Despite large supplies of fresh water and the natural ability of water to cleanse itself over time, populations had become so concentrated by 1850 that outbreaks of life-threatening diseases were traced to bacteria in the polluted water. Since that time, the practice of wastewater collection and treatment has been developed and perfected, using some of the most technically sound biological, physical, chemical, and mechanical techniques available. As a result, public health and water quality are protected better today than ever before. The modern sewer system is an engineering marvel. Homes, businesses, industries, and institutions throughout the modern world are connected to a network of below-ground pipes which transport wastewater to treatment plants before it is released to the environment.
Wastewater is the flow of used water from a community.
The amount of wastewater handled by the treatment plant varies with the time of day and with the season of the year. In some areas, particularly communities without separate sewer systems for wastewater and runoff from rainfall, flow during particularly heavy rains or snowmelts can be much higher than normal. What happens in a wastewater treatment plant is essentially the same as what occurs naturally in a lake or stream. A treatment plant uses a series of treatment stages to clean up the water so that it may be safely released into a lake, river, or stream. In primary treatment, sand, grit, and the larger solids in the wastewater are separated from the liquid.