Everything You Need To Know To Find The Best Waste To Biogas

Waste-to-energy

This decomposition mentioned above, happens in an anaerobic environment, so the process resulting in biogas is also known as anaerobic digestion ' a natural form of waste-to-energy that uses the process of fermentation to break down organic matter. Animal manure, food scraps, wastewater, and sewage are examples of organic matter that can generate biogas through anaerobic digestion. Due to the high methane content (typically 50-75%), biogas is flammable, and therefore produces a deep blue flame and can be used as an energy source.

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What is biogas?

Biogas is a gas produced from organic materials like animal waste, and food scraps.
It is created through a process called anaerobic digestion, where bacteria break down these materials in the absence of oxygen. This digestion produces a mixture of gases, primarily methane, and carbon dioxide, which can be used as a source of energy.

Biogas is considered a renewable energy source because the organic materials used to produce it can be replenished. It can be used for various purposes, such as heating, cooking, and generating electricity.
Biogas is also a cleaner alternative to traditional fossil fuels since it produces fewer greenhouse gas emissions when burned.

In summary, biogas is a gas made from organic materials that can be used as an environmentally friendly energy source. A more sustainable planet starts with what you do in your own backyard and HomeBiogas has created advanced systems that can help.

What is biogas made of?

Since biogas results from a natural process occurring in a sealed environment, controlling its composition can be challenging. That's why the methane-carbon dioxide ratio can vary. The most common ratio is 60% CH4 (methane) and 40% CO2 (carbon dioxide), but you can expect biogas to contain methane in a proportion of 45 to 75% and carbon dioxide from 55 to 25%. 

Biogas advantages and disadvantages

Generating and using biogas has advantages and disadvantages, like all other energy sources. You should carefully consider these practical aspects when analyzing whether to invest in a biogas plant. 

Among the most popular benefits of biogas, we can mention: 

1. It is a renewable, clean source of energy that relies on a carbon-neutral process, meaning that no new amounts of carbon are released into the atmosphere when using biogas. 

2. It helps divert food waste from landfills, positively impacting the environment and economics. 

3. It reduces soil and water contamination from animal manure and human feces, maintaining a healthy and safe environment for many communities worldwide. 

4.  It reduces the amount of CH4 (methane) emitted to the atmosphere, countering climate change with a possible immediate impact on the environment. 

5. A bi-product is organic fertilizer which is a cost effective way to grow healthy crops.

Some of the disadvantages of relying on biogas as a source of energy can be:

1. Biogas production depends on a biological process, so it can't be completely controlled. 

2. It works better in warm climates, meaning that biogas isn't accessible equally worldwide. 

What kind of waste can produce biogas? 

All organic waste can be used to produce biogas. You can use raw materials such as agricultural waste, municipal waste, plant material, manure, human feces, sewage, garden (green) waste, or food waste. For human waste, a Bio-toilet is recommended.

Is biogas good or bad? 

Biogas is an excellent source of clean energy, meaning that it has a lower impact on the environment than fossil fuels. While not having a zero impact on the ecosystems, biogas is carbon-neutral. That's because biogas is produced from plant matter, which has previously fixed carbon from carbon dioxide in the atmosphere. A balance between the carbon released from biogas and the amount absorbed from the atmosphere is maintained.

The Ecology of Biogas

Biogas is known as an environment-friendly energy source because it alleviates two major environmental problems simultaneously:

1. The global waste epidemic releases dangerous levels of methane gas every day.

2. We rely on fossil fuel energy to meet global energy demand.

The biogas production process utilizes nature's elegant tendency to recycle substances into productive resources to convert organic waste into energy. Biogas generation recovers waste materials that would otherwise pollute landfills, prevents the use of toxic chemicals in sewage treatment plants, and saves money, energy, and material by treating waste on-site. 

Moreover, biogas usage does not require fossil fuel extraction to produce energy. Instead, biogas takes a problematic gas and converts it. More specifically, the methane content present in decomposing waste is converted into carbon dioxide. Methane gas has approximately 20 to 30 times the heat-trapping capabilities of carbon dioxide. In simple words, when a rotting loaf of bread converts into biogas, the loaf's environmental impact will be about ten times less potent than if it was left to rot in a landfill.

Biogas Digesters

As opposed to letting methane gas release to the atmosphere, biogas digesters are the systems that process waste into biogas, and then channel that biogas so that the energy can be productively used. There are several types of biogas systems and plants that have been designed to make efficient use of biogas. While each model differs depending on input, output, size, and type, the biological process that converts organic waste into biogas is uniform.

As opposed to letting methane gas release into the atmosphere, biogas digesters are systems that process waste into biogas and then channel that biogas so that the energy can be productively used. 

There are several types of biogas systems and plants that have been designed to make efficient use of biogas. While each model differs depending on input, output, size, and type, the biological process that converts organic waste into biogas is uniform. Biogas digesters receive organic matter, which decomposes in a digestion chamber. The digestion chamber is fully submerged in water, making it an anaerobic (oxygen-free) environment. The anaerobic environment allows for microorganisms to break down the organic material and convert it into biogas.

All-Natural Fertilizer

Because the organic material decomposes in a liquid environment, nutrients in the waste dissolve into the water and Because the organic material decomposes in a liquid environment, nutrients in the waste dissolve into the water and create a nutrient-rich sludge, typically used as fertilizer for plants. This fertilizer output is generated daily and therefore is a highly productive by-product of anaerobic digestion.

Biological breakdown

Organic matter ferments with the help of bacterial communities to produce biogas. Four stages of fermentation move the organic material from its initial composition into a biogas state.

1. The first stage of the digestion process is the hydrolysis stage. In the hydrolysis stage, insoluble organic polymers (such as carbohydrates) are broken down, making them accessible to the next stage of bacteria called acidogenic bacteria.

2. The acidogenic bacteria convert sugars and amino acids into carbon dioxide, hydrogen, ammonia, and organic acids.

3. At the third stage, the acetogenic bacteria convert the organic acids into acetic acid, hydrogen, ammonia, and carbon dioxide. This process makes the final step possible with the help of methanogens.

4. The methanogens convert these final components into methane and carbon dioxide, which can be used as flammable, green energy.

History of Biogas

This anaerobic process of decomposition (or fermentation) of organic matter happens all around us in nature and has been happening for a very long time. The bacteria that break down organic material into biogas are some of the oldest multi-celled organisms on the planet. Human use of biogas, of course, doesn't go that far back. Anecdotal evidence traces the first uses of biogas to the Assyrians and the Persians in the 10th and 16th centuries. More recently, the 20th century has brought about a renaissance of both industrial and small-scale biogas systems.

In the 18th century, it became clear to Flemish chemist Jan Baptise van Helmont that decomposing organic matter produced a combustible gas. Soon after, John Dalton and Humphrey Davy clarified that this flammable gas was methane. The first significant anaerobic digestion plant dates back to in Bombay. In , the UK used anaerobic digestion to convert sewage into biogas, then used to light street lamps. For the next century, anaerobic digestion was primarily used as a means to treat municipal wastewater. When the price of fossil fuels rose in the 's industrial anaerobic digestion plants increased in popularity and efficiency.

Both India and China began developing small-scale biogas digesters for farmers around the 's. The goal was to decrease energy poverty in rural areas and make cleaner cooking fuels more accessible in remote areas. Close to one-third of the global population still uses firewood and other biomass for energy, causing devastating health and environmental problems. 

In India, the popular model is the floating drum digester, and China's preferred biogas model is the fixed dome digester.

Since then, family-sized biogas units have been gaining more attention and popularity as both a means of reducing household waste and providing clean, renewable energy to families throughout the world. In the past 15 years, countries around the globe have been adopting biogas programs to make both household biogas systems and larger anaerobic digestion plants accessible, efficient, and convenient. As landfills get illegally overloaded, and the release of methane poses more worrying problems, the benefits of biogas systems become more relevant and important.

Many Uses of Biogas:

Biogas can be produced with various types of organic matter, and therefore there are several types of models for biogas digesters. Some industrial systems are designed to treat: municipal wastewater, industrial wastewater, municipal solid waste, and agricultural waste.

Small-scale systems are typically used for digesting animal waste. And newer family-size systems are designed to digest food waste. The resulting biogas can be used in gas, electricity, heat, and transportation fuels.

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For example, in Sweden, hundreds of cars and buses run on refined biogas. The biogas in Sweden is produced primarily from sewage treatment plants and landfills.

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Another example of the diversified uses of biogas is the First Milk plant. One of the UK's biggest cheesemakers is building an anaerobic digestion plant to process dairy residues and convert them into bio-methane for the gas grid. New anaerobic digestion plants like these with fascinating stories keep popping up every day.

Small-Scale Biogas Systems

Small-scale or family-size biogas digesters are most frequently found in India and China. However, the demand for such units is growing fast thanks to more advanced and convenient technologies, such as HomeBiogas. As the modern world produces more and more waste, individuals are eager to find ecological ways to treat their trash.

Traditional systems typically found in India and China focus on animal waste. Due to a lack of energy in rural areas combined with a surplus of animal manure, biogas digesters are very popular, practical, and even life-changing. In many developing countries, biogas digesters are even subsidized and advocated by the government and local ministries, who see various biogas benefits. In addition to having clean, renewable energy that provides gas in the kitchen, many families make extensive use of the fertilizer by-product that biogas digesters provide.

In African countries, some biogas users even turn a profit by selling the bio-slurry by-product produced by biogas systems. This bio-slurry is different from the liquid fertilizer that is made daily. Bio-slurry refers to the most decomposed stage of the organic matter after it has been broken down in the digester. Bio-slurry sinks to the bottom of the biogas system, and with the help of modern units like HomeBiogas, is quickly emptied once accrued (usually an annual process). This bio-slurry is, in fact, a nutrient-dense sludge that provides lots of benefits to soil and can increase the productivity of vegetable gardens.

Biogas is a technology that mimics nature's ability to give back. Both industrial-size and family-size biogas units are becoming incredibly popular and relevant in today's world. As the application grows, biogas can make a significant impact on reducing greenhouse gases. Biogas is applicable both in underdeveloped and industrialized countries as a clean energy source and a renewable means of treating organic waste.

The Future of Biogas

As the world continues to seek sustainable energy solutions, the potential of biogas as a renewable, clean, and versatile energy source cannot be underestimated. Governments and private sectors should invest in research and development to improve the biogas production and utilization technologies. With the right support and incentives, biogas companies like HomeBiogas can significantly meet the growing global energy demand while reducing greenhouse gas emissions and promoting a greener, cleaner future.

Conclusion

In conclusion, biogas offers a promising solution to some of the most pressing environmental and energy challenges we face today. By embracing this sustainable energy source, we can help build a cleaner, greener future for future generations.

Table of Contents

The United States produces more than 70 million tons of organic waste each year. While source reduction and feeding the hungry are necessary priorities for reducing needless food waste, organic wastes are numerous and extend to non-edible sources, including livestock manure, agriculture wastes, waste water, and inedible food wastes. When these wastes are improperly managed, they pose a significant risk to the environment and public health. Pathogens, chemicals, antibiotics, and nutrients present in wastes can contaminate surface and ground waters through runoff or by leaching into soils. Excess nutrients cause algal blooms, harm wildlife, and infect drinking water. Drinking water with high levels of nitrates is linked to hyperthyroidism and blue-baby syndrome. Municipal water utilities treat drinking water to remove nitrates, but it is costly to do so.

Organic wastes also generate large amounts of methane as they decompose. Methane is a powerful greenhouse gas that traps heat in the atmosphere more efficiently than carbon dioxide. Given equal amounts of methane and carbon dioxide, methane will absorb 86 times more heat in 20 years than carbon dioxide. To reduce greenhouse gas emissions and the risk of pollution to waterways, organic waste can be removed and used to produce biogas, a renewable source of energy. When displacing fossil fuels, biogas creates further emission reductions, sometimes resulting in carbon negative systems. Despite the numerous potential benefits of organic waste utilization, including environmental protection, investment and job creation, the United States currently only has 2,200 operating biogas systems, representing less than 20 percent of the total potential.

Introduction
 

What is biogas?

Biogas is produced after organic materials (plant and animal products) are broken down by bacteria in an oxygen-free environment, a process called anaerobic digestion. Biogas systems use anaerobic digestion to recycle these organic materials, turning them into biogas, which contains both energy (gas), and valuable soil products (liquids and solids).

Figure 1: Anaerobic digestion process (Graphic by Sara Tanigawa, EESI).

Anaerobic digestion already occurs in nature, landfills, and some livestock manure management systems, but can be optimized, controlled, and contained using an anaerobic digester. Biogas contains roughly 50-70 percent methane, 30-40 percent carbon dioxide, and trace amounts of other gases. The liquid and solid digested material, called digestate, is frequently used as a soil amendment.

Some organic wastes are more difficult to break down in a digester than others. Food waste, fats, oils, and greases are the easiest organic wastes to break down, while livestock waste tends to be the most difficult. Mixing multiple wastes in the same digester, referred to as co-digestion, can help increase biogas yields. Warmer digesters, typically kept between 30 to 38 degrees Celsius (86-100 Fahrenheit), can also help wastes break down more quickly.

After biogas is captured, it can produce heat and electricity for use in engines, microturbines, and fuel cells. Biogas can also be upgraded into biomethane, also called renewable natural gas or RNG, and injected into natural gas pipelines or used as a vehicle fuel.

The United States currently has 2,200 operating biogas systems across all 50 states, and has the potential to add over 13,500 new systems.

The Benefits of Biogas

Stored biogas can provide a clean, renewable, and reliable source of baseload power in place of coal or natural gas. Baseload power is consistently produced to meet minimum power demands; renewable baseload power can complement more intermittent renewables. Similar to natural gas, biogas can also be used as a source of peak power that can be rapidly ramped up. Using stored biogas limits the amount of methane released into the atmosphere and reduces dependence on fossil fuels. The reduction of methane emissions derived from tapping all the potential biogas in the United States would be equal to the annual emissions of 800,000 to 11 million passenger vehicles. Based on a waste-to-wheels assessment, compressed natural gas derived from biogas reduces greenhouse gas emissions by up to 91 percent relative to petroleum gasoline.

In addition to climate benefits, anaerobic digestion can lower costs associated with waste remediation as well as benefit local economies. Building the 13,500 potential biogas systems in the United States could add over 335,000 temporary construction jobs and 23,000 permanent jobs. Anaerobic digestion also reduces odors, pathogens, and the risk of water pollution from livestock waste. Digestate, the material remaining after the digestion process, can be used or sold as fertilizer, reducing the need for chemical fertilizers. Digestate also can provide additional revenue when sold as livestock bedding or soil amendments.

Biogas Feedstocks
 

Food Waste

Around 30 percent of the global food supply is lost or wasted each year. In alone, the United States produced roughly 133 billion pounds (66.5 million tons) of food waste, primarily from the residential and commercial food sectors. To address this waste, EPA's Food Recovery Hierarchy prioritizes source reduction first, then using extra food to address hunger; animal feed or energy production are a lower priority. Food should be sent to landfills as a last resort. Unfortunately, food waste makes up 21 percent of U.S. landfills, with only 5 percent of food waste being recycled into soil improver or fertilizer. Most of this waste is sent to landfills, where it produces methane as it breaks down. While landfills may capture the resultant biogas, landfilling organic wastes provides no opportunity to recycle the nutrients from the source organic material. In , the EPA and USDA set goals to reduce the amount of food waste sent to landfills by 50 percent by . But even if this goal is met, there will be excess food that will need to be recycled. The energy potential is significant. As just one example, with 100 tons of food waste per day, anaerobic digestion can generate enough energy to power 800 to 1,400 homes each year. Fat, oil, and grease collected from the food service industry can also be added to an anaerobic digester to increase biogas production.

Landfill Gas

Landfills are the third largest source of human-related methane emissions in the United States. Landfills contain the same anaerobic bacteria present in a digester that break down organic materials to produce biogas, in this case landfill gas (LFG). Instead of allowing LFG to escape into the atmosphere, it can be collected and used as energy. Currently, LFG projects throughout the United States generate about 17 billion kilowatt-hours of electricity and deliver 98 billion cubic feet of LFG to natural gas pipelines or directly to end-users each year. For reference, the average U.S. home in used about 10,812 kilowatt-hours of electricity per year.

Livestock Waste

A 1,000-pound dairy cow produces an average of 80 pounds of manure each day. This manure is often stored in holding tanks before being applied to fields. Not only does the manure produce methane as it decomposes, it may contribute to excess nutrients in waterways. In , livestock manure management contributed about 10 percent of all methane emissions in the United States, yet only 3 percent of livestock waste is recycled by anaerobic digesters. When livestock manure is used to produce biogas, anaerobic digestion can reduce greenhouse gas emissions, reduce odors, and reduce up to 99 percent of manure pathogens. The EPA estimates there is the potential for 8,241 livestock biogas systems, which could together generate over 13 million megawatt-hours of energy each year.

Wastewater Treatment

Many wastewater treatment plants (WWTP) already have on-site anaerobic digesters to treat sewage sludge, the solids separated during the treatment process. However, many WWTP do not have the equipment to use the biogas they produce, and flare it instead. Of the 1,269 wastewater treatment plants using an anaerobic digester, only around 860 use their biogas. If all the facilities that currently use anaerobic digestion'treating over 5 million gallons each day'were to install an energy recovery facility, the United States could reduce annual carbon dioxide emissions by 2.3 million metric tons'equal to the annual emissions from 430,000 passenger vehicles.

Crop Residues

Crop residues can include stalks, straw, and plant trimmings. Some residues are left on the field to retain soil organic content and moisture as well as prevent erosion. However, higher crop yields have increased amounts of residues and removing a portion of these can be sustainable. Sustainable harvest rates vary depending on the crop grown, soil type, and climate factors. Taking into account sustainable harvest rates, the U.S. Department of Energy estimates there are currently around 104 million tons of crop residues available at a price of $60 per dry ton. Crop residues are usually co-digested with other organic waste because their high lignin content makes them difficult to break down.

Biogas End Uses
 

Raw Biogas and Digestate

With little to no processing, biogas can be burned on-site to heat buildings and power boilers or even the digester itself. Biogas can be used for combined heat and power (CHP) operations, or biogas can simply be turned into electricity using a combustion engine, fuel cell, or gas turbine, with the resulting electricity being used on-site or sold onto the electric grid.

Digestate is the nutrient-rich solid or liquid material remaining after the digestion process; it contains all the recycled nutrients that were present in the original organic material but in a form more readily available for plants and soil building. The composition and nutrient content of the digestate will depend on the feedstock added to the digester. Liquid digestate can be easily spray-applied to farms as fertilizer, reducing the need to purchase synthetic fertilizers. Solid digestate can be used as livestock bedding or composted with minimal processing. Recently, the biogas industry has taken steps to create a digestate certification program, to assure safety and quality control of digestate.

Renewable Natural Gas

Renewable natural gas (RNG), or biomethane, is biogas that has been refined to remove carbon dioxide, water vapor, and other trace gases so that it meets natural gas industry standards. RNG can be injected into the existing natural gas grid (including pipelines) and used interchangeably with conventional natural gas. Natural gas (conventional and renewable) provides 26 percent of U.S. electricity, and 40 percent of natural gas is used to produce electricity. The remainder of natural gas is used for commercial purposes (heating and cooking) and for industrial ones. RNG has the potential to replace up to 10 percent of the natural gas used in the United States.

Compressed Natural Gas and Liquefied Natural Gas

Like conventional natural gas, RNG can be used as a vehicle fuel after it is converted to compressed natural gas (CNG) or liquefied natural gas (LNG). The fuel economy of CNG-powered vehicles is comparable to that of conventional gasoline vehicles and can be used in light- to heavy-duty vehicles. LNG is not as widely used as CNG because it is expensive to both produce and store, though its higher density makes LNG a better fuel for heavy-duty vehicles that travel long distances. To make the most of investments in fueling infrastructure, CNG and LNG are best suited for fleet vehicles that return to a base for refueling. The National Renewable Energy Laboratory estimates RNG could replace five percent of the natural gas used to produce electricity and 56 percent of the natural gas used to produce vehicle fuel.

Federal Policies Supporting the Biogas Industry
 

The Renewable Fuel Standard

Production of cellulosic biofuel (in gallons)
by fuel type Ethanol Renewable CNG Renewable LNG 2,181,096 81,490,266 58,368,879 3,805,246 116,582,508 71,974,041 * 3,536,721 56,916,606 34,224,820 * As of July

The Renewable Fuel Standard (RFS) was created by Congress as part of the Energy Policy Act. The RFS requires the blending of renewable fuels into the U.S. transportation fuel supply. Currently about 10 percent of the gasoline supply is provided by renewable fuel, primarily ethanol. The RFS sets fuel volumes for a variety of fuel categories: biomass-based diesel, advanced biofuel, cellulosic biofuel, and renewable fuel as a whole. Each category has a required minimum reduction in greenhouse gases.

EPA approved biogas as a qualifying cellulosic feedstock under the RFS in . Cellulosic biofuels must be 60 percent less greenhouse gas-intensive than gasoline. Currently, most of the cellulosic fuel volumes are being met through the use of RNG as a vehicle fuel. Compliance with the RFS is tracked through renewable identification numbers (RINs) that can be traded, and RINs for cellulosic biofuels can earn RNG producers $40/MMBtu (as of September ). According to biogas producers, the RFS has become an important driver of investment in the industry.

As part of the approval of biogas, the EPA updated the RFS to allow biogas-derived electricity used as vehicle fuel to qualify for RINs, or 'e-RINs.' However, as of , the EPA has not approved any producer requests to start generating e-RINs, despite biogas production already exceeding current transportation electricity demand.

The Farm Bill

Programs under the Farm Bill's Energy Title (IX) have been crucial for growth in the biogas industry. Under the Farm Bill, the USDA's Bioenergy Program for Advanced Biofuels provides payments to producers to promote the production of advanced biofuels refined from sources other than corn starch. The program currently receives $15 million per year in mandatory funding with $20 million available per year in discretionary funding through .

The Rural Energy for America Program (REAP) provides grants and loan guarantees to agricultural producers and rural small businesses to promote renewable energy production and energy efficiency improvements. The program has mandatory funding of $50 million per year through , and $100 million available in discretionary funds.

The Biomass Research and Development Initiative is a joint program between the USDA and DOE. With $3 million in mandatory funding through fiscal year and $20 million in discretionary funding through fiscal year , the Biomass Research and Development Board awards grants, contracts, and financial assistance to projects that stimulate research and development of biofuels and bio-based products. However, these programs have consistently seen reductions in funding through the appropriations process.

Other Agency Programs

AgSTAR is a joint program between the EPA, USDA, and DOE. The program promotes the use of anaerobic digesters on livestock farms to reduce methane emissions from animal waste. The AgSTAR program supports the planning and implementation of anaerobic digester projects, and includes state and non-governmental partners.

The EPA's Landfill Methane Outreach Program (LMOP) encourages the waste industry to recover and use biogas generated from organic waste in landfills. LMOP forms partnerships with communities, utilities, landfill owners, and other stakeholders to provide technical assistance and seek financing for landfill biogas projects.

Conclusion
 

Biogas systems turn the cost of waste management into a revenue opportunity for America's farms, dairies, and industries. Converting waste into electricity, heat, or vehicle fuel provides a renewable source of energy that can reduce dependence on foreign oil imports, reduce greenhouse gas emissions, improve environmental quality, and increase local jobs. Biogas systems also provide an opportunity to recycle nutrients in the food supply, reducing the need for both petrochemical and mined fertilizers.

Biogas systems are a waste management solution that solve multiple problems and create multiple benefits, including revenue streams. The United States currently has the potential to add 13,500 new biogas systems, providing over 335,000 construction jobs and 23,000 permanent jobs. However, to reach its full potential, the industry needs consistent policy support. Reliable funding of Farm Bill energy title programs and a strong Renewable Fuel Standard encourage investment and innovation in the biogas industry. If the United States intends to diversify its fuel supply and take action against climate change, it should strongly consider the many benefits of biogas.

Author: Sara Tanigawa

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