Emit­ting bricks: Hu­man waste can be en­gi­neered into build­ing ma­te­ri­als

Las Vegas Review-Journal - - | NEWS & PUZZLES - By Joanna Klein New York Times News Ser­vice

De­pend­ing on the amount of biosolids used, how they were treated and how long they sat around, the biosolid bricks were safe, durable and in some ways en­ergy ef­fi­cient.

It may be un­pleas­ant to con­tem­plate the ul­ti­mate fate of all the ma­te­rial from your own body that you flush down the pipes. But it’s time we talk about biosolids — the dis­in­fected left­overs from the wa­ter treat­ment process.

This sandy ma­te­rial con­tains nu­tri­ent-rich or­ganic con­tent that’s good for agri­cul­ture. But it also makes nice bricks, ac­cord­ing to Ab­bas Mo­ha­jerani, a civil en­gi­neer at Royal Mel­bourne In­sti­tute of Tech­nol­ogy Univer­sity in Aus­tralia. He’s talk­ing about the kind we use for build­ing.

“Biosolids bricks look the same, smell the same and have sim­i­lar phys­i­cal and me­chan­i­cal properties as nor­mal fired clay bricks,” he said.

And as long as it’s done lo­cally, he thinks that re­cy­cling stock­piles of left­over biosolids into bricks could save land and en­ergy, and re­duce car­bon emis­sions.

World­wide, hu­mans pro­duce vast quan­ti­ties of biosolids. In a sin­gle day, New York City alone makes 1,200 tons, or about 50 truck­loads. And the amount of biosolids is grow­ing as pop­u­la­tions ex­pand around the planet.

The old so­lu­tion was to dump them into the sea or a land­fill. But more treat­ment plants and stricter reg­u­la­tions are prompt­ing peo­ple to find clever ways to re­cy­cle the dried sludge. About 50 to 70 per­cent of it is now used, mostly to boost soil qual­ity or fer­til­ize crops. But the rest re­mains un­used or stock­piled. In the United States, it’s es­ti­mated that nearly a third of the 7 mil­lion to 8 mil­lion tons of biosolids pro­duced each year still end up in land­fills. As or­ganic par­ti­cles in the waste de­com­pose, green­house gases such as car­bon diox­ide es­cape and can con­trib­ute to global warm­ing.

And then there are bricks.

The world makes tril­lions of them each year. The soil it takes to make them is enough to fill 1,000 holes, each as big as a soc­cer field and nearly as deep as the Em­pire State Build­ing is tall. And it takes a lot of en­ergy, too.

Other re­searchers have tried mix­ing bricks with biosolids and other waste prod­ucts. Mo­ha­jerani had ex­per­i­mented al­ready with cig­a­rette butts. So turn­ing waste into a build­ing ma­te­rial didn’t seem so far-fetched.

Over the course of half a decade, he and a team of re­searchers col­lected biosolids from two waste­water treat­ment plants in Mel­bourne and mixed them with soil to make hy­brid bricks of vary­ing pro­por­tions. They fired them for 10 hours, at nearly 2,000 de­grees Fahren­heit, and cooled them, then com­pared them in tests to nor­mal bricks.

The team’s find­ings, pub­lished this month in the jour­nal Build­ings, ranked the biosolid bricks sim­i­lar in qual­ity to those cur­rently on the mar­ket. And the re­searchers pro­posed that in­cor­po­rat­ing just 15 per­cent biosolids into all the bricks made around the world each year would elim­i­nate all of our left­overs.

De­pend­ing on the amount of biosolids used, how they were treated and how long they sat around, the biosolid bricks were safe, durable and in some ways en­ergy ef­fi­cient.

Be­cause or­ganic ma­te­rial burns up when placed in a fur­nace, biosolid bricks re­quire as lit­tle as half the en­ergy to fire as nor­mal bricks do (de­pend­ing on how much or­ganic ma­te­rial is in the bricks). The burned or­ganic ma­te­rial also leaves be­hind spa­ces in the biosolid bricks, mak­ing them lighter, more por­ous and filled with gas. And be­cause gases are poor ther­mal con­duc­tors, heat passes through biosolid bricks more slowly. That makes them bet­ter in­su­la­tors, which could re­sult in sav­ings on heat­ing and cool­ing costs, Mo­ha­jerani said.

But the trade-off is strength. Although biosolid bricks met in­dus­try re­quire­ments, they were typ­i­cally not as sturdy as reg­u­lar bricks.

In a re­lated anal­y­sis of the po­ten­tial pro­duc­tion process, the re­search team de­ter­mined that mak­ing bricks with biosolids would be bet­ter for the en­vi­ron­ment over­all, even though biosolid bricks re­quire more wa­ter and could pro­duce other forms of pol­lu­tion.

To limit the car­bon foot­print and en­sure sus­tain­abil­ity, brick pro­duc­tion ide­ally would take place close to treat­ment plants and biosolids stock­piles, Mo­ha­jerani said. “Other­wise, I don’t think it is likely on a large scale in the near fu­ture.”

RMIT UNIVER­SITY VIA THE NEW YORK TIMES

Ab­bas Mo­ha­jerani, a civil en­gi­neer at Royal Mel­bourne In­sti­tute of Tech­nol­ogy Univer­sity in Aus­tralia, holds a brick made with biosolid waste, or treated waste­water sludge. Con­vert­ing biosolids into build­ing ma­te­ri­als could keep a lot of left­overs of the waste process out of land­fills, and pro­vide other en­vi­ron­men­tal ben­e­fits, too.

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