Landfill Liners and Alternative Daily Cover

The old garbage dumps of days gone by are no more. Today’s waste disposal solutions are increasingly sophisticated. Environmental regulation, recycling, and the development of plastics – of all things – have contributed to far more tightly managed landfills, with goals inching towards zero waste.

Garbage dumps used to be large holes, usually on the edge of town, where garbage could be buried. While this was an improvement on how people have historically dealt with their trash – by throwing it out the window, into rivers and fields, or alongside the road – it was still a health hazard, an increasingly offensive thing as populations grew, and an environmental burden.

 

In the United States, the Resource Conservation and Recovery Act, passed by the US Congress in 1976, changed how garbage is processed, managed and stored. The garbage dumps of the past were simply places where garbage was buried. Today’s landfills are much more complexly engineered sites.

They are extensively planned locations that are constantly monitored. This move toward increasingly more environmentally sound methods has also increased the efficiency of these sites. Before selecting a site for a landfill, city planners must work with engineers to determine what the effects a landfill will have in the long term.

An additional safety measure came when the EPA examined using alternative materials for landfill “daily cover”. Landfills are required to be covered at the end of each working day, and the original method was to use a layer of soil. This was obviously wasteful of resources, and used up the landfill quickly.

Since the EPA report in 1993, landfills and state regulations have increasingly adopted alternative daily cover (ADC), typically turning to geosynthetic materials such as polyethylene and PVC, which work well both to contain and to filter, and can be manufactured in very large and custom-fitting sheets.

Geomembranes and geotextiles (the “geo” part simply means working with the land) had already been used as part of the liner underneath the landfill. It now became possible to use them as the top cover also.

Landfill Bottom Liners and Top Covers

One of the biggest issues surrounding landfills is their impact on the environment, particularly the potential of contaminants reaching the groundwater supply. To prevent this, a bottom liner is used. While it is well known that placing large qualities of garbage in one location can have long lasting consequence, scientists and engineers continue to work toward better solutions that are more environmentally friendly.

The EPA constantly works to regulate how landfills are designed and managed so that any new discoveries of more environmentally friendly methods can be incorporated quickly. Currently for landfill liners, it requires multiple layers of materials be used for landfills.

The underlying liner of new landfill sites will often consist of a soil or clay layer combined with a geotextile – a synthetic permeable membrane that screens solids out from the ever-present liquid descending from the trash, the “leachate”. This liquid is a severe pollutant and is contained and directed to a treatment process by yet another geosynthetic layer, this one impermeable. And underneath this layer will often be another impermeable layer of dense clay.

Landfill daily cover used to be almost as elaborate, taking 6 inches of soil or clay for each day’s landfill cap. With the continued improvement of geosynthetic materials, these over-engineered solutions can be replaced by a more plastic material. Landfill covers made of a synthetic reinforced polyethylene can create greater safety for the environment, combined with being easier to use, and less costly than other alternative daily covers. They can also be re-used.

Daily cover must contain gasses generated by the garbage, control odor and dust, minimize windblown litter, discourage birds, and prevent pests and the sp[read of disease. Geomembranes do all these things very well, as well as reducing fire risk, improving community tolerance of the landfill, and most importantly, shedding surface water efficiently – thus avoiding adding to the leachate.

The light yet tear-resistant qualities of geosynthetic materials make them easy for operators to install. To further reduce the risk of tears or holes, manufacturers can create the liner in very large or even one piece to fit the landfill size.

The benefit of using this type of cover is that it reusable. This saves cities a lot of money. Also, because operators don’t have to add additional materials to landfill, the lifespan of the site is extended. The combination of a good landfill liner and an alternative daily cover significantly decreases the long term impact the landfill has on the environment.

The federal government provides oversight of landfill operations to ensure that improvements are made Landfilthat make them more environmentally friendly. This involves tracking recycling and composting efforts. Both government and operators are also exploring ways of generating energy from waste processes.

The United States generates 262.4 metric tons of solid waste each year. That number has grown each year – but efforts in recycling and composting have caused it to plateau, and since 2005, the growth has been minimal.

Bottom Line

Landfills are becoming better about preserving the environment. Their efforts, coupled with increased recycling efforts, are improving how waste is managed in the United States. The development of synthetic materials for landfill liners and alternative daily cover has significantly advanced the design and management of landfills.

Recycling of Polyvinyl Chloride

Polyvinyl chloride is one of the most widely used plastics worldwide. A major problem in the recycling of polyvinyl chloride is the high chlorine content in raw PVC and high levels of hazardous additives added to the polymer to achieve the desired material quality. As a result, PVC requires separation from other plastics before mechanical recycling. PVC products have an average lifetime of 30 years, with some reaching 50 or more years.  This means that more PVC products are reaching the end-of-life and entering the waste stream, and the amount is likely to increase significantly in the near future.

PVC Recycling Methods

Currently, PVC is being recycled by either one of the two ways:

  • Mechanical recycling – This involves mechanically treating the waste (e.g. grinding) to reduce it into smaller particles.  The resulting granules, called recyclate, can be melted and remolded into different products, usually the same product from which it came.
  • Feedstock recycling – Chemical processes such as pyrolysis, hydrolysis and heating are used to convert the waste into its chemical components.  The resulting products – sodium chloride, calcium chloride, hydrocarbon products and heavy metals to name a few – are used to produce new PVC, as feed for other manufacturing processes or as fuel for energy recovery.

In mechanical recycling, because no chemical reaction is involved, the recyclate retains its original composition. This poses a recycling challenge because PVC products, depending on their application, contain different additives.  For example, rigid PVC is unplasticized whereas flexible PVC is added plasticizers because this additive increases the plastic’s fluidity and thus, its flexibility. Even products used for the same application may still differ in composition if they have different manufacturers.

When different kinds of PVC waste are fed to a mechanical recycler, the resulting product’s composition is difficult to predict, which is problematic because most PVC products, even recycled ones, require a specific PVC content.  In order to produce a high-quality recylate, the feed ideally should not be mixed with other kinds of plastic and should have a uniform material composition.Material recycling is therefore more applicable for post-industrial waste than for post-consumer waste.

Feedstock recycling is seen to be complementary to conventional mechanical recycling as it is able to treat mixed or unsorted PVC waste and recover valuable materials.  However, a study showed that feedstock recycling (or at least the two that was considered) incurred higher costs than landfilling, primarily due to the low value of the recovered products. This provides little incentive for recyclers to pursue PVC recycling.  This may change in the future as more stringent regulations to protect the environment are enacted.  Some countries in Europe have already banned PVCs from landfills and PlasticsEurope is targeting a “zero plastic to landfill” in Europe by 2020.

Post-industrial waste is relatively pure and comes from PVC production and installation, such as cut-offs from laying of cables or scraps from the installation of window frames.  These are easily recycled since they can be collected directly from processors or installers or even recycled by producers themselves as raw material to manufacture the same product.

Post-consumer waste contains mixed material and has been used for different applications.  These are products that have reached the end-of-life or are replaced due to damage, like pipes from underground, window frames being replaced for renovation and electric cables recovered from demolition. These would require further sorting and cleaning, adding cost to the recycling process.  The recyclate produced is usually of lower quality and consequently of decreased economic value.

Recent Developments

Europe is leading the way for a more sustainable use of PVC with programs, such as RecoVinyl and VinylPlus, where recycling is advanced as one of the ways to use resources more efficiently and to divert as much waste as possible from landfills. Recovinyl, created in 2003, is an initiative of the European PVC industry to advance the sustainable development of the PVC industry by improving production processes, minimise emissions, develop recycling technology and boost the collection and recycling of waste.

Having been successful in all of its goals, including an increase in recycling of PVC across Europe to over 240,000 tonnes a year, in 2011 the PVC industry redefined the role of Recovinyl as part of the ambitious new ten-year VinylPlus sustainable development programme. VinylPlus works in partnership with consumers, businesses, municipalities, waste management companies, recyclers and converter, as well as the European Commission and national and local governments. The goal is to certify those companies who recycle PVC waste and those accredited converting companies who purchase recyclate to manufacture new products and applications.

Even if some types of PVC recycling are not feasible or economically viable at present, it will likely be reversed in the future as governments, manufacturers, consumers and other stakeholders create programs that innovate and find ways to achieve a sustainable future for the PVC industry.