Our Better Nature: Turning Farts into Fuel – The Upside of Biogas

Even if its precise definition isn’t at the tip of our tongues, we all get the drift of what the term biogas means: there’s biology involved, and the result is gas. If you’re ever on the same flight as the national sauerkraut-eating team on their way home after taking gold in Europe, the biogas will be unmistakeable. And inescapable. More common (and less fictional) examples of biogas include cows’ belches, and the myriad bubbles that swarm to the water’s surface if you wade into a marsh.

Composed chiefly of methane (CH₄) at concentrations that range from 50 to 60 percent, biogas is highly combustible. In fact, it can be used in place of natural gas for home-heating and to fuel internal-combustion engines to generate electricity. Formed by microbes under anaerobic (oxygen-free) conditions, CH₄ is a greenhouse gas that is more than 28 times as potent than carbon dioxide at trapping heat in Earth’s atmosphere.

Methane is valuable when harnessed and put to good use, but makes the world hotter when it’s released into the air. This is one of the reasons it’s crucial to “harvest” biogas that is naturally released by landfills and manure pits. Someday, maybe even cow burps, which are a major source of greenhouse gas emissions, will be captured and used.

Methane itself is colorless and odorless, but biogas is not pure methane. In the context of biogas, one generally finds CH₄ in the company of dodgy pals like hydrogen sulfide (H₂S), which is responsible for the rotten-egg smell of farts and swamp gas. Not only is H₂S a stinker, at high levels it’s toxic and flammable as well.

Another contaminant is ammonia, which forms corrosive nitrogen oxides. In addition to being greenhouse gases, nitrogen oxides cause or worsen the symptoms of emphysema, asthma, and bronchitis when we breathe them in. Landfill biogas is frequently tainted by siloxanes found in lubricants and detergents. Siloxanes are also hazardous to breathe. Before biogas can be used as fuel in commercial engines to generate power, these impurities must be filtered out.

Even if biogas did not yield perks like heat and electricity, we’d still have to extract it from landfills to keep the darned things from blowing up. Methane accumulates in landfills as organic matter decomposes in oxygen-deprived conditions underground. This led to a spate of biogas explosions, some quite destructive, in landfills across the U.S. and Europe in the 1960s through the 1980s.

Although such events are less frequent now due to advances in landfill gas collection systems, landfill fires and explosions continue. Cases in Atlanta, Georgia and Sioux City, Iowa in 2018, and in Pittsburgh, Pennsylvania in 2020, are reminders that even though biogas can generate electricity for us, not everyone has gotten the memo about the need to manage it.

Biogas is also made in something called a methane digester, which I thought was another word for a cow. Despite its name, it doesn’t digest methane. It allows animal manure, sewage, and household garbage to break down, or “be digested,” anaerobically. The resulting methane, which would otherwise have been released to the atmosphere, is collected and used for heat, electrical generation, and other applications. In addition, digester-sourced biogas, which is nearly pure methane, can be injected into the natural-gas grid or compressed into liquid and shipped to world markets.

In its essence, a methane digester is an airtight vessel that is filled with animal manure, food scraps, spoiled hay, or other cheap, abundant organic waste. Since plenty of bacteria are already in the organic matter, you don’t need to supplement them. The only element that’s missing is time. It can take anywhere from 5 to 90 days for your methane to get “ripe,” depending on the type of vessel, what you put in it, and of course, climate (digesters work faster in Ecuador than in Alaska). In large-scale digesters, new material is continually moved through the vessel, whereas backyard setups need to be periodically cleaned out and recharged. The residue left over when the process is done is typically used for fertilizer.

These days, livestock farmers are being encouraged to install methane digesters as an additional source of income or to offset heating costs. Digesters reduce greenhouse gas emissions, and manure processed in a digester retains more nitrogen than manure stored in open-air lagoons. It’s not brain surgery, but there is a learning curve, as well as labor inputs.

Digester technology works on a very small scale as well. Backyard units that run on household waste are common in developing areas of the world and are gaining traction in western Europe. The Chinese have been involved with methane digestion since about 1960, and in the 1970s, roughly six million home digesters were given to Chinese farmers. Home digesters are popular in India, Pakistan, Nepal, and parts of Africa. In Germany, Europe’s foremost biogas producer, the government gives incentives and subsidies to farmers and others to help them adopt digester technology.

In the U.S., rural residents can buy home biogas kits online, as long as local regulations don’t prohibit their use. If you’re handy, instructions for making your own backyard methane digester are available.

Biogas technology is growing as a discipline at many universities.  If you’ve eaten too much sauerkraut, you’ll just have to let digestion run its course. Away from others, please.