The Tweet: “It takes 91% less energy to recycle a plastic bag than a paper one.”

This fact is based on figures from the Wall Street Journal, and while there is a mistake in the tweet, the message it conveys is an important one. We might use certain materials believing they have better environmental qualities than they in fact do. To add to this, the majority of waste in the UK and US still goes to landfill and our energy recovery programmes are inadequate.

The energy required to recycle a material is measured in British Thermal Units (BTU, 1 BTU approximately equals 1055 joules). According to a 1989 report from the Society of Plastics Industry the energy required to recycle one plastic bag is 17 BTUs compared to 1444 BTUs for a paper bag. If these figures are accurate, a plastic bag requires 1.2% of the energy required to recycle a paper bag.

The actual figures from the Wall Street Journal state that it takes “91% less energy to recycle a pound of plastic than it does to recycle a pound of paper,” not per individual bag like the tweet suggests. This would mean that pound for pound plastic bags require 9% of the energy required to recycle a paper bag. The discrepancy between the two figures of 1.2% and 9% can be explained by the fact that individual plastic bags weigh less than paper ones.

The reasons for using plastic bags over paper ones are accumulating. According to the Wall Street Journal:

• The production of paper bags generates 70% more air- and 50 times more water-pollutants than production of plastic bags.
• At a landfill about 95% of garbage is buried beneath layers of soil, making it difficult for air and sunlight to make contact, which prevents paper from degrading.
• For every seven trucks needed to deliver paper bags, only one truck is needed for the same number of plastic bags, helping to save energy and reduce emissions.
• Plastic bags generate 80% less waste than paper bags.
• Plastic grocery and retail bags make up a tiny fraction (less than 0.5%) of the U.S. municipal solid waste stream.
• Plastic bags generate only 50% of the GreenHouse Gas (GHG) emissions of composted paper bags.
• The production of plastic bags consumes less than 4% of the water needed to make paper bags.

William Rathje, a researcher from the University of Arizona who spent three decades studying the science behind modern refuse concluded that landfills “are not vast composters; rather, they are vast mummifiers.” Biodegradation does take place, but the pace is incredibly slow. Landfill sites are designed to compress as much waste into as small an area as possible, reducing the amount of air around the waste. Rathje and his colleagues would use old newspapers to date the refuse they were studying because the paper would remain in tact for decades.

The 1989 report also provided figures for how much energy is required to make each individual bag; 594 BTUs for a plastic one and 2511 BTUs for a paper one. This is more than four times as much energy per bag. Plastic bags may be synonymously associated with litter and landfill sites, but despite this they are more energy efficient than paper ones.