Aftercare
In order to reduce the environmental impact on the coastal waters surrounding Stige Island, environmental protection measures were required. Therefore a system for collection of leacthate was established in 2003. It is integrated with a monitoring system designed to ensure that at least 58% of the nitrogen contents is recovered - a target set by the local supervising authority, Funen County. Besides the leacthate collection system also gas is being collected from the landfill.
Collection of leacthate
A drainage system is encircling the old landfill and a unique monitoring system involving new innovative technologies has been designed. The monitoring system comprises an infiltration control system. It enables modelling of the water in order to calculate the amount of nitrogen leakage. One of the keystones in the monitoring system is the infiltration control system. This system is unique, and it comprises the location of lysiometres and Time Domain Reflexion (TDR)-probes, to account for variations in rainfall, vegetation, soil composition, ground slope and orientation.
Collection of drainage water
During the closure of Stige Island, a system has been established for collecting, monitoring and discharging surface water at the landfill. This is to ensure that any polluted surface water cannot leave the landfill in an uncontrolled fashion. The pure surface water is discharged to Odense Fjord. If surface water from an area of the landfill is found to be polluted, it is transferred directly to the leachate collecting system.
Gas extraction at Stige Island
The former landfill, Stige Island, has the largest dump gas plant in Denmark. The gas formed from the biological processes that take place in dumped refuse is collected via vertical boreholes in the island. The gas provides electricity and district heating in Odense via a combined heat and power plant.
Electricity and heat for households in Odense
The amount of gas will continiously decrease as the waste is decomposing. Annual production in 2002 accounted for around 8,100,000 m3 of dump gas, yielding 11,300,000 kWh of electricity and 14,200,000 kWh of heat. This covers the annual electricity requirements of approximately 5,000 households and the annual heat requirements of nearly 900 households.
25 km of suction pipes
The gas is collected via 160 vertical boreholes. The total length of the boreholes is more than 2,000 metres. A suction pipe system measuring 25 km in length links the boreholes to 4 pump modules, which are each able to pump up a maximum of 720 cubic metres of gas from the dump per hour. In the pump module, the gas is compressed to a gauge pressure of 1 bar and is transferred to the custom-built combined heat and power plant over a distance of about 4 km via an underground plastic gas pipeline.
4 gas engines comprising 16 cylinders
The gas is utilised in 4 gas engines each comprising 16 cylinders. Each gas engine powers a generator, which produces electricity. The engine's cooling system generates surplus energy together with heat from the exhaust gas and is used for district heating production. The gas engines and the generators each have an electricity output of 736 kW.
