How are gas emissions monitored at landfill sites?

What we call the environment is everything that surrounds us, from the air we breathe to the water we drink, to the urban or rural landscapes we immerse ourselves in. Landfill sites do also fall under the ‘environment’ handle, and they have the potential to create wide reaching effects on their immediate environment as well as further afield.

Environmental protections are taken very seriously in the UK, and there are strict guidelines in how gas emissions are to be handled at landfill sites. Landfill gas (LFG) is a natural byproduct produced by the decomposition process of organic matter which makes up a large portion of the total waste entering the landfill each year.

While it has a single name, LFG is composed of two main gases: about 50% carbon dioxide and 50% methane, though there are sometimes other trace gases in the mix. The combination of carbon dioxide and methane is particularly problematic for the environment as they are both known to have damaging environmental effects.

Carbon dioxide is the most common greenhouse gas behind water vapour, while methane is one of the most potent. They’re known as greenhouse gases as they have an insulating effect on the planet. When solar radiation enters the atmosphere some of it is reflected back into space by reflective surfaces such as polar ice, glaciers and sand, but a considerable amount doesn’t make it that far.

This unabsorbed and unreflected solar radiation becomes trapped in the atmosphere by greenhouse gases which means that global mean temperatures are gradually rising. It is this fact that makes proper LFG management vital as it helps contribute to a reduction of overall greenhouse gas emissions annually.

LFG detection

Regular monitoring must take a high priority at the landfill as LFG can escape directly from the surface of the landfill or can leak out of gas capping and collection systems which are designed to reduce emissions. As well as surface loss and permeation through gas management systems, landfill gas can also escape laterally by leaching into the surrounding earth or becoming dissolved into the water table.

Landfills, therefore, have the potential to contribute to local pollution and global emissions of carbon dioxide and methane, so proper monitoring must be carried out at various points in the waste management system to ensure levels are within acceptable parameters at all times. Current landfill gas monitoring guidance states that:

• Appropriate measures must be taken to monitor and control the accumulation of gas
• Migration of landfill gas must be controlled
• Landfills must collect LFG which is produced by the waste
• Collected gas must be either treated or put to use
• Gas management should have minimal risk to the environment and the health and safety of site operatives
• Gas that cannot be used should be flared

There are four main ways that gas emissions are monitored at landfill sites including passive and active sampling, remote sampling and monitoring, and continuous monitoring.

Active landfill gas sampling

In active LFG monitoring systems, a volume of gas is passed through a solution or filter within a specific time frame to ascertain the present gas levels. The contents of the filter or the chemical solution are analysed in a lab to give an average reading of gas emissions over time. As this method produces an average it can’t be used to identify isolated events such as leaks.

Passive gas monitoring

Passive monitoring is usually done by exposing a chemical solution to the ambient air conditions for a period of several weeks so that it can adsorb pollutants. The pollutant concentration is measured to give the average LFG emissions overtime, and as with active monitoring it is not possible to pinpoint events.

Continuous monitoring

Continuous monitoring produces real time data on LFG emissions as samples are collected and analysed to give average readings over short periods of time.

Remote gas monitoring

Monitoring gas emissions remotely is a little more complex and produces real time readings to detect trends in emissions and identify events. It uses methods such as long-path infrared spectroscopy.

It is possible to take readings using sampling equipment, handheld devices, and sensors placed at key locations throughout the waste management system.