The Fort Worth, Texas, Village Creek Water Reclamation Facility is big — it is rated at 166 mgd.

So to be meaningful, an energy savings program also has to be big. Fort Worth officials decided a $35 million investment would do the job. It appears they were right: The program launched in 2010 is already several million dollars ahead of schedule on savings.

The utility entered a performance contract with Johnson Controls for $35 million with an energy savings guarantee of $41 million over 13 years. Major parts of the project included improvements in the aeration system such as new diffusers and switching to dissolved oxygen control; a heat recovery steam generation system and installation of steam-driven blowers; SCADA system replacement; digester mixer upgrades; and construction of a high-strength waste co-digestion facility.

Heat recovery

The Village Creek plant, with 110 employees, serves nearly 900,000 residents in 23 communities. The plant’s average flow is about 100 mgd; its size creates some unique opportunities. Among these is the use of steam to operate blowers for the aeration process.

Jerry Pressley, plant superintendent, believes Village Creek is the first wastewater treatment plant to use the process. “The combustion turbines we use to burn our methane gas are not very thermally efficient,” Pressley says. “There’s a lot of waste heat. Our consultants found a way to take that waste heat, enhance it and add to it to generate the amount of steam that would be necessary to run the steam-driven turbines.”

The steam powers blowers that can replace two 25,000 cfm electric blowers. The plant also uses methane from its 14 anaerobic digesters to generate electricity. The methane, burned in two 5.2 MW Solar Taurus 60 turbines paired with Kato Engineering generators (Nidec Motor Corp.) can meet 65 to 70 percent of plant power requirements. Before the steam system came online, the plant produced about 50 percent of its electricity.

Village Creek enhances methane production by adding high-strength liquid food waste to the digesters. The material comes from a variety of sources, including soft drink bottlers, food waste processors, and a biodiesel producer. Ovivo USA linear mixers in six of the 1.2- to 1.4-million-gallon digesters blend the food waste in. The plant produces about 85 dry tons of biosolids per day — low for a facility its size, according to Pressley. Nearly all the biosolids are land-applied on farms in seven surrounding counties.

Driving down demand

While ramping up power production, Village Creek made changes to reduce the need for electricity. “They really are two sides of the same coin,” Pressley says. “We reduced our baseline power demand by a variety of fairly straightforward efforts: changing air handling, some motor exchanges, and lighting upgrades to more energy-efficient LED systems. We installed an automated ROAM system (Acuity Brands Lighting) that enables us to turn off lights throughout the plant.”

A major part of the project with Johnson Controls was an upgrade of the aeration system with more than 75,000 9-inch fine-bubble membrane diffusers from SSI Aeration. Other smaller-scale changes are ongoing.  

“We’ve made a conscious effort to reduce power demand throughout the plant as we have the opportunity,” Pressley says. “As our operations and maintenance budgets allow, we continue to replace older lighting with LEDs.” The team is also replacing older pumps and motors with more efficient models.

Toward net zero

As recent investments in energy production and conservation pay off, Fort Worth officials are wondering how far they should go down the path to net-zero energy. One vision that guided energy investments was that the plant would eventually be off the grid.

“We’ve stepped back from that a little bit,” Pressley says. “We’re trying to make the best decisions about where we would like to be in terms of our cogeneration and onsite power production. We’re looking at the cost of power generation and what our needs are and what’s that sweet spot between our power production efforts and what we buy off the grid.”

Net zero isn’t off the table: “We’re conducting some additional studies to determine long-term viability. It’s not easy. It’s not cheap. We have to make a business decision on the investment that it would take to get there.

“Maintaining the connection to the grid is important for a lot of reasons. Our size puts us at a level that affords us some priority if power is lost. We get power from two different substations with three different feeds into the facility. That’s nice for redundancy.”

The core business

Ana Pena-Tijerina, engineering manager for the Fort Worth Water Department, added a couple of other concerns: “As large as we are and as old as this facility is, we face challenges every day with aging infrastructure. We have to put a lot of thought into how we use the funding that’s available. We are evaluating everything and making sure we make the best decisions.”

Given that the price of electricity from local utility Oncor Electric is relatively low, investing in energy production may not always be the best use of resources. “There are many lessons learned through the years. Energy systems are complicated. We should not forget our core business, which is treating water.”