Remember the story of the three little pigs? Only the brick house was strong enough to resist the big bad wolf’s huffs and puffs. Bricks and cement are strong and popular building materials used the world over. Unfortunately, the process to make them spews out lots of pollution. Now, scientists are learning how to make these construction materials more Earth-friendly with a surprising ingredient: poop. Â
In some cases, those feces come from grazing animals such as cows. Their manure is full of plant fibers. Recycling sludge — the material from sewage-treatment plants — also works. Sludge is processed human wastes. It gets removed as wastewaters are cleaned. Rich in nutrients, sludge and manure are sometimes used as fertilizers. But they also may contain infectious microbes or even heavy metals. And these can make safe disposal of those wastes a challenge. For various reasons, large quantities of sludge get buried in landfills each year.
All around the world, researchers are exploring different ways to not only keep sludge out of landfills but also to put it to good use. Some places burn the sludge, creating ash. This kills pathogens and reduces its volume, making its disposal easier.
But sludge and sludge ash are both rich in silicon, aluminum and calcium. These are ingredients used in making cement and bricks. Making construction materials with sludge could put this waste to use and keep it out of landfills. At the same time, it could reduce the pollution created by the standard processes used to make cement and bricks.
Sludgy cement
To John Zhou, dumping potentially useful sludge into landfills seemed a waste. He’s an environmental engineer at the University of Technology in Sydney, Australia. Sludge contains materials such as silica that function like cement, he knew. And cement is a key ingredient in the concrete used for sidewalks, walls, buildings and more. Concrete’s recipe includes cement mixed with gravel, sand…
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