Composting

Technology Strengths, Weaknesses and Critical Indicators

Compost Technologies:

  • Requires manure fiber moisture content <80%
  • Volume reduction of 30 to 50% typical
  • Produces a stable, odor free product with market value
  • Requires significant space and time to create highest product value
  • Different technologies and approaches result in a wide range of compost characteristics

Overall Summary

Primary Application

  • More and more dairies are using recycled manure solids (RMS) or composted solids, for bedding in free stall barns to reduce costs and complexity associated with manure treatment when sand or other bedding is used.
  • Compost operations are typically integrated with a solids separator that separates manure solids / fiber from raw slurry.
  • Operations are sized for dairies of all sizes that harvest manure as raw slurry with typical solids content of ~10%.
  • When not used as bedding, compost is typically land applied or sold.
  • There are other uses for composted solids, such as being used as a replacement for peat moss in potting soils.

Economic/Return on Investment Considerations

  • Capital costs are moderate to high depending on the technology selected.
  • Operating costs can be high because tractors and specialized turning equipment are used for turning the solids and there is usually one person who is responsible for this operation on a medium to large size dairy.
  • When used for bedding, ~60% of the composed solids are required, leaving 40% that can be sold to other producers for bedding or for sale typically to the nursery industry to be mixed with potting soil.

Industry Uptake

  • Composted solids require 4-6 weeks of curing before being used.
  • Thousands of dairies are separating solids, but it is estimated that hundreds are composting for bedding recovery.

Technology Maturity

  • Mature technology for both solid separation and composting.

Primary Benefits

  • Cost savings from avoided purchase of sand or other type of bedding such as sawdust.
  • Decreased cost and complexity of managing sand laden manure.
  • Decreased GHG emissions up to 33%+ because solids are kept out of the basin or lagoon where they would decompose and form methane and there are no GHG emissions associated with trucking of sand or other bedding material to the farm.
  • Decreased pathogens by up to 2/3rds compared to RMS that are not composted.
  • Slight storage reduction benefits (0-33%+) by taking the RMS from ~ 30 – 35% dry matter to ~40 – 45% dry matter.

Secondary Benefits

  • Potential revenue stream is created if a market can be found for composted RMS.
  • Decreased carbon footprint of the dairy because manure is separated and composted for bedding and other uses.
  • Some dairy operators report improved cow comfort and cleanliness using RMS solids for bedding.

How it works

  • RMS are captured after raw slurry goes through a screw press, slope or vibrating screen separator with rollers.
  • RMS are transported to the composing area and windrowed or passed through a rotary drum composter.
  • Residence time in the windrow is usually 3-6 weeks depending on climate conditions, this is the time required for biological (natural) heating to occur and get the solids up to at least 55 °C. Primary composting through a rotary drum may be 2-3 weeks or less.
  • Some vendors recommend that the solids stay in the windrow until they reach 70 °C.
  • The composting process will lead to modest reduction in moisture (usually resulting in dry matter content of 40 – 45%), only a slight increase in dry matter content, but leading to significant reduction in pathogens and, therefore, presumably reductions in cow health concerns.
  • This reduction in moisture results in both a slight volume reduction and improved bedding quality.
  • Some producers may pass the compost through a secondary composting cycle for additional treatment, further pathogen reduction and more stable product.

Pretreatment and/or Post-treatment Required

  • No pretreatment is required for the raw slurry before going through solids separation.

Limitations

  • These operations emit exhaust directly into the air with no emission control devices.
  • Research into long term manure composting shows significant potential for volatilization of ammonia nitrogen (8-43%).
  • Odor release is probable through emissions of volatile carbon and sulfur compounds during the turning process.

Other Considerations

  • Keys to success are a commitment to making a composting operation work. There are many dairies that have converted successfully to RMS bedding and have not encountered significant increases in mastitis or somatic cell count.
  • Justification for composting most often comes via cost savings and reduced complexity of manure management.

Technology Providers in order of 9-Point Scoring System

The XACT BioReactors are large scale in-vessel composters that convert huge volumes of solid organic waste into compost in as little as 3 to 7 days. Additionally, XACT is offering designer microbial additives which can target specific bacteria.  For example, somatic cell count in the dairy industry is a major…
RePeet™ the renewable peat-free alternative is the first real answer to the ever growing challenges facing the peat moss industry and its customers. RePeet™ is the soil amendment solution that the U.S. horticultural industry has been waiting for. It is a true peat moss replacement having undergone a life similar…
LuckNow is pleased to be a part of the process of turning compost and sludge into useable products such as potting soil.  LuckNow will custom modify any of their four-auger or vertical mixers to handle mixing of compost and sludge.
Cocoa’s composting process transforms organic waste materials including dairy, swine, poultry and horse manure as well as agricultural residuals like hay, silage, straw, and used bedding into high-quality Cocoa Compost Fertilizers, that are enriched to optimize soil performance and maximize crop yields.   The Cocoa Process provides rigorous quality control procedures to ensure uniform, pathogen free Cocoa…
 Aveterra’s ACS auger-driven composting systems are designed to transform manure, yard and food waste into certified organic compost and soil amendments. ACS gantry and auger movements are programmed to keep the composting process progressing at optimal speed while ensuring the material reaches temperature, killing weed seeds, pathogens, and larvae. ACS…
Agrilab Technologies Inc. standard products include the Drum Dragon, Hot Skid, Hot Box and AerSkid units.  This technology incorporates aeration to accelerate the composting process for manure, bedding, forest residuals, food scraps and other biomass.  AGT equipment is modular to meet a range of scales and applications. On-site and remote…