The inputs and outputs of today’s cities reflect important 19th-century decisions about infrastructure as well as 20th-century developments.

As shown in Figure 7.2 in the textbook, three major types of household waste leave the home as two waste streams.

In some communities, storm runoff and/or industrial wastes join the flow of municipal wastewater in the sanitary sewer system.

The three main objectives of sewage treatment serve the larger goal of producing a waste stream that can safely be released into a body of water.

The processes used in municipal wastewater treatment (sewage treatment) are designed to achieve its three main objectives.

Nothing ever goes away; sewage treatment produces treated effluent and also a new byproduct, sludge, which itself must be treated and then put somewhere.

In less densely populated areas, water is used to carry toilet waste to a septic system.

A composting toilet offers an alternative to the use of water to carry sewage, thus recognizing the value of both clean water and human waste.

The Clean Water Act sets standards for sewage treatment, standards for sewage effluent, and limits on metals and pathogens in sludge.

Safe community drinking water is of critical importance in public health; conversely, unsafe water delivers a health hazard to large groups of people.

In the United States today, some people use private well water; others either treat or supplement their publicly supplied tap water.

Federal drinking water standards are in place for some biological hazards, turbidity, and a large number of chemical contaminants.

Nothing ever goes away; much of our “stuff ” eventually becomes trash—a waste stream that is mundane but still challenging to manage.

Source reduction is a new twist on an old idea.

Recycling diverts recyclable materials from the municipal solid waste stream.

In the United States, municipal solid waste that is not recycled is either incinerated or placed in a landfill.

Municipalities may also produce other wastes.

Federal regulations govern the disposal of municipal solid waste.

The world is rapidly becoming more urban.

Despite having adequate systems in support of the “urban metabolism,” the built environment of more developed countries also creates some health hazards, both indoors and out.

People living in industrialized countries engage in a wide range of activities and use many products that are useful or convenient or pleasant, but may also carry some health risk.

Among the various hazards discussed in Section 7.7, the potential health risks of certain consumer products and services—including various personal care and household products, cell phones, and tanning salons—were not well documented before they came on the market.

The IPAT equation provides a way to conceptualize the impact of development on ecosystems.

At a global scale, we face daunting challenges.