Landfill gas is created by landfills, which account for 16% of the human-caused (anthropogenic) methane emissions in America. This is not what many people worry about when they think of greenhouse gases, it’s important. Thanks to the work of many nonprofits, government programs, and corporations that work in the transportation industry, though, we have a way to use this gas to help lower emissions.
Ann Vail, Executive Director of Louisiana Clean Fuels, explained to me that landfill gas can be turned into renewable natural gas (RNG). In 2015, LCF held a webinar about renewable natural gases and how it’s made. Although since 2015 several laws (and prices) have changed, the information about the fuel is still a good basic introduction into how it’s made and how our communities are working toward making it cleaner.
Note: All emission estimates from the Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990–2017.
Many large-vehicle fleets (buses, UPS trucks, etc.) now use compressed natural gas (CNG). When RNG is cleaned, it becomes chemically identical to the natural gas that we use in other applications, such as fuel for fleet vehicles, electric power plants, and heating for some homes. Using natural gas as a vehicle fuel produces less greenhouse gas emissions than diesel or gasoline due to the fact that methane is the shortest hydrocarbon. Even better if it’s RNG created from landfill emissions.
There are 5 steps that turn landfill gas into renewable natural gas that can be used as fuel for vehicles.
1. Organic Materials
You start with organic materials, which are mostly biologic waste such as food waste, manure, paper products, and tree trimmings.
Biogas is extracted from landfills, or put into special containers known as anaerobic digesters. Once you have the gases, you are also left with biosolids that can be used as an additive to the compost.
3. RNG Fuel
The next step is to clean the biogas, which means the removal of carbon dioxide, H2S Siloxanes, and Volatile Organic Compounds (VOCs). Raw landfill gas is typically around 60% CO2 and 40% CH4, with the previously mentioned impurities in the parts per million/billion range. It’s typically cleaned to the point that CH4 concentration is above 94% and it’s ready to be used as a vehicle fuel. (94% is a requirement to be sold as a vehicle fuel.)
4. Fueling Stations
Sometimes fueling stations are on the site where RNG is produced, or the RNG can be shipped by truck to fueling stations. RNG can also be used to produce electricity, which is a common practice for wastewater treatment plants where they power the entire wastewater treatment plant with electricity produced onsite by burning biogas.
Natural gas engines work exactly like traditional gas engines and only require minor modification to operate on natural gas. Many natural gas vehicles are bi-fuel vehicles, which means they both have a gasoline tank and a CNG tank so that they can run on either fuel at the flip of a switch.
Not only does the use of RNG reduce greenhouse gas emissions from the landfill, but it replaces the gasoline or diesel that would otherwise be used with a lower-emission fuel.
This doesn’t mean that we have the green light to keep wasting food or other organic material. No, it means that there are innovative solutions being put forth that help offset some of the damage we have done, the vast contributions we have made toward the destruction of our own environment.
To close, note that landfills aren’t the only thing that RNG can be sourced from. Wastewater treatment plants, livestock farms (an increasingly common source), and dedicated food waste digesters are also sources for RNG. Even dairy farms are moving toward capturing methane from manure and turning that into RNG that they then can add into the natural gas pipeline.
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