The Water And Wastewater Industry

The water and wastewater industry is a major part of the nation’s infrastructure. Its proper operation is essential to protect human health and the environment. The industry comprises public and private utilities that produce, treat or deliver water. It also includes sewage systems, which convey waste water from homes and businesses. Some of these systems are decentralized and others are centralized. A centralized system is comprised of pipes, chambers, manholes and pumping stations that convey sewage from a sewage treatment plant to the environment or to a wastewater reuse plant.

Biological Treatment

In many mechanical bar screen, microorganisms (bacteria and protozoa) consume biodegradable soluble organic contaminants and other substances in the sewage. The organisms grow and reproduce in a controlled aerobic or anaerobic process. This process is known as primary treatment.

Other chemicals in sewage are removed through secondary treatment. This is accomplished by adding specific chemical compounds, called coagulants and flocculants, to the sewage. These chemicals help to bind the organic solids into larger groups that can be separated by a sedimentation process. The final product of this treatment is called biological sludge.

The sludge is then sent to a disposal site. Some sludge is used as a soil amendment or to help make other products, such as fertilizers. A small amount of sludge may be returned to the municipal sewer system for reuse, if it has been properly treated to remove all hazardous constituents.

In densely populated areas, it is not practical to treat all the wastewater at the source of production. To reduce costs, some cities choose to dump raw sewage directly into lakes, rivers and oceans. These communities are often violating two federal acts — the Fisheries Act and the Environmental Protection Act.

Chemical treatments, such as oxidation, precipitation and filtering, can be used to further clean the wastewater. Oxidation, for example, transforms iron (II) cations into poorly-soluble iron (II) oxides by adding oxygen to the wastewater. Phosphorus can be precipitated as calcium, iron or aluminum hydroxides, and nitrogen can be removed using nitrifying bacteria.

Most industrial processes generate wastewater. These sources of wastewater include battery manufacturing, electric power plants, gas and oil refineries, food processing and canning industries, paper mills, metal smelters, pulp and paper producers and woodworking factories.

While most industrial sources of wastewater are regulated, there is a growing movement to minimize or eliminate the generation of wastewater through industrial redesign and by recycling wastewater within the production process.

Most municipalities have a wastewater collection and treatment system. The system includes a network of pipes, chambers, manholes, pumps and screening devices that collect and transport sewage to a treatment plant. This is also referred to as a sewage system, or combined sewer and stormwater system. The system may also include on-site sewage facilities and septic tanks in rural areas. These are referred to as on-site or decentralized systems. Sewage is transported from these onsite systems to centralized wastewater treatment plants by the sewerage system.