As wastewater networks in the U.S. continue to age, concerns about the overall integrity of the nation's treatment plants and piping systems have grown more pressing. An article in Water & Wastes Digest estimated more than $30 billion in corrosion damage occurs within wastewater handling systems each year, a cost that is expected to rise moving forward. Part of the problem is that most wastewater treatment plants were built using concrete and metal, materials which are highly susceptible to corrosion and require perpetual maintenance to remain operational.
"More than $30 billion in corrosion damage occurs within wastewater handling systems each year."
As wastewater flows through piping, transfer lines, tanks and process equipment, the metal components become degraded through natural electrochemical reactions, such as reduction-oxidation. Over time, these reactions create weak spots on the metal's surface, leading to greater vulnerabilities in the network's infrastructure. Because these treatment plants and handling systems often process highly volatile liquids, corrosion response is always an ongoing process. But the frequency of major incidents seems to be speeding up.
Corrosion devastates major Louisville sewer pipe
In April 2018, workers in Louisville, KY, found that corrosive gases had eaten away at the concrete lining of an important sewer pipe. According to a local radio station, WFPL 89.3, the affected pipe is responsible for carrying around 40 percent of Jefferson County's wastewater. In total, the repair efforts lasted just over eight months and cost the city about $20 million dollars. Repair crews were forced to pry up part of Main Street in downtown Louisville to fully fix the problem, which caused substantial traffic congestion for several months.
"When we started the work in August, we actually had an enormous void under Main Street," Tony Parrot, Executive Director of the Metropolitan Sewer District, told WFPL 89.3 in regard to the repair efforts. "It was about 50-foot wide, 60-foot long, 25-foot deep void."
This incident represents a broader trend with the city's aging sewer system, as wastewater overflows have been polluting Louisville waterways for some time. In response, federal officials have issued a consent decree which mandates the complete repair of the city's sewer system by 2024.
Treated sewage spills into Barnegat Bay due to corroded piping
On October 9th, officials from the Ocean County Utilities Authority discovered a failure with one of the local treatment plant's wastewater outfall pipes, located close to the Bayville section of Berkeley, NJ. Upon initial inspection, utility investigators found that a hole in the steel piping had caused treated sewage to leak into Barnegat Bay for almost six weeks. In an interview with the Asbury Park Press, a spokeswoman from the New Jersey Department of Environmental Protection mentioned that initial measurements showed the 1-inch cavity was leaking at a rate of 50 gallons per minute. OCUA officials believe the leak was the result of corrosion within the aging wastewater infrastructure, though investigations are still ongoing.
While environmental protection officials and utility regulators do not believe this leak is a threat to public health, they have been quick to point out that similar incidents have plagued the wastewater system in the past. Between 2003 and 2006, four near-identical leaks were repaired in the same network. Keith Marcoon, Executive Director of the OCUA, reassured the public that the leak was sealed on Nov. 20 and repairs are currently underway. The outfall pipe is buried beneath 7 feet of seabed, requiring an extensive excavation process to fully address the pipe's corrosion problem.
Wastewater treatment experts deploy a number of methods to control corrosion, such as cathodic protection systems. But to address these incidents in the future, experts must conduct thorough corrosion testing and environmental testing to ensure the materials are more reliable in the long term.