XLPE – cross-linked polyethylene.
x-rays – 1. Electromagnetic radiation with a very short wavelength (0.01 to 12 nanometers), shorter than ultraviolet radiation. 2. An image created by short-term exposure of an object to x-rays used in spectrometry analysis and medical therapy.
yield – l. The amount of product water produced by a water treatment process. 2. The quantity of water (expressed as a rate of flow-GPM, GPH, GPD, or total quantity per year) that can be collected for a given use from surface or groundwater sources. The yield may vary with the use proposed, with the plan of development, and also with economic considerations.
zeolites – Hydrated sodium alumina silicates, either naturally-occurring mined products or synthetic products, with ion exchange properties. Zeolites were formerly used extensively for residential and commercial water softening but have been largely replaced by synthetic organic cation resin ion exchangers of polystyrene divinylbenzene substrate. Modified zeolites such as manganese greensand and synthetic manganese zeolites are still used as catalyst/oxidizing filters for the removal of iron, hydrogen sulfide, and manganese.
zeolite softening – A term formerly used for the removal of calcium and magnesium hardness from water by base exchange using natural or synthetic zeolites. Since the introduction of synthetic organic cation exchange resins, the more correct term is cation exchange softening. Zeolite softening was also called base exchange.
zero discharge water – A discharge limit applied to manufacturing and commercial establishments in which only normal human sanitary waste waters may be discharged to the municipal sewerage system. All other types of waste water, such as that water used in manufacturing processes, are not included in zero discharge water; but they must be recycled, and the resulting waste product from such water must be taken to an alternate and approved disposal facility.
zero soft water – water produced by the cation exchange process and measuring less than 1.0 grain per U.S. gallon (17. 1 ppm or 17. 1 mg/L) as calcium carbonate. zeta potential-The electrical potential which exists across the interface of all solids and liquids. The potential represents the difference in voltage between the surface of the diffuse layer surrounding a colloidal particle and the bulk liquid beyond. Also known as electrokinetic potential.
zone of aeration – The comparatively dry soil or rock located between the ground surface and the top of the water table.
zone of saturation – The layer in the ground in which all available interstitial voids (cracks, crevices, holes) are filled with water. The level of the top of this zone is the water table. SEE ALSO water table.
zooplankton – Small, usually microscopic animals (such as protozoans), found in lakes and reservoirs.