Bricks from bacteria

Materials World magazine
,
1 Jul 2010

Bricks, grown at room temperature from bacteria, sand, and urea,
could drastically reduce the construction industry’s carbon footprint,
their developer claims.

The bio-manufactured bricks, created by Professor Ginger Krieg Dosier,
at the American University of Sharjah in Abu Dhabi, UAE, are produced
by layering sand with Sporosarcina pasteurii, a non-pathogenic common
soil bacterium naturally found in wetlands.

The bacteria are mixed with a solution of urea and calcium chloride.
They use urea as a source of energy, producing ammonia and carbon
dioxide, increasing the pH level of the solution, says Dosier. The rise
in pH forms a mineral precipitate, combining calcium chloride with
carbon dioxide. The bacteria can then act as nucleation sites,
attracting mineral ions from calcium chloride to the cell wall, forming
calcite crystals. The mineral growth fills gaps between the sand
grains, cementing them.

Rather than being fired in a kiln, the chemical reaction dries and
hardens the material at temperatures of 20-30ºC, reducing energy costs.
Dosier claims that the resulting material is as strong as a fired clay
brick.

Wetting, drying, freeze-thaw and abrasion resistance tests are yet to
be conducted, as is a comparison with un-fired clay bricks in terms of
their eco-credentials.


Up to now, the process has only been tested using sand from the UAE,
but Dosier is keen to test aggregates from other countries for
compatibility with the bacteria. ‘These soils will include small
percentages of clay’, she explains, ‘But they will need to be
specifically graded for this process as fine particles will block
[bacteria] penetration.’

While the new brick presents countless design possibilities, there are
hurdles in terms of large-scale production. Firstly, this process is
slow (taking one week to dry and harden) and, secondly, the chemical
processes release ammonia and a small amount of carbon dioxide.
Microbes convert the ammonia to nitrates, which can poison groundwater.
To solve this problem, Dosier plans to design a system that will
capture emissions and recycle them back into the production cycle.

Pete Walker, Professor of Innovative Construction Materials at the
University of Bath, UK, sees promise in the work, but recognises there
is still plenty of research to be done.

‘A rigorous lifecycle assessment [is needed] to make sure there are no
hidden negative environmental impacts,’ he says. ‘But perhaps the
biggest concern relates to any potential health risks. What happens if
not all the bacteria is converted or activated in the chemical process?
Are these bacteria going to cause any concern to the structure of the
building or its inhabitants?’

Walker also insists that the technique has to be economically viable
before it can make its way into industry, and these biological bricks
currently cost over five times the amount of one made from clay
(US$2.70 per bio-manufactured brick compared to US$0.5 for a
traditional clay brick).

Dosier says she is working to address these issues, and is looking for industrial partners to take the work further.