Anaerobic Digestion at the Omrin Ecopark Leeuwarden, Netherlands
The following was reported in the Energy from Waste Supplement to the CIWM/s Wastes Management magazine after a study tour during 2006. We thought that inclusion here may of interest to our readers, showing as it does how an AD Plant can be integrated into an eco-park facility, based at a landfill site.
For copyright reasons we have only included an extract here from the much longer article in the supplement. The information is published as in 2006, so the article will not reflect subsequent changes.
The eco-park is considered to be primarily an Energy from Waste Facility, however, it receives a large tonnage of construction waste annually, includes an MBT Plant and Anaerobic Digestion Facility and is just one of the many processes used at the site to treat waste. Finally, there is a landfill on site which we presume accepts all the remaining residual waste from all activities.
The extract follows:-
“The MBT plant processes 220 000 tonnes per year of waste, which represents all household and most commercial waste. The MBT process involves the deposit of wastes into the plant by a grab, which goes through a series of drum screens to sort the materials by size and air blows off the lighter fractions (eg plastic film, tissue paper), while metals are extracted by magnets and eddy current separators.
The larger fractions, typically paper and plastic, are separated for use as fuel and added to the light fraction that is blown off and baled as a refuse derived fuel. This is sent to Germany and burnt at a cement kiln. There appeared to be some commercial or regulatory uncertainty over this process and the operator of the cement kiln was only able to offer one-year duration contracts for receipt of the material, and at a significant cost (€70/tonne 2006).
After removal of the large and light fraction and metals, the predominantly finer, organic rich residue is washed by steam to remove inorganic material like glass, sand and stone, and then processed in an anaerobic digestion facility.
The anaerobic digestion plant uses a thermophilic process (with added heat) operating at 55°C, which degrades the organic fraction under controlled conditions and captures the biogas generated. This type of digestion process is preferred because of faster processing time and higher gas yield rates.
The process produces enough biogas to generate electricity to power the plant and export into the grid. The digester tanks are flushed from the top and bottom as part of the process and the wastes are mixed and digested in the process to produce a solid digestate and a liquid effluent, in addition to the biogas.
The liquid effluent together with the landfill leachate is treated on site.*
The solid digestate is applied as a base and top layer for landfill.*
The construction and demolition waste is processed at a dedicated sorting facility where materials are sorted by hand on picking belts or by wheeled loaders. The concrete and rubble is crushed and graded for use as secondary aggregate and the wood is separated into three grades:
- unpainted, solid wood is used for manufacture of chipboard
- painted wood, hardboard and softwood are exported to Italy for use in the manufacture of MDF
- treated woods are sent for disposal as hazardous waste.
In the Netherlands 95 percent of construction and demolition waste is reported to be recycled.
The Ecopark also accepts waste electrical and electronic equipment, which is sent for recovery by specialist operators.”
- End of Extract -
* If anyone reading this page has current knowledge of this facility, it would be interesting to hear whether subsequently the digestate in solid and liquid forms has been used for other uses. Technology providers generally cite the products of Anaerobic Digestion as just that and say that these can be sold as a revenue stream. Clearly, at the time of the visit the physical output from AD was a liability on the system.
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