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The Salt That Could Save the World's Sewers from Crumbling

A simple change in water treatment could be key to saving important infrastructure—and could save billions of dollars annually.
August 14, 2014, 7:40pm
Image: Flickr/Ben Salter

Our sewer systems are, quite literally, crumbling.

Most of the underground networks that haul away our waste and protect cities from (most) diseases and (some) bad odors are now more than 100 years old and cost the U.S. about $14 billion in maintenance every year.

The primary culprit is hydrogen sulfide found in wastewater, which forms sulfuric acid when exposed to air and corrodes concrete sewer pipes. This sulfide problem is nothing new and waste management services spend a lot of money to remove the acid after it forms and repair the pipes, but new research says that the problem could actually be prevented during the water treatment process, and that replacing and repairing the pipes isn't actually necessary.


A study published today in Science by Zhiguo Yuan of the Advanced Water Management Centre at the University of Queensland suggests that by simply changing the sulfates, or salts, used to clean drinking water, water treatment plants could preemptively prevent sewer corrosion.

All water naturally contains some amount of sulfate from the environment, but water treatment plants add aluminum or iron salts to coagulate and remove solids and other natural organic matter to make the water safe for drinking.

Yuan's two-year survey of drinking water and sewage in South East Queensland, Australia found that added aluminum sulfate accounted for 52 percent of all sulfate in the drinking water, an amount consistent with industry standards worldwide.

When the water reaches the sewer pipes, bacteria in the oxygen-less environment reduces the sulfate to hydrogen sulfide. The study concluded that this is the leading cause of sewer corrosion.

Simply switching to chloride-based chemicals, which many water utilities around the world are already using, could cut sewer pipe maintenance costs 30 to 50 percent, Yuan said.

The solution seems simple, but could be made tough by institutional barriers. Though water supply and water sanitation are all a part of one system, they are usually treated as separate utilities by the government.

"Such partitioning into 'clean' and 'dirty' water is not only administrative but fundamental and is found at all levels, from operators to research," Wolfgang Rauch, a professor at the University of Innsbruck, wrote in an accompanying Science article. Rauch suggested the research not only provides a solution to the sulfide problem, it also highlights the advantages of a more holistic view of urban water management.

"Understanding processes, interlinkages, and consequences in the complete urban water cycle allows identification of optimal solutions," Rauch suggested, pointing to how removing phosphates from laundry detergent over the past 30 years has helped decreased phosphorus in wastewater.

Unfortunately, cutting through red tape is usually easier said than done, and Rauch said that some other solution to the sulfide problem is likely to prevail.

"There is a long history of making wrong decisions in complex technical systems if the components are viewed in a segregated way," he wrote.

And making a wholesale change in how wastewater is treated is certainly dicey from a political, and, potentially, a public health standpoint. In other words, I wouldn't hold your breath waiting for things to change—bit-by-bit repair jobs probably aren't going anywhere anytime soon.