Composting and Anaerobic Digestion


Anaerobic digestion

Anaerobic digestion (AD) is a process in which biodegradable waste is decomposed in the absence of oxygen in a sealed environment over a period of 25-30 days (rather than 20+ years if in landfill). This prevents methane (24 times more polluting than CO2) from escaping into the atmosphere. AD produces:

  • Biogas (mainly methane plus CO2);
  • A digestate which can be liquid or solid. This can be used as a nutrient-rich soil conditioner.

There are many benefits to biogas and biomethane production including:

  • Reduction of organic waste entering landfill
  • Reduction in greenhouse gas emissions of 75-200% compared to fossil fuels
  • Prevention of methane emissions
  • Reduction of waste transportation, when the AD plant is located near the site of waste production
  • Stops effluent (e.g. from intensive rearing units) from entering water courses - helping to meet the Water Framework Directive.


Biogas is produced by the process of anaerobic digestion (AD) from biodegradable organic residues including agricultural slurries, food, vegetable and garden wastes, sewage and source-segregated municipal waste.

Biogas is normally produced as a mix of 60% methane and 40% CO2

Biogas can be used to generate electricity with some surplus heat,

Biogas can be upgraded, by removing the CO2, to produce biomethane (at least 95% methane) and can power gas vehicles or be injected into the gas grid. Biomethane powered vehicles are well established on the continent but not in the UK.


Our composting and AD services

Cambridge Eco Ltd can provide specialist technical advice on composting in the following ways:

* Design of horticultural and field trials

* Feasibility and case studies

* Compost standards, PAS100 certification and quality protocols

* Compost and AD digestate utilisation and application

* Knowledge of current legislation regarding compost and AD digestate application to agriculture

Specialist areas:

* In depth knowledge of composting of a wide variety of organic wastes

* Assessing the effects of compost on agricultural land, including crop production, soil carbon, organic matter and nutrient cycling

* Using compost as a peat substitute for horticultural crops

* Utilisation of composts to suppress soil-borne pathogens


Click here for useful composting and anaerobic digestion links.