Researchers in Michigan are trying to determine if liquid septage can super-charge the breakdown of garbage inside landfills. Is septage the secret ingredient needed to turn a regular landfill into a bioreactor landfill – producing more biogas and freeing up space for even more garbage?
Starting in 2005 the research team associated with Smiths Creek Landfill in Michigan constructed a septage receiving area to screen septage, store it and then pump it into infiltration pipelines buried in one portion of the landfill.
The first step is our Honey Monster septage receiving station. The system monitors, grinds, screens, cleans and removes unwanted trash and solids as septage is unloaded from tanker trucks (known as honey wagons in the industry). Haulers swipe their access card to activate the system, connect a discharge hose to a 4” (100mm) cam lock connector and start the flow from their truck.
Once finished the system calculates the total volume and prints a receipt for the driver. This data is later downloaded by the billing office so they can send the hauler an invoice. The Honey Monster also performs a wash down cycle to ensure it is ready to go for the next load that arrives.
“The Honey Monster is working as advertised – no complaints,” said Matt Williams, Manager of the landfill. “The drivers unload in about 5-6 minutes and everything is working fine. We simply check it once a day.”
One of the project designers, Xianda Zhao PE of CTI & Associates, is watching the injection process very closely and feels it is still too early to judge whether the bioreactor landfill is viable.
“The Honey Monster removes the bigger solids and it’s working fine,” said Xianda. “We’re collecting a large amount of gas, but we’re not certain yet how much more gas compared to traditional decomposition.”
The Michigan Department of Environmental Quality (MDEQ) is phasing out the land application of septage so the Honey Monster at Smiths Creek Landfill is a convenient location for St. Clair County septage haulers. The landfill expects to receive 23,000 gallons per day on average.
Once the Honey Monster screens out the trash the septage flows into two holding tanks where material further settles. It is then pumped through piping and injected into gravel beds deep inside the landfill where it percolates through the compacted garbage. The mixture of garbage and septage starts a biological chain reaction – speeding up decomposition.
According to Matt, there are two key benefits of a bioreactor landfill:
- More biogas in a quicker amount of time
- Increased settlement of garbage means more landfill capacity
“It certainly helps with decomposition of trash and is a very cool system,” said Matt. “But we don’t know yet if this is commercially viable. What we’re doing is a research project.”
The bioreactor cell covers roughly 7 acres and septage passes through 700,000 cubic yards of garbage. The landfill owner, Saint Clair County, invested roughly $1.5 million over the last three years into the project and charges septage haulers $0.05 per gallon– an average fee for the region. Septage bioreactor cells are also certified and licensed by MDEQ.
“What we’re doing is a pilot project – it’s still too early to tell,” said Xianda. “The one thing we know – the septage has not caused any problems in the landfill.”
The landfill is more convenient for local haulers than the nearest wastewater treatment plant which is 25 miles away.
“We hope this project will prove that a bioreactor is an environmentally safe way to handle septage since the injected liquid is contained in the cell,” said Matt.