ATS Glossary

 

 

activated sludge.  Name of a wastewater treatment process as well as the biologically active sediment produced by it.  The activated sludge process combines alternating aerobic and anaerobic treatments of wastewater, either in a single vessel, called a sequencing batch reactor, or in linked aeration chambers and settling tanks, called clarifiers.  After forced mixing of septic tank effluent with air, solids are allowed to settle during a quiescent period to form the sludge, which provides a suitable environment in which anaerobic bacteria can reduce nitrate to nitrogen.  See also suspended-growth process. 

 

aeration.  Generally, the addition or augmentation of oxygen either in water or soil.  Aeration is a component of secondary treatment of sewage or industrial wastewater.  It enables aerobic bacteria to carry out nitrification.

 

aerobic.  With oxygen in the environment, or occuring only in the presence of oxygen, as in aerobic bacteria.  In a conventional septic system, aerobic bacteria reside primarily in the leaching field.  Most alternative sewage systems compensate for their smaller leaching fields by using forced aeration of some sort to ensure that aerobic bacteria will thrive.  See also nitrification.

 

aerobic treatment unit (ATU).  On-site unit that mixes air with wastewater.  Most ATUs use a suspended-growth process (similar to the extended aeration of activated sludge) or a fixed-film process (similar to a trickling filter).  They usually are marketed, delivered, and installed as self-contained modules or packages. 

 

alternative (on-site sewage) treatment systems (ATS).  Systems intended to provide acceptable treatment and dispersal of wastewater in cases where a conventional on-site wastewater treatment system cannot be installed because of limited space for leaching fields and such environmental constraints as high water tables, shallow soils, and those with slow percolation rates, such as clays and tight silts.  Alternative systems, also referred to as I/A Technology and as nonconventional on-site wastewater treatment systems, come in many forms and include such components as aerobic treatment units, mound systems, peat filters, sand filters, and trickling filters, among others.   

 

American National Standards Institute (ANSI).  Organization founded in 1981 by five engineering societies and three government agencies to promote the voluntary adoption of industrial guidelines and to oversee accreditation programs for products in a great many fields, including wastewater treatment.  ANSI's overarching mission is to enhance both the global competiveness of U.S. business and the quality of U.S. life. See also National Sanitation Foundation.

 

anaerobic.  Without oxygen, or without enough oxygen to sustain aerobic bacteria.  In a conventional sewage system, anaerobic bacteria reside primarily in the septic tank.  Anaerobic bacteria work much less quickly than aerobic bacteria and so treat effluent only partially before it flows into the leaching field.  See also denitrification and primary treatment.

 

anoxia.  Lack of dissolved oxygen.  This condition can occur in fresh water (rivers, lakes, streams, etc.) or salt water, typically in areas that have limited water exchange or high levels of primary productivity (plant growth and decomposition) and bacteria growth within the water column.  Anoxia is a natural phenomenon and may result if the rate of oxidation of organic matter by bacteria is greater than the supply of dissolved oxygen or if eutrophication has rapidly increased.  In extreme circumstances, oxygen-deprived waters formulate what are called dead zones.  The most notable case of a dead zone in Connecticut is western Long Island Sound.

 

ANSI.  See American National Standards Institute.

 

ATS.   See alternative treatment system. 

 

ATU.  See aerobic treatment unit.

 

batch reactor.  Tank in which sewage is treated in batches.  After solids settle out of  the sewage, the batch is aerated (see aeration) and mixed, then allowed to settle again for additional anaerobic treatment.  See also sequencing batch reactor.

 

biochemical oxygen demand (BOD).  A standard measure of the content of sewage.  BOD refers to the amount of oxygen required by aerobic bacteria to decompose carbon-based organic substances, including fecal matter, detergents, fats, and food particles.  Effluent in a septic tank is treated anaerobically (without oxygen) because sewage entering it is so high in BOD that any oxygen is quickly removed.  BOD in the tank is reduced by anaerobic digestion and settling of solids.  The BOD of the sewage that flows from the tank to the leaching field in a conventional septic system also supports the growth of the field’s biomat, where anaerobic microorganisms consume many bacteria and viruses before they can pass into groundwater.  Alternative systems generally include an extra unit between the septic tank and the field, or a separate area within the tank, where oxygen is introduced to increase BOD removal, thus making it possible to dispose of treated effluent in tight soils and reduce the size of leaching fields.  Five-day BOD, or BOD-5, represents the amount of oxygen consumed by bacteria during a five-day period; this is the most common measure of the strength of effluent eventually released from conventional sewage treatment systems to surface waters or streams.  Effluent with a high BOD can deplete oxygen in receiving waters, changing ecosystems and causing fish kills.  See also tertiary treatment and total suspended solids.   

 

biocrust. See biomat.

 

bioformat.  See biomat.

 

biomat.  Short for biological mat: the layer of biological growth and inorganic material that develops at the interface between a leaching field and the soil beneath and around it; also called the clogging mat, clogging zone, biocrust, bioformat, and slime layer.  The biomat typically extends about an inch into the soil.  If excavated, it is easily seen as a gray or blackish, jelly-like layer along the bottom and sides of the leaching field.  The biomat provides an environment in which anaerobic microogranisms attack poisons and viruses (see biochemical oxygen demand).  It also controls the rate at which treated effluent moves from the field into coarse-to-medium-textured soils.  It may not control flows through fine clay soils, which are less permeable than the biomat itself.  

 

blackwater.  Wastewater from toilets and kitchen sinks.  See also RUCK system.

 

BOD.  See biochemical oxygen demand.

 

bottomless ISF.  See intermittent sand filter.

 

BPR.  Biologic Phosphorus Removal.  See enhanced (or biologic) phosphorus removal.

 

cesspool.  Drywell for receiving untreated wastewater, including fecal material, with either an open bottom and/or perforated sides.  Construction of cesspools with a capacity to serve 20 or more persons per day was banned by federal regulations in 1999. Existing cesspools of this size were supposed to be replaced by sewers or alternative treatment systems by 2005.       

 

CF.  See continuous flow system.

 

CFSGAS.  See continuous-flow-suspended-growth aerobic system.

 

clarifier.  Chamber, also called a sedimentation tank or settling tank, in which solids settle out of wastewater, usually by gravity.  

 

clear zone.  Cloudy zone of effluent in a septic tank that is clear in comparison with organic solids that settle to the bottom of the tank and the scum of greases, oil, and other lighter-than-water particulates that rise to the top.  See effluent.     

 

clogging mat or zone.  See biomat.

 

cluster system.  Sewage treatment system under some form of common ownership and management that serves two or more houses or other structures but less than an entire community.  Cluster systems are commonly used to treat wastewater in housing developments.

 

continuous-flow (CF) system.  Method of  treating sewage without interruption of intake, as opposed to an intermittent flow system.  CF systems usually include a chamber that has been partitioned to separate the turbulent aeration area from the quiescent settling zone.  See also continuous-flow-suspended-growth aerobic system.

 

continuous-flow-suspended-growth aerobic system (CFSGAS).   System for treating high-strength wastewaters that operates without interruption of intake in a series that includes both the fixed-film and suspended-growth components, also known as a couple contact aeration, dual process, enhanced, or high-biomass system.  Such combined systems can be loaded at higher rates than can either component by itself, but the U.S. Environmental Protection Agency (EPA) recommends that they be installed only if management service is available on-site.  See also continous-flow system.

 

conventional on-site treatment system.  Traditional system, consisting of a septic tank, pipe, distribution box, and leaching field and relying on gravity to distribute the effluent.  See also on-site wastewater treatment system. 

 

couple contact aeration system.  See continuous-flow-suspended-growth aerobic system.

 

D-box.  See distribution box.

 

DMR.  See Discharge Monitoring Report.

 

decentralized system.  An alternative treatment and/or cluster system for collecting, treating, and dispersing or reclaiming wastewater from a small community or service area.

 

Decentralized Wastewater Management District (DWMD).  A town-based wastewater management program, enabled by Connecticut statute, for which a town replaces the Connecticut Department of Energy and Environmental Protection (DEEP) as the permitting authority for subsurface sewage disposal. 

 

denitrification.  The anaerobic counterpart of nitrification, denitrification is the reduction of oxidized forms of nitrogen, such as nitrite and nitrate, which are common substances in wastewater, to nitrogen gas and water.  Anaerobic bacteria in the biomat mediate the process of detrification by feeding on carbon in organic waste.  Efficient, reliable denitrification is the ultimate goal of sewage treatment.

 

Discharge Monitoring Report (DMR).  A report form provided or approved by the Commissioner of the Connecticut DEEP for use by a permittee to submit discharge monitoring data to the DEEP relating to compliance with limits and conditions established in the individual permit for a facility.

 

dispersal system.  System that receives treated wastewater and distributes it, typically by means of perforated pipes or spray nozzles, onto a fixed-film filter or, at the end of the treatment process, the surface of the land, into the groundwater, or into the air.

 

dissolved oxygen (DO).  Oxygen in water, wastewater, or another liquid.  Dissolved oxygen enters water from photosynthesis and the atmosphere and is used in respiration.  Because adequate dissolved oxygen levels are necessary to maintain healthy aquatic biota, DO is a common indicator of water quality.  Dissolved oxygen is particularly sensitive to water temperature:  the cooler the water, the higher the DO concentration.  DO concentrations may also vary due to turbidity, flow, and respiration.  The amount usually is expressed in milligrams per liter (mg/l), parts per million (ppm), or percent of saturation.  See also biochemical oxygen demand.

 

dissolved solids.  The fraction of solids dissolved in water.  See total suspended solids.

 

distribution box (D-box).  Unit that receives effluent from a septic tank, divides the flow, and channels it in approximately equal amounts into disposal lines in the leaching field.

 

DMR.  See Discharge Monitoring Report.

 

DO.  See dissolved oxygen.

 

dose.  A controlled amount of wastewater, discharged on a regular schedule by a pump in what is often referred to as a dosing tank or pump chamber.  The pump may be set to run for a certain period of time at a certain time for day or for a certain number of minutes every so many hours.  For example, a system may be “on” and process sewage for 3-5 minutes every 25-27 minutes.  Typically, smaller dosing feeds with longer resting periods in between will result in better nitrification than larger doses over shorter periods.  In theory, pumped dosing is better than steady-flow gravity for distributing effluent to leaching fields and other treatment units while giving receiving systems time to rest between applications.  But dosing presents many practical difficulties — e.g., pumps may malfunction, alarms may fail or not be heard, owners may turn off systems, and dosing schedules may not jibe well with changes in patterns of usage.  

 

dosing feed.  The volume of sewage that is processed in a particular amount of time.  See dose.

 

dosing tank.  See dose.

 

drainfield.  See leaching field.

 

drip dispersal.  Method of distributing wastewater evenly for processing.  See trickling filter system.

 

dual process system.  System for treating high-strength wastewaters that combines the fixed-film and suspended-growth processes in a single unit rather than in a series, as in a continuous-flow-suspended-growth aerobic system.

 

DWMD.  See Decentralized Wastewater Management District.

 

effluent.  Sewage, water, or another liquid, whether in its natural state or partially treated.  Sewage commonly is divided into three types:  primary effluent, also called septic tank effluent (STE), meaning the partially treated wastewater in the clear zone of a septic tank; secondary effluent, which has been treated further, typically in a leaching field; and tertiary effluent, which has received additional treatments (see effluent polishing) to reduce  or eliminate potential hazards to people.  See also primary treatment, secondary treatment, and tertiary treatment.

 

effluent filter (or screen).  Removable, cleanable, PVC filter, inserted into the outlet of a septic tank in order to trap solids that might be transported into the leaching field or other components of the sewage treatment system.  Such a filter has slots of different sizes, one inside another, catching fine particles while also preventing floating matter from exiting the tank.  An outlet filter improves the performance of a septic system and extends its life.  Connecticut began requiring installation of outlet filters in 2000.  See also primary treatment and total suspended solids.   

 

effluent polishing.  Disinfection of effluent by chlorination, ozonation, or ultraviolet light; a final stage in wastewater treament, more common in southern states than Connecticut.  Polished effluent is known in large treatment plants as tertiary effluent.  See also septic tank effluent and tertiary treatment.

 

enhanced (or biologic) phosphorus removal (EPR or BPR).  Additional treatments to remove phosphorus from effluent in a leaching field before it is dispersed on the surface of the land or into streams or other flowing waters.  Such treatments include subsurface irrigation and plantings in a shallow layer of soil (six inches in Connecticut) over the leaching field.  Phosphorous that is converted to biomass will be released again when the organizms die, however, resulting in no net loss of this element in the environment.  See also phosphorous.

 

enhanced system.  See continuous-flow-suspended-growth aerobic system.

 

environmental sensitivity.  The relative susceptibility of water or other environments to adverse impacts of wastewater discharges.  Adverse impacts generally are characterized as low, acute (immediately and signficantly disruptive), or chronic (gradual but having serious effects over a long term).

 

EPR.  See enhanced (or biologic) phosphorus removal.

 

eutrophication.  Excessive productivity (plant growth and decomposition) in aquatic systems, leading to algae blooms, fish kills, and anoxia.  Eutrophication is caused by excessive loading in a body of water of organic and mineral nutrients, particularly nitrogen and phosphorus, often as a result of runoff of sewage and agricultural fertilizers.  As plant and algae growth explode, oxygen supply is decreased, causing fish and other aquatic creatures to die of suffication.  Eutrofication can devastate an entire community, decrease biodiversity, increase toxicity concentrations, and foster the growth of exotic and nuisance species.  See also limiting nutrient.

 

FC.  See fecal coliform.

 

fecal coliform (FC).  Fecal coliform bacteria form part of the coliform bacteria group that consists of several genera of bacteria belonging to the family enterobacteriaceae.  Most bacteria from this family are harmless; they live in soil, water, and the digestive systems of animals.  Fecal coliform are present in the intestinal tracts of humans and other warm-blooded animals.  The presence of fecal coliform bacteria in aquatic environments indicates contamination from the fecal material of humans or animals.  Fecal coliform by themselves are typically not pathogenic; they are indicator organisms, showing the presence of other pathogens.  Fecal coliform may be killed either by boiling water or disinfection with chlorine.

 

fixed activated sludge system.

 

fixed-film (or fixed-medium) process.   Treatment of septic tank effluent by filtering it through a permeable medium with large surface areas for supporting aerobic bacteria and other microorganisms that carry out the nitrification (textile, blocks of foam, plastic cylinders).  Air is supplied to the chamber containing the filter by either natural or forced ventilation.  A layer or film of slime grows on the media beds, supporting the aerobic bacteria.  (The layer may become thick enough to support some anaerobic bacteria, in which case denitrification also will take place.)  Natural-media filters generally are constructed on-site, while synthetic ones are produced off-site or assembled on-site from modular components.  Synthetic filters weigh less than natural ones and can be smaller than natural ones with similar capacities.  They are not as dense as natural ones, however, and so are more susceptible to temperature variations.  Also, they are relatively new and less is known about their life spans.  See also rotating biologal contactoror and trickling filter system.  

 

flat-sheet membrane system.  See plate-and-frame membrane system.

 

graywater.  Wastewater from bathroom sinks, bathtubs, showers, dishwashers, clothes washers, and other non-toilet sources.  See also RUCK system.

 

high-biomass system.  See continuous-flow-suspended-growth aerobic system.

 

hydraulic conductivity.  As applied to soils, the ability of the soil to transmit water through its pores.

 

I/A.  Innovative/Alternative Technology.  See alternative treatment system.

 

IF.  See intermittent-flow system.

 

intermittent-flow (IF) system.  Treatment of sewage in two units that operate in parallel, with one open for intake while the other goes through alternating cycles of aeration and settling.  See also continuous-flow system.

 

intermittent sand filter (ISF).  The basic components of an ISF system are a primary treatment unit (a septic tank or other sedimentation system), a pump chamber, and a sand filter.  Effluent is pumped intermittently (that is, in doses) onto the surface of the filter, usually through perforated pipes or spray nozzles that distribute it evenly.  The effluent then percolates in a single pass through the sand to an underdrain, which transports it to a line either for further treatment or disposal.

 

ISF.  See intermittent sand filter.

 

large-capacity septic system.  On-site sewage treatment system that serves 20 or more persons per day.  Such systems are subject to the EPA's Underground Injection Control Regulations. 

 

leaching field.   Underground structure in which septic tank effluent is processed and disposed; also called a drainfield or, more technically, a soil absorption system.  A leaching field typically consists of a series of four-inch diameter perforated PVC pipes, placed in two- to three-foot-wide trenches.  Regulations governing trenches vary from place to place, according to usage and soil characteristics.  In Connecticut, trenches must be at least 12 inches apart and 18 inches above impermeable soil and ground water or 48 inches above bedrock.  The perforated pipes are set on top of gravel, which is also used as backfill around them.  The gravel permits adequate drainage and reduces root growth near the pipes.  Untreated building paper or straw over the gravel prevents fine soil particles from flowing into the gravel.  Finally, a topsoil cover on the leaching field prevents contact with the wastewater and reduces infiltration from rainwater.  Leaching fields may fail for a variety of reasons.  For example, they may become anaerobic if not well aerated, if there is too small a separation between the bottom of the field and groundwater, or if overloaded (by too much rain, say, or even a constantly running toilet) so that the available oxygen, necessary for supporting aerobic  bacteria, is displaced by water.  See also biomat, mound system, secondary treatment, and travel time.

 

limiting nutrient.  A chemical necessary for primary production (plant growth) but available in smaller quantities for algae and other plants to increase their productivity.  A limiting nutrient is consumed or processed before other nutrients, and thus the absence of a limiting nutrient prevents growth.  Phosphorus, a chemical prevalent in fertilizers, is typically the limiting nutrient in aquatic ecosystems.  Reducing the amount of phosphorus loading into surface waters will reduce the risk of eutrophication.  See also phosphorus.

 

MBR.  See membrane bioreactor.

 

membrane bioreactor (MBR).   Extremely fine filter that catches solid particulates and bacteria as effluent is forced through it in an aerated tank or sequencing batch reactor.  Originally employed for cleaning water in chemical and biotechnology processes, membranes have been developed for many other applications, including removal of pollutants from residential and commercial sewage.  Membranes serve the same function as clarifiers, or settling tanks, but have a smaller footprint than other systems because they work faster and so can operate with tanks that are 30-50 percent less in volume.  Membranes are commonly divided into four categories, depending on the size of the material removed.  From smallest to largest, they are Reverse Osmosisis (RO), Nanofiltration (NO), Ultrafiltration (UF), and Microfiltration (MF).  The first two are employed to remove salts from water; they work by osmosis.  The second two are intended to remove larger particles from septic tank effluent; they act as physical barriers, filtering effluent through membranes, typically hollow fibers with microscopic pores that are assembled in compartmentalized cells or modules of different sorts.  The main types of module are the tubular membrane and the plate-and-frame (or flat-sheet) membrane systems.  In both cases fibers are packed densely in order to provide the largest possible surface area within the smallest possible volume.  UF membranes typically filter out particulates ranging from 0.003 to 0.1 micron in diameter; MF membranes filter out particulates of 0.05 to 1 micron, where a micron equals one billionth of a meter (a human hair, by contrast, is about 100 microns in diameter).  Effluent may be pumped through UF and MF membranes at relatively low pressure, compared with the pressure in the RO and NO processes, or pulled through them by vacuum force.  MBR systems offer a number of advantages over other technologies:  They may result in higher water quality and less sludge, thus lowering disposal costs, and they may deal better with low temperatures and uneven wastewater flows (at schools, for instance).  The need for regularly cleaning them may lead to higher maintenance costs, however.

 

MF.   Microfiltration. (MF).  See membrane bioreactor.

 

microbial digestion.  See secondary treatment.

 

microfiltration.  See membrane bioreactor.

 

mound system.  Above-grade leaching field in a mound made of  fill or aggregate.  A mound system may be used when it is impossible to construct a conventional on-site treatment system because of such constraints as steepness of slope, a high water table, soil that is too sandy, or closeness of ledge rock to the surface.  When built on slopes, mounds parallel contours of the land and are much longer than they are wide.  Effluent may be dispersed from the septic tank to the mound by gravity if the slope is steep enough; otherwise a pump must be used.  Compare with raised-bed system.    

 

nanofiltration (NO).  See membrane bioreator.

 

National Pollutant Discharge Elimination System (NPDES).  Permitting program established by the Federal Water Pollution Control Act Amendments of 1972.  Details of the program are covered in Section 402 of the Clean Water Act.  This program strengthened existing policies by incorporating harm-based and technology-based regulations applicable to point source discharges into navigable (or surface) waters.  Discharges are illegal unless authorized by an NPDES permit.

 

National Sanitation Foundation (NSF).  A nonprofit, nongovernmental organization dedicated to developing standards, product certifications, and risk-management practices for public health and safety.  Founded in 1944, the NSF focuses mainly on developing standards for water, food, indoor air quality, and the environment.  Its Water Quality Index (WQI), which includes measures of biochemical oxygen demand, dissolved oxygen, fecal coliform, pH, and other factors, is commonly used to compare the quality of various bodies of water.  The NSF is accredited by the American National Standards Institute. 

 

nitrification.  The transformation by aerobic bacteria of ammonia (NH3) in sewage waste to oxidized forms of nitrogen, in particular nitrite (NO2) and nitrate (NO3).  Nitrites and nitrates are fairly harmless; they are even used as food preservatives.  But they also are plant nutrients and are used in fertilizers to increase crop yields.  Ideally, the sewage treatment process concludes with denitification.  If the entire process is not completed successfully, nitrogen will get into surface waters and groundwaters, leading to algae blooms and dead zones.  Nitrogen-oxygen compounds also cause air pollution and contribute to acid rain.  See denitrification and eutrophication.

 

nitrogen.  Atmospheric gas that does not support life directly but whose compounds, including all proteins, are essential to it.  Nitrogen circulates continually in freshwater ecosystems as well as septic systems in many chemical states.  Most of the nitrogen in a septic system is excreted by humans in the form of organic nitrogen and urea.  Anaerobic bacteria break down the nitrogen in urea and other organic materials fairly quickly into ammonia (NH3) — that is, 1 part nitrogen and 3 parts hydrogen (the hydrogen is present in water).  See also denitrification, nitrification, and phosphorous.

 

NO.  Nanofiltration. See membrane bioreactor.

 

nonpoint source pollution.  Pollution from water runoff as opposed to discharges from a pipe or other single source.

 

NPDES.  See National Pollutant Discharge Elimination System.

 

NSF.  See National Sanitation Foundation.

 

on-site wastewater treatment system.  System that relies on natural processes and/or mechanical components to collect, treat, and disperse or discharge wastewater from a single dwelling or building.  See also alternative treatment system and conventional on-site treatment system.

 

operating permit.   A renewable and revocable permit to operate and maintain an on-site or cluster system for treating wastewater in compliance with specific operational or performance requirements.

 

OWTS.  See on-site wastewater treatment system.

 

peat filter.  System that functions like a sand filter except the wastewater is filtered through two to three feet of compacted peat instead of sand.  Effluent is either pumped or gravity-fed through the layer of peat after passing through the septic tank.  The peat acts like a sponge, absorbing the effluent and dispersing it in all directions as it percolates slowly through the filter.  The effluent then may be recirculated, discharged into another treatment unit, or allowed to drain into the soil or a small leaching field.  Peat systems may be constructed on-site or assembled from preconstructed modules.  Moisture and temperature levels of peat systems are relatively constant, allowing  microbes to survive during periods when the systems are inactive and making these system especially suitable to use in colder climates.  They may have to be replaced anywhere from five to 15 years after installation, however.

 

pH.  Abbreviation for potentia hydrogenii (potential of hydrogen).  The pH scale is used for measuring the relative acidity or alkalinity of a solution.  The scale ranges from near 0 for such strong acids as hydrochoric acid to near 14 for very strong alkaline, or base, solutions such as lye.  A pH of 7 is neutral. Because the scale is logarithmic, a difference of 1 means an increase or decrease in the amount of acidity by a factor of 10.  Most surface water in the United States is slightly acidic because of industrial emissions such as sulfur dioxide.  Most aquatic biota can survive in waters with a pH between 6.5 and 9.0.

 

phosphorus.  Companion nutrient to nitrogen and the primary limiting nutrient in aquatic ecosystems because it is not typically abundant in an accessible form for assimilation.  In general, phosphorus is more important to algae growth in fresh water, causing the green scum seen in many ponds, while nitrogen is more responsible for algae growth in salt water.  Phosphorus also can contaminate drinking water, which is why it has been banned from inclusion in detergents in some jurisdictions.  Both the U.S. Environmental Protection Agency and the Connecticut Departmental of Energy and Environmental Protection have begun giving more attention to phosphorus, but very few alternative treatment systems address its removal.  See also eutrophication.

 

pipe (also called a sewer or soil pipe).  Connector between a building and the septic tank in a conventional on-site treatment system.

 

plate-and-frame (or flat-sheet) membrane system.  One of the two (with the tubular membrane systemem) main types of membrane modules.  As the name implies, membranes in this system are sandwiched between stacked support plates.  Plate-and-frame membranes may be either spiral-wound or pillow-shaped.  Spiral-wound membranes are wrapped, along with support material, in layers around a central drain.  The design permits dense packing, thus maximizing membrane surface area in a minimum amount of space.  Spiral-wound membranes are used only in nanofiltration and reverse osmosis applications, where flows are high and suspended solids are minimal or nonexistent.  Pillow-shaped membranes are so-called because of the shape that two membranes take when packed around a supporting plate.  In this system, effluent flows through the membranes from inside out.  Then it is collected in the space between pillows and carried away by drains.  See membrane bioreactor.

 

primary treatment.  Removal of large particles from raw sewage through gravity separation and/or screening.  On-site systems commonly use a septic tank for this treatment.  The tank may be equipped with an effluent filter to capture particles that are too small or too light to settle.  The partially, nonchemically treated liquid discharged from primary treatment is called primary effluent.  See also effluent, secondary treatment, and tertiary treatment.

 

pump chamber (or tank).  Watertight chamber containing a pump that sends wastewater from the septic tank to another unit, such as a clarifier or sand filter, for secondary treatment.  The chamber usually is underground, with an opening above grade to provide access for maintenance and repairs.  The pump is set to operate on a schedule, discharging effluent in doses.  Storage capacity of the chamber is an important consideration in system design:  The unit must be large enough to allow effluent accumulated during peak periods of usage to be dosed over a period of time.  

 

pumped discharge ISF.  See intermittent sand filter.

 

raised-bed system.  Above-grade mound of fill or aggregate into which septic tank effluent is pumped and partially treated.  Raised-bed systems differ from mound systems in that they are constructed over soil that can accept septic tank effluent, whereas all treatment in a mound system must take place within the mound.

 

RBC.  See rotating biological contactor.

 

recirculating sand filter (RSF).  Initially developed in Massachusetts for the purpose of reducing nitrogen discharge from on-site systems, RSF come in a variety of sizes and configurations.  The four main components of such a system are the septic tank, pump chamber, sand filter, and leaching field.  Septic tank effluent is sent from the pump chamber to the sand filter.  As the effluent percolates through the sand filter, aerobic bacteria process ammonia into nitrate (see nitrification).  A portion of the treated effluent may be returned to the pump chamber or the septic tank for further processing while the rest is piped into the leaching field.  See also intermittent sand filterer.

 

reverse osmosis (RO).  See membrane bioreactor.

 

RO.  Reverse osmosis. See membrane bioreactor.

 

rotating biological contactor (RBC).  One of two principal fixed-film treatment processes; see also trickling filter.  In an RBC system, aerobic bacteria on rotating plastic disks are exposed alternately to wastewater and to air.  The disks, mounted on a horizontal shaft and immersed about halfway in septic tank effluent, revolve slowly (one to two revolutions per minute) in channels.  The effluent is oxygenated to some extent by turbulence at the disk-water interface.  Excess biomass continuously sloughs from the disks, and some suspended biomass develops within the channels, eliminating the need for a clarifierer.  To remove nitrogen, an aerobic RBC may be coupled with an anaerobic unit in which the disks are submerged completely within the effluent.  

 

RSF.  See recirculating sand filter.

 

RUCK system.  Treatment system that works by separating a household’s wastewater into two streams:  blackwater (toilet and kitchen-sink wastes) and graywater (all other flow) for discharge into separate septic tanks.  The system has no mechanical parts, depending only on gravity.  Blackwater flows from its septic tank to the aerobic RUCK filter.  The filter consists of several layers of in-drains that are overlain by layers of sand and filter cloth.  The sand and in-drain media support the growth of aerobic bacteria for the nitrification process.  Once the effluent has percolated through the filter, it is collected by a drain at the bottom and discharged into the graywater septic tank.  Denitrification of the effluent is achieved by passive mixing of the RUCK filter-treated blackwater and the carbon-rich graywater in the separate anaerobic septic tank.  After this third treatment, the effluent flows to the leaching field for final disposal.  An entire RUCK system includes two septic tanks, the RUCK filter, and a conventional leaching facility, all of which operate underground.  The system requires little maintenance aside from periodic pumping of the blackwater septic tank.  Because each component has to be lower in elevation than the previous one, however, the leaching field must be relatively deep.  A minimum of 10 feet from the land surface to groundwater is needed in order for the leaching facility to be located deep enough to accommodate gravity flow.

 

sand filter.   Packed bed of sand for straining septic tank effluent or settled wastewater.  Sand filters are produced in many sizes and configurations and have been used in many applications, ranging from single-family homes to large commercial establishments and small communities.  Sand provides a better environment for aerobic bacteria to accomplish nitrification than plastic or synthetic filters.  Sand never freezes if buried more than four feet and will remove most pathogens and deactivate viruses if a few feet in thickness.

            The typical filter consists of a box, often of concrete or wood, with an impermeable PVC lining, containing washed sand, typically 24-36 inches deep, over a gravel underdrain.  (Bottomless sand filters, without an impermeable liner, are, in effect, leaching fields.)  The sand must meet certain specifications, which vary from locality to locality, of size, uniformity, and fineness; anthracite and mineral tailings may be used in place of sand.  The filter may be buried, usually with a layer of pea gravel on top, or open to the atmosphere.  When buried, a lightweight filter fabric is placed over the gravel to prevent silt from flowing into the sand while permitting air and water to pass through.  Open-air sand filters commonly have wooden tops for protective and aesthetic purposes.  Effluent may be distributed over the filter by gravity or pumping.  Whichever, it must be evenly dispersed over the sand surface.  Contained filters come in two forms:  single-pass, or intermittent sand filters, and recirculating sand filters.    

 

SAS.  Soil Absorption System. See leaching field.

 

SBR.  See sequencing batch reactor.

 

secondary effluent.  See effluent.

 

secondary treatment.  Also called microbial digestion, most secondary treatment processes move primary effluent (see effluent) through an aerated environment (e.g., in tanks or the soil) that contains aerobic bacteria.  Secondary treatment includes three main wastewater treatment processes: (1) Reduction of pathogenic populations.  Most of the microorganisms in sewage that cause diseases also reside within the human digestive system, which is an anaerobic environment.  Not being well adapted to aerated environments, these bacteria eventually perish due to exposure to oxygen.  Other organisms, such as predators of pathogens, typically survive in an aerobic environment, but will be removed by physical filtration as the effluent passes through sand, peat, or other media with small pores. (2) Removal of dissolved organic substances and organic particles.  The aerobic bacteria in the aerated secondary-treatment medium consume and metabolize these organic compounds.  (3) Removal of biodegradable components and small particulate contaminants, which are captured in the fine pores of the various filtering media and processed by aerobic bacteria. 

            The discharge from a secondary-treatment unit is called secondary effluent.  In a once-through treatment system, the secondary effluent drained from the bottom of the filter may be either dispersed to a leaching field or move on to tertiary treatment for further processing.  In comparison, a recirculating system draws effluent from the bottom of the treatment tank and directs a portion of it back to a dosing or recirculation tank.  See also dose, primary treatment, and tertiary treatment.

 

sedimentation tank.  See clarifier.

 

septic tank.  Buried, watertight tank for receiving and partially treating raw wastewater.  Modern tanks usually are rectangular boxes made of concrete, fiberglass, or high-density polyethylene.  Tanks for residences generally hold 1,000 to 1,500 gallons, depending on the number of bedrooms in the house.  Tanks for commercial systems vary in size according to flow.  Solids and floatables separate in the tank, heavier particulates forming a sludge layer at the bottom while grease and other lighter materials float to the top, creating a layer of scum.  The cloudy effluent in the middle is called the clear zone. Anaerobic bacteria flourish in the septic tank, where there is little oxygen.  These bacteria begin to decompose organic contaminants, breaking them down into liquids and gases.  The gases, mainly methane and hydrogen sulfide, normally are vented through the building's rooftop plumbing stack.  This initial stage of the sewage treatment process is called primary treatment.  Because solids and scum tend to accumulate faster than they decompose, the clear zone is gradually compressed and the system can become clogged if incoming wastewater forces effluent out of the tank before the solids have been able to settle sufficiently.  Performance of the system can be improved by installation of an effluent filter on the tank outlet.  Septic tanks should function almost indefinitely, however, if pumped out every three to five years.

  

septic tank effluent (STE).   See effluent.

 

sequencing batch reactor (SBR).  Unit used in the activated sludge process that provides alternating aerobic and anaerobic treatments in a single vessel.  SBRs include intermittent-flow and continuous-flow systems.  See also batch reactor and membrane bioreactor.

 

sewer pipe.  See pipe.

 

slime layer.  See biomat.

 

soil absorption system.  See leaching field.

 

soil pipe.  See pipe.

 

STE.  Septic tank effluent; see effluent.

 

suspended-growth (or culture) process.  Suspended-growth systems encourage growth of aerobic bacteria by rapidly circulating septic tank effluent in an air-filled chamber.  Vigorous mixing causes the bacteria to remain in suspension while they digest biodegradable compounds.  Suspended-growth systems usually are produced in self-contained modules or packages, commonly called aerobic treatment units.  These systems generally can be designed to fit in smaller spaces than fixed-film systems treating an equal volume of wastewater, but they do not handle drastic changes in flow or remove organic material and suspended solids as well as fixed-film systems do.  See also activated sludge and continuous-flow-suspended-growth-aerobic system.

 

tertiary effluent.  See tertiary treatment.

 

tertiary treatment.  Third step in treating wastewater, which may be required to remove contaminants.  Tertiary treatment may also include disinfection (or effluent polishing) with chlorine, ozone, or ultraviolet light to remove disease-causing viruses, bacteria, and other microbes.  Effluent that has received advanced treatment and has been disinfected is called tertiary effluent.

 

total suspended solids (TSS).  Standard measure of the effectiveness of treating domestic sewage.  The suspended solids are small organic and inorganic particles in wastewater, usually measured as mg TSS/liter of water.  If carried to the leaching field, the particles may clog the small spaces between the grains of soil in the field.  TSS can be reduced in several ways.  Simplest is to place an effluent filter on the outlet of the septic tank.  Alternative treatment systems can also reduce TSS, typically by means of settling tanks, or clarifiers, and/or filters of sand or other media.  See also biochemical oxygen demand.

 

travel time.  Number of days required for effluent from a leaching field to reach surface water or a well that supplies drinking water.  Distance will vary from site to site, depending on soil types and groundwater flows.  A few feet of unsaturated soil usually provide sufficient protection.  The standard rule of the Connecticut DEEP is that travel time must be at least 21 days.

 

trickling filter system.  Treatment method in which septic tank effluent is distributed evenly over the surface of well-ventilated, fixed-film media, such as beds of rock, gravel, polyurethane foam, peat, or plastic.  The effluent usually is distributed in timed doses by drip dispersal, typically by spraying from one or more nozzles or by means of perforated pipes.  After passing downward through the filtering media, the effluent may be discharged into a leaching field or, if additional denitrification is desired, a portion of it may be sent back to the septic tank or to a clarifier, where the remaining solids and biomass are allowed to settle out before the effluent is cycled for a second time through the filter.

 

TSS.  See total suspended solids.

 

tubular membrane system.  One of the two (with plate-and-frame membrane systems) main types of membrane modules.  Tubular systems come in different grades of fineness.  They include tubular membranes, with diameters of about 5 to 15 mm; capillary membranes, with diameters of about 0.5 to 5 mm, and hollow-fiber membranes, with diameters of less than 1 micron (a billionth of a meter).  The larger the membrane, the lower the packing density.  Tubular membranes are most suitable where levels of solids are high, liquids are viscous, and cleaning and maintenance are important issues.  Capillary membranes can be packed much more closely than tubular membranes but are more susceptible to clogging.  Hollow-fiber membranes can be packed still more tightly, but they are so small that their use is limited almost entirely to nanofiltration and reverse osmosis applications, where levels of suspended solids are extremely low.  See membrane bioreactor.  

 

UF.  Ultrafiltration.  See membrane bioreactor.

 

ultrafiltration (UF).  See membrane bioreactor.

Water Pollution Control Authority (WPCA).  A quasi-municipal corporation that, under Connecticut law, may exercise “the power to acquire, construct, maintain, supervise, manage, [and] operate a sewer system and perform any act pertinent to the collection, transportation, and disposal of sewage.”  Any municipality in the state may by ordinance establish a WPCA.  The WPCA is also authorized to prepare a municipal water pollution control plan.

 

water pollution control plan.  A strategic plan that summarizes wastewater management issues in a municipality, and sets forth general goals and objectives and specific implementation measures.  For non-sewered areas, the plan should describs the means by which municipal programs are carried out to avoid community wastewater pollution problems.  A water pollution control plan must identify areas with existing or planned sewer service, as well as areas where the municipality wants to avoid the installation of municipal sewers.  The plan must also identify where “community sewerage systems” and Decentralized Wastewater Management Districts are allowed, and conversely, disallowed.

 

WPCA.  See Water Pollution Control Authority.