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Glossary of Terms - P

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P alkalinity - Phenolphthalein alkalinity of water as determined by titration with standard acid solution to the phenolphthalein endpoint (pH approx. 8.3). Includes carbonate and hydroxide alkalinity. (See total alkalinity.)

packed bed - A bed of filter or ion exchange medium which is completely retained so that no bed expansion can occur and no backwash step is used to reclassify the filter or resin. Packed beds are usually part of the design features in ion exchange water softeners used to obtain high capacity and increased regeneration efficiency.

particle size - As used in water industry standards, this term refers to the size, expressed in microns, of a particle suspended in water as determined by the smallest dimension.

parts per billion (ppb) - A measure of proportion by weight which is equivalent to one unit weight of solute (dissolved substance) per billion unit weights of the solution. This measurement is often used as a measure of concentration when analyzing water for contaminants. Since one liter of water weighs one billion micrograms, one ppb is the equivalent of one microgram per liter when used in water analysis.

parts per million (ppm) - A measure of proportion by weight which is equivalent to one unit of weight of solute (dissolved substance) per million weights of solution. Since one liter of water weighs one million milligrams, one ppm is equal to one milligram per liter (mg/L). Milligram per liter is the preferred unit of measure in water or waste water analysis.

pathogens - Microorganisms that can cause disease in other organisms or in humans, animals, and plants. They may be bacteria, viruses, or parasites and are found in sewage, in runoff from animal farms or rural areas populated with domestic and/or wild animals, and in water used for swimming. Fish and shellfish contaminated by pathogens, or the contaminated water itself, can cause serious illnesses.

P.E. - portable exchange.

percentage values - These are needed to calculate specific resin capacities for this water supply. They are also to calculate DI water quality.

peristaltic pump - A self-priming pump that achieves pumping action by moving a system of rollers against a flexible tube. The pumped fluids (e.g., chemical feeds) are never exposed to the air or to the mechanical moving parts. The roller design prevents siphoning by providing a constant seal on the pumping tube.

permanent hardness - See non-carbonate hardness.

permanganate - Generally refers to potassium permanganate, a chemical compound used in water treatment. (See potassium permanganate.)

pH - A measure of the degree of the acidity or the alkalinity of a solution as measured on a scale ("pH scale") of 0 to 14. The midpoint of 7.0 on the pH scale represents neutrality--that is, a "neutral" solution is neither acid nor alkaline. Numbers below 7.0 indicate acidity; numbers above 7.0 indicate alkalinity. It is important to understand that pH is a measure of intensity, not of capacity. That is, pH indicates the intensity of alkalinity or acidity in the same way temperature tells how hot something is but not how much heat the substance carries.

More specifically, pH is the negative of the logarithm of the hydrogen ion concentration of a solution. The hydrogen ion concentration is the weight of hydrogen ions, in grams, per liter of solution. In neutral water, for example, the hydrogen ion concentration is 107- grams per liter; the pH is therefore 7.

Since it is hydrogen that is responsible for acidity and alkalinity, the abbreviation "pH" stands for "potential of hydrogen." The neutral point of 7.0 actually indicates the presence of equal concentrations of free hydrogen and hydroxide ions.

phosphate - A salt of phosphoric acid. In the water industry, polyphosphates are used as sequestering agents to control iron and hardness and as coating agents to control corrosion by formation of a thin passivating film on metal surfaces.

The complex phosphates also are a group of sequestering agents widely used in detergent formulations (except where phosphates are banned by law) because of their superiority in chemical water softening, sequestering, and other builder functions.

Waters containing concentrations of iron, manganese, calcium, or magnesium sometimes can be treated with a sequestering agent such as polyphosphate and kept from depositing these mineral precipitates or scales for a period of time. However, polyphosphate sequestering is not permanent, and therefore may not be as effective as actually removing the iron, manganese, and hardness minerals, as is done with iron filters and ion exchange water softening, for example. The sequestering value of polyphosphates is destroyed when they revert (hydrate) to orthophosphate. Polyphosphate reversion or hydration to orthophosphate occurs naturally in water with time. Intentions would be for this reversion not to happen and not to drop the sequestered water hardness, iron, and manganese out until after it reaches the waste water. But, the polyphosphate reversion process can be accelerated by various uncontrolled conditions, such as low pH, high temperature, and the presence of the oxides of certain heavy metals, including iron, calcium, copper, and zinc in water. It is important in phosphate feed water treatment operations to: 1)maintain a stable pH within the phosphate product's performance rage. 2) determine the polyphosphate composition or blend that is most compatible with the specific water quality objectives and conditions, and 3) apply the appropriate dosage of phosphate to accommodate the system demand. Because of the difficulty in maintaining phosphate stabilities in the presence of varying pH, time, temperature, and metal oxides in most natural water supplies, the actual removal of iron, manganese, and water hardness is generally a more assuredly effective water treatment method.

physical stability - A measure of the ability of an ion exchanger or filter medium to resist breakdown by physical forces such as crushing, attrition, or high temperatures to which it may be subjected in use.

pK - A measure of the completeness of an incomplete chemical reaction, using a logarithmic scale. Also used to express the extent of dissociation of weak acids and complex ions. The weaker the electrolyte, the larger is its pK. The strengths of different acids may be compared by using pK values. Mathematically speaking, pK is the negative of the logarithm of the ionization (dissociation) constant (pKeq) of a chemical compound.

pneumatic tank - A pressurized holding tank which is part of a closed water system (such as for a household well system) and is used to create a steady flow of water and avoid water surges created by the pump kicking on and off.

POE - Point of entry.

point-of-entry (POE) treatment - Full service water treatment applied to the water entering a house or building for the purpose of reducing contaminants in the water distributed throughout the house or building (outside faucets may be excepted from treatment).

point-of-use (POU) treatment - Water treatment applied to a single tap used for the purpose of reducing contaminants in water at that one outlet. POU treatment is often used to treat water for drinking and cooking only.

polyvinyl chloride - A thermoplastic polymer resin material (-CH2CHCl-) that is rigid and practically chemically inert. Commonly used for water pipes and fittings, as well as numerous other services such as siding, gutters, raincoats, chemical containers, flooring, toys, tennis court surfaces, and films and package coatings for food containers.

population equivalent - A unit of measure used to express the strength of waste water from any source. (That is, not from household waste water only.) In making such calculations, 0.17 pounds of BOD (biological oxygen demand) per capita per day is often used as the standard figure. Thus, waste water with 17 pounds of BOD per day would have a population equivalent of 17 divided by 0.17 or 100 people.

porosity - A measure of the volume of pores in a material. Porosity is calculated as a ratio of the interstices of a material (e.g., the volume of spaces between the media particles in a filter bed) to the volume of its mass, and is expressed as a percentage.

portable exchange (PE) tanks - Tanks containing up to two cubic feet of ion exchanger products or filter media which are rented to homeowners or business clients with the beds fully-regenerated and ready for use. Portable exchange tanks do not have the valve controls required for regeneration. Upon exhaustion (determined by predetermined calendar days, meter, or monitoring device), the tanks are returned to a central regeneration plant where the resin or other media in each tank is reprocessed and restored for reuse. Portable exchange tanks may be available with water softening or deionization resins, mixed ion exchange media, manganese zeolite, activated alumina, and activated carbon. Portable exchange tanks are used for both household and commercial applications.

positive charge - The electrical potential of an atom which has lost one or more electrons, therefore leaving it with more protons than electrons. Cations carry positive charges. (See electron, cation).

post-chlorination - The application of chlorine to a water following other water treatment processes.

potable (drinking) water - A water supply which meets USEPA and/or state water quality standards and that is considered safe and fit for human consumption.

potassium chloride (KCl) - A colorless potassium salt which can be used as a regenerant in cation exchange water softeners and dealkalizers.

potassium permanganate (KMnO4) - Dark purple, odorless crystals (with a blue metallic sheen) that dissolve in water to produce a purple-red color. Potassium permanganate is a powerful oxidizing agent that is used in water treatment as both an oxidizer and a disinfectant. It is also an effective regenerant for manganese oxidizing filters.

POU - Point-of-use.

ppm - Parts per million.

ppb - Parts per billion.

ppt - Parts per trillion.

pre-chlorination - The application of chlorine to a water prior to other water treatment processes.

precipitate - 1. As a verb: to cause a dissolved substance to form a solid which comes out of solution and can be removed by settling or filtering. For example, the reduction of dissolved iron by oxidation, precipitation and filtration. 2. As a noun: the solid formed when a dissolved substance comes out of solution in such a way that it can be settled or filtered out. 3. As a verb: to cause moisture to condense and be deposited as rain, sleet, snow, etc.

precoat - The application of a granular filter medium, such as diatomaceous earth or powdered activated carbon to a membrane or screen or other filtration surface, prior to the service cycle of a filter.

pressure control - A switch which operates on changes in pressure. Usually this is a diaphragm pressing against a spring. When the force on the diaphragm overcomes the spring pressure, the switch is actuated (activated).

pressure differential - The difference in the pressure between two points in a water system. The difference may be due to the difference in elevation and/or to pressure drop resulting from water flow.

pressure drop - 1. A decrease in the water pressure (in psi) which occurs as the water flows. Pressure drop may occur for several reasons: internal friction between the molecules of water, external friction between the water and the walls of the piping system, or rough areas in the channel through which the water flows. 2. The difference between the inlet and outlet water pressure during water flow through a water treatment device such as a water conditioner. Abbreviated P and measured in pounds per square inch gauge pressure. Same as head loss.

psi - Pounds per square inch.

psig - Pounds per square inch guage.

public water system - A system for the provision to the public of piped water for human consumption, if such system has at least 15 service connections or regularly serves an average of at least 25 individuals daily at least 60 days out of the year. Such term includes: 1. any collection, treatment, storage, and distribution facilities under control of the operator of such system and used primarily in connection with such system; and 2. any collection or pretreatment storage facilities not under such control which are used primarily in connection with such system. A public water system is either a "community water system" or a "non-community water system."

PVC - Polyvinyl chloride.

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