Biomethane Injection into the Grid: RHI Opportunities to the Waste Water Treatment Sector Wusterhaus

Gomez, E. and Schulte-Schulze Berndt, A., Schmack CARBOTECH GmbH



With the amendment of the renewable obligation certificates (ROCs) on 2009 to the electricity produced by cogeneration units on waste water treatment plants (WWTP), a drastic decrease on the incentives for the WWT-sector creates an interesting opportunity to seek chances on the next renewable heat incentive system of 2011.

With the planned tariff for the injection of biomethane into the gas grid, a better and more feasible perspective is given to the sewage gas produced by sludge fermenters on WWTP. Through the upgrading of biogas into biomethane, injected gas will not only be prized with incentives but additionally handled with a price on the market; this creates -on the long term- an advantage for the WWT-Sector over the electricity fluctuating price being a more stable market with reliable profiting.

The presentation will focus on the biogas and sewage gas cleaning and upgrading methods with well-proven technologies which provide an alternative for the efficient employment of this fuel gas to maximize its potential on the UK renewable energy market.


Biogas, Biomethane, Carbotech, Grid, Natural Gas, PSA, Schmack, Viessmann


In Europe by far the most common method of using the sewage gas from WWTP is the production of electricity and heat with CHP plants or in boilers for the generation of heat.  A disadvantage of CHP plants are the relative low efficiency, which in optimal cases the energy produced as electricity and heat will achieve a realistic performance of 80% while the rest can be regarded as lost energy. The UK government has realised, among other issues, this disadvantage and therefore the support scheme ROC for electricity production reduced in particular cases such as for sewage gas, with the purpose of a more effective usage of the gas produced, the upcoming Renewable Heat Incentives (RHI) intends to persuade the WWT-Industry to upgrade the sewage gas to natural gas quality for injecting it into the grid.

Therefore the most promising alternative for using biogas is the injection into the natural gas grid, not only because of the energy efficiency improvement but also the long term economical stability regarding the natural gas selling price towards the electricity price.  With many alternatives for electrical production from conventional fossil resources to renewable sources (wind turbines, solar energy, hydropower, etc), the price development will steadily decrease while the natural gas prices with less alternatives of production/extraction becomes an attractive alternative for selling the generated gas from WWTP.

Through the decades of dependency from fossil fuels has brought positive and negative aspects, which from one side is the predicted shortage from natural gas in the near future but from the other side is the good infrastructure that countries like the United Kingdom with its gas grid has achieved.  With one of the top networks in the world, the alternative of gas production through anaerobic digestion and the injection into the grid becomes an interesting role to the potential gas producers from sewage and biogas plants.

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