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Symbols and Acronyms

paddle aerator   A device, similar in form to a paddle wheel, that is used in the aeration of water.

panel board  One or more panel units designed for assembly into a single panel, including buses, and with or without switched and/or automatic overcurrent devices. Panel boards are used to control light, heat, or power circuits of small individual or grouped loads. They are designed to be set in a cabinet box or in or against a wall or partition and are accessible from the front only (see switchboard).

Parshall flume  A calibrated device developed by Parshall for measuring the flow of liquid in an open conduit consisting essentially of a contracting length, a throat, and an expanding length. At the throat is a sill over which the flow passes at Belanger’s critical depth. The upper and lower heads are each measured at a definite distance from the sill. The lower head need not be measured unless the sill is submerged more than about 67%.

partial pressure  The pressure exerted by each gas independently of the others in a mixture of gases. The partial pressure of each gas is proportional to the amount (percent by volume) of that gas in the mixture.

particles  Generally, discrete solids suspended in water or wastewater that can vary widely in size, shape, density, and charge.

parts per million (ppm)  The number of weight or volume units of a minor constituent present with each 1 million units of a solution or mixture. The more specific term, milligrams per liter (mg/L), is preferred.

pathogenic bacteria  Bacteria that cause disease in the host organism by their parasitic growth.

pathogens  Pathogenic or disease-producing organisms.

peak  (1) The maximum quantity that occurs over a relatively short period of time. Also called peak demand, peak load. (2) The highest load carried by an electric generating system during any specific period. It is usually expressed in kilowatts (kW).

peak load  (1) The maximum average load carried by an electric generating plant or system for a short time period such as 1 hour or less. (2) The maximum demand for water placed on a pumping station, treatment plant, or distribution system; expressed as a rate. (3) The maximum rate of flow of wastewater to a pumping station or treatment plant. Also called peak demand.

period  (1) The interval required for the completion of a recurring event. (2) Any specified duration of time.

peripheral weir  The outlet weir extending around the inside of the circumference of a circular settling tank over which the effluent discharges.

permeability  (1) The property of a material that permits appreciable movement of water through it when it is saturated; the movement is actuated by hydrostatic pressure of the magnitude normally encountered in natural subsurface water. Perviousness is sometimes used in the same sense as permeability. (2) The capacity of a rock or rock material to transmit a fluid. See also permeability coefficient.

permeability coefficient  A coefficient expressing the rate of flow of a fluid through a cross section of permeable material under a hydraulic or pressure gradient. The standard coefficient of permeability used in the hydrologic work of the U.S. Geological Survey (USGS), known also as the Meinzer unit, is defined as the rate of flow of water in gallons per day (gpd) at 60 °F through a cross section of 1 ft (0.3 m) under a hydraulic gradient of 100%. See also field permeability coefficient.

pervious  Possessing a texture that permits water to move through perceptibly under the head differences ordinarily found in subsurface water. See also permeability.

pH  A measure of the hydrogen-ion concentration in a solution, expressed as the logarithm (base 10) of the reciprocal of the hydrogen-ion concentration in gram moles per liter (g/mole/L). On the pH scale (0 to 14), a value of 7 at 25 °C (77 °F) represents a neutral condition. Decreasing values indicate increasing hydrogen-ion concentration (acidity); increasing values indicate decreasing hydrogen-ion concentration (alkalinity).

phase  Any portion of a physical system separated by a definite physical boundary from the rest of the system. The three physical phases are solid, liquid, and gas; colloids are the dispersed phase and liquids are the continuous phase.

phenolic compounds  Hydroxyl derivatives of benzene. The simplest phenolic compound is hydroxyl benzene (C6H5OH).

phosphate  A salt or ester of phosphoric acid. See also orthophosphate, phosphorus.

phosphorus  An essential chemical element and nutrient for all life forms. Occurs in orthophosphate, pyrophosphate, tripolyphosphate, and organic phosphate forms. Each of these forms and their sum (total phosphorus) is expressed as milligrams per liter (mg/L) elemental phosphorus. See also nutrient.

phosphorus removal  The precipitation of soluble phosphorus by coagulation and subsequent flocculation and sedimentation.

photosynthesis  The synthesis of complex organic materials, especially carbohydrates, from carbon dioxide, water, and inorganic salts with sunlight as the source of energy and with the aid of a catalyst, such as chlorophyll.

photosynthetic bacteria  Bacteria that obtain their energy for growth from light by photosynthesis.

physical analysis  The examination of water and wastewater to determine physical characteristics such as temperature, turbidity, color, odors, and taste.

physical-chemical treatment  Treatment of wastewater by unit processes other than those based on microbiological activity. Unit processes commonly included are precipitation with coagulants, flocculation with or without chemical flocculents, filtration, adsorption, chemical oxidation, air stripping, ion exchange, reverse osmosis, and several others.

physical treatment  Any treatment process involving only physical means of solid–liquid separation, for example, screens, racks, clarification, and comminutors. Chemical and biological reactions do not play an important role in treatment.

phytoplankton  Plankton consisting of plants, such as algae.

pin floc  Small floc particles that settle poorly.

pipe  A closed conduit that diverts or conducts water or wastewater from one location to another.

pipe diameter  The nominal or commercially designated inside diameter of a pipe, unless otherwise stated.

pipe fittings  Connections, appliances, and adjuncts designed to be used in connection with pipes; examples are elbows and bends to alter the direction of a pipe; tees and crosses to connect a branch with a main; plugs and caps to close an end; and bushings, diminishers, or reducing sockets to couple two pipes of different dimensions.

pipe gallery  (1) Any conduit for pipe, usually of a size to allow a person to walk through. (2) A gallery provided in a treatment plant for the installation of conduits and valves and used as a passageway to provide access to them.

piping system  A system of pipes, fittings, and appurtenances within which a fluid flows.

piston pump  A reciprocating pump in which the cylinder is tightly fitted with a reciprocating piston.

plant hydraulic capacity  The level of flow into a plant above which the system is hydraulically overloaded.

plastic media  Honeycomb-like products, manufactured from plastics of various compositions, with high surface area;volume ratios that are used in trickling filters in place of crushed stone. The product is available in large modules fabricated from sheets that may be cut to size on-site, and small discrete pieces to be loosely packed in the filter bed. See also trickling filter.

plate press  A filter press consisting of a number of parallel plate units lined with filter cloth that rests on drainage channels in the plates. Pressure is exerted by the pumping of solids into chambers created between the cloths. The operation is carried out in batches.

plug flow  Flow in which fluid particles are discharged from a tank or pipe in the same order in which they entered it. The particles retain their discrete identities and remain in the tank for a time equal to the theoretical detention time.

plumbing  (1) The pipes, fixtures, and other apparatus inside a building for bringing in the water supply and removing the liquid and waterborne wastes. (2) The installation of the foregoing pipes, fixtures, and other apparatus.

plumbing fixtures  Receptacles that receive liquid, water, or wastewater and discharge them into a drainage system.

plunger pump  A reciprocating pump with a plunger that does not come in contact with the cylinder walls, but enters and withdraws from it through packing glands. Such packing may be inside or outside the center, according to the design of the pump.

pneumatic ejector  A device for raising wastewater, sludge, or other liquid by alternately admitting it through an inward swinging check valve into the bottom of an airtight pot and then discharging it through an outward swinging check value by admitting compressed air to the pot above the liquid.

point gauge  A sharp-pointed rod attached to a graduated staff or vernier scale used for measuring the elevation of the surface of water. The point is lowered until the tip barely touches the water and forms a streak in flowing water and a meniscus jump in still water. It can also be used in a still well and can operate on an electric current with a buzzer or light that will operate when contact with the water is made.

polishing  A general term for those treatment processes that are applied after conventional ones. See also advanced waste treatment, tertiary treatment.

pollution  (1) Specific impairment of water quality by agricultural, domestic, or industrial wastes (including thermal and atomic wastes) to a degree that has an adverse effect on any beneficial use of the water. (2) The addition to a natural body of water any material that diminishes the optimal economic use of a water body by the population it serves and has an adverse effect on the surrounding environment.

polychlorinated biphenyls (PCBs)  A class of aromatic organic compounds with two six-carbon unsaturated rings, with chlorine atoms substituted on each ring and more than two such chlorine atoms per molecule of PCB. They are typically stable, resist both chemical and biological degradation, and are toxic to many biological species.

polyelectrolyte flocculants  Polymeric organic compounds used to induce or enhance the flocculation of suspended and colloidal solids and thereby facilitate sedimentation or the dewatering of sludges.

polyelectrolytes  Complex polymeric compounds, usually composed of synthetic macro­molecules that form charged species (ions) in solution; water-soluble polyelectrolytes are used as flocculants; insoluble polyelectrolytes are used as ion exchange resins. See also polymers.

polymers  Synthetic organic compounds with high molecular weights and composed of repeating chemical units (monomers); they may be polyelectrolytes, such as water-soluble flocculents or water-insoluble ion exchange resins, or insoluble uncharged materials, such as those used for plastic or plastic-lined pipe and plastic trickling filter media.

polyvinyl chloride (PVC)  An artificial polymer made from vinyl chloride monomer (CH2:CHCl); frequently used in pipes, sheets, and vessels for transport, containment, and treatment in water and wastewater facilities. See also polymers.

population dynamics  The ever-changing numbers of microscopic organisms within the activated sludge process.

population equivalent  The estimated population that would contribute a given amount of a specific waste parameter (BOD5, suspended solids, or flow); usually applied to industrial waste. Domestic wastewater contains material that consumes, on the average, 0.17 lb of oxygen/cap/d (0.08 kg/cap·d), as measured by the standard BOD test. For example, if an industry discharges 1 000 lb of BOD/d (454 kg/d), its waste is equivalent to the domestic wastewater from 6 000 persons (1 000/0.17 5 approximately 6 000).

pore  As applied to stone, soil, or other material, any small interstice or open space, generally one that allows the passage or adsorption of liquid or gas.

pore space  Open space in rock or granular material.

porosity  (1) The quality of being porous or containing interstices. (2) The ratio of the aggregate volume of interstices in a rock or soil to its total volume; usually stated as a percentage.

positive-displacement pump  Pump type in which liquid is induced to flow from the supply source through an inlet pipe and inlet valve. Water is brought into the pump chamber by a vacuum created by the withdrawal of a piston or pistonlike device, which, on its return, displaces a certain volume of water contained in the chamber and forces it to flow through the discharge valve and pipe.

postaeration  The addition of air to plant effluent to increase the oxygen concentration of treated wastewater.

postchlorination  The application of chlorine to wastewater following treatment.

power (apparent)  The mathematical product of the volts and amps of a circuit. The product generally is divided by 1000 and designated as kilovolt amperes (kVA).

power (electric)  The time rate of transferring or using electrical energy, usually ex­pressed in kilowatts (kW).

power (reactive)  That portion of apparent power that does no work. It is usually measured in kilovars. Reactive power must be supplied to most types of magnetic equipment, such as motors, ballasts, transformers, and relays. Typically, it is supplied by generators or by electrostatic equipment such as capacitors.

power requirements  The rate of energy input needed to operate a piece of equipment, a treatment plant, or other facility or system. The form of energy may be electrical, fossil fuel, other types, or a combination.

preaeration  A preparatory treatment of wastewater consisting of aeration to remove gases, add oxygen, promote flotation of grease, and aid coagulation.

prechlorination  The application of chlorine to wastewater at or near the treatment plant entrance. Often used after bar screens and grit chambers to control odors in primary settling tanks.

precipitate  (1) To condense and cause to fall as precipitation, as water vapor condenses and falls as rain. (2) The separation from solution as a precipitate. (3) The substance that is precipitated.

preliminary treatment  Unit operations, such as screening, comminution, and grit removal, that prepare the wastewater for subsequent major treatment.

press filter  A press operated mechanically for partially dewatering sludge. See also filter press, plate press.

pressure  (1) The total load or force acting on a surface. (2) In hydraulics, unless otherwise stated, the pressure per unit area or intensity of pressure above local atmospheric pressure expressed in pounds per square inch (psi) or kilograms per square centimeter (kg/cm2).

pressure filter  (1) An enclosed vessel having a vertical or horizontal cylinder of iron, steel, wood, or other material containing granular media through which liquid is forced under pressure. (2) A mechanical filter for partially dewatering sludge. See also filter press, plate press.

pressure gauge  A device for registering the pressure of solids, liquids, or gases. It may be graduated to register pressure in any units desired.

pressure-relief valve  Valve that opens automatically when the pressure reaches a preset limit to relieve stress on a pipeline.

pressure tank  A tank used in connection with a water distribution system for a single household, for several houses, or for a portion of a larger water system that is airtight and holds both air and water and in which air is compressed and the pressure so created is transmitted to the water.

pretreatment  Treatment of industrial wastewater at its source before discharge to municipal collection systems.

primary effluent  The liquid portion of wastewater leaving the primary treatment process.

primary sedimentation tank  The first settling tank for the removal of settleable solids through which wastewater is passed in a treatment works. Sometimes called a primary clarifier.

primary sludge  Sludge obtained from a primary sedimentation tank.

primary treatment  (1) The first major treatment in a wastewater treatment facility, used for the purpose of sedimentation. (2) The removal of a substantial amount of suspended matter, but little or no colloidal and dissolved matter. (3) Wastewater treatment processes usually consisting of clarification with or without chemical treatment to accomplish solid–liquid separation.

primary voltage  The voltage of the circuit supplying power to a transformer, as opposed to the output voltage or load-supplied voltage, which is called secondary voltage. In power supply practice, the primary is almost always the high-voltage side and the secondary the low-voltage side of the transformer.

propeller pump  A centrifugal pump that develops most of its head by the propelling or lifting action of the vanes on the liquid. Also called an axial-flow pump.

propeller-type impeller  An impeller of the straight axial-flow type.

proportional weir  A special type of weir in which the discharge through the weir is directly proportional to the head.

protozoa  Small one-celled animals including amoebae, ciliates, and flagellates.

publicly owned treatment works  Wastewater treatment plant.

pump  A mechanical device for causing flow, for raising or lifting water or other fluid, or for applying pressure to fluids.

pump curve  A curve or curves showing the interrelation of speed, dynamic head, capacity, brake horsepower, and efficiency of a pump.

pump efficiency  The ratio of energy converted into useful work to the energy applied to the pump shaft, or the energy difference in the water at the discharge and suction nozzles divided by the power input at the pump shaft.

pumping head  The sum of the static head and friction head on a pump discharging a given quantity of water.

pumping station  (1) A facility housing relatively large pumps and their appurtenances. Pump house is the usual term for shelters for small water pumps. (2) A facility containing lift pumps to facilitate wastewater collection or reclaimed water distribution.

pump pit  A dry well or chamber, below ground level, in which a pump is located.

pump stage  The number of impellers in a centrifugal pump; for example, a single-stage pump has one impeller; a two-stage pump has two impellers.

putrefaction  Biological decomposition, usually of organic matter, with the production of foul-smelling products associated with anaerobic conditions.

putrescibility  (1) The relative tendency of organic matter to undergo decomposition in the absence of oxygen. (2) The susceptibility of wastewaters, effluent, or sludge to putrefaction. (3) The stability of a polluted, raw, or partially treated wastewater.