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November, 2002 Just what is a Coliwasa anyway? Contributed by Mr. Mike McGinness* No, it's not an Italian dessert, a new computer operating system, or the latest dance! Coliwasa (or CoLiWaSa) is an acronym for Composite Liquid Waste Sampler, designed to help collect a vertical core from non-homogeneous liquids. (You may recall from the last E-Newsletter that a thief uses the same principle but applies to solids sampling.) Coliwasa samplers permit a more representative sampling of multiphase liquids and fluid-like sludges. A wide range of viscosity, corrosivity, volatility, and solids contents can be sampled in drums, tanks, and settling ponds. Coliwasa samplers are commercially available in various non-reactive material construction designs and are suitable for sampling liquids, viscous materials, and heavy sludges. Here is a picture of one type of Coliwasa.
How it works: The Coliwasa is a two-part device with a straw-like outer tube and a solid rod-like inside piece with an end seal that keeps the liquids out of the tube until the seal at the bottom is released. Lower it slowly into the container at a rate that allows representative sample collection, which generally occurs when the liquid level in the container is equal to that in the sample tube. Once the sample tube is full, closing the seal allows the Coliwasa to retain the sample for withdrawal. Allow sufficient time for all fluids to drain into the sample collection jar. Remove the jar, then cap it, label it, and store it appropriately.Advantages of a Coliwasa:
Limitations of a Coliwasa:
Moral: While a Coliwasa sampler has drawbacks, it is an improvement over grab sampling. We cannot always get a truly random sample, but we can reduce the bias in our samples by improving our equipment and procedures. Sampling Challenge: What sampling assumptions are involved in the use of Coliwasa samplers? More information about sampling equipment and procedures for solids, liquids, and gases is available in the Short Course at Texas Tech University and in the short introductory book A Primer for Sampling Solids, Liquids, and Gases, by Dr. Patricia L. Smith. * Mr. McGinness has been
an independent environmental compliance consultant for 15 years with his
own company, Custom Process Systems & Service Company, working
principally in the areas of hazardous waste water treatment, discharge,
and pollution prevention process control of solvent and water based
cleaning processes. He has earned two US patents as well as two U.S.
Department of Energy, Innovative Concepts, Process Development and
Demonstration Grants. Mr. McGinness has a B.S. in Chemical Engineering
from the University of Houston and is currently the V.P. of Technology and
Co-Founder of EcoShield Environmental Systems, Inc.
(http://www.ecoshieldenv.com) Send This Information To a Friend "Your decisions are
only as good as your samples." Newsletters | About
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