Dewatering Glossary

A

activated sludge process - A biological wastewater treatment process  in which a mixture of wastewater and biologically enriched sludge is mixed and aerated to facilitate aerobic decomposition by microbes.

activated sludge - The biologically active solids in an activated sludge process wastewater treatment plant.

aeration - The addition of air or oxygen to water or wastewater, usually by mechanical means, to increase dissolved oxygen levels and maintain aerobic conditions.

aerobic digestion - Sludge stabilization process involving direct oxidation of biodegradable matter and oxidation of microbial cellular material.

anaerobic digestion - Sludge stabilization process where the organic material in biological sludges are converted to methane and carbon dioxide in an airtight reactor.

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B

belt press - A dewatering device utilizing two opposing synthetic fabric belts,  revolving over a series of rollers to “squeeze” water from the sludge.

bench test - A small scale test or study used to determine whether a technology is suitable for a particular application.

biosolids - Solid organic matter recovered from municipal wastewater treatment that can be beneficially used, especially as a fertilizer. “Biosolids” are solids that have been stabilized within the treatment process, whereas “sludge” has not.

body feed - Coating or bulking material added to the influent of material to be treated. This adds “body” to the material during filtration cycle.

bulking sludge - A poor or slow settling activated sludge that results from the prevalence of filamentous organisms.

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C

cake - Dewatered sludge material with a satisfactory solids concentration to allow handling as a solid material.

centrate - The liquid remaining after solids have been removed in a centrifuge.

centrifuge - A dewatering device relying on centrifugal force to separate particles of varying density such as water and solids.

chemical sludge - Sludge resulting from chemical treatment processes of inorganic wastes which are not biologically active.

clarifier - A settling tank used to remove suspended solids by gravity settling. Commonly referred to as sedimentation or settling basins, they are usually equipped with a motor driven chain and flight or rake mechanism to collect settled sludge and move it to a final removal point.

coagulant - A chemical added to initially destabilize, aggregate, and bind together colloids and emulsions to improve settleability, filterability, or drainability. 

composite sample - A combination of individual samples of water or wastewater taken at predetermined intervals to minimize the effect of variability of individual samples.

composting - Stabilization process relying on the aerobic decomposition of organic matter in sludge by bacteria and fungi.

contact stabilization process - Modification of the activated sludge process where raw wastewater is aerated with activated sludge for a short time prior to solids removal and continued aeration in a stabilization tank.

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D

decant - Separation of a liquid from settled solids by removing the upper layer of liquid after the solids have settled.

digester - A tank or vessel used for sludge digestion.

dissolved solids - Solids in solution that cannot be removed by filtration with a 0.45 micron filter.

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E

effluent - Partially or completely treated water or wastewater flowing out of a basin or treatment plant.

emulsion - A mixture made up of dissimilar elements, usually of two or more mutually insoluble liquids that would normally separate into layers based on the specific gravity of each liquid.

endothermic - A process or reaction which is accompanied by the absorption (drawing in) of heat.

environment - Water, air, and land, and the interrelationship that exists among and between water, air and land and all living things.

exothermic - A process or reaction which is accompanied by the creation of heat.

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F

ferric chloride - An iron salt commonly used as a coagulant. Chemical formula is FeCl3.

filter - A device utilizing a granular material, woven cloth or other medium to remove pollutants from water, wastewater or air.

filter aid - A polymer or other material added to improve the effectiveness of the filtration process.

filter cake - The layer of solids that is retained on the surface of a filter.

filter press - A dewatering device where sludge is pumped onto a filtering medium and water is forced out of the sludge, resulting in a “cake”.

filtrate - Liquid remaining after removal of solids with filtration.

filtration rate - A measurement of the volume of water applied to a filter per unit of surface area in a given period of time.

flocculation - Gentle stirring or agitation to accelerate the agglomeration of particles to enhance sedimentation or flotation.

fly ash - The noncombustible particles in flue gas. Often used as a body feed or solidification chemical.

free oil - Non-emulsified oil that separates from water, in a given period of time.

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G

grab sample - A single water or wastewater sample taken at a time and place representative of total discharge.

gravity belt thickener -  A sludge dewatering device utilizing a filter belt to promote gravity drainage of water. Usually precedes additional dewatering treatment.

gravity filter – A filter that operates at atmospheric pressure.

gravity thickening - A sedimentation basin designed to operate at high solids loading rates.

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H

hydrated lime - The calcium hydroxide product that results from mixing quicklime with water. Chemical formula is CaOH2.

hydrogen sulfide - A toxic gas formed by the anaerobic decomposition of organic matter. Chemical formula is H2S.

hydrophilic - Having an affinity for water.

hydrophobic - Having an aversion to water.

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I

in situ - Treatment or disposal methods that do not require movement of contaminated material.

incineration - The process of reducing the volume of a material by burning and reducing to ash if possible.

inclined plate separator - A series of parallel inclined plates that can be used to increase the efficiency of clarifiers and gravity thickeners.

indirect reuse - The beneficial use of reclaimed water into natural surface waters or groundwater.

industrial wastewater - Liquid wastes resulting from industrial processes.

influent - Water or wastewater flowing into a basin or treatment plant.

inorganic compound - Compounds that contain no carbon or contain only carbon bound to elements other than hydrogen.

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J

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K

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L

land application - The disposal of wastewater or municipal solids onto land under controlled conditions.

land disposal - Application of municipal wastewater solids to the soil without production of usable agricultural products.

landfill -  A land disposal site that employs an engineering method of solid waste disposal to minimize environmental hazards and protect the quality of surface and subsurface waters.

leachate - Fluid which trickles through solid materials or wastes and contains suspended or dissolved materials or products of the solids.

lime - The term generally used to describe ground limestone (calcium carbonate), hydrated lime (calcium hydroxide), or burned lime (calcium oxide).

lime stabilization - The addition of lime to untreated sludge to raise the pH to 12 for a minimum of 2 hours to chemically inactivate microorganisms.

listed hazardous waste - The designation for a waste material that appears on an EPA list of specific hazardous wastes or hazardous waste categories.

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M

makeup water - Fluid introduced in a recirculating stream to maintain an equilibrium of temperature, solids concentration or other parameters. Also refers to the quantity of water required to make a solution.

membrane - A thin barrier that permits passage of particles of a certain size or of particular physical or chemical properties.

micro-filtration -  A low pressure membrane filtration process which removes suspended solids and colloids generally larger than 0.1 micron diameter.

milligrams per liter - (mg/L) A common unit of measurement of the concentration of a material in solution.

miscible - Capable of being mixed together.

mixed liquor suspended solids - Suspended solids in the mixture of wastewater and activated sludge undergoing aeration in the aeration basin.

municipal waste - The combined solid and liquid waste from residential, commercial and industrial sources.

municipal wastewater treatment plant – (MWTP) Treatment works designed to treat municipal wastewater.

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N

nano-filtration - A specialty membrane filtration process which rejects solutes larger than approximately one nanometer (10 angstroms) in size.

natural organic matter - Organic matter present in natural waters.

neutralization - The chemical process that produces a solution that is neither acidic nor alkaline. Usually with a pH between 6 and 8.

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O

organic - Relating to, or derived from a living thing. A description of a substance that contains carbon atoms linked together by carbon-carbon bonds.

organic matter - Substances containing carbon compounds, usually of animal or vegetable origin.

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P

paint filter test - Test to determine free water content of sludge or dewatered solids sample Usually used as the criteria for admission to a landfill.

parts per million - (ppm) A common unit of measure used to express the number of parts of a substance contained within a million parts of a liquid, solid, or gas.

pasteurization - A process for killing pathogenic organisms by applying heat for a specific period of time.

permeate - The liquid that passes through a membrane.

pH – Represents the percentage of Hydrogen and is a term used to describe the activity of the Hydrogen ion. The activity is essentially equal to the concentration of the Hydrogen ion, therefore a pH of 0-7 is acid , 7 is neutral (water) , and 7-14 is an alkaline. 

physical-chemical treatment - Treatment processes that are non-biological in nature.

pin floc - Small flocculated particle size.

plate-and-frame press - A batch process dewatering device in which sludge is pumped under high pressure through a series of parallel plates, in which a chamber is created between the plates. Each plate is fitted with filter cloth and the solids are collected in the chambers and the water is filtered from the sludge.

point source discharge - A pipe, ditch, channel or other container from which pollutants may be discharged.

pollutant - A substance, organism or energy form present in amounts that impair or threaten an ecosystem to the extent that its current or future uses are prevented.

polymer – Chemical used for flocculation in dewatering. Also known as a "polyelectrolyte" which is a substance made of giant molecules formed by the union of simple smaller molecules.

post treatment - Treatment of finished water or wastewater to further enhance its quality.

precipitate - A solid that separates from a solution.

precipitation - The phenomenon that occurs when a substance held in solution passes out of solution into a solid form.

preliminary treatment - Treatment steps including comminution, screening, grit removal, pre-aeration, and/or flow equalization which prepares wastewater influent for further treatment.

pressure filter - Filter unit enclosed in a vessel that may be operated under pressure.

primary clarifier - Sedimentation basin that precedes secondary wastewater treatment.

primary sludge - Sludge produced in a primary waste treatment unit.

primary treatment - Treatment steps including sedimentation and/or fine screening to produce an effluent suitable for biological treatment.

process wastewater - Wastewater generated during manufacture or production processes.

process water - Water that is used for, or comes in contact with an end product or the materials used in an end product.

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Q

quicklime - A calcium oxide material produced by calcining limestone to liberate carbon dioxide, also called “calcined lime” or “pebble lime”, commonly used for pH adjustment. Chemical formula is CaO.

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R

raw sewage - Untreated wastewater and its contents.

raw sludge - Undigested sludge recently removed from a sedimentation basin.

raw water - Untreated surface or groundwater.

reclaimed water - Wastewater that has been treated to a level that allows for its reuse for a beneficial purpose.

reclamation - The process of improving or restoring the condition of land or other material to a better or more useful state.

recycling - The process by which recovered materials are transformed into new products.

residence time - The period of time that a volume of liquid remains in a tank or system.

respiration - Intake of oxygen and discharge of carbon dioxide as a result of biological oxidation.

return activated sludge - Settled activated sludge that is returned to mix with raw or primary settled wastewater.

rotary drum screen - Cylindrical screen used to remove floatable and suspended solids.

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S

screenings press - A mechanical press used to compact and/or dewater material removed from mechanical screening equipment.

scrubber - A device used to removal particulates or pollutant gases from combustion or chemical process exhaust streams.

scum - Floatable materials found on the surface of primary and secondary settling tanks consisting of food wastes, grease, fats, paper, foam, and similar matter.

secondary clarifier - A clarifier following a secondary treatment process, designed for gravity removal of suspended matter.

secondary sludge - The sludge from the secondary clarifier in a wastewater treatment plant.

secondary treatment - The treatment of wastewater through biological oxidation after primary treatment.

sedimentation - The removal of settleable suspended solids from water or wastewater by gravity in a quiescent basin or clarifier.

sedimentation basin - A quiescent tank used to remove suspended solids by gravity settling. Also called clarifiers or settling tanks, they are usually equipped with a motor driven rake mechanism to collect settled sludge and move it to a central discharge point.

septic - Condition characterized by bacterial decomposition under anaerobic conditions.

settleability - The tendency of suspended solids to settle.

settleable solids - That portion of suspended solids which are of a sufficient size and weight to settle to the bottom of an Imhoff cone in one hour.

settled sludge volume - Volume of settled sludge measured at predetermined time increments for use in process control calculations.

sewage - Liquid or waterborne wastes polluted or fouled from households, commercial or industrial operations, along with any surface water, storm water or groundwater infiltration.

sewer gas - A gas mixture produced by anaerobic decomposition of organic matter usually containing high percentages of methane and hydrogen sulfide.

shock load - A sudden hydraulic or organic load to a treatment plant, also descriptive of a change in the material being treated.

slop oil - Separator skimmings and tramp oil generated during refinery startup, shutdown or abnormal operation.

sludge - Accumulated and concentrated solids generated within a treatment process that have not undergone a stabilization process.

sludge blanket - The accumulated sludge suspended in a clarifier or other enclosed body of water.

sludge dewatering - The removal of a portion or majority of the water contained in sludge by means of a filter press, centrifuge or other mechanism.

sludge drying bed - A closed area consisting of sand or other porous material upon which sludge is dewatered by gravity drainage and evaporation.

slurry – A mixture of a solid and a liquid that facilitates the transfer of the solid into a treatment solution.

solid waste - Garbage, refuse, sludge and other discarded material resulting from community activities or commercial or industrial operations.

solubility - The amount of a substance that can dissolve in a solution under a given set of conditions.

stabilization pond - A large shallow basin used for wastewater treatment by natural processes involving the use of algae and bacteria to accomplish biological oxidation of organic matter.

subnatant - Liquid remaining beneath the surface of floating solids.

supernatant - Liquid above the settled sludge layer in a sedimentation basin.

surfactant - A surface-active agent such as a detergent which, when mixed with water, generally increases its cleaning ability, solubility, and penetration, while reducing its surface tension.

suspended solids - Solids captured by filtration through a  0.45 micron filter membrane.

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T

tertiary treatment - The use of physical, chemical, or biological means to improve secondary wastewater effluent quality.

thickening - A procedure used to increase the solids content of sludge by removing a portion of the liquid.

total dissolved solids - The weight per unit volume of all volatile and non-volatile solids dissolved in a water or wastewater after a sample has been filtered to remove colloidal and suspended solids.

total solids - The sum of dissolved and suspended solids in a water or wastewater. 

total suspended solids - The measure of particulate matter suspended in a sample of water or wastewater. 

toxic - Capable of causing an adverse effect on biological tissue following physical contact or absorption.

treatability study - A study in which a waste is subjected to a treatment process to determine treatment and/or to determine the treatment efficiency or optimal process conditions for treatment.

turbidity - A qualitative measurement of water clarity which results from suspended matter that scatters or otherwise interferes with the passage of light through the water.

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U

ultra-filtration - A low pressure membrane filtration process which separates solutes up to 0.1 micron size range.

up-flow clarifier - Clarifier where flocculated water flows upward through a sludge blanket to obtain floc removal by contact with flocculated solids in the blanket.

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V

vapor - The gaseous phase of a material that is in the solid or liquid state at standard temperature and pressure.

volatile - A substance that evaporates or vaporizes at a relatively low temperature.

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W

waste activated sludge - Excess activated sludge that is discharged from an activated sludge treatment process.

wastewater - Liquid or waterborne wastes polluted or fouled from households, commercial or industrial operations, along with any surface water, storm water or groundwater infiltration.

water reclamation - The restoration of wastewater to a state that will allow its beneficial reuse.

WPCF - Water Pollution Control Facility 

WTP - Water Treatment Plant

WWTP - Wastewater Treatment Plant

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X

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Y

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Z

Zero discharge - A facility that discharges no liquid effluent to the environment.

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Copyright © 2002 Onyx Industrial Services Inc. - National Separations Division
Last modified: July 25, 2006