United States EPA 542-B-94-004
Environmental Protection September 1994
Agency
Solid Waste and Emergency Response (5102W)
wEPA
Innovative Site
Remediation
Technology
Chemical Treatment
Volume 2
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INNOVATIVE SITE
REMEDIATION TECHNOLOGY
CHEMICAL TREATMENT
One of an Eight-Volume Series
Edited by
William C. Anderson, P.E., DEE
Executive Director, American Academy of Environmental Engineers
1994
Prepared by WASTECH®, a multiorganization cooperative project managed
by the American Academy of Environmental Engineers® with grant assistance
from the U.S. Environmental Protection Agency, the U.S. Department of
Defense, and the U.S. Department of Energy.
The following organizations participated in the preparation and review of
this volume:
! Air & Waste Management \«**J American Society of
Association \™ Civil Engineers
P.O. Box 2861 345 East 47th Street
Pittsburgh, PA 15230 New York, NY 10017
American Academy of f M/M, Hazardous Waste Action
Environmental Engineers® Ss Coalition
130 Holiday Court, Suite 100 1015 15th Street, N.W., Suite 802
Annapolis, MD 21401 Washington, D.C. 20005
American Institute of ^(^ Water Environment
Chemical Engineers ^Federation
345 East 47th Street 601 Wythe Street
New York, NY 10017 Alexandria, VA 22314
Published under license from the American Academy of Environmental
Engineers®. © Copyright 1993 by the American Academy of Environmental
Engineers®.
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Library of Congress Cataloging in Publication Data
Innovative site remediation technology/ edited by William C. Anderson
200p. 15.24 x 22.86cm.
Includes bibliographic references.
Contents: — [2] Chemical treatment [3] Soil washing/soil flushing
— [4] Stabilization/solidification
— [6] Themal desorption.
1. Soil remediation. I. Anderson, William, C., 1943-
II. American Academy of Environmental Engineers.
TD878.I55 1994 628.5'5 93-20786
ISBN 1-883767-02-4 (v. 2) ISBN 1-883767-04-0 (v. 4)
ISBN 1-883767-03-2 (v. 3) ISBN 1-883767-06-7 (v. 6)
Copyright 1994 by American Academy of Environmental Engineers. All Rights Reserved.
Printed in the United States of America. Except as permitted under the United States
Copyright Act of 1976, no part of this publication may be reproduced or distributed in any
form or means, or stored in a database or retrieval system, without the prior written
permission of the American Academy of Environmental Engineers.
The material presented in this publication has been prepared in accordance with
generally recognized engineering principles and practices and is for general
information only. This information should not be used without first securing
competent advice with respect to its suitability for any general or specific applica-
tion.
The contents of this publication are not intended to be and should not be
construed as a standard of the American Academy of Environmental Engineers or of
any of the associated organizations mentioned in this publication and are not
intended for use as a reference in purchase specifications, contracts, regulations,
statutes, or any other legal document
No reference made in this publication to any specific method, product, process,
or service constitutes or implies an endorsement, recommendation, or warranty
thereof by the American Academy of Environmental Engineers or any such
associated organization.
Neither the American Academy of Environmental Engineers nor any of such
associated organizations or authors makes any representation or warranly of any
kind, whether express or implied, concerning the accuracy, suitability, or utility of
any information published herein and neither the American Academy of E^nviron-
mental Engineers nor any such associated organization or author shall be responsible
for any errors, omissions, or damages arising out of use of this information.
Book design by Lori Imhoff
Printed in the United States of America
WASTECH and the American Academy of Environmental Engineers are trademarks of the American
Academy of Environmental Engineers registered with the U.S. Patent and Trademark Office.
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CONTRIBUTORS
This monograph was prepared under the supervision of the WASTECH*
Steering Committee. The manuscript for the monograph was written by a task
group of experts in chemical treatment and was, in turn, subjected to two peer
reviews. One review was conducted under the auspices of the Steering Committee
and the second by professional and technical organizations having substantial
interest in the subject.
PRINCIPAL AUTHORS
Leo Weitzman, Ph.D., Task Group Chair
President
LVW Associates, Inc.
Kimberly Gray, Ph.D.
Assistant Professor
Department of Civil Engineering
and Geological Sciences
University of Notre Dame
Frederick K. Kawahara, Ph.D.
Research Chemist
Risk Reduction Engineering Laboratory
U.S. Environmental Protection Agency
Robert W. Peters, Ph.D., P.E., DEE
Environmental Systems Engineer
Energy Systems Division
Argonne National Laboratory
John Verbicky, Ph.D.
Chemfab Corporation
REVIEWERS
The panel that reviewed the monograph under the auspices of the Project
Steering Committee was composed of:
Peter B. Lederman, Ph.D., P.E.,
DEE, P.P., Chair
Center for Environmental Engineering
and Science
New Jersey Institute of Technology
John Herrmann
Senior Technical Advisor
Water and Hazardous Waste Treatment
Research Division
U.S. Environmental Protection Agency
B. Mo Kim, Ph.D.
Environmental Laboratory
General Electric Company
Joseph F. Lagnese, Jr., P.E., DEE
Private Consultant
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STEERING COMMITTEE
Frederick G. Pohland, Ph.D., P.E., DEE
Chair
Weidlein Professor of Environmental
Engineering
University of Pittsburgh
William C. Anderson, P.E., DEE
Project Manager
Executive Director
American Academy of Environmental
Engineers
Paul L. Busch, Ph.D., P.E., DEE
President and CEO
Malcolm Pirnie, Inc.
Representing, American Academy of
Environmental Engineers
Richard A. Conway, P.E., DEE
Senior Corporate Fellow
Union Carbide Corporation
Chair, Environmental Engineering
Committee
EPA Science Advisory Board
Timothy B. Holbrook, P.E.
Engineering Manager
Groundwater Technology, Inc.
Representing, Air & Waste Management
Association
Walter W. Kovalick, Jr., Ph.D.
Director, Technology Innovation Office
Office of Solid Waste and Emergency
Response
U.S. Environmental Protection Agency
Joseph F. Lagnese, Jr., P.E., DEE
Private Consultant
Representing, Water Environment
Federation
Peter B. Lederman, Ph.D., P.E., DEE, P.P.
Center for Env. Engineering & Science
New Jersey Institute of Technology
Representing, American Institute of
Chemical Engineers
Raymond C. Loehr, Ph.D., P.E., DEE
H.M. Alharthy Centennial Chair and
Professor
Civil Engineering Department
University of Texas
James A. Marsh
Office of Assistant Secretary of Defense
for Environmental Technology
Timothy Oppelt
Director, Risk Reduction Engineering
Laboratory
U.S. Environmental Protection Agency
George Pierce, Ph.D.
Editor in Chief
Journal of Microbiology
Manager, Bioremediation Technology Dev.
American Cyanamid Company
Representing the Society of Industrial
Microbiology
H. Gerard Schwartz, Jr., Ph.D., P.E., DEE
Senior Vice President
Sverdrup Corporation
Representing, American Society of Civil
Engineers
Claire H. Sink
Acting Director
Division of Technical Innovation
Office of Technical Integration
Environmental Education Development
U.S. Department of Energy
Peter W. Tunnicliffe, P.E., DEE
Senior Vice President
Camp Dresser & McKee, Incorporated
Representing, Hazardous Waste Action
Coalition
Charles O. Velzy, P.E., DEE
Private Consultant
Representing, American Society of
Mechanical Engineers
William A. Wallace
Vice President, Hazardous Waste
Management
CH2M Hill
Representing, Hazardous Waste Action
Coalition
Walter J. Weber, Jr., Ph.D., P.E., DEE
Earnest Boyce Distinguished Professor
University of Michigan
iv
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REVIEWING ORGANIZATIONS
The following organizations contributed to the monograph's review and
acceptance by the professional community. The review process employed by each
organization is described in its acceptance statement. Individual reviewers are, or
are not, listed according to the instructions of each organization.
Air & Waste Management
Association
The Air & Waste Management
Association is a nonprofit technical and
educational organization with more than
14,000 members in more than fifty
countries. Founded in 1907, the
Association provides a neutral forum
where all viewpoints of an environmen-
tal management issue (technical,
scientific, economic, social, political,
and public health) receive equal
consideration.
This worldwide network represents
many disciplines: physical and social
sciences, health and medicine, engineer-
ing, law, and management. The
Association serves its membership by
promoting environmental responsibility
and providing technical and managerial
leadership in the fields of air and waste
management. Dedication to these
objectives enables the Association to
work towards its goal: a cleaner
environment.
Qualified reviewers were recruited
from the Waste Group of the Technical
Council. It was determined that the
monograph is technically sound and
publication is endorsed.
The reviewers were:
James R. Donnelly
Director of Environmental Services and
Technologies
Davy Environmental
Paul Lear
OHM Remediation Services, Corp.
American Institute of
Chemical Engineers
The Environmental Division of the
American Institute of Chemical Engi-
neers has enlisted its members to review
the monograph. Based on that review
the Environmental Division endorses
the publication of the monograph.
American Society of Civil
Engineers
Qualified reviewers were recruited
from the Environmental Engineering
Division of ASCE and formed a Sub-
committee on WASTECH®. The mem-
bers of the Subcommittee have
reviewed the monograph and have
determined that it is acceptable for
publication.
Hazardous Waste Action
Coalition
The Hazardous Waste Action Coali-
tion (HWAC) is an association dedi-
cated to promoting an understanding of
the state of the hazardous waste practice
and related business issues. Our mem-
ber firms are engineering and science
firms that employ nearly 75,000 of this
country's engineers, scientists, geolo-
gists, hydrogeologists, toxicologists,
chemists, biologists, and others who
solve hazardous waste problems as a
professional service. HWAC is pleased
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to endorse the monograph as technically
sound.
The lead reviewer was:
James D. Knauss, Ph.D.
Hatcher-Sayre, Incorporated
Water Environment
Federation
The Water Environment Federa-
tion is a nonprofit, educational orga-
nization composed of member and
affiliated associations throughout the
world. Since 1928, the Federation
has represented water quality spe-
cialists including engineers, scien-
tists, government officials, industrial
and municipal treatment plant opera-
tors, chemists, students, academic
and equipment manufacturers, and
distributors.
Qualified reviewers were re-
cruited from the Federation's Hazard-
ous Wastes Committee and from the
general membership. A list of their
names, titles, and business affilia-
tions can be found listed below. It
has been determined that the docu-
ment is technically sound and publi-
cation is endorsed.
The reviewers were:
Roger R. Hlavek
Chemical Engineer
Naval Air Warfare Center —
Aircraft Division
Murali Kalavapudi
Senior Environmental Engineer
Energetics, Incorporated
Byung R. Kim*
Principal Staff Engineer
Ford Research Laboratory
Edward R. Maziarz
Environmental Engineering
Consultant — Industrial Wastes
ALCOA
Charles D. Sweeney
Director
CDS Laboratories, Inc.
Arnold S. Vernick, P.E., DEE
Associate
Geraghty & Miller, Inc,
Scott E. Walters
Environmental Chemisl
Pennsylvania Department of
Environmental Resources
Robert C. Wichser
Chief Utility Engineer
Richmond Virginia Department of
Public Utilities
*WEF lead reviewer
vi
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ACKNOWLEDGMENTS
The WASTECH® project was conducted under a cooperative agreement
between the American Academy of Environmental Engineers® and the Office
of Solid Waste and Emergency Response, U.S. Environmental Protection
Agency. The substantial assistance of the staff of the Technology Innovation
Office was invaluable.
Financial support was provided by the U.S. Environmental Protection
Agency, Department of Defense, Department of Energy, and the American
Academy of Environmental Engineers®.
This multiorganization effort involving a large number of diverse profes-
sionals and substantial effort in coordinating meetings, facilitating communica-
tions, and editing and preparing multiple drafts was made possible by a
dedicated staff provided by the American Academy of Environmental Engi-
neers® consisting of:
Paul F. Peters
Assistant Project Manager & Managing Editor
Karen M. Tiemens
Editor
Susan C. Richards
Project Staff Assistant
J. Sammi Olmo
Project Administrative Manager
Yolanda Y. Moulden
Staff Assistant
I. Patricia Violette
Staff Assistant
VII
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viii
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TABLE OF CONTENTS
Contributors iii
Acknowledgments vii
List of Tables xiii
List of Figures xiv
1.0 INTRODUCTION 1.1
1.1 Chemical Treatment 1.1
1.2 Development of the Monograph 1.2
1.2.1 Background 1.2
1.2.2 Process 1.3
1.3 Purpose 1.4
1.4 Objectives 1.4
1.5 Scope 1.4
1.6 Limitations 1.5
1.7 Organization 1.6
2.0 PROCESS SUMMARY 2.1
2.1 Process Identification and Description 2.2
2.1.1 Substitution Processes 2.2
2.1.2 Oxidation Processes 2.3
2.1.3 Chemical Precipitation Processes 2.4
2.1.4 Design and Other Considerations 2.5
2.1.5 Materials Handling 2.5
ix
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Table of Contents
2.1.6 Costs 2.7
2.2 Potential Applications 2.7
2.2.1 Substitution Processes 2.8
2.2.2 Oxidation Processes 2.9
2.2.3 Precipitation Processes 2.9
2.3 Process Evaluation 2.9
2.4 Limitations 2.10
2.4.1 Substitution Processes 2.10
2.4.2 Oxidation Processes 2.10
2.4.3 Precipitation Processes 2.11
2.5 Technology Prognosis 2.11
3.0 PROCESS IDENTIFICATION AND DESCRIPTION 3.1
3.1 Substitution Processes 3.6
3.1.1 Low-Temperature Substitution Processes 3.9
3.1.1.1 KPEG Process 3.10
3.1.1.2 GRC Process 3.12
3.1.1.3 KGME/DECHLOR 3.13
3.1.2 High-Temperature Substitution Processes 3.16
3.2 Oxidation Process Descriptions 3.20
3.2.1 Chemical Oxidation Processes 3.21
3.2.2 UV Photodegradation/Photolysis 3.21
3.2.3 Advanced Oxidation Processes 3.24
3.3 Precipitation Processes 3.29
3.3.1 Hydroxide Precipitation 3.31
3.3.2 Carbonate Precipitation 3.35
3.3.3 Sulfide Precipitation 3.37
3.3.4 Xanthate Precipitation 3.45
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Table of Contents
3.3.5 Combined Precipitation Treatment 3.48
3.4 Scientific Basis 3.52
3.4.1 Substitution Processes 3.52
3.4.2 Oxidation Processes 3.54
3.4.2.1 Photolysis 3.56
3.4.2.2 UV-Hydrogen Peroxide 3.57
3.4.2.3 Ozonation and Advanced Oxidation Processes 3.58
3.4.3 Precipitation Processes 3.59
3.5 Status Of Development 3.61
3.6 Environmental Impact 3.62
3.6.1 Substitution Processes 3.63
3.6.2 Oxidation Processes 3.64
3.7 Pre- and Posttreatment Requirements 3.65
3.7.1 Substitution Processes 3.66
3.7.2 Oxidation Processes — Posttreatment Requirements 3.66
3.8 Special Health and Safety Considerations 3.68
3.9 Design Data and Unit Sizing 3.69
3.9.1 Substitution Processes 3.69
3.9.2 Oxidation Processes 3.70
3.9.3 Precipitation Processes 3.79
3.9.4 Materials of Construction 3.81
3.10 Operational Requirements and Considerations 3.82
3.11 Materials Handling 3.83
3.12 Information Required to Consider and Employ the Process 3.84
3.13 Unique Planning and Management Needs 3.88
3.14 Cost 3.90
3.14.1 Fixed Costs 3.91
xi
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Table of Contents
3.14.2 Variable Costs 3.92
3.14.3 Estimated Costs of Various Treatment Methods 3.94
3.14.4 Equipment Sizing and Cost - Oxidative Processes 3.94
4.0 POTENTIAL APPLICATIONS 4.1
5.0 PROCESS EVALUATION 5.1
6.0 LIMITATIONS 6.1
6.1 Substitution Processes 6.1
6.2 Oxidation Processes 6.1
6.2.1 UV-Ozonation — Treatment of Water 6.2
6.2.2 UV-Oxidation — Treatment of Paniculate 6.3
6.2.3 UV-Hydrogen Peroxide — Treatment of Water 6.3
6.2.4 UV-Hydrogen Peroxide — Treatment of Soils and Sedi-
ments 6.5
6.3 Precipitation Processes 6.5
7.0 TECHNOLOGY PROGNOSIS 7.1
Appendices
A. Emerging Technologies A.1
A.1 The Base Catalyzed Decomposition (BCD) Process A.I
A.2 Iron (II) Catalyzed H2O2 Oxidation (Fenton's Reagent) A.3
A.3 Photocatalysis in Semiconductor Systems A.8
A.4 Ionizing Radiation A. 10
A.5 Sonication A. 11
A.6 Iron(VI)-Ferrate A. 11
B. Case Study Of Romulus Removal Action B.I
C. List Of References C.I
D. Suggested Reading List D.I
xii
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LIST OF TABLES
Table Title Page
2.1 Applicability of chemical treatment techniques. 2.2
2.2 Summary listing of major design and other considerations. 2.6
3.1 Chemical treatment processes addressed. 3.5
3.2 Contaminants and media that have been chemically treated. 3.6
3.3 Results of KPEG Process Guam application. 3.10
3.4 Logarithm of stability constants reported for cadmium. 3.32
3.5 Advantages and limitations of metal hydroxide and metal
sulfide precipitation. 3.34
3.6 Results after treatment of plant wastewaters. 3.36
3.7 Sites of operation of GRC Process. 3.62
3.8 Sites of operation, high temperature chemical treatment
processes. 3.63
3.9 List of solubility products for various heavy metal
compounds. 3.80
3.10 Cost of treatment. 3.95
3.11 Economic comparisons of groundwater treatment systems. 3.98
4.1 Amenable to treatment (rule of thumb). 4.2
4.2 Summary of removals of heavy metal achieved using
various chemical precipitation techniques. 4.11
A. 1 BCD treatment of 2,4-D; 2,4,5-T. A.2
A.2 Relative oxidizing strength of oxidants. A. 12
B.I Cost breakdown for Romulus immediate removal action. B.2
xiii
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LIST OF FIGURES
Figure Title Page
3.1 Chemical"dechlorination"ofPCB. 3.8
3.2 Simplified mechanical flow diagram of KPEG field-scale
treatment system at Guam, U.S.A. 3.11
3.3 GRC Process flow diagram. 3.13
3.4 KGME/DECHLOR Process flow diagram. 3.15
3.5 Rotating kiln processor. 3.17
3.6 Simplified sectional diagram showing the four internal
zones-ATP. 3.18
3.7 Process flow diagram, ATP SoilTech. 3.19
3.8 The Ultrox System. 3.27
3.9 Solubilities of metal hydroxides and metal sulfides as a
function of solution pH. 3.33
3.10 Free-radical chain reaction of ozone decomposition. 3.58
3.11 Ozone decomposition catalyzed by hydrogen peroxide. 3.59
3.12 Resonance structures for O3. 3.61
3.13 Distribution of heavy metals under equilibrium conditions. 3.72
3.14 Schematic representation of direct and indirect reaction
pathways of O3. 3.73
3.15 Cross section of a grain of PCB-contaminated soil. 3.87
3.16 (a) Construction costs of ozonation systems. 3.96
(b) Breakdown of ozonation system construction costs. 3.97
4.1 Influence of pH on rate constants for ozone and various
inorganic compounds. 4.4
xiv
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Chapter 1
INTRODUCTION
This monograph on chemical treatment is one of a series of eight on
innovative site and waste remediation technologies that are the culmination
of a multiorganization effort involving more than 100 experts over a two-
year period. It provides the experienced, practicing professional guidance
on the application of innovative processes considered ready for full-scale
application. Other monographs in this series address bioremediation, soil
washing/soil flushing, solvent chemical extraction, stabilization/ solidifica-
tion, thermal desorption, thermal destruction, and vacuum vapor extraction.
1.1 Chemical Treatment
The term chemical treatment, as used in this monograph, refers to the use
of reagents to destroy or chemically modify target contaminants by means
other than pyrolysis or combustion. The monograph addresses processes
that chemically treat contaminated soils, groundwaters, surface waters, and,
to a limited extent, concentrated contaminants. Chemical treatment is a
means of converting hazardous constituents into less environmentally ob-
jectionable forms in order to meet treatment objectives.
This monograph addresses substitution, oxidation, and chemical precipi-
tation processes. It addresses processes within these classes that are suffi-
ciently advanced for full-scale application. There are a number of emerging
technologies within these classes that are in the research or an early devel-
opment stage, not yet ready for full-scale application, that appear to be very
promising technologically. Six such technologies are briefly addressed in
Appendix A.
1.1
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Introduction
1.2 Development of the Monograph
1.2.1 Background
Acting upon its commitment to develop innovative treatment technolo-
gies for the remediation of hazardous waste sites and contaminated soils
and groundwater, the U.S. Environmental Protection Agency (EPA) estab-
lished the Technology Innovation Office (TIO) in the Office of Solid Waste
and Emergency Response in March, 1990. The mission assigned TIO was
to foster greater use of innovative technologies.
In October of that same year, TIO, in conjunction with the National Ad-
visory Council on Environmental Policy and Technology (NACEPT), con-
vened a workshop for representatives of consulting engineering firms, pro-
fessional societies, research organizations, and state agencies involved in
remediation. The workshop focused on defining the barriers that were im-
peding the application of innovative technologies in site remediation
projects. One of the major impediments identified was the lack of reliable
data on the performance, design parameters, and costs of innovative pro-
cesses.
The need for reliable information led TIO to approach the American
Academy of Environmental Engineers®. The Academy is a long-standing,
multidisciplinary environmental engineering professional society with
wide-ranging affiliations with the remediation and waste treatment profes-
sional communities. By June 1991, an agreement in principle (later formal-
ized as a Cooperative Agreement) was reached. The Academy would man-
age a project to develop monographs describing the state of available inno-
vative remediation technologies. Financial support would be provided by
the EPA, U.S. Department of Defense (DOD), U.S. Department of Energy
(DOE), and the Academy. The goal of both TIO and the Academy was to
develop monographs providing reliable data that would be broadly recog-
nized and accepted by the professional community, thereby eliminating or,
at least, minimizing this impediment to the use of innovative technologies.
The Academy's strategy for achieving the goal was founded on a
multiorganization effort, WASTECH® (pronounced Waste Tech), which
joined in partnership the Air and Waste Management Association, the
American Institute of Chemical Engineers, the American Society of Civil
Engineers, the American Society of Mechanical Engineers, the Hazardous
1,2
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Chapter 1
Waste Action Coalition, the Society for Industrial Microbiology, and the
Water Environment Federation, together with the Academy, EPA, DOD,
and DOE. A Steering Committee composed of highly respected representa-
tives of these organizations having expertise in remediation technology
formulated the specific project objectives and process for developing the
monographs (See page iv for a listing of Steering Committee members).
By the end of 1991, the Steering Committee had organized the Project.
Preparation of the monograph began in earnest in January, 1992.
1.2.2 Process
The Steering Committee decided upon the technologies, or technological
areas, to be covered by each monograph, the monographs' general scope,
and the process for their development and appointed a task group composed
of five or more experts to write a manuscript for each monograph. The task
groups were appointed with a view to balancing the interests of the groups
principally concerned with the application of innovative site and waste
remediation technologies — industry, consulting engineers, research, aca-
deme, and government (see page iii for a listing of members of the Chemi-
cal Treatment Task Group).
The Steering Committee called upon the task groups to examine and
analyze all pertinent information available, within the Project's financial
and time constraints. This included, but was not limited to, the comprehen-
sive data on remediation technologies compiled by EPA, the store of infor-
mation possessed by the task groups' members, that of other experts willing
to voluntarily contribute their knowledge, and information supplied by pro-
cess vendors.
To develop broad, consensus-based monographs, the Steering Committee
prescribed a twofold peer review of the first drafts. One review was con-
ducted by the Steering Committee itself, employing panels consisting of
two members of the Committee supplemented by at least four other experts
(See Reviewers, page iii, for the panel that reviewed this monograph). Si-
multaneous with the Steering Committee's review, each of the professional
and technical organizations represented in the Project reviewed those mono-
graphs addressing technologies in which it has substantial interest and com-
petence. Aided by a Symposium sponsored by the Academy in October,
1992, persons having interest in the technologies were encouraged to par-
ticipate in the organizations' review.
1.3
-------
Introduction
Comments resulting from both reviews were considered by (he Task
Group, appropriate adjustments were made, and a second draft published.
The second draft was accepted by the Steering Committee and participating
organizations. The statements of the organizations that formally reviewed
this monograph are presented under Reviewing Organizations on page v.
13 Purpose
The purpose of this monograph is to further the use of innovative chemi-
cal treatment site remediation and waste processing technologies, that is,
technologies not commonly applied, where their use can provide better,
more cost-effective performance than conventional methods. To this end,
the monograph documents the current state of a number of innovative
chemical treatment technologies.
7.4 Objectives
The monograph's principal objective is to furnish guidance for experi-
enced, practicing professionals and users' project managers. The mono-
graph is intended, therefore, not to be prescriptive, but supportive. It is
intended to aid experienced professionals in applying their judgment in
deciding whether and how to apply the technologies addressed under the
particular circumstances confronted.
In addition, the monograph is intended to inform regulatory agency per-
sonnel and the public about the conditions under which the processes it
addresses are potentially applicable.
1.5 Scope
The monograph addresses innovative chemical treatment technologies
that have been sufficiently developed so that they can be used in full-scale
1.4
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Chapter 1
applications. It addresses all aspects of the technologies for which suffi-
cient data were available to the Chemical Treatment Task Group to describe
and explain the technologies and assess their effectiveness, limitations, and
potential applications. Laboratory- and pilot-scale studies were addressed,
as appropriate.
The monograph's primary focus is site remediation and waste treatment.
To the extent the information provided can also be applied to production
waste streams, it will provide the profession and users this additional ben-
efit. The monograph considers all waste matrices to which chemical treat-
ment processes can be reasonably applied, such as soils, liquids, and slud-
ges.
Application of site remediation and waste treatment technology is site
specific and involves consideration of a number of matters besides alterna-
tive technologies. Among them are the following that are addressed only to
the extent essential to understand the applications and limitations of the
technologies described:
• site investigations and assessments;
• planning, management, specifications, and procurement;
• regulatory requirements; and
• community acceptance of the technology.
1.6 Limitations
The information presented in this monograph has been prepared in accor-
dance with generally recognized engineering principles and practices and is
for general information only. This information should not be used without
first securing competent advice with respect to its suitability for any general
or specific application.
Readers are cautioned that the information presented is that which was
generally available during the period when the monograph was prepared.
Development of innovative site remediation and waste treatment technolo-
gies is ongoing. Accordingly, postpublication information may amplify,
alter, or render obsolete the information about the processes addressed.
1.5
-------
Introduction
This monograph is not intended to be and should not be construed as a
standard of any of the organizations associated with the WASTECH®
Project; nor does reference in this publication to any specific method, prod-
uct, process, or service constitute or imply an endorsement, recommenda-
tion, or warranty thereof.
7.7 Organization
This monograph and others in the series are organized under a uniform
outline intended to facilitate cross reference among them and comparison
of the technologies they address. Chapter 2.0, Process Summary, provides
an overview of all material presented. Chapter 3.0, Process Identification,
provides comprehensive information on the processes addressed. Each pro-
cess is fully analyzed in turn. The analysis includes a description of the
process (what it does and how it does it), its scientific basis, status of devel-
opment, environmental effects, pre- and posttreatment requirements, health
and safety considerations, design data, operational considerations, and com-
parative cost data to the extent available. Also addressed are process-unique
planning and management requirements, and process variations.
Chapter 4.0, Potential Applications, Chapter 5.0, Process Evaluation, and
Chapter 6.0, Limitations, provide a synthesis of available information and
informed judgments on the processes. Each of these chapters addresses the
processes in the same order as they are described in Chapter 3.0. Chapter
7.0, Technology Prognosis, identifies likely future applications of the pro-
cesses.
1.6
-------
Chapter 2
PROCESS SUMMARY1
Chemical treatment, for the purposes of this monograph, refers to the use
of reagents to destroy or chemically modify contaminants by means other
than pyrolysis, wet oxidation, or combustion. This monograph addresses
techniques used to chemically treat contaminated soils, groundwaters, sur-
face waters, and, to a limited extent, concentrated contaminants.
These technologies embrace a wide variety of processes used in treating
wastes and contaminated materials. They consist of a series of techniques
that can be selectively applied to destroy or modify organic and inorganic
contaminants. The selection varies depending on the particular contami-
nants and media. The systems and processes usually have to be modified
from one site to the next. Chemical treatment is usually employed as a pre-
or posttreatment process in site remediation and seldom as a stand-alone
process.
Chemical treatment processes convert hazardous constituents into less
objectionable environmental forms in order to meet treatment objectives.
The ideal goal for a treatment process is the complete mineralization of the
target contaminants, for example, the reduction of polychlorinated biphe-
nyls (PCBs) to sodium chloride, carbon dioxide, and water. This outcome
is relatively rare, however, and the goal set for most chemical treatment
processes is more modest — the conversion of selected contaminants into
less toxic or unregulated, i.e., not governed by state or federal regulations,
chemical forms. In many cases, the long-term environmental effect of the
chemical reagents and reaction products may not be well understood, and it
may not be known whether they will remain stable for long periods. This
uncertainty leads to tradeoffs between present cost and the risk of future
adverse environmental impact. The toxicity of the reaction products of all
chemical treatment methods, especially those of substitution reactions,
1. This chapter is a summary of Chapters 3.0 through 7.0. Sources are cited, where
appropriate, in those chapters — Ed.
2.1
-------
Process Summary
needs to be addressed. For example, replacing chlorine atoms on a con-
taminant with a glycol structure of methoxyethoxy moiety (as iin one of
polyethylene glycol processes described in the text) may produce a mol-
ecule that may not be regulated at the time of treatment, but it may not be
less toxic than the original compound.
2.1 Process Identification and Description
Although chemical treatment processes potentially span the full range of
chemistry, only the following techniques have been applied in site and
waste remediation:
• Substitution;
• Oxidation; and
• Precipitation.
See table 2.1 for a list of the contaminants, by media, that might be
treated by each technique.
2.1.1 Substitution Processes
Substitution reactions have been used to treat soils contaminated with
chlorinated organic compounds, such as PCBs or chlorodibenzodioxins.
Table 2.1
Applicability of Chemical Treatment Techniques
Technique Media Contaminants
Substitution Soil, oils, and debris Halogenated and other
Processes Generally not applicable to substituted organics, such as
aqueous streams PCD and dioxms
Oxidation Processes Aqueous streams, dilute Relatively low concenti ations of
paniculate suspensions, and organics
some debns
Precipitation Only aqueous streams Inorganic contaminants
Processes
2.2
-------
Chapter 2
Substitution reactions do not mineralize the halogenated organic com-
pounds, but, instead, convert the compounds into substituted forms that are
within regulatory standards. In most cases, the chlorine or other group that
is characteristic of the target compound is substituted by another functional
group that converts the contaminant to a nonregulated form.
The substitution processes that have been used or appear to be developed
sufficiently to be used for site and waste remediation fall into two broad
classes: (1) low-temperature processes in the 130 to 160°C (260 to 320°F)
range and (2) high-temperature processes in the 200 to 345 °C (400 to
650°F) range.
Three innovative low-temperature substitution processes were identified
and are addressed in this monograph — the potassium polyethylene glycol
(KPEG) Process, the Galson Research Corporation (GRC) Process, and the
KGME/DECHLOR Process. Of these, only the GRC Process has been used
commercially. The KPEG Process was used once at the pilot-scale. The
KGME/DECHLOR Process is, at present, in the pilot-scale phase of devel-
opment and it appears that it will be applicable to site and waste
remediation.
One apparently successful high-temperature process (SoilTech Anaero-
bic Thermal Processor (ATP)), which combines chemical treatment with
pyrolysis, and is addressed in this monograph. Its reactor subjects the
treated material first to temperatures of 200° to 340°C (400 to 650°F) and
then to temperatures of 480 to 600°C (900 to 1,100°F).
One emerging substitution reaction technology, Base Catalyzed Decom-
position (BCD), has been identified. It, along with other emerging tech-
nologies, is discussed in Appendix A.
2.1.2 Oxidation Processes
In the oxidative degradation of organic compounds, an organic com-
pound is converted by means of an oxidizing agent into new materials typi-
cally having either a higher oxygen or lower hydrogen content than the
original compound. Oxidative processes that appear applicable use ozone
and hydrogen peroxide (individually or together) in conjunction with ultra-
violet light to destroy organic contaminants in an aqueous stream.
2.3
-------
Process Summary
The oxidation processes addressed in this monograph are ozone-based
advanced oxidative processes (AOPs). These processes, based on free radi-
cal, chain reaction chemistry, combine ozonation with ultraviolet (UV)
photolysis. Some compounds that are resistant to destruction or are only
slowly destroyed by UV irradiation alone or UV in combination with either
ozone or hydrogen peroxide are rapidly destroyed, and to a greater extent,
by all three agents. Following are the AOPs addressed:
• Rayox — This process has been shown to be effective in treating
a wide variety of halogenated compounds, volatile compounds,
and other organics; and
• Ultrox — This process has been used in treating a variety of
organic constituents in aqueous streams.
The following emerging oxidation technologies are addressed in appen-
dix A:
• Iron (II) Catalyzed H2O2 Oxidation (Fenton's Reagent);
• Photocatalysis in Semiconductor Systems;
• Ionizing Radiation;
• Sonication; and
• Iron (VI) Oxidation.
A case study of the use of hypochlorite in treating cyanide- contaminated
material is provided in Appendix B. This process is well established and of
relatively limited applicability, but the case study is presented for the useful
information it provides on the cost of treatment.
2.1.3 Chemical Precipitation Processes
Chemical precipitation entails transforming a soluble compound into an
insoluble form through the addition of chemicals, to a point of supersatura-
tion. The process is routinely used in treating wastewaters. Its application
in site remediation is less common, but it appears to have potential for re-
moving toxic metals.
Precipitation is largely used for the treatment of aqueous materials con-
taminated with toxic inorganic elements and compounds. In treating soils,
it would normally be classified as a stabilization rather than a chemical
treatment process.
2.4
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Chapter 2
The following precipitation processes are addressed:
• Hydroxide;
• Carbonate;
• Sulfide;
• Xanthate; and
• Combined precipitation treatment.
2.1.4 Design and Other Considerations
Many of the general design considerations for chemical treatment pro-
cesses are similar to those of other remediation processes. Design consider-
ations unique to chemical treatment are addressed in this monograph. See
table 2.2 (on page 2.6) for a summary listing of some unique design consid-
erations along with health and safety considerations and pre- and posttreat-
ment requirements.
2.1.5 Materials Handling
Once the fundamental requirement of performance needs is met, the
principal concern in selecting a chemical treatment system is meeting mate-
rial handling requirements. The system must accommodate wastes, often
abrasive and corrosive, of varying characteristics. In many cases, the
wastes may be incompatible with particular designs. For example, high
concentrations of suspended solids may make it impossible to use UV-
based processes because turbidity will attenuate UV transmission through
the suspension.
Fugitive emissions are an important consideration. Conveyors and other
materials-moving equipment must often be modified to minimize fugitive
emissions. A conveyor that releases a small amount of dust may be accept-
able for transporting gravel, but not for transporting a contaminated mate-
rial.
Another important design consideration lies in recognizing that most
wastes are heterogeneous. The system must be capable of treating extremes
in waste composition and contaminant concentrations. If, for example, the
system is designed to handle wastes having average characteristics, it will
fail when it is fed waste having characteristics outside this limited range.
2.5
-------
Process Summary
Table 2.2
Summary Listing of Major Design and Other Considerations
Substitution
Processes
Oxidation
Processes
Precipitation
Processes
Design
Considerations
• Highly alkaline •
reagents will attack
aluminum and .
magnesium system
components, forms H2
gas
• Elastomeric seals are
subject to attack by
reagents
• Reactor size depends
on residence time
required
• System design •
depends on residence ,
time requirements and
level of degradation
needed
• Performance depends
on UV lamp geometry,
wavelength of UV,
and optical path length
• Efficiency of ozone
generation depends on
type and pretreatment
of feed gas-air or
oxygen
• Solubility products of •
target species and ,
precipitating reagent
must be below their
concentrations in
solution
• If multiple substances
are present.
coprecipitation can
occur
Requirements
Conduct treatability
studies
Dewater and filter oils
Delump and screen
soils
Drain and dry solids
.uid soils
Filter liquid streams
Pretreatment may be
needed to prevent
excessive fouling of
UV lamps
Filter liquid streams
pH adjustment
Posttreatment Health & Safety
Requirements Considerations
• Neutralize excess •
caustic
• Remove excess
reagents by
washing
•
• Residual ozone in •
offgas must be
destroyed
• Effluent may
require pH •
adjustment, solids
removal, or ,
removal of
residual H2O2
• Effluent may
require further
treatment, i.e.,
biotreatment or
adsorption
• Highly site «
specific
• Must consider
sludge volume
and stability
• Cost savings may
result from metals
recovery
Uncertainty
about long-
term effects of
substitution
products
Avoid
aluminum and
magnesium for
matenal of
construction
Handling of
strong
oxidizing
agents
Control of
hydrogen gas
Ozone is a
toxic gas and a
fire hazard
Potential for
H2S formation
in sulfide
precipitation
Heterogeneity of wastes presents a problem for all remediation processes,
but chemical treatment processes are particularly vulnerable because of
competing reactions, stoichiometric relationships among reactants, and the
possibility that trace materials can poison reactions, especially catalytic or
chain reactions.
2.6
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Chapter 2
2.1.6 Costs
Major components of fixed cost are equipment amortization, marketing,
permits and approvals, and shipping and setting up equipment. Major com-
ponents of variable cost are reagent purchase and recovery, utilities, labor,
travel and subsistence, and analytical costs.
Most remediation systems tend to be highly specialized. The system is
designed for a given application and its cost must be amortized over one or
a few projects. One way to minimize this effect is to design the system so
that it can be assembled from readily available, reusable components.
While the system may be highly specialized, the components can be used
from one project to the next. Chemical treatment systems lend themselves
to this approach. The components are generally readily available and can be
rearranged for different applications. In addition, the systems tend to be
compact. They are relatively inexpensive to ship, set up, and knock down.
Reagent cost, unique to chemical treatment processes, is usually a sig-
nificant part of the overall cost, and reagent recovery is an economic (as
well as environmental) necessity. In addition, the typical chemical treat-
ment process requires highly trained workers, usually unavailable locally.
Consequently, the labor and travel costs for a chemical treatment
remediation are generally higher than those of other remediation operations.
2.2 Potential Applications
Chemical treatment is rarely used alone. Typically, it is used as part of a
treatment train — as a pretreatment technique to enhance the efficiency of
subsequent processes or in posttreatment of an effluent. Following are ex-
amples of applications:
• Oxidation techniques have been used in wastewater treatment to
"soften" organic compounds to improve their biodegradability;
and
• Chemical dechlorination can be used to treat the chlorinated
organics that are removed from soil through solvent extraction
or thermal desorption.
2.7
-------
Process Summary
The waste matrix is a major factor in any remediation. With soils, such
variables as the quantity and quality of the natural organic material, mineral
content, and amorphousness of clays result in a high variability of perfor-
mance among sites as well as within a particular site. Designs based on
"average characteristics of a soil" will often encounter operating difficulties
when a "nonaverage" soil is encountered. Nevertheless, the following gen-
eral rules appear to apply, although with numerous site- and process-spe-
cific exceptions:
• Solids tend to be more difficult to treat than liquids;
• The larger the particle size of nonporous materials in the matrix,
the easier it is to treat the contaminants. Larger particulates
make the contaminants more accessible to the reagent and per-
mit a clean separation of the reagent after treatment (the oppo-
site tends to be true of porous materials, such as organic soils);
and
• The cost of treatment of substitution processes increases with
contaminant concentration. For oxidation processes, the rela-
tionship is less clear. Precipitation processes typically do not
apply to low-concentration contaminants.
Chemical treatment should be considered for use at sites where one or
more of the following conditions exist:
• The remediation is mainly driven by one or a few specific kinds
of contaminants that can be chemically modified;
• The quantities of material to be treated or local concerns pre-
clude the transport of the contaminants to an off-site: treatment
location;
• Established processes, such as incineration, are unacceptable
technically or because of local concerns; and
• The quantity of material to be treated is small or the contaminant
concentrations are low. The economics of such a site favor the
low-capital, high-operating cost approach.
2.2.1 Substitution Processes
Substitution processes should be considered for treating oils or soils and
other solids that are contaminated with a particular class of compound, such
2.8
-------
Chapter 2
as PCBs. They do not appear to be effective in treating aqueous streams.
Substitution processes are most effective in treating halogenated aromatic
compounds. Possible additional applications include treating halogenated
aliphatics, nitrogen-bearing compounds, and sulfonated compounds.
2.2.2 Oxidation Processes
Oxidation processes should be considered for treating aqueous streams
and some slurries that are considered hazardous because they contain low
concentrations of organic constituents. The most likely applications are
treatment of groundwater or surface water streams that are contaminated
with such compounds as cyanides and light organics.
2.2.3 Precipitation Processes
Precipitation processes, by their nature, are limited to liquid systems.
They should be considered for treating materials that are hazardous because
they contain toxic metal compounds in an aqueous solution. Precipitation is
applicable whenever the target metal is present in a soluble form and can be
chemically converted to a less soluble form.
2.3 Process Evaluation
Both oxidation and precipitation processes are commercially available
for treating drinking water and wastewater. Therefore, it is believed these
processes would be effective in treating contaminated groundwaters. Their
use for this purpose is a matter of transfer of the technology to another ap-
plication, rather than de novo development of technology .
For over a decade, substitution processes have been available for the
treatment of soils and sludges contaminated with PCBs and other chlori-
nated organics. They have not been used extensively for the following
reasons:
• Existing technologies, such as incineration and landfilling have
been cheaper and more widely available; and
• An initial field test of the technology identified design problems,
but no additional funding for follow-up work was available.
2.9
-------
Process Summary
It appears these problems are being resolved or eliminated. Incineration
and landfilling are, at times, rejected. In addition, the costs quoted by the
vendors of several substitution processes (GRC, SoilTech/ATP, and
KGME/DECHLOR), are beginning to approach those of incineration. Fi-
nally, the design problems are being addressed and solved.
2.4 Limitations
2.4.1 Substitution Processes
Although substitution reactions can occur in the presence of water, large
quantities of water will interfere with the desired chemical reactions and
consume excessive quantities of reagent. Therefore, substitution processes
are not now practical for treating aqueous wastes. Although the processes
can operate in the presence of water, the processes are generally impractical
because their operating temperatures above 100°C boil the water out of the
reaction system, increase heat requirements, and reduce efficiency. They
may be operated under pressure in order to maintain a temperature above
the system's boiling point. However this requires special pressure vessels
and other process equipment.
Commercial substitution reactions presently available do not mineralize
halogenated organic compounds. Instead, they convert the compounds into
substituted forms that are within regulatory standards. This means that they
are applicable only in treating regulated contaminants, such as PCBs and
dioxins. They are not applicable in treating general types of contaminants,
such as hydrocarbons or unsubstituted organic compounds, such as benzene.
2.4.2 Oxidation Processes
Of the three classes of processes addressed here, oxidation processes
actually destroy or mineralize the target organic contaminants. In doing so,
however, they consume relatively large quantities of ozone and/or hydrogen
peroxide.
Advanced oxidation processes using ultraviolet light to form free radicals
were developed to overcome this limitation. Since advanced oxidation
2.10
-------
Chapter 2
processes are based on hydroxyl free radical chemistry, chemical interac-
tions are highly nonspecific and nonselective. Rates of destruction vary
with such factors as the nature of the contaminant mixture, pH, concentra-
tion of contaminants, presence of scavengers, and inorganic nature.
Oxidation processes do not work well in the presence of free radical
scavengers, such as bicarbonate and carbonate ions. The scavengers con-
sume the ozone and hydrogen peroxide, and inhibit the effect of the UV
radiation. The presence of such scavengers requires higher doses of oxidiz-
ers and larger UV fluxes.
Another important factor is penetration of UV light through the wastewa-
ter stream. Light penetration is attenuated by high particle concentrations.
Consequently, the technique, in general, is not well suited to treating soils.
A similar problem is optical fouling of the quartz tubes containing the UV
light source. This occurs gradually, over the course of the treatment, and
can significantly reduce process performance and efficiency. Some form of
tube cleaning should be incorporated in all such processes.
2.4.3 Precipitation Processes
Precipitation reactions are limited to the treatment of inorganic materials
in aqueous media. They are routinely used in the treatment of wastewaters,
but their application in site remediation is less common.
One potential limitation lies in the collection and handling of precipi-
tates. Their handling must be addressed in a treatability study conducted
before the treatment method is selected.
2.5 Technology Prognosis
Under proper conditions, discussed in this monograph, chemical treat-
ment can be a useful treatment technology. The following are likely appli-
cations of the processes addressed in this monograph:
• Substitution processes, especially the high temperature substitu-
tion processes, will be used to treat soils and sludges contami-
nated with PCBs, pentachlorophenols, chlorodibenzodioxins,
and chlorodibenzofurans;
2.11
-------
Process Summary
Oxidation and precipitation processes will be used to treat water
from pump-and-treat applications; and
Precipitation processes will be commonly used to treat aqueous
streams that are contaminated with toxic metals.
-------
Chapter 3
PROCESS IDENTIFICATION AND
DESCRIPTION
Chemical treatment, for the purposes of this monograph, refers to the use
of reagents to destroy or chemically modify target contaminants by means
other than pyrolysis or combustion. The monograph addresses techniques
used to chemically treat contaminated soils, groundwaters, surface waters,
and, to a limited extent, concentrated contaminants. Chemical treatment is
a means of converting hazardous constituents into less environmentally
objectionable forms in order to meet treatment objectives.
Embracing a wide variety of processes used in treating wastes and con-
taminated materials, chemical treatment is not a "technology" in the same
sense as is, for example, incineration. Instead, it consists of a series of tech-
niques that can be selectively applied to destroy or modify organic and
inorganic contaminants. The selection varies depending on the particular
contaminants and media. The systems and processes usually have to be
modified, at least to some extent, from one site to the next.
Chemical treatment has been successful in a number of applications. The
following instances are limited to those for which data exist from (1) an
actual remediation, (2) a scale equivalent to a remediation, or (3) a pilot
study whose results can be scaled up to a remediation application:
• treatment of polychlorinated biphenyls (PCBs),
chlorodibenzodioxins (dioxin) and pentachlorophenol (PCP) in
soil;
• treatment of cyanides in water and on debris;
• treatment of phenols in groundwater;
• treatment of nonsubstituted and chlorinated hydrocarbons in soil
and in groundwater;
• precipitation of toxic metals from groundwater;
3.1
-------
Process Identification and Description
• treatment of PCBs in mineral oil; and
• destruction of low-level organic compounds in groundwater.
Chemical treatment is rarely used as the sole process. It may be used as
a pretreatment technique to enhance the efficiency of subsequent processes
or as a posttreatment step in treating an effluent. Following are examples of
such applications:
• Various advanced oxidation techniques have been successfully
employed to soften organic compounds to improve their biode-
gradability;
• Chemical dechlorinadon can be used to treat the contaminated
eluate from solvent extraction of chlorinated organics from soil;
and
• Chemical destruction can be used to treat the offgases from a
vapor phase extraction process.
The ideal goal for a treatment process is the complete mineralization of
the contaminants — for example, reduction of a PCB to sodium chloride,
carbon dioxide and water. Although mineralization can result from certain
oxidation processes, this outcome is relatively rare and has been commer-
cially achieved with but a few readily oxidizable compounds. Therefore,
the actual goal set for chemical treatment processes is more modest — for
example, the conversion of selected contaminants into chemical forms that
are less toxic or unregulated.
In many cases, the long-term stability or environmental effect of the
chemical reagents and the reaction products may not be well understood
and it may not be known whether they will remain stable for long periods.
This uncertainty results in tradeoffs between present costs and the risk of
future liability or future adverse environmental impact. As considered here,
chemical treatment has the following specific goals:
• Convert the hazardous constituents into a less toxic or environ-
mentally less objectionable form. For example, the replacement
of chlorine on a PCB or chlorodibenzodioxins (dioxin) molecule
with an aryl or alkyl group (using, for example, sodium
napthalenide reagent) or with another functional group (as with a
polyethylene glycol). The addition of the group to the PCB or
dioxin molecule converts it to an unregulated substance;
3.2
-------
Chapter 3
• Convert the hazardous constituents into a less mobile form, for
example, by precipitation;
• Convert the hazardous constituent into a form that is more ame-
nable to subsequent treatment by another process. An example
is the partial oxidation of contaminants in groundwater to con-
vert refractory (difficult to degrade) organics into compounds
that are amenable to biodegradation; and
• Convert the hazardous constituent into a more mobile form,
thereby making it amenable to a second treatment process that is
to remove the modified hazardous constituents from the nonhaz-
ardous matrix. (While mobilization is conceptually possible, no
such commercial or near-commercial chemical processes were
identified).
An important consideration when using chemical treatment is the nature
of the material leaving the treatment process. Chemical treatment requires
that reagents be mixed with the contaminated material. When the reagents
destroy or modify the target contaminants (e.g., Cr*6, PCBs, dioxins), the
"decontaminated material" still contains chemical reaction products and any
residual reagents, which may be toxic or hazardous. Even if they are not,
their presence may have a significant environmental impact, such as a high-
oxygen demand, on the surrounding ecosystem. If the "treated" material is
returned to the site, the residual reagents (which will usually be mobile)
may be cause for concern. It might not be possible to dispose of the treated
material because of health and safety regulations.
An example of this concern arises in the treatment of organic contami-
nants by substitution processes. As explained below, all commercial substi-
tution processes convert the contaminant into an unregulated form by
replacing one or more halogen atoms on the target molecule (a PCB, for
example) with another functional group, such as an ether. The resultant
compound is, at present, unregulated, but its environmental impact still
needs to be considered. Complete replacement with hydrogen (as claimed
for the Base Catalyzed Decomposition (BCD) process) may not always be
desirable. For example, if all chlorine atoms on chlorobenzene are replaced
with hydrogen, benezene, a known carcinogen, is formed. One must ap-
proach chemical treatment with knowledge of the chemical transformations,
regulatory requirements, and environmental ramifications.
3.3
-------
Process Identification and Description
Chemical treatment, by its nature, is technique-oriented rather than pro-
cess-oriented. That is, to determine the proper treatment method, it is first
necessary to identify the target contaminant and determine its reactivity and
accessibility. Chemical knowledge is used to ascertain the kind of chemical
reactions to which the target cornpound(s) is amenable, evaluate the avail-
able equipment, and select or design the appropriate treatment system. This
orientation is reflected in the grouping of technologies addressed in this
monograph by the kind of chemical reactions they use, that is, by substitu-
tion processes, oxidation processes, and precipitation processes (see table
3.1 on page 3.5).
While substitution reactions can occur in the presence of water, large
quantities of water will interfere with the desired chemical reactions and
consume excessive quantities of reagent. As a result, these reactions have
not, to date, been applied to the treatment of aqueous systems.
Oxidation embraces a broad class of chemical reactions that are well
established methods for treating aqueous liquids containing small amounts
of organics or cyanide. One can effectively oxidize low concentrations of
contaminants by appropriate use of oxidation reactions; some materials,
such as cyanides, can even be mineralized. Commonly used oxidizing
agents are ozone (O3), hypochlorite, and hydrogen peroxide (H2O2). Air is
frequently used as the oxidizing agent in wet-air oxidation and incineration
processes. Reactions using ozone, hydrogen peroxide, ultraviolet (UV)
light, and hypochlorite are oxidation processes.
Chemical precipitation involves transforming a soluble compound into
an insoluble form through the addition of chemicals such that a supersatu-
rated environment exists. Precipitation is largely used for the treatment of
aqueous materials contaminated with toxic inorganic elements and com-
pounds. Its use in the treatment of soils would normally be considered to be
stabilization. The process has been routinely used for the treatment of
wastewaters. Its application in remediation is less common, but data from
wastewater applications indicate that it is applicable. No specific use of the
process was found that would qualify it as an "innovative technology" (see
Section 1.3). Its underlying principles are presented here in the interest of
aiding in transferring the technology from the field of wastewater treatment
to the treatment of groundwater, surface waters, and other liquids in
remediations.
3.4
-------
Chapter 3
Table 3.1
Chemical Treatment Processes Addressed
•SUBSTITUTION PROCESSES
ESTABLISHED TECHNOLOGIES
- Sodium metal/aromatic/ether
- NaPEG* - developed in early 1980s — no successful field tests conducted
INNOVATIVE TECHNOLOGIES
Low Temperature PEG reagents
- KPEG/APEG
- APEG Plus - Galson Research (GRC)
- DECHLOR/KGME - Chemical Waste Management (CWM)
High Temperature Chemical Reactions
- Soiltech Anaerobic Thermal Processor (ATP) - Canonie Engineering
EMERGING TECHNOLOGY
High Temperature Chemical Reactions
- Base Catalyzed Dechlorination (BCD) - EPA/RREL
•OXIDATION PROCESSES
INNOVATIVE TECHNOLOGIES
- Ozonation
- H2O2 or Ozone with UV
EMERGING TECHNOLOGIES
- Iron (II) Catalyzed Oxidation, (H2O2/FeII), Fenton's Reagent
- Sonication
- Ionizing Radiation
•CHEMICAL PRECIPITATION PROCESSES
ESTABLISHED TECHNOLOGIES
- Hydroxide Precipitation
- Carbonate Precipitation
- Sulfide Precipitation
- Xanthate Precipitation
- Combined Precipitation Treatment
" The NaPEG process is discussed as a precursor process which, while not commercially sucessful on its
own, illustrates the technical basis for other processes which were operated commercially
An established method of chemical treatment is the use of sodium or
calcium hypochlorite (NaOCl or Ca(OCl)2) for disinfection, by destroying
low concentrations of organics in water and for the destruction of cyanides
by oxidation. A discussion of the treatment of cyanide-contaminated film
chips as part of the emergency removal action at the PBM Enterprises site
in Romulus, Michigan is included in Appendix B. This application is not
considered an innovative process; destruction of cyanides by hypochlorite is
3.5
-------
Process Identification and Description
established technology and chemistry. The case study, however, illustrates
when chemical treatment is applicable and provides a concrete example of
the costs of such an application.
For operational reasons, not every technology can be applied to media
encountered in remediation — soil, debris, water, and oil. See table 3.2.
Table 3.2
Contaminants and Media that have been Chemically Treated
SOILS
• PCB, dioxins, PCP
DEBRIS
• cyanides
WATER
• cyanides
• phenols
• metals (precipitation)
OTHER
• PCB and dioxins m mineral oil
3.1 Substitution Processes
Commercial processes based on substitution reactions have successfully
treated soils, sludges, and oils contaminated with halogenated organics,
such as PCBs, chlorodibenzodioxins (dioxins), or chlorodibenzofurans
(dibenzofurans). It is claimed that an emerging process, the BCD Process,
discussed in Appendix A, is capable of also treating hazardous sulfur-bear-
ing and nitrogen-bearing compounds. However, only laboratory data on
this application are available at present. Substitution reactions have been
used successfully in remediations (up to 36,000 tonne (40,000 ton)) to treat
soils contaminated with chlorinated organic compounds. Examples of treat-
ment are:
• Conversion of PCBs on soil and in oils to unregulated, substi-
tuted chlorobiphenyls; and
3.6
-------
Chapter 3
• Conversions of chlorodibenzodioxins and chlordibenzofurans on
soil and in oil to substituted chlorodibenzodioxins and
chlordibenzofurans which may be subject to less stringent regu-
lation.
Of the two substitution processes listed in table 3.1 (on page 3.5) under
"established technology," the first, Sodium metal/aromatic/ether, is a highly
specialized process used commercially in the early to mid-1980s to treat
PCB-contaminated mineral oils. The process destroys the PCBs dissolved
in the mineral oil by using a reagent prepared by reacting sodium metal, a
polycyclic aromatic compound, and an ether. The commonly used aromatic
compounds were naphthalene or biphenyl. The commonly used ethers were
tetrahydrofuran or one of the diethers, such as ethyleneglycol dimethyl
ether (commercial name — Diglyme). The resulting reagent is deactivated
by water. Its use, therefore, is limited to high purity organic media.
The second of the established substitution processes, sodium polyethyl-
ene glycol (NaPEG), was developed in the late 1970s but was not used be-
yond the laboratory scale, except for a few unsuccessful field trials.
Sodium polyethylene glycol is formed by reacting sodium hydroxide
(NaOH) with polyethylene glycol. The resultant reagent is mixed with the
contaminated material and the NaPEG, in principle, replaces one or more
chlorines on the target molecule.
Subsequent research indicated that a similar substitution reaction using
potassium polyethylene glycol (KPEG) is preferable to the NaPEG
(Brunelle and Singleton 1983, 1985). The KPEG reagent is prepared in the
same way as the NaPEG reagent except that potassium hydroxide (KOH) is
used instead of sodium hydroxide. The processes are described in greater
detail by Weitzman (1982), Brown et al. (1982), and Smith and Bubbar
(1979).
All substitution processes reviewed appear to fall into two broad catego-
ries:
• Low temperature processes operating in the 130 to 160°C (260
to 320°F) range; and
• High temperature processes operating in the 200 to 345 °C (400
to 650°F) range.
One high temperature process (SoilTech Anaerobic Thermal Processor
(ATP)), discussed later, combines chemical treatment with pyrolysis. In the
3.7
-------
Process Identification and Description
reactor, the treated material is subjected to temperatures of 200 to 345 °C
(400 to 650°F) in the first zone and then to temperatures of 480 to 600°C
(900 to 1,100°F) in the second zone.
Figure 3.1 illustrates the chemistry of substitution reactions. It shows a
PCB molecule before and after treatment with (in this case) polyethylene
glycol reagent. As can be seen, treatment converts the PCB molecule into a
unregulated substituted chlorobiphenyl. Figure 3.1 shows only one level of
substitution. Clearly, the chemical reaction can substitute additional chlo-
rine atoms on the PCB molecule. The type of functional group that replaces
the chlorine atom is determined by the process chemistry.
Figure 3.1
Chemical "Dechlorination" of PCB
Cl
Cl
HOCH2[CH2OCH2;inCH2OK
y no'-istrc
ci ci
; >OCH2[CH2OCH2lnCH2OH
Cl
Reprinted by permission of the National Ground Water Association from "Groundwater Treatment With Ultraviolet Light and
Hydrogen Peroxide" by M.A Rowland in the 1989 Outdoor Action Conference Copyright 1989 by the National Ground
Water Association.
Different chemical processes substitute different functional groups for
the chlorine. For example, the processes using polyethylene glycol (KPEG
and Galson Research Corporation (GRC)) replace the chlorine with the
glycol structure; it is claimed that the BCD Process replaces it with hydro-
gen. Note that data documenting this result have not, to date, been obtained
from the developer of the BCD Process .
3.8
-------
Chapter 3
The main application of the substitution processes has been in the treat-
ment of oils and soils contaminated with halogenated aromatics, mainly
PCBs and PCP. The PCBs in the environment are always associated with
chlorobenzenes, which have also been treated successfully by substitution
processes.
No field data was found on the treatment of halogenated organic com-
pounds other than on the treatment of chlorinated aromatic compounds.
Informal discussions with chemists who have worked with substitution
reactions led to the impression that:
• Aliphatic compounds appear to be more difficult to treat than
aromatic compounds;
• Fluorinated compounds appear to be more difficult to treat than
their corresponding chlorinated compounds; and
• Brominated and iodine compounds appear to be less difficult to
treat than their corresponding chlorinated compounds.
Although no actual data substantiating these claims was found, this ob-
servation may be useful for preliminary evaluations of various processes.
3.1.1 Low-Temperature Substitution Processes
Three low-temperature substitution innovative processes applicable in
remediation were identified: KPEG, GRC, and KGME/DECHLOR Pro-
cesses. The core of each process is a heated, agitated reactor. Heat is nec-
essary to maintain the 130 to 160°C (260 to 320°F) temperatures needed for
the reaction. In the KPEG Process, heat is also necessary to lower the vis-
cosity of the polyethylene glycol (PEG)-400 reagent, a viscous fluid that is
difficult to mix into the soil. In the KPEG and GRC Processes, the reactor
is capable of accepting and discharging soils. The KGME/DECHLOR
Process is designed to treat the contaminated oily extract from a thermal
treatment process (Chemical Waste Management's X*TRAX Process), and
not to treat soil.
The KPEG Process was used only for a demonstration of the chemistry.
For this demonstration, the treated soil leaving the reactor did not require
treatment beyond neutralization of the reagent to achieve an acceptable pH.
The PEG and products of the reaction remained with the soil. As a result,
this process did not require equipment to clean the soil. Polyethylene gly-
3.9
-------
Process Identification and Description
col is a food additive and is biodegradable. Its subsequent biodegradation
in the environment must, however, be monitored to assure that excessive
oxygen demand is not placed on the ecosystem. The GRC Process has an
extensive system for washing the residual reagent and reaction products
from the soil. The washing serves two purposes: (1) mitigating the environ-
mental impacts discussed above and (2) reducing cost by recovering the
PEG. Polyethylene glycol is an expensive material, costing approximately
$2.25/kg ($1.00/lb), and its recovery and reuse is crucial to the economic
viability of the process. See table 3.3 for the extent of destruction of PCBs
achieved by the process.
Table 3.3
Results of KPEG Process Guam Application
PCB Concentration in Soil (ppm)
Sample
1
2
3
Before
treatment
3,276
3,828
3,651
After
treatment
13.9
1.01
331
%
Reduction
99.57
99.97
99.91
PCB in
Condensate
(ppm)
0.831
0.176
3.50
3.1.1.1 KPEG Process
The process shown in figure 3.2 (on page 3.11) was a batch process em-
ploying a combination of PEG-400 (polyethylene glycol with an approxi-
mate molecular weight of 400) and KOH to react with the aromatic
chlorides in contaminated soils and sludges. Contaminated solids were
mixed with the solution of KOH in polyethylene glycol and heated to 150 to
180°C (300 to 360°F) for four hours. This resulted in deactivation of PCBs;
that is, one or more of the chloride moieties on the PCBs were replaced by
alkoxy ethylene units. At the conclusion of the operation the reaction mix-
ture was highly alkaline. After cooling, the mixture was neutralized by the
addition of sulfuric acid and was discharged to a collection hopper made of
steel. It was stored until approval was obtained for its release to the envi-
ronment.
3.10
-------
Chapter 3
Figure 3.2
Simplified Mechanical Flow Diagram of KPEG
Field-Scale Treatment System at Guam, U.S.A.
Reprinted by permission of the Hazardous Material Control Resources Institute from "Industrial Plant Expansion
Groundwater and Soil Cleanup* by J.E Edwards and T. Bonham in the 5th National Conference on Hazardous Wastes
and Hazardous Materials. Copyright 1988 by Hazardous Material Control Resources Institute
The reactor was a 3,000-L (793-gal) jacketed vessel with a working ca-
pacity of 1,900 L (490 gal). It was equipped with a 75-hp motor and a gear
box stirrer capable of providing mixer shaft speeds of 30 and 60 rev/min. A
nitrogen purge was maintained on the system for safety. The reactor was
heated by circulating heat transfer fluid through the jacket. All wettable
parts of the system were made of 316 stainless steel. (Ferguson and Rogers
1990).
The results were similar to those of other processes; substitution of the
aromatic chloride by the alkoxyethoxy moiety for the aromatic chloride
occurs, except that, it is claimed, all chlorine atoms on the PCB were re-
placed. No proof of such complete substitution is given, although complete
3.11
-------
Process Identification and Description
substitution is not necessary in order to convert the PCB into a unregulated
form. The treated soil leaving the KPEG process was saturated with PEG
after this demonstration. It was described by one observer as similar to
quicksand.
3.1.1.2 GRC Process
The GRC Process (also called the alkaline polyethylene glycol (APEG)
Plus Process) was developed by the Galson Remediation Company
(Peterson 1986). It uses KPEG mixed with dimethyl sulfoxide (DMSO) as
the reagent. The DMSO extracts the contaminant from the soil, reduces the
PEG's viscosity, and catalyzes the substitution reaction (GRC 1992). The
first system employing DMSO and KPEG was designed for liquids, PCB-
contaminated transformer oil. A specially-designed second system was
subsequently used to treat contaminated soils.
Before treatment, the site is prepared by excavating and stockpiling the
contaminated soil. The contaminated soil is screened to less than 1.5 cm
(0.6 in.) and sent through a shredder; larger particles are removed by the
separator and washed. Screened particles are loaded and conveyed to a wet
slurry mixing feed system where they are reacted with reagents (Peterson
1986).
The soil/reagent mixture is heated to 150°C (SOOT) and reacted for sev-
eral hours in the presence of a 45% aqueous solution of potassium hydrox-
ide (1 part), polyethylene glycol (4 parts), DMSO (1 part), and the
chloroaromatic contaminant. In clay soils, the recipe calls for \25 Ib of
reagent mixture per 100 Ib of soil. If the contaminant soil is sandy, then 60
Ib of reagent mix is used with 100 Ib of soil. The level of contaminant, soil
type, water content (which should be less than 30% in clay soil), and size of
soil particles all affect the separating conditions.
After treatment is completed, free reagent is separated by cleeantation.
This is followed, as shown in figure 3.3 (on page 3.13), by a series of
washes with water to remove the residual KPEG reagent. Note that both
PEG and KPEG are miscible with water. After washing, the clean soil is
partially dried and discharged. The washwater is distilled to recover the
PEG, DMSO, and potassium hydroxide. The residue from the (distillation
consists of the reaction products potassium chloride and hydroxylated(s)
polychlorobiphenyls.
3.12
-------
Chapter 3
Figure 3.3
GRC Process Flow Diagram
f
Wash Water
Makeup
f Salts
and Reaction Products
3.1.1.3 K6ME/DECHLOR
The KGME/DECHLOR Process was developed by Chemical Waste
Management (CWM) (Friedman and Halpern 1992a) to treat oils contami-
nated with PCBs, polychlorodibenzodioxins (PCDDs), and
polychlorodibenzofurans (PCDFs). The process is coupled with CWM's
X*TRAX Process to treat soil. X*TRAX is a thermal treatment system that
removes oils and oily contaminants from soil and other solids. X*TRAX
removes the contaminated oil from the soil and the oil is treated by the
KGME/DECHLOR Process.
The KGME/DECHLOR Process employs the reaction of 2-
methoxyethanol with either KOH in the presence or absence of an
nonaqueous hydrogen donor (aprotic) solvent, forming potassium polyeth-
3.13
-------
Process Identification and Description
ylene glycol methylethers (GME) (KGME). The KGME reacts with
haloaromatics, replacing one or more halogens with the 2-methoxyethoxy
moiety and are converted to methoxyethoxy aryls. That is, the chlorine
atoms attached to the aryl nucleus are replaced with the methoxyethoxy
moiety, forming ethers at the aryl nucleus.
Details of the reaction are found in the CWM brochure (Friedman and
Halpern 1992a, 1992b). To produce KGME, 2-methoxyethanol is reacted
with potassium hydroxide in a suitable reaction vessel containing haloge-
nated aryls at 110 to 150°C (230 to 300°F) during a one to four hour period.
The treated oil phase, which contains the reaction products and traces of
unreacted PCBs, is transferred to a storage tank. Samples are taken for
analysis, and if the PCB concentration is unacceptable, the batch is returned
to the reactor for a more vigorous treatment. If the PCB concentration is
acceptable, the batch is discharged. The final disposition of the treated oil
depends on whether other regulated Resource Conservation and Recovery
Act (RCRA) hazardous constituents are present.
Aroclors, 1254 and 1250, are reduced from initial concentrations of
250,000 mg/L to <50 mg/L and sometimes to <5 mg/L. Lower Aroclors,
e.g. 1016, 1242 and 1248, can also be transformed to non-PCBs, but gener-
ally require greater concentrations of reagent, higher temperatures, and/or
longer reaction times.
Chemical Waste Management is currently using a pilot-scale KGME/
DECHLOR system depicted in figure 3.4 (on page 3.15). The major com-
ponents consist of a 380-L (100-gal) reactor, thermal fluid healer/chiller, a
1,900 L (500 gal) decantation tank, storage tanks of 1,900 L (500 gal) ca-
pacity, and pumps.
Chemical Waste Management indicates that the system converts PCBs
into substituted ethers with methoxyethoxy moieties at somewhat greater
efficiency than does KPEG at 115°C (239°F). But at a higher temperature,
150°C (300°F), there is only a very slight improvement. No data are avail-
able for KPEG reaction at 150°C. An important point is noted in the CWM
report, which states:
"The dehalogenation shown was performed on a waste
which contained 722 ppb of PCDDs and 2725 ppb of PCDFs
prior to treatment. After 1.25 hours at 115°C (one equiv alent
KGME/equivalent Cl; 0.5 equivalent of 2-methoxy ethanol
excess), the chlorinated dioxins and furans were reduced to
3.14
-------
Chapter 3
below limits of detection (51 ppb). A similar treatment with
KPEG resulted in a comparable destruction of dioxins; how-
ever, the levels of tetrachlorinated dibenzofurans were actu-
ally increased (from 30 to 251 ppb)."
It should be noted that methoxy ethanol is being tested as a possible
teratogen. Larger molecules, such as methoxyethoxy-ethanol, are listed as
irritants.
The KGME/DECHLOR Process is currently limited in application to
liquid wastes with less than 25% water. Solid materials contaminated with
PCBs require a pretreatment step, such as X*TRAX or soil washing, in
order to remove the PCBs and to provide a treatable liquid matrix.
Figure 3.4
DECHLOR/KGME Process Flow Diagram
Nitrogen —
Quench
& wash
•Atmosphere
Liquid
Liquid
Reagent
Waste
Oil
*-
i
f \
Reactor
/
(PCBs)
queous
'aste
Aqueous
Storage
Tank
V )
, Off-Site
Disposal
3.15
-------
Process Identification and Description
3.1.2 High-Temperature Substitution Processes
Two high-temperature substitution processes were evaluated — the ATP
(SoilTech) Process, addressed here, and the BCD Process, an emerging
technology, addressed in Appendix A.
The ATP Process, developed by SoilTech, Inc., was evaluated under the
U.S. Environmental Protection Agency's (US EPA's) Superfund Innovative
Technology Evaluation (SITE) program. It has treated 36,000 tonne
(40,000 ton) of PCB-contaminated soil at the Wide Beach (Brant, NY)
Superfund site and PCB-contaminated dredge spoils at Waukegan Harbor,
Illinois as part of a demonstration. The process is based on a thermal des-
orption process patented by Taciuk (dePercin 1991; Taciuk 1979, 198la,
1981b). The system can treat 9 tonne (10 ton) of soil per hour.
Figure 3.5 (on page 3.17) shows the Taciuk reactor, as depicted in the
patent. Note that the referenced patent is for use of the reactor to extract oil
from shale; the system used for remediation may differ in some details.
Figure 3.6 (on page 3.18) is a simplified diagram of the reactor. See figure
3.7 (on page 3.19) for a flow diagram of the entire system.
The reactor is a rotating cylinder consisting of a core (called here "the
reactor") surrounded by an annular space through which hot combustion
gases flow. Crushed and sized contaminated soil, mixed with a solution of
diesel fuel, recycle oil from the process, and APEG (whether sodium or
potassium, is not specified) is fed to the reactor (on the left of figure 3.5 on
page 3.17) (A). The solids flow to the far end (B), then drop into the outer
chamber and flow back to the discharge. A fossil fuel burner (B) is
mounted at the point where the solids drop into the annular chamber.
The reactor and the annular chamber are each divided into two thermal
zones by a baffle. The region to the left of the baffle in the reaictor, called
the "preheat zone," is maintained at a temperature of 200 to 340°C (400 to
650°F). The region to the right of the baffle, called the "retort zone," is
maintained at a temperature of 480 to 620°C (900 to 1,1 SOT). In the annu-
lar chamber, the region to the right of the baffle is called either the coking
or combustion zone, depending on whether it refers to the portion of the
kiln which is below or above the solids bed in the rotating annulus. The
region to the left of the baffle is referred to as the cooling zone:. The tem-
perature in the combustion zone (and presumably coking zone) of the reac-
tor is 650 to 760°C (1,200 to 1,400T), and in the cooling zone, 260 to
430°C (500 to SOOT).
3.16
-------
Chapter 3
CD
o
in CD
CO O.
>
= .c
O
O
3.17
-------
Process Identification and Description
Figure 3.6
Simplified Sectional Diagram Showing the Four Internal Zones — ATP
Flue Gas*-...,. <<—
Discharge
Low Temp.
Steam and
Hydrocarbon
Vapors Flow **•*•».
Feed__ —'
Stocks
Hydrocarbon
-—'/* and Steam
Vapors Flow
Gas Streams Solid Streams Coked Solids
Spent Solid_
.._ Auxiliary
'Burners
'•--.„ Combustion
Air Flow
The flow of solids and gases in the reactor is complex. The organic con-
stituents vaporize in the preheat zone and those that do not vaporize crack
to lower molecular weight compounds in the retort zone. In addition, the
reagent, by dechlorinating the PCB, also contributes to its destruction.
Offgases from the retort zone flow out of the reactor to condensers and air
pollution control equipment, as shown in figure 3.6. The condensate is
physically separated into an aqueous phase and heavy and light nonaqueous
phases. The nonaqueous phase is spread on the soil feed and recycled back
into the reactor. The aqueous phase is treated by a carbon adsorption sys-
tem. Spent carbon from the two systems is recycled back into the reactor.
The hot, granular solids exiting the reactor pass through the fossil fuel
burner flame before dropping into the annular chamber. The burner ignites
residual organics on the soil. Gases from the burner mix with those of the
3.18
-------
Chapter 3
o
1
LL.
I
O
2
a.
3.19
-------
Process Identification and Description
burning organics in the annular region and pass into the combustion zone of
the furnace.
Figure 3.7 (on page 3.19) is a process flow diagram of the complete sys-
tem. The ATP Process combines features of thermal desorption,1 thermal
destruction (incineration), and chemical reaction in one unit.
Forty thousand tons of PCB-contaminated soil was treated at the Wide
Beach Development Superfund site. The concentration of PCBs was re-
duced from the 100 to 600 mg/L range to less than 10 mg/L. The treatment
was performed in 1990-91 at a cost of $245/ton. The only question that
might be asked about the process is what fraction of destruction of PCBs
took place because of thermal decomposition versus chemical decomposi-
tion? The process achieved an acceptable level of destruction of the target
contaminants. The physical condition of the treated soil was not reported.
However, because the treatment process is basically a thermal system, the
product is, most likely, a dry, granular solid.
3.2 Oxidation Process Descriptions
Chemical oxidation processes are used in many industrial processes
(RadTech 1992) and in the treatment of potable water to remove a broad
range of natural and synthetic organic compounds. Many of these technolo-
gies are commercially available and can be readily applied in the
remediation of groundwater and even soil. Oxidation processes fall into
three broad categories: (1) chemical oxidation, (2) photodegradation/pho-
tolysis, and (3) a combination of chemical oxidation and photolysis. The
emerging technologies, discussed in Appendix A, do not clearly fit these
categories.
Oxidation processes have been used exclusively to degrade organic com-
pounds in aqueous media and some soils; however, it would appear possible
to use the technique also to change the oxidation state of metals and convert
them to less toxic or less soluble forms that will precipitate.
1 See the monograph in this series, Innovative Site Remediation: Thermal Desorption,
wherein the ATP Process is addressed as a thermal desorption process.
3.20
-------
Chapter 3
3.2.1 Chemical Oxidation Processes
Chemical oxidation processes use merely a chemical oxidizing agent to
react with the contaminant. The following are commonly used as oxidizing
agents:
• hypochlorite, either sodium or calcium (NaOCl or Ca(OCl)2);
• hydrogen peroxide; and
• ozone.
Hypochlorite treatment is a well-established technology that has been
used extensively to destroy pathogens in drinking water. A case history of
its use in remediation to destroy cyanides is given in Appendix B. Its use,
however, will likely remain limited because it is relatively expensive and
because it can convert organic constituents to traces of chloromethanes and
chlorethanes.
Ozone and hydrogen peroxide are excellent oxidizing agents that can be
used somewhat interchangeably for the destruction of organic compounds.
They are both strong oxidizing agents capable of destroying most
nonhalogenated and some halogenated compounds in aqueous media. For
example, both have been commonly used to destroy cyanides in wastewater.
Similarly, they can be used to destroy low concentrations of easily oxidiz-
able organic compounds in groundwater.
As compounds involved become refractory (hard to destroy or chemi-
cally react) or as the concentration increases, the amount of oxidizing agent
required becomes high. Although ozone and hydrogen peroxide are both
oxidizing agents, they are not completely interchangeable. The chemical
pathways they follow in oxidizing organic compounds are somewhat differ-
ent. This is especially true in the presence of UV light, as explained in the
next subsection. An understanding of the fundamental chemistries involved
is necessary to design an efficient treatability study, and in most cases the
treatability studies should include consideration of ozone and peroxide both
individually and in combination.
3.2.2 UV Photodegradation/Photolysis
Ultraviolet light can initiate oxidation reactions either through simple
photodegradation, with low-intensity UV light, or through photolysis, with
high-intensity UV light. A major potential application of photolysis is the
3.21
-------
Process Identification and Description
use of natural sunlight to degrade organics in soil and waters. Photolysis is
a true oxidative process. The high-intensity UV light forms OH" radicals
that attack and oxidize the organic contaminants.
While photodegradation can be used to destroy some compounds, total
destruction of most compounds has not proven feasible. Dissociation of
chemical bonds occurs only when the UV light wavelength matches the
absorption bands of the contaminants. Each contaminant has a unique opti-
mal wavelength for photodissociation; and as a contaminant degrades par-
tially, the wavelength that will degrade the product molecule is usually
different from that which degrades the original compound.
Another difficulty with solar photodegradation is that the absorption
bands and wavelengths are usually not the same for the various by-products
of photooxidation and therefore, the reaction products are themselves re-
fractory. A good example of this difficulty is the "pinkwater" lhat results
from exposure of trinitrotoluene (TNT) production wastewater to sunlight.
The pinkwater contains partial products of oxidation of the original con-
taminants and is in its own right an environmental problem.
The type of UV light source used for photodegradation is critical to the
process's success. This is equally true for simple photodegradation pro-
cesses or advanced oxidation processes, discussed in Subsection 3.2.3.
Photodissociation of organic compounds by direct photolysis requires
photon energies from 4 eV to 7 eV (1 eV = 1.6 x 1019 Joules), which corre-
sponds to wavelengths from 300 nm to 175 nm. Complex structures and
mixtures of organic compounds require a very dense structure of UV emis-
sion lines to be completely degraded to innocuous products because each
molecule has a set of unique absorption bands that can vary in width (1 to
20 nm) and dictate an optimal wavelength for photodissociation. For ex-
ample, benzene's molar extinction coefficient is 47,000 at a wa.velength of
184 nm, 7,000 at 202 nm, and at wavelengths between 230 to 270 nm,
benezene absorbs light relatively weakly with an extinction coefficient, (e =
300) (see Subsection 3.4.2.1). In contrast, acetone has strong absorbance at
a wavelength 220 nm (e = 16,000), but is very weak at 318 nm (e = 30)
(Wekhof, 1991).
First generation UV light sources are able to generate only a few lines in
the far UV region. Mercury vapor lamps emit their strongest emission at
254 nm. Medium- to high-pressure mercury vapor lamps with input powers
greater than 80 watt/cm have additional strong lines at 248, 265, 280, 297,
3.22
-------
Chapter 3
and 302 nm. Given this limited availability of emission lines, it is apparent
that even high-power, medium pressure mercury vapor lamps are incapable
of cleaving bonds in contaminants such as benzene.
Metal halide lamps, which are medium- or high-pressure mercury lamps
containing dopants, such as iodides and magnesium, have a higher emission
line density in the far UV region. Dopants, which can be selected to fill
specific wavelength gaps between the mercury lines, allow customizing the
spectrum of the lamp to a particular application. These types of lamps are
far more efficient than first generation mercury vapor lamps, which require
the addition of an oxidant for efficient toxic degradation. The efficiency of
doped mercury lamps, however, can be enhanced through the addition of
peroxide and/or a photocatalyst.
Even mercury lamps containing dopants lack a sufficient number of UV
lines to insure complete destruction of mixtures of toxic chemicals. If
doped mercury lamps are considered second generation technologies, con-
tinued innovation has brought about the development of a third generation
lamp that provides an UV continuum with pulsed devices. The most simple
and cost-effective types of broad UV spectrum lamps for environmental
applications are xenon and custom-built flashlamps (Wekhof, 1991). Op-
eration of the xenon flashlamp entails converting the xenon gas to a plasma
by a short pulse of electric current. In order to increase the UV output be-
low 300 nm, xenon flashlamps must be operated outside their rated range of
current density (6 to 14 kA/cm2 vs. 1 to 5 kA/cm2), which will significantly
shorten lamp life by a factor of 100 or more.
In water, direct photolysis occurs readily of compounds that have suffi-
cient solubilities and are exposed to specifically energetic light. The effects
of pH and ionic strength on the process are relatively minor. Organic de-
struction in air, however, is about 5 times faster than in water (Wekhof,
1991). This is due to the following factors:
• Water absorbs UV light more than does air;
• Recombination of photoproducts to yield the parent compound
is less in air than in water because of diffusional properties; and
• Ozone is formed in the gaseous system because of the presence
of oxygen.
Although UV radiation does not penetrate solid matrices, such as soils,
direct or indirect photolysis can be used effectively in soil systems by creat-
3.23
-------
Process Identification and Description
ing an organic or surfactant film on the surface of particles to solubilize the
contaminants at the interface. In addition to transporting contaminants to
the surface, organic solvents/surfactants may also play the role of H+ -do-
nors in the degradation pathway. In addition, in soil irradiation shallow
depth and periodic mixing are necessary.
3.2.3 Advanced Oxidation Processes
Advanced oxidation processes, based on free radical, chain reaction
chemistry, combine ozonation with UV photolysis and hydrogen peroxide.
Some compounds (e.g., methanol) that are resistant to destruction or are
only slowly destroyed by UV radiation alone or with the addition of either
O3 or H2O2 are rapidly destroyed to a far greater extent in the presence of all
three agents, suggesting that a synergy exists in the chemistry of this pro-
cess.
Over the past 15 years, the oxidation of a large number of organic con-
taminants in wastewater throughout the use of a combination of ultraviolet
light and hydrogen peroxide has been examined. While ultraviolet light and
hydrogen peroxide are each capable of causing some degradation of organic
materials by themselves, the synergistic effect of combining the two meth-
ods expands their utility and effectiveness (Ansari, Kahn, and Ali 1985).
The complete mineralization of 2,4-Dinitrotoluene (2,4-DNT) proceeds
through sidechain oxidation, hydroxylation of the benzene ring, and ben-
zene ring cleavage in the presence of ultraviolet light and hydrogen perox-
ide. The degradation of 2,4-DNT proceeds rapidly at H2O2:2,4-DNT mole
ratios above 13:1 (Ho 1986). Initial concentrations of 75 mg/L of 2,4-DNT
in water can be reduced to below detection limits of 1 mg/L in 45 minutes
or less. During the oxidative degradation of 2,4-DNT, the pH of the reac-
tion medium is reduced from approximately 6.4 to approximately 2.6.
Guittonneau et al. (1990) showed that p-chloronitrobenzene undergoes
oxidative degradation with UV/H2O2 treatment at ambient temperatures.
Sundstrom and Klei (1986) demonstrated the oxidative degradation, under
the influence of UV/H2O2 treatment, of a wide range of organic compounds
in water, including o-dichlorobenzene, m-dichlorobenzene, chlorobenzene,
phenol, toluene, carbon tetrachloride, chloroform, ethylene dibromide, and
dichloromethane. In addition, the reduction of the pentachlorophenol con-
tent of contaminated groundwater from 10 mg/L to less than 1 mg/L has
also been described (Edwards and Bonham 1988). The partial oxidation of
3.24
-------
Chapter 3
arginine to a variety of amino acids and urea was reported by Ansari, Kahn,
and Ali (1985). Although 1,1,1-trichlorethane and Freon 113 do undergo
oxidative degradation when treated with the UV/H2O2 system, overall deg-
radation of these compounds is significantly slower than the degradation of
other organics such as perchloroethylene (Camp 1991).
Since the chemistry of advanced oxidation processes is essentially that of
the hydroxyl free radical, they are extremely effective treatment processes
for most contaminants. For example, the dechlorination of a highly chlori-
nated aliphatic compound, chlorendic acid, can be accomplished with
ozone, but the rate is enhanced significantly under conditions which favor
the formation of hydroxyl radicals: UV light, high pH, and low bicarbonate
concentration (Stowell and Jensen 1991). The degradation rates of volatile
organochlorine compounds (trichloroethane, trichloroethylene, and
tetrachloroethylene) by ozonation were increased by a factor of 10 with UV
irradiation (Kusakabe et al. 1991).
Recently, two advanced oxidation processes that appear to be able to
treat a range of refractory compounds, including pentachlorophenol, were
introduced. They are the Rayox (Solarchem Environmental Systems, San
Diego, Calif.) and Ultrox (Santa Ana, Calif.) Processes. The fundamental
feature of both is the use of a combined UV/ozone or UV/ozone/H2O2 to
generate OH» radicals.
Rayox Process. The Rayox Process uses a proprietary reactor design that
improves mass and radiation transfer, permits staged treatments, and en-
ables automatic cleaning of the UV components. The process uses propri-
etary UV light sources termed by the vendor as Solarchem UV lamps.
These lamps have a range of intensities and emission characteristics
matched to the pollutants treated. The process also utilizes proprietary
catalysts termed the ENOX catalysts, to enhance the production efficiency
of OH» radicals and oxidation selectivity. The Rayox Process has twice the
number of controllable process variables as early oxidative process technol-
ogy, and the user can select process conditions to favor radical reactions,
direct photolysis reactions, or a combination of the two. The process train
can use either a batch or continuous flow reactor depending on type and
amount of contamination, flow rate, and degree of removal desired.
According to the vendor, the Rayox UV/ozone/H2O2 Process has been
shown to be effective in treating most halogenated and volatile compounds,
PCBs and dioxins, pesticides, organic corrosive chemicals, nitrogenated
3.25
-------
Process Identification and Description
aromatic and aliphatic compounds, cyanides, and iron. The process has
been applied in treating the following:
• gasoline in groundwater for destruction of benzene, toluene,
ethylbenzene, xylene (BTEX);
• multi-contaminant leachates (carbon tetrachloride, benzene,
toluene, xylene (BTX), chlorinated solvents, ketones, chloro-
form, etc.);
• wood preservation industrial wastewaters (phenols, PCP), diox-
ins, polyaromatic hydrocarbons (PAHs));
• chlorinated and nonchlorinated solvents (trichloroethylene
(TCE), tetrachloroethene (PCE), dichloroethane (DCA), 1,4-
Dioxane, etc.); and
• explosives in process waters (TNT, DNT, nitroglycerine (NG),
ethylene glycol dinitrate (EGDN), etc.).
When used at an US EPA superfund site, >99% volatile organic com-
pound (VOC) destruction was achieved, and in a groundwater remediation,
>99.99% BTX degradation was effected (US EPA 1990). Successful treat-
ment of process water and groundwater containing mixed pesticides, PAHs
from coal gasification, complexed (including iron) cyanides, dyes, and
bleach plant effluent has been reported by the manufacturer.
No schematic or operational information was received for the Rayox
Process, but it appears to be similar in its major features to the Ultrox Pro-
cess, described below.
Ultrox Process. The Ultrox Process uses a combination of ozone, hydro-
gen peroxide, and UV irradiation to treat a variety of organic constituents in
aqueous streams. See figure 3.8 (on page 3.27). The system can be ob-
tained in a variety of sizes with reactors ranging in capacity from 1,100 to
14,800 L (300 to 3,900 gal). The reactor is made of stainless steel. It con-
tains vertical, low temperature mercury lamps inside quartz tubes. Four to
eight reactors can be staged in series, the number depending on treatment
conditions. Lamps may be mounted in all or only some of the reactors. The
process can operate under intermittent, continuous, or batch flow conditions
and may be fully automated, with periodic monitoring.
The reactor uses ozone and/or hydrogen peroxide. The ozone is gener-
ated either from air (producing a stream containing 2% ozone by weight) or
3.26
-------
Chapter 3
Figure 3.8
The Ultrox System
Air
JL
C Catalytic
Ozone
Decomposer
Treatment
Tank Offgas
/
Hydrogen Peroxide
1 Hydrogen peroxide is combined with contaminated water.
2 Ozone is generated and injected into the treatment tank.
3 Contaminated water is pumped to the treatment tank and irradiated with ultraviolet light. The light reacts
with the ozone gas and hydrogen peroxide, producing hydroxyl radicals which destroy organic contaminants.
4 Water flows from left to right through a series of treatment chambers.
5 Residual ozone in the offgas is converted to oxygen by a catalytic decomposer, eliminating any release of
ozone.
6 Treated water flows to discharge.
oxygen (yielding 6% ozone by weight) in the range of 4 to 44 kg/day (10 to
100 Ib/day). The ozone is bubbled into the base of the reactor. Hydrogen
peroxide may replace ozone, or be used in combination with ozone and is
directly metered into the influent line. The offgas from the reactor is col-
lected for destruction of residual O3 and VOCs by a patented catalytic pro-
cess, D-TOX™. The D-TOX™ uses O3 to oxidize the susceptible organics
and also uses two additional catalysts to destroy remaining VOCs and re-
3.27
-------
Process Identification and Description
sidual O3. A sorber made of a mixture of bases is located at the end of the
catalytic train to remove any remaining organic material or acids.
The Ultrox Process was demonstrated in 1988 under the SITE program
(US EPA 1989). The treated wastewater contained 44 organic contami-
nants, three of which, TCE, 1,1-DC A, and 1,1,1-trichloroethane (1,1,1-
TCA), were chosen as indicator parameters for the test. Efficiency in
removing the TCE was about 99%, the 1,1-DCA, about 58%, and the 1,1,1-
TCA, about 85%. Measured efficiencies in removing the total VOCs were
about 90%.
Both chemical oxidation and stripping resulted in removal of some com-
pounds from the water phase. Stripping accounted for 12 to 75% of the
total removal of 1,1,1-TCA and for 5 to 44% of 1,1-DCA. Stripping ac-
counted for less than 10% of the TCE and vinyl chloride removed and neg-
ligible amounts of other VOCs present.
The ozone destruction system reduced ozone concentrations; in the gas
stream to less than 0.1 ppm and reduced the VOCs, which were stripped
into the gas stream, to nondetectable concentrations. Very little removal of
total organic carbon (TOC) was observed, indicating partial oxidation of
organics without complete conversion to carbon dioxide and water.
According to the vendor, the Ultrox AOP is capable of treating contami-
nation typical of that experienced in the petroleum industry (leaking fuel
storage tanks, refinery equipment leaks, spills at transfer terminals, and
pipeline failures) and is effective in treating compounds, such as benzene,
toluene, xylene, ethyl benzene, and methyl-t-butyl ether (MTBE). As to the
chemical industry, the Ultrox system is capable of degrading benzene,
phenols, TCE, PCE, and chlorinated or phosphated pesticides. This tech-
nology is also applicable in treating compounds typically found in contami-
nation experienced in the aerospace industry, such as Freon 113.
Contamination commonly experienced in the woodtreating industry, such as
creosote, PAHs, and dioxins can be handled by the Ultrox system. In
groundwaters, the following contaminants can be degraded by the Ultrox
system:
• benzene • perchloroethylene (PCE)
• toluene • xylene
• creosote • pentachlorophenol (F'CP)
3.28
-------
Chapter 3
• 1,2-dichloroethylene • bis(2-chloroethyl)ether
• dichloroethylene • pesticides
• dioxins • polynuclear aromatics (PNA)
• dioxanes • 1,1,1 -trichloroethane (1,1,1 -TC A)
• Freon 113 • trichloroethylene (TCE)
• methylene chloride • tetrahydrofuran
• methyl isobutyl ketone • vinyl chloride
• poly chlorinated biphenyls (PCBs) • methyl-butyl ether (MTBE)
• tetrachloroethylene
Industrial wastewaters containing the following compounds are also
effectively treated:
• amines • methyl ethyl ketone
• analines • methyl isobutyl ketone
• chlorinated solvents • methylene chloride
• chlorobenzenes • pesticides
• creosotes • phenol
• complex cyanides • RDX
• hydrazine compounds • trinitrotoluene (TNT)
• isopropanol • polynitrophenols
3.3 Precipitation Processes
Chemical precipitation involves transforming a soluble compound into
an insoluble form through the addition of chemicals, such that a supersatu-
rated environment exists (i.e., the solubility product is exceeded). It should
be noted that there is a fine distinction between chemical precipitation and
stabilization/solidification (S/S) operations. In S/S operations, the contami-
nants are incorporated into a cement-like matrix, rendering the contami-
nants less prone to leaching. Sludges are chemically treated by mixing a
3.29
-------
Process Identification and Description
binder material to improve the physical and chemical stability of the sludge.
Materials such as portland cement, silicates, poz/olanic materials, and fly
ash have been used as S/S agents. The purpose of S/S technologies is to
minimize the leaching potential of the contaminants.2 Similarly, this is the
goal of chemical precipitation operations, that is, to make the contaminant
less soluble. S/S techniques are used to immobilize heavy metals, but they
have also been used to immobilize organic contaminants as well. In gen-
eral, organics with low water solubility are immobilized fairly, well through
S/S operations, while higher solubility organics are not (Connor 1990).
Chemical precipitation techniques are rarely used to precipitate; organic
compounds from solution, although organics can adsorb onto precipitate
forms, such as hydrous metal oxides.
Chemical precipitation is the most common technique used for treatment
of metal-containing waters (US EPA 1980; Peters, Ku, and Bhattacharyya
1985; Patterson 1988; Patterson and Minear 1975). Oxidation/reduction
plus precipitation being a closely-related technique is also used (Patterson
1988). Alternative techniques, including selective sorption/desorption and
differential precipitation, have focused primarily on opportunities for recov-
ery of metals and sludge beneficiation and extraction (Patterson 1988).
Clifford, Subramonian, and Sorg (1986) cite the following advantages of
precipitation/coprecipitation contaminant removal processes:
• low cost for high volume;
• often improved by high ionic strength; and
• reliable and well-suited for osmotic control.
Limitations include the following:
• stoichiometric chemical addition requirements;
• high water content sludge must be disposed;
• part per billion effluent contaminant levels may require two-
stage precipitation;
• processing is not readily applied to small, intermittent flows; and
• coprecipitation efficiency depends on initial contaminant con-
centration and surface area of the primary floe.
2 See the monograph in this series, Innovative Site Remediation: Stabilization/Solidifi-
cation.
3.30
-------
Chapter 3
Precipitation can be broadly divided into two categories: chemical pre-
cipitation, and coprecipitation/adsorption. Chemical precipitation is a com-
plex phenomenon resulting from the induction of supersaturation
conditions. Precipitation proceeds through three stages: nucleation, crystal
growth, and flocculation. Metal salt solubility can be predicted (at equilib-
rium) from thermodynamic calculations. These thermodynamic calcula-
tions cannot assess the kinetic rate, the influence of precipitate induction
parameters, or the degree of supersaturation required to induce nucleation.
It is important to note that the stability constants reported in the technical
literature can vary by several orders of magnitude. See, for example, table
3.4 (on page 3.32). Patterson (1988) points out that the shape of the cad-
mium hydroxide solubility curve (as a function of pH) can vary signifi-
cantly, depending on the particular stability constants chosen.
Chemical precipitation processes offer significant potential for removing
soluble ionic species from solution, particularly heavy metals. The tech-
nique is not generally applicable in treatment of contaminated soils. It can,
however, be used to treat industrial wastewaters and contaminated
groundwaters (ex situ). This technique is applicable for removing soluble
ionic species from aqueous solutions. Chemical precipitation can also be
used as a pretreatment technique to remove heavy metals from solution
before biodegradation of hazardous organic compounds.
There are five basic precipitation techniques that can be used to remove
heavy metals from solution. Each are discussed in the following five sub-
sections.
3.3.1 Hydroxide Precipitation
In hydroxide precipitation, heavy metals are removed by adding an al-
kali, such as caustic or lime, adjusting the wastewater pH to the point where
the metal(s) exhibits minimum solubility. In general, the solubilities of
metal hydroxides in solution decrease with increasing pH to a minimum
value beyond which (the isoelectric point) the metals become more soluble
because of their amphoteric nature. See figure 3.9 (on page 3.33).
Newkirk, Warner, and Barros (1981) observe that the minimum solubilities
as quantified under ideal conditions differ considerably with those observed
in actual practice because of the influences of complexing agents (and other
contaminants that may be present), temperature, and ionic strength. Fur-
ther, Bowers, Chin, and Huang (1981) observe that in heterogeneous sys-
3.31
-------
Process Identification and Description
Table 3.4
Logarithm of Stability Constants Reported for Cadmium
Reference Source
Stability
Constant
K,
Kj
K3
*4
K*
Smith and
Martell
(1976)
3.90
7.70
8.75
8.70
-14.65
Baes and
Mesmer
(1976)
3.92
7.65
8.70
8.65
-13.65
Sillen and
Martell
(1971)
5.00
8.90
11.60
...
-13.60
Snoeyink
and Jenkins
(1980)
4.16
8.40
9.10
8.80
-13.60
Dean (1979)
4.17
8.33
9.02
8.62
-13.60
Sawyer and
McCarty
(1978)
6.08
8.70
8.38
8.42
(-13.60)
Chemical Reactions Involved:
Cd(OH)2(s)<=> Cd+2 + 2 OH-
Cd*2 + OH- <==> CdOH+
Cd+2 + 2OH- <==> Cd(OH)2°
Cd+2 + 3OH- <===> Cd(OH)3-
Cd+2 + 40H- <==> Cd(OH)4-2
Solubility Constant Expression:
Stability Constant Expressions:
[CdOtf]
A.. — ~
K,=-
[Cd(OH)20] [Cd(OH)20]
K,=
K4 =
[Cd(OH)"][OH-]
[Cd(OH\} _ [Cd(OH\]
[Cd(O//)2O][0tf
[Cd(OH)r\OH-\ KtK2K3\
Adapted from Patterson 1988
terns, coprecipitation and complexation of more than one species may be
occurring.
The metals precipitate as metal hydroxides and can be removed by floc-
culation and sedimentation/filtration operations. The extent of precipitation
depends on the solubility product (Ks) of the metal hydroxide and the equi-
librium (stability) constants, Kt's, of the metal hydroxyl constants, plus the
stability constants for other complexing agents that may be present
(ethylenediamine tetraacetic acid (EDTA), nitrilotriacetic acid (NTA), cit-
rate, tartrate, gluconic acid, cyanide, ammonia, etc.). The effectiveness of
the solid/liquid separation is heavily dependent on the physical properties
3.32
-------
Figure 3.9
Solubilities of Metal Hydroxides and Metal
Sulfldes as a Function of Solution pH
Chapter 3
I
100-
80
60
40
20-
10.0-
8.0'
6.0-
4.0-
2.0-
1.0-
0.8
0.6
0.4-
0.2-
0.10
0.08.
0.06-
0.04-
0.02-
0.01-
0.008-
0.006-
0.004-
0.002-
0.001
Pb(OH),
CdS
CuS
PbS
100
-80
-60
-40
-20
-10.0
-8.0
-6.0
-4.0
-2.0
-1.0
-0.8
-0.6
-0.4
-0.2
-010
-0.08
-0.06
-0.04
-0.02
-0.01
-0.008
-0.006
-0.004
-0.002
0.001
0
10
12
14
3.33
-------
Process Identification and Description
(size, density, etc.) of the metal hydroxide precipitates. Widespread use of
this technique is due to its relative simplicity, low cost of precipitant (lime),
and ease of pH control (Peters, Ku, and Bhattacharyya 1985; Peters and Ku
1987). See table 3.5 for a summary of advantages and limitations of metal
hydroxide precipitation. Clifford, Subramonian, and Sorg (1986) observe
that a staged precipitation process can be used for mixed-metal wastes be-
cause of the variation in the pH of their minimum hydroxide solubilities.
Arumugam (1976) studied hydroxide precipitation for recovery of chro-
mium from spent tanning liquor. The process was found to be the cheapest
for the removal and recovery of chromium. The optimum pH for maximum
removal with lime was pH 6.6; removal of chromium exceeded 98% at that
pH. The precipitated chromium hydroxide was separated by settling, filtra-
Table 3.5
Advantages and Limitations of Metal Hydroxide
and Metal Sulflde Precipitation.
Advantages of Hydroxide Precipitation
• Ease of automatic pH control
• Well proven and accepted in industry
• Relatively simple operation
• Low cost precipitant (lime)
Limitations of Hydroxide Precipitation
• Hydroxide precipitates tend to resolubilize if the
solution pH is changed
• The removal of metals by hydroxide
precipitation of mixed metal wastes may not be
effective because the minimum solubilities for
different metals occur at different pH conditions
• The presence of complexing agents has an
adverse effect on metal removal
• Chromium (VI) is not removed by this technique
• Cyanide interferes with heavy metal removal by
hydroxide precipitation
• Hydroxide sludge quantities can be substantial
and are generally difficult to dewater due to their
amorphous particle structure
• Little metal hydroxide precipitation occurs at
pH<6
• Processing is not stable for large flow and
concentration variations in the influent
• Start-up and shutdown times are longer than
those for packed-bed and membrane processes
Advantages of Sulfide Precipitation
• Attainment of a high degree of metal removal
even at low pH (pH = 2 to 3)
• Low detention time requirements in the reactor
due to the high reaction rates of sulfides
• Feasibility of selective metal removal and
recovery exits
• Metal sulfide sludge exhibits letter thickening
and dewatering characterisbcs than the
corresponding metal hydroxide sludge
• Metal sulfide precipitation is less influenced by
the presence of complexes and chelating agents
than is the corresponding metal hydroxide
precipitation
• Metal sulfide sludge is reportedly three times
less subject to leaching at pH I) as compared
with metal hydroxide sludge ('Whang et al.
1981.)
• Metal sulfide sludges generally have smaller
volumes and are easier to dew.iter than the
corresponding metal hydros ide sludge
Limitations of Sulfide Precipitation
• Potential for H2 S gas evolution
• Possibility of sulfide toxicity
• Process is relatively complex and expensive as
compared with hydioxide precipitation
3.34
-------
Chapter 3
tion, and then was redissolved in sulfuric acid to form chromium sulfate,
which can be recycled for further tanning. Lime was more economical than
other alkalies (NaOH, Na2CO3, and NH4OH).
Sheffield (1981) investigated lime precipitation for removal of copper,
iron, nickel, chromium, and lead. These metals, from electroplating shops,
were successfully removed by precipitation with a hydroxide (such as lime)
or soda ash with addition of sulfate or sulfide to enhance removal of the
copper/iron complexes.
The batch precipitation of cadmium, zinc, and nickel both by hydroxide
and sulfide precipitation for various pH conditions, reaction times, and type
and concentration of complexing agents were studied. The complexing
agents investigated were ammonia, citrate, phosphate, tartrate, and EDTA.
The metal hydroxide precipitates tended to be amorphous and colloidal,
causing the resulting sludge to be voluminous. The presence of complexing
agents severely inhibited metal hydroxide precipitation (Peters and Ku
1985). Generally, higher pH conditions enhanced the nucleation rate and
improved the resulting particle size distribution (Peters and Ku 1985; Peters
et al. 1984; Peters, Ku, and Bhattacharyya 1984; Ku 1986). In the absence
of chelating agents, extremely low residual zinc and cadmium concentra-
tions (Zn <0.5 mg/L, Cd <0.3 mg/L) were obtained.
Hydroxide precipitation of heavy metals is well suited for automatic pH
control and is an effective treatment technique in industry. As an example
of the effectiveness of hydroxide precipitation, removal efficiencies ex-
ceeded 98% for Cd2+, Pb2+, and Cr3* when spiked well waters and river wa-
ters were used (US EPA 1978; Sorg, Csanady, and Logsdon 1978; Sorg
1979).
Rabosky and Altares (1983) presented a case history of full-scale waste-
water treatment for a small chrome-plating shop. Caustic soda was used to
adjust the wastewater pH to between 9.5 and 10.0 in order to precipitate the
metals as metal hydroxides. For the copper-containing wastewaters, the
precipitation was performed at pH 10.5 using NaOH. See table 3.6 (on
page 3.36) for typical results.
3.3.2 Carbonate Precipitation
Carbonate precipitation of heavy metals has been shown to be an effec-
tive treatment alternative to hydroxide precipitation. Carbonate precipita-
3.35
-------
Process Identification and Description
Table 3.6
Results After Treatment of Plant Wastewaters
Parameter
Nickel
Copper
Lead
Zinc
Iron
Manganese
Chromium (total)
Chromium( +6)
Cyanide
Oil and Grease
Phenol
Suspended Solids
Concentration,
Before Treatment
18.9
5.7
0.20
1.35
8.4
1.45
8.5
4.5
11.1
1 10
<0.001
6-10
(mg/L)
After
Treatment
0.63
0.89
0.02
0.06
2.8
0.05
0.04
<0.01
<0.001
1.2
<0.001
8.0
Adapted from Rabosky and Altares 1983
tion can be accomplished using soda ash (sodium carbonate). Carbonate
precipitation has the following advantages over conventional hydroxide
precipitation (Patterson, Allen, and Scala 1977; Clifford, Subramonian, and
Sorg 1986):
• Optimum treatment occurs at lower pH conditions;
• Metal precipitates are reported to be denser than the liquid, fa-
cilitating solids separation; and
• Sludges have better dewatering characteristics.
Sodium bicarbonate can be used also to precipitate heavy metals out of
solution (Barber 1978). Such treatment has the dual advantage of precipi-
tating the metal carbonate while holding pH within a narrow range at nearly
optimum conditions. Although sodium bicarbonate is not as efficient in
removing metal from solution as other bases, it has the advantage of neu-
tralizing excess acidity, which helps in meeting wastewater discharge stan-
dards. The sodium bicarbonate acts as a buffer, maintaining alkalinity near
the optimum pH level. Some metals, such as zinc, do not readily precipi-
3.36
-------
Chapter 3
tate, regardless of the amount of carbonate added. By mixing soda ash
(sodium carbonate), sodium bicarbonate, and lime (calcium hydroxide),
however, it is possible to precipitate zinc as zinc hydroxide, while using the
carbonates to stabilize pH. Sodium bicarbonate treatment has the additional
advantage of easy handling, simple application, ability to function in con-
tinuous flow operation, and moderate cost (Barber 1978).
Patterson, Allen, and Scala (1977) studied the feasibility of carbonate
precipitation in the removal of heavy metals. For nickel and zinc, no ben-
efit was realized by using carbonate precipitation as opposed to hydroxide
precipitation; the optimum pH for metal removal corresponded to pH values
predicted by the theoretical metal hydroxide solubility diagram. No advan-
tages in terms of denser sludges or better filtration characteristics were ob-
served for the zinc carbonate or nickel carbonate systems. Beneficial
results were observed using carbonate precipitation in cadmium and lead
removal. Comparable residual cadmium concentrations were observed at
approximately two pH units lower with carbonate treatment than with hy-
droxide treatment. The cadmium carbonate precipitates had approximately
the same filtration rate as the cadmium hydroxide system. Treatment
equivalent to that for lead hydroxide at pH 10.5 was obtained with the lead
carbonate system at pH 7.5 and a total carbonate concentration of 0.08
moles/L, or at pH 10 and a total carbonate concentration of 0.002 moles/L.
The lead carbonate system yielded a denser precipitate with improved filter-
ability characteristics than did the lead hydroxide system.
Additional laboratory carbonate precipitation studies have been per-
formed by Me Anally, Benefield, and Reed (1984) and McFadden,
Benefield, and Reed (1985), in which combined chemical treatment was
performed for removal of nickel from solution. These studies are described
in Subsection 3.4.5.
3.3.3 Sulfide Precipitation
Sulfide precipitation has been demonstrated to be an effective alternative
to hydroxide precipitation for removal of heavy metals from industrial
wastewaters (Bhattacharyya, Jumawan, and Grieves 1979; Bhattacharyya,
Jumawan et al. 1981; Bhattacharyya, Shin et al. 1981; US EPA 1980; Kim
1981; Kim and Amodeo 1983; Ku 1982, 1986; Ku and Peters 1986, 1988;
Peters et al. 1984; Peters, Ku, and Bhattacharyya 1984, 1985; Peters,
Eriksen, and Ku 1985; Peters and Ku 1984, 1985, 1987, 1988). See table
3.37
-------
Process Identification and Description
3.5 (on page 3.34) for a listing of advantages and limitations of this tech-
nique. Avoiding sulfide reagent overdose prevents formation of the odor-
causing H2S. In currently operated soluble sulfide systems, wliich do not
match demand, the process tanks must be enclosed and vacuum evacuated
to minimize sulfide odor problems.
Bench-scale studies involving metal sulfide precipitation showed that
sulfide precipitation is an extremely effective treatment in removing metals
such as, Cd, Cu, Pb, Zn, As, and Se (Bhattacharyya, Jumawan, and Grieves
1979; Bhattacharyya, Jumawan et al. 1981; Bhattacharyya, Shin et al.
1981). Overall separation and precipitate settling rates were optimal for
understoichiometric addition of sulfide (=0.60 x the theoretical stoichiomet-
ric sulfide requirement) and pH >8.0 (Bhattacharyya, Jumawan, and
Grieves 1979). Bhattacharyya, Shin et al. (1981) observed essentially com-
plete removal of zinc using sulfide precipitation (l.Ox) for pH >4. Measure-
ments taken on H2S loss (as gas) showed H2S was negligible, attributable to
the preference of the metal sulfide reaction over the H+-S2 reaction. Nickel
precipitation with sulfide was found to be a strong function of reaction time
for pH <10 in open systems. This was attributed to nickel dissolution caus-
ing the formation of Ni(SOH)2 and NiSO4 in the presence of oxygen.
The particle size distributions of ZnS, CdS, and NiS precipitation were
studied, because removal efficiency and ease of removing the sludge are
coupled. Both heavy metal removal and particle size distributions (PSDs)
were reported (Ku 1986; Peters et al. 1984; Peters, Ku, and Bhattacharyya
1984; Peters and Ku 1987). Using sulfide precipitation, virtually all the
zinc was removed at pH 8 to 10 (residual Zn <0.30 mg/L; removal effi-
ciency >99.7%). Few particles greater than 20 urn in size were observed;
the dominant particle size of the precipitates was only 5 to 7 um, causing a
cloudy appearance in the reactor suspension and making sedimentation and
filtration operations difficult. This suggested that the use of a flocculant or
coagulant aid would be advantageous. Although very high super saturations
were achieved, the kinetic order was low (i <1.02) for continuous ZnS pre-
cipitation (Peters et al. 1984). Little effect was observed on the resulting
PSD by varying the reactor detention time. Increasing the suspended solids
concentration increased both the particle growth rate and the precipitate
dominant size, yielding a more favorable PSD. The presence of calcium
improved the settling characteristics of both the Cd-Ca-Na2S and the Cd-
CaS slurry systems. The metal sulfide reactions were extremely rapid;
chemical equilibrium was achieved within 5 minutes reaction time. A
3.38
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Chapter 3
phase transformation from an amorphous, kinetically-favored precipitate to
a more crystalline, thermodynamically-favored precipitate was indicated for
the ZnS system as the precipitate aged. Patterson, Allen, and Scala (1977)
and Patterson and Minear (1975) have also noted such phase transforma-
tions. Particle size, rather than completeness of the solid phase formation,
often controls the apparent removal effectiveness.
The batch precipitation of zinc, cadmium, and nickel using both hydrox-
ide and sulfide precipitation at various pH conditions, with and without
complexing agents, has been studied (Peters and Ku 1985,1988; Ku and
Peters 1988). Addition of EDTA inhibited zinc removal in both hydroxide
and sulfide treatment because of the formation of stable metal chelates; the
effect was more pronounced for the Zn(OH)2 system (Peters and Ku 1985).
Tartrate severely hindered both zinc hydroxide and zinc sulfide precipita-
tion, resulting in the formation of very fine precipitates; this was confirmed
when no zinc removal occurred even with a settling time of 30 minutes
(Peters and Ku 1988). For removal of cadmium, virtually no change in
residual cadmium concentration was observed in the presence of tartrate
(compared with a control containing no complexing agents) because of the
formation of low-stability complexes. Extremely low residual metal con-
centrations can be achieved using sulfide precipitation in the absence of
chelating agents, as compared to similar hydroxide precipitation conditions
(Peters and Ku 1985). The presence of phosphate enhanced the PSD be-
cause of a flocculation/agglomeration mechanism. The presence of ammo-
nia has a minimal effect on metal sulfide removal and precipitation kinetics.
The presence of EDTA severely inhibited CdS precipitation. Equilibrium
conditions were reached quickly, within 5 minutes reaction time, for the
ZnS and CdS systems (Peters and Ku 1985), while equilibrium was
achieved after 40 minutes reaction time for the NiS system because of the
oxidation of sulfide in the open system (Ku and Peters 1988).
Peters, Ku, and Bhattacharyya (1984) and Ku and Peters (1986) also
addressed the effect of chelating agents on metal sulfide precipitation;
EDTA forms very strong metal chelates that interfere with ZnS precipita-
tion. Weak chelating agents, such as citrate, gluconic acid, and tartrate,
form weak metal chelates; formation of the metal sulfide precipitate domi-
nates in these cases. Removal of copper was nearly complete even in the
presence of EDTA.
3.39
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Process Identification and Description
Hohman (1985) selectively precipitated Cd from a Cd-Fe wastewater at
pH 2 by employing a stoichiometric sulfide dose only for the cadmium ions.
At pH 6, Fe3+ was selectively removed from Cd through hydroxide precipi-
tation. The CdS precipitation step goes to completion within 1 minute reac-
tion time, while FeS precipitation is much slower. At high sulfide levels,
FeS resolubilizes on formation of soluble species or colloids.
Laboratory studies were performed on a synthetic Pb-containing waste-
water and a metal finishing plant effluent sample in Madras, India
(Kamaraj, Jacob, and Srinivasan 1989; Kamaraj et al. 1990), Employing a
soluble sulfide precipitation technique, removal of lead (in the absence of
chelating agents) approached 100% for a sulfide dosage corresponding to
0.6x theoretical stoichiometric requirement. Removal exceeded 96% for pH
in the range of 3 to 10. Ammonia had little effect on the removal of heavy
metals from solution. Using 800 mg/L of EDTA, the removal of lead from
the synthetic system was reduced to about 80%. Removal of Ni, Cr, Zn,
Ag, and Cd exceeded 95% for pH >7. For sulfide dosages of 70% of the
stoichiometric requirement, removal of the heavy metals exceeded 95%.
In a similar study, Kamaraj et al. (1991) investigated the effects of sul-
fide dosage, solution pH, and the presence of chelating agents (EDTA and
cyanide) on treatment of a synthetic wastewater containing lead, cadmium,
and silver. Stoichiometric sulfide dosage at pH 5, in the absence of chelat-
ing agents, resulted in maximuin removals of Cd, Pb, and Ag (98, 73, and
100%, respectively). The maximum removal of Pb, Cd, and Ag occurred at
pH 8, 4, and 4, respectively. To simulate an industrial wastewater, SO42
was added to form a solution containing 1000 mg/L SO42,40 mg Pb/L, 10
mg Cd/L, and 4 mg Ag/L. Maximum removal of lead, occurring at pH 8,
was 95%, while maximum removal of Cd, occurring at pH 2 to 4, was
100%; similarly, maximum removal of Ag was 96% at pH 2. For a stoi-
chiometric sulfide dosage at pH 8, the removal of Pb, Cd, and Ag with 100
mg/L EDTA present was 20, 82.4, and 72%, whereas with 10 mg/L cyanide
(in place of the EDTA), the removal was 95.2, 96.8, and 64%. As a com-
parison, when a stoichiometric sulfide dosage was employed, the removal
of Pb, Cd, and Ag was 90.4, 100, and 72%. When cyanide was present, the
requirement for sulfide ions was increased to achieve maximum removal of
all the heavy metals, except lead, in the presence of chelating agents.
There are two main processes for sulfide precipitation of heavy metals
(US EPA 1980): soluble sulfide precipitation (SSP) and insoluble sulfide
3.40
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Chapter 3
precipitation (ISP), the difference being the way in which the sulfide ion is
introduced into the wastewater. This US EPA publication provides an ex-
cellent description and review of sulfide precipitation processes. In the SSP
Process, sulfide is added to the wastewater in the form of a water-soluble
sulfide reagent, such as sodium sulfide (Na2S) or sodium hydrosulfide
(NaHS). The addition of the solution may be monitored by periodic analy-
ses of metal contents or it may be controlled by means of a feedback control
loop employing ion specific electrodes. The process can be operated either
in batch or continuous mode.
In the ISP Process, a slightly soluble ferrous sulfide (FeS) slurry is added
to the wastewater, supplying the sulfide ions required to precipitate the
heavy metals. Since most of the heavy metals are less soluble than ferrous
sulfide, they will precipitate as metal sulfides. Since the FeS has a very low
solubility with a sulfide concentration of 0.02 JJg/L, emission of H2S is
minimized. In practice, FeS is freshly prepared by mixing FeSO4 and
NaHS. Among the advantages of the ISP Process is the absence of any
detectable H2S gas and reduction of Cr*6 to Cr+3. Among its disadvantages
is the considerably larger stoichiometric reagent consumption and genera-
tion of large quantities of sludge because of the ferrous hydroxide formation
(US EPA 1980). The addition of FeS is not automatically controlled in
response to metals content. The rate of FeS addition is determined by jar
tests on the wastewater before it enters the sulfide precipitation tank. The
process normally requires 2 to 4 times the stoichiometric amount of FeS
(US EPA 1980). The use of an excessive amount of FeS adds to the chemi-
cal cost of the process; it also contributes to the production of large amounts
of sludge. The Sulfex Process (Scott 1979) produces almost three times
more sludge than the conventional hydroxide precipitation process (Kim
1981).
In the SSP Process, the high sulfide concentration often causes rapid
precipitation of metal sulfides (high nucleation rates) resulting in small
particulate fines and hydrated colloidal particles which have poor settling
characteristics and poor filterability. In the presence of chelating agents,
hydroxide precipitation is not possible, even at high pH. With sulfide pre-
cipitation, heavy metal removal is possible even with chelating agents
present, although the metal sulfide precipitation is influenced by the pres-
ence of chelating agents (Ku and Peters 1986, 1988; Peters and Ku 1984,
1985, 1987, 1988; Peters, Ku, and Bhattacharyya 1984). In the absence of
chelating agents, little metal hydroxide precipitation occurs when the pH is
3.41
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Process Identification and Description
below 6. Metal sulfide precipitation can be conducted over a very wide pH
range, typically from pH 2 to pH 12 (see figure 3.9 on page 3.33). Because
metal sulfides are less soluble than the corresponding metal hydroxides,
better removal efficiencies are achieved over a broad pH range. In addition,
metal sulfides are less amphoteric than the corresponding metal hydroxides
and are, therefore, less likely to resolubilize. Metal sulfide sludges usually
have smaller volumes and are easier to dewater than metal hydroxide slud-
ges.
An alternative to using FeS in the ISP Process involves addition of cal-
cium sulfide (CaS) (Kim 1981; Kim and Amodeo 1983). Under this tech-
nique, the problems of delivery of the insoluble sulfide ions and the
generation of large amounts of sludge can be minimized through addition of
CaS. The addition of CaS as a slurry produces easily settleable precipitates.
Calcium sulfide particles act as nuclei for production of metal sulfide par-
ticles, and the dissolved calcium ions function as a coagulant. Since cal-
cium is mostly dissolved in the wastewater after reaction, the increase in the
sludge volume is minimal. For this same reason, the CaS dosage require-
ment is nearly stoichiometric (in contrast to the overstoichiometric dosage
requirement for FeS).
Whang, Young, and Pressman (1981) designed a soluble sulfide precipi-
tation system for the Tobyhanna Army Depot in Tobyhanna, Pennsylvania.
The Depot operates an electroplating facility which discharged its wastewa-
ters along with other wastewaters from the Depot to a trickling filter plant.
The wastewaters from the electroplating facility included three primary
streams:
• cyanide-bearing wastewater, containing cadmium, copper, and
cyanide;
• chromium-bearing wastewater, containing sodium, chromate,
and other additives; and
• other alkaline and acidic wastewater, containing sodium, nickel,
aluminum, tin, iron, lead, zinc, chloride, sulfate, nitrate, phos-
phate, and other additives.
In addition to these streams, the plating facility also periodically dumped
spent solutions (ranging from once per month to once per year). The flow
from the facility averaged 67,500 L/day (18,000 gal/day), consisting of
7,500 L/day (2,000 gal/day) of chromium-bearing wastewaters, 15,000 L/
3.42
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Chapter 3
day (4,000 gal/day) of cyanide-bearing wastewaters, and 45,000 L/day
(12,000 gal/day) of acid/alkaline wastewaters. This system was installed at
the Depot and has been in use since late 1981.
A full-scale SSP plant (Resta et al. 1978) was constructed by the U.S.
Army at the Belvoir Research and Development Center in Fort Belvoir,
Virginia, and became operational in February, 1983. Safety features of the
plant included neutralization of the wastewater pH prior to sulfide addition,
automatic control of the sulfide feed via a specific ion probe, addition of
ferrous sulfate to remove the excess sulfide, hydrogen peroxide oxidation of
the residual effluent sulfide, and covering and ventilation of the process
tanks. Removal exceeding 90% was observed for Cd, Cr, Cu, Ni, and Zn,
with removal of Pb exceeding 80%. The sludge generated averaged 0.3 L
of sludge/1,000 L of wastewater treated; the solids content of the filter cake
averaged 23.4% without the use of any sludge conditioners. The sludge
samples were determined to be nonhazardous by the Extraction Procedure
Toxicity test. Chemical costs in 1978 averaged $0.08/1,000 L ($0.30/1,000
gal) of wastewater treated, causing the process operational cost to be $0.19/
1,000 L ($0.71/1,000 gal) excluding manpower and energy costs.
Peters and Ku (1984) investigated the continuous precipitation of copper,
nickel, chromium, and zinc from synthetic and actual industrial plating
wastewaters by both hydroxide and sulfide treatment. For a zinc-nickel
wastewater, slightly lower residual and enhanced floe size were observed in
sulfide treatment than in hydroxide treatment. Low pH treatment (pH = 7.2
to 7.4) resulted in incomplete removal of nickel; zinc precipitation was
preferential to that of nickel. At higher pH levels (pH = 10), removal of
both nickel and zinc exceeded 98% through either hydroxide or sulfide
treatment. Larger sulfide dosages and higher pH conditions resulted in
greater metal removal and larger settling velocities. Chromium was not
effectively removed from the Cu-Ni-Cr-Zn wastewater through hydroxide
treatment. Increasing the sulfide dosage resulted in lower residual heavy
metal concentrations for Cu, Cr, and Zn, while the nickel concentration
increased because of the formation of fine floes. At pH 10.0, in sulfide
treatment, removal exceeded 97%, 98%, 55%, and 83% for Zn, Cu, Cr, and
Ni, respectively. The understoichiometric addition of sulfide showed great
promise as a treatment technique to achieve extremely low metal residuals,
while minimizing the potential for H2S gas evolution and sulfide toxicity
problems.
3.43
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Process Identification and Description
In a more scientific investigation, Bhattacharyya, Jumawan et al. (1981)
found sulfide precipitation using Na2S to be highly effective in removing
Cd, Cu, Pb, Zn, As, and Se from complex wastewaters. Full-scale plant
data were obtained at the Boliden Metall Corporation's metal smelting plant
in Skelleftehamn, Sweden. The full-scale plant was put into operation in
1978 and was designed to precipitate As, Cu, Cd, Hg, Pb, and 2ji as sulfides
at pH 3 to 5 by recycling to "roaster"; the fluoride was removed separately
by lime treatment (at pH >10) forming CaF2. The wastewater was first
partially neutralized (to pH 2.5 to 3.0) with addition of NaOH, after which
Na2S was added (as a 15% Na2S solution). The reagent dosages were con-
trolled by monitoring pH. The sulfide precipitate was removed by sedimen-
tation (after polymer addition) and post-filtration. The wastewaters treated
also contained fluoride, which was removed by precipitation with lime (us-
ing a 10% lime slurry) following the metal sulfide precipitation. Five sepa-
rate tests were performed to determine the extent of heavy metals and
arsenic removal and to establish the performance of the individual vessels.
The process had been in operation for nearly a year at the time of publica-
tion.
For this plant's wastewater, removal of Cd, Cu, and Zn exceeded 98%,
with removal of As and Se being 98% and >92%. The residual concentra-
tions achieved for Cd, Cu, and Zn were consistently in the range of 0.05 to
0.10 mg/L. When only hydroxide treatment was used, the settling rates and
metal separations were consistently lower than those obtained by sulfide
precipitation. The Cd, Zn, and Se removal was much poorer, even at pH
10.5, using hydroxide treatment. At pH 8.5, the residual metal concentra-
tions of Se, Cd, and Zn were 9, 2, and 5 mg/L. At pH 10.5, the residual Cd
and Zn concentrations decreased to 0.6 and 1.1 mg/L. The settling rate of
the sludges was a function of pH and sulfide dosage. Poor settling veloci-
ties resulted from hydroxide precipitation and overstoichiometric sulfide
precipitation. The settling rate, at 0.6x the stoichiometric requirement of
sulfide, was twice that obtained using hydroxide precipitation. This com-
bined hydroxide-sulfide treatment at pH 8 to 9 was shown to be effective
for removal of Cd, Cu, Hg, Fe, Pb, Zn, and As in both synthetic wastewater
and for full-scale treatment of wastewater. Even with sulfide overdoses at
low pH, no H2S gas loss was observed.
3.44
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Chapter 3
3.3.4 Xanthate Precipitation
In xanthate treatment, metal contaminants exchange with sodium ions
contained in the xanthated material to form an insoluble complex. The
xanthate acts as an ion exchange material, removing heavy metals and re-
placing them with sodium and magnesium. The heavy metals-laden mate-
rial can be removed from solution by sedimentation and filtration.
Compared with metal hydroxide precipitation, xanthate treatment offers the
following advantages (Federal Remediation Technologies Roundtable
1992):
• a higher degree of metal removal;
• less sensitivity to fluctuations in pH (metal xanthates do not
exhibit amphoteric solubilities);
• less sensitivity to the presence of complexing agents;
• improved sludge dewatering properties; and
• the capability of selectively removing metals.
Wing and Rayford (1977) state that the process will probably not be
economical for initial metal concentrations exceeding 100 mg/L, although
xanthate treatment could be used as a secondary treatment to further lower
the metal concentration to below discharge limits.
The process was developed by the U.S. Department of Agriculture
(Wing, Doane, and Russel 1975; Wing et al. 1978; Wing 1974; Wing and
Rayford 1975, 1976). Xanthates are sulfonated organic compounds. The
xanthate-metal precipitation process can be represented as follows:
ROCSSNa + M+ NaOH )ROCSS-M + Na+ [3.1]
or
2(ROCSSNa) + M2+ NaOH >ROCSS-M-SSOCR + 2Na+ [3.2]
where M+ or M2+ are the metal ions and NaOH indicates that the reaction
occurs at high pH.
Whereas hydroxide precipitation is effective over a pH range of approxi-
mately 9 to 12, xanthate precipitation is effective over a much wider pH
range (= 3 to 12), with maximum effectiveness above pH 7. Solutions with
3.45
-------
Process Identification and Description
pH less than 3 rapidly decompose the xanthates (Wing 1974). The hierar-
chy for selective removal of some cations and heavy metals by xanthate
treatment is in the following order: Na « Ca-Mg-Mn < Zn < Ni < Cd < Pb-
Cu-Hg (Flynn, Carnahan, and Lindstrom 1980). This technique still pro-
duces significant quantities of sludge which must be handled in accordance
with RCRA and other applicable regulations.
Wing (1974) observed that contaminants could be introduced when water
was treated with starch xanthates and a cationic polymer; possible contami-
nants include small ionic species (Cl from the cationic polymer, and Na+,
OH", and CO32 from the xanthate), small nonionic species (CS2 and COS
from the xanthate), and the polyelectrolytes themselves. The piresence of
sequestrants (diglycolate, NTA, polyphosphate, or citrate were used in this
study) at concentration levels of 0.1 g/L did not affect efficiency in remov-
ing mercury. Starch xanthate effectively treated 11 other metals: Cd2+, Cr3*,
Cu2+, Fe2+, Fe3+, Pb2+, Mn2+, Hg2+, Ni2+, Ag+, and Zn2+. The treatment can be
performed using either batch or continuous precipitation. Wing and
Rayford (1976) reported that the insoluble starch xanthate-metal sludge
settled rapidly and dewatered to 50 to 90% solids content after filtration or
centrifugation. A preliminary estimate of the cost to make the insoluble
starch xanthate was $0.68/kg ($0.30/lb). Other starch-based products
ranged in price from $0.68 to $1.69/kg ($0.30 to $0.75/lb). The chemical
cost of treating a 50 mg/L Cu-EDTA rinse with lime and polymer was esti-
mated to be $0.02/1,000 L ($0.07/1,000 gal) (Wing and Rayford 1976).
Wing and Rayford (1977) conducted bench-scale studies on synthetic
wastewater that contained heavy metals using insoluble starch xanthate
treatment. The heavy metals investigated included Ag+, Au3+, Cd2+, Co2+,
Cr3+, Cu2+, Fe2+, Hg2+, Mn2+, Ni24, Pb2+, and Zn2+. The initial heavy metal
concentrations ranged from 26 to 104 mg/L. The residual metal concentra-
tion was generally below the effluent discharge standards. Wing and
Rayford (1976) showed that other starch-based products were effective in
removing heavy metal; these products were insoluble starch xanthate, car-
boxyl cross-linked starch, polyethylenimine cross-linked starch, and tertiary
amine and quaternary ammonium cross-linked starch.
Wing (1974) conducted bench-scale studies on a synthetic mercury-
containing wastewater in the presence of various sequestrants (diglycolate,
NTA, polyphosphate, citrate) and with a control containing no sequestrants.
The presence of the sequestrants at a concentration level of 0.1 g/L did not
3.46
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Chapter 3
adversely affect the removal of mercury. Treatment of the mercury solution
having initial pH in the range of 3 to 11 was effective for removal of Hg.
Starch xanthate and cationic polymer could be added in either order for
effective removal of Hg. The more slowly the starch xanthate was added to
the solution, the more effectively it complexed with mercury, indicating that
the complexation was not an instantaneous reaction. Slower precipitation
generally produces fewer and larger particles, resulting in a sludge which is
more easily filtered. Reaction times required were on the order of five min-
utes. When a larger bench-scale system (95 L (25 gal)) was used, a solution
containing 31,770 ng/L Cu2+ was reduced to a residual level of 22 jig/L Cu2+
with a 5 minute contact time, and to a level of 20 ng/L with a 120 minute
contact time.
In a laboratory investigation, Bricka and Cullinane (1987) prepared sev-
eral synthetic sludges containing the contaminant cations Cd, Cr, Hg, and
Ni. The wastes were treated through hydroxide and xanthate (cellulose and
starch) precipitation. The treated sludges were subjected to Extraction Pro-
cedure (EP) Toxicity tests. All the solidified sludges passed the EP Toxic-
ity test, except for the solidified hydroxide sludge, which failed the test for
Hg. The unsolidified cellulose xanthate sludge failed the EP Toxicity test
for Ni and Cd, while the unsolidified hydroxide sludge failed for every
metal tested. The xanthate-precipitated sludges appear to effectively immo-
bilize heavy metals.
Fender, MacGregor, and Patterson (1982) studied sulfide precipitation of
zinc-laden foundry wastewaters. The wastewater pH was adjusted with
lime to provide pH ranging from 8.5 to 11.0. Ferrous sulfide (at a dosage of
750 mg/L) was added to each sample. The residual lead and iron concentra-
tions were consistently less than 0.1 mg/L when initial metal concentrations
in the wastewater were 21.1 and 0.1 to 1.0 mg/L, respectively. The zinc
concentration decreased from 775 mg/L to a level of 1.7 to 3.7 mg/L; how-
ever, this removal was still inadequate. Two-stage, hydroxide-sulfide pre-
cipitation was investigated in pilot-scale treatability studies. The best
treatment occurred with lime at pH 9.6 with 20 mg/L FeS added to the su-
pernatant. This resulted in a final filtered effluent concentration of 0.05 mg
Zn/L.
3.47
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Process Identification and Description
3.3.5 Combined Precipitation Treatment
In a very broad sense, each precipitation system (with the exception of
metal hydroxide precipitation) involves a combined precipitation system.
This is because the precipitations are generally performed at a particular
pH. For pH >6, metal hydroxide precipitation is possible. Metals are pref-
erentially removed from solution by sulfide precipitation. Hov/ever,
coprecipitation of metal sulfides and metal hydroxides is possible. The
majority of investigations involving combined precipitation systems have
been bench-scale studies.
McAnally, Benefield, and Reed (1984) studied the effectiveness of
soluble sulfide and carbonate in reducing nickel in a synthetic nickel-plating
wastewater. Employing jar tests, the investigators determined optimum pH
range for nickel removal from the synthetic wastewater to be 10.0 to 11.0.
Optimum nickel removal occurred at pH 11 where a residual total nickel
concentration of 0.1 mg/L was obtained with a sulfide:nickel weight ratio of
2.0 and a carbonate:nickel weight ratio of 20.0. At pH 10, a similar degree
of removal (0.2 mg/L residual total Ni) was obtained using a CO32: Ni2+
ratio of 10.0 and a S2: Ni2+ ratio of 0.5. The excellent results in removing
nickel were probably due to a coprecipitation phenomenon. To treat the
synthetic nickel wastewater, the pH was adjusted by drop-by-drop addition
of IN NaOH, and an equivalent amount of IN CaCl2 solution was added to
simulate lime addition. The carbonate was added in the form of NaHCO3.
Such conditions likely led to the precipitation of calcium carbonate
(CaCO3), which has been shown to be an excellent adsorbent for Cd, Pb,
and Zn (Chang and Peters 1985; Faust and Schultz 1983; Peters and Chang
1984, 1985). Coprecipitation and adsorption of Ni(OH)2 and NiS onto the
CaCO3 surfaces may have caused the excellent results in removing Ni.
However, McAnally, Benefield, and Reed (1984) did not report the residual
calcium concentrations needed to confirm this supposition.
In a similar study, McFadden, Benefield, and Reed (1985) investigated
the effect of iron as a coprecipitator of nickel as well as the effects of car-
bonate addition, pH adjustment, and polymer addition. For pH adjustment,
along with carbonate addition, optimum nickel removal occurred when the
total carbonate concentration (CT) was 50 mg/L at pH 11. These conditions
resulted in the soluble and total nickel concentrations of <0.10 and 0.10 mg/
L. All three CT concentrations, employing (50, 100, and 200 mg/L) at pH
10 and 11, effected removal of at least 96% of the total nickel and 99% of
3.48
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Chapter 3
the soluble nickel. The investigators suggested that the calcium may pro-
vide a nucleus for CaCO3 formation, thereby increasing settleability, al-
though they do not report the final residual calcium concentrations of the
treated wastewater. The initial Ca2+ concentrations were the same as those
employed by McAnally, Benefield, and Reed (1984). Coprecipitation of Ni
onto the CaCO3 surfaces may indeed be an explanation for the high percent-
ages of nickel removal observed.
Nickel removal through hydroxide precipitation was the most efficient
for the synthetic wastewater at pH 10 to 11, depending on the Fe:Ni ratio
and CT (McFadden, Benefield, and Reed 1985). Both the soluble and total
nickel concentrations at pH 10 (Fe:Ni = 2, and CT = 0), were reduced to
<0.10 mg/L. Identical results ensued at pH 11 (Fe:Ni = 2, and CT = 100
mg/L as CaCO3). At pH 9, the best overall removal was effected with a
Fe:Ni ratio of 1.0 and CT = 50 mg/L as CaCO3, where the total and soluble
residual nickel concentrations were 0.20 and 0.10 mg/L. For the actual
wastewater, the most efficient soluble nickel removal occurred at pH 10
with a Fe:Ni ratio of 0.7 and CT = 0, resulting in total and soluble nickel
concentrations of 0.30 and 0.25 mg/L, respectively. Use of anionic and
cationic polymers did not enhance the removal of nickel appreciably. For
the actual wastewater, the lowest cost to treat the wastewater was $ 0.14/
1,000 L ($ 0.53/1,000 gal) (in 1985 dollars) for conditions of pH 10, Fe:Ni
ratio of 0.7, and CT = 0.
When ferrous sulfide was used as a coprecipitator, heavy metals (Cu, Cd,
Ni, Cr, and Zn) in the influent wastewater were shown to be significantly
reduced in concentration (Schlauch and Epstein 1977). FeS treatment was
found to be superior to conventional hydroxide precipitation employing
lime as the precipitant.
Chang and Peters (1985) observed that cadmium could be very effec-
tively removed through conventional lime softening operations; the maxi-
mum contaminant level of 0.01 mg/L for Cd could be met with pH in the
range of 7.3 to 11.0. Calcite was the only morphological form observed in
the continuous CaCO3 precipitation. The residual calcium concentration
increased = 30 to 40 mg/L in the presence of cadmium, indicating an inhibi-
tory effect on CaCO3 precipitation. Removal of cadmium was attributed
primarily to physical adsorption onto the CaCO3 sludges.
Talbot (1984) described a process using less than stoichiometric addition
of sulfide, giving a combined hydroxide-sulfide treatment. At pH 8.0, the
3.49
-------
Process Identification and Description
Talbot Process reduced the cadmium concentration in a solution from 15.0
mg/L to <0.05 mg/L, while hydroxide treatment provided a residual concen-
tration of 4.8 mg/L. For a water containing 2.9 mg/L Hg, conventional
hydroxide treatment did not remove any mercury, while the Talbot Process
lowered the mercury level to <0.001 mg/L at pH 8.0. The operating cost of
the Talbot Process is comparable to that of conventional hydroxide precipi-
tation. A smaller quantity of sludge is generated by the Talbot Process
(compared with conventional hydroxide precipitation), thereby lowering
sludge disposal costs.
The Talbot Process basically involves the understoichiometric addition
of sulfide to the wastewater. Bhattacharyya, Jumawan, and Grieves (1979)
also observed that adding 60% of the theoretical requirement of sulfide
provided effective removal of heavy metals (Cu, Cd, Hg, Pb, and As). Pe-
ters, Eriksen, and Ku (1985) also observed that understoichiometric addi-
tion of sulfide, even in an amount as low as 0.5 x stoichiometric
requirement, likewise provided excellent removal of zinc and cadmium and
decreased the resulting sludge volume. They suggested that metals could be
selectively precipitated, removed, and recovered from a mixed-metal waste-
water by properly controlling the solution pH, sulfide dosage, chelant dos-
age, type of chelant, and temperature in a cascading series of reactors. For
example, zinc can be selectively precipitated at pH 6.0, with stoichiometric
sulfide dosage and addition of EDTA (Peters, Eriksen, and Ku 1985).
Pugsley et al. (1970) were the first investigators to observe that selective
removal of a particular heavy metal could be effected in a cascading reactor
system through proper control of the dosage rates. A preliminary estimate
for the sulfide treatment of plating wastewater was approximately $2.45/
1000 L ($9.27/1,000 gal) which compared favorably with the $2.50/1,000 L
($9.45/1,000 gal) approximate cost of treating it by conventional hydroxide
precipitation (Peters, Eriksen, and Ku 1985). Considerable cost savings can
be realized also through reuse, recycle, and recovery of the waste metals
from the plating process.
Higgins and Slater (1984) observed that treating a mixture of metals is a
somewhat more effective measure than treating metals individually. Sulfide
treatment lowered the solubility of nickel and cadmium. Ferric hydroxide
precipitates reduced the metal solubilities through the incorporation of other
metals into an amorphous precipitate and the provision of surface sites for
adsorption. Addition of ferrous sulfate to an alkaline environment (pH
between 7 and 10) caused the iron to precipitate as iron hydroxide and aided
3.50
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Chapter 3
in the flocculation of solids in the process. Such treatment was very effec-
tive in reducing hexavalent chromium to the trivalent form. A combination
of ferrous sulfate and sodium sulfide produced a sludge that was easily
removed, yet minimized sludge production.
Pilot-plant studies (Maruyama, Hannah, and Cohen 1975) employing
lime addition (260 mg/L giving rise to a pH of 10.0) plus 20 mg/L ferrous
sulfate were used to treat a nickel wastewater initially containing 5 mg/L
Ni. The residual nickel concentration was reduced to 0.35 mg/L after sedi-
mentation and filtration. Hydroxide precipitation (at pH 11.5, Ca(OH)2
dosage = 600 mg/L) resulted in a residual nickel concentration of 0.15 mg/L
after sedimentation and filtration. Leckie, Merril, and Chow (1985) like-
wise observed that trace elements of cadmium, zinc, lead, arsenic, selenium,
silver, chromium, copper, and vanadium could be removed by adsorption/
coprecipitation with amorphous iron oxyhydroxide. In both anion and cat-
ion adsorption, iron dose and solution pH were the two adsorption control-
ling parameters.
Of the three precipitation processes, carbonate precipitation produced the
smallest sludge volume. Neither the hydroxide sludges nor the sulfide slud-
ges thickened well in the clarifier. When subjected to acidification, the
hydroxide sludge was the least stable, while the sulfide sludge was the most
stable.
Brantner and Cichon (1981) compared the use of hydroxide, carbonate,
and sulfide treatments in removing heavy metals (Zn, Cr, Cd, Cu, and Pb).
Effective zinc removal was achieved with all three chemical precipitate
processes. For low soluble zinc levels in the clarifier overflow, it appeared
that zinc removal was not limited by solubility, but rather by the effective-
ness of the separation of solids and liquid. The inability of carbonate pre-
cipitation to consistently effect low residual zinc concentrations was
attributed to the kinetics of zinc carbonate formation, causing the solubility
of zinc hydroxide to govern the removal of zinc. Chromium was effectively
removed only through sulfide precipitation. Precipitation of cadmium and
copper was very effectively achieved through all three processes. Lead was
effectively removed through carbonate and sulfide precipitation, causing a
residual filtered lead concentration of <0.1 mg/L; hydroxide precipitation
resulted in a mean effluent level of 0.2 mg/L.
3.51
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Process Identification and Description
3.4 Scientific Basis
3.4.1 Substitution Processes
In the early 1980s, several groups of investigators (Brunelle and Single-
ton 1983; Rogers 1983; Klee, Rogers, and Tiernan 1984; Kornel and Rogers
1987; Franklin Research Center 1982; Neuman and Sasson 1983; Friedman
and Halpern 1992b) described the reaction of PCBs with the phase transfer
catalyst, PEG, in the presence of KOH. The destruction of the halogenated
carbon compounds by PEG in the presence of a base, such as KOH, was
found to be a promising technique for pollution control.
For example, Brunelle and Singleton (1983) described the use of PEG
and poly(ethylene glycol) methylethers (PEGMs) and their reactions as
nucleophiles with PCBs and similar chlorinated aromatics under basic and
mild reaction conditions. In this reaction, partial dechlorination of PCBs
occurred with PEG, producing aryl polyglycols in two hours at 100°C
(212°F). The rate of reaction of PCBs with KOH/PEG was faster than that
with KOH/PEGM; KOH is more effective than NaOH as a basic when used
with an equivalent amount of PEG. Possibly, PEG functions as a phase
transfer agent, complexing the potassium ion and transporting it into the
organic phase (Bailey and Koleske 1976; Yanagida, Takahashi, and
Okahara 1977). An alternative possibility is that the PCB is extracted into
the glycol phase followed by the reaction in the polar glycol phase. Effi-
cient stirring is important to the success of the reaction.
The Franklin Institute (Franklin Research Center 1982) developed a re-
lated process. They found that PCBs could be destroyed by reaction with
sodium metal and PEG at 165 to 180°C (329 to 356°F) and theorized that
sodium PEG was the active reagent. Brunelle and Singleton (1983) com-
pared the two methods. The investigators used a 10-fold excess of NaPEG
in a solventless reaction with Aroclor 1260, and 60% reaction occurred after
two hours at 75°C (170°F) under nitrogen. Air bubbled through the reaction
mixture, giving only 23% reaction. A 5-fold excess of KOH/PEG under the
same conditions resulted in 100% destruction of PCBs. In this study,
PEGM provided better detoxification than PEG and a "no water" situation
was better than when 15% water was present.
The use of PEGMs as phase transfer catalysts (Brunelle and Singleton
1983) in the alkoxylation of mono- and dichlorobenzene has been reported
by Neuman and Sasson (1983). Using polyethylene glycol of mean mo-
3.52
-------
Chapter 3
lecular weight of 6000, (PEG-6000) with n-pentanol in addition to the basic
hydroxide with o- and p-dichlorobenzenes, the investigators produced cor-
responding ortho- and para- pentoxy chlorobenzene and other products.
Differences in the affinity of tertiary and secondary alkoxides for the glycol
catalyst were noted when compared with that of the primary type. The
method of Brunelle, Franklin Research Center, Kornel, Rogers', and Sparks,
and that of Neuman involved reaction of PEG with alkali metal hydroxides,
displacing the resistant chloride in the aromatic chloride via nucleophilic
displacement and, possibly, holding fast the remaining residue in the water
soluble and/or in organic solvents. The reaction mechanism could be either
an addition-elimination sequence (Macomber et al. 1983) or an S,^ mecha-
nism (Bunnett 1978).
The S^j mechanism involves a chain reaction with electron transfer to
the aromatic nucleus followed by expulsion of the chloride ion (Cl~) and
combination with stabilization of the aromatic radical nucleus. The elec-
tron-donating nucleophile should have a low ionization potential in order to
accommodate the aromatic rings' electron affinity. It is a radical chain
mechanism with nucleophilic substitution. Equation [3.6], below, is the
summation of the preceding equations, where X" is a chloride (Macomber et
al. 1983).
[3.3]
[3.4]
[RY]~ + RX -> RY + [RX]~ [3.5]
RX+Y--+RY+X- [3.6]
In order for chlorinated aromatics to undergo the above addition-elimi-
nating sequence, the aromatic halide would be required to have electron
withdrawing groups (multiple of 4, 5, or 6 chlorides) substitution in order to
activate the aromatic ring for the above addition-elimination mechanism.
Acyclic PEG shows complexing properties of ether oxygens with metals
in a manner similar to those of crown-ethers (Balasubramanian and
Chandani 1983). PEG with a general structure HO(CH2CH2-O)nH differs
from crown-ethers essentially in that the macrocyclic ring is opened and the
3.53
-------
Process Identification and Description
molecule is laid out. In the solution state, hydrodynamic evidence (Bailey
and Koleske 1976) indicates that PEG chains are randomly coiled or in an
unordered conformation in several solvents. Yanagida, Takahashi, and
Okahara (1977) have shown that linear PEG can complex several alkali
salts and can effect phase transfer into organic solvents with efficiencies
comparable to those obtained with 18-crown-6. Complexation does not
seem to occur when PEG of molecular weight of less than 300 (PEG-200) is
used. This suggests that more than six ethylene oxide moieties are neces-
sary for complexation (Balasubramanian and Chandani 1983).
Laboratory, pilot-scale, and full-scale data on the use of substitution
reactions to treat contaminated materials are available for the following
media and contaminants:
SOILS
• PCBs, dioxins, PCP
DEBRIS
• cyanides
WATER
• cyanides
• phenols
• metals (precipitation)
OTHER
• PCBs and dioxins in mineral oil
Chemical treatment is rarely used upon high concentrations of target
compounds in any medium usually because of the large amounts of reagent
normally required and, consequent high reagent costs. Another difficulty,
because some of the chemical reactions are very energetic, lies in control-
ling them at high concentrations. Note that this is not a firm rule. For ex-
ample, KPEG reagents have been used to commercially treat small
quantities of high concentration PCB waste at 0.1 to 10% of chlorinated
biphenyls.
3.4.2 Oxidation Processes
This section on oxidation processes focuses primarily on organic destruc-
tion and assesses those technologies that appear to be both innovative and
3.54
-------
Chapter 3
feasible for application to multiphase pollution in the near future. Such
traditional oxidants as chlorine or permanganate are not addressed because
they are not innovative and are not appropriate for use at many hazardous
waste sites. This discussion is centered mostly on excited state and free
radical processes involving various activated oxygen species; primary
among them is the hydroxyl free radical, OH». These species are common,
short-lived, kinetic intermediates in a wide range of oxidation reactions,
including enzymatic and combustion reactions.
Excited states are energetically rich intermediates produced by photo-
chemical processes involving molecular absorption of light or photons.
Excited state species exhibit a reactivity generally much higher than their
ground state analogues and hence, are inherently unstable. Cleavage of
chemical bonds generates free radical molecular fragments, which bear
unpaired electrons. They exhibit significantly higher reactivities than the
parent molecule and, like excited states, are inherently unstable. Free radi-
cals and excited states are formed with energy absorption by a substrate. An
example of this is the photolysis or radiolysis of water (Singh 1986):
,. _y- or e~—irradiation ^rr „ _, _ rr ro „,
HJO- > H» + OH» + H~O + e + H~O* [3.7]
2 Vac-UV photolysis 2 "> 2
where H2O* represents an excited state species.
Because of their high reactivities, these species undergo further reactions
to produce other radicals or reactive species:
H2O* -» //• + OH* [3.8]
OH* + OH* -> H2O2 [3.9]
H2O+ + H2O -» H3O+ + OH* [3.10]
This sequence of radical formation (initiation), successive radical forma-
tion (propagation), and ultimate return to stable species (termination) is
called a chain reaction (Lowry and Richardson 1981). Chain reactions have
the central advantage of being energy-efficient. At sufficiently high tem-
peratures, most chemical bonds will break, forming radicals. At lower tem-
peratures, less than 200°C (400°F), an initiator that produces radicals easily
under milder conditions is needed.
3.55
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Process Identification and Description
3.4.2.1 Photolysis
According to quantum theory, light is composed of discrete particles
called quanta or photons that carry an amount of energy e determined by its
wavelength (A,) or its frequency (\)) according to:
e = hc/h=hv [3.11]
where h is Planck's constant and c is the speed of light in a vacuum. Atoms
and molecules can absorb a quantum only when the energy of the quantum
matches an energy transition to a higher state (Lowry and Richardson
1981). A single quantum can bring about a single transition only if it is
adequately and specifically energetic (proper wavelength). The intensity of
light, on the other hand, influences the number of molecules able to undergo
a transition, but does not change the nature of the transition.
Different wavelengths of light produce different kinds of molecular tran-
sitions. Higher vibrational or rotational levels are induced by infrared exci-
tation. High-energy ultraviolet radiation can cause ionization by the
removal of an electron from the molecule. Longer wavelength UV and
visible light may promote a molecule from its ground state to an excited
state.
One mole of photons is called an Einstein, and the energy of an Einstein
of light at a certain wavelength can be calculated. For example, the energy
contained in an Einstein of 200 nm light is 143 kcal, as opposed to that of
700 nm light which is only 40 kcal. The bond energies of C-C and C-H are
approximately 100 kcal/mole, which is equivalent to the energy contained
in an Einstein of 286 nm light (Lowry and Richardson 1981). Saturated
hydrocarbons absorb light only below 200 nm and their photochemistry is
not very interesting, because in their excited states these molecules frag-
ment indiscriminately through sigma bond cleavage. Molecules having
unsaturated bonds and/or hetero atoms such as N or O are more photo-
chemically active. With increasing conjugation there is a decrease in the
energy of the lowest transition.
Although there may be many transitions possible for an excited state, not
all transitions are equally probable. The extinction coefficient, e, of a com-
pound is an experimentally determined parameter indicating the probability
of a certain transition at a certain wavelength. The greater the extinction
3.56
-------
Chapter 3
coefficient, the more favorable the transition and the more strongly the
compound will absorb at that wavelength.
3.4.2.2 UV-Hydrogen Peroxide
For certain organic compounds, UV light itself is capable of initiating
bond cleavage processes, leading to degradation. The range of compounds
that undergo degradation in the presence of UV light alone, however, is
somewhat limited. The rate of UV-initiated degradation can be slow, and
the extent of degradation can be incomplete. In contrast, the application of
a combination of ultraviolet light and hydrogen peroxide in aqueous media
produces hydroxyl radicals (OH»). Hydroxyl radicals are potent oxidizing
agents that rapidly attack a wide range of organic materials and are capable
of completely oxidizing dissolved organic contaminants in water to carbon
dioxide, water, and salts (Heeks, Smith, and Perry 1991).
The process initially involves the UV-catalyzed decomposition of hydro-
gen peroxide into hydroxyl radicals:
H2O2 uv ) 2OH* [3.12]
As in any photochemically initiated process, the overall efficiency of the
generation of products (in this case, hydroxyl radicals) is a function of the
quantum yield () process:
Quantum Yield (<1>) = (Moles Substrate Reacted)/(Moles Photons Ab-
sorbed):
, (Moles Substrate Reacted)
O = - = [3.13]
(Moles Photons Absorbed)
The quantum yield of photochemical reactions depends upon many fac-
tors including the optical path length of medium, the molar extinction coef-
ficient and concentration of the substrate, and the intensity and wavelength
of light source employed. The optical path length of the medium should be
as large as possible to provide maximum light flux in optimizing the quan-
tum yield of the process. Suspended solids, colloids, and particulates that
will reflect and absorb light should be minimized. Large molar extinction
coefficients in the substrate being irradiated will lead to greater quantum
yields. The molar extinction coefficient of any substrate is dependent upon
3.57
-------
Process Identification and Description
the wavelength of light with which it is irradiated. For hydrogen peroxide,
the molar extinction coefficient at 254 nm is approximately 19.6 M 'cnr1
(Smith 1988). Consideration of these factors is essential in order to select
the optimum light source to be used in the process. Once generated, the
highly reactive hydroxyl radicals degrade organic materials in much the
same way as hydroxyl radicals generated by other means.
3.4.2.3 Ozonation and Advanced Oxidation Processes
There are two modes of action in ozonation processes, illustrated in fig-
ure 3.10 and figure 3.11 (on page 3.59). That of figure 3.10 is along a slow
Figure 3.10
Free-Radical Chain Reaction of Ozone Decomposition
From Babkxi, G., Bellamy. W.D., Bourbigot. M.. Daniel. F.B.. Dore, M., Eita. R. Goidon, G . Langlais, B. Laplanche, A.,
Legube. B., Martin, G., Masschetein, W.J., Pacey. G., Reckhow. D.A.. Vantresque. C., Fundamental Aspects. 11,17,21,
in Ozone in Water Treatment Application and Engineering, Langlais, B., Reckhow, DA, Brink, D.R., Eds., Lewis
Publishers, a subsidiary of CRC Press, Boca Raton, Florida, 1991. With Permission.
3.58
-------
Chapter 3
Figure 3.11
Ozone Decomposition Catalyzed by Hydrogen Peroxide
From Babton, G., Bellamy. W.D., Bourbigot, M., Daniel. F.B., Dore, M., Ert, R, Giordon, G , Langlais, B, Laplanche, A.,
Legube. B., Martin, G., Masschetein, W.J., Pacey, G., Reckhow, D.A.. Ventresque, C., Fundamental Aspects. 11,17.21,
in Ozone in Water Treatment Application and Engineering, Langlais, B., Reckhow, DA.. Brink, D.R., Eds., Lams
Publishers, a subsidiary of CRCPress, Boca Raton, Florida, 1991. With Permission.
reaction route that involves direct interaction with molecular ozone. This is
a highly selective pathway and often does not result in complete mineraliza-
tion of contaminants. The pathway depicted in figure 3.11 entails ozone
decomposition in a series of reactions producing various free radicals, the
most reactive among them being the hydroxyl radical (OH«). This reaction
is initiated, and its rate is limited by, ozone reaction with hydroxide. In
order to enhance the kinetics and energetics of OH« generation, ozone de-
composition can be catalyzed by the addition of hydrogen peroxide and/or
simultaneous use of UV irradiation (see figures 3.10 and 3.11). The result-
ing radical is highly reactive and attacks a wide variety of organics, oxidiz-
ing them to mineralization.
3.4.3 Precipitation Processes
Metals exist in aqueous systems in a variety of forms, including soluble,
insoluble, inorganic, metal-organic complexes, reduced, oxidized, free
3.59
-------
Process Identification and Description
metal, precipitated, adsorbed, and complexed. In any solid-liquid suspen-
sion, an equilibrium exists between the free ions of a given metal, the
soluble ligands, and the solid phase. Soluble ligands may be inorganic or
organic in nature, whereas the solid phase may consist of sludge plus metal
precipitates. Treatment processes must be selected to remove the existing
form of the metal. In general, there are five categories of metal species in
aqueous systems: (1) free ions, (2) metal-hydroxyl complexes, (3) metal-
ligand complexes, (4) adsorbed metals, and (5) the solid phase. These
metal speciation categories are summarized below:
(1) Free ions, M+n
(2) Metal-hydroxyl complex
\M(OH)."-J]
M+n+j OH-<===>M(OH)n-J; Kj=^--^ [3.14]
1 ' [M+nOH-
(3) Metal-ligand complex
\ML"~im]
M+n+iUm<===>MLrm; K, = l ' J
(4) Adsorbed metal
v - \-MS\
(5) Solid phase
MAn <===> M+n + nA~; Ksp = [M+n \A~ ]" [3.17]
where:
K. is the concentration equilibrium constant for the metal-hydroxyl
complex equilibrium; j is a numerical coefficient.
K is the concentration equilibrium constant for the metal-ligand
complex equilibrium; i is a numerical coefficient.
KA is the concentration equilibrium constant for the adsorbed metal
equilibrium; A stands for adsorbed metal.
3.60
-------
Chapter 3
Ksp is the concentration equilibrium constant for the solid phase
equilibrium; sp stands for solid phase.
See figure 3.12 for a conceptual model of metal speciation and distribu-
tion.
Figure 3.12
Resonance Structures for 03
8+ • • 8
From Bablon, G., Bellamy, W.D., Bourbigot, M., Daniel, F.B., Dore, M., Erb, F., Gordon, G., Langlais, B, Laplanche, A.,
Legube, B., Martin, G , Masschelein, W.J., Pacey, G., Reckhow, D.A., Ventresque, C , Fundamental Aspects, 11, 17, 21,
in Ozone in Water Treatment Application and Engineering, Langlais, B., Reckhow, D.A., Brink, D.R., Eds, Lewis
Publishers, a subsidiary of CRC Press, Boca Raton, Florida, 1991 With Permission.
3.5 Status Of Development
Except for the PEG Process, the substitution processes described herein
are available for commercial application. As discussed earlier, a pilot sys-
tem of the PEG Process was tested at the site in Guam but no further activ-
ity occurred. Table 3.7 (on page 3.62) lists the treatment projects conducted
by the GRC Process. As can be seen, most of the treatments have been
performed on either PCB-contaminated liquids or at pilot-scale on contami-
nated soils. Table 3.8 (on page 3.63) shows the processes conducted using
high temperature substitution.
According to the developer, the low temperature substitution reactions
have not been highly successful in laboratory tests for the treatment of halo-
genated aliphatic compounds. The high temperature processes, because
they rely on pyrolysis as well as on substitution reactions, should be effec-
3.61
-------
Process Identification and Description
Table 3.7
Sites of Operation of GRC Process
Site
ITS
Wide Beach
AmTeeh
GE, Moreau
NCBC
Montana Pole
Western Processing
Niagara Mohawk
Bengart-Memel
Niagara Mohawk
Date
1992
1988
1988
1987
1987
1986
1986
1986
1986
1984-5
Contaminant
PCB Soil
PCBSoil
dioxin Sludge
PCB Soil
Dioxin Soil
Dioxin Oil
Dioxin Oil
PCB Oil
PCB Soils
PCB Oil
Size/Concentration
150-ton demo.
10 runs @ 200 Ib each
260 to< 2 ppm
2500 gal @ 1 .1% to < Ippb
Pilot Test 7000 to <10 ppm
Pilot Test 350 ppb
9000 gal 100 ppm to <1 ppb
5500 gal @ 15% water, to <1 ppb
6000 gal to <2 ppm
12 tons to <10 ppm
Pilot Test to <2 ppm
Other demonstrations conducted under EPA sponsorship
tive in treating aliphatics. Since the SoilTech/ATP process uses the chemis-
try of the BCD Process to treat the chlorinated organic compounds, similar
results are expected for both.
3.6 Environmental Impact
The impact of chemical treatment processes on the land and water is
limited to that of the material leaving the process, either treated soil or
treated water. Posttreatment of the soil or aqueous streams can limit the
impacts to acceptable levels. The impact of oxidation or precipitation pro-
cesses on the air is slight to nonexistent, making them highly attractive
because air pollution control devices can increase the cost of competing
technologies by a factor of two or more.
3.62
-------
Chapter 3
3.6.1 Substitution Processes
The potential effect of substitution processes on the air must be carefully
evaluated. The processes can and should be designed to essentially elimi-
nate air emissions, because they will not do it naturally. It is generally as-
sumed that contaminants, such as PCBs, are nonvolatile at temperatures at
which low-temperature destruction processes operate (130 to 160°C (270 to
320°F) for PCBs). This assumption is wrong; PCBs do have finite vapor
pressures at these temperatures,
A review of the Alternative Treatment Technology Information Center
(ATTIC) data base (US EPA 1992a) revealed that the vapor pressures of
common Aroclors (commercial mixtures of PCBs and chlorobenzene iso-
mers) at 100°C are in the range of 0.5 to 3 Torr (mm Hg). Mid-weight
'Aroclors, those that were most commonl) used, have a vapor pressure of
about 1 Torr. Assuming ideal vapor pressure behavior, whenever a mixture
of water and a PCB are heated to just 100°C, 1 mole of the PCB will be
evaporated for every 760 moles of water. This ratio is independent of con-
centration of PCBs. Perry (1965) provides for more information on steam
stripping and steam distillation. A typical molecular weight for an Aroclor
is approximately 270. The molecular weight of water is 18. Hence, at
100°C, for every kg of water evaporated, 1/760 x 270/18 = 0.02 kg or 20 g
of PCBs will also evaporate.
Table 3.8
Sites of Operation, High Temperature Chemical Treatment Processes
Site
Wide Beach
Development
Superfund Site,
Brant, NY
Waugegan
Harbor, IL
Australia
U.S. Navy
Date
1991-'92
1992
1993
(sch.)
1993
(sch.)
Process/
Contaminant
ATP/PCB
ATP/PCB
BCD/PCB
BCD/PCB
Size/
Concentration
40,000 yd3, Soil
100-600ppm
Demonstration
10 tph dredge spoils
99.9999% destruction
2-2,000 L batch
systems for liquids
1-tph soil 25 -
6,500ppm
sch. - scheduled for the projected date
3.63
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Process Identification and Description
This calculation is based on the assumption that the water does not
change the PCBs' vapor pressure. In fact, PCBs are highly hydrophobic,
and the presence of water will result in a vapor pressure that is higher than
this value. Thus, the volatilization rate of PCBs is, most likely, higher than
the above estimate. In addition, it is expected that the vapor pressure of
PCBs will increase at a greater rate than that of water as the temperature
increases. In conclusion, significant quantities of PCBs will volatilize in
any process operating at a temperature above 100°C. High temperature
substitution processes take advantage of this phenomenon, collecting the
condensate, separating the oily phase which contains the PCBs, and recy-
cling the collected oil back into the reactor.
3.6.2 Oxidation Processes
The typical compounds identified after natural waters are oz,onated are
saturated aliphatic acids and diacids, aliphatic aldehydes, alkanes, and some
aromatic acids. These compounds are also identified in oxidation by
KMnO4 or in hydrolysis by NaOH. These results suggest that the ozonation
of complex solutions may not result only in oxidation products, but may
cause the release of compounds from macromolecular structures or generate
by-products that are susceptible to subsequent hydrolysis or precipitation.
While ozonation destroys the mutagenic and carcinogenic activity of
many compounds (e.g., polyaromatic amines and polycyclic aromatic hy-
drocarbons), it has also been observed to change the route of a compound's
mutagenicity and produce mutagenic by-products. Two by-products shown
by the Ames test to have direct mutagenic effects are glyoxal and glyoxylic
acid. Overall, however, the ozonation of water is considered to produce far
fewer potentially deleterious by-products than chlorination.
Ozone in the gas phase has long been recognized as a dangerous and
toxic compound. In animal studies, inhalation of molecular ozone imparts
chromosomal damage and inhibits DNA replication. In mammals, ozone's
high redox potential and extreme reactivity result in damage to many bio-
chemical components. Since the lung is vulnerable to gaseous ozone,
ozonation must be conducted in closed systems and the offgas must be de-
stroyed. The effects of aqueous ozone on mammals have not been exten-
sively studied. Studies of several species of fish have shown ozone to be
lethal to a number of them, but there is not much toxicity associated with
common by-products.
3.64
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Chapter 3
Ozone is a stronger oxidant than the halogen/halide redox couples and
thus, it is thermodynamically possible to oxidize chloride, bromide, and
iodide. In the presence of bromide ions, for instance, ozonation leads to the
formation of hypobromite, which is partially oxidized into bromate ions. In
the presence of NOM, ozonation will produce bromonated organic com-
pounds, such as, bromoform, bromoacetic acid, and dibromoacetic acid.
The generation of these compounds presents the same set of concerns as
other halogenated organic compounds because of their potential toxicity.
One advantage of direct UV photolysis is that complete destruction of
compounds can be accomplished without any threatening chemical residue,
if the energetic specifications for the photodissociation of the contaminant
are met. Since this requires a special set of conditions (pulsed UV con-
tinuum or certain mixtures of compounds (dioxins + solvents)), more often
parent compound degradation creates a suite of by-products. Careful atten-
tion should be paid to the identity of these compounds, which, in many
cases (TNT, PCBs, dioxins), is extremely difficult to determine. Fre-
quently, additional treatment, such as bioremediation or carbon adsorption,
will be required, especially when solvents are present. If dangerous by-
products accumulate, addition of oxidants to the UV system will usually
result in more complete destruction of the parent compound and its break-
down products.
3.7 Pre- and Posttreatment Requirements
Liquid streams fed to oxidation processes are pretreated by filtration to
remove sediment and other particulates. Oxidation processes using UV
light are particularly sensitive to turbidity; if the light cannot penetrate the
liquid, loss of efficiency will result. Deposits on the UV lamps will also
result in a decrease of process efficiency. Some deposition and fouling is
unavoidable, and a well-designed system will make provisions for regular
cleaning of the lamp surfaces. In cases of extreme deposition, some form of
pretreatment of the incoming aqueous stream may be necessary to control
fouling.
No general guidance to posttreatment of the aqueous streams issuing
from oxidation processes can be given. The requirements are highly site
3.65
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Process Identification and Description
specific. Consider for example, an oxidation process used as a method of
treating groundwater from a pump-and-treat operation. If the groundwater
is contaminated with only small amounts of chloromethanes or
chloroethanes, posttreatment will usually be unnecessary. If, on the other
hand, the contaminants include highly refractory compounds, the oxidation
process might be used to pretreat the compounds and make them more ame-
nable to biological treatment.
3.7.1 Substitution Processes
Contaminated oil to be treated by substitution processes usually does not
require pretreatment. Reagent usage, however, can often be reduced and
process performance improved by dewatering and filtering the oil prior to
treatment.
The key to a successful treatment of contaminated soil is to maximize the
contaminant's accessibility to the reagent. Therefore, delumpirig and
screening prior to treatment is highly desirable.
Posttreatment of soils or other waste streams is generally nol required
with the commercially available processes, as they incorporate the posttreat-
ment in the operation itself. Needless to say, new processes that treat con-
taminated soils using substitution reactions (such as the BCD Process) must
incorporate sufficient posttreatment of the soil to neutralize excess caustic
and remove contaminants and reagents.
3.7.2 Oxidation Processes — Posttreatment Requirements
Since ozone is both a toxic gas and a fire hazard, it is mandatory that the
residual O3 in the effluent and offgases of an ozonation system be destroyed
before release. There are three basic methods for destroying the ozone:
• Thermal treatment at temperatures between 300 to 350°C (570
to 660°F) for 3 seconds. This will destroy 99% of this ozone.
Heat recovery may be incorporated in this type of system be-
cause of the resulting high temperatures and energy consump-
tion;
• Catalytic thermal destruction wherein lower temperatures can be
used (30 to 50°C (90 to 120°F)). Catalysts may be metal (plati-
num or palladium) or metal oxides (aluminum or manganese
3.66
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Chapter 3
oxide) for full-scale applications and hydroxides or peroxides
for pilot scale. The main disadvantage of this method is catalyst
sensitivity to chlorine, sulfides, and nitrogen; and
• Destruction of ozone by passing the gas stream through an acti-
vated carbon bed or column.
Posttreatment of by-products, of course, varies with their nature. For
example, waters treated with ozone often require biostabilization because
the biodegradability of the background organic material is enhanced. This
can be effected through use of biological activated carbon or other types of
biological filters. A thorough evaluation to determine by-product identities
and toxicities should be made before releasing effluents into the environ-
ment.
In most systems where UV photolysis has been applied, posttreatment
was not required. This is largely because such systems are used to treat
relatively low concentration streams and, in a situation where incomplete
destruction was observed, oxidants could probably be added to insure com-
plete contaminant destruction via an alternate reaction pathway. It is pos-
sible, however, that for concentrated or complex systems, posttreatment of
the effluent, by biological methods for example, would be desirable. Post-
treatment may be necessary for applications where polymerization occurs.
Polymerization of the organics would form a precipitate that would necessi-
tate a solid-liquid separation step.
It is postulated that the UV/H2O2 treatment of organic contaminants in
water produces a variety of small molecule organic acid intermediates
which ultimately can be mineralized upon extended oxidation (Ogata,
Tomizawa, and Takagi 1981). This must be verified, however, for the par-
ticular matrix, contaminant, and reactor system. As a precaution, offgases
and effluent streams from the UV/H2O2 oxidation process should be dis-
charged through a secondary carbon bed filtration system to account for
process failures or effluent variability. The final effluent composition
should be monitored to ensure that discharge requirements are met. When
designed and operated properly, the UV/H2O2 oxidation process should not
have any adverse environmental impact. The effluent from the UV/H2O2
oxidation process may require pH adjustment, solids removal, and the re-
moval of residual hydrogen peroxide.
3.67
-------
Process Identification and Description
If engineered so that proper dose is applied, AOPs are capable of effect-
ing very high levels of contaminant destruction with virtually no by-prod-
ucts. The only major posttreatment step required is the destruction of ozone
in the offgas. This step is usually a part of the commercial process, and, in
the Ultrox systems, (see Subsection 3.2.1) the gas treatment system is also
capable of treating any VOCs that carry over in the offgas.
3.8 Special Health and Safety
Considerations
Special worker health and safety considerations consist of those normally
required in handling (1) PCBs and other materials of environmental and
health concern and (2) corrosive materials, both caustic (the reagent) and
acid (for neutralization) (American Chemical Society 1979; US! Dept. of
Health, Education, and Welfare 1977).
The long-term effects of the products of the substitution reactions are not
certain. Specifically, the health effects of substituted PCBs,
chlorodibenzofurans, and chlorodibenzodioxins are not known. All pro-
cesses, except the KPEG Process used in Guam, either destroy the products
in the system (BCD, ATP) or collect the product for subsequent proper
disposal (GRC, KGME/DECHLOR).
Oxidative processes use strong oxidizing agents to break down the or-
ganic constituents, introducing a significant health and safety concern. The
resulting materials handling requirements are reasonably well understood.
The processes also use highly alkaline materials to treat chlorinated organ-
ics. Sodium and potassium hydroxide can react with aluminum, forming
hydrogen. Any alkaline process should be designed to safely vent or con-
trol hydrogen gas. Even though use of aluminum in the treatment system
must be scrupulously avoided, aluminum metal is often present in contami-
nated soil and debris.
The potential dangers in using ozone are even greater when oxygen is
used as the feed gas. Although the system can be shut down if a leak devel-
ops, other safety measures should be taken, such as installation of self-
contained breathing apparatuses.
3.68
-------
Chapter 3
3.9 Design Data and Unit Sizing
3.9.1 Substitution Processes
The parameters under which the substitution processes described herein
operate do not impose special design considerations. For example, the resi-
dence times of one to three hours in the reactor for the GRC, KGME/
DECHLOR, ATP Reactor, and BCD chemical processes are long enough to
allow the reactions to occur unless some form of interfering material is
present. Because of the possibility that some material may be present that
could interfere with the chemical reactions, it is necessary to conduct
treatability studies to evaluate the efficacy of the process. The high level of
control that substitution reactions allow provides a high degree of certainty
that the results of a properly-designed treatability study will translate reli-
ably to field conditions.
The unit sizing or throughput of the process is largely determined by
such factors as the type of soil or oil and the presence of water. Contami-
nant concentration is only a factor when it is very high.
Reactor size is determined largely by solid or slurry residence time. For
all substitution processes, solids residence times are in the one to three-hour
range. The reagent to soil ratios are from 1:1 to 2:1 by weight for the low-
temperature KPEG Process, whereas, for the high-temperature BCD Pro-
cess, the catalyst PEG weight ratio is 1 to 10% for a 50 Ib process. For a 10
Ib reaction in the KPEG Process, the ratio is 0.1 to 10%. The excess re-
agent is necessary as a phase transfer catalyst, which extracts the contami-
nant from the soil and allows it to react with the reagent. The reactor
volume must be large enough to accommodate both the soil and reagent.
The reactor for the low-temperature substitution processes must also be
large enough to allow sufficient agitation.
In essence, the substitution process "reaction" requires, along with the
proper temperature, sufficient residence time in the reactor and adequate
mixing in the vessel. It is also necessary to continuously collect the con-
densate, which may, or may not, be recycled in the reactor depending upon
its makeup and value. After these steps, the treated effluent is discharged.
3.69
-------
Process Identification and Description
3.9.2 Oxidation Processes
The UV/hydrogen peroxide oxidation process is carried out in a recircu-
lating batch reactor or continuous flow-through reactor configuration. Sys-
tem design is dependent upon the residence time requirements of the
specific oxidation being undertaken and the level of degradation to be
achieved. An analysis of the configurations for lamp arrays and reactor
shapes in photochemical reactor design that optimize UV light flux has
been reviewed by Smith (1988). Galvanized and aluminum reactors dis-
played no observable rate differences (Barr 1976). The internal reflectivity
of the reactor vessel chamber may be an important design feature of the
system, if significant quantities of light pass through the reaction medium.
The premixed hydrogen peroxide aqueous influent (with the pH adjusted,
if needed) is pumped through the reaction chamber and passed by a series
of UV lamps sealed in quartz tubes. Although the UV/H2O2 oxidation pro-
cess is effective over a relatively broad pH range, the photolytic degradation
of hydrogen peroxide is both mildly pH and temperature dependent. The
rate of hydrogen peroxide photolytic decomposition is approximately twice
as fast at pH 11 than at pH 3 (Sundstrom and Klei 1986) and increases by a
factor of two in going from 17°C (63°F) to 35°C (95°F). The residence
time in the reaction vessel must be sufficient to achieve complete oxidation
of the initial contaminants and their oxidation by-products. Residence
times from several minutes to several hours may be required.
Lamp geometry is another design consideration. Cylindrical lamps can
be placed in the center of annular reactors or around the circumference of
cylindrical reactors. Quartz must be used for those surfaces through which
UV light passes before coming into contact with contaminants. On small
scales, processing chambers can be placed alongside lamps and encircled by
a UV reflector. This is the configuration used with a pulsing UV continuum
in the Wekhof Process. The choice of geometry depends largely on the
degree of light penetration (or attenuation) through the fluid. Since UV
light cannot penetrate particles, a thin film flow over, for example, an irra-
diated weir could be used. For soils of shallow depths, frequent turning and
the addition of either solvents or surfactants to bring contaminants to the
surface are usually required.
The kind of lamp used determines the wavelength of the resultant UV
light. It is necessary to match the wavelength to the reagents as closely as
possible. Hydrogen peroxide absorbs light most efficiently at 254 nm.
3.70
-------
Chapter 3
More than 80% of the total output of low pressure mercury arc lamps is
centered at a wavelength of 254 nm, making them preferable for most hy-
drogen peroxide photochemical processes.
Clearly, the greater the optical path length, the more likely a quantum of
light is to strike the desired target molecule and initiate the chemical reac-
tion. Filtration or other means of clarifying the influent is, therefore, a nec-
essary part of any process utilizing UV light.
The aqueous stream to be treated is typically premixed with a 50% solu-
tion of hydrogen peroxide and fed into an oxidation reaction chamber con-
taining the UV light source. Generally, excess hydrogen peroxide is used in
the process, and the initial level of peroxide added is established in a labora-
tory- or bench-scale treatability study. The hydrogen peroxide level is di-
rectly proportional to the rate of oxidation observed and the level of
peroxide added may require adjustment according to compositional changes
in the influent or reactor performance.
The amount of hydrogen peroxide used depends upon the balance be-
tween reaction rate and peroxide efficiency. It is generally best to start the
process at the lowest effective level of peroxide that results in complete
mineralization and then, to increase its concentration to achieve the desired
reaction rate. Excess hydrogen peroxide must be destroyed or removed
from the effluent prior to discharge.
In general, AOPs operate at ambient, or slightly above ambient, tempera-
tures and produce activated oxygen species, such as the hydroperoxy and
hydroxyl radicals (Aieta et al. 1990). The term "activated oxygen species"
is loosely applied to the following array of species: singlet oxygen, super-
oxide anion, peroxy radicals, hydroxyl radical, hydrogen peroxide, and
organic hydroperoxides. It is important to note that a high degree of
interconversion exists among these species, and the rates of production
depend on the reaction conditions (Singh 1986).
Ozone is a powerful oxidizing agent, widely used in the treatment of
water. Initially, because of this quality, its principal use was in disinfecting
drinking water, but over time O3 was found to be highly effective in many
other water treatment applications. Ozone is now considered a multipur-
pose treatment chemical, and its use as an integrated process can effect
removal of color, control of taste and odor, oxidize iron and manganese,
enhance coagulation, control algal growth, minimize production of disinfec-
tion by-products, and provide biological stabilization.
3.71
-------
Process Identification and Description
The mechanisms by which ozone accomplishes these various treatment
objectives are, for the most part, poorly understood. It is generally believed
that ozone modifies organic structure in a way that enhances the overall
treatment or removal process. The lack of knowledge results mostly be-
cause the chemical quality of natural waters, especially the nature of the
natural organic matrix, is extremely difficult to define. Based on funda-
mental chemical considerations, however, ozone is known to be very reac-
tive with a broad range of synthetic organic compounds (SOCs), and there
is degree of certainty that ozone should be effective in destroying certain
types of SOCs.
In aqueous solutions, there are two types of interactions between ozone
and various compounds:
• Direct molecular reaction; and
• Indirect reaction with radical by-products of ozone decomposi-
tion.
In the first route, direct interaction (see figure 3.13) is highly selective.
It occurs only at certain sites or functionalities and only under certain solu-
tion conditions. The second pathway, indirect interaction, is nonselective
and is thought to be mediated primarily by the hydroxyl free radical.
Figure 3.13
Distribution of Heavy Metals Under Equilibrium Conditions
3.72
-------
Chapter 3
Figure 3.14
Schematic Representation of Direct and
Indirect Reaction Pathways of O3
Direct Oxidation of Substrate __
>-Products
CO*
Radical Consumption 3
HC03
Reprinted from Water Research Volume 10, Number 5, J. Hoigne, and H. Bader, Role of Hydroxyl Radical Reaction in
Ozonation Processes in Aqueous Solutions, Copyright 1976, with kind permission from Pernamon Press Ltd.,
Headington Hill Hall, Oxford, 0X3 OBW, UK.
Given the resonance structures of ozone, shown in figure 3.14, it is evi-
dent that ozone possesses the attributes of a dipole, an electrophile, and a
nucleophile. Ozone's dipolar structure makes it capable of 1-3 dipolar
cyclo addition to unsaturated bonds, also referred to as the Criegee mecha-
nism, ultimately yielding carbonyl compounds (aldehydes and ketones) and
hydrogen peroxide. Electrophilic reactions with ozone are limited to mol-
ecules having strong electronic densities, such as certain aromatic com-
pounds. The substituents on aromatic rings exert a major influence on
ozone attack. Aromatic substitution by electron donor groups such as OH
or NH2 causes an enhanced electronic density on carbons located in ortho
and para positions, which, in a sense, activates these sites to electrophilic
attack by O3. Electron withdrawing substitutions such as COOH and NO2
have an opposite effect on aromatic reactivity with ozone and direct attack
to the least deactivated position that is located meta to the substitution.
Electrophilic interactions lead to hydroxylated products that will readily
undergo further reaction with ozone. Typically, aliphatic products with
3.73
-------
Process Identification and Description
carbonyl and carboxyl functional groups are among the final products. Nu-
cleophilic interactions are common at sites showing electronic depletion,
most often produced by electron withdrawing groups. Overall, interactions
with molecular ozone are highly specific, slower than those of the indirect
pathways, and favored by low pH (J.M. Montgomery Consulting Engineers
1985). The ionic state of a substrate has significant influence as well.
Rates of interaction with molecular ozone are greater for non-ionic and
anionic species than for cationic compounds. Rate constants for direct reac-
tion with ozone in water have been measured for 45 potential organic con-
taminants (e.g., solvents, haloalkanes, esters, aromatics, and pesticides).
These data illustrate that steric factors are also important in limiting reactiv-
ity for complex molecules (Yao and Haag 1991). In general, direct reaction
with ozone is limited to unsaturated aromatic and aliphatic compounds and
is influenced by the type and position of functional group substitutions
(Langlais, Reckhow, and Brink 1991).
Under ambient conditions, ozone is relatively unstable and will rather
quickly undergo decomposition. The stability of dissolved ozone is a func-
tion of pH, ultraviolet light, ozone concentration, and the concentration of
radical scavengers. Ozone decomposition is faster under alkaline conditions
and occurs in a chain reaction process. It is generally accepted that O3 de-
composition is base-catalyzed, and that the free-radical initiating step is the
rate-determining step in the process. Although the hydroxide ion is consid-
ered the primary initiator under the process conditions in many water sys-
tems, there are many other compounds that can initiate the process, which
involves inducing the formation of a superoxide ion radical, O2:. In addition
to hydroxide, some common inorganic ions that can serve as initiators are
hydroperoxide and ferrous ions. Under acidic conditions, the O atom
formed in the thermal dissociation of ozone is a precursor of the initiation
of O3 decomposition (Sejested et al. 1991). Examples of initiating organic
compounds are glyoxylic acid, formic acid, and humic substances. Ultra-
violet radiation at 253.7 nm also causes ozone decomposition, as does the
combination of H2O2/HO2-. These latter initiators are often used in combi-
nation with ozone and constitute the basis of AOPs (Langlais, Reckhow,
and Brink 1991).
Promoters of free-radical reactions are all those inorganic and organic
compounds capable of regenerating the superoxide ion from the hydroxyl
radical. Common promoters are compounds such as aryl groups, formic
acid, glyoxylic acid, primary alcohols, humic substances, and phosphates.
3.74
-------
Chapter 3
The superoxide ion will, in turn, react with ozone, playing a promoter's
role.
Inhibitors of free-radical interactions terminate chain reactions by con-
suming hydroxyl radicals without regenerating the superoxide anion. Typi-
cal inhibitors are bicarbonate and carbonate ions, alkyl groups, tertiary
alcohols, and humic substances. The observation that humic substances are
capable of initiating, promoting, and terminating the chain reaction of O3
decomposition results because these compounds are complex macromol-
ecules substituted with many different functional groups.
Since the rate-limiting step in the O3 decomposition chain reaction is the
initiation step, AOPs have been developed to enhance decomposition kinet-
ics. These techniques are particularly effective at neutral pH and when high
concentrations of radical scavengers (inhibitors) are present. The two most
frequently used AOPs combine O3 with either hydrogen peroxide or UV
light.
As a weak acid, H2O2 partially dissociates in water into the hydroperox-
ide ion, HO2. In contrast with the slow reaction between H2O2 and O3, HO2
is highly reactive with O3. The increasing O3 decomposition rate that oc-
curs with increasing pH is further accelerated in the presence of H2O2, since
its equilibrium is shifted toward the conjugate base, HO2~. Figure 3.11 (on
page 3.59) is a diagram of H2O2/HO2 induced decomposition of ozone.
The overall reaction in the formation of ozone is: 3 O2 <—> 2O3. This
is a thermodynamically unfavorable reaction requiring a large input of en-
ergy. Unlike molecular oxygen, ozone cannot be liquefied by compression.
It can be dissolved in liquid oxygen up to 30% by weight, but beyond that it
becomes explosive. For these and other reasons, ozone is generated on site
in most applications.
The production of ozone requires the dissociation of molecular oxygen
into oxygen radicals, which then react with molecular oxygen to form
ozone. Ozone generation is an equilibrium process in which conditions for
generation also influence destruction. Oxygen radicals, for example, pro-
mote the destruction, as well as production, of ozone. Therefore, it is impor-
tant to determine and maintain an optimum concentration of oxygen
radicals in order to produce efficient conversion.
The splitting of oxygen requires significant inputs of energy. Electrical
discharges or photon quantum energy are typical energy sources. The high
3.75
-------
Process Identification and Description
voltage source of electrons most widely used for ozone generation is silent
corona discharge, but chemonuclear sources and electrolytic processes are
sometimes used. Ultraviolet light, of wavelengths lower than 200 nm, or
gamma-rays are possible photon quantum energy sources.
In the corona discharge, a high voltage alternating current (6 to 20 kv) is
passed across a dielectric discharge gap containing a dry, oxygen-bearing
feed gas. The efficiency of ozone generation depends on the type of feed
gas used. Ozone concentrations of 1.5 to 2.5% by weight can be achieved
by using air, and by using high-purity oxygen, ozone concentrations can be
increased to the 3 to 5% range. Pretreatment of air or high-purity oxygen
feed gas removes dust, moisture, oil, and, in some cases, nitrogen. The
elimination of moisture is imperative in order to obtain high yields. When
air is used, water vapor promotes the formation of nitric acid, which causes
corrosion, and production of hydroxyl free radicals, which consume oxygen
radicals and ozone. Use of an air feed is complicated, costly, and mainte-
nance-intensive. Use of liquefied oxygen eliminates most of the pretreat-
ment needs and, at a cost of approximately $0.08/m3 ($3.00/ft3), may be an
economically attractive alternative, especially for small to mid- size applica-
tions (Kawamura 1991).
There are three basic kinds of ozone generators used in water treatment
applications: low-, medium- and high-frequency units with variable or con-
stant voltage. The low- and medium-frequency units are reliable, widely
used, and readily supplied. Less heat is generated with these units, so cool-
ing requirements are also decreased. Cooling systems are integral parts of
ozone generator designs, since 90 to 95% of the supplied power is con-
verted to heat. Power consumption is an important consideration because,
in general, heat generation increases with power consumption.
Ozone is not highly soluble in water. Dissolution of ozone follows
Henry's Law and, as such, is proportional to the partial pressure of ozone in
the gas phase. Given ozone's low solubility and low concentration in the
gas phase, its transfer from the gas to the liquid phase is a critical step af-
fecting process efficiency. Following are the several kinds of contactors
designed to optimize gas transfer:
• concurrent and countercurrent diffused bubbles;
• positive pressure injection (U-tube);
• negative pressure (Venturi tube);
3.76
-------
Chapter 3
• turbine mixer tank; and
• packed tower.
Tank depths are in the range of 5.5 to 6 m (18 to 20 ft), effecting a trans-
fer efficiency of at least 95%. With high ozone concentrations, approxi-
mately 10% by weight, transfer can be accomplished with a hydraulic
eductor and an in-line static mixer. The countercurrent bubble contactor
has been used most often in water treatment because of its efficiency and
cost-effectiveness. Ozone contact tanks are covered to contain the off gas
and are normally built of concrete.
Extensive modelling has been done in evaluating gas transfer as a func-
tion of different operational parameters and reactor design (Langlais,
Reckhow, and Brink 1991). Typically, however, since ozone contact pro-
duces a minimum of 95% gas transfer and the reaction kinetics of ozone are
very rapid, contact times of 3 to 10 minutes are considered sufficient. Pilot
testing is performed where time and budget permit, but selection of dose
and contact time are often based on rule-of-thumb.
Since 3 to 10% of the ozone is not transferred to the liquid, ozone in the
offgas may be present at a level of 1 g/m3 and must be destroyed. In an
eight-hour work day, the maximum ambient ozone concentration allowable
by the Occupational Safety and Health Administration (OSHA) is 0.002 g/
m3. Techniques available for destroying the offgas are thermal destruction,
with or without a catalyst, and catalytic thermal destruction. Simple ther-
mal destruction is used in air-feed gas systems. Catalytic thermal destruc-
tion improves energy efficiency, but care must be taken to protect the
catalyst from exposure to chlorine and its derivatives, sulfides, and nitro-
gen. In some cases, the offgas is recycled back to the feed, but this requires
reconditioning.
In summary, the design of ozonation processes involves the selection of:
• a feed gas system;
• feed gas pretreatment;
• an ozone generator;
• contactor; and
• offgas destruction system.
An excellent discussion of design criteria is provided by Kawamura
(1991).
3.77
-------
Process Identification and Description
Destruction efficiency of UV photolysis depends on the type of organic
compound. The rate of the photodissociation process, F, can be calculated
according to the following:
Y = Q?on\mgl Ls\
where: O is the photon flux within an absorption band (photons/
cm2-sec)
a is the cross-sectional area for a photodissociation of a con-
taminant (10 n to 1016 cm2) calculated for each absorption
band.
n is the contaminant concentration (mg/L)
At a UV flux of 0.1 W/cm2/nm (typical for the Wekhof Process) a rate of
toxic destruction, F = 1 mg/L-sec, is possible. Although similar fluxes can
be obtained with traditional mercury vapor lamps, the emission lines typi-
cally do not match the absorption bands of the various contaminants.
Therefore, it is wavelength, not power, that is limiting.
One way of improving UV efficiency is by using pulsed UV sources.
Pulsed sources have the advantage of producing pulses of very high photon
fluxes that can be thousands of times greater than emissions from continu-
ous sources. The pulsed sources operate at about the same average power
level as the continuous sources, but they do so in short pulses of high inten-
sity radiation. The short, high intensity pulses favorably alter the kinetics
of the photochemistry. There are basically three design parameters for
photon fluxes: peak power, RMS power, and average power. Peak power
is defined as the energy of a single pulse divided by the duration of the
pulse and is usually in orders of magnitude greater than the average power.
The RMS power expresses the effectiveness of the repeated pulsed action of
the peak power at some repetition rate, R. The average power is the com-
bined energy of all the pulses delivered in one second at the specified rep-
etition rate.
Optimum destruction of contaminants is accomplished by determining
the proper combination of these parameters within the following ranges —
the ratio of RMS power to average power should fall into a range of 1:10 to
1:100 and the ratio of average power to peak power should be within
1:1000 to 1:10,000 with an average power density of 0.1 W/cin2/nm in the
treated medium. The latter ratio is related to the plasma temperature and
3.78
-------
Chapter 3
shifts the peak of UV generation to a absorption band region for a targeted
contaminant (Wekhof 1991).
3.9.3 Precipitation Processes
The key to effective precipitation lies in assuring that the solubility prod-
ucts of the target species and the reagent used to precipitate them are below
their concentrations in the solution. See table 3.9 (on page 3.80) for a list of
values of solubility products of various metal hydroxide, metal carbonate,
and metal sulfide species.
When a solid phase is precipitated from solution, impurities that are nor-
mally soluble under the conditions of the precipitation may adsorb onto
nuclei or crystals and be removed with the parent solid as a single phase.
This phenomenon is known as coprecipitation and is a concern when de-
signing a precipitation system involving multiple substances.
Coprecipitation/adsorption is a coprocess for removing contaminants
from wastewaters. The following five major kinds of coprecipitation have
been identified (Kolthoff 1932; Salutsky 1959; Christian 1977; Patterson
1988):
• Surface adsorption. Impurities are not incorporated into the
internal crystal structure, but instead stay adsorbed to the outer
surface of the precipitate. This adsorption involves a primary
adsorbed ion layer that is held tightly, and a counterion layer
that is held more or less loosely. Surface properties of the form-
ing solid phase (including electrostatic charge) serve to attract or
repel secondary constituents in the surrounding aqueous matrix;
• Occlusion. Impurities are not incorporated in the crystal lattice,
but are adsorbed during the growth of the crystals and give rise
to the formation of imperfections in the crystal. Adsorption
phenomena during the growth of the crystals are primarily re-
sponsible for the degree of occlusion;
• Isomorphic inclusion (or mixed crystal formation). The impu-
rity fits nicely into the crystal lattice of the precipitate and be-
comes incorporated into the lattice in place of a lattice ion of
similar dimension and chemical characteristics. Thus, the impu-
rity becomes permanently incorporated into the crystal lattice,
resulting in a mixed crystal;
3.79
-------
Process Identification and Description
Table 3.9
List of Solubility Products for Various Heavy
Metal Compounds
Compound
CdCO3
Cd(OH)2-fresh
Cd(OH)2-aged
CdS
CoC03
Co(OH)2- fresh
Co(OH)3
a-CoS
B-CoS
Cr(OH)3
CuCO3
Cu(OH)2
CuS
FeCO,
Fe(OH)2
Fe(OH)3
FeS
HgjCO,
Hg(OH)2
Hg2S
HgS (red)
HgS (black)
MnCO3
PK,
11.28
13.6
13.7*
26.1
12.84
14.8
43.8
20.4
24.7
30.2
30.17*
9.86
9.60*
19.66
18.80*
35.2
36.10*
10.50
10.70*
15.1
14.74*
37.4
37.22*
17.2
18.39*
16.05
23.7
47.0
52.4
51.8
10.74
9.40*
K*
5.2x10 -12
2.5x10 -14
2.0x10 -14
8.0x10 -2?
1.4x10 -13
1.6x10 15
1.6x10 -"
4.0x10 -21
2.0x10 "25
6.3x10 -31
6.7x10 '31
1.4x10 -|0
2.5x10 -10
2.2x10 -20
1.6x10 -19
6.3x10 -*
8.0x10 '"
3.2x10-"
2.0x10-"
8.0x10 -16
1.8x10 •"
4.0x10 -3S
6.0xlO'38
6.3x10 '1S
4.0x10 -19
8.9x10-"
2.0x10 -M
l.OxlO-47
4.0x10 -"
1.6x10 'H
1.8x10-"
4.0x10 -10
Compound
Mn(OH)2
MnS - amorphous
MnS - crystalline
MnS
NiCO3
Ni(OH)2 - fresh
a-NiS
B-NiS
V-NiS
NiS
PbCO3
Pb(OH)2
PbS
Sn(OH)2
Sn(OH)4
SnS
SrCO3
ZnCO,
Zn(OH)2
a-ZnS
B-ZnS
ZnS
PK,P
12.72
12.70*
9.6
12.6
15.15*
8.18
6.85*
14.7
15.80*
18.5
24.0
25.7
20.52*
13.13
12.82*
14.93
14.38*
27.9
28.15*
27.85
56.0
250
9.96
10.84
10.52*
16.92
16.35*
23.8
21.6
22.8*
K,
1.9x10 -13
2.0x10 -13
2.5x10 -">
2.5x10 -13
7.0x10 -16
6.6x10 '9
1.4xlO-7
2.0x10 -15
1.6x10 -16
3.2xlO'19
l.OxlO-24
2.0x10 -2*
3.0x10 "21
7.4x10 -14
1.5x10 13
1.2x10 -15
4.2xlO-15
8.0x10 -2"
7.0xlO'29
14X10'28
l.OxlO-56
1.0x10 "25
1.1x10-'°
1.4x10-"
3.0x10-"
1.2x10-"
4.5x10'"
1.6x10 -M
2.5x10 -22
1.6x10 -23
Adapted from Dean 1979, and Benefield, Judkms, and Weand 1982
•Benelield, Judkms, and Weand 1982.
3.80
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Chapter 3
• Mechanical entrapment. This form involves the physical enclo-
sure of a small portion of the mother liquor with tiny hollows or
flaws which form during the rapid growth and coalescence of
the crystals. The pockets remain filled with the mother liquor
and eventually become completely enclosed by the precipitate;
and
• Postprecipitation. The precipitate is allowed to stand in contact
with the mother liquor, and a second substance will slowly form
a precipitate with the precipitating reagent. This type of precipi-
tate contamination is closely related to surface adsorption.
Regardless of the kind of coprecipitation, the initial incorporation of the
impurity into the solid phase is the result of adsorption. This adsorption
may be due to chemisorption, resulting from the coordination between the
impurity and one or more constituent ions of the crystal lattice, or
physisorption, resulting from electrostatic interactions, Van der Waal's
forces, or dipole-dipole interactions. Chang (1985) and Chang and Peters
(1985) presented data on the coprecipitation/adsorption of cadmium, lead,
and zinc onto CaCO3 sludges.
Patterson (1988) observed that little effort had been made to control
coprecipitation. Possible control mechanisms include pH control (which
influences the surface charge of the precipitate solid and the speciation of
the soluble phases), control of the oxidation state of the soluble species,
selection of coprecipitant salt and dosage, and process configuration.
3.9.4 Materials of Construction
In designing chemical processes, materials of construction often present
a challenge, since the materials may be exposed to the following:
• highly reactive reagents;
• solvents specifically chosen to dissolve heavy organic com-
pounds;
• agents specifically designed to mobilize metals; and
• highly abrasive conditions.
Highly reactive reagents are of particular concern when selecting elasto-
meric seals and gaskets for chemical treatment processes for halogenated
organic compounds. The reagents are chosen to specifically attack the or-
3.81
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Process Identification and Description
ganic halogen. Most common elastomers, specifically designed for chemi-
cally resistant seals and gaskets, are based on halogenated polymers. Many
dechlorination reagents will, for example, attack fluorochlorocarbon (i.e.,
Teflon™) gaskets, even though the material is recommended for use in
contact with some of the solvents used in such a reaction.
Metals used in construction of oxidative processes must be selected for
their resistance to oxidation. The first choice, therefore, is some type of
stainless steel; however, many stainless steels are especially prone to chlo-
ride embrittlement. In addition, many stainless steels are susceptible to acid
damage. Therefore, if the pH cannot be maintained in an acceptable range,
a material that resists acid attack must be used.
While low pH is most commonly associated with corrosion problems,
high pH is also a matter of concern. Chemical dechlorination (i.e., sodium
adduct, KPEG, etc.) involves the use of highly alkaline reagents which will
aggressively attack aluminum and magnesium. Many nonferrous metals are
attacked by strong caustic agents; that most commonly encountered is alu-
minum, which is often used in tankers because of its light weight. Alumi-
num tankers can, inadvertently, end up as part of the treatment train in a site
remediation. Copper is attacked by chloride salts, as well. The designer
must be aware of these possibilities and guard against them.
Finally, the designer must consider mechanical wear as well as chemical
resistance. Many wastes contain high concentrations of suspended solids.
Many of the solids, especially in remediation wastes, are of a mineral nature
and are highly abrasive. This can create a particularly acute problem with
seals. Soil treatment systems are especially susceptible to abrasive attack.
Furthermore, seal failure is especially dangerous in a chemical treatment
system, since the system may contain highly reactive materials..
3.10 Operational Requirements and
Considerations
As does any on-site process, chemical treatment processes require utili-
ties and cooling water at the site. Chemical processes are typically compact
and can be relatively self-contained. Thus, they do not require extensive
site preparation or construction.
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Chapter 3
3.77 Materials Handling
The chemical treatment process selected must satisfy engineering re-
quirements that are usually dictated by materials handling considerations.
This is especially true for solids treatment, but materials handling can be a
significant consideration in treating aqueous streams as well. The mixtures
of waste and reagent can be abrasive and corrosive. Some processes may
require that treatment take place at pressures other than atmospheric, and,
therefore, the waste and reagents must be fed through pressure locks. Each
process dictates unique materials handling techniques. In addition, the
process must accommodate wastes of varying characteristics.
Another important consideration in materials handling is the control of
fugitive emissions. Conveyors and other materials moving equipment from
the construction or minerals-processing industries must often be modified
for use in waste treatment systems so that fugitive emissions are minimized.
A conveyor that releases a small amount of dust may be acceptable for
transporting gravel, but its potential use in transporting a contaminated
material must be carefully evaluated. Fugitive emissions present a particu-
lar problem for chemical treatment systems. They do not incorporate a
means of treating air from hoods or shrouds, because unlike incinerators,
they usually do not require large volumes of air. A covered conveyor trans-
ferring waste to an incinerator can be ducted to the incinerator's air intake
duct. Use of the same conveyor in a chemical treatment system might dic-
tate that the air from it be ducted to an air pollution control device.
Contaminated wastes and materials are, by their nature, highly heteroge-
neous. Any process designed to cope with an "average" material, no matter
how well the waste is characterized, must also be capable of treating the
off-average material to some extent. If not, frequent breakdowns will re-
sult. Preprocessing (e.g., blending and shredding) can help, but rarely can it
provide a truly homogeneous material continuously over time.
Inhomogeneity of wastes usually translates into an unacceptable level of
downtime. To avoid this problem, often the wastes to be treated are
sampled over space and time. Each sample is analyzed or samples are com-
bined and analyzed. The results of the analyses are then used to establish
the "waste characteristic," and the treatment process is built to handle this
average material.
3.83
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Process Identification and Description
Inhomogeneity of field materials presents problems for all treatment
processes, but the problem is especially acute in chemical treatment pro-
cesses, since the chemistry is often highly sensitive to trace materials in the
waste. In selecting a process, it is essential that one examine the wastes to
be treated in order to determine difficulties likely to be incurred under alter-
native treatment schemes.
Materials handling does not present a particular problem for the oxida-
tion and precipitation processes addressed herein, except, possibly, in the
collection and handling of precipitates from these processes. (Note that
precipitates can form in oxidation as well as in precipitation processes.)
The handling of precipitates present widely varying problems, and no gen-
eral guidance can be given. Their handling must be part of the treatability
study conducted before the treatment method is selected.
3.12 Information Required to Consider
and Employ the Process
Following are factors that must be considered in deciding whether any
given site or waste is a candidate for chemical treatment by a substitution
process:
• accessibility of contaminants lo the treatment process;
• materials handling;
• materials of construction;
• coupling with other processes;
• heterogeneity of inputs;
• treatment objectives; and
• cost-effectiveness.
The treatment objectives must be clearly established before a process is
chosen. The level of destruction of the target contaminants is important, but
the treatment objectives must be extended to other contaminants, both haz-
ardous and nonhazardous. This is important when considering any
remediation process, but especially when considering chemical treatment
3.84
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Chapter 3
processes, since in most of them the contaminated material is mixed with
reagents.
The kind of issues surrounding treatment objectives can be illustrated by
considering treatment using KPEG to destroy chloro-p-dioxins (dioxins) on
soil. The contaminated soil is mixed with the KPEG reagent, diluted in a
solvent, and the mixture is heated to approximately 200°C (390°F). Once
the dioxins are reacted, the mixture is cooled. It is now a slurry of KPEG,
solvent, soil, and the products of the chemical reaction.
The mixture is highly alkaline and must be neutralized with acid. This
step is clearly necessary because the alkaline material is hazardous and
cannot be released. The neutralization step converts the excess KPEG to a
potassium salt and the original polyethylene glycol, PEG. The PEG is not
hazardous; in fact, PEGs of lower molecular weight are used as food addi-
tives. The solvent, however, may be hazardous. The question that now
must be addressed is, how much subsequent treatment is required to remove
the PEG and solvent so that the treated soil may be disposed?
The PEG is costly, so a high degree of PEG recovery is essential for the
process's economics. One process recovers the vast majority of the PEG
and solvent with a second treatment step, soil washing. But this step does
not remove all of the PEG or solvent. Does the soil from the soil washing
process require additional treatment (say, by bioremediation) prior to dis-
posal? These questions illustrate how the selection of a given treatment
scheme, especially one involving chemical treatment, hinges on the level of
desired performance. It also illustrates that the designer must look beyond
the environmental impact of just the one or a few contaminants that are of
particular concern in a given situation. In many situations, the concern lies
with a relative few toxic contaminants, but the designer must consider also
the nontoxic pollutants such as biochemical oxygen demand (BOD), chemi-
cal oxygen demand (COD), NOx, particulates, etc.
By its nature, chemical treatment requires that reagents be brought into
intimate contact with the contaminant. To illustrate, consider PCBs on soil.
Soil is a complex, highly variable combination of silicates, carbonates, or-
ganic matter, and numerous other constituents. In addition to chemical
differences among soils, the physical states also vary widely. The particles
can be coarse or fine, and they can be solid, highly porous or anything in
between. Naturally-occurring soils will usually contain significant quanti-
ties of water. A typical clay or loamy soil that appears dry to the touch can
contain in excess of 20% water by weight.
3.85
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Process Identification and Description
Contaminated soils are even more complex. As an example, consider a
soil contaminated with a hydrophobic material, say PCBs. The following
points should be taken into account when possible cleanup procedures are
considered:
• The PCBs contaminate the soils in two unique ways;: (1) on the
surface; and (2) embedded in the pores of the soil particles;
• Only rarely are PCBs found in the environment in pure form.
Most PCBs were blends of PCB isomers and chlorobenzenes.
The blends are usually mixed with mineral oils that were used as
dielectric fluids as well. The mineral oils were either paraffinic
(aliphatic) or aromatic based;
• Generally, PCBs in the environment have "aged," changed with
time. The aging consists of some oxidation of the less stable
organic constituents, especially the mineral oils, dechlorination,
and biodegradation of the lower chlorinated PCBs, and preferen-
tial volatilization of the lighter components. The combination of
these processes leads to a change in the PCB isomer mix remain-
ing in the soil; and
• The PCBs and the mineral oil base in which they are typically
found are highly hydrophobic. Typical maximum solubility in
water is on the order of 0.05 to 0.1 mg/L.
It is reasonable, therefore, to postulate that a grain of soil in a typical
environmental sample of soil contaminated with a PCB will resemble that
in figure 3.15 (on page 3.87). The soil grain's surface may be coated with
the PCB liquid. The PCB liquid is also present in its pores, but it appears
likely that the pores also contain water, creating a pattern of alternating
layers of PCB and water.
Now, assume that a hypothetical reagent that readily destroys PCBs has
been discovered. Fundamental kinetics dictate that the reagent and the PCB
must be in the same phase. If this does not occur, then the chemical reac-
tion (no matter how fast its rate) will be heterogeneous. The reaction rates
will be limited by mass transfer of the PCB across the two-phase barrier and
the destruction will be very slow.
If, on the other hand, the reagent solution can dissolve the PCB, the sur-
face of the PCB will be dissolved and will react. But if the solution is hy-
drophobic, it will be unable to penetrate the droplets of water in the soil
3.86
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Chapter 3
Figure 3.15
Cross-Section of a Grain of PCB-Contaminated Soil
pores. The PCB in the pores will not be accessible to the reagent and,
therefore, it will not be destroyed.
Chemical processes that treat PCB-contaminated materials overcome the
problem because of two characteristics: (1) they are soluble in both organic
and aqueous phases and (2) they operate at temperatures above the boiling
point of water so that the water and PCBs are driven out of the pores, bring-
ing the PCBs into contact with the reagent. For example, APEG reagents
dissolve in both water and the organic phases. As a result, they can diffuse
into the pores and destroy the PCBs. Furthermore, the processes are run at
temperatures above the boiling point of water.
Consider how these facts relate to the treatment of soils using solid re-
agents. First, consider the contaminant on the surface of the soil. The
solid reagent reacts with the contaminant on the surface of the soil, but there
must be a mechanism for the contaminant to transfer from the soil particle
to the reagent particle. Such a transfer is not impossible, but it is very slow.
Contaminant in the pores is simply not accessible to the reagent. In order
for a solid reagent to work, the contaminant must be mobilized either by
heat (which vaporizes it) or by a solvent. The solvent, termed a phase trans-
fer catalyst, is, therefore, an essential ingredient for any liquid-phase solid-
solid reaction.
3,87
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Process Identification and Description
Although the problem of accessibility is most obvious in soils, it occurs
in all media. For example, oxidation of organic contaminants in aqueous
media by ozone requires that the ozone cross the liquid-gas barrier. The
rate of ozone diffusion is much slower than the oxidation reaction. As a
result, the destruction of organics by ozone will generally be mass-transfer
limited. Improvements in the system's performance will come by increas-
ing the surface area of contact, either by decreasing gas bubble size or in-
creasing the system pressure.
3.13 Unique Planning and Management
Needs
Chemical treatment is effective in treating selected contaminants that are
in dilute form in another medium, such as soil, water, or nonhazardous oil.
Understanding the principal advantages, and disadvantages, of chemical
treatment is the key to determining the conditions under which it should be
applied. Following are the principal advantages:
• Relatively low capital cost. The treatment system c an often be
assembled from standard, off-the-shelf components;
• Very low levels of air emissions. Because most chemical treat-
ment systems operate in the liquid phase, the potential for air
emissions is minimized;
• Potential for a high level of quality control (QC). The reaction
products can be tested and analyzed as part of an on-line QC
program to assure satisfactory destruction of the contaminants;
• Relatively high degree of public acceptance. The processes do
not suffer from a popular stigma as does, for example, incinera-
tion, largely because of the low levels of air emissions that result
and the high level of quality control that can be exacted; and
• Comparatively small size. Typically, systems with significant
throughputs can be mounted on trailers and operated at the con-
taminated site with minimal construction and little on-site as-
sembly.
3.88
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Chapter 3
Following are the principal disadvantages of chemical treatment:
• Relatively high operating costs, especially for treating materials
with high concentrations of contaminants. The cost of chemical
treatment is highly sensitive to the amount of reagent consumed.
Because highly skilled operators are required on site, labor costs
also tend to be higher than for simpler technologies;
• Highly sensitive to the overall composition of the material being
treated. Water or other materials present in the contaminated
material may interfere with some of the desired chemical reac-
tions. The stream(s) to be treated must be relatively homoge-
neous;
• Risk of undesirable side reactions. The long-term environmental
and health effects of the products of some chemical reactions
used in treating contaminants are not well known; and
• Residual reagents. Except for some of the processes used to
treat aqueous streams with H2O2 or O3, residual reagents remain
in the treated stream. This is of special concern when treating
soils where the reagents must be removed by treating them ther-
mally, through solvent extraction, or through soil washing.
In view of its principal advantages and disadvantages, chemical treat-
ment should be considered as a method of treatment at sites where one or
more of the following conditions exist:
• The object is mainly the treatment of one or a few specific kinds
of contaminants that can be chemically modified;
• Transport of the contaminants to an off-site location for treat-
ment is precluded by the volume of material to be treated or
because of other considerations;
• Established on-site processes, such as incineration, are not tech-
nically feasible or are otherwise precluded; and
• The quantity of material to be treated is small or the contaminant
concentrations are low and the economics of treatment, there-
fore, favor the low capital, high operating cost approach.
Political and social factors, rather than economic considerations, are
often determinants in the selection of a treatment process. The lowest cost,
environmentally-sound remediation may not be acceptable for a given site.
3.89
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Process Identification and Description
In such circumstances, chemical treatment may be selected in pilace of other
techniques, although the economics may not be in its favor.
The overriding planning and management need for effective implementa-
tion of any remediation process is proper scheduling. This need is espe-
cially acute, however, in planning chemical treatment, because the
chemicals required are generally not locally available. Limited on-site stor-
age space makes delivery schedules especially crucial to effective opera-
tions.
3.14 Cost
This section focuses on how the incremental cost of the chemical process
affects total treatment cost. It is keyed to the major components of fixed
and variable cost listed below:
• FIXED COST COMPONENTS
• equipment amortization
• sales
• obtaining required permits and approvals
• preparing the system for the specific job
• shipping, setup, and knockdown
• site capping and restoration
• VARIABLE COST COMPONENTS
• reagent purchase
• handling and disposal cost of treatment and treated materials
• utilities
• labor, travel, and subsistence
• chemical analyses
3.90
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Chapter 3
3.14.1 Fixed Costs
Because of the unique nature of chemical treatment, many of these com-
ponents weigh in differently than they would in other remediation pro-
cesses, such as incineration or stabilization.
The first factor that impacts chemical treatment is the amortization of the
equipment. As previously discussed, chemical treatment systems tend to be
highly site specific. That is, a given treatment train incorporating chemical
treatment methods will be assembled to work on a specific site and then
dismantled. In most cases, it is unlikely that the same treatment train will
be used at a second site. As a result, the treatment system must be amor-
tized over only one job. The cost per ton of material treated by a system
which costs, for example, $3 million to build and to treat 30,000 tons of
material at a site will be $11 I/tonne ($100/ton). The cost per ton does not
include the cost of money (interest on capital). If the remediation takes
three years between the time the equipment is built and the remediation is
completed, and we assume a 10% annual cost of capital, the amortized cost
of the equipment for this remediation is $145/tonne ($130/ton) of material
treated.
Since typical disposal costs are currently on the order of $111 to $5507
tonne ($100 to $500/ton), the amortization cost for this hypothetical system
makes a significant impact on the cost of remediation. Clearly, chemical
treatment systems must either be usable at many sites, or they must be rela-
tively inexpensive to build. At present, with the exception of the KPEG
Processes, the former alternative does not appear likely. Chemical treat-
ment trains are highly specialized. Therefore, in order for chemical treat-
ment systems to be economically competitive, the equipment must consist
of easily-assembled, readily-available, reusable components.
Cost of sales is far more difficult to quantify a priori than amortization
cost and is not unique to chemical treatment methods. It is significant,
however, and must be included as a part of the overall cost of treatment
when planning a remediation project.
Also difficult to quantify, permit costs are usually a significant fraction
of the overall treatment cost. Permit costs have two components, direct and
indirect. The direct permit costs are preparation of the permit application
and the required testing and reporting. The indirect components are the cost
of delays and responding to public comment. Examination of the history of
3.91
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Process Identification and Description
several chemical treatment applications (i.e. Weitzman 1982; Peterson
1986; and operators of the ATP/SoilTech process) has led to the conclusion
that chemical treatment systems encounter far less public opposition and
fewer delays than do incineration processes, resulting in lower permitting
costs than incineration.
Chemical treatment systems tend to be compact. They typically do not
require large foundations (as do transportable incinerators) and are built on
standard over-the-road equipment. They are, therefore, relatively inexpen-
sive to ship, setup, and knockdown. The total cost of these activities is typi-
cally on the order of $10,000 to $20,000. These estimates are based on the
authors' field experience and discussions with vendors.
Site capping and restoration can be a costly part of a remediation, these
costs are not unique to chemical treatment. They are highly dependent on
the characteristics of the particular site.
3.14.2 Variable Costs
Reagent cost is unique to chemical treatment processes. It is usually a
very significant factor in the overall cost. Consider the treatment of 27,000
tonne (30,000 ton) of soil. The KPEG Processes require that the soil be
mixed with relatively large volumes of reagent dissolved in a carrier. If, for
purposes of order-of-magnitude cost estimation, it is assumed mat each ton
of soil is mixed with one ton of reagent, then it will be necessary to process
27,000 tonne (30,000 ton) of reagent. Reagent recovery will be considered
below. Typical reagent costs are $2.25 to $11.25/kg ($1 to $5/lb). Assum-
ing the lower cost, and neglecting, for the moment, reagent recovery, the
reagent cost for the treatment is $60,000,000 or $2,200/tonne ($2,000/ton).
Clearly, some form of reagent recovery is economically necessary. Ignore,
for the purpose of this analysis, the environmental impact of such an enor-
mous reagent release. At 90% reagent recovery, the cost of reagent is $2207
tonne ($200/ton) of material treated; at 95% recovery it is $110/tonne
($100/ton), and at 99% recovery $22/tonne ($20/ton).
It is extremely difficult to maintain 99% reagent recovery for a highly
heterogeneous process. Ninety-five percent reagent recovery is still very
difficult to achieve, although more realistic than the 99%> claimed by one
vendor. One can refine the reagent cost estimate by making the analysis
site- and technology-specific, but it is apparent that in all cases, the cost of
reagent is a significant part of the total remediation cost.
3.92
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Chapter 3
The above analysis is based on the use of quantities of reagent that would
normally be needed to treat contaminated soils. The relatively large reagent
volumes are necessary to overcome the mass transfer problems. In water
treatment, far smaller quantities of reagent are required, on the order of
0.1%, making the cost of reagent far more manageable; however, it is still a
significant factor when the cost of chemical treatment is compared to the
cost of alternative technologies for many applications.
For most chemical treatment processes, utility costs are relatively low,
typically less than $1.10/tonne ($1.00/ton) of material treated.
Labor, travel, and subsistence costs for chemical processes are generally
higher than for other remediation operations. This is because the typical
chemical treatment process requires highly trained workers. It is usually
impossible to hire them locally. One must, therefore, add approximately
$150 per day for travel and subsistence, corresponding to $18.75 per hour
of operation. Assume that a typical soil treatment system requires three
operators per shift. Assume further an average cost per operator is $45/hr,
fully loaded, and a throughput of 9 tonne/hr (10 ton/hr). Adding (and
rounding) the travel and subsistence cost increases the cost of labor for the
operation to $64/hr per operator, or a cost of labor of about $21/tonne ($197
ton), if the system is operating eight hours per shift. System malfunctions,
delays, and breakdowns reduce the time for treatment and proportionately
increase the labor cost. For example, a system which, because of break-
downs and other reliability problems, is operating only 50% of the time
would have double the labor costs per ton than that based on an estimate of
100% reliability. If we assume 50% time on-line, the labor cost for chemi-
cal treatment would increase to $42/tonne ($38/ton).
The above cost estimate does not include the cost of labor for excavation
and materials transfer, which would be required regardless of the technol-
ogy used. This cost varies with process reliability and is another factor
making process reliability an important consideration in the selection of a
remediation process. (Treatment system reliability, of course, is an impor-
tant factor in the evaluation of all remediation processes, not just chemical
treatment.) The excavation and materials handling equipment and person-
nel stand idle, while the system is inoperative. The cost attributed to such a
decrease in productivity should be factored into the total cost of the treat-
ment process.
3.93
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Process Identification and Description
Chemical treatment requires frequent sampling of both feed and pro-
cessed materials and analysis of the samples for key constituents. The sam-
pling and analysis is necessary both to assure that the process is destroying
the target contaminant and to monitor the general performance. These costs
cannot be quantified here, but one must take them into account in assessing
the total cost of a chemical treatment operation.
While system reliability has its greatest impact on labor costs, it also
affects other costs, such as rental of tank trucks, compressors, generators,
and other equipment. In comparative analyses of treatment methods, sys-
tem reliability is often determinative. The more complicated the process,
the more significant downtime is likely. Chemical treatment systems use
relatively simple equipment. If the equipment is properly selected for the
application, it is likely that the system will have less downtime than systems
applying alternative innovative technologies.
3.14.3 Estimated Costs of Various Treatment Methods
Reliable cost data on treatment methods are very difficult to obtain, since
the ultimate cost is highly site specific. See table 3.10 (on page 3.95) for
available cost data.
3.14.4 Equipment Sizing and Cost - Oxidative Processes
Excellent discussions of the practical aspects of ozonation are provided
by Kawamura (1991) and Langlais, Reckhow, and Brink (1991). The most
practical ozone generators are either low- or medium-frequency. Selection
of a generator is usually based on the following factors:
• reliability and maintenance;
• energy cost differential;
• turn-down ratio;
• cooling water temperature;
• benefits of oxygen-enriched feed gas; and
• owner preference.
Following are key design elements and operating factors affecting equip-
ment sizing and cost:
• size of the ozone generators;
3.94
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Chapter 3
Table 3.10
Cost of Treatment
Process
PEG Process
GRC Process
DECHLOR/KGME
ATP
BCD
Romulus Remediation
Treatment Cost per ton
of material treated
unknown
$200-500
N/A
$254
N/A
$1,358
Source
Vendor claim
Vendor claim
Field Data
N/A - Not available
• number of generators, cost of energy, and cost of O2;
• type of feed gas treatment;
• reliability of each component;
• operation and maintenance costs;
• ozone contactor design;
• offgas treatment; and
• whether UV light or hydrogen peroxide is used to catalyze de-
composition of O3.
Major manufacturers of ozone generators are Quantum (Emery),
Welsback Ozone System, Griffin, Technics, PCI Ozone and Control, Asea
Brown Boveri (ABB), Infilco Degremont Inc. (IDI), Trailigas, Schmidding-
Werke (Megos), Mitsubishi, and Toshiba. Design criteria and a detailed
example of design calculations can be found in Kawamura (1991). An
extensive review of the economics of ozonation systems is presented by
Bellamy et al. (1991). See also figures 3.16 a and b (on pages 3.96 and
3.97).
Wekhof (1991) presents cost comparisons for a 100-fold destruction of
20 mg TCE/L and 20 mg benzene/L in a wastewater using the following
3.95
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Process Identification and Description
Figure 3.16a
Construction Costs of Ozonation Systems
10,000
1000
\ i T TT irr
Low Frequency, Air
Medium Frequency, Air
Medium Frequency, O2
I I I I I I 11
I I I I I I I
100
1000
Ozone Generation Capacity (Ib/d)
10,030
Complete ozone system (includes generation, building, and contactor).
Reprinted by Permission of Susumu Kawamura from "Water Treatment Principles and Design* by James M Montgomery
Consulting Engineers, Inc. Published by John Wiley and Sons. Copyright 1989 by Susumu Kawi
sumu Kawamura
technologies: air stripping with offgas vapor phase activated carbon
(Westates Carbon, Inc., Los Angeles, CA); conventional UV/hydrogen
peroxide (PSI, Tucson, AZ); Wekhof Process using a 20 kW UVERG
(pulsed UV lamp) system. The comparison is summarized in table 3.11 (on
page 3.98). The pulsed UV system was considerably less expensive than
conventional air stripping/offgas scrubbing. The system also enjoys an
economic advantage over conventional advanced oxidation processes. For
soils, the pulsed system's operational costs are much greater — in the range
of $120 to $250/m3 ($92 to $191/yd3). It requires 24 hours to process 1 m3
(1.3 yd3) of soil using a 100 kW pulsed system and mobile systems are
available. In contrast, treatment of highly contaminated soils by
bioremediation takes between months and years and incineration is costly
and destroys the soil.
3.96
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Chapter 3
The issue of equipment sizing is, as always, resolved through a site-
specific tradeoff between investment capital and operating costs. Pilot- and
commercial-scale UV/H2O2 oxidation systems for the treatment of contami-
nated groundwater have been designed and operated. Reactor capacities in
the range of 57 to 830 L (15 to 220 gal) have been constructed and operated
(Heeks, Smith, and Perry 1991; Andrews 1980). Flow rates through the
oxidation reactors are designed to meet effluent contaminant levels by con-
trolling residence times. UV/H2O2 reactor systems have been operated at
flow rates of 4 to 37 L/min (1 to 10 gal/min). The selection of reactor vol-
ume, throughput, and residence time will be dictated by the rate of oxida-
tion of contaminants, which can be controlled to a reasonable degree by the
concentration of hydrogen peroxide in the influent. Operating systems have
been constructed by several vendors including Peroxidation Systems, Inc.
and Solarchem Environmental Systems.
Figure 3.16b
Breakdown of Ozonation System Construction Costs
10,000
1000
100
I I I I TTTTI
Complete System
\III I 1 T_
I I I I I I 11
I I I I I I I
100
1000
Ozone Generation Capacity (Ib/d)
10,000
Ozone system components.
Reprinted by Permission of Susumu Kawamura from 'Water Treatment Principles and Design* by James M Montgomery
Consulting Engineers, Inc. Published by John Wiley and Sons. Copyright 1989 by Susumu Kawamura.
3.97
-------
Process Identification and Description
Capital and operating costs are dependent on the scale of the operation,
contaminant levels, oxidation rates, post- and pretreatment and equipment
utilization rates. Cost estimates for groundwater treatment of $0.41 and
$1.32/m3 ($1.57 and $5.00/1,000 gal) of wastewater treated at process
throughputs of 1 nrVmin (250 gal/min) and 0.1 mVmin (25 gal/min) for the
treatment of groundwater containing approximately 6,000 ppm of VOCs
have been generated (Heeks, Smith, and Perry 1991). A pilot-plant opera-
tion with a 0.04 m3/min (10 gal/min) throughput rate has been projected to
entail a capital investment of approximately $100,000 and an annual operat-
ing cost of $20,000.
Treatment costs, of course, depend largely on the specific set of condi-
tions attending each application, such as, nature of initial concentration and
contaminant, and flow and target concentrations. For initial concentrations
less than 100 mg/L, the Rayox system reduces contaminant levels three to
Table 3.11
Economic Comparisons of Groundwater Treatment Systems
Item
Equipment
Installation
Capital Cost
Electricity
Carbon
Chemicals
Lamps Cost
Maintenance
Amortization
Total Operating
Total Cost
$/m3
($/l,OOOgal)
Air Stripping And
Activated Carbon
$100,000
$20,000
$120,000
$5,120
$ 274,300
$0
$0
$15,600
$24,000
$319,020
$1.60
($ 6.07)
Mercury Vapor Lamp
UV With H2O2
$ 1 15,000
$ 20,000
$ 135,000
$ 34,500
$0
$ 12,000
$ 38,400
$ 6,750
$27,000
$118,650
$0.59
($ 2.24)
Pulsed Xenon Lamp
UV With H2O2
$ 115,000
$ 15,000
$ 120,000
$ 1 1 ,400
$0
$6,000
$ 17,800
$6,000
$ 25,000
$ 66,200
$0.33
$1.26
Costs projected according to the following assumptions
Contaminant- 20 mg/L benzene plus 20 mg/L ICE
Flow rate 380 L/min (100 gal/mm)
Operating costs are given tor 1 year round the clock operation
Reprinted by permission of the American Institute of Chemical Engineers from Treatment of Contaminated
Water, Air and soil with UV Hashlamps" by A. Wekhof In Environmental Progress, Volume 10, number 4.
Copyright 1991 by American Institute of Chemical Engineers. All rights reserved.
3.98
-------
Chapter 3
five orders of magnitude at a cost of approximately $0.79/m3 ($3.00/1,000
gal). As initial concentrations increase from 100 to 1,000 mg/L, the costs
rise to $2.64/m3 ($10/1,000 gal).
Direct operating and maintenance costs of the Ultrox Process are re-
ported by the manufacturer for a number of applications. The costs range
from $0.11 to $1.32/m3 ($0.40 to $5.00/1,000 gal). In general, it was found
that this process was much less costly than alternatives, such as activated
carbon. In one application, a comparison of various treatment strategies for
groundwater contamination with TCE and other trace VOCs (total VOC
concentration = 7.0 mg/L) found that the capital costs of air stripping with
vapor phase granular activated carbon were less than the Ultrox Process, but
the operation and maintenance costs of the Ultrox system were one-third to
one-half that of the alternatives.
3.99
-------
-------
Chapter 4
POTENTIAL APPLICATIONS
Chemical treatment processes are potentially applicable under the fol-
lowing conditions:
• Substitution processes — where materials are considered haz-
ardous because they contain a specific class of contaminants,
especially halogenated aromatic compounds. They also may be
used in treating materials containing halogenated aliphatics,
nitrogen-bearing compounds, and sulfonated compounds;
• Oxidation processes — where materials are considered hazard-
ous because they contain low concentrations of organic constitu-
ents in water or in a dilute slurry; and
• Precipitation processes — where materials are considered haz-
ardous because they contain toxic metal compounds in aqueous
solution.
There are rules-of-thumb as to the degree to which some organic com-
pounds are amenable to chemical treatment. Nonchlorinated organic com-
pounds are commonly treated by oxidation reactions, while chlorinated
compounds are treated by dechlorination/substitution reactions. See table
4.1 (on page 4.2) for lists of compounds in the approximate order to which
they are amenable to treatment. Compounds falling into classes at the top
of the table tend to be more readily treatable than those at the bottom. The
nature of the contaminant to be treated is a major determinant whether
chemical treatment is practical under any given condition.
As to inorganic contaminants, the question becomes whether a more
desirable form of the metal to be treated exists chemically, i.e., different
oxidation state, less soluble, more soluble, less toxic, etc. The determina-
tion must be made on a metal-specific basis and no general rules appear to
apply. Organic compounds containing fluorine tend to be more stable and,
hence, more difficult to treat chemically than their chlorinated counterparts.
4.1
-------
Potential Applications
Table 4.1
Amenable to Treatment (Rule of Thumb)
Nonchlorinated
(Oxidation Processes)
Easiest to Treat Phenols, Alcohols
Ketones, Organic Acids
Aroman'cs
Uosaturated Aliphatics
Saturated Aliphatics
V
Hardest to Treat Flourinated Compounds
Chlorinated
(Substitution Processes)
Media
Chlorophenols Homogeneous Debris
i
Chlor. Aroniatics
Chlor. Unsaturated Ah'phatics
Chlor. Saturated Aliphatics
Brominated and Iodine Compounds
i
Sand
V
Clay
Brominated and iodinated compounds tend to be more amenable to chemi-
cal treatment.
The foregoing are merely guidelines based on the fundamental chemistry
of the classes of compounds, supported, however, by the results of studies
of the several treatment processes. To understand the likelihood of the
success of a given chemical process, it is necessary to consider its scheme
of attacking the target molecule. Consider, for example, a nonchlorinated
phenol. It consists of a partially oxidized benzene ring. The -OH group on
the benzene ring reduces the inherent stability of the benzene ring and
makes the molecule more susceptible to further oxidation. Aromatic com-
pounds that do not include a phenol group, such as benzene or naphthalene,
are very stable and far more difficult to oxidize. The degree of difficulty
progresses down the list.
Chlorinated (or, more generally, halogenated) organic compounds are
typically treated by processes that attack the chlorine atom on (he molecule,
rather than oxidize the whole molecule. A possible exception is the lower
chlorinated chlorophenols that can be oxidized by processes analogous to
those for phenol. Clearly, chemical processes that attack the chlorine atom
on the molecule are totally unsuitable for treatment of materials contami-
nated with nonhalogenated compounds.
There is also an important rule-of-thumb relating to the medium to be
treated. Obviously, solids tend to be more difficult to treat than liquids.
4.2
-------
Chapter 4
Furthermore, the greater the contaminant concentration, the more difficult
the contaminant is to treat. There are, however, treatability characteristics
within the solids class. Table 4.1 (on page 4.2) lists various solid media in
order of increasing difficulty of chemical processing; the larger the particle
size, and the less hydrophilic the material, the easier it is to treat the media.
This is because larger particles and less hydrophilic materials make the
contaminant more accessible to the reagent and allow clean separation of
the reagent from the matrix after treatment.
Within these classes of media, the difficulty of treatment increases with
an increase in the water content of the solids. Contaminated sand as a
dredge spoil would tend to be more difficult to treat than the same contami-
nated sand if it were removed from a dry area. The water tends to (1) dilute
the reagents, (2) encapsulate hydrophobic contaminants, (3) make the solids
clump together, and (4) interfere with many chemical reactions.
Although several oxidation processes have been applied directly to the
treatment of contaminated soils on a laboratory scale, the oxidation reac-
tions themselves are most likely to occur in the liquid phase and are more
efficient in degrading aqueous phase organic compounds. Therefore, al-
though direct treatment of contaminated soils on a large scale may prove to
be physically impractical (Watts, Tyre, and Miller 1991), indirect treatment
of soil contaminants with chemical oxidation may be feasible when phase
transfer from the solid to aqueous phase can be effectively achieved.
Chemical oxidation has also been evaluated as a pretreatment step in the
biological degradation of contaminants in soil matrices (Kelly, Gauger, and
Srivastava 1990; US EPA 1990).
Ozone is commonly used in water treatment to oxidize many inorganic
compounds. Generally, the rate of oxidation is first-order with respect to
both reactants. For many compounds, the rate varies with pH, as shown in
figure 4.1 (on page 4.4).
Elevated levels of reduced iron and manganese are frequently found in
groundwaters. While not posing a health threat, such concentrations are not
desirable and interfere with other processes or uses of the groundwater. In a
pump-and-treat scenario, for example, high iron and manganese levels in
contaminated groundwater interfere with adsorption processes (e.g., acti-
vated carbon or ion exchange) and bioremediation techniques. Therefore,
removal is required to assure the effectiveness of these processes.
4.3
-------
Potential Applications
Figure 4.1
Influence of pH on Rate Constants for Ozone
and Various Inorganic Compounds
10'°-
106-
104-
102-
1 —
io-2 -J
OH
so2-
NO,
CIO
NH,C1
ci-
i i r
6
pH
\ \
10
Reprinted from Water Research Volume 19, Number 8, J Hoigne, H Bader, W R Haag, and J. Staehelm, Rate
Constants of Reactions with Ozone with Organic and Inorganic Compounds in Water, Part 3 Inorganic Compounds and
Radicals, Copyright 1985, with kind permission from Pergamon Press Ltd., Headington Hill Hall, Oxfoid, 0X3 OBW, UK.
4.4
-------
Chapter 4
Reduced iron or the ferrous ion (Fe+2) is easily oxidized by oxygen or
ozone to Fe+3 in a stoichiometric ratio of 0.43 mg O3/mg of Fe+2. The oxida-
tion of Mn+2 to Mn44 requires stronger oxidation conditions than does the
oxidation of iron, but ozone is sufficiently energetic. Actual removal of
both iron and manganese is accomplished by the formation of an insoluble
hydroxide precipitate. Therefore, in addition to ozonation, a solid-liquid
separation unit is needed. There are many techniques to remove solids and,
depending on flows and space availability, tray or tube settlers, a sedimen-
tation tank, or a porous media filter may be appropriate. The oxidation and
precipitation steps in this removal process will be influenced, or even se-
verely hampered, by the presence of significant amounts of natural organic
material. Higher ozone doses are required and, possibly, coagulant use
would be necessary to destabilize the hydroxide precipitates.
The oxidation of ammonia to nitrate is possible with ozone added in a
4:1 molar ratio with ammonia.
4O3 + M/3 -> NO~ + 4O2 + #30+ [4.1]
The rate of this reaction is slow, particularly at pH values less than nine.
Unless the system is adequately buffered, the pH decreases with reaction.
Oxidation occurs more rapidly in the presence of bromide, which has a
catalytic effect independent of pH. Nitrite, too, is quickly oxidized by
ozone to nitrate and each mg of NO2 consumes 1 .4 mg of O3. Sulfide will
be oxidized to sulfate at a rate of 6 mg O3 per mg of S 2. The reaction rate
increases with the degree of deprotonation, or negative charge, of the inor-
ganic species.
For the purposes of hazardous waste treatment, ozonation is probably
more applicable to the destruction of synthetic organic compounds. Atten-
tion must be paid to the inorganic matrix because ozone demand will be
exerted by the compounds described above. Carbonate species, the major
ion of most water systems, are potent scavengers of hydroxyl free radicals.
Both of these factors will diminish ozone's effectiveness and increase ozone
consumption.
In natural waters, organic compounds are present in either a dissolved or
particulate state. The concentration of dissolved organic carbon (DOC) in
most natural surface and groundwaters is in the range of 2 to 10 mg/L and
of this, 95% is derived from natural sources. Natural organic matter is com-
4.5
-------
Potential Applications
posed of various biopolymers, such as amino acids and proteins, fulvic
acids, carbohydrates, lipids, etc. Synthetic organic compounds are usually
present in comparatively small proportions, around 5% of the DOC, and
consequently are referred to as micropollutants. Micropollutants can be
present as untransformed aromatic or aliphatic hydrocarbons, chlorinated
solvents, phenols, substituted or nonsubstituted polyphenols, pesticides,
plasticizers, or surfactants. When released into the environment, these com-
pounds can be modified by hydrolysis, photolysis, or biological; transforma-
tions to by-products that may be environmentally harmful.
Most synthetic organic compounds are hydrophobic and have very low
solubilities in water. High concentrations of natural organic matter (NOM)
can increase these solubilities either through partitioning, complexation, or
by a cosolvent-like effect. Usually, synthetic organic compounds (SOCs)
are found in higher concentration in the particulate organic phase (biomass),
in sediments, and on soils. In complex media, meaning multicomponent
and multiphase systems, reactivity with ozone must be very high for degra-
dation to occur.
Direct reaction will occur at carbon multiple bonds (C=C, G=C-O-R,
-C=C-X), or at atoms carrying negative charge (N, P, O, S, and nucleo-
philic carbons). Ortho- and para-activated aromatic compounds substituted
with OH, CH3 or OCH3 are predicted to show strong initial reactivity in
contrast to lesser reactivity, in cases where NO2, COOH, or CHO are substi-
tuted. These chemical reactivity predictions would also hold for other elec-
trophilic oxidants, but among these, ozone is more reactive. If the mode of
reaction is due to radical species such as the hydroxyl radical, reactions are
nonselective.
Continued reaction beyond the initial reaction depends upon the structure
of the primary by-products, but, in most cases, additional reaction will oc-
cur, especially in the case of the radical pathway. The feasibility of using
ozonation for organic destruction can be evaluated by considering relatively
simple rules of organic chemistry. A very thorough review of ozone's be-
havior toward a wide range of organic compounds present in natural waters
can be found in Langlais, Reckhow, and Brink 1991, the salient points of
which are briefly summarized below.
Saturated aliphatic hydrocarbons and halogenated derivatives are largely
an unreactive group of compounds with respect to direct interactions with
ozone. Alkenes are more reactive, but this reactivity is depressed with sub-
4.6
-------
Chapter 4
stitution of electrophilic groups, such as halogens. Cleavage of carbon
double bonds produces aldehydes and acids. In the case of ethylene, rates
of reaction are much lower with hydrogen replacement by chlorine. In gen-
eral, alcohols, ethers, aldehydes, and carboxylic acids are also relatively
unreactive with ozone, and their degradation requires hydroxyl radicals.
Destruction of these unreactive compounds requires advanced oxidation
processes to stimulate radical reactions. Ozone, in combination with either
H2O2 or ultraviolet (UV) light, would enhance the rates of destruction 1 to
50 fold.
Ozone reactivity with an aromatic compound depends on the
compound's substituents. Interaction may occur with the ring, with side-
chains, or competitively at both sites. To reiterate, direct ozone attack is
most favorable as an electrophilic reaction at ortho or para positions relative
to electron donor substitutions (e.g., OH), or at the meta position for elec-
tron withdrawing substituents (e.g., Cl). Mononuclear and polynuclear
aromatic compounds are degradable with ozone. With naphthalenes, the
first step in degradation is 1-3 cyclo addition to break one of the aromatic
rings and subsequent reaction of the resulting side chains to produce a suite
of by-products (Legube 1985, 1986). In general, the reaction scheme be-
tween ozone and mono- or polynuclear aromatic hydrocarbons involves
oxidation of the aromatic ring to produce phenols, quinones, and/or aro-
matic acids. Further breakdown of the aromatic ring occurs, producing
short-chain aliphatic acids and aldehydes. Less reactive aromatic com-
pounds (chlorobenzenes, nitrobenzenes, chlorinated furans, and dioxins)
require the use of advanced oxidative processes (AOPs) to direct the reac-
tion efficiently along the free radical pathway.
Phenolic compounds are a common class of aromatic pollutants found in
water. In general, phenolic compounds are susceptible to interactions with
ozone due to the presence of the OH substitution, which is both electron-
donating and ionizing. Therefore, reaction between ozone and phenolic
compounds is favored by increasing pH; overall reaction rates have been
seen to increase by an order of magnitude for each unit increase in pH. At
higher pH, it is expected that the mechanism of O3 interaction is a combina-
tion of direct and indirect reaction. Approximately 4 to 6 moles of ozone
are required per mole of phenol for ring cleavage. While phenols are rap-
idly and easily oxidized by ozone, the suite of by-products can bear greater
toxicity than the parent compounds. At sufficient ozone dose and contact
times, these by-products are usually destroyed, yielding a final set of oxida-
4.7
-------
Potential Applications
tion products including glyoxylic, oxalic and formic acids, and glyoxal.
The extent and rate of reaction can be improved with AOPs.
Amines are another family of compounds that reacts with ozone. Elec-
trophilic interactions are promoted by the electron-donating influence of
nitrogen. This can be offset, though, by the presence of electron withdraw-
ing groups such as nitro groups or nitrosamines. Analysis of by-products
suggests that there are four types of interactions between amines and ozone:
• direct oxidation of the nitrogen group;
• oxidation of the a-carbon;
• deamination or splitting of the C-N bond; and
• secondary condensation or polymerization reactions among
parent compounds and reaction by-products.
Rates of reaction with compounds such as urea and dimethyl nitrosamine
are very slow and can be enhanced with advanced oxidation processes (see
also Subsection 3.3.1, Photolysis Systems).
Ozonation of pesticides has been reasonably well studied, and a good
review of the literature has been written by Reynolds (1989). The term
pesticide encompasses a broad range of agents and chemistries. General
predictions of the destructive capacity of ozone can be made by considering
the organic structure of the pesticide. Organochlorine pesticides are not
very reactive with ozone, and AOPs are usually applied to improve rates of
destruction. Organophosphates, on the other hand, are much more reactive.
The P=S bonds are oxidized to form P=O, and continued reaction yields
phosphoric acid. Phenoxyacetic herbicides interact with ozone along lines
similar to that of phenolic compounds (Benitez, Beltran-Heredia, and
Gonzalez 1991). Heterocyclic nitrogenous herbicides, such as atrazine, are
not very reactive. Direct interaction with pyridine is slow, but higher rates
of reaction have been observed via the free radical mechanism which pro-
duces by-products that are very easily degraded (Andresozzi et al. 1991). A
study, evaluating ozonation of a pesticide waste and rinsate (containing
atrazine, cyanazine, metoalchlor, and paraquat) prior to circulation through
a biologically active soil column, demonstrated that herbicidal activity was
eliminated, and no mutagenic activity was found (Somich, Muldoon, and
Dearney 1990).
Surfactants, as a group, are not particularly reactive with ozone. Their
presence in water, even at relatively low levels (1 to 3 mg/L), interferes
4.8
-------
Chapter 4
with gas transfer. There are four general classes of surfactants: nonionic,
anionic, cationic, and ampholytic. A frequently used anionic surfactant that
is fairly reactive with ozone is alkylbenzene sulfonate. In this case, ozone
enhances the biodegradability of the compound. Reaction with anionic
forms is favored over neutral and cationic surfactants. Increasing pH in-
creases rates of reaction. In a study of the ozonation of polyethoxylated
nonyl phenol, modification of the polyethoxylated side chain indicated that
the reaction was essentially hydrogen abstraction at one of the ethoxylated
units followed by depolymerization (Calvosa et al. 1991). Nonionic surfac-
tants yield polyethylene glycols and polyethers as products of ozonation.
These products, in turn, show very low reactivities with ozone. Overall,
reactions between ozone and surfactants are slow, and in mixtures, other
compounds of higher reactivity will consume ozone first.
Colored compounds such as dyes or NOMs typically display chemical
attributes (anionic with conjugated aromatic structures), making them rela-
tively reactive with ozone. Ozonation can result in some color loss, but can
also yield a broad suite of by-products. The complexity of the molecules
dictates dose and contact time requirements.
In summary, there are a number of trends that should be considered when
assessing the usefulness of ozone in destroying SOCs:
• In engineering applications, significant degradation occurs only
with compounds having ozonation rate constants, KQ, greater
than 103 M^S'1;
• Ozone reacts preferentially with nucleophilic sites (O, N, P, S
substitutions, C=C);
• Destruction of parent compounds by ozone typically yields com-
pounds more oxidized, polar, and biodegradable; the total or-
ganic carbon (TOC) of water, however, may not change.
Therefore, monitoring TOC is not an adequate method of evalu-
ating process efficiency;
• In some cases, ozonation by-products can have higher toxicities
than the parent compounds. In addition, ozone can modify com-
plexation behavior of trace materials (e.g. metals) causing their
release into solution. Efforts should be made to evaluate by-
product identity and toxicity; and
4.9
-------
Potential Applications
• Slow or poor reactivity with ozone can be enhanced! by AOPs
that involve combined use of Qjl\LŁ>2, or O3/UV, or O^/Hflj/
UV.
Ozone is a potent biocide and is often used as a primary disinfectant in
treatment schemes. It is not considered an adequate final disinfectant and,
because it is short-lived, it does not impart any residual disinfectant to wa-
ter. Furthermore, ozone usually renders the natural organic matrix more
biodegradable, which leads to biological regrowth in distribution systems.
For this reason, biostabilization is often required after ozonation. While it
is not certain how ozone inactivates microorganisms, it seems likely that the
site of inactivation is the cytoplasmic membrane, and if residual ozone is
able to cross this membrane, ozone would be highly reactive with the cyto-
plasm and nucleic acids.
Precipitation processes are applicable whenever the concentration of a
target metal in an aqueous stream is greater than the solubility of its least
soluble compound. Solubility products need to be considered when the
stream contains more than one metal. See table 4.2 for a listing of sources
reporting the successful removal of a variety of metals from aqueous
streams by precipitation.
Table 4.2
Summary of Heavy Metal Removals Achieved Using
Various Chemical Precipitation Techniques.
Metal
pH
Hydroxide Precipitation
Ba 10-11
9.2
10.5
11.6
10.5
10.3
Cd 8.5-11.3
11.2-11.3
Cd
6.0-10.0
10.0
Metal Concentration
(mg/L)
Initial Residual
7.0-8.5 —
10.0-12.0 —
10.0-12.0 —
10.0-12.0 —
7.5 —
17.4 —
0.3 —
10 —
100 <0.3
100 <0.3
100 2.0
100 5.0
Removal
Efficiency
(%)
>90
84
93
82
88
95
>98
>98
>99.7
>99.7
98.0
95.0
Comments Reference
Klot plant tests EPA 1978
Full-scale tests EPA 1978
Synthetic plating Peters and Ku 1984
wastewater
4.10
-------
Chapter 4
Table 4.2 cont.
Summary of Heavy Metal Removals Achieved Using
Various Chemical Precipitation Techniques.
Metal
Cd
Cr
Cr+3
Cr*
Cu
Pb
Hg
Ag
Zn
Zn
pH
8.0
8.6
9.4
10.4
11.9
6.6
9.5-10.0
9.5-10.5
10.6-11.3
9.5-10.5
9.5-11.6
10.5
9.5-10.5
8.5-11.3
6.0
7.4
8.8
10.5
11.9
12.3
10.7-11.4
9.4
9.3-11.3
9.0
11.5
10.0
6.2
7.5
8.3
9.5
11.0
11.8
10.0
10.0
Metal Concentration Removal
(mg/L) Efficiency
Initial Residual (%) Comments
—
2350
126
5
0.2
0.3
—
Cr*3:5125 Cr*3:26.0 >98.0
Cr*3:1.40 Cr*3:0.3 78.6
Cr*:2.23 Cr^:<0.01 >99.5
Cr*3:4.0 Cr+3:0.03 99.3
Cr**:4.5 Cr**:<0.01 >99.7
0.15
0.15
0.15
0.45
5.7
0.15
9.3ug/L
9.3 Mg/L
0.15
0.15
100
100
106
106
106
106
106
106
106
106
—
0.08
0.89
1700
25.6
6.0
0.6
280
1050
—
0.3
32.0
1900
27.5
0.55
0.25
0.68
0.95
0.25
0.34
0.76
46.0
0.38
0.40
0.65
41.0
>98.0
>70.0
<10.0
82.2
84.4
>98.0
60-80
30
<5
70
90
99.7
68.0
99.76
99.68
99.28
56.60
99.64
99.62
99.39
61.32
10mg/LCO32
10 mg/L CO, 2
10mg/LCO32
55 mg/L CO3 2
100 mg/L CO3 2
Nickel/Chrome rinse
Full scale plant
—
Copper rinse
Full scale plant
15 mg/L CO3 2
15 mg/L CO3 2
15 mg/L CO3 2
40 mg/L CO,-2
123 mg/L CO,2
275 mg/L CO,'2
—
—
No chelants present:
300 mg/L EDTA
12 mg/L CO,'2
12 mg/L CO, 2
30 mg/L CO,'2
35 mg/L CO,2
65 mg/L CO,-2
25 mg/L CO,'2
Reference
Patterson et al.
1977
Arumugam 1976
EPA 1978
Rabosky and
Altares 1983
EPA 1978
Patterson et al.
1977
EPA 1978
EPA 1978
Peters & Ku 1985
Patterson et al.
1977
No chelants present:
0.025-um filter Ku & Peters 1986
0.45-um filter
2.5-Mm filter
11.0-Mm filter
100 rpg/L Arprppnia present:
0.025-Mm filter
0.45-Mm filter
2.5-Mm filter
11.0-Mm filter
4.11
-------
Potential Applications
Table 4.2 cont.
Summary of Heavy Metal Removals Achieved Using
Various Chemical Precipitation Techniques.
Metal
Zn
Ni
Mixed Metals:
Cu
Ni
Pb
Mixed Metals:
Fe
Pb
Sn
Mixed Metals:
Cu
Pb
Sn
pH
10.0
10.0
10.0
10.0
10.0
10.0
6.8
7.4
8.3
9.4
11.0
12.3
>8.5
8.5-91
8-10
Metal Concentration
(mg/L)
Initial Residual
106
106
106
106
106
106
106
106
106
106
106
106
106
106
106
106
106
106
106
106
—
—
—
—
—
—
60.0
1.9
1.2
20-60
0.1
1.0
20-150
0.5-1.0
0.1-0.5
0.48
0.88
37.0
>100
0.45
1.04
25.0
>100
>100
5.8
4.5
>100
7.0
6.2
>100
>100
>100
>100
>100
>100
1450
930
15
0.5
0.3
0.5
0.9
0.3
0.4
0.3-2 4
0.5
0.5
0.5-2.0
<0.05
0.1
Removal
Efficiency
(%) Comments Reference
99.55
99.17
65.09
<5.66
99.58
99.02
76.41
<5.66
<5.66
94.53
95.75
<5.66
93.40
94.15
<5.66
<5.66
<5.66
<5.66
<5.66
<5.66
—
—
—
—
—
—
98.5
84.2
667
>96
—
>50
>97.5
90-95
<80
100 mg/L Citrate present:
0.025-um filter ICu & Peters 1986
0.45-nm filter
2.5-um filter
11.0-ujn filter
100 mg/L Tartrate present:
0.025-pm filter
0.45-(im filter
2.5-um filter
11.0-um filter
No cheiants present:
5-min settling
15-min settling
30-min settling
100 mg/L Ammonia present:
5-min settling
15-min settling
30-min settling
100 mg/L Citrate present
5-min settling
15-min settling
30-min settling
100 mg/L Tartrate present:
5-min settling
15-min settling
30-min settling
19 mg/L CO3-2 Patterson et al. 1977
30 mg/L CO3 2
38 mg/L CO3-2
38 mg/L CO3'2
90 mg/L CO3'2
225 mg/L CO3-2
Electroplating Sheffield 1981
plant data
Electroplating
plant data
Printed circuit
board manufacturer
4.12
-------
Chapter 4
Table 4.2 cont.
Summary of Heavy Metal Removals Achieved Using
Various Chemical Precipitation Techniques.
Metal
Mixed Metals:
Cd
Cr
Cu
Pb
Zn
pH
9.7-10.2
Metal Concentration
(mg/L)
Initial Residual
1.66 0.04
1.11 0.97
0.29 0.03
1.7 0.2
31.0 0.28
Removal
Efficiency
(*)
97.6
12.6
89.7
88.2
99.1
Comments Reference
Brantner and
— Cichon 1981
Carbonate Precipitation
Cd
Cd
Ni
Pb
Pb
Zn
7.2
8.4
9.5
10.7
11.9
8.1
8.4
8.7
10.0
10.8
11.7
7.2
8.2
9.0
10.5
11.5
12.5
5.6
6.1
6.8
10.1
11.6
12.3
7.5
8.4
9.2
10.5
11.4
12 .4
6.6
8.3
9.1
10.0
10.8
11.9
12.5
— 440
— 7.5
— 0.6
— 0.35
— 0.5
— 5.0
— 1.2
— 1.7
— 0.25
— 0.25
— 0.35
— 800
— 60.0
— 3.8
— 27
— 1.4
— 1.4
— 4.6
— 43.6
— 17.4
— 0.6
— 10.0
— 1260
— 1.0
— 2.0
— 3.6
— 8.0
— 6.0
— 150
— 260
— 0.95
— 0.75
— 0.60
— 0.85
— 1.60
— 49.6
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
5 mg/L C03'2 Patterson et al. 1977
5 mg/L CO3 2
10mg/LCO32
50 mg/L CO3'2
225 mg/L CO3'2
1200 mg/L CO3 2
2800 mg/L CO3 2
3350 mg/L CO3'2
4200 mg/L CO3'2
4400 mg/L CO3'2
4300 mg/L CO3-2
1500 mg/L CO3-2
3000 mg/L C03-2
3500 mg/L CO3-2
5500 mg/L CO3-2
5500 mg/L CO3'2
5500 mg/L CO3-2
10 mg/L CO3-2
15 mg/L C03'2
20 mg/L CO3'2
55 mg/L CO3'2
55 mg/L CO3'2
55 mg/L CO3 2
1200 mg/L CO3 2
4000 mg/L CO3'2
4650 mg/L CO3-2
5500 mg/L C03-2
5500 mg/L C03-2
5500 mg/L C03'2
Sample not analyzed for CO3"2
Sample not analyzed for CO3"2
Sample not analyzed for CO3"2
5500 mg/L CO,'2
6500 mg/L CO3 2
5500 mg/L COj'2
3500 mg/L CO,'2
4.13
-------
Potential Applications
Table 4.2 cont.
Summary of Heavy Metal Removals Achieved Using
Various Chemical Precipitation Techniques.
Metal pB Metal Concentration Removal
(mg/L) Efficiency
Initial Residual (*) Comments
Reference
Mixed Metals: 7.8-8.S
Cd
Cr
Cu
Pb
Zn
1.37
0.67
0.18
1.4
26
0.04
0.60
<0.03
<0.1
1.18
97.1
10.4
>83.3
>92.9
95.4
Brantner &
Cichon 1981
Sulfide Precipitation
Cu
Cu
Cu
Cu
Cu
Cu
4.0
6.0
8.0
10.0
4.0
4.0
4.0
4.0
3.0
4.0
6.0
8.0
10.0
4.0
8.0
8.0
4.0
10.0
4.0
6.0
8.0
10.0
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
0.08
0.08
0.05
0.05
1.3
0.6
0.3
0.2
0.9
0.8
0.6
0.6
1.0
0.08
0.85
0.65
0.25
0.15
0.05
0.7
0.4
0.1
0.5-1 0
0.08
<0.05
0.65
0.45
0.40
0.50
99.92
99.92
99.95
99.95
98.7
99.4
99.7
99.8
99.1
99.2
99.4
99.4
99.0
99.92
99.15
99.35
99.75
99.85
99.95
99.3
99.6
99.9
>99.0
99.92
>99.95
99.35
99.55
99.60
99.50
No chelants.S'2 =1.05x Peters et al. 1984a
No chelants,S-2 =1.05i.
No chelants,S2 =1.05i.
No chelants,S-2 =1.05i.
100 mg/L EDTA, Bhattacharyya et al.
S-2=1.0x 1981D
100 mg/L Gluconic Add,
S-2=1.0x
100 mg/L Citrate, S'^l.Ox
100 mg/L Tartrate,S '^=1 .Ox
100 mg/L EDTA, Peters et al. 1984a
S2=1.05x
100 mg/L EDTA.S 2 =1.05x
100 mg/L EDTA.S-2 =1.05x
100 mg/L EDTA.S 2 =1.05x
100 mg/L EDTA.S 2 =1.05x
Nochelants, Ku 1982
S'2=1.05x
100 mg/L EDTA, S'2 =1.05x
100 mg/L Citrate, S'2 =1.05x
100 mg/L Gluconic Arid, S'2 =1.05x
100 mg/L Tartrate, S'2 =1.05x
No chelants,S 2 = 1.05*
100 mg/L EDTA,S2=1.05x
100 mg/L Citrate, S'2=1.05x
100 mg/L Tartrate, S'2 =1.05*
100 mg/L EDTA, Peters et al. 1984
S-2=1.05x
No Chelants present Peters & Ku 1987
S2= l.OSx
No Chelants present S'2 = l.OSx
100 mg/L Citrate S 2 = l.OSx
100 mg/L Citrate S'2 = l.OSx
100 mg/L Citrate S 2 = l.OSx
100 mg/L Citrate S'2 = l.OSx
4.14
-------
Chapter 4
Table 4.2 cont.
Summary of Heavy Metal Removals Achieved Using
Various Chemical Precipitation Techniques.
Metal
pH
Metal Concentration
(mg/L)
Removal
Efficiency
Initial Residual (%)
Cd
Cd
Zn
Zn
Zn
4.0-10.0
4.0
9.0
4.0
8.0
3.0
4.0
8.0
10.0
4.0
6.0
8.0
10.0
4.0
8.0
10.0
10.0
10.0
10.0
10.0
500
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
106
106
106
106
106
106
106
106
106
106
106
106
106
106
106
106
106
106
106
0.01
1.2
0.16
0.1
0.5
0.3
0.9
12.0
0.3
0.2
0.15
16.5
15.0
12.8
12.0
8.0
12.0
0.10
0.10
0.36
26.0
0.22
0.24
0.84
25.0
0.35
0.80
33.0
>100
0.16
0.20
16.5
>100
>100
4.2
3.6
>99.99
98.8
99.84
99.9
99.5
99.7
99.1
88.0
99.7
99.8
99.85
83.5
85.0
87.2
88.0
92.0
88.0
99.91
99.91
99.66
75.47
99.79
99.77
99.21
76.42
99.67
99.24
68.87
<5.66
99.85
99.81
84.43
<5.66
<5.66
96.04
96.60
Comments Reference
S 2 = 1 .05x Peters et al. 1984a
100 mg/L EDTA, Bhattacharyya et al.
S 2 = l.Ox 1981b
No chelants, CaS Kim 198 1
precipitation
No chelants, S'2 = l.OSx Peters and Ku 1987
100 mg/L Citrate S 2 = l.OSx
No chelants S-2= l.OSx
100 mg/L Citrate S'2 = l.OSx
No chelants, S 2 = l.OSx Peters et al. 1984a
No chelants, S'2= l.OSx
No chelants, S'2 = l.OSx
No chelants, S2 = l.OSx
100 mg/L EDTA, S'2 = l.OSx
100 mg/L EDTA, S'2 = l.OSx
100 mg/L EDTA, S2 = l.OSx
100 mg/L EDTA, S 2 = 1 .OSx
100 mg/L EDTA, Bhattacharyya et al..
S'2=1.0x 198 Ib
100 mg/L EDTA, Peters et al. 1984b
S2 = l.OSx 120
No Chelants present:
0.025-um filter Ku & Peters 1986
0.45-um filter
2.5-um filter
11.0-um filter
100 mg/L Ammonia present:
0.025-um filter
0.45-um filter
2.5-um filter
11.0-um filter
100 mg/L Citrate present:
0.025-um filter
0.45-um filter
2.5-um filter
11.0-um filter
100 mg/L Tartrate present:
0.025-um filter
0.45-um filter
2.5-um filter
11.0-um filter
No Chelants present:
5-min settling
IS-min settling
30-min settling
4.15
-------
Potential Applications
Table 4.2 cont.
Summary of Heavy Metal Removals Achieved Using
Various Chemical Precipitation Techniques.
Metal pH
Zn 10.0
10.0
10.0
Zn 8.0
Mixed Metals: 8.0
Cd
Cr
Cu
Ni
Zn
Mixed Metals:
Zn 10.8
Fe
Pb
Zn 11.1
Fe
Pb
Zn 10.6
Fe
Pb
Zn 10.4
Fe
Pb
Zn 10.85
Fe
Pb
Zn 10.7
Fe
Pb
Metal Concentration Removal
(mg/L) Efficiency
Initial Residual (%) Comments Reference
106
106
106
106
106
106
106
106
106
100
100
100
100
100
100
2.06
2.61
1.82
3.50
5.8
813
<0.1
23.5
813
<0.1
23.5
813
<0.1
23.5
813
<0.1
23.5
813
<0.1
23.5
813
<0.1
23.5
>100
5.6
4.4
>100
>100
>100
>100
>100
>100
0.35
0.60
0.70
0.85
0.75
0.80
0.10
0.32
004
0.07
0.41
6.66
<0.1
0.09
6.74
<0.1
<0.03
3.90
<0.1
0.03
4.59
<0.1
0.10
4.40
<0.1
0.03
4.64
<0.1
004
<5.66
94.72
95.85
<5.66
<5.66
<5.66
<5.66
<5.66
<5.66
99.65
99.40
9930
99.15
99.25
99.20
95.1
87.7
97.8
98.0
92.9
99.2
—
99.6
99.2
—
>99.8
99.5
—
99.8
99.4
—
99.6
99.45
—
99.8
99.4
—
99.8
100 mg/L Ammonia present:
5-min settling Ku & Peters
15-min settling
30-mm settling
100 mg/L Citrate present:
5-min settling
15-min settling
30-mm settling
100 mg/L Tartrate presem :
5-min settling
15-min settling
30-min settling
1986
No chelants S 2 = l.OSx Peters and Ku 1987
23 mg/L Citrate S'2 = l.OSx
92 mg/L Citrate S'2 = 1 05x
225 mg/L Citrate S'2 = l.OSx
450 mg/L Citrate S'2 = l.OSx
900 mg/L Citrate S'2 = l.OSx
Wastewater from Kesta et al.
electroplating and melal
finishing operation at
Ft. Belvoir, VA
Fender et al
Pure hydroxide
treatment
50 mg/L FeS
100 mg/L FeS
500 mg/L FeS
1000 mg/L FeS
2000 mg/L FeS
1978
. 1982
4.16
-------
Chapter 4
Table 4.2 cont.
Summary of Heavy Metal Removals Achieved Using
Various Chemical Precipitation Techniques.
Metal pH
Mixed Metals: 8.0
Zn
Pb
Cd
Cu
Hg
Fe
Mixed Metals: 8.S
Cd
Cu
Zn
Pb
Fe
Se
As
Cd 8.0.-8.5
Cu
Zn
Pb
Fe
Se
As
Cd 8.0-8.5
Cu
Zn
Pb
Fe
Se
As
Mixed Metals:
Cd 8.0-8.5
Cu
Zn
Pb
Fe
Se
As
Mixed Metals:
Cu 8.0
Zn
Cu 8.0
Zn
Cu 8.0
Zn
Cu 8.0
Zn
Metal Concentration Removal
(mg/L) Efficiency
Initial Residual (%) Comments
30-60
20-40
3-16
3-5
2-4
5-20
10.5
297
85.5
39.0
149
3.0
100
10.5
297
85.5
39.0
149
3.0
100
10.5
297
85.5
39.0
149
3.0
100
10.5
297
85.5
39.0
149
3.0
100
100
100
100
100
100
100
100
100
—
—
—
—
—
—
0.6
0.5
3.1
0.7
<0.5
<1.0
6.8
<0.05
0.2
0.9
0.4
<0.5
<1.0
2.0
<0.05
0.1
0.05
0.4
<0.5
1.2
11.0
<0.05
<0.05
<0.05
0.3
<0.5
1.0
21.0
0.4
0.3
0.3
15.0
0.4
27.0
0.5
74.0
51-75
97-99
99
90
99
2-26
99.4
99.8
96.4
98.2
>99.7
>66.7
93.2
>99.5
99.9
98.9
99.0
>99.7
>66.7
98.0
>99.5
>99.9
99.4
99.0
>99.7
60.0
89.0
>99.5
>99.9
>99.5
99.2
>99.7
66.7
79.0
99.6
99.7
99.7
85.0
99.6
73.0
99.5
26.0
S'2 = 0.6x, full scale
plant
Copper smelting plant
scrubber wastewater;
Reference
Bhattacharyya et
al. 1981a
Bhattacharyya et
al. 1979
hydroxide treatment only
S-2 = 5 mM
S-2 = 8 mM
S'2 = 12 mM
No EDTA, S'2= l.OSx
100 mg/L EDTA,
S-2 = l.OSx
200 mg/L EDTA,
S-2= l.OSx
200 mg/L EDTA,
S'2 = 0.8x
Bhattacharyya et
al. 198 Ib
Peters et al. 1984b
4.17
-------
Potential Applications
Table 4.2 cont.
Summary of Heavy Metal Removals Achieved Using
Various Chemical Precipitation Techniques.
Metal pH Metal Concentration Removal
(mg/L) Efficiency
Initial Residual (%) Comments
Inference
Mixed Metals: 9.0
CM
Cu
Cr
Pb
Zn
Mixed Metals:
Zn 8.0
Cu
Cr
Ni
Zn 8.0
Cu
Cr
Ni
Zn 8.0
Cu
Cr
Ni
Zn 8.0
Cu
Cr
Ni
Zn 10.0
Cu
Cr
Ni
Zn 10.0
Cu
Cr
Ni
Zn 10.0
Cu
Cr
Ni
Zn 10.0
Cu
Cr
Ni
Mixed Metals: 8.0-8.4
Cd
Cr
Cu
Pb
Zn
7.95
18.6
1.34
3.5
47.0
24.5
62.4
28.0
1.04
24.5
62.4
28.0
1.04
24.5
62.4
28.0
1.04
24.5
62.4
28.0
1.04
24.5
62.4
28.0
1.04
24.5
62.4
28.0
1.04
24.5
62.4
28.0
1.04
24.5
62.4
28.0
1.04
3.3
0.52
0.35
4.5
93.0
<0.05
<0.05
<0.05
<0.5
<0.05
2.4
1.45
13.6
0.36
1.70
1.325
8.8
0.30
0.40
1.40
9.6
0.30
0.39
1.475
8.0
0.20
0.5
14.4
8.0
0.15
0.53
12.2
2.05
0.175
0.605
12.4
1.75
0.175
1.2
10.8
1.50
0.20
0.06
<0.05
<0.03
<0.1
0.68
>99.4
>99.7
>96.2
>85.7
>98.9
90.2
97.7
51.4
65.4
93.0
97.9
68.6
71.1
98.4
97.75
65.7
71.1
98.4
97.6
71.4
80.8
97.9
76.9
91.6
85.5
97.8
80.4
92.7
83.1
97.5
80.1
93.8
83.1
95.1
82.7
94.6
80.8
98.2
>98.2
>91.4
>97.7
99.3
CaS precipitation IKirn 1981
Industrial plating Peters and Ku 1 984
waslewaler; hydroxide
treatment only
S 2 = 0.83x
S-2=1.0x
S2=l.lx
Hydroxide
treatment only
S-2 = 0.83x
S-1 = 1.0x
S-2=l.lx
FeS Dose = 1.5x Urantner &
Cichon 1981
4.18
-------
Chapter 4
Table 4.2 cont.
Summary of Heavy Metal Removals Achieved Using
Various Chemical Precipitation Techniques.
Metal pH
Metal Concentration Removal
(mg/L) Efficiency
Initial Residual (%) Comments Reference
Combined Precipitation Treatment
Ni 6 10 8.2
7 10 9.5
8 10 6.8
9
10
11
6
7
8
9
10
11
6
7
8
9
10
11
6
7
8
9
10
11
6
7
8
9
10
11
6
7
8
9
10
11
6
7
8
9
10
11
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
4.0
0.2
0.1
7.3
7.8
8.3
1.6
0.05
0.1
9.8
8.8
8.9
2.3
0.12
0.05
9.7
9.6
8.7
6.4
0.1
0.05
7.0
9.4
7.8
1.5
0.1
0.05
8.7
8.4
8.8
3.2
0.3
0.05
10.0
9.5
9.2
4.8
0.1
0.05
18
5
32
60
98
99
27
22
17
84
99.5
99
2
12
11
77
98.8
99.5
3
4
13
36
99
99.5
30
6
22
85
99
99.5
13
16
12
68
97
99.5
0
5
g
52
99
99.5
Hydroxide treatment McAnally et al.
only 1984
OH treatment, C,. = 50 mg/L
OH treatment, C, = 100 mg/L
OH treatment, C,. = 200 mg/L
SfS mg/L, CV=0
S^Smg/L, C^SOmg/L
Sf=5 mg/L, C^lOOmg/L
4.19
-------
Potential Applications
Table 4.2 cont.
Summary of Heavy Metal Removals Achieved Using
Various Chemical Precipitation Techniques.
Metal pH
Ni 6
7
8
9
10
11
6
7
8
9
10
11
6
7
8
9
10
11
6
7
8
9
10
11
6
7
8
9
10
11
6
7
8
9
10
11
6
7
8
9
10
11
6
7
8
9
10
11
Metal Concentration Removal
(mg/L) Efficiency
Initial Residual (%) Comments
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
9.2
9.4
9.1
4.8
0.15
0.05
9.1
7.6
7.7
4.6
0.1
0.05
8.9
7.8
8.1
4.5
0.1
0.05
9.1
9.2
8.6
6.8
0.9
0.05
9.2
8.8
8.5
6.6
0.1
0.05
9.7
8.2
1.0
3.1
0.1
0.05
9.3
6.1
5.2
2.8
0.15
0.1
9.5
9.2
9.1
3.4
0.15
0.05
8
6
9
52
98.5
99.5
9
24
23
52
99
99.5
11
22
19
55
99
99.5
9
8
14
32
91
99.5
8
12
15
34
99
99.5
3
18
90
69
99
99.5
7
39
48
72
98.5
99
5
8
9
66
98.5
99.5
SjsS mg/L,
Cr=200mg/L
8^10 mg/L, 0^=0
Reference
VlcAnally et al.
1984
S^IO mg/L, Cj=5Q mg/L
87=10 mg/L, C.,^100 rngO,
87=10 mg/L, 0^200 mgtL
87=20 mg/L, CT=0
87=20 mg/L, CT=SO mg/L
87=20 mg/L, CT=IOO mg/L
4.20
-------
Chapter 4
Table 4.2 cont.
Summary of Heavy Metal Removals Achieved Using
Various Chemical Precipitation Techniques.
Metal pH
Ni 6
7
8
9
10
11
Ni 6
6
6
6
9
9
9
9
10
Metal Concentration Removal
(mg/L)
Initial
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
Residual
8.5
9.0
8.8
5.4
0.3
0.05
8.2
8.2
4.9
6.7
7.6
9.2
9.5
8.8
9.9
9.6
9.3
8.9
9.5
9.0
8.8
8.8
7.7
0.5
0.35
0.35
2.0
1.7
0.2
0.3
2.8
1.9
0.3
0.22
6.8
2.0
0.12
0.20
0.20
0.10
<0.10
<0.10
Efficiency
(%)
15
10
12
46
97
99.5
18
18
51
33
24
8
5
12
1
4
7
11
5
10
12
12
23
95
96.5
96.5
80
83
98
97
72
81
97
97.8
32
80
98.8
98
98
99
>99
>99
Comments Reference
5^20 mg/L, McAnally et al.
CjrfOO mg/L 1984
CT = 0, Fe/Ni = 0 McFadden et al.,
CT = 0,Fe/Ni=0.5 1985
CT = 0,Fe/Ni=1.0
CT = 0, Fe/Ni=2.0
CT=50 mg/L, Fe/NM)
Cf=50 mg/L, Fe/Ni=0.5
CT=50 mg/L, Fe/Ni= 1.0
CT=50 mg/L, Fe/Ni=2.0
CT=100 mg/L, Fe/Ni=0
CT=100mg/L,Fe/Ni=0.5
C^lOOmg/L, Fe/Ni=1.0
CT=100 mg/L, Fe/Ni=2.0
0^200 mg/L, Fe/Ni=0
CT=200 mg/L, Fe/Ni=0.5
0^200 mg/L, Fe/Ni=1.0
CT=200 mg/L, Fe/Ni=2.0
Cj = 0, Fe/Ni = 0
CT = 0, Fe/Ni=0.5
CT = 0, Fe/Ni=1.0
C,. = 0, Fe/Ni=2.0
Cj=50 mg/L, Fe/Ni=0
C^SO mg/L, Fe/Ni=0.5
CT=50 mg/L, Fe/Ni=1.0
C^SO mg/L, Fe/Ni=2.0
CT=100 mg/L, Fe/Ni=0
CT=100mg/L,Fe/Ni=0.5
Cr=100ing/L, Fe/Ni=1.0
CT=100mg/L,Fe/Ni=2.0
Cf=200 mg/L, Fe/Ni=0
CT=200 mg/L, Fe/Ni=0.5
CT=200 mg/L, Fe/Ni=1.0
CT=200 mg/L, Fe/Ni=2.0
CT = 0, Fe/Ni = 0
CT = 0, Fe.Ni=0.5
Cr = 0,Fe/Ni=1.0
CT = 0, Fe/Ni=2.0
4.21
-------
Potential Applications
Table 4.2 cont.
Summary of Heavy Metal Removals Achieved Using
Various Chemical Precipitation Techniques.
Metal pH
Ni 10
10
10
Ni 10.0
Cd 6.90
7.32
7.60
7.76
8.04
9.44
10.38
10.84
7.42
7.45
7.66
7.%
8.66
9.74
10.62
11.01
Metal Concentration
(mg/L)
Initial Residual
10
10
10
10
10
10
10
10
10
10
10
10
5.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
<0.10
<0.10
<0.10
<0.10
0.14
0.10
<0.10
<0.10
<0.10
<0.10
<0.10
<0.10
0.35
0.08
Ca=147.5
<0.01
Ca=129.5
<0.01
Ca=] 19.4
99
>99
>99
>99
98.6
99
>99
>99
>99
>99
>99
>99
93
92
>99
>99
>99
>99
>99
>99
>99
>99
>99
>99
>99
>99
>99
>99
>99
CT= 50 mg/L, Fe/Ni=0 McFadden et al.
Cj= 50mg/L,Fe/Ni=0.5 1985
C,= 50mg/L,Fe/Ni=ljB
C,= 50mg/L,Fe/Ni=2j»
C,=100 mg/L, Fe/Ni=0
Cr=100 mg/L, Fe/Ni=0. 5
Cr=100 mg/L, Fe/Ni= 1.0
Cj=100 mg/L, Fe/Ni=2.0
CT=200mg/L,Fe/Ni=0
Cj=200 mg/L, Fe/Ni=0. 5
CJ=200 mg/L, Fe/Ni= 1.0
Cj=200 mg/L, Fe/Ni=2.0
FeSO4 = 20 mg/L Maruyama et al.,
1975
Ca,=150 mg/L Chang & Peters,
as CaCO3 1985
Ca;=250 mg/L
asCaCO3
4.22
-------
Chapter 4
Table 4.2 cont.
Summary of Heavy Metal Remoyals Achieved Using
Various Chemical Precipitation Techniques.
Metal pH
Cd 7.36
7.41
7.57
7.62
7.64
8.03
9.58
10.81
7.79
8.05
9.42
10.%
11.30
7.82
8.21
8.82
10.47
11.07
11.39
Metal (
(
Initia
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
5.0
5.0
5.0
5.0
5.0
5.0
5.0
5.0
5.0
5.0
5.0
Concentration
mg/L)
1 Residual
<0.01;
Ca=191.6
ND
Ca=156.7
ND
Ca=117.0
ND
Ca=92.1
ND
Ca=106.5
ND
Ca=37.1
ND
Ca= 10.3
ND
Ca = 2.7
0.02
Ca=148.9
0.01
Ca=110.0
<0.01
Ca= 38.7
ND
Ca = 52.2
<0.01
Ca= 32.2
0.02
Ca=115.8
0.02
Ca= 75.0
<0.01
Ca=40.5
ND
Ca=11.2
ND
Ca = 14.4
0.02
Ca=10.6
Removal
Efficiency
(%) Comments Reference
>99 Caj=350 mg/L Chang & Peters
as CaCO3 1985
>99
>99
>99
>99
>99
>99
>99
98 Ca,=150 mg/L
as CaCO3
99
>99
>99
>99
98 Ca,=250 mg/L
asCaCO,
98
>99
>99
>99
98
4.23
-------
Potential Applications
Table 4.2 cont.
Summary of Heavy Metal Removals Achieved Using
Various Chemical Precipitation Techniques.
Metal pH
Cd 7.67
7.97
8.38
10.09
10.66
10.95
11.30
Mixed Metals:
Zn 8.0
Ni
Pb
Cd
Cu
Hg
Zn
Ni
Pb
Cd
Cu
Hg
Metal Concentration
(mg/L)
Initial Residual
5.0
5.0
5.0
5.0
5.0
5.0
5.0
50
15
15
15
15
2.9
50
15
15
15
15
2.9
0.03
Ca=208.1
<0.01
Ca=119.4
ND
Ca = 67.2
<0.01
Ca= 22 8
0.01
Ca= 14.8
<0.01
Ca= 15.3
ND
Ca = 10.8
0.57
1.8
<0.05
<0.05
<0.03
<0.001
0.04
<0.05
<0.05
<0.05
<0.03
<0.001
Removal
Efficiency
(%) Comments Reference
97 Ca,=350 mg/L Chang & Peters,
as CaCO3 1985
>99
>99
>99
99
>99
>99
98.9 Talbot 1985
88.0
>99.7
>99.7
>99.8
>99.9
99.9
>99.7
>99.7
>99.7
>99.8
>99.9
4.24
-------
Chapter 5
PROCESS EVALUATION
Both oxidation and precipitation processes appear to be excellent choices
for use in the treatment of groundwaters containing the types of contami-
nants discussed in Chapter 4.0. Systems are commercially available for
drinking water and wastewater treatment. The need, therefore, is for trans-
fer of existing technology to another application, rather than development
of a new technology.
For over a decade, substitution processes have been available for the
treatment of soils and sludges contaminated with polychlorinated biphenyls
(PCBs) and other chlorinated organics. They have not been used exten-
sively because other methods and technologies, such as landfilling and in-
cineration, have been cheaper and more readily available. Where local
community concerns prevented the use of existing technologies, the "do
nothing" alternative often has been employed. This situation has resulted in
very little economic incentive to invest in the development of these tech-
nologies. A number of substitution processes now appear to be available at
costs approaching those of incineration, specifically, Galson Research Cor-
poration (GRC), SoilTech/Anaerobic Thermal Processor (ATP), and
KGME/DECHLOR coupled with a thermal treatment system for soils.
The Base Catalyzed Decomposition (BCD) Process, which appears to be
similar to the SoilTech/ATP Process, but operates at lower temperatures
and uses an improved reagent, is an emerging technology. It is discussed in
Appendix A.
5.1
-------
-------
Chapter 6
LIMITATIONS
Chemical treatment processes are highly specialized. The selected pro-
cess must not only be effective in treating the particular contaminants in a
particular matrix, but it must also be chemically compatible with the other
constituents of the matrix.
6.1 Substitution Processes
Substitution processes are applicable only in treating substituted organic
contaminants, such as halogenated or sulfur bearing organics. In fact, they
have been successfully applied only in the treatment of chlorinated aromatic
compounds, such as polychlorinated biphenyls (PCBs) and
chlorodibenzodioxins. The processes are further limited when water is
present. In the treatment of contaminated soils, the processes described
herein can tolerate some water, but water increases the reagent require-
ments. In high temperature substitution processes, water increases the re-
moval of contaminants by competing mechanisms, such as steam stripping,
and increases fuel requirements.
6.2 Oxidation Processes
Advanced oxidation processes were developed in order to overcome
many of the limitations encountered in general oxidation processes. Since
this technology is based on hydroxyl free radical chemistry, chemical inter-
actions are highly nonspecific and nonselective. Because of the high reac-
tivity of hydroxyl radicals, most contaminants in most aqueous streams are
very effectively destroyed. The matrix limitations encountered in using
6.1
-------
Limitations
these technologies are similar to those encountered in devising strategies
based on hydroxyl radical chemistry. The biggest concern is the presence
of scavengers, such as bicarbonate and carbonate ions. At high concentra-
tions, higher doses of ozone, hydrogen peroxide, and ultraviolet (UV) radia-
tion are required. Another important factor is penetration of UV light
through the wastewater stream. Light penetration is attenuated b*y high
particle concentrations, and, therefore, the technique general!)' is not well
suited to treating soils. Rates of destruction will vary with such factors as
the nature of the contaminant mixture, pH, concentration of contaminants,
presence of scavengers (carbonates and natural organic material), and the
inorganics present.
6.2.1 UV-Ozonation — Treatment of Water
Depending on the reaction conditions (pH, ions, temperature, etc.), or-
ganic compounds interact with ozone via multiple pathways. Ionic strength
and pH do not affect gas transfer, although the solubility of ozone increases
with decreasing temperature. The kinetic regime of ozone reactions is
highly dependent on pH and ozone partial pressure. For example, the deg-
radation kinetics of p-nitrophenol are very slow at pH 2, but they increase
with pH until an instantaneous rate is achieved at pH 8.5 (Beltran, Gomez-
Serrano, and Duran 1992). A similar trend is observed with increasing
ozone partial pressure. These results have important implications for design
of ozone contactors because, under extreme conditions, mass transfer of
ozone can be controlling and interfacial areas should be maximized. At
intermediate pH, rates of mass transfer and chemical reaction are about
equal. For nitrophenols, ozone decomposition or free radical pathways
become major only above a pH of 12.4. Therefore, to select this pathway,
ozone decomposition requires catalysis by either UV light or hydrogen
peroxide. In general, high pH favors ozone decomposition and has a favor-
able effect also on substrate ionization by causing deprotonation, which
produces either uncharged or negatively-charged species.
A major consideration in applying ozonation in remediation is the pres-
ence of competitive substrates and inhibitors or scavengers. For groundwa-
ter in particular, the inorganic matrix can have a profound effect on ozone
efficiency. Bicarbonate and carbonate ions scavenge hydroxyl radicals,
terminating the decomposition chain reaction and stabilizing molecular
ozone. Once again, advanced oxidation processes are usually required to
6.2
-------
Chapter 6
7
offset this effect. Some ions, iron(II) for example, will enhance ozone ki-
netics by initiating decomposition.
The natural organic matter (NOM) exerts very complex effects on
ozonation efficiency. This class of ill-defined compounds can participate in
initiation, propagation, and termination interactions. The extent of these
interactions will vary regionally and seasonally. Moreover, NOM is usually
present at much higher concentrations than synthetic organic pollutants. In
general, micropollutant destruction in the presence of even low to moderate
amounts of NOM requires relatively high ozone doses, and AOPs would
typically be used.
6.2.2 UV-Oxidation — Treatment of Particulate
Degradation of polyaromatic hydrocarbons (PAHs) adsorbed onto a
silica gel was studied in a fluidized-bed reactor simulating atmospheric
interactions (Alebic-Juretic, Cuitas, and Klasinc 1990). Rates of degrada-
tion were influenced by the degree of surface coverage and enhanced on the
surface of the acidic silica gel. These findings suggest that the type of sur-
face is important and that reaction is via electrophilic substitution.
Ozonation in heterogeneous aqueous systems has not been widely studied
and it is expected that ozone effectiveness would be diminished by the pres-
ence of solids because of a quenching effect and mass transfer limitations.
A major difference between atmospheric and aqueous particles lies in the
higher concentrations of NOM and other potential scavengers in aqueous
systems.
Although UV radiation does not penetrate solid matrices such as soils,
direct or indirect photolysis can be used effectively in soil systems. Shal-
low depths and periodic mixing are needed with soil irradiation.
6.2.3 UV-Hydrogen Peroxide — Treatment of Water
A number of water soluble, organic contaminants in groundwater have
been successfully oxidated through the UV/H2O2 Process (Camp 1991;
Edwards and Bonham 1988; Rowland 1989; US EPA 1992b). While the
process appears to be effective in treating most of the contaminants in
groundwater studied to date, there are a number of limitations that can af-
fect its effectiveness in treating contaminated water.
6.3
-------
Limitations
Interference with transmission of light energy from the source (lamp)
through the aqueous medium to the substrate being photolyzecl can ad-
versely affect the efficiency of the UV/H2O2 Process. Optical fouling of the
quartz tubes containing the UV light source over the course of the treatment
process can significantly reduce process performance and efficiency. An
example of this difficulty has been described by Camp (1991) in the treat-
ment of chlorinated hydrocarbons in groundwater containing less than a 0.1
mg/L of iron. Camp reported iron deposition rates of 0.009 to 0.085 mg Fe/
cm2hr in the treatment of groundwater containing tetrachloroelhene (PCE).
The resultant loss in light transmission translated to a reduction in overall
process efficiency, which worsened over the course of several days. Re-
moving the deposited iron from the quartz tubes improved process perfor-
,mance. The efficiency of PCE destruction decreased as the inlervals be-
tween cleanings of the quartz tubes increased. The iron deposition process
was thought to be an oxidative precipitation or flocculation of iron. There-
fore, the presence of even relatively low concentrations of dissolved miner-
als may adversely impact light transmission and process efficiency. The
quartz tubes containing the light source may need to be cleaned periodi-
cally, and the effect on operating costs, labor, maintenance, and downtime
of the process, will need to be considered.
Dissolved carbonate (CO3~2) and bicarbonate (HCO3) ions at relatively
high concentrations (=4 mmol/L) can significantly reduce the rate of degra-
dation of organic contaminants (Guittonneau et al. 1990). Both carbonate
and bicarbonate ions react with hydroxyl radicals as scavengers with bimo-
lecular rate constants in the range of IxlO7 8 L mol 'S ', which is competi-
tive with the rate constants for the reaction of hydroxyl radicals with most
organic substrates. Therefore, pH adjustments with carbonate bases prior to
the oxidation reaction should be avoided. If necessary, sodium hydroxide
(NaOH) should be used.
Since hydroxyl radicals are potent and nonselective oxidizing agents, the
presence of other dissolved organics in water may require the use of higher
levels of hydrogen peroxide beyond the amounts required to degrade the
contaminants of interest.
Virtually all of the organic contaminants which undergo UV/H2O2 oxida-
tion produce intermediate products that must also undergo subsequent oxi-
dation. These by-products, depending upon their nature, may require ex-
tended oxidation and thus may impact reactor productivity by increasing the
total residence time for complete mineralization.
6.4
-------
Chapter 6
These process limitations need to be addressed in treatability studies and
matrix analysis and characterization to determine the suitability and cost of
applying the UV/H2O2 oxidation process to a site remediation.
6.2.4 UV-Hydrogen Peroxide — Treatment of Soils and Sedi-
ments
Since photochemical reaction efficiency depends upon the optical path
length of medium in which it is carried out, direct application of the UV/
HjOj oxidation process to soils is not practical. If, however, the contami-
nants of interest can be effectively transferred to an aqueous phase of rea-
sonably high optical path length, the UV/H2O2 oxidation then can be effec-
tively carried out on soils or sediments. This approach has been applied to
lagoon sediments contaminated with water soluble explosives waste
(Wentsel, Sommerer, and Kitchens 1981). The presence of high levels of
water soluble organics, other than the contaminants to be degraded, can
result in the need for higher levels of hydrogen peroxide than desired and,
therefore, increase costs.
6.3 Precipitation Processes
Precipitation processes are limited to the treatment of inorganic materials
in aqueous media.
6.5
-------
-------
Chapter 7
TECHNOLOGY PROGNOSIS
Under proper conditions, discussed in this monograph, chemical treat-
ment can be a useful site remediation technology. The following are likely
applications of the processes addressed in this monograph:
• Substitution processes, especially the high temperature pro-
cesses, will be used to treat soils and sludges contaminated with
polychlorinated biphenyls (PCBs), pentachlorophenol (PCP),
chlorodibenzodioxins, and chlorodibenzofurans;
• Oxidation and precipitation processes will be used to treat water
from pump-and-treat applications; and
• Precipitation processes will be commonly used to treat sludges
and aqueous streams that are contaminated with toxic metals and
other cations.
7.1
-------
-------
Appendix A
APPENDIX A
Emerging Technologies
There are a number of chemical technologies that are at a research or an
early developmental stage. Although there are some questions about their
economic feasibility, they appear to be very promising technologically. Six
such technologies are briefly discussed below.
A. 1 The Base Catalyzed Decomposition
(BCD) Process
The BCD, a chemical reaction method similar in many ways to the
anaerobic thermal processor (ATP) process, is under development by the
Risk Reduction Engineering Laboratory (RREL) at the U.S. Environmental
Protection Laboratory, Cincinnati, Ohio. This process has been tested in the
laboratory for treating a variety of contaminants including polychlorinated
biphenyls (PCBs); 2,4-D and 2,4,5-T (see table A.I on page A.2);
tetrachlorodibenzo-p-dioxin (TCDD), tetrachlorodibenzofurans (TCDF),
lindane, endrin, dieldrin, and other chlorinated compounds. (Kornel,
Rogers, and Sparks 1991a, 1991b, and 1991c).
In these tests, 10 mL of oil (Sun Par LW 107 boiling range: 327° to
387°C) contaminated with 2,4-D, and 2,4,5-T were combined with 1.0 g
NaOH and l.Og of catalyst in a 50 mL round bottom flask. A vertical con-
denser was attached to the reaction flask, and the mixture was heated and
maintained at 330 to 340°C (630 to 640°F) for one hour under conditions of
refluxing solvents (Kornel, Rogers, and Sparks 199la, 1991b, and 1991c).
After three hours, the mixture was cooled and 50 mL of distilled water was
added to dissolve sodium chloride formed during the reaction. Water ex-
A.l
-------
Emerging Technologies
Table A. 1
BCD Treatment of 2A-D; 2 A5-T
Herbicide
2,4-D
2,4-D
2,4,5-T
2,4,5-T
Weight Of
Sample (mg)
1,005
1,009
1,004
1,018
Theoretical
324.6
325.7
420.0
427.6
Actual
373.7
335.4
421.1
450.7
% Chlorine
Balance
115.0
102.9
100.3
105.4
TCDD in Liquid Herbicide Formulation
Tests
2-1
2-2
2-3
2-4
2-5
2-6
Ratio of
Formulation:Oil
1:3
1:3
110
2:0
1:3
1:1
Treatment
Time (hrs)
4
4
3
83
8
3
TCDD Concentration (ppb)
Before" After***
11.3
11.3
4.8
8.2
11.3
18.3
0.13
0.017
0.005
0.01
0.01
0.002*
Detection limit of high resolution MS
Calculated in the initial reaction mixture
* In the final reaction mixture
tract was filtered, diluted to 100 mL with distilled water and analyzed for
chloride by ion chromatography. Experimental results shown in Table A. 1
confirmed the conversion of the aromatic chloride to sodium c hloride for
2,4-D and 2,4,5-T.
It was claimed that the BCD process totally dechlorinates 2,4-D and
2,4,5-T at 10% starting concentrations. The developers claimed that the
reaction completely replaced the chlorine with hydrogen, but no indepen-
dent verification of this phenomenon has been published.
The BCD chemistry was used to destroy up to 100,000 ppm of PCBs in
dielectric fluids. The treatment was similar to the one described above.
Gas chromatography showed an absence of biphenyl, and the presence of
pentachloro-, hexachloro-, and heptachloro-biphenyl in the untreated mix-
ture. Similar analysis of the reacted mixture showed the presence of biphe-
A.2
-------
Appendix A
nyl and absence of the chlorobiphenyls. Chlorine balance accounts for the
chlorine present as the mineralized salt.
A.2 Iron (II) Catalyzed H2O2 Oxidation
(Fenton's Reagent)
Iron II can potentially be used as a catalyst to improve the performance
of hydrogen peroxide as an oxidizing agent. While no large-scale or pilot
application of this technology has been found, there appears to be no chemi-
cal impediment to the procedure. This type of chemical oxidation is fre-
quently used in the laboratory and the costs appear to make its application
in remediation worth considering.
Among the most commonly used metal catalysts for the decomposition
of hydrogen peroxide in aqueous media is iron (Fe2+). This basic process
was first reported by Fenton (1984) in describing the oxidation of tartaric
acid. The combination of various iron salts with hydrogen peroxide has
come to be known as Fenton's Reagent. The resultant oxidation process
has also come to be referred to as the Fenton Process.
The catalytic reaction of iron with hydrogen peroxide in the Fenton Pro-
cess is believed to proceed through a series of redox reactions (Watts, Tyre,
and Miller 1991) represented by the following equations, which produce
powerful oxidizing agents in the form of hydroxyl radicals (HO) and
perhydroxyl radicals (HO2»).
Fe2 + H2O2 -» Fe3 + HO~ + HO* [A.I]
Fe2+HO' -> Fe3+HO~ [A.2]
[A.3]
Fe2++H++O2 [A.4]
Intermediate oxidation by-products can be formed under Fenton Process
conditions and these must be taken into account in the mass balance of the
process and for their environmental impact.
A.3
-------
Emerging Technologies
Fenton's Reagent consists of the combination of hydrogen peroxide
(H2O2) and iron(II) salts (Fe2+). The most common source of ferrous ion
used in the laboratory process is ferrous sulfate, typically obtained as its
heptahydrate (FeSO4»7H2O). Commercially, ferrous sulfate is available as a
moist bulk product with a specified range of water content. Hydrogen per-
oxide is commercially available in a range of concentrations from 30 to
70% by weight in water. Typically, hydrogen peroxide is most easily and
safely handled at concentrations of 10 to 30% by weight in water. Higher
concentrations can react violently with organic material.
The Fenton oxidation is normally carried out by first establishing the
ferrous ion concentration at the desired level in the reaction medium by the
addition of a ferrous salt. The reaction medium is then adjusted to pH 2 to
5 by the addition of a suitable acid, such as hydrochloric acid (HC1), or a
base, such as sodium hydroxide (NaOH). The reaction medium is then
agitated vigorously while hydrogen peroxide is slowly added to the reaction
(Walling 1975). The reaction is normally carried out at ambient tempera-
tures. In most cases, the optimum initial pH is three, although Fenton's
reaction has been observed to produce OH efficiently at neutral pH (Zepp,
Faust, and Hoigne 1992). Furthermore, the authors of this study found that
light accelerated the reaction by photo-regenerating Fe(II).
In a slight modification of the Fenton's reaction, the complete mineral-
ization of phenoxyacetic herbicides was observed in an iron(III)/H2O2 sys-
tem (Pignatello 1992).
The degradation reaction was sensitive to pH, reaching an optimum
around pH 2.7. The reaction was adversely affected by the pre:sence of
methanol and chloride, which exerted a scavenging effect on the hydroxyl
radical, and by sulfate, which complexed Fe3+. In this case, too, the rate of
degradation was increased significantly by light. A partial explanation of
the observed phenomena was that photoreduction of the iron monohydroxo-
complex (FeOH2+) produces Fe2+ and OH". The ferrous ion in the presence
of H2O2 generated hydroxyl radical in the conventional Fenton's reaction.
Photo-assisted mineralization of the herbicides was nearly complete in 2
hours at a H2O2:herbicide ratio of 5:1, suggesting that dioxygem was also
involved in the degradation pathway.
During the course of the reaction, oxygen gas is liberated as the hydro-
gen peroxide undergoes decomposition. This gas evolution can become
violent if the hydrogen peroxide is added too rapidly. The gas evolved
A.4
-------
Appendix A
during the addition of hydrogen peroxide can potentially entrain volatile
organic contaminants and should therefore be scrubbed appropriately prior
to discharge into the environment.
The specific concentrations of ferrous ion and hydrogen peroxide re-
quired for complete mineralization of various contaminants will be depen-
dent upon a number of factors related to the specific compounds and matrix
to be treated. In the treatment of contaminated aqueous streams, the total
dissolved carbon loading will determine the amount of hydrogen peroxide
required for treatment. This requirement is a direct reflection of the nonse-
lective nature and high reactivity of the hydroxyl radicals generated in the
Fenton Process. Thus, the target compounds of interest and any other dis-
solved carbon sources will all consume hydrogen peroxide in the process.
The concentration of ferrous ion used in this process is based on the
amount of hydrogen peroxide required for complete oxidation. Typical
ferrous ion to hydrogen peroxide concentration ratios fall in the range of
1:200 to 1:1,000 by weight. In adding ferrous salts to the reaction medium,
one should take into account the concentration of indigenous iron species.
In the direct treatment of soils, the presence of naturally occurring ores
containing ferrous ions, such as magnetite, may be sufficient to eliminate
the need for ferrous salt addition (Vasilenko and Fedosoua 1987). The time
required to complete the process, again, depends upon the amount of con-
taminant and indigenous carbon to be oxidized, as well as the concentration
of ferrous ion and hydrogen peroxide used. Typical reaction times fall in
the range of one to several hours.
Upon completion of the oxidation process, excess hydrogen peroxide
may require removal or destruction. Finally, the concentration of soluble
iron species in the treated medium may require adjustment to acceptable
discharge levels by sequestering or precipitating of soluble iron species.
The range of contaminants treatable by the Fenton oxidation process is,
in principle, quite broad. Several classes of organic compounds have been
degraded on a laboratory scale, including polyaromatic hydrocarbons
(PAHs), pesticides, aromatic hydrocarbons, phenols, chlorinated aromatics,
chlorinated hydrocarbons, and lignins. The complete mineralization of
benzo(a)pyrene and phenanthrene has been reported using Fenton oxidation
(Kelley, Gauger, and Srivastava 1990). Phenol degradation using Fenton's
Reagent has been reported by Osaki, Sugihara, and T. Kaji (1990). Chlo-
robenzene and chlorophenol are degraded by Fenton's Reagent via a num-
A.5
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Emerging Technologies
her of complicated pathways, the more direct involving hydroxylation, ring
cleavage, and mineralization (Sedlak and Andren 1991). Oxygen was
present, the more direct pathway was favored, and less H2O2 was required.
Gold, Kutsuki, and Morgan (1983) reported the rapid degradation of 14C-
labeled lignins, and a similar polymer degradation has been investigated by
Matsuzuru et al. (1982) using Fenton's Reagent to degrade powdered cation
exchange resins. Watts, Tyre, and Miller (1991) studied the laboratory-
scale degradation of Dieldrin, Trifluralin, pentachlorophenol, and n-
hexadecane in the Fenton Process. In that study, Trifluralin arid pentachlo-
rophenol were rapidly degraded by the iron/hydrogen peroxide system,
while dieldrin and n-hexadecane were degraded more slowly. Decoloriza-
tion of a wide variety of dyes has been demonstrated, and the best results
were found below pH 3.5 (Kuo 1992), at which about 90% of the chemical
oxygen demand and about 97% of the color was removed.
Water. Fenton oxidation is a very effective process for the treatment of
contaminated wastewater. The strong oxidizing conditions produced in the
process generally lead to the mineralization of all soluble organic com-
pounds. This means that nonhazardous, naturally occurring organics are
degraded along with the contaminant of interest and will, therefore, con-
sume additional reagents beyond the amount required to degrade the target
compounds. Water containing high levels of soluble or suspended organic
matter may require very large amounts of reagents. The presence of useful
forms of dissolved iron can, in principle, be used to advantage in reducing
the amount of ferrous salts required to carry out the process.
Soils. The degradation of contaminants in soil matrices has been demon-
strated in laboratory and field studies. The limitations described for treat-
ment of water are also applicable to soils. In addition, soils containing a
high level of organic matter can lead not only to use of very large amounts
of reagent, but also to slower rates of contaminant degradation.
Under conditions that lead to complete mineralization of the target con-
taminant, the by-products of the Fenton process should be water and stable
oxides that pose no threat to the environment. Conditions leading to com-
plete mineralization, however, will need to be established for each matrix
and contaminant type to be treated. The process parameters of stoichiom-
etry, pH, and reagent concentration will need to be determined in an appro-
priate treatability study. Under Fenton conditions, the partial oxidation of
certain organics can lead to undesirable by-products. An example of this
A.6
-------
Appendix A
has been reported by Heindl and Hutzinger (1987), who found that partial
Fenton oxidation of trichlorobenzenes can lead to the formation of
polychlorodibenzofurans (PCDFs) and polychlorodibenzodioxins (PCDDs).
When contaminants are completely mineralized in the Fenton oxidation,
the only posttreatment requirements would be the adjustment of the matrix
pH, the removal of iron to meet discharge permit levels, and the removal of
any excess hydrogen peroxide. Complete mineralization should be verified
by mass balance and analysis prior to discharge.
There have been only a few instances of full-scale remediation using the
Fenton oxidation. One example is found in EPA's computerized on-line
information system (COLIS). In this case 6,400 kg (14,000 Ib) of phenol
leaked from a railcar in Charleston, South Carolina, in May 1978. Runoff
from the leak was collected and transferred to two 500,000 gal elastomer-
lined and covered concrete bunkers where 50% H2O2 was metered into the
bunker and circulated with hydrated ferric sulfate. Phenol was oxidized
within 2 days, and initial concentrations, which ranged from 700 to 2,700
ppm, were reduced to less than 5 ppm.
Tate (1991) reported a one day full-scale production test by Environmen-
tal Health Research and Testing (EHRT) of an oxidation process which was
used to treat soil containing up to 20,000 ppm hydrocarbon contamination
at the Hamilton Army Airfield in Novato, California. The results of the test
demonstrated the reduction of hydrocarbons to below 100 ppm. Full-scale
remediation of this 18,000 m3 (24,000 yd3) site using Fenton technology
under the supervision of the US Army Corps of Engineers was recently
confirmed by a representative of Environmental Health Safety and Testing
(Purbaugh 1992). Production throughput, according to EHRT, was approxi-
mately 1,200 m3 (1,500 yd3) per day based on a one shift operation. The
remediation required six months to complete at an estimated cost of $1577
m3 ($120/yd3). The EHRT could not offer engineering details beyond those
contained herein because of proprietary considerations.
Technical grade hydrogen peroxide (35% by weight in water) is commer-
cially available in tank car volumes at a cost of approximately $0.55/kg
($0.25/lb), and ferrous sulfate is available in moist bulk forms at a cost of
$37/tonne ($34.00/ton). For matrices containing low levels of hazardous
organic compounds and other organic material, the cost of reagents required
to treat the matrix should be in the range of $22 to $55/tonne ($20 to $507
ton). Some field work using Fenton's reagent has been conducted by the
A.7
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Emerging Technologies
Institute of Gas Technology in Chicago, IL. This work came to the authors'
attention after the monograph was written and was not included.
A.3 Photocatalysis in Semiconductor Sys-
tems
Semiconductors are materials that undergo a charge separation when
irradiated with sufficiently energetic light. Electrons in the valence band of
a semiconductor particle are excited to the conduction band by the absorp-
tion of a quantum of ultraband gap light, leaving behind a positive hole.
These charges may recombine or migrate to the surface of the particle
where they can engage in interfacial redox reactions. This phenomenon has
been extensively applied in solar power generation and organic synthesis, as
well as in other industrial uses (Heller 1987). Only relatively recently, how-
ever, has it come to the attention of environmental engineers. It has been
demonstrated that photocatalysis can reduce metals or oxidize (in many
cases, completely mineralize) almost every class of organic compound
(Schiavello 1988; Ollis 1985; Ollis, Pelizzetti, and Serpone 1989; Pelizzetti,
Minero and Maurino 1990). A novel photocatalytic method was recently
reported for detoxifying cyanide wastes (Bhakta et al. 1992).
Some common examples of semiconductors are titanium dioxide (TiO2),
zinc oxide (ZnO), and cadmium sulfide (CdS). The anatase form of TiO2
has received the most attention in the treatment of low levels of contami-
nants in either liquid or gaseous phases, because it appears to be more reac-
tive and is commercially available at low cost (i.e. Degussa). Ultraviolet
light having wavelengths less than 380 nm is required to induce the charge
separation in TiO2, and it has been demonstrated that solar radiation, the
spectrum of which is 5% ultraviolet (UV), can drive these degradation reac-
tions (Matthews 1987; Pilizzetti et al. 1988; Gerischer and Heller 1992;
Manilal et al. 1992).
There is extensive literature on photocatalysis, and the theoretical basis
of this process is well-established. It is interesting, however, that the exact
mechanism by which organic compounds are destroyed remains unknown.
It is conventional thinking that oxygen is required to sweep trapped elec-
trons on the surface, inhibiting charge recombination and allowing oxida-
A.8
-------
Appendix A
tion to occur at the trapped positive hole. Oxidation may result from the
transfer of an electron from an adsorbed organic compound, or it may be
mediated by the hydroxyl free radical produced by the oxidation of water.
Most kinetic treatments of photocatalysis are based on the assumption that
the hydroxyl free radical is the primary oxidant and utilize Langmuir-
Hinshelwood rate forms (Matthews 1988; Turchi and Ollis 1990). The rate-
limiting step has been suggested to be electron scavenging by oxygen
(Gerischer and Heller 1991) and some recent reports suggest that oxygen
plays a more intrinsic role in the degradation processes than simply electron
sweeping (Stafford et al. 1993; Barreto, Gray, and Anders 1994),
Most investigations of semiconductor photocatalysis have been con-
ducted with single components in TiO2 slurry systems and under batch labo-
ratory conditions. Typically, a mercury vapor lamp is used to induce the
charge separation of the semiconductor. An alternative process has been
demonstrated whereby a colored pollutant can sensitize semiconductors by
injecting electrons with visible light excitation (Dieckmann, Gray, and
Kamat 1992 a, b). Application of photocatalysis necessitates the develop-
ment of a reactor utilizing immobilized semiconductors, and TiO2 has suc-
cessfully been attached to glass mesh, to the inside of a glass coil, and to
alumina (Matthews 1987; Magrini et al. 1992). A patented Nulite
photoreactor uses stationary TiO2 attached to a fiberglass mesh (Al-Ekabi et
al. 1991).
Groundwaters or waters having inorganic ions or metals present can be
treated effectively with photocatalysis, although rates may be adversely
affected, and some loss of catalytic activity with time has been observed
(Abdullah, Low, and Matthews 1990; Magrini et al. 1992). Using a pilot-
scale, continuous flow slurry reactor that is powered by a parabolic solar
collector, trichlorethylene (TCE) contamination in a groundwater located at
a Superfund site in Livermore, California, has been reduced from 5,000 ppb
to the detection limit of 5 ppb (U.S. Water News 1991, 12). Similarly, fa-
vorable reports have been made for the treatment of volatile organic com-
pounds (VOCs) in the gas phase (Environment Today 1992, 10-11). Sus-
pended solids may affect reaction rates by attenuating light penetration into
the reactor and by partitioning contaminants. A preliminary comparison of
projected operating costs among activated carbon, UV/ozone and UV/
photocatalysis found that, for medium to high flows, photocatalysis is com-
petitive with carbon and appears to be more economical than UV/ozone
(Ollis et al. 1989). A more recent cost assessment based on the Livermore
A.9
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Emerging Technologies
pilot study found that photolysis is more cost-effective than carbon, but that
catalyst improvements are required for it to be competitive with UV/perox-
ide (Turchi 1992). Actual operating costs for the Nutech reactor are
claimed to be very reasonable at $0.24/m3 ($0.18/yd3).
A.4 Ionizing Radiation
A recent innovation in the treatment of industrial and municipal wastes is
the use of high-energy radiation, which interacts with matter to produce
ions, free radicals, and other short-lived reactive species (Singh, Kremers et
al. 1985; Singh, Sagert et al. 1985). In an aqueous system, irradiation with
"•"Co produces the ionizing event, forming, reducing (the aqueous electron)
and oxidizing (the hydroxyl free radical) species in equal proportions.
These radicals can then interact with contaminants and induce the same
kind of reactions that have been discussed in the text of this monograph
(see, for example, Singh et al. 1985; Kurucz et al. 1990; Nickelsen et al.
1992; Farooq et al. 1993). There also appear to be some advantages for the
use of radiolysis in treating compounds in an adsorbed state (Dickson and
Singh 1986). A pilot-scale study has been conducted over the last five
years in Miami, Florida, by researchers at the University of Miami and
Florida International University with funding from the National Science
Foundation. This group has demonstrated that hazardous organic com-
pounds can be effectively removed from aqueous solution economically,
although treatment costs are highly dependent on the required dose and
flow rate (Kurucz et al. 1990). Pulsed electron beams, produced by com-
pact and inexpensive induction accelerators, appear to be a cost-effective
means for removing a broad spectrum of toxic organic contaminants, and
new accelerator technology is making this a very competitive technology
(Science Research Laboratory, Inc., Somerville, Mass.).
Currently, radiolytic processes are used extensively in the curing of plas-
tics where ionizing radiation replaces thermal or catalytic techniques and
results in lower emissions. This is an excellent example of waste minimiza-
tion. In general, capital and operating costs of electron beam processing are
highly variable, but capital costs are normally high for conventional elec-
tron beams, and processing rates must be high to achieve reasonable unit
costs (Cleland 1992).
A.10
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Appendix A
A.5 Sonication
Ultrasonic waves in liquids can produce and accelerate many chemical
reactions inside, at the interface, or at some distance from cavitating gas
bubbles. High temperatures and pressures exist inside a collapsing bubble
and at the interface. Hydroxyl hydrogen free radicals are produced in the
thermal decomposition of water. Pyrolysis and radical reactions can occur
simultaneously and appear to be responsible for the destruction of p-
nitrophenol in aqueous solution (Kotronarou, Mills, and Hoffmann 1991).
The destruction of parathion by ultrasonic irradiation has been reported also
(Kotronarou, Mills, and Hoffmann 1992). The characteristics of
pentachlorophenate degradation by means of sonochemical treatment at 530
kHz has been explained recently (Petrier et al. 1992). SRI International of
Menlo Park, California, is in the process of scaling up a sonication process
to enhance the photocatalysis (Environment Today 1992, 10-11). In this
application, it is thought that ultrasound enhances primarily mass transfer,
and a commercial sonication reactor would range from 10 to 50 kHz. A
pilot-scale system is under development and is funded by DOE's Innovative
Technologies Program.
A.6 lron(VI)-Ferrate
Iron(VI)-Ferrate (not to be confused with Fenton's Reagent) is a high
oxidation state of iron that is present in water as a divalent anion, FeO42" and
can be obtained commercially as a potassium salt under the trade name,
TRU/Clear from Analytical Development Corporation (Colorado Springs,
CO). Theoretically, ferrate possesses the properties of a strong oxidant (see
table A.2 on page A. 12), as well as the typical complexation and precipita-
tion properties associated with iron(III). There has been limited research on
the use of this chemical in water and wastewater treatment as a disinfectant,
oxidant, and coagulant. For the most part, its use has remained of academic
interest because, at a cost of $56/kg ($25/lb), it is extremely expensive, and
until recently, it had not been found to be superior to other more affordable
oxidation/precipitation strategies. Although the mechanism is not known,
ferrate has been shown to produce better removal rates and less sludge in
treating of waters contaminated with radioactive elements, especially the
A.ll
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Emerging Technologies
Table A.2
Relative Oxidizing Strength of Oxidants
Oxidant
Fluorine
Hydroxy Radical
Atomic Oxygen
Ferrate
Ozone
Hydrogen Peroxide
Perhydroxyl Radical
Hypochlorous Acid
Chlorine
Chemical/
Species
F2
HO
O-
Fe042-
°3
HjOj
HCO
HOC1
C12
Oxidation Potential*
(Volts)
3.06
2.80
2.42
2.20
2.07
1.77
1.70
1.49
1.36
Relative Oxidation
Strength
2.25
2.05
1.78
1.62
1.52
1.30
1.25
1.1
1.00
•Source: Rica 1981
transuranic elements. A bibliography of work utilizing potassium ferrate is
available from Analytical Development Corporation (4405 N. Chestnut
Street, Colorado Springs, CO 80907, 719-260-1711).
A.12
-------
Appendix B
APPENDIX B
Cose Study Of Romulus Removal Action
The Comprehensive Environmental Response, Compensation, and Li-
ability Act (CERCLA) Immediate Removal Project at PBM Enterprises of
Romulus, Michigan, conducted in 1985, is an excellent example of the ap-
plication of chemical treatment in a site remediation (Powers 1985). Silver
had been recovered from photographic film by a cyanide solution process at
the site. Operation ceased in September, 1984. At that time, the site con-
tained 421 tonne (464 ton) of film chips contaminated with up to 1,000 ppm
cyanide stored in 17 semi-trailers and two roll-off boxes and about 7,570 L
(2,000 gal) of cyanide- or hypochlorite-contaminated liquid wastes. In
addition, about 60 m3 (80 yd3) of contaminated soil was excavated for treat-
ment. (Cyanide-contaminated soil and surface waters were also found at
the site, but these were not part of the emergency removal effort.) Incinera-
tion was considered, but was ruled out because of considerations of safety,
cost, regulatory, and the public attitude. It was decided to treat the liquids
and chips chemically by oxidation with sodium hypochlorite, a method of
destroying cyanide that is commonly used in the metal plating and process-
ing industries.
The treatment system was a batch process using sodium hypochlorite in
conjunction with pH adjustments to oxidize the sodium cyanide in the fol-
lowing reaction:
2NaCN + SNaOCl + H^O^>N,+ 2NaHCO, + SNaCl [B.I]
The specific process had been developed by Mid-America Services of
Riverdale, Illinois, and had been used to treat 7.3 million kg (16 million Ib)
of cyanide-contaminated film chips in 1984. On-site remediation opera-
tions were started on April 11, 1985 and completed on October 8, 1985.
Cyanide levels were reduced to less than 20 ppm in all streams except for
B.I
-------
Case Study Of Romulus Removal Action
the contaminated soils in which the posttreatment cyanide level was ap-
proximately 60 ppm.
Treatment was conducted in roll-off boxes lined with poly vinyl chloride
(PVC) membrane. About 15 m3 (20 yd3) of contaminated film chips were
loaded into a treatment vessel and then about 13,200 L (3,500 gal) of caus-
tic and hypochlorite solution were added. The mixture was agitated by
blowing compressed air through it for two to three hours, and the reaction
was monitored. When the reaction was completed, the waste hypochlorite
solution was drained into a holding tank and the chips rinsed by adding
water to the tank, agitating, and draining. The drained chips were tested for
cyanide and, if under 20 ppm, approved for disposal as a nonhazardous
.waste. The spent hypochlorite solution and rinse liquid were disposed of.
The semitrailers, in which the chips and the drums were stored, were also
decontaminated with hypochlorite solution. All the wood was removed
from the semitrailers and, along with the drums, decontaminated in the roll-
off boxes. The semitrailer shells were vacuum cleaned and then sprayed
Table B.I
Cost Breakdown for Romulus Immediate Removal Action
Item
Labor
Travel and Subsistence
Capital Equipment
Shipping
Materials (mainly reagent)
Sampling and Analysis
Disposal Costs
Subcontract Services
Other
Total
Cost ($1,000)
235
39
213
48
71
3
45
28
8
680
Cost, $ per Ton*
469
78
425
95
142
6
90
56
16
1,358
•Based on 501 tons treated
In addition, ERA performed $124,000 of project management and $3,000 of analytical services m-house or
through other government contractors.
(From Powers 1985)
B.2
-------
Appendix B
with hypochlorite solution to destroy any residual cyanide. The spent re-
agent and rinsewater were trucked to a chemical waste treatment facility
where it was treated and disposed as a hazardous waste. The treated chips
and soil were disposed as nonhazardous wastes.
Problems encountered during the treatment included (1) delivery of poor
quality hypochlorite solution, (2) leaks in the PVC liners of field-patched
fiberglass vessels, (3) spillage of hypochlorite solution because a plumber
inadvertently failed to turn a pump off after a test, and (4) frequent failure
of rented air compressors. These problems are not characteristic of chemi-
cal treatment operations. They are, however, illustrative of the kinds of
problems encountered in the field.
The total cost of the remediation was $698,000, including that for re-
moval and disposal of treated materials and liquid wastes. Additional costs
of $127,000 were incurred by EPA for management of the program. While
it is difficult to attribute the various cost elements to component treatments,
it is reasonable to assume that the vast majority of the cost was associated
with treatment of the cyanide-contaminated film chips. The cost of treat-
ment was, therefore, approximately $1,600 per tonne ($1,500 per ton). See
table B.I (on page B.2) for a cost breakdown.
B.3
-------
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Appendix C
APPENDIX C
List Of References
Abdullah M., G. Low, and R. Matthews. 1990. Effects of common inor-
ganic anions on rates of photocatalytic oxidation of organic carbon over
illuminated titanium dioxide. J. Phys. Chem. 94:6820-5.
Aieta, E.M., E.S. Wong, J. Kuo, and J.M. Montgomery. 1990. Advanced
oxidation processes: state of the art review. In Proc. Am. Chem. Soc. Sym-
posium on Emerging Technologies for Hazardous Waste Treatment. Atlan-
tic City.
Al-Ekabi H., A. Safarzadeh-Amiri, W. Sifton, and J. Story. 1991. Advanced
technology for water purification by heterogeneous photocatalysis. Interna-
tional], of Environ, and Poll. 1(1/2): 125-36.
Alebic-Juretic A., T. Cvitas, and L. Klasinc. 1990. Heterogeneous polycy-
clic aromatic hydrocarbon degradation with ozone on silica gel carrier. Env.
Sci. and Tech. 24:62-66.
Andresozzi R., A. Insola, V. Caprio, and M. G. D'Amore. 1991. Ozonation
of pyridine in aqueous solution: mechanistic and kinetic aspects. Water
Research 25:655-9.
Andrews, C.A. 1980. Photooxidative treatment of TNT contaminated waste
waters. Report No. WQEe/C 80-137. Naval Weapons Support Center.
Ansari, A.S., LA. Khan, and R. Ali. 1985. UV degradation of arginine in
the presence of hydrogen peroxide: involvement of hydroxyl radical in the
photolytic process. J. Radial. Res. 26:321-9.
Arumugam, V. 1976. Recovery of chromium from spent chrome tan liquor
by chemical precipitation. Indian J. Environ. Health 18(1): 47-57.
Baes, C.F., and R.E. Mesmer. 1976. Hydrolysis of cations. New York: John
Wiley and Sons.
C.I
-------
List of References
Bailey, F.E. and J.V. Koleske. 1976. Polyethylene oxide. New York: Acad-
emy Press.
Balasubramanian, D. and B. Chandani. 1983. A poor chemists crown. J.
Chem. Ed. 60(1):77.
Barber, N.R. 1978. Sodium bicarbonate helps metal plant meet federal stan-
dards. Indus. Wastes 24(1) :26, 29.
Barr, W.A. 1976. An evaluation of the engineering design parameters of
hydrogen peroxide, UV oxidation of refractories in waste water. Report No.
USNA-EPRD-31. Annapolis, Md.: US Naval Academy.
Barreto R., K. Gray, and K. Anders. 1994. Photocatalytic degradation of
methyl-tert-butyl ether in TiO2 slurries: a proposed reaction scheme. Water
Research. In review.
Bellamy W.D., B. Langlais, G. Lykins, K. Rakness, C.M. Robson, and P.
Schulhof. 1991. Economics of ozone systems: new installations and retro-
fits. In Ozone in water treatment: application and engineering, ed. B.
Langlais, D.A. Reckhow, and D.R. Brink, 491-541. Denver: American Wa-
ter Works Assoc. Research Foundation.
Beltran F., V. Gomez-Serrano, and A. Duran. 1992. Degradation kinetics of
p-nitrophenol ozonation in water. Water Research 26:9-17.
Benefield, L.D., J.F. Judkins, Jr., and B.L. Weand. 1982. Process chemistry
for water and wastewater treatment. Englewood Cliffs, N.J.: Prentice-Hall,
Inc.
Benitez F., J. Beltran-Heredia, and T. Gonzalez. 1991. Kinetics of the reac-
tion between ozone and MCPA. Water Research 25:1345-9.
Bhakta D., S. Shukla, M.S. Chandrasekharalah, J.L. Margrave. 1992. A
novel photocatalytic method for detoxification of cyanide wastes. Env. Sci.
Tech. 26:625-6.
Bhattacharyya, D., A. Jumawan, G. Sun, C. Sund-Hagelberg, and K.
Schwitzebel. 1981. Precipitation of sulfide: bench-scale and full-scale ex-
perimental results. In AIChE Sympos. Series, Water-1980 77(209): 31-42.
Bhattacharyya, D., A.B. Jumawan, and R.B. Grieves. 1979. Separation of
toxic heavy metals by sulfide precipitation. Sep. Sci. Technol. 14:441-52.
C.2
-------
Appendix C
Bhattacharyya, D., J.H. Shin, G.H. Sun, and A.B. Craig, Jr. 1981. Applica-
tion of sulfide precipitation for the removal of heavy metals from industrial
wastewaters. In Proc. 2nd World Congress ofChem. Engrg. VL548-52.
Bowers, A.R., G. Chin, and C.P. Huang. 1981. Predicting the performance
of a lime-neutralization/precipitation process for the treatment of some
heavy metal-laden industrial wastewaters. In Proc. 13th Mid-Atlantic Indus.
Waste Con/. 13:51-62.
Brantner, K.A., and E.J. Cichon. 1981. Heavy metals removal: comparison
of alternative precipitation processes. In Proc. 13th Mid-Atlantic Indus.
Waste Conf. 13:43-50.
Bricka, R.M., and M.J. Cullinane, Jr. 1987. Comparative evaluation of
heavy metal immobilization using hydroxide and xanthate treatment. In
Proc. 42nd Purdue Indus. Waste Conf. 42:809-818.
Brown, J.F., M.E. Lynch, J.C. Carnahan, and J. Singleton. 1982. Chemical
destruction of PCBs in transformer oil. In Proc. Detoxification of Hazard-
ous Waste, 201. ACS. New York. Aug., 1981.
Brunelle, D.J. and D.A. Singleton. 1983. Destruction/removal of PCBs from
non-polar media. Reaction of PCB with poly(ethylene glycol)/KOH.
Chemosphere 12:183.
Brunelle, D.J. and D.A. Singleton. 1985. Chemical reaction of polychlori-
nated biphenyls on soils with poly(ethylene glycol)/KOH. Chemosphere
14(2): 173-181
Bunnett, J.F. 1978. Aromatic substitution by the SRNI; mechanism. Ace.
Chem.Res. 11:413.
Calvosa L., A. Monteverdi, B. Rindone, and G. Riva. 1991. Ozone oxida-
tion of compounds resistant to biological degradation. Water Research
25:985-93.
Camp, D.W. 1991. Effect of Lamp-Coating Mineral Deposits on UV-Oxida-
tion of Ground Water. UCRL-JC-107037. Lawrence Livermore National
Laboratory. Livermore, Ca.
Chang, T.-K. 1985. Coprecipitation and adsorption for removal of cad-
mium, lead, and zinc by the lime-soda ash water softening process. Ph.D.
diss., Purdue University, West Lafayette, Ind.
C.3
-------
List of References
Chang, T.-K., and R.W. Peters. 1985. Removal of cadmium from contami-
nated groundwaters through coprecipitation and adsorption in lime soften-
ing operations. In Proc. 17th Mid-Atlantic Indus. Waste Conf. 17:455-74.
Christian, G.D. 1977. Analytical Chemistry. 2d ed. New York: John Wiley
and Sons.
Cleland M.R. 1992. High power electron accelerators for industrial radia-
tion processing. In Radiation processing of polymers, ed. A. iSingh and J.
Silverman, 23-42. New York: Manser Publishers.
Clifford, D,, S. Subramonian, and T.J. Sorg, 1986. Removing dissolved
inorganic contaminants from water. Env. Sci. Tech. 20(11): 1072-80.
Connor, J.R. 1990. Chemical fixation and solidification of hazardous
wastes. New York: Van Nostrand Reinhold Publishing Co.
Dean, J.A., ed. 1979. Lange's handbook of chemistry. 12th ed. New York:
McGraw-Hill Book Co.
dePercin, P, 1991. Remedial action, treatment, and disposal of hazardous
waste. In Proc. Seventeenth Annual Hazardous Waste Research Symposium,
511. RREL, Cincinnati. EPA/600/9-91/002. US EPA. April.
Dickson L.W. and A. Singh. 1986. A review of applications of radiolysis in
the adsorbed state. In Proc. 7th Canadian Nuclear Society Conference.
Toronto.
Dieckmann M.S., K.A. Gray, and P.V. Kamat. 1992. Photocatalyzed degra-
dation of adsorbed nitrophenolic compounds on semiconductor surfaces.
Wat. Sci. Tech. 25(3):277-9.
Dieckmann M.S. 1993. unpublished results. University of Notre Dame.
Edwards, I.E. and T. Bonham. 1988. Industrial plant expansion: groundwa-
ter and soil cleanup. In Proc. 5th National Conference on Hazardous
Wastes and Hazardous Materials. Las Vegas, Nev.
Farooq S., C. Kurucz, T. Waite, and W. Cooper. 1993. Disinfection of
wastewaters: high energy electron vs. gamma irradiation. Water Research
27(7): 117-1184.
Faust, S.D., and C.M. Schultz. 1983. The efficacy of removal of heavy met-
als from water by calcite. J. Environ. Sci. Health. A18(l): 95-102.
Federal Remediation Technologies Roundtable. 1992. Synopses of federal
demonstration of innovative site remediation technologies. 2d ed.
C.4
-------
Appendix C
Fender, R.G., A. MacGregor, and K.E. Patterson. 1982. Sulfide precipita-
tion investigation and system design for zinc foundry wastewater. In Proc.
14th Mid-Atlantic Indus. Waste Conf. 14:268-277.
Fenton, H.J. 1984. Oxidation of tartaric acid in the presence of iron. /.
Chem. Soc. 65:899-910.
Ferguson, T.L., and C.J. Rogers. 1990. Field applications of the KPEG
process for treating chlorinated wastes. Project Officers Report. Order No.
Pb 89 212 724/AS and Comprehensive Report on the KPEG Process for
Treating Chlorinated Wastes Order No. PB90 163 643. EPA/600/S2-90/
026. Risk Reduction Engineering Laboratory. Cincinnati. July.
Flynn, C.M., Jr., T.G. Carnahan, and R.E. Lindstrom. 1980. Adsorption of
heavy metal ions by xanthated sawdust, report of investigations - 8427.
Reno, Nev.: US Bureau of Mines.
Franklin Research Center. 1982. Technical and cost of hazardous wastes
detoxification. Proposal No. 22. Prepared for US EPA. Philadelphia.
Friedman, A.J. and Y. Halpern. 1992a. Chemical Waste management, Inc.
Geneva, Research Center 1950 S. Batavia Avenue, Geneva, IL 60134.
Friedman, A.J. and Y. Halpem. 1992b. The KGME process. Patent Pending.
Gerischer H. and A. Heller. 1991. The role of oxygen in photooxidation of
organic molecules on semiconductor particles. J. Phys. Chem. 95:5261-7.
Gerischer H. and A. Heller. 1992. Photocatalytic oxidation of organic mol-
ecules at TiO2 particles by sunlight in aerated water. /. Electrochem. Soc.
139(1): 113-8.
Gold, M.H., H. Kutsuki, and M.A. Morgan. 1983. Oxidative degradation of
lignin by photochemical and chemical radical generating systems.
Photochem. Photobiol. 38:647-51.
GRC, Environmental, Inc. 1992. Alkaline dechlorination using dimethyl
sulfoxide. East Syracuse, New York. June
Guittonneau, S., J. DeLaat, J.P. Duguet, C. Bonnel, and M. Dore. 1990.
Oxidation of parachloronitrobenzene in dilute aqueous solution by O3 + UV
and H2O2 + UV: a comparative study. Ozone Sci. andEng. 12:73-94.
Heeks, R.E., L.P. Smith, and R.M. Perry. 1991. Oxidation technologies for
groundwater treatment. In ACS Symposia Series 468:110-32.
C.5
-------
List of References
Heindl, A and O. Hutzinger. 1987. Search for industrial sources of PCDD/
PCDF, HI. Short-chain chlorinated hydrocarbons. Chemosphere 16:1949-
57.
Heller A. 1987. Industrial aspects of semiconductor photochemistry. New J.
ofChem. 11(2): 187-9.
Higgins, I.E., and V.E. Slater. 1984. Combined removal of Cr, Cd, and Ni
from wastes. Environ. Prog. 3(1): 12-25.
Ho, P.C. 1986. Photooxidation of 2,4-d dinitrotoluene in aqueous solution
in the presence of hydrogen peroxide. Environ. Sci. Technol. 20(3): 260-7.
Hohman, S.C. 1985. Sulfide precipitation of metals in aqueous systems:
selective precipitation and sludge stability. M.S. Thesis, University of Ken-
tucky, Lexington.
Kamaraj, P., S. Jacob, and S. Srinivasan. 1989. Removal of heavy metals
from wastewater by sulphide precipitation technique. Bull. Electrochem.
5(8): 572-4.
Kamaraj, P., S. Jacob, N. Sathyamurthy, and D. Srinivasan. 1990. Short
communication: removal of heavy metals from waste water by sulphide
precipitation process. Indian J. Technol. 28: 718-20.
Kamaraj, P., S. Jacob, N. Sathyamurthy, and D. Srinivasan. 1991. Sulphide
precipitation technique in the removal of heavy metals. Indian J. Environ.
Health 33(2): 208-12.
Kawamura S. 1991. Integrated design of water treatment facilities. New
York: John Wiley and Sons, Inc.
Kelly, R.L., W.K. Gauger, and V.J. Srivastava. 1990. Application of
Fenton's reagent as a pretreatment step in biological degradation at
polyaromatic hydrocarbons. In Proc. Inst. of Gas Tech. Annual oil, gas,
coal and Environmental Biotechnology Symposium. New Orleans.
Kim, B.M. 1981. Treatment of metal containing wastewater with calcium
sulfide. In AIChE Sympos. Series, Water 1980 77(209): 39-48.
Kim, B.M., and P.A. Amodeo. 1983. Calcium sulfide process for treatment
of metal-containing wastes. Environ. Prog. 2(3): 175-80.
Klee, A., C.J. Rogers, and T. Tiernan. 1984. Ind. Environ. Res. Lab. Report,
EPA-600/2-84-071. Cincinnati: US EPA. (Avail. NTIS, Order No. PB.84-
170059, 75pp.)
C.6
-------
Appendix C
Kolthoff, I.M. 1932. Theory of coprecipitation - the formation and proper-
ties of crystalline precipitates. J. Phys. Chem. 36(3): 860.
Kernel, A. and C.J. Rogers. 1987. Chemical destruction of halogenated
aliphatic hydrocarbons, reacting with an alkali metal glycolate. U.S. Patent
4,675,464.
Kernel, A., Rogers, C.J., and H.L. Sparks. 1991a. Method for the destruc-
tion of halogenated organic compounds in a contaminated medium, poly-
ethylene glycol with alkali metal hydroxide. U.S. Patent No. 5,019,175.
May 28
Kornel, A., Rogers, C.J., and H.L. Sparks. 1991b. Method for the destruc-
tion of halogenated organic compounds in a contaminated medium, adding
alkali metal carbonates. U.S. Patent No. 5,039,350. Aug. 13.
Kornel, A., Rogers, C.J., and H.L. Sparks. 1991c. Method for the base cata-
lyzed decomposition of halogenated and nonhalogenated organic com-
pounds in a contaminated medium. U.S. Patent No. 5,064,526. Nov. 12.
Kotronarou A., G. Mills, and M.R. Hoffmann. 1991. Ultrasonic irradiation
of p-nitrophenol in aqueous solution. J. Phys. Chem. 95:3630-8.
Kotronarou A., G. Mills, and M.R. Hoffmann. 1992. Decomposition of
parathion in aqueous solution by ultrasonic irradiation. Env. Sci. Tech.
26:1460-2.
Ku, Y. 1982. Sulfide precipitation of heavy metals: development of reaction
equilibrium model and establishment of chelating agents effect on precipita-
tion. M.S. Thesis, University of Kentucky, Lexington.
Ku, Y. 1986. Removal of heavy metals by sulfide precipitation in the pres-
ence of complexing agents. Ph.D. diss., Purdue University, West Lafayette,
Ind.
Ku, Y., and R.W. Peters. 1986. The effect of weak chelating agents on the
removal of heavy metals by precipitation processes. Environ. Prog. 5(3):
147-53.
Ku, Y., and R.W. Peters. 1988. The effect of complexing agents on the
precipitation and removal of copper and nickel from solution. Paniculate
Sci. and Technol. 6(4): 441-66.
Kuo, W.G. 1992. Decolorizing dye wastewater with Fenton's reagent. Wa-
ter Research 26:881-6.
C.7
-------
List of References
Kurucz C., T. Waite, W. Cooper, and M. Nickelsen. 1990. Full-scale elec-
tron beam treatment of hazardous wastes-effectiveness and costs. In Proc.
45th Industrial Waste Conference. Chelsea, Mich.: Lewis Publishers.
Kusakabe K., S. Aso, T. Wada, J. Hayashi, S. Morooka, and K. Isomura.
1991. Destruction rate of volatile organochlorine compounds in water by
ozonation with ultraviolet radiation. Water Research 25(10): 1199-203.
Langlais B., D.A. Reckhow, and D.R. Brink. 1991. Ozone in water treat-
ment: application and engineering. Denver: American Water Works Assoc.
Research Foundation.
Leckie, J.O., D.T. Merrill, and W. Chow. 1985. Trace element removal
from power plant waste streams by adsorption/ coprecipitation with amor-
phous iron oxyhydroxide. In AIChE Sympos. Series, Separation of Heavy
Metals and Other Trace Contaminants 81(243): 28-42.
Legube B. 1985. Identification of a few organics and attempted quantifica-
tion upon disinfection with ozone of a biologically treated waste water. In
Proc. Intl. Conf, The Role of Ozone in Water and Wastewater Treatment,
ed. R. Perry and R. E. Mclntyre. Selper, LTD. London.
Legube B. 1986. Ozonation of naphthalene in aqueous solution a) Part 1:
Ozone consumption and ozonation products; b) Part 2: Kinetics studies of
the initial reaction step. Water Research 20:197.
Lowry T.H. and K.S. Richardson. 1981. Mechanism and theory in organic
chemistry. 2d ed. New York: Harper and Row Publishers.
Macomber, R.S., M. Orchin, G. Garrett, and H. Braus. 1983. Im-house re-
port on KPEG technology fields of new KPEG Reactor on PCDD contami-
nated soils. Contract No. 68-03-2846 EPA, Modification, No. 46. Univer-
sity of Cincinnati, Ohio. Feb. 24, 1987.
Magrini K., R. Goggin, A. Watt, and A. Taylor. 1992. Water composition
effects on the photocatalytic oxidation of aqueous trichloroethylene. Paper
presented at Spring Meeting of the American Chemical Society, April, in
San Francisco.
Manilal V., A. Haridas, R. Alexander, and G. Surender. 1992.
Photocatalytic treatment of toxic organics in wastewater: toxicity of
photodegradation products. Wat. Res. 26(8): 1035-8.
C.8
-------
Appendix C
Maruyama, T., S.A. Hannah, and J.M. Cohen. 1975. Metal removal by
physical and chemical treatment processes. /. Water Pollut. Contr. Fed.
47(5): 962-75.
Matsuzuru, H., M. Toshikuni, A. Yamanaka, and N. Moriyama. 1982. Oxi-
dative degradation of powdered cation exchange resin by Fell. Catalyzed
hydrogen peroxide 23. Report Number JAERI-M-82-087. Japan Atomic
Energy Institute.
Matthews R.W. 1987. Solar-electric water purification using photocatalytic
oxidation with TiO2 as a stationary phase. Solar Energy 38(6): 405-13.
Matthews R.W. 1988. Kinetics of photocatalytic oxidation of organic sol-
utes over titanium dioxide. J. of Catalysis 111:264-72.
McAnally, S.L., L. Benefield, and R.B. Reed. 1984. Nickel removal from a
synthetic nickel-plating wastewater using sulfide and carbonate for precipi-
tation and coprecipitation. Sep. Sci. Technol. 192(3): 191-217.
McFadden, F., L. Benefield, and R.B. Reed. 1985. Nickel removal from
nickel plating wastewater using iron, carbonate, and polymers for precipita-
tion and co-precipitation. In Proc. 40th Purdue Indus. Waste Conf. 40:417-
29.
J.M. Montgomery Consulting Engineers. 1985. Water treatment principles
and design. New York: John Wiley and Sons, Inc.
Neuman, R. and Y. Sasson. 1983. Mechanism of base catalyzed reactions in
phase-transfer systems with polyethylene glycol as catalysts. Tetrahedron
20:3734-37.
Newkirk, D.D., M.G. Warner, and S. Barros. 1981. Treatability studies on
heavy metal removal in selected inorganic chemical industries. In Proc.
36th Purdue Indus. Waste Conf. 36:17-28.
Nickelsen M., W. Cooper, C. Kurucz, and T. Waite. 1992. Removal of ben-
zene and selected alkyl-substituted benzenes from aqueous solution utiliz-
ing continuous high-energy electron irradiation. Env. Sci. Tech. 26:144-52.
Ogata, Y., K. Tomizawa, and K. Takagi. 1981. Photooxidation of formic,
acetic and proprionic acids with aqueous hydrogen peroxide. Canadian J. of
Chemistry 59:14.
C.9
-------
List of References
Ollis D.F., E. Pelizzetti and N. Serpone. 1989. Heterogeneous
photocatalysis in the environment: application to water purification. In
Photocatalysis -fundamentals and applications, ed. N. Serpone and E.
Pelizzetti, 603-637. New York: Wiley.
Ollis, D. 1985. Contaminant degradation in water. Env. Sci. Tech. 19(6):
480-4.
Osaki, S., S. Sugihara, and T. Kaji. 1990. Treatment of radioactive waste
phenol with Fenton's oxidation, Radioisotopes. 39:174-7.
Patterson, J.W. 1988. Metal treatment and recovery. In Metal speciation:
theory, analysis, and application, ed. J.R. Kramer and H.E. Allen, 333-345.
Chelsea, Mich: Lewis Publishers, Inc.
Patterson, J.W., and R.A. Minear. 1975. Physical-chemical methods of
heavy metals removal. In Heavy metals in the aquatic environment, ed. P. A.
Krenkel, 261-276. Oxford, England: Pergamon Press.
Patterson, J.W., H.E. Allen, and JJ. Scala. 1977. Carbonate precipitation
for heavy metals pollutants. /. Water Pollut. Control Fed. 49(12): 2397-
410.
Pelizzetti E., C. Minero and V. Maurino. 1990. Adv. Colloid Interface Sci.
32:271-316.
Perry, J.H., C.H. Chilton, and S.D. Kirkpatrick. 1963. Chemical engineers'
handbook. New York: McGraw Hill Book Company.
Peters, R.W., and T.-K. Chang. 1984. Removal of heavy metals by
coprecipitation and adsorption on the lime-soda ash water softening pro-
cess. In Proc. 15th Annual Meeting of the Fine Particle Society. Orlando,
Ha. August 19-22.
Peters, R.W, and T.-K. Chang. 1985. The effect of particle size distribution
and morphology of CaCO3 precipitation in the presence of Zn and Cd. In
Proc. 16th Annual Meeting of the Fine Particle Society. Miami Beach, Fla.
April 22-26.
Peters, R.W., and Y. Ku. 1984. Removal of heavy metals from industrial
plating wastewaters by sulfide precipitation, 279-311. In Proc. Industrial
Wastes Symposia, 57th Water Pollution Control Federation Annual Confer-
ence.
C.10
-------
Appendix C
Peters, R.W., and Y. Ku. 1985. Batch precipitation studies for heavy metal
removal by sulfide precipitation. In AIChE Sytnpos. Series, Separation of
Heavy Metals and Other Contaminants 81(243): 9-27.
Peters, R.W., and Y. Ku. 1987. The effect of citrate, a weak complexing
agent, on the removal of heavy metals by sulfide precipitation, 147-169. In
Metals speciation, separation, and recovery, ed. J.W. Patterson and R.
Passino. Chelsea, Mich.: Lewis Publishers, Inc.
Peters, R.W., and Y. Ku. 1988. The effect of tartrate, a weak complexing
agent, on the removal of heavy metals by sulfide and hydroxide precipita-
tion. Paniculate Sci. and Technol. 6(4): 421-39.
Peters, R.W., E. Eriksen, and Y. Ku. 1985. Segregated removal of heavy
metal species from mixed-metal plating wastewaters by selective precipita-
tion. In Proc. 1985 Triangle Conference on Environmental Technology.
Raleigh, N.C. April 3-4.
Peters, R.W., Y. Ku, and D. Bhattacharyya. 1984. The effect of chelating
agents on the removal of heavy metals by sulfide precipitation. In Proc.
16th Mid-Atlantic Indus. Waste Conf. 16:289-317.
Peters, R.W., Y. Ku, and D. Bhattacharyya. 1985. Evaluation of recent
treatment techniques for removal of heavy metals from industrial wastewa-
ters. In AIChE Sympos. Series, Separation of Heavy Metals and Other Con-
taminants 81(243): 165-203.
Peters, R.W., Y. Ku, D. Bhattacharyya, and L.-F. Chen. 1984. Crystal size
distribution of sulfide precipitation of heavy metals, industrial crystalliza-
tion, 84:111-23. In Proc. 9th Sympos. Indus. Crystal. The Hague, Nether-
lands. September 25-28.
Peterson, R.L. 1986. Method for decontaminating soil. U.S. Patent No.
4,574,013. March 4.
Pignatello, J.J. 1992. Dark and photo-assisted Fe3+-catalyzed degradation
of chlorophenoxy herbicides by hydrogen peroxide. Env. Sci. and Tech.
26:944-51.
Powers, R.E. 1985. On scene coordinator's report, CERCLA immediate
removal project. Romulus, Mich.: PBM Enterprises. Dec. 16.
Pugsley, E.B., C.Y. Cheng, D.M. Updegraff, and L.W. Ross. 1970. Re-
moval of heavy metals from mine drainage in Colorado by precipitation.
Chem. Engrg. Prog. Sympos. Series, Water -1970 67(107): 75-89.
C.ll
-------
List of References
Purbaugh, T. 1992. Telephone conversation with J. Verbicky. June 6.
Rabosky, J.G., and T. Altares, Jr. 1983. Wastewater treatment of a small
chrome plating shop: a case history. In Proc. 38th Purdue Indus. Waste
Conf. 38:449-56.
Reynolds G. 1989. Aqueous ozonation of pesticides: a review. Ozone Sci.
Engrg. 11:339.
Rice, R.G. 1981. Ozone for the treatment of hazardous materials. In Proc.
WATER-J980 Symposium Series. American Institute of Chemical Engi-
neers. 29(77): 79-107.
RadTech. 1992. Proceedings of RadTech North America Conference.
Rogers, C.J. 1983. Incineration treatment of hazardous waste. In Proc. 8th
Annual Research Syymposium, 197-201. EPA600/9 83-003, PB83-210450.
Res. Dev. (Rep.). Cincinnati: US EPA.
Rowland, M.A. 1989. Groundwater treatment with ultraviolet light and
hydrogen peroxide. In Proc. National Water Well Association Outdoor
Action Conference, 659-672.
Salutsky, M.L. 1959. Precipitates: their formation, properties, and purity. In
Treatise on analytical chemistry, ed. I.M. Kolthoff and P.J. Elving, Part I,
Vol. I, Sec. B. New York: Interscience.
Sawyer, C.N., and P.L. McCarty. 1978. Chemistry for environmental engi-
neering. 3d ed. New York: McGraw-Hill Book Co.
Schiavello, M., ed. 1988. Photocatalysis and environment. Dortrecht:
Kluwer.
Schlauch, R.M., and A.C. Epstein. 1977. Treatment of metal finishing
wastes by sulfide precipitation. EPA Report. EPA 600/2-77-049. Cincin-
nati: US EPA
Scott, M.C. 1979. An EPA demonstration plant for heavy metals removal
by sulfide precipitation, 126. In Proc. 2nd Conf. Adv. Pollut. Contr.for
Metal Fin. Indus. EPA 600/8-79-014.
Sedlak, D.L. and A.W. Andren. 1991. Oxidation of chlorobenzene with
Fenton's reagent. Env. Sci. and Tech. 25:777-82.
Sehested K., H. Corfitzen, J. Holcman, C.H. Fischer, and E.J. Hart. 1991.
The primary reaction in the decomposition of ozone in acidic aqueous solu-
tions. Env. Sci. and Tech. 25:1589-96.
C.12
-------
Appendix C
Sheffield, C.W. 1981. Treatment of heavy metals at small electroplating
plants. In Proc, 36th Purdue Indus. Waste Conf. 36:485-92.
Sillen, L.G., and A.E. Martell. 1971. Stability constants of metal ion com-
plexes. London: Chemical Society.
Singh A. 1986. Chemical and biochemical aspects of activated oxygen:
singlet oxygen, superoxide anion, and related species. In Handbook of free
radicals and antioxidants in biomedicine, ed. J. Miguel, A.T. Quintanilha,
and H. Weber, Vol. 1,17-27. CRC Press.
Singh A., N. Sagert, J. Borsa, H. Singh, and G. Bennett. 1985. The use of
high-energy radiation for the treatment of wastewater: a review. In Proc.
8th Wastewater Treatment Conference, Environment. Montreal, Canada.
Nov.
Singh A., W. Kremers, P. Smalley, and G. Bennett. 1985. Radiolytic
dechlorination of polychlorinated biphenyls. Radiat. Phys. Chem. 25(1): 11-
9.
Smith, O.K. 1988. Application of UV lamp technology for water treatment
or sterilization. By-products and environmental impact. Report No. 647 U
588. Canadian Electrical Association.
Smith, J.F. and G.L. Bubbar. 1979. The chemical destruction of polychlori-
nated biphenyls by sodium naphthalenide. Report from the Guelph-Water-
loo Centre for Graduate Work in Chemistry, Department of Chemistry,
University of Waterloo. Waterloo, Ontario: University of Waterloo.
Smith, R.M., and A.E. Martell. 1976. Critical stability constants. New
York: Plenum Press, Inc.
Snoeyink, V.L., and D. Jenkins. 1980. Water chemistry. New York: John
Wiley and Sons, Inc.
Somich C.J., M.T. Muldoon, and P.C. Dearney. 1990. On-site treatment of
pesticide waste and rinsate using ozone and biologically active soil. Env.
Sci. and Tech. 24:745-9.
Sorg, T.J. 1979. Treatment technology to meet the interim primary drinking
water regulations for organics: part 4. /. Am. Water Works Assoc. 71(8):
454-66.
C.13
-------
List of References
Sorg, T.J., M. Csanady, and G.S. Logsdon. 1978. Treatment technology to
meet the interim primary drinking water regulations for inorganics: part 3.
J. Am. Water Works Assoc. 70(12): 680-91.
Stafford U., K.A. Gray, P. Kamat, and A. Varma. 1993. An in-situ diffuse
reflectance FTIR investigation of photocatalytic degradation of 4-
chlorophenol on a TiO2 powder surface. Chem. Phys. 205(1): 55-61.
Stowell J. and Jensen J. 1991. Dechlorination of chlorendic acid with
ozone. Water Research 25(1) 83-90.
Sundstrom, D.W. and H.E. Klei. 1986. Destruction of hazardous com-
pounds by ultraviolet catalyzed oxidation with hydrogen peroxide. Report
#PB87-149357. NTIS.
Taciuk, W. 1979. Process for thermal cracking a heavy hydrocarbon. U.S.
Patent 4,180,455. Dec. 25.
Taciuk, W. 1981a. Process for recovery of hydrocarbons from inorganic
host materials comprising oil sands containing clay and bitumen. U.S.
Patent 4,280,879. July 28.
Taciuk, W. 1981b. Apparatus and process for recovery of hydrocarbons
from inorganic host materials. U.S. Patent 4,306,961. Dec. 22.
Talbot, R.S. 1984. Co-precipitation of heavy metals with soluble sulfides
using statistics for process control. In Proc. 16th Mid-Atlantic Indus. Waste
Conf. 16:279-88.
Tate, B. 1991. New oxidation process scrubs contaminated soil. US Army
Corps of Engineers, Engineer Update. July.
Turchi C. speaker. 1992. Pilot-scale study of the solar detoxification of
VOC contaminated groundwater. Paper presented at 7992 Summer Meeting
of the American Institute of Chemical Engineers. Minneapolis,.
Turchi C.S. and D.F. Ollis. 1990. Photocatalytic degradation of organic
water contaminants: mechanisms involving hydroxyl radical attack. /. of
Catalysis 122:178-92.
Ultrox Process Brochures. 2435 South Anne Street, Santa Ana, Ca.
US EPA. 1978. Manual of treatment techniques for meeting the interim
primary drinking water regulations. EPA 600/8-77-005.
C.14
-------
Appendix C
US EPA. 1980. Summary report: control and treatment technology for the
metal finishing industry; sulfide precipitation. EPA 625/8-80-003.
US EPA. 1989. Technology evaluation report and the applications analysis
report. Superfund innovative technology evaluation program. EPA/540/5-
89/012, EPA/540/A5-89/012. Ultrox International.
US EPA. 1990. Handbook on in-situ treatment of hazardous waste contami-
nated soils, 22-23. EPA/540/2-90/002.
US EPA. 1992a. Alternative Treatment Technology Information Center
(ATTIC) (data base). Office of Solid Waste and Emergency Response,
Technology Innovation Office. Washington, D.C.
US EPA. 1992b. Synopses of federal demonstrations of innovative site
remediation technologies 58. Federal Remediation Technologies
Roundtable Report. Contract No. 68-W2-004.
US EPA. 1992c. SoilTech Anaerobic Thermal Processor, Outboard Marine
Corporation site. EPA 540/MR-92/078
US EPA. 1992d. Technology evaluation report, SoilTech/Anaerobic ther-
mal processor technology. EPA/540/XX-XX/XXX. SITE Demonstration
Bulletin, RREL Draft Report.
Vasilenko, I.I. and A.N. Fedosoua. 1987. Liquid phase heterocatalytic oxi-
dation of phenol by hydrogen peroxide on magnetite. Zhurnal Prikladnoi
Khimii 60(4): 870-3.
Walling, C. 1975. Fenton's reagent revisited. Ace. Chem. Res. 8:125-31.
Watts, R.J., B.W. Tyre, and G.C. Miller. 1991. Treatment of four
biorefractory contaminants in soils using catalyzed hydrogen peroxide. /.
Environ. Qual. 20:832-8.
Weitzman, L. 1982. Treatment and destruction of polychlorinated biphenyls
and PCB-contaminated materials. In Proc. Detoxification of Hazardous
Waste, 131. ACS. New York. Aug., 1981.
Wekhof A. 1991. Treatment of contaminated water, air and soil with UV
flashlamps. Env. Progress 10(4): 241-7.
C.15
-------
List of References
Wentsel, R.S., S. Sommerer, and J.F. Kitchens. 1981. Engineering and
development support of general decon technology for the DAKCOM instal-
lation restoration program, task 2. Literature review on treatment of con-
taminated lagoon sediment- phase I. Report under US Army T'oxic and
Hazardous Materials Agency contract No. DAAK11-80-C-0027. Alexan-
dria, Va.: Atlantic Research Corporation.
Whang, J.S., D. Young, and M. Pressman. 1981. Design of soluble sulfide
precipitation system for heavy metals removal. In Proc. 13th Mid-Atlantic
Indus. Waste Conf. 13:63-71.
Wing, R.E. 1974. Heavy metal removal from wastewater with starch xan-
thate. In Proc. 29th Purdue Indus. Waste Conf. 29:348-56.
Wing, R.E., and W.E. Rayford. 1976. Starch-based products effective in
heavy metal removal. In Proc. 31st Purdue Indus. Waste Conf. 31:1068-79.
Wing, R.E., and W.E. Rayford. 1977. Heavy metal removal processes for
plating rinse waters. In Proc. 30th Purdue Indus. Waste Conf. 30:838-52.
Wing, R.E., L.L. NaVickis, B.K. Jusberg, and W.E. Rayford. 1978. Re-
moval of heavy metals from industrial wastewaters using insoluble starch
xanthates. EPA 600/2-78-085. Cincinnati: US EPA, Office of Research and
Development.
Wing, R.E., W.N. Doane, and C.R. Russell. 1975. Insoluble starch xanthate:
use in heavy metal removal. /. Appl. Polym. Sci. 19:.
Yanagida, S., K. Takahashi, and M. Okahara. 1977. Metal ion complexation
of noncyclic poly(oxyethylene) derivatives. Part IV para transfer catalysis
of poly(oxyethylene) dimethyl ethers. Bull. Chem. Soc. Japan 50:1386.
Yao, C.C.D. and W.R. Haag. 1991. Rate constants for direct reactions of
ozone with several drinking water contaminants. Water Research 25:761-
73.
Zepp, R.G., B.C. Faust, and J. Hoigne. 1992. Hydroxyl radical formation in
aqueous reactions pH 3-8, of iron II with hydrogen peroxide: the Photo-
Fenton Reaction. Environmental Science and Technology 26:313-9.
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Appendix D
APPENDIX D
Suggested Reading List
Exner, J.H., ed. 1981. Detoxification of hazardous waste. Ann Arbor,
Mich.: Ann Arbor Science.
US EPA. 1991. Bibliography of federal reports and publications describing
alternative and innovative treatment technologies for corrective action and
site remediation. Federal Remediation Technologies Roundtable. EPA/540/
8-91/007. Office of Solid Waste and Emergency Response, Technology
Innovation Office. Washington, D.C. May.
US EPA. 1991. Innovative treatment technologies, overview and guide to
information sources. EPA/540/2-91/002. Technology Innovation Office,
Office of Solid Waste and Emergency Response. Washington, D.C. Oct.
US EPA. 1991. Innovative treatment technologies, semi-annual status re-
port, No. 2. EPA/540/2-91/001. Technology Innovation Office, Office of
Solid Waste and Emergency Response. Washington, D.C. Sept.
US EPA. 1991. Selected alternative and innovative treatment technologies
for corrective action and site remediation a bibliography of EPA informa-
tion resources, fall update. EPA/540/8-91/092. Technology Innovation
Office, Office of Solid Waste and Emergency Response. Washington, D.C.
Nov.
US EPA. 1991. Synopses of federal demonstrations of innovative site
remediation technologies. Federal Remediation Technologies Roundtable.
EPA/540/8-91/009. Washington, D.C. May.
US EPA. 1991. Papers presented at Third Forum on Innovative Hazardous
Waste Treatment Technologies: Domestic and International. Dallas. June
11-13. EPA/540/2-91/015. Office of Solid Waste and Emergency Response,
Technology Innovation Office and Risk Reduction Engineering Laboratory,
Cincinnati. Washington, D.C. Sept.
D.I
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Suggested Reading List
US EPA. 1992. Literature survey of innovative technologies for hazardous
waste site remediation 1987—7997. Preliminary Draft. Office of Solid
Waste and Emergency Response, Technology Innovation Office. Washing-
ton, D.C. Feb.
D.2
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