Anaerobic Digestion

In the UK, demand for anaerobic digestion systems and the consulting expertise required to develop them is growing.  Mannvit offers full-service engineering consulting for anaerobic digestion systems, support facilities and infrastructure through its UK office.

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Anaerobic digestion refers to the use of organic waste to both produce renewable energy (electricity and heat), and to reduce the bulk of organic waste.  By creating energy and reducing waste, digesters are both an appealing solution to common problems and an attractive investment.  For farmers, food processors and other agriculture industries, energy from an anaerobic digester reduces or eliminates the need to purchase energy, surplus energy fed into the electric or gas grid provides income in the form of a feed in tariff, and the reduction in waste volume protects against rising landfill taxes and gate fees. 

Mannvit UK services:

  • Structural and mechanical design
  • Chemical engineering
  • Civil engineering
  • Feasibility studies
  • Site investigations
  • Cost estimates
  • Contract documents
  • Bid evaluations
  • Environmental impact assessments and reports
  • Project management
  • Project planning
  • On-site inspections
  • Mass flows and BMW balance determination
  • Legislative and environmental compliance
  • Management and support of the tendering process
  • Design and construction management
  • Process testing and optimisation
  • Product quality assurance
  • Product and market identification
  • Troubleshooting

Engineering an anaerobic digestion installation includes determining technology and design parameters that are well matched to the type and supply of organic waste, the nature of the heat and / or energy demand, and land-use issues.  Making the most of the natural resources and managing the overall project requires a variety of interrelated services and disciplines.

Anaerobic digester installations must be designed and built to avoid odour, to properly accommodate sludge and effluent substrate, and to use organic waste as efficiently as possible. 

Power Delivery:
Power delivery includes both the transmission of power over high voltage transmission lines, and the supplier/customer purchase agreement for power consumption.  Grid connections are needed to supply power beyond the immediate area, whether to execute contracts with green energy suppliers, and to supply the national grid.  Power Purchase agreements (PPAs) are contracts stipulating the pricing, supply expectations and operational parameters for a power supplier / power consumer relationship.  Power suppliers in a PPA can be public, power companies or private industry.  Mannvit services include extensive experience in power transmission.

Financial Incentives and Compliance:
The financial driver for anaerobic digestion and other renewables in the UK is the Feed in Tariff (FIT).  With FITs, renewable energy projects become a much more attractive proposition and can be considered for their investment merit in addition to their benefits as an environmentally friendly energy source.  FIT incentives have three primary components, and the tariffs for the primary component, generation, is set by a schedule according to the type of renewable energy, and the production capacity.  The three components of FIT incentives are Power generation, Offset, and Export.   

Power generation tariffs are paid to owners of a renewable energy source in direct proportion to the amount of power being generated.   

Offsets are for energy used by the owners of the power source and are equivalent to simply not paying the market rate for the power generated.  This is in addition to the tariff.   

Export of power can earn additional income.  Power that is generated above and beyond the need for on-site use can be exported back to the grid, earning additional revenue.

Revenue from Anaerobic Digestion
Anaerobic digestion plants can be developed for farmers and food processors to generate revenue and reduce waste disposal costs. Revenue from an anaerobic digestion plant can be achieved through:

  • Selling electricity to the National Grid
  • Offsetting electricity and heating bills
  • The Government Feed in Tariff (FIT) incentive
  • Gate Fees for waste intake and landfill tax savings

Renewable Feed in Tariffs (FITs) in the UK (Table 1)
Payments to anyone who owns a renewable electricity system, for every kilowatt hour they generate. The tariff applies for 20 years and is index linked. The “generation” tariff is paid on the total output of the renewable generation system whether you feed it into the grid or use it yourself.

The “export” tariff is a bonus payment for every kilowatt-hour (kWh) your system exports to the electricity grid.

AD Size

Generation Tariff p/kW

<500kWe capacity


>500kWe capacity


Table 1: FIT: AD Generation / Export Tariff over 20 year

Landfill Tax Escalator (Table 2)

Implemented by the UK in response to the EU Landfill Directive. The landfill tax element of gate fees will rise by £8 per year until 2013 in a drive to reduce waste volume.



Landfill Tax (£/tonne)









Table 2: Landfill Tax Escalator

Anaerobic Digestion systems usually takes circa 12 months or more to construct and commission once a feasibility study is complete or planning permission has been granted.

Grid connections
It is likely that electricity will be exported to the 11kV distribution system which is extensive in rural areas and can support between 1–3 MW.