ined taking into account improved understanding of sludge particles' behavior and sediment quality criteria now being developed.
Digested sludge may be a beneficial resource; when it can be recycled feasibly in a beneficial way, it certainly should be. Sometimes, however, the extra costs of energy and facilities and the cross-media impacts of dewatering the sludge and transporting it to places where it can be used beneficially may not outweigh the environmental costs of ocean disposal.
All of the foregoing discussion focused primarily on water and sediment quality and the development of appropriate engineering works and management strategies to produce the desired water and sediment quality while still disposing of wastewater and storm water. The integrated approach obviously requires that full consideration be given to the cross-media impacts of various actions for disposal of wastewater with respect to the land and the atmosphere. Some examples of these cross-media consequences are presented in Table 4.10. There are, of course, other examples as well, but the points are illustrative.
One general point is worth more attention. The building and operation of treatment plants, including the facilities for the processing of sludge, consume materials in their construction and use energy to operate. Materials extraction and production (such as steel for reinforcing bars or copper for windings in motors) have significant environmental costs and consume an important resource base. Energy to run plants requires the extraction of fuels and contributes CO2 to the atmosphere, which may affect global warming. Digested sludge produces methane but this energy is not free. If the treatment plant, through energy conservation, were to have a surplus of electric power generated from the methane, then it could be put into the power grid and substituted for other sources. Secondary treatment is an energy-intensive process, the full environmental impacts of which should be considered along with the benefits and costs.
As a final example, the city of Los Angeles was recently required to stop discharging digested sludge to the ocean via a seven-mile sludge outfall and instead now has an EPA-approved disposal system consisting of dewatering and incineration even though the Los Angeles basin is one of the most severely impacted air pollution regions in the country. The option of moving the ocean discharge point much further offshore to water over 1,000-feet-deep has been predicted to have low cost and few offshore impacts. It was rejected by the EPA because the Clean Water Act prohibited such a project regardless of the environmental consequences of alternative options (LA/OMA 1980, Brooks 1983).