Wastewater Management

Sources of Wastewater

Wastewater is collected in sewerage networks (if available) or in small decentralized systems such as privy houses, pit latrines, septic tanks, and so on. Most cities throughout the world have sewerage systems that allow for the collection of both wastewater and runoff resulting from rain. Runoff carries a mixture of water, sediments, oil, and grease from streets that is combined with wastewater from human-related activities that produce liquid wastes. Sources of wastewater from human-related activities are classified as point source or direct, and nonpoint source or diffuse. Examples of direct sources are the discharges from domestic residences, public properties such as governmental buildings, private commercial properties, industrial and mining facilities, and livestock farms. Examples of diffuse sources are agricultural areas. Each of these sources can add different types and concentrations of contaminants to water.

Wastewater Constituents

Wastewater is composed primarily of water. Alongside water, there are high concentrations of chemicals, toxic compounds, and organic and inorganic matter. When wastewater is accumulated and is left untreated, the decomposition of the organic matter that it contains leads to nuisance conditions, including the production of malodorous gases. Untreated wastewater contains a large number of pathogenic organisms (bacteria, viruses, parasitic worms, etc.) that come from human and animal intestinal tracts. These organisms are the leading causes of epidemics such as typhoid, cholera, hepatitis A, dengue fever, among others and bacteriological and viral diseases. Wastewater also contains nutrients, such as nitrogen and phosphorus, that exist naturally in the environment. However, the high concentrations of these nutrients in wastewater can stimulate unwanted growth of algae and other aquatic invasive species. Wastewater may also contain heavy metals and different types of toxic compounds that are known carcinogens. Because of these reasons, the highest priority of wastewater management has been to adequately remove potential nuisance conditions that can severely affect public and environmental health.

Brief History

Wastewater problems are very old. But it was not until the mid to late 18th century that management of water quality and wastewater began. Events such as the Broad Street cholera epidemic in London led to the enactment of the first regulations to protect public health and drinking water from wastewater discharges. The “sanitary idea” of Edwin Chadwick in London proposed that wastewater must be collected via sewerage networks away from the highly populated centers and the community water supply sources. The collected untreated wastewater was then discharged untreated into water bodies further downstream of communities. Engineers during these times favored the construction of drinking water treatment plants instead of having to [Page 3051]spend money in treating wastewater prior to its being discharged.

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