United States Office of EPA 832-R-04-001 Environmental Protection Office of Management September 2004 Agency Washington DC 20460 Primer for Municipal Systems Primer for Municipal Wastewater Treatment Systems

Clean Water Act Requirements for Wastewater Treatment 4

The Need for Wastewater Treatment 5

Effects of Wastewater on 5

Some of the Key Challenges Faced by Wastewater Treatment Professionals Today 6

Collecting and Treating Wastewater 6 Centralized Collection 6 Systems 7 System 9 : 8 -Demanding Substances 8 8 Nutrients 8 Synthetic Organic and Inorganic Chemicals 8 Thermal 8

Wastewater Treatment 9 Primary Treatment 9 Preliminary Treatment 9 Primary Sedimentation 11 Basic Wastewater Treatment Processes 10 Physical 10 Biological 10 Chemical 10 11 Attached Growth Processes 11 Suspended Growth Processes 12 13 Treatment 14 Slow Rate 14 Rapid Infiltration 15 Overland Flow 15 Constructed 15 Disinfection 16 16 16 Radiation 16

Pretreatment 16

Advanced Methods of Wastewater Treatment 17 Control 17 Biological Control 18 Coagulation-Sedimentation 18 19

The Use or Disposal of Wastewater Residuals and 19 Land Application 20 20 Beneficial Use Products from Biosolids 21

Decentralized (Onsite or Cluster) Systems 21 Treatment 22 Conventional Septic Tanks 22 Aerobic Treatment Units 22 Media Filters 22 Dispersal Approaches 23 Field 23 Mound System 23 Drip Dispersal System 24 Evapotranspiration Beds 24 Management of Onsite/Decentralized Wastewater Systems 24

Asset Management 24 Operation 25 Maintenance 25

Common Wastewater Treatment Terminology 25

Clean Water Act Requirements for Wastewater Treatment

The 1972 Amendments to the Federal Water Control Act (Public Law 92- 500–, known as the Clean Water Act (CWA), established the foundation for wastewater control in this country. The CWA’s primary objective is to ‘restore and maintain the chemical, physical and biological integrity of the nation’s .’

The CWA established a control program for ensuring that communities have clean water by regulating the release of contaminants into our country’s waterways. Permits that limit the amount of pollutants discharged are required of all municipal and industrial wastewater dischargers under the National Discharge Elimination System (NPDES) permit program. In addition, a construction grants program was set up to assist publicly- owned wastewater treatment works build the improvements required to meet these new limits. The 1987 Amendments to the CWA established Revolving Funds (SRF) to replace grants as the current principal federal funding source for the construction of wastewater treatment and collection systems.

Over 75 percent of the nation’s is served by centralized wastewater collection and treatment systems. The remaining population uses septic or other onsite systems. Approximately 16,000 municipal wastewater treatment facilities are in operation nationwide. The CWA requires that municipal wastewater treatment discharges meet a minimum of ‘secondary treatment’. Over 30 percent of the wastewater treatment facilities today produce cleaner discharges by providing even greater levels of treatment than secondary.

4 Primer for Municipal Wastewater Treatment Systems

The Need for Wastewa- produced can greatly alter people to use the water for ter Treatment the amount and complexity beneficial purposes. Past Wastewater treatment is of industrial and approaches used to control needed so that we can challenge traditional control must use our and treatment technology. The be modified to accommodate for fishing, swimming and application of commercial current and emerging issues . For the first and , Effects of Wastewater on half of the 20th century, combined with Water Quality pollution in the Nation’s from growing development The basic function of the urban waterways resulted in activities, continues to be a frequent occurrences of low source of significant pollution wastewater treatment plant dissolved oxygen, fish kills, as runoff washes off the is to speed up the natural algal blooms and bacterial land. processes by which water contamination. Early efforts Water pollution issues now purifies itself. In earlier in water pollution control dominate public concerns years, the natural treatment prevented human about national water quality process in streams and from reaching water supplies and maintaining healthy was adequate to or reduced floating debris . Although a perform basic wastewater that obstructed shipping. large investment in . As our population Pollution problems and their pollution control has helped and grew to their control were primarily local, reduce the problem, many present size, increased not national, concerns. miles of streams are still levels of treatment prior Since then, population impacted by a variety of to discharging domestic and industrial growth have different pollutants. This, wastewater became increased demands on our in turn, affects the ability of necessary. natural , altering the situation dramatically. Progress in abating pollution has barely kept ahead of , changes in , technological developments, changes in , , and many other factors. Increases in both the quantity and variety of goods

5 (Data form U.S. Service multi wastewater inventories: 2000 USEPA Clean Watershed Needs Survey)

Collecting and Treating Wastewater Population Receiving Different Levels of Wastewater Treatment The most common form of pollution control in the 220 consists of 200 a system of sewers and 180 wastewater treatment . 160 2 The sewers collect municipal No Discharge 140 Greater than wastewater from , Secondary 120 , and industries Secondary 100 Less than and deliver it to facilities Secondary 80 1 for treatment before it is Raw Discharge 60 discharged to water bodies

ulation Served (millions) 40 or land, or reused. p 20 Po 0 Centralized Collection During the early days of our Before the CWA nation’s history, people living After the CWA in both the and the

1 Raw discharges were eliminated by 1996 countryside used cesspools 2 Data for the "no-discharge" category were unavailable for 1968 and privies to dispose of domestic wastewater. Cities began to install wastewater Some of the key challenges faced by wastewater collection systems in the late treatment professionals today: nineteenth century because of an increasing awareness  Many of the wastewater treatment and collection facilities are now old and worn, and require further improvement, of waterborne disease and repair or replacement to maintain their useful ; the popularity of indoor and flush .  The character and quantity of contaminants presenting problems today are far more complex than those that pre- The use of collection sented challenges in the past; systems brought dramatic improvements to public  Population growth is taxing many existing wastewater treatment systems and creating a need for new plants; health, further encouraging the growth of metropolitan  Farm runoff and increasing provide ad- areas. In the year 2000 ditional sources of pollution not controlled by wastewater treatment; and approximately 208 million people in the U.S. were  One third of new development is served by decentralized served by centralized systems (e.g., septic systems) as population migrates further collection systems. from metropolitan areas.

6 Combined Sewer Systems Many of the earliest sewer systems were combined sewers, designed to collect both sanitary wastewater and storm water runoff in a single system. These combined sewer systems were designed to provide storm from and roofs to prevent flooding in cities. Later, lines were added to carry domestic wastewater away from homes and businesses. Early sanitarians thought that these combined systems provided adequate health protection. We now know that the overflows designed to release excess flow during also release pathogens and other pollutants. Simplified Urban

7 Pollutants Oxygen-Demanding Substances

Dissolved oxygen is a key element in water quality that is necessary to support aquatic life. A demand is placed on the natural supply of dissolved oxygen by many pollutants in waste- water. This is called biochemical oxygen demand, or BOD, and is used to measure how a plant is working. If the , the treated wastewater produced by a treatment plant, has a high content of organic pollutants or , it will demand more oxygen from the water and leave the water with less oxygen to support fish and other aquatic life. and ammonia are “oxygen-demanding” substances. Oxygen-demand- ing substances are contributed by domestic sewage and agricultural and industrial wastes of both plant and animal origin, such as those from processing, paper mills, tanning, and other processes. These substances are usually destroyed or converted to other compounds by if there is sufficient oxygen present in the water, but the dis- solved oxygen needed to sustain fish life is used up in this break down process.


Disinfection of wastewater and chlorination of drinking water supplies has reduced the oc- currence of such as , , and dysentery, which remain problems in underdeveloped countries while they have been virtually eliminated in the U.S. Infectious micro-organisms, or pathogens, may be carried into surface and by sewage from cities and institutions, by certain kinds of industrial wastes, such as tanning and meat packing plants, and by the contamination of storm runoff with animal wastes from pets, livestock and wild animals, such as geese or deer. Humans may come in contact with these pathogens either by drinking contaminated water or through swimming, fishing, or other contact activities. Modern disinfection techniques have greatly reduced the danger of water- borne disease.


Carbon, nitrogen, and phosphorus are essential to living organisms and are the chief nutri- ents present in natural water. Large amounts of these nutrients are also present in sewage, certain industrial wastes, and drainage from fertilized land. Conventional secondary bio- logical treatment processes do not remove the phosphorus and nitrogen to any substantial extent -- in fact, they may convert the organic forms of these substances into form, making them more usable by plant life. When an excess of these nutrients overstimulates the growth of water plants, the result causes unsightly conditions, interferes with drinking water treatment processes, and causes unpleasant and disagreeable tastes and in drinking water. The release of large amounts of nutrients, primarily phosphorus but occasionally ni- trogen, causes nutrient enrichment which results in excessive growth of . Uncontrolled algae growth blocks out and chokes aquatic plants and animals by depleting dis- solved oxygen in the water at night. The release of nutrients in quantities that exceed the affected waterbody’s ability to assimilate them results in a condition called or cultural enrichment.

Inorganic and Synthetic Organic Chemicals

A vast array of chemicals are included in this category. Examples include detergents, house- hold cleaning aids, heavy , pharmaceuticals, synthetic organic pesticides and her- bicides, industrial chemicals, and the wastes from their manufacture. Many of these sub- stances are toxic to fish and aquatic life and many are harmful to humans. Some are known to be highly poisonous at very low concentrations. Others can cause taste and prob- lems, and many are not effectively removed by conventional wastewater treatment.


Heat reduces the capacity of water to retain oxygen. In some areas, water used for cooling is discharged to streams at elevated from power plants and industries. Even discharges from wastewater treatment plants and storm water retention ponds affected by summer heat can be released at temperatures above that of the receiving water, and elevate the . Unchecked discharges of can seriously alter the of a , a stream, or estuary.

8 Wastewater Treatment Preliminary Treatment In 1892, only 27 American As wastewater enters a cities provided wastewater treatment facility, it typically treatment. Today, more flows through a step called than 16,000 publicly-owned preliminary treatment. A wastewater treatment plants screen removes large floating operate in the United States objects, such as rags, cans, and its territories. The bottles and sticks that may construction of wastewater clog , small pipes, and treatment facilities Workers install sewer line down stream processes. The blossomed in the 1920s and screens vary from coarse to Sanitary Sewer Systems again after the passage of fine and are constructed with Sanitary sewer collection the CWA in 1972 with the parallel or bars systems serve over half the availability of grant funding with openings of about half people in the United States and new requirements an inch, while others may today. EPA estimates that calling for minimum levels be made from mesh screens there are approximately of treatment. Adequate with much smaller openings. 500,000 miles of publicly- treatment of wastewater, along with the ability to owned sanitary sewers provide a sufficient supply Screens are generally placed with a similar expanse of of clean water, has become in a chamber or and privately-owned sewer a major concern for many inclined towards the flow of systems. Sanitary sewers communities. the wastewater. The inclined were designed and built screen allows debris to be to carry wastewater from Primary Treatment caught on the upstream domestic, industrial and The initial stage in the surface of the screen, and commercial sources, but treatment of domestic allows access for manual not to carry storm water. wastewater is known as or mechanical cleaning. primary treatment. Coarse Nonetheless, some storm Some plants use devices are removed from “the ability to water enters sanitary sewers known as comminutors or the wastewater in the through cracks, particularly barminutors which combine primary stage of treatment. provide a sufficient in older lines, and through the functions of a screen and In some treatment plants, roof and drains. a grinder. These devices supply of clean primary and secondary Due to the much smaller catch and then cut or shred stages may be combined volumes of wastewater water continues to into one basic operation. the heavy and floating that pass through sanitary At many wastewater material. In the process, the be a major national sewer lines compared to treatment facilities, influent pulverized matter remains combined sewers, sanitary passes through preliminary in the wastewater flow to be concern” sewer systems use smaller treatment units before removed later in a primary pipes and lower the cost of primary and secondary tank. collecting wastewater. treatment begins.

9 Basic Wastewater Treatment Processes Physical Biological Chemical Physical processes were In , bacteria and Chemicals can be used to some of the earliest methods other small organisms in create changes in pollutants to remove solids from water consume organic that increase the removal wastewater, usually by matter in sewage, turning of these new forms by passing wastewater through it into new bacterial cells, physical processes. Simple screens to remove debris , and other chemicals such as , and solids. In addition, by-products. The bacteria lime or iron can be solids that are heavier than normally present in water added to wastewater to water will settle out from must have oxygen to do cause certain pollutants, wastewater by gravity. their part in breaking down such as phosphorus, to floc Particles with entrapped the sewage. In the 1920s, or bunch together into large, air float to the top of water scientists observed that these heavier masses which can and can also be removed. natural processes could be be removed faster through These physical processes are contained and accelerated physical processes. Over the employed in many modern in systems to remove organic past 30 years, the chemical wastewater treatment material from wastewater. industry has developed facilities today. With the addition of oxygen synthetic inert chemicals to wastewater, masses of know as to grew and further improve the physical rapidly metabolized organic separation step in wastewater pollutants. Any excess treatment. Polymers are microbiological growth often used at the later could be removed from stages of treatment to the wastewater by physical improve the settling of excess processes. microbiological growth or biosolids.

After the wastewater has of grit and entering a any additional material that been screened, it may flow treatment plant can cause might damage equipment or into a grit chamber where serious operating problems, interfere with later processes. sand, grit, cinders, and small such as excessive wear of The grit and screenings stones settle to the bottom. pumps and other equipment, removed by these processes Removing the grit and gravel clogging of aeration devices, must be periodically that washes off streets or or taking up capacity in tanks collected and trucked to a land during storms is very that is needed for treatment. for disposal or are important, especially in In some plants, another incinerated. cities with combined sewer finer screen is placed after . systems. Large amounts the grit chamber to remove

10 secondary treatment are attached growth processes and suspended growth processes.. Primary Sedimentation Secondary Treatment Attached Growth With the screening After the wastewater has Processes completed and the grit been through Primary In attached growth (or fixed removed, wastewater still Treatment processes, it film) processes, the microbial contains dissolved organic flows into the next stage of growth occurs on the surface and inorganic constituents treatment called secondary. of stone or media. along with suspended Secondary treatment Wastewater passes over solids. The suspended solids processes can remove up to the media along with air to Solids removed from automated screens consist of minute particles of 90 percent of the organic matter that can be removed matter in wastewater by from the wastewater using biological treatment with further treatment processes. The two most such as sedimentation or common conventional gravity settling, chemical methods used to achieve coagulation, or . Pollutants that are dissolved or are very fine and remain suspended in the wastewater are not removed effectively by gravity settling.

When the wastewater enters a sedimentation tank, it slows down and the suspended solids gradually sink to the bottom. This mass of solids is called primary . Various methods have been devised to remove primary sludge from the tanks. Newer plants have some type of mechanical equipment to remove the settled solids from sedimentation tanks. Some plants remove solids continuously while others do so at intervals. Aerated Grit Chamber

11 media bed material. New Suspended Growth facilities may use beds made Processes of plastic balls, interlocking Similar to the microbial sheets of corrugated plastic, processes in attached growth or other types of synthetic systems, suspended growth media. This type of bed processes are designed material often provides to remove biodegradable more surface area and organic material and a better environment for organic nitrogen-containing promoting and controlling material by converting

Sequencing Batch biological treatment than ammonia nitrogen to provide oxygen. Attached Reactor rock. Bacteria, algae, fungi unless additional growth process units include and other microorganisms treatment is provided. In trickling filters, biotowers, grow and multiply, forming suspended growth processes, and rotating biological a microbial growth or slime the microbial growth is contactors. Attached growth layer (biomass) on the suspended in an aerated processes are effective at media. In the treatment water mixture where the air removing biodegradable process, the bacteria use is pumped in, or the water is organic material from the oxygen from the air and agitated sufficiently to allow wastewater. consume most of the organic oxygen transfer. Suspended matter in the wastewater as growth process units include A is simply food. As the wastewater variations of activated a bed of media (typically passes down through the sludge, oxidation ditches and rocks or plastic) through media, oxygen-demanding sequencing batch reactors. which the wastewater passes. substances are consumed by The media ranges from the biomass and the water The suspended growth three to six feet deep and leaving the media is much process speeds up the allows large numbers of cleaner. However, portions of aerobic bacteria and microorganisms to attach of the biomass also slough other microorganisms that and grow. Older treatment off the media and must settle break down the organic facilities typically used out in a secondary treatment matter in the sewage by stones, rocks, or slag as the tank. providing a rich aerobic environment where the microorganisms suspended in the wastewater can work more efficiently. In the aeration tank, wastewater is vigorously mixed with air and microorganisms acclimated to the wastewater in a suspension for several hours. This allows the bacteria Trickling Filters 12 Brush Aerators in an Oxidation Ditch

Centerfeed well of a for removing excess biomass

of mechanical aeration and forced aeration can also be used. Also, relatively pure oxygen, produced by several different manufacturing processes, can be added to provide oxygen to the aeration tanks. and other microorganisms to run the aeration system. From the aeration tank, to break down the organic The effectiveness of the the treated wastewater matter in the wastewater. process flows to a sedimentation The microorganisms grow can be impacted by elevated tank (secondary clarifier), in number and the excess levels of toxic compounds in where the excess biomass biomass is removed by wastewater unless complex is removed. Some of the settling before the effluent industrial chemicals are biomass is recycled to the is discharged or treated effectively controlled through end of the aeration further. Now activated an industrial pretreatment tank, while the remainder is with millions of additional program. “wasted” from the system. aerobic bacteria, some of The waste biomass and the biomass can be used An adequate supply of settled solids are treated again by returning it to an oxygen is necessary for the before disposal or as aeration tank for mixing with activated sludge process to biosolids. incoming wastewater. be effective. The oxygen Lagoons is generally supplied by A wastewater The activated sludge mixing air with the sewage or is a process, like most other and biologically active scientifically constructed techniques, has advantages solids in the aeration pond, three to five feet and limitations. The units tanks by one or more of deep, that allows sunlight, necessary for this treatment several different methods. are relatively small, requiring Mechanical aeration can be less space than attached accomplished by drawing growth processes. In the sewage up from the addition, when properly bottom of the tank and operated and maintained, spraying it over the surface, the process is generally thus allowing the sewage free of flies and odors. to absorb large amounts of However, most activated oxygen from the . sludge processes are more Pressurized air can be forced costly to operate than out through small openings attached growth processes in pipes suspended in the due to higher use wastewater. Combination

13 Wastewater Lagoon

Land Treatment Slow Rate Infiltration Land treatment is the In the case of slow rate controlled application of infiltration, the wastewater wastewater to the where is applied to the land and physical, chemical, and moves through the soil biological processes treat where the natural filtering algae, bacteria, and oxygen the wastewater as it passes action of the soil along to interact. Biological and across or through the soil. with microbial activity and physical treatment processes The principal types of land plant uptake removes most occur in the lagoon to treatment are slow rate, contaminants. Part of the improve water quality. The overland flow, and rapid water evaporates or is used quality of water leaving the infiltration. In the arid by plants. The remainder is lagoon, when constructed western states, pretreated either collected via drains or and operated properly, is municipal wastewater has for surface discharge or considered equivalent to the been used for many years allowed to percolate into the effluent from a conventional to irrigate crops. In more groundwater. secondary treatment system. recent years, land treatment However, winters in cold has spread to all sections of Slow rate infiltration is climates have a significant the country. Land treatment the most commonly used impact on the effectiveness of many types of industrial land treatment technique. of lagoons, and winter wastewater is also common. The wastewater, which is storage is usually required. sometimes disinfected before Whatever method is application, depending on Lagoons have several used, land treatment can the end use of the crop and advantages when used be a feasible economic the method, can correctly. They can be used alternative, where the land be applied to the land by for secondary treatment area needed is readily spraying, flooding, or ridge or as a supplement to available, particularly and furrow irrigation. The other processes. While when compared to costly method selected depends on treatment ponds require advanced treatment plants. cost considerations, terrain, substantial land area and Extensive research has been and the type of crops. Much are predominantly used conducted at land treatment of the water and most of the by smaller communities, sites to determine treatment nutrients are used by the they account for more performance and study than one-fourth of the the numerous treatment plants, while other pollutants municipal wastewater processes involved, as are transferred to the soil treatment facilities in this well as potential impacts by adsorption, where many country. Lagoons remove on the environment, e.g. are mineralized or broken biodegradable organic groundwater, , down over time by microbial material and some of the and any crop that may be action. nitrogen from wastewater. grown.

14 Biologically Degradable Wastewater Treated in the U.S. has increased since 1940, however, treatment efficiency has improved so that pollution has decreased.

80,000 Influent BOD5

Effluent BOD5 70,000 Removal Efficiency BOD5 R BOD5

60,000 emoval Efficiency (%) Efficiency emoval

50,000 Constructed Wetlands

40,000 Wetlands are areas where the water saturates the 30,000 ground long enough to BOD5 Loading (metric tons/day) support and maintain 20,000 vegetation such as reeds, bulrush, and 10,000 cattails. A “constructed

0 wetlands” treatment system is 1940 1950 1960 1970 1980 1990 1996 2016 designed to treat wastewater Year by passing it through the 1 165 gal/capita-day is based on data in the Clean Water Needs Surveys for 1978 wetland. Natural physical, through 1986 and accounts for residential, commercial, industrial, , and infiltration and inflow components. chemical, and biological wetland processes have been Rapid Infiltration Overland Flow recreated and enhanced in constructed wetlands The rapid infiltration This method has been used designed specifically to treat process is most frequently successfully by the food wastewater from industries, used to polish and recover processing industries for wastewater for small communities, storm many years to remove solids, reuse after pretreatment by runoff from urban and bacteria and nutrients from secondary and advanced agricultural areas, and acid wastewater. The wastewater treatment processes. It is mine drainage. Significant is allowed to flow down a also effective in cold or water quality improvements, gently-sloped surface that is wet weather and has been including nutrient reduction, successfully used in Florida, planted with vegetation to can be achieved northeastern and arid control runoff and . Constructed Wetlands southwestern states. Large Heavy are well amounts of wastewater suited to the overland flow are applied to permeable process. As the water flows soils in a limited land area down the slope, the soil and and allowed to infiltrate its microorganisms form a and percolate downward gelatinous slime layer similar through the soil into the in many ways to a trickling water table below. If the filter that effectively removes water is to be reused, it can solids, pathogens, and nutri- be recovered by wells. The ents. Water that is not cost-effectiveness of this absorbed or evaporated is process depends on the soil’s ability to percolate a large recovered at the bottom of volume of water quickly and the slope for discharge or efficiently, so suitable soil reuse. drainage is important.

15 Land Treatment - Rapid Infiltration

Pretreatment The National Pretreatment Program, a cooperative effort of Federal, state, POTWs and their industrial dischargers, requires industry Disinfection chlorine gas is used less to control the amount of Untreated domestic frequently now than in the pollutants discharged into wastewater contains micro- past. municipal sewer systems. organisms or pathogens that Pretreatment protects the Ozone produce human diseases. wastewater treatment Ozone is produced from Processes used to kill or facilities and its workers oxygen exposed to a high deactivate these harmful from pollutants that may voltage current. Ozone is organisms are called create hazards or interfere very effective at destroying disinfection. Chlorine is the with the operation and and bacteria and most widely used performance of the POTW, decomposes back to oxygen but ozone and ultraviolet including contamination of rapidly without leaving radiation are also frequently , and reduces harmful by products. Ozone used for wastewater effluent the likelihood that untreated is not very economical due to disinfection. pollutants are introduced into high energy costs. the receiving waters. Chlorine Ultraviolet Radiation Chlorine kills micro- Ultra violet (UV) disinfection Under the Federal organisms by destroying occurs when electromagnetic Pretreatment Program, cellular material. This municipal wastewater chemical can be applied to energy in the form of light in plants receiving significant wastewater as a gas, a the UV spectrum produced industrial discharges must or in a solid form similar to by arc lamps develop local pretreatment swimming pool disinfection penetrates the wall of programs to control chemicals. However, any exposed microorganisms. free (uncombined) chlorine The UV radiation retards the industrial discharges into remaining in the water, ability of the microorganisms their sewer system. These even at low concentrations, to survive by damaging programs must be approved is highly toxic to beneficial their genetic material. UV by either EPA or a state aquatic life. Therefore, disinfection is a physical acting as the Pretreatment removal of even trace treatment process that Approval Authority. More amounts of free chlorine leaves no chemical traces. than 1,500 municipal by dechlorination is often Organisms can sometimes treatment plants have needed to protect fish repair and reverse the developed and received and aquatic life. Due to destructive effects of UV approval for a Pretreatment emergency response and when applied at low doses. Program. potential safety concerns,

16 Advanced Methods of secondary are called industrial cooling and Wastewater Treatment advanced treatment. processing, recreational uses As our country and the and water recharge, and demand for clean water Advanced treatment even indirect augmentation have grown, it has become technologies can be of drinking water supplies. more important to produce extensions of conventional cleaner wastewater effluents, secondary biological Nitrogen Control yet some contaminants are treatment to further Nitrogen in one form more difficult to remove stabilize oxygen-demanding or another is present in than others. The demand substances in the wastewater, municipal wastewater and for cleaner discharges has or to remove nitrogen and is usually not removed by been met through better phosphorus. Advanced secondary treatment. If and more complete methods treatment may also discharged into lakes and of removing pollutants at involve physical-chemical streams or estuary waters, wastewater treatment plants, separation techniques nitrogen in the form of in addition to pretreatment such as adsorption, ammonia can exert a direct demand on oxygen and /, or stimulate the excessive which helps limit types of membranes for advanced growth of algae. Ammonia wastes discharged to the filtration, exchange, in wastewater effluent can be sanitary sewer system. and . In toxic to aquatic life in certain Currently, nearly all WWTPs various combinations, these instances. provide a minimum of processes can achieve any secondary treatment. In degree of pollution control By providing additional some receiving waters, the desired. As wastewater is biological treatment beyond discharge of secondary purified to higher and higher the secondary stage, treatment effluent would degrees by such advanced nitrifying bacteria present still degrade water quality treatment processes, the in wastewater treatment can and inhibit aquatic life. treated effluents can be biologically convert ammonia Further treatment is needed. reused for urban, landscape, to the non-toxic nitrate Treatment levels beyond and agricultural irrigation, through a process known as . The nitrification process is normally sufficient to remove the associated with ammonia in the effluent. Since nitrate is also a nutrient, excess amounts can contribute to the uncontrolled growth of algae. In situations where nitrogen must be completely removed from effluent, an Monitoring a discharger as part of a Pretreatment Program 17 Nitrification Process Tank

additional biological process can be added to the system to convert the nitrate to nitrogen gas. The conversion of nitrate to nitrogen gas is accomplished by bacteria in a process known as . Effluent with nitrogen in the form of nitrate is placed into a tank Biological Phosphorus Coagulation- devoid of oxygen, where Control sedimentation carbon-containing chemicals, Like nitrogen, phosphorus A process known as chemical such as , are added is also a necessary nutrient coagulation-sedimentation or a small stream of raw for the growth of algae. is used to increase the wastewater is mixed in with Phosphorus reduction is removal of solids from the nitrified effluent. In this often needed to prevent effluent after primary oxygen free environment, excessive algal growth and secondary treatment. bacteria use the oxygen Solids heavier than water attached to the nitrogen in before discharging effluent settle out of wastewater by the nitrate form releasing into lakes, and gravity. With the addition of nitrogen gas. Because estuaries. Phosphorus removal can be achieved specific chemicals, solids can through chemical addition become heavier than water and a coagulation- and will settle. sedimentation process discussed in the following Alum, lime, or iron salts CHEMICAL section. Some biological are chemicals added to treatment processes the wastewater to remove called biological nutrient phosphorus. With these removal (BNR) can also chemicals, the smaller achieve nutrient reduction, particles ‘floc’ or clump removing both nitrogen together into large masses. and phosphorus. Most of The larger masses of the BNR processes involve particles will settle faster modifications of suspended when the effluent reaches the growth treatment systems nitrogen comprises almost so that the bacteria in these next step--the sedimentation 80 percent of the air in the systems also convert nitrate tank. This process can earth’s atmosphere, the nitrogen to inert nitrogen gas reduce the concentration of release of nitrogen into the and phosphorus in the by more than 95 atmosphere does not cause solids that are removed from percent. any environmental harm. the effluent.

18 Although used for years in Carbon adsorption consists enforce the need to employ the treatment of industrial of passing the wastewater environmentally sound wastes and in water effluent through a bed or residuals management treatment, coagulation- canister of techniques and to sedimentation is considered granules or powder which beneficially use biosolids an advanced process remove more than 98 whenever possible. Biosolids because it is not routinely percent of the trace organic are processed wastewater applied to the treatment of substances. The substances solids (“sewage sludge”) municipal wastewater. In adhere to the carbon surface that meet rigorous standards some cases, the process and are removed from the allowing safe reuse for is used as a necessary water. To help reduce the beneficial purposes. pretreatment step for other cost of the procedure, the Currently, more than half advanced techniques. This carbon granules can be of the biosolids produced process produces a chemical cleaned by heating and used by municipal wastewater sludge, and the cost of again. treatment systems is disposing this material can applied to land as a soil The Use or Disposal of conditioner or and be significant. Wastewater Residuals and Biosolids the remaining solids are incinerated or landfilled. ADSORPTION When pollutants are removed Ocean dumping of these from water, there is always solids is no longer allowed. something left over. It may be rags and sticks caught on Prior to utilization or the screens at the beginning disposal, biosolids are of primary treatment. It may stabilized to control odors be the solids that settle to and reduce the number of the bottom of sedimentation disease-causing organisms. tanks. Whatever it is, there Sewage solids, or sludge, are always residuals that when separated from the Biosolids Digestor must be reused, burned, Carbon adsorption buried, or disposed of in Carbon adsorption some manner that does not technology can remove harm the environment. organic materials from wastewater that resist removal by biological The utilization and disposal treatment. These resistant, of the residual process solids trace organic substances can is addressed by the CWA, contribute to taste and odor Conservation problems in water, taint fish and Recovery Act (RCRA), flesh, and cause foaming and other federal laws. and fish kills. These Federal laws re-

19 wastewater, still contain Stabilization of solids may are transported to the soil around 98 percent water. also be accomplished by treatment areas. The slurry They are usually thickened composting, heat treatments, or dewatered biosolids, and may be dewatered or the addition containing nutrients and to reduce the volume to of lime or other alkaline stabilized organic matter, is be transported for final materials. After stabilization, spread over the land to give processing, disposal, or the biosolids can be safely nature a hand in returning beneficial use. Dewatering spread on land. grass, trees, and flowers to processes include drying barren land. Restoration of Land Application beds, presses, the countryside also helps plate and frame presses, In many areas, biosolids control the flow of acid and centrifuges. To improve are marketed to farmers as drainage from mines that fertilizer. Federal regulation dewatering effectiveness, endangers fish and other (40 CFR Pert 503) defines the solids can be pretreated aquatic life and contaminates minimum requirements with chemicals such as lime, the water with acid, salts, for such land application ferric chloride, or polymers and excessive quantities of practices, including to produce larger particles metals. contaminant limits, field which are easier to remove. management practices, Incineration Digestion is a form of treatment requirements, stabilization where the Incineration consists of monitoring, recordkeeping, burning the dried solids volatile material in the and reporting requirements. to reduce the organic wastewater solids can Properly treated and residuals to an ash that decompose naturally and the applied biosolids are a can be disposed or reused. potential for odor production good source of organic Incinerators often include is reduced. Digestion without matter for improving soil heat recovery features. air in an enclosed tank structure and help supply Undigested sludge solids (anaerobic solids digestion) nitrogen, phosphorus, and have significant value as has the added benefit of micronutrients that are a result of their high organic producing gas required by plants. content. However, the water which can be recovered and Biosolids have also been content must be greatly Land Application of Biosoilds used as a source of energy. used successfully for many reduced by dewatering or years as a soil conditioner drying to take advantage and fertilizer, and for of the fuel potential of restoring and revegetating the biosolids. For this areas with poor soils due to reason, pressure filtration construction activities, strip dewatering equipment is or other practices. used to obtain biosolids Under this biosolids which are sufficiently dry management approach, to without continual treated solids in semi- reliance on auxiliary . liquid or dewatered form In some cities, biosolids are

20 Composted Biosolids

systems and cluster systems. An onsite system is a wastewater system relying on natural processes, although sometimes containing mechanical components, to collect, treat, disperse or reclaim wastewater mixed with refuse or refuse- (i.e. cadmium, mercury, from a single dwelling or derived fuel prior to burning. and ) and persistent building. A and Generally, waste heat is organic compounds from soil adsorption field is an recovered to provide the contaminating the residuals example of an onsite system. greatest amount of energy of wastewater treatment and A wastewater collection and efficiency. limiting the potential for treatment system under some beneficial use. form of common ownership Beneficial Use Products that collects wastewater from from Biosolids Effective stabilization two or more dwellings or Heat dried biosolids pellets of wastewater residuals buildings and conveys it to have been produced and and their conversion to a treatment and dispersal used extensively as a biosolid products can be system located on a suitable fertilizer product for costly. Some cities have site near the dwellings or care, turf production, citrus produced fertilizers from buildings is a cluster system. groves, and vegetable biosolids which are sold to Decentralized systems production for many years. help pay part of the cost include those using Composting of biosolids of treating wastewater. alternative treatment is also a well established Some use technologies like media approach to solids composted, heat dried, filters, management that has been or lime stabilized biosolid systems, aerobic treatment adopted by a number of products on parks and other units, and a variety of soil communities. The composted public areas. dispersal systems. Soil -like product has shown dispersal systems include Egg-shaped Digestors particular promise for use Decentralized (Onsite in the production of soil and Cluster) Systems additives for revegetation of topsoil depleted areas, and A decentralized wastewater as a potting soil amendment. system treats sewage from homes and businesses Effective pretreatment that are not connected to of industrial wastes a centralized wastewater prevents excessive levels treatment plant. of unwanted constituents, Decentralized treatment such as systems include onsite

21 pressure systems such as water prior to dispersal in the bottom of the tank, low pressure and drip into the environment; a referred to as septage, must dispersal systems. These soil dispersal component be removed and disposed of systems treat and disperse which assures that treated properly. relatively small volumes water is released into the of wastewater, and are environment at a rate which Aerobic Treatment Units generally are found in can be assimilated; and a Aerobic treatment units rural and suburban areas. management system which are also used to provide While septic tanks and soil assures proper long term onsite wastewater treatment. absorption systems have operation of the complete They are similar to septic significant limitations, system. Disinfection tanks, except that air is decentralized systems can of the treated effluent introduced and mixed with effectively protect water may be provided prior the wastewater inside the quality and public health to dispersal. A typical tank. Aerobic (requiring from groundwater and onsite system consists of a oxygen) bacteria consume surface water contamination septic tank followed by an the organic matter in the if managed properly (i.e. effluent distribution system. sewage. As with the typical properly sited, sized, Alternative treatment systems septic system, the effluent designed, installed, include aerobic treatment discharge from an aerobic operated, and maintained). and sand filtration systems. system is typically released Nitrate concentrations in through a sub-surface groundwater that exceed the Conventional Septic distribution system or may be drinking water standards can Tanks disinfected and discharged cause health problems. A septic tank is a tank buried directly to surface water. in the ground used to treat Aerobic treatment units also Treatment sewage without the presence require the removal and Onsite wastewater systems of oxygen (anaerobic). The proper disposal of solids that contain three components: sewage flows from the accumulate in the tank. a treatment unit which treats Septic tank and distribution box plumbing in a or small business establishment into Media Filters the first of two chambers, Media filters are used to where solids settle out. The provide further treatment liquid then flows into the of septic tank effluent, second chamber. Anaerobic and provide high levels of bacteria in the sewage break nitrification. They can be down the organic matter, designed to pass the effluent allowing cleaner water once or multiple times to flow out of the second through the media bed. chamber. The liquid typically Media, such as sand, acts as discharges through a sub- a filter. The media is placed surface distribution system. two to three feet deep above Periodically, the solid matter a liner of impermeable

22 Onsite aerobic treatment unit Mound System When the soil is not conducive to or when the groundwater level is high, a mound system is commonly used. A mound system is a distribution system constructed above the original ground level by using granular material such as sand and gravel to receive the septic tank effluent before it flows to the native soil below. The material such as plastic further treat or distribute the effluent flows to a dosing or . Septic tank treated effluent. The most tank that is equipped with a effluent is applied to the filter common alternative dispersal . Here the effluent is surface in intermittent doses systems include low pressure stored until there is sufficient and is further treated as it pipe, mounds, drip disposal, liquid. Once the liquid is slowly trickles through the and evapotranspiration beds. pumped out, it moves evenly media. In most media filters, throughout the mound before wastewater is collected in Absorbtion Field reaching less permeable an underdrain then either When soil conditions permit, soil or ground water. The pumped back to the filter the most common method granular material acts as bed or to other types of to disperse septic tank or a treatment medium and treatment. aerobic system effluent is an improves the removal of Mound system under construction absorption field consisting (photo courtesy of Ayres Associates) Dispersal Approaches of a series of perforated Traditional onsite systems parallel pipes laid in trenches include treatment units on gravel or crushed stone followed by a drainfield or or as a direct discharge to absorption field. Wastewater the soil through trenches. from the treatment unit is Typically, effluent flows into dispersed through a suitable the absorption field from soil layer where it receives a distribution box which additional treatment by the maintains an even flow of soil microorganisms and effluent to the absorption filtering of the field. From there, the soil. If the soil is unsuitable effluent drains through the for the installation of a soil stone and into the soil which absorption field, alternative provides further treatment. methods can be used to

23 Licensed wastewater treatment plant operator

the existing systems do not perform adequately due to a lack of management. Therefore, EPA promotes the sustained management of decentralized wastewater systems to enhance their performance and reliability. EPA strongly encourages communities to establish management programs for the maintenance of onsite systems in addition to where pretreated wastewater improving local requirements evaporates from the soil for onsite system siting and surface or is transpired by system design. Communities plants into the atmosphere. benefit from effective Usually, ET beds are used in onsite system management Sewer line maintenance arid climates and there is no programs by enjoying discharge either to surface pollutants in ways that improved protection of public or ground water. Vegetation may not be provided by health and local surface is planted on the surface of substandard native soils. water and groundwater the sand bed to improve the resources, preserving rural Drip Dispersal System process and areas, protecting Where soils are very thin or enhances the owners’ investments through have reduced permeability, aesthetics of the bed. increased system service drip dispersal systems can life, and avoiding the need be utilized. The typical drip Management of Decen- tralized Systems to finance costly central system operates like drip wastewater collection and irrigation at a moderately Ensuring performance of treatment systems. high pressure. The decentralized wastewater components of a drip system treatment systems is an Asset Management include filters to remove issue of national concern America’s public water- solids, a network of drip because these systems are based – its tubes to disperse liquid into a permanent component , wastewater, soil, tanks to hold liquid, and of our nation’s wastewater and storm water facilities, controllers to regulate the infrastructure. Twenty- and collection/distribution flow to the drip system. five percent of households systems – is integral to our nationwide and one-third economic, environmental Evapotranspiration Beds of the new homes being and cultural vitality. Evapotranspiration (ET) bed constructed are served by Much of this country’s is an onsite dispersal system onsite systems. Many of public wastewater system

24 infrastructure has crossed water quality and human Common Wastewater the quarter-century mark, health. Most systems are in Treatment Terminology dating back to the CWA operation every day of the Activated Sludge is a suspended construction grant funding year, or shine. Licensed growth process for removing organic matter from sewage of the 1970s. Many of our and trained operators are by saturating it with air and collection systems date from responsible for the day- microorganisms that can break down the organic the end of War II and to-day performance of the matter. the population boom of the wastewater system. Their Advanced Treatment involves post war era. The oldest responsibilities include treatment levels beyond secondary treatment. portions of the collection budget and business system pipe network exceed administration, public Aeration Tank is a chamber for injecting air and oxygen into 100 years of service. relations, analytical testing, water. Significant parts of this and mechanical Aerobic refers to a life or a infrastructure are severely as well as overseeing the process that occurs in the stressed from overuse and collection system and presence of oxygen. the persistent under-funding wastewater treatment Aerobic Treatment Units provide wastewater processes. of repair, rehabilitation, treatment by injecting and replacement. In an air into a tank, allowing aerobic bacteria to treat the increasing number of Maintenance wastewater. communities, existing Wastewater collection and Algae are aquatic plants which systems are deteriorating, treatment systems must grow in sunlit waters and yet the demand for provide reliable service release oxygen into the water. Most are a food new infrastructure to and avoid equipment for fish and small aquatic accommodate growth breakdowns. Most animals, but some cause water quality problems. presses unabated. A equipment breakdowns can be avoided if system Alternative System A revitalized approach to wastewater treatment or managing capital wastewater operators inspect the collection system utilized in lieu of a conventional assets for cost effective equipment, including system. performance is emerging sewer lines and , regularly. Preventive Anaerobic refers to a life or a in this country. This asset process that occurs in the management approach maintenance uses data absence of free oxygen. focuses on the cost effective obtained through the Bacteria are small living sustained performance of the inspections in a systematic organisms which help consume the organic way to direct maintenance wastewater collection and constituents of sewage. activities before equipment treatment system assets over Barminutor is a device mounted their useful life. failures occur. A good on bar screens in a program will reduce wastewater treatment plant to shred material, such Operation breakdowns, extend as rags and debris, that Wastewater collection and equipment life, be cost- accumulates on the bars. treatment systems must effective, and help the Bar Screen is composed of parallel bars that remove be operated as designed system operators better larger objects from to adequately protect perform their jobs. wastewater.

25 Black Water is the term given and biological integrity of Digestion of solids takes place in to domestic wastewater that the Nation’s waters.” tanks where volatile organic carries animal, human, or materials are decomposed food wastes. Coagulation is the clumping by bacteria, resulting together of solids to make in partial gasification, Biological Nutrient Removal them settle out of the liquefaction, and (BNR) is the use of bacteria sewage faster. Coagulation mineralization of pollutants. to remove nutrients from of solids is improved by the wastewater. use of chemicals such as Disinfection is the killing of lime, alum, iron salts, or pathogenic microbes Biomass is microbial growth. polymers including , viruses, helminths, Biosolids are treated sewage Combined Sewers carry both and protozoans. sludge solids that have sewage and stormwater been stabilized to destroy runoff. Dispersal/Percolation involves pathogens and meet a volume of wastewater rigorous standards allowing Comminutor is a device to catch applied to the land, for safe reuse of this material and shred heavy solid matter penetrating the surface, as a soil amendment. at the headworks of the and passing through the wastewater treatment plant. Biotower is a unit in which the underlying soil. waste is allowed to fall Composting is the natural Dissolved Oxygen (DO) is through a tower packed with biological decomposition the amount of free oxygen synthetic media on which of organic material in the in solution in water, or there is biological growth presence of air to form wastewater effluent. similar to the trickling filter. a stabilized, -like Adequate concentrations material. BOD (Biochemical Oxygen of dissolved oxygen are necessary for fish and other Demand) is a measure Conventional Systems are aquatic organisms to live of oxygen consumed in wastewater treatment and to prevent offensive biological processes that systems that have been odors. break down organic matter traditionally used to collect in water. municipal wastewater in Eligible Costs are those sewers and convey it to a Carbon Adsorption is a method wastewater reduction central facility for treatment activities that can be funded to treat wastewater in which prior to discharge to surface activated carbon removes with waters. Either primary or (SRF) loans. trace organic matter that secondary treatment may be resists degradation. provided in a conventional Effluent is the treated liquid that Chlorination is the process system. comes out of a treatment of adding chlorine gas or plant after completion of the Denitrification is the reduction treatment process. chlorine compounds to of nitrite to nitrogen gas. wastewater for disinfection. Denitrification is carried Eutrophication is the normally Chlorinator is a device that adds out in wastewater treatment slow aging process by chlorine, in gas or liquid tanks by bacteria under which a lake evolves form, to wastewater to kill anoxic conditions. The into a bog or marsh and infectious bacteria. bacteria use the nitrate for ultimately disappears. energy, and in the process, During eutrophication, the Clarifier also known as a settling release nitrogen gas. The lake becomes enriched tank, removes solids from nitrogen gas, a major with nutrients, especially wastewater by gravity settling constituent of air, is released nitrogen and phosphorus, or by coagulation. to the atmosphere. which support the excess production of algae and Clean Water Act (Federal Diffused Air is a technique by other life. Water Pollution Control Act) which air under pressure Eutrophication may be originally enacted in 1948 is forced into sewage in accelerated by many human and amended in 1972, 1981 an aeration tank. The air activities. and 1987, the Clean Water is pumped into the tank Act has as its objective the through a perforated pipe Evapotranspiration is the restoration and maintenance and moves as bubbles uptake of water from the of the “chemical, physical, through the sewage. soil by evaporation and by

26 transpiration from the plants Inorganic refers to compounds Mound System is an effluent growing thereon. that do not contain carbon. disposal system involving a mound of soil built up on the Floc is a clump of solids formed Interceptors are large sewer original ground surface to in sewage by biological or lines that collect the flows which effluent is distributed. chemical action. from smaller main and trunk sewers and carry them to the National Pollutant Discharge Flocculation is the process treatment plant. Elimination System by which clumps of solids (NPDES) is a program in sewage are made to Intermittent involves established by the Clean increase in size by chemical a bed of sand or other Water Act (CWA) that action. fine-grained material to requires all wastewater which wastewater is applied discharges into “waters of Gray Water refers to domestic intermittently in flooding the United States” to obtain wastewater composed of doses. a permit issued by the US water from sinks, Environmental Protection , Lagoon is a shallow pond in Agency (EPA) or a state (does not include which algae, aerobic and agency authorized by the wastewater). anaerobic bacterial purify EPA. wastewater. is a mechanical Nitrification is the biochemical device which shreds Land Application is the oxidation of ammonium to wastewater solids and raises controlled application of nitrate. the fluid pressure level high wastewater or biosolids onto enough to pass wastewater the ground for treatment Nitrogenous Wastes are wastes through small diameter and/or reuse. that contain a significant pressure sewers. concentration of nitrogen. Lateral Sewers are small pipes Grit Chamber is a small that are placed in the Nutrients are elements or designed to ground to receive sewage compounds essential as permit the settling of coarse, from homes and businesses raw materials for plant heavy inorganic solids, such and convey it to main, trunk and animal growth and as sand, while allowing the and interceptor sewer lines development. lighter organic solids to pass leading to the wastewater through the chamber. Organic Matter is the treatment plant. carbonaceous material Groundwater is the zone Mechanical Aeration uses contained in plants or beneath the ground surface mechanical energy to inject animals and wastes. saturated with water that has air from the atmosphere into seeped down through soil Overland Flow is land treatment water to provide oxygen to and rock. which involves the controlled create aerobic conditions. application of wastewater Impervious means resistant to Media Filters involves a bed of onto grass-covered gentle penetration by fluids or by sand or other fine-grained slopes, with impermeable . surface soils. As water flows material to which wastewater over the grass-covered soil is applied, generally to Incineration involves combustion surface, contaminants are physically remove suspended of the organic matter in removed and the water is solids from sewage. sewage sludge, producing a collected at the bottom of Bacteria on the media residual inert ash. the slope for reuse. decompose additional Infiltration is the penetration of wastes. Treated water drains Oxidation involves aerobic water through the ground from the bed. Solids that bacteria breaking down into sub-surface soil or the accumulate at the surface organic matter and oxygen passing of water from the must be removed from the combining with chemicals in soil into a pipe, such as a bed periodically. sewage. sewer. Microbes is shorthand for Oxidation Pond is an aerated Influent refers to water, microorganisms. man-made pond used for wastewater, or other liquid wastewater treatment. flowing into a , Million Gallons Per Day (MGD) basin or treatment plant, or is a measurement of the Ozonation is a disinfection any unit thereof. volume of water. process where ozone is

27 generated and added to Pump is a mechanical device Septage refers to the residual wastewater effluent to kill for raising or lifting water or solids in septic tanks or pathogenic organisms. other fluid, or for applying other on-site wastewater pressure to fluids in pipes. treatment systems that must Pathogens are disease-causing be removed periodically for microorganisms, including Receiving Waters are disposal. pathogenic bacteria, viruses, waterbodies (i.e. rivers, helminths, and protozoans. lakes, oceans, or other Septic Tanks are a type of onsite water courses) that receive wastewater treatment system Percolation is the movement discharges of treated or in which the organic waste of water through sub- untreated wastewater. is decomposed and solids surface soil layers, usually settle out. The effluent continuing downward to the Rotating Biological Contactor flows out of the tank to a groundwater. (RBC) is a wastewater soil adsorption field or other treatment process involving Permeability is a measure of dispersal system. large, closely-spaced the ease with which water Sequencing Batch Reactors penetrates or passes through plastic discs rotated about a (SBR) are a variation soil. horizontal shaft. The discs alternately move through of the activated sludge Phosphorus is a nutrient that the wastewater and the air, process where all treatment is essential to life, but in developing a biological processes occur in one tank excess, contributes to the growth on the surface of the that is filled with wastewater eutrophication of lakes and discs that removes organic and drawn down to other water bodies. material in the wastewater. discharge after treatment is complete. Pollution results when Sanitary Sewer is the collection contaminants in human, system for transporting Settleable Solids are solids that animal, vegetable, mineral, domestic and industrial are heavier than water and chemical or thermal waste wastewater to municipal settle out of water by gravity. or discharges reach water, wastewater treatment Sewers are a system of pipes making it less desirable facilities. Stormwater is not that collect and deliver for domestic, recreation, directed into this system but wastewater and/or industry, or uses. is handled by a separate stormwater to treatment system. is a long chain organic plants or receiving waters. compound produced by Secondary Treatment is the Soil Absorption Field is a the joining of primary units second stage in most subsurface area containing called monomers. Polymers wastewater treatment are used to improve settling a trench or bed with a systems in which bacteria minimum depth of 12 of suspended solids, remove consume the organic matter solids from wastewater, inches of clean stones and in wastewater. Federal a system of piping through and improve dewatering of regulations define secondary biosolids. which treated wastewater treatment as meeting effluent is distributed into the Pressure Sewers are a system minimum removal standards surrounding soil for further of pipes in which the water, for BOD, TSS, and pH in treatment and disposal. wastewater or other liquid is the discharged effluents transported under pressure from municipal wastewater Slow Rate Land Treatment supplied by pumps. treatment facilities. involves the controlled application of wastewater Pretreatment involves treatment Sedimentation Tanks are to vegetated land at a few of wastes or wastewater by wastewater treatment tanks inches of liquid per week. industries performed prior in which floating wastes are to the discharge to the sewer skimmed off and settled Storm Sewers are a separate system. solids are removed for system of pipes that carry disposal. rain and snow melt from Primary Treatment is the buildings, streets and yards initial stage of wastewater Seepage is the slow movement to surface waters. treatment that removes of water through small floating material and cracks or pores of the soil, Suspended Solids are the small material that easily settles or out of a pond, tank or particles suspended in water out. pipe. or wastewater.

28 Transpiration is the process is the smallest form of by which is a which can released to the atmosphere reproduce within host cells. by living plants. Wastewater Treatment Plant is Trickling Filter is a fixed film a facility involving a series process that involves a tank, of tanks, screens, filters, and usually filled with a bed of other treatment processes rocks, stones or synthetic by which pollutants are media, to support bacterial removed from water. growth used to treat wastewater. Water Table is the elevation of groundwater or saturated Ultraviolet Radiation (UV) is a soil level in the ground. disinfection process where wastewater is exposed to UV light for disinfection.

For more information see: www.epa.gov.owm