A Massive Amount of Energy is Hidden in Our Waste
Renewable energy is everywhere. It’s not just from the sun shining, wind blowing, or rivers flowing downstream. It could be in the wood chips below the trees in your backyard, the garbage you threw out last week or in the burrito you didn’t finish at Chipotle. It could be in the landfills that lay on the other side of the golf course or in the stinky parts of the dairy farms, hog farms, or waste treatment plants outside of town. Energy can also hide in old auto tires, plastic water bottles, and pistachio shells.
People have known how to create heat by burning wood and garbage for millennia. But burning these items releases harmful contaminants into the sky and pollutes the air we breathe. The good news is, there are more sustainable ways to extract the energy in these things by separating out their component elements.
Breaking Down Waste Elements
We know that natural gas is a hydrocarbon, a compound consisting of carbon and hydrogen atoms. Natural gas is mostly made of methane (CH₄) obtained from fossil fuels that used to be plants millions of years ago. Those plants matched hydrogen with carbon taken in during photosynthesis to grow and through years of compression underground formed a concentrated hydrocarbon fuel.
Now here’s the interesting part: most of the everyday items that end up in landfills also contain hydrocarbons that can be accessed to create energy, and not just through burning.
From Toxic to Treasure
Wood, agriculture waste, food waste, municipal solid waste in landfills, dairy, chicken and hog manure, and human biosolids all contain hydrocarbons that will be released as methane into the atmosphere when left to decompose. Methane is a greenhouse gas that is 30 times worse than carbon dioxide for climate change.
But we now know that if we gather that methane from these decomposing feedstocks, we can clean it up. We can inject it back into natural gas pipelines, displacing fossil fuels that release carbon that had been in the ground for millions of years, not pulled from the atmosphere last year by the plants the cow, hog, pig (or person) ate last month. That’s considered to be carbon neutral and thus sustainable.
It also reduces the pressure on landfills which is a crucial issue in hundreds of municipalities across the US. And when you burn the methane in a stove or boiler, the methane is separated into carbon monoxide (CO) and oxygen (O₂), both of which are not harmful greenhouse gases.
Feeding the Waste Masses
Food waste is becoming an enormous problem for both municipalities that are running out of landfill space and for the environment. Over 100 million tons of food waste is generated annually in the US, which is the equivalent of 450,000 Statues of Liberty. Around 38% of grain products are lost, 50% of seafood, 52% of fruits and vegetables, 22% of meat, and 20% of milk.
This food, which is worth over $160 billion in the US alone, is being dumped into landfills where it emits around 8% of global greenhouse gasses. California has started to prohibit organic waste that emits harmful methane from being sent to landfills across the state, forcing it to be processed in compost piles or other processes. Many other states are starting to follow suit.
Even more methane comes from animals that provide meat and animal products. According to the latest USDA agriculture census data (2012), each year there are 69 million beef cattle, 200 million hogs, and 8.4 billion broiler chickens sold in the US. These animals create over 335 million tons of manure by dry weight, which will emit harmful methane if left to decompose.
Fueling the Flames
In its ongoing Billion-Ton Report, the USDA projected the potential for more than one billion dry tons of biomass to be available by 2030. That includes excess forest resources, agriculture waste, and construction and demolition waste.
All over California and the American West, excess fallen wood and vegetation are contributing to the wildfire threat. Removing that and turning it into woody biomass for energy that offsets fossil fuels is a double-win.
In the Eye of the Beholder
All of these products have the potential to create problems if not disposed of properly, including overcrowded landfills and methane emissions through decomposition. But all of these items have value as well. They can be turned into energy that displaces fossil fuels.
The energy content varies substantially between these feedstocks. Cattle and pig slurry can contain 15-25 cubic meters of biogas per ton, while baking waste (650 m3/ton) and waste greases (600 m3/ton) can have much more. Food waste also varies wildly. Potato peels can produce 68 m3/ton of biogas while molasses is nearly 500 m3/ton with average food waste emitting 200 m3/ton of biogas.
There are various ways to get at this biogas, or renewable natural gas, as it’s called when it’s upgraded and ready for the pipeline.
If it’s buried in a landfill, the gas emitted can be captured through a system of pipes within the garbage dump.
Cow, poultry, and swine manure, along with most organic waste, can be put into capped anaerobic digester tanks or lagoons that capture the biogas as it’s emitted.
Woody biomass, construction waste, municipal solid waste, plastics and other materials containing hydrocarbons that are harder to get at can be processed through biomass conversion technologies like gasification and pyrolysis.
These technologies use various levels of heat and pressure to separate the internal components of the materials and reconstitute them as syngas that can be used as fuel and biochar/carbon black that can be used as an agriculture amendment or filtration medium.
The Waste-to-Value Solution
There are hundreds of anaerobic digesters currently installed all over the world at dairies converting cow manure into biogas. The same is starting to happen at poultry and swine facilities. Several major projects are underway to start converting plastics, tires, woody biomass, and municipal solid waste into valuable fuels and bi-products.
At Nexus PMG, tapping into this hidden potential within our waste is a key part of our mission to build a better world. Providing infrastructure development and advisory services to waste-to-value projects is our specialty. If you see an opportunity to turn waste into value, let us know.