic between hydrogen, sugar and oil production from algae all at the same time needs extensive research.
   
   Harvesting:
   
   Dry harvesting: Good for attaining a solid biomass. This is only good when you want to get all of the biomass out of the water. This is only necessary if you want the cellulose, protein, carbohydrates and lipids all the same. You can either sell the biomass or separate the components first then sell them or process them into various end products. Drying algae is very energy intensive and all possible forms of waste heat should be used.
   
   Wet Harvesting: The best method because it employs a continuous live harvest method that doesnt kill the algae. Instead the desired component (oil or sugar) is continuous "milked" from the algae while it is still in the water. This allows the algae a longer life and better reproduction and oil production rates from each cell. Some methods for live extraction include electrolysis, ultrasonic cavitation or using natural conditions. Nanoparticles (tiny sponges) can be used to suck the oil out of algae as well.
   
   Processing into the various products is next but the most common method for deisel production is transesterfication. Pyrolysis and hydropyrolysis are also being used right now. There are many other methods but these to my knowledeg are most common or most promising. I hope this helps!

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2. 

   bioreactor 3 months ago #

   I suggest you to investigate about hydrogen production by microalgae. I think that can be a newfangled thesis topic.

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