Photo by Ralf Geithe - Getty Images
Biogas plant next to a rapeseed field.
Biogas plant next to a rapeseed field.
From rural Uganda to Madison, Wisconsin, renewable natural gas (RNG) is an important source of clean energy that also has other major environmental benefits.
What is RNG? It’s a gas derived from organic waste material such as livestock manure, food waste, garden and lawn clippings and other animal and plant-based material. It is often concentrated on farms, in landfills and in waste treatment facilities.
The big difference between “natural gas” and renewable natural gas is that the former is a fossil fuel and the latter is a clean energy resource derived from current waste products.
I first encountered the use of renewable natural gas as a clean energy resource when I was doing a 2006 research project on dairy cooperatives in Uganda. I met a middle-aged widow who was raising two daughters from the proceeds of a two-or-three-cow dairy farm. She sold the milk to her local co-op and used the cow manure to produce biogas. She had learned a simple technique from a dairy co-op advisor on how to build a small manure digester and to pipe the gas into her house. The biogas provided the energy for two small lamps and a gas cooking stove. She was able to pay the school fees for her daughters from the sale of milk and to provide lighting for them to study in the evenings.
Biogas and its more purified product, renewable natural gas (RNG), can be generated by an anaerobic digester that can be as simple as the one used by the Ugandan dairy farmer or it can be a multi-million-dollar processing facility.
Renewable natural gas is a valuable environmental resource not only in communities in developing countries but those in developed countries as well, including Madison Wisconsin, where I live.
“Natural Gas” and Renewable Natural Gas
Many people have the misconception that “natural gas” is a clean fossil fuel. In fact, it’s a dirty, nonrenewable source of energy. Natural gas is made up of almost 90% methane, a potent greenhouse gas, and is a major contributor to global warming. Natural gas produces slightly more than half as much carbon dioxide as coal when it is combusted, but it is prone to leak significant amounts of methane into the atmosphere at the wellhead, during its distribution, and at the point of combustion. Some scientists have concluded that because of this leakage, natural gas may be just as bad for global warming as coal.
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Renewable natural gas, in contrast, is carbon neutral because it is derived from an ongoing recycling of plant and animal products. It also has the benefit of reducing methane emissions from landfills, livestock, food scraps, and other degradable waste products.
According to the American Biogas Council, there is a cornucopia of benefits from RNG and other biomass processing. “Biogas systems protect our air, water, and soil by recycling organic waste into renewable energy and soil products, while reducing GHG emissions.
“In the U.S., there is an urgent need to manage the millions of tons of food, water and animal waste. The main benefits of biogas systems come from the fact that they are recycling all this material while also producing renewable energy and soil products which displace fossil fuels.
“When you put these and other benefits together, we can prevent tons of carbon emissions from entering our air, prevent nutrients from entering our waterways, create healthier soils with natural, non-fossil fuel-based fertilizers, and produce reliable, baseload renewable energy.”
The American Biogas Council identifies substantial growth opportunities for these biogas-related benefits. In the United States alone, the Council projects that more than 15,000 new biogas systems could be developed. Worldwide, there is massive potential for these systems.
Two Brief Examples of Biogas and RNG Use
East Africa
In East Africa (including Uganda), farmers and local communities are turning organic waste into biogas for cooking, lighting, and other household uses, while at the same time reducing carbon dioxide and methane emissions.
Since the vast majority of households in developing countries use dirty and unhealthy fuels such as bottled natural gas or scarce resources such as wood or charcoal for cooking and heating, biogas is an excellent clean energy alternative.
Madison, Wisconsin
My favorite thing about living in Madison is the chain of lakes that runs through the city and the surrounding countryside. This beautiful resource, however, is not what it used to be. Seventy years ago, the lakes were crystal clear – excellent for swimming, boating, and picnicking along the shorelines. Today, the lakes are plagued with weeds and periodic blooms of blue-green algae that are toxic to humans and animals. On several summer days each year, the lakes stink because of the decaying vegetation.
The primary cause of this deterioration of the lakes' quality? Phosphorus runoff from the increasingly large nearby dairy farms that provide nutrients for the weeds and algae. In the past few decades, far more phosphorus has been imported to the Madison-area watershed in the form of chemical fertilizers and animal feed than has been exported from it as dairy, meat, and grain products.
Thus, the mess the lakes are in today.
What does this lake problem have to do with renewable natural gas? Anaerobic digesters can radically reduce the amount of phosphorus runoff as well as the amount of methane generated by cow manure, landfills, and other sources of waste.
In fact, for the first time in the past seven decades or so, the Madison-area watershed is on the verge of exporting more phosphorus per year than it imports because of two recently installed manure digesters and one planned for 2024 or 2025, all of which will not only extract RNG from manure, but also remove harmful chemicals such as phosphorus. The long-term result will be increasingly clear lakes as well as the reduction of harmful methane emissions into the atmosphere.
The county landfill also has a new state-of-the-art processing facility that converts methane from landfills into RNG. The facility inserts this renewable gas—and that generated by manure digesters and other sources—into natural gas pipelines which allow the clean energy fuel to be used locally as well as transported to other parts of the country.
Conclusion
Renewable natural gas needs to become a better-understood and more frequently utilized resource for creating a clean energy future on small dairy farms in Uganda as well as in metropolitan areas in the United States and other countries.
