Co-digestion

Co-fermentation is a microbiological process whereby organic matter from biomassa is fermented under anaerobic conditions by methane-forming bacteria. The resulting biogas is burned in a CHP (combined heat and power unit) and converted into electricity and heat. This energy can be used at location or delivered to others, for example an energy company. The fermented manure can be used as animal fertilizer in agriculture.

Principle

From the mixing pit all manure from the farm is brought via a manure-pump into the fermentor. In the fermentor the manure is stirred with the help of electric mixers. The manure remains in the fermentor for a minimum of 30 days. Other products can also be added to the mixture in the fermentor, in which case we speak of co-fermentation. This is done to enhance the output. One can think here of chicken manure, corn, leftover feed from the farm, wheat, vegetables and fruit. These and other products are on the so called ‘positive list’ provided by the ministry of agriculture in the Netherlands.

From the fermentor the mixture (manure + co-product) is conducted to the second fermentor, here the fermented manure cools off. After the second fermentor the manure can eventually be stored in a normal manure silo or be spread directly onto the fields.

The methane gas released during this process is stored above the fermentor under the membrane cover specially designed for this purpose. In this gas-storage space a small amount of air is added to the biogas in order to remove the sulphur. Then a gas motor and generator convert the gas into electricity and heat. The heat produced is used partly to create warmth for the fermentation process. The remaining heat can be stored in a warm-water buffer. A small part of the electricity can be applied for private use and the rest is conducted onto the grid.

This technique has been known for many years, and there is extensive international experience in its use. In recent years substantial subsidies have been given in the Netherlands to encourage the production of sustainable energy from biomass, which makes the fermentation of biomass economically feasible.
International experience indicates that this is a reliable process which now can be applied on a farm without any problem.

Environmental benefits

Methane has a greenhouse effect 21 times stronger than CO2. By converting methane into CO2 and water (by means of incineration through the CHP) the emission of manure is greatly reduced, with great positive effects for the environment. This is underlined by the number of subsidies granted for manure fermentation according to the ROB (reduction of gases other than CO2). Along with the reduction of greenhouse gases the production of odors is also reduced, partly thanks to the closed process.

The sustainable energy produced also contributes to a reduced consumption of fossil fuels by normal power plants. Moreover, the residue is often better than ordinary manure and can be used as a replacement for fertilizer in agriculture. Another advantage of fermented manure as a fertilizer is that the minerals are easily absorbed by plants. This results in better utilization as well as a lower chance of having it rinsed away. Manure that has been fermented also contains a significant amount of organic matter. As a replacement for artificial fertilizer in agriculture this makes it even more advantageous.

Subsidy

Regulations for stimulating the environmental quality of electricity-production have been in effect since July 1, 2003, and facilitate subsidy for sustainable energy.

Moreover the purchase of fermentation installations is also subsidized. This is a fiscal arrangement. According to the energy-investment deduction regulations, an extra 44% of the investment of the fiscal profit can be deducted and spread over three years before the investment and three years following.

Permits

For the building of a fermentation-installation a number of permits are needed.

According to the WRO (law of environmental planning) an exemption from the zoning plan and a building permit are often required. 
One of the most important laws in the area of environment is the WM (Environmental or Conservation Law). This law means that everyone in the Netherlands is required to have adequate concern for the environment. If anyone knows (or can be expected to know) that his actions or neglect can harm the environment he must where possible prevent or limit these effects. 
In article 10 of the conservation law allowance is made for the use of manure-fermentation installations on farms. This can be seen as part of normal agrarian operations.
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E Kwadraat Consultants

Manure-fermentation can also enhance your operational management.
Think here not only of the financial advantages, but also of the improved manure quality, a lower fossil-energy consumption and a contribution to sustainable energy.

Our consultants can help you to judge whether a fermentation-installation would be a worthwhile expansion for your business. After taking inventory of the possibilities they can, along with regulating permits, also help with the following:

  • Financial aspects, such as estimating the advantages in your specific circumstances
  • Supervision of the building
  • Consultation with the bank
  • Consultation with the energy customers
  • Putting together the menu
  • Contracts for delivery of co-products like manure, corn, etc.
  • Contracts for disposal of fermented manure
  • Supervision of technical processes of fermentation

We can also begin with a QuickScan. We hereby make an estimate of the possibilities of your business. A calculation based on your data, an explanation of the latter and taking stock with your local authority will provide a clear picture of your situation.