ABSTRACT
In 2010, 50% of the world’s population lived in cities, as compared with 20%, 10 years before (WHO, 2014). More than 60% of the population will live in urban areas by the year 2030, making this an increasingly significant component in the global environment. Cities account for 70% of the world’s energy consumption and greenhouse gas emissions. Urban centers, together with their suburbs, constitute what is now called the built environment. This built environment includes (a) the various physical structures that serve the community; (b) the resultant products and discharges associated with the various industrial, municipal, and domestic activities such as wastepiles, dumps, aeration ponds, gravel pits; (c) the infrastructure, such as pipelines, transmission towers, roads, runways, bridges; (d) the various utilities necessary to service the community, such as power plants, gas plants, wastewater treatment plants, reservoirs; (e) the other kinds of resources associated with, and necessary to sustain the urban population and the welfare of the community (e.g., parks, lakes, forests, recreational and sporting facilities). By its very nature, the man-made environment that defines the built environment is often in conflict with the natural environment and in particular with the goals of sustainability of the land environment and its natural resources. The general perception is that urban centers consume significant resources and pollute the air, land, and water. Populations within the cities require clean air, clean water, sewage and waste management systems, adequate food supply, housing, and transportation. It is estimated that more than 200 million people live in cities that do not have access to clean drinking water and that more than 400 million people live in cities that do not have access to solid waste collection services and facilities. It is often argued that these demands are currently not well met, and that the demand deficit will continue to escalate with time. For example, in Accra, Ghana, only 5% of the inhabitants have access to a sanitation network, whereas 50% do not have a septic tank or access to public lavatories (Fauchon, 2012). In Lima, Peru, 90% of the sewage (more than 16 m3/s), is discharged directly into the sea. Some typical types of urban problems are summarized in the illustration shown in Figure 7.1.
