This video segment from a WPSU documentary Liquid Assets describes the process by which water contaminated with raw sewage can be purified to be clean enough for rivers and seas, or even drinking. Until fairly recently, wastewater management was a very simple process and all that was required was a body of flowing water. Then came the deliberate movement of sewage to the ocean or the river to avoid its accumulation in the city. Boston was a pioneer of this system. But with changing circumstances, even this method proved insufficient and wastewater treatment systems became necessary.
Households, businesses, industries and agriculture produce wastewater. It consists of soluble and insoluble particles, organic particles, gases, toxins and bacteria. Treating wastewater is an expensive process with a slow rate of return. Many developing nations have little or no investment in this infrastructure. Even in developed countries, it is a relatively recent introduction to a city’s hygiene management. But before the wastewater treatment plants came the sewage system, which began with Boston.
Boston’s original waste management system allowed wastewater to run naturally down its hills. But eventually, this water started accumulating. Conditions worsened to the point where the government decided to take action and the first modern sewage system of the United States came into being. Now, huge pipes were taking the sewage away from the residents but this waste was left untreated.
In the U.S. wastewater treatment plants were not common until the latter part of the 20th century, because flowing water was considered sufficient to dilute and dispose of the waste. With increasing population, consumption and pollution, this system became insufficient. Hence, cities had to take the next step in hygiene. It takes huge investments to ensure that wastewater and drinking water treatment plants function properly to maintain a safe water supply. Today with evolving technologies, the waste travels through multiple stages of treatment - removing tons of solids, settling out microscopic particles and introducing bacteria that consume and decompose the toxic material. In some treatment plants the water is further disinfected, through the use of ultraviolet light or ozonation.
Wastewater treatment is important not only for human hygiene and health, but also for the plants and animals that live in the water. If too much untreated sewage and other organic matter is added to a lake or a stream, dissolved oxygen levels will drop too low to support sensitive species of fish and other aquatic life. Wildlife in the region surrounding a water resource may drink that water and people may use it for recreation. Water is an important influence on the quality of life and it needs to be conserved during times of scarcity. Treated water may be used again for consumption in households, in agriculture, in industry and for irrigation. In this way, purified water can add to the available water resources of a city and be an especially great benefit to an expanding community.
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