The animals that make up corals are anthozoans, a class of invertebrate within the phylum Cnidaria, which includes a diverse assortment of creatures like jellies, hydroids, and sea anemones. In this mostly marine and entirely carnivorous club you can either float or anchor yourself to a surface, and many do both within their lifespan.
When corals anchor themselves, they do so as attached polyps in large colonies, and they do it by using calcium carbonate, or lime, as a cement. The Great Barrier Reef along Australia's northeastern coast is a huge collection of these colonies, built on the 10,000-year-old ruins of their ancestors' exoskeletons.
Their method for building their homes is worlds away from the way humans have been making cement and concrete, but one company has developed an innovative method for using seawater (which corals also utilize to make calcium) to both make cement and sequester carbon dioxide. But first, we'll look at how corals make their homes.
Coral reef communities in general, and coral polyps in particular, exhibit that characteristic so common in these crowded, diverse environments: interdependence. When real estate is expensive, you find a way to make a living (ask any of my fellow Californians). Stiff competition makes for some pretty creative methods, however, and often they include the mutually beneficial relationship called symbiosis.
The carnivorous corals can't go it alone so they have co-evolved with an algae boarder, a paying house guest who supplies most of their energy needs through photosynthesis. The algae are there for the same reason as everyone else: clear, calm and relatively warm water. For their tithing of sugars they receive the shelter and protection of the corals' limestone fortress. They also receive a daily nutritious dose of nitrates and phosphates from the corals' waste. While this mutualism is beneficial to both parties, it isn't entirely unforced. The corals excrete a digestive solution that causes the algae cell walls to leak their precious food. It's estimated that 80 percent of the algae's sugars go to the corals. An entire ecosystem is based on this relationship that translates the energy of the sun into the building of a massive underwater world.
Corals are extremely sensitive to small changes in the magic formula that makes up their habitat. Even slight changes in temperature, salinity, light and nitrogen can kill them outright. It has been estimated that half of the world's reefs could die out within 50 years. How we reduce and reverse the air pollution that is causing climate change will be critical to the survival of these shallow seas ecosystems. Ironically, the corals themselves may provide part of the answer for us.
Unlike their human counterparts, anthozoans don't make their cementitious homes by mining fossil rock. They don't grind it up, cook it to over 1,450 degrees C and then pound the baked material back into a pulverized dust. No, they just take in plain seawater, and precipitate out calcium and magnesium at normal temperatures and pressure. The calcium is turned into a crystal form of carbonate called aragonite. They secrete this lime out a little at a time while they are multi-tasking with other things like gathering food and having sex. No worries.
I think we could use some pointers from our salty friends, especially since cement production is the third largest source of GHG emissions in the U.S., according to the U.S. Environmental Protection Agency. The $11.9 billion industry produced approximately 110.3 million metric tons of cement in 2007, from 116 plants in 36 states. Yearly global production of cement dwarfs this figure: it is reckoned by the Portland Cement Association to be approximately 1.25 billion metric tons, with much of it spurred by development in China and India. Sobering indeed, when you consider that every ton of cement produced is matched by another ton of carbon dioxide (CO2) put into our atmosphere. Happily, there are some companies that are developing ways to make cement production more like the coral's methods.
The Calera Corporation operates a small facility on the central California coast that is testing some of these biomimetic processes. Located next to the Moss Landing Power Plant, the facility has been making small batches of cement by processing CO2 gas through seawater to make first carbonic acid and then carbonates. Their process is proprietary and in patent development, but, if successful, could revolutionize how we make cement and, perhaps more importantly, how we capture and sequester carbon.
It is an elegant scheme: Take a waste product, CO2, that is so damaging but ubiquitous that governments like the state of California are forced to regulate its reduction. Use this waste as a feedstock, process it through the most abundant substance on earth, seawater, and produce a material that not only can be used for building but permanently entombs the offending carbon. To power part of your processing use the free waste heat from the power plant itself. When you are done, return the unheated, unpoisoned seawater back safely, or pass it on as a pretreated (and money saving) stock for desalinization.
As an example, the Moss Landing plant is a gas-fired electricity generating facility that produces about 1,000 megawatts of power. While it is doing this it is also pumping out about 30,000 parts per million of CO2 into the air. Calera claims that it can capture most of this carbon and sequester a half-ton of carbon for every ton of cement that it makes. Company officials are currently describing their product as a supplementary cementitious material admixture, rather than as a replacement for Portland cement. It is being promoted as a replacement for fly ash, which can be increasingly hard to obtain, and as a better performing portion of a greener concrete mix when 50 percent recycled materials are specified.
The eventual possibilities sound a lot like the interdependent material cycling in coral colonies that we have just discussed, and the industrial ecology practiced in Kalundborg, Denmark. There, for instance, the city's power plant shunts several by-products to waiting, intentionally located industries, including “waste” heat, fly ash, heated seawater, and gypsum (another ingredient, by the way, in Portland cement). A similar symbiotic arrangement of power plant, carbon capture cement plant and desalinization plant seems worthy of study.
This process holds even greater promise for what the U.N. Intergovernmental Panel on Climate Change considers a critical option for reducing climate-changing air pollution: Carbon capture and sequestration. Most any power plant will do as a source of stock; in fact, the dirtier the better. We have a wealth of this waste-turned-resource in the United States. Approximately 2.5 billion metric tons of CO2 were produced in 2006, by 2,775 power plants. Of these, 600 were coal-fired plants that spewed 5 times more pollution (or should we say grey gold?) than the Moss Landing operation. The Calera process would take sequestration one step further by recycling the carbon into a very useable and worthwhile product.
Since Calera potentially provides at least three benefits, pollution abatement, seawater treatment and cement production, the company seems to have the opportunity to engage in several separate markets. This may offer the chance to be as innovative at the business table as at the manufacturing plant. Indeed, a recent article in the Harvard Business Review noted that the company was considering giving the cement away for free while making its income from carbon capture. Whatever their eventual business model, I'm sure the anthozoans will be pleased at their success.
Tom McKeag teaches bio-inspired design at the California College of the Arts and University of California, Berkeley. He is the founder and president of BioDreamMachine, a nonprofit educational institute that brings bio-inspired design and science education to K12 schools.
Coral photos - horizontal by http://www.flickr.com/photos/hamed/ / CC BY 2.0; verical by http://www.flickr.com/photos/robertpaulyoung/ / CC BY 2.0