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Symbols and Acronyms

Manning formula   A formula for open-channel flow published by Manning in 1890. It gives the value of c in the Chezy formula. See also Manning roughness coefficient.

Manning roughness coefficient  The roughness coefficient in the Manning formula for determination of the discharge coefficient in the Chezy formula.

manometer  An instrument for measuring pressure. It usually consists of a U-shaped tube containing a liquid, the surface of which moves proportionally in one end of the tube with changes in pressure in the liquid in the other end; also, a tube-type of differential pressure gauge.

mass spectrometer  A device that permits observation of the masses of molecular fragments produced by destructible bombardment of the molecule with electrons in a vacuum; coupled with gas chromatography (GC-MS), mass spectrometry can yield very specific compound identification.

mass spectrometry  A means of sorting ions by separating them according to their masses.

mean  (1) The arithmetic average of a group of data. (2) The statistical average (50% point) determined by probability analysis.

mean cell residence time (MCRT)  The average time that a given unit of cell mass stays in the activated-sludge aeration tank. It is usually calculated as the total mixed liquor suspended solids in the aeration tank divided by the combination of solids in the effluent and solids wasted.

mechanical aeration  (1) The mixing, by mechanical means, of wastewater and activated sludge in the aeration tank of the activated-sludge process to bring fresh surfaces of liquid into contact with the atmosphere. (2) The introduction of atmospheric oxygen into a liquid by the mechanical action of paddle, paddle wheel, spray, or turbine mechanisms.

mechanical aerator  A mechanical device for the introduction of atmospheric oxygen into a liquid. See also mechanical aeration.

mechanically cleaned screen  A screen equipped with a mechanical cleaning apparatus for removal of retained solids.

mechanical rake  A machine-operated mechanism used for cleaning debris from racks located at the intakes of conduits supplying water to hydroelectric power plants, water supply systems, or for other uses, and conveying wastewater to pumps or treatment processes.

median  In a statistical array, the value having as many cases larger in value as cases smaller in value.

membrane filter test  A sample of water is passed through a sterile filter membrane. The filter is removed and placed on a culture medium and then incubated for a preset period of time. Coliform colonies, which have a pink to dark-red color with a metallic sheen, are then counted using the aid of a low-power binocular wide-field dissecting microscope. The membrane filter test is used to test for the presence and relative number of coliform organisms.

mercaptans  Aliphatic organic compounds that contain sulfur. They are noted for their disagreeable odor and are found in certain industrial wastes.

mercury gauge  A gauge in which the pressure of a fluid is measured by the height the fluid pressure will sustain a column of mercury.

mesh  One of the openings or spaces in a screen. The value of the mesh is usually given as the number of openings per linear inch. This gives no recognition to the diameter of the wire; thus, the mesh number does not always have a definite relationship to the size of the hole.

mesophilic  That group of bacteria that grow best within the temperature range of 20 to 40 °C (68 to 104 °F).

mesophilic digestion  Digestion by biological action at 27 to 38 °C (80 to 100 °F).

mesophilic range  Operationally, that temperature range most conducive to the maintenance of optimum digestion by mesophilic bacteria, generally accepted as between 27 and 38 °C (80 and 100 °F).

metabolism  (1) The biochemical processes in which food is utilized and wastes formed by living organisms. (2) All biochemical reactions involved in cell synthesis and growth.

metazoan  A group of animals having bodies composed of cells differentiated into tissues and organs and usually having a digestive cavity lined with specialized cells.

meter  An instrument for measuring some quantity such as the rate of flow of liquids, gases, or electric currents.

methane (CH4)  A colorless, odorless, flammable, gaseous hydrocarbon present in natural gas and formed by the anaerobic decomposition of organic matter, or produced artificially by heating carbon monoxide and hydrogen over a nickel catalyst. See also anaerobic digestion.

methane bacteria  A specialized group of obligate anaerobic bacteria that decompose organic matter to form methane.

methane fermentation  A reaction sequence that produces methane during the anaerobic decomposition or organic waste. In the first phase, acid-forming bacteria produce acetic acid; in the second, the methane bacteria use this acid and carbon dioxide to produce methane. Fermentation results in the conversion of organic matter into methane gas.

mgd  Million gallons per day; a measure of flow equal to 1.547 cu ft/sec, 681 gpm, or 3 785 m3/d.

mg/L  Milligrams per liter; a measure of concentration equal to and replacing ppm in the case of dilute concentrations.

microbial activity  The activities of microorganisms resulting in chemical or physical changes.

microbial film  A gelatinous film of microbial growth attached to or spanning the interstices of a support medium. Also called biological slime.

microorganisms  Very small organisms, either plant or animal, invisible or barely visible to the naked eye. Examples are algae, bacteria, fungi, protozoa, and viruses.

microscopic  Very small, generally between 0.5 and 100 mm, and visible only by magnification with an optical microscope.

microscopic examination  (1) The examination of water to determine the presence and amounts of plant and animal life, such as bacteria, algae, diatoms, protozoa, and crustacea. (2) The examination of water to determine the presence of microscopic solids. (3) The examination of microbiota in process water, such as the mixed liquor in an activated-sludge plant.

mist  Fine liquid droplets of such small size that gravity separation is hindered. Fog is a water mist.

mixed-flow pump  A centrifugal pump in which the head is developed partly by centrifugal force and partly by the lift of the vanes on the liquid. This type of pump has a single inlet impeller; the flow enters axially and leaves axially and radially.

mixed liquor  A mixture of raw or settled wastewater and activated sludge contained in an aeration tank in the activated-sludge process. See also mixed liquor suspended solids.

mixed liquor suspended solids (MLSS)  The concentration of suspended solids in activated-sludge mixed liquor, expressed in milligrams per liter (mg/L). Commonly used in connection with activated-sludge aeration units.

mixed liquor volatile suspended solids (MLVSS)  That fraction of the suspended solids in activated-sludge mixed liquor that can be driven off by combustion at 550 °C (1022 °F); it indicates the concentration of microorganisms available for biological oxidation.

mixed-media filter  A filter containing filtering media of different particle size or density.

mixing basin  A basin or tank in which agitation is applied to water, wastewater, or sludge to increase the dispersion rate of applied chemicals; also, tanks used for general mixing purposes.

mixing chamber  A chamber used to facilitate the mixing of chemicals with liquid or the mixing of two or more liquids of different characteristics. It may be equipped with a mechanical device that accomplishes the mixing.

mixing channel  A channel provided in a water or wastewater treatment plant; the hydraulic characteristics of the waterway or its construction features are such that chemicals or liquids are thoroughly mixed.

modified aeration  A modification of the activated-sludge process in which a shortened period of aeration (1.5 to 3 hours) is used with a reduced quantity of suspended solids (200 to 500 mg/L MLSS) in the mixed liquor. Sludge settling is usually poor; high suspended solids concentration may be expected in effluent.

moisture  Condensed or diffused water collected on or excluded to a surface.

moisture content  The quantity of water present in soil, wastewater sludge, industrial waste sludge, and screenings, usually expressed in percentage of wet weight.

mole  (1) Molecular weight of a substance, normally expressed in grams. (2) A device to clear sewers and pipelines. (3) A massive harbor work, with a core of earth or stone, extending from shore into deep water. It serves as a breakwater, a berthing facility, or a combination of the two.

monitoring  (1) Routine observation, sampling, and testing of designated locations or parameters to determine the efficiency of treatment or compliance with standards or requirements. (2) The procedure or operation of locating and measuring radioactive contamination by means of survey instruments that can detect and measure, as dose rate, ionizing radiations.

Monod equation  A mathematical expression first used by Monod in describing the relationship between the microbial growth rate and concentration of growth-limiting substrate.

most probable number (MPN)  That number of organisms per unit volume which, in accordance with statistical theory, would be more likely than any other number to yield the observed test result or would yield the observed test result with the greatest frequency. Expressed as density of organisms/100 mL. Results are computed from the number of positive findings of coliform group organisms resulting from multiple portion decimal dilution plantings. Used commonly for coliform bacteria.

motor controller  A specialized type of controller whose typical functions performed by a motor controller include starting, accelerating, stopping, reversing, and protecting motors.

moving average  Trend analysis tool for determining patterns or changes in treatment process. For example, a 7-day moving average would be the sum of the datum points for 7 days divided by 7.

mudballs  (1) Accretions of siliceous incrustations on the exterior surface of sand grains. From these incrustations grow numerous filamentous organisms over which there is a gelatinous coating. Mudballs are approximately spherical in shape and vary in size from that of a pea up to 1 or 2 in. (2.5 to 5.1 cm) or more in diameter. They are formed principally by the retention and gradual building up of growths that are not completely removed by the washing process. (2) Balls of sediment sometimes found in debris-laden flow and channel deposits.

mud blanket  A layer of flocculant material that forms on the surface of a sand filter.

multimedia filter beds  A filtration apparatus consisting of two or more media, such as anthracite and sand, through which wastewater flows and by which it is cleansed. Media may be intermixed or segregated.

multiple-hearth incinerator  A countercurrent-type of incinerator frequently used to dry and burn partially dried sludges. Heated air and products of combustion pass by finely pulverized sludge that is continuously raked to expose fresh surfaces.

multiple-stage sludge digestion  The progressive digestion of waste sludge in two or more tanks arranged in series.

multistage pump  A centrifugal pump with two or more sets of vanes or impellers connected in series in the same casing. Such a pump may be designated as two-stage, three-stage, or more, according to the number of sets of vanes used. The purpose is to increase the head of the discharging fluid.

municipal wastewater treatment  Generally includes the treatment of domestic, commercial, and industrial wastes.