Plumbing Enzymes Glossary Of Terms

This glossary describes terms as they have been used within the Wastewater Treatment Plant Operator Training Program Basic Course. For further or more complete definitions, other references should be examined.


The activated sludge process is a method of biological treatment which produces a high quality effluent. It is a secondary process, usually following primary treatment. The activated sludge removes the 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.


One of the advanced wastewater treatment methods. It involves the removal of a pollutant, such as organics, by making it stick to the surface of a solid, like carbon. (ADsorption is not to be confused with ABsorption. In absorption, one substance is taken into the body of another, like water into a sponge.)


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.


A very shallow waste stabilization pond that has dissolved oxygen throughout it so that treatment can occur by aerobic decomposition.


These are the bacteria that cause aerobic decomposition. Conditions are provided so that it is the aerobic and facultative bacteria that work.


Bacteria that live and reproduce in an environment containing no dissolved oxygen. Anaerobic bacteria contain their oxygen supply by breaking down chemical compounds which contain no dissolved oxygen.


Decomposition and decay of organic material in an environment containing no dissolved oxygen.


A digester designed to make use of anaerobic-process bacteria to decompose the sludge and reduce the volume of sludge to be handled. The anaerobic digester is completely sealed so that no air gets into it.


A deep waste stabilization pond. These ponds usually don’t have any dissolved oxygen throughout the liquid, and anaerobic decomposition occurs. These ponds can smell pretty badly, and are thus restricted in use.


These are the bacteria that live and work when there is no dissolved oxygen present. Anaerobic Bacteria, and facultative bacteria in the anaerobic state, result in anaerobic decomposition.


Bacteria are living organisms, microscopic in size. Most bacteria use organic matter for their food. Under proper conditions, they multiply with great rapidity.


A bar screen is 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.


A measure of the amount of organics, or food available in the wastewater.


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 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.


In the chlorine contact chamber or tank, the chlorine must have enough time in contact with the 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 we add enough chlorine so that there will be, at the 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.


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 a 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.


The network of sewers collecting wastewater from the community and bringing it to your plant is called the collection system.


Combined sewage is 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 my be sized in proportion to the flow at the time of sampling.


This refers to the changing of water vapor into water droplets.


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.


The theoretical time required for a given flow of waste water to pass through a tank, or the amount of time that the wastewater is in the tank.


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.


By disinfection, we mean the killing of microorganisms in the water. The point is to kill the pathogenic organisms or bacteria that are harmful to man. Note that not all of the organisms in the water are killed by disinfection. Any process that produces a harsh environment for the organisms can be used for disinfection. Most plants use chlorine.


Atmospheric oxygen dissolved in water or wastewater. It is usually abbreviated D.O.


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 your plant are called downstream users.


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.


Wastewater or other liquid – raw or partially or completely treated – Flowing from a tank, treatment process, or treatment plant.


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.


Larger particles that have formed from the coming together or joining of smaller particles as a result of biological or chemical activity.


An action resulting in the gathering of fine particles to form larger particles that are heavier and more easily settled.


When you collect all of your 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.


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.


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.


Wastewater or other liquid – raw or partially treated – flowing into a reservoir, tank treatment process, or treatment plant.


Waste material such as sand, salt, iron, calcium, and other mineral materials which are not converted in large quantities by organism action. Inorganic wastes are substances of mineral origin and may contain carbon and oxygen, whereas organic wastes are substances of animal or vegetable origin and contain carbon and hydrogen along with other elements.


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 is referred to as the mixed liquor


Municipal sewage contains all of domestic sewage, as well as some of the industrial wastes.


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.


Our example in the program was the number of red dots for every million yellow dots. P.P.M. refers to 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 litre (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.)


pH is an expression of the intensity of the alkaline or acidic strength of water. The pH may range from 0 to 14, where 0 is the most acid, 14 the most alkaline, and 7 neutral. Natural waters usually have a pH between 6.5 and 8.5.


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.


A wastewater treatment process consisting of a rectangular or circular tank which allows those substances in wastewater that readily settle or float to be separated from the water being treated.


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 stat 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.


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, an disposed of either by burning or burial.


Refers to that portion of the wastewater that floats to the surface. It is composed mainly of grease and oil, and is called the secondary clarifier.


The clarifier or sedimentation tank included as part of the secondary treatment process is called the secondary clarifier.


Secondary treatment consists of two processes. The first process biologically decomposes or converts dissolved or suspended organic materials into a more settleable form. The second process separates the solids from the liquid. The remaining liquid becomes the effluent. Some systems return the biological solids to the process for reuse.


Refers to the settling out of suspended materials from a liquid.


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.


See wastewater.


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.


See digester.


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.


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.


Refers to treatment phases or processes that follow secondary treatment. They are often referred to as advanced or physical-chemical wastewater treatment methods.


Well-mixed liquor is put into a one-litre 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.


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.


A basin used for wastewater treatment by biological decomposion of organic matter. The kind of treatment activity occurring depend son 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.


Refers to all waterborne waste materials. Normal domestic wastewater is a mixture of about 99.9% water and 0.1% solids. Just about half of the dissolved solids are organic, and the other half inorganic. Normal domestic sewage contains inorganic solids, gasses, and microorganisms as well. Fresh wastewater is usually gray in color and has a musty, or unpleasant smell.


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.