A landfill in Bilbao, Spain, demonstrated how biogas generated from decomposing municipal waste can be captured, treated and used to produce electricity instead of being released into the atmosphere, The Economic Times reported.
The Artigas landfill, which received around 700 tonnes of waste every day from Bilbao and neighbouring towns, had a waste stream equivalent to that generated by a population of about 800,000 people, according to a CORDIS report.
A biogas recovery and power generation system was installed at the site to collect methane-rich gas produced during waste decomposition and use it for electricity generation. During its first year of operation, from November 1992 to October 1993, the plant generated 4.4 million kWh of electricity.
The electricity generated was sold to Iberdrola, which purchased around 4.1 million kWh during the first year at an average price of 10.6 pesetas per kWh.
How the system worked
The Artigas facility had 21 gas collection wells connected to 12 gas lines. The wells were between 10 and 18 metres deep and transported the landfill gas to a main collector located inside the engine house.
The collected biogas contained an average of about 52% methane. The system was capable of recovering around 600 cubic metres of biogas per hour, while the engines consumed approximately 500 cubic metres per hour.
Before being supplied to the engines, the gas was treated to remove particles and other contaminants. Excess gas that could not be used by the engines was sent to a flare for controlled combustion.
Moisture was another concern because water present in the gas could damage the engines. The biogas therefore passed through a dehumidification system before entering the power-generation units.
The plant used two internal combustion engines, each driving a 450 kW alternator, giving the facility a combined generation capacity of about 900 kW. The electricity was passed through a 2,000 kVA booster transformer before being supplied to the Iberdrola grid.
Gas capture also addressed landfill risks
The project was not limited to electricity generation. Capturing landfill gas also helped address some of the environmental and safety problems associated with the accumulation of gas inside waste sites.
According to the report, removing the gas reduced the risk of explosive mixtures developing within the landfill. It also helped protect vegetation around the site because methane can displace oxygen around plant roots.
Gas collection additionally helped reduce unpleasant odours associated with the landfill.
The biogas was regularly monitored, with the Institute of Renewable Energies analysing the gas and condensates passing through the collection system from 1990. Tests showed average methane concentrations of around 50%, while oxygen levels ranged from 0.72% to 8.65%.
The gas also contained compounds including benzene, toluene and ethylbenzene. As a result, additional equipment was used to condition the gas before it reached the engines.
The Artigas project demonstrated that waste deposited in a landfill could provide a second resource through the recovery of methane-rich biogas. By collecting, cleaning and conditioning the gas and using it to generate electricity, the project combined landfill gas management with renewable energy production.
