Water Purification Methods - Final Rinsing Surgical Instruments
Source Water - Rinse Cycles Washer Decontaminators Disinfectors
Problems associated with low quality source water can include poor quality cleaning as well as the staining, pitting and corrosion of surgical instruments. If poor quality source water is used for the "Final Rinse" cycle of an automated surgical instrument washer (decontaminator, disinfector) mineral residues can remain on the instruments. This residue will then be baked onto the instruments during the "Hot Air Dry" cycle that follows. The problems caused by poor quality source water can be treated chemically using washer chemicals or by installing a DI or RO water purification system. To determine the quality of source water testing should be performed during mid summer and mid winter due to the normally wide deviations of water conditions.
Keywords:
Deionization
Deionized water (DI) de-ionized water, DI Water
Reverse osmosis (RO), RO Water
Water purification the removal of contaminants
Disinfection Disinfecting Water
Neutral pH Values
Final Rinse Water
Surgical Instrument Washer Instrument Stains
Surgical Instrument Residue
Deionization
Process utilizing specially-manufactured ion exchange resins which remove ionized salts from water can theoretically remove 100% of salts. Deionization typically does not remove organics, virus or bacteria, except through “accidental” trapping in the resin and specially made strong base anion resins which will remove gram-negative bacteria.
Deionized water (DI water or de-ionized water) also spelled deionized water, see spelling differences) is water that lacks ions, such as cations from sodium, calcium, iron, copper and anions such as chloride and bromide. This means it has been purified from all other ions except H3O+ and OH−, but it may still contain other non-ionic types of impurities such as organic compounds. This type of water is produced using an ion exchange process. Deionized water is similar to distilled water, in that it is useful for scientific experiments where the presence of impurities may be undesirable.
Reverse osmosis (RO) is the process of pushing a solution through a filter that traps the solute on one side and allows the pure solvent to be obtained from the other side. More formally, it is the process of forcing a solvent from a region of high solute concentration through a membrane to a region of low solute concentration by applying a pressure in excess of the osmotic pressure. This is the reverse of the normal osmosis process, which is the natural movement of solvent from an area of low solute concentration, through a membrane, to an area of high solute concentration when no external pressure is applied. The membrane here is semipermeable, meaning it allows the passage of solvent but not of solute. The membranes used for reverse osmosis have a dense polymer barrier layer in which separation takes place. In most cases the membrane is designed to allow only water to pass through this dense layer while preventing the passage of the solute (such as salt). This process requires that a high pressure be exerted on the high concentration side of the membrane, usually 2–14 bar (30–200 pounds per square inch) for fresh and brackish water, and 40–70 bar [(600–1000 psig)] for seawater, which has around 24 bar (350 psi) natural osmotic pressure which must be overcome.
Water purification is the removal of contaminants
from raw water to produce drinking water that is pure enough for human consumption or for industrial use. Substances that are removed during the process include parasites ( such as Giardia or Cryptosporidium) , bacteria, algae, viruses, fungi, minerals (including toxic metals such as Lead, Copper etc.), and man-made chemical pollutants. Many contaminants can be dangerous—but depending on the quality standards, others are removed to improve the water's smell, taste, and appearance. A small amount of disinfectant is usually intentionally left in the water at the end of the treatment process to reduce the risk of re-contamination in the distribution system.
Many environmental and cost considerations affect the location and design of water purification plants. Groundwater is cheaper to treat, but aquifers usually have limited output and can take thousands of years to recharge. Surface water sources should be carefully monitored for the presence of unusual types or levels of microbial/disease causing contaminants. It is not possible to tell whether water is safe to drink just by looking at it. Simple procedures such as boiling or the use of a household charcoal filter are not sufficient for treating water from an unknown source. Even natural spring water—considered safe for all practical purposes in the 1800s—must now be tested before determining what kind of treatment is needed.
pH adjustment
The manufacturers of Surgical Instruments unanimously recommend using Neutral pH chemicals when cleaning surgical Instruments. If the water is acidic, lime or soda ash is added to raise the pH. Lime is the more common of the two additives because it is cheaper, but it also adds to the resulting water hardness. Making the water slightly alkaline ensures that coagulation and flocculation processes work effectively and also helps to minimize the risk of lead being dissolved from lead pipes and lead solder in pipe fittings. The pH should approximate 7 when being used to clean surgical instruments.
pH values
pH is a logarithmic measurement of proton presence; the true pH of deionized water is 7.0, because the ionization constant of water (KW) ~ 10-14, so p[KW] = 14, and pH + pOH = p[KW]. In practice, the indication from chemical indicators can give a value of usually between pH 5.0 and pH 9.0 depending on the indicator used (the indication being the ions introduced by the indicator itself, its solvent and its impurities). Electronic pH meters will output an unpredictable value since the absence of ions in the liquid means that the two parts of the electrode are insulated from each other and thus would generate no EMF. In practice since absolutely pure water is an unattainable goal, the liquid will contain a very small amount of ions, but the current this would allow the probe to generate will be far smaller than that required to operate the metering circuit. pH meter electrodes should not be immersed in deionized water for prolonged periods as the lack of any ions 'sucks' them out of the electrode degrading its performance. Deionized water should be used for cleaning only rarely as the effect is cumulative. Electrodes should be cleaned using proper cleaning solution (usually very acidic), and rinsed between samples in a pH neutral liquid such as tap water or pH 7.0 buffer solution (but ideally in the next sample to be tested). Deionized water will quickly acquire a pH when exposed to air. Carbon dioxide, present in the atmosphere, will dissolve in the water, introducing ions and giving an acidic pH of around 5.0. The limited buffering capacity of DI water will not inhibit the formation of carbonic acid H2CO3. Boiling the water will remove the carbon dioxide to restore the absence of a pH value.
Disinfection is normally the last step in purifying drinking water. Water is disinfected to destroy any pathogens which pass through the filters. Possible pathogens include viruses, bacteria, including Escherichia coli, Campylobacter and Shigella, and protozoans, including G. lamblia and other Cryptosporidia. In most developed countries, public water supplies are required to maintain a residual disinfecting agent throughout the distribution system, in which water may remain for days before reaching the consumer. Following the introduction of any chemical disinfecting agent, the water is usually held in temporary storage - often called a contact tank or clear well to allow the disinfecting action to complete.
1. Chlorine- The most common disinfection method is some form of chlorine or its compounds such as chloramine or chlorine dioxide. Chlorine is a strong oxidant that kills many micro-organisms.
Because chlorine is a toxic gas, there is a danger of a release associated with its use. This problem is avoided by the use of sodium hypochlorite, which is either a relatively inexpensive solid that releases free chlorine when dissolved in water or a liquid (bleach)that is typically generated on site using common salt and high voltage DC. Handling the solid, however, requires greater routine human contact through opening bags and pouring than the use of gas cylinders which are more easily automated. The generation of liquid sodium hypochlorite is both inexpensive and safer than the use of gas or solid chlorine. Both disinfectants are widely used despite their respective drawbacks. A major drawback to using chlorine gas or sodium hypochlorite is that they react with organic compounds in the water to form potentially harmful levels of the chemical by-products trihalomethanes (THMs) and haloacetic acids, both of which are carcinogenic and regulated by the U.S. Environmental Protection Agency (EPA). The formation of THMs and haloacetic acids is minimized by effective removal of as many organics from the water as possible before disinfection. Although chlorine is effective in killing bacteria, it has limited effectiveness against protozoans that form cysts in water. (Giardia lamblia and Cryptosporidium, both of which are pathogenic).
2. Chlorine dioxide is another fast-acting disinfectant. It is, however, rarely used, because it may create excessive amounts of chlorate and chlorite, both of which are regulated to low allowable levels. Chlorine dioxide also poses extreme risks in handling: not only is the gas toxic, but it may spontaneously detonate upon release to the atmosphere in an accident.
3. Chloramines are another chlorine-based disinfectant. Although chloramines are not as effective as disinfectants, compared to chlorine gas or sodium hypochlorite, they are less prone to form THMs or haloacetic acids. It is possible to convert chlorine to chloramine by adding ammonia to the water along with the chlorine: The chlorine and ammonia react to form chloramine. Water distribution systems disinfected with chloramines may experience nitrification, wherein ammonia is used a nitrogen source for bacterial growth, with nitrates being generated as a byproduct.
4. Ozone (O3) is a relatively unstable molecule of oxygen which readily gives up one atom of oxygen providing a powerful oxidising agent which is toxic to most water borne organisms. It is a very strong, broad spectrum disinfectant that is widely used in Europe. It is an effective method to inactivate harmful protozoans that form cysts. It also works well against almost all other pathogens. Ozone is made by passing oxygen through ultraviolet light or a "cold" electrical discharge. To use ozone as a disinfectant, it must be created on site and added to the water by bubble contact. Some of the advantages of ozone include the production of relatively fewer dangerous by-products (in comparison to chlorination) and the lack of taste and odor produced by ozonation. Although fewer by-products are formed by ozonation, it has been discovered that the use of ozone produces a small amount of the suspected carcinogen Bromate, although little Bromine should be present in treated water. Another one of the main disadvantages of ozone is that it leaves no disinfectant residual in the water. Ozone has been used in drinking water plants since 1906 where the first industrial ozonation plant was built in Nice, France. The U.S. Food and Drug Administration has accepted ozone as being safe; and it is applied as an anti-microbiological agent for the treatment, storage, and processing of foods.
5. UV radiation (light) is very effective at inactivating cysts, as long as the water has a low level of colour so the UV can pass through without being absorbed. The main drawback to the use of UV radiation is that, like ozone treatment, it leaves no residual disinfectant in the water.
Because neither ozone nor UV radiation leaves a residual disinfectant in the water, it is sometimes necessary to add a residual disinfectant after they are used. This is often done through the addition of chloramines, discussed above as a primary disinfectant. When used in this manner, chloramines provide an effective residual disinfectant with very little of the negative aspects of chlorination.
Other water purification techniques
Other popular methods for purifying water, especially for local private supplies are listed below. In some countries some of these methods are also used for large scale municipal supplies. Particularly important are distillation (de-salination of seawater) and reverse osmosis.
1. Boiling: Water is heated hot enough and long enough to inactivate or kill micro-organisms that normally live in water at room temperature. Near sea level, a vigorous rolling boil for at least one minute is sufficient. At high altitudes (greater than two kilometers or 5000 feet) three minutes is recommended. US EPA emergency disinfection recommendations In areas where the water is "hard" (that is, containing significant dissolved calcium salts), boiling decomposes the bicarbonate ions, resulting in partial precipitation as calcium carbonate. This is the "fur" that builds up on kettle elements, etc., in hard water areas. With the exception of calcium, boiling does not remove solutes of higher boiling point than water and in fact increases their concentration (due to some water being lost as vapour). Boiling does not leave a residual disinfectant in the water. Therefore, water that has been boiled and then stored for any length of time may have acquired new pathogens.
2. Carbon filtering: Charcoal, a form of carbon with a high surface area, absorbs many compounds including some toxic compounds. Water passing through activated charcoal is common in household water filters and fish tanks. Household filters for drinking water sometimes contain silver to release silver ions which have a bactericidal effect.
3. Distillation involves boiling the water to produce water vapour. The vapour contacts a cool surface where it condenses as a liquid. Because the solutes are not normally vaporised, they remain in the boiling solution. Even distillation does not completely purify water, because of contaminants with similar boiling points and droplets of unvaporised liquid carried with the steam. However, 99.9% pure water can be obtained by distillation. Distillation does not confer any residual disinfectant and the distillation apparatus may be the ideal place to harbour Legionnaires' disease.
4. Reverse osmosis: Mechanical pressure is applied to an impure solution to force pure water through a semi-permeable membrane. Reverse osmosis is theoretically the most thorough method of large scale water purification available, although perfect semi-permeable membranes are difficult to create. Unless membranes are well-maintained, algae and other life forms can colonise the membranes.
5. Ion exchange: Most common ion exchange systems use a zeolite resin bed to replace unwanted Ca2+ and Mg2+ ions with benign (soap friendly) Na+ or K+ ions. This is the common water softener.
6. Electrodeionization: Water is passed between a positive electrode and a negative electrode. Ion selective membranes allow the positive ions to separate from the water toward the negative electrode and the negative ions toward the positive electrode. High purity deionized water results. The water is usually passed through a reverse osmosis unit first to remove non-ionic organic contaminants.
7. The use of iron in removing arsenic from water. See Arsenic contamination of groundwater Water purification solutions.
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The manufacturers of stainless steel surgical instruments are consistent in their recommendations for the "proper sequence of cleaning treatments" to optimize the care of surgical instruments and the sterilization of reusable surgical instruments.
Surgical Instrument Detergents Cleaners Lubricants:
The foundation of their recommendations are based on a sequence of chemical and mechanical treatments which include using: Neutral pH chemicals, combination cleaning agents (enzymatic instrument cleaners, enzyme surgical instrument detergents), cold water pre-wash, elevated temperature detergent cleaning, redundant purified water rinses, and elevated temperature (above boiling point) hot air drying.
Water Purification Methods
Final Rinsing Surgical Instruments
Source Water for Rinsing Surgical Instruments
Rinse Cycles Washer Decontaminators Disinfectors
