The process by which one substance is physically taken into and included with another substance.
Activated Sludge Process
A method of biological treatment which produces a high quality effluent. It is a secondary process, usually following primary treatment. The activated sludge removes finely divided, suspended and dissolved organic matter remaining in the wastewater. When we talk about activated sludge, we are referring to the biological communities of microorganisms which are developed in the aeration tank. If supplied with enough dissolved oxygen, they will aerobically decompose organics in the waste water. Activated sludge is settled from wastewater and returned to the aeration tank for reuse.
Exposure that will result in significant response shortly after exposure (typically a response is observed within 48 or 96 hours).
The adhesion of molecules to the surface of solid bodies or liquids with which they are in contact. It involves the removal of a pollutant, such as organics, by making it stick to the surface of a solid, like carbon.
Removal of dissolved and suspended materials remaining after normal biological treatment when required for water reuse or for the control of eutrophication in receiving waters.
Growing in the presence of oxygen, as in aerobic bacteria or aerobic treatment.
Bacteria which live and reproduce only in an environment containing dissolved oxygen.
A digester designed to make use of aerobic-process bacteria to decompose and reduce the volume of sludge to be handled. The sludge is continuously aerated without the addition of new food other than the sludge itself. After about 20 days, the material is considered stable enough for ultimate disposal.
Aerobic treatment unit
A container of various configurations that provides for aerobic degradation or decomposition of wastewater constituents by bringing the wastewater into direct contact with air by some mechanical means.
A sewage system other than a conventional gravity system or a conventional pressure distribution system. Properly operated and maintained alternative systems provide equivalent or enhanced treatment performance as compared to conventional gravity systems.
Growing in the absence of oxygen, as in anaerobic bacteria in a septic tank.
The process by which nitrate-nitrogen is converted biologically to nitrogen gas in the absence of oxygen. The process is also known as anoxic denitrification.
A written statement of acceptability, in terms of the requirements in local and state regulations issued by the local health officer.
Biological treatment processes in which the microorganisms responsible for the conversion of the organic matter or other constituents in the wastewater to gases and cell tissue are attached to some inert medium, such as rocks, slag, or specifically designed ceramic or plastic materials. Attached-growth treatment processes are also known as fixed-film processes.
Bacteria are living organisms, microscopic in size. Most bacteria use organic material.
Usually a set of parallel bars placed at an angle in a channel so that the wastewater flows through the bars. Larger objects entering the plant collect on these bars and can be removed. Screening is usually the first step in pre-treatment.
Biochemical oxygen demand (BOD)
A standard test that measures the strength of wastewater by determining the quantity of oxygen that is naturally consumed by the wastewater under standard conditions. Generally it is measured in mg/L.
Chemical oxygen demand (COD)
A standard test that measures the amount of the organic matter in wastewater that can be oxidized (burned up) by a very strong chemical oxidant.
Exposure that will result in sub lethal response over a long term, often one-tenth of the life span or more.
This refers to the addition of chlorine, usually to treated wastewater, for the purpose of disinfection – to kill off most of the harmful bacteria that may still be in the liquid at this point.
Chlorine Contact Basin
Chlorine solution is mixed with treated wastewater in a container called a chlorine contact tank or basin. The main purpose of these tanks is to provide sufficient mixing and sufficient contact time for the disinfection to take place.
Chlorine Contact Time
In the chlorine contact chamber or tank, the chlorine must have enough time in contact with bacteria to be able to kill them. The amount of time that we give for this is called chlorine contact time. Usually the contact time is 20 to 30 minutes, although more time is not unusual.
The amount of chlorine to be used for disinfection depends on how much treatment the wastewater has already received. Usually enough chlorine is added so that there will be, at least, 0.5 parts per million of chlorine in the mixture after 20 minutes of contact time. The actual amount and contact time will be specified by the regulatory agency.
Any process or combination of processes, the primary purpose of which is to reduce the concentration of suspended matter in a liquid. Term formerly used as a synonym of settling or sedimentation. In recent years, the latter terms are preferable when describing the settling process.
Sometimes also called a settling tank or sedimentation basin. It is a tank or basin in which wastewater is held for a period of time, during which the heavier solids settle to the bottom. Lighter materials which float to the water surface are removed by a surface skimming device. If the unit is placed as part of primary treatment, it is called a primary clarifier. Similarly, clarifiers in the secondary treatment phase are called secondary clarifiers.
This is a more complex physical-chemical wastewater treatment process, which uses chemicals to help settle out some of the smaller particles in the wastewater.
One type of bacteria. The presence of coliform-type bacteria is an indication of possible pathogenic bacterial contamination. Fecal coliforms are those coliforms found in the feces of various warm-blooded animals, whereas the term coliform also includes other environmental sources.
The network of sewers collecting wastewater from the community and bringing it to your plant is called the collection system.
A mixture of municipal (or sanitary) sewage and storm waters when both are collected in the same sewers.
Besides screening and grit removal, pre-treatment also usually involves shredding. There are machines available, like the comminutor, that cup up or shred material while it is still in the wastewater stream. The cutup material is left in the wastewater.
When samples are collected at regular intervals (e.g., hourly), and then combined, a composite sample is obtained. This reduces the effect of variation in individual samples. Individual samples may have equal volumes, or may be sized in proportion to the flow at the time of sampling.
This refers to the changing of water vapors into water droplets.
Individual components, elements, or biological entities such as suspended solids or ammonia nitrogen.
In this variation of the activated sludge process, pre-treated wastewater is mixed with return activated sludge in a contact basin for about 30 minutes to 1 hour. Then the solids are allowed to settle. The resulting supernatant is the plant effluent. The resulting sludge is aerated for two to six hours to decompose the organics that are present. The sludge is then returned to the contact basin.
Constituents added to the water supply through use.
Decentralized wastewater management
Collection, treatment, and disposal/reuse of wastewater from individual homes, clusters of homes, isolated communities, industries, or institutional facilities, as well as from portions of existing communities at or near the point of waste generation.
The anaerobic biological reduction of nitrate-nitrogen to nitrogen gas. Also removal of total nitrogen from a system.
The estimated length of time before the system will have to be replaced or rehabilitated.
The period of time that a water or wastewater flow is retained in a basin, tank, or reservoir for storage or completion of physical, chemical, or biological reaction.
This is a process of removing all or a portion of the water from a water-solids mixture. This is done to reduce the volume of the sludge that requires further handling. For example, digested sludge could be spread on sand drying beds to allow the water to drain from the sludge.
A tank in which sludge is placed to allow sludge digestion to occur. Digestion may occur under anaerobic or aerobic conditions.
Both aerobic and anaerobic digester produces gasses. As the anaerobic digester is usually completely sealed, these gasses are important, especially since anaerobic digester gas is about 70% methane and 30% carbon dioxide. When mixed with air, digester gas is extremely explosive. The methane gas is often used as the energy source for heating the plant. The main gas produced in aerobic digestion is carbon dioxide. The gasses produced are not offensive, and therefore it is only necessary to cover aerobic digesters for heat preservation.
Biological decomposition of the organic matter within the sludge without the addition of new food. Digestion reduces sludge volume, and makes the sludge easier to dewater. Properly digested sludge is stable and inoffensive.
The process of destroying pathogenic organisms in water and wastewater.
The concentration of oxygen (normally a gas) dissolved in water. It is a function of temperature and pressure. The colder the water, the more oxygen it will hold. In general, fish require 5.0 mg/L in a stream.
Dissolved solids are the ones that are actually in solution in the liquid. In normal domestic wastewater, just about half of the dissolved solids are organic, and the rest of the dissolved solids are inorganic.
These are human and household wastes. Human wastes are the most important in terms of public health because they may contain organisms which produce disease in man. Household wastes include that from laundry, bathing, washing, cooling foods, and dishwashing. Most of these particles contain soap. Kitchen wastes also have particles of food or grease that enter the wastewater system.
Domestic sewage is that containing human and household wastes. This is the kind of wastewater coming from residential areas where there is little or no industry.
Treated plant effluent usually goes into a river, lake, or stream. Users of this water downstream from the plant are called downstream users.
A pipe or conduit that carries untreated runoff water to nearby waterways to reduce flooding of pavements. Not to be confused with sewers which carry wastewater.
Sludge can be dewatered by spreading the sludge on specially constructed beads of sand or fine stone. The water drains through this bed, leaving the sludge on top.
A well which is a bored, drilled, or driven shaft or hole whose depth is greater than its width and is designed and constructed specifically for the disposal of storm water.
Wastewater, partially or completely treated, flowing out of a reservoir, tank, treatment component, or disposal component.
The process by which a water body becomes over-enriched with nutrients. While this is a naturally-occurring process, it can be accelerated by human activities and generally results in a less-diversified and less-desirable water body.
An advanced physical – chemical wastewater treatment method that works through the use of electricity.
This activated sludge treatment variation is usually provided for a small – sized treatment facility. Whereas contact stabilization has a relatively short aeration time, in extended aeration the liquid is aerated longer. This means that the amount of sludge produced in this system is reduced, because more time is allowed for decomposition.
When moisture evaporates, it changes into water vapor. This process is called evaporation.
Facultative bacteria can use either dissolved oxygen or oxygen obtained from food materials. In other words, facultative bacteria can survive and function actively in both the aerobic or anaerobic conditions.
The most common type of pond in current use. The upper portion is aerobic, while the bottom layer is anaerobic. Algae supply most of the oxygen to the upper layer.
Biological treatment processes in which the organisms can function in the presence or absence of molecular oxygen.
Inability of water to penetrate the soil.
Indicator bacteria common to the digestive systems of warm-blooded animal that is cultured in standard tests to indicate contamination from sewage or level of disinfection. Generally measured as colonies/100 mL.
See attached-growth processes.
Larger particles that have formed from the coming together or joining of smaller particles as a result of biological or chemical activity.
To cause (soil) to form small lumps or masses.
An action resulting in the gathering of fine particles to form larger particles that are heavier and more easily settled.
Flow rate (or discharge or “Q”)
Minimum design pumping rate required to deliver effluent in a timely fashion to a gravity system and to pressurize a pressure manifold of low pressure pipe laterals.
When collecting all of the testing or sample liquid at the same time, it is called a grab (or catch) sample. Grab samples can only give you information about the liquid at the location and time of sampling. Grab samples should be collected at the same time and location every day, so that comparing results for each day is more accurate.
Grease interceptor (trap)
In plumbing, a receptacle designed to collect and retain grease and fatty substances normally found in kitchen or similar wastes. It is installed in the drainage system between the kitchen or other point of production of the waste and the building sewer.
That portion of the wastewater stream that originates in sinks, tubs, showers, laundry; i.e., all portions of the wastewater stream excluding toilet wastes.
The heavy inorganic material present in wastewater. Examples are sand and gravel. Settled solids in the grit chamber are called grit.
Sewers are often below groundwater level, and if the joints between sections of the sewers are not tight or if there are cracks in the sewers, groundwater might be entering into the sewers.
Hydraulic Loading Rate
An empirically-derived design and operating parameter that relates to ponding, surface shearing rate, and hydraulic detention time. Usually reported in units of volume of wastewater (including recycle) per unit cross-sectional area per day.
Whenever water is exposed to the atmosphere, the sun causes it to evaporate and rise as a water vapor. Moisture is also given off to the air by plants by transpiration. The moisture in the air forms clouds. When the clouds cool, the water vapor condenses into water droplets or snow. When heavy enough, the rain or snow precipitates. Water that falls to the earth is taken up by oceans, lakes and rivers, or it soaks into the ground to flow through it until it is again exposed. When the water is exposed to the warm air, it begins to evaporate, and the hydrologic or water cycle starts again.
Industrial wastes are another important part of wastewater. In many areas, industrial or manufacturing wastes are collected with other community wastewater for treatment and disposal. Sometimes the amount and kind of waste will require separate collection and disposal systems.
(1) The flow or movement of water through the interstices of pores of soil or other porous medium.
(2) Groundwater seeping into a collection system.
Direct rain flow, such as rooftop drains, into a collection system.
Wastewater, partially or completely treated, or in its natural state (raw wastewater) that flows into a reservoir, tank, treatment component, or disposal component.
The minerals, salts, etc. present in wastewater not attributed to carbon molecules of the organic. Examples include iron, silver, lead, sodium.
The condition that limits treatment capacity usually either groundwater or bedrock.
Any of various pasty materials used as protective coatings or cements.
Media (Trickling Filter)
The material in a trickling filter over which settled wastewater is sprinkled and then flows over and around during treatment. Slime, consisting of microorganisms, grows on the surface of the media and treats the wastewater. Rock or plastic media are most commonly used.
Besides other things, wastewater also contains countless numbers of living organisms, most of them too small to be seen except under a microscope. These are of two general types: bacteria, and other more complex living organisms.
The contents of the aeration tank as well as the aeration tank effluent are referred to as the mixed liquor.
Municipal sewage contains all of domestic sewage, as well as some of the industrial wastes.
The oxidation of ammonia-nitrogen to nitrate-nitrogen in wastewater by biological or chemical reactions.
The minerals and other materials that provide food for living organisms. Traditionally, nitrogen, phosphorous, and potassium are thought of as the most important elemental nutrients for streams and lakes.
The molecules, cells, etc. in wastewater from living organisms based on elemental carbon.
Waste material which comes from animal or vegetable sources. Organic waste generally can be consumed by bacteria and other small organisms as food.
This is a variation of the extended aeration process. Raw or pre-treated wastewater flows to an oxidation ditch which is usually a race-track affair. Cylindrical brush rotors in the oxidation ditch turn, aerating the liquid and causing it to move within the track. The liquid from the oxidation ditch flows to a final clarifier. Activated sludge from the final clarifier is returned to the oxidation ditch.
A measurable factor such as temperature.
Parts Per Million (P.P.M.)
The number of units of the smaller component for each million units or parts of the larger component. In wastewater terminology, one P.P.M. is roughly equal to one milligram per liter (one mg/l).
Microorganisms which are harmful to man. Bacteria or viruses which can cause disease like typhoid, cholera, dysentery and others. (There are many types of bacteria which do not cause disease and which are not called pathogens.)
Seepage through a permeable material.
Having pores or openings that permit liquids or gases to pass through.
A measure of the acid or base quality of water that is the negative log of the hydrogen ion concentration. The scale ranges from 1-14. A pH of 7.0 is neutral with 13.0 being very basic and 1.0 being very acidic.
Any interference with use or reuse of water, or failure to meet quality requirements.
Chlorination at the headworks of the plant; influent chlorination prior to plant treatment process.
Use of racks, screens, comminutors, and grit removal devices to remove metal, rocks, sand and similar materials which may hinder operation of a treatment plant.
The clarifier or sedimentation tank included as part of the primary treatment process.
Removal of a portion of the suspended solids and organic matter from the wastewater.
A tank or compartment following the septic tank which contains a pump, floats, and volume for storage of effluent. Effluent is pumped from the pump chamber to another pretreatment process or to the disposal component. In certain types of pressure distribution systems, this may also be called a “surge tank.” If a siphon is used in lieu of a pump, this will be called a “siphon chamber”.
At points in the wastewater collection system where it is not possible to provide sufficient slope from the source of the wastewater to the treatment plant, pumping stations are used to pump the wastewater up so that gravity flow can start again. For example, a pumping station would be used to move wastewater over a hill.
A stream, river, lake, or ocean into which treated or untreated wastewater is discharged.
A portion of material or water identical in content to that in the larger body of material or water being sampled.
Residual chlorine is the amount of chlorine remaining after a given contact time and under specified conditions.
Return Activated Sludge
Sludge collected in the secondary clarifier of the activated sludge process has a large number of hungry or active bacteria in it, and can be used again. The activated sludge collected from the clarifier is returned to the aeration tank, where it is again mixed with incoming wastewater and air. Return activated sludge is an important part of the activated sludge process.
See representative sample.
A sampling dipper has a long handle to make it easier to collect samples from tanks and channels.
These are the places from which you sample. They should be places where the liquid is well mixed.
Refer to the materials collected on the bar screen. They are removed from the bar screen either mechanically or by hand, and disposed of either by burning or burial.
A layer of wastewater particles floating on the liquid surface in a septic tank.
Removal of biodegradable organics and suspended solids. Disinfection is also typically included in the definition of conventional secondary treatment.
Refers to the settling out of suspended materials from a liquid.
The semi-liquid material that is pumped out of septic (or interceptor) tanks, consisting of liquid, scum, and sludge.
A condition produced by the absence of dissolved oxygen in an aquatic environment. This promotes the growth of anaerobic process organisms. The wastewater turns black, giving off foul odors.
A water-tight pretreatment receptacle receiving the discharge of sewage from a building sewer or sewers, designed and constructed to permit separation of settleable and floating solids from the liquid and detention and anaerobic digestion of the organic matter prior to discharge of the liquid.
Suspended solids, in mL/L, that will settle out of suspension within a specified period of time.
Untreated wastes from toilets, baths, sinks, lavatories, laundries, and other plumbing fixtures in places of human habitation, employment, or recreation.
A pipe or conduit that carries wastewater. Not to be confused with drain pipes which carry untreated runoff water to nearby waterways to reduce flooding of pavements.
In a properly operated secondary clarifier, the solids that have flocculated settle to the bottom. This produces a layer of light, fluffy solids which extend from the bottom of the clarifier for several feet. This layer is called the sludge blanket.
Soil absorption capacity
In subsurface effluent disposal, the ability of the soil to absorb water.
Refers to the killing off of all microorganisms in the liquid. In wastewater treatment, we disinfect rather than sterilize. That is, not all of the microorganisms in the liquid are killed off.
Stream Assimilation Capacity
Refers to the amount of waste that a stream or other receiving water can handle or deal with through natural process without significant undesirable effects on the receiving water.
Refers to the rainwater which is not absorbed by the ground. If this rain or storm water enters the sewer system, and your plant is not designed to handle such flows, you could run into treatment problems.
When solids settle to the bottom of a container, the clear liquid formed in the upper portion is the supernatant. If a scum layer also develops, then the supernatant is the clear liquid between the settled and floating solids.
Suspended solids, both organic and inorganic, are the ones that are in suspension in the water. Most of these solids will settle if allowed to stand. Different standing times will allow different amounts of suspended solids to settle.
Biological treatment processes in which the microorganisms responsible for the conversion of the organic matter or other constituents in the wastewater to gases and cell tissue are maintained in suspension within the liquid.
Removal of residual suspended solids, usually by granular medium filtration. Disinfection is also typically a part of tertiary treatment. Nutrient removal is often included in this definition.
30-Minute Settling Test
Well-mixed liquor is put into a one-liter graduated cylinder and allowed to sit for 30 minutes. After this time, the amount of sludge settled is measured. The top part is the supernatant. This test gives some information on the settleability and nature of the sludge.
The mineral, cells, etc. left in wastewater after evaporation of the water fraction at 103°C. Usually measured in mg/L.
Total suspended solids
The mineral, cells, etc. in wastewater retained on a standard filter paper after filtration followed by drying at 103°C. Usually measured in mg/L.
The adverse effect which a biologically active substance has, at some concentration, on a living entity.
Any element in water or wastewater that, for reasons associated with natural distribution, industrial uses, solubility, or other factors, is present at very low concentrations.
Refers to the process of moisture being given off to the air by plants.
A treatment process in which wastewater trickles over media that provide the opportunity for the formation of biological slimes which treat the wastewater.
Treatment standard 1
A thirty-day average of less than 10 mg/L of biochemical oxygen demand (BOD), 10 mg/L of total suspended solids (TSS), and a thirty-day geometric mean of less than 800 fecal coliform colonies per 100 mL.
Treatment standard 2
A thirty-day average of less than 10 mg/L of biochemical oxygen demand (BOD), 10 mg/L of total suspended solids (TSS), and a thirty-day geometric mean of less than 800 fecal coliform colonies per 100 mL.
Total suspended solids (TSS)
A measurement of the solids that either float on the surface of, or are in suspension in, water or wastewater. A measure of wastewater strength often used in conjunction with biochemical oxygen demand (BOD).
Some regulatory terminology means sewage in which the total suspended solids (TSS) content does not exceed 430 mg/L, the five-day biochemical oxygen demand (BOD) does not exceed 380 mg/L, and the content of fats, oils, and greases (FOG) does not exceed 75 mg/L.
Waster Stabilization Pond
A basin used for wastewater treatment by biological decomposition of organic matter. The kind of treatment activity occurring depends on the depth of the pond. Aerobic ponds are too shallow to be common in Canada. Deep ponds (8-12 Feet) usually work by anaerobic decomposition. Because of their smell, they are usually only used in sparsely populated areas. Ponds that have an aerobic top layer and an anaerobic bottom layer are called facultative ponds. They are the most common. The effluent from waste stabilization ponds is usually quite low in bacteria, especially if the effluent flows from one pond to another. A long detention time, usually a month or more, is needed, and disinfection may also be required.
The liquids generated from industrial processes, sanitary fixtures and appliances, food handling, etc.
Processing of wastewater for reuse.
A wall or plate specially designed to allow liquid to leave the tank at slow speed, to prevent particles form flowing out of the tank.
(1) Complete recycling of water. (2) Discharge of essentially pure water. (3) Discharge of a treated effluent containing no substance at a concentration higher than that found normally in the local environment.
Please note that this information was adapted from the Northern Arizona University
Department of Civil and Environmental Engineering.