Technologies: Within-Vessel Composting

Commercial vendors are promoting within-vessel (also known as in-vessel) composters to California businesses and institutions, such as restaurants, hotels, grocery stores, universities, prisons, and dairies, as a solution to managing that generate large quantities of food waste generated on-site. The following information may be helpful when evaluating whether this type of technology is suitable for your facility.

CalRecycle strongly recommends that food waste generators contact local government’s environmental/public health agencies for assistance in meeting local program requirements based on the type of technology and proposed end use for the products created.

How Within-Vessel Composters Work

Within-vessel composting is a way of composting materials, such as food or landscape wastes, within an enclosed drum, silo, bin, container, etc. to control emissions and maintain uniform conditions of temperature and moisture,. There are a wide variety of products and manufacturers on the market, and a significant variation among the technologies available. Before purchasing any technology, extensive research is recommended.

Things to Consider

  • Conduct a waste audit to understand the type and amount of organic waste you generate. This will help as you research and find a properly sized composter.
  • Composters can handle anywhere from 50 lbs. to thousands of pounds of materials per day.
  • The composter may require electricity or water connections. They are typically installed in commercial or industrial settings where food waste or other organic waste are close by. The goal is to manage the wastes on-site.
  • Most composters need bulking agents such as wood pellets, almond hulls, sawdust, leaves or wood chips.
  • Most have a rotation device to turn the materials and some monitor temperature, moisture, oxygen, and odor.
  • While materials may break down quickly, the material that comes out of the composter (output material) is not mature compost. Compost is the result of complex chemical and biological changes that take weeks or months, not hours or days. Mature compost has reached a stage of reduced biological activity as indicated by reduced temperature and rate of respiration below that of active compost. Most output material requires additional curing outside of the composter to finish the composting process.
  • Know how much space is available on-site to store the composter, equipment, and finished compost.
  • Removing food from the waste stream can lead to reduced hauling and disposal costs.
  • Lab analysis may be required to determine if the finished material meets state and local laws for land application or compost.

Evaluating the Cost and Return on Investment

When considering the purchase of an within-vessel composter product, calculate the initial and ongoing costs and compare it with the cost of separated organics collection services. Although vendors are promoting these as cost-efficient solutions, this may not always be the case.

Research the true cost of the equipment and maintenance:

  • Upfront costs (i.e., shipping and installation)
  • Electrical and/or water connections
  • Ongoing general maintenance and repairs
  • Ongoing costs such as bulking agents or finished compost testing (if sent off-site as a composting product)
  • Staff time allocated to operations

Solid Waste Handling and Transportation Requirements

Local governments may license solid waste self-haulers. Check with your local government’s environmental/public health agencies to determine how to comply with local program requirements.

Environmental Health Standards for Compost

Materials processed from within-vessel composting units may need additional curing time to cool or stabilize before being used as compost and to avoid odor and nuisance issues. Work with your local government to determine how to comply with local rules for composting on-site.

Land Application Requirements for Material Sent Off-site

If material is sent off-site for land application, a lab analysis is recommended to ensure the material meets the requirements for land application. If compostable material fails to meet the requirements, the receiving end-user may be considered an illegal solid waste activity and be subject to enforcement action. Check with your local government’s environmental/public health agencies for assistance in meeting local program requirements.

California Water Board requirements may also apply. Consult with your Local Enforcement Agency and the Regional Water Quality Control Board to determine what is required.

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For more information contact: Food Scrap Management,