As the Michigan Department of Environment Quality phases out land-applied septage and restricts where haulers can offload it, pumpers working many miles from limited receiving facilities face the question, “What am I going to do with it?”
The Smiths Creek Landfill in Smiths Creek, Mich., may have the answer.
A study by the Watershed Management Advisory Group showed that St. Clair County had no septage receiving facility, and identified Smiths Creek Landfill as a potential site. At the same time, engineers at CTI and Associates Inc., an environmental engineering firm in Brighton, Mich., worked with Larry O’Keefe, former landfill manager, to develop the concept of operating a portion of the landfill as a bioreactor.
The research, development and demonstration project gives Smiths Creek Landfill the opportunity to study the beneficial effects of injecting liquid from dewatered septage into the bioreactor instead of standard landfill leachate (water that seeps through the garbage). The project also gives haulers their only municipal disposal location in St. Clair County.
When Pumper interviewed Matt Williams, landfill and environmental manager, the bioreactor had operated for 10 days and only one pumper was providing septage.
Pumper:
Who invented what is being called the Viridis Septage Bioreactor Landfill technology from Viridis Waste Control LLC in Dublin, Ohio?
Williams:
The inventors are Larry and Jan O’Keefe, Te-Yang Soong, Ph.D., P.E., director of solid waste services at CTI, and Morgan Subbarayan, president of CTI.
Pumper:
Does the bioreactor also handle grease trap waste?
Williams:
At this point, we accept only residential septage because we need the anaerobic organisms in it. If the project proves successful, we’ll look at expanding it to include commercial septage. We don’t accept portable restroom waste either.
Pumper:
What is the capacity of the septage receiving facility?
Williams:
It handles up to 10,000 gallons per load. Our projected capacity is 23,000 gpd.
Pumper:
May pumpers from outside St. Clair County use the facility?
Williams:
Not yet, because solid waste plans need upgrading. For example, we have almost completed modifying St. Clair County’s solid waste plan to accept septage from surrounding counties. However, those counties haven’t begun to modify their solid waste management plans to export septage. When that is done, we will allow haulers from other counties to discharge here.
Pumper:
What is inside the receiving facility built at the landfill?
Williams:
It has an unloading bay, processing building, underground lift stations, and biofilter building. The covered unloading bay has one cam lock fitting extending through the wall to which pumpers connect their discharge hoses. They swipe their ID card through the reader in our control panel, hit the green start button, and discharge their load.
In the processing building, septage flows through a rock trap where heavy items fall out, then into a Muffin Monster from JWC Environmental in Costa Mesa, Calif. Besides removing the inorganics, the grinder homogenizes the load. Next, it passes through an inline pH meter before reaching the JWC Honey Monster, a modular dewatering system that screens solids down to 6 mm and separates the liquid. An auger on the screen directs solids up a discharge chute and into a bag. Full bags are buried in the landfill. The amount of dewatered waste is minimal, maybe 1 to 2 percent of the septage volume.
To control odors and any hydrogen sulfide emissions, a blower in the biofilter building draws air from the processing building and forces it through a biofilter. The filter media is 50 percent compost and 50 percent wood chips.
Pumper:
What happens to the dewatered liquid?
Williams:
It discharges out the bottom of the Honey Monster and flows into two 4,100-gallon concrete lift stations. Each tank has a float-activated 7.5-hp Gorman-Rupp sewage pump that sends 200 gpm through a 2,500-foot force main to two 50,000-gallon flexible bladder tanks at the top of the landfill. The discharge piping that connects the tanks to the bioreactor cell is hooked to a manifold. We simply open a valve to the appropriate line and liquid gravity feeds to the bioreactor.
Pumper:
How large is the bioreactor and how is the liquid dispersed into it?
Williams:
The bioreactor, a 7-acre section of the landfill called a cell, will hold 700,000 cubic yards of degradable garbage. We’re injecting liquid from dewatered septage into the east half now.
Injecting large amounts of liquid into a cell to facilitate decomposition makes it a bioreactor. To the best of our knowledge, this is the first time liquid from dewatered septage has been used. We’ve been filling this cell since December 2005, and it will take almost three more years before we reach its capacity.
We fill the cell in lifts, or layers, and build the bioreactor infrastructure simultaneously by laying 3-inch high-density polyethylene, or HDPE, perforated lines for injecting septage and leachate, and 4-inch perforated HDPE pipe for extracting landfill gas. The pipes lie in a bed of washed, evenly graded and naturally rounded stone with as many voids as possible. By dewatering the septage, we prevent solids from clogging the pipes and beds.
Pumper:
How thick are the lifts?
Williams:
The bottom lift, reserved for injection lines, is 10 to 30 feet thick depending on the slope. The bottom has a slight grade, directing landfill leachate to a collection point where we can pump it out. Successive lifts are 10 feet thick, and gas extraction lines and injection lines are installed on alternating lifts.
Pumper:
How does your gas extraction system work?
Williams:
The entire landfill contains 36 vertical gas extraction wells. Landfill gas is about 50 percent methane and 50 percent carbon dioxide. Pipes connect the wells to a common pipe attached to a large vacuum blower. Each well has a valve to regulate how much vacuum we apply based on the amount of gas produced. The extracted gas is routed through a 30-foot-high flare stack and burned so we don’t release methane into the atmosphere.
Pumper:
Why don’t you use the methane as an alternative energy source?
Williams:
Until recently, our landfill wasn’t producing enough volume to make it economically feasible to convert methane into another form of energy. The bioreactor, however, will produce a high volume of gas faster than normal, making our landfill attractive to developers. We are in the process of selecting a developer who can generate electricity from the gas or clean it to the quality of a high Btu natural gas. The waste heat from the conversion process could heat our offices, maintenance shop, or maybe even the energy-producing facility.
Another reason our methane is attractive to developers is because state regulations require Michigan power companies to use a certain percentage of alternative or renewable energy. This technology can be used anywhere there is septage and garbage.
Pumper:
How much does it cost?
Williams:
St. Clair County has invested about $1.5 million in the engineering and construction of the septage-bioreactor facility. The additional infrastructure, including injection and extraction piping, will increase that figure.
Pumper:
What is your septage disposal fee and how does it compare with what municipal treatment plants charge?
Williams:
Our fee is five cents a gallon with no minimum set volume. The nearest treatment plant that accepts septage is in Mount Clemens, 25 miles to the south. Haulers say the discharge fee is the same. It remains to be seen how attractive our price will be.
Pumper:
Is the bioreactor the answer to inexpensive septage disposal and reuse of waste?
Williams:
It’s too early to know. We hope the project will prove that the bioreactor is an environmentally safe way to handle septage, since the injected liquid is contained in the cell. In fact, leaching through the garbage actually cleans it a little. We should have the data showing whether septage outperforms landfill leachate in degrading garbage in two to three years. I’m confident the technology will work well due to the nature of septage and the microbes in it.
Is it the most cost-efficient way of doing it? The answer depends on the location of the landfill and the availability of other septage disposal options. I believe it will be a site-by-site situation based on the conditions at each landfill.
Our vision for this project is twofold, to meet the need created by regulatory agencies and to be economically viable for haulers. It’s one thing for governments to dictate, “You have to go there.” We want haulers to want to come because it is a desirable disposal option.
