Landfills are a fact of life for all of us, collectively we manage to create hundreds of millions of tons of refuse every year. All manner of waste, both household and industrial ends it life at landfills. Nowadays this tipping is extremely regulated for a whole batch of environmental issues and reasons. Many years of research by universities have been funded by government and private agencies that have helped develop our understanding and regulate these landfills as safely as possible. It has also been discovered that the methane from landfills can be used to produce energy, albeit with a major disagreement between groups in the benefits versus environmental impacts argument. This article is aimed at helping the average person to understand how a landfill works, which waste products degrade well, which don’t degrade at all and why the process is longer in a landfill and ways to accelerate the process are being used.
A landfill site is the oldest form of waste management as it’s early operation was simply to have all the tipping organized into one place and buried under a mound of earth. Today, the term landfill site no longer simply means a large empty crater in the ground for dumping of waste, but will actually include infrastructure for processing and separation of various wastes ( recycling) and in some cases the use of bioreactors to produce energy.
What is a landfill and how is it constructed?
A landfill is basically a depression in the ground that has been specifically chosen for its geological properties to aid with containing the waste without contamination leaking out into the local environment and water systems.
A membrane or liner is laid across the area to contain the waste and the leachate ( contaminated water from the waste). Think of it as a giant double skinned bath tub, with a slight gradient so that the leachate can be collected at the lowest point and transferred to a safe sewage facility for processing. Old clay quarries for brickworks are ideally suited as the clay is used as a barrier and saves a lot of time and effort transporting to a new site. The official description from the Environment Protection Agency (EPA) is as follows: Modern landfills are well-engineered facilities that are located, designed, operated, and monitored to ensure compliance with federal regulations.
What are the problems?
- 1. Some of the chemicals can gradually leak through the clay in what is called diffusion.
- 2. Clay can also have it’s own flaws and weaknesses to allow escape.
- 3. The best liners are made of high density polyethylene, but these also can be degraded by some household chemicals which cause brittleness and leads to cracking.
- 4. The leachate collection system can become clogged up with silt or by the growth of micro organisms. The piping can degrade or corrode itself and end up becoming crushed under the weight of the tons of trash above it.
- 5. The covers are continually being weathered, rain, wind snow etc. which opens the soil covering to dry out and crack. Burrowing animals and insects gain can cause weaknesses. These weaknesses can both allow further rainwater in to become contaminated and also allow gases and odors to escape into the surrounding air.
Under all of the federal and state laws, there has to be continual testing and monitoring of these sites for fear of contaminating ground and water supplies. This continues long after a landfill site is completely filled.
Degradation of the waste in a landfill.
In 2010, America produced 250 million tons of waste of which 85 million tons was recycled. This gives a 34.1% recovery rate. The table below shows the life expectancy of general items discarded into the trash and into the landfills:
Banana 3-4 weeks
Paper bag 1 month
Cotton rag 5 months
Wool sock 1 year
Cigarette butt 2-5 years
Leather boot (or shoe) 40-50 years
Rubber sole of leather boot (or shoe) 50-80 years
Tin can 80-100 years
Aluminum can 200-500 years
Plastic 6-pack rings 450 years
Plastic jug 1 million years
Styrofoam cup Unknown? Forever?
Glass bottle Unknown? Forever
Due to the way the landfills are designed, the degradation times are increased as water is drained from the landfill, As the waste becomes more compacted, biodegradation is decreased with the lack of oxygen and water. Researchers at the University of Arizona mined a landfill to understand this in more detail. What they found was that the whole process was far more static than they imagined, hotdogs and pasties were still identifiable after 15 years in the ground because of the lack of oxygen and water.
Curbside waste collections are making an ever increasing dent into the content within these landfills, many areas also benefitting from green waste collections which are taken sites to compost naturally.
Landfills as energy sources.
This is quite a contentious issue so, for the sake of this article, the following information is copied directly from the respective websites. The readers are left to make their own opinion or follow the links for further reading on the subject.
From the EPA website:
Energy recovery from waste is the conversion of non-recyclable waste materials into useable heat, electricity, or fuel through a variety of processes, including combustion, gasification, pyrolization, anaerobic digestion, and landfill gas (LFG) recovery. This process is often called waste-to-energy (WTE).
Energy recovery from waste is part of the non-hazardous waste management hierarchy. Converting non-recyclable waste materials into electricity and heat generates a renewable energy source and reduces carbon emissions by offsetting the need for energy from fossil sources and reduces methane generation from landfills.
From the Grassroots Recycling Network website:
Bioreactor landfills emphasize the production of methane gas, a greenhouse gas 23 times more effective at trapping heat than carbon dioxide. To generate sufficient energy, a bioreactor landfill also depends upon the ability to capture the majority of these emissions. However, estimates of the collection efficiency of landfill gas systems differ widely among experts and models, and due to heterogeneity of the waste mass, there may be no clear model of landfill gas production and capture. The U.S. EPA assumes 75% gas collection efficiency at landfills but measured efficiencies have been reported as low as 9 percent. The 2006 Intergovernmental Panel on Climate Change (IPCC) report on greenhouse gas inventories suggests a default estimate of recovery efficiency of 20 percent. The IPCC cites studies measuring collection efficiencies ranging from 9-90 percent, representative of the many uncertainties involving modeling gas generation and collection efficiency. Even the waste industry attests methane emissions are not accurately tabulated. Given the discrepancy of gas collection and generation data, it is probable bioreactor landfills continue to be net contributors to climate change, not a tool to prevent greenhouse gas emissions.
The design of modern landfills has the effects on the environment in mind, from leakage into the ground, to waste blowing away across the surrounding area, to trying to control the methane produced into the atmosphere. So whilst no system can realistically claim to be 100% foolproof, the regulated landfills are as safe as we could all hope for until a viable and workable alternative is found. To this end, there is much research being sponsored around the world in finding better solutions.
But having lived only 6 miles away from a landfill site at Brogborough, England, I can tell you first hand that on a hot day with a breeze, you can detect a slight odor from the site. On a perfectly still summer’s day, you can see a slight haze over the site as you approach it. This is why I support any efforts to divert waste from landfills, especially waste that does not degrade but could be recycled for other uses.
To this end, I urge all readers to think about their waste, a second bin for recyclable items and find someone willing to collect it if curbside collections are not available to you.
As for energy production, I am sat on the fence over this at the moment. I would like to see a consistently high recovery rate and see some scientific statistics of any effects on the atmosphere. Reducing CO2 for methane, at face value, seems to be replacing one problem with another. I am a supporter of alternate energies to reduce the dependency on fossil fuel, just not at any cost.