List of Water Treatments
Tap – On demand source; no feedwater waste occasional lab use, general office use, potable, sanitation Quality and content varies according to location Contains VOCs and microbial contaminants Boiling water will kill microorganisms, however it does not remove dissolved ions or particulates.
Filtered – On demand source; occasional lab use, potable Two chief filters of use to conservators are particulate filters and activated charcoal filters.: Amount of feedwater waste correlates with type of filter used. Waste is generally lower than distilled, deionized or reverse osmosis processes. Varying degrees of VOCs and microbial contaminants are removed depending on the filter employed.
Distilled – prepared by heating tap water to create steam. The condensate is collected as product. Distilled is not an on demand source, so it must be made in advance and stored. If the storage container is not made of an inert material, plasticizers will leach out of it and recontaminate the water. Distillation removes all metals, anions, cations, and microorganisms. Distillation eliminates nearly all VOCs. Distillation produces small amounts of water very slowly and uses large amounts of energy and is wasteful of water. Up to 95% waste of feed water; 5% pure product
Deionized can produce moderate volumes of purified water on-demand. While it doesn't produce absolutely pure water, it is convenient and quick, and may be sufficient for many applications. It is an excellent system for removing dissolved solids and gases, although it has a generally poor rating for other impurities. Amount of feedwater waste is much lower than distilled or reverse osmosis, however filters that are re-usable require considerable amounts of water for cleaning purposes. For ultrapure product, deionization systems are often combined with reverse osmosis (RO) systems.
ElectroDeIonized (EDI) water is a continuous water treatment process that removes ionizable species from liquids using voltage applied across a cell. It differs from conventional deionization techiniques in that it is does not require the use of acid, caustic soda, or other chemicals. Deionization can be done continuously and inexpensively using electodeionization.
Reverse Osmosis – depending on system, approx 75% of feedwater is recovered as pure water. While the percentage of feedwater to recovered water is large, the process is very efficient in removing contaminants: RO can remove mineral salts as well as contaminants such as bacteria and pesticides. Reverse osmosis eliminates nearly all VOCs and provides high quality purified water which is suitable for many routine laboratory purposes Product may be prepared in advance and stored for use. The amount of water on demand may be limited by the size of the storage container. If the storage container is not made of an inert material, plasticizers will leach out of it and recontaminate the water.
High Efficiency Reverse Osmosis (HERO) is a proprietary system originally developed to provide ultrapure water. This process was developed for the microelectronics industry. HERO has several potential advantages over conventional RO including greater water recovery – between 95% to 99 %, higher quality product, higher quantity output, and generally lower costs. This is achieved by chemical pretreatment of the feed water undergoing RO. More efficient system than RO, so costs are about 20%–40% less than operating a conventional RO system.
ElectroDeIonization (EDI) is commonly used in conjunction with reverse osmosis (RO) process for ultrapure water. The combination is known as Reverse Osmosis ElectroDeIonization (RO/EDI). Feedwater is first treated by RO. Recovered water is then sent through an electrodeionization cell where voltage is applied across the cell. Output is ultrapure water.
Ultraviolet oxidation is another method that works well as an addition to other systems. It does a good job eliminating bacteria. It works by the use of ultraviolet radiation at the biocidal wavelength of 254 nanometers, which is ‘murder’ on bacteria. For more in depth discussion of water quality and application, see the Paper Conservation Catalogue, Chapter 16 Water; Quality/Purity (pp. 13 – 16 or 16.3.1).
This wiki was created and is maintained by the Sustainability Committee (formerly the Committee on Sustainability in Conservation Practice). It is intended to provide information for AIC members and other interested parties. Any treatment should be carried out by a qualified conservator(find a conservator ). Please send comments and suggestions for sustainable practices to sustainability(a)conservation-us.org.