Water pollutants can come from point sources or non-point sources. A point source pollutant is one that reaches the water from a single pipe or channel, such as a sewage outlet or drain pipe. Nonpoint sources are large, unconfined areas from which pollutants enter a body of water. Surface runoff from farms, for example, is a non-point source of pollution, carrying animal waste, fertilizers, pesticides, and sediment to nearby waterways.
Urban stormwater drainage, which can carry sand and other granular materials, oil residues from cars, and chemicals to de-ice roads, is also considered a dispersed source due to the many places where it enters waterways. or lakes. Point source pollutants are easier to control than dispersed source pollutants, as they flow to a single point where treatment processes can remove them from the water. This control is generally not possible for nonpoint source pollutants, which cause much of the overall water pollution problem. The best way to reduce nonpoint source water pollution is to apply appropriate land use plans and development standards.
General types of water pollutants include pathogens, oxygen-requiring wastes, plant nutrients, synthetic organic chemicals, inorganic chemicals, microplastics, sediments, radioactive substances, oil, and heat. Wastewater is the main source of the first three types. Farms and industrial structures are also sources for some of them. Eroded soil sediment is considered a pollutant because it can damage aquatic ecosystems and heat (particularly from cooling water from power plants) is considered a pollutant due to the negative effect it has on dissolved oxygen levels and aquatic life in rivers and lakes.
Characteristics of the wastewater
Types of wastewater
There are three types of wastewater or wastewater: domestic wastewater, industrial wastewater, and stormwater. Domestic wastewater carries used water from houses and apartments; it is also called sanitary sewer system. Industrial wastewater is the water that is used in manufacturing or chemical processes. Rainwater, or rainwater, is the runoff from precipitation collected in a system of pipes or open channels.
Domestic wastewater is just over 99.9% water by weight. The remainder, less than 0.1 percent, contains a wide variety of dissolved and suspended impurities. Although they represent a very small fraction by weight of wastewater, the nature of these impurities and the large volumes of wastewater into which they are transported make the disposal of domestic wastewater a major technical problem. The main impurities are putrescible organic materials and plant nutrients, but it is highly likely that domestic sewage also contains pathogenic microbes. Industrial wastewater usually contains specific and easily identifiable chemical compounds, depending on the nature of the industrial process. Rainwater carries organic materials, suspended and dissolved solids, and other collected substances as they travel through the ground.
The amount of putrescible organic material in wastewater is indicated by the biochemical oxygen demand or BOD; The more organic matter in the wastewater, the higher the BOD, which is the amount of oxygen that microorganisms require to break down organic substances in the wastewater. It is one of the most important parameters for the design and operation of treatment plants. Industrial wastewater can have BOD levels many times higher than domestic wastewater. Stormwater BOD is of particular concern when mixed with domestic wastewater in combined sewer systems (see below).
Dissolved oxygen is an important factor in water quality for lakes and rivers. The higher the dissolved oxygen concentration, the better the water quality. When sewage enters a lake or stream, the decomposition of organic materials begins. Oxygen is consumed as microorganisms use it in their metabolism. This can quickly deplete the available oxygen in the water. When dissolved oxygen levels drop too low, trout and other aquatic species soon die. In fact, if the oxygen level drops to zero, the water will become septic.