Addressing End of Life Issues of Bioplastics
There are many benefits that plastics offer to the world, but the overall perception that people have concerning plastics is negative. Some of the primary concerns with plastic consumption are the environmental pollution and sustainability of the plastic life cycle.
In a recent study by the American Chemistry Council, people were asked about their perceptions of various packaging materials. Nearly 1/3 of the people surveyed had an unfavorable view of plastics, as opposed to only 7% that had an unfavorable view of paper or cardboard. In fact, of all the materials surveyed, plastics were ranked at the bottom of the list. Consumers clearly expressed negative perceptions about plastics in relations to the impact on the environment. The top three reasons against plastic in order were: Not biodegradable, bad for the environment and not all plastics are recyclable. All three of those concerns are end of life cycle issues. (1)
The weakest point in the plastic life cycle is at the end of the products useful life and disposal. Although the industry is committed to recycling, currently 55% of all municipal solid waste and 85% of plastic waste ends up in landfills. (3) Landfills are the least desired management strategy for plastics. “A more significant problem for land filling is that plastic wastes now constitute about 10% by weight and about 20% by volume of the municipal waste stream. Since plastics are essentially nondegradable, their volume will not shrink and plastics may eventually consume a disproportionate amount of landfill space.” (Rustagi, 2011) None of the material resources from plastic products are recovered. Long term risks of contamination of soils and ground water by some additives and breakdown by products in plastics pose continual organic pollutants. (Hopewell. J, et al., 2009)
“Plastic production has continued to climb every year since the 1950’s. The outlook for 2015 is 6 billion pounds of plastic production. Globally, 450 billion pounds of plastics are consumed, which averages out to be 65lbs of plastics usage per person annually.” (Mosko. S, 2013) In addition, the world’s population has recently hit 7 billion people, and is expected to hit over 9 billion by the year 2050. It’s vital to manage waste issues that will result from this dramatic population growth. (4)
Recycling Issues for Bioplastics
Biodegradable polymers have the disposal options of landfilling, incineration, anaerobic digestion, home and industrial composting and recycling. (Yates, et al.,2013) One of the problems is that bioplastics are not easily recyclable. Most people have the misconception that all the plastic they put in their recycling bins are 100% recycled into new plastic products. However, only 10% of plastic waste gets recycled in the USA, and up until recently, a good portion of that was actually sent to over to China. This should be looked at in a positive light by seeing it as an opportunity to look at plastic as a valuable resource instead of scrap and should spawn creativity to find new end of life uses for this “unwanted” plastic.
Another perception is that bioplastics are automatically considered to be a total contaminant to current recycling streams. “The increased use of bioplastics and biocomposites may have further serious implications for the recycled plastics industry, as it could potentially lead to the contamination of collected conventional plastics by bioplastics, affecting the quality and physical integrity of the resulting materials.” (Soroudi et al, 2013) “Regarding the recycling of PET mixed with PLA, the limitations of NIR sorting systems, not only their difficulty in identifying polymers with special colors or structures, but also their high costs.” (Soroudi et al, 2013) However, according to a recent study conducted by the National Packaging Consortium in Italy, up to 10% of starch based shopping bags could be combined with traditional PE shopping bags with negligible impact on the technical performance of recycled PE. The results were the same when up to 10% of flexible, compostable packaging material was combined with common plastic packaging. (6) Given the increasing popularity of PLA and bioplastic packaging entering the market, the recyclability complications represent a challenge for recyclers to cope with a more diverse stream of plastics. Thus recycling does not offer the flexibility and economics needed for complete utilization of the waste plastic streams.
Solution…A Two Prong Approach
The chart below shows recycling in conjunction with energy recovery and how they work together. The model has two complementary approaches to resource management ; in one scenario the plastic material ends up as a new product; in the other scenario the material ends up in a Waste- to- Energy facility and is converted to fuel or electricity.
On the left side of the diagram is recycling. Once the plastics and the materials leave the household, they are placed in recycling bins and sent to a recycling center for separation, cleaning, grinding, reprocessing and pelletizing. The resin pellets are then made into new products.
On the right side of the diagram, there is the energy recovery cycle. Plastics leave the home, but these plastics are not candidates for recycling. The plastic waste is placed in a bin for pick up, and is transported to an energy recovery facility where it is processed through methods such as, combustion, gasification, or pyrolysis. These processes can produce a ratio of co-products such as oil, syngas and/or electricity. “Because plastics are typically derived from petroleum or natural gas, they can generate almost as much energy as fuel oil, although the much higher amount of energy initially required to produce the plastic is lost. (Rustagi, 2011) “The amount of energy recovered can also depend on whether it is used for electricity generation, combined heat and power, or as a solid refuse fuel for co-fueling of blast furnaces or cement kilns. A process called Liquefaction can convert the plastic waste into diesel fuel, alternatively gasification or pyrolysis can produce hydrogen rich syngas or heavier crude oils.” (Hopewell. J, et al., 2009) Pyrolysis is especially appropriate for products or waste streams that contain waste plastics, organic waste and inorganic solid waste materials because the pyrolysis process can convert any organic material into a hydrocarbon rich bio-oil that can be further refined into products conventionally produced from petroleum. These non-recyclable organic waste residues have high conversions yields to liquid and gases in the pyrolysis process.”(Adrados, 2012) In both cases of reuse and energy recovery, waste plastic is converted into a valuable resource (fuel or electricity) through thermo-chemical processes.
The recycling industry in the US started in the 1980’s, however after nearly 30 years, the U.S. has some of the lowest recycling rates in the developed world. The average annual recycling for the USA is around 8% and Europe has a 24% recycling rate. (Mosko.S, 2013)
“Recycling biopolymers may be more favorable energetically than composting, however, the sorting and cleaning processes may make this impractical and if biodegradation has been triggered, the degraded material will be unsuitable for recycling. Incineration (with sufficient energy recovery efficiency) may be an end of life option which does not require biodegradation of the materials, but could have lower environmental impacts than industrial composting.” (Yates, et al., 2013)
In the future, energy recovery is expected to gain more popularity in the US for several reasons. First, as recyclable plastics are processed over and over, they lose some of their mechanical properties and can no longer be effectively recycled for input into new products. Secondly, as recycling capacity is likely to increase, it won’t be sufficient or logistically feasible to process the amount of waste that an expanding population will continue to produce. Third, the intrinsic energetic value of non-recyclable plastics is a valuable resource to produce energy. We need to control our energy costs and improve our energy solutions, and plastics can help achieve this goal. Energy recovery through waste-to-energy processes provides a clean alternative and sustainable energy source that will be there as long there is a waste supply. From the chart above, the U. S. lags far behind other European nations in recycling and waste- to- energy. The U.S. has only 86 waste-to-energy plants in 25 states, compared to over 400 waste-to-energy plants in Europe. Europe is leading the trend in sustainable plastic solutions, however there are leading states within the USA that are catching on to the waste to energy movement, such as Connecticut, Massachusetts and Hawaii. (8) Surprisingly, California has one of the highest recycling rates, but one of the smallest waste to energy rates and ranks only 14 out of 50 states for avoiding landfilling.