Friday, February 24, 2012

Ion Exchange Basic Concepts

Basic Concepts
Ion Exchange Reactions

Ion exchange is a reversible chemical reaction where an ion (an atom or molecule that has lost or gained an electron and thus acquired an electrical charge) from solution is exchanged for a similarly charged ion attached to an immobile solid particle. These solid ion exchange particles are either naturally occurring inorganic zeolites or synthetically produced organic resins. The synthetic organic resins are the predominant type used today because their characteristics can be tailored to specific applications.

An organic ion exchange resin is composed of high-molecular-weight polyelectrolytes that can exchange their mobile ions for ions of similar charge from the surrounding medium. Each resin has a distinct number of mobile ion sites that set the maximum quantity of exchanges per unit of resin.

Most plating process water is used to cleanse the surface of the parts after each process bath. To maintain quality standards, the level of dissolved solids in the rinse water must be regulated. Fresh water added to the rinse tank accomplishes this purpose, and the overflow water is treated to remove pollutants and then discharged. As the metal salts, acids, and bases used in metal finishing are primarily inorganic compounds, they are ionized in water and can be removed by contact with ion exchange resins. In a water deionization process, the resins exchange hydrogen ions (H+) for the positively charged ions (such as nickel. copper, and sodium). and hydroxyl ions (OH-) for negatively charged sulfates, chromates. and chlorides. Because the quantity of H+ and OH ions is balanced, the result of the ion exchange treatment is relatively pure, neutral water.

Thursday, February 23, 2012

NOM - Natural Organic Matter's effect on Water Treatment

Drinking water treatment – understanding the processes and meeting the challenges

Don Bursill
Water Science and Technology: Water Supply Vol 1 No 1 pp 1–7 
© 2001 IWA Publishing and the authors D. Bursill

Cooperative Research Centre for Water Quality and Treatment, Salisbury, South Australia

Abstract On and follow Natural organic matter (NOM) derived from soil and vegetation in water catchments is the key factor influencing most, if not all water treatment processes. The structure of the NOM and its involvement in water treatment processes requires better understanding. It seems likely that a better understanding of NOM reactions could lead to far better predictive capacity for water treatment designers and operators. Certainly the removal of NOM as a first step to the production of drinking water has many attractions. This paper provides an overview of work done by the author and many of his colleagues to advance this issue. 

Keywords drinking water treatment, natural organic matter, membranes, activated carbon, MIEX®

Tuesday, February 21, 2012

Read a free sample from the Practical Boiler Water Treatment Handbook

ISBN-13/EAN: 9780820601717
ISBN: 0820601713
Author: Natarajan Manivasakam
Chemical Publishing
Book - Hardback
Pub Date: Sept 22, 2011
572 pages

Click the "Look Inside" button above to view your free sample of this book
Available Here or from any major online retailer


What is Reverse Osmosis

Reverse Osmosis, also known as Hyper-filtration by the industry, represents state-of-the-art in water treatment technology. Reverse Osmosis (RO) was developed in the late 1950's under U.S. Government funding, as a method of desalinating sea water. Today, reverse osmosis has earned its name as the most convenient and thorough method to filter water. It is used by most water bottling plants, and by many industries that require ultra-refined water in manufacturing. Now this advanced technology is available to homes and offices for drinking water filtration.

How It Works

In short, it is the process by which water molecules are forced through a 0.0001 micron semi-permeable membrane by water pressure. Long sheets of the membrane are ingeniously sandwiched together and rolled up around a hollow central tube in a spiral fashion. This rolled-up configuration is commonly referred to as a spiral wound membrane or module. They are available in different sizes for processing different quantities of water. Typically, a module for home water treatment is as small as 2" diameter and 10" long, while one for industrial use may be 4" diameter and 40" long.

Condensate Polishing: Basic Principles

Condensate polishing


Fossil-fuelled (coal, oil, gas) and nuclear power stations produce electricity with turbines powered with high pressure steam. A schematic representation of this steam circuit is shown in the picture below. After going through the turbine, the steam is condensed and recycled.

Power station steam circuit
A power station steam circuit 

To avoid deposits on the turbine blades and corrosion in the steam circuit, the steam must be extremely pure. However, being permanently recycled, the condensate collects corrosion and erosion products from the boiler and pipework, as shown in the picture. The contaminants in the condensate must have a concentration of a few µg/L (ppb) or less. Therefore, the condensate, in many (but not all) power stations, is treated with ion exchange resins, ion exchange being the only process capable of achieving these low residual values.

Many new power stations are being built, particularly in emerging countries such as India and China, so that the number of condensate polishing project has increased tremendously since the beginning of the 21st Century. Whilst ion exchange processes for water demineralisation were mainly developed in Europe, the champions of condensate polishing design are largely American.

A Reverse Osmosis Starter

Reverse osmosis (RO) is a membrane-technology filtration method that removes many types of large molecules and ions from solutions by applying pressure to the solution when it is on one side of a selective membrane. The result is that the solute is retained on the pressurized side of the membrane and the pure solvent is allowed to pass to the other side. To be "selective," this membrane should not allow large molecules or ions through the pores (holes), but should allow smaller components of the solution (such as the solvent) to pass freely.

In the normal osmosis process, the solvent naturally moves from an area of low solute concentration (High Water Potential), through a membrane, to an area of high solute concentration (Low Water Potential). The movement of a pure solvent to equalize solute concentrations on each side of a membrane generates osmotic pressure. Applying an external pressure to reverse the natural flow of pure solvent, thus, is reverse osmosis. The process is similar to other membrane technology applications. However, there are key differences between reverse osmosis and filtration.

The predominant removal mechanism in membrane filtration is straining, or size exclusion, so the process can theoretically achieve perfect exclusion of particles regardless of operational parameters such as influent pressure and concentration. Reverse osmosis, however, involves a diffusive mechanism so that separation efficiency is dependent on solute concentration, pressure, and water flux rate.[1] Reverse osmosis is most commonly known for its use in drinking water purification from seawater, removing the salt and other substances from the water molecules.