Saturday, December 17, 2011

In Search of the Green Helix

You know what sucks? 40,000 kids dying everyday as a result of inadequate nutrition. That sucks. Unfortunately, unless we start getting creative or stop reproducing so much, this horrendous statistic is only going to get worse. Our planet can only support so many people.

According to the Economist, the world’s population should stabilize around 9 billion. Not everyone agrees with this analysis, but even if this conservative estimate proves to be accurate, and we really should hope that it does, then that means adding another 30% to the 6 billion souls the earth is already struggling to support.

The reason we should be worrying (and many are) about this is because the finite resources on our little blue sphere are rapidly dwindling. If everyone consumed as much resources as the average American we would need about 2.5 earths, and the middle class in the developing world, and their desire for western luxuries is growing quickly. China is buying up huge swaths of arable land in Africa to help supply its 1.3 billion citizens with food but a great deal of the ‘Forgotten Continent’s’ land is also threatened by the creeping menace of desertification. Companies that mine potash, the base for most fertilizers, are seen as some of the best prospects around to invest in. Add to that the changing weather patterns and glacial melt that is caused by global warming and it starts looking like future wars might be fought over farm land and fresh water instead of oil.

So what do we do? One strategy that could help is to grow more edible algae. Specifically spirulina. A lot of you may already be familiar with this little green helix. Humans have been using it for over a millennia and it has been at health food stores in the US for decades. In spite of this it has yet to receive a true, large-scale following.
This is unfortunate because this incredible stuff is some of the densest complete protein you can get. It doubles its biomass every 2 to 5 days and provides 400 times more protein per acre than beef. It thrives in warm temperatures and can grow in high alkaline water (up to a PH of 11) and brine; environments where almost nothing else can survive. This means it can grow in deserts and coastal areas and, unlike most crops, does not require the clearing of any fertile land. Because of its high quantities of vitamins and minerals --particularly vitamin A, iron and zinc- when a group of 500 malnourished children in southern India received a supplemental tablespoon of spirulina a day for 150 days the prevalence in new cases of common eye disease dropped from 80% to 10%.

Goverments all over the world, particularly in Asia, started to recognize the algae potential as early as the 1970s and began large-scale, commercial production. Our lovely green friend, however, has yet to find more than a niche market in rich countries.

The government of India has set a good example in the developing world with an inter-departmental program, called the All India Coordinated Project on Algae. The AICPA is designed to encourage small-scale algae production across the country for both human and livestock consumption. The project is a start but it, along with the rest of the Indian agricultural sector, still has a long way to go before it reaches its potential. Even though the subcontinent has enough arable land to become a major food exporter, because of politics and lack a of resources, it is barely self-sufficient.

So, up in northeast India, we have decided to do our own small part to trying to help the situation. I am going to figure out a way to both grow spirulina and trap carbon!

The only issues to overcome are to figure out a way to pump CO2 through the water, circulate it enough to get the maximum yield of algae, and heat the water- the northeast is cold in the winter. Now, these wouldn’t be problems if we had money; you could just build a green house and buy CO2 canisters. But money is tight and the point of this project is to make a sustainable example that’s easy to replicate.

So my idea is to kill 4 birds with one stone. I want to use the exhaust from our 35 kW generator to heat the water, circulate it, provide the necessary CO2 and trap some of the carbon from the exhaust in the spirulina. My idea, which is still very much that, is to get a barrel of water, fill it with spirulina, snake a heat transfer pipe carrying the exhaust through the tank and bring the exhaust to a gas separator to isolate the CO2, then bubble it through the water. If the water is not circulated enough by the bubbles then I’m thinking to use a paddle wheel that is either powered by the generator itself or by the exhaust. I would use the exhaust by putting a spin-wheel in the tube; which would then drive a crankshaft to spin the paddle wheel. The carbon from the generators emissions would be trapped in the spirulina itself, which is 3 times as efficient at fixing carbon as a forest of equal area.

There are several hurdles in between me and my fully-functioning, model mini-spirulina farm. Probably the biggest is the gas separator. I have no idea if you can even make something that can effectively filter diesel exhaust, let alone how to build one. It’s also very important to get this part right as the algae absorbs everything you put in the water. A catalytic converter, if it’s not already in the generator, would help but would still leave me a long ways from isolating the CO2. The other problems aren’t so much whether or not I can do it, but how. I need to figure out how much water the exhaust can heat (the generator uses about 6 liters of diesel an hour), how best to position and shape the heat transfer tube and how to set up the tank itself. The problem there is that the more I insulate the tank the less sunlight it will get and visa versa. Spirulina needs a lot of sunlight and temperatures between 25C and 40C to grow. The generator is also in a brick shed so attaching the tank directly to the unit won’t work.

My formal education in physics stopped in high school, and in thermodynamics it’s non-existent, so I don’t even know where to start on figuring out the heat problem. Physics message boards require a greater understanding of the terminology than I have and, since I don’t have time to teach myself thermodynamics, I have enlisted the help of several of my elite network of physicist friends (made up of a very smart cousin and an equally gifted Beloiter). However, I am also appealing to you, the reader. If you or anyone you know has any knowledge that might help with this I would very much appreciate any guidance. I’ll even carve your name into the tank.

1 comment:

  1. Travis,

    I think you have a theoretically good idea, but to kill all the birds with your hypothetical stone is too expensive and technically challenging for your situation. I would suggest forgetting about the carbon sequestration and focus on growing the algae. I imagine the air quality in your area is pretty bad and will have enough CO2 that the algae (assuming it grows on the surface of the water) will absorb said CO2 from the air. Without knowing what kind of generator you have and the local atmospheric temperature, pressure, chemical composition and humidity, I can't do a detailed thermodynamic analysis of the system you describe. However, using the exhaust from the "geney" (generator) to warm the water would not be too difficult.

    For the tank you should try to get double-paned windows, with a vacuum or air between the panes. Try to find plastic panels instead of glass as plastic does not let heat pass as readily as glass. This will also allow light to enter your greenhouse assuming the plastic is colorless and transparent. If you don't have double-paned windows you could bury the tank with only the top surface exposed to the air above.

    To transport the exhaust through your greenhouse, you can use standard steel piping similar to the outlet on the muffler of the geney. Something you should be aware of, by routing the exhaust through more piping you will decrease the efficiency of the geney because you are altering the back-pressure to a non-optimal value. This means your fuel consumption will increase.

    To control the temperature of the water in which the algae will grow, i recommend installing a door on the exhaust pipe (i.e. a relief valve) that releases exhaust so that if the outside air temp changes you can adjust the amount of high-temp gas flowing through the pipes inside the greenhouse. You'll have to experiment with the door to achieve optimum water temperature.

    Increase the surface area of the pipe in the water to increase the heat transfer quantity to the water in the greenhouse tank.

    What sort of nutrients does the spirulina need to eat?

    I feel like I'm forgetting something to tell you, but I hope this helps. My email is if you have any more questions.