James G. Speight - Encyclopedia of Renewable Energy

The specific type of metal contamination found in a contaminated soil is related to the operation that occurred at the site. The range of contaminant concentrations and the physical and chemical forms of contaminants will also depend on activities and disposal patterns for contaminated wastes on the site. Other factors that may influence the form, concentration, and distribution of metal contaminants include soil and groundwater chemistry and local transport mechanisms.

Finally, in order to evaluate the impact of a chemical that has been released to the environment, the chemical must be characterized in terms of the transport and transformation in that system (atmosphere, water, or land) and the potential for the transport of the chemical from one system to another or from one system to the other two. The assessment should focus on areas with which a released chemical is most likely to have contact. For a meaningful characterization, the environment must be viewed as a series of interacting compartments and it must be determined whether a chemical will remain and accumulate in the local area of the origin of the chemical. The potential for the chemical to be physically, chemically, or biologically transformed in the system of its origin (such as by hydrolysis, oxidation, or other transformation; Chapter 8) or be transported to another system such as by volatilization or by precipitation. The chemical could also be transferred by deposition and runoff to surface water that provides drinking water.

Each of these scenarios defines a pathway from the air emission to contact with a person, and each pathway has an associated route of contact. The true potential for exposure cannot be quantified until the pathways and routes that account for a substantial fraction of the intake and uptake for the receptor population have been identified. The likelihood of any pathway depends on the chemical properties of the substance released, where and how it is released, and environmental conditions. Sometimes the exposure increases along a pathway (such as bioaccumulation), but more often the exposure may decrease.

Thus, characterizing transportation pathways begins at the source of the agent release. In some situations, the source may be obvious and can be defined and characterized from air or soil concentrations. In many cases, such as contamination of water supplies, sources and emissions may be multiple and poorly characterized. However, classification of a potential transportation route should, as much as possible, be based on the released volume, duration of the release, and the rate of emission.

In order to fully understand the impact of a released chemical on the environment, the potential for chemical transformation of the spilled chemical which may occur as a result of biotic or abiotic processes, can significantly reduce the concentration of a substance or alter its structure in such a way as to enhance or diminish its toxicity or change its toxic effect. For example, for many airborne organic compounds, transformation processes, such as photolytic decomposition and oxidation/reduction reactions, can result in conversion to other compounds. For organic chemicals, the half-life of the chemical for any given transformation process provides a useful index of persistence in environmental media. For example, the photochemical half-life can vary from day to night, and specific information on the rates and pathways of transformation for individual chemicals of concern must be obtained directly from experimental determinations or derived indirectly from information on chemicals that are structurally similar to the released chemical.

Despite these environmental impacts, renewable energy technologies compare extremely favorably to fossil fuels, and remain a core part of the solution to future energy requirements. Renewable energy is going to be an important source for power generation in the near future because the resources again and again produce useful energy. Wind power generation is considered as having lowest water consumption, lowest relative greenhouse gas emission, and most favorable social impacts. It is considered as one of the most sustainable renewable energy sources, followed by hydropower, photovoltaic, and then geothermal. As these resources are considered as clean energy resources, they can be helpful for the mitigation of greenhouse effect and global warming effect.

However, by understanding the components of the environment and the current and potential environmental issues associated with each renewable energy source, the reader can understand the means to effectively avoid or minimize these impacts as they become a larger portion of energy supply. For this reason, this encyclopedia is an all-inclusive work that also presents not only the environmental components but also the various environmental aspects of the generation and use of renewable energy. Other issues arise that are similar to those produced by the use of fossil fuels – contamination of the atmosphere, water, and the land – but the degree of the contamination is not the same.

However, it would be a serious omission if recognition of some of the potential properties and effects of renewable fuels such as biogas and bio-oil and were omitted from this work. For example, biogas and bio-oil could cause harm to the environment is used without any form of treatment. The gas needs to be cleaned of objectionable environmentally harmful constituents and the bio-oil (from whatever the source) needs to be processed to provide useable products. Accordingly, it has been necessary to include options for gas cleaning and options for bio-oil refining (such as hydrotreating and hydrocracking) so that the reader may understand the conditioning of these products into environmentally benign use.

The dynamics are now coming into place for the establishment of an alternate energy industry and it is up to various levels of government not only to promote the establishment of such an industry but to lead the way, recognizing that it is not only supply and demand but the available and variable technology. The processes for recovery of the raw materials and the processing options have changed in an attempt to increase the efficiency of energy production.

In addtion, there are several interrelationships between conventional fuels and alternate fuels, especially in the areas of fuel production and fuel refining. Accordingly, it has been found necessary to include segments for the conventional fuel industries that are applicable to the alternate fuels industries. As ready reference, the articles in this encyclopedia have been assembled to assist the reader to understand the options that are available for the production of alternate energy, especially alternate fuels, and such processes from the conventional fuels industries and also from the unconventional fuels are, where they are applicable to renewable fuels, also included.

The Scrivener Encyclopedia of Renewable Energy was compiled because the need was recognized for an extensive work on the nature of renewable energy sources. This will be a convenient-to-use encyclopedia that will be a suitable companion for the researcher, teacher, and manager. Also, in order for help the reader understand the nature of renewable energy sources ( Table 1), the encyclopedia contains segments that will allow the reader to compare renewable energy sources with the (to date) more conventional fossil fuels resources and how the conventional processing units that will be necessary to process renewable energy sources that are in the form of gases, liquid and solid.

Table 1 Simplified categorization and nomenclature of the various energy sources.

The encyclopedia also contains a section on further reading for those readers who require further information on any of the subjects.