Glossary
Activated carbon A highly porous form of charcoal that, after being subjected to intense heat, can be used to adsorb large quantities of specific contaminants in water. The granules (granular activated carbon [GAC]) have a high capacity, given the enormous surface area, to selectively remove trace and soluble contaminants from water.
Absorption The uptake of water or dissolved chemicals by a cell or an organism; the process by which one substance is trapped throughout the volume of another, usually a liquid, by solution or chemical reaction.
Acre-foot A unit for expressing large quantities of water and defined as equivalent to the volume of water to cover one acre of land to a depth of one foot.
Activated sludge Refers to a biological process; a wastewater treatment method in which carbonaceous organic matter of wastewater provides an energy source for the production of new cells for a mixture of microorganisms. Bacteria make up about 95 percent of the activated sludge biomass. In addition, certain microorganisms obtain energy by oxidizing ammonia nitrogen to nitrate nitrogen in the process known as nitrification.
Adsorption A physical process by which contaminants are held on the surface of a solid substance for example, activated carbon.
Advanced treatment Purification processes used after or during secondary wastewater treatment to remove nutrients or additional solids and dissolved organics; also called tertiary treatment.
Aeration A physical treatment process in which air is thoroughly mixed with water or wastewater for purification.
Aerobic In the presence of air or available molecular oxygen.
Algae Microscopic single-celled plants that contain chlorophyll and live floating or suspended in water; phytoplankton. The biological activities of algae significantly affect the pH and dissolved oxygen of water.
Algal bloom Visible overgrowth of algae in lakes or reservoirs, due to eutrophication.
Alum Aluminum sulfate, one of the most commonly used chemical coagulants used for water treatment.
Anaerobic In the absence of air or available molecular oxygen.
Anion A negatively charged ion in an electrolyte solution, for example, chloride (Cl-).
Aquifer A geologic formation that exhibits the permeability (porosity and fractures) to transmit and yield groundwater in amounts sufficient to be used as a usable water supply (see also Groundwater).
Bacteria Microscopic single-celled plants that do not contain chlorophyll and do not nourish themselves by photosynthesis.
Best available technology (BAT) The best technology treatment techniques or other means that the EPA administrator finds, after examination for efficacy under field conditions and not solely under laboratory conditions, are available (taking cost into consideration). For the purpose of setting maximum contaminant levels for synthetic organic chemicals, any BAT must be at least as effective as granular activated carbon (GAC).
Best available technology economically achievable Technology-based standard established by the Clean Water Act (CWA) as the most appropriate means available on a national basis for controlling the direct discharge of toxic and nonconventional pollutants to navigable waters. In general, BAT effluent limitations guidelines represent the best existing performance of treatment technologies that are economically achievable within an industrial point source category or subcategory.
Best management practices (BMPs) Structural, nonstructural, and managerial techniques that are recognized to be the most effective and practical means to control non-point source pollutants, yet are compatible with the productive use of the resource to which they are applied. BMPs are used in both urban and agricultural areas.
Biochemical oxygen demand (BOD) The amount of oxygen required by microorganisms (mainly bacteria) to decompose (biodegrade) organic matter in water. BOD is a measure of the amount of organic pollution.
Biosolids The solid materials resulting from wastewater treatment that meets government criteria for beneficial use, such as for fertilizer and soil amendments. Biosolids consist mostly of living organisms but can contain other contaminants as well. Accordingly, treatment and processing are required under stringent EPA (see Part 503 Rule) and state regulations. Biosolids are one of the most studied materials that have ever been regulated by the EPA. The term biosolids is distinct from sewage sludge in that biosolids are a by-product of sludge that can be beneficially and safely recycled.
Black water Liquid and solid human body waste and the carriage water generated through toilet usage.
Cation A positively charged ion in an electrolyte solution; for example, sodium ion (Na+).
Centrifugal pump A mechanical device that adds energy to a liquid using a rapidly rotating impeller in a specially shaped casing. As the rotating impeller spins the water, centrifugal force builds up enough pressure to force the water through the discharge outlet. Centrifugal pumps are a common type of pump used for water treatment and distribution.
Chloramines Compounds formed by the reaction of hypochlorous acid (or aqueous chlorine) with ammonia.
Chlorine residual The amount of chlorine compounds that remain in water or wastewater after disinfection, providing continued sanitary protection in the distribution system.
Clarifier A large circular or rectangular sedimentation basin or settling tank in which heavier suspended solids settle to the bottom and the clarified water or wastewater is drawn off the top; also called settling basins or sedimentation basins.
Coagulants Treatment chemicals that cause very fine particles to clump together into larger particles, thereby facilitating the separation of solids from the water by settling, skimming, draining, or filtering. The chemicals neutralize the electrical charges of the suspended particles, causing destabilization (collision) and clumping (flocculation).
Coagulation The process of adding coagulant chemicals in the formation of settleable flocs.
Combined sewer A pipeline infrastructure that transports a mixture of surface runoff, human domestic wastes (sewage), and sometimes industrial wastes. Wastewater and runoff in a combined sewer may occur in excess of the sewer capacity and cannot be immediately treated.The excess is frequently discharged directly to a receiving water body without treatment, or to a holding basin for subsequent treatment and discharge.
Consumptive use That part of water withdrawn from available supplies that is evaporated, transpired by plants, incorporated into products, used on crops, consumed by humans or livestock, or otherwise removed without direct return to an immediate water resource system or environment; also referred to as water consumed.
Contaminant Any physical, chemical, biological, or radiological substance or matter in water (definition in CFR Section 141.2 146.3).
Conventional filtration The mainstay of traditional water treatment for substantial particle removal (filtration). The process is generally as follows: coagulant chemicals, flash mixing, coagulation, flocculation, sedimentation, and filtration.
Corrosion inhibitor A substance that slows the rate of corrosion of metal plumbing materials by water, especially lead and copper materials.
Desalination The removal of salts from saline water to provide freshwater.
Disinfection The process designed to kill or inactivate most microorganisms in water, including essentially all pathogenic bacteria. Chlorine is, by far, the most prevalent oxidant used in disinfection in the United States. However, the concern over carcinogenic by-products of the chlorine disinfection method has created strong interest in disinfection alternatives, such as chlorine dioxide, chloramines, ozone, mixed oxidants, and ultraviolet radiation. It should be noted that most disinfectants have the potential for harmful by-products under the right conditions.
Disinfection by-product A compound formed by the reaction of a water treatment disinfectant with natural organic matter (a “precursor” found in all surface and groundwaters) in a water supply.
Effluent Water or some other liquid (raw, partially or completely treated) flowing from a reservoir, basin, treatment process, or treatment plant.
Electrodialysis The process where the salts are extracted from the feedwater by using a membrane with an electrical current to separate the ions.The positive ions go through one membrane, while the negative ions flow through a different membrane, leaving the end freshwater product.
Eutrophication The degradation of water quality due to an increase in the nutrient (primarily nitrogen and phosphorus) levels of a lake or other body of water that results in excessive plant (principally algae) growth and decay. Low dissolved oxygen in the water is a consequence of eutrophication. Cultural eutrophication is the subset caused by human activities.
Filtration A process for removing particulate matter from water by passage through porous media; technically distinct from separation.
Flocculation The gathering together of fine particles in water by gentle mixing after the addition of coagulant chemical to form clusters or flocs.
Geographic information system (GIS) A computerized database system containing information on natural resources and other factors that can be analyzed and displayed in spatial or map format. GIS technology is increasingly used in watershed management.
Greywater Wastewater, other than sewage, from water usage in activities such as clothes and dish washing, bathing, and sinks.
Groundwater Subsurface water that is present below the water table in soils and geologic formations that are fully saturated (see also Aquifer).
Hard water Specifically refers to the total concentration of calcium and magnesium (salts) in water (measured in terms of grains per gallon [gpg]).Water hardness is a relative scale ranging from soft water (under 1 gpg or 17.1 mg/L) to very hard water (over 10.5 gpg or 180 mg/L).
Heavy metals Metallic elements with high atomic weights, for example, mercury, zinc, copper, silver, chromium, cadmium, arsenic, and lead. They are of particular concern because they can damage living things at low concentrations and tend to bioaccumulate in the food chain.
Industrial sources Nonmunicipal sources generating wastewater that is discharged to surface waters. The types of wastewaters generated at a facility depend on the specific activities undertaken at a particular site, and may include manufacturing or process wastewaters, cooling waters, sanitary wastewater, and stormwater runoff.
In-situ infrastructure rehabilitation The replacement and repair of water, wastewater, and/or stormwater pipeline systems through in-place rehabilitation techniques as opposed to more costly and disruptive traditional approaches. So-called trenchless rehabilitation and replacement technologies include cured-in-place pipe (CIPP), fold-and-form pipe, slip lining, pipe bursting, microtunneling, and horizontal directional drilling (HDD).
Ion exchange A water treatment process in which ions are preferentially adsorbed from a solution for equivalently charged ions attached to resin (small solid structures).
Irrigation The controlled application of water for agricultural or vegetative purposes through constructed systems to supply water requirements not satisfied by precipitation.
Large water system A water system that serves more than 50,000 persons.
Maximum contaminant level (MCL) The maximum permissible level of a contaminant in water that is delivered to the free-flowing outlet of the ultimate user of a public water system, except in the case of turbidity, where the maximum permissible level is measured at the point of entry to the distribution system.
Maximum contaminant level goal (MCLG) The maximum level of a contaminant in drinking water at which no known or anticipated adverse effect on the health of persons would occur, and which allows an adequate margin of safety. MCLGs are nonenforceable health goals.
Membrane bioreactor (MBR) A membrane bioreactor is a combination of suspended-growth activated sludge biological treatment and membrane separation treatment. The use of MBR in wastewater applications has grown rapidly as a cost-effective alternative to secondary clarifiers (conventional activated sludge) and tertiary filters.
Micron A unit of length equal to one millionth of a meter or one thousandth of a millimeter. One micron equals 0.00004 of an inch.
National Pollutant Discharge Elimination System (NPDES) A national program in the United States under Section 402 of the Clean Water Act for regulation of discharges of contaminants from point sources to receiving water bodies; discharges are authorized by an NPDES permit, which is the regulatory agency document issued by either a federal or state agency.
Non-point source pollution Pollutants or contaminants discharged over a wide land area such as a watershed as opposed to a specific, identifiable point source. These are forms of diffuse pollution caused by sediment, nutrients, and organic and toxic substances (such as pesticides) originating from land-use activities, which are carried to lakes and streams by surface runoff. Non-point sources include agricultural stormwater runoff, return flows from irrigated agriculture, city streets, residential property, construction, land disposal, and saltwater intrusion.
Organic matter Carbon compound-based substances made by living organisms (plant and animal residue). A precursor in the formation of trihalomethanes when combined with chlorine in the water disinfection process.
Osmosis The passage of a liquid from a weak solution to a more concentrated solution across a semipermeable membrane. The membrane allows the passage of the solvent (water) but not the dissolved solids (solutes).
Ozone disinfection The disinfection of water or wastewater, utilizing ozone (O3) as an alternative to other disinfection methods. The oxidation potential of ozone is second only to fluorine. Accordingly, it is an effective disinfectant for a wide range of pathogens and achieves the primary disinfection goal for the categories regulated under the Surface Water Treatment Rule (SWTR). Ozone is highly unstable and therefore must be generated on-site.
Pathogen A disease-producing agent in a living organism; viruses, bacteria, parasites, or fungi that cause disease.
Part 503 rule The federal biosolids rule contained in 40 CFR Part 503; biosolids that are to be land applied must meet these strict regulations and quality standards governing their use and disposal.The Part 503 rule has different provisions for each class of biosolids (Class A and Class B) but generally contains numerical limits for metals in biosolids, pathogen and vector attraction reduction standards, management practices and frequency of monitoring, and record keeping and reporting requirements for land-applied biosolids.
pH A measure of the relative acidity or alkalinity of water (or liquid). Mathematically, pH is the logarithm (base 10) of the reciprocal of the hydrogen ion concentration, [H+]; that is, pH = Log (1/[H+]). Pure water is neutral, with a pH of 7. Natural waters usually have a pH between 6.5 and 8.5.
Point-of-entry (POE) Refers to a water treatment device applied to potable water entering a house or building for the purpose of reducing contaminants in the drinking water distributed throughout the house or building.
Point-of-use (POU) Refers to a water treatment device applied to a single tap used for the purpose of reducing contaminants in drinking water at that one point of use.
Point-of-use-reuse (POUR) Refers to the emergence of sustainable techniques, particularly with respect to decentralized wastewater treatment systems. The premise of POUR technology is the on-site separation and biological treatment of household wastewater and reuse/recycling; a decentralized analogy to a membrane bioreactor at a centralized wastewater treatment plant.
Point source pollution Pollutants or contaminants that are discharged from a single stationary source, location, or fixed facility such as an industrial effluent discharge or sewage outflow pipe. NPDES: Any discernible, confined, and discrete conveyance, including but not limited to, any pipe, ditch, channel, tunnel, conduit, well, discrete fissure, container, rolling stock concentrated animal feeding operation (CAFO), landfill leachate collection system, vessel or other floating craft from which pollutants are or may be discharged.
Potable water Water of a quality that is safe and satisfactory for drinking and cooking.
Primary wastewater treatment The first stage of the wastewater treatment process, where mechanical methods are used to remove pollutants. Solid material in wastewater settles out during this process.
Prior appropriations doctrine A property rights system for allocating water to private interests utilized by the early settlers and miners and prevalent in the relatively arid western states. John Locke is attributed with laying the foundation for the American doctrine of prior appropriation.The prior appropriations doctrine is based on the concept of “first in time, first in rights.” The first person to take a quantity of water had a senior priority right to the water. The embedded principle of “beneficial use,” however, required that a person’s right is limited to the amount of water actually put to beneficial use; appropriative rights can be lost through non-use. In addition, the rights can be separated from the land and sold or transferred. The prior appropriations doctrine is contrasted with the riparian rights doctrine.
Publicly owned treatment works (POTW) A treatment works, as defined by Section 212 of the CWA, that is owned by the state or municipality. This definition includes any devices and systems used in the storage, treatment, recycling, and reclamation of municipal sewage or industrial waste liquids. It also includes sewers, pipes, and other conveyances only if they convey wastewater to a POTW treatment plant. Privately owned treatment works, federally owned treatment works, and other treatment plants not owned by municipalities are not considered POTWs.
Public water system A system for the provision to the public of piped water for human consumption, if such system has at least 15 service connections or regularly serves an average of at least 25 individuals at least 60 days out of the year.The term includes: (1) any collection, treatment, storage, and distribution facilities under control of the operator of such system and used primarily in connection with such system; and (2) any collection or pretreatment storage facilities not under such control that are used primarily in connection with such system. A public water system is either a “community water system” or a “noncommunity water system.”
Reclaimed wastewater Municipal wastewater effluent that is treated to for a specific, beneficial use; also called recycled or reused water.
Recycled water Water that is used more than once before it is discharged into the hydrologic cycle.
Reverse osmosis (RO) An advanced method of water or wastewater treatment that relies on a semipermeable membrane to separate water from constituent contaminants. Pressure is used to reverse the normal osmotic process, resulting in the solvent’s moving from a solution of higher concentration to one of lower concentration. The membrane allows the passage of the solvent (water) but not the dissolved solids (solutes).
In desalination, the process of removing salts from water using a membrane.With RO, the product water passes through a membrane with a pore size that salts are unable to pass through.The rejected salt waste brine is removed and must be disposed of.
Riparian rights doctrine A system for allocating water to private interests based on rights of the owner whose land abuts water. The doctrine has its origins in English common law and is prevalent in the eastern United States, where surface water is relatively more abundant. Riparian water rights differ from state to state and often depend on whether the water is a river, lake, or ocean. Specifically, persons who own land adjacent to a stream (riparian) have the right to make reasonable use of the stream; riparian users of a stream share the flow among themselves with no application of priority of use (compare to the Prior appropriations doctrine). Riparian water rights cannot be sold or transferred for use on nonriparian land.
Secondary wastewater treatment Treatment following primary wastewater treatment involving the biological process of reducing suspended, colloidal, and dissolved organic matter in effluent from primary treatment systems. Secondary wastewater treatment generally removes 80 to 95 percent of the biochemical oxygen demand and suspended matter and may be accomplished with biological or chemical-physical methods. Activated sludge and trickling filters are common in secondary treatment and remove about 90 percent of the oxygen-demanding substances and suspended solids. Disinfection is the final stage of secondary treatment.
Salinity The total amount of minerals (salts) dissolved in water and measured by TDS (see definitions of freshwater, brackish water, and seawater under Total dissolved solids).
Sanitary sewer A sewer that transports only wastewaters (from domestic residences and/or industries) to a wastewater treatment plant.
Septic system An on-site system designed to treat and dispose of domestic sewage; a typical septic system consists of a tank that receives wastes from a residence or business and a system of tile lines or a pit for disposal of the liquid effluent that remains after decomposition of the solids by bacteria in the tank.
Sewer system An infrastructure network of underground systems of conduits (pipes and/or tunnels) that collect and transport wastewaters and/or runoff; gravity sewers carry free-flowing water and wastes; pressurized sewers carry pumped wastewaters under pressure.
Softener A point-of-entry device that reduces water hardness by replacing calcium and magnesium ions with sodium ions.
Surface water All water naturally open to the atmosphere (rivers, lakes, reservoirs, streams, impoundments, seas, estuaries, etc.) and all springs, wells, or other collectors that are directly influenced by surface water.
Tertiary wastewater treatment The additional treatment of effluent beyond that of primary and secondary treatment. It involves specific biological, physical, and chemical separation processes to remove organic and inorganic substances that resist conventional treatment and may involve alternative disinfection methods such as ozone or ultraviolet radiation.
Total dissolved solids (TDS) All of the solid material dissolved in water. TDS is measured on a sample of water that has passed through a very fine mesh filter to remove suspended solids.The water passing through the filter is evaporated, and the residue represents the dissolved solids.
Freshwater: Water with <1,000 mg/L of TDS; generally, however, more than 500 mg/L of TDS is undesirable for drinking and many industrial uses. Brackish water:Water with >1,000 to 25,000 mg/L of TDS Seawater:Water with >25,000 mg/L of TDS
Total Maximum Daily Load (TMDL) The total pollutant loading from point and non-point sources that a water body can assimilate. Assimilative capacity is the amount of pollutants that a water body may absorb while maintaining corresponding water quality classification and standards, including protection of aquatic life and human health.
Transmission lines The pipeline infrastructure that transports raw water from its source to a water treatment plant. After treatment, water is pumped into transmission pipelines that are connected to the distribution infrastructure grid system.
Turbidity The cloudy appearance of water caused by the presence of suspended and colloidal matter. Technically, turbidity is an optical property of the water based on the amount of light reflected by suspended solid particles.Turbidity can significantly impact the efficacy of treatment methods and water quality.
Ultraviolet (UV) disinfection The disinfection of water or wastewater by using UV light as an alternative to other disinfection methods. A UV disinfection system transfers electromagnetic energy from a mercury arc lamp to an organism’s genetic material, thereby destroying the cell’s ability to reduce.
Volatile organic compounds (VOCs) Volatile organic compounds are compounds that have a high vapor pressure and low solubility. The most frequently occurring VOCs in groundwater are perchloroethylene (industrial solvent), methyl tertiary butyl ether (fuel oxygenate), and chloroform (by-product of chlorination). Maximum contaminant levels for many VOCs have been established by the EPA and the states because of adverse human health effects.
Wastewater The used water and solids from a community (including used water from industrial processes) that is not suitable for use unless it is treated and flows to a treatment plant. Stormwater, surface water, and groundwater infiltration also may be included in the wastewater that enters a wastewater treatment plant.The term sewage usually refers to household wastes but is being replaced by the term wastewater.
Water rights A highly specialized type of real property that legally varies widely from the local to federal level and by type, such as natural rights, appropriative rights, or sovereign control. In the context of the institutional structure governing a market-driven, efficient allocation of water, water rights must be well defined, enforceable, and transferable.
Watershed The land area that drains water (contributes runoff) to a particular stream, river, or lake.There are an infinite number of watersheds on Earth.
Watershed management The optimization, through integrated planning, of the water resource goals of an area defined by a natural drainage basin (watershed). Central to the term is a holistic approach to a broad array of goals, including sustainability, water quality, cost effectiveness, and human health, as well as innovation in implementation tools and protocols such as geographic information systems, land use, Total Maximum Daily Load studies, and watershed-based National Pollutant Discharge Elimination System permits.