With the aggregation of millions of people in large urban centers, there is an unprecedented amount of human waste to be treated. In this treatment, pathogenic microbes (bacteria, viruses, protozoa, and parasitic worms) must be removed or reduced to harmless levels. It is well known that in any community, at any time, there are always small numbers of people who are either manifestly ill, in some stage of illness but not demonstratively so, or healthy carriers of diseases. Together, these are indications of a community’s normal background of pathogenic microorganisms in which feces are in the sewage. As a result, sewage is a great threat to human health, especially for those who come in contact with water drawn from sewage contaminated sources.
Generally, sewage consists of 99.9% water and 0.02% solids. Although the amount of solids may seem small, in comparison to the amount of water that is flowed in a large city such as Washington D.C, solids amount to 200 tons/day (Benarde). Of this 40-50% is protein, 40-50% consist of carbohydrates, and the remaining 5-10% is fat (Benarde). All these substances are broken down from fecal matter. Fecal matter is known to be the leading cause of death, with a toll of 10 million a year. Some examples of diseases are typhoid and cholera; these are very common in third world countries, due to the lack of sanitation. In modern industrialized countries, sanitation is taken to higher step than in developing countries. For example in the United States, drinking water runs through a series of treatment steps before it is flowed into households, as for third world countries, water is usually pumped by a well with no treatment at all. Because of this, serious diseases develop in untreated, unsanitary water.
In the United States, several steps are performed before water can reach a household. The first process to treat water is the primary treatment, sewage goes to a treatment plant, in the treatment plant the untreated water flows through coarse and fine screens to trap floating objects such as fecal solids and other items. The coarse screens consist of a bank of vertical bars set approximately 1 inch apart. Behind the screens is a comminutor, which grinds the remaining solids to a size that should prevent damage to the machinery that later are used to filter (Benarde).
The following step is secondary treatment, depending on the type of secondary treatment to be given; the sewage will pass to either a bio-filter or an activated sludge aeration tank. Both are based on the stabilization or neutralization or organic waste by biological action. Although pathogenic microorganisms are partially removed in the settling process and filtration and aeration mechanically remove others, it is the process of chlorination that destroys the great majority of organisms. In addition, chlorine leaves a residual in the water system can further disinfect, as water is discharged into the watercourse.
Water supplies were...