The Sioux Falls Solution

Dave McElroy

Earlier this year, the U.S. Environmental Protection Agency's Landfill Methane Outreach Program recognized Sioux Falls, S.D.'s landfill gas-to-energy (LFGTE) project with one of the program's annual awards. The project, which supplies gas from the Sioux Falls Regional Sanitary Landfill (SFRSL) to a boiler at a nearby ethanol production plant, also has received an award from the Solid Waste Association of North America and is the first LFGTE facility in South Dakota. The project earned its moment in the sun after nearly a decade of work by the city to find a beneficial use for the gas produced by the site.

Careful Planning

In the early 2000s, Sioux Falls officials began exploring possible uses for landfill gas (LFG) produced by SFRSL, which currently receives about 160,000 tons of municipal solid waste (MSW) per year. Roughly 4 million tons of MSW already has been disposed of at the site.

Before it could find an end user for the LFG, though, the city had to prove that it could reliably and effectively capture the gas. Therefore, in 2005, after consulting with engineering firm R. W. Beck's St. Paul, Minn., office, Sioux Falls installed 19 dual-phase wells (DPWs) at the landfill. "Dual-phase" indicates that the wells collect both LFG and leachate. LFG is sent to a flare, which began operating in early 2006, and the leachate is pumped to an underground storage tank that is then trucked to a wastewater treatment plant (two, 1-million-gallon leachate ponds have since been constructed to help manage the large amount of leachate being pumped out of the landfill).

In 2007, an additional 23 DPWs were installed and provided additional flow to the existing flare. By 2008, LFG flow averaged around 900 to 1,000 standard cubic feet per minute.

After the gas collection and control system had proven itself, Sioux Falls officials began looking for LFG users. R.W. Beck completed an LFG utilization feasibility study for the city, which was co-funded by the South Dakota Department of Environment & Natural Resources to serve as guidance for other South Dakota landfills. The feasibility study is available for download from the association's Web site at www.sdswma.org.

The LFG feasibility study looked at a variety of possible uses for LFG, such as electricity generation, direct use or high Btu use, as well as private or third-party ownership options. In the end, the direct-use application of LFG to fire an industrial boiler was chosen in part because of the return on investment and consistent demand for LFG.

Officials looked at piping the LFG into Sioux Falls for use by the city or a local business such as a greenhouse or private asphalt plant. Around that same time, the L. P. Gill Landfill in Jackson, Neb., had entered into a LFG supply agreement with an ethanol plant near the site. Because the city has a good relationship with Leonard Gill, owner of the landfill, we were able to evaluate that project and use it as a template.

Soon, the city entered into discussions with locally based POET Biorefining, which produces ethanol fuel, about supplying LFG to the firm's Chancellor, S.D., production plant, located about 11 miles from SFRSL. The timing proved good for both sides since the plant's capacity was being expanded from 50 million gallons per day to 105 million gallons per day. Although the majority of POET's facilities are powered by clean-burning natural gas, the company diligently looks for opportunities to use renewable energy. An agreement between Sioux Falls and POET was signed in April 2008.

Dubuque, Iowa-based Unison Solutions built and installed the gas compressor system that treats the LFG before it is delivered to the ethanol plant. The system includes two 250-horsepower compressors, drying equipment and filtering equipment. No sulfur or siloxane treatment equipment was needed because the boiler at the ethanol plant was able to handle the untreated LFG.

As part of the agreement with the ethanol plant, the city had to deliver LFG by July 2009. However, LFG delivery actually began ahead of schedule in February 2009, primarily due to the fact that pipeline installation took just two months. West Concord, Minn.-based Ellingson Cos. installed the 12-inch SDR 11 pipe primarily using a unique plow system that eliminated the need for conventional excavation machinery except at the beginning and end of each plow run. Before installation, the HDPE pipe was welded together with a track-wheeled Fast Fusion welder. The pipe was installed with a minimum of four feet of cover over the top of the pipe. No sand or bedding material was used around the pipe. Road crossings and creek crossings were excavated using directional drilling equipment.

Because the gas was dried to a dew point of 40 degrees or less, no condensate lift stations were installed along the hilly pipeline route. The pipeline has now been in operation for more than a year and has had no problems associated with accumulating condensate.

After the LFG is delivered to plant via the pipeline, it is used to fire a boiler that produces steam that powers ethanol production. The boiler also can be fired with wood chips and other wood waste from SFRSL and other landfills.

LFG sales to POET grossed almost $1 million in its first year of operation. Sioux Falls-based Mickelson & Co. was used to evaluate the city's options for carbon offsets associated with the destruction of methane. Sioux Falls entered into a multi-year agreement with San Francisco-based TerraPass for the sale of its verified emission reduction credits. To date, the city has generated more than $500,000 in verified emission reduction credits. The estimated payback period for the LFG project is four years.

"POET has been a very innovative and cooperative partner," says Mark Cotter, director of public works for Sioux Falls. "Based on the success of this project, we are looking at additional ways to work together to expand waste-to-energy opportunities in South Dakota".

The City's landfill gas project has allowed for an additional revenue source while waste receipts have fallen off as has been experienced by many landfills around the country.

Dave McElroy is the superintendent of the Sioux Falls Regional Sanitary Landfill.

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