Water Purifiers Proaudio55 (Own work) [CC BY-SA 3.0 ( via Wikimedia Commons

Water Purification: Local water is never sufficiently pure for medical and laboratory use. All water must be treated to;  Remove bacteria, viruses and micro- organisms  Improve turbidity  Alter pH  Remove minerals & ions

Clinical Use Samples preparation Mixed with medicine for patients (IV solutions) Equipment that requires deionized water Patient washing Food preparation

Clinical Use Water impurities: –Parasites –Bacteria –Viruses –Organic compounds –Ions

Common treatment methods: Filtering Boiling Distillation Sterilization Reverse Osmosis UV light Carbon filtering Deionization

Water Purification Common treatment methods: Filtering Boiling Distillation Sterilization Reverse Osmosis UV light Carbon filtering Deionization Ultrafiltration

Principles of Operation Parts: –Inlet –Outlet –Vent –Filter –Drains

Principles of Operation Distillation –Heating water in a still to its boiling point and condensing the resulting steam to water again

Principles of Operation Distillation limitations –“Bumping” can take place (liquid water shoots out of the boiler directly into the condenser) –Large amount of energy and water Robert Malkin (2006), Medical Instrumentation in the Developing World [pdf]. Retrieved from library.ewh.org

Principles of Operation Ion Exchange –A harmless water ion is used to replace a harmful one –Greatly impact the water treatment industry (1903) –Used to remove lead, mercury, and other heavy metals from water

Principles of Operation Ion Exchange –Reversible process in which impurity ions present in the water are replaced by ions released by an ion-exchange resin beads –Softening and deionization methods Robin Muller (2009), Ion Exchanger [photograph]. Retrieved from auscher.jpg

Principles of Operation Softening Ion Exchange –Reduce water hardness prior to reverse osmosis processing –Contain beads that exchange two sodium ions for every calcium or magnesium ion removed from the "softened" water Fuse School (2014), Making Hard Water Soft [video]. Retrieved from

Principles of Operation Deionization Ion Exchange –Exchange either hydrogen ions for cations or hydroxyl ions for anions

Principles of Operation Deionization limitations –Cannot be used to remove particles, pyrogens (fever causing substances) or bacteria –Can release resin particles into the water (which serve as a culture medium for bacteria growth)

Principles of Operation Electrodeionization –Combination of electrodialysis and ion exchange –Effectively deionizes water –Requires prefiltration to prevent clogging of the cells

Principles of Operation Electrodeionization Commonshelper2 (2009), Electrodialysis [image]. Retrieved from

Principles of Operation Ultraviolet (UV) Radiation –Mercury, low-pressure lamps generate 254 nm of ultraviolet light –Destroys the DNA and other proteins in the bacteria, parasites and viruses (sterile water)

Principles of Operation Ultraviolet (UV) Radiation –Besides 254 nm, some lamps generate both 185 nm UV light to decomposes the organic molecules SteriPen Traveler UV Light Sterilizes In Seconds $60 Coronium [CC BY-SA 2.5 ( CC BY-SA 3.0 ( sa/3.0) or GFDL ( via Wikimedia Commons

Principles of Operation Ultraviolet (UV) limitation –Dead organisms are not removed from the water –Particles or clumps of microorganisms can cause shadowing

Principles of Operation Carbon Adsorption –Controlled by the diameter of the pores in the carbon filter and by the diffusion rate of organic molecules through the pores –Removes nonionic, organic molecules and free chlorine –Sterilize intravenous solutions, serums and antibiotics

Principles of Operation Carbon Adsorption –Protects other purification media in the system that may be sensitive to oxidants –Placed upstream (before the ion- exchange filter)

Principles of Operation Carbon Adsorption advantages –Long life Carbon Adsorption limitations –Can release carbon particles into the water

Principles of Operation Filtration –Removes particles from the water based on their size –Depth, screen and surface approaches

Principles of Operation Filtration - Depth –Matted fibers or materials compressed to form a matrix that retains particles by random adsorption or entrapment –Used as prefilters because they are economical and can remove nearly all (perhaps 98%) of the suspended solids

Principles of Operation Filtration - Surface –Multiple layers of media –Very efficient, removing almost all of the suspended solids (99.99%) –Used as either prefilters or clarifying filters HealthBody 2014), How to Make a Survival Water Filter [video]. Retrieved from

Principles of Operation Filtration - Screen –Single layer, uniform structures which retain all particles larger than a controlled pore size –Particles are retained on one surface of the screen filter

Principles of Operation Filtration –Depth filters are often used to pre-treat water by removing up to 98% of the suspended impurities in water that might foul or clog other parts of the filter system – Surface filters remove up to 99.9% of suspended contaminants and may be used as a pre-filter or a final clarifying filter –Screen filters are placed at the end of the filtration system to remove the last remaining traces of resin, carbon and microorganisms

Principles of Operation Filtration advantages –Almost no maintenance Filtration limitations –Filters must be replaced occasionally –Will not remove dissolved inorganics, pyrogens (fever-producing substance), colloidals (gold, silver, zinc and copper) or viruses

Principles of Operation Ultrafiltration –Pore sizes lie in the range μm (100 to 10 times smaller than typical screen or surface filters)

Principles of Operation Ultrafiltration removes: –Particulates –Micro-organisms including all parasites and bacteria and some viruses –Inorganic colloids –Large organic molecules including pyrogens Ultrafiltration limitations: –Can not remove dissolved inorganics, such as calcium, sodium and chloride

Principles of Operation Reverse Osmosis –Most economical and efficient method for purifying –Removing 90% to 99% of all contaminants –Reverse osmosis membranes is even finer than ultrafiltration –The semi-permeable membrane rejects salts (ions) by a charge phenomena action

Principles of Operation Reverse Osmosis Colby Fisher (2013), Simplified RO Schematic [image]. Retrieved from

Principles of Operation Reverse Osmosis rejects: –Practically all particles –Bacteria –Viruses –Organics greater than 300 Daltons in molecular weight

Principles of Operation Reverse Osmosis limitations –Slow flow rates

Commercial Examples Proaudio55 (Own work) [CC BY-SA 3.0 ( via Wikimedia Commons

Commercial Examples Google Shopping (2016), Medical Water Purifiers [screenshot]. Retrieved from google.com

Clogged filters -Low flow rate -Some can be cleaned by backflushing with pure water Leaks -Repair with epoxy or a silicone sealant (temporally) -Replace tubing (definitive) Common Problems

Deionizer fails -Regenerate or replace resin bed Deposits plug system -Clean deposits Common Problems

Flow rate test: -Check with a measuring cup or graduated cylinder and a watch Purity test: -Check protein content in a spectrophotometer -Check ion content by measuring the conductivity Test Procedures Sterility test: -Cell culture check

Testing: Water systems are usually not tested regularly in developing nations Flow can be tested easily Some portions of a system can be checked visually Most functions will require specialized equipment You may be able to work with lab staff or director to help solve problems or recommend routine testing

Questions ?