Anaerobic Digestion

Technology 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.

Limitations

  • 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.

Technology Providers in order of 9-Point Scoring System

Symbiont works with manufacturing facilities on biogas, an alternative and renewable fuel. Anaerobic treatment of high strength industrial waste and municipal biosolids is a proven biological treatment process, which generates biogas.   Utilizing biogas is as a fuel in boilers is one of the many common applications for this fuel.…
With experience across the RNG industry, Meska Solutions can assist you in turning a waste stream into a revenue stream.   They help with Dairy Farm Evaluations for an RNG Projects often offering the following service without any upfront costs: Provide Technical due diligence and Financial Modeling to determine whether an…
Generate Capital builds, owns, operates and finances assets in: Sustainable Water, Waste & Agriculture (anaerobic digesters, wastewater treatment, desalination, food waste management, recycling/reuse, precision agriculture, farm automation, irrigation, sensors & meters). Sustainable Energy (microgrids, solar, energy storage, lighting, HVAC systems, fuel cells, geothermal, biomass & biogas, building automation & sensors,…
Figure 8 Environmental provides a manure management system called CLARA. CLARA removes over 90% of total suspended solids from irrigation flush water, allowing for the treated water to be recycled back through your flush system. It also can substantially reduce lagoon size requirements by 100% and eliminate the need for…
From project concept through commissioning, EnTech Solutions partners with dairy farmers to produce marketable, renewable energy from agricultural waste. Their team of renewable natural gas experts have proven experience in anaerobic digestion and modular gas processing solutions to help drive value throughout the project lifecycle.   EnTech Solutions also supplies…
Clarke Energy can offer comprehensive engineering, procurement and construction (EPC) services complimenting the supply and maintenance of a gas engine or other power generation equipment. Clarke Energy adds value to the core power solution through engineering, installation and maintenance services. Their supply can range from the sale of a single…
BioMass Solution is focused in the three main areas. First and foremost they are a project development company. Their core strength is matching technologies in their portfolio with problematic waste streams. They work on net new projects or can evaluate add-on technology enhancements to current deployments.   Through their technology…