Effluent is

wastewater Wastewater is water generated after the use of freshwater, raw water, drinking water or saline water in a variety of deliberate applications or processes. Another definition of wastewater is "Used water from any combination of domestic, industrial ...

from sewers or industrial outfalls that flows directly into surface waters either untreated or after being treated at a facility. The term has slightly different meanings in certain contexts, and may contain various

pollutant A pollutant or novel entity is a substance or energy introduced into the environment that has undesired effects, or adversely affects the usefulness of a resource. These can be both naturally forming (i.e. minerals or extracted compounds like o ...

s depending on the source. Treating wastewater efficiently is challenging, but improved technology allows for enhanced removal of specific materials, increased re-use of water, and energy production from waste.

Definition

Effluent is defined by the

United States Environmental Protection Agency The Environmental Protection Agency (EPA) is an independent executive agency of the United States federal government tasked with environmental protection matters. President Richard Nixon proposed the establishment of EPA on July 9, 1970; it ...

(EPA) as "wastewater–treated or untreated–that flows out of a treatment plant, sewer, or industrial outfall. Generally refers to wastes discharged into surface waters". The ''Compact Oxford English Dictionary'' defines effluent as "liquid waste or sewage discharged into a river or the sea". Wastewater is not usually described as effluent while being

recycle Recycling is the process of converting waste materials into new materials and objects. The recovery of energy from waste materials is often included in this concept. The recyclability of a material depends on its ability to reacquire the p ...

d, re-used, or treated until it is released to surface water. Wastewater percolated or injected into

groundwater Groundwater is the water present beneath Earth's surface in rock and soil pore spaces and in the fractures of rock formations. About 30 percent of all readily available freshwater in the world is groundwater. A unit of rock or an unconsolidated ...

may not be described as effluent if

soil Soil, also commonly referred to as earth or dirt Dirt is an unclean matter, especially when in contact with a person's clothes, skin, or possessions. In such cases, they are said to become dirty. Common types of dirt include: * Debri ...

is assumed to perform treatment by filtration or

ion exchange Ion exchange is a reversible interchange of one kind of ion present in an insoluble solid with another of like charge present in a solution surrounding the solid with the reaction being used especially for softening or making water demineralised, ...

; although concealed flow through fractured bedrock, lava tubes, limestone caves, or gravel in ancient

stream channel In physical geography, a channel is a type of landform consisting of the outline of a path of relatively shallow and narrow body of water or of other fluids (e.g., lava), most commonly the confine of a river, river delta or strait. The word is c ...

s may allow relatively untreated wastewater to emerge as springs.

Description

Effluent in the artificial sense is in general considered to be

water pollution Water pollution (or aquatic pollution) is the contamination of water bodies, usually as a result of human activities, so that it negatively affects its uses. Water bodies include lakes, rivers, oceans, aquifers, reservoirs and groundwater. ...

, such as the outflow from a

sewage treatment Sewage treatment (or domestic wastewater treatment, municipal wastewater treatment) is a type of wastewater treatment which aims to remove contaminants from sewage to produce an effluent that is suitable for discharge to the surrounding e ...

facility or an

industrial wastewater Industrial wastewater treatment describes the processes used for Wastewater treatment, treating wastewater that is produced by industries as an undesirable by-product. After treatment, the treated industrial wastewater (or effluent) may be reuse ...

discharge. An effluent sump pump, for instance, pumps waste from toilets installed below a main sewage line. In the context of

waste water treatment plants Sewage treatment (or domestic wastewater treatment, municipal wastewater treatment) is a type of wastewater treatment which aims to remove contaminants from sewage to produce an effluent that is suitable for discharge to the surrounding envir ...

, effluent that has been treated is sometimes called ''secondary effluent'', or ''treated effluent''. This cleaner effluent is then used to feed the

bacteria Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one Cell (biology), biological cell. They constitute a large domain (biology), domain of prokaryotic microorganisms. Typically a few micrometr ...

biofilters Biofiltration is a pollution control technique using a bioreactor containing living material to capture and biologically degrade pollutants. Common uses include processing waste water, capturing harmful chemicals or silt from surface runoff, an ...

. In the context of a

thermal power station A thermal power station is a type of power station in which heat energy is converted to electrical energy. In a steam-generating cycle heat is used to boil water in a large pressure vessel to produce high-pressure steam, which drives a stea ...

and other industrial facilities, the output of the cooling system may be referred to as the effluent cooling water, which is noticeably warmer than the environment and is called

thermal pollution Thermal pollution, sometimes called "thermal enrichment", is the degradation of water quality by any process that changes ambient water temperature. Thermal pollution is the rise or fall in the temperature of a natural body of water caused by hum ...

. In

chemical engineering Chemical engineering is an engineering field which deals with the study of operation and design of chemical plants as well as methods of improving production. Chemical engineers develop economical commercial processes to convert raw materials int ...

practice, effluent is the stream exiting a

chemical reactor A chemical reactor is an enclosed volume in which a chemical reaction takes place. In chemical engineering, it is generally understood to be a process vessel used to carry out a chemical reaction, which is one of the classic unit operations in chem ...

. Effluent may carry pollutants such as fats/oils/greases, chemicals, detergents, heavy metal rinses, solids, and food waste. Possible sources include a wide range of manufacturing industries, mining industries, oil and gas extraction, and service industries.

Pollution control regulation

United States effluent guidelines

In the United States, the Clean Water Act requires all direct effluent discharges to surface waters to be regulated with permits under the

National Pollutant Discharge Elimination System The Clean Water Act (CWA) is the primary federal law in the United States governing water pollution. Its objective is to restore and maintain the chemical, physical, and biological integrity of the nation's waters; recognizing the responsibiliti ...

(NPDES). Indirect dischargers–facilities which send their wastewater to municipal sewage treatment plants–may be subject to pretreatment requirements. NPDES permits require discharging facilities to limit or treat effluent to the levels that result from using the most effective treatment technologies possible at a practical cost to mitigate the effects of discharges on the receiving waters. EPA has published technology-based regulations, called "

effluent guidelines Effluent Guidelines (also referred to as Effluent Limitation Guidelines (ELGs)) are U.S. national standards for wastewater discharges to surface waters and publicly owned treatment works (POTW) (also called municipal sewage treatment plants). The U ...

", for 59 industrial categories. The agency reviews the standards annually, conducts research on various categories, and makes revisions as appropriate. Noncompliance with these standards and all other conditions in the permits is punishable by law. Each year, effluent guidelines regulations prevent billions of pounds of contaminants from being released into bodies of water. EPA regulations require effluent limitations to be expressed as mass-based limits (rather than concentration-based limits) in the permits, so that discharging facilities will not use dilution as a substitute for treatment. In cases where setting mass-based limits are infeasible, the permit authority must set conditions in the permit that prohibit dilution.EPA. "Calculating NPDES permit conditions." ''Code of Federal Regulations'',

Pretreatment

When pretreating effluent, it is difficult to reduce expenses, increase productivity, adhere to stringent standards, and prevent discharge of byproducts. Furthermore, depletion of clean, fresh, accessible water is a global issue, but evolving technology can help prevent this because improving treatment methods allows for re-use of water. Additionally, waste-to-energy technology transforms organic matter into usable electricity, heat, or fuel. Treatments also exist to remove certain elements, compounds, salts, and minerals from effluent.

References