You would expect something called “renewable natural gas” to be more like natural gas than any other fuel. What makes it renewable? It’s a kind of biogas, as is natural gas. But it comes from a different source. Consideration of its uses and benefits, then, becomes part of the larger question of biogas pros and cons.

Natural gas, a fossil fuel, has flowed through our pipelines for more than a century. It resulted from the decomposition of organic matter millions of years ago. We use it to generate electricity, heat buildings and water, and cook food. As compressed natural gas or liquified natural gas, it serves as transportation fuel.

Vast quantities of natural gas are trapped beneath the earth’s surface. Its chief component, methane, is a potent greenhouse gas. Much of it escapes into the atmosphere during the process of extracting it from the ground

When we think of biogas, we usually mean something else. It arises from landfills and other manmade sources. It’s largely methane but not as pure as natural gas.

Processing it, however, results in what’s known as renewable natural gas. In that form, it is interchangeable with conventional natural gas. It can be sent through the same pipelines and put to all the same uses.

Renewable natural gas comes from a variety of sources:

• Landfills
• Livestock manure
• Wastewater treatment plants
• Food waste

Modern landfills place waste in an environment with no air. Anaerobic bacteria feast on the organic portion of it and excrete biogas. Elsewhere, anaerobic digesters accomplish the same purpose.

Cellulose from agricultural wastes and energy crops can also be turned into usable biofuels, including biogas and ethanol. Technological and economic problems have so far prevented their commercialization.

The process of making biogas

As long as anything lives, eats, and dies, the world will never run short of biogas. It is an infinitely renewable energy source. Collecting renewable natural gas prevents methane from escaping into the atmosphere. Producing it directly reduces greenhouse gases and therefore global warming.

Almost any organic waste can produce biogas through anerobic digestion. That is, organic wastes are sealed in a reactor containing a variety of microbes that thrive in the absence of air. Most often, different kinds of organic materials become feedstock at the same time. This process, called co-digestion, enables low-yielding, difficult wastes to be combined with higher-yielding wastes to increase biogas production from the less promising material.

It doesn’t require a large land area or cost much to set up anaerobic digesters. Therefore, producing biogas can be especially helpful in rural areas. Small biodigesters are already available for home use.

Whatever solids remain once anerobic digestion is complete make an excellent organic fertilizer. It doesn’t have the harmful, toxic effects of petrochemical fertilizer. It can play an important role in regenerative agriculture.

Uses of renewable natural gas

Like natural gas itself, renewable natural gas can be used to generate electricity, heat buildings, cook food, and power motor vehicles. It also has some of the same advantages and disadvantages. And, of course, it has the additional advantages of not having to be extracted from deep underground.

According to a joint report from the Environmental Protection Agency, the Department of Agriculture, and the Department of Energy in 2014, the US can support at least 13,000 facilities to make biogas from landfill gas, manure, and sewage treatment plants. That many facilities could produce up to 654 billion cubic feet of biogas every year. If that sounds like a lot, it’s enough to power 3 million homes. That’s a small percentage of the homes in this country.

Viewed another way, all the organic waste sent to landfills or incinerated in a year has as much energy as 6 billion gallons of diesel fuel. Again, that seems like a lot, but it’s only 15% of the diesel used in heavy-duty trucks and buses.

Biofuels, therefore, can replace some but nowhere near all the fossil fuels we burn.

Environmental benefits of renewable natural gas

Generation of renewable natural gas turns a toxic waste product into something useful. It therefore contributes to the concept of a circular economy. Instead of making something, using it, and discarding it, the circular economy makes something, uses it, and makes something else from whatever remains after it’s no longer useful.

Capturing and using what would otherwise become greenhouse gases in the atmosphere results in negative net-zero carbon emissions. That is, diverting gases from landfills, livestock, and other sources and making renewable natural gas reduces global warming.

The example of farms

I have lost track of the number of stories I have read about successful pilot projects to turn farm animal manure into energy. But nothing ever seems to come of them. There are probably lots of reasons why hog and cattle growers don’t routinely extract energy from all that manure. For one thing, they have too much else to do to keep up with it.

But now, private companies are contracting with farmers to do the work. Vanguard Renewables, a New England company, operates farm-based biogas systems. The first ones converted manure emissions to electricity, which it sells to the grid. More recently, it has started one to convert the methane to renewable natural gas, which it sells through existing natural gas pipelines.

Companies like Vanguard deal with manure without adding to the farmers’ workloads. Both the farms and companies make money from it.

The example of motor vehicles

Renewable natural gas has particular advantages as a motor fuel. Today’s fleet of trucks and buses on American roads includes about 175,000 natural-gas powered vehicles. The EPA has estimated that the capturing all the methane that now goes into the atmosphere could power 200,000 trucks.

In California, nearly 90% of all the gas used in natural gas vehicles already comes from renewable natural gas. Many people look to electric vehicles as a way to combat pollution from transportation. But as long as so much of our electric grid depends on burning fossil fuels, burning renewable natural gas in a vehicle might actually pollute less.

Problems with renewable natural gas, real and imagined

Like everything else, biogas has its pros and cons. It appears that the advantages of renewable natural gas outweigh the disadvantages. But it presents the same problems as natural gas and at least one of its own.

Indoor air quality

It is estimated that energy usage in buildings accounts for almost 40% of global carbon emissions. Burning fossil fuels for heating, hot water, and cooking accounts for most of it. Many environmentalists look to building electrification to mitigate the problems associated with burning natural gas.

Increased indoor air pollution is among the more serious problems. It comes from:

• particulate matter
• nitrous oxides
• methane leakage
• carbon monoxide
• other combustion byproducts

Indoor air pollution leads to poor respiratory health. For example, children raised in homes with a gas furnace, water heater, dryer, and stove suffer significantly more asthma than children raised in all-electric homes.

Although extremely rare, natural gas mains sometimes explode, with deadly results and costly destruction of property.

The state of the renewable natural gas industry

Commercial production of biogas is in its infancy. Most companies are small local or regional companies such as Vanguard.

Production of renewable natural gas has started to attract the attention of larger players, however. Dominion Energy, a Virginia-based natural gas utility, and Smithfield Farms, the largest pork producer in the world, have established a joint venture called Align RNG. It will produce renewable natural gas at nearly all of Smithfield’s hog finishing farms.

Second only to Iowa as the largest American pork producer, North Carolina has more than 2,000 hog farms and about 9 million pigs. Smithfield contracts with 90% of them.

Align RNG will cover all those lagoons and install anaerobic digesters to extract the biogas. If other utilities and meat-packing companies enter into similar joint ventures, it will solve the air and water pollution all those lagoons cause, as well as producing a lot of saleable gas.

Actually, Align RNG isn’t the first large-scale utility partnership to produce natural gas from hog waste in North Carolina. A state law passed in 2007 required that utilities derive at least 0.2% of their electricity from hog and poultry waste. So Duke Energy contracted buy renewable natural gas from a company called Optima KV. The 80,000 BTU that Duke will purchase over a 15-year period will displace that much natural gas used at two of Duke’s power plants.

That large corporations have started to show interest bodes well for the future, but creation of a viable biogas industry requires technical, financial, social, and regulatory conditions that do not yet exist.

Involvement of the natural gas industry

Earthjustice and the Sierra Club have issued a joint report that dismisses renewable natural gas as “the gas industry’s deceptive effort to keep our homes and buildings tethered to gas combustion.”

It’s quite true that industries have long defended themselves against criticism on environmental grounds using misleading arguments and false information. Some corporate sustainability initiatives amount to greenwashing.

But it’s also quite true that too many environmentalists mindlessly take the position that if industry benefits from something, it must therefore be bad for society.

The gas industry considers renewable natural gas equivalent to wind or solar as a renewable resource. Since it comes from organic waste, I find it difficult to argue with that position. But it doesn’t follow that using a combustible fuel indoors has all the same benefits of powering the same space with wind or solar.

Most of my sources have mentioned that renewable natural gas is relatively inexpensive. The Earthjustice/Sierra Club report claims that it costs 4 to 17 times as much as fossil fuel natural gas. It also focuses entirely on using gas in buildings and doesn’t speak to vehicle fuel at all. I haven’t attempted to compare these two applications.

Sources:

Could Renewable Natural Gas Be the Next Big Thing in Green Energy? / Jonathan Mingle, Yale Environment 360. July 25, 2019
The pros and cons of biogas: is it the answer to a circular economy? / Power Technology. January 28, 2020
Renewable natural gas production / US Department of Energy Alternative Fuels Data Center Rhetoric vs. reality: the myth of “renewable natural gas” for building decarbonization / Sasan Saadat, Matt Vespa, and Mark Kresowik in Earthjustice. July 14, 2020
What does negative net zero carbon mean? AskWaves explains how renewable natural gas can take GHG emissions negative / Alan Adler, Freight Waves. April 11, 2021