“It’s synthetic sandstone. All that’s happening is crystals are growing around sand grains.”
The way in which Professor Ginger Dosier describes her innovative process that has recently won the Metropolis “Next Generation” design competition is accurate, but perhaps slightly over-simplified.
I never ceased to be amazed by friendly bacteria. We may have an instinctively negative view of our super-abundant microbial colleagues, but many of them are really helpful, and we’d be in a bad way without them. Take, for example, the bacteria that munch on natural crude oil in ocean water or in sand; take the wondrous critter, bacillus pasteurii, that can turn sand into sandstone and heal cracks in concrete. And now here, although appearing under a different name, is bacillus pasteurii again.
Ginger Dosier is an architect at the American University of Sharjah, in the United Arab Emirates, but an architect with a difference: she is interested in designing her own building materials and thereby participating directly in influencing the performance of a building. She has chosen the most basic of building materials, the brick; as she comments, “Bricks are so humble, they are the lowest common denominator in architecture. Bricks were designed around our hands; one is used for holding the brick and the other for the trowel. I wanted something that would slip right into the system and the entire construction system would not have to be redefined.” And what she has done is potentially of huge importance, because bricks may be humble, but their manufacture consumes large amounts of energy and creates more atmospheric pollution than the entire aviation industry. A standard brick must be fired in a kiln at temperatures greater than 1000 degrees centigrade; making a couple of bricks generates more than a kilogram of carbon dioxide – and it’s estimated that perhaps 1.2 trillion bricks are manufactured around the world every year. Dosier’s solution is don’t bake the brick, grow it.
And this is where our old friend, bacillus pasteurii plays the leading role. Although the reports of the brick-making process describe the bacteria used as sporosarcina pasteurii, it would seem that this is just an alternative (stage?) name for bacillus pasteurii - why the microbiologists can’t make up their minds is beyond me, but there we are. Bacillus pasteurii, if treated right, produces calcite that can glue sand grains together (or mend concrete, for that matter); the process is referred to as microbial-induced calcite precipitation, or MICP. Treating the bacteria right requires feeding them which is where the urine comes in – urea [(NH2)2CO] can be made synthetically or from urine, and provides nutrition for the bacteria. Water is also necessary, as is calcium chloride.
The process for making a brick is relatively straightforward: put dry sand into a mould, add the cultured bacteria, water, urea, and calcium chloride, and wait for about a week – other than the 37 degrees centigrade at which the bacteria must be prepared, no heating is required. But it took Dosier two years to find the right proportions of materials, the right microbes, and the right chemistry, and her eventual success was another example of laboratory serendipity:
Then one afternoon, she threw together a bunch of scraps from some old, ill-fated tests, for kicks. Practically forgetting about it, she revisited experiment No. 112 a week later, only to discover that the medium had transformed into a “baby brick,” as she tells it, a four-by-two-by-one-centimeter proof of concept. “I was shocked to find that it had worked,” she says, “and glad that I took detailed lab notes.” The magic formula was in allowing the right concentration of bacteria to fester just long enough.
Currently, her bricks are small - about 3cm long, 1.5cm wide and a centimetre deep – but she’s working on scaling up. And scaling up to any kind of commercial mass production process is yet another, hardly trivial, step. But the potential is huge. Dosier contemplates the ability to program a brick’s exact composition and then “ fabricate it layer by layer on a 3-D printer. The technology poses countless design possibilities. Ball-shaped bricks: Why not?” (Metropolis).
But, as usual, it’s still not quite that simple:
Microbial-induced calcite precipitation spews tremendous amounts of ammonia, as scientists affiliated with Delft University of Technology, in the Netherlands, discovered recently when they tried the chemical process on contaminated sand and soil. “High ammonia concentrations result in environmental eutrophication and eventually, via microbial conversion to nitrate, the poisoning of groundwater,” the Delft researcher Henk Jonkers writes in an e-mail. If the bacteria continues to convert ammonia to nitrous oxide, he adds, it can produce a greenhouse gas 320 times more powerful than CO2.
Dosier is thinking about emissions capture in the manufacturing process, another complex and multi-disciplinary challenge, but she’s up for it: having come so far as an architect learning and working in different worlds, she deserves to succeed.