Tennessee WWTP Goes Chlorine-Free

After more than a year’s study into a new wastewater disinfection process, the Tullahoma Utilities Board (TUB) has received state approval to replace the chlorine used to treat the city’s wastewater with an organic disinfectant.

With that approval, TUB’s wastewater treatment plant has become the first in Tennessee to fully implement the use of peracetic acid.

Peracetic acid (PAA) – manufactured by adding hydrogen peroxide to acetic acid (the principal component of vinegar) – has been used for decades in the food and medical industries, but has only gained attention in the U.S. wastewater industry in recent years as water systems began exploring chlorine-free disinfection methods.

Since roughly 1910, the industry has relied on hazardous chlorine gas as a disinfectant because it reduces disease-causing microorganisms – in particular, E. coli – reliably at a reasonable cost; but it does not come without disadvantages.

Because chlorine residuals are harmful to aquatic life, regulations often require wastewater plants to dechlorinate prior to discharge. In Tullahoma, where wastewater effluent discharges into the low water flow of Rock Creek, dechlorination was essential.

Supervisor Jeff Totherow checks the newly installed peracetic acid pump at the Tullahoma Utilities Board’s wastewater treatment plant. TUB is the first in the state to replace its gaseous chlorine disinfectant with liquid peracetic acid.
– Staff Photo by Chris Barstad

“Our permit says that if you can detect chlorine in our discharge, we’re in violation. So we had to use another dangerous chemical, sulfur dioxide, to take the chlorine out,” said TUB Wastewater Department Manager Scott Young.  “Instead of having one highly dangerous chemical down there, we had two highly dangerous chemicals.”

Now, both of those dangerous gases have been removed from the plant in favor of liquid PAA, which reacts quickly and dissipates rapidly. And because it does not persist in the environment or affect effluent toxicity, it does not need to be removed as chlorine does.

“This system is just so simple,” said Young. “It’s literally just a little pump and a tank, where before we had masses and masses of equipment. And we were working on it all the time.”

The amount of time and money spent working on the plant’s chlorination-dechlorination system was one of the driving factors in the utility’s investigation into a new disinfection method.

When Tullahoma’s wastewater treatment plant was installed in 1985, it was the first Sequential Batch Reactor (SBR) treatment system of its kind in the U.S. and the largest in the world. At the time, it was supported by the Environmental Protection Agency (EPA) as an “innovative, alternative” to existing systems and 85 percent of its construction was funded by grant money.

Though Young said that system does have a lot of advantages, one of the drawbacks of the continuous influent, intermittent discharge system is the amount of water that must be treated at one time.

“The way we put batches out in 100,000 gallons, our plant is tough to disinfect,” said TUB General Manager Brian Skelton. “Most plants that are four times our size are not putting out the volume of water we are.”

To treat the water in large batches rather than in a constant flow, multiple cylinders of both chlorine and sulfur dioxide had to be employed and fitted with automatic shutoff equipment. That equipment, Young said, had become obsolete and was no longer supported by the manufacturer, so TUB was “looking at about $100,000 to replace it.”

By switching away from the chlorination system, Young said, “that’s a cost we didn’t have to endure.”

At 91 cents per pound, the cost of liquid PAA is significantly higher than the cost of chlorine gas, but Young said the savings incurred by retiring the outdated equipment – both in maintenance and replacement costs — would offset the expense and likely break even in the long run.

“It’s actually an expensive chemical,” said Young. “It actually costs more than the chlorine and the sulfur dioxide. But we’ve been spending something in the neighborhood of $20,000 a year just keeping that equipment going.”

And the hope is that as more wastewater treatment plants begin switching to PAA, a higher demand for the product will drive the price down.

Though TUB’s wastewater treatment plant was the first in the state to convert to the new disinfecting agent, it may not be alone for long.

Nationwide, the wastewater industry is investigating alternatives to chlorine disinfection amid rising concerns about harmful chlorination byproducts. Though there are other effective alternatives on the market, such as ultraviolet (UV) treatment, PAA has an advantage in that the capital costs to retrofit existing chlorine facilities are very low.

In Tullahoma, those costs are nearly nonexistent.

“For us, it’s almost nothing because PeroxyChem is supplying the equipment,” said Young.

Philadelphia-based PeroxyChem LLC provided the chemical for the Tullahoma plant’s state-required toxicity study and has already put the new PAA system in place.

After comparing the company’s price to other suppliers, TUB directors voted unanimously Tuesday night to enter into a three-year agreement with PeroxyChem for the continued supply of PAA.

“We’re going to be their showcase now,” said Skelton. “They are going to bring people from wastewater plants all over to Tullahoma to see this because we successfully got this implementation approved by the state of Tennessee.

“Because we have such a low-flow stream, they are going to look at us more critically than 98 percent of the other wastewater plants in the state, and because of that, it will make it much easier for almost all others to get permitted.”

Removing chlorine from the treatment plant represents an additional boon to TUB as a move away from the hazardous gases also removes the plant from the emergency response umbrella of the EPA’s Risk Management Program (RMP) for toxic or flammable substances – a program that required regular reporting and annual training with the city fire department.

“Because we no longer have the chlorine, we’re no longer subject to the risk management plan,” said Young.

“That helps our fire department and first responders out,” board member Bob Lindeman said Tuesday.

“A lot of work went into this. It’s something that really makes TUB look first class, which we are.”

The wastewater treatment plant, located at 1012 S. Franklin St., operates and is regulated under the EPA and State of Tennessee through the National Pollutant Discharge Elimination System (NPDES) permit program.

Source: The Tullahoma News

Media

Taxonomy

• Wastewater Treatment
• water treatment