Both technologies are extremely important to achieving high quality water characteristics, and both are complex - each posing a different set of challenges in scaling up to commercial size operations. You will fmd that most equipment
ION EXCHANGE AND CARBON ADSORPTION 433
Chemical
Methane Series
suppliers have the expertise to tailor their equipment and processes to specific applications, but that in many situations, pilot scale testing will be required.
The overview of these technologies presented in this chapter should give you a flavor for the applications and general principles. For carbon adsorption, we can add one more helpful piece of information. Table 11 provides you with some representative organic chemicals that can be removed from water using activated carbon systems. Following this table is a short glossary of important terms for ion excliange and carbon adsorption.
Formula Molecular Boiling Point Weight @ 760 mm
Hg, "C
CnH2n+2
Table 1 1. Representative Organic Chemicals and Typical Retentivities on Activated Carbons
~~
Decane Acetylene Series Acetylene Propyne
~ ________ ~
C1d-b 142.28 I 231 .O 25
CnH2n-I
C*H, 26.04 -88.5 2
c3H, 40.06 -23.0 5
Avg.
Retentivity in % at 20"
1 Cand760
Hg
I
Pentyne C5H8
1
~~
68.11 56.0 12
5 8 12 16 23 25 25
Butyne I C,& I 54.09 I 27.0 I 8
434 WATER AND WASTEWATER TREATMENT TECHNOLOGIES
ION EXCHANGE A N D CARBON ADSORPTION 435
Chemical Formula Molecular Weight
Formaldehyde HSCHO 30.03
Acetaldehyde CH&HO 44.05
Boiling Point Avg.
Q 760 mm Retentivity in % at 20°
C and 760 Hg, "C
mmHg
-21.9 3
21 .o 7
SHORT GLOSSARY
Acidity: An expression of the concentration of hydrogen ions present in a solution.
Adsorbent: A synthetic resin possessing the ability to attract and to hold charged particles.
Adsorption: The attachment of charged particles to the chemically active group on the surface and in the pores of an ion exchanger.
Alkalinity: An expression of the total basic anions (hydroxyl groups) present in a solution. It also represents, particularly in water analysis, the bicarbonate, carbonate, and occasionally, the borate, silicate, and phosphate salts which will react with water to produce the hydroxyl groups.
Anion: A negatively charged particle or ion. Anion interchange: The displacement of one negatively charged particle by another on an anion-exchange material.
Attrition: The rubbing of one particle against another in a resin bed; frictional wear that will affect the site of resin particles.
Backwash: The countercurrent flow of water through a resin bed (that is, in at the bottom of the exchange unit, out at the top) to clean and regenerate the bed after exhaustion.
Base exchange: The property of the trading of cations shown by certain in- soluble naturally occurring materials (zeolites) and developed to a high degree of specificity and efficiency in synthetic resin adsorbents.
Batch operation: The utilization of ion-exchange resins to treat a solution in a container wherein the removal of ions is accomplished by agitation of the solution and subsequent decanting of the treated liquid.
Bed: A mass of ion-exchange resin particles contained in a column. Bed depth: The height of the resinous material in the column after the exchanger has been properly conditioned for effective operation. Bed expansion: The effect produced during backwashing when the resin particles become separated and rise in the column. The
436 WATER AND WASTEWATER TREATMENT TECIINOMGIES
expansion of the. bed due to the increase in the space between resin particles may be controlled by regulating backwash flow.
Bicarbonate alkalinity: The presence in a solution of hydroxyl (OH-) ions resulting from the hydrolysis of carbonates or bicarbonates. When these salts react with water, a strong base and a weak acid are produced, and the solution is alkaline.
Breakthrough: The first appearance in the solution flowing from an ion-ex- change unit of unabsorbed ions similar to those which are depleting the activity of the resin bed. Breakthrough is an indication that regeneration of the resin is necessary.
Capacity: The adsorption activity possessed in varying degrees by ion-ex- change materials. This quality may be expressed as kilograins per cubic foot, gram- milliequivalents per gram, pound-equivalents per pound, gram-milliequivalents per milliliter, and so on, where the numerators of these ratios represent the weight of the ions adsorbed and the de- nominators represent the weight or volume of the adsorbent.
Carbonaceous exchangers: Ion-exchange materials of limited capacity pre- pared by the sulfonation of coal, lignite, peat, and so on.
Carboxylic: A term describing a specific acidic group (COOH) that contrib- Utes cation-exchange ability to some resins.
Cation: A positively charged particle or ion. Channeling: Cleavage and furrowing of the bed due to faulty operational procedure, in which the solution being treated follows the path of least resistance, runs through these furrows, and fails to contact active groups in other parts of the bed.
Chemical stability: Resistance to chemical change which ion-exchange resins must possess despite contact with aggressive solutions.
Color-throw: Discoloration of the liquid passing through an ionexchange material;
the flushing from the resin interstices of traces of colored organic reaction intermediates.
Column operation: Conventional utilization of ion-exchange resins in columns through which pass, either upflow or downflow, the solution to be treated.
Cycle: A complete course of ion-exchange operation. For instance, a complete cycle of cation exchange would involve regeneration of the resin with acid, rinse to remove excess acid, exhaustion, backwash, and finally regeneration.
Deashing: The removal from solution of inorganic salts by means of adsorption by ion-exchange resins of both the cations and the anions that comprise the salts. See deionization.
Deionization: Deionization, a more general term than deushing, embraces the removal of all charged constituents or ionizable salts (both inorganic and organic) from solution.
ION EXCHANGE AND CARBON ADSORFTION 437
Demineralizing: See deadzing.
Density: The weight of a given volume of exchange material, backwashed and in place in the column.
Dissociation: Ionization.
Downflow: Conventional direction of solutions to be processed in ion-ex- change column operation, that is, in at the top, out at the bottom of the column.
Dynamic system: An ion-exchange operation wherein a flow of the solution to be treated is involved.
Efficiency: The effectiveness of the operational performance of an ion ex- changer.
Efficiency in the adsorption of ions is expressed as the quantity of regenerant required to effect the removal of a specified unit weight of adsorbed material, for example, pounds of acid per kilogram of salt removed.
Effluent: The solution which emerges from an ion-exchange column. Electrolyte:
A chemical compound which dissociates or ionizes in water to
produce a solution which will conduct an electric current; an acid, base, or salt.
Elution: The stripping of adsorbed ions from an ion-exchange material by the use of solutions containing other ions in concentrations higher than those of the ions to be stripped.
Equilibrium reactions: The interaction of ionizable compounds in which the products obtained tend to revert to the substance from which they were formed until a balance is reached in which both reactants and pacts are present in definite ratios.
Equivalent weight: The molecular weight of any element or radical expressed as grams, pounds, and so on divided by the valence.
Exchange velocity: The rate with which one ion is displaced from an ex- changer in favor of another.
Exhaustion: The state in which the adsorbent is no longer capable of useful ion exchange; the depletion of the exchanger's supply of available ions. The exhaustion point is determined arbitrarily in terms of: (1) a value in parts per million of ions in the effluent solution; and (2) the reduction in quality of the effluent water determined by a conductivity bridge which measures the resistance of the water to the flow of an electric current.
Fines: Extremely small particles of ion-exchange materials.
Flow rate: The volume of solution which passes through a given quantity of resin within a given time. Flow rate is usually expressed in terms of feet per minute per cubic foot of resin or as millimeters per minute per millimeter of resin.
Freeboard: The space provided above the resin bed in an ion-exchange column to allow for expansion of the bed during backwashing.
438 WATER AND WASTEWATER TREATMENT TECHNOLQGIES
Grain: A unit of weight; 0.0648 grams; 0.000143 pounds.
Grains per gallon: An expression of concentration of material in solution. One grain per gallon is equivalent to 17.1 parts per million.
Gram: A unit of weight; 15.432 grains; 0.0022 pounds.
Gram-milliquivalents: The equivalent weight in grams, divided by 1,000.
Greensands: Naturally occurring materials, composed primarily of complex silicates, which possess ion-exchange properties.
Hardness: The scale-forming and lather-inhibiting qualities which water, high in calcium and magnesium ions, possesses.
Hardness as calcium carbonate: The expression ascribed to the value obtained when the hardness-forming salts are calculated in terms of equivalent quantities of calcium carbonate; a convenient method of reducing all salts to a common basic for comparison.
Head loss: The reduction in liquid pressure associated with the passage of a solution through a bed of exchange material; a measure of the resistance of a resin bed to the flow of the liquid passing through it.
Hydraulic classification: The rearrangement of resin particles in an ion-ex- change unit. As the backwash water flows up through the resin bed, the particles are placed in a mobile condition wherein the larger particles settle and the smaller particles rise to the top of the bed.
Hydrogen cycle: A complete course of cation-exchange operation in which the adsorbent is employed in the hydrogen or free acid form.
Hydroxyl: The term used to describe the anionic radical (OH-) which is responsible for the alkalinity of a solution.
Influent: The solution which enters an ion-exchange unit.
Ion: Any particle of less than colloidal size possessing either a positive or a negative electric charge.
Ionization: The dissociation of molecules into charged particles.
Ionization constant: An expression in absolute units of the extent of dissociation into ions of a chemical compound in solution.
Ion exchange: See fundamental description beginning page 273. Kilograin: A unit of weight; 1,000 grains.
Leakage: The phenomenon in which some of the influent ions are not ad- sorbed and appear in the effluent when a solution is passed through an underregenerated exchange resin bed.
Negative charge: The electrical potential which an atom acquires when it gains one or more electrons; a characteristic of an anion.
ION EXCHANGE AND CARBON ADSORPTION 439
pH: An expression of the acidity of a solution; the negative logarithm of the hydrogen-ion concentration (PH 1 very acidic; pH 14, very basic; pH 7, neutral), pOH: An expression of the alkalinity of a solution; the negative logarithm of the hydroxyl-ion concentration.
pK: An expression of the extent of dissociation of an electrolyte; the negative logarithm of the ionization constant of a compound.
Physical stability: The quality which an ion-exchange resin must possess to resist changes that might be caused by attrition, high temperatures, and other physical conditions.
Positive charge: The electrical potential acquired by an atom which has lost one or more electrons; a characteristic of a cation.
Raw water: Untreated water from wells or from surface sources.
Regenerant: The solution used to restore the activity of an ion exchanger. Acids are employed to restore a cation exchanger to its hydrogen form; brine solutions may be used to convert the cation exchanger to the sodium form. The anion exchanger may be rejuvenated by treatment with an alkaline solution.
Regeneration: Restoration of the activity of an ion exchanger by replacing the ions adsorbed from the treated solution by ions that were adsorbed initially on the resin.
Rejuvenation: See regeneration.
Reverse deionization: The use of an anion-exchange unit and a cation-ex- change unit-in that order-to remove all ions from solution.
Rinse: The operation which follows regeneration; a flushing out of excess regenerant solution.
Siliceous gel zeolite: A synthetic, inorganic exchanger produced by the aqueous reaction of alkali with aluminum salts.
Static system: The batch-wise employment of ion-exchange resins, wherein (since ion exchange is an equilibrium reaction) a definite endpoint is reached in which a finite quantity of all the ions involved is present. Opposed to a dynamic, column- type operation.
Sulfonic: A specific acidic group (S03H) on which depends the exchange activity of certain cation adsorbents ,
Swelling: The expansion of an ion-exchange W which occurs when the re- active groups on the resin are converted from one form to another.
Throughput volume: The amount of solution passed through an exchange W before exhaustion of the resin is reached.
Upflow: The operation of an ion-exchange unit in which solutions are passed in at the bottom and out at the top of the container.
440 WATER AND WASTEWATER TREATMENT TECHNOMGES
Voids: The space between the resinous particles in an ion-exchange bed.
Zeolite: Naturally occurring hydrous silicates exhibiting limited base exchange.
RECOMMENDED RESOURCES FOR THE READER
Recommend that you sugthe following Web sites for detailed equipment information on ion exchangers and carbon adsorption.
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Ion Exchange Chromatography - Basic principles of ion exchange chromatography and studies conducted from Texas A&M University.
http : //ntri.tamuk. edu/fplc/ion.html.
Ion Exchange - Encyclopedia article - good general introduction. (Encarta@
Concise Encyclopedia Article). . .http://encarta.msn.com/index/conciseinde.
Indian Ion Exchange and Chemical Industries - Produces reverse osmosis and demineralization systems, base exchange softeners, clarifiers and filters, degassers and de-aerators, filtration and micro filtration systems, effluent treatment plant.. .http://www.indianionexchange.com .
Dionex Corporation - Manufacturers of liquid chromatography systems (IC and HPLC), chromatography software data systems, reversed-phase and ion-exchange columns, and accelerated solvent extraction systems. . . http : //www . dionex .corn.
Remco Engineering - Manufacturer of systems for water treatment, waste water recycling, heavy metal recovery and filtration. Provides some good general information plus vendor specific. htcp://www.remco.com .
Purolite Corporation - London company offers ion exchange products and polymeric absorbents. Find corporate info, offices worldwide, products, services, and contacts.. .http://www.purolite.com..
Ion Exchange for Introduction to Biochemical Engineering - General and company specific information - “Ion exchange can be defined as a reversible exchange of ions between a solid and a liquid in which there is no substantial change in the structure of the solid (Dowex Dow Chemical)”.
The solids are the ion exchange resin., etc. http://www.rpi.edu/dept/chem- eng/Biotech .
Ion Exchange Resins - SpectralGel Ion Exchange resins are ion exchange media for use in low-pressure liquid chromatography. They are based on a polystyrene/divinylbenzene support and are available for both anion and cation exchange applications. This site will give you a reasonable
ION EXCHANGE AND CARBON ADSORPTION 441
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background on resin selection criteria and some economic factors for comparisons to other technologies. http://www . lplc. com/misc/ionex.htm..
Ion exchange for Metal Recovery - A discussion of the trade-offs Author Karrs, Stanley R. Buckley, Deborah Morey Document Type Proceedings article Source 7th AESF/EPA Conference on Pollution Control in the Metal Finishing Industry Subject Resource. Although specific to the metal industry, still some very good technical data that will assist you on resin selection for ion exchange applications. Also, some good schematics of process operations. http://es.epa.gov/techpubs/0/7250.html.
Application of Ion Exchange to Materials Recovery - A compilation of links to internet recycling resources provided by Allan Barton of Murdoch University, author of Resources Recycling and Recovery. Visit this at the following URL.. , http: //wwwscience .murdoch. edu. adteachin.
Ion Exchange Resins - Very good site for you to visit! Contains cost comparisons between RO and ion exchange systems for several design cases. http://www.rohmhaas.com/ionexchange.
Comparison with Reverse Osmosis and Ion Exchange -Another great site to visit for comparison with reverse osmosis and ion exchange The BioDentmProcessReverse OsmosisIon Exchange THE BioDentm PROCESS The BioDentm process has several important advantages over other nitrate treatment systems : http : //www . nitrateremoval. com. .
Ion Exchange Simulation - Uses the Java applet that simulates an ion exchange experiment. Select from topics for information on using the applet. Setting up the experiment Running the simulation.
http ://www .rit. edu/ - pac86 12/webionex/web.
JCE 1996 (73) 639 [Jul] Visible Ion Exchange Demonstration for Large or Small Lecture Halls - Visible Ion Exchange Demonstration for Large or Small Lecture Halls Jerry A. Driscoll Department of Chemistry, University of Utah, Salt Lake City, UT 84112 This demonstration is a colorful illustration of how an ion exchange column works. Some great visual graphics! http: //jchemed. chem. wisc. edu.
Ion Exchange Resin Cross Reference Guide - American L.B. Science &
Technology Group Co., Ltd. is a group of manufacturer & manufacturer representative specializing in electronic and mechanical and water treatment products. http: //www . americanlb. com/resin/res. html.
Care & Use of Vydac VHP Ion-Exchange Columns - Guide to Column Care and Use Vydac VHP Protein Ion-Exchange Columns (300VHP, 301VHP, 400VHP) Vydac VHP-Series Protein Ion-Exchange columns consist of a polystyrene-divinylbenzene copolymer bead with a chemically attached hydrophilic surface. A thorough treatment of the theory and some experimental data. http://www .vydac.com/vydacpubs/CMGuides/.
442 WATER AND WASTEWATER TREATMENT TECHNOLOGIES
17. IEXTOOLS (TM) Ion Exchange Software - IexTools Ion exchange is extensively used in ultrapure (high-purity) water manufacturing. Ion exchange is used in the following industries: power, microelectronics, food, water treatment (potable, wastewater), and hydrometallurgy.
http: //www dtrapureh2o .com/product 1 .htm.
The Zeolite Researchers' List: Catalysis, ion-exchange and separation -
List of researchers in the field of zeolites (including URLs and e-mail- adresses). Subfield: Catalysis, ion-exchange and separation.
http : //www .tn. utwente . nl/cdr/Staff/Haral .
Adsorption and ion exchange group - Loughborough University - adsorption and ion exchange group loughborough university department of chemical engineering The adsorption and ion exchange group is concerned with research into environmental pollution control, especially the removal of trace toxic metals and organochemicals. You will find abstracts of research and links to research articles. http://www- staff. lboro. ac.W - cgbs2.
Home Water Treatment Using Activated Carbon - Discussion and guidelines from a 1997 article from the Michigan State University Extension. http://www.msue.msu.edu/msue/imp/modwq/w .
Water Treatment FAQ - By Patton Turner. Excellent overview of all water treatment methods and associated problems.
http://www .providenceco-op.com/waterfaq.
Treatment Systems for Household Water Supplies - Activated Carbon Filtration - 1992 article from the North Dakota State University Extension Service explaining in detail what activated charcoal systems can and cannot do. http: //www .ext .nod&. edu/extpubs/h2oqual.
Activated Carbon for Process Water Treatment: Activated Carbon from CPL Carbon Link - Activated carbon from CPL Carbon Link for liquid and gas phase purification by adsorption. Activated carbons for all applications including chemical, water, air, solvent recovery, gold recovery, food, automotive, industrial, catalysis.. http://www.activated-carbon.com.
Carbochem - Supplies carbon and other chemical products based in copper, cerium, nickel, and cobalt. http://www.carbochem.com.
Water Quality and Treatment Handbook, 5th Edition - State-of-the-art handbook of community water supplies The leading source of information on water quality, water treatment, and quality control for 60 years is now available in an up-to-the-minute new edition. Go to this site for detailed contents of this important publication. http://preview.mcgraw- hill.com/info/com.
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