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35 TOTAL SYSTEMS APPROACH TO FOAM CONTROL IN INDUSTRIAL WASTEWATER Brian S. Johnson, Senior Chemist Nalco Chemical Company Naperville, Illinois 60563 INTRODUCTION Foam control is important to industrial processes. Without proper foam control, production processes are often slowed; unwanted foam is a general nuisance, and a safety hazard. Sometimes foam is desirable, such as: ore floatation, Styrofoam, beer, fire extinguishing, etc. But, even desirable foams need to be disposed of after use. Breaking the foam greatly reduces the volume of waste material. Proper plant design can minimize foaming using mechanical methods. Sometimes this is not practical or simply not thought of. Traditional approaches to foam control has concentrated on selection of the proper antifoam chemical. How to best apply or control the antifoam chemical was a secondary consideration. This paper covers the three aspects of foam control: antifoam selection, application, and dosage control. Focus will be on wastewater treatment. BACKGROUND Foaming is an interfacial phenomenon. Foams occur because bubbles are stabilized by surfactant molecules. In this paper, a bubble is defined as a rounded thin envelope of liquid surrounding a gas phase, i Surfactants are molecules that are active at the air/water interface. This activity is attributed to the dual nature of the surfactant. Part of the molecule is not water soluble. This is called the hydrophobic or lipophilic 'tail'. The other portion is hydrophilic. The hydrophilic portion interacts with the water molecule and is generally polar. This portion is called the head group. Foams are formed because the bubbles' elasticity (E) is increased. This is given by:2 (I) dlnA where InA is the natural logarithm of the surface area (A) and 7 is the surface tension. The units of surface tension are energy per area (ergs/cm2). As the surface tension differential (d-y) increases, the elasticity increases. Bubbles with low surface tension differentials are less elastic, more brittle and easily broken. Bubbles with high elasticity are readily adaptable to forces trying to break the bubble. Increasing the bubble elasticity decreases the rate of bubble breakage, which increases foam. Air bubbles are created by turbulence as the liquid passes through pumps, weirs, etc. Gas bubbles are also produced by fermentation processes. The foam is created when these bubbles are stabilized by surface active molecules. Pure liquids cannot foam. When two, pure liquid, air bubbles touch they immediately coalesce. The pure liquid, forming the bubble, does this to minimize surface area. A surfactant impurity can stabilize the interface by impeding the touching of the bubble interfaces. Surface tension is lowered by the presence of a surfactant. Less energy is required to make the same amount of extra surface area. Without a stabilizing surfactant, the generated foam quickly drains allowing the bubbles to touch. This leads to bubble coalescence. Foam Stabilizing Mechanisms Foams can be stabilized by several mechanisms. The major mechanisms are: slow interfacial or lamella drainage, and 2-D diffusion of the foaming surfactant. The lamella is the liquid region between two air bubbles. Foam breaking is the result of lamella drainage, allowing bubbles to coalesce. When the lamella drains, the liquid goes to a 'plateau border.'' The plateau border is illustrated in Figure la. This plateau border is the liquid region between three bubbles. In any foam, the plateau regions contain most of the liquid. If flow to the plateau border is impeded, then bubble 48th Purdue Industrial Waste Conference Proceedings, 1993 Lewis Publishers, Chelsea, Michigan 48118. Printed in U.S.A. 341
Object Description
Purdue Identification Number | ETRIWC199335 |
Title | Total systems approach to foam control in industrial wastewater |
Author | Johnson, Brian S. |
Date of Original | 1993 |
Conference Title | Proceedings of the 48th Industrial Waste Conference |
Conference Front Matter (copy and paste) | http://earchives.lib.purdue.edu/u?/engext,21159 |
Extent of Original | p. 341-348 |
Collection Title | Engineering Technical Reports Collection, Purdue University |
Repository | Purdue University Libraries |
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Description
Title | page 341 |
Collection Title | Engineering Technical Reports Collection, Purdue University |
Repository | Purdue University Libraries |
Rights Statement | Digital object copyright Purdue University. All rights reserved. |
Language | eng |
Type (DCMI) | text |
Format | JP2 |
Capture Device | Fujitsu fi-5650C |
Capture Details | ScandAll 21 |
Transcript | 35 TOTAL SYSTEMS APPROACH TO FOAM CONTROL IN INDUSTRIAL WASTEWATER Brian S. Johnson, Senior Chemist Nalco Chemical Company Naperville, Illinois 60563 INTRODUCTION Foam control is important to industrial processes. Without proper foam control, production processes are often slowed; unwanted foam is a general nuisance, and a safety hazard. Sometimes foam is desirable, such as: ore floatation, Styrofoam, beer, fire extinguishing, etc. But, even desirable foams need to be disposed of after use. Breaking the foam greatly reduces the volume of waste material. Proper plant design can minimize foaming using mechanical methods. Sometimes this is not practical or simply not thought of. Traditional approaches to foam control has concentrated on selection of the proper antifoam chemical. How to best apply or control the antifoam chemical was a secondary consideration. This paper covers the three aspects of foam control: antifoam selection, application, and dosage control. Focus will be on wastewater treatment. BACKGROUND Foaming is an interfacial phenomenon. Foams occur because bubbles are stabilized by surfactant molecules. In this paper, a bubble is defined as a rounded thin envelope of liquid surrounding a gas phase, i Surfactants are molecules that are active at the air/water interface. This activity is attributed to the dual nature of the surfactant. Part of the molecule is not water soluble. This is called the hydrophobic or lipophilic 'tail'. The other portion is hydrophilic. The hydrophilic portion interacts with the water molecule and is generally polar. This portion is called the head group. Foams are formed because the bubbles' elasticity (E) is increased. This is given by:2 (I) dlnA where InA is the natural logarithm of the surface area (A) and 7 is the surface tension. The units of surface tension are energy per area (ergs/cm2). As the surface tension differential (d-y) increases, the elasticity increases. Bubbles with low surface tension differentials are less elastic, more brittle and easily broken. Bubbles with high elasticity are readily adaptable to forces trying to break the bubble. Increasing the bubble elasticity decreases the rate of bubble breakage, which increases foam. Air bubbles are created by turbulence as the liquid passes through pumps, weirs, etc. Gas bubbles are also produced by fermentation processes. The foam is created when these bubbles are stabilized by surface active molecules. Pure liquids cannot foam. When two, pure liquid, air bubbles touch they immediately coalesce. The pure liquid, forming the bubble, does this to minimize surface area. A surfactant impurity can stabilize the interface by impeding the touching of the bubble interfaces. Surface tension is lowered by the presence of a surfactant. Less energy is required to make the same amount of extra surface area. Without a stabilizing surfactant, the generated foam quickly drains allowing the bubbles to touch. This leads to bubble coalescence. Foam Stabilizing Mechanisms Foams can be stabilized by several mechanisms. The major mechanisms are: slow interfacial or lamella drainage, and 2-D diffusion of the foaming surfactant. The lamella is the liquid region between two air bubbles. Foam breaking is the result of lamella drainage, allowing bubbles to coalesce. When the lamella drains, the liquid goes to a 'plateau border.'' The plateau border is illustrated in Figure la. This plateau border is the liquid region between three bubbles. In any foam, the plateau regions contain most of the liquid. If flow to the plateau border is impeded, then bubble 48th Purdue Industrial Waste Conference Proceedings, 1993 Lewis Publishers, Chelsea, Michigan 48118. Printed in U.S.A. 341 |
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