07/03/18. Laboratory Water and Water Purification Systems. Water in the Laboratory. Sources of Water and Water Contamination. Contaminants in Water

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1 Laboratory Water and Water Purification Systems KMU 392 Chemical Process Industries March 2018 Water in the Laboratory Water is the most commonly used solvent in laboratories and constitutes often more than 99% of the mass of solutions used in experimentations. The quality of water used in the lab is therefore critical for the success of the tests performed. Tap water has far too many contaminants to be used in laboratories or for scientific purposes. Purification processes are necessary! H 2 O Sources of Water and Water Contamination Surface water (rivers, lakes, streams, reservoirs, oceans) Ground water Contaminants in Water Contaminant is any substances you do not want in your water. These are also called impurities. Particulates, Dissolved inorganic (solids and gases), Dissolved organics, Microorganisms, DNA, RNA and pyrogens. Inorganic Ions: cations, such as sodium, calcium, magnesium or iron, and anions, such as bicarbonate, chloride and sulfate. Organics: biologically originated molecules including humic acids, tannins, and synthetic phthalates esters plasticizers. Particulates and Colloids: soft particulates (vegetal debris) and hard particulates (sand, rock). Bacteria and their by-products: living microorganisms, by-products, such as pyrogens and nucleases. Gases: nitrogen, oxygen and carbon dioxide. 1

2 Laboratory Water Quality Standards Technical standards on water quality have been established by a number of organizations For laboratory applications; The American Society for Testing and Materials (ASTM ) The International Organization for Standardization (ISO 3696) For clinical laboratories: Type 3 Lab Water Grades Type 3 water is the lowest laboratory water grade, recommended for glassware rinsing, heating baths and filling autoclaves, or to feed Type 1 lab water systems. The Clinical and Laboratory Standards Institute (CLSI) Type 2 Lab Water Grades Type 1 Lab Water Grades Type 2 water is the grade used in general laboratory applications such as buffers, ph solutions and microbiological culture media preparation; as feed to Type 1 water systems, clinical analyzers, cell culture incubators and for preparation of reagents for chemical analysis or synthesis. Type 1 water is the grade required for critical laboratory applications such as HPLC mobile phase preparation, blanks and sample dilution in GC, HPLC, AA, ICP-MS and other advanced analytical techniques; preparation of buffers and culture media for mammalian cell culture and IVF (in vitro fertilization); production of reagents for molecular biology applications (DNA sequencing, PCR); and preparation of solutions for electrophoresis and blotting. Water specifications based on the different water types Examples of different standards ISO specification for water for laboratory use: ISO 3696: 1987 ASTM standard specification for Reagent Grade Water: ASTM D Parameters: Conductivity (µs/cm) Resistivity (MΩ-cm) Acidity/Alkalinity (ph) Total dissolved solids (TDS) Total organic carbon (TOC) Chemical oxygen demand (COD) Biological oxygen demand (BOD) Colony forming units per milliliter (CFU/ml) Etc Important parameters BECAUSE... Ions are primary contaminants Purity Presence of Ions Ultrapure water: Max. Conductivity=0.056 µs/cm Min. Resistivity=18.31 MΩ-cm Pharmacopoeia requirements for purity of 'purified water' *Requires the use of 0.2µm membrane filter ** Prepared by distillation *** Requires the use of a 0.45µm membrane filter 2

3 Lab Water Systems Distilled and Bidistilled Water Systems Type II and Type III Method: Distillation Deionized Water Systems Type I Method: Ion-exchange columns Ultrapure Water Systems Type I Methods (combinations of two or three methods are applied) Ion Exchange Activated Carbon Reverse Osmosis Ultrafiltration Microporous Filters Ultraviolet (UV) Radiation Distilled and Double Distilled Water Systems Distilled Water (dh 2 O) Distillation is probably the oldest method of water purification. Water is first heated to the boiling point. The water vapor rises to a condenser where cooling water lowers the temperature so the vapor is condensed, collected and stored. Double Distilled Water (ddh 2 O) Prepared by double distillation of water. Usage (Type II and Type III) General laboratory applications such as buffers, ph solutions Glassware rinsing, heating baths and filling autoclaves Most of inorganic compounds Particulates Microorganisms CO 2 Silica Ammonia Volatile organic compounds Distilled versus Double Distilled Water Systems Removes a broad range of contaminants and therefore useful as a first purification step. Reusable. Contaminants are carried to some extent into the condensate (Inorganic contaminants are able to migrate along the thin water film that forms on the inner walls of the still) Requires careful maintenance to ensure purity (Distillation is a slow process, during this time, recontamination may occur) Consumes large amounts of tap water (for cooling) and electrical energy (for heating) Not environment-friendly. (a still requires regular cleaning of the boiling pot with HCl) Ion exchange: Deionized Water Systems The ion-exchange process percolates water through spherical, porous bead resin materials (ion-exchange resins). Ions in the water are exchanged for other ions fixed to the beads. The two most common ion-exchange methods are softening and deionization. The softeners contain beads that exchange two sodium ions for every calcium or magnesium ion removed from softened water. Deionization (DI) beads exchange either hydrogen ions for cations, or hydroxyl ions for anions. The cation-exchange resins, which are made of polystyrene chains crosslinked by divinylbenzene with covalently bound sulfonic acid groups, will exchange a hydrogen ion for any cations (e.g., Na +, Ca ++, Al +++ ). The anion-exchange resins, which are made of polystyrene polymer chains with covalently bound quaternary ammonium groups, will exchange a hydroxyl for any anions (e.g., Cl-, NO3-, SO4 -- ). Usage (Type I) Preparation of analytical solutions Diluting samples Production of reagents for biochemical analysis H + from the cation exchanger unites with OH - of the anion exchanger to form pure water. These resins may be packaged in separate bed exchangers or in mixed units. 3

4 Dissolved inorganic compounds Polar organic compounds Dissolved gases Particulates Microorganisms Neutral organic compounds Ultrapure Water Systems Ultrapure water is defined by international regulations and standards, such as ASTM or ISO. Removes dissolved inorganics (ions) effectively, allowing resistivity levels above 18.0 MΩ 25 C Regenerable (by acids and bases) Relatively inexpensive initial capital investment. Limited capacity: once all ion binding sites are occupied, ions are no longer retained Does not effectively remove organics, particles, pyrogens or bacteria. Chemically regenerated DI beds can generate organics and particles. Single use, virgin resins require good pretreated water quality to be economically efficient. Possible contaminations of the water are efficiently removed which is measurable by the conductivity. The production of ultrapure (Type 1) water demands a combination of different water purification techniques, each removing specific contaminants. Ion Exchange Activated Carbon Reverse Osmosis Ultrafiltration Microporous Filters Ultraviolet (UV) Radiation These water purification techniques are organized in an optimized process sequence to make sure that the highest water purity level is reached. Activated Carbon One gram of activated carbon has a surface of up to 1000 m 2. Organic molecules dissolved in water may enter the pores and bind to their walls due to van der Waals forces. Important parameters: diameter of the pores in the carbon filter the diffusion rate of organic molecules through the pores. Activated carbon used in water purification is available in two forms: Natural activated carbon produced by treating vegetal products at high temperature. Synthetic activated carbon is made by the controlled pyrolysis of polystyrene spherical beads. Activated carbon is usually used in combination with other treatment processes. Dissolved organic compounds Removes dissolved organics and chlorine effectively. Long life due to high binding capacity. Does not efficiently remove ions and particulates. Can generate carbon fines. Particulates Microorganisms Dissolved inorganic compounds Reverse Osmosis Reverse osmosis is the most economical method of removing 95 % to 99 % of all contaminants. Natural osmosis occurs when solutions with two different concentrations are separated by a semi-permeable membrane. Osmotic pressure drives water through the membrane. In Reverse osmosis, hydraulic pressure is applied to the concentrated solution to counteract the osmotic pressure. Pure water is driven from the concentrated solution at a flow rate proportional to applied pressure. Reverse osmosis membranes reject all particles, bacteria and organics greater than 200 Dalton molecular weight at a rate close to 99%. Reverse osmosis is a cross-flow separation process. Feed flows tangentially along the membrane surface, thereby producing two streams: permeate and concentrate. Reverse osmosis membranes are manufactured from cellulose acetate or thin-film composites of polyamide on a polysulfone substrate. The semi-permeable membrane rejects salts (ions) by a charge phenomenon action. Parameters: Pressure (2-17 bar) Temperature (For every 1 C below 25 C product water quantity is reduced by 3%) Flow rate Ionic rejection (the greater the charge, the greater the rejection) 4

5 Particles Pyrogens and microorganisms Colloids Dissolved inorganics Effectively removes all types of contaminants Requires minimal maintenance Operation parameters are easy to monitor Dissolved gases Slow flow rates per surface: requires large membrane surfaces or an intermediate storage device. Requires good pretreatment to avoid rapid membrane damage by water contaminants: scaling (CaCO 3 deposits on the surface) fouling (deposits of organics or colloids on the surface) piercing (membrane cut by hard particulates) Microporous Filters Microporous filters can be classified in three categories: depth, surface and screen. Depth filters are matted fibers or materials compressed to form a matrix that retains particles by random adsorption or entrapment. Surface filters are made from multiple layers of media. When fluid passes through the filter, large particles accumulate primarily on the surface of the filter. Screen filters (also called microporous membrane filters) are uniform structures which, like a sieve, retain all particles larger than the precisely controlled pore size on their surface. For example, 0.22 µm membrane filters, which retain all bacteria, are routinely used to sterilize intravenous solutions, serums and antibiotics. Depth filters are usually used as prefilters, surface filters may be used either as prefilters or clarifying filters, screen filters are used at the last step of purification to remove the last remaining contaminants. Eliminated (depending on filter type/pore size) All particulates All microorganisms Dissolved inorganics Dissolved organics Pyrogens Screen filters are absolute filters that remove all particles and microorganisms greater than their pore size. Efficient operation throughout their lifetime Maintenance is limited to replacement. Ultrafiltration Ultrafiltration is a separation process using membranes with pore sizes in the range of 0.1 to micron. An ultrafiltration membrane functions as a molecular sieve. It separates dissolved molecules on the basis of their size often reported as the molecular weight by passing a solution through an infinitesimally fine filter. They will clog when the surface is covered by contaminants. Will not remove dissolved inorganics, organics or pyrogens. Not regenerable. Ultrafilters are available in several selective ranges and types. The ultrafilter is a tough, thin, selectively permeable membrane that retains most macromolecules above a certain size (Nominal Molecular Weight Limit, or NMWL). In water purification, ultrafilters are routinely used to provide pyrogen-free and nuclease-free water for critical cell culture or molecular biology experimentation. A highly porous material with extremely small pores of 0.02 µm Eliminated Particles Pyrogens Enzymes Microorganisms and viruses Monovalent ions Multivalent ions Effectively removes most particles, and retain them above the ultrafilter surface Efficient operation throughout their lifetime Their lifetime can be extended by a regular water flush at high speed Will not remove dissolved inorganics or organic substances. May clog when challenged by an excessive level of high-molecularweight contaminants. 5

6 Lab Water Systems Commercial Reverse Osmosis Water Purification Systems Water distillation system Pressure Vessels for Ion Exchange Resin or Carbon Filtration Membrane filter cartridge for ultrafiltration Barnstead nanopure diamond ultrapure water system RO Membrane for Ultra Pure Water 6