As the ever-increasing cost and capacity limitations of landfills in North America is forcing. municipalities to find a solution to reduce volume and costs, the value proposition of Mechanical Biological Treatment is to be considered.
By Gaelan Brown and Aurel Lubke
A growing number of landfills in North America are nearing their capacity limits, with waste disposal costs rapidly increasing in most urban areas. In many U.S. regions, the cost for landfill disposal and hauling is above $100 per ton.
Ever-increasing costs to get new landfills permitted and developed are accelerating the problem, with many states being forced to haul their trash to a neighboring state. Landfill diversion efforts of recyclable or compostable materials are making progress in many regions, but landfill capacity and cost issues are still worsening.
Meanwhile, nearly half of the trash sent to North American landfills consists of organic materials, which emit large volumes of methane, a potent greenhouse gas, due to the anaerobic nature of landfills.
According to the EPA, in 2021 landfills in the U.S. emitted an equivalent of 122 million tons of CO2 into the atmosphere, which may be an underestimation. Europeans estimate a landfill produces between 1 and 1.7 tons of CO2 equivalents of GHG emission to atmosphere, per ton of municipal solid waste (MSW) disposed of in the landfill. With almost 150 million tons being landfilled each year, this puts emissions somewhere in the range of 150 to 250 million tons of CO2 equivalent into our atmosphere.
Mechanical Biological Treatment
A solution to this problem, which can reduce landfill volumes by up to 90 percent and drastically reduce greenhouse gas emissions, is Mechanical Biological Treatment, or MBT. MBT has proven itself over the last 35 years throughout the European Union, becoming one of the primary ways to process MSW.
MBT is a process in which mixed MSW is put through an enclosed controlled composting process, in combination with mechanical sorting processes to separate organic materials from recyclables and non-recyclables.
After the initial biological degradation process is complete, it is much easier to mechanically sort the materials into organics, recyclable, and landfill or incinerator portions, because the composted organics have been reduced to inert dehydrated material by the composting process.
This is the primary difference between MBT and a MRF: MBT offers a solution for the organic fraction that also enables separation from the rest of the waste stream, lowering the cost of disposal.
The composted portion of an MBT process is typically a low-value compost product, but this material can still be a beneficial source of carbon for field crops or an emissions-free alternate daily cover for a landfill.
A Primary Method in Europe
As mentioned earlier, over the last 20 years MBT has become a primary method of MSW treatment in Europe. One of the first MBT facilities in Europe was built in Salzburg Austria in 1976, which is
currently processing more than 80,000 tons per year of MSW with the MBT process.
MBT has been a big success in Europe in terms of eliminating volatile organics going into landfills, reducing GHG emissions and creating opportunities for recycling. This has been driven primarily by EU legislation known as The Landfill Directive, enacted by the EU Parliament in 2002.
The Landfill Directive outlawed the landfilling of organic waste unless the organic waste is inert. Inert is defined and measured by the national interpretation of each EU nation, but this essentially means the material cannot generate methane because it has fully decomposed into stable base elements.
The good news for North America is that European taxpayers funded the development of a solution that is now a proven and predictable way to reduce landfill costs for municipalities.
Adapting to Waste Streams
The only alternative to MBT is incineration. While incineration also does not produce methane and creates valuable energy, there are several drawbacks. First and foremost, incineration is expensive, due to the numerous emissions incinerators generate. All these emissions need to be managed with complicated and expensive scrubbing technologies.
Additionally, incineration does not capture and recycle any of our waste, and about 25 percent of the incinerated waste stream comes out as ash that is highly contaminated with heavy metals and other toxins that still need to be disposed of.
The future of recycling is wide open. As the different recycling industries are developing, there are more and more types of materials that can be captured from waste streams for recycling, creating jobs, investments, and reducing resource mining. MBT facilities can easily adapt to these new waste streams, adding in different sorting technologies to capture and recycle them.
One clear example of this is biodegradable plastics. The vast majority of which are currently being landfilled. If sent to an incinerator these would be burned just like any other plastic creating toxic ash. Instead with MBT, this waste stream has a second chance to be transformed back into inert soil. The more future oriented solution that captures the most value is MBT.
How Does MBT Work?
First, mechanical sorters and conveyors are used to separate the waste into the wet organics fraction, and the dry recycling fraction. The organics fraction of municipal solid waste (OFMSW), is composted, then mechanically separated again to remove any remaining recyclable material. The final product is called Compost-Like Output, or CLO.
The CLO fraction represents about 50 percent of the waste stream, typically. The oversize fraction holds recyclable material, such as beverage and food cans, PET bottles, paper, and cardboard as well as inert materials like glass or stone.
If the mix of plastic and paper cannot be recycled, it is dried, shredded, and can then be used as RDF/SRF (Refuse Derived Fuel for incinerators)—for example, in cement factories or pyrolysis plants to upgrade to gasified aviation fuel.
Composting of the OFMSW typically consists of loading the waste into a large, contained chamber, with a computerized compost aeration system built in. When the compostable material has the right oxygen levels (typically 15 percent or higher), thermophilic composting microbes kick into overdrive to rapidly break down the material, sterilize pathogens, and evaporate moisture.
The MBT process is completely contained, with the aeration system exhausted into a biofilter, which captures odors and VOC emissions. Any leachate from the MSW is captured in special sump-traps built into the aeration channels in the floor. All leachate is used again as irrigation water, making the entire process zero discharge.
After two to three weeks of data-optimized aeration, the organics portion of the MSW is reduced by 40 to 50 percent and dried down below 40 percent moisture content for further sorting. This makes it easy to run the MSW through various types of mechanical sorting equipment to sort out the glass, metal, and plastic from the composted material.
Before landfilling the final organic fraction, the product undergoes a maturation process just like in composting, to secure that not only the material is inert, but also that the lab results are returned to confirm the compliance with the landfilling criteria.
Closing Thoughts on MBT
MBT saves additional GHG emissions by enabling advanced recycling, instead of landfilling or incineration. A good MBT plant will save more than 1 ton of GHG emissions per ton of MSW processed. These emissions are respected by the UNFCCC and incentivized by allowing the harvest of carbon credits for North American landfills.
Another advantage to MBT is that the organic fraction can be separated quite easily from the non-organic fraction at the transfer station. This simplifies logistics, keeps your recycling plants clean, and lowers trucking costs.
Waste from an MBT plant is deposited at the landfill at about 15 percent moisture content, keeping the landfill dry and saving a lot of money for landfill aftercare, while also reducing the overall volume of material that is landfilled by as much as 90 percent.
The MBT process means that a landfill with only 10 years of capacity now has 100 years of capacity. This also means the landfill operator can retain income at the landfill while doing the aftercare of the old landfill. (As we know: closing a landfill is very expensive, as you need to pay someone for 100 years to treat the leachate, prevent fires, manage gaseous emissions, etc.) MBT can be executed on levels of 20,000to/year up to 500,000to/year or more.
In Europe the MBT process has been developed in a government-driven way. Governments decided that compostable materials cannot go to landfills. However, some organic materials cannot be sorted by source-separation, such as baby diapers, so the organic portions of mixed MSW still had to be dealt with.
In North America, the value proposition of MBT is going to be more focused on saving money for municipalities, commercial waste generators and taxpayers. The ever-increasing cost and capacity limitations of landfills in North America is forcing municipalities to find a solution to reduce volume and costs. | WA
Gaelan Brown is an independent communications and business development consultant working with organizations focused on technology and sustainability. He is author of the book The Compost Powered Water Heater and is a freelance writer for a variety of publications with a focus on renewable energy and composting technology. He has held senior management roles or management consulting roles with companies such as groSolar, 1% for the Planet, Green Mountain Technologies, Agrilab Technologies, and Ansa Coffee. He can be reached at [email protected].
Aurel Lubke is CEO of Compost-Systems GmbH, based in Austria. He has been designing and building advanced composting facilities and composting equipment for more than 35 years, including more than 100 industrial facilities around the world. He can be reached at [email protected]
For more information, visit https://compostingtechnology.com/composting-facility-design/mechanical-biological-treatment-mbt/ or www.compost-systems.com/en/references.
Resources
www.epa.gov/lmop/frequent-questions-about-landfill-gas
www.youtube.com/watch?si=anp1Bg1lIykT2gMW&v=FMrjYkB2YE&feature=youtu.be&themeRefresh=1