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Biogas: How the U.S. can Power 46 Million Homes with Energy from Food Scraps, Grass Clippings, and Feces

If the U.S. used all of their untapped organic ‘waste’ – humanure, livestock manure, dog & cat manure, grass clippings & leaves, and food waste – they would generate about $54.4 billion in clean Biogas energy every year, at no extra cost.

Biogas-EndAllDisease

Biogas is a combustible gas mixture generated when organic matter, such as animal (and human) manure, food scraps, leaves, and grass clippings, are broken down by bacteria at warm temperatures (30-60°C) in an anaerobic environment (without oxygen). 

When organic waste is fed into an anaerobic digester, it functions like a big concrete stomach, converting it into biogas, and rich garden fertilizer.  Paul Sellew, CEO of Harvest Power Inc., said in a Boston Ted Talk that the compost derived from food waste his facility “improves the soil, has beneficial organisms that fight disease in soil, holds water to minimize irrigation, has micro and macronutrients, contains everything the plant  needs to grow, is affordable, and locally available.”

Surprisingly, biogas has been used by humans for thousands of years.  It was used to heat bath-water in 10th century Assyria, and in Persia during the 16th century AD.  In Chinese literature the use of biogas dates back 2,000-3,000 years, and the Italian merchant traveller Marco Polo used to cover sewage ponds to produce bio-gas.  It is estimated that there are currently 2 million bio-gas digesters operating in India, which many people use to power their homes.

Benefits of Biogas

  • Generates electricity 24/7
  • Can be produced from any organic waste source.
  • Diverts waste from landfills.
  • Creates new jobs
  • Can be delivered through existing natural gas pipelines
  • Can be filtered, then compressed to make fuel for cars, buses, and trucks.
  • The end product is a nutrient-rich, odour-free fertilizer
  • Reduces greenhouse gas emissions

How Much Power can the U.S. Generate with Untapped Biogas?

Now let’s go on an adventure and calculate how much Biogas Americans are wasting each year in Landfills.  We are going to do some simple math to find out first hand, approximately how much of the United States could be powered simply by tapping unused energy sources.

Toilet - EndAllDisease

Humanure Potential Energy

Due to the efficiency of the human digestive system, the amount of biogas that can be yielded from human waste is limited in comparison with livestock manure and other feedstocks.

On average, one human produces 2.2 lbs (0.998kg) of urine and 0.5 lbs (0.227 kg) of fecal matter or a total of 2.7lbs (1.224 kg) waste in one day.

  • 2.7lbs (fecal matter per person, per day) x 365 (days in 1 year)
    = 985.5 lbs (fecal matter per person, per year)

In 2013, the United States had a population of 313.9 million people.

  • 313.9 million (U.S. population) x 985.5 lbs (fecal matter per person, per year)
    = 309,348,450,000 lbs (309 billion pounds U.S. fecal matter per year)
    _
    Convert 309,348,450,000 lbs to tons
    (1 ton = 2000lbs)
    309,348,450,000lbs (U.S. fecal matter) ÷ 2000 (lbs per ton)
    = 154,674,225 tons (154,674,225 tons U.S. fecal matter per year)

Author David House states in The Biogas Handbook that 1 ton of human waste produces about 0.6 cubic meters of biogas.

  • 154,674,225 tons (U.S. fecal matter) x 0.6 m³ (Biogas per ton)
    = 92,804,535 (Biogas per year from human feces)

Each cubic meter (m3) of biogas contains the equivalent of 6 kWh of calorific energy.

  • 92,804,535 x 6 kWh (per cubic metre of biogas)
    = 556,827,210 kWh

In 2012, the average annual electricity consumption for a U.S. residential utility customer was 10,837 kWh.

  • 556,827,210 kWh (Energy per year from human feces) ÷ 10,837 kWh (average U.S. home)
    = 51,382 homes

Therefore, 51,379 homes can be powered completely by the energy generated from humanure in the United States.

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dog-pooping

 

Animal Manure Potential Energy

 

Livestock Animals

According to the USDA, 1.37 billion tons of solid animal waste produced every year in the U.S.  This animal waste leeches into the environment and has devastating impact, polluting rivers, lakes, and estuaries across America.
Methane yield from manure varies depending on the animal, and their diets, but methane yield from pig manure has been assumed to be 22m³ per ton.  Solid cow manure has a potential of 40 m³ of methane per ton.  We’re going to meet somewhere in the middle and use 30m³ to calculate the potential energy that can be extracted from animal manure.
  • 1,370,000,000 (1.37 billion tons of waste) x 30m³ (Methane per ton)
    = 41,100,000,000 m³ (41.1 billion cubic metres)

Each cubic meter (m3) of methane contains 10.83 KWh of energy.

  • 41,100,000,000 m³ (41.1 billion cubic metres) x 10.83 kWh (in each cubic metre of Methane)
    = 445,113,000,000 kWh (Livestock manure energy per year)

In 2012, the average annual electricity consumption for a U.S. residential utility customer was 10,837 kWh.

  • 445,113,000,000 kWh (Livestock manure energy per year) ÷ 10,837 kWh (average U.S. home)
    = 41,073,452 homes

Therefore, 41 million homes (41,073,452) can be powered completely by the energy generated from livestock manure in the United States.

Dogs & Cats

A study on the biogas potential of dog waste found that 7 kg of dog waste produced 178 L of biogas in 50 days.

How much biogas in 1 year?

  • 178 ?_
    50    365x=1,299.4 Litres (biogas from 7kg dog waste in 1 year)

How much cubic metres of biogas is 1,299.4 Liters?

  • 1 cubic metre = 1000 liters
  • 1,299.4 Litres (biogas from 7kg dog waste in 1 year ÷ 1000 (liters in 1 cubic metre)=1.2994 m³ (biogas from 7kg dog waste in 1 year)

How much biogas from 1 ton of dog waste in 1 year?

  • 1.2994 x  ___?___
    7kg____907.185kg= 168.4 m³ (biogas from 1 ton of dog waste in 1 year)

According to Maine Scientist Will Brinton, “American dogs and cats produce 10 million tons of waste a year”.

How much biogas can be produced with all dog and cat waste in America?

  • 168.4 m³ x 10,000,000
    = 1,683,994,556

Each cubic meter (m3) of biogas contains the equivalent of 6 kWh of calorific energy.

  • 1,683,994,556 (biogas per year from dogs and cats) x 6 kWh (in every cubic meter)
    = 10,103,967,336 kWh (Dog and Cat Waste Energy Per Year)

In 2012, the average annual electricity consumption for a U.S. residential utility customer was 10,837 kWh.

  • 10,103,967,336 kWh (Dog and Cat Waste Energy Per Year) ÷ 10,837 kWh (average U.S. home)
    = 932, 358 homes

Therefore, almost 1 million homes (932,358) can be powered completely by the energy generated from dog & cat waste in the United States.

grass clippings and leaves

Grass Clippings and Leaves Potential Energy

Ordinary lawn clippings yield one of the highest volumes of biogas per ton.  One tonne of organic waste can produce 125 cubic metres of methane, the energy equivalent of one barrel of oil.  Every year we dispose of 24 million tons of leaves and grass clippings.

  • 24,000,000 tons (leaves & grass clippings) x 125 (methane per ton)
    = 3,000,000,000 (methane per year in leave & grass clippings)

Each cubic meter (m3) of methane contains 10.83 kWh of energy.

  • 3,000,000,000 (leaves & grass clippings) x 10.83 kWh (energy per m3)
    = 32,490,000,000 kWh

In 2012, the average annual electricity consumption for a U.S. residential utility customer was 10,837 kWh.

  • 32,490,000,000 kWh (leaves & grass clippings energy per year) ÷ 10,837 kWh (average U.S. home)
    = 2,998,062 homes

Therefore, almost 3 million homes (2,998,062) can be powered completely by the energy generated from the grass clippings and leaves that people throw out every year in the United States.

 food-waste-shot1

Food Waste Potential Energy

As of July 12, 2013, the United States is disposing of 95% of their food waste in landfills and incinerators.

According to the EPA, “Over 36 million tons of food waste reach landfills each year in the United States”.  Accounting for food waste in the home, restaurants, industrial food production, and grocery stores, all of this food that does not get eaten can be recycled and converted into energy using Biodigesters.

Digesting 1 ton of food waste can generate about 300 kWh of energy.

36,000,000 tons (food waste in US per year) x 300 kWh (energy per ton of food)
=10,800,000,000 kWh (U.S. energy per year from food waste)

In 2012, the average annual electricity consumption for a U.S. residential utility customer was 10,837 kWh.

  • 10,800,000,000 kWh (food waste) ÷ 10,837 kWh (average U.S. home)
    = 996, 586 homes

Therefore, almost 1 million homes (996,586) can be powered completely by the energy generated from food waste in the United States.

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How many households in America can Biogas Power?

Estimated Number of U.S. Households (2009): 117,538,000

Biogas Energy Sources:

  • Humanure: 51,379 homes
  • Livestock Animals: 41,073,452 homes
  • Dogs & Cats: 932, 358 homes
  • Grass Clippings & Leaves: 2,998,062 homes
  • Food Waste: 996, 586 homes

Total U.S. homes that can be powered completely using organic matter that is currently thrown in the garbage: 46,051,837 homes

By adding up all of the kWh generated from the organic matter above, we find that in total, generating Biogas from these sources would generate 499,063,794,546 kWh of energy.

At the mid-peak time of day, hydro currently costs about 10.9 cents per kWh.

  • 499,063,794,546 kWh x 10.9 cents/kWh
    = $54,397,953,605

Therefore, if the U.S. used all of their untapped organic matter – humanure, livestock manure, dog & cat manure, grass clippings & leaves, and food waste – they would generate about $54.4 billion in clean energy every year, for free.

How to Make Your Own Biogas Digester

The best part about a home Biogas digester is that, instead of being dependent on large corporations, you are in charge of your own energy production.  “Just one cubic metre of biogas, says Li Xia, Deputy Director of the Guangxi Rural Energy Office in China, “can meet the daily energy needs of rural households, mainly for cooking 3 meals.”

Interesting Facts about Biogas

  • More than 500 landfill–to–energy projects are currently operating in the United States, and another 500 landfills are good candidates for turning their methane into an energy resource, which would produce enough electricity to power nearly 688,000 homes across the nation.
  • Germany, the 4th largest economy in world, recycles 70% of its organic waste and has thousands of these facilities in operation.  In 2009, Germany produced enough electricity from biogas to power 3.5 million homes.
  • Sweden has been operating a biogas-powered train since 2005. It shuttles passengers between two cities that are 75 miles apart.

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