Biogas

Anaerobic digestion produced biogas is an environmentally friendly, renewable fuel. Before use, it is important to clean or upgrade the gas to make it functional in gas appliances such as engines and boilers.

Biogas includes methane, carbon dioxide, and other trace gases. The production of biogas happens when manure is kept in an anaerobic environment. The produced methane can be utilized right away to create electricity and/or heat, or go through a cleanup process to create renewable natural gas for the grid or vehicle fuel.

Biogas Production

Biogas production relies on anaerobic bacteria to transform manure and other organic material into biogas and liquid effluent. There are three stages to the process of biogas production.

  1. Liquefaction
    Liquefying bacteria convert insoluble, fibrous materials such as carbohydrates, fats, and proteins into soluble substances. Water, some fibrous material, and other inorganic material also can accumulate in the digester or pass through the digester unchanged. Undigested materials make up the low-odor, liquefied effluent.
  2. Acid Production
    Acid-forming bacteria convert the soluble organic matter into volatile acids--the organic acids that can cause odor production from stored liquid manure.
  3. Biogas Production
    Methane-forming bacteria convert those volatile acids into biogas--a gas composed of about 60 percent methane, 40 percent carbon dioxide, and trace amounts of water vapor, hydrogen sulfide, and ammonia. Not all volatile acids and soluble organic compounds are converted to biogas; some become part of the effluent.

Biogas Resources

Newly developed Renewable Natural Gas (RNG) site for a dairy farm

Biogas utilization

Overview of options with CHP comparison (2021)

  • Reciprocating IC engine-generator sets
  • Microturbines
  • Fuel cells
  • Gas turbines
  • Boilers
  • Renewable natural gas (RNG)

Engine-generator sets

Absorption Chilling: Turning Biogas-Fueled Engine Waste Heat into Chilled Water (2020)

Emissions from Biogas-Fueled Distributed Generation Units (2016)

Obtaining Utility Interconnection of On-site Generation (2009)

 

Fuel cells

Feasibility of Fuel Cells for Biogas Energy Conversion on Dairy Farms (2005)

Hydrogen sulfide removal from biogas

Performance and Economic Results for Two Full-Scale Biotrickling Filters to Remove H2S from Dairy Manure-Derived Biogas (2019)

Hydrogen Sulfide Removal from Biogas fact sheet series (2017)

Case studies

Desulfurization

Case studies

Related resources

Sulfur Flow Characterization

The flow of sulfur through eight dairy farms in New York State, inputs to animals, digester influent and effluent and biogas, were studied from January 2007 to March 2008. Digesters on five farms were traditional plug flow, two were horizontal and mixed and one was vertical with a mixer. Food waste was added to the digester at two dairy farms and there was pre-separation of solids at two farms. On the farms that did not use food waste, 88 percent of the sulfur entering the digester came from the total mixed ration (TMR), 5 percent from drinking water and 7percent from bedding. Where food waste was used 73 percent came from the TMR, 10 percent from food waste, 13 percent from water and 4 percent from bedding. One farm using food waste had a high sulfur content drinking water which shifted these percentages. The concentration of hydrogen sulfide in the biogas ranged from 1,020 to 6,730 ppm. Digesters with no pretreatment of influent averaged 11.1 pounds of sulfur entering the digester for each 100 cow-days, those with pretreatment averaged 4.8 while those with food waste averaged 13.8. On average, 25 percent of the sulfur entering the digester was removed in the biogas.