C)Transport processes

Transport processes include the impact of emissions caused by the extraction and production of fuel used in trains, ships and planes and by the conversion of fuel to mechanical energy during transport. Environmental impacts are expressed per one metric ton(1000 kg) of goods transported over a distance of 1 km (1 ton-km).

Transport by road: For transport of materials by road, where the capacity of a truck may be limited not by weight but by the volume of low-density materials, the environmental impact may also be expressed per cubic meter (m³) transported per kilometer (m³-km). Capital goods, like the production of trucks and road or rail infrastructure, and the handling of cargo planes on airports, are included as they are not negligible.

Rail transport: The impacts for rail transport are based on the average European ratio of diesel to electric traction and average load level of a car.

Air transport (cargo planes): A loading efficiency for European average conditions is assumed and account is taken of a possible empty-return journey.

Energy: The energy indicators refer to the extraction and production of fuels and to energy conversion and electricity generation. The European industry average efficiency is used and account is taken of the mix of various fuels used in Europe to generate electricity. Also, Eco-indicators have been determined for high-voltage electricity that is used in industrial processes and for low-voltage electricity, used in residential, commercial, and light industry applications. This accounts for line transmission losses.

In addition to Europe-average indicators, Ei-99 also provides specific indicators for a number of countries. The large differences between countries are explained by the vintage and efficiency of different technologies used to produce electricity. One of the IE term papers in this class will deal with determining equivalent indices for the U.S. industry.

d) Recycling or disposal of used materials

In the recent past, the only concern about used materials and products was where to dispose them so they could not be seen or smelled. There was little consideration as to their properties, value or effects on the environment. Even today, well meaning people who truly want to protect the environment can be passionate about what should be done with what they consider to be a generic material, called wastes. Industrial ecologists, such as the Ei-99 developers and faculty in this school, are trying to shed some scientific light on this difficult subject. Wastes, and in particular what is called municipal solid wastes (MSW), consist of all phases and practically all materials that exist on this planet. Taking such materials and burying them in a common “grave”, as is presently done for most MSW, is an insult to the Earth and also to human intelligence. Yet, in the U.S. it is encouraged by federal legislation.

Of course, the first thing to consider in process/product design is how to minimize the materials/energy to be used in production and marketing/distribution of a product (packaging, etc.). However, you cannot make an omelet without having egg shells to dispose of. For as long as people want to be fed, clothed, housed, and entertained, there will be used materials to dispose of.

Municipal Solid Wastes

With regard to MSW, the higher density materials (metals, glass, and ceramics) do not decompose nor burn and are the easiest to separate physically and recycle. However, if their sorting is done manually, a large fraction still ends up in landfills. Glass and ceramics are inert materials but metals in landfills continue to oxidize for centuries after a landfill closes.

Manual sorting of papers and plastics can result in some recycling of these materials while the rest goes to landfills. Paper and plastics are recycled to some extent but, in most U.S. communities, nearly two thirds end up in landfills. They range from "difficult to impossible" to decompose so they lie in a landfill for decades or centuries. Their gradual decomposition results in a reduction of volume so that the cover and walls of a closed landfill may subside with time resulting in rupture of mechanical barriers (liners, etc.) and seepage of corrosive solutions into the groundwater or adjacent surface waters. Also, any organic material such as papers (cellulose) and food/plant wastes that is buried in a landfill continues to decompose anaerobically (i.e., in the absence of oxygen) with time and produce methane gas which is a greenhouse gas (GHG) that is about 20 times more potent than carbon dioxide. During the active life of a landfill, some of this gas may be collected and used; after the landfill closure, any methane gas generated is emitted to the atmosphere.

However, this paper/plastics composite material has a "heating value" that is nearly the same as some U.S. coals. Therefore, it can be used as an alternative fuel to fossil fuels for generating electricity. In fact, it is used as such in Waste-to-Energy plants in enlightened communities in the U.S. and many other developed countries. Nearly 16% of the U.S. MSW is processed to recover energy.

The remaining class of materials are food and plant wastes. This is what is called the "wet" stream of MSW. This material cannot be recycled and if combusted has a very low heating value. However, the “wet” stream decomposes easily aerobically (i.e., in the presence of oxygen) to produce a compost product that can be used as a soil conditioner) or anaerobically, in a bioreactor, to produce methane gas and a compost product.