Energetic utilization of solid domestic waste landfill methane

Professor, Doctor of Technics, Zolotaryov G.M, General Director, Environment and Life Safety International Academy of Sciences

Annually, about 350-400 kg of solid domestic wastes to be specified per a person tends to be accumulated at housing and communal sector. All the accumulated solid domestic wastes are disposed at the polygons. With the Russian Federation population numbered by 142 million, about 60 million tons of solid wastes are accumulated. More than 10 million tons are the wastes of biological origin – sewage sediments. By their energy potential, the above domestic wastes are equivalent to 20 million tons of fuel oil that may be utilized per one year. Therefore, utilization of domestic wastes for the purpose of electric energy generation may be considered as the matter of urgent character.

Last years, domestic wastes are utilized for generation of electric energy that is produced at waste-processing factories. Besides, an amount of electric energy may be generated at the expense of previously buried domestic wastes.           

The process of buried waste gassing may continue for more than 100 years. Gassing cycle is reduced twice upon reaching the period of 25 years. At the same time, the landfill gas is not only fire-hazardous and explosive, but also harmful to health. Methane emissions result in increasing of thermal effect subject to Kioto agreement regulations. Therefore, degassing of used domestic waste landfills is indispensable condition to be considered for proper functioning of housing and communal sector either from the standpoint of ecological safety and from the one of energy conservation.

As for the other countries, they widely use the new waste biogas energetic technologies.

A network of vertical gas drain holes is joined to the gas pipelines, where the vacuum-compressor station produces vacuum to be required for absorbing of landfill gas and pressure that feeds gas to the piston plant. Biogas is burnt in the gas-piston motor that is joined to the electric energy generator via its half-coupling.

For example, in USA the landfill of 14 ha area containing 1.0 million tons of domestic wastes and 0.5 million tons of industrial wastes was used for extraction of biogas in amount of 60 million m³ per year or 6868 m³/h. Along with it, electric energy in amount of 13.1 MW-hour was generated.

Useful service life of the landfill biogas extraction energotechnological complex made up 8 years (from 1978 to 1985). In 1985, more than 30 units of solid waste biogas extracting plants were operated in USA.

In Germany, company “G.A.S. Energietechnologie” carries out operational inspection of 400 MW output facilities functioning at the expense of landfill gas, biogas and shaft methane. At private sector a number of low-capacity plants to be used for generation of electric power are operated.

In Great Britain, some cement and brick firing plants operating on the biogas extracted out of the landfill stock are used. By now, great experience related to landfill biogas utilization is accumulated.

A number of solid domestic waste polygons including “Timokhovo” (64 hectares), “Salaryevo” (50 hectares), “Shcherbinka” (50 hectares), “Iksha” (40 hectares) and “Khmetyevo” (25 hectares) are positioned within the area of Moscow region. All the above solid domestic waste polygons may be modified and with the electric power generated plants constructed, large volumes of extracted waste biogas may be utilized. In total, the volume of biogas rated in 1.3 billion m³ per year may be extracted within the solid waste disposal area of 300 hectares. The above amount of biogas will make it possible to generate the electric power of 2.5 million mW-h/ year. With electric energy to be specified in amount of 1.0 ruble per 1 kW-h sold, the rate of profit will total 2.5 billion rubles per year.

Polygon “Torbeyevo” (Lyuberetzky district, Moscow region) is projected for supply and installation of imported energotechnological equipment for the purpose of testing the new biogas extracting and energetic technology.

Biogas is collected from the vertical holes. A network of holes is drilled at the solid waste buried depth by means of mobile drilling unit. Then, the perforated pipe of 250 mm diameter is fit in the borehole.

The hole clearance is filled with granular material (e.g. haydite). The hole clearance upper portion is plugged with cement preventing hole aeration and biogas discharge.

Biogas comes from the holes to the collector via degassing pipeline. The vacuum compressor produces vacuum to make biogas coming to the drying filter and then to the gas collector. From the gas collector the amount of purified biogas is delivered to the gas engine connected to the electric generator. For the purpose of safety, gas excess is flared in the gas collector flue. Gas-piston plant is installed as a container-type unit with the output of 1000 kW.

When starting up the gas-piston unit consumes electric mains power. Upon starting up the gas-piston unit supplies 10.5 kV power. Single polygon “Torbeyevo” may be used for installation of several gas-piston units.

Solid domestic waste polygon biogas is generated as a result of anaerobic decomposition of organic remains and consists of methane - 40-50%, carbon dioxide – 35-45%, and nitrogen – 5-15%. Solid domestic wastes contain approximately 150 to 250 kg of carbon compounds per one ton. These kinds of substances are subject to biological decomposition and conversion in biogas with the help of active microorganisms. Upon waste disposal, within the period of approximately one-two years the process of stable, anaerobic, methane fermentation is commenced. Thermal value of biogas emitted by polygon wastes is approximately 5.9 kW per 1 m³ of biogas, thus making up one half of natural gas thermal value. While decomposing, the wastes in amount of 1 ton are capable to emit approximately 150-200 m³ of gas to be utilized for 15-25 years. At polygon “Torbeyevo”, with its base area of 12.0 hectares and height of 12.0 hectares that covers the landfill volumes of 2.0 million m³, the amount of 200.0 million m³ may be extracted. With the above volumes of biogas burnt, the amount of 300 million kW-h power (300 million rubles per year) may be produced. 

 For the purpose of waste disposal, the clay-coated bench is constructed. Wastes being stacked are disposed with their layer thickness of maximum 2 m. Then the waste layer is compacted by means of heavy-duty tractor Caterpillar. Any layer shall have density specified within the range of 0.7 – 0.8 t/m³. Upon compacting the solid domestic waste layer is filled with clay to be used for layer waterproofing. Open waste storage is filled as a separate bench. In summer seasons, around the wastes being disposed at a certain bench, flocks of birds that may be considered as sources of infection are gathered. To reduce risk of infection carried by rodents and birds, it is recommended annually fill the disposed layer of wastes with soil or clay. But, due to some technological problems, it is often hard to make.

The matter of domestic waste biological resources located within the area of Moscow region should be resolved by means of geological analysis of biogas reserves. For the purpose of that, it is preferable to invest funds and arrange any solid waste polygon biogas exploration and extraction joint venture. Due to the technology of solid domestic waste biogas extraction, not only economic, but also ecological nature conservation problems may be resolved.

Upon extracting biogas the ground area may be used for planting of trees and arrangement of any green space. In this case, the disposed area may be reduced from 1000 m to 500 m and used for housing development.