Waste-to-Energy Conversion

All human activity produces waste . It is important to manage this waste properly, for both economic and environmental reasons. Waste is defined as any solid, liquid or gaseous substance that cannot be used or recovered by its producer. Reducing the negative impact of an activity on people and the environment means minimizing waste production. Waste can be a raw material for other uses. In such cases, it is worthwhile exploiting this possibility, provided it is economically profitable or satisfies environmental regulations. In the latter case, the activity must be financed by the community in the form of grants or subsidies. The ultimate aim of waste management is to recover what can be recovered, and end up with final waste that will have to be disposed of in one way or another.

There are many ways of recovering or managing the waste produced by our civilization. The production of energy or energy sources is one possible way. This article is the first in a series dedicated to this type of recovery. It is a general introduction to this complex field. It introduces subjects that will be covered in greater technical, regulatory and economic detail in subsequent articles written by specialists.

First, we'll show that energy production is just one of the ways in which waste can be valorized. Then, using two unconventional examples, we'll show how we can obtain an energy source from waste. The first example will focus on nuclear waste from current nuclear power plants (slow neutron reactors), which is a potential fuel for future power plants (fast neutron reactors). The second will look at the production of a fuel from the carbon dioxide produced by the combustion of fossil fuels. To achieve this valorization, we need to supply more energy than we can subsequently recover. These examples represent two extremes: with nuclear waste from current power plants, it is possible to produce much more energy than is possible with current technology, whereas with carbon dioxide, a great deal of energy has to be expended to resynthesize a fuel. After introducing the main waste streams that can be used for energy recovery, we will briefly describe their energy recovery options. The section on meat-and-bone meal will be a little more developed than the others, as this waste can lead to fatal diseases in 100% of cases for cattle (BSE) or for a human being (Creutzfeldt-Jakob). This waste...