Biosolids from treated sewage could be used as bricks

Answering the call of nature is, well, natural. The end result of going to the toilet regularly, however, is copious amounts of so-called biosolids, which is left after sewage sludge is treated.

In the U.S., a country of 330 million people, upwards of 7 million dry tons of biosolids are generated annually at the 16,500 or so municipal wastewater treatment facilities. In the E.U. another 9 million tons are produced. Of all that vast volume, about 55% is turned into fertilizers, but another 30% of these biosolids gained from sewage treatment is left unused, ending up in stockpiles where millions of tons of biosolids are stored.

A team of researchers from Australia’s RMIT University has come up with a new use for these unused biosolids: turning them into bricks. Doing so would be “a practical and sustainable proposal for recycling all the leftover biosolids worldwide,” they explain in a new study.

That way not only could leftover biosolids be put to good use, they argue, but we would also help reduce the environmental impacts of brick production.

“The annual production of 1,500 billion bricks globally requires over 3.13 billion cubic metres of clay soil — equivalent to over 1,000 soccer fields dug 440m deep or to a depth greater than three times the height of the Sydney Harbour Bridge,” the researchers explain. “Utilisation of only 15 percent of biosolids in brick production would reduce the carbon footprint of brick manufacturing whilst satisfying all the environmental and engineering requirements for bricks.”

If treated human feces, in the form of biosolids, are mixed into bricks with at contents of up to 25%, the resulting bricks have proved strong enough while at the same time biosolid-fortified bricks are more porous than traditional bricks, which makes them better as insulators by letting less heat escape.

Better yet: it requires less energy to fire a brick made with biosolid, which could lower carbon footprints from brick manufacturing. If 15% of biosolids were used in 15% of brick production worldwide, we could recycle all the 5 million tonnes of leftover biosolids produced each year in the U.S., the E.U., Australia, New Zealand and Canada, the researchers say.

“Using biosolids in bricks could be the solution to these big environmental challenges,” explains Abbas Mohajerani, an engineer at the university. “It’s a practical and sustainable proposal for recycling the biosolids currently stockpiled or going to landfill around the globe.”