Reusable vs. Disposable Cups

In his blog post entitled Reusable vs. Disposable Cups: Saving Money and Energy (July, 2009, http://greenresearch.com/2009/07/16/reusable-vs-disposable-cups-saving-money-and-energy), author David Schatsky discusses the environmental impacts of disposable cups (paper, plastic, polystyrene foam) versus reusable cups (glass, ceramic, higher grade reusable plastic). Schatsky focuses on the impact related to the energy involved in each type of cup. His blog post derives most of its information from one particular study. The study Schatsky cites is entitled Reusable and Disposable Cups: An Energy-Based Evaluation. It was performed by Martin B. Hocking, a chemist at the University of Victoria, and was published in the journal Environmental Management, Vol. 18, No. 6.

From findings in the study, Schatsky highlights many of the energy break-even ratios of the different cup types. For example, polystyrene foam cups require relatively little energy to manufacture, where as ceramic cups require much energy. Therefore, a ceramic cup needs to be reused many times before its energy requirement balances with the energy required to manufacture that number of singly-used foam cups. In this case, the break-even point is 1006 uses (Schatsky, 2009).

Hocking’s study uses a thorough set of equations for determining the total energy involved in all aspect of each cup’s life. These include extracting and processing the raw materials, manufacturing the cups, and washing the reusable varieties. The energy expenditure of each cup type is expressed as a value of kilojoules per gram. It is from these values, along with variables such as the number of uses before washing or disposing, that Hocking arrives at his break-even ratios. These ratios compose the majority of results from the study.

Schatsky accurately summarizes results from the study using data, without making any particularly strong claims that aren’t supported by such data. However, when discussing energy requirements for paper cups, he does use language that is overly strong and subjective. He twice refers to paper as being “an energy hog”. This description goes beyond the data provided in Hocking’s study, and stands out as very opinionated, in an article that is generally results-based.

Hocking performed a number of sensitivity tests in his study, calculating how changes in certain variables affect the break-even ratios. Schatsky does discuss these tests and their results in his article. For example, he notes that if energy in the washing process is reduced by 50%, the breakeven for reusable plastic versus polystyrene falls to 59 versus the 450 from standard energy requirements (Schatsky, 2009). Schatsky goes even further to note that energy efficiency in dish washing has improved since publication of the study, thus highlighting how this limiting variable would affect results if more current data were used to calculate washing energy.

There is one particular limiting factor in Hocking’s study, though, which Schatsky does not discuss in his article. Hocking’s method for determining energy requirements for the manufacture of disposable cups requires that this energy value be compared to the equivalent amount of electricity for washing reusable cups. Such a comparison requires values for the efficiency of electricity production in the area where the manufacturing and washing are done. Efficiency values vary from country to country. For example, Canada has an average electrical generating efficiency of 57.3%, compared to the US at 38% (Hocking, 1994). Values from other countries range from 33.0% to 99.6%. However, Hocking uses the efficiency value from Canada when calculating all energy requirements. Therefore, the actual requirements would vary depending on the country where the manufacture and washing occur.

References:

Schartsky, David, Reusable vs. Disposable Cups: Saving Money and Energy, 2009, http://greenresearch.com/2009/07/16/reusable-vs-disposable-cups-saving-money-and-energy.

Hocking, Martin, Reusable and Disposable Cups: An Energy-Based Evaluation, 1994, Environmental Management, Vol. 18, No. 6.