A dozen sewage plants in Louisiana discharge sewage into the marshes. Is it helpful or harmful?

Jacob Groby is so confident in the quality of the wastewater treated by the Mandeville Wastewater Plant that on a recent Thursday morning, he stood next to a discharge pipe and shook his hands.

Water, which had only recently been flushed down someone’s toilet or run through their kitchen sink, pooled in his palms. He took a whiff.

“It doesn’t smell like a thing,” he said. “And it’s obvious.”

The plant, which filters “biosolids” from Mandeville’s wastewater, recently dodged a bullet.

A bill introduced by Rep. Rep. Kim Coates, R-Pontchatoula, would have forced the plant and others like it to undergo a costly upgrade. But after adjournment, the bill was amended to only require signage in the marsh noting that treated sewage is present, before it was sent to Gov. Jeff Landry’s desk. It became law this month without the governor’s signature.

Coates’ bill was introduced because not everyone shares Groby’s faith in the process Mandeville and about a dozen other plants in the state use to treat wastewater, which relies on a method somewhat unique to Louisiana called “wetland assimilation “. Adjacent natural wetlands, on the north shore of Lake Pontchartrain, are considered to be part of the treatment process. When sewage is discharged into the marsh, it still contains relatively high levels of nitrogen and phosphorus – plant food, basically – which act as fertilizer and promote plant growth.

Some environmentalists are concerned that treated sewage may have seeped through wetlands and into Lake Pontchartrain.

Conventional treatment plants have stricter standards for their wastewater and discharge directly into larger or cheaper waterways, such as rivers or lakes.

For supporters of the process, like Groby, who runs the plant as Mandeville’s utilities supervisor, leaving a little extra stuff in the wastewater is the whole point.

“The wetland serves as our speed bump for hurricanes,” Groby said. “And the general idea for the wetland project is to take the solids and nutrient-rich water for further growth of grasses and trees to reduce storm surges.”

It’s also cheaper than conventional wastewater treatment, “but that’s a secondary benefit,” said John Day, an emeritus professor of coastal sciences at LSU and founder of Comite Resources, a company that designs and monitors these types of plants. of treatment. “The thing about freshwater marshes … is that if you have salt water in them, they can collapse.”

The addition of fresh water from the treatment plant, according to Day, removes saltwater, which is increasingly invading the marshes due to sea level rise from climate change. As vegetation near the treatment plant grows, Day says, it removes planet-warming carbon dioxide from the atmosphere. Day thinks he can sell carbon credits based on that crop growth, which industry can buy to offset pollution.

For opponents, this process is stressing ecosystems that are already threatened by a variety of other stressors.

“A wetland can only take so much,” said Carlton Dufrechou, who once ran the Pontchartrain Conservancy and now heads the Causeway Commission. “You and I could tolerate a little whiskey. But if we put too much whiskey in our system, we won’t assimilate it.”

Coates told the House Natural Resources Committee that she has seen changes in the marsh into which the Hammond sewage treatment plant discharges, which uses the same process as Mandeville. A marsh she could once wade through has now “turned into open water,” she said. “We don’t need to dump it out there in natural wetlands.”

“I was taking pictures and I noticed that sewage was building up in some places,” said Ed Bodker, a longtime Ponchatoula resident who previously worked as an environmental program manager for the Louisiana Department of Transportation.

Over the years, he said, the swamp deteriorated. Day, whose company designed the plant, blames the marsh’s decline on the nutria infestation.

But, Bodker says, “None of [wetlands assimilation plants] they’ve kept their promises, as far as I can tell.”

Groby said redesigning his plant, as originally required by Coates’ bill, would have been expensive.

“We got a quick and dirty engineering estimate of what it would cost to meet Rep. Coates’ proposed bill,” Groby said. “25 million dollars.”

What happens after you fry

Sewage treatment plants usually work like this: First, they filter waste that is flushed down the toilet that cannot be treated. The sewage is then passed through a series of pools filled with bacteria that digest the organic matter, before being disinfected, either with chemicals or ultraviolet light.

Newer plants will filter plant nutrients before discharging treated wastewater into water bodies.

No other state in the U.S. has as many wetland assimilating plants as Louisiana, according to research by Taylor Sloey, a biology professor at Old Dominion University in Virginia.

“My biggest concern is: What is the long-term game here?” Sloey said. “Maybe they work well for 20 or even 50 years. But at some point, you reach a tipping point where the system is stressed and you can have environmental collapse.”

Outdated infrastructure

Louisiana has an aging wastewater treatment infrastructure. Many of the state’s wastewater treatment plants, whether they rely on wetland assimilation or not, are failing to meet federal and state standards.

“It’s probably about 50-50,” said Josiah Cox, CEO of Central States Water Resources, a company that buys struggling treatment plants in half the US. [wetlands assimilation plants] are really well maintained and doing great, and half of them aren’t.”

After Coates’ bill was returned by municipalities and others, including Day and Groby who testified against the bill, no significant changes to the plants would be required.

Signs posted around wetlands will read: “Caution: Treated Sewage Discharge.”