How Do Landfills Work? (Animated Guide)
The trash tossed in dumpsters goes through a long journey that normally ends in a landfill.
A landfill is a place where waste and disposable materials are stored. Landfills in the past (also known as dumps) went unmonitored, easily bred contamination, and attracted disease-carrying pests. Today, landfills are regulated and waste management employees go through several steps to safely store waste. Some of the byproducts of trash decomposition that normally would pollute the atmosphere, like methane, are now being captured and used to generate electricity.
The most recent report from the EPA in 2015 found that Americans created 262.4 million tons of trash that year. The massive amount of trash produced makes proper waste management crucial to ensure a safe, clean environment for all.
So, where does all of that trash go and how does it get there? Read on below to learn exactly how landfills work.
How Do Landfills Work?
Modern landfills are built using a layering system designed to safely isolate waste and monitor any byproducts, leaks and anything else that can harm the environment. Isolating the trash from air and water is vital for preventing contamination.
We can learn more about how landfills work by examining each layer.
Cells (Old and new)
Each day, trash is compacted a cell in order to make the most of the space available in the landfill. The day’s work cell is also known as the daily workface. Here, trash is organized in layers or lifts then compacted accordingly.
Heavy machinery like bulldozers and compaction equipment are used to compress the trash and place it in the landfill. A six inch layer of dirt covers the cell after it’s made and is then compacted once more. This layer helps contain odors and prevent unwanted pests. Some landfills are considering alternatives like tarps or cement emulsions to save space.
The Liner System
The bottom layer of the landfill consists of a liner that keeps trash and byproducts separate from the environment and groundwater. Some facilities use more than one type, but at any landfill you’ll find at least one of the below liners.
- Compact clay liners: These liners are normally made of dense, compacted clay solid enough to prevent waste, liquid or gas leaks from seeping into the environment.
- Plastic liners: These liners are made of dense plastic and other synthetic materials, normally 30 to 100 mils thick. Plastic liners are typically used in municipal solid waste (MSW) landfills.
In some cases, landfills use clay to first line the bottom, then plastic (or another synthetic material) on top to reinforce it.
Learn more about the different types of landfills.
The Drainage System
On top of the liner, you’ll find a storm water drainage system that filters out both the liquids produced by trash and the water collected from rain and snow. This layer is important because it separates produced liquids from solid waste. Another drainage system is used to specifically filter out the liquid produced by trash, called leachate, from any rainwater and the rest of the landfill.
We explain the different drainage systems below.
A storm water drainage system uses a pipes to keep rainwater out of the landfill using a number of structures:
- Drainage ditches: Storm water is collected through a pipe system and is carried from the landfill to drainage ditches around the landfill. These ditches are normally lined with concrete or gravel.
- Collection ponds: Next, the water is carried from the ditches to collection ponds, sometimes called sed ponds, where suspended soil particles settle out. Here, the storm water is also tested for leachate chemicals.
- Off-site: Finally, storm water is pumped or permitted to flow off site and back into the environment after it has been sufficiently filtered and the soil particles have settled.
A leachate collection system filters waste liquids from the landfill using pipes, packs of gravel and layers of sand on the bottom of the landfill. Leachate is also treated during this process, since the liquid is normally acidic after picking up contaminants while it seeped through the landfill.
The leachate collection system is similar to the storm water drainage system.
- Leachate collection ponds: Perforated pipes throughout the landfill collect leachate and carry it to leachate collection ponds, also called sumps. Here, the leachate is tested for chemical levels and allowed to settle.
- Sent for treatment: Afterwards, the leachate is released to an onsite treatment facility or off-site wastewater treatment plant. Some landfills recirculate the leachate into the landfill so it soaks into the waste and does not reappear. This reduces the amount of leachate in the landfill, but increase the concentration of contaminants.
- Release: The treated leachate is then released into local bodies of water after it’s deemed safe and clean.
Alternatively, waste can be tested for liquids before it enters the landfill. This is done by passing waste through standard paint filters. Trash is rejected if any liquid passes through the filter and drips in a five to 10 minute period.
Groundwater monitoring stations test water in the environment around the landfill for leachate chemicals using pipes that directly reach the water itself. These systems normally have wells upgradient (uphill) and downgradient (downhill) of the landfill to test water quality.
- Upgradient wells: These wells test water before it moves under the disposal area to get a baseline measurement of the water’s quality before it passes.
- Downgradient wells: These wells test water after it’s passed the disposal area to see if there’s been contamination or any other impact to the groundwater.
Gas Collection System
The gas collection system uses extraction wells and pipes throughout the landfill to carry landfill gas that’s generated when waste decomposes to treatment areas where it is then vented, burned or converted into energy.
Gas is a byproduct of waste decomposition and is generally made up of equal parts methane and carbon dioxide with hints of nitrogen and oxygen. If left untreated, the methane can explode or burn in the short term and contribute to global warming in the long term. Carbon dioxide normally filters out naturally as a part of the liquid filtering processes.
A landfill is permanently capped with a plastic liner when it is full. After it’s capped, the landfill is covered with two feet of soil. Then, vegetation (normally grass and plants without penetrating roots) is planted on top to prevent soil erosion due to rainfall and wind. The landfill is monitored for 30 years to ensure there is no detrimental impact to the environment.
Types of Landfills
It’s crucial to learn what items you can actually dispose of in dumpsters and what items need to be thrown away in special receptacles. Getting this right means making sure everything is transported to the proper type of landfill, especially hazardous materials. Below are a few common types of landfills.
- Municipal solid waste (MSW) landfill: These landfills hold waste generated by households, hotels, and similar areas. This waste is non-hazardous.
- Construction and demolition (C&D) landfill: These landfills contain material produced during the process of construction, renovation and demolition. Materials in this category include concrete, wood and glass. C&D landfill waste is also considered non-hazardous.
- Hazardous waste landfill: As the name implies, these landfills hold hazardous waste. This category includes wood-preserving wastes and spent solvent wastes, according to the EPA.
How Modern Landfills are Becoming More Sustainable
As you can see, today’s landfills are a far cry from the disease-ridden dumps from years before. The industry is also exploring other ways to make landfills cleaner, safer and more environmentally friendly in addition to the processes we’ve already mentioned. See below to learn a few ways landfills are becoming more sustainable.
A simple way to reduce a landfill’s ecological footprint is by separating waste into its respective disposal areas before it reaches a landfill. For example, properly disposing of hazardous materials can ensure it’s safely discarded and doesn’t come in contact with other waste or people.
Proper segmentation is also helpful for organic waste. This type of waste, like food and greens, releases lots of gasses and odors into the air. Landfills can do their part by having a separate, green drop-off area. The EPA also suggests that individuals can do their part by composting at home.
Trash to Energy
As we’ve mentioned, some landfills are converting gas created at their sites into electricity. This helps lessen our reliance on fossil fuels, like oil. Below are three common ways landfill gas energy is converted and used.
- Electricity: Gas is used as fuel to generate electricity at power plants either at the landfill or nearby.
- Alternative fuel: Gas is carried to an industrial or commercial facility and used in place of or in combination with fossil fuels.
- Processed gas: Gas is filtered to natural gas quality and transferred for use in places natural gas is normally applied, like kitchen stoves.