“Paper or plastic?” This question has come to symbolize the choice between sustainable and non-sustainable manufacturing processes. Do you know the “right” answer? Are you sure? If so, why are you sure? It is unavoidable that the first question sets off a chain reaction of other questions. We must also answer questions about the assumptions we used to generate the first answer and the relative risks associated with these choices!
Most people would answer that paper bags are better than plastic bags. At first, it seems obvious. Paper bags are made from trees and trees are renewable. Plastic bags are made from petroleum which is non-renewable. But what about the manufacturing process itself? Paper production generates a significant amount of environmental discharge including toxic chlorinated chemicals. Thus, water pollution from paper production is a significant problem. Plastic production must be efficient due to the rising costs of the petroleum it is made from. In short, lower petroleum use by a plastic manufacturer results in higher profits but global competition minimizes profits. However, no manufacturing process is perfectly efficient and air pollution is always a by-product.
Now the situation seems less clear. Which is “really” better: an inefficient, highly polluting, paper manufacturing plant that begins with a renewable resource or a highly efficient, plastic manufacturing plant that begins with a non-renewable resource? Recycling seems to give the advantage to paper. But this assumes the presence of a recycling center and high public participation. Be honest, when is the last time you recycled or reused a paper bag?
The need to answer these questions has motivated an approach called “Life Cycle Assessment” (LCA). The overarching philosophy is a “cradle to grave” approach. The analysis begins with the extraction of raw materials, continues through manufacture and use and ends with disposal or recycling. The point is to consider the cumulative environmental and economic effects for all stages. Different approaches to this goal have lead to different methods and standardization is needed. In the USA, the effort to standardize LCA has been led by the Society of Environmental Toxicology and Chemistry (SETAC) and the Environmental Protection Agency (EPA).
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The first step is a materials balance, also known as a mass balance. The first question is: What are all the materials input to the process? For example, soft woods, petroleum, chemicals, metals, packaging, etc. At the end, the mass of the finished product and wastes output by the process must balance with the materials input. As materials pass through the manufacturing process, they require energy at each step. In short, if it moves, it needs energy. Thus, total energy consumption can be calculated for the process. The point of this rather “finicky” approach is to identify inefficiencies. Material inefficiencies are identified by excessive waste generation. Energy inefficiencies are identified by excess waste heat. The generation of waste heat is a result of the “infamous” second law of thermodynamics, also known as entropy. Inefficiencies are only bad when they are unrecognized. An inefficient step in the process presents the opportunity for improvement. The closer you look, the more you find.So what is the answer to our paper vs. plastic question? Sorry gentle reader but there is no simple answer. First, you must consider the relative risks of the water pollution associated with paper production vs. the air pollution associated with plastic production. Which is more important in your community? The risks should be considered in the context of other sources of pollution affecting you. The efficiency of the individual plants must also be considered. A modern, plastic plant may have significant advantages over an aging paper mill, especially in a community where the rate of paper recycling is low and other sources of air pollution are minimal.
We live in a world of increasing penalties for environmental pollution and increasing costs of energy. The quest for increased efficiency and the corresponding decrease in waste and costs is driving a transition in today’s economy. Waste emissions and energy costs are major components of the risk of doing business. Thus, LCA is gaining acceptance among both engineers and managers. Life Cycle Assessment is a method of efficiency and risk analysis and will be an increasingly important factor in planning and decision making for government and businesses.
Bradley R. Clark holds a B.S in Chemistry form SVSU, a M.A. in Mathematics and is completing a M.S. in Alternative Energy from Wayne State University. He started the renewable energy consulting business ENERGISYS and is working in close association with Carbon Credit Environmental Services. bclark@getcarboncredtico2.com |
