Biogas And Air Pollution: Friend Or Foe?

Biogas is a combustible gaseous fuel that is collected from the microbial degradation of organic matter in anaerobic conditions. It is principally a mixture of methane (CH4) and carbon dioxide (CO2) along with other trace gases. Biogas can be used as a clean energy alternative to burning polluting wood, dung, or fossil fuels, which can release toxic air pollutants into households and the atmosphere. However, the question arises: does biogas cause air pollution? This is especially pertinent given that biogas impurities can be detrimental to the environment and human health.

Biogas can be used to replace natural gas for cooking, heating, and electricity generation

Biogas, which is composed mostly of methane and carbon dioxide, can be used as a renewable fuel for electricity generation, heating, and cooking. Raw biogas can be burned directly as fuel for heating or electricity generation for onsite use, but it must be treated to produce renewable natural gas (RNG) before it can be used in place of fossil natural gas. RNG can be used to produce compressed natural gas (CNG) or injected into natural gas pipelines. RNG treatment includes removing moisture and reducing nitrogen, carbon dioxide, and trace amounts of other gases. The U.S. National Renewable Energy Laboratory estimates that RNG could replace up to 5% of the natural gas used to produce electricity and 56% of the natural gas used to produce vehicle fuel.

Biogas can also be upgraded into biomethane, which can be used as a renewable fuel in place of petroleum natural gas. In California, the combustion exhaust from biomethane exhibited low levels of toxicity, similar to natural gas exhaust. However, DNA damage and mutagenicity produced by exposure to combustion exhaust from a cooking stove were slightly higher for biomethane than for petroleum natural gas. More thorough testing is needed to determine how the feedstock and production methods for biogas and biomethane can be enhanced to reduce toxicity.

Biogas is produced by anaerobic decomposition or thermochemical conversion of biomass. Anaerobic bacteria occur naturally in soil, in bodies of water such as swamps and lakes, and in the digestive tracts of humans and animals. Biogas forms in and can be collected from municipal solid waste landfills and livestock manure holding ponds. It can also be produced under controlled conditions in special tanks called anaerobic digesters. The digestate, or material remaining after anaerobic digestion, is rich in nutrients and can be used as a fertilizer.

Biogas can reduce methane and black carbon emissions

Biogas is a promising bioenergy alternative that can be recovered from waste and wastewater in the context of environmental sustainability and a circular economy. It is made when biomass, such as organic waste, manure, food waste, and agricultural residue, is fermented or put through anaerobic digestion. This process, which occurs in an oxygen-free environment, produces gas that is 50-75% methane.

Biogas can be used to reduce methane emissions and air pollution. It can be burned for refrigeration, cooking, heating, lighting, and electricity generation. When biogas is used in place of fossil fuels, further emission reductions can be achieved, sometimes resulting in carbon-negative systems. For example, biogas can replace fuels such as wood and charcoal, reducing black carbon emissions and forest degradation.

Biogas can also help reduce methane emissions from livestock manure, which is a significant source of methane. In 2015, livestock manure management contributed about 10% of all methane emissions in the United States. When treated with anaerobic digesters, livestock manure can reduce greenhouse gas emissions, odors, and up to 99% of manure pathogens.

In addition to reducing methane emissions, biogas can also help reduce black carbon emissions. By recycling organic waste and using it to produce biogas, we can displace the use of biomass and fossil fuels, reducing black carbon emissions and improving air quality. According to Charlotte Morton, Chief Executive of the World Biogas Association, biogas can reduce global GHG emissions by 10% and deliver 50% of the Global Methane Pledge by 2030.

Overall, biogas has the potential to be a valuable climate and clean air energy solution, helping to slow climate change, improve global health, and increase energy access.

Biogas impurities can cause corrosion and clogging in gas pipelines

Biogas is a mixture of methane (CH4) and carbon dioxide (CO2) along with other trace gases. It is produced by the microbial decomposition of organic waste under anaerobic conditions. The use of biogas offers benefits such as a decrease in greenhouse gas emissions and a reduction in the dependence on fossil fuels. However, raw biogas contains various impurities that can cause issues in pipelines.

The presence of siloxanes in biogas can lead to the formation of siloxane dioxide particles, which have abrasive and adhesive properties that cause excessive wear and tear on co-generator engines. Halogenated hydrocarbons, such as chlorine, bromine, and fluorine-based compounds, are frequently found in landfill biogas and are corrosive. During combustion, these compounds can form dioxins and furans, which pose public health risks.

To address these issues, biogas purification processes are necessary. Water removal is typically the first step, followed by the removal of toxic and harmful compounds. Various technologies are available for biogas cleaning and upgrading, such as membrane permeation, cryogenic technology, water scrubbing, and pressure swing adsorption. The specific methods employed depend on the application and the required purity levels.

In summary, biogas impurities can cause corrosion and clogging in gas pipelines, emphasizing the importance of purification processes to ensure safe and efficient utilization. By removing impurities, the negative impacts on pipelines can be mitigated, and the benefits of biogas as a renewable energy source can be fully realized.

Biogas can be made from food waste, yard trimmings, and organic solid waste

Biogas is a type of combustible natural gas that can be made from food waste, yard trimmings, and other organic solid waste. It is created by breaking down the bacteria in organic waste in an "anaerobic digestion" process, which occurs in a purpose-built vessel, free of oxygen. This process can happen naturally in some landfills, natural environments, and even in livestock manure processing factories. However, it can be optimized, controlled, and contained using an anaerobic digester.

The process of creating biogas from food waste involves placing food waste and organic waste scraps into a reactor, where bacteria break down the waste, creating a chain of chemical reactions that result in biogas formation. This biogas can be used for cooking, heating, and electricity generation, among other applications. The liquid and solid digested material, called "digestate," can also be used as a soil amendment or fertilizer, further contributing to sustainable practices.

Biogas production offers several benefits, including waste reduction, energy generation, and environmental protection. By converting waste into energy, biogas helps reduce the amount of waste sent to landfills, which not only saves space but also mitigates the environmental impact of waste decomposition. Additionally, biogas can displace fossil fuels, leading to reduced greenhouse gas emissions and improved air quality. According to Abadi et al. (2016), the use of biogas technology can help address the environmental and health concerns associated with cooking fires, which are currently the leading environmental cause of death worldwide.

However, it is important to address the impurities that may be present in biogas, such as carbon dioxide, hydrogen sulphide, and siloxanes. These impurities can have detrimental effects on equipment and the environment. For example, hydrogen sulphide is corrosive to pipelines and storage facilities, and its combustion produces sulfur dioxide, a major air pollutant. Therefore, it is essential to implement removal technologies and adhere to standards, such as the European biomethane standard, to minimize the negative impacts of these impurities.

In summary, biogas offers a promising alternative energy source that can be derived from food waste, yard trimmings, and organic solid waste. While it provides numerous benefits, including waste reduction and environmental protection, it is crucial to manage the impurities in biogas to ensure its sustainable and safe utilization.

Biogas can be collected from landfills, covered lagoons, or enclosed tanks

Biogas is a mixture of methane (CH4) and carbon dioxide (CO2), with trace amounts of other gases. It is produced by the microbial degradation of organic matter in anaerobic conditions. Biogas can be collected from landfills, covered lagoons, or enclosed tanks called anaerobic digesters.

Landfills are a significant source of biogas, as they contain large amounts of organic waste that breaks down to produce methane. Food waste, in particular, makes up 21% of US landfills, and it is the easiest type of organic waste to break down into biogas. The US Environmental Protection Agency (EPA) and the USDA have set goals to reduce food waste in landfills, but even if these goals are met, there will still be excess food waste that can be converted into biogas. The EPA's Landfill Methane Outreach Program (LMOP) encourages the waste industry to recover and use biogas generated from organic waste in landfills, and provides technical assistance and financing for landfill biogas projects. In 2023, the EPA announced a final rule that established biofuel volume requirements and standards for cellulosic biofuel for 2023-25 as part of the RFS program.

Biogas can also be collected from covered lagoons, also known as manure lagoons, which are commonly used by dairy farms and livestock operations. The biogas that forms in these lagoons can be captured and used for energy.

Finally, biogas can be collected from enclosed tanks called anaerobic digesters. These tanks are used by many municipal sewage treatment plants and manufacturers, such as paper mills, food processors, and breweries, as part of their waste treatment processes. The biogas produced in these digesters can be used to heat the digesters themselves, enhancing the anaerobic digestion process and destroying pathogens. It can also be used to generate electricity, either for use at the facility or to sell to the electric power grid.

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