How One Plant Beat Phosphorus Limits and Avoided a Plant Upgrade

A Texas team avoids a costly plant upgrade for phosphorus removal by working with industrial and commercial customers to reduce their inputs.
How One Plant Beat Phosphorus Limits and Avoided a Plant Upgrade
The team at the Walnut Branch Wastewater Treatment Plant includes, from left, Brandon McBride, chief operator; Eugene Robinson, operator; Gilbert Ybarbo, superintendent; Jose Nava, operator; Rene Porras, pretreatment coordinator; and Jestin Peeples, operator in training.

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When the time came to renew ITS NPDES permit, the team in the City of Seguin received an unpleasant surprise.

In 2010, as part of a focus on reducing phosphorus discharges, the Texas Commission on Environmental Quality proposed a limit of 1 mg/L. Seguin’s wastewater treatment plants had been discharging about 10 mg/L.

Seeing the significant and unplanned cost to comply, the Seguin team asked for a conversation with TCEQ officials, says Gilbert Ybarbo, plant superintendent. As talks progressed, the regulators admitted they were mainly interested in dropping effluent phosphorus below 5 mg/L, the threshold for harm to the Guadalupe River, the plant’s receiving stream.

After more discussion, the state agreed not to impose the limit for three years, giving the city team time to study the problem and consider options costing less than a plant process upgrade. In the end, the Seguin team not only beat the proposed 5 mg/L limit, but avoided having a phosphorus limit in its current permit. That saved customers millions of dollars.

The team did it by working closely with customers upstream to reduce phosphorus inputs to the system. Money saved by avoiding a plant upgrade can instead be devoted to improving and expanding existing treatment facilities.

On the grow

Seguin, a fast-growing city of about 26,000, lies 35 miles northeast of San Antonio. It is a county seat dating to the 1800s, and is home to many commuters who drive 40 minutes to San Antonio or 45 minutes to Austin.

In the last decade, the city has gained local employers, notably an engine factory, a commercial bakery supplying grocery stores and other retail outlets, a water bottling company, and a poultry processing plant. There are seven permitted industrial users and nearly 100 restaurants.

Also among the 8,500 sewer connections in Seguin’s 25-square-mile service area are the homes of many retirees. Along with the industrial growth has come a housing boom, says Emery Gallagher, director of the city’s water and wastewater utilities. In 2012, the utility expanded its service area to include rural communities outside Seguin’s border.

Wastewater flows to the Geronimo Creek and Walnut Branch treatment plants. Geronimo is the newer and smaller plant, built in 1987 east of the city. It will handle the community’s growth, and the site includes enough land to expand it as needed. Walnut Branch was built in the 1950s. The city grew to surround the plant, but there is still enough land to double its size.

Walnut Branch is designed for 4.9 mgd and has an average flow of 2.8 mgd. Geronimo is designed for 2.13 mgd and has an average flow of 1.2 mgd. The annual wastewater operations budget is about $3 million.

Handling that budget and plant operations is a team of eight: Ybarbo; Rene Porras, pretreatment coordinator; Brandon McBride, chief operator at Walnut Branch; Gilbert Perez, chief operator at Geronimo; Jamie Alvarez, Jose Nava, and Eugene Robinson, plant operators; and Jestin Peeples, operator in training.

In transition

“We have two influent locations for the Walnut Branch plant,” Ybarbo says. One is a lift station and a force main serving the western part of the city, and the other is a gravity-fed pipe for the east side. They join just above the bar screen. Sludge and scum that accumulate there are pumped to aerobic digesters.

The wastewater then goes to the aeration basins outfitted with Enviroquip (Ovivo) diffusers and on to the secondary clarifiers (also Ovivo). Secondary effluent flows through V-notch weirs into a gravity trough that feeds the chlorination chamber. A dechlorination chamber follows, and a 30-inch pipe takes the treated water to the Guadalupe River.

The plant is staffed on a single shift from 7 a.m. to 3:30 p.m. For unstaffed hours, an alarm system is hardwired to sensors or floats. If an alarm is triggered, the system automatically dials the cellphones of all staff members. A SCADA system is in the budget to support the plant’s expansion and growing sophistication.

Geronimo uses the same basic process but includes a large oxidation ditch with Passavant Mammoth Rotor brushes (Evoqua). Its bar screen comes from Infilco Degremont (SUEZ).

Biosolids from both plants are dewatered and landfilled.

Minding P’s and Q’s

After the TCEQ granted a reprieve on the phosphorus limit, the question for the Seguin team was how to study alternatives for phosphorus reduction. The team worked with representatives from TRC, the city’s consulting engineering firm, to develop a sampling and monitoring plan.

They began with nine points, but as the process went on they realized they could make do with six points. That was easier for Porras, the pretreatment coordinator, because he did much of the field work. The sample points were established to test influent at the plant and at all of the city’s main sewer trunk lines so that the team could determine what section of the city, and thus which customers, were the main phosphorus contributors.

The monitoring revealed that the largest source of phosphorus was the poultry plant, followed by the engine plant, and then a number of connections that included restaurants. The team set out to talk to the customers and explain the problem.

“Rene and I did a lot of legwork with both the poultry plant and the engine plant,” Ybarbo says. “We provided plans to the commercial users. We televised lines and did smoke testing, or used ink dye where smoke testing was not an option, to find cross connections. We looked at floor scrubbers and identified the types of detergent they were using.”

The poultry plant in particular was responsive. For example, the facility installed a system of pipes and pumps to collect used marinade, which was high in phosphorus. The team there also replaced phosphorus-containing cleaners and sanitizers. The engine factory replaced its high-phosphorus cleaners with low- or no-phosphorus products. “The payout was that, since we didn’t have to impose a permit limit, they didn’t have to install any large new treatment system or use chemicals to remove phosphorus,” Porras says.

Of course, if the city had installed equipment at its own treatment plants to remove phosphorus, that would have added to all customers’ bills. “And not only is there the cost of the equipment, but there’s a continuing cost, too,” says Gallagher. “With engineering fees, I think we easily could have reached $1 million to $2 million on equipment, and that was three years ago. Then add the chemical costs, about $120,000 annually. And we would have more solids to deal with. That’s another $150,000 to $200,000.”

Clearing the FOG

While the industrial sources were large and easy to see, restaurant grease was another important part of the phosphorus problem. Here, the key to the solution was Porras’ monitoring program. Many of the salts and seasonings used in restaurants contribute phosphorus to the wastewater stream, he says.

“What did the trick with the restaurants was a change in detergents and making sure their grease traps are serviced regularly,” Porras says. “But the trap is the more important part. If it’s being cleaned properly, none of the detergent or anything else enters the wastewater stream.”

Previously, it was common for these traps to overflow, and phosphorus-containing seasonings that came off food during cooking would flow into the sewer. Trap maintenance benefited restaurants because frequent pumping meant they were not regularly spending money to have plumbers unclog blocked drains, Ybarbo says.

The key to managing trap pumping is a good spreadsheet combined with the city’s pumping ordinance. Restaurants are required to send in their receipts from pumping contractors.

Porras enters the information into a spreadsheet so that he can monitor the servicing without driving around the city to inspect traps.

Only four haulers deal with the restaurants in Seguin. “And we have a good rapport with the haulers, so if there’s a question about whether a particular restaurant was pumped recently, we can call the hauler and get the information we need,” Gallagher says. If the spreadsheet shows that a restaurant isn’t up to date, a phone call to the hauler handles that.

In reviewing manifests from last year, Porras found proper grease trap pumping kept about 250,000 gallons of grease waste out of the city system.

Essential education

Critical to the end result was education. “Once our team educated the industrial users, they were on board with us about the phosphorus limit,” says Gallagher. “Once they understood what we were trying to achieve, and what the alternative would cost the city and them, they worked closely with us. They wanted to be good neighbors, too, and we would never have been able to make this happen without their help.”

With new customers, the utility is taking a proactive approach. Instead of regulating later, utility staff members meet with new customers before a project begins. “They have to submit a permit application to us, and we work with them to evaluate the impact of what they’re proposing to do,” Gallagher says. “Our goal is to be impact-neutral from the beginning.”

Initial tests reveal how much phosphorus a commercial customer will generate, and that in turn dictates the Seguin team’s approach. Even if a customer’s phosphorus contribution will be minimal, the team provides educational material about the problems phosphorus can cause. Ybarbo observes, “Staying in front of it can really help reduce problems after the fact.”


Reuse water yields power — and revenue

In the arid Southwest, there are better things to do with treated wastewater than send it downriver toward the ocean. The utility in Seguin, Texas, found a customer and a source of revenue in the Rio Nogales Power Project, which operates a natural-gas-fired power plant in the city.

“Last year we sold them about 335 million gallons of reuse water and another 720 million gallons of potable water,” says Emery Gallagher, director of water and wastewater utilities. All the water is for the plant’s cooling towers. The city does no polishing of the water. Instead, the power plant team adjusts the pH and other parameters to match its requirements.

A new owner recently took over the plant and is especially interested in resource conservation. Previously, power plant cooling used about 32 percent reclaimed water and 68 percent potable water. Now it’s about 40 percent reclaimed water and 60 percent potable. Water used by the power plant flows to the Geronimo Creek treatment plant and discharges into the Guadalupe River.

“We’ve talked about enhancing that reuse and installing filters so the power plant can run completely on reused water,” Gallagher says. Filters are not in use now and would be part of the long-term plan. At the moment, the utility is doing a study to determine what water quality the power plant needs and what the utility might do to meet that need.

Providing this service produces positive cash flow for the city. Within the next 10 years, two trends should further benefit the city, Gallagher says. First, the growth of Seguin will increase the amount of wastewater, and the Walnut Branch plant will be expanded to handle it. Second, the power plant should be running more, and using more cooling water, because of the owner’s plan to comply with air pollution rules by decommissioning an old coal-fired power plant.

As the utility adapts to provide more reclaimed water, potable water not sold to the power plant may be sold to other customers, or that capacity may be held in reserve for future growth. “Cities throughout the nation are always looking at water,” says Gallagher. “Once you secure those water resources, you keep them.”



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