NEWS OF TH E WEEK
FIXING A SOURCE OF SEWER CORROSION CIVIL ENGINEERING: Switching water-
treatment chemicals could reduce sulfides that degrade cement pipes
The concrete pipes that make up sewer systems are being eaten by sulfuric acid.
ODAY’S UNDERGROUND sewer infrastructure
COURTESY OF ZHIGUO YUAN
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is the result of more than 100 years of investment. In the U.S., for example, the sewer system is now valued at an estimated $1 trillion. But that investment is under a chemical threat from sulfideinduced concrete corrosion, according to a research report. The problem is largely preventable by eliminating sulfate—the source of the sulfide—from watertreatment operations, the study’s authors say. The sewer sulfide problem has been around since sewers were first built, according to Ilje Pikaar, Keshab R. Sharma, and Zhiguo Yuan of the University of Queensland, in Australia. To better understand the current impact of chemicals on sewer pipes, the researchers performed a two-year sampling campaign along with a water-treatment industry survey and conducted a computer model scenario analysis (Science 2014, DOI: 10.1126/science.1251418).
WORMS INSPIRE NEW BIOADHESIVE ACS MEETING NEWS: Researchers
mimic wet adhesives made by sandcastle worms
ANDCASTLE WORMS are pretty good chemists.
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Without advanced degrees, they have figured out how to biosynthesize glue components they use to build their underwater tubular shelters. Inspired by the worms, Russell J. Stewart of the University of Utah and coworkers are creating similar adhesives that might be used to make in utero surgery safer or to block blood vessels that feed tumors. “It’s a classic example of borrowing successfully from nature,” comments biomedical sealants specialist Jeffrey M. Karp of Brigham & Women’s Hospital, in Boston. When doctors examine or perform surgery on developing fetuses, the amniotic membranes that protect fetuses in the womb can rupture. The membranes often fail to heal, so the procedures carry a significant risk of preterm delivery. Existing medical adhesives fall short in addressing this surgical problem. Some adhesives swell too much FRED HAYES/U OF UTAH
Two sandcastle worms’ heads poke out of tubular shelters (white) the worms build, while a third worm is temporarily tubefree.
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As Yuan and coworkers explain, anaerobic bacteria in biofilms and sediments reduce sulfate in sewage to hydrogen sulfide, which is bad enough because of its noxious odor and toxicity. But in sewers H2S is oxidized by aerobic bacteria on pipe surfaces exposed to air. The corrosive sulfuric acid formed eats away the calcium silicate-based concrete pipes at a rate of several millimeters per year. Water and human and industrial waste naturally contain sulfate, the researchers note. But about half of the sulfate in wastewater comes from aluminum sulfate or ferric sulfate added as a coagulant during water treatment to help remove colloidal solids and natural organic matter. By switching to sulfate-free coagulants, such as polyaluminum chloride or ferric chloride, much of the sulfide problem could be solved, Yuan says. Engineers estimate the average life span of sewers at 50 to 100 years, which leads to necessary annual investments of 1 to 2% of the replacement cost for repairs, note environmental engineers Wolfgang Rauch and Manfred Kleidorfer of the University of Innsbruck, in Austria, who wrote a commentary to accompany the report. “Any technological improvement that helps increase the service life of sewers by one year would save globally more than $1 billion per year,” Rauch and Kleidorfer say. Replacing sulfate in water treatment, they add, “is a simple source control measure that can at least counteract if not solve the sulfide problem.”—STEVE RITTER
when they cure and may cause further damage. Others “are ineffective in the flexible, moist, and biochemically active conditions of the human body or are acutely cytotoxic,” says Nick Aldred of Newcastle University, in England, who is an expert on barnacle adhesives. Stewart told a Division of Agricultural & Food Chemistry session at last week’s American Chemical Society national meeting that he hopes a sandcastleworm-inspired adhesive his group is developing will provide an effective alternative for existing adhesives. Sandcastle worms produce highly charged polyelectrolyte glue components and combine oppositely charged components enzymatically to construct their shelters. Obtaining the glue directly from the worms or producing it recombinantly hasn’t proved practical. So Stewart and coworkers instead synthesize oppositely charged polyelectrolytes and combine them to form water-immiscible polymer solutions called complex coacervates. They then apply the coacervates to biological tissues and cross-link them enzymatically to cure them into adhesives that bond to the tissues. The patented technique is in preclinical testing for use in fetal surgery. Stewart and coworkers “have made astounding progress in quickly moving from understanding the key concepts of wet adhesion by the sandcastle worm to the point where they are able to synthesize a polymer that mimics it,” said Anne Marie Power of the National University of Ireland, who studies barnacle wet adhesion. “It could address a real surgical problem.”—STU BORMAN
AUGUST 18, 2014
