Mitigating methane emissions and off-setting some natural gas demand with bio-methane produced from food waste and dairy manure

Bio-methane produced from all available food waste and dairy manure in the US annually would offset about .74 percent of annual natural gas demand. The bigger savings come in mitigated methane emissions; around 100 Heartland-scale anaerobic digestion facilities can eliminate about 0.41 percent annually of the approximately seven billion tons of overall US greenhouse gas emissions. 

Most manure just sits around. Anaerobic digesters take those piles and place them in large covered tanks and convert waste into an energy source. Chemical engineers examined the carbon footprint of anaerobic digestion.

Methane is far more damaging as a greenhouse gas than carbon dioxide — 25 times more so. The gas, which is produced by decomposing organic materials in the absence of air, not only traps heat efficiently but is also a health and safety hazard because it’s so concentrated in landfills. About half of the landfills in the US collect and burn methane, mitigating the danger but still contributing to atmospheric methane and carbon dioxide levels. Animal manure decomposition on farms is the main contributor of methane emissions in agriculture.

Repurposing that wasted gas is the focus of a new study published in the journal Environmental Progress and Sustainable Energy by chemical engineers from Michigan Technological University. Specifically, they examined the carbon footprint of anaerobic digestion — composting organics without air — which can be used to redirect methane into a usable energy source.

“We found that bio-methane produced through anaerobic digestion emits far less than its fossil natural gas equivalent,” says Sharath Ankathi, the paper’s lead author and a PhD student at Michigan Tech. Studying each product’s carbon footprint is a way to assess its social, environmental and economic impact — in other words how sustainable it is — which Ankathi says is “defined as helping current generations without compromising their needs or the needs of future generations.”

Ankathi’s faculty advisor is David Shonnard, a professor of chemical engineering who leads the Sustainable Futures Institute on campus. They also collaborated with James Potter from AG Energy USA, and together the team focused on a case study of a biogas facility in Colorado. Their primary tool is a life cycle assessment (LCA).

Ankathi and Shonnard dug into the piles of organic waste coming into Colorado’s Heartland Biogas Facility LLC and assessed the process that turns food waste from restaurants in Denver and manure from dairy farms near the facility into bio-methane, an energy source. This is the first study that looks at the entire anaerobic digestion life cycle of both food waste and dairy manure and that includes avoided landfill emissions.

Methane emissions account for 11 percent of the country’s overall greenhouse gas emissions; both manure and food waste are significant contributors. In the US, 97 percent of food waste is buried and decomposes in landfills while manure is most commonly placed in open-to-the-sky lagoons, storage pits, slurries, deep beds for cattle and swine, or poultry high-rise houses. Dairy cows are the most significant contributor to methane emissions from manure decomposition.

Anaerobic digesters take those uncovered piles of sitting manure and place them in large covered tanks. Bacteria are used to break down the solids and liquids; the key is ensuring the breakdown doesn’t come in contact with oxygen. Food waste on its own is not as efficient in anaerobic digestion, so blending it with manure solves two problems with one process. The end products are a liquid digestate, which can be used for fertilizer or industrial uses, and bio-methane, which can be used like natural gas.

In their analysis, the team found that bio-methane produced from all available food waste and dairy manure in the US annually would offset about .74 percent of annual natural gas demand. The bigger savings come in mitigated methane emissions; around 100 Heartland-scale anaerobic digestion facilities can eliminate about 0.41 percent annually of the approximately seven billion tons of overall US greenhouse gas emissions.

Sharath K. Ankathi, James S. Potter, David R. Shonnard. Carbon footprint and energy analysis of bio-CH4 from a mixture of food waste and dairy manure in Denver, ColoradoEnvironmental Progress & Sustainable Energy, 2017; DOI: 10.1002/ep.12762

Michigan Technological University. “Bio-methane transforms from landfill waste to energy source.” ScienceDaily. ScienceDaily, 11 October 2017. <


There are still lots of things to be independently studied but we absolutely know three things: (1) the human population is growing at an alarming rate; (2) our expanding population is becoming wealthier, and(3) our population has to be fed.

It’s because of the newfound wealth of so many people around the world that we are moving farther away from a financially enforced vegetarian diet and demanding more animal products. Access to meat is no longer restricted to people in economically developed regions or the privileged few in third world nations. To meet the demand, the production of beef, pork poultry and seafood is straining the resources of world agriculture, though. It has caused some influential organizations to ‘point with alarm’ at the supposed burden animal protein is putting on our natural resources.

Elsevier, a Dutch-based magazine publisher which defines itself as a global information analytics business, reports “a new study published in Global Food Security found that livestock place less burden on the human food supply than previously reported. Even stronger, certain production systems contribute directly to global food security because they produce more highly valuable nutrients for humans, such as proteins, than they consume.” (Elsevier, by the way, publishes Global Food Security).

The surprising new study questions an idea accepted by many that livestock production creates an unacceptable natural resource drain that must be stopped as soon as possible. The feed that ag animals consume should be used by humans, they say. The water they require is essentially stealing it from a thirsty planet and their waste material including whatever they belch into the atmosphere is poisoning the environment. Cows, say some, are a primary reason for global warming, even more pernicious than all the cars, truck and buses in the world combined.

Anne Mottet, Ph.D., lead investigator of the study, said “As a Livestock Policy Officer working for the Food & Agriculture Organization (FAO) of the United Nations, I have been asked many times by the press to report on the negative environmental impacts of livestock. Doing so, I came to realize that people are continually exposed to incorrect information that is repeated without being challenged, in particular about livestock feed. There is currently no official and complete international database on what livestock eat. This study contributes to filling this gap and to provide peer-reviewed evidence to better inform policy makers and the public.”

What are animal agriculture’s benefits? Meat makes up 18% of global calories, 25% of global protein consumption and provides essential micro-nutrients, such as vitamin B12, iron and calcium. Livestock use large areas of pasture, of course, but most of that land can’t be used for anything else. Replacing all that animal protein with fruits, nuts, grains and vegetables would require an enormous amount of probably unavailable arable land.

Although previous studies claim grain needed to raise 1 kg of beef is between 6 kg and 20 kg. Mottet’s study says an average of only 3 kg are needed to produce 1 kg of meat. Looking at the difference in species, cattle rely on grazing and forages so they need even less, just 0.6 kg of protein from human food to produce 1 kg of protein in milk and meat. An incredible 86% of livestock feed is not suitable for human consumption. It’s an efficient use of “leftovers” the study says that would “quickly become an environmental burden as the human population grows and consumes more and more processed food.”

FAO estimates that we will need as much as 70% more animal products by mid-century to supply world demand. Land needed to raise animals, they say, will increase even if feed conversion ratios are improved. Feed formulation, genetic selection and better veterinary services “have improved conversion ratios. Continued progress is needed to make the system more sustainable but it is essential to improve the recycling of food wastes and by-products into livestock feed as well as to increase feed crops yields.”

Mottet’s conclusion is “Animal production, in its many forms, plays an integral role in the food system, making use of marginal lands, turning co-products into edible goods, contributing to crop productivity and turning edible crops into highly nutritious, protein-rich food.”
Let’s not self-lynch by placing our heads in the ‘anti-ag’ noose created by non-meat-eaters. More realistically designed third party studies need to be made. Too much research has been developed and financed by organizations with an unsympathetic agenda. Is livestock production the evil environmental killer claimed by certain activist groups? I don’t think so.