Glossary of Terms - S
A B C D E F G H I J K L M N O P Q R S T U V W Z
sacrificial anode - An anode made of suitable metal placed in a water heater tank to protect the tank from corrosion. Anodes of metals such as aluminum, magnesium, or zinc are sometimes installed in water heaters and other tanks to control corrosion of the tank. The introduction of the anode creates a galvanic cell in which the magnesium or zinc will go into solution (be corroded) more quickly than the metal of the tank, thereby imparting a cathodic (negative) charge to the tank metal(s) and thus preventing tank corrosion. This corroding of the anode metal is called "the sacrifice of the anode".
Safe Drinking Water Act - The national legislation first passed by the U.S. Congress and signed into law by the President in 1974 and amended in 1986.
The SDWA directs the U.S. Environmental Protection Agency to promulgate and enforce standards for safe drinking water necessary to protect public health at public water systems serving 25 or more people for an average of 60 days per year. The law also contains provision for delegating primary enforcement responsibility to states and for protecting underground sources of drinking water.
saline water - Water containing an excessive amount of dissolved salts, usually over 1,000 mg/l.
salt - 1. Chemistry A chemical compound formed by the neutralization of an acid with a base. For example, H2SO4 (acid) + 2NaOH (base) = Na2SO4 (salt) + 2H2O (water). 2. Water Treatment Sodium chloride (NaCl) or potassium chloride (KCl), both of which are used in solution during the regeneration of cation exchange water softeners and some dealkalizers. 3. Common table salt, which is sodium chloride (NaCl).
salt mushing - See mushing.
sanitize - To reduce the number of bacterial contaminants to safe levels as judged by public health requirements. To make clean and free or inactivation of dirt, filth, and conditions injurious to health. Generally considered to reduce germ count by 50 to 99.9 percent. The USEPA requires that sanitizing claims must show a 99.9 percent microbial reduction in five minutes.
scale - A deposit of mineral solids on the interior surfaces of water lines and containers, forming when water containing the carbonates or bicarbonates of calcium and magnesium is present, especially when heated. To see what scale looks like in a pipe click here. Picture of Scale.
sedimentation - The process in which solid suspended particles settle out of water, usually when the water has little or no movement. Also called "settling".
semi-permeable membrane - Typically a thin, organic film which allows the passage of some ions or materials while preventing the passage of others. Some membranes will only allow the passage of cations. (See electrodialysis.) Some membranes reject most dissolved substances, but allow the passage of water. (See reverse osmosis.)
septic - A condition produced by bacteria when all oxygen supplies are depleted. If severe, bottom deposits appear and water turns black, gives off foul odors, and the water has a greatly increased chlorine demand.
sequestering agent - 1. A chemical that forms complexes with metallic ions in solution so that the metallic ions may no longer be precipitated. For example, calcium soap precipitates are not produced from hard water treated with sodium hexametaphosphate. Note however, the tendency for condensed phosphate polymers, such as hexametaphosphates, may be to hydrate in water, especially under conditions of high temperature or high pH, and thereby revert to a simpler and stable phosphate form, such as orthophosphate which can no longer sequester the hardness and metal ions. 2. Any agent that prevents an ion from exhibiting its usual properties because of close combination with an added material. (See chelating agent.)
sequestration - A chemical reaction in which certain ions are bound into a stable, water soluble compound, thus preventing undesirable action by the ions. (See chelate.)
service run - That portion of the operating cycle of a water conditioning unit in which treated water is being delivered, as opposed to the period when the unit is being backwashed, recharged or regenerated.
service unit - A term sometimes applied to softeners or filters which are regenerated or backwashed at a central point, then transported to the point of use for connection to the water system. (See PE, portable exchange.)
shielded - The separation of metallic parts by an electrical nonconductor; insulated by other than an air gap.
silica gel or siliceous gel - A synthetic hydrated sodium aluminosilicate with ion exchange properties, once widely used in ion exchange water softeners. (See zeolite, gel zeolite.)
sludge - The solids which are separated from water during processing.
slug - An temporary abnormally high concentration of an undesirable substance which passes through a water system, usually brief or intermittent in nature, and often related to an upset of a system. For example, a slug of iron may occur during high flow which disturbs and suspends previously deposited iron precipitates.
soap - One of a class of chemical compounds which possesses cleansing properties; formed by the reaction of a fatty acid with a base or alkali. Sodium and potassium soaps are soluble and useful, but can be converted to insoluble calcium and magnesium soaps (curd) by the presence of these hardness ions in water.
soap curd - The insoluble precipitate that forms when soap is used in hard water.
soda ash (Na2CO3) - the common name for sodium carbonate, a chemical compound used to neutralize acid water, and as an alkalinity builder in some soap and detergent formulations, and in the lime-soda ash water softening process.
sodium (Na+) - A metallic element found abundantly in compounds in nature, but never existing alone. Sodium compounds are highly soluble and do not form curds when used with soaps or detergents. Many sodium compounds are used in the water treatment industry. Most notable is the use of sodium chloride as a regenerant in the cation exchange water softening process.
sodium chloride (NaCl) - The chemical name for common salt, widely used in the regeneration of ion exchange water softeners.
sodium cycle - The cation exchange process in which sodium on the ion exchange resin is exchanged for hardness and other ions in water. Sodium chloride is the common regenerant used in this process.
sodium hydrosulfite (Na2S2O4) - A crystalline salt which is a strong reducing agent and the main ingredient in several resin cleansers that are used to clean iron-fouled ion exchange resin beds.
sodium hydroxide (NaOH) - A strong alkaline compound used as a regenerant for anion exchange resin in deionization systems and for the pH modification of low pH (acid) water. Sodium hydroxide is also called caustic, caustic soda, or lye.
sodium hypochlorite (NaOCl) - Liquid bleach; used as a source of chlorine in water treatment. Laundry bleach available from grocery stores is 5.25 percent chlorine and commercial strength bleach available from swimming pool suppliers or chemical companies is usually 12.5 percent chlorine.
soft water - Any water which contains less than 1.0 gpg (17.1 mg/l) of hardness minerals, expressed as calcium carbonate
softened water - Any water that is treated to reduce hardness minerals to 1.0 gpg (17.1 mg/l) or less, expressed as calcium carbonate.
solar salt - Common salt which is produced by solar evaporation in shallow ponds or lagoons and used in water softener regeneration.
solenoid shutoff valve - An electrical device operated by a magnetic coil to make the valve either open for flow or close to shut off water flow. This type of valve is used extensively for flow control and direction on many water processing systems.
solute - The substance which is dissolved in and by a solvent. Dissolved solids, such as the minerals found in water, are solutes.
solution feeder - A device, such as a power driven pump or an eductor system, designed to feed a solution of a water treatment chemical into the water system, usually in proportion to flow. (See chemical feeder.)
solvent - The liquid, such as water, in which other materials (solutes) are dissolved. (See solute.)
specific conductance - The measure of the electrical conductance of water or a water solution at a specific temperature, usually 25oC. (See resistance.)
specific gravity - The ratio of the weight of a specific volume of a substance compared to the weight of the same volume of pure water at 4oC.
specific resistance - The measure of the electrical resistance of water or a water solution at a specific temperature, usually 25oC. (See resistance.)
sphericity - A measure of the roundness and wholeness of an ion exchange resin product or other bead form absorbent or filter medium.
spore - A small reproductive body, often single-celled, capable of reproducing the organism under favorable conditions. The spore is sometimes considered the resting stage of the organism. Among the organisms that may produce spores are algae, bacteria, and certain protozoa’s. In water, most spores resist adverse conditions which would readily destroy the parent organism.
stability index - See Langelier's Saturation Index.
Standard Methods - The abbreviation for the name of the reference book "Standard Methods for the Examination of Water and Wastewater", widely used in water and waste water testing and analysis.
static - Fixed in position, resting, or without motion, as opposed to dynamic or moving.
static system - A system or process in which the reactants are not flowing or moving.
sterilization - A process in which all living organisms are destroyed. (See disinfection.)
sulfate-reducing bacteria - A group of bacteria which are capable of reducing sulfates in water to hydrogen sulfide gas, thus producing obnoxious tastes and odors. These bacteria have no sanitary significance, and are classed as nuisance organisms.
sulfonic acid (-SO2OH) - A specific acidic group which forms the exchange site active group in certain cation exchange resins and gives these resins their ion exchange capability.
sulfur (S) - A yellowish solid element. The term is also commonly used to refer to sulfur water (water containing hydrogen sulfide gas).
superchlorination - The addition of excess amounts of chlorine to a water supply to speed chemical reactions or insure disinfection with short contact time. The chlorine residual following super-chlorination is high enough to be unpalatable, and thus de-chlorination is commonly employed before the water is used.
supernatant - Liquid removed from settled sludge. Supernatant commonly refers to the liquid between the sludge on the bottom and the water surface of a basin or container.
surface-active agent - A surface-active substance that when added to water lowers surface tension and increases the "wetting" capabilities of the water. Reduced surface tension allows water to spread and to penetrate fabric or other substances to be washed or cleaned. There are three categories of surfactants: detergents, wetting agents, and emulsifiers. "Surfactant" is a contraction for surface-active agent.
surface tension - The result of attraction between molecules of a liquid which causes the surface of the liquid to act as a thin elastic film under tension. Surface tension causes water to form spherical drops, and to reduce penetration into fabrics. Soaps, detergents and wetting agents reduce surface tension and increase penetration by water.
surfactant - A contraction of the term "surface-active agent".
suspended solids - Solid particles in water which are not in solution.
swelling - In the water treatment context, the expansion of certain ion exchange resins when converted into specific ionic state.
syndet - A contraction of the term "synthetic detergent".
synthetic detergent - A synthetic cleaning agent, such as linear alkyl sulfonate and alkyl benzene sulfonate. Synthetic detergents react with water hardness, but the products are soluble.