Industrial wastewater treatment covers the mechanisms and processes used to treat wastewater produced as a by-product of industrial or commercial activities. After treatment, treated industrial wastewater (or effluents) may be reused or released in a sanitary sewer or in surface water from the environment. Most industries produce some wastewater although recent trends in the developed world have been to minimize such production or to recycle such wastewater into the production process. However, many industries continue to rely on processes that produce wastewater.
Fossil fuel power plants, particularly coal, are an important source of industrial wastewater. Many of these plants discharge wastewater with significant levels of metals such as lead, mercury, cadmium and chromium, as well as arsenic, selenium and nitrogen compounds (nitrates and nitrites). Wastewater streams include flue gas desulphurisation, fly ash, bottom ash and mercury flue gas control. Plants with air pollution controls, such as wet scrubbers, typically transfer the captured contaminants to the wastewater stream.
Ash ponds, a type of surface reservoir, are a treatment technology widely used in coal plants. These ponds use gravity to deposit large particles (measured as total suspended solids) of the wastewater from the power plant. This technology does not treat dissolved contaminants. Power plants use additional technologies to control contaminants, depending on the type of test in the plant. These include dry-ash management, closed-loop ash recycling, chemical precipitation, biological treatment (as an activated sludge process), membrane systems, and evaporation-crystallization systems. Technological advances in ion exchange membranes and electrodialysis systems have enabled a high efficiency treatment of flue gas desulfurization wastewater to meet the recent EPA discharge limits [3]. The treatment approach is similar for other large-scale industrial wastewater.