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Glossary of Environment and Microbiology Terms

Are you experiencing difficulty understanding the terms in various articles involving cleanup of our environment? When someone starts discussing F/M ratios and MCRTs, are you too embarrassed to ask what they are talking about? Well this glossary was designed for you.


A (Back to Top of Page)
 Abiotic factors:  Non living; moisture, soil, nutrients, fire, wind, temperature, climate
 Absorption:  The taking in or soaking up of one substance into the body of another by molecular or chemical action (as tree roots absorb dissolved nutrients in the soil).
 Absorption Field: A system of properly sized and constructed narrow trenches partially filled with a bed of washed gravel or crushed stone into which perforated or open joint pipe is placed. The discharge from the septic tank is distributed through these pipes into trenches and surrounding soil.While seepage pits normally require less land area to install, they should be used only where absorption fields are not suitable and well-water supplies are not endangered.
 Acid:  A substance that dissolves in water with the formation of hydrogen ions, contains hydrogen which may be replaced by metals to form salt, and/or is corrosive.
 Acidity:  The capacity of water or wastewater to neutralize bases. Acidity is expressed in milligrams per liter of equivalent calcium carbonate. Acidity is not the same as pH.
 Activated sludge:  Sludge particles produced in raw or settled wastewater (primary effluent) by the growth of organisms (including zoogleal bacteria) in aeration tanks in the presence of dissolved oxygen. The term "activated" comes from the fact that the particles are teeming with fungi, bacteria, and protozoa. Activated sludge is different from primary sludge in that the sludge particles contain many living organisms which can feed on the incoming wastewater.
 Adsorption:  The gathering of a gas, liquid, or dissolved substance on the surface or interface zone of another substance.
 ADP:  Adenosine diphosphate. See ATP.
 Aeration:  The process of adding air to water. In wastewater treatment, air is added to freshen wastewater and to keep solids in suspension.
 Aeration tank:  The tank where raw or settled wastewater is mixed with return sludge and aerated. This is the same as an aeration bay, aerator, or reactor.
 Aerobe:  An organism that requires free oxygen for growth.
 Alkaline substance:  Chemical compounds in which the basic hydroxide (OH-) ion is united with a metallic ion, such as sodium hydroxide (NaOH) or potassium hydroxide (KOH). These substances impart alkalinity to water and are employed for neutralization of acids. Lime is the most commonly used alkaline material in wastewater treatment.
 Alum: Astringent crystalline double sulfate of an alkali. K2SO4AL2 (SO4)3 24H2O. Used in the processing of pickles and as a flocking agent. Excess aluminum in the environment can be hazardous.
 Ammonia oxidation:  Test drawn during manufacturing process to evaluate the ammonia oxidation rate for the nitrifiers.
 Ambient temperature:  Temperature of the surroundings.
 Anaerobe:  An organism that lives and reproduces in the absence of dissolved oxygen, instead deriving oxygen from the breakdown of complex substances.
 Anhydrous:  Very dry. No water or dampness is present.
 Antibiotic resistance When antibiotics are incorrectly used (to treat bacteria that are not sensitive to the specific antibiotic or to treat viruses, which NEVER respond to antibiotics) and are not taken for the full term prescribed (usually from 5 to 21 days, depending on the specific antibiotic and disease being treated), surviving pathogenic organisms develop immunity to the antibiotic and pass it along to descendants and might choose to pass the trait along to unrelated bacteria via a process known as horizontal gene transfer.
 Anion:  A negatively charged ion in an electrolyte solution, attracted to the anode under the influence of a difference in electrical potential. Chloride is an anion.
 API separator:  A facility developed by the Committee on Disposal or Refinery Wastes of the American Petroleum Institute for separation of oil from wastewater in a gravity differential and equipped with means for recovering the separated oil and removing sludge
 Aseptic:  Free from living germs of disease, fermentation or putrefaction.
 Assimilate:  To take in, similar to eating food.
 Attached growth
 Wastewater treatment processes in which the microorganisms and bacteria treating the wastes are attached to the media in the reactor. The wastes being treated flow over the media. Trickling filters, bio-towers, and RBCs are attached growth reactors. These reactors can be used for removal of BOD, nitrification, and denitrification.
 ATP:  Adenosine triphosphate. Chemical energy generated by substrate oxidations is conserved by formation of high-energy compounds such as adenosine diphosphate (ADP) and adenosine triphosphate (ATP) or compounds containing the thioester bond
 Autotrophy:  A unique form of metabolism found only in bacteria. Inorganic compounds (e.g., NH3, NO2-, S2, and Fe2+) are oxidized directly (without using sunlight) to yield energy. This metabolic mode also requires energy for CO2 reduction, like photosynthesis, but no lipid-mediated processes are involved. This metabolic mode has also been called chemotrophy, chemoautotrophy, or chemolithotrophy.
 AWT:  Advanced Waste Treatment - any process of water renovation that upgrades treated wastewater to meet reuse requirements.

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 Bacteria:  Living organisms, microscopic in size, which usually consist of a single cell. Most bacteria use organic matter for their food and produce waste products as a result of their life processes.
A light-dependent, anaerobic mode of metabolism. Carbon dioxide is reduced to glucose, which is used for both biosynthesis and energy production. Depending on the hydrogen source used to reduce CO2, both photolithotrophic and photoorganotrophic reactions exist in bacteria.
 Batch process:  A treatment process in which a tank or reactor is filled, the wastewater (or solution) is treated or a chemical solution is prepared and the tank is emptied. The tank may then be filled and the process repeated. Batch processes are also used to cleanse, stabilize or condition chemical solutions for use in industrial manufacturing and treatment processes.
 Bench scale analysis:  Also known as: "bench test". A method of studying different ways of treating wastewater and solids on a small scale in a laboratory. While some competitors of Alken-Murray Corporation will experiment with treatments by selling a product that they "hope" will work and then advising the client to change products every month as one treatment after another fails to deliver the desired results, Alken-Murray will examine information provided on the appropriate diagnostic survey form, by either the client or authorized distributor, to select standard products, blends of standard products or totally customized blends for the authorized distributor to test against freshly collected samples of pollution from the client's project, with tests performed locally in the distributor's laboratory. Sometimes a distributor will test up to 25 different treatment options to finally achieve a sufficiently high quality result to deliver a confidence level sufficient to ensure that the positive bench test results will scale up to deliver similar results when scaled up to pilot or full-scale application. If Alken-Murray and its authorized distributor cannot achieve this result from bench scale testing as many potential treatments as Valerie could devise from initially submitted information, the distributor will usually enlist the aid of an accredited, independent drinking water or environment pollution testing laboratory, paid for by the client, to see if some undisclosed or previously unencountered compounds are inhibiting bacterial performance. If nothing new is disclosed from these new chemical analysis, the client is advised to consider alternative treatments (incineration, chemical reaction, filtering, etc.) from other vendors, but if one or more new pollutants ARE discovered, Alken-Murray research staff examine the chemistry of the new pollutants to study its shape for possible attach by enzymes that have been discovered in previous screenings. If Sigma-Aldrich or another laboratory chemical supply company carries the chemical(s) in pure form, Alken-Murray will purchase enough to prepare a broth media, featuring the new pollutant(s) as sole source of organic carbon, so that any growth or reproduction will indicate potential talent for digesting the new pollutant(s). Following filter-sterilizing or autoclaving, ten mL of the broth is dispensed into sterile, fifteen mL, screw-cap test tubes. Each tube is then inoculated with a single colony picked from a 24-hour-old TSA plate growth of a stock Alken-Murray collection strain, selected for demonstrating the ability to digest related or similarly shaped chemical compounds, in the past. Inoculated test tubes are incubated at their optimal temperature for up to 7 days, with a well-mixed sample tested spectrophotometrically for signs of growth and reproduction daily. Five mL from the original 10 mL broth media in a test tube showing strong growth is inoculated into 100 ml of fresh broth media, using the same recipe with the pollutant(s) as sole organic carbon source, contained in a 250 mL Erlenmeyer flask, incubated at the selected strain's optimum temperature, with shaking at 200 rpm. A chemical analysis protocol is selected to enable measurement of the pollutant(s) in the broth media. Appropriate samples are withdrawn to perform chemical analyses on the pollutant(s) in the media and the growth rate of the inoculated strain in each flask. If pollutant(s) disappear at a similar rate as the growth rate of the culture, the strain is then tested for synergy with other strains known to be required to digest known pollutants in client's polluted site, with these results guiding actual new custom formulas sent to distributor to test with fresh samples of client's pollution project. If final results of one of the new formulas delivers a confidence level sufficient to ensure that positive bench test results will scale up properly to a full-scale application, a new Alken-Murray product is officially named and the sale is made. This close cooperation between Alken-Murray Corporation and its authorized disttibutors is responsible for our strong reputation for a high success rate worldwide.
 Benzene:  An aromatic hydrocarbon which is a colorless, volatile, flammable liquid. Benzene is obtained chiefly from coal tar and is used as a solvent for resins and fats in dye manufacture.
 Binary fission:  During binary fission, a single cell divides transversely to form two new cells called daughter cells. Both daughter cells contain an exact copy of th geneticinformation contained in the parent cell.
Biocatalysis: Chemical reactions mediated by biological systems (microbial communities, whole organisms or cells, cell-free extracts, or purified enzymes aka catalytic proteins).
 Biotic potential:  All the factors that contribute to a species
increasing its number. Reproduction, migration, adaptation etc.
 BOD:  Biochemical Oxygen Demand - the rate at which microorganisms use the oxygen in water or wastewater while stabilizing decomposable organic matter under aerobic conditions. In decomposition, organic matter serves as food for the bacteria and energy results from this oxidation.
 BOD test:  A procedure that measures the rate of oxygen use under controlled conditions of time and temperature. Standard test conditions include dark incubation at 20 C for a specified time (usually 5 days).
 Biofilm:  A slime layer which naturally develops when bacteria attach to an inert support that is made of a material such as stone, metal, or wood. There are also non-filamentous bacteria that will produce an extracellular polysaccharide that acts as a natural glue to immobilize the cells. In nature, nonfilament-forming microorganisms will stick to the biofilm surface, locating within an area of the biofilm that provides an optimal growth environment (i.e., pH, dissolved oxygen, nutrients). Since nutrients tend to concentrate on solid surfaces, a microorganism saves energy through cell adhesion to a solid surface rather than by growing unattached and obtaining nutrients randomly from the medium. Pseudomonas and Nitrosomonas strains are especially well known for their ability to form a strong biofilm.
 Bioflocculation:  The clumping together of fine, dispersed organic particles by the action of certain bacteria and algae.
 Biomass:  A mass or clump of living organisms feeding on the wastes in wastewater, dead organisms and other debris.
 Biostimulation: Any process that increases the rates of biological degradation, usually by the addition of nutrients,oxygen, or other electron donors and acceptors so as to increase the number of indigenous microorganisms available for degradation of contaminants.
 Bio-Tower:  An attached culture system. A tower filled with a media similar to rachet or plastic rings in which air and water are forced up a counterflow movement in the tower.
 Blinding:  The clogging of the filtering medium of a microscreen or a vacuum filter when the holes or spaces in the media become sealed off due to a buildup of grease or the material being filtered.
 Buffer:  A solution or liquid whose chemical makeup neutralizes acids or bases without a great change in pH.
 Bulking sludge:  Clouds of billowing sludge that occur throughout secondary clarifiers and sludge thickeners when sludge becomes too light and will not settle properly. In the activated sludge process, bulking is usually caused by filamentous bacteria. Alken-Murray can cure this condition by applying Alken Nu-Bind and Clear-Flo 7015 to the system.

C (Back to Top of Page)

 Cation exchange
 The ability of a soil or other solid to exchange cations (positive ions such as calcium) with a liquid.
 Cess Pools: This system is similar to a septic tank. in performance. Sewage water usually seeps through the open bottom and portholes in the sides of the walls. These can also clog up with overuse and the introduction of detergents and other material which slow up the bacterial action.
 CFU: Viable micro-organisms (bacteria, yeasts & mould) capable of growth under the prescribed conditions (medium, atmosphere, time and temperature) develop into visible colonies (colony forming units) which are counted. The term colony forming unit (CFU) is used because a colony may result from a single micro-organism or from a clump / cluster of micro-organisms.
 Chemoautotroph: An organism that obtains its energy from the oxidation of chemical compounds and uses only organic compounds as a source of carbon. Example: nitrifiers.
 Chemotroph:  An organism that obtains its energy from the oxidation of chemical compounds.
 Chemical precipitation:  Precipitation induced by addition of chemicals; the process of softening water by the addition of lime and soda ash as the precipitants.
 Chloramines:  Compounds formed by the reaction of hypochlorous acid (or aqueous chlorine) with ammonia.
 Chlorination:  The application of chlorine to water or wastewater, generally for the purpose of disinfection, but frequently for accomplishing other biological or chemical results.
 Ciliates:  A class of protozoans distinguished by short hairs on all or part of their bodies.
 Citric Acid  Derived from citrus fruit or by fermentation of crude sugar, also used as antioxidant, sequestrant, dispersing agent. Helps adjust pH. No toxicity in diluted amounts.
COD:  Chemical oxygen demand - the amount of oxygen in mg/l required to oxidize both organic and oxidizable inorganic compounds.
 Clarification:  A process in which suspended material is removed from a wastewater. This may be accomplished by sedimentation, with or without chemicals, or filtration.
 Clarifier:  Settling tank, sedimentation basin. A tank or basin in which wastewater is held for a period of time, during which the heavier solids settle to the bottom and the lighter material will float to the water surface.
 Coagulants:  Chemicals which cause very fine particles to clump (floc) together into larger particles. This makes it easier to separate the solids from the water by settling, skimming, draining, or filtering.
 Coliform bacteria:  Non-pathogenic microbes found in fecal matter that indicate the presence of water pollution; are thereby a guide to the suitability for potable use.
 Colloids:  Very small, finely divided solids (particles that do not dissolve) that remain dispersed in a liquid for a long time due to their small size and electrical charge.
 Combined available
 The concentration of chlorine which is combined with ammonia (NH3) as chloramine or as other chloro derivatives, yet is still available to oxidize organic matter.
 Combined sewer:  A sewer designed to carry both sanitary wastewaters and storm or surface-water runoff.

 When two organisms coexist, with one organism deriving food or other benefits from another, without causing harm to the other organism. Often this relationship offers two-way benefits. For a more powerful version of this co-operation see synergism.

A natural consortium of commensal bacteria residing in saliva and the digestive system of fish, crustaceans and mammals, including humans, are necessary for proper digestion of foods into simple water-soluble compounds that can easily pass through intestinal walls to feed the host's body.

A natural consortium of commensal bacteria will take up residence in the skin and coat of mammals, reducing objectionable odors from sweat and excess production of natural oils, meant to lubricate and protect the skin from the environment, when disinfectants are avoided in soaps, shampoos and skin care products. These commensal bacteria will try to protect their natural home by mechanically preventing invasion by pathogenic (disease-causing fungi and bacteria). Many natural commensal bacteria are exploited by pharmaceutical companies to produce antibiotics, used to cure some of the worst pathogenic organisms, but incorrect use and overuse of antibiotics is leading some pathogenic organisms to develop resistance to the most commonly used antibiotics. Natural commensal bacteria will produce a coctail of antibiotics or will vary the antibiotics they produce to discourage pathogens they encounter from developing resistance.

 Comminution:  Shredding. A mechanical treatment process which cuts large pieces of waste into smaller pieces so that they won't plug pipes or damage equipment.
 Contact stabilization:  Contact stabilization is a modification of the conventional activated sludge process. In contact stabilization, two aeration tanks are used. One tank is for separate reaeration of the return sludge for at least four hours before it is permitted to flow into the other aeration tank to be mixed with the primary effluent requiring treatment.
 Conventional treatment:  The preliminary treatment, sedimentation, flotation, trickling filter, rotating biological contactor, activated sludge and chlorination of wastewater.
 Conversion:  Changing from one substance to another. As food matter is changed to cell growth or to carbon dioxide.
 CRT:  Cell residence time - the amount of time in days that an average "bug" remains in the process. Also termed "sludge age".

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 DAF:  Dissolved air flotation - one of many designs for waste treatment
 Declining growth:  A growth phase in which the availability of food begins to limit cell growth.
 Degradation:  A growth phase in which the availability of food begins to limit cell growth.
 Denitrification:  An anaerobic biological reduction of nitrate nitrogen to nitrogen gas, the removal of total nitrogen from a system, and/or an anaerobic process that occurs when nitrite ions are reduced to nitrogen gas and bubbles are formed as a result of this process. The bubbles attach to the biological floc in the activated sludge process and float the floc to the surface of the secondary clarifiers. This condition is often the cause of rising sludge observed in secondary clarifiers or gravity thickeners. (See Nitrification)
 Detritus: Dead plant and animal matter, usually consumed by bacteria, but some remains.
 D/I unit:  Deionizing unit, frequntly used to maintain water quality in aquariums. Advantages: does not waste water like the R/O unit, is designed to be hooked up to either a faucet or household piping system, the anion & cation resins can be regenerated (with another expensive unit) indefinitely, and these systems allow a larger water flow (up to 2,000 gallons a day), than an R/O system, but cost dramatically more too.
 Diatomaceous earth:  A fine, siliceous (made of silica) "earth" composed mainly of the skeletal remains of diatoms (single cell microscopic algae with rigid internal structure consisting mainly of silica). Tests prove that DE leaches unacceptable amounts of silicate into the water for fish health. If used as a filter substance, a silicone removing resin should be employed afterwards.
 Diffused Air Aeration:  A diffused air activated sludge plant takes air, compresses it, and then discharges the air below the water surface of the aerator through some type of air diffusion device.
 Digester:  A tank in which sludge is placed to allow decomposition by microorganisms. Digestion may occur under anaerobic (most common) or aerobic conditions.
 Disinfection:  The process designed to kill most microorganisms in wastewater, including essentially all pathogenic (disease-causing) bacteria. There are several ways to disinfect, with chlorine being the most frequently used in water and wastewater treatment plants.
 Dissolved solids:  Chemical substances either organic or inorganic that are dissolved in a waste stream and constitute the residue when a sample is evaporated to dryness.
 Distributor:  The rotating mechanism that distributes the wastewater evenly over the surface of a trickling filter or other process unit.
 DO: Dissolved Oxygen - a measure of the oxygen dissolved in water expressed in milligrams per liter.
 DOUR: Dissolved Oxygen Uptake Ratio, reported as mg DO/L/hour, a test that is used to measure how much oxygen is being consumed by the microbes in a wastewater treatment plant, to assure that the biomass is receiving sufficient dissolved oxygen.

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 Ecology:  The study of all aspects of how organisms interact with each other and/or their environment
 Ecosystem:  Groupings of various organisms interacting with each other and their environment.
 E-coli:  Escherichia coli - one of the non-pathogenic coliform organisms used to indicate the presence of pathogenic bacteria in water.
 Effluent:  Wastewater or other liquid - raw (untreated), partially or completely treated - flowing from a reservoir, basin, treatment process, or treatment plant.
 EGL:  Energy grade line - a line that represents the elevation of energy head in feet of water flowing in a pipe, conduit, or channel.
 Electrolytic process: A process that causes the decomposition of a chemical compound by the use of electricity.
 Endogenous respiration: A reduced level of respiration (breathing) in which organisms break down compounds within their own cells to produce the oxygen they need.
 Enteric: Of intestinal origin, especially applied to wastes or bacteria. 
 Enzyme: Organic substances (proteins) produced by living organisms and act as catalysts to speed up chemical changes.
 Environmental resistance: All biotic and abiotic factors combining to limit explosion.
 Equalizing basin: A holding basin in which variations in flow and composition of liquid are averaged. Such basins are used to provide a flow of reasonably uniform volume and composition to a treatment unit. Also called a balancing reservoir.
 Estuaries: Bodies of water which are located at the lower end of a river and are subject to tidal fluctuations. 
 Eucaryotes:  The kingdom that describes ALLorganisms (plants, fungi, animals, fish, birds, etc.) that have an organized nucleus surrounded by a nuclear membrane. The other major kingdom is the Procaryotes (containing only the primitive bacteria and Archae)

F (Back to Top of Page)

 Facultative anaerobe: A bacterium capable of growing under aerobic conditions or anaerobic conditions in the presence of an inorganic ion ie. SO4, NO3. 
 Facultative pond: The most common type of pond in current use. The upper portion (supernatant) is aerobic, while the bottom layer is anaerobic. Algae supply most of the oxygen to the supernatant. 
 FAME: Fatty Acid Methyl Ester, a means of identifying bacteria by analysis of the fatty acids in their cells. This is often done as an initial screening until a company, such as Alken-Murray Corporation, is sure that a bacterial strain is one they wish to use commercially, and then 16S rRNA identification may be completed for a more definite identification and fingerprint of the strain, to keep competitors from copying that strain.
 Fermentation: A type of heterotrophic metabolism in which an organic compound rather than oxygen is the terminal electron (or hydrogen) acceptor. Less energy is generated from this incomplete form of glucose oxidation than is generated by respiration, but the process supports anaerobic growth.  
 Filamentous organisms: Organisms that grow in a thread or filamentous form. Common types are Thiothrix, Actinomycetes, and Cyanobacteria (aka blue-green algae). This is a common cause of sludge bulking in the activated sludge process. Variously known as "pond scum", "blue-green algae", or "moss", when it appears in a pond/lake, and confused with algae because it looks a lot like algae. Cyanobacteria forms a symbiotic relationship with some varieties of algae, making the combination very difficult to combat in lakes and ponds. Filamentous organisms and Actinomycetes will naturally stick to solid surfaces. Common types of Cyanobacteria are: Oscillatoria, Anabaena, and Synechococcus. Other filament formers include: Spirogyra, Cladophora, Rhizoclonium, Mougeotia, Zygnema and Hydrodictyon. Nocardia is another filament former, which causes foaming and interferes with flocculation in a waste treatment plant.
 Filter aid: A chemical (usually a polymer) added to water to help remove fine colloidal suspended solids. 
 Floating matter: Matter which passes through a 2000 micron sieve and separates by flotation for an hour. 
 Floc: Clumps of bacteria and particulate impurities or coagulants that have come together and formed a cluster. Found in aeration tanks and secondary clarifiers. 
 Flocculation: The process of forming floc particles when a chemical coagulant or flocculent such as alum or ferric chloride is added to the wastewater.
 F: Food - represents BOD in the F/M ratio. Expressed in pounds. 
 FOG:  Fats, Oils and Greases. A measure of the non-petroleum based fats in waste treatment.
 F/M: A ratio of the amount of food to the amount of organisms. Used to control an activated sludge process.
 Flow equalization system: A device or tank designed to hold back or store a portion of peak flows for release during low-flow periods.  
 Food chain: Very simple pathway of nutrient flow. Ex. Carnivore > herbivore > plant .

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 Gasification: The conversion of soluble and suspended materials into gas during anaerobic decomposition. In clarifiers the resulting gas bubbles can become attached to the settled sludge and cause large clumps of sludge to rise and float on the water surface. In anaerobic sludge digesters, this gas is collected for fuel or disposed of using a waste gas burner. 
Generation time:  The time required for a given population to double in size. This time can be as short as 20 minutes or as long as a week. 
 Genetic engineering;

 Scientists isolate a strand of DNA responsible for specific desired talents, but other undesirable traits, such as being slow-growing, finicky, delicate or belonging to a pathogenic organism, make the source strain unsuitable for large-scale commercial growth to produce desired raw enzymes or end product. This isolated strand of desired DNA is often coupled with a gene for resistance to a specific antibiotic that is not native to a selected, safe, fast-growing, robust production strain so that exposing the genetically engineered cell to high levels of the antibiotic will kill off ALL clone offspring cells that did not incorporate the desired plasmid.

The USEPA FIFRA regulations PROHIBIT the uncontrolled release of genetically engineered organisms into the environment, to reduce the risk of unstable, engineered strains passing antibiotic resistance, immunity to chlorine bleach, survival of autoclaving or radiation exposure, etc. to unrelated species in the environment, potentially reducing our ability to effectively treat extremely dangerous pathogenic organisms, via horizontal gene transfer to Bacillus anthracis, Corynebacterium diptheriae, Streptococcus pyogenes, Clostridium botulinum, Clostridium tetanai, Legionella pneumoniae etc. , increasing the spread of Anthrax, Diptheria, Flesh-eating disease, Rheumatic fever, Botulism and Tetanus, Legionnaire's Disease, the diseases caused by the species named above.

Glyoxylate cycle:  A modification of the Krebs cycle, which occurs in some bacteria. Acetyl coenzyme A is generated directly from oxidation of fatty acids or other lipid compounds.  
 Gram positive: Bacterial cells which retain the crystal violet stain during a staining procedure. Most strains of bacilli are gram positive.
 Gram negative: Bacteria cells which lose the crystal violet during the decolorizing step and are then colored by the counterstain. Pseudomonas and Thiobacillus are examples of gram negative strains. 
 Grit: The heavy material present in wastewater, such as sand coffee grounds, eggshells, gravel and cinders. 

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 Halophilic or Halotolerant: Bacteria which thrive in a highly salt environment, up to 25% NaCl.
 Headworks: The facilities where wastewater enters a wastewater treatment plant. The headworks may consist of bar screens, comminutors, a wet well and pumps. 
 Heterotroph: A microorganism which uses organic matter for energy and growth. 
 HRT: Hours of Retention Time. 
 Horizontal Gene Transfer

The process by which bacteria and Archaea transfer genes to other bacteria or Archaea, especially obvious when a sudden environmental change forces resident bacteria or Archaea to seek a faster method of evolution than will occur slowly due to mutations of native DNA. Methods used include:

  1. conjugation - One cell binds to another cell, often unrelated, opening a connection through which it can pass a strand of DNA, copied from its primary DNA, into a separate contained packet of DNA, called a plasmid, to the recipient cell, without risking spilling cell contents from either donor or recipient cell into the environment. Conjugation is often a two-way transfer that enhances survival of both participants. If bacteria develop antibiotic resistance due to improper application of antibiotics (incorrect selection of treatment antibiotic, insufficient dosage to kill ALL bacteria exposed to the antibiotic), escaping bacteria may choose to pass antibiotic resistance along in plasmids to other bacteria they encounter in their environment (whether they normally live in hospitals, sewage systems, lakes, ponds, rivers or turf that is grazed by livestock.
  2. DNA scavenging - One cell samples DNA strands strewn about during cell wall breakdown following death of bacterial cells that were intolerant of primary environmental conditions (temperature, pH, salinity, available food sources, antibiotics produced by native bacteria to keep them dominant, etc.), sometimes delivering beneficial enzyme pathways to the resident species. When horizontal gene transfer happens naturally in the environment, huge leaps in adaptation can occur, creating new species very distinct from parental strains. I
 House Sewer: The pipeline connecting the house and drain and the septic tank.
 Humus:  The dark organic material in soils, produced by the decomposition of soils. The matter that remains after the bulk of detritus has beenconsumed (leaves, roots). Humus mixes with top layers of soil (rock particles), supplies some of the nutrients needed by plants -increases acidity of soil; inorganic nutrients more soluble under acidic conditions, become more available, EX. wheat grows
best at pH 5.5-7.0. Humus modifies soil texture, creates loose, crumbly texture, that allows water to soak in and nutrients retained; permits air to be incorporated into soil.
 Hydraulic loading: Hydraulic loading refers to the flows (MGD or m3/day) to a treatment plant or treatment process. 
 Hydrogen sulfide gas: Hydrogen sulfide is a gas with a rotten egg odor. This gas is produced under anaerobic conditions. Hydrogen sulfide is particularly dangerous because it dulls your sense of smell so that you don't notice it after you have been around it for a while and because the odor is not noticeable in high concentrations. The gas is very poisonous to your respiratory system, explosive, flammable, and colorless. 
 Hydrolysis: The process in which carbohydrates and starches are simplified into organic soluble organics, usually by facultative anaerobes.
 Hygroscopic: Absorbing or attracting moisture from the air. 


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