Anaerobic Digestion

Solution Strengths, Weaknesses and Critical Indicators

Anaerobic Digestion:

  • Long usable life and can be run reliably
  • Creates energy and generates environmental credits
  • Proper feeding & system monitoring is required to avoid system downtime
  • Proven technology for odor control
  • Proven technology for GHG reduction
  • Proven technology for pathogen reduction
  • Different types of systems produce varying gas production rates
  • Requires proper preparation of the feedstock
  • Requires other technologies for energy utilization
  • Requires other technologies for digestate handling
  • Requires other technologies to prevent nitrogen loss
  • Complex systems may require expertise not available on-farm

Overall Summary

 Primary Application

  • Dairy farms with over 500 cows or farms with meaningful organics for co-digestion.
  • Vacuumed/scraped manure, manure slurries, bedded pack that is diluted with digester effluent.

 Economic/Return on Investment Considerations

  • Economics are almost always a challenge; on a value of renewable energy basis, AD is hard to justify, at present received prices for electricity and gas.
  • AD does provide several non-monetary benefits to a farm (see below).

 Industry Uptake

  • 200 dairy-based U.S. installations and thousands worldwide.

Technology Maturity

  • Refined, standard designs available from multiple technology providers.

Primary Benefits

  • Odor reduction – 70 to 95% reduction of indicator acids.
  • Manure organic matter reduction – 35%.
  • Renewable electrical energy production – 2,000 kWh/cow possible each year.
  • Pathogen reduction – 90%+ elimination of fecal coliform organisms as a typical indicator pathogen.
  • Greenhouse gas emission reduction – amount varies by location and farm-specific, but reductions can be large, on the order of 67%+.
  • Nutrient preservation/transformation – key crop nutrients in manure are not consumed by AD and the nutrient form is more plant available than when not digested.
  • Contributes to society’s goal for organic landfill diversion – co-digestion easily achieved enhancing above benefits.

Secondary Benefits

  • Pre-treatment for tertiary treatments like ammonia stripping.
  • Post treatment of waste separation can produce adequate recycled manure solids for bedding livestock.
  • Renewable thermal heat production – 13,500 Btu’s/cow or more possible each year.
  • Nutrients converted for a more plant available form.
  • Increased crop yields possible.
  • Possible reduction of impact on water quality.

How it Works

  • Raw or pre-treated manure is conveyed into a gas tight vessel on a regular basis (daily or more often) that operates at a set temperature (38 ⁰C in most cases).
  • Naturally occurring microbes in manure break solids down into energy-rich biogas.
  • Biogas is used to fuel engine-generators to make electricity or is cleaned to make a natural gas replacement.
  • Some of the produced gas, or heat produced by an engine-generator set is used to heat the digester making it a net energy production system.

 Pre-treatment and/or Post-treatment Required

  • Pre-treatment not required when organic material is used to bed stalls and/or when manure is not substantially diluted. Pre-treatment to remove bedding sand is required with sand-bedded stalls.
  • Pre-treatment may be used to remove excess moisture from influent from barns where hydraulic flushing is used.
  • Post-treatment not required but may be employed based on overall goals of the manure treatment system.


  • Does not reduce volume.
  • Does not work well with raw manure containing bedding sand.
  • Does not work with highly diluted manure due to cost and heat demands for a large vessel.

Other Considerations

  • Currently, most systems are farmer managed, more consistent results may be achieved by dedicated operators.
  • Adding co-digestible material will increase the nutrient content of the digestate and will need to be addressed in the nutrient management plan.
  • A portion of nutrients are converted from organic to inorganic. More nutrients are available for immediate update by crops, so nutrient management plans should be updated to reduce the potential for water quality concerns.

Solutions Providers in order of 9-Point Scoring System

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Bia provides all the essential elements of a successful waste to energy project. The start by securing a site with the required specifications for the construction and operation of their project. They acquire all permits required for construction and operation, and source various waste streams for successful operation and optimized…
Renewable Natural Gas (RNG) PAR is developing RNG projects in several regions of the US utilizing best-in-class anaerobic digester (AD) technology to convert agricultural wastes into Renewable Natural Gas. The main benefits of these RNG projects are that they recycle waste materials while also producing renewable energy and soil products…
Shell is constructing multiple projects to turn organic waste into renewable natural gas (RNG). RNG, or biomethane, is a pipeline-quality gas that is fully interchangeable with conventional natural gas and thus can be used in natural gas vehicles. The use of RNG in the form of compressed natural gas (R-CNG)…
HoSt is a global player in the supply of turnkey agricultural biogas plants, also known as farm scale biogas plants. HoSt has supplied a large number of agricultural biogas plants for the anaerobic digestion (AD) of manure and agricultural products (e.g. corn, straw and grass) in combination with waste from…
Biogas can be a valuable commodity if you have the right systems in place. Mead & Hunt can help you design and construct anaerobic digestion systems that make beneficial use of biogas. Their turnkey systems remove impurities to generate renewable natural gas (RNG), a pipeline-quality gas that is fully interchangeable…
Gruppo Energy Future provides solutions for all types of organic waste. From food waste to livestock manure, they have technology to handle any challenging feedstock. Their systems include “wet” Anaerobic Digesters for both agricultural and urban organics, Organic Repurposing Facilities (ORF’s), High-Solids Anaerobic Digesters, and more.
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LF Bioenergy is a new breed of Renewable Natural Energy developer. Unlike many developers they… Build real partnerships with farmers Live in the Ag world and Energy industry Design around your farm’s operations Staff their facilities with highly trained operators Integrity is at the center of what they do. They…