Landfill gas contains many different gases. Methane and carbon dioxide make up 90 to 98% of landfill gas. The remaining 2 to 10% includes nitrogen, oxygen, ammonia, sulfides, hydrogen and various other gases. Landfill gases are produced when bacteria break down organic waste. The amount of these gases depends on the type of waste present in the landfill, the age of the landfill, oxygen content, the amount of moisture, and temperature. For example, gas production will increase if the temperature or moisture content increases. Though production of these gases generally reaches a peak in five to seven years, a landfill can continue to produce gases for more than 50 years.
Odors in landfill gas are caused primarily by hydrogen sulfide and ammonia, which are produced during breakdown of waste material. For example, if construction and demolition debris contain large quantities of plasterboard (also called drywall or gyprock), large amounts of hydrogen sulfide can be formed. Hydrogen sulfide has the foul smell of rotten eggs, while ammonia has a strong pungent odor. Humans can detect hydrogen sulfide and ammonia odors at very low levels in air, generally below levels that would cause health effects.
Many landfill operators are now installing engineering gas containment and extraction systems to utilise the landfill gas to produce power to export to the power grid or for powering operations with energy and waste heat.
The hydrogen sulfide (H2S) gas component in the collected methane gas, will produce sulfur dioxide emissions if burnt and corrode and foul power generation equipment.
Landfills that have a lot of plasterboard will find that they need to install expensive scrubbers to remove the H2S from the gas stream before it can be used for power generation or heating.
Sulphur compounds are corrosive in the presence of free water or the moisture found within the engine oil and/or landfill gas. These compounds can lead to wear on engine piston rings and cylinder linings. Gas recirculation systems may increase the availability of moisture within the engine system. This also affects oil quality, leading to the need for more frequent oil changes.
Sulphur compounds are corrosive in the presence of free water or the moisture found within the engine oil and/or landfill gas. These compounds can lead to wear on engine piston rings and cylinder linings. Gas
recirculation systems may increase the availability of moisture within the engine system. This also affects oil quality, leading to the need for more frequent oil changes.
- unlined landfills in sulphate-rich geological materials such as gypsum (CaSO4.2H2O) quarries or gypsiferous soils;
- landfills where large quantities of gypsum plasterboard or sulphate-enriched sludges (e.g. from wastewater treatment or flue gas desulphurisation) have been buried;
- landfills where sulphate-rich soils have been used as intermediate cover materials;
- landfills where construction and demolition (C&D) debris containing substantial quantities of gypsum wallboard has been ground down and recycled as daily or intermediate cover.
Typically, landfill gas contains <100 ppm v/v H2S but, at landfills where the sulphate loading is high, values for H2S can be several thousand ppm v/v.