Village Creek Water Reclamation Facility is a leader in the energy recovery arena in the wastewater sector. The treatment plant opened in 1958 and has always been dedicated to using resources efficiently – that includes energy recycling.
Since the early 1960s, methane produced during anaerobic digestion has been captured to generate electricity. The original internal combustion engines were replaced in 2001 with two 5.2-megawatt, cleaner burning, turbine engines.
Low-grade landfill gas, which would otherwise be wasted through flaring, has been purchased, as needed, since 2001. This supplements the methane gas produced as by-product of the treatment process.
The more efficient turbines were supplying about 50 percent of the facility’s electricity before the latest energy efficiency project began in 2008.
Fort Worth and Johnson Controls Inc. have partnered on a $35 million infrastructure renewal project. The ultimate goal is to make Village Creek Water Reclamation Facility a net zero energy facility.
The project achieves the goals through improving electrical efficiencies, converting some processes to alternative energy sources and improving methane gas production.
Improvements paying off ahead of schedule
The Energy Savings Performance Contract for the Village Creek Water Reclamation Facility is a $35 million initiative. Johnson Controls Inc. has guaranteed the city it will save $41 million in electricity costs over 13 years.
The project has significantly benefited Fort Worth’s goal to establish Village Creek WRF as a Net Zero Energy Facility.
To date, this project has reduced electrical consumption by 39 percent, which has taken more than $2.6 million off the plant’s electric bills annually. Also, Oncor Electric provided $1.3 million in rebates to the water/wastewater utility because of its electric demand reductions.
Financially, the project has far exceeded anticipated savings. Johnson Controls has guaranteed $4.1 million in savings to date, but actual savings are $7 million. This almost $3 million windfall belongs entirely to the city’s water utility.
These Village Creek WRF improvements have helped Fort Worth achieve the energy reduction goals set by the Texas Legislature. The legislation was originally adopted in 2001 and amended in 2007 and 2013.
The current legislation mandates public agencies located in the 41 nonattainment counties reduce electricity use by 5 percent per year through 2021.
The legislation requires ambitious, fundamental changes in energy use to help the state comply with federal Clean Air Act standards.
To date, the reduced electrical consumption has lowered the facility’s carbon footprint by nearly 58,000 metric tons of greenhouse gas emissions, or the equivalent of 137 million vehicle miles traveled.
Village Creek Water Reclamation Facility energy reductions from process improvements were enhanced by lighting and air conditioning improvements funded through a U.S. DOE Energy Efficiency & Conservation Block Grant.
How the Improvements Fit Together
Solids are sent to digesters, where anaerobic bacteria break down the organics into stable compounds and reduce pathogens. Biogas, which is about 65 percent methane, is produced as a byproduct during this process.
Linear Motion Mixers
The addition of linear motion mixers to six of the 14 anaerobic digesters improved performance. Functioning like a giant plunger, this improves the circulation and breakdown of solids during anaerobic digestion. The result is more methane and less solids from the process.
Having the linear motion mixers allows the treatment facility to accept high-strength liquid food waste, such as from soft drink bottlers. The high-strength waste is a terrific food source for the anaerobic bacteria, resulting in more methane production.
The methane produced in the digesters and methane purchased from a landfill is converted into electricity by two 5.2-kilowatt turbine engines. The plant does not yet produce enough gas to power both turbines. Some of the heat is used keep the digesters at 98 degrees all year.
Heat Recovery Steam Generator
Most of the heat exhaust from the gas turbines was wasted to the atmosphere, with some captured to heat the digesters and administration building. Now it is all captured, condensed and reheated to create a new energy source – high pressure steam.
Process Air is used in secondary wastewater treatment to accelerate the biological reactions that are the basis of cleaning wastewater. Generating air for this process typically can account for 60 percent of a plant’s energy demand. Now two electrical blowers have been retrofitted with two steam blowers, powered by the heat recovery steam generator.
Aeration Basin Diffusers
Feeding air to the aerobic bacteria speeds up the natural process of cleaning the wastewater. All 1,500 diffusers in thirteen basins were replaced with new, more efficient ones.
Preliminary studies indicate creating these low oxygen level zones has reduced the air demand in six aeration basins by 30 percent. A recycle stream within each basin from the downstream end to the anoxic zone allows the re-use of the oxygen present in the bacteria in the wastewater.
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