TREATMENT TECHNOLOGY BACKGROUND DOCUMENT
             Larry  Rosengrant
              Section Chief

               Laura Lopez
             Project Officer
  U.S. Environmental  Protection Agency
          Office of Solid Waste
             401  M  Street,  SW
          Washington, DC  20460
               January 1991
                                'iVl Printed on Recycled Paper

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                               TABLE OF CONTENTS


Section                                                           Page No.


EXECUTIVE SUMMARY  	     viii

      Applicability  	     xi
      Underlying Principles of Operation 	     xiii
      Description of the Treatment  Process 	     xiv
      Waste Characteristics Affecting Performance (WCAPs)  ...     xv
      Design and Operating Parameters   	     xvii


                          I.  TREATMENT TECHNOLOGIES

A.    DESTRUCTION TECHNOLOGIES

      1.    BIOLOGICAL TREATMENT 	     1

      1.1   Applicability  	     1
      1.2   Underlying Principles of Operation ...  	     1
      1.3   Description of Biological Treatment Processes  ...     3
      1.4   Waste Characteristics Affecting Performance  (WCAPs).     8
      1.5   Design and Operating Parameters   	     11
      1.6   References	     16

      2.    CHEMICAL OXIDATION  	     17

      2.1   Applicability	'.  .  .     17
      2.2   Underlying Principles of Operation 	     18
      2.3   Description of Chemical Oxidation Processes   ....     21
      2.4   Waste Characteristics Affecting Performance  (WCAPs).     23
      2.5   Design and Operating Parameters   	     24
      2.6   References	     28

      3.    CHEMICAL REDUCTION  	     29

      3.1   Applicability	     29
      3.2   Underlying Principles of Operation 	     29
      3.3   Description of Chemical Reduction Process   	     30
      3.4   Waste Characteristics Affecting Performance  (WCAPs).     32
      3.5   Design and Operating Parameters   	     33
      3.6   References	     37
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                         TABLE OF CONTENTS (CONTINUED)


Section                                                           Page No.


      4.    ELECTROLYTIC OXIDATION OF CYANIDE  	     38

      4.1   Applicability	     38
      4.2   Underlying Principles of Operation 	     38
      4.3   Description of Electrolytic Oxidation of Cyanide
              Process	     39
      4.4   Waste Characteristics Affecting Performance (WCAPs).     39
      4.5   Design and Operating Parameters  	     40
      4.6   References	     43

      5.    INCINERATION	     44

      5.1   Applicability	     44
      5.2   Underlying Principles of Operation 	     45
      5.3   Description of Incineration Process  	     46
      5.4   Waste Characteristics Affecting Performance (WCAPs).     54
      5.5   Design and Operating Parameters  	     57
      5.6   References	     63

      6.    WET AIR OXIDATION	     64

      6.1   Applicability	     64
      6.2   Underlying Principles of Operation 	     66
      6.3   Description of Wet Air Oxidation Process	     66
      6.4   Waste Characteristics Affecting Performance (WCAPs).     67
      6.5   Design and Operating Parameters  	     70
      6.6   References	     73

B.    TECHNOLOGIES THAT REDUCE THE SOLUBILITY OR LEACHABILITY
      OF METALS

      1.    AMALGAMATION	     74

      1.1   Applicability	     74
      1.2   Underlying Principles of Operation 	     74
      1.3   Description of Amalgamation Treatment Processes  .  .     75
      1.4   Waste Characteristics Affecting Performance (WCAPs).     75
      1.5   Design and Operating Parameters  	     77
      1.6   References	     80
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                         TABLE OF CONTENTS (CONTINUED)


Section                                                           Page No.


      2.    CHEMICAL PRECIPITATION 	     81

      2.1   Applicability	     81
      2.2   Underlying Principles of Operation  	     82
      2.3   Description of Chemical Precipitation Process   ...     83
      2.4   Waste Characteristics Affecting Performance  (WCAPs).     85
      2.5   Design and Operating Parameters 	      89
      2.6   References	      93

      3.    ENCAPSULATION	      94

      3.1   Applicability	      94
      3.2   Underlying Principles of Operation   	      94
      3.3   Description of Encapsulation  Processes   	      94
      3.4   Waste Characteristics Affecting Performance  (WCAPs).     96
      3.5   Design and Operating Parameters	     98
      3.6   References	..	     101

      4.    STABILIZATION OF METALS	     102

      4.1   Applicability	     102
      4.2   Underlying Principles of Operation  	     102
      4.3   Description of Stabilization  Process  	     104
      4.4   Waste Characteristics Affecting Performance  (WCAPs).     104
      4.5   Design and Operating Parameters   	     106
      4.6   References	     110

      5.    VITRIFICATION	     Ill

      5.1   Applicability	     Ill
      5.2   Underlying Principles of Operation  	     112
      5.3   Description of Vitrification  Processes  	     113
      5.4   Waste Characteristics Affecting Performance  (WCAPs).     115
      5.5   Design and Operating Parameters   	     119
      5.6   References	     124
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                         TABLE OF CONTENTS (CONTINUED)


Section                                                           Page No.

                           II.  REMOVAL TECHNOLOGIES
A.    RECOVERY, REUSE, AND/OR SEPARATION TECHNOLOGIES FOR
      ORGANICS

      1.    CARBON ADSORPTION   	      125

      1.1   Applicability	      125
      1.2   Underlying Principles of Operation  	      125
      1.3   Description of  Carbon Adsorption Process 	      125
      1.4   Waste Characteristics Affecting Performance  (WCAPs).      129
      1.5   Design and Operating Parameters  	      130
      1.6   References	      133

      2.    DISTILLATION TECHNOLOGIES	      134

      2.1   Applicability	      134
      2.2   Underlying Principles of Operation  	      135
      2.3   Description of  Distillation Processes   	      137
      2.4   Waste Characteristics Affecting Performance  (WCAPs).      146
      2.5   Design and Operating Parameters  	      150
      2.6   References	      156

      3.    EXTRACTION TECHNOLOGIES  	      157

      3.1   Applicability	      157
      3.2   Underlying Principles of Operation  	      157
      3.3   Description of  Extraction Processes  	      158
      3.4   Waste Characteristics Affecting Performance  (WCAPs).      164
      3.5   Design and Operating Parameters  	      166
      3.6   References	      170

      4.    FUEL SUBSTITUTION	      171

      4.1   Applicability	      171
      4.2   Underlying Principles of Operation  	      174
      4.3   Description of  Fuel Substitution Process 	      174
      4.4   Waste Characteristics Affecting Performance  (WCAPs).      177
      4.5   Design and Operating Parameters  	      179
      4.6   References	      183
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                         TABLE OF CONTENTS (CONTINUED)


Section                                                           Page No,


B.    RECOVERY AND/OR SEPARATION TECHNOLOGIES FOR METALS

      1.    ACID LEACHING	     184

      1.1   Applicability	     184
      1.2   Underlying Principles of Operation 	     184
      1.3   Description of Acid Leaching  Process 	     185
      1.4   Waste Characteristics Affecting Performance (WCAPs).     186
      1.5   Design and Operating Parameters  	     188
      1.6   References	     190

      2.    FILTRATION TECHNOLOGIES  	     191

      2.1   Applicability	     191
      2.2   Underlying Principles of Operation 	     191
      2.3   Description of Filtration Processes  	     192
      2.4   Waste Characteristics Affecting Performance (WCAPs).     194
      2.5   Design and Operating Parameters  	     196
      2.6   References	     200

      3.    HIGH TEMPERATURE METALS RECOVERY 	     201

      3.1   Applicability  .  .	     201
      3.2   Underlying Principles of Operation 	     202
      3.3   Description of High Temperature Metals Recovery
              Process	     202
      3.4   Waste Characteristics Affecting Performance (WCAPs).     205
      3.5   Design and Operating Parameters  	     206
      3.6   References	     210

      4.    ION EXCHANGE	     211

      4.1   Applicability	     211
      4.2   Underlying Principles of Operation 	     211
      4.3   Description of Ion Exchange Process  	     212
      4.4   Waste Characteristics Affecting Performance (WCAPs).     213
      4.5   Design and Operating Parameters  	     217
      4.6   References	     220
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                         TABLE OF CONTENTS (CONTINUED)


Section                                                            Page  No,


      5.    RETORTING	      221

      5.1   Applicability	      221
      5.2   Underlying  Principles of Operation  	      221
      5.3   Description of  Retorting Process  	      222
      5.4   Waste Characteristics Affecting Performance  (WCAPs).      225
      5.5   Design and Operating Parameters   	      227
      5.6   References	      228
                 III.  TECHNOLOGIES APPLICABLE TO HIXED WASTE
                            (RADIOACTIVE/HAZARDOUS)


INTRODUCTION 	      229

A.    TECHNOLOGIES FOR WASTES CONTAINING ORGANICS AND
      INORGANICS OTHER THAN METALS  	      231

      1.    Carbon Adsorption   	      231
      2.    Distillation Technologies   	      231
      3.    Extraction Technologies   	      232

B.    TECHNOLOGIES FOR NIXED WASTES CONTAINING METALS  	      233

      1.    Acid Leaching	      233
      2.    Chemical Precipitation  	      233
      3.    Filtration	      233
      4.    High Temperature Metals Recovery  	      233
      5.    Ion Exchange	      234
      6.    Stabilization of Metals   	      234

C.    TECHNOLOGIES FOR MIXED WASTES IN  SPECIAL TREATABILITY
      GROUPS	      235

      1.    Amalgamation	      235
      2.    Encapsulation	      235
      3.    Vitrification	      236
      4.    Incineration	      237

REFERENCES	      238
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                         TABLE OF CONTENTS (CONTINUED)


Section                                                           Page No.
APPENDIX A  List of Best Demonstrated Available Technology  (BOAT)
            Background Documents and Associated BDAT(s)   ....     A-l
                                LIST OF FIGURES

Figure                                                             Page No.

  1   Activated Sludge System   	     4
  2   Trickling Filter System   	     7
  3   Anaerobic Digestion	     9
  4   Continuous Chemical Reduction System	     31
  5   Liquid Injection Incineration System  	     49
  6   Rotary Kiln Incineration  System   	     50
  7   Fluidized Bed Incineration System   	     52
  8   Fixed Hearth Incineration System  	     53
  9   Continuous Wet Air Oxidation System  	     68
 10   Continuous Chemical Precipitation System  	     84
 11   Circular Clarifier Systems    	     86
 12   Inclined Plate Settler System   	     87
 13   Carbon Adsorption Systems  	     127
 14   Plot of Breakthrough  Curve	     128
 15   Batch Distillation System-	     138
 16   Fractionation System  	     140
 17   Steam Stripping System 	     142
 18   Thin Film Evaporation System	     143
 19   Screw Flight Dryer 	     145
 20   Two-Stage Mixer-Settler Solvent Extraction  System   ....     160
 21   Packed and Sieve Tray Solvent Extraction  Columns  	     162
 22   High Temperature Metals Recovery  System   	     203
 23   Two-Step Cation/Anion Ion Exchange  System  	     214
 24   Retorting Process (Without a Scrubber and Subsequent
        Wastewater Discharge)   	     223
 25   Retorting Process (With a Scrubber  and Subsequent
        Wastewater Discharge)   	     224
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                               EXECUTIVE SUMMARY

      This  document  provides  a  discussion   of  the  treatment  technologies
applicable to wastes that are subject to the Land Disposal Restrictions (LDR),
which were mandated  by  Congress  as part of the 1984 Hazardous and Solid Waste
Amendments (HSWA) to the  Resource  Conservation and  Recovery Act (RCRA).  This
document does not include every  possible technology that may be used to treat
wastes  subject  to  the  LDR,  but  discusses those  most  commonly  used.   The
technologies  discussed  include  those  that   are   demonstrated  (commercially
available)  and  have  been proven  to substantially  diminish the  toxicity of
hazardous constituents  and/or to  reduce the  likelihood  of  migration of such
constituents from the waste of concern.  These  technologies  include those that
treat wastewaters* and  those that  treat  nonwastewaters.

      Treatment performance data from technologies  discussed in this document
were  the basis  for  the  determination  of the  Best  Demonstrated   Available
Technology (BOAT),  from which  the Land Disposal  Restrictions treatment  standards
were promulgated (as numerical standards or methods  of treatment).  Information
supporting the  development of these  treatment standards may be  found  in the
applicable background documents prepared for EPA's Office of Solid Waste, Waste
Treatment Branch.   These BOAT background documents  contain  information on the
following:   industries  affected  and  waste characterization,  applicable and
demonstrated treatment technologies for the wastes of concern, determination of
BOAT, and treatment  performance  data with design and operating conditions.
*For  the  purpose  of the  Land  Disposal   Restrictions   rule, wastewaters  are
 defined  as  wastes  containing  less  than  or  equal   to   1  percent  (weight
 basis)  filterable  solids  and  less  than  or  equal   to   1  percent  (weight
 basis)  total  organic  carbon  (TOC).  Wastes  not  meeting  this  definition
 are classified as nonwastewaters.
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      The  methodology EPA  used to  develop the  BOAT treatment  standards is
described in two separate documents:  Generic Quality Assurance Project  Plan for
Land Disposal  Restrictions  Program ("BOAT") (USEPA  1990)  and Methodology for
Developing  BOAT Treatment  Standards  (USEPA  1990).   The  second  document also
discusses the petition process to be followed in  requesting  a  variance  from the
BDAT treatment  standards.

      Appendix A lists the  background documents developed  for  the BDAT  program,
identifying  the technologies  and  the  types of constituents treated  (e.g.,
organics, inorganics, metals,  etc.) when present in actual  treatment performance
data.

      The  treatment  performance data and  the  design and operating  data  (see
Section 5  of this  executive summary for a  discussion  of  design  and operating
data) contained in these documents may be  used to help determine  whether a
treatment  system  has  been designed and  operated  properly.    The  treatment
performance  data  from these  background documents may be used to  compare the
performance  of a  treatment  system  of  concern  treating  the  same  or similar
constituents  (provided  the  waste matrices  are not significantly dissimilar).
Comparisons can be  made  of the destruction or removal  efficiencies,  the  level of
treatment  achieved,  and  the design and operating  parameters  of  a system  (for
example,  feed  rate,  temperature,   and  oxygen  concentration  for incineration
systems or concentration of nutrients, dissolved oxygen, residence time,  etc. for
biological treatment systems).

      One  document  that  may be particularly helpful  is  the F039 (Multisource
Leachate) background document, Volumes A through  E (USEPA  1990).  This  document
contains comprehensive treatment performance data covering the complete list of
P and U  waste code constituents.  The nonwastewater data, for the most  part, were
derived from 11 incineration test burns  for the organics and from stabilization
treatment for the metals.  The wastewater data were derived from various sources
such  as EPA's  Office of  Water's  Industrial  Technology  Division  (ITD),  the

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National  Pollutant Discharge  Elimination System  (NPDES), Water  Engineering
Research  Laboratory  (WERL),  and other  data  sources available  to  the Agency.
These  above-mentioned  data were generally considered to  represent long-term
sampling, with  many  data  sets  meeting  EPA's criteria for quality assurance/
quality control.   Hence,  treatment performance data  from  the F039 background
document  and other BOAT documents  may be  used as  a  basis  for comparison when
evaluating the performance of other treatment systems.

      The Agency wishes to point out  that additional information on treatment
technologies may  be  obtained  through EPA's Alternative  Treatment Technology
Information Center (ATTIC), operated by  the Office  of Environmental Engineering
and Technology Demonstration.  The ATTIC  is an information retrieval  network that
provides  up-to-date technical  information on innovative treatment methods for
hazardous wastes.    The ATTIC  provides  information on  innovative treatment
technologies, cost analysis,  and migration  and  sampling  data bases; provides
information on experts who can be contacted for assistance; and  is  a source for
locating  and ordering documents.

      Also,  the EPA Office of Waste Programs Enforcement has  tapes  and manuals
for Inspectors of  Incinerators  (only  available to  EPA personnel).   Information
include  an  introduction  to  incinerator  design,  air pollution  control,  and
regulatory  guidance.   Further  information may be obtained  by  contacting the
Regional  RCRA training coordinator.

      The treatment technologies presented in this  document have been organized
into three  separate groups according  to how  they treat waste  and to what types
of waste they are  applicable:  (1) treatment technologies that destroy or reduce
the  migration  of  wastes;  (2) removal  technologies  that  separate or recover
constituents for  recycle/reuse or treatment;  and  (3) technologies that treat
mixed  waste,  i.e.,  hazardous/radioactive  waste.    Although  some  of  the
technologies can belong to more than one group, each  technology  has been placed
in the group where it is most commonly  used.

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      The remainder of this introduction describes the purpose and contents of
each  of   the  various   elements   presented  in  each   technology  section:
applicability, underlying principles of operation, description of the technology,
waste characteristics  affecting performance, and design and operating parameters.
Specifically  explained  are what  information is  provided in  each  technology
subsection, how the Agency  uses this  information  as  part of its BOAT program,
and, when applicable,  how the  Agency intends to modify the treatment technology
discussions as more treatment data and information become available.

1.    Applicability

      (a)   Information Provided.  The applicability section contains information
on the general application of  the treatment technology to various wastes.  EPA's
analysis of applicability is  performed in  consideration of the parameters and
constituents known to  affect treatment selection.  That is, in order to identify
whether a treatment technology was applicable to any particular waste stream, the
Agency considered all  parameters and characteristics associated  with a hazardous
waste that could affect the selection  of a  treatment technology.  EPA uses the
acronym  PATS  (i.e.,   parameters   affecting  treatment   selection)  for  these
parameters.

      EPA's list of PATS,  shown in Table 1,  identifies all known  constituents and
parameters that are needed to  select a technology or technology train  for a given
waste.

      It is important to point out that in  developing this list,  EPA's goal was
to determine the demonstrated  technology or  treatment technology train that would
best  treat  all of  the constituents  in the  waste  (i.e., achieve  the  lowest
concentration  in  the  residual).   Accordingly, EPA will  add  components  to the
treatment train as long as they are demonstrated and will  achieve statistically
significant reduction in  the  concentrations of  the  constituents.  (Note:  the
statistical analysis that the Agency  uses  to determine whether  a significant

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          Table  1   List  of Parameters  Affecting Treatment Selection

      BOAT list metals content
      BOAT list organics content
      Content of other BOAT constituents  (sulfides and  fluorides)
      Biological  oxygen demand (BOD)
      Btu content
      Presence of complexed metals
      Cyanide content
      Filterable solids content
      Oil and grease content
      Oxidation state
      pH
      Total  organic carbon  (TOC) content
      Total  organic halides (TOX) content
      Viscosity
      Water content
      Selectivity value
      Sublimation temperature
      Ash fusion temperature
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reduction in constituents  has  occurred  is  referred to as Analysis of Variance
(ANOVA).   Refer to  the Methodology  for Developing  BOAT  Treatment Standards
document for further information.)

      (b)   EPA's Use of This  Information.  EPA uses  the PATS as the basis for
making decisions regarding whether a particular technology is "demonstrated" for
a particular waste.   The Agency is performing treatment tests on  specific wastes
to "demonstrate" the treatment of the waste  using the technology, to develop
treatment standards,  and  to  set the criteria by  which  other wastes  can be
regulated using the demonstrated technology.

      The PATS analysis  will  sometimes  show that  several  technologies are
applicable for treating the waste.  EPA will prioritize these technologies  based
on its analysis of available data and information  regarding the effectiveness of
the various technologies.  For organics, EPA's preference will  be  technologies
that recover or destroy the compounds; for  metals,  the Agency's  preference will
be technologies that result in recovery of the metals.

      In some instances, analysis of a particular parameter  affecting treatment
selection will  not be possible or would  be  meaningless with  regard  to selecting
a treatment system.   For example,  the BOD of  a contaminated  soil is essentially
meaningless since the soil  is not likely  to  be  treated in a  biological wastewater
treatment system.

      (c)   Use of New  Data and  Information.   As data become available either
from industry or through EPA's  BOAT data collection program,  EPA  will modify the
PATS analysis to further refine specific concentration ranges for which various
technologies can handle various parameters.
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2.    Underlying Principles of Operation

      (a)   Information Provided.  For each treatment technology EPA provides the
fundamental theory of operation  of the technology.  This section is not meant to
provide a  detailed  discussion on the specific  complex physical,  chemical,  or
biological  mechanisms by  which treatment  occurs.   Instead,  the  discussion
describes the mechanisms involved so that one can understand what characteristics
can  affect the performance  of  the technology.   For  example,  the  underlying
principle of chemical precipitation is that  metals  in wastewater are removed by
adding  a  treatment  chemical  to form  a  metal  precipitate  that  is  generally
insoluble and therefore settles out of solution.  Formation of the precipitate
and the  settling mechanism are the principles controlling technology performance.

      (b)   Use of Information Provided.  The theory of operation is necessary
as  the  precursor  to  analyzing which  waste characteristics  can affect  the
performance  of a  given treatment  technology.    That  is,  the principles  of
treatment  operation  are used as the  rationale  and basis on  which  the Agency
determines what waste characteristics can affect performance.  Accordingly, waste
characteristics affecting performance (WCAPs), which are discussed below, must
be understood from the standpoint of how  each waste characteristic inhibits or
interferes with the  fundamental operation of the treatment technology.

3.    Description of the Treatment Process

      This section provides a brief description of the principal  components of
a treatment technology.  It is intended to provide  a basic understanding of the
equipment  used and  the treatment  sequence.    This  presentation  relates  the
discussion on underlying principles of operation with the later discussion of the
design  and  operating  parameters   important  to   effective  waste  treatment.
Simplified  block diagrams  are  provided  in  this  section.    The information
presented  is general in nature to avoid attempting  to  show all  combinations and
permutations that are possible  in describing a particular technology.
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4.    Waste Characteristics Affecting Performance fWCAPs)

      (a)   Information  Provided.   The  WCAPs are  based  on  the  underlying
principles of the treatment technology.  For example, the underlying principle
of chemical  precipitation  is formation of the insoluble metal  precipitate and the
settling of the precipitate out of solution.  WCAPs for this technology are those
parameters  that  affect the  chemical reaction  of the  metal  compound  or the
solubility of the metal  precipitate (i.e., formation)  and/or affect the  ability
of the precipitated compound to settle.  The  WCAPs  include  (a)  the concentration
and type  of metals, (b) the concentration of  total  dissolved solids,   (c) the
concentration of  complexing agents, and (d) the concentrations of oil and  grease.
The  first three parameters  can   affect  precipitate  formation,  and the  last
parameter can affect settling rate.

      EPA's selection of WCAPs for the various treatment systems is based on a
literature review, as well as  information obtained during  plant  sampling visits
that test the treatment technology.  EPA is  aware  that in  some cases analytical
methods are  not  available to measure the specific  waste characteristics that
affect  treatment.    In  such  instances,   EPA  measures the parameter  that most
closely approximates the actual parameter of concern.  For  example, a WCAP for
steam stripping  is  the  relative  volatility of a  component.  Because relative
volatility cannot  be measured,  EPA uses boiling  point  as the best measure of
assessing the WCAP  of relative volatility.

      The analysis  of waste characteristics affecting performance is conducted
where EPA already  has determined from a  PATS  analysis  that an untested waste
could be  treated effectively  by  the  same BOAT  technology as another waste for
which treatment performance data  are available.  The  WCAP  analysis  is then used
to  determine  whether the treatment  standards  from the  tested waste  can be
transferred to the  untested waste.  Simply stated, this analysis compares, for
two separate wastes, the characteristics  that affect the  level  of treatment that
can be  achieved.   Where this comparison  shows that  the untested  waste can be

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treated as well or better, the Agency will transfer the treatment standards to
the untested waste.

      For example, for wastes that  can  be  treated using chemical precipitation,
if the Agency tests a waste containing lead at a given level, it will transfer
the treatment standards developed from the  test to a second lead-containing waste
if the second waste meets the following WCAP-based conditions:

      •  The lead concentration is similar to that of the tested waste;
      •  The second waste has a lower total dissolved solids level;
      •  The concentration and type of other metals  are similar to those of the
         tested waste; and
      •  The untested waste has a concentration  of oil and grease similar to or
         less than that of the tested waste.

      (b)   'Use of Information Provided.  In applying the WCAP analyses, it is
important to remember that the technology itself and the associated design and
operating conditions are fixed (i.e.,  they are  fixed at the  values that existed
for the already tested waste).  EPA does  not  assume that,  where WCAPs for the
untested waste show that  it would be significantly harder to  treat, the addition
of another  treatment  component  or  a change in  design and operating conditions
will result in the untested waste  achieving the  same performance  as that of the
previously  tested waste.   EPA is  aware that  modifying the treatment system or
operating conditions could result  in similar  treatment.  However, the Agency is
not  certain,  without  demonstrating  through  testing,  that  treatment  levels
associated  with BOAT  standards  (normally  in  the low (<10)  part per million or
part per billion range) can be achieved by simply changing treatment conditions.
Accordingly,  EPA  is  very  cautious in  its  decisions  to  transfer  treatment
standards where the WCAP analysis  shows that treatment modifications are needed
from the previously tested waste.
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      (c)   Use of New Data and  Information.   In  developing the WCAPs for the
various  treatment technologies,  EPA  found  little  and,  in  some cases,  no
information  on  the  relative  importance  of  the  various  WCAPs  for  a  given
technology (i.e.,  which waste characteristics have the most significant impact
on treatment performance).  Where information was available with regard to the
specific WCAPs that are important when assessing the performance of  a particular
technology, EPA was unable to find any supporting data that would quantify the
relative impact of each of the WCAPs on treatment performance.

      As data become available either from industry or through EPA's BOAT data
collection program,  EPA  may  modify  the WCAP  analysis  to  further  refine the
parameters  identified as  affecting  treatment  technology  performance.    As
previously noted,  before  it adopts a new WCAP, the Agency must understand how the
parameters affect  treatment relative to the underlying principles of operation.

5.    Design and Operating Parameters

      EPA uses design and  operating  information  in several  ways.   First, this
information  is  used, in  conjunction with the  Agency's BOAT  data collection
program, in determining whether a particular  treatment system  is well designed.
That is, the Agency assesses  design  data prior to  determining whether to test a
particular piece  of  equipment  or treatment  train for  potential  use  in the
development of BOAT treatment standards.  EPA obtains operating data during the
course of an  Agency-sponsored  treatment  test to ensure that  the  treatment system
is well operated.   Secondly, EPA expects facilities to provide the appropriate
design and operating  data when submitting treatment data to  be considered  in the
development of the BOAT treatment standards.  Again,  the Agency assesses these
data  to determine whether the  treatment  system was  well  designed  and well
operated.

      For example, some of the critical  design and operating parameters  for steam
stripping include  the number of equilibrium stages  in the column,  the temperature

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at which the unit is  designed to operate, and how well  the design temperature is
controlled.  In evaluating performance data from a steam stripping operation, the
Agency would examine  the design specifications (e.g., the basis for  selecting the
number of  stages and design temperature)  for the treatment  unit in order to
determine the extent  to which  the hazardous constituents could be expected to
volatilize.  After the design specifications  are established, the Agency would
collect data  (e.g.,  hourly  readings  of the column temperature) throughout the
operation of  the treatment  process demonstrating  that  the unit  was operating
according to design specifications.  If the data collected vary considerably from
the design requirements, that variation could  form the basis  for  determination
that the treatment unit was  improperly operated.   If the  temperature  data show,
for  example,  that  for significant  periods  of  time  the  temperature varied
considerably from the design requirements,  the Agency would not use  these data
to determine the levels of performance achievable  by BOAT.

      Finally, EPA requires facilities petitioning for a  treatment variance to
submit the plant's design values  and the  operating data  during the time of the
treatment period to ensure that the treatment system was  well  designed  and well
operated.
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 I.  TREATMENT TECHNOLOGIES





A.  DESTRUCTION TECHNOLOGIES

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                           1.  BIOLOGICAL TREATMENT

1.1         Applicability

      Biological treatment can  typically  be  divided into two classifications:
aerobic  biological  treatment  and  anaerobic biological  treatment.   Aerobic
biological treatment  takes place  in  the  presence  of  oxygen,  while anaerobic
biological treatment is an oxygen-devoid process.

      Aerobic  biological  treatment  is  a  treatment technology  applicable to
wastewaters containing biodegradable organic constituents and some  nonmetallic
inorganic constituents including sulfides  and cyanides.  Four of the  most common
aerobic  biological  treatment  processes  are  (a)  activated  sludge,   (b) aerated
lagoon,  (c) trickling filter,  and (d)  rotating biological contactor  (RBC).  The
activated sludge and aerated  lagoon processes are suspended-growth processes in
which microorganisms are maintained in suspension with the liquid. The trickling
filter and the RBC are attached-growth processes in which microorganisms grow on
any inert medium such as rocks, slag, or specifically designed ceramic or plastic
materials.  This section discusses these  four processes as well  as the powdered
activated carbon (PAC)  adsorption process, which  is a variation of the activated
sludge treatment.

      Anaerobic digestion  is best  suited to wastes  with a moderate  to high pH,
nonhalogenated hydrocarbons, moderate to low organic loadings,  and  low to  zero
biological oxygen demand.   The waste should also  be  in a  semisolid or sludge
form.   Anaerobic biological   treatment  typically takes place  in an anaerobic
digester.

1.2         Underlying Principles of Operation

      The basic principle of operation for aerobic biological  treatment processes
is that living, oxygen-requiring microorganisms decompose organic and  nonmetallic
inorganics constituents into carbon dioxide,  water,  nitrates,  sulfates, simpler


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low-molecular-weight organic byproducts, and cellular biomass.  Wastes that can
be degraded  by  a  given species or genus of  organisms  may  be very limited.  A
mixture of organisms may be required  to  achieve effective treatment, especially
for wastes containing mixtures  of organic compounds.  Nutrients  such as nitrogen
and phosphorus are also required to aid in the biodegradation process.

      The  aerobic  biodegradation  process can be  represented by  the following
generic equation:

       Cx",  *  °2  +
Microorganisms  produce enzymes  that catalyze  the  biodegradation reactions,
degrading the organic waste to obtain energy for cell metabolism and cell growth.

      Aerobic biological treatment of wastewaters containing organic constituents
results in the net accumulation of a biomass of expired microorganisms consisting
mainly of cell  protein.   However, the  cellular  biomass or sludges  may  also
contain  entrained  constituents  from  the  wastewater  or  partially  degraded
constituents.  These sludges must be periodically removed ("wasted") to maintain
proper operation of the aerobic biological treatment system.

      The basic principle of operation of anaerobic biological treatment  is  that
microorganisms  in  the  absence of oxygen  transform organic  constituents and
nitrogen-containing compounds  into carbon dioxide and methane gas.   Often other
nutrients  such as nitrogen and phosphorus  are necessary to  aid digestion.  The
anaerobic  biological  treatment  process  can be  described  by  the following
equation:
       r   u      microorganisms .  rn    ,   ru
       Cx  Hy  +     nutrients   >  C02  +   CH4
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1.3         Description of Biological Treatment Processes

1.3.1       Activated Sludge

      The activated sludge process is currently  the most widely used biological
treatment process.  This is partly the result  of the  fact that recirculation of
the biomass, which is an integral  part of the  process, allows microorganisms to
adapt to changes in wastewater composition with a relatively short acclimation
time and also allows a greater degree of control over the acclimated bacterial
population.

      An activated sludge system consists of  an equalization basin, a settling
tank, an aeration basin, a clarifier, and a  sludge recycle line.  Wastewater is
homogenized in an equalization  basin  to reduce variations in  the feed, which may
cause process upsets of the microorganisms  and diminish treatment efficiency.
Settleable solids are then removed in a settling tank.

      Next, wastewater  enters  an  aeration  basin,  where an aerobic bacterial
population  is  maintained in suspension  and oxygen,  as well  as  nutrients, is
provided.  The contents  of the basin are referred to as the mixed liquor.  Oxygen
is supplied to the aeration  basin by mechanical or diffused aeration, which also
aids in  keeping  the microbial  population in  suspension.  The mixed liquor is
continuously  discharged from the  aeration  basin  into a clarifier,  where the
biomass  is separated from the treated wastewater.  A portion of the biomass is
recycled to the aeration basin to maintain an optimum concentration of acclimated
microorganisms in the aeration  basin.  The remainder of the separated biomass is
discharged or "wasted."  The biomass may be further dewatered on sludge drying
beds or by sludge filtration (which is further  discussed in Section II.B.2) prior
to disposal.  The clarified effluent  is discharged.  A schematic diagram of an
activated  sludge treatment  system  is  shown  in Figure 1.
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            OXYGEN
              AND
           NUTRIENTS
WASTEWATER
INFLUENT
EQUALIZATION
TANK


8ETTLINO
TANK
               I
            AERATION
             BASIN
  BASIN
EFFLUENT
                    SLUDGE  RECYCLE
TREATED
EFFLUENT
TO DISPOSAL
                                                 WASTE  SLUDGE
                                                 TO SLUDGE
                                                 FILTRATION
                                                 AND DISPOSAL
Figure 1  Activated Sludge System

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      The  recycled biomass  is referred  to as  activated  sludge.    The  term
"activated"  is  used  because  the  biomass contains  living  and  acclimated
microorganisms that metabolize and assimilate organic material  at a higher rate
when  returned .to  the  aeration   basin.    This  occurs   because  of  the  low
food-to-microorganism ratio in the sludge from the clarifier.

      An important  variation  on the activated sludge  process  is  the Powdered
Activated  Carbon  Treatment (PACT)  process.   This  process  offers  a combined
treatment and pretreatment system in which noncompatible and  toxic constituents
are adsorbed onto  activated carbon, while microorganism-compatible waste remains
in solution.  Powdered activated carbon is added  directly  to  the aeration basin
of the activated sludge treatment system. Overall removal  efficiency  is improved
because compounds  that are not readily biodegradable  or  that are toxic to the
microorganisms are  adsorbed onto the surface of  the powdered activated carbon.
The  carbon is removed  from  the  wastewater in  the  clarifier along  with the
biological sludge.  Usually, the activated carbon is recovered,  regenerated, and
recycled.

1.3.2       Aerated Lagoon

      Like an activated  sludge system,  an'aerated lagoon  is  a  suspended-growth
process.   The  aerated lagoon  system consists of a large  pond  or tank that  is
equipped with  mechanical aerators  to  maintain  an aerobic  environment  and  to
prevent  settling   of  the  suspended biomass.    Initially,  the  population  of
microorganisms in an  aerated  lagoon  is much lower than  that  in  an  activated
sludge system because  there  is no sludge recycle.  Therefore,  a significantly
longer residence time is  required to achieve  the same effluent quality.  However,
this longer residence time may be an advantage when complex organic chemicals are
to be degraded.  Also, the microorganisms in aerated lagoons  are more  resistant
to  process upsets  caused  by  feed  variations  than  those  in activated sludge
systems because of the larger  tank volumes and longer residence  times used.  The
effluent  from  the aerated lagoon  may  flow  to  a  settling  tank for removal  of
suspended  solids.   Alternatively,  the  mechanical  aerators  in the system may  be
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shut off for a period of time to facilitate settling prior to discharge of the
effluent.  The settled solids are generally dewatered prior to disposal.

1.3.3       Trickling Filters

      A trickling filter is an attached-growth biological treatment process.  The
system consists of an equalization basin, a settling tank, a filter medium, an
influent wastewater distribution system,  an under drain system,  a clarifier, and
a recirculation line.  The filter medium consists  of  a bed of an inert material
to which the microorganisms attach themselves and through which the wastewater
is percolated.  Rocks or synthetic material  such as plastic rings and saddles are
typically  used  as  filter  media.   Following  equalization  and  settling  of
settleable solids in the wastewater, it is distributed over the top  of the filter
medium  by  a rotating  distribution arm  or a fixed  distributor   system.   The
wastewater forms a thin layer as it flows downward through the filter and over
the microorganism layer on the surface of the medium.  As the distribution arm
rotates, the microorganism layer is alternately exposed  to a flow  of wastewater
and a  flow of  air.    In  the  fixed distributor system,  the  wastewater flow is
cycled on and off at a specified dosing  rate to ensure that an adequate supply
of oxygen  is available  to  the microorganisms.    Oxygen from  air reaches  the
microorganisms through the void spaces in the medium. Figure 2 is a diagram of
a trickling filter system.

      A trickling filter system is  typically used as a roughing  filter  to reduce
the organic loading  on  a downstream activated sludge process.  Trickling filters
can be  used for the  treatment  of wastewaters that  could  potentially produce
"bulking"  sludge  (i.e.,  a sludge with  poor settling characteristics  and poor
compactability in an activated sludge process) because the microbial solids that
slough off the trickling filter medium are relatively dense and can be readily
removed in a clarifier.
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WASTEWATER
    INFLUENT
1
             WASTE  DISTRIBUTOR
11       11
                                 PLASTIC OR ROCK
                                                                     TREATED
                                                                     EFFLUENT
                                                                     TO  CLARIFIER
                          Figure 2  Trickling Filter System

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1.3.4       Rotating Biological Contactor

      A  rotating  biological  contactor  (RBC)  consists  of a  series  of closely
spaced, parallel disks that are rotated  at an average rate of 2  to 5 revolutions
per minute while  submerged to  40  percent  of their diameters in a contact tank
containing wastewater.   The disks  are constructed  of  polystyrene,  polyvinyl
chloride, or similar materials.   Each  disk  is covered  with  a biological slime
that degrades dissolved organic constituents present in  the wastewater.  As the
disk is rotated out of  the tank,  it carries a film of  the wastewater into the
air, where oxygen is available  for aerobic biological decomposition.  As excess
biomass is produced, it sloughs off the disk and  is separated from the treated
effluent in a  clarifier.   The  sloughing off  process is similar to that which
occurs in a trickling filter.  There is no  recycle of sludges or recirculation
of  treated  effluent in an RBC process.  Several RBCs are  often  operated in
series, with the effluent  from  the last RBC being discharged.  Biological solids
are usually dewatered prior to disposal.

1.3.5       Anaerobic Biological Treatment

      In anaerobic  biological  treatment, the  influent sludge  is  settled and
equalized,   then pumped to  the anaerobic  digester  (Figure  3) along  with an
alkaline adjustment additive.  There may or may not be mechanical agitation of
the digester.  After an adequate residence  time to allow for proper digestion,
the digester contents are  allowed  to settle.   The supernatant  is pumped to an
aerobic treatment area (typically  to an activated sludge unit),  while the sludge
is taken to disposal areas or subjected to additional treatment, such as drying
or incineration.

1.4         Waste Characteristics Affecting Performance (WCAPs)

      In determining whether  biological  treatment  will achieve the same  level of
performance on an untested waste that it achieved on a previously tested waste
and whether performance levels can be transferred, EPA examines the following
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INFLUENT
 SLUDGE
  SLUDGE
EQUALIZATION
   TANK
             ALKALINITY
             ADJUSTMENT
              ADDITIVE
                                               FLAME
GAS COMPRESSION
                                                    FLOATING I
                                                     COVER   •
                                                          MIXERS
                                          MEAT
                                                                 SUPERNATANT TO
                                                                 ACTIVATED SLUDGE
                                                                        SLUDGE
                                                                        EFFLUENT
                                                                                   PUMP
                                       EXCHANGER   DIGESTER CONCRETE)
                                      RECYCLE SLUDGE
                                                                                  SLUDGE
                                                                                  HOLDING
                                                                                   BASIN
                                                      PUMP
                                            Figure 3  Anaerobic Digestion

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waste characteristics:   (a)  the ratio of the  biological  oxygen demand to the
total organic carbon content, (b) the concentration  of surfactants,  and  (c) the
concentration of toxic constituents and waste characteristics.

1.4.1       Ratio of Biological Oxygen Demand to Total Organic Carbon Content

      Because organic  constituents in the  waste effectively serve  as  a food
supply for the microorganisms, it is necessary  that  a  significant percentage be
biodegradable.  If they are not, it will  be  difficult  for  the microorganisms to
successfully  acclimate to  the waste  and  achieve  effective treatment.   The
percentage  of biodegradable  organics can  be  estimated  by  the ratio  of the
biological oxygen demand (BOD) to the  total organic carbon (TOC)  content.  Since
the biological oxygen demand  is a measure of the amount of oxygen required for
complete  microbial  oxidation of biodegradable  organics,  the BOO  analysis is
mostly  relevant  to  aerobic  biological  treatment.    (In  anaerobic biological
treatment, BOD is one of the  main restrictive characteristics in that BOD must
be relatively low or zero.)  If the ratio of BOD to  TOC in an untested waste is
significantly lower than that  in the tested waste, the  system may not achieve the
same  performance  and  other,  more  applicable  technologies  may  need  to  be
considered for treatment of the untested waste.

1.4.2       Concentration of  Surfactants

      Surfactants can affect biological treatment performance by forming  a film
on  organic   constituents,   thereby  establishing  a  barrier   to  effective
biodegradation.   If the concentration of surfactants  in  an  untested waste is
significantly higher than that  in the tested waste, the system may  not achieve
the same  performance and other, more applicable technologies  may  need to be
considered for treatment of the untested waste.
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1.4.3       Concentration of Toxic Constituents and Waste Characteristics

      A number of constituents  and waste characteristics have been  identified as
potentially toxic to microorganisms.  Specific toxic concentrations have not been
determined  for most  of these  constituents and  waste characteristics.   The
constituents  and  waste characteristics  found  to  be  potentially  toxic  to
microorganisms include  metals  and  oil  and grease,  ammonia,  and phenols.  High
concentrations of dissolved solids are treated more  effectively by  anaerobic
treatment than by aerobic treatment.  If the concentration of toxic constituents
and waste characteristics in an untested waste is significantly higher than that
in the tested waste,  the system may not achieve  the  same  performance and other,
more applicable  technologies may  need  to be considered  for treatment of the
untested waste.

1.5         Design and  Operating Parameters

      In assessing the effectiveness of the design and operation of a biological
treatment  system,  EPA  examines  the  following  parameters:   (a)  the amount of
nutrients,  (b)   the  concentration  of   dissolved  oxygen,   (c) the  food-to-
microorganism  ratio,  (d)  the   pH,  (e) the  biological  treatment temperature,
(f) the  mean   cell  residence  time,  (g) the hydraulic loading  rate,  (h) the
settling time, and (i)  the  degree  of mixing.

      For  many  hazardous   organic  constituents,  analytical  methods  are not
available or the constituent cannot be  analyzed in the waste  matrix.   Therefore,
it would normally be  impossible  to measure  the effectiveness  of the biological
treatment system.  In  these  cases EPA tries to identify measurable  parameters or
constituents that would act as  surrogates in order  to  verify  treatment.

      For organic constituents,  each compound  contains a measurable  amount of
total organic  carbon  (TOC).  Removal of TOC  in the  biological  treatment system
indicates removal of organic constituents.  Hence,  TOC analysis is likely  to be
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an adequate surrogate analysis where the specific organic constituent cannot be
measured.

      However, TOC analysis may  not be  able to adequately detect treatment of
specific organics  in matrices that  are heavily organic-laden  (i.e.,  the TOC
analysis may  not  be  sensitive enough to detect changes  at the milligrams per
liter (mg/1) level in matrices where total organic concentrations are hundreds
or thousands  of  mg/1).    In  these  cases other surrogate  parameters  should be
sought.  For  example,  if a specific analyzable constituent  is expected to be
treated  as  well  as  the  unanalyzable constituent,  the  analyzable constituent
concentration should be monitored as a surrogate.

1.5.1       Amount of Nutrients

      Nutrient addition  is important in controlling the growth of microorganisms
because an  insufficient amount of nutrients results in poor microbial growth with
poor biodegradation of organic constituents.  The principal inorganic nutrients
used are nitrogen  and phosphorus.   In  addition,  trace  amounts  of potassium,
calcium, sulfur,  magnesium,  iron,  and  manganese  are  also  used  for  optimum
microbial growth.  The percent distribution of  nitrogen and phosphorus added to
microorganisms  varies  with  the  age   of  the organism   and  the  particular
environmental conditions.  The total amount of nutrients  required  depends on the
net mass of organisms produced.

      EPA monitors the amount  of  nutrients added and their method  of addition to
the wastewater to  ensure that a sufficient supply is provided  to  achieve an
effective growth of microorganisms.

1.5.2       Concentration of Dissolved Oxygen

      A  sufficient concentration  of dissolved  oxygen   (DO)  is  necessary to
metabolize and degrade dissolved  organic constituents in  aerobic treatment.  The
DO concentration  is controlled by adjusting the  aeration rate.  The aeration rate
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must be  adequate  to provide a sufficient DO concentration  to satisfy the BOD
requirements of the  waste,  as well as to provide  adequate  mixing to keep the
microbial  population in suspension  (for  activated sludge  and  aerated lagoon
processes).  The  reverse  is true for anaerobic treatment,  in that DO must be
absent for  anaerobic treatment to occur.   EPA  monitors  the DO concentrations
continuously,  if  possible,  to  ensure  that the  system  is operating  at the
appropriate design condition and to diagnose operational problems.

1.5.3       Food-to-Microorganisra Ratio

      The  food-to-microorganism  (F/M)  ratio, which applies only to  activated
sludge systems, is a  measure of the amount of biomass available to metabolize the
influent organic loading to the aeration unit.   This ratio can be  determined by
dividing the influent BOD concentration by the concentration of  active biomass,
also referred to as  the  mixed liquor volatile suspended solids (MLVSS).  The F/M
ratio is controlled by adjusting the wastewater  feed rate or the sludge  recycle
rate.  If the F/M  ratio  is too high, too few microorganisms will  be available to
degrade  the organics.   EPA  periodically  analyzes the  influent  BOD and the
aeration unit's MLVSS concentrations to ensure  that the  system  is  operating at
the appropriate design  condition.

1.5.4       pH

      Generally,  neutral or slightly alkaline  pH favors microorganism  growth.
The optimum range for most microorganisms used  in  biological  treatment  systems
is between 6 and 8.   Treatment effectiveness is generally insensitive to  changes
within this  range.   However, pH values outside the  range can  lower  treatment
performance.  EPA monitors the pH continuously,  if possible, to  ensure that the
system  is  operating at  the  appropriate  design  condition  and  to diagnose
operational problems.
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1.5.5       Biological Treatment Temperature

      Microbial growth can occur under a wide range of temperatures,  although the
majority of the microbial species used in aerobic biological treatment processes
are  active between  20 and  35*C  (68  to  95*F).   For anaerobic  systems,  the
temperature  is typically between  30  and  70*C  (86  to  158*F).    The  rate of
biochemical reactions in cells increases with  temperature up  to a maximum above
which the rate of activity declines  and microorganisms either die off or become
less active.  EPA monitors the biological treatment temperature continuously, if
possible,  to  ensure that the system  is  operating at the  appropriate design
condition and  to diagnose operational problems.

1.5.6       Mean Cell Residence Time

      In activated sludge,  aerated lagoon,  and anaerobic  digestion  systems, the
mean cell residence time (MCRT) or sludge age is  the length of time organisms are
retained in the unit before  being drawn off as waste sludge.   By controlling the
MCRT, the growth phase of the microbial  population can be controlled.   The MCRT
must be long enough to allow  the organisms in the unit to reproduce.   The MCRT
is determined by dividing the total active microbial mass  in  the unit (MLVSS) by
the total quantity of microbial mass withdrawn daily (wasted). EPA  monitors the
MCRT to  ensure that a sufficient number of microorganisms  are  present in the
unit.

1.5.7       Hydraulic Loading Rate

      The  hydraulic loading  rate  determines  the  length of  time  the organic
constituents are  in  contact with  the microorganisms and, hence,  the extent of
biodegradation  that  occurs.   In  trickling  filters,  the hydraulic  loading rate
also determines the shear velocities on the microbial layer.  Excessively high
hydraulic loading rates may  wash away the microbial layer  faster than it  can grow
back.   However, the hydraulic  loading rate  must  be high enough  to  keep the
microbes moist and to remove dead or dying microbes that have  lost their ability
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to cling to the filter media.  For all aerobic biological treatment processes,
the hydraulic loading rate is controlled  by  adjusting the wastewater feed rate.
In addition, for RBCs, the hydraulic  loading rate can be controlled by changing
the disk speed or adjusting the submersion depth.   EPA monitors the wastewater
feed rates  to  ensure that  the  hydraulic loading provides  sufficient  time to
achieve an effective biodegradation of organic constituents in the wastewater.

1.5.8       Settling Time

      Adequate settling time must be  provided to separate the biological solids
from the mixed  liquor.  Activated sludge systems cannot  function properly if the
solids cannot  be effectively  separated and  a portion  returned to the aeration
basin.  EPA monitors the settling time to ensure effective solids removal.

1.5.9       Degree of Mixing

      Mixing  provides  greater  uniformity   of the  wastewater   feed  in  the
equalization basin  to reduce variations  that may cause  process  upsets of the
microorganisms  and  diminish  treatment efficiency.   For activated  sludge and
aerated lagoon systems,  sufficient aeration  in the aeration  unit provides mixing
to  ensure  adequate  contact  between  the  microorganisms  and  the  organic
constituents in the wastewater.   The  quantifiable degree  of mixing is a complex
assessment that includes,  among other factors, the amount of energy supplied, the
length of time the material is mixed,  and the related turbulence  effects of the
specific size and shape of the mixing unit.   The degree of  mixing  is beyond the
scope  of simple measurement.   EPA,   however,  evaluates  the degree  of mixing
qualitatively by considering whether mixing  is provided and whether the type of
mixing device  is  one that could be expected  to achieve  uniform  mixing of the
wastewater.
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1.6         References


Barley, J.,  and  Ollis,  D.  1977.   Biochemical  engineering fundamentals.   New
      York:  McGraw-Hill  Book Co.

Burchett,  M.,  and Tshobanoglous,  G.    1974.   Facilities  for controlling  the
      activated  sludge  process  by  mean cell  residence time.   Journal  Water
      Pollution Control Federation.  Vol. 46, no. 5  (May 1974), p. 973.

Clark, J.W., Viessman,  W.,  and Hammer, M.   1977.   Water supply and  pollution
      control.  New York:  Harper & Row, Publishers.

Eckenfelder  Jr.,  W.W.,   Patoczka,  J., and  Watkins,  A.    1985.    Wastewater
      treatment.  Chemical engineering.  September 2,  1985.

Johnson, S.J.   1978.   Biological treatment.   Unit  operation for treatment  of
      hazardous industrial wastes.  Park Ridge, N.J.:  Noyes  Data Corporation.

Kobayashi, H., and Rittmann, B.  1982.  Microbial removal of  hazardous  organic
      compounds.    Environmental  Science  and  Technology.   Vol.  16,   no.  3,
      pp.  170-183.

Metcalf & Eddy,  Inc.  1979. Wastewater  engineering:  treatment, disposal,  reuse.
      New  York:  McGraw-Hill Book Co.

Nemerow, N.L.  1978.  Industrial water pollution origins, characteristics,  and
      treatment.  Reading, Mass.:  Addison-Wesley Publishing  Company.

Perry, R.,  and  Green, D.   1984.   Chemical engineers' handbook.  6th  ed.  New York:
      McGraw-Hill Book Co.      ""

Rittmann,  B.   1987.  Aerobic  biological treatment.   Environmental Science  and
      Technology.  February 1987.  p.  128.

USEPA.  1985.  U.S.  Environmental Protection Agency.   Final report.  Assessment
      of treatment technologies for hazardous waste and their  restrictive waste
      characteristics.  Vol  1.  Washington, O.C.:  U.S.  Environmental Protection
      Agency.

USEPA.  1986.  U.S. Environmental Protection Agency.  Best demonstrated  available
      technology  background  document  for F001-F005  spent solvents.   Vol.  1,
      EPA/530-SW-86-056.   pp.   4-43.    Washington,  D.C.:   U.S. Environmental
      Protection Agency.
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                            2.  CHEHICAL OXIDATION

2.1         Applicability

      Chemical  oxidation  is   a  treatment  technology  used  to  treat  wastes
containing organics.  It is also  used to  treat  sulfide wastes  by converting the
sulfide  to  sulfate.    The  destruction  of  cyanides  in   wastes   is  usually
accomplished  by  chemical  oxidation.   Chemical  oxidation can also  be  used to
change the  oxidation  state of metallic compounds  to valences that  are less
soluble,   such as  converting  arsenic  in wastes  to the  relatively insoluble
pentavalent state.

      Chemical  oxidation  is   applicable  to   dissolved  cyanides   in  aqueous
solutions, such as wastewaters from metal plating and finishing operations, or
to inorganic sludges from these operations  that contain cyanide compounds.  For
cyanides, chemical oxidation is most applicable  to solutions containing less than
500  mg/1  of  cyanides  when the  cyanides  are   in  a form  that  can  be easily
disassociated in water to yield free cyanide ions.  If cyanides are present in
water as  a tightly bound complex ion  (e.g., ferrocyanide),  only limited treatment
may occur.  If the waste contains greater than  500 mg/1 of  cyanide,  but no more
than about 100,000  mg/1,  electrolytic oxidation may be more appropriate.  See
Section I.A.4.

      Chemical  oxidation  may  also  be  used  for  destruction of  the  organic
component of organometallic compounds in wastes, thus freeing the metal component
for treatment by chemical precipitation or stabilization.  Organic compounds such
as EDTA,   NTA, citric acid, glutaric  acid, lactic acid, and  tartrates are often
used  as   chelating  agents to  prevent metal   ions  from  precipitating  out in
electroless  plating solutions.   When these  spent plating solutions  require
treatment for metals removal  by  chemical precipitation,  the organic chelating
agents must  first  be destroyed.   Chemical  oxidants, potassium permanganate in
particular, are effective in releasing metals  from complexes with these organic
compounds.


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2.2         Underlying Principles of Operation

      The basic principle of operation for chemical  oxidation is  that  inorganic
cyanides,  some dissolved  organic  compounds,  and  sulfides  can  be chemically
oxidized to yield carbon dioxide, water, salts,  simple organic acids, and, in the
case of sulfides, sulfates.  Metallic ions such as  arsenites can  be oxidized to
higher, less soluble valences such as arsenates.  The principal chemical oxidants
used are hypochlorite,  chlorine gas, chlorine dioxide,  hydrogen peroxide, ozone,
and potassium permanganate. The reaction chemistry for each is discussed below.

2.2.1       Oxidation with Hypochlorite or Chlorine (Alkaline  Chlorination)

      This type of oxidation is carried out using sodium hypochlorite (NaOCl),
calcium  hypochlorite  (Ca(OCl)2),  chlorine gas  (C12),  or  sometimes   chlorine
dioxide gas  (C102).   The  reactions  are normally conducted under slightly  or
moderately alkaline conditions.  Alkaline chlorination  of cyanide is a two-step
process usually operated at a pH of 10 to 11.5 for the first  step and 8.5 for the
second step.   The toxic gas cyanogen  chloride  (CNC1)  is formed as a reaction
intermediate in the first step  of this  process and may be liberated if  the pH is
less than 10 and incomplete reaction occurs. Example reactions for the  oxidation
of cyanide, phenol,  and sulfide using  sodium hypochlorite are  shown below:

            Cyanide:  CN" + NaOCl  -> OCN" + NaCl  (Step  1)
                      20CN" + 3NaOCl -» CO/" + C02 + N2  +  3NaCl  (Step 2)

            Phenol:   C6HSOH +  14NaOCl  - 6C02 +  3H20 + 14NaCl

            Sulfide:  S" + 4NaOCl  -» SO/ +  4NaCl

            Arsenic:  H3As03 +  NaOCl  -* H3As04 + NaCl

      Chlorine  dioxide  also   oxidizes the  same  pollutants  under  identical
conditions.  Chlorine dioxide  first hydrolyzes  to form a mixture of chlorous


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(HC102) and chloric (HC103)  acids.  These acids act as the oxidants, as shown in
the equations below,  for phenol:

                        2C102 + H20 - HC102 + HC103
                    C6H5OH + 7HC102 - 6C02  + 3H20 + 7HC1
                    3C6H5OH + 14HC103 - 8C02 + 9H20 +  14HC1

2.2.2       Peroxide  Oxidation

      Peroxide oxidizes the same  constituents that  alkaline chlorination
oxidizes under similar conditions.   The relevant  reactions are the following:

            Cyanide:  2CN'  * 5H202 - 2C02 + N2 + 4H20 + 20H'

            Phenol:   C6H5OH + 14H202 -» 6C02  •»• 17H20

            Sulfide:  S" +  4H202 -» SO/  + 4H20

2.2.3       Oxidation with  Ozone  (Ozonation)

      Ozone  is  an effective  oxidizing  agent  for  the  treatment  of organic
compounds  and  for  the oxidation of cyanide  to cyanate.  Cyanogen  gas  (C2N2)  is
a reaction intermediate in this  reaction.  Further oxidation of cyanate  to carbon
dioxide  and nitrogen compounds  (N2  or NH3) occurs  slowly  with  ozone.   The
oxidation  of cyanide  to cyanate proceeds by the following reaction:

                              CN"  + 03 -» CNO~ +  02

      The  rates   of  ozonation  reactions   can  be  accelerated   by   supplying
ultraviolet (UV) radiation  during treatment.  Some  literature sources indicate
that  even the  cyanide complexes most  difficult to  treat,  the  iron-cyanide
complexes, can be  oxidized  completely.
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2.2.4       Oxidation with Potassium Permanganate

      Potassium permanganate can  also  be  used  to oxidize  the same constituents
as the other chemical  oxidants.   The reactions of potassium permanganate with
phenol and sulfide at acidic  pHs  and with  cyanide at pH 12 to 14 are as follows:

      Phenol:   3C6H5OH + 28KMn04  +  28H* - 18C02 + 28Mn02 + 23H20 + 28K*

      Sulfide:  5S" + 8KMn04  +  24H*  -> 5S04" + 8Mn*2 +  12H20 +  8K*

      Cyanide:  CN" + 2KMn04  +  Ca(OH)2  -> CNO" + K2Mn04 + CaMn04 + H20

In cyanide oxidation using potassium permanganate, cyanide  is oxidized only to
cyanate.  Further oxidation of  cyanate  can be accomplished by acid hydrolysis or
by the use of another oxidizing agent.

2.2.5       S02/Air Oxidation

      Cyanide can be oxidized to cyanate  in an aqueous solution by bubbling air
containing from 1 to 10 percent S02  through  the waste.  The S02 is also oxidized
to sulfate  in  this reaction.  This treatment  process occurs  by  the  following
reaction:

                       CN' +  S02 + 02 + H20 -» CNO" + H2S04

This  oxidation  reaction  requires the  use of  a  soluble copper  salt  catalyst.
Copper sulfate (CuS04)  is most  often used. S02/air oxidation is used frequently
in the treatment of wastewaters from gold  production, which contain both cyanide
and thiocyanate, because S02/air oxidizes  cyanide more strongly than thiocyanate
while alkaline chlorination and other common oxidizing agents oxidize thiocyanate
more  strongly than  cyanide.  As with potassium permanganate, further  oxidation
of cyanate  can be  accomplished  by acid  hydrolysis  or by  the use of another
oxidizing agent.


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2.3         Description of Chemical Oxidation Processes

2.3.1       Alkaline Chlorination

      Alkaline chlorination can  be accomplished by either batch or continuous
processes.   For  batch  treatment, the wastewater  Is  transferred to a reaction
tank, where the pH 1s adjusted and  the oxidizing agent Is added.   In some cases,
the tank may  be  heated to increase the reaction  rate.   For oxidation of most
compounds, a slightly to moderately alkaline pH is used.  It is  important that
the tank be well mixed for effective treatment to occur.  After  treatment, the
wastewater is either directly discharged or transferred to another process for
further treatment.

      In the continuous process, automatic instrumentation is used to control pH,
reagent addition, and temperature.  An oxidation-reduction potential  (ORP) sensor
is usually used  to measure the extent of reaction.

      In both types of processes,  agitation is typically provided to maintain
thorough mixing.  Typical residence times for these and other oxidation processes
range from 1 to  2 hours.
                             •
2.3.2       Peroxide Oxidation

      The peroxide oxidation process is run under similar conditions, and with
similar equipment, to those used  in the alkaline chlorination process.  Hydrogen
peroxide is added as a liquid solution.

2.3.3       Ozonation

      Ozonation can be  conducted  in a batch or continuous process.  The ozone for
treatment is produced onsite because of the hazards  of transporting and storing
ozone as well as  its short shelf life.   The  ozone gas is supplied to  the reaction
vessels  by  injection   into the  wastewater.  The  batch process  uses  a single


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reaction tank.  As with  alkaline chlorination, the amount of ozone added  and the
reaction time used are determined by the type and concentration of the oxidizable
contaminants, and vigorous mixing should be provided for complete oxidation.

      In continuous operation,  two  separate tanks may be used for reaction.  The
first tank receives an excess dosage of ozone.  Any excess ozone remaining at the
outlet of the second tank 1s recycled to the first tank, thus ensuring  that an
excess  of ozone  is maintained  and  also  that no  ozone  is released  to the
atmosphere.   As  with alkaline chlorination, an ORP  control  system is  usually
necessary to ensure that sufficient ozone is being added.

2.3.4       Permanganate Oxidation

      Permanganate oxidation is conducted in tanks in a manner  similar  to that
used for alkaline chlorination, as discussed previously.  Potassium permanganate
is normally dissolved in an  auxiliary  tank and added as a solution. As with the
other oxidizing agents, ORP (for continuous processes) and excess oxidizing agent
(for batch processes) are monitored to measure the extent of reaction.

2.3.5       S02/Air Oxidation

      S02/air oxidation of cyanide depends on efficient mixing  of air with the
waste to  ensure an  adequate  supply of oxygen.   Because of this factor, the
equipment requirements for this process are similar to those  for ozonation.  S02
is sometimes  supplied with the air  by  using flue gas containing S02 as  the air
source.   Otherwise, sulfur in the +4 oxidation   state  can   be  fed  as  gaseous
sulfur  dioxide  (S02),  liquid  sulfurous  acid (H2S03),  sodium  sulfite  (Na2S03)
solution, or sodium bisulfite (NaHS03)  solution.  Sodium bisulfite solution, made
by dissolving  sodium metabisulfite (Na2S205) in water,  is  the  most frequently
used source of S02.  This process  is usually run continously, with the addition
of oxidizing agent and acid/alkali being controlled through continuous monitoring
of ORP and pH, respectively.
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2.4         Waste Characteristics Affecting Performance (WCAPs)

      In determining whether chemical oxidation will achieve the same level of
performance on an untested waste that it achieved on a previously tested waste
and whether performance  levels  can  be transferred,  EPA examines the following
waste characteristics:   (a) the concentration of other oxidizable contaminants
and (b) the concentration of metal salts.

2.4.1       Concentration of Other Oxidizable Compounds

      The presence of other oxidizable compounds in addition to  the constituents
of concern will  increase  the demand for oxidizing agents and, hence, potentially
reduce the effectiveness  of the treatment process.  As a surrogate for the amount
of oxidizable organics present, EPA analyzes for total organic carbon (TOC) in
the waste.  Inorganic reducing compounds such as  sulfide may also create a demand
for additional oxidizing agent;  EPA  also attempts to identify and analyze for
these constituents.  If TOC and/or inorganic reducing compound concentrations in
the untested waste are significantly higher than those in  the tested  waste, the
system may not achieve the same performance. Additional oxidizing  agent may be
required  to effectively oxidize  the waste  and achieve the  same treatment
performance, or  other,  more applicable  treatment technologies  may need to be
considered for treatment of the untested waste.

2.4.2       Concentration of Metal Salts

      Metal  salts,  especially  lead  and  silver  salts,  will  react  with the
oxidizing  agent(s)  to form metal  peroxides,  chlorides,   hypochlorites,  and/or
chlorates.   These reactions can  cause an  excessive  consumption of oxidizing
agents and potentially interfere with the  effectiveness of treatment.

      An   additional   problem   with   metals  in  cyanide  solutions  is   that
metal-cyanide complexes  are  sometimes formed.   These complexes  are  negatively
charged metal-cyanide ions that are extremely soluble.  Cyanide in the complexed
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form may not be oxidizable, depending on the strength  of the metal-cyanide bond
in  the  complex and  the type  of  oxidizing  agent  used.    Iron  complexes (for
example, the ferrocyanide  ion,  Fe(CN)6"4)  are the most stable of the complexed
cyanides.

      If the concentrations of metal salts and/or metal-cyanide complexes in the
untested waste  are significantly higher  than  those  in the  tested waste, the
system may not achieve the same performance.  Additional oxidizing  agent  and/or
a different oxidizing agent may be required to effectively  oxidize the waste and
achieve  the  same  treatment  performance,  or other, more  applicable treatment
technologies may need to be considered  for treatment  of the untested waste.

2.5         Design and Operating Parameters

      In assessing the effectiveness of the design and operation of a chemical
oxidation system,  EPA examines the following parameters:  (a) the residence time,
(b) the amount and type of oxidizing agent, (c)  the degree of mixing, (d)  the pH,
(e) the oxidation temperature,  and  (f)  the amount and type of catalyst.

      For  many hazardous  organic  constituents,  analytical  methods  are not
available or the constituent cannot  be analyzed in the  waste matrix.  Therefore,
it would normally be impossible to measure  the  effectiveness of the chemical
oxidation  treatment  system.   In these  cases EPA  tries  to identify measurable
parameters or constituents that would act  as surrogates to verify  treatment.

      For  organic  constituents, each  compound  contains  a  measurable amount of
total organic carbon (TOC).  Removal of  TOC in  the chemical oxidation treatment
system will  indicate removal  of organic constituents.  Hence, TOC analysis is
likely  to  be   an adequate   surrogate  analysis  where  the  specific   organic
constituent cannot be measured.

      However, TOC analysis  may not be  able to adequately detect treatment of
specific organics in matrices  that are heavily organic-laden  (i.e.,  the TOC
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analysis may not be sensitive enough to detect changes at the milligrams/liter
(mg/1)  level  in matrices where  total  organic concentrations  are  hundreds or
thousands of mg/1).   In these cases other surrogate parameters  should be sought.
For example, if a specific analyzable constituent is expected to be treated as
well as the unanalyzable constituent, the analyzable constituent concentration
should be monitored as a surrogate.

2.5.1       Residence Time

      The  residence  time  impacts  the  extent   of volatilization  of  waste
contaminants.  For a batch system, the residence time is controlled by adjusting
the treatment time in the reaction tank.  For a continuous system, the waste  feed
rate is controlled to make sure that the system is  operated at  the appropriate
design residence time.  EPA monitors the residence  time to ensure that sufficient
time is provided to effectively oxidize the waste.

2.5.2       Amount and Type of Oxidizing Agent

      Several factors influence the choice of oxidizing agents and the amount to
be  added.   The  amount  of oxidizing agent required  to  treat a given amount of
oxidizable constituent(s) will vary with the  agent chosen.   Enough oxidant  must
be  added to ensure complete oxidation;  the specific amount depends on the  type
of  oxidizable  compounds  in  the waste and  the  chemistry  of  the  oxidation
reactions.   Theoretically,  the amount  of  oxidizing agent to  be added  can be
computed from oxidation reaction stoichiometry; in  practice, an excess of oxidant
should be used.  Testing for excess oxidizing agent will determine whether the
reaction has  reached completion.   In continuous processes, oxidizing agent is
added by automated feed methods.  The amount of oxidizing agent needed is usually
measured and controlled automatically by an oxidation-reduction  potential (ORP)
sensor.   EPA examines the  amount  of oxidant added to the chemical oxidation
system to ensure that it  is sufficient to effectively oxidize the waste and, for
continuous  processes,  examines how  the facility ensures  that the particular
addition rate is maintained.  EPA also tests for excess oxidizing agent for batch
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processes and continuously monitors the ORP for continuous processes to ensure
that excess oxidizing agent, if possible, is supplied.

2.5.3       Degree of Mixing

      Process tanks  must be  equipped with mixers  to ensure  maximum contact
between the oxidizing agent and the waste solution.  Proper mixing also limits
the production  of  any solid precipitates from  side  reactions  that may resist
oxidation.  Mixing  also provides an even distribution of  tank contents and a
homogeneous  pH  throughout  the  waste,  improving  oxidation  of  wastewater
constituents.   The quantifiable  degree  of mixing  is  a complex assessment that
includes, among other factors,  the amount of energy supplied,  the length of time
the material is mixed, and the related turbulence effects of the specific size
and shape of the tank.   This  is  beyond  the scope  of simple measurement.  EPA,
however, evaluates  the  degree of mixing  qualitatively  by  considering whether
mixing is provided and  whether the  type of mixing device is  one that could be
expected to achieve uniform mixing of the waste solution.

2.5.4       pH

      Operation at the optimal  pH maximizes the chemical oxidation reactions and
may,  depending  on  the   oxidizing  agent  being  used, limit  the  formation  of
undesirable reaction byproducts or the escape of cyanide from  solution as HCN,
CNC1, or C2N2 gas.   The  pH  is  controlled  by the addition of  caustic, lime, or
acid to the solution.   In most cases,  a slightly  or moderately alkaline pH is
used, depending on the type  of  oxidizing agent being used  and  the compound being
treated  (see  Section 2.2,  Underlying Principles  of Operation).   In alkaline
chlorination treatment of organics, a slightly  acidic pH may be selected as an
optimum.   In  permanganate  oxidation,  a pH  of 2 to 4 is often selected.   EPA
monitors the pH  continuously, if possible,  to ensure that the system is operating
at the appropriate design condition and to diagnose operational problems.
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2.5.5       Oxidation Temperature

      Temperature  affects the  rate  of reaction  and the  solubility  of the
oxidizing agent in the waste.  As the temperature is  increased, the solubility
of  the  oxidizing  agent,  in  most  instances,  is  increased  and  the  required
residence  time,   in  most  cases,  is reduced.    EPA  monitors the  oxidation
temperature continuously,  if possible, to ensure that the system is operating at
the appropriate design condition and to diagnose operational problems.

2.5.6       Amount and Type of Catalyst

      Adding a catalyst that promotes oxygen transfer and thus enhances oxidation
has the  effect of lowering the necessary  reactor temperature and/or  improving the
level of destruction of oxidizable compounds.  For waste constituents that are
more difficult to  oxidize,  catalyst addition may  be  necessary to effectively
destroy the constituent(s) of concern. Catalysts typically used for this  purpose
include copper bromide and  copper  nitrate.    If  a catalyst  is required, EPA
examines the  amount  and  type added, as well as the method of addition of the
catalyst to the waste, to ensure that effective oxidation  is achieved.
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2.6         References


Gurnham, C.F.   1985.   Principles of industrial waste treatment.  New York:   John
      Wiley and Sons.

Gurol, M.D., and Holden,  I.E.   1988.  The effect of copper and iron  complexation
      on removal of cyanide by ozone.  Ind. Enq. Chem. Res.  27(7):1157-1162.

McGraw-Hill.   1982.   Encyclopedia of science and technology.  Vol. 3,  p.  825.
New   York:  McGraw-Hill Book Co.

Metcalf &  Eddy,  Inc.   1986.   Briefing:   Technologies applicable  to  hazardous
      waste.  Prepared for U.S. Environmental Protection Agency,  Hazardous Waste
      Engineering Research  Laboratory.   Cincinnati,  Ohio:   U.S. Environmental
      Protection Agency.

Nutt, S.G., and Zaidi, S.A.   1983. Treatment  of  cyanide-containing wastewaters
      by the copper-catalyzed S02/air oxidation process.  In  Proceedings of the
      38th  Industrial Waste  Conference.  Purdue University,  West Lafayette,
      Indiana, May 10-12, 1983.   Stoneham, Mass.:  Butterworth  Publishers.

Patterson,  J.W.   1985.  Industrial  wastewater  treatment technology.    2nd ed.
      Stoneham, Mass.:  Butterworth  Publishers.

Schroeter,  J.,  and  Painter, C.   1987.    Potassium permanganate oxidation  of
      electroless  plating   wastewater.    Carus   Chemical  Company,  1001 Boyce
      Memorial Drive,  P.O.  Box 1500, Ottawa,  Illinois  61350.

Weast, R.C., ed.  1978. Handbook  of  chemistry and physics.  58th ed. Cleveland,
      Ohio:  CRC Press.
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                            3.  CHEMICAL REDUCTION

3.1         Applicability

      Chemical reduction  is  a treatment technology  used  to reduce hexavalent
chromium  and  selenate  ions  to  the  less  soluble  trivalent chromium  ion  and
elemental selenium,  respectively.   It is  also  used  to treat oxidizing wastes
containing  reducible   organics   and   inorganic  oxidizers  such  as  calcium
hypochlorite, hydrogen peroxide (and other  peroxides), and nitric acid.  Because
this technology frequently requires that  the pH  be in the acidic range,  it  would
not normally be applicable to wastes that contain significant amounts of cyanide
or sulfide.   In  such wastes,  lowering of  the pH  can result in the release  of
toxic gases such as  hydrogen cyanide or  hydrogen sulfide.

      Hexavalent chromium is usually present in wastes from the plating industry,
metal surface preparation processes, the chromium pigments industry, and leather
tanning  processes.    Selenates are  frequently  found  in  some  mining  and  ore
processing  wastes.   Organic  and  inorganic oxidizers  are  found in propel 1 ant
explosives  and in the chemical manufacturing  industries.

3.2         Underlying  Principles  of Operation

      The basic principle of chemical  reduction is to reduce the valence of the
oxidizer in solution. "Reducing agents" used to  effect the reduction include the
sulfur  compounds sodium  sulfite  (Na2S03), sodium  bisulfite (NaHS03), sodium
metabisulfite  (Na2S205), sulfur dioxide (S02), and sodium hydrosulfide  (NaHS).
The  ferrous form of iron (Fe*2)  is a popular  reducing agent  in  many cases.
Elemental magnesium  (Mg), zinc (Zn), and  copper  (Cu) are also effective  reducing
agents.  Frequently, hydrazine (N2H2)  is  used as a reducing agent also. Typical
reduction reactions  are as follows:
f:\document\15254031.01.005                   29

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      H202   +
Hydrogen Peroxide
               2H*
              2Fe>2    -
            Ferrous iron
                                               2H20
                                                            *3
                                                         2Fe
                                                          Ferric  Iron
4Zn
N0
                          10H*  -*
 Metallic Zinc  Nitrate  Ion
     3Na2S03
     Sodium
     Sulfite
   Chromic Acid
                                                             3H20
                                   Zinc  Ion    Ammonium  Ion
                                3H2S04  -  (Cr*3)2(S04)3  + 3Na2S04
                                Sulfuric  Chromium       Sodium
                                Acid      Sulfate        Sulfate
                                                                   4H20
      H2Se03
                 2S0
    Selenic Acid  Sulfite  Ion
              -»    2S04    +
                 Sulfate Ion
                                                 H20
                                                          Se
                                                          Elemental  Selenium
These reactions are usually accomplished at pH values  from  2  to  3
3.3
            Description of Chemical Reduction  Process
      The chemical  reduction treatment process can  be  operated in a  batch  or
continuous  mode.    A batch  system consists  of a  reaction tank,  a  mixer  to
homogenize the contents of the tank,  a  supply of reducing agent, and a source of
acid and base for  pH control.  A continuous chemical reduction treatment system,
as shown in Figure  4, usually  includes a  holding tank upstream of the  reaction
tank  for flow  and  concentration  equalization.   It also  typically  includes
instrumentation to automatically control  the amount of reducing agent  added and
the pH of the reaction tank.  The amount  of reducing agent is controlled by the
use of  a sensor called an  oxidation-reduction  potential  (ORP) cell.   The ORP
sensor   electronically  measures,  in  millivolts,   the   level   to which  the
oxidation/reduction  (redox)  reaction has  proceeded  at Figure 4 any given time.
It  must  be  noted,  however,  that  the   ORP  reading  is  very  pH dependent.
Consequently, if the pH is  not maintained  at  a  steady value,  the ORP will vary
somewhat, regardless of the  level  of chemical reduction.
f:\document\15254031.01.005
                                      30

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                                                                                TREATED EFFLUENT
                                                                                TO SETTLING,
                                                                                FURTHER
                                                                                TREATMENT.
                                                                                AND/OR DISPOSAL
                        REDUCTION
                      REACTION TANK
                     PRECIPITATION
                         TANK
      	  ELECTRICAL CONTROLS

      G)
        |   MIXER
                        Figure 4  Continuous Chemical  Reduction System

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      When  chemical  reduction is  used  for treating  hexavalent  chromium, the
trivalent  chromium that  is  formed  is  either  reused  or further  treated by
stabilization  and  land  disposed.    Likewise,  for  selenium reduction,  the
precipitated elemental selenium may be recovered or stabilized and disposed of.

3.4         Waste Characteristics Affecting Performance (WCAPs)

      In determining whether  chemical reduction will  achieve  the same level of
performance on an untested waste that it achieved on a previously tested waste,
and whether performance  levels  can be transferred, EPA examines the following
waste characteristics:   (a) the concentration of other reducible compounds and
(b) the concentration of oil  and grease.

3.4.1       Concentration of  Other Reducible Compounds

      The  presence of  other  reducible  compounds  (also  called  oxidizers) in
addition to the  BOAT  list  constituents  of concern will increase the demand of
reducing agents,  thereby potentially  reducing the effectiveness of the treatment
process.   As  a  surrogate  for the  amount of organic  oxidizers present in the
waste, EPA might  analyze for total organic carbon (TOC) in  the waste.  Inorganic
oxidizing  compounds  such as  ionized metals (e.g.,  silver,  selenium,  copper,
mercury) may  also create a demand  for additional  reducing  agent.   EPA might
attempt  to identify  and analyze  for  these metal constituents.   If  TOC or
inorganic oxidizer concentration in  the  untested waste  is significantly higher
than  that  in  previously  tested  wastes, the system may  not  achieve  the  same
performance as  that  achieved previously.    Additional  reducing agent  may be
required to effectively reduce the  untested waste and achieve the  same treatment
performance,  or  other,  more  applicable  treatment  technologies may  need to be
considered for treatment of the untested waste.
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3.4.2       Concentration of Oil and Grease

      EPA believes that oil and grease compounds could cause monitoring problems
because of fouling of instrumentation (e.g., electrodes for pH and ORP sensors).
If the concentration of oil  and grease in  an  untested waste is significantly
higher than that in a tested waste, the untested system may not achieve the same
performance.   Therefore,  other,  more applicable  treatment or  pretreatment
technologies may need to be considered for treatment of the untested waste.

3.5         Design and Operating Parameters

      In assessing the effectiveness of the design and operation of a chemical
reduction system,  EPA examines the following parameters:  (a)  the  residence time,
(b) the amount and type of reducing agent, (c) the degree of  mixing,  (d) the pH,
and (e) the reduction temperature.

      For  many hazardous  organic  constituents,  analytical  methods  are  not
available or the constituent cannot be  analyzed in the waste  matrix.  Therefore,
it would  normally be impossible to measure  the  effectiveness of the chemical
reduction  treatment  system.   In these cases EPA  tries to identify measurable
parameters or constituents that would  act as surrogates to verify treatment.

      For  organic  constituents,  each  compound  contains a measurable amount of
total organic carbon  (TOC).   Removal  of TOC in  the chemical reduction treatment
system indicates removal of organic constituents.  Hence, TOC analysis  is likely
to be  an  adequate  surrogate  analysis where the  specific organic constituent
cannot be  measured.

      However, TOC  analysis may  not  be able to adequately detect treatment of
specific  organics  in matrices that  are heavily organic-laden  (i.e.,  the TOC
analysis may  not  be sensitive enough  to detect  changes at  the  milligrams per
liter (mg/1) level  in matrices where total organic concentrations are hundreds
or thousands  of mg/1).   In  these cases other  surrogate  parameters should be
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sought.   For example,  If a specific  analyzable  constituent is expected to be
treated  as  well as  the  unanalyzable constituent,  the analyzable constituent
concentration should be monitored as  a surrogate.

3.5.1       Residence Time

      The residence  time  affects  the extent of reaction of waste contaminants
with reducing agents.  For a batch system, the residence time  is controlled by
adjustment of the treatment time in the reaction tank.  For a continuous  system,
the waste feed rate is controlled to make sure that the system is operated at the
appropriate design residence time.   EPA monitors the residence time to  ensure
that sufficient time is provided to effectively reduce the  waste.

3.5.2       Amount and Type of  Reducing Agent

      Several factors influence the choice of reducing agents  and the amount to
be added.   The  amount of  reducing  agent required to  treat a given amount of
reducible constituent will  vary with the agent chosen.  Enough reducing agent
must be added to ensure complete reduction;  the specific amount will depend on
the type of reducible compounds in the waste and  the  chemistry of the reduction
reactions.   Theoretically, the amount  of reducing  agent  to  be  added  can be
computed from reduction  reaction stoichiometry.  In practice, however, an excess
of  reducing agent  should be  used.   Testing for  excess  reducing  agent,  if
possible, will determine whether the  reaction has reached completion.

      In  continuous  processes,  the  addition of  reducing  agent  is   usually
accomplished by automated feed methods.   The amount  of reducing agent needed is
usually metered  and controlled automatically by an oxidation-reduction potential
(ORP) sensor.  EPA examines the amount of reduction  agent  added to the chemical
reduction system to ensure that  it is  sufficient to effectively reduce the waste
and,  for continuous  processes, examines  how the  facility  ensures  that the
particular  addition  rate  is maintained.   EPA may also  test  for excess reducing
agent in the system effluent.  For continuous processes, EPA monitors the ORP to
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ensure that  enough reducing agent  is supplied.   EPA may also  monitor pH to
determine  whether it  is  controlled  to  the appropriate  optimum range.   For
continuous systems, pH  is monitored  to  ensure  that it is kept steady to avoid
changes in ORP caused by pH variations.

3.5.3       Degree of Mixing

      Process  tanks  must be  equipped with  mixers to ensure  maximum  contact
between the reducing  agent and the waste oxidizing solution.   Proper mixing also
homogenizes any solid  precipitates  that  may be present,  or that may form from
side reactions, so that they can also be reduced if necessary.  Mixing provides
an even distribution  of tank contents  and a homogeneous pH throughout  the waste,
improving  reduction  of wastewater  constituents.    The quantifiable  degree of
mixing is a complex assessment that includes, among other  factors, the amount of
energy supplied,  the length of time the  material  is mixed,  and the  related
turbulence effects of the specific size  and  shape of  the  tank.   This  is beyond
the scope of simple measurement.  EPA, however, evaluates the degree of mixing
qualitatively,  using  engineering judgment,  by considering  whether  mixing is
provided and whether the type of mixing device  is  one  that could  be expected to
achieve uniform mixing  of the waste solution.

3.5.4       pH

      For batch and continuous  systems,  the  pH  affects the reduction  reaction.
The  reaction  speed  is usually  significantly reduced   at  higher  pH  values
(typically above  4.0).   It  is  worth  noting  that  some reduction  reactions may
proceed  better under alkaline  conditions,  in  which  case pH must be properly
controlled to the appropriate alkaline range.  For a batch system, the pH can be
monitored intermittently during treatment.   For  a continuous system,  the  pH must
be continuously monitored because it affects the ORP reading.  EPA monitors the
pH to ensure that  the system is operating at the appropriate design condition and
to diagnose operational problems.
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3.5.5       Reduction Temperature

      Temperature  affects  the rate  of  reaction and  the  solubility  of the
reactants in the waste.  As the temperature is increased, the solubility of the
reactants, in most  instances,  is  increased and the required residence time, in
most cases,  is reduced.  EPA may monitor the reduction temperature to ensure that
the system  is operating  at  the appropriate  design  condition  and  to diagnose
operational problems.
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3.6         References
McGraw-Hill.   1982.   Encyclopedia  of science  and technology.    Vol.  9,  pp.
      714-718.  New  York:   McGraw-Hill  Book Co.

Nebergall et al.  General chemistry.  5th ed.  Lexington, Mass.:  D.C.  Heath and
      Company.

Patterson, J.W.   1985.   Industrial wastewater treatment technology.  2nd  ed.
      Stoneham, Mass.:   Butterworth  Publishers.
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                     4.   ELECTROLYTIC OXIDATION OF CYANIDE

4.1         Applicability

      Electrolytic  oxidation  is  a  treatment  technology with  demonstrated
applicability  to the treatment  of  wastes  containing high  concentrations of
cyanide  in  solution.   Because  of excessive retention  time  requirements,  the
process is often  applied as preliminary treatment for highly concentrated cyanide
wastes, prior to more conventional chemical cyanide oxidation.

      This  treatment technology  is  used in  industry for the  destruction of
cyanide  in  (a)  concentrated spent plating  solutions  and stripping  solutions,
(b) spent heat treating  baths, (c) alkaline descalers,  and (d)  metal passivating
(rust-inhibiting)  solutions.   Electrolytic oxidation  has  been demonstrated
successfully for treatment of wastes containing concentrations of cyanide up to
100,000 mg/1.   However,  for concentrations of  cyanide lower  than  500  mg/1,
chemical oxidation treatment may  be  more efficient  (see  Section  I.A.2).

4.2         Underlying  Principles of Operation

      The basic principle of operation for electrolytic  oxidation of  cyanide is
that  concentrated  cyanide  waste  subject  to  an  electrolytic  reaction  with
dissolved oxygen  in  an  aqueous solution  is  broken down to  the gaseous  products
carbon dioxide (C02), nitrogen (N2), and ammonia (NH3).  The process is conducted
at elevated temperatures for periods ranging from several hours to over a week,
depending on  the initial cyanide concentration  and the desired  final cyanide
concentration.   The theoretical  destruction  process  that takes  place  at  the
anodes is described  by  the  following reaction:

                           Electricity
  2CN'   +    202         	>    2C02     +      N2     +   2e~
cyanide     oxygen                        carbon        nitrogen    electrons
  ion                                    dioxide
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      The  effectiveness   of   electrolytic   oxidation  is  dependent  on  the
conductivity of the waste, which is a function of several waste characteristics
including  the  concentration of  cyanide  and other  ions  in solution.   As the
process continues, the waste becomes less capable of conducting electricity as
the cyanide concentration  is  reduced,  causing  the  electrolytic reaction to be
much less efficient at longer retention times.

4.3         Description of Electrolytic Oxidation Process

      Typically,  electrolytic  destruction  of cyanide takes place  in a closed
cell.  This cell  consists  of  two electrodes suspended in an aqueous solution,
with  direct  current   (DC)  electricity  supplied  to  drive  the   reaction  to
completion.   The  temperature  of  the bath containing  the cyanide waste  is
maintained  at  or  above  52*C  (125'F).   Sodium chloride  may  be added  to the
solution as an electrolyte (conductor)  to increase the conductivity  of the waste
being treated.  Since the reaction may take days or weeks,  water is usually added
to the tank periodically to make up for losses due to evaporation from the heated
tank.  This is necessary to ensure that the electrodes remain fully  submerged so
that  a  full  flow  of current  is maintained in the  solution during  treatment.
Following  treatment,   the  treated  waste   is  usually  further treated   in  a
conventional chemical  oxidation  system to destroy residual cyanides.

4.4         Waste  Characteristics Affecting Performance  (WCAPs)

      In determining whether electrolytic oxidation will  achieve the same level
of performance on  an untested waste  that it achieved a previously  tested waste
and whether performance  levels  can be transferred, EPA examines the following
waste characteristics:  (a) the concentration of other oxidizable materials and
(b) the concentration of reducible metals.
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4.4.1       Concentration of Other Oxidizable Materials

      The  presence  of  oxidizable  organic*  (such  as   oil   and  grease  and
surfactants) and the presence of inorganic ionic species in a reduced state (such
as trivalent chromium  or  sulfide)  may increase the treatment time required to
achieve  destruction  of  cyanide  because  these   materials  may   be  oxidized
preferentially to the cyanide in solution.  If concentrations of other oxidizable
materials  are  significantly higher  in  the untested waste than  in the tested
waste, the system may not achieve the same performance.  Longer reaction time may
be required to  oxidize cyanide  and achieve the same treatment performance, or
other, more  applicable treatment  technologies  may need  to  be considered for
treatment of the  untested waste.

4.4.2       Concentration of Reducible Metals

      The electrolytic process may cause some of the more  easily reduced metals
in the waste, such  as  copper, to plate out  onto the  cathode  as the pure metal.
The plating of metals onto the cathode may result  in changes  in current density
and, hence, may change the  rate of cyanide  oxidation.  If the  concentration of
reducible metals  in the untested waste is significantly higher than that in the
tested waste, the system  may  not achieve the same performance and other, more
applicable treatment technologies may need to be considered for treatment of the
untested waste.

4.5         Design  and Operating Parameters

      In  assessing  the  effectiveness  of the  design  and  operation of  an
electrolytic oxidation system,  EPA examines the following parameters:  (a) the
oxidation  temperature,  (b)  the  residence time, (c) the pH,  (d) the electrical
conductivity, (e) the electrode spacing and surface area,  and (f)  the  degree of
mixing.
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4.5.1       Oxidation Temperature

      For the electrolytic process, elevated temperatures are used.  Normal
temperatures range from 52 to 93'C (125 to 200*F).  The temperature can be raised
by increasing the  flow of steam to the coils  or  jacket  supplying heat to the
reactor contents.   EPA monitors the oxidation  temperature  to ensure that the
system  is  operating   at  the  appropriate  design  condition  and  to  diagnose
operational problems.

4.5.2       Residence Time

      Electrolytic oxidation is  usually a  batch process.   The time allowed to
complete the reaction is an important factor in electrolysis  and  is  dependent on
the  initial  concentration  of  the  waste  and  the  desired  final  cyanide
concentration.   The  rate of  cyanide  destruction  decreases  as  the  cyanide
concentration decreases (i.e.,  the  rate  of cyanide  destruction asymptotically
approaches zero).  Typical residence times range from periods of several hours
to more than a week.   EPA  observes  the  residence time to ensure that sufficient
time is provided to effectively destroy the cyanides in the wastes.

4.5.3       pH

      Typical solutions for electrolytic oxidation have a pH ranging from  11.5
to 12.0.  The pH must be maintained in  the  alkaline range to prevent liberation
of toxic  hydrogen cyanide.   Typically,  pH  is controlled by the  addition of
caustic or  lime.   EPA monitors the pH to  ensure  that  the treatment system is
operating  at the  appropriate  design  condition  and  to  diagnose  operational
problems.

4.5.4       Electrical Conductivity

      The solution must have  an electrical conductivity high enough to allow the
reaction  to  proceed  at an acceptable  rate.    If the conductivity  is not  high


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enough, it can  be improved by adding an electrolyte such as sodium chloride.  The
conductivity  of the  waste  during  the  reaction  is  normally  determined  by
monitoring both the current and voltage of the cell.  EPA monitors the electrical
conductivity to ensure that the treatment system is operating at the appropriate
design condition.

4.5.5       Electrode Spacing and Surface Area

      The spacing and  surface area of the electrodes directly impact the current
flowing  through the  waste.   The  reaction  rate  is  increased  by  both closer
electrode  spacing  and more  electrode surface area  because  each increases the
current density in  the cell.  EPA observes the electrode spacing and surface area
to ensure that  sufficient current density is provided to effectively destroy the
cyanides in the waste.

4.5.6       Degree of Mixing

      Electrolytic destruction of cyanides  requires good mixing in the reaction
vessel.  Mixing helps  ensure  an adequate  supply of oxygen (from the air) for the
electrochemical reaction (see Section 4.2, Underlying Principles of Operation),
enhances mass  transfer  to promote  the oxidation reaction, and  keeps suspended
solids in  suspension.   Mixing may  be provided  by the bubbling of air from the
bottom of  the  reactor,  or an external source of  mixing may be provided.  The
quantifiable degree of mixing is  a complex assessment that includes, among other
factors, the amount of energy  supplied, the length  of  time the material  is mixed,
and the related turbulence effects of the size  and shape of  the reaction vessel
used.  The degree  of  mixing  is  beyond the  scope  of simple measurement.   EPA,
however,  evaluates the degree of mixing qualitatively by considering whether
mixing is  provided and  whether  the type  of  mixing device is one that could be
expected to achieve uniform mixing  of the waste.
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4.6         References


Cushnie, G.C.,  Jr.   1985.   Electroplating  wastewater pollution control  tech-
      nology,  p. 205.  Park Ridge, N.J.:   Noyes  Publications.

Easton, J.K.  1967.   Electrolytic decomposition of concentrated  cyanide plating
      wastes.  Journal Water Pollution Control  Federation  39(10):1621-1626.

Patterson, J.W.  1985.  Industrial wastewater treatment technology. 2nd ed., pp.
      123-125.  Stoneham, Mass.   Butterworth Publishers.

Pearson, G.J.,  and  Karrs, S.R.   1984.   Electrolytic cyanide destruction.   In
      Proceedings for plating  and surface finishing,  pp. 2 and  3.

Roy, C.H.   1981.  Electrolytic wastewater treatment.  In  a  series  of American
      Electroplaters Society,  Inc., illustrated lectures,  pp. 8-10.
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                               5.  INCINERATION

5.1         Applicability

      Incineration  is  a treatment technology  applicable to  the  treatment of
wastes containing a wide range of organic  concentrations  and low concentrations
of water,  metals,  and  other inorganics.    The four most  common incineration
systems are liquid  injection, rotary kiln, fluidized bed, and fixed hearth.

      Liquid injection incineration is applicable to wastes having sufficiently
low viscosity values (less than 750 saybolt universal seconds (Sus) such that the
waste  can be  atomized  in  the  combustion  chamber.    However,  viscosity is
temperature dependent so that while liquid injection may  not be  applicable  to a
waste at ambient conditions, it may become applicable when the waste is heated.
In addition, the  number of waste particles and the concentration of  suspended
solids need to  be sufficiently low to avoid clogging  of the burner nozzle (or
atomizer openings).

      Rotary kiln,  fluidized bed,  and  fixed hearth incineration are applicable
to wastes having a wide range of viscosity, particle size, and suspended  solids
concentration.

      Incineration  of  highly explosive constituents may require treatment in
units  that are  specially  designed  and  fitted with  certain  explosion-proof
equipment.  Incinerators for corrosive waste should be equipped,  if necessary,
with pollution control  devices to  remove  corrosive gases that may be  generated
from the burning  of corrosive waste.   The incineration of hazardous waste  must
be performed in accordance  with the incinerator design  and emissions regulations
in 40 CFR 264, Subpart  0.
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5.2         Underlying Principles of Operation

      The  basic  principle  of  operation  for  incineration   is  the  thermal
decomposition of organic  constituents  via cracking and oxidation reactions at
high temperatures (usually between 760 and 1550*C  (1400 and 3000'F) to convert
them into carbon dioxide and water vapor along with nitrite oxides,  nitrates, and
ammonia (for nitrogen-containing wastes);  sulfur oxides and sulfate (for sulfur-
containing wastes); or halogen acids (for halogenated wastes).

      In liquid injection  incineration  the organic constituents in the waste are
volatilized and the chemical bonds are destabilized. Once the chemical bonds are
broken, these constituents react with oxygen to  form carbon dioxide, water vapor,
and other aforementioned compounds.

      In rotary kiln  and fixed hearth incineration, two chambers are  involved in
the incineration process.  In the primary chamber, the organic constituents in
the waste  are volatilized.   During  this volatilization  process,  some  of the
organic constituents  oxidize to form carbon dioxide  and  water vapor.   In the
secondary chamber,  the chemical  bonds are destabilized, resulting in  the organic
constituents reacting with oxygen to form carbon dioxide,  water vapor, and other
aforementioned compounds.

      In fluidized bed incineration, a single  chamber contains the fluidizing
sand and  a  freeboard section above the  sand.   The fluidized  bed aids  in the
volatilization and  combustion of the organic waste constituents.  The sand  in the
bed provides a sufficient  heat capacity to volatilize organic constituents.  The
forced air used to fluidize the bed provides sufficient oxygen and  turbulence to
enhance the  reactions of organics with  oxygen to  form  carbon dioxide,  water
vapor, and other aforementioned compounds.  Additional  time for conversion  of the
organic constituents  is provided by the freeboard  above the fluidized bed.
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5.3         Description of Incineration Processes

      The physical form of the waste determines the appropriate feed method into
the incineration system.  Liquids are pumped into the combustion chamber through
nozzles or via specially designed atomizing burners.  Wastes containing suspended
particles may need to be screened to avoid clogging  of  small nozzle or atomizer
openings.  Sludges  and  slurries  are fed using positive displacement pumps and
water-cooled  injection  ports.    Bulk solid  wastes  may require  shredding for
control of particle size.  Wastes may be fed to the combustion  chamber via rams,
gravity  feed,  air lock feeders,  vibratory or  screw feeders,  or belt feeders.
Containerized waste is gravity-fed or ram-fed.

      Although sustained combustion is possible with waste heat content as low
as 2230 kcal/kg (4010 Btu/lb), wastes are typically blended to a net heat content
of  4450 kcal/kg  (8000  Btu/lb)  or  higher or  auxiliary  fuel  is used  in the
combustion chambers to raise the heat content  to  a  level sufficient to sustain
the combustion process.

      Following incineration of wastes, fly ash  particulates, acid gases (halogen
acids),  and  other gaseous  pollutants  (nitric oxides  (NOJ  and  sulfur oxides
(SOJ)  are further  treated in an  air pollution  control  system.   Particulate
emissions  from most waste combustion systems generally have particle diameters
less than 1 micron and require high-efficiency collection systems to minimize air
emissions.  The most common air pollution control  system used  includes a quench
(for gas cooling and conditioning),  followed  by a  high-energy  venturi scrubber*
(for particulate and acid  gas removal), a packed bed  or plate tower absorber (for
acid gas removal),  and  a  demister (for vapor mist plume elimination).

      Packed  bed  or plate  tower  scrubbers  are commonly  used without venturi
scrubbers  in the  air pollution control systems at liquid  injection incinerator
*A venturi is a short tube or duct with a tapering  constriction that  causes  an
 increase in the velocity of fluid flow and a corresponding decrease in pressure.
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facilities,  where absorption  of gaseous  pollutants  is  more  important  than
particulate control.    (Wastes burned in liquid injection incinerators typically
have a low ash content and, hence, generate  a low level of fly ash particulates.)

      Some  liquid injection  incinerator  facilities  do  not  employ  any  air
pollution control system because the wastes  burned contain low levels of both ash
and halogen content, thereby generating low  (i.e., untreatable) levels of fly ash
particulates and acid gases.

      Many air pollution  control  system designs  in  recent  years have begun to
incorporate waste heat boilers as a substitute for gas quenching as a means of
energy recovery.   Wet  electrostatic  precipitators (ESP), ionizing wet scrubbers
(IWS), and fabric filters  are also being incorporated into newer  systems because
these devices have high removal  efficiencies for small particles  and a lower
pressure drop than that of venturi scrubbers.

      The inorganic constituents of wastes (noncombustible ash) are not destroyed
by  incineration.   These  materials,  depending on their composition,  exit the
incinerator  as   either  bottom  ash   from  the  combustion  chamber  or  fly  ash
particulates suspended  in the combustion gas  stream.  Bottom ash is typically
either air-cooled or quenched with water following discharge from the combustion
chamber.    This   waste  is  then  stabilized  (if levels   of  Teachable  metal
constituents of concern are found) and/or land disposed.

      Fly ash particulates,  as well  as  acid gases and other gaseous pollutants,
are entrained in  the  scrubber waters of the  air pollution control  system and
collected in the sumps of recirculation tanks.  Here the acids are neutralized
with caustic  and much of the water  is returned to  the air  pollution control
system.  Eventually, a portion or all  of these scrubber waters  are discharged for
treatment and disposal when the total dissolved solids level becomes excessively
high.  Scrubber waters are discharged either  to a settling  tank  or lagoon or to
a  chemical  precipitation  system  (if treatable  levels of soluble  metal  con-
stituents  of  concern  are found)  to remove  these  solids  prior  to  their land

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disposal.  Depending on the nature of the remaining dissolved constituents and
their  concentrations,  treated  scrubber waters  may  be returned  to  the  air
pollution control  system, further treated in filtration processes,  or discharged.

      Below are descriptions  of the incineration processes  for  the four most
common incinerator systems.

5.3.1       Liquid Injection

      In a liquid  injection incineration  system, a burner or nozzle atomizes the
waste and injects  it  into the combustion chamber, where it is incinerated  in the
presence of air or oxygen.  A forced-draft system supplies the combustion chamber
with  air to provide  oxygen for  combustion  and  turbulence for mixing.   The
combustion  chamber  is  usually  a  cylinder  lined with  refractory (i.e.,  heat-
resistant) brick and  can be fired horizontally, vertically upward, or vertically
downward.  Figure 5 illustrates a liquid injection incineration  system.

5.3.2       Rotary K1ln

      A  rotary kiln  is a  slowly rotating, refractory-lined  cylinder that  is
mounted at a slight  incline from the horizontal.  Solid wastes enter  at the high
end of the kiln,  and  liquid or gaseous  wastes  generally enter through  atomizing
nozzles in the afterburner section of the kiln.   A forced-draft system supplies
the kiln with  air to provide  oxygen for combustion  and turbulence for mixing.
Rotation of the kiln enhances  the exposure of the solids to the heat, thereby
aiding their volatilization as well  as providing additional mixing of the  solids
with  air combustion.   In addition,  the rotation causes the ash  to move  to the
lower end  of the  kiln,  from which it is removed.  Rotary kiln systems usually
have a secondary combustion chamber or afterburner following the kiln  for further
combustion of  the volatilized  waste constituents.   Figure 6 is  a diagram of a
rotary kiln incineration system.
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                                               FLY ASH PARTICIPATES
                                              AND COMBUSTION  GASES
                                         TO AIR POLLUTION CONTROL SYSTEM
                                              AND/OR THE  ATMOSPHERE
    AUXILIARY FUEL	^BURNER
                       AIR-
LIQUID OR GASEOUS
  WASTE  INJECTION
-HBURNER
                                                         t
                PRIMARY
              COMBUSTION
                CHAMBER
AFTERBURNER
 (SECONDARY
 COMBUSTION
  CHAMBER)
                                                         I
                                            BOTTOM ASH TO STABILIZATION
                                               AND/OR LAND DISPOSAL
                 Figure 5  Liquid Injection Incineration System

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                                                 FLY  ASH PARTICULARS
                                               AND COMBUSTION GASES  TO
                                                AIR POLLUTION CONTROL
             UOUIO OR GASEOUS
               WASTE INJECTION
       AUXILIARY
           FUE
  SOLID
 WASTE
INFLUENT
                                                    BOTTOM ASH TO
                                                    STABILIZATION
                                                AND/OR LAND  DISPOSAL
               Figure  6   Rotary Kiln Incineration  System
                                      50

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5.3.3       Fluidized Bed

      A fluidized bed incinerator consists of a column containing inert particles
such as sand, which is referred to as the bed.  Air, driven by  a blower, enters
the bottom of the bed to fluidize the sand.  Air passage through  the bed provides
oxygen for combustion and promotes rapid and uniform mixing of the injected waste
material within the fluidized bed.  The fluidized bed has an extremely high heat
capacity (approximately three times that of flue  (combustion) gases at the same
temperature),  thereby  providing a large  heat  reservoir.  The injected waste
reaches incineration temperature  quickly  and  transfers the  heat of combustion
back to the bed.   The freeboard above the fluidized bed provides additional time
for  combustion  of  organic  constituents.    Because  of the excellent  mixing
properties associated with  fluidized  bed incinerators, they can  operate at lower
temperatures more effectively than other incinerators.  Figure 7 is a diagram of
a fluidized bed  incineration system.

5.3.4       Fixed Hearth Incineration

      Fixed hearth  (also called controlled air or starved air)  incineration is
a two-stage  combustion process.   Waste is ram-fed  into the  first stage,  or
primary chamber,  and burned at less  than stoichiometric conditions  (not enough
oxygen for complete combustion).   The resultant  smoke and pyrolysis products,
consisting primarily of volatile hydrocarbons and  carbon monoxide, along with the
typical products of combustion, pass to the secondary  chamber.   Here additional
air  is  injected to complete  the  combustion process.   This  two-stage process
generally yields low fly ash particulate and carbon monoxide (CO) emissions.  The
primary chamber combustion  reactions  and resultant combustion  gas velocities are
maintained  at  low  levels  by the  starved  air  conditions so  that  particulate
entrainment and carryover in the combustion gases are  minimized.   Figure 8 is a
diagram of a fixed  hearth incineration system.
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  BOTTOM ASH TO STABILIZATION
     AND/OR LAND  DISPOSAL
                                             FLY ASH
                                             PARTICIPATES
                                             AND COMBUSTION
                                             GASES TO AIR
                                             POLLUTION
                                             CONTROL SYSTEM
                                            MAKE-UP
                                            SAND
                                             AIR
Figure 7  Fluidized Bed Incineration System
                   52

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                                                                 AIR
                                                        FLY  ASH PARTICIPATES
                                                        AND  COMBUSTION  GASES
                                                           TO AIR POLLUTION
                                                           CONTROL  SYSTEM
                      AIR
in
              WASTE
           INJECTION
BURNER
                                                                 i
                                        PRIMARY
                                      COMBUSTION
                                       CHAMBER
                                           I
                                      SECONDARY
                                     COMBUSTION
                                       CHAMBER
BURNERM-
AUXILIARY
FUEL
                              BOTTOM ASH TO STABILIZATION
                                  AND/OR LAND DISPOSAL
                                      Figure 8  Fixed Hearth  Incineration System

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5.4         Waste Characteristics Affecting Performance (WCAPs)

      In  determining whether  incineration  will   achieve  the  same  level  of
performance on an untested waste that it achieved on a previously tested waste
and whether performance  levels can  be transferred, EPA examines the  following
waste characteristics:    (a) the  thermal conductivity  of the  waste,  (b) the
component boiling points, (c)  the  component  bond dissociation energies,  (d) the
heating value of the waste, (e) the concentration of explosive constituents, and
(f) the concentration of noncombustible constituents.

5.4.1       Thermal  Conductivity of the Waste

      A major factor determining whether a particular constituent will volatilize
is the transfer of heat through the waste.   For rotary kiln, fluidized bed, and
fixed hearth  incineration, heat is transferred through the waste by radiation,
convection, and conduction.

      EPA examined all  three methods of heat transfer.  For a given incinerator,
heat transferred  through  various  wastes  by  radiation and convection  is more  a
function of the design and type of incinerator than of the waste being treated;
therefore,  EPA believes  that  conduction would be the  primary cause of heat
transfer differences between wastes.   Heat flow by conduction  is proportional to
the temperature  gradient across the  material.   The proportionality  constant,
referred to  as the thermal conductivity, is  a  property  of the material to be
incinerated.

      Thermal conductivity measurements,  as part of a treatability comparison for
two different wastes to be treated by a single incinerator, are most meaningful
when applied  to wastes  that  are  homogeneous  (i.e., uniform  throughout).   As
wastes exhibit greater degrees of nonhomogeneity,  thermal conductivity becomes
less accurate in predicting treatability because the  measurement essentially
reflects heat  flow  through regions having the greatest conductivity (i.e., the
path of  least resistance) and not  heat flow through all  parts of the waste.
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Nevertheless, EPA believes that thermal conductivity may provide the best measure
of performance transfer.   If  the  thermal  conductivity of an untested waste is
significantly lower than that of the tested waste, the system may not  achieve the
same performance.  Higher temperatures may be  required to  improve  heat transfer
through the  waste and achieve the same treatment performance,  or other, more
applicable treatment technologies  may need to be considered for treatment  of the
untested wastes.

5.4.2       Component Boiling Points

      Following  transfer  of  heat  to a  constituent  within  a waste,  the
constituent's removal depends on its  volatility.  EPA recognizes,  however, that
volatilities are  difficult  to measure or calculate directly  for  the types of
wastes generally treated by incineration  because the wastes usually consist of
a mixture of components.   However,  because the volatilities of components are
usually inversely  proportional  to their  boiling points  (i.e.,  the  higher the
boiling point, the lower the volatility),  EPA uses the boiling points of waste
components as a surrogate waste characteristic for volatility.  If the boiling
points of waste components in the untested waste are significantly higher than
those in  the tested waste, the system may not achieve  the same performance.
Higher temperatures may be required to volatilize less volatile components and
achieve the  same  treatment  performance  or  other,  more  applicable treatment
technologies may need to be considered for treatment of the untested wastes.

5.4.3       Component Bond Dissociation Energies

      The activation energy is the amount of heat energy needed to destabilize
molecular  bonds  so  that  the  exothermic combustion  reactions  can  proceed.
Typically, the activation energy required  for  incineration  of  solids is greater
than that required for liquids, and the activation energy  required for liquids
is higher than that  required  for  gases.   However,  the activation energies for
components are difficult to measure  or calculate  directly and usually must be
determined empirically.  The  bond dissociation energy is the amount of  energy


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needed to break each of the individual  bonds  in a molecule.  Theoretically, the
bond dissociation  energy  and the activation energy  are  equivalent.   However,
other energy effects including interactions between different molecular bonds may
have  a  significant  influence on  the  activation  energy.    Nevertheless,  EPA
believes that  bond dissociation energy  is the best  indicator  for activation
energy and therefore uses  it as a surrogate waste characteristic.  If the bond
dissociation energies of waste components  in an untested waste are significantly
higher than  those in  the  tested waste,  the  system  may not achieve  the same
performance.  Higher temperatures may be required to destabilize molecular bonds
for waste components with  high bond dissociation energies and achieve the same
treatment performance, or other, more applicable treatment technologies may need
to be considered for treatment of the untested waste.

5.4.4       Heating Value  of the Waste

      The amount of heat released from  the exothermic combustion reactions of  a
waste is referred to as its heating value. To maintain combustion, the heating
value of a waste must  be sufficient to heat incoming waste up to the appropriate
design incineration temperature and provide the necessary activation energy for
additional  combustion reactions to  occur.   Higher  waste  heating  values are
required for higher incineration temperatures and higher amounts of excess oxygen
to sustain combustion without auxiliary fuel consumption.  Low heating values for
an  organic  waste  are usually  caused  by high  concentrations  of  water  or
halogenated  compounds.    If  the  heating  value  of  an   untested   waste  is
significantly lower than that  of the tested waste, the system may not achieve the
same performance.  Auxiliary fuel may be required to  provide the necessary heat
to maintain combustion and  achieve the same treatment performance, or other, more
applicable treatment technologies may need to be considered for  treatment of the
untested waste.
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5.4.5       Concentration of Explosive Constituents

      Explosive  constituents  may  interfere  with the  smooth operation  of an
incinerator, causing process upsets  resulting  in ineffective treatment of the
waste.  If the concentration of explosive constituents in an untested waste is
significantly higher than that in the tested waste, the system may not achieve
the same performance and other, more  applicable treatment technologies may need
to be considered for treatment of the untested waste.

5.4.6       Concentration of Noncombustible Constituents

      Noncombustible constituents Include water, metals, and other inorganics.
High concentrations of noncombustible constituents result in low waste heating
values, requiring  auxiliary fuel; large  quantities of bottom  ash,  requiring
stabilization treatment (if treatable levels  of Teachable metal constituents of
concern  are  present)   and/or disposal;   and  large  quantities  of  fly  ash
particulates and volatile metals in the combustion gases, requiring removal in
an air pollution control  system and treatment in a settling  tank  or lagoon or by
means of a chemical precipitation system (if treatable levels of soluble metal
constituents of concern are  present) followed by disposal.  Volatile metals such
as arsenic  may  also fuse to  the  refractory walls  in the  combustion chamber,
inhibiting  effective operation  of the  incinerator.   If the concentration of
noncombustible constituents in an  untested  waste is significantly higher than
that in the tested  waste, the system may  not achieve the same performance and
other, more  applicable treatment technologies may  need to  be  considered for
treatment of the untested waste.

5.5         Design  and Operating Parameters

      In  assessing  the  effectiveness  of  the  design   and  operation  of  an
incineration system, EPA examines the  following parameters:  (a) the incineration
temperature,  (b) the  concentration  of  excess  oxygen  in  the combustion  gas,
(c) the concentration  of  carbon monoxide  in  the  combustion gas, (d) the waste


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feed rate, and (e)  the degree of waste/air mixing.  In addition, incineration of
hazardous waste must be performed in accordance with the  incineration design and
emissions  regulations  in  40 CFR 264,  Subpart  0.   For  many  hazardous organic
constituents, analytical  methods are not available  or the constituent cannot be
analyzed  in  the  waste  matrix.   Therefore, it  would normally be impossible to
measure the effectiveness of the incineration treatment  system.   In these cases
EPA tries  to  identify measurable parameters or constituents  that would act as
surrogates to verify treatment.

      For organic constituents,  each constituent contains a  measurable  amount of
total organic carbon (TOC).  Removal of TOC in the incineration treatment system
indicates removal of organic constituents. Hence,  TOC analysis  is likely to be
an adequate surrogate analysis  where the specific organic constituent cannot be
measured.

      However, TOC  analysis may not  be able  to adequately  detect treatment of
specific  organics  in matrices  that  are heavily organic-laden  (i.e.,  the TOC
analysis  may  not be sensitive  enough to  detect  changes at the milligrams per
liter (mg/1) level  in matrices where total organic  concentrations are hundreds
or thousands  of mg/1).    In  these  cases other  surrogate parameters  should be
sought.   For example,  "if a specific analyzable  constituent  is  expected to be
treated  as well  as  the  unanalyzable constituent,   the  analyzable constituent
concentration should be monitored as a  surrogate.

5.5.1        Incineration Temperature

      Temperature  provides  an  indirect  measure of  the energy available (i.e.,
Btu/hr)  to  both  volatilize  organic  waste  constituents  and  overcome  their
activation  energy.   As  the  design  temperature   in  the  combustion chamber
increases,  more constituents  with  lower  volatilities  and  higher  activation
energies  will  be  destroyed.    EPA  monitors  the incineration  temperature
continuously to  ensure that  the system is operating at the appropriate design
condition  and to diagnose operational problems.
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5.5.2       Concentration of Excess Oxygen in the Combustion Gas

      A sufficient supply of oxygen must be supplied to the combustion chamber
to effectively incinerate the organic waste constituents. The stoichiometric or
minimum theoretical oxygen requirement to completely  combust the waste is based
on the amounts of combustible constituents in the waste.  If perfect mixing could
be achieved and  the waste burned instantaneously,  only the stoichiometric amount
of oxygen would be needed  for  complete combustion.   However,  neither of these
phenomena occur in commercial  incinerators.   The  amount of excess  oxygen in a
given  incinerator  depends on the  degree of  waste/air  mixing  achieved  in the
combustion chamber and  the  desired degree of  combustion gas cooling.  Because
excess air (oxygen) supplied to the combustion chamber acts as  a diluent in the
combustion process, it reduces the overall temperature in the incinerator (i.e.,
maximum theoretical incineration temperatures are achieved at zero percent excess
air).   This  temperature  reduction might be desirable  to limit  refractory
degradation when high-heating value wastes are being burned. However, when low-
heating-value wastes  are being burned, excess  air should  be minimized to keep the
system temperature as high as possible.  Even  with high-heating-value waste, it
is desirable  for equipment design considerations to limit  the  amount of excess
air to some extent  so that combustion chamber volume and downstream air pollution
control system sizes can be limited.

      An inadequate supply of oxygen, on the other hand, will lead to ineffective
incineration  with  higher concentrations  of  carbon monoxide (CO)  and  organic
products of incomplete combustion  (PICs),  resulting in a heavier load  on the air
pollution control  system. Typically, 20 to 60 percent excess oxygen is required
to   provide   adequate  waste/oxygen   contact  and,   subsequently,   effective
incineration  of the waste.  EPA monitors the concentration of  excess oxygen in
the combustion gas continuously to ensure that the system is  operating at the
appropriate design condition and to diagnose operational problems.
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5.5.3       Concentration of Carbon Monoxide 1n the Combustion Gas

      The concentration  of  carbon monoxide in the combustion  gas provides an
indication of the extent  to which organic  waste  constituents are converted to
carbon dioxide and water  vapor.  Higher carbon monoxide levels are  an indication
of ineffective incineration with the presence of greater amounts of unreacted or
partially reacted organic waste constituents in the combustion gas, resulting in
a heavier load  on the air  pollution  control  system.   Higher  carbon monoxide
levels can result from an insufficient incineration temperature; an inadequate
supply of excess  oxygen;  a  waste feed rate that  is  too high,  resulting in an
insufficient residence time  for the waste; and improper mixing in the combustion
chamber.  EPA monitors the concentration of  carbon monoxide in the combustion gas
continuously to ensure that the  system is  operating  at the appropriate design
conditions and to diagnose operational problems.

5.5.4       Waste Feed Rate

      The waste  feed rate determines  the  residence  time of the  waste in the
combustion chamber.   Sufficient  residence  time must  be provided  to allow for
volatilization of the organic waste  constituents,  mixing with  oxygen in the
combustion chamber,  and  completion  of the  combustion reactions.   The total
residence time required for  these  processes to occur depends on  the incineration
temperature, the amount of excess  oxygen provided in the combustion chamber, the
degree  of waste/air mixing in  the combustion chamber, the size  and  type of
incinerator used, the  physical form  of the waste, and the waste particle size
(which determines the amount of waste surface area available for heat transfer).
Typical incinerator residence times range from approximately 2 seconds for liquid
and  gaseous   wastes  in  liquid  injection  incinerators  and the  afterburner,
freeboard, and secondary combustion chambers of rotary kiln,  fluidized  bed, and
fixed hearth  incinerators to 30 minutes to 1 hour for  solid wastes  in  a rotary
kiln incinerator.  EPA monitors the waste feed rate continuously to  ensure that
sufficient residence  time is  provided to effectively  incinerate organic waste
constituents.
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5.5.5       Degree of Waste/Air Mixing

      The  incineration  temperature,  the  amount of  excess  oxygen,   and  the
residence time required to achieve effective incineration  of  a waste all depend
to some extent on the degree of waste/air mixing in the combustion chamber.  For
liquid  injection incinerators, the  degree  of  waste/air  mixing  is  primarily
determined by the specific burner design  and the degree of atomization of the
waste/air mixture achieved.    The degree of atomization  is dependent on the
viscosity of the liquid waste and the amount  of solid impurities present. If the
waste viscosity exceeds 750 Sus or the amount of solid impurities is too high,
the degree  of  atomization may not be  fine enough,  resulting  in  ineffective
incineration.

      For rotary kiln  incineration, the degree of waste/air mixing is determined
by the airflow  rate into the kiln as well as the rate of rotation (revolutions
per minute (RPM)) of the kiln.   As the  airflow rate  is increased, the degree of
waste/air  mixing is  improved  although  this  also  reduces  the  incineration
temperature and residence time of the combustion  gases.  Increasing the rate of
rotation of the kiln also improves waste/air mixing;  however,  the residence time
of the waste  solids is  also  reduced.   Typical  rotation  rates for rotary kilns
range from 0.3  to 1.5 meters per minute (1 to 5 feet  per minute).

      For fluidized bed incineration, the degree of waste/air mixing is indicated
by the pressure drop through the bed caused by the airflow  rate used to  fluidize
the bed.  The higher  the pressure  drop,  the  greater  the degree of mixing in the
fluidized bed.  However, this  also reduces the incineration temperature and the
residence time  of the waste solids and combustion gases.

      For fixed hearth incineration, the degree of waste/air mixing is determined
by  the  airflow  rate  into the combustion  chamber.   As  the airflow  rate  is
increased,  the  degree of  waste/air  mixing  is  improved.   However,  this  also
reduces the  incineration temperature and  the residence  time of the combustion
gases.
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      The quantifiable degree of waste/air mixing is a complex assessment  that
is  difficult  to  express  in  absolute  terms.   However,   for  liquid  injection
incineration, EPA evaluates the degree of mixing qualitatively by examining the
burner design and determining whether it could be expected to  achieve  effective
atomization  of  the  waste/air  mixture.    For  rotary  kiln  incineration,   EPA
estimates the degree of mixing  by monitoring  the  airflow  rate into  the  kiln as
well as the kiln's rate of rotation to ensure that effective mixing of the waste
and air is achieved.   For fluidized bed  incineration, EPA estimates the degree
of  mixing by  monitoring  the  pressure  drop  through the bed to ensure  that
effective mixing of waste and air is achieved.   For  fixed hearth incineration,
EPA estimates  the degree of mixing by  monitoring  the airflow  rate into  the
combustion  chamber to ensure  that  effective mixing  of   the  waste  and  air  is
achieved.
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5.6         References


Ackerman, D.G., McGaughey, J.F., and Wagoner, D.E.  1983.  At sea  incineration
      of PCB-containinq wastes on board the M/T vulcanus.  600/7-83-024.  U.S.
      Environmental Protection Agency, Washington, D.C.

Bonner,  I.A.,  et  al.    1981.    Engineering  handbook  for hazardous  waste
      incineration.    Prepared  by  Monsanto  Research  Corporation   for  U.S.
      Environmental Protection Agency.  PB 81-248166.

Moller, J.J., and  Christiansen,  O.B.   1984.   Dry scrubbing of hazardous waste
      incinerator  flue  gas  by spray dryer absorption.   In Proceedings of  the
      77th annual APCA meeting.

Novak, R.G.,  Troxler,  W.L., and Dehnke,  T.H.   1984.   Recovering energy from
      hazardous waste incineration, Chemical engineering progress  91:146.

Oppelt, E.T.  1987.  Incineration of hazardous  waste,  JAPCA vol.  37,  no. 5,  May
      1987.

Santoleri,  J.J.    1983.   Energy  recovery—a  by  product  of  hazardous  waste
      incineration systems.   In Proceedings of the 15th Mid-Atlantic Industrial
      Waste Conference on Toxic  and Hazardous Waste.

Vogel, G.,  et al.   1983.   Composition  of hazardous  waste  streams  currently
      incinerated.  Prepared by  Mitre Corp.  for U.S.  Environmental  Protection
      Agency.

Vogel, G., et al.   1986.   Incineration and cement kiln capacity for  hazardous
      waste treatment.  In Proceedings of the 12th Annual Research  Symposium on
      Incineration and Treatment of Hazardous Wastes.  Cincinnati,  Ohio.
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                             6.   WET AIR OXIDATION

6.1         Applicability

      Wet air  oxidation is  a  treatment technology  applicable  to wastewaters
containing organics and oxidizable  inorganics such as cyanide.  The process is
typically used to oxidize sewage sludge,  regenerate spent activated carbon, and
treat process wastewaters.   Wastewaters treated using this technology include
pesticide  wastes,  petrochemical   process  wastes,  cyanide-containing  metal
finishing wastes, spent caustic wastewaters containing phenolic compounds, and
some organic chemical production wastewaters.

      This technology differs from  other treatment technologies generally used
to treat wastewaters containing organics in the  following ways.  First, wet air
oxidation  can   be   used   to  treat  wastewaters  that  have  higher  organic
concentrations  than  are  normally   handled  by  biological   treatment,  carbon
adsorption,  and  chemical  oxidation but may be too  dilute  to  be effectively
treated by thermal  processes such  as incineration.   Wet air oxidation is most
applicable for waste streams containing dissolved or suspended organics in the
500 to 50,000 mg/1 range.   Below 500 mg/1,  the rates of wet air oxidation of most
organic constituents are too slow for efficient  application  of this technology.
For these more dilute waste streams, biological  treatment, carbon adsorption, or
chemical oxidation may be more applicable.   For  more  concentrated  waste streams
(above  50,000 mg/1),   thermal  processes  such   as   incineration  may be  more
applicable.   Second, wet  air  oxidation  can  be applied  to wastes  that have
significant  concentrations of metals  (roughly  2 percent),  whereas biological
treatment, carbon  adsorption,  and  chemical  oxidation may  have  difficulty in
treating such wastes.

      It is  important to point  out  that wet air oxidation proceeds by a series
of reaction steps and the intermediate  products  formed are not always  as readily
oxidized  as  are  the original  constituents.   Therefore, the process does not
always achieve complete oxidation of the organic constituents.  Accordingly, in

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applying  this technology  it  is  important  to assess  potential  products of
incomplete  oxidation  to determine  whether  further treatment  is necessary or
whether this technology is appropriate at all.

      Studies of the wet air oxidation  of different compounds have led to the
following empirical observations concerning a compound's susceptibility to wet
air oxidation based on its chemical structure:

      1.  Aliphatic  compounds,  even  with  multiple  halogen  atoms,  can  be
          destroyed   within   conventional   wet  air   oxidation  conditions.
          Oxygenated   compounds  (such   as   low-molecular-weight  alcohols,
          aldehydes,  ketones,  and  carboxylic  acids)   are  formed,  but  these
          compounds are readily biotreatable.

      2.  Aromatic hydrocarbons, such as toluene, acenaphthene,  or pyrene, are
          easily oxidized.

      3.  Halogenated aromatic  compounds  can  be oxidized provided there is at
          least  one  nonhalogen functional  group present  on  the  ring (e.g.,
          pentachlorophenol  (-OH) or 2,4,6-trichloroaniline  (-NH2)).

      4.  Halogenated aromatic compounds,  such as 1,2-dichlorobenzene, and PCBs,
          such  as  Aroclor   1254,   are  resistant  to wet air  oxidation  under
          conventional conditions.

      5.  Halogenated ring compounds, such as the pesticides  aldrin, dieldrin,
          and endrin,  are expected to be  resistant to conventional  wet air
          oxidation.

      6.  DDT can be oxidized, but results in the  formation  of intractable  oils
          in conventional wet air oxidation.
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      7.  Heterocyclic  compounds  containing oxygen,  nitrogen,  or  sulfur are
          expected to be destroyed by wet air oxidation because the 0, N, or S
          atoms provide a point of attack for oxidation reactions to occur.

6.2         Underlying Principles of Operation

      The basic principle of operation for wet air oxidation is that the enhanced
solubility of  oxygen  in water at high temperatures  and  pressures  aids in the
oxidation of  organics.   The  typical  operating temperature  for the  wet air
oxidation treatment  process  ranges  from 175  to  325*C  (347  to 617*F).   The
pressure is maintained at a level high enough to prevent excessive evaporation
of the  liquid  phase at the  operating temperature,  generally  between  300 and
3000 psi. At these elevated temperatures  and pressures, the solubility of oxygen
in water is dramatically increased, thus providing a strong driving force for the
oxidation.   The  reaction  must take  place  in  the  aqueous phase  because the
chemical reactions involve both oxygen (oxidation)  and water  (hydrolysis).  The
wet air oxidation process for  a specific organic compound generally involves a
number of oxidation and hydrolysis reactions  in series, which degrade  the initial
compound by steps into  a series of compounds of simpler structure.  Complete wet
air oxidation results in the conversion of organic compounds into carbon dioxide,
water   vapor,    ammonia   (for   nitrogen-containing   wastes),   sulfate   (for
sulfur-containing wastes), and halogen acids (for halogenated wastes).

      However,  treatable quantities of partial degradation products may remain
in the treated  wastewaters from wet air oxidation.  Therefore, effluents  from wet
air oxidation  processes may be given subsequent treatment including biological
treatment, carbon adsorption,  or chemical oxidation  before being discharged.

6.3         Description of Wet Air Oxidation Process

      A conventional  wet air oxidation system consists of a high-pressure liquid
feed  pump,  an  oxygen  source   (air compressor  or  liquid  oxygen vaporizer),  a
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reactor, heat exchangers, a vapor-liquid separator, and process regulators.  A
basic flow diagram is shown in Figure 9.

      A typical batch wet air oxidation process proceeds as follows.  First, a
copper  catalyst  solution  may  be  mixed  with  the  aqueous  waste  stream  if
preliminary testing indicates that a catalyst is necessary.  The waste is then
pumped into the reaction chamber.  The aqueous waste is pressurized  and heated
to the design  pressure  and temperature.  After reaction  conditions have been
established, air is fed to the reactor for the duration of the design reaction
time.  At the completion of the wet air oxidation process, suspended solids or
gases are removed and the remaining treated aqueous waste is either  discharged
directly to disposal  or fed to a  biological  treatment,  carbon adsorption, or
chemical oxidation treatment system if further treatment is necessary prior to
discharge to disposal.

      Wet  air  oxidation can  also be  operated  in  a  continuous process.   In
continuous operation, the waste  is pressurized, mixed  with pressurized air or
oxygen, preheated in a series of heat exchangers by the  hot  reactor  effluent and
steam, and fed  to the reactor.   The waste feed  flow rate controls the reactor
residence  time.   Steam  is  fed into the  reactor  column to  adjust the column
temperature. The treated waste is separated  in a gas-liquid separator, with the
gases  treated  in an  air pollution  control  system  and/or discharged  to the
atmosphere, and the liquids either further treated, as mentioned above, and/or
discharged to disposal.

6.4         Waste Characteristics Affecting Performance (WCAPs)

      In determining  whether wet  air  oxidation  will  achieve the same level of
performance on an untested waste that  it achieved on a previously  tested waste
and whether performance  levels can be transferred,  EPA examines the following
waste characteristics:  (a)  the chemical oxygen demand and  (b)  the concentration
of interfering substances.
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      PRESSURIZED
      WASTEWATER
      INFLUENT
t
                  PRESSURIZED
                     AIR OR
                    OXYGEN
CO
 FEED HEAT
EXCHANGERS
                                                            REACTOR
                      STEAM
VENT GASES TO
AIR POLLUTION
CONTROL SYSTEM
AND/OR THE
ATMOSPHERE
                                                      STEAM
                                                      GAS-LIQUID
                                                      SEPARATOR
                                                                                     TREATED
                                                                                     EFFLUENT
                                                                                    TO FURTHER
                                                                                    TREATMENT
                                                                                      AND/OR
                                                                                     DISPOSAL
                              Figure 9  Continuous Uet Air Oxidation System

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6.4.1       Chemical Oxygen Demand

      The chemical oxygen demand (COD) of the waste is a measure of the oxygen
required for complete oxidation of the oxidizable waste constituents.  The limit
to the amount of  oxygen  that  can be  supplied  to the waste is dependent on the
solubility of oxygen in the aqueous waste  and  the rate of dissolution of oxygen
from the gas phase to the liquid  phase.  This  sets  an upper limit on the amount
of oxidizable compounds that can be treated by wet air oxidation.  Thus, high-COO
wastes may require dilution for effective  treatment to occur.   If the COD of the
untested waste is  significantly higher than that of the tested waste, the system
may not achieve the same performance. Pretreatment of the waste or dilution as
part of treatment may be needed to reduce  the  COD to within levels treatable by
the dissolved oxygen concentration and to achieve the same treatment performance,
or other, more applicable treatment technologies may need to be considered for
treatment of the untested waste.

6.4.2       Concentration of  Interfering Substances

      In some cases,  addition of a water-soluble  copper  salt  catalyst to the
waste before  processing is necessary  for efficient oxidation  treatment  (for
example, for oxidation of  some halogenated  organics).   Other metals have been
tested and have been  found  to  be less effective.  Interfering  substances for the
wet air  oxidation process are essentially  those that  cause  the  formation of
insoluble  copper  salts when  copper  catalysts are  used.   To be  effective in
catalyzing the oxidation  reaction, the copper ions must be dissolved in solution.
Sulfide, carbonate, and other  negative ions that form insoluble copper salts may
interfere  with  treatment  effectiveness   if  they  are  present  in  significant
concentrations in wastes for which copper  catalysts are  necessary for effective
treatment.   If an  untested waste  for which  a  copper catalyst is necessary for
effective  treatment  has  a concentration  of interfering substances  (including
sulfide,  carbonate,  or  other  anions  that  form  insoluble  copper  salts)
significantly higher than that in a tested waste, the system may  not achieve the
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same performance and other, more applicable treatment technologies may need to
be considered for treatment of the untested waste.

6.5         Design and Operating Parameters

      In assessing the effectiveness  of  the  design  and operation of a wet air
oxidation system,  EPA examines  the  following parameters:   (a) the oxidation
temperature, (b)  the residence time, (c)  the excess oxygen concentration, (d) the
oxidation pressure, and (e)  the amount and type of catalyst.   For many hazardous
organic constituents,  analytical methods are not available or the constituent
cannot  be  analyzed  in the  waste  matrix.   Therefore,  it  would  normally be
impossible  to  measure the  effectiveness of  the wet  air  oxidation treatment
system.   In  these  cases  EPA  tries to  identify  measurable  parameters or
constituents that  would act as  surrogates to verify treatment.

      For organic  constituents,  each  compound contains a measurable amount of
total organic carbon (TOC).  Removal  of  TOC  in the wet air oxidation treatment
system indicates removal  of organic constituents.  Hence,  TOC  analysis is likely
to be  an  adequate  surrogate  analysis where  the  specific  organic constituent
cannot be measured.

      However, TOC  analysis  may  not  be  able to adequately detect treatment of
specific organics  in matrices that  are heavily organic-laden  (i.e.,  the TOC
analysis may  not be sensitive enough to detect  changes  at the milligrams per
liter (mg/1) level  in matrices where  total organic concentrations are hundreds
or thousands  of mg/1).   In  these  cases  other  surrogate parameters should be
sought.  For  example,  if a specific  analyzable  constituent  is expected to be
treated as  well  as  the  unanalyzable constituent,  the analyzable constituent
concentration should be monitored as  a surrogate.
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6.5.1       Oxidation Temperature

      Temperature is  the  most important parameter affecting  the  system.   The
design temperature  must be  high  enough to  allow the oxidation  reactions to
proceed at  acceptable rates.   Raising  the temperature increases  the wet air
oxidation rate  by enhancing  oxygen solubility  and  oxygen diffusivity.   The
process is normally operated  in the temperature  range of  175 to 325*C (347 to
617*F), depending on the hazardous constituent(s) to be treated.  EPA monitors
the oxidation temperature continuously,  if possible,  to ensure that the  system
is operating  at  the  appropriate design condition  and  to  diagnose operational
problems.

6.5.2       Residence Time

      The residence time impacts the extent of oxidation of waste contaminants.
For a batch system, the-residence time is controlled directly by adjusting the
treatment time in the  reaction  tank.   For a continuous system,  the waste  feed
rate is controlled to make sure that the system is operated at the appropriate
design residence time.  Generally, the reaction rates are relatively fast for the
first 30 minutes  and  become slow after 60  minutes.   Typical  residence times,
therefore, are approximately 1 hour.  EPA  monitors the  residence time  to ensure
that sufficient time is provided to effectively oxidize the waste.

6.5.3       Excess Oxygen Concentration

      The system must be designed to supply adequate amounts  of oxygen for the
compounds to be  oxidized.  An estimate of the amount of oxygen needed can be  made
based on  the COD content of the untreated waste; excess oxygen should be supplied
to ensure  complete oxidation.   The source of oxygen is  compressed  air  or a
high-pressure pure oxygen stream.   EPA monitors the excess oxygen concentration
(the concentration of  oxygen  in  the gas  leaving  the reactor) continuously, if
possible, by sampling the vent gas from  the gas-liquid  separator to ensure  that
an effective amount of oxygen or air is being supplied to the waste.

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6.5.4       Oxidation Pressure

      The design pressure must be high enough to prevent excessive evaporation
of water  and volatile  organics  at the  design  temperature.   This  allows the
oxidation reaction to occur  in  the aqueous phase,  thereby  improving treatment
effectiveness.  Typical  oxidation  pressures  range  from 900 to 3000 psig.  EPA
monitors the oxidation  pressure  continuously,  if possible, to ensure that the
system  is  operating  at  the  appropriate design  condition  and  to  diagnose
operational problems.

6.5.5       Amount and Type of Catalyst

      Adding a catalyst  that promotes oxygen transfer and thus enhances oxidation
has the effect of lowering the necessary reactor temperature and/or improving the
level of destruction of oxidizable compounds.  For waste constituents that are
more  difficult  to oxidize,  the addition  of a  catalyst  may  be necessary to
effectively destroy the  constituent(s)  of concern.  Catalysts typically used for
this  purpose include copper  bromide  and  copper nitrate.    If  a catalyst is
required,  EPA  examines  the  amount  and  type added,  as well  as  the  method of
addition of  the  catalyst to the waste,  to ensure  that effective oxidation is
achieved.
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6.6         References
Detrich, M.J.,  Randall,  T.L.,  and Canney, P.J.   1985.   Wet air  oxidation  of
      hazardous organics  in wastewater.   Environmental  Progress 4:171-197.

Randall, T.L.   1981.   Wet oxidation  of toxic and hazardous compounds,  Zimpro
      technical bulletin  1-610.   Presented at the 13th  Mid-Atlantic Industrial
      Waste Conference, June 29-30, 1981, University of Delaware, Newark, Del.

USEPA.  1990.  U.S. Environmental Protection Agency, Office of Solid Waste.  Best
      demonstrated available technology (BOAT) background document addendum for
      acrvlonitrile wastes.   Washington, D.C.:  U.S. Environmental  Protection
      Agency.
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    I.  TREATMENT TECHNOLOGIES (CONTINUED)
B.  TECHNOLOGIES THAT REDUCE THE SOLUBILITY OR
            LEACHABILITY OF METALS

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                               1.  AMALGAMATION

1.1         Applicability

      The term amalgamation refers to two types of processes that can  be  used as
treatment for mercury wastes.  Neither amalgamation process significantly  reduces
the Teachability of mercury; both processes only convert  it into a more easily
processed form.  In both processes, a solid alloy of mercury and a base metal,
such as zinc, is formed.  This alloy can be subsequently  processed by retorting
to recover mercury.

      The two processes differ from each other in the types of wastes managed.
The first process is applicable only to solutions containing dissolved  mercury
salts.  The principal  current  use  for the process is in treatment  of wastewaters
containing organomercury  salts.   The  second  process is  usable only for wastes
rich  in elemental mercury.   Since the use of  this  second process  is merely a
convenience  to  avoid  handling mercury in liquid  form,  its use  is negligible.
Both processes are applicable only to wastes  containing mercury where selective
recovery of the mercury is deemed viable.

1.2         Underlying Principles of Operation

      The amalgamation processes  depend on the ability of mercury to form  low-
melting-point solid alloys with metals such as copper and zinc,  which have the
thermodynamic capability of simultaneously reducing mercuric and mercurous salts
to elemental mercury.   Basically, an excess of  the less noble metal (zinc or
copper) is  contacted  with a  waste  containing  mercury or mercury  salts.   The
chemical  reaction  reducing the  mercury  in  the  mercury  salts  occurs  and the
elemental  mercury liberated forms  an alloy with  the excess metal added.  For  zinc
and mercuric nitrate, the reaction may be written:
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            Hg(N03)2 + Zn - Zn(N03)2 + Hg

            Hg + Zn •» mercury zinc amalgam

1.3         Description  of Amalgamation Treatment Processes

      The two types of amalgamation processes are operated as  follows:

      1.  The aqueous replacement process (solution process) involves  addition
          of  excess  base  metal,  such  as  zinc,  to  a wastewater  solution
          containing dissolved mercury salts.  The elemental zinc, or other base
          metal, reacts  with the mercuric or mercurous  salts to  form elemental
          mercury, which subsequently alloys with the  excess  base metal  to form
          a solid  amalgam (or alloy) that can  be recovered  by  filtration  and
          then  sent for mercury  recovery  if  applicable.   Generally,  finely
          divided  zinc   (zinc dust)  is  used.   The  high  surface area of  this
          material  allows for rapid reaction and  alloy  formation.

      2.  The  nonaqueous process, which  is seldom used, involves  contacting
          waste  liquid  mercury  with  finely  divided  zinc  powders.  The  mass
          rapidly  solidifies  into a  solid  amalgam,  which may be more  easily
          managed  than  liquid  mercury.    This  type  of  process is typically
          limited  in utility only to waste scrap  elemental mercury.


1.4         Waste  Characterization Affecting Performance  fWCAPs)

      In  determining  whether  amalgamation  will  achieve the  same  level  of
performance on an  untested waste that it achieved on  a  previously tested waste
and whether performance  levels  can  be transferred,  EPA examines the following
waste characteristics:   (a) the chemical form of  the  mercury,  (b) the  solution
pH,  (c)  the presence  of solids,  and (d)  the  presence  of  other  interfering
materials.


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1.4.1       Chemical Form of the Mercury

      The solution process requires that the mercury be present in the form of
a dissolved mercury salt.  As a result,  the  process  is not applicable to wastes
containing insoluble mercury  compounds.   The nonaqueous process is applicable
only to waste scrap mercury in elemental form.

1.4.2       Solution pH

      The solution process involves reactions of finely divided zinc with mercury
salts in solution.  Reactions such as  those  consuming zinc by  reaction with the
acidic  content  of  wastewaters are  undesirable.   Therefore,  the  pH  of the
wastewater solution should be adjusted to near neutral value before the process
is used.  This characteristic does not apply to the  second process, where  scrap
liquid mercury is a required feedstock.

1.4.3       Presence of  Sol Ids

      The solution process is  aimed at recovery  of  a solid amalgam that can be
shipped to mercury reprocessors.  The presence of other solids in the amalgam may
be undesirable.  Therefore,  if mercury is to be recovered, wastewater solutions
should be filtered to remove  extraneous solids  before the process is used.  This
characteristic does not  apply  to the  second  process.

1.4.4       Presence of  Interfering Materials

      The solution process requires a clear solution as  a feedstock.  Solutions
containing oils,  greases, and emulsified  or  suspended materials need  to be
pretreated before use of the  process.   The presence of many other dissolved
salts, such as those of copper, which  can react with zinc, is  also undesirable,
but  does  not exclude  use of  the  process.    The presence  of  such  salts will
increase the amounts of  zinc required for process operation.
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      The nonaqueous process requires elemental mercury as  a  feedstock.   Scrap
mercury  contaminated  with  oils,  greases, and  emulsion  is  better managed  by
retorting  directly since  these  interfering substances  may  inhibit  amalgam
formation.

1.5         Design and Operating Parameters

1.5.1       Solution Process Design and Operating Parameters

      In assessing the effectiveness of the design and operation of  a solution
process, EPA examines the following parameters:   (a)  temperature,  (b)  degree  of
mixing, (c) zinc usage,  (d) solution pretreatment, and (e)  residual  mercury  in
the treated wastewater.

1.5.1.1     Temperature

      The solution process  is normally operated at ambient  temperature but can
be run at  temperatures up to about 60*C to  enhance the reaction rate between zinc
and dissolved  mercury salts.   EPA will  examine  the basis  for  the   choice  of
operating  temperature  and  temperature  monitoring equipment  to  ensure  proper
process operation.

1.5.1.2     Degree of Mixing

      Finely divided zinc powder is normally added  to the solution containing the
mercury compound.   To ensure adequate contact  between  the zinc particles and
mercury ions present in solution, good agitation  is needed.  EPA will examine the
equipment  used to  determine that  the  treatment  vessel  contains the  proper
stirring equipment.
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1.5.1.3     Zinc Usage

      Sufficient zinc must be added to the solutions to ensure that all of the
mercury  present  is converted  to  an  amalgam.    To  achieve  this  end,  the
concentration  of  mercury  in  the solution  to be  processed  must  be  known to
estimate the minimum amount of zinc to be added.   EPA will examine  a facility's
calculations for zinc addition for individual batches to ensure proper operation.

1.5.1.4     Solution Pretreatment

      In a properly operated  unit,  the mercury-containing solutions  processed
should be clear and free  of oil, grease, and suspended  solids  when  introduced to
the processing equipment.  EPA will inspect the solutions entering the process
to ensure that proper pretreatment is being used.

1.5.1.5     Residual Mercury Levels in Treated Liquid Phase

      One final design and operating parameter  of importance is the concentration
of mercury in the treated water after amalgam  removal.   For a properly designed
and operated unit, both the entering and final mercury concentrations  should be
determined on a batch-by-batch basis.   EPA will examin'e  these records  to ensure
proper operation.   EPA will  also determine proper operation by examination of
capabilities  for  posttreatment to  precipitate  any residual  mercury  from the
treated  wastewaters prior to their  discharge.    Amalgamation  processes are
normally  used as  part   of treatment trains  devoted  to  recovering  elemental
mercury.  The reaction of zinc with mercury salts  in solution occurs rapidly at
higher mercury salt concentrations but may become very slow as the concentration
falls to low levels.  As  a result, treated solutions are likely  to  contain  some
residual mercury salts requiring  separate treatment.
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1.5.2       Nonaqueous Process Design and Operating Parameters

      The nonaqueous (solid) process  Is very rarely used on a significant  scale.
Generally, waste  mercury  is  either  retorted  or redistilled  as  such without
formation of amalgams.  There  are, however, a few instances in which it might be
desirable to amalgamate elemental mercury, the most important of which is when
the mercury  1s contaminated  by radioisotopes.   The  solid process  involving
amalgamation  with zinc  is basically  simple,  and  there  are two  design and
operating parameters of concern:  (a) the amount  of zinc used and (b)  the adequacy
of the mixing.

1.5.2.1     Amount of Zinc Used

      The properties of the final amalgam prepared will depend on  the ratio of
zinc powder to mercury used.   Mercury  and zinc form amalgams over a  very wide
composition range.  However,  it  is necessary to  add sufficient zinc so that an
alloy  that  is  solid at  room temperature  is  obtained.    This  entails   using
sufficient zinc to ensure that an amalgam with  at least 25 percent  zinc content
is obtained.

1.5.2.2     Adequacy of Mixing

      To  form  uniform zinc-mercury  amalgams,  the  constituents  need  to  be
uniformly mixed.    Historically, such  amalgams  have  been  prepared  in   small
quantities.    If a  facility desires to  process  mercury by this route  in  higher
volumes, a specially designed mixing  system may be needed.  EPA will examine the
design and operation of the mixing system to determine whether adequate  mixing
is likely to be achieved.
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1.6         References


Mellor,  J.W.,  1948.   Comprehensive  treatise  on  theoretical  and  inorganic
      chemistry.  Vol. 4, pp.  1022-1049.   London,  U.K.:  Longmans Green.

Signer, W., and Nowak M.,  1978.  Mercury compounds.  In Kirk-Othmer encyclopedia
      of  chemical  technology.  Vol.  15,  pp.  157-171.   New  York:  John  Wiley
      Interscience.

Rissmann, E.F., and Schwartz, S.,  1989.  Treatment of wastes containing arsenic,
      selenium,  thallium,  and mercury compounds.   In Proceedings of  the 44th
      Industrial  Waste Conference. Purdue University, pp. 643-648.  Ann Arbor,
      Mich.:   Lewis  Publishers.
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                          2.  CHEMICAL PRECIPITATION

2.1         Applicability

      Chemical precipitation is  a treatment technology applicable to wastewaters
containing a wide range of dissolved and other metals, as well  as  other inorganic
substances  such as  fluorides.    This technology  removes  these metals  and
inorganics from solution  in the form of insoluble solid precipitates. The solids
formed are then separated from the wastewater by settling, clarification, and/or
polishing filtration.

      For  some wastewaters,  such  as  chromium plating baths  or plating baths
containing cyanides, the metals exist in  solution  in a very soluble form.  This
solubility can be caused  by the metal's oxidation state (for example, hexavalent
chromium  wastewaters)  or  by  complexing  of  the  metals  (for  example,  high
cyanide-containing wastewaters). In both cases, pretreatment, such as hexavalent
chromium reduction or oxidation of the metal-cyanide complexes,  may be required
before the  chemical  precipitation  process  can be  applied effectively.   In the
case of arsenic, the arsenic-containing solution is  normally  treated first with
oxidizing  agents  such  as alkali  hypochlorite solution  to  convert the lower-
valence  arsenic compound  to arsenate.    The arsenic  ion   is  then  typically
precipitated out as  ferric  arsenate.   Some compounds must be reduced prior to
precipitation.   For instance,  selinites   and  selenates  are  oxidants  and are
readily reduced to elemental selenium, which is insoluble in  aqueous solutions.
Sulfur dioxide, sulfides, sulfites, and ferrous ion  are  all  effective for this
reduction reaction.

      Chemical precipitation may also be applicable to mixed waste for separating
radionuclides  from  other  hazardous  constituents  in  wastewaters.   Specific
conditions  of  pH, temperature,  and  precipitating  reagent addition  are required
to selectively remove part or all of the radioactive  component as a precipitate.
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2.2         Underlying Principles of Operation

      The basic principle of operation  of chemical precipitation  is that metals
and inorganics in wastewater are removed by the addition of a precipitating agent
that converts the soluble metals and inorganics to insoluble precipitates.  These
precipitates are settled, clarified, and/or  filtered out of solution, leaving a
lower concentration of metals and inorganics in the wastewater.  The principal
precipitation agents used  to  convert soluble metal  and inorganic compounds to
less soluble forms  include lime (Ca(OH)2),  caustic (NaOH), sodium sulfide (Na2S),
and, to a lesser extent,  soda ash (Na2C03), phosphate  (P04"), and ferrous sulfide
(FeS).

      The solubility of a particular compound depends on the extent to which the
electrostatic forces holding the ions of the compound together can be overcome.
The solubility changes  significantly with temperature, with most metal compounds
becoming more soluble as the temperature increases.  Additionally,  the solubility
is affected by other constituents present in  the wastewater, including other ions
and complexing agents.  Regarding specific ionic forms,  nitrates,  chlorides, and
sulfates are,  in general, more soluble than hydroxides, sulfides, carbonates, and
phosphates.

      Once  the  soluble metal and  inorganic compounds have  been converted to
precipitates, the effectiveness of  chemical  precipitation  is determined by how
successfully the precipitates are physically removed.  Removal usually relies on
a  settling  process;  that  is,  a   particle  of a  specific  size,  shape,  and
composition will settle at a specific velocity,  as described by Stokes'  Law.  For
a batch  system,  Stokes'  Law is a good  predictor of settling time because the
pertinent particle  parameters essentially remain constant.   In  practice, however,
settling time for  a batch  system  is normally determined by empirical  testing.
For a continuous system, the theory of  settling is complicated by such factors
as turbulence, short-circuiting of the  wastewater, and  velocity gradients, thus
increasing the importance of empirical tests  to accurately  determine appropriate
settling times.

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2.3         Description of Chemical Precipitation Process

      The equipment and  instrumentation required for chemical precipitation vary
depending  on  whether the  system  is  batch  or  continuous.   Both  systems  are
discussed below.

      For a batch system,  chemical  precipitation requires  a feed system for the
treatment  chemicals  and a  reaction  tank where  the waste can be  treated  and
allowed to settle.  When lime is used, it is usually added to the reaction tank
in a slurry form.  The supernatant liquid is generally analyzed before discharge
to ensure that settling of precipitates  is adequate.

      For a continuous  system,  additional tanks are necessary,  as well  as the
instrumentation to ensure  that the  system is operating properly.  A  schematic of
a  continuous  chemical   precipitation  system  is  shown  in  Figure  10.   In this
system, wastewater is fed into an equalization  tank,  where  it is mixed to provide
more uniformity, thus minimizing the  variability in  the type and concentration
of constituents sent to the  reaction  tank.

      Following equalization, the wastewater is pumped to  a reaction tank where
precipitating  agents   are   added.    This  is  done   automatically by  using
instrumentation that senses the pH of  the  system  for hydroxide precipitating
agents, or the oxidation-reduction potential (ORP) for nonhydroxide precipitating
agents, and then  pneumatically adjusts  the  position of the treatment chemical
feed valve until the design pH or ORP  value is achieved.  (The  pH and ORP values
are affected by  the  concentration  of hydroxide and  nonhydroxide precipitating
agents, respectively, and  are thus  used as indicators of their  concentrations in
the reaction tank.)

      In the reaction tank, the wastewater and precipitating agents are mixed to
ensure commingling of the metal  and inorganic constituents to be removed and the
precipitating agents.   In  addition, effective dispersion  of the precipitating
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      WASIEWATCR
      INFLUENT	
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                       *4
                    COUALIIATION
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                  ELECTHICAL  CONTROLS
                  UIIER
                                                                     rRECIPIIAIMa
                                                                        AQfHT
                                                                        FEED
                                                                        • tlTCM
    COAGULANT  OR
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                                           Figure 10   Continuous  Chemical Precipitation System

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agents throughout the tank is necessary to properly monitor and thereby control
the amount added.

      Following  reaction  of  the  wastewater with  the  stabilizing  agents,
coagulating or flocculating compounds are added to chemically assist the settling
process.  Coagulants and flocculants increase the particle size and density of
the precipitated  solids, both  of which increase the  rate of settling.   The
coagulant or  flocculating agent  that  best  improves  settling characteristics
varies depending on the particular precipitates to be settled.

      Settling can be conducted in a large  tank by relying solely  on gravity or
can be  mechanically assisted  through  the  use of  a circular  clarifier  or an
inclined plate  settler.   Schematics of the  two  settling  systems  are shown in
Figures 11 and 12.  Following the addition of coagulating or flocculating agents,
the wastewater is fed to a large settling tank, circular clarifier, or inclined
plate settler,  where the precipitated  solids are  removed.   These  solids are
generally further treated in  a sludge filtration system to  dewater  them prior to
disposal.  Sludge filteration  is  discussed in Section II.B.2 of this document.

      The supernatant  liquid  effluent  can  be further treated  in a polishing
filtration  system  to remove precipitated  residuals  both in  cases  where the
settling system is underdesigned and in cases where  the particles  are difficult
to settle.   Polishing filtration is discussed in Section II.B.2 of this document.

2.4         Waste Characteristics Affecting  Performance (WCAPs)

      In determining whether chemical precipitation  will achieve the  same  level
of performance on an untested waste that it achieved on a previously tested  waste
and whether performance  levels can be  transferred,  EPA examines  the following
waste  characteristics:    (a) the  concentration  and  type of  metals,  (b) the
concentration  of  total   dissolved  solids   (TDS),   (c)   the  concentration of
complexing agents, and (d) the concentration  of oil and grease.
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    BOTTOMS TO SLUDGE
FILTRATION  AND  DISPOSAL
                                                                             TREATED EFFLUENT
                                                                             TO POLISHING
                                                                             FILTRATION
                                                                             ANO/OR  DISPOSAL
WASTTWATIR
INFLUINT
           CENTER FEED CLARIF1ER  WITH SCRAPER SLUDGE REMOVAL SUSTEM
WASTEWATCR
   INFLUENT
                      RIM  FEED - CENTER TAKEOFF CLARIF1ER WITH
                    HYDRAULIC SUCTION SLUDGE REMOVAL SYSTEM
                  TREATED
                  EFFLUENT
                  •TO POUSMING
                  FILTRATION
                  ANO/OR DISPOSAL
                                                                       BOTTOMS TO
                                                                       SLUDGE FILTRATION
                                                                       AMD DISPOSAL
                                                                            WASTEWATER
                                                                            INFLUENT

                                                                            TREATED
                                                                            EFFLUENT
                                                                            TO POLISHING
                                                                            FILTRATION
                                                                            ANO/OR  DISPOSAL
                                                       BOTTOMS TO SLUDGE FILTRATION AND DISPOSAL
                          RIM  FEED - RIM TAKEOFF CLARIF1ER
                         Figure 11  Circular Clar1f1er Systems
                                         86

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WASTEWATER
INFLUENT
                                                                  TREATED
                                                                  EFFLUENT
                                                                  TO POLISHING
                                                                  FILTRATION
                                                                  AND/OR  DISPOSAL
                                                          BOTTOMS TO
                                                          SLUDGE FILTRATION
                                                          AND  DISPOSAL
                   Figure 12  Inclined  Plate Settler System
                                     87

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2.4.1       Concentration and Type of Metals

      For most metals, there is a specific  pH  at which the metal precipitate is
least soluble.  As a result, when a waste contains a mixture of many metals, it
is not possible to operate a treatment system at a single pH or ORP value that
is optimal  for  the removal  of  all metals.   The extent to which  this affects
treatment depends  on  the  particular  metals to be  removed  and their respective
concentrations.   One  alternative is to operate multiple  precipitations, with
intermediate settling, when the optimum pH occurs at markedly different  levels
for the metals present.  If  the concentration  and type of metals in an untested
waste differ from  and are significantly higher than those in the tested  waste,
the  system  may not  achieve the  same  performance.   Additional  precipitating
agents, alternate pH/ORP values, and/or multiple precipitations may be required
to achieve the same treatment performance,  or other, more applicable treatment
technologies may need to be considered for treatment of the untested waste.
                                                 •
2.4.2       Concentration of Total Dissolved Solids

      High  concentrations of total  dissolved solids (TDS) can  interfere with
precipitation reactions, as well as inhibit  settling.  Poor precipitate formation
and   flocculation   are  results  of   high  TDS  concentrations,   and   higher
concentrations of  solids are found in the treated wastewater residuals.   If the
TDS concentration  in an untested waste is significantly  higher than that  in the
tested  waste,  the system  may  not   achieve  the  same performance.     Higher
concentrations  of precipitating  agents may be required  to  achieve  the same
treatment performance, or other, more applicable treatment technologies may need
to be considered for  treatment of the  untested waste.

2.4.3       Concentration of Complexing Agents

      A metal  complex consists of a metal   ion surrounded  by  a  group of other
inorganic or organic ions or molecules  (often called ligands).   In the complexed
form, metals  have a  greater  solubility.   Also,  complexed metals  inhibit the

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reaction of  the  metal  with the precipitating agents  and  therefore may not be
removed as effectively  from  solution  by chemical  precipitation.   However, EPA
does not have  analytical  methods to  determine  the  concentration of complexed
metals in wastewaters.  The Agency believes that the best indicator for complexed
metals is to analyze  for  complexing  agents,  such  as cyanide, chlorides,  EDTA,
ammonia, amines,  and methanol,  for  which  analytical methods  are available.
Therefore,  EPA uses the concentration of complexing  agents as a surrogate  waste
characteristic for the concentration  of metal complexes.   If the concentration
of complexing agents in an untested waste is significantly higher than that in
the  tested  waste, the  system may not  achieve  the same  performance.   Higher
concentrations of precipitating  agents  may be required  to achieve  the same
treatment performance, or  other, more  applicable treatment technologies  may need
to be considered  for treatment of the untested waste.

2.4.4       Concentration of  Oil and  Grease

      The concentration of oil and grease in a waste  inhibits the settling of the
precipitate by creating emulsions that require  a long  settling  time.  Suspended
oil  droplets in  water  tend to suspend particles such as  chemical  precipitates
that would otherwise settle out  of solution.  Even with the use  of coagulants or
flocculants,  the  settling of  the   precipitate  is  less   effective.    If the
concentration of oil and grease in an  untested waste  is significantly higher than
that  in  the tested waste,  the system  may  not achieve  the  same  performance.
Pretreatment  of  the  waste  may  be   required  to   reduce   the  oil  and grease
concentration  and  achieve the  same  treatment  performance,  or  other,  more
applicable treatment technologies may need to be considered for  treatment of the
untested waste.

2.5         Design and Operating  Parameters

      In assessing the effectiveness  of  the  design  and operation  of a  chemical
precipitation  system,  EPA examines  the  following  parameters:    (a) the  pH/ORP
value; (b)  the precipitation temperature; (c) the residence time;  (d) the amount

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and type of precipitating agents, coagulants, and flocculants;  (e)  the degree of
mixing; and (f) the settling time.

2.5.1       pH/ORP Value

      The pH/ORP value in continuous chemical precipitation systems is used as
an indicator of the concentration of precipitating agents in the reaction tank
and thus is used to regulate their addition  to  the tank.  The pH/ORP value also
affects  the solubility of  metal precipitates  formed and  therefore  directly
impacts  the effectiveness  of  their removal.   EPA  monitors the  pH/ORP value
continuously,  if possible,  to  ensure  that the  system  is operating  at  the
appropriate design condition and to diagnose operational problems.

2.5.2       Precipitation Temperature

      The  precipitation  temperature  affects   the   solubility  of  the  metal
precipitates.  Generally, the lower  the temperature,  the lower the  solubility of
the  metal   precipitates and  vice  versa.    EPA monitors  the  precipitation
temperature continuously,  if possible, to ensure that the system  is operating at
the appropriate design condition and to diagnose operational problems.

2.5.3       Residence Time

      The residence time impacts the  extent of the  chemical reactions to form
metal precipitates  and,  as  a  result,  the  amount of  precipitates  that  can be
settled out of  solution.   For  batch systems, the residence time is controlled
directly by adjusting the treatment time in  the reaction tank.  For continuous
systems, the wastewater feed rate is controlled to make sure that  the system is
operating at the appropriate design residence time.   EPA monitors the residence
time to  ensure that sufficient  time  is provided to  effectively   precipitate
metals and  inorganics from the wastewater.
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2.5.4       Amount and Type of Precipitating Agents,  Coagulants, and Flocculants

      The amount and type of precipitating agent used to effectively treat the
wastewater depends on the  amount and type of metal  and  inorganic constituents in
the wastewater to be treated.  Other design and operating parameters,  such as the
pH/ORP value, the precipitation temperature,  the residence time, the amount and
type of coagulants and flocculants, and the settling time,  are determined by the
selection of precipitating agents.  The addition of coagulants and flocculants
improves the settling rate of the  precipitated metals  and inorganics and allows
for smaller  settling  systems (i.e.,  lower settling time) to achieve  the same
degree of settling as a much  larger system.   Typically, anionic polyelectrolyte
flocculating agents are most effective with metal  precipitates, although cationic
or nonionic polyelectrolytes also are effective.  Typical doses range from 0.1
to 10 mg/1 of  the  total  influent  wastewater stream.  Conventional coagulants,
such as alum (aluminum sulfate), are also effective, but must be dosed at much
higher concentrations  to achieve the same result.   Therefore, these coagulants
add  more  to  the  settled  sludge  volume   requiring  disposal   than  do  the
polyelectrolyte flocculants.   EPA  examines  the amount  and type of precipitating
agents, coagulants, and flocculants added, and their method  of addition to the
wastewater, to ensure  effective precipitation.

2.5.5       Degree of  Mixing

      Mixing provides  greater  uniformity of the wastewater feed and disperses
precipitating  agents,  coagulants,  and flocculants throughout the wastewater to
ensure the most rapid  precipitation reactions and settling of precipitate solids
possible.   The  quantifiable degree of  mixing  is  a complex  assessment that
includes, among other things, the  amount  of energy supplied,  the length of time
the material is mixed, and the related turbulence effects of the specific size
and shape of the tank.  This is beyond  the scope  of simple measurement.  EPA,
however, evaluates the degree of mixing qualitatively  by considering whether
mixing is provided and whether the type  of mixing device is one that could be
expected to achieve uniform mixing of the wastewater.

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2.5.6       Settling Time

      Adequate  settling time must be provided to make  sure that removal of the
precipitated  solids  from the wastewater  has  been completed.   EPA monitors the
settling time to  ensure effective solids removal.
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2.6         References


Cherry, K.F. 1982. Plating waste treatment,  pp. 45-62.  Ann Arbor,  Mich.:  Ann
      Arbor Science Publishers, Inc.

Cushnie,  G.C.,  Jr.  1985.  Electroplating  wastewater  pollution  control  tech-
      nology,   pp. 48-62, 84-90.  Park Ridge, N.J.: Noyes Publications.

Cushnie, G.C., Jr. 1984. Removal of metals from wastewater;  neutralization and
      precipitation,   pp. 55-92.  Park Ridge, N.J.: Noyes Publications.

Gurnham, C.F.  1955. Principles of industrial  waste  treatment,  pp.  224-234.  New
      York: John Wiley and Sons.

Kirk-Othmer.  1980.  Flocculation.   In Encyclopedia of chemical  technology. 3rd
      ed.,  vol.  10, pp. 489-516.  New York:  John Wiley and Sons.

USEPA.  1983.   U.S. Environmental Protection  Agency.  Treatability manual: Vol.
      Ill,   Technology  for  control/removal   of   pollutants,   p.  111.3.1.3.2.
      EPA-600/2-82-001C.   Washington,  D.C.:   U.S.  Environmental  Protection
      Agency.
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                               3.   ENCAPSULATION

3.1         Applicability

      Encapsulation processes refer to a family of processes wherein high-solids
nonwastewaters are mixed with  an  organic  polymeric substance or with asphalt.
The mixture is then allowed to cure into a solid mass prior to disposal.  These
processes are applicable to a wide variety of wastes.  They are not applicable
to wastes containing materials that decompose at  high temperatures or to wastes
containing oxiders that can react with the  binder materials. Also, some aromatic
solvents such as  xylene and toluene can diffuse through  the encapsulating agent.
Oils, greases, and some chelating agents  may interfere with  the hardening and
solidification of the encapsulating material.  EPA believes that encapsulation
technologies  are applicable  primarily  to  wastes containing  hazardous  metal
constituents.  Encapsulation may immobilize hazardous organics as well as metals;
however, incineration is more applicable to organics since incineration destroys
organics completely, whereas encapsulation can only immobilize them.

3.2         Underlying Principles of Operation

      There are a number of very similar encapsulation processes that differ from
each other only  in the encapsulating agent used.   In all  of the processes, the
waste is first dried to remove  moisture.  The waste is then usually reheated and
mixed with  hot asphalt or  thermoplastic  material such  as polyethylene.   The
mixture is then  cooled to solidify  the mass.  The  ratio  of matrix (fixative or
encapsulating  agent) to waste  is  generally high  (i.e., 1:1  or 1:2 fixative to
waste on a dry basis).  The matrix, once solidified, coats the waste to minimize
leaching.

3.3         Description of Encapsulation  Processes

      Encapsulation  processes  can  take  the  form  of  macroencapsulation,
microencapsulation, or both.  Microencapsulation is the containment of individual

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waste particles  in  the polymer or asphalt matrix.   Macroencapsulation is the
encasement of a mass  of  waste  in  a thick polymer coating.   The waste mass may
have been microencapsulated prior to macroencapsulation.

3.3.1       Hicroencapsulation

      Microencapsulation  processes  typically   involve  the  following  unit
operations in series:

      •  Predrying of the waste to remove entrained moisture.

      •  Mixing of  the heated  waste with molten encapsulating agent  (asphalt,
         polyethylene, thermosetting resins).

      •  Cooling of the hot mixture to allow the mixed mass to harden into a
         solid mass.

      Generally, ratios  of matrix  to waste  used are high compared to those of
pozzolanic stabilization processes (i.e., for encapsulation  the ratio  is in the
1:1 to 1:2 range).   Mixing  is  generally  done at 120 to  130°C depending on the
melting characteristics of the  matrix and the type of equipment used  for mixing.
A  few  processes  differ  from the  above description  in  that polymerization of
monomers mixed with waste is conducted at ambient or near ambient temperatures
in  the  presence  of  catalysts.    The monomer  (or  monomeric  mixture)  then
polymerizes at room temperature, coating the individual waste particles.

3.3.2       Macroencapsulation

      The macroencapsulation process of hazardous waste  solids usually involves
two steps.  In the first  step, the hazardous wastes may be chemically treated by
using low-cost dehydrating agents such as lime,  kiln dust,  or Portland cement.
This operation does not increase the volume  of the solids significantly because
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only a small amount of dehydrating agent is needed to dewater the solids.  The
resulting mixtures are friable, and they can easily be ground.

      In the second step, the dehydrated sludges are ground and the particles may
be microencapsulated,  typically  by a polybutadiene binder.   Then the mass is
macroencapsulated, or coated, typically by high-density polyethylene.

      The typical apparatus for macroencapsulation processes  features  heated or
cooled molds, a method of waste and  hardened product manipulation,  and hydraulics
for mold  actuation.   The molds typically contain electrical band heaters and
water cooling channels.  After the  polymer coating hardens, the mold  is split to
facilitate product demolding.

3.4         Waste Characteristics  Affecting Performance (WCAPs)

      In  determining whether encapsulation will  achieve the  same  level  of
performance on an untested waste that  it achieved on a previously tested waste
and whether  performance  levels  can be transferred,  EPA examines the  following
waste characteristics:  (a) the water content  of the waste; (b) the presence of
oxiding  agents in the  waste; (c) the presence  of certain  organic  solvents;
(d) the presence of oils,  greases,  and  chelating agents; and (e) the presence of
thermally unstable materials  in the waste.   These  characteristics are  described
below.

3.4.1       Water Content

      The processes normally  require a dry  solid  waste.  Wet  solids need to be
dried  at elevated  temperature,  or  chemically  treated,  to  remove  entrained
moisture  before  they  can  be  mixed with molten polymers, asphalt, or  monomeric
mixtures.  The presence of free water  interferes  with the elevated temperature
encapsulation  processes  by forming  steam  during the mixing and preventing  a
smooth coating of the particles.   In ambient temperature processes, water may
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react  with the  polymerization  catalyst,  preventing  it  from  initiating the
polymerization reactions.

3.4.2       Presence of Oxidizing Agents

      Strong oxidization salts such as nitrites, chlorates,  or perchlorates will
react with the organic matrix materials and slowly deteriorate the matrix.   These
oxidants may also react spontaneously with the heated matrix material to  cause
a fire  or explosion.   Wastes containing  such  strong oxidants  should  not be
managed by polymer encapsulation processes.

3.4.3       Presence of Organic Solvents

      Organic  solvents,   particularly  aromatic  solvents,  may  be  capable of
dissolving the polymer matrix material.   They will  also cause significant air
emissions due to  volatilization during the mixing of the heated waste and matrix
materials.  The  process  should not  be  used on wastes containing such solvents
unless the wastes have been pretreated to remove such materials.

3.4.4       Presence of Oils,  Greases, and Chelating Agents

      Oils, greases, and organic  chelating agents  are likely  to dissolve in and
migrate through  the polymeric  matrices used for encapsulation.  They may  also,
to   some   extent,   coat   individual   waste   particles   and   prevent    firm
microancapsulation  binding between  waste  particles  and  the  polymer  matrix
surrounding them.  Because of  the ability of these organics to diffuse through
polymeric matrices, wastes containing oils, greases, and organic chelating agents
should not be managed by  polymer encapsulation.

3.4.5       Presence of Thermally Unstable Materials

      Hydrated salts are  likely  to  decompose  during  the initial hot mixing of
matrix  and waste materials,  liberating  water  vapor.   These salts will   also

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rehydrate during cooling  and  thus  interfere  with the uniform coating of waste
particles by the matrix polymer.  Wastes containing hydrated salts  should not be
managed by this  process.   Salts  that are known to cause such problems include
hydrated sodium sulfate, magnesium sulfate, and hydrated metal chlorides.  The
soluble hydrates need to be removed from the waste by chemical  or physical means
before the wastes are managed by polymer microencapsulation.

3.5         Design and Operating Parameters

      There are five design and operating parameters for this  set  of processes:
(a) the choice of the polymeric matrix material,  (b)  the mixing equipment used,
(c) the ratio of polymer to waste used, (d) process temperature control, and (e)
air emissions control.  These are described in the following  paragraphs.

3.5.1       Choice of Polymeric Matrix

      Several polymeric matrices  are available for use  in these  encapsulation
processes.  These include  asphalt, polyethylene, thermosetting plastics (such as
urea formaldehyde type resins),  and resins that can be polymerized  under ambient
temperature in the presence of a catalyst.  The choice  of  the polymeric matrix
determines the temperature and equipment to be used and  strongly influences the
needed cure time.  It also determines to  some degree  the choice of wastes that
can be accepted  because of differences  in the properties of the polymers.  EPA
will examine the basis  for the choice of polymer matrix, available test data, and
the wastes being accepted  for processing.

3.5.2       Mixing Equipment Used

      For microencapsulation,  polymers  or monomers and catalysts must be well
mixed with wastes to ensure that uniformly coated waste  particles  are  produced.
EPA will examine the design and operating characteristics  of  the  mixing system
to ensure that  it is capable of generating uniform mixes.
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3.5.3       Ratio of Polymer to Waste Used

      Sufficient polymer  must  be used  to  ensure that the  waste  is uniformly
coated.  Generally,  a  1:1 or 1:2 polymer-to-waste ratio  on a weight basis is
used.  EPA will  examine the basis  for the choice  of polymer-to-waste  ratio used
to ensure that sufficient polymer is being added.

3.5.4       Process Temperature Control

      To achieve uniform  mixing,  the encapsulation matrix must be in a liquid
state.  The melting points of the different thermoplastic polymers will differ
from each other.  During mixing of the molten polymer  and waste, the temperature
needs to be maintained above the thermoplastic polymer melting point and below
the point at which  polymer vaporization or  thermal decomposition begins.  Thus,
for a given thermoplastic polymer, there is only  a certain temperature range in
which the process can be satisfactorily operated.  For thermosetting  resins the
temperature selected must be appropriate  to  cause  polymerization (hardening)
after thorough mixing.   EPA will examine data on the properties of  the polymers,
including  decomposition,  to ensure  that  a  proper  operating  temperature was
selected.  EPA will  also examine  the  temperature  control instrumentation in use
to ensure that it is operating properly.

3.5.5       Air Emissions Control

      Heating of mixtures  of waste with polymers or asphalt can cause the release
of hydrocarbon air emissions that may include  volatile components  of  the waste,
plasticizers present in the polymers, polymer decomposition products, and low-
molecular-weight ingredients of the asphalt.  In a properly operating system, air
emissions testing may be  needed during at  least  initial  operation to determine
levels of emissions and to assess the need  for air emissions control.  EPA will
examine  such  air monitoring data  to determine whether  air emissions control
systems are appropriate.   The Agency will also examine the  air emissions control
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systems  in  use  to  ensure  that they  are  operating  and  in  proper  operating
condition.
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3.6         References


Pierce, J., and Vesilind, P.A. 1981.  Hazardous waste management,  pp. 82-4. Ann
      Arbor, Mich.:   Ann Arbor Science Publishers.

Rich, G.,  and  Cherry, K. 1987.   Hazardous  waste treatment technologies.  Chap-
      ter 6, pp. 9-3.   Northbrook,  111.: Purdue Publishing Company.
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                          4.   STABILIZATION  OF  METALS

4.1         Applicability

      Stabilization is a treatment technology  applicable to wastes containing
Teachable metals and having a high filterable solids content, low total organic
carbon  (TOC)  content, and  low oil  and  grease content.   This  technology is
commonly used  to treat residuals  generated from  treatment of wastes  such as
electroplating wastewaters, incineration ash  residues, and characteristic D-metal
wastes such as  cadmium (0006), chromium (0007),  lead (0008), and mercury (0009).
For wastes with recoverable levels of metals, high temperature metals recovery
and retorting technologies may be  applicable.

      Stabilization  refers  to  a broad  class  of treatment  processes  that
immobilize  hazardous  constituents  in  a  waste.    Related  technologies  are
encapsulation and thermoplastic binding.  However, EPA considers stabilization
technologies to be distinct from the other technologies in that their operational
principles  are  significantly different.    Stabilization  typically  requires  a
chemical reaction between the waste  and  the  stabilizing  agent  for effective
treatment, while thermoplastic binding and encapsulation usually employ physical
containment of hazardous particulates by the encapsulating agent.

4.2         Underlying Principles  of Operation

      The basic principle of operation for stabilization is that leachable metals
in a waste  are immobilized following the addition of stabilizing agents and other
chemicals.  The Teachability is reduced  by the  formation  of a lattice structure
and/or  chemical  bonds  that  chemically bind  the metals to the solid matrix and
thereby limit the amount  of metal  constituents that can be leached when water or
a mild acid solution comes into contact with the waste material.  Stabilization
is most effective when the waste metal  is  in its  least soluble state, thereby
decreasing the potential  for leaching.  For example, hexavalent chromium  is much
more soluble and  more  difficult to stabilize than trivalent chromium.


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      The  two principal  stabilization  processes  used  are  cement-based  and
lime/pozzolan-based processes.  A  brief  discussion of each is provided below.
In both cement-based and lime/pozzolan-based techniques, the stabilizing process
can be modified through the  use of additives,  such as silicates, that control
curing  rates,  reduce permeability,  and  enhance the  properties of  the solid
material.

4.2.1       Portland Cement-Based Process

      Portland cement  is  a  mixture  of  powdered  oxides of  calcium,  silica,
aluminum, and iron, produced by kiln  burning  of materials rich in calcium and
silica at high temperatures (i.e., 1,400 to 1,500*C (2,552 to 2,732*F)}.  When
the anhydrous cement  powder is mixed with water, hydration occurs and the cement
begins  to  set.   The  chemistry  involved  is  complex because  many  different
reactions occur depending on the composition of the cement mixture.

      As the cement begins  to set, a colloidal gel of indefinite  composition and
structure is formed.   Over time, the gel  swells and forms a matrix composed of
interlacing, thin, densely packed  silicate fibrils.   Constituents present  in the
waste slurry (e.g., hydroxides and carbonates of various metals) are incorporated
into the interstices of the  cement  matrix.   The high pH of the cement mixture
tends to keep metals  in the form of insoluble hydroxide and carbonate  salts.  It
has been hypothesized that metal  ions may also  be incorporated into the crystal
structure of the cement matrix, but this hypothesis has  not been verified.

4.2.2       Lime/Pozzolan-Based Process

      Pozzolan, which contains finely divided,  noncrystalline  silica  (e.g., fly
ash or components of cement kiln dust),  is a material  that  is not cementitious
in itself, but becomes so  upon  the addition  of lime.   Metals in the waste are
converted to  insoluble  silicates  or hydroxides and  are incorporated into the
interstices of the binder matrix, thereby inhibiting  leaching.
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4.3         Description of Stabilization Process

      The stabilization process consists of a weighing device, a mixing unit, and
a curing vessel or  pad.   Commercial  concrete mixing and handling equipment  is
typically used in stabilization  processes.   Weighing conveyors, metering cement
hoppers, and mixers  similar to concrete batching plants have been adapted in some
operations.  When extremely dangerous materials are  treated, remote-control and
in-drum mixing equipment, such as that used with nuclear waste,  is employed.

      In most stabilization processes, the waste, stabilizing agent,  and other
additives, if used,  are mixed in a mixing  vessel  and  then transferred to a curing
vessel or pad and  allowed  to cure.  The actual  operation  (equipment requirements
and process sequencing) depends on several factors  including the nature of the
waste, the quantity of the waste, the location  of the waste in relation to the
disposal site,  the  particular stabilization  formulation  used,  and the curing
rate.   Following curing,  the stabilized  solid formed  is  recovered from the
processing equipment and  disposed of.

4.4         Waste Characteristics Affecting Performance (WCAPs)

      In  determining   whether  stabilization  will   achieve  the   same  level   of
performance on an untested waste that it achieved on a previously tested waste
and whether  performance  levels  can  be transferred,  EPA examines the  following
waste characteristics:    (a)  the  concentration of  fine  particulates,  (b) the
concentration of  oil  and grease, (c) the  concentration  of organic  compounds,
(d) the concentration of sulfate and chloride compounds, and (e)  the  solubility
of the metal compound.

4.4.1       Concentration of Fine Particulates

      For both cement-based and lime/pozzolan-based processes, very  fine solid
materials (i.e., those that pass through a No. 200 mesh  sieve  (less  than  74 /j m
particle size)) weaken the bonding  between waste  particles and the  cement  or


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lime/pozzolan binder by coating the particles.  This coating inhibits chemical
bond formation, thereby decreasing the resistance of the material to leaching.
If the concentration of fine particulates in  an  untested waste  is significantly
higher  than  that  in  the  tested  waste,  the  system  may  not achieve  the same
performance.   Pretreatment of  the  waste may be  required to  reduce  the fine
particulate concentration and achieve the same treatment performance, or other,
more applicable treatment technologies may need to be considered for treatment
of the untested waste.

4.4.2       Concentration of 011 and Grease

      Oil and grease in both cement-based and  lime/pozzolan-based systems result
in the  coating  of waste particles  and  the weakening of  the  bond  between the
particle and  the  stabilizing agent, thereby decreasing the  resistance of the
material to leaching.   If  the  concentration  of  oil  and grease  in the untested
waste is significantly higher than that  in the tested waste, the system may not
achieve the same performance.  Pretreatment may be required to reduce the oil and
grease concentration and achieve the same treatment performance,  or other, more
applicable treatment technologies may need to be considered for treatment  of the
untested waste.

4.4.3       Concentration of Organic Compounds

      Organic compounds in the waste interfere with  the stabilization chemical
reactions and bond formation, thus inhibiting  curing of the stabilized material.
This interference  results in a stabilized waste having decreased resistance to
leaching.  If the total organic  carbon  (TOC)  content of the untested waste is
significantly higher than that of the tested waste,  the system  may not achieve
the same performance.  Pretreatment may be required to reduce the TOC and achieve
the same treatment performance, or other, more applicable treatment technologies
may need to be considered for treatment  of the untested waste.
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4.4.4       Concentration of Sulfate and Chloride Compounds

      Sulfate and chloride compounds interfere with the stabilization chemical
reactions, weakening  bond strength  and prolonging  setting and  curing time.
Sulfate and chloride compounds may reduce the dimensional stability of the cured
matrix, thereby  increasing Teachability potential.   If  the  concentration of
sulfate and chloride compounds in the untested waste is significantly higher than
that  in  the  tested waste,  the system  may  not achieve  the same  performance.
Pretreatment may be required to reduce  the sulfate and chloride concentrations
and achieve the same treatment  performance,  or  other, more applicable treatment
technologies may need to be considered  for treatment of the untested waste.

4.4.5       Solubility of the Metal Compound

      The metal to  be  stabilized  should be  in  its least soluble state, or the
stabilized  waste   may  exhibit  a  potential   for  increased  Teachability.
Pretreatment may be required to chemically reduce or oxidize  the metal to a lower
solubility state and  achieve maximum stabilization  performance.   For example,
hexavalent chromium is much more  soluble and more difficult to stabilize than
trivalent chromium.

4.5         Design  and Operating Parameters

      In  assessing  the  effectiveness  of  the  design  and   operation of   a
stabilization system,  EPA examines  the following parameters:  (a) the amount and
type  of  stabilizing  agent  and additives,  (b) the  degree  of  mixing,   (c) the
residence time, (d) the stabilization temperature  and humidity, and (e)  the form
of the metal compound.

4.5.1       Amount  and Type of Stabilizing Agent  and Additives

      The stabilizing agent and additives used  will  determine  the chemistry and
structure of the stabilized material and therefore  its Teachability.  Stabilizing


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agents  and  additives  must  be carefully  selected based  on the  chemical  and
physical characteristics  of the waste to  be  stabilized.    To  select  the most
effective type of stabilizing  agent and additives, the waste should be tested in
the  laboratory  with   a  variety  of  these materials  to  determine the  best
combination.

      The amount of stabilizing agent and  additives is a critical parameter in
that sufficient stabilizing materials are  necessary to properly bind the waste
constituents  of  concern,  making  them  less  susceptible  to  leaching.    The
appropriate  weight ratios  of stabilizing  agent and  additives   to waste  are
established empirically by  setting  up a  series  of laboratory tests that allow
separate leachate testing  of different  mix  ratios.   The ratio of  water to
stabilizing agent  (including water in waste) will also impact the strength and
leaching characteristics of the stabilized material.   Too much water will cause
low strength; too little will  make mixing difficult and, more important, may not
allow the chemical reactions  that bind the hazardous constituents to be fully
completed.    EPA evaluates  the amount of  stabilizing  agent, water,  and other
additives used in the stabilization process to ensure that sufficient stabilizing
materials are added to the waste to effectively immobilize the waste constituents
of concern.

4.5.2       Degree of Mixing

      Mixing  is necessary  to ensure  homogeneous  distribution of  the waste,
stabilizing  agent,  and  additives.   Both  under-mixing   and  overmixing  are
undesirable.    The  first  condition  results  in  a   nonhomogeneous  mixture;
consequently, areas will exist within the  waste where waste particles are neither
chemically bonded to the stabilizing agent nor  physically held within the lattice
structure.    Overmixing,  on  the other hand, may  inhibit  gel formation and ion
adsorption in some stabilization systems.  Optimal mixing  conditions are usually
determined  through laboratory tests.  The  quantifiable degree of mixing is a
complex  assessment that  includes,  among  other  factors,  the amount of energy
supplied, the length of time  the material  is mixed, and the  related turbulence


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effects of the specific size  and shape of the mix tank or vessel.  The degree of
mixing is beyond the scope of simple measurement.  EPA, however, evaluates the
degree of mixing  qualitatively by considering whether  mixing  is  provided and
whether  the  type  of mixing  device  is one  that  could be expected  to achieve
homogeneous distribution of the waste, stabilizing agent, and additives.

4.5.3       Residence Time

      The residence time or duration of curing  ensures  that the waste particles
have had sufficient time in which  to incorporate  into lattice structures and/or
form  stable  chemical  bonds.   The  time  necessary for  complete stabilization
depends on the waste and the stabilization process used.  The performance of the
stabilized waste (i.e.,  the levels of waste constituents in the leachate) will
be highly dependent on whether complete stabilization  has  occurred.   Typical
residence times range  from 7 to 28 days.   EPA monitors the  residence time to
ensure that sufficient  time is provided to effectively stabilize the waste.

4.5.4       Stabilization Temperature and Humidity

      Higher  temperatures  and lower  humidity  increase the rate  of curing by
increasing the rate of evaporation of water from the stabilization  mixtures.  If
temperatures  are  too  high,  however,  the  evaporation  rate can  be excessive,
resulting in too little water being available for completion of the stabilization
reaction.  EPA monitors the stabilization temperature and humidity continuously,
if possible,  to ensure that  the  system  is  operating at the appropriate design
conditions and to diagnose operational problems.

4.5.5       Form of  the  Metal Compound

      Ideally, the waste metal to be  stabilized  should be in its least soluble
state to reduce leaching of the stabilized waste.  Pretreatment  such  as chemical
oxidation or  chemical  reduction may be required  to oxidize or reduce the metal
to a  state of lower  solubility.  Additionally, the solubility of the metal can
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be decreased  by precipitating it  with  an appropriate compound.   For example,
ferric arsenate  is less  soluble  and  less Teachable than calcium arsenate.   EPA
can monitor  solubility  of the  metal  by performing  a standard  leaching test
(Extraction Procedure (EP)  or Toxicity Characteristic Leaching Procedure (TCLP)).
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4.6         References


Ajax Floor  Products  Corp.  n.d.   Product  literature:   technical data sheets,
      Hazardous Waste Disposal  System.  P.O. Box 161, Great Meadows,  N.J. 07838.

Austin, G.T. 1984.   Shreve's chemical  process industries.  5th ed. New  York:
      McGraw-Hill Book Co.

Bishop, P.L.,  Ransom, S.B., and  Grass,  D.L.   1983.   Fixation  mechanisms  in
      solidification/stabilization   of  inorganic   hazardous  wastes.      In
      Proceedings of  the 38th  Industrial Waste Conference. May 10-12, 1983,  at
      Purdue University, West  Lafayette, Indiana.

Conner,  J.R.     1986.   Fixation  and  solidification  of wastes.    Chemical
      Engineering.  Nov. 10, 1986.

Cullinane,  M.J.,  Jr., Jones,  L.W.,  and Malone,  P.G.   1986.   Handbook  for
      stabilization/solidification  of hazardous  waste.   U.S.  Army Engineer
      Waterways Experiment Station.  EPA report no.  540/2-86/001.   Cincinnati,
      Ohio:  U.S. Environmental Protection Agency.

Electric Power Research Institute. 1980.   FGD sludge disposal,  annual.  2nd ed.
      Prepared by Michael  Baker Jr.,  Inc. EPRI CS-1515 Project  1685-1.   Palo
      Alto, Calif.: Electric Power Research  Institute.

Malone, P.G.,   Jones, L.W.,  and  Burkes,   J.P.  Application of solidification/
      stabilization technology to electroplating  wastes.   Office of Water and
      Waste Management.   SW-873.   Washington,  D.C.:  U.S. Environmental Pro-
      tection Agency.

Mishuck, E., Taylor,  D.R.,  Telles,  R., and Lubowitz, H.   1984.  Encapsulation/
      fixation (E/F)  mechanisms.   Report  no.  DRXTH-TE-CR-84298.    Prepared  by
      S-Cubed under Contract no. DAAK11-81-C-0164.

Pojasek RB. 1979. Sol id-waste  disposal:  solidification.   Chemical  Engineering
      86(17):  141-145.

USEPA.   1980.    U.S. Environmental  Protection Agency.   U.S. Army Engineer
      Waterways  Experiment  Station.    Guide  to  the  disposal  of  chemically
      stabilized and  solidified waste.  Prepared for MERL/ORD  under  Interagency
      Agreement No.  EPA-IAG-D4-0569.   PB 81  181  505.  Cincinnati,  Ohio:   U.S.
      Environmental Protection Agency.
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                               5.   VITRIFICATION

5.1         Applicability

      Vitrification  technologies  include  glass  and  slag vitrification  and
elevated-temperature  calcination  processes.   Vitrification  processes involve
dissolving the  waste at high  temperatures  into glass or  a  glass!ike matrix.
Calcination involves merely heating the material at high temperatures.

      High-temperature vitrification is applicable to nonwastewaters containing
arsenic* or other  characteristic  toxic metal  constituents that are relatively
nonvolatile  at the  temperatures  at   which  the process   is  operated.   This
technology is  also applicable to many wastes containing organometallic compounds,
where  the  organic  portion  of the  compound can  be  completely oxidized  at
process-operating conditions.  Afterburners may  be required to convert  unburned
organics to carbon dioxide.

      The process is not generally applicable  to volatile metallic compounds or
to wastes containing  high  levels  of  constituents  that will interfere  with the
vitrification process.  High levels of chlorides and other  halogen salts should
be avoided  in  the wastes being processed because  they  interfere with glassmaking
processes and cause corrosion problems.

      Calcination  processes are  applicable  to  inorganic  wastes that do not
contain volatile constituents.
*Volatile arsenic compounds  are usually converted to nonvolatile arsenate salts
 such  as  calcium arsenate  prior  to  use of this process.  In ordinary glass-
 making,  arsenic  volatilization  problems   are minimized  by  adding arsenic
 as arsenate salts.
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5.2         Underlying Principles of Operation

      The basic principles of operation for vitrification technologies depend on
the technology used.  In glass  and slag  vitrification  processes,  the  waste con-
stituents become chemically bonded inside a glasslike  matrix in many  cases.  In
all instances, the waste becomes  surrounded by a glass matrix that immobilizes
the waste constituents  and retards or  prevents  their reintroduction into the
environment.  Arsenates are converted to silicoarsenates, and other  metals are
converted to silicates.

      High-temperature calcination processes remove water of hydration from the
toxic metal-bearing solids, convert hydroxides present to oxides,  and  sinter the
material, reducing its surface area to a minimum.  Conversion of hydroxides to
oxides and minimization of available  surface area retard  surface  reactions that
would reintroduce the material  into  the environment.   Calcination may also be
accompanied by chemical  reaction if a material  such as lime  is blended with the
waste before it is heated.  For example,  lime will  react  with arsenic oxides at
higher temperatures  to  form calcium arsenate,  and  this  material will then be
sintered  at  elevated  temperatures.    Brief  descriptions of  each of  the
high-temperature processes are given in the following  subsections.

5.2.1       Glass Vitrification

      In  the  glass  vitrification process,  the  waste and  normal  glassmaking
constituents are first blended together and then fed  to  a glassmaking furnace,
where the mixed feed materials  are introduced into  a pool of molten glass.  The
feed materials then  react  with  each  other  to form  additional molten  glass, in
which particles of the waste material become dissolved or suspended.   The molten
glass is subsequently cooled.  As  it cools, it solidifies into a solid mass that
contains  the  dissolved  and/or  suspended  waste constituents.   Entrapment and
chemical  bonding  within  the   glass matrix  render   the  waste constituents
unavailable for reaction.
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5.2.2       Slag Vitrification

      Slag vitrification differs from glass vitrification in that finely ground
slag from metal-refining processes and waste  are  premixed  and fed  to the same
type of furnace as  that  used for glassmaking.   The  slag  liquifies at the process
temperature  (1100  to 1200'C),  and the  waste constituents either  dissolve or
become suspended in the molten slag.   Subsequent cooling of the slag causes it
to  solidify,  trapping  the waste  inside a glasslike  matrix  and rendering it
unavailable for chemical reaction or migration into the environment.

5.2.3       High-Temperature Calcination

      In  the  high-temperature calcination process, the waste is  heated  in a
furnace or kiln to between 400 and 800'C.  In some instances, the waste may be
blended with lime prior to heating.  In those cases, chemical  reaction may occur
during the calcining  process.   Water present  as either free  water  or water of
hydration is evaporated, and  hydroxides  present are thermally  decomposed to the
corresponding oxides  and water vapor.  At the higher temperatures,  the surface
area of the dehydrated  material is decreased by thermal sintering.   Conversion
of  hydroxides to  oxides  and  substantial  losses  of  surface area  render the
material  less  reactive in  the  environment  and  lower  the Teachability of
characteristic toxic  metals  present.  In general, the higher the  calcination
temperatures  used,  the more  complete the loss of  water and the  greater the
accompanying  loss of  surface area, resulting in lower  Teachability potential.

5.3         Description of Vitrification Processes

      This  chapter  discusses  three   types  of  high-temperature  stabilization
processes,  which  differ  considerably  from  each  other.    Individual  process
descriptions  are given  in the  following subsections.
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5.3.1       Glass Vitrification

      Soda ash,  lime, silica, boron oxide, and other glassmaking constituents are
first blended with the waste  to  be treated.   The amount of waste added to the
blend  is  dependent on  the waste  composition.   Different metal  oxides  have
differing solubility limits in glass matrices.   The blended waste and glass raw
material mixture is then fed to a conventional, heated glass electric furnace.

      The introduced material  typically is added through a port at the top of the
furnace and falls into a pool  of  molten glass.   The  glass constituents dissolve
in the  molten  glass  and form additional glass.   Molten glass is periodically
withdrawn  from the bottom of the furnace  and cooled.   This  material  then
solidifies on cooling  into  solid blocks of glasslike material.   Organics  present
in the  feed mixture undergo combustion at the normal operating temperatures of
1100 to 1400'C and are fully oxidized to carbon dioxide and water vapor.

      The top of the furnace is normally cooled so that  volatile materials, such
as arsenic  oxides,  that are present in the  feed  mixtures  can condense on the
cooled  surface  and  fall back  into  the  melt, where  they  can  undergo chemical
reaction to form silicoarsenates involved in the glassmaking process.   Most of
the arsenic  used in  making glass  by  this  method is present  as  salts  such as
calcium arsenate.   This  approach  was introduced  into the glass  industry to
minimize fugitive arsenic  losses.

      Gases, such as carbon dioxide, that are liberated during the glassmaking
process exit the furnace through  the top and are generally wet-scrubbed prior to
reentering the atmosphere.

5.3.2       Slag Vitrification

      The slag vitrification process  is basically similar to glass vitrification
except  that granulated slag, instead of  the  normal  glassmaking  constituents, is
blended with the waste for feed to  the system.  A pool of liquid slag  is  present


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in the furnace, and the blended raw material mix typically is introduced at the
top of the furnace and falls into this molten slag.  The granulated slag-waste
mixture liquifies to form additional slag.  Slag is periodically withdrawn from
the slag pool and cooled into blocks.

      The type of furnace used  for glass vitrification can also  be  used for slag
vitrification.  The operating parameters are similar.

5.3.3       High-Temperature Calcination

      In the high-temperature calcination process, wastes containing inorganic
compounds are fed to ovens or kilns, where  they are heated to high temperatures
(i.e., 500 to 900*C) to drive off water of hydration and to convert hydroxides
present to the  corresponding  oxides.   This process is primarily applicable to
inorganic wastes that contain nonvolatile constituents.

      The waste is heated  in  the  oven  or kiln  to the  desired  temperature,
moisture  and water of hydration  are  driven off;  and, at  the  500  to 900*C
temperature  range,  hydroxides  decompose  to the  corresponding oxides and water
vapor.  The  high-temperature  treatment also  significantly reduces the  surface
areas of the oxides formed by sintering,  thereby reducing the reactivity of the
material. After the waste material has  been calcined at an elevated temperature,
it  is  withdrawn from  the  oven or  kiln,  cooled,  and either land disposed or
forwarded to another process,  such  as  stabilization, for further treatment.

5.4         Haste Characteristics Affecting Performance fWCAPs)

      The waste characteristics affecting performance are different  for  the two
vitrification  processes  and the  calcination  process.    Accordingly,  they are
discussed separately in  the following  subsections.
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5.4.1       Waste Characteristics Affecting Performance (WCAPs)

      In  determining whether  vitrification will  achieve  the  same  level  of
performance on an untested waste  as  on  a previously tested waste, and whether
performance  levels  can  be  transferred,  EPA  examines  the  following  waste
characteristics  that  affect  performance  of  the  vitrification  processes:
(a) organic content of the waste, (b) concentrations of specific metal ions in
the waste, (c) concentrations of compounds in  the waste  that interfere with the
glassmaking process, and  (d) moisture content of the waste.

5.4.1.1     Organic Content

      At process  operating temperatures  (1100 to 1400'C), organics  are combusted
to carbon dioxide, water, and  other  gaseous products.   The combustion process
liberates heat, reducing  the external energy requirements for the process.

      The amount of heat liberated by combustion is  a function of  the Btu value
of the waste.  The  Btu content merely  changes  the  energy input needs for the
process and does  not  affect waste treatment performance.  The amount of material
that may not oxidize completely is a  function  of the organic halogen content of
the waste.   The  presence of  these  halogenated organics does  impact process
performance because sodium chloride has  a low solubility in glass.  The presence
of high  chlorides  results  in  a  porous glass  that is  undesirable.    If the
halogenated organic content of  an untested waste is the same as or less than that
present  in  an already   tested  waste,   the system  should  achieve  the  same
performance for organic destruction.

5.4.1.2     Concentrations of  Specific  Metal Ions

      Most metal  oxides have solubility  limits in glass  matrices.  Hence, their
concentration determines the amount of glass-forming materials or slag with which
they must be  reacted  in  this  process to generate a  nonleaching slag or glass.
The solubility limits of  most  common metal  oxides and salts in glass are found


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in the Handbook  of  Glass  Manufacture  and other treatises on glass production.
Oxides for  which extensive  solubility  information is  available  are alumina,
antimony oxide,  arsenic oxides,  barium  oxide,  cadmium oxide, chromium oxides,
copper oxides, cobalt oxides,  iron oxides, lead oxides,  manganese oxides, nickel
oxides, selenium oxides, tin oxides, and zinc oxides.  Analysis for individual
metal concentrations  in  the waste can  be  performed  according to EPA-approved
methods.   If the  concentrations of specific metals in an untested waste are less
than those in a tested waste,  then the same ratio of slag or  glass raw materials
to waste  may be used for vitrification purposes.  If, however,  the concentration
of metal  is greater than that in  the tested waste,  a different formulation must
be used.

5.4.1.3     Concentrations of Deleterious  Materials

      Some  waste constituents,  such  as  chlorides,  fluorides,  and  sulfates,
interfere with the  vitrification process  if they  are  present at high levels.
These salts have  limited solubilities in  glass; therefore, when they are present,
additional  glass-forming  raw materials  must be  added  to compensate  for their
presence.   The solubility  limits of various  salts in  glasses are discussed in
references  on glass  production  such as  the  Handbook  of  Glass  Manufacture.
Generally, if the concentrations  of such  materials in an untested waste are lower
than those in a tested waste, then the same ratio of glass-forming constituents
to waste may  be  used.   Reducing  agents  such  as carbon or ferrous salts reduce
arsenates and selenates to  lower valence  compounds that  are more volatile.  These
compounds  should not  be  present  in  significant quantities in arsenic-  or
selenium-containing wastes to be vitrified.

5.4.1.4     Moisture Content

      Materials fed to the vitrification process should be reasonably  dry (i.e.,
contain less than 5  percent free moisture).  If  a waste has excess moisture above
this level, it should be thermally dried  before it is blended with glass-forming
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materials; otherwise, it may  react violently when introduced to  the molten glass
or slag pool.

5.4.2       Waste Characteristics Affecting Performance of High-Temperature
            Calcination

      In determining whether high-temperature calcination will  achieve the same
level of performance on  an untested  waste  as on a previously tested waste and
whether performance levels can be transferred,  EPA examines  the following waste
characteristics that impact the performance of  the high-temperature calcination
process:  (a) the organic content of the waste,  (b) the moisture content of the
waste, and (c)  the inorganic composition of the waste.  These characteristics are
discussed below.

5.4.2.1     Organic Content

      Calcination temperatures normally used are too  low to  initiate combustion
of some  types  of organic compounds.   However, they  are high  enough to cause
volatilization of organics, which have to be removed from process off-gases.  For
these reasons,  the presence of significant levels of organics is undesirable but
can be handled  with appropriate air pollution controls.  Organics, per se, do not
interfere  with  the  conversion  of  oxides  to  hydroxides  or with  sintering
processes.  Afterburners may  be required on vitrification units managing high-
organic-content wastes to ensure complete combustion of the organics present.

5.4.2.2     Moisture Content

      Excess water that has to be removed from the waste by heating increases the
amount of time  needed  to bring the  waste to the calcination temperature.  For
this reason, wastes with high moisture content should be dewatered prior to the
use of this process.
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5.4.2.3     Inorganic Composition

      Calcination temperatures are normally selected based on the temperatures
at which  hydroxides  are thermally decomposed to  the  corresponding oxides and
water vapor.  To  select an  optimum operating  temperature,  one should know the
approximate composition of the waste.  A few toxic metal  oxides  have  fairly low
volatilization temperatures. Arsenic oxide, selenium dioxide, and mercuric oxide
all volatilize below 500*C.  High-temperature calcination should not be used for
wastes that contain  these volatile constituents unless the wastes are blended
with materials such as lime, which will  react with the  constituents before they
can vaporize.  Nonvolatile arsenic compounds such as ferric and calcium arsenates
can be calcined without concern for vaporization  of material.

5.5         Design and  Operating  Parameters

      The design  and  operating  parameters  for  the vitrification processes are
similar to each other,  but differ  considerably  from those for high-temperature
calcination.    The   following  subsections  discuss   these  two  technologies
separately.

5.5.1       Design and  Operating  Parameters for Vitrification Processes

      In  assessing  the  effectiveness  of  the  design   and operation  of   a
vitrification system, EPA examines the following  parameters:  (a)  the composition
of the vitrifying agent, (b) the operating  temperature, (c)  the  residence time,
and (d) the vitrification furnace  design.

5.5.1.1     Composition of the Vitrifying  Agent

      Slag and various  glassmaking formulations are used as  vitrifying agents.
The choice of the vitrifying agent is determined by the solubility  of the waste
constituents  to  be   vitrified.    Different inorganic oxides  have  differing
solubilities in various glass matrices.


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      For slags, the presence of carbon or other reducing agents is undesirable
when arsenic-bearing or selenium-bearing wastes are vitrified.  Carbon or ferrous
salts in the slag reduce arsenates in the waste to arsenic trioxide, which has
a low  volatilization temperature.   In  a similar manner,  these  same reducing
agents  reduce  selenates   to   elemental  selenium,   which  also  has  a  low
volatilization temperature.  When slags are  used for vitrifying arsenic-bearing
and selenium-bearing wastes, EPA monitors the composition of the granulated slags
to  ensure  that they  do  not contain  significant  concentrations of  carbon or
ferrous salts.

      In glass vitrification, various glassmaking formulations can be used.  EPA
examines  the  proposed  formulations  to ensure  that  the   toxic   metal  ion
concentrations of the final  product do not exceed solubility limits.   Hence, EPA
examines  the material  balances  based  on   waste  composition  and  glassmaking
additives and the published solubility limits for metal oxides in various glasses
to ensure that the vitrified product is  indeed a glass containing the solubilized
toxic waste constituents.

5.5.1.2     Operating Temperature

      Vitrification furnaces are normally operated in  the 1100 to 1400*C range.
The  exact operating  temperature  is  usually  selected  based on the  desired
composition of the final  product. Furnaces are  normally equipped with automatic
temperature  control  systems.  EPA examines  the basis of choice  for operating
temperatures and the nature  and physical condition of the temperature monitoring
and control equipment to ensure  that the system is being properly operated.

5.5.1.3     Residence Time

      Sufficient time must be allowed for the materials added  to glass furnaces
to reach operating temperatures  and then undergo the chemical reactions needed
to produce glasses.  Residence times are normally on the order of 1  to 2 hours
for  processes operated  at  1100  to  1200*C.   For  glasses  or slags requiring
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slightly  higher temperatures,  slightly  longer residence  times  are usually
selected.  EPA examines the basis for the facility's choice of residence times
to ensure that the system is well operated.

5.5.1.4     Vitrification Furnace Design

      Vitrification furnaces normally incorporate the following design  features:

      •  Withdrawal of the product in liquid form  from  the base of  the furnace.

      •  Maintenance of a liquid pool of product in the furnace.

      •  Addition of product constituent mix at the top of the furnace.

      •  Design of the top area of the furnace  in a manner that  allows for
         cooling of this  area.  (This is important  because volatile  constituents
         of the input feed may  vaporize from the melt.  The  cool  top area allows
         these constituents to condense and fall back  into the melt.)

      •  Presence and proper operation of an air emissions control  afterburner
         and scrubbing system to manage vent gas emissions  from the system such
         as volatilized noncombusted organics and  hydrogen chloride vapors from
         combustion of any chlorinated organics present.
      EPA examines the furnaces to be used for waste vitrification to ensure that
the design  features  mentioned above are  present  since  they are important  for
proper operation of the systems.
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5.5.2       Design  and  Operating Parameters  for  High-Temperature Calcination
            Systems

      In  assessing  the  effectiveness  of  the  design   and   operation   of  a
high-temperature calcination process, EPA examines the following parameters:
(a) the operating temperature,  (b) the residence time,  and (c)  the  air emission
control units in place on the ovens or kilns used.

5.5.2.1     Operating Temperature

      Calcination temperatures of from 500 to 900*C have  been used  in industry.
The calcination  temperature selected is generally a temperature above which  metal
hydroxides  present  will  decompose  to  the corresponding  oxides.   Data on
decomposition temperatures of some metal hydroxides are given  in Table 2.  The
temperature chosen is normally high enough to cause extensive sintering (surface
area loss) of the oxides formed, while at the same time not volatilizing  these
materials.   EPA examines the technical  basis for selection  of the calcining
temperature  to  determine whether the  system is properly operated.   EPA  also
examines the temperature monitoring  and  control  systems  in place  to determine
whether they are properly operated and reliable.

             Table 2  Metal  Hydroxide Decomposition  Temperatures
      Metal hydroxide                  Decomposition temperature  (*C)
      Cadmium hydroxide                             300
      Chromic acid                                  400
      Lead hydroxide                                145
      Nickel hydroxide                              230
      Zinc hydroxide                                125
Source:  Weast 1977.
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5.5.2.2     Residence Time

      Calcination  is  generally a batch  process,  and sufficient  time must be
allowed for samples to be brought to the operating  temperature.  Residence times
of several  hours are normally  used to minimize the effects of heat-up  time.  EPA
examines the  technical  basis  for the choice of residence  time to ensure that
sufficient  heating at  the required  temperature  is  allowed to  complete the
dehydration and sintering processes.  Residence time is a function of the time
needed to bring the calcination furnace or kiln to the desired temperature and
the time  needed to complete  the dehydration  and sintering processes  at the
selected temperature.

5.5.2.3     Air Emission Control Systems

      During the calcination process, water vapor  is  driven  off as it is formed
by the decomposition of hydroxides present in the waste.  These hot  gases exit
the calcination furnace or kiln as they are formed.   Some particulates from the
waste material, as well as organics present in the waste, may become entrained
in  these  vent  gases.   Therefore,   for  air pollution  control  purposes,  the
calcination units must be equipped with wet  or dry particulate collection systems
that  are  properly designed and  operated.   If wastes  containing organics are
processed by high-temperature calcination, the calcination  furnaces  need to be
equipped with afterburners to combust organic vapors  emitted.   EPA examines the
design basis, physical condition, and maintenance  of  these air emission control
units to determine whether  they are properly designed, maintained,  and operated.
EPA also examines  the system  of management in  use for handling and  subsequent
treatment of the collected particulates to ensure that these finely divided waste
particles are properly managed.
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5.6         References


Penberthy,  L.    1984.   Electric  melting  of glass.    In  Handbook  of  glass
      manufacture. Vol. I, pp. 387-399.  New  York:  Ashlee Publishing  Co.

Penberthy, L.  1981.  Method and apparatus  for converting hazardous material  to
      a  relatively  harmless condition.   U.S. Patent  4299.611.   November  10,
      1981.

Steitz, W.R., Hibscher,  C.W.,  and Mattocks,  G.R.   1984.  Electric melting  of
      glass.  In Handbook of glass manufacture. Vol. I, pp. 400-428. New York:
      Ashlee Publishing Co.

Tooley, F.V.  1984.   Raw materials.  In Handbook of glass manufacture.   Vol.  I,
      pp. 19-56.  New York:  Ashlee Publishing Co.

Twidwell,  L.G.,  and Mehta,  A.K.   1985.   Disposal of arsenic bearing  copper
      smelter flue dust.  In  Nuclear and chemical waste management.  Vol. 5,  pp.
      297-303.    Butte,  Mont.:    Montana  College  of  Mineral   Science  and
      Technology.

Weast, R.C., ed.  1978.  Handbook of chemistry and  physics. 58th  ed. Cleveland,
      Ohio:  CRC Press.
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                                   II.   REMOVAL TECHNOLOGIES
                 A.   RECOVERY,  REUSE*, AND/OR SEPARATION TECHNOLOGIES
                                           FOR ORGANICS
*The Agency encourages  pollution prevention efforts  such as those  in recovery and reuse practices (see 40  CFR
Part 261.1  for  the  definition of reuse,  reclaimation,  and  recycling).   However, the  Agency recognizes that
currently  there is some confusion over the definition of what constitutes a solid  waste that has led to  the
proliferation  of  so-called  "sham  recycling"  by  some  facilities.   Sham recycling  are  illegitimate waste
management  practices whereby hazardous waste materials  having  no  saleable value (no market  for reuse)  are
claimed to be recycled/reused in order to escape the stringent RCRA hazardous waste definitions.

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                             1.   CARBON  ADSORPTION

1.1         Applicability

      Carbon  adsorption  is a treatment technology used  to  treat wastewaters
containing dissolved organics at concentrations less than about 5 percent and,
to a lesser extent, dissolved metal  and  other  inorganic contaminants.  The most
effective metals removal is achieved with metal complexes.

      The two most  common carbon adsorption processes are  the granular activated
carbon (GAC), which  is  used  in  packed  beds,  and the powdered activated carbon
(PAC), which  is  added  loosely to wastewater.   This  section  discusses the GAC
process; the PAC process is discussed in Section  I.A.I of this document, i.e.,
Biological Treatment.

1.2         Underlying Principles of Operation

      The basic principle of operation for carbon adsorption is the mass transfer
and  adsorption of  a molecule  from a  liquid  or gas onto  a  solid  surface.
Activated carbon is  manufactured  in such a way as to produce extremely porous
carbon particles whose internal  surface area is very large (500  to 1,400 square
meters per gram of carbon).  This porous structure attracts and  holds  (adsorbs)
organic molecules as well  as certain metal and  inorganic molecules.

      Adsorption occurs because (a)  the contaminant has a low  solubility in the
waste, (b) the contaminant has  a greater affinity for the carbon than for the
waste, or (c) a combination of the two.   The amount of contaminants  that can be
adsorbed by activated carbon ranges from 0.10  to  0.15 gram per  gram of carbon.

1.3         Description of Carbon Adsorption Process

      In GAC  systems,  the  carbon is packed in  a  column  and  the wastewater is
passed through the carbon bed(s).  The flow can be either  down or up  through the


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vertical  column(s).   Figure 13 shows  two  carbon adsorption systems.   In the
carbon adsorption process, the wastewater is  passed  through  a stationary bed of
carbon.   The  contaminants  in  the  wastewater are  adsorbed most  rapidly and
effectively by the upper layers of carbon  during the initial  stages of operation.
These  upper  layers  are  in  contact  with   the wastewater  at   its  highest
concentrations of contaminants.  The small  amounts of the contaminants that are
not adsorbed in the first few layers of  the activated carbon bed are  removed from
solution in the lower or downstream portion of the bed.  Initially, none of the
contaminants escapes from the carbon bed.

      As the wastewater  flows  down the column (or  the  location  in the column
where the majority of  adsorption  is occurring)  and  the  adsorption capacity is
reached in the  top layers,  the  adsorption  zone moves  down  the  column.   As the
adsorption zone approaches the end of the carbon bed,  the concentration in the
effluent  rapidly  approaches the  influent  concentration.    This  point  in the
process is referred to as breakthrough.  A  breakthrough curve (Figure 14) shows
the plot  of  the ratio of  effluent  to  influent  concentrations versus  time of
process operation.   At breakthrough, the adsorptive capacity of the carbon bed
is exhausted,  and little additional removal   of  contaminants occurs.   Treated
wastewater is then either treated further in  another carbon adsorption column,
if necessary, or disposed of.

      Once the carbon bed is spent and can no longer remove contaminants from the
waste, it is  taken off-line.  The activated carbon is then either regenerated by
thermal  or  chemical  methods  for  further  use or treated by  incineration and
disposed of.   If carbon adsorption  is used  to  treat very  toxic  or hazardous
materials, the  spent carbon usually  is incinerated and disposed of directly.

      Regeneration  is  accomplished thermally   by  heating  the   carbon   to  a
temperature  (between  1,500  and  1,700'F)  at   which  most of  the  adsorbed
contaminants are volatilized and destroyed  but which is not  high enough to burn
the surface of  the carbon.  About 4  to 9 percent of the carbon is lost in this
process.  Steam can also be used to  regenerate carbon by volatilizing adsorbed


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    WASTEWATER
      INFLUENT
ro
-•4
                            TREATED
                           EFFLUENT
                          TO DISPOSAL
                                                  GRANULAR
                                                  ACTIVATED
                                                   CARBON
                                                                 ;•»«.:
           OOWNFLOW SERIES ARRANGEMENT
                                            TREATED
                                            EFFLUENT  WASTEWATER
                                            TO           INFLUENT
                                            DISPOSAL
UPFLOW  SERIES  ARRANGEMENT
                                        Figure  13  Carbon Adsorption Systems

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                                     WASTEWATER
                                       INFLUENT
ro
oo
u
1
                       ADSORPTION
                             ZONE

                                       EFFLUENT
                                                      \J
                                                      I
 V*
1
B
 \f
J
                                   1.0


                    RATIO OF
              EFFLUENT TO INFLUENT
                CONCENTRATIONS   0.6
              WITH RESPECT TO TIME
                                                                   B
                                                              TIME
                                        Figure 14  Plot of Breakthrough Curve

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organics for subsequent condensation, recovery, and reuse or for treatment and
disposal.  Chemical  regeneration  involves the use of an acid,  alkali, or organic
solvent  to  redissolve contaminants  for  subsequent recovery and  reuse  or for
further  treatment  and disposal.   There  is  a  loss  of performance  with each
regeneration of  spent carbon because metals  (such  as calcium,  magnesium, and
iron) plug small  pores in the carbon  and  prevent some  organic contaminants from
being  desorbed  at  the  thermal  regeneration  temperature.    In  each  thermal
regeneration  process,  some  carbon  becomes  spent,  requiring  treatment  and
disposal.  As a result, makeup carbon has to  be added  to the regenerated carbon
being placed back in  service.

      The number of  times that the carbon  can  be regenerated is determined  by the
extent of its physical  erosion and the loss of its adsorptive capacity.  Isotherm
tests  can be  performed  on the  regenerated  carbon  to  determine adsorptive
capacity; such tests  can thus aid in predicting the number of times the carbon
can be regenerated.

1.4         Waste Characteristics Affecting  Performance (WCAPs)

      In determining  whether carbon  adsorption will  achieve the same level of
performance on an untested waste  as it achieved on a previously tested waste and
whether performance levels can be transferred,  EPA examines  the  following waste
characteristics:  (a)  the waste type and concentration of adsorbable contaminants
and (b) the concentrations  of suspended solids  and oil and grease.

1.4.1       Waste Type and  Concentration of Adsorbable Contaminants

      The concentration of adsorbable contaminants is  a measure  of the fraction
of the wastewater constituents that  can be expected to be adsorbed by a carbon
adsorption column.   Concentrations of organics in the wastewater greater than
about  5  percent  result  in  excessive  activated  carbon  consumption  requiring
frequent regeneration.  At  the higher organic concentrations other treatment
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technologies, such as wet air oxidation,  solvent extraction, or incineration, may
be more appropriate.

      Although all organics can  be adsorbed to some degree, activated carbon has
a greater affinity  for  aromatic than  for aliphatic compounds and for nonpolar
than  for polar   compounds.    If the  type  and  concentration  of   adsorbable
contaminants in an untested waste are  significantly less  adsorbable  and higher,
respectively, than  in  the tested waste,  the system may  not  achieve the same
performance.

1.4.2       Concentrations of Suspended Sol Ids and Oil and Grease

      Suspended solids and oil and grease can reduce the effectiveness of carbon
adsorption  by  clogging and  coating  the  pores,  as well  as  by  competing for
adsorption  sites,  thereby interfering  with  the treatment  of contaminants of
concern.  EPA has  information  showing that this treatment interference occurs
with suspended  solids  at levels greater  than  about 50 mg/1  and with oil and
grease at above 10 mg/1.

1.5         Design and Operating Parameters

      In assessing  the  effectiveness  of the design and  operation of a carbon
adsorption system, EPA examines  the  following parameters:   (a)  the type and pore
size of the  carbon  particles,  (b)  the adsorption temperature, (c) the pH, and
(d) the hydraulic loading rate.

      For many  hazardous  organic  constituents,  analytical  methods  are not
available or the constituent cannot  be analyzed in the  waste matrix.   Therefore,
it would  normally be  impossible to  measure  the effectiveness  of  the carbon
adsorption treatment system.   In these  cases EPA tries to identify  measurable
parameters  or  constituents  that  would  act  as  surrogates in  order to verify
treatment.
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      For organic constituents,  each  compound  contains  a measurable amount of
total organic carbon (TOC).  Removal of TOC in the carbon adsorption treatment
system will  indicate removal of organic  constituents.   Hence, TOC analysis is
likely  to  be  an  adequate  surrogate  analysis  where   the   specific  organic
constituent cannot be measured.

      However, TOC analysis may not be able to adequately detect treatment of
specific  organics  in  matrices  that are  heavily organic-laden  (i.e.,  the TOC
analysis may not be sensitive enough to detect changes at the milligrams/liter
(mg/1) level  in matrices where total  organic concentrations  are hundreds or
thousands of mg/1).  In these cases,  other surrogate parameters should be sought.
For example, if a specific analyzable constituent is expected to  be  treated as
well as the unanalyzable constituent, the analyzable constituent  concentration
should be monitored as a surrogate.

1.5.1       Type and Pore Size  of Carbon Particles

      Activated carbon is made from a variety  of  substances (e.g., coal, wood),
ground to many different  sizes,  and  manufactured with a number of different  pore
sizes.  The pore size  determines the surface area available for  adsorption  and,
hence, the  carbon's  adsorptive  capacity.   The  type  and pore  size of carbon
particles exhibit different  adsorptive capacities for different  contaminants.
Another  property  that  is  important in assessing the effectiveness of carbon
particles is  the  iodine  number; this value is  an  indicator  of the  adsorptive
capacity for low-molecular-weight-organics.  Laboratory bench testing is used to
determine the most effective type and pore size of carbon  particles for treating
particular  wastewaters.   EPA  examines  the type  and  pore size  of  the carbon
particles used to ensure that effective adsorption is achieved.

1.5.2       Adsorption Temperature

      As the temperature  increases,  the solubility of the  contaminants generally
increases as well,  which  results in  less effective adsorption.  EPA monitors the
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temperature continuously, if possible,  to ensure that the system is  operating  at
the appropriate design condition and to diagnose operational problems.

1.5.3       pH

      The pH  impacts  both the solubility of  the  various contaminants and the
potential for chemical bonding to occur.  EPA monitors the pH continuously,  if
possible, to  ensure that  the system  is  operating at  the  appropriate design
conditions and to diagnose operational problems.

1.5.4       Hydraulic Loading Rate

      The amount  of time that the waste contaminants  are in contact with the
carbon particles  (i.e., residence time) impacts the extent to which  adsorption
occurs.   Higher  residence times generally  improve adsorption  performance but
require longer carbon  beds to maintain the same  overall throughput.  Typical
residence times for GAC adsorption systems range from 30 to  100  minutes.   For a
given size carbon bed,  the residence  time  can  be  determined by the  hydraulic
loading rate.  Typical hydraulic loading rates for downflow  adsorption systems
range from 0.5 to  8.0 gal/min-ft2, while upflow systems typically operate around
15 gal/min-ft2.    EPA  monitors  the  hydraulic  loading  rate  to  ensure  that
sufficient time is  provided to effectively  adsorb contaminants.
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1.6         References


Authur D.  Little, Inc.  1977.  Physical, chemical  and biological  treatment
      techniques  for  industrial  wastes. Vol. I., pp. 1-1  to  1-18 and 1-37 to
      1-41.  NTIS, PB275-054.

DeJohn, P. B.  1975.  Carbon from lignite or coal:  Which  is better?  Chemical
      Engineering. .April 28.

Eckenfelder, W.W. Jr., Patoczka, J., and Watkins  A.  1985. Wastewater treatment.
      Chemical Engineering. September 2, 1985.

GCA Corp.   1984.  Technical  assessment of  treatment  alternatives for wastes
      containing  halogenated  orqanics.   Prepared for  U.S. Environmental Pro-
      tection Agency, Contract No. 68-01-6871,  pp. 150-160.

Metcalf &  Eddy,   Inc.  1985.  Briefing:   Technologies applicable  to   hazardous
      waste.   Prepared  for  U.S.  Environmental  Protection Agency,  Office of
      Research and Development, Hazardous Waste Engineering  Research Laboratory.
      Section 2.13.

Patterson,  J.  W.  1985.  Industrial wastewater  treatment  technology.  2nd ed.
      Stoneham, Mass.:  Butterworth Publishers,  pp. 329-340.

Touhill,   Shuckrow & Assoc.  1981.   Concentration technologies  for   hazardous
      aqueous waste treatment.  NTIS, PB81-150583. pp. 53-55.

USEPA.  1973.  U.S. Environmental Protection Agency.   Process design manual for
      carbon adsorption.  NTIS,  PB227-157.  pp. 3-21 and 53.

USEPA.  1982.  U.S. Environmental Protection Agency.  Development  Document for
      the Porcelain Enameling Point Source Category, pp. 172-241.  Washington,
      D.C.: U.S.  Environmental Protection Agency.

USEPA.   1986.    U.S.  Environmental   Protection Agency.     Best  demonstrated
      available  technology  (BOAT)  background  document  for  F001-F005   Spent
      Solvents.  Vol.  1,  EPA/530-SW-86-056,  p.  4-4.   Washington,  D.C.:   U.S.
      Environmental Protection Agency.

Versar.  1985  .   Versar,  Inc.   An Overview of Carbon Adsorption.  Draft  final
      report  prepared  for  U.S.  Environmental  Protection  Agency,  Exposure
      Evaluation Division, Office of Toxic Substances.  Contract No. 68-02-3968,
      Task No. 58.
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                         2.   DISTILLATION TECHNOLOGIES

2.1         Applicability

      Distillation is a thermal treatment technology applicable to  the treatment
of wastes  containing organics that  are  volatile enough to  be  removed by the
application of  heat.   Constituents that are not  volatilized may  be reused or
incinerated as  appropriate.   The four most  common  distillation processes are
batch distillation, fractionation, steam stripping, and thin film evaporation.
Thermal drying  is  also included in this  section  because  of its similarity to
distillation  processes.   Thermal  drying uses  heat to volatilize  water from
wastes.

      Batch distillation can  be  used to  treat  wastes having a relatively high
percentage of volatile organics.  In general, batch distillation  is applied to
spent solvent wastes where the wastes are highly concentrated in the  solvent and
yield  significant  amounts  of recoverable materials  upon  separation.   Batch
distillation is particularly applicable for wastes that have both  very  volatile
and  very  nonvolatile components  since  the separation  of  that combination of
components  is  amenable to  the  relatively unsophisticated  batch  distillation
equipment.

      Fractionation is typically applied  to wastes containing greater than about
7 percent organics.  It is  designed to achieve  the highest degree  of distillate
purity of  the separated  components.   Fractionation can be operated to produce
multiple product streams for recovery of more than one organic  constituent from
a waste while generating relatively small  amounts of  residue to be land disposed.
In general, this technology is used where recovery  of  multiple constituents is
desired and where the waste contains minimal amounts of suspended solids.

      Steam stripping  is a form of distillation  applicable  to the treatment of
wastewaters containing organics that are volatile enough to  be removed by the
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application of heat using steam as the heat  source.  Typically, steam stripping
is applied where the waste contains less than 1 percent volatile organics.

      Thin film evaporation  is  typically  applied  to wastes containing greater
than 40 percent organics.  However, the feed stream  to the  thin film evaporator
must contain low concentrations of suspended solids.

      Thermal  drying is  a  treatment  technology applicable  to  solid wastes
typically having  a filterable  solids  content  of approximately  40  percent or
greater.  Thermal  drying removes water and volatile  organics from a solid waste
through evaporation.  Thermal dryers  operate in  the range of 300 to 700*F and
usually  have mechanical  agitation to  improve heat  transfer.   Use  of this
technology results in a smaller volume of waste with reduced concentrations of
water and volatile organics.

      A thermal dryer or "sludge dryer" is an enclosed device that is typically
used to dehydrate  sludge.   The  dryer's input (from  wastes and auxiliary fuel)
usually does not exceed 1500 Btu per pound of wastes treated, compared  to 3,300
to 19,000 Btu per pound for  incineration.

2.2         Underlying Principles  of Operation

      The basic principle of operation for  distillation processes, i.e., batch
distillation, fractionation, thin film evaporation,  and  steam stripping,  is the
volatilization of  hazardous components through the application  of  heat.  The
components that are volatilized are then condensed  and typically either  reused
or further treated, usually by liquid injection  incineration.  In thermal drying,
the basic principle  of  operation  for drying is the  removal of a liquid  from  a
solid  waste  by  evaporation.    This  is  similar  to  distillation   in  that
volatilization of organic constituents also occurs.  However, the primary purpose
of thermal drying is to volatilize water.  Liquid  constituents  will vaporize as
a  result of applied  heat.   In  thermal   drying,  the  rate  at  which  liquid
evaporation occurs depends on the thermal  conductivity of  the  solid waste to be


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dried  and  the  boiling  points  of the  volatile  liquid  constituents  to  be
evaporated.

      An integral  part of the theory of the distillation process is the principle
of vapor-liquid equilibrium.  When  a liquid mixture of two or more components is
heated, the vapor  phase present above the liquid phase becomes more concentrated
in the more volatile constituents  (those  having higher vapor  pressures).   The
vapor  phase above  the  liquid phase  is then  removed and  cooled  to yield  a
condensate that is also more  concentrated  in  the more volatile components.  The
degree of  separation of components depends on  the relative differences  in the
vapor  pressures of the constituents; the  larger the difference in  the vapor
pressures, the more easily the separation can be accomplished.

       If the difference between the vapor pressures is extremely large, a single
separation cycle or a single "equilibrium stage" of vaporization and condensation
may achieve a significant  separation of  the constituents.   In  such cases, batch
distillation  or  thin   film  evaporation  would  be  used.     Typically,  batch
distillation units and  thin film  evaporation  units  contain  only one equilibrium
stage  and  are  thus  limited  in   the degree  of  separation  by the  relative
volatilities of the constituents.

       If the difference between  the vapor pressures of volatile components is
small,  then  multiple   equilibrium stages  are  needed  to achieve  effective
separation.   In  practice, the  multiple  equilibrium  stages  are  obtained by
stacking  "trays"  or placing  "packing" into a  column.   Essentially,  each tray
represents  one  equilibrium  stage.   In  a  packed  steam stripping  column or
fractionation column, the  individual equilibrium stages are  not discernible, but
the number of equivalent trays can be calculated from mathematical relationships.
The vapor phase from a  tray rises to the tray above it, where  it condenses; the
liquid phase falls to the  tray below it,  where it is again heated and separated.

      The  vapor-liquid equilibrium of the waste components can be expressed as
relative volatility, which is the ratio of the vapor-to-liquid  concentrations of
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a constituent  divided by the  ratio  of the vapor-to-liquid  concentrations of
another constituent.  The relative volatility  is a direct indicator of the ease
of separation.   If the  numerical value  is  1,  then separation  is  impossible
because the constituents have  the same  concentrations  in  the vapor  and liquid
phases.   When  the relative volatility  is  1,  the  liquid mixture  is  called an
azeotrope.  Separation becomes increasingly easier as the value of the relative
volatility becomes increasingly different from unity.

2.3         Description of Distillation Processes

2.3.1       Batch Distillation

      A batch distillation unit usually consists of a steam-jacketed vessel, a
condenser, and a product receiver. As  the name implies, it is a batch process,
not a continuous process.  Figure  15 is a schematic showing the major components
of a batch distillation  unit.   The steam jacket provides  the heat required to
vaporize  the volatile constituents in  the liquid fraction of  the waste.   The
rising vapor is collected in the  condenser, cooled,  and condensed.  The liquid
product stream is then routed  to  the product receiver.

       It  is important to note  that this technology treats wastes by vaporizing
constituents,  not destroying  them.    Accordingly,  an  integral  part  of  this
technology is a condensation system to collect the organics, as well as an air
emission  control  system  to  collect  or  destroy  those  organics that  are not
condensed.  The  cooling  load of  the condenser is calculated in the design to
ensure that the product recovery rate is  maximized and emissions from condenser
venting are minimized. The "bottoms," which are the  least volatile constituents
of the waste, are withdrawn from  the bottom of the batch still.  Because  batch
distillation is used to remove the volatile organics from wastes, the bottoms are
reduced in volatile organic  content.   However,  prior  to disposal, the bottoms
generally require additional  treatment, such as incineration,  for residual, less
volatile  organics.
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                            VENT  OF NON-CONDENSED  VAPORS
                            TO AIR POLLUTION CONTROL SYSTEM
                                AND/OR THE  ATMOSPHERE
WASTE
INI-LUbNI
i
i
J
(

L
                                                  CONDENSER
       'A/////////////,
            BATCH STILL
                                   HEATED
                                   JACKET
PRODUCT
RECEIVER

RECOVERED
ORGANICS
TO  REUSE
OR  FURTHER
TREATMENT
STILL  BOTTOMS
 TO REUSE OR
 INCINERATION
                  Figure 15  Batch Distillation System
                             138

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2.3.2       Fractionation

      Fractionation is a continuous process conducted in a unit that consists of
a  reboiler,   a column  containing  stripping  and  rectification  sections,  a
condenser, and a  "reflux"  system.  Figure  16 is  a schematic showing the major
components of a fractionation unit.   The  reboiler is a device  that provides the
heat required to vaporize the liquid  fraction of  the waste.  It supplies enough
heat to maintain the liquid in the column at its boiling point.   The stripping
and rectifying sections are composed of a set of trays in a vertical column.  The
discrete trays may be  replaced by loose packing consisting of plastic, metal, or
ceramic  geometric  shapes  that  provide  surface  area  for  the  continuous
boiling/condensing that  takes place  in  the  column.   In the stripping section,
vapor rising  from the boiler is  contacted with  the downflowing  liquid feed.
Through this  contact,  the  constituents  with lower boiling points (i.e., those
that are  more volatile)  are concentrated in the  vapor.   In the rectification
section,  the  vapor rising above  the feed  tray  is  contacted  with downflowing
condensed liquid product (reflux).  Through  this contact, the vapor is further
enriched in the constituents with  lower  boiling points  (i.e.,  the more volatile
constituents).   The rising vapor  is collected  at  the  top of  the  column and
condensed in  a condenser.   The liquid product stream,  except for the portion
returned  to the  column as  reflux, is then  routed to a  product  receiver.  The
"bottoms," which are the least volatile components (i.e., those with the highest
boiling points),  are continuously withdrawn from the   reboiler.   Because the
liquid composition varies slightly from one equilibrium stage to  the  next,  it is
also  possible  to withdraw  streams   of  differing  quality  (sometimes  called
"fractions")  from different locations throughout  the column.   This is typically
done in refining petroleum, resulting in different grades or "cuts" of petroleum
products.

2.3.3       Steam Stripping

      Steam stripping is a continuous process conducted in a unit that consists
of a boiler,  a stripping column, a condenser, and a collection tank,  as shown in


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                          VENT OF NON-CONDENSED VAPORS
                         TO AIR POLLUTION CONTROL SYSTEM
                              AND/OR  THE ATMOSPHERE

                                       i
                              REFLUX

                                               CONDENSER
  WASTE
INFLUENT'
                                t
                            RECTIFIER
                             SECTION
                             STRIPPER
                             SECTION
PRODUCT
RECEIVER
                                            RECOVERED  ORGANICS
                                                 TO  REUSE
                                I
                                  REBOIL

                                                       BOTTOMS
                                                       TO REUSE OR
                                                       INCINERATION
                                       REBOILER
                  Figure 16 Fractional!on System
                                  140

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Figure 17.  The boiler provides the heat required to vaporize the liquid fraction
of the waste.  The  stripping column is composed of a  set  of trays or packing
placed in a vertical column.

      The steam  stripping  process uses multiple equilibrium  stages,  with the
initial waste mixture entering  at  the top, the uppermost equilibrium stage.  The
boiler is located beneath the lowermost equilibrium stage, allowing  the vapor to
move upward in the column,  coming  into  contact with the  falling liquid.  As the
vapor  comes  into contact  with the  liquid  at each  stage, the  more  volatile
components are removed or  "stripped" from the liquid  by the vapor phase.  The
concentration  of  the  emerging  vapor  is  enriched  in  the  more  volatile
constituents, and the liquid exiting the bottom of the boiler ("bottoms"), which
is predominantly  water, contains high concentrations of the  lower vapor pressure
constituents.  This effluent  from the bottom of  the  stripper  is  reduced in
organic  content  but may  still require  additional treatment such as  carbon
adsorption or biological treatment.  The steam and organic vapors exiting the top
of the column are condensed.  As  condensed liquids, the organic components are
usually immiscible with water.   The two  immiscible  phases are  then separated in
a product receiver.  Organics  in  the organic phase are typically recovered or
disposed of in a liquid injection  incinerator, while the aqueous condensate is
recycled to the stripper.

2.3.4       Thin Film Evaporation

      Thin film  evaporation is a  continuous process conducted in  a unit that
typically  consists  of a  steam-jacketed cylindrical  vessel   and  a condenser.
Figure 18 is a schematic showing the major components of a thin film evaporator.
The steam-heated  surface of the cylindrical vessel provides  the heat  required to
vaporize the volatile constituents in the waste.  The evaporator walls are heated
from the  outside as the feed  trickles  down  the  inside walls in  a thin film.
Unique to this form of distillation is  the distribution  device that  spreads the
thin film over the heated surface.   The  feed rate of waste is controlled to allow
the more volatile material adequate time to vaporize.  The heat transfer from the


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STEWATER
 INFLUENT
                       VENT OF NON-CONDENSED  VAPORS
                      TO AIR POLLUTION  CONTROL SYSTEM
                           AND/OR  THE ATMOSPHERE
               k^
               k    -»•»-»•» -^ -x -v
               NSTRIPPINGX;
               \ COLUMN
                                     1

                                             CONDENSER
                                    RECYCLE
                                                       RECEIVER
RECOVERED
ORGANICS
TO REUSE
OH TREATMENT
                                                         TREATED  EFFLUENT
                                                         TO FURTHER
                                                         TREATMENT
                                                         ANO/OR DISPOSAL
                     Figure 17 Steam Stripping System
                                    142

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                ROTATING
                  DRIVE
  WASTE
INFLUENT
   LIQUID
     FILM
           VENT OF
  NON-CONDENSED  VAPORS  TO
AIR  POLLUTION  CONTROL SYSTEM
   AND/OR THE  ATMOSPHERE
                                        1

                                                CONDENSER
      HEATED
      JACKET
PRODUCT
RECEIVER

RECOVERED
ORGANICS
TO REUSE
                                     BOTTOMS TO
                                     REUSE OR
                                     INCINERATION
                 Figure 18  Thin Film Evaporation System
                                   143

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heating medium (steam) to the waste is determined by their relative temperatures,
the heat transfer rate of the vessel materials, and the thermal  properties of the
waste stream forming the film.   The rising  vapor is collected  at the top of the
column, cooled,  and condensed in  a  condenser.   The  condensed  liquid product
stream is then routed to a product  receiver.  The "bottoms," which are the least
volatile components of the waste,  are continuously withdrawn from the bottom of
the thin film evaporator.  Because thin film evaporation is used to remove the
volatile  organics from wastes,  the  bottoms  are reduced in  volatile organic
content.  However,  prior  to disposal, the  bottoms  usually  require additional
treatment, such as  incineration, for residual, less volatile organics.

2.3.5       Thermal Drying

      A wide  range  of batch  and  continuous dryers  is available.   One commonly
used continuous type is the screw-flight dryer, the major components of which are
shown in  Figure  19.  The  screw-flight dryer consists of a screw surrounding a
hollow shaft enclosed in a trough.  Heat transfer  fluid is  heated to temperatures
as high as  750*F  and circulated,  usually  countercurrent  to  the flow of waste,
through the hollow shaft.  Heat transfers  from the shaft to the  screw blades, and
then into the  feed  material, causing  water and  organics  to  be driven off in a
vapor form.  The  dried cake  is discharged  from the dryer.

      The dryer  is  designed  to  create good contact between  the screw and feed
material.   The screw is  usually  equipped  with  breaker bars  to  ensure proper
shearing of the input materials and to prevent the  screw surfaces from fouling.

      Vapors emerging from this  system are managed in one  of two ways, depending
on  their  composition.    If  the  vapors contain  only water,   they  are usually
directly  vented  to the atmosphere.   However, if the  vapors  contain volatile
organics, they are generally passed through  a water-cooled condenser system.  The
recovered organic liquids from the condenser unit are then forwarded to another
process for treatment or recovery.
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            FEED IN
BREAKER BARS
                                                                                                             STEAM IN
            SCREWS
in
HOLLOW
SHAFT
 DRIED
MATERIAL
                                       Figure  19   Screw Flight Dryer

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2.4         Waste Characteristics Affecting Performance (WCAPs)

      In determining  whether distillation technologies will  achieve the same
level of performance  on  an  untested  waste as  on a previously tested waste and
whether performance levels can be transferred,  EPA examines  the  following waste
characteristics:  (a)  the component boiling points, (b) the thermal conductivity,
(c) the concentration of volatiles,  (d) the concentration of suspended solids,
(e) the surface tension, and  (f) the oil and grease content.  The  above-mentioned
waste  characteristics   affecting  performance  vary  for  each  distillation
technology.

      The WCAPs for each specific distillation process are  as follows:

      •  Batch distillation:  thermal  conductivity, component boiling points, and
         concentration of volatiles.

      •  Fractionation, steam stripping,  and thin  film evaporation:  concen-
         tration of suspended solids, component boiling points, concentration of
         volatiles, surface  tension, and  oil and grease content.

      •  Thermal drying:  thermal conductivity and component boiling points.
2.4.1       Component Boiling Points

      As  noted earlier,  the greater  the  ratio  of  volatility of  the waste
constituents, the more easily the separation of these  constituents  can proceed.
This ratio is called relative volatility.   EPA recognizes, however, that relative
volatilities cannot be measured or calculated directly  for the  types of wastes
generally treated by distillation processes because  such wastes  usually consist
of a myriad of components,  all with different vapor pressure-versus-temperature
relationships.    However,  because  the  volatility  of  components  is  usually
inversely proportional  to  their boiling  points (i.e.,  the  higher the boiling


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point, the lower the  volatility), EPA uses the boiling point  of waste components
as a surrogate waste  characteristic for relative volatility.   If the differences
in boiling points between the more volatile and less volatile constituents are
significantly smaller in the  untested waste than in the tested waste, the system
may not achieve the  same performance and more rigorous operating conditions or
other, more  applicable treatment technologies  may need to  be  considered for
treatment of the untested waste.

2.4.2       Thermal  Conductivity of the Waste

      A major factor  determining whether a particular constituent will volatilize
is the potential  for  transfer of heat  through the waste.  For  batch distillation,
heat transfer is accomplished principally by conduction from  the external source
of  heat  (with some  convection  within the waste).   For thermal  drying,  heat
transfer is accomplished primarily by conduction  rather than convection  since the
wastes  are  usually  not  liquids.   Thermal conductivity is   not  as  critical   a
consideration with other forms of distillation because the wastes are  broken up
into thin films, which  conduct heat relatively rapidly.

      Heat flow by conduction is proportional  to the temperature gradient across
the  material.   The proportionality  constant,   referred  to  as the thermal
conductivity, is a property of the material to  be distilled (or dried  in the case
of thermal drying).  With regard to convection,  EPA believes  that the  amount of
heat  transferred  by  convection  is  not  dependent  on the waste's thermal
conductivity.  Convection will usually be more a  function of the system design
than  of  the waste itself  (i.e.,  how well the  waste can be mixed  during the
process).

      Thermal conductivity measurements, as part of a treatability comparison for
two different wastes  to be treated by a single batch distillation  unit, are most
meaningful  when  applied  to  wastes  that   are   homogeneous  (i.e.,  uniform
throughout).   As  wastes  exhibit greater  degrees  of  nonhomogeneity, thermal
conductivity  becomes  less   accurate  in  predicting treatability because the
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conductivity  becomes less  accurate  in  predicting  treatability because  the
measurement essentially reflects heat flow through regions having the greatest
conductivity (i.e., the path of least resistance)  and not heat flow through all
parts of the waste.   Nevertheless,  EPA  believes  that thermal  conductivity may
provide the  best  measure  of performance  of  heat transfer.   If the thermal
conductivity of an untested  waste is significantly lower than that of the tested
waste,  the system may  not achieve  the  same  performance,  and other,  more
applicable treatment technologies may need to be considered for treatment of the
untested waste.

2.4.3       Concentration of Volatile Components

      The  concentration  of volatile  components  is  a  measure of the maximum
fraction of the waste that can be expected to volatilize during a distillation
process. A relatively low concentration of volatile components  implies  that most
of  the waste  may  become  bottoms  (i.e.,  relatively  nonvolatile).    If  the
concentration  of  relatively  volatile  components in  the  untested  waste  is
significantly lower than that in the  tested waste, the untested system may not
perform  adequately.   More rigorous  operating  conditions,  such  as  higher
temperatures, higher residence times, etc., may be required to volatilize less
volatile components and achieve the same treatment performance,  or other, more
applicable treatment technologies may need to be considered for treatment of the
untested waste.

2.4.4       Concentration of Suspended Solids

      Wastes   containing   large  amounts  of   suspended   solids—organic  or
inorganic—may  have  an adverse  effect on distillation  treatment systems.   For
example, in thin  film evaporation,  large amounts of  suspended solids may coat
heat  transfer  surfaces,  thereby  disturbing  the  uniform  film  and  inhibiting
volatilization  of constituents.   In  fractionation and  steam  stripping, large
amounts of suspended solids may clog column  internals and coat heat tranfer
surfaces,  thereby inhibiting heat  transfer and  mass  transfer of constituents
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between the vapor and liquid phases.  If the concentration of suspended solids
in the untested waste  is significantly higher than that in the tested waste, the
system may not achieve the same performance.  Filtration may be required prior
to distillation processes to reduce the  concentration of suspended solids and
achieve the  same  treatment performance,  or other, more applicable treatment
technologies may need to be considered for treatment of the untested waste.

2.4.5       Surface Tension

      The surface  tension  of the waste is a measure of the tendency  of the waste
to foam and to  "wet" the heat and mass transfer surfaces.  The higher the surface
tension of the  liquid, the  higher  its tendency  to foam.   Also, higher surface
tensions will  not  allow a  film  of  the  waste to coat heat and  mass transfer
surfaces as  well  as  low  surface  tensions  will.   The  likelihood  of foaming
requires special  column  design or the   incorporation  of defoaming compounds.
Packed columns  are usually  less susceptible to  foaming than are tray columns.
Waste with high surface tensions that cannot effectively wet column packing or
evaporator walls  will not  form  the thin  films that  enhance heat  and  mass
transfer.  If the  surface  tension  of the  untested waste is significantly higher
than that of the tested waste,  the  system may not achieve the same performance.
Defoaming compounds and/or the use of a packed column  may be required to reduce
foaming and achieve the same  treatment performance,  or other,  more applicable
treatment technologies may need to  be considered  for treatment of the untested
waste.

2.4.6       Concentration of Oil and Grease

      High  concentrations  of  oil   and   grease  may clog steam  stripping and
fractionation  equipment,  thereby  reducing their  effectiveness.   In thin film
evaporation,  high  concentrations  of oil and grease  may result  in  the waste
coating  the evaporator  walls, preventing  a  uniform film  from  forming and
inhibiting volatilization of waste components.   If the concentration of oil and
grease  in  the  untested waste is significantly  higher  than  that  in the tested
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applicable treatment technologies may need to be considered for treatment of the
untested waste.

2.5         Design and Operating  Parameters

      In assessing the effectiveness of the design and operation of distillation
technologies, EPA may examine the  following parameters:  (a) the temperature and
pressure, (b) the  differential  pressure,  (c)  the liquid and vapor  flow rates,
(d) the  internal  column  design,  (e)  the number  of separation stages,  (f)  the
residence time, (g) the surface area, and (h) the  mechanical  system design.

      The  above-mentioned  design  and  operating  parameters  vary  for  each
distillation technology.  The design and operating conditions for each specific
distillation process are as  follows:

      •  Batch distillation:  temperature and pressure, and  residence time.

      •  Fractionation:  number of  separation stages,  liquid  and vapor flow
         rates, temperature  and pressure,  differential pressure, and internal
         column design.

      •  Steam stripping:   number of separation stages, liquid  and  vapor  flow
         rates, temperature  and pressure, and internal  column  design.

      •  Thin film evaporation:   evaporator surface  area,  temperature and
         pressure, residence time, and the speed and design  of the waste disposal
         mechanism.

      •  Thermal dryer:  temperature and pressure,  residence time, and the design
         and speed of the screw mechanism.
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      To evaluate  the  effectiveness of design and  operating  variables,  it is
necessary to measure the concentrations of the components to be separated in both
the feed system and the  process  residuals (e.g.,  overheads and bottoms).  For
many hazardous organic  constituents, analytical methods are not available  or the
constituent cannot be analyzed in the waste matrix.  Therefore,  it would  normally
be impossible to measure  the effectiveness of treatment of distillation  systems.
In these cases EPA tries  to identify measurable parameters  or constituents that
would act as surrogates to verify treatment.

      For organic  constituents,  each  compound  contains a  measurable amount of
total organic carbon (TOC).  Removal of TOC in  the  distillation  treatment  system
will indicate removal of  organic  constituents.  Hence, TOC  analysis  is likely to
be an adequate surrogate  analysis where the  specific organic constituent  cannot
be measured.

      However, TOC  analysis may  not be able to adequately detect treatment of
specific organics  in matrices that  are heavily organic-laden;  that  is, the TOC
analysis may  not  be sensitive enough to  detect changes at the milligrams per
liter (mg/1) level  in matrices where total organic  concentrations are  hundreds
or  thousands  of mg/1.   In these  cases  other surrogate  parameters should be
sought.  For  example,  if a specific  analyzable constituent  is expected  to be
treated  as  well  as the  unanalyzable  constituent,  the analyzable  constituent
concentration might be monitored as a surrogate.

2.5.1       Temperature and Pressure

      These parameters are  integrally related to  the vapor-liquid  equilibrium
conditions.  In steam stripping and fractionation, the temperature  at any point
in the column is an indicator of the constituent  concentrations at  that  point,
thus revealing whether the separation  of components  is taking place  as expected.
Overall  column  pressure  influences the  boiling  point of the liquid at  any
location in the column.  For example, through application of a  partial vacuum to
the column, the temperatures required to  achieve  the  desired separation  can be
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reduced because  liquids volatilize at  lower temperatures when  pressures are
reduced.  EPA monitors the temperature  and  pressure of a steam stripping column
and a fractionation column continuously,  if possible, to ensure that the system
is operating at  the  appropriate  design  conditions  and  to diagnose operational
problems.

      In  thin  film  evaporation,  to achieve  the desired  volatilization, the
evaporator may be operated at pressures below atmospheric (slight vacuum).  At
vacuum conditions, lower  temperatures  can  be used,  requiring less heat input,
because boiling  points  decrease  as  pressure decreases.   EPA monitors the thin
film evaporator  temperature  as  well as the  pressure (if  pressures other than
atmospheric are  used) continuously, if  possible, to  ensure that the system is
operating  at  the  appropriate design  condition and  to  diagnose operational
problems.

      In  batch  distillation  and in thermal  drying,  temperature  provides  an
indirect measure of  the energy  available  (i.e.,  Btu/hr)  to vaporize the  waste
constituents. As the design temperature increases,  more constituents with  lower
volatilities will be removed from the waste.  Pressure is  integrally related to
the boiling point of the  waste  and  the subsequent  vaporization of the organic
constituents.  As the pressure is lowered  below  atmospheric  (i.e.,  as vacuum is
increased),  the  boiling  point   of  the waste  will  also  be  lowered,  thereby
requiring less heat  input  to  volatilize waste constituents.   EPA monitors the
distillation  temperature  as  well   as  the  pressure  (if  pressures  other than
atmospheric are used) to ensure  that the system  is  operating  at the appropriate
design conditions and to diagnose operational problems.

2.5.2       Differential Pressure

      In fractionation, measuring the differential  pressure between the top and
bottom of the column  indicates whether the  flow rate of either the liquid or the
vapor phase is excessive.   For instance,  a high  pressure drop across the column
may indicate a condition  of  "flooding,"  in which the liquid phase cannot flow
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down through  the column as  fast as feed  Is  entering,  causing  backing  up or
"flooding" to occur.   EPA  monitors  the pressure drop across the fractionation
column continuously, if possible, to ensure that the  system  is operating at the
appropriate design condition and to diagnose operational problems.

2.5.3       Liquid and Vapor Flow Rates

      For steam stripping and fractionation, the vapor-liquid equilibrium data
are  also  used  to  determine  the  liquid   and  vapor  flow  rates  that  provide
sufficient contact and residence time between the liquid and  vapor streams.  The
appropriate flow rates are  affected by the column  diameter.  EPA monitors the
liquid and vapor flow rates to ensure  that sufficient contact time between the
liquid and vapor streams is provided to effectively separate the organics from
the wastewater, and to ensure that the  column does  not "flood" (i.e., the vapor
or liquid flow  is  so  high  that  the  vapor  cannot exit the top of the column as
rapidly as it  is generated and/or the liquid cannot  run out the bottom  as rapidly
as it is fed into the column).  Also see Differential Pressure,  above.

2.5.4       Internal Column Design

      In  steam  stripping and fractionation, column  internals  are designed to
accommodate the physical  and chemical properties of  the waste to be fractionated.
Two types of internals may be used in steam stripping and fractionation:  trays
and packing. Tray types  include bubble  cap, sieve,  valve, and turbo-grid.  Trays
have several advantages over packing.  They are less  susceptible to blockage by
solids, they  have  a lower capital  cost for large-diameter  columns  (more than
approximately 3  feet), and  they accommodate a  wider  range of liquid and vapor
flow rates.   Compared to trays, packing has the advantages of having a lower
pressure drop  per theoretical stage, being more resistant to corrosive  materials,
having a lower capital cost for  small-diameter  columns  (less than approximately
3 feet),  and being  less  susceptible to foaming because of a more uniform flow
distribution  (i.e.,  lower local variations in  flow  rates).  EPA examines the
internal  column  design of a steam stripping or fractionation column to ensure


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that the  system is designed  to handle potential operational  problems (e.g.,
corrosion, foaming, channeling).

2.5.5       Number of Separation Stages

      The number  of separation stages  in  a steam  stripping  or fractionation
column  required  to  achieve  the  desired  separation  of  the  more  volatile
constituents from the  less volatile constituents is calculated from vapor-liquid
equilibrium data,  which are determined empirically.  Using the theoretical number
of stages,  one  can determine the  actual  number of stages  through  the use of
empirical tray efficiency data, typically supplied by equipment manufacturers.
EPA examines the actual number of stages in the  steam stripping or fractionation
column to ensure that the system is designed to achieve an effective degree of
separation of organics from the wastewater stream.

2.5.6       Residence Time

      The residence time determines the necessary energy  input  into the system
as well  as the degree  of  volatilization achieved for organic constituents.  The
residence time  requirement  is  dependent on  the distillation  or evaporation
temperature (or dryer  temperature  in the case of thermal  drying)  and the thermal
conductivity  of the waste.   EPA observes  the residence time  to  ensure that
sufficient time is provided to effectively volatilize  organic constituents from
the waste.  In the case of thermal drying, the residence  time must be sufficient
to effectively evaporate  the volatile  liquid constituents and,  hence, to dry the
waste.

2.5.7       Evaporator Surface Area

      In thin film evaporation,  the evaporator  surface area  required to achieve
the desired volatilization  of organic components from the waste is calculated
from the  vapor-liquid equilibrium  data,  which  are determined empirically, and
from waste liquid  flow rates.  EPA examines the surface area of the evaporator
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to  ensure  that  sufficient  surface  area  is  provided  to  achieve  effective
volatilization of the more volatile organic components.

2.5.8       Mechanical System Design

      Both thin film evaporation and thermal drying have rotating parts.  For the
evaporator, the speed and design of the feed distributor will help determine how
well the feed will  coat  the evaporator surfaces.  For the dryer, the size, screw
flight, spacing, and speed of the screw mechanism will affect residence time and
heat transfer.   Typically,  higher rotational  speed will distribute  feed more
effectively in an evaporator and will  provide more mixing turbulence in a dryer
(for improved  heat  transfer).   However,  increased  speed will  reduce  residence
time in the dryer and will cause earlier mechanical failure in both evaporators
and dryers  (i.e., the bearings  and shafts  will wear more rapidly).
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2.6         References


DeRenzo, D.J., ed.  1978.  Unit operation for treatment of hazardous  industrial
      wastes.  Park Ridge, N.J.:  Noyes  Data  Corporation,

Kirk-Othmer.  1965.  Encyclopedia of chemical technology.  2nd ed., vol.  7,  pp.
      204-248.  New York:  John Wiley and Sons.

McCabe, W.L., Smith, J.C., and Harriot,  P.   1985.  Unit operations of chemical
      engineering,  pp.  533-606.  New York:   McGraw-Hill  Book Co.

Perry, R.H. and Chilton,  C.H.  1973.  Chemical  engineers7 handbook.  5th ed.,  pp.
      13-1 to 13-60.  New York:  McGraw-Hill  Book Co.

Rose, L.M.   1985.   Distillation  design  in  practice.    pp.  1-307.    New  York:
      Elsevier.

Van Winkle, M.  1967.  Distillation,  pp.  1-684.  New York:  McGraw-Hill Book Co.

Water Chemical  Corporation.   1984.  Process design  manual  for stripping  of
      organics.   PB84-232628.   pp. 1-1  to  F4.   Prepared for the  Industrial
      Environmental  Research  Laboratory, Office of  Research  and Development,
      U.S. Environmental Protection Agency.
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                          3.   EXTRACTION TECHNOLOGIES

3.1         Applicability

      Extraction  technologies  (i.e.,  solvent  extraction  and  critical   fluid
extraction) are used to treat wastes containing a variety of organic constituents
and a broad range of total organic content.   Extraction technologies have been
demonstrated for treatment of API separator sludges and other hydrocarbon-bearing
wastes generated  by the petroleum and  petrochemicals  industries.   In theory,
these technologies are also applicable to wastes of similar composition generated
by other industries  such as the organic  chemicals industry.

      In solvent extraction,  the selection of an extraction fluid (solvent)  is
dependent on the solubility of the organic waste constituents  in the extraction
fluid.

      Critical fluid extraction is  applicable  to wastes containing organics that
are soluble  in  pressurized  fluids  such as carbon dioxide,  propane, butane,  or
pentane  (extraction  fluids).   Compounds that have been successfully extracted
from  wastes  by this process  include  aliphatic  hydrocarbons,  alkenes,  simple
aromatics such as benzene and toluene,  polynuclear aromatics, and phenols.

3.2         Underlying Principles  of Operation

      The  basic principle  of  operation in  extraction  technologies  is that
constituents  are  removed  from a waste  by mixing  the waste with an extraction
fluid  (solvent)  that will  preferentially dissolve  the  waste constituents  of
concern from the waste.   In the simplest extraction  systems, two components  are
mixed:   (a)  the waste stream  to  be extracted  and  (b) extraction  fluid.   The
extraction  fluid and waste  stream are  mixed  to  allow  mass transfer of  the
constituent  (the solute) from the  waste  stream  to the extraction fluid.
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        Except for the waste constituents that are to be extracted, the waste must
 be  immiscible  in the  extracted  fluid,  so that  after mixing, the two  immiscible
 phases can physically separate  by gravity.  Separation of  the  extraction  fluid
 phase  and the  waste stream  phase occurs under  quiescent conditions,  relying  on
 the density differences  between the  two phases.

        The extraction  fluid, which  now contains the extracted  contaminants,  is
 called the extract; the extracted waste stream from which the contaminants have
 been removed is called the raffinate.  The extract can be either the heavy  (more
• dense) phase or the light (less dense) phase.   In  theory, the maximum degree  of
 separation that can be achieved is provided by the selectivity value,  which  is
 the ratio of the equilibrium concentration of the contaminants in the extraction
 fluid  to the  equilibrium concentration of the contaminants in  the waste.  The
 solvent extraction process  can  be either batch or continuous.

        In critical fluid  extraction,  the extraction fluids  used are compounds
 that are usually gases at ambient conditions.   Since  the  extraction fluid  being
 used is  a  gas, it is  first  pressurized, which converts  it to  a liquid.  As a
 liquid, it leaches (dissolves) the organic constituents out of the complex  waste
 with which it  is mixed.   The enhanced  solubilities of  various organic compounds
 in hydrocarbons and other extraction  fluids at high pressure aid  in their removal
 from a waste.   The process is  usually carried out  at  or  near  the  extraction
 fluid's  "critical pressure," which is  the pressure above which the liquid form
 of  the extraction fluid  cannot be  gasified,   no matter  how  much the  fluid  is
 heated.   (In  fact, above the critical pressure liquid  and  gas phases become
 physically indistinguishable, in that  two phases do  not  really exist.)

 3.3         Description  of  Extraction  Process

 3.3.1       Solvent Extraction

        The  simplest,  least effective  solvent extraction unit is a  single-stage
 system (mixer-settler system).  The solvent and the  liquid waste  stream are  mixed


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together; the raffinate  and  extract  are separated by settling without further
extraction.

      The more effective multistage contact extraction is  basically  a series of
batch mixer-settler  units.   The waste  stream is contacted with  solvent in a
series of successive steps or stages.  Raffinate from the first extraction stage
is contacted with fresh  solvent in a second stage, and  so on.

      In countercurrent, multistage  extraction  columns, fresh solvent and the
waste stream  continuously enter at opposite ends of  a column consisting of a
series of extraction stages.  Extract and raffinate layers  pass continuously and
countercurrently from stage  to stage through the system.

      Several types of extraction systems  are used for  contact and  separation.
Three of the most common  systems--mixer-settler systems, extraction columns, and
centrifugal contactors — are  discussed below.

3.3.2       Mixer-Settler Systems

      Single-stage mixer-settler systems  are  extraction systems composed of a
mixing chamber for  phase dispersion,  followed by a settling chamber for phase
separation.  Mixer-settler systems  are typically used to treat solids or highly
viscous wastes and can handle difficult-to-mix components.  The vessels may be
either vertical or horizontal.   Dispersion in  the mixing chamber occurs by pump
circulation,  nonmechanical   in-line  mixing,  air  agitation,  or  mechanical
stirring.   In a  two-stage  mixer-settler  system  (a  simple  multistage contact
extractor), as shown in  Figure 20,  the  extract from the first stage is sent to
a recovery unit to separate the solvent from the remaining extract containing the
organic  constituents of concern.    The  recovered  solvent  is  used,  and  the
remaining extract is either  reused or further treated  in  an incineration unit.
The  raffinate from  the first  stage  is  sent  to the second-stage  unit  for
additional extraction.  Recycled solvent from recovery of the  first-stage extract
and/or fresh solvent makeup  is added to the first-stage raffinate before it is
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                                         RECYCLED SOLVENT FROM
                                         RECOVERY/FRESH  SOLVENT
                                         MAKEUP
en
o
                                                    RECYCLED
                                                     SOLVENT
                                     EXTRACT TO RECOVERY
       RECYCLED
     TO PROCESS
               TO
            DISPOSAL
                           RAFFINATE

                            *-^^--

                            EXTRACT
RAFFINATE
^—^"

EXTRACT
STAGE 2
                                                                                  EXTRACT TO
                                                                                  RECYCLE OR
                                                                                  DISPOSAL
                                Figure  20  Two-Stage Mixer-Settler Solvent Extraction System

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mixed  and  sent  to the  second stage.   The  extract  from  the  second  stage,
containing mainly  solvent,  is  recycled  to  the first-stage unit as the solvent
stream.  The resulting raffinate from the second  stage  may require filtering to
remove solids before it is sent to further treatment (if  required).  If solids
collected during filtration contain treatable  levels  of hazardous constituents,
they will require further treatment, such as stabilization (for metals) and/or
incineration (for organics) prior to disposal.

      Parameters such as the density or  specific constituent concentrations in
the extract may be monitored to determine when the  second-stage extract must be
sent to solvent recovery and when fresh or recycled solvent must be added to the
first-stage unit.

3.3.3       Extraction Columns

      Extraction columns are continuous flow, countercurrent, multistage contact
systems.  Two types of extraction columns are packed extractors and sieve-tray
extractors.   Figure 21 presents schematics  of these  two types  of extraction
columns.  A packed extractor  contains plastic or ceramic materials in various
geometric shapes or structured packings  of wire gauze or mesh.   Mass transfer of
the contaminants from the waste to the extract  is promoted because  of breakup and
distortion of both phases  as they contact the packing, resulting in the intimate
mixing of the waste and the solvent.

      The  sieve-tray extractor  is  similar to  the sieve-tray column  used in
fractionation distillation.   Tray  perforations  cause  the formation  of liquid
droplets that aid the mass transfer process  by  allowing  for more intimate contact
between the solute  and the  solvent.

3.3.4       Certrifugal Contactors

      Centrifugal  contactors are based on the application of centrifugal  force
to increase rates of countercurrent flow and enhance  separation of the phases.
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     SOLVENT
at
IS)
        WASTE
      INFLUENT
                                         TREATMENT  AND/OR
                                         DISPOSAL
                                                      SOLVENT.
\PACKINQ
  SUPORT
                                       HAhHNAIt TO
                                       TREATMENT AND/OR
                                       DISPOSAL
                                EXTRACT  AND SOLVENT
                                TO  SEPARATOR
                                , AND RECOVERY UNIT
                         PACKED EXTRACTOR
                         EXTRACT  AND SOLVENT
                         TO  SEPARATOR
                         AND RECOVERY UNIT
                     B. SIEVE TRAY EXTRACTOR
                           Figure 21  Packed and Sieve Tray Solvent Extraction Columns

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Centrifugal units are used when short contact times are required, such as when
unstable materials  are being  processed.   One  type of  centrifugal  contactor
consists of a drum that rotates around a shaft equipped  with annular passages at
each end for  feed and raffinate.   The light  phase  is  injected under pressure
through  a  shaft  and is  then routed  to the  periphery of  the  drum  through
perforations.   The  heavy phase is  also  charged through the shaft,  but  it is
channeled to  the  center  of the drum through  perforations.   Centrifugal  force
acting on  the phase-density difference promotes dispersion  as the  phases are
forced through the perforations.  Centrifugal extractors provide short contact
time, have minimal space requirements, and easily handle emulsified materials and
fluids with small density differences.

3.3.5       Critical Fluid Extraction

      A critical fluid extraction system consists of a blending tank,  one or more
extraction  vessels,  one  or  more  decanters,  one  or  more  filters,  and  an
evaporation unit. Organic wastes such as oil refinery sludges are first combined
in a blending tank and mixed well  to yield a homogeneous, pumpable mixture.  This
mixture  is  then pumped under  pressure  to  an extraction vessel  filled  with a
liquified gas such as carbon dioxide, propane, butane, or pentane and is mixed
under pressure to extract (dissolve) hydrocarbon components  from the waste into
the  liquified gas extraction  fluid.  After  the  hydrocarbon  components  of the
waste  dissolve  in  the  pressurized  liquid,  the   resulting  solution  is
gravity-separated in a decanter into a wastewater (or waste  solids) stream and
an extraction fluid-rich  stream.   The  wastewater stream, containing inorganic
solids, is sometimes filtered  under pressure to remove the insoluble components.
The extraction fluid-rich stream is fed to  a  pressurized  evaporation unit.  The
extraction fluid  (carbon dioxide,  propane,  butane,  or pentane)  is evaporated by
dropping  the  pressure  and  is   subsequently  recovered,  repressurized,  and
recondensed for reuse. The  residue from the evaporation,  consisting  of a liquid
hydrocarbon mixture, is then reprocessed or reused,  blended with fuels for heat
recovery, or incinerated.   If  the extracted waste stream still exceeds treatment
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requirements, it may be extracted again with  fresh  extraction  fluid at the high
pressure conditions.

      If inorganic residuals (or waste solids) filtered from the waste/solvent
mixture contain treatable levels of hazardous  constituents such as certain metals
(e.g., chromium, lead) or organics, they will  require further  treatment such as
stabilization or incineration prior to disposal.

3.4         Waste Characteristics Affecting Performance (WCAPs)

      In determining whether extraction processes will achieve the  same level of
performance on  an  untested waste as on  a  previously tested waste and whether
performance  levels  can be transferred,  EPA  examines  the   following  waste
characteristics:   (a) the  concentration of  extractable hydrocarbons,  (b) the
solubility of the waste constituents of concern in the extraction fluid, (c) the
surface tension, and  (d) the alkalinity of the waste.

3.4.1       Concentration of Extractable Hydrocarbons

      The  concentration of  extractable  hydrocarbons  in  the  waste  feed  is  a
measure of the maximum fraction of the waste that can be expected to be extracted
in the  process.  A  relatively low concentration  of  extractable  hydrocarbons
implies that most of  the waste may become wastewater or waste  solids (i.e., is
nonextractable).   Total extractable  hydrocarbon  content can  be  estimated by
measurement of the  total organic carbon (TOC)  content.  If the TOC of an untested
waste is significantly lower than that of the tested waste,  the untested system
may  not remove as  much  hydrocarbon  as  the  tested system.   More rigorous
extraction  conditions such  as  higher temperatures and  pressures,   additional
mixing, and longer  settling times  may be required to extract  less extractable
components and achieve the  same treatment performance,  or other, more  applicable
treatment technologies may  need to be  considered for treatment  of the untested
waste.
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      Critical fluid extraction  processes  are  designed to extract hydrocarbon
components from mixed oily and organic waste  liquids  and sludges.  For critical
fluid extraction to be economically applied, the waste should contain at least
a few  percent by weight  of  extractable  hydrocarbons.   This  process  has been
demonstrated on wastes containing from 5  to 34  percent  hydrocarbons.  For lower
concentrations, batch distillation or conventional solvent extraction may be more
economical.   Also,  critical  fluid  extraction is  not economical  for wastes
containing  high  concentrations  of  extractable  hydrocarbons  (higher  than
95 percent).  These wastes are more amenable to fractionation treatment.

3.4.2       Solubility of the Haste Constituents of Concern in the
            Extraction Fluid

      The constituents in the waste feed  that are to  be extracted determine the
type of extraction fluid that is best suited for the process.  For example, polar
organic molecules  (e.g.,  phenol) in an organic feed can  be  extracted with an
aqueous solvent.   Organic constituents  in  aqueous  feeds  can  be extracted with
various organic solvents.  Metal-containing wastes can be extracted with acids
(e.g.,  trialkylphosphoric and carboxylic  acids)  or amine  solvents.    If the
solubility of the waste constituents of concern in the extraction fluid  in the
untested waste is  significantly lower than that  in the tested waste, the untested
system may not achieve adequate performance.  Use of another extraction  fluid may
be required to increase the solubility of the waste  constituents of concern and
achieve the  same  treatment  performance,  or other,  more  applicable treatment
technologies may need to  be considered for treatment of the untested waste.

3.4.3       Surface Tension

      The surface tension of the  waste is a measure of the  tendency of  the waste
to foam.  The higher the surface tension  of the liquid, the higher its tendency
to foam.  If foaming is likely,  the system design must  be modified or defoaming
compounds  may be  required.   For  column  extractors,  packed  columns  are less
susceptible to  foaming  than  are tray columns.  If  the surface tension of the
untested  waste is  significantly higher  than  that  of the tested  waste,  the

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untested system may not achieve adequate performance.  Defearning compounds and/or
the use of a packed column may be required to reduce foaming and achieve the same
treatment performance, or other, more applicable treatment technologies may need
to be considered for treatment of the untested waste.  Foaming has not been found
to affect the performance of critical  fluid extraction processes.

3.4.4       Alkalinity of the Waste

      In critical fluid extraction, when carbon  dioxide is used as the extraction
fluid, high alkalinity will  interfere  with the process  because carbon dioxide
will react to form carbonates and bicarbonates.  This will result  in  excessive
carbon  dioxide  consumption.   For  wastes  having  high  alkalinity  levels,  an
extraction fluid other than carbon dioxide  should be  used  in  the critical fluid
extraction process.   The same  problem does  not arise  if a  hydrocarbon fluid
(propane, butane,  or  pentane)  is used.  If carbon dioxide was the  extraction
fluid  used  on  a tested  waste  and  the  alkalinity  of  the  untested waste is
significantly higher  than that of the  tested waste,  the system  may  not achieve
the same performance.  Use of another extraction fluid may be required to achieve
the same treatment performance, or other, more applicable treatment  technologies
may need to be considered for treatment of the untested waste.  Alkalinity of  the
waste  has not  been  found to affect  the performance of  conventional solvent
extraction processes.

3.5         Design and Operating Parameters

      In  assessing the effectiveness of the design and operation of extraction
systems,  EPA examines the following parameters:  (a) the number of separation
stages, (b) the extraction temperature  and pH,  (c) the degree of mixing, (d)  the
residence time,  (e) the settling time, and (f)  the extraction  pressure.

      For  many  hazardous  organic  constituents,  analytical  methods  are   not
available or the constituent cannot  be  analyzed in the waste matrix.  Therefore,
it would  normally  be  impossible to measure the effectiveness of the extraction


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treatment system.  In these cases, EPA tries to identify measurable parameters
or constituents that would act as surrogates to verify treatment.

      For organic constituents,  each  compound  contains a measurable amount of
total organic carbon (TOC).  Removal of TOC in the extraction treatment system
implies removal of organic constituents.  Hence, TOC analysis is likely  to  be an
adequate surrogate  analysis  where the specific organic  constituent cannot be
measured.

      However, TOC analysis may  not  be  able to adequately detect treatment of
specific organics in matrices that are heavily organic-laden; that  is, the TOC
analysis may  not  be  sensitive enough to detect changes  at the milligrams per
liter (mg/1) level in matrices where total organic concentrations are  hundreds
or thousands  of mg/1.    In  these cases, other surrogate  parameters should be
sought.  For  example,  if a specific analyzable constituent is expected to be
treated  as  well as  the  unanalyzable constituent, the analyzable  constituent
concentration should be monitored as a surrogate.

3.5.1       Number of Separation Stages

      For solvent extraction columns, the number of theoretical  stages  required
to achieve the desired separation of hazardous  constituents from a liquid waste
into the selected extraction fluid is calculated from solvent equilibrium data,
which are determined empirically.  Using the theoretical number  of  stages, one
can then determine the  actual  number of stages through the use of empirical tray
efficiency data typically supplied by equipment manufacturers.  EPA examines the
actual number of stages in a solvent extraction column system to ensure  that the
system is designed to achieve an effective degree  of  extraction.

3.5.2       Extraction Temperature and pH

      Temperature  and  pH changes can  affect equilibrium  conditions   (pH will
affect equilibrium  when  the  waste  or the  extraction fluid is aqueous) and,
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consequently, the performance of the solvent  extraction system.  Critical fluid
extraction is normally performed at ambient temperature although it is possible
to use higher temperatures when  necessary.  In all  cases,  temperatures used must
be below the critical temperature* of the extraction fluid used to ensure that
the  fluid  is present in  the extraction vessel  in  the  liquid phase  (so that
maximum contact with the waste  can be achieved).  EPA monitors the temperature
and pH (as applicable) continuously, if possible, to ensure that the system is
operating  at the  appropriate  design conditions  and to  diagnose  operational
problems.

3.5.3       Degree of Mixing

      For  mixer-settler  solvent extractors,  mixing determines the  amount of
contact between the two immiscible phases and, accordingly, affects the degree
of mass  transfer  of the constituents  to  be  extracted.   Intense  agitation to
provide  high  rates  of  mass  transfer,  however,  can  produce solvent  waste
dispersions that are difficult  to separate into distinct phases. The waste must
be premixed  before introduction into the critical  fluid extraction  system to
ensure a uniform,  pumpable  blend of material.   The  waste is normally mixed in
tanks or other vessels.   Any well-designed and well-operated system should have
such waste blending equipment.  The quantifiable degree of mixing is a complex
assessment  that includes,  among  other  things,  the  amount of mixing  energy
supplied, the length of time the material is mixed,  and  the related turbulence
effects of the  specific size and shape of the tank vessel.  This is beyond the
scope of simple measurement.  During the  fluid extraction, the  extraction fluid
and waste need  to  be mixed  to ensure maximum contact and, hence,  efficiency of
extraction.  Any well-designed  system  should include a pressurized extraction
vessel that is equipped with an  operable mixing system.  EPA, however, evaluates
the degree of mixing qualitatively by considering whether the  type of mixing
*The critical temperature of a substance  is that  temperature above  which  the
 the substance cannot be liquified, no matter how high the operating  pressures.
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device provided is one that could be expected to achieve  adequate uniform mixing
of the waste.

3.5.4       Residence Time

      The  residence  time  in  the  extraction  vessel   impacts  the  extent of
extraction of organic contaminants from the waste.  Residence time will vary with
the solubility  of the organic contaminants  in the solvent  and  the degree of
mixing.  For a batch  solvent extraction system, the residence time  is  controlled
directly  by adjusting the  treatment time  in  the  extraction  vessel.   For a
continuous solvent extraction system, the waste feed  rate is controlled to ensure
that  the  system  is  operating  at the  appropriate design residence  time.  In
critical fluid extraction, as with conventional  solvent extraction,  the residence
time  in the  extraction  vessel  impacts  the  extent of extraction  of organic
contaminants  from the waste.   EPA monitors  the residence time to ensure  that
sufficient time is provided to effectively extract the organic contaminants from
the waste.

3.5.5       Settling  Time

      For  mixer-settler  solvent extractors  and  critical   fluid  extractors,
adequate  settling time must be  provided  to make sure  that separation of  the
phases has been effectively completed.  EPA monitors the settling time to ensure
effective phase separation.

3.5.6       Extraction Pressure

      Critical  fluid  extraction  systems  operate  at  pressures   at  which  the
extraction fluids will be liquids  at ambient  temperatures.  Pressure is normally
monitored by  means  of gauges  and recorders  attached to the  extraction vessel.
EPA monitors  the  extraction pressure continuously,  if possible, to  ensure that
the system  is operating at  the  appropriate design condition  and to  diagnose
operational problems.
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3.6         References


CF Systems  Corporation.    1988.   CF  Systems  units to  render refinery wastes
      non-hazardous.

De Renzo,  D.J., ed.  1978.  Unit operations for treatment of hazardous  industrial
      wastes.  Park Ridge, N.J.:  Noyes Data Corporation.

Gallacher, L.V.   1981.   Liquid ion exchange  in  metal  recovery and  recycling.
      Third Conference on Advanced Pollution Control  for the Metal  Finishing
      Industry.  USEPA 600/2-81-028.  pp. 39-41.

Hackman, E.   1978.   Toxic organic chemicals,  destruction and waste  treatment.
      pp.  109-111.  Park Ridge, N.J.:  Noyes Data Corporation.

Hanson, C.  1968.   Solvent extraction  theory, equipment,  commercial operations,
      and economics.  Chemical Engineering. August 26,  1968,  p. 81.

Humphrey,  J.L., Rocha, J.A., and Fair, J.R.   1984.  The essentials of extraction.
      Chemical Engineering. September 17, 1984,  pp. 76-95.

Johnston,  K.   1978.   Supercritical  fluids.   In  Kirk-Othmer encyclopedia  of
      chemical  technology.    Supplement  Vol.   I,  pp.  872-983.     New  York:
      Wiley-Interscience.

Lo, Teh C.,  Baird, M.H.I., and Manson,  C., eds.   1983.   Handbook  of  solvent
      extraction,  pp. 53-89.  New York:  John Wiley and  Sons.

Perry, R.H.,  and  Chilton,  C.H.   1973.  Chemical  engineer's handbook. 5th  ed.,
      pp.  15-1 to  15-24.  New York:  McGraw-Hill Book Company.

Weast, R.C., ed.   1978.   Handbook  of chemistry and physics.  58th ed.  Cleveland,
      Ohio:  CRC Press.
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                             4.   FUEL SUBSTITUTION

      Fuel substitution involves using hazardous waste as a fuel in  industrial
furnaces  or  in  boilers.    The  hazardous  waste  may  be  blended  with other
nonhazardous wastes (e.g., municipal sewer sludge) and/or fossil fuels.

      On December 31, 1990, EPA promulgated regulations to control emissions from
industrial  furnaces  and  boilers  from treatment  of  hazardous  waste.    Permit
requirements are similar  to  those for incineration, in that controls limit  the
emissions of total organic carbons, toxic metals,  HC1, and wastewaters.  Like  the
incinerator  regulations  (40 CFR 264, Subpart  0),  the  boiler  and   furnace
regulations (40 CFR 266, Subpart H) require 99.99 percent destruction  and removal
efficiency  of  principal  organic   hazardous  constituents   (POHCs).    These
regulations  will  also minimize  products  of  incomplete  combustion   (PICs),
including carbon  monoxide  (CO).  These regulations will also minimize  particulate
emissions by regulating the  metal emissions.

4.1         Applicability

      Fuel substitution has  been used with industrial waste solvents,  refinery
wastes, synthetic fibers/petrochemical wastes, and waste oils.   It  can  also be
used  when combusting  other waste  types produced during  the  manufacture  of
Pharmaceuticals,  pulp and paper,  and pesticides.  These wastes can be handled in
a solid,  liquid,  or gaseous  form.

      Industrial  furnaces include a  variety of industrial processes that produce
heat and/or products by burning fuels. They include blast furnaces, electric  arc
smelting  furnaces, cement kilns, lime kilns, smelters, coke ovens,  and  halogen
acid  furnaces  (HAFs).   Industrial  boilers  are units wherein  fuel  is   used  to
produce steam for process  and plant  use.  Industrial boilers  typically use coal,
oil, or gas as the primary fuel source.
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      The parameters that affect the applicability of fuel substitution are the
following:

      •  Halogen content of the waste;
      •  Inorganic solids content (ash content) of the waste, particularly heavy
         metals;
      •  Heating value of the waste;
      •  Viscosity of the waste (for liquids);
      •  Filterable solids concentration (for liquids); and
      •  Sulfur content.

4.1.1       Halogen Content of the Waste

      If halogenated organics  are burned, halogenated acids and free halogen are
among the products of combustion.   These released corrosive gases may require
subsequent treatment prior .to venting to the atmosphere.   Also,  halogens and
halogenated acids formed during combustion are likely to severely corrode boiler
tubes and other process equipment.  To minimize such problems, halogenated wastes
are blended into fuels only at very  low concentrations.  High chlorine content
can also lead  to  the  incidental production (at very low concentrations) of other
hazardous  compounds such  as  polychlorinated  biphenyls   (PCBs),   chlorinated
dibenzo-p-dioxins  (CDDs),  chlorinated  dibenzofurans  (CDFs),  and  chlorinated
phenols.

4.1.2       Inorganic Solids Content of the Waste

      High inorganic solids content (i.e.,  ash content) of wastes  may cause two
problems:  (1) scaling in the boiler  and (2) particulate air  emissions.  Scaling
results  from  deposition  of  inorganic  solids  on  the walls  of  the  boiler.
Particulate emissions are produced by noncombustible inorganic  constituents that
flow out of the boiler with the gaseous combustion products.  Because of these
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problems, wastes with significant concentrations of inorganic materials  are not
usually  handled  in boilers unless  the  boilers have  an  air pollution  control
system.

      Industrial  furnaces  vary in their  tolerance to inorganic constituents.
Heavy metal concentrations, found in both  halogenated  and nonhalogenated wastes
used as fuel, can cause  environmental concern because they may be emitted in the
gaseous emissions  from  the combustion process,  in the ash residues, or in any
produced solids.  The partitioning of the heavy metals  to  these  residual  streams
primarily  depends  on the  volatility of the metal, waste  matrix',  and  furnace
design.

4.1.3       Heating Value  of the  Waste

      The  heating  value of the waste must  be  high enough  (either alone or  in
combination with other fuels) to maintain combustion temperatures consistent with
efficient waste  destruction and operation of the boiler  or furnace.  For many
applications, only supplemental fuels having minimum heating values  of 4,400  to
5,600 kcal/kg (8,000 to  10,000  Btu/lb) are considered to be feasible.  Below this
value, the unblended fuel would not be likely to maintain a stable flame,  and its
combustion would release insufficient energy to provide needed  steam  generation
potential  in the boiler or the necessary  heat  for  an  industrial  furnace.  Some
wastes with heating values  of  less than  4,400 kcal/kg (8,000 Btu/lb)  can  be used
if sufficient auxiliary fuel is used to  support combustion or if special  designs
are  incorporated into  the  combustion device.   Occasionally,  for wastes with
heating  values  higher than virgin fuels,  blending with  auxiliary fuel  may  be
required to prevent overheating or overcharging of the combustion device.

4.1.4       Viscosity of the Waste

      In combustion devices designed to  burn liquid fuels,  the  viscosity of the
liquid  waste must  be  low  enough that  it  can  be  atomized  in the  combustion
chamber.  If the  viscosity  is too high, heating  the  storage tanks may be required
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prior to combustion.   For atomization of liquids,  a viscosity of 165 centistokes
(750 Saybolt Universal Seconds (Sus)) or less is typically required.

4.1.5       Filterable Solids Concentration

      Filterable materials suspended  in  the  liquid fuel  may prevent or hinder
pumping or atomization and if so other technologies may need to be considered.

4.1.6       Sulfur Content

      A waste's sulfur content may affect whether it can be burned or not because
the waste may emit sulfur oxide into the  atmosphere.  For  instance, the EPA has
promulgated sulfur oxide emission regulations for certain  new source industrial
boilers (40 CFR 266,  Subpart H).  Air pollution control  devices are  available to
remove sulfur oxides from the stack gases.

4.2         Underlying Principles of Operation

      For a boiler and most industrial  furnaces there are two distinct principles
of operation.  Initially,  energy  in  the form of heat is  transferred  to the waste
to  achieve  volatilization of  the various waste constituents.    For liquids,
volatilization energy may also be supplied by  using pressurized atomization.  The
energy used  to  pressurize the  liquid  waste  allows the  atomized  waste to break
into  smaller  particles,  thus  enhancing  its  rate  of  volatilization.    The
volatilized  constituents  then  require  additional  energy to destabilize  the
chemical bonds, allowing the constituents  to react with oxygen  to form carbon
dioxide and water vapor.  The energy needed to destabilize the chemical bonds is
referred to as  the energy of activation.

4.3         Description of Fuel Substitution Process

      Since a number of  industrial applications can use  fuel substitution, there
is  no  one  process description that  will  fit all  of these applications.   The
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following section, however, provides a general description of industrial kilns
(one form of industrial furnace) and industrial boilers.

4.3.1       Kilns

      Combustible wastes have the potential  to be used as fuel in kilns and,  for
waste liquids, are often used with oil to co-fire kilns.  Coal-fired  kilns  are
capable of handling some solid wastes.  In  the case of cement kilns,  there  are
usually no residuals requiring land disposal since any ash formed becomes part
of the product or is removed by particulate collection systems and recycled back
to the kiln.   The only  residuals  may be low levels of unburned gases  that escape
with combustion products.   If this is the case, air pollution control  devices  may
be required.

      Three types of kilns are particularly applicable: cement kilns,  lime kilns,
and lightweight  aggregate kilns.

4.3.1.1     Cement Kilns

      The cement kiln  is  a rotary furnace,  which  is a refractory-lined steel
shell  used  to  calcine a  mixture of  calcium,  silicon,  aluminum,  iron,   and
magnesium-containing minerals.   The  kiln  is normally  fired by  coal  or oil.
Liquid  and  solid  combustible  wastes  may  then   serve   as auxiliary  fuel.
Temperatures within the kiln are typically  between 1,380 and 1,540*C  (2,500 to
2,800'F).   To  date,  only  liquid hazardous  wastes have been burned  in cement
kilns.

      Most cement kilns have a dry particulate collection device  (i.e., either
an electrostatic precipitator  or a baghouse), with  the  fly ash collected  and
recycled  back  to the  kiln.    Buildup  of metals  or other  noncombustibles  is
prevented through their incorporation  into  the  product cement.   Many  types of
cement require a source of chloride so that  most halogenated liquid hazardous
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wastes currently can be burned in cement kilns.  Available information shows that
scrubbers are not used.

4.3.1.2     Lime Kilns

      Quick lime (CaO) is manufactured in  a  calcination  process using limestone
(CaC03)  or dolomite  (CaC03 and MgC03).   These raw materials are also heated  in
a refractory-lined  rotary kiln, typically  to temperatures of  980 to  1,260*C
(1,800 to 2,300'F).   Lime kilns are less likely to burn hazardous wastes  than are
cement kilns because product  lime is often added to potable water systems.  Only
one  lime  kiln  in  the United  States  currently  burns  hazardous waste.   That
particular facility  sells its product lime  for use as flux or as refractory  in
blast furnaces.

      As with cement kilns, any  fly ash collected is recycled back  to  the lime
kiln; thus, no residual  streams  are produced by the kiln.  Available  information
shows that scrubbers are not used.

4.3.1.3     Lightweight Aggregate Kilns

      Lightweight aggregate kilns heat  clay to produce  an expanded  lightweight
inorganic material used in Portland cement formulations  and other applications.
The kiln has a normal temperature range of 1,100  to  1,150*C (2,000  to 2,100'F).
Lightweight aggregate kilns are less amenable to  combustion of hazardous wastes
as  fuels  than  are  the  other kilns described above because  these kilns lack
material to adsorb  halogens.   As a result,  burning of halogenated  organics  in
these kilns would likely require afterburners to  ensure  complete destruction  of
the  halogenated organics  and scrubbers to  control  acid gas  production.  Such
controls  would  produce  a  wastewater  residual   stream  subject  to treatment
standards.
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4.3.2       Industrial Boilers

      A boiler is a closed vessel in which water is transformed into steam by the
application of heat.   Normally,  heat is supplied by the combustion  of pulverized
coal, fuel oil,  or gas.   These  fuels  are fired into a combustion chamber with
nozzles and burners  that  provide mixing with air.   Liquid  wastes, and granulated
solid wastes in the  case  of grate-fired boilers, can be burned as auxiliary fuel
in  a  boiler.    However,  few grate-fired boilers  burn hazardous  wastes.  For
liquid-fired boilers, residuals requiring land disposal are generated only when
the boiler is shut down  and cleaned.  This is generally done  once or twice per
year.   Other residuals  from  liquid-fired boilers  would be  the  gas emission
stream, which would  consist  of any products of incomplete  combustion,  along with
the normal combustion products.  For example, chlorinated wastes would  produce
acid gases.  If this  is the case, air pollution control devices may be required.
For solid-fired  boilers, an ash normally is  generated.   This ash may  contain
residual  amounts  of  organics  from  the   blended  waste/fuels,  as  well  as
noncombustible materials.   Land disposal  of this  ash would require compliance
with applicable  BOAT  treatment  standards.

4.4     Waste Characteristics Affecting Performance  (WCAPs)

      In determining  whether  fuel  substitution will  achieve the same level of
performance on  an untested  waste as on  a  previously tested waste and  whether
performance  levels  can   be transferred,  EPA  examines   the  following waste
characteristics:  (a)  the component boiling points, (b) the thermal conductivity
of the waste, and (c) the component bond dissociation energies.

4.4.1       Component Boiling Points

      The  term  relative  volatility refers to the  ease with which a substance
present in a solid or liquid waste will vaporize from that  waste upon application
of  heat from  an external  source.   Hence,  it  bears a relationship  to the
equilibrium vapor pressure of the substance.
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      EPA  recognizes that  the relative  volatilities cannot  be  measured  or
calculated directly for the types of wastes generally treated in an industrial
boiler  or  furnace.   The Agency  believes  that the  best measure  of relative
volatility is the boiling point of the  various hazardous  constituents and will,
therefore,  use  this   parameter   in   assessing  volatility  of  the  organic
constituents.

4.4.2       Thermal Conductivity of the Waste

      Consistent with the underlying principles of combustion in aggregate kilns
or boilers, a major factor with regard  to whether  a particular constituent will
volatilize is the transfer of  heat through the waste.   In  the case of industrial
boilers burning  solid fuels,   heat  is  transferred through  the waste  by three
mechanisms:  radiation,  convection, and conduction.   For  a given boiler, it can
be  assumed that the  type of waste will  have  a minimal  impact  on  the  heat
transferred from radiation.   With  regard  to convection,  EPA believes that the
range of  wastes  treated would  exhibit similar properties  with  regard  to the
amount of heat transferred by  convection.   Therefore,  EPA will not  evaluate the
radiation or convection  heat transfer properties  of wastes in  determining similar
treatability.  For solids, the third heat transfer mechanism, conductivity, is
the one principally operative  and most likely to  change  between wastes.

      Using  thermal  conductivity  measurements  as   part   of  a   treatability
comparison for two different  wastes  through a  given  boiler  or furnace is most
meaningful when  applied to wastes that are  homogeneous.    As  wastes exhibit
greater degrees of nonhomogeneity, thermal conductivity becomes less accurate in
predicting treatability because the measurement essentially  reflects heat flow
through  regions  having  the   greatest  conductivity   (i.e.,  the path  of least
resistance) and not heat flow  through all parts of the waste. Nevertheless, EPA
has not identified a better alternative to thermal  conductivity, even for wastes
that are nonhomogeneous.
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4.4.3       Component Bond Dissociation Energies

      Given an excess of  oxygen,  an  organic waste in an industrial furnace or
boiler would be expected to convert to carbon dioxide and water vapor provided
that the activation energy  is  achieved.   Activation energy is the quantity of
heat  (energy)  needed  to  destabilize  molecular bonds  so that  the oxidation
(combustion) reaction will  proceed to  completion.   As a measure of activation
energy,  EPA  is   using  bond  dissociation  energies.    In  theory,  the  bond
dissociation  energy would  be  equal  to  the  activation energy;  in practice,
however, this is  not always  the case because of molecular interaction bonds.  In
some instances, bond dissociation energies will not be  available and will have
to be estimated,  or other energy  effects  will  have a significant  influence on
activation energy.

4.5         Design and Operating Parameters

      In assessing  the effectiveness  of  the design  and operation  of  a fuel
substitution system, EPA examines  the following  parameters:   (a) the combustion
temperature, (b)  the residence time,  (c)  the degree of mixing,  (d)  the air feed
rate, (e) the fuel feed rate, and (f) the steam pressure/rate of production.

      For  many hazardous  organic  constituents,   analytical  methods  are  not
available or the  constituent cannot be analyzed in the waste matrix. Therefore,
it  would normally  be  impossible  to measure  the  effectiveness   of  the fuel
substitution treatment system.   In these cases, EPA tries to identify measurable
parameters or constituents that would act as surrogates to verify  treatment.

      For organic constituents, each  compound  contains  a measurable amount of
total organic carbon (TOC).  Removal of TOC  in the  fuel substitution treatment
system will indicate removal of organic  constituents.  Hence, TOC analysis is
likely  to  be an  adequate  surrogate  analysis  where   the   specific  organic
constituent cannot be measured.
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      However, TOC analysis may  not  be able to adequately detect treatment of
specific organics  in matrices that  are heavily organic-laden  (i.e.,  the TOC
analysis may not be sensitive enough to detect changes at the milligrams/liter
(mg/1)  level  in  matrices where  total  organic concentrations  are hundreds or
thousands of mg/1).  In these cases, other surrogate parameters should be sought.
For example, if a specific analyzable constituent is expected to  be  treated as
well as the unanalyzable constituent, the analyzable constituent  concentration
should be monitored as a surrogate.

4.5.1       Combustion Temperature

      Industrial  boilers are generally designed based on  their steam  generation
potential  (Btu output).   This  factor  is  related to  the  design  combustion
temperature, which,  in turn, depends  on the amount  of fuel  burned and its Btu
value.  The  fuel feed rates and combustion temperatures of industrial boilers are
generally fixed based on the Btu values of  fuels normally handled  (e.g., No.  2
versus No.  6 fuel oils).   When wastes are  to be blended with fossil fuels for
combustion,  the blending, based on Btu  values, must be such that  the resulting
Btu value of the mixture is close to that of the fuel value used  in  the design
of the  boiler.   Industrial furnaces also are  designed  to operate at specific
ranges  of  temperature  to  produce  the  desired  product  (e.g.,  lightweight
aggregate).   The  blended  waste/fuel mixture  should be capable of  maintaining the
design temperature range.

4.5.2       Residence Time

      A sufficient residence time of combustion products  is normally necessary
to  ensure   that  the  hazardous  substances   being  combusted   (or formed during
combustion)   are  completely oxidized.   Residence  times  on the  order of a few
seconds  are generally  needed at normal  operating  conditions.   For  industrial
furnaces as  well  as  boilers,  the  residence time is a function of the size of the
furnace and the fuel feed rates.  For most  boilers and furnaces,  the residence
time usually exceeds a few seconds.


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4.5.3       Degree of Mixing

      Boilers are designed so that fuel and air are intimately mixed.  This helps
to ensure that complete combustion takes place.  The shape of the boiler and the
method of fuel and air feed influence the turbulence required for  good  mixing.
Industrial furnaces also are designed for turbulent mixing where fuel and air are
mixed.

4.5.4       Air Feed Rate

      An important operating parameter in boilers and many  industrial  furnaces
is the oxygen content in the flue gas, which is a function of the air feed rate.
Stable  combustion  of  a  fuel   generally  occurs  within a  specific  range   of
air-to-fuel ratios.  An  oxygen  analyzer in the combustion gases  can  be  used  to
control the feed ratio of air to fuel  to  ensure complete thermal  destruction  of
the waste and efficient  operation of the boiler.  When  necessary,  the  air feed
rate can  be  increased or decreased to maintain  proper fuel-to-oxygen  ratios.
Some industrial furnaces do not completely combust fuels (e.g.,  coke ovens and
blast furnaces);  hence,  oxygen  concentration  in  the flue gas is a meaningless
variable.

4.5.5       Fuel  Feed Rate

      The rate at which  fuel is injected  into  the boiler or industrial  furnace
will determine the thermal output of the  system per unit of time (Btu/hr).   If
steam is produced, steam pressure monitoring will indirectly determine  whether
the fuel feed rate is adequate.   However,  various  velocity  and mass measurement
devices can be used to monitor  fuel flow directly.

4.5.6       Steam Pressure or Rate of Production

      Steam pressure in boilers provides a direct  measure  of the thermal output
of  the  system and is directly  monitored  by  use  of in-system pressure  gauges.
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Increases  or decreases  in  steam pressure  can be  effected  by increasing  or
decreasing the  fuel  and  air feed rates within certain operating design limits.
Most industrial  furnaces do not  produce  steam;  instead they  produce  a product
(e.g., cement,  aggregate)  and monitor the rate of production.
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4.6         References


Bonner,  T.A.,  et  al.     1981.    Engineering  handbook  for  hazardous  waste
      incineration.    Prepared  by  Monsanto  Research  Corporation  for  U.S.
      Environmental Protection Agency  PB 81-248163.

Castaldini C., et al.   1986.  Disposal of hazardous wastes in industrial  boilers
      or furnaces.  Park Ridge, N.J.:  Noyes  Publications.

USEPA.   1990.   Office of Solid Waste.   Standards for owners and  operators  of
      hazardous  wastes  in  boilers  and  industrial   furnaces;  proposed  and
      supplemental  proposed  rule,  technical  corrections,  and  request  for
      comments.  55 FR 17862, April  27,  1990.

Versar.    1984.    Estimating  PMN  incineration  results.    EPA  Contract  No.
      68-01-6271, Task No. 66.  Draft  report for  Exposure  Evaluation Division,
      Office  of  Toxic  Substances.    Washington, D.C.:    U.S.  Environmental
      Protection Agency.
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   II.  REMOVAL TECHNOLOGIES (CONTINUED)
B.  RECOVERY AND/OR SEPARATION TECHNOLOGIES
                 FOR METALS

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                               1.   ACID LEACHING

1.1         Applicability

      Acid leaching is a treatment technology used to treat wastes in solid or
slurry form  containing metal constituents  that are soluble  in  a  strong acid
solution or can be converted by reaction with a strong acid to a soluble form.
This process has been  used  to  recover metals such as mercury, copper, nickel,
silver, and cadmium from  inorganic wastes  generated in the primary metals and
inorganic chemicals industries.

      The acid leaching process is most effective  with wastes  having high (over
1,000 ppm) levels of metal constituents.  Wastes containing lower levels of such
contaminants are more difficult to process  because the low metal concentrations
require longer contact times.

      Acid leaching can also be used to extract heavy metals or radionuclides
from mixed wastes,  principally  soils,  separating the material  into its hazardous
and radioactive components.   This  process has greater utility  when combined with
unit operations such as ion exchange,  solvent extraction,  chemical precipitation,
and filtration.

      Another  type of leaching process,  alkaline leaching,   is  used  to treat
wastes containing  metal  constituents that are  soluble  in  a  strong caustic or
alkaline  solution.  This  process  is  mainly useful in recovering aluminum from
bauxite ore.   Generally,  the following information  on  acid  leaching would be
applicable to alkaline leaching.

1.2         Underlying Principles  of Operation

      The basic principle of operation for acid leaching is that  solubilities of
various metals in acid solutions aid  in their removal from a waste.  The process
concentrates  the  constituent(s)  leached  by  the  acid  solutions.    These
constituents can then be filtered  to remove residual solids  and neutralized to

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precipitate  solids  containing  high  concentrations  of  the  constituents  of
interest,  which   can   be   further  treated  in  metals  recovery  processes.
Alternatively, the acid  solutions  can  be electrolyzed to recover pure metals.
An  acid  leaching  system usually consists  of a solid/liquid  contacting unit
followed by a  solid/liquid  separator.   The most frequently used acids include
sulfuric (H2S04), hydrochloric  (HC1), and nitric (HN03).   Although any  acidic pH
can theoretically be used, acid leaching processes are normally run  at  a pH from
1 to 4.

1.3         Description  of Acid Leaching Process

      Acid  leaching  processes  can  be  categorized  into   two  major   types:
(a) treatment by percolation of the acid through the  solids  or  (b) treatment by
dispersion of the solids within the acid solution.  Both treatments are followed
by  subsequent  separation of  the solids  from the liquid.   In both  types of
systems, sufficient acid must be supplied to keep the pH at  the level  needed to
effectively leach the metals from the waste.

1.3.1       Percolation  Processes

      Percolation is typically conducted in batch tanks.   Batch percolators are
large tanks ranging in size up to 50,000 gallons.   First,  the solids are  placed
in the tank,  and  then acid is added.  The acid percolates through the solids and
drains out through  screens  or a porous medium  in  the tank bottom.    Following
treatment, the solids are removed and further treated using stabilization,  and/or
they are land disposed.

1.3.2       Dispersed-Solids Processes

      Acid leaching by dispersion of fine  solids into the acid is performed in
batch tanks.   The untreated  waste and the acid are mixed in the  reaction tank to
ensure effective contact between the solids and the acid.  Following mixing, the
suspension may be pumped to  stirred  holding  tanks, where the leaching  is allowed
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to proceed to completion.  The treated solids are then usually separated from the
acid by filtration and  further treated using stabilization,  and/or they are land
disposed.

1.4         Waste Characteristics Affecting Performance (WCAPs)

      In  determining whether  acid   leaching  will  achieve  the  same  level  of
performance on an untested waste that it achieved on a previously tested waste
and whether  performance  levels  can  be transferred,  EPA examines the  following
waste characteristics:   (a)  the  solid waste particle size,  (b)  the alkalinity of
the waste,  (c)  the  solubility of metal constituents  in  the acid, and  (d) the
concentration of leachable metals.

1.4.1       Solid Waste Particle Size

      Both the  solubility  reaction  rate of the  acid  with  the hazardous metal
constituents in the waste and the rate of transport of acid to and from the site
of  the  hazardous constituents  are   affected  by the  size  of  the  solid waste
particles.  The smaller the particles,  the  more rapidly they will  leach  because
of the increased surface area of the waste  that is  exposed  to  the acid.   If the
particle size of the untested waste is greater  than that of the tested waste, the
system may not achieve  the  same  performance.  Grinding the untested waste may be
required to reduce the  particle  size  and achieve the same treatment performance,
or it may be  necessary  to consider other, more  applicable treatment technologies
for treatment of the untested waste.

1.4.2       Alkalinity of the Waste

      The neutralizing capacity (or  alkalinity) of  the waste solids affects the
amount of  acid  that must  be added to the waste to achieve  and/or maintain the
desired reactor pH.  In addition to  dissolving the waste contaminants, the acid
will also dissolve some of the alkaline bulk solids; therefore,  highly alkaline
wastes require more acid or a  stronger acid to maintain pH during treatment.  If


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the alkalinity In an untested waste is  greater than that in a tested waste, the
system may  not achieve  the  same  performance.   Use of  additional  acid  or a
stronger acid  may  be required to compensate for the  increased  alkalinity and
achieve the  same treatment  performance,  or other,  more  applicable treatment
technologies may need to be considered for treatment of the untested waste.

1.4.3       Solubility of the Metal Constituents in the Add

      The metal constituents  must dissolve in the acid to form soluble salts for
the process to be effective.   Thus, the acid selected should be one that forms
soluble salts for all of the constituents to be removed.   If the solubility of
a metal constituent(s)  of concern in  an  untested  waste  is less  than  that of
another constituent(s) of concern in a previously tested waste in the same acid,
or less than the solubility of the same metal(s) tested with a different acid,
the system may  not  achieve the same performance.  Use of  another acid may be
required to increase the solubilities of the metal constituent(s) of concern and
achieve the  same treatment  performance,  or other,  more  applicable treatment
technologies may need to be considered for treatment of the untested waste.

1.4.4       Concentration of Leachable Metals

      The amount of Teachable metals is a measure of the maximum fraction of the
waste that can be expected to leach in the acid leaching system.   A relatively
low concentration of Teachable metals implies that most of  the waste will remain
in  the  solid or  slurry waste residues  (i.e.,  it  is  nonleachable).    If the
concentration of Teachable metals  in  the  untested  waste  is significantly less
than that in the tested waste, the  system  may not achieve the same performance.
Use of a higher concentration of acid or a  stronger acid may be required  to leach
less Teachable components and achieve  the  same treatment performance, or other,
more applicable treatment technologies may need to be considered for treatment
of the untested waste.
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1.5         Design and Operating Parameters

      In assessing  the effectiveness of  the  design and operation  of an acid
leaching system, EPA examines  the following parameters:  (a)  the residence time,
(b) the type and concentration of acid used,  (c) the pH, and  (d) the degree of
mixing.

1.5.1       Residence Time

      The extent of reaction and dissolution of the contaminants in  the acid is
directly related to the contact  time.  EPA monitors the residence time  to ensure
that sufficient time is provided to effectively leach the metal  contaminants from
the waste.

1.5.2       Type and Concentration of Add Used

      If the hazardous  constituents to be removed in the acid leaching system are
already present in  the waste in soluble form, or are solubilized by pH reduction,
then any acid that will reduce the pH to the desired value may be used.  However,
if chemical reaction is necessary to form soluble species, then the  appropriate
acid, as well  as the  appropriate  concentration of the acid,  must  be used to
ensure effective leaching of the metal constituents.   EPA examines the type and
concentration of acid used to ensure that the  acid solution  selected is capable
of effectively  leaching the metal constituents from the waste.

1.5.3       pH

      For dispersed solids systems, the feed of acid to the  leaching reactor is
based on  pH monitoring  and  control  because   the  reaction  rate is highly pH
dependent.  Therefore,  a pH should be determined,  based on the residence time and
amount of hazardous metal  constituents in the  waste,  that provides for complete
dissolution of metal  constituents.  For percolation systems, pH monitoring of the
acid percolating through the tank (i.e.,  leaving the  system)  should  ensure that
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enough acid  is  being  added.   EPA monitors the pH to ensure that the  system  is
operating  at the  appropriate design  conditions  and  to  diagnose  operational
problems.

1.5.4       Degree of Mixing

      Mixing  provides greater  contact between the  acid  and  the  solid  waste
particles, ensuring more  rapid  leaching of metal  contaminants from the  waste.
The quantifiable degree of mixing is a complex assessment that includes,  among
other factors, the amount  of energy  supplied, the length of time the material  is
mixed, and the related turbulence effects of the specific  size and  shape  of the
tank.  Although the  exact degree of mixing  is beyond simple measurement,  EPA
evaluates it by considering whether mixing is  provided and whether the type  of
mixing device  is  one  that could be expected  to  achieve  uniform mixing  of the
waste solution.
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1.6         References
Kirk-Othmer.  1978.  Encyclopedia of chemical technology.  Vol.  2,  pp.  140-144.
      New York:  John  Wiley and Sons.

McCabe, L., and Smith, J.   1976.  Unit operations of chemical engineering.   3rd
      ed., pp. 607-610.   New York:   McGraw-Hill Book Co.

Perry, R.H., and Chilton,  C.H.   1973.   Chemical engineers' handbook.   5th  ed.,
      pp. 19-41 to  19-43.   New  York:   McGraw-Hill Book Co.
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                          2.   FILTRATION TECHNOLOGIES

2.1         Applicability

      Filtration technologies (i.e., polishing filtration and sludge filtration)
are used to remove particles  from waste streams  that  are predominantly water or
to remove water from wet solids and sludges.

      Polishing filtration is a treatment technology applicable to wastewaters
containing  relatively   low   concentrations   of  solids  (usually  less  than
1,000 mg/1).  This type of filtration  is typically used  as a polishing step for
the  supernatant   liquid  following   chemical   precipitation  and  settling/
clarification of wastewaters  containing metal  and other inorganic precipitates.
Polishing filtration removes particles  that are difficult to  settle because of
their  size  and/or  density,  as  well  as  precipitated   particles  from  an
underdesigned settling system.

      Sludge  filtration,  also  known   as  sludge dewatering  or cake-formation
filtration, is a technology used on wastes that contain high  concentrations of
suspended solids,  usually higher than 1 percent (10,000 mg/1).  Sludge filtration
is commonly applied to waste  sludges,  such  as  clarifier solids,  for dewatering.
Typically,  these  sludges  can  be dewatered  to  19  to   50  percent  solids
concentration using this technology.

2.2         Underlying Principles of Operation

      The basic principle of operation for sludge and polishing filtration is the
removal/separation of particles from a mixture of fluid and particles by a medium
that permits  the  flow of the  fluid  but retains  the particles.   Usually, the
larger the particles, the easier they  are to remove  from the  fluid.

      Extremely small particles,  in the colloidal size range, may not be  removed
or filtered effectively in a  sludge or polishing filtration  system  and thus may


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appear in the wastewater passing through the  filter.  To mitigate this problem,
the wastewater can be  treated  prior  to  filtration  to modify the particle size
distribution  and/or   particle   electrostatic   charge   by  using  appropriate
precipitants, coagulants, flocculants,  and filter  aids.   The selection of the
appropriate precipitant and coagulant is important  because they  affect the type
of waste particles formed.   For example,  lime (calcium hydroxide) precipitation
usually produces larger, less gelatinous particles (which are easier to remove
from  aqueous wastes   by  using  filtration)  than  does  caustic soda  (sodium
hydroxide) precipitation.   For particles that become too small  or too highly
charged  to  remove effectively,  the  use of coagulants  and  flocculants  both
decreases particle charge  and  increases the size  of the  particles.   Also, if
pumps are used,  shear  can  be minimized by lowering  the  pump speed or using a
low-shear type of pump.  Excessive shear breaks up agglomerated particles, making
them smaller  and more  difficult to filter.  Filter  aids  such as diatomaceous
earth are used  to precoat  cloth-type  filter media and to  provide an initial
filter cake onto which  additional solids can  be deposited during the filtration
process.  The presence  of the precoat  aids in the removal  of small particles from
the  solution  being filtered.    These  particles adhere  to,  and  are  actually
filtered by, the precoat solids during the filtration process.

2.3         Description of  Filtration Processes

2.3.1       Polishing  Filtration Processes

      During  polishing filtration,  wastewater  may  flow  by  gravity  or under
pressure to the filter.  The two most common  polishing filtration processes are
cartridge and granular  bed filtration.  Both processes remove particles that are
much smaller than the  pore  size of the filter medium by straining, adsorption,
and coagulation/flocculation mechanisms; these processes are also capable of
producing an effluent with a low level  of solids  (typically  less than 10 mg/1).
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2.3.1.1     Cartridge Filtration

      Cartridge filters can be used for relatively low waste feed flows.  In this
process, a hollow, cylindrically shaped cartridge with a matted cloth-type filter
medium  is  placed within  a sealed vessel.   Wastewater is  pumped through the
cartridge wall until the  flow drops  excessively or until  the pumping pressure
becomes too high because of plugging  of the filter medium.   The sealed  vessel is
then opened,  and the  plugged  cartridge  is  removed and  replaced with a new
cartridge.  The plugged  cartridge  is  then cleaned and/or disposed of.   Cartridge
filters can be assembled in a parallel arrangement to increase the overall system
flow.

2.3.1.2     Granular Bed Filtration

      For relatively large volume flows,  granulated media  such as sand,  garnet,
or anthracite  coal  are  used singly  or in combination to trap suspended solids
within the pore  spaces  of the media.  Dual  and multimedia filter arrangements
allow higher flow rates  and efficiencies.  Typical hydraulic loading rates range
from 2 to 5 gal/sq ft-min for single-medium filters and  from 4 to 8 gal/sq ft-min
for multimedia filters.

      In this  process,  wastewater is either  gravity-fed or pumped through the
granular bed media  and filtered until either the flow drops excessively or the
pumping  pressure  becomes  too high because of  plugging of the granular filter
media.  Granular media filters are usually cleaned by backwashing with previously
filtered water in an upflow manner to expand the bed, loosen the  media  granules,
and resuspend  the entrapped filtered solids.  The  backwash water, which may be
as much as 10  percent of the volume of the filtered wastewater, is then returned
to the head of the wastewater treatment system so that the filtered solids in the
backwash water can be settled out of solution and the water refiltered prior to
discharge.
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2.3.2       Sludge Filtration Process

      For sludge filtration, waste is pumped  through  a cloth-type filter medium
(also known as pressure filtration, such as that performed with  a plate-and-frame
filter); drawn by vacuum through the cloth or metal mesh medium (also known as
vacuum  filtration,  such  as that  performed with  a vacuum drum  filter);  or
gravity-drained and mechanically pressed through  two continuous  fabric belts
(also known as belt filtration, such as that performed with a belt filter press).
In all  cases, the  solids  "cake" builds up on the  filter medium  and acts as a
filter  for subsequent solids removal.

      For  a  plate-and-frame filter,  removal  of the  solids is accomplished by
taking  the  unit  off-line,  opening the  filter, and using mechanical or manual
methods to scrape off  the solids  (a batch process).  For  the vacuum  filter, cake
is removed  continuously  by using an adjustable knife mechanism  to scrape the
sludge  from the vacuum drum as the drum rotates.   For the belt filter, the cake
is continuously removed by  a discharge roller and blade,  which  dislodge the cake
from the belt.  For a specific sludge,  the plate-and-frame  filter will usually
produce the driest cake (highest percentage of solids).  The belt filter produces
a drier cake than does a vacuum filter,  but usually not  as dry as that produced
by a plate-and-frame filter.  Dewatered solids  are  further treated  in processes
such as sludge drying, incineration,  solvent  extraction  (if treatable levels of
organics are present), stabilization (if treatable  levels  of Teachable metals are
present), and/or disposal.  The liquid filtrate that penetrates the filter medium
is further treated in  processes such as polishing  filtration, carbon adsorption,
and biological treatment,  and/or it  is  disposed of.

2.4         Waste Characteristics Affecting Performance  (WCAPs)

      In determining  whether  polishing  and  sludge filtration will   achieve the
same level of performance  on an  untested waste as  on a previously  tested waste
and whether performance levels can be transferred, EPA examines the following
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waste characteristics:   (a)  the  solid  waste  particle size and (b) the type of
solid waste particles.

2.4.1       Solid Waste Particle Size

      Extremely small  particles,  in the colloidal range,  may not be filtered
effectively in a polishing filter and thus may appear in the filtrate.

      In sludge filtration, the smaller the particle size, the more the particles
tend to  go  through the  filter  media.   This  is  especially true  for  a vacuum
filter.  For a pressure filter (such as  a plate and frame),  smaller particles may
require higher pressures for equivalent fluid throughput because the smaller pore
spaces between  particles  collected on the filter medium  create resistance to
flow.  If the  solid waste particje size distribution of  an untested waste is
significantly lower than  that of the tested waste, the system may not achieve the
same performance.   In  practice, it is usually difficult to  measure particle size
accurately  and  representatively.   However,  it  can  be said  that individual
particles formed  by  chemical  precipitation  are  typically much  smaller than
particles  formed   mechanically   (e.g.,  by  erosion,   grinding,   or abrasion).
Pretreatment of the waste with  coagulants and flocculants  may  be required to
increase the particle  sizes and achieve the  same treatment performance,  or other,
more applicable treatment technologies may need to be considered  for treatment
of the untested waste.

2.4.2       Type of Solid Waste Particles

      Some  solids  formed during metal precipitation  are  gelatinous in nature
because of  high levels of electrostatic  charge.   Such solids are difficult to
filter by polishing filtration and may be  impossible to dewater  effectively by
sludge filtration.  In most cases,  solids  can  be made less  gelatinous  by use of
the appropriate coagulants and coagulant dosage prior  to  settling/clarification,
or after settling/clarification but prior  to  filtration.   In addition, the use
of  lime  instead of  caustic  in  chemical  precipitation  of  metals reduces the


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formation of gelatinous solids.  Also,  in the  case  of sludge filtration, adding
filter aids, such as lime or diatomaceous earth, to a gelatinous sludge increases
its  filterability  significantly.    Finally, precoating  filter  media  with
diatomaceous earth prior to sludge filtration assists in dewatering gelatinous
sludges.  If solids in an untested waste are significantly more gelatinous than
those in  the tested waste, the  system may not  achieve adequate performance.
Pretreatment of the  waste with  coagulants  may be  required  to  decrease the
gelatinous  nature  of  the waste and achieve the same treatment performance, or
other,  more applicable treatment  technologies may need to  be considered for
treatment of the untested waste.

2.5         Design and Operating  Parameters

      In assessing the effectiveness of the design  and operation of a polishing
filtration system, EPA examines the following parameters:  (a)  the type  and size
of  the  filter;  (b)  the   filtration  pressure;  (c) the  amount  and   type  of
coagulants, flocculants, and filter aids used; (d) the  hydraulic loading rate;
and (e) the pore size of the filter media.

2.5.1       Type and Size of Filter

      The type  and size of the filtration  system used is dependent on  the rate
of feed, the nature of the particles to be removed/separated,  the desired solids
concentration in the filtrate  (usually just for polishing filtration) and  in the
filter cake (in  sludge filtration), the amount  and concentration of solids  in the
feed, and the required  downtime  for  solids removal and  maintenance.    As noted
earlier, with polishing filtration,  cartridge filtration  is  limited   to lower
volume  wastewaters and those  with lower  solids  concentrations as compared to
granular bed filtration.  For granular bed filtration, when more than one medium
is  used (dual   and multimedia filter  arrangements such as  sand,  garnet, and
anthracite coal), a higher  capacity can be expected  for the same size filter bed.
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      In sludge  filtration,  typically a pressure filter  (such  as  a plate and
frame) will  yield a drier cake than a belt or vacuum filter and will  also be more
tolerant of variations  in  influent  sludge  characteristics.   Pressure filters,
however, are  characterized by  batch  processes requiring downtime for solids
removal.   When  cake  is  built  up  to the maximum  depth physically possible
(constrained  by  filter geometry)  or  to  the  maximum  design   pressure,  the
filtration system 1s taken off-line  while  the  cake  1s removed.   (An alternate
unit can be  put on-line while  the  other  is  being cleaned.)   Belt and vacuum
filters are  continuous systems (i.e., cake discharges continuously), but each of
these filters  is usually  much  larger  than  a pressure  filter  with  the same
capacity.

      For all  filtration processes,  the  larger  the  filter, the  greater its
hydraulic capacity (overall throughput) and the longer the filter  runs between
solids removal.  EPA examines the type and size of the filter chosen to ensure
that it is capable of achieving effective filtration of the wastewater.

2.5.2       Filtration Pressure

      Pressure  impacts  both  the design pore size of  the  filter media and the
design feed flow rate (hydraulic loading rate).  The higher the  feed pressure,
the longer the run will  be prior to  solids  removal in  polishing  filtration.  In
sludge filtration, at higher pressures the  cake will  be drier  and the runs will
usually be longer prior  to cake discharge.  However,  for gelatinous  solids, such
as some metal  hydroxides,  excessive  pressure may  cause  the  solids to clog the
filter pores and prevent additional  polishing or sludge filtration.  Also, high
pressures may force particles through the filter medium, especially early in  a
filter run,  resulting in ineffective filtration.   In vacuum sludge filtration,
the maximum amount of vacuum typically  applied ranges from  20 to 25 inches of
mercury.   (The  absolute  maximum amount of  vacuum  that  can  theoretically be
applied is 29.9 inches  of mercury,  or atmospheric  pressure.)   For belt filters,
neither hydraulic  pressure  nor  vacuum is applied to  the  waste  feed (although
mechanical  pressure  is  applied).   For plate-and-frame  and  vacuum filtration
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systems, EPA monitors the filtration pressure (or vacuum) applied to the waste
feed continuously, if possible, to  ensure  that  the  system is operating at the
appropriate design condition and to diagnose operational problems.

2.5.3       Amount and Type of Coagulants, Flocculants, and Filter Aids

      Coagulants, flocculants, and filter aids may be mixed with the waste feed
prior to filtration.  Coagulants and flocculants affect the type and size of the
particles in the waste  and,  hence,  their ease of removal.  In vacuum filtration
their effect  is particularly significant  since they may make the  difference
between  no  cake formation  and  the forming of  a relatively  dry  cake.   In a
pressure filter,  coagulants,  flocculants,  and  filter  aids  can significantly
improve overall throughput and cake dryness.  Filter aids, such as diatomaceous
earth, can  be  precoated on all sludge  filters  for  particularly difficult-to-
filter sludges (those containing a high concentration of gelatinous solids).  The
precoat layer acts somewhat like a filter  in that sludge solids are trapped in
the precoat pore spaces.  In polishing filtration, filter  aids  both improve the
effectiveness of filtering gelatinous particles and increase the time that the
filter can stay on-line.

      Coagulants, flocculants, and filter aids are particularly useful when the
sludge (in the case of  sludge filters) and  wastewater  (in  the case of polishing
filtration)  have  a  high  percentage of  very  small  particles  or  when  the
concentration  of  solids in  the  waste  feed or  wastewater is  low.   Inorganic
coagulants include alum, ferric sulfate, and lime.  Organic flocculants, which
are  called  polyelectrolytes,  are  anionic, cationic,  or nonionic  in  nature.
Diatomaceous earth is the most commonly  used filter aid.  The  use of coagulants,
flocculants, and filter aids increases the  amount of solids requiring disposal.
Polyelectrolyte flocculant usage,  however,  usually does not increase the solids
volume significantly because the required  dosage  is  relatively  low.   If the
addition of coagulants,  flocculants, and filter aids is required, EPA examines
the amount and type added to the waste,  along with their method of addition, to
ensure effective dewatering and filtration.


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2.5.4       Hydraulic Loading Rate

      Lower hydraulic loading  rates generally improve filtration  performance.
For sludge filtration,  higher  hydraulic loading rates for a given size  filter
yield greater  overall  throughput but result  in  the  formation of wetter  cakes
(lower percent  solids)  and,  for plate-and-frame filters, shorter cycle  times.
For polishing filtration, higher hydraulic loading rates yield greater  throughput
but result in shorter cycle times.  EPA monitors the  hydraulic loading rate  to
ensure  effective  dewatering  and  filtration  of waste  sludge  and   effective
filtration of wastewater.

2.5.5       Pore Size of the Filter Media

      For  polishing filtration  systems,  the  pore size  of  the  filter  media
determines  the  particle  size  that  will  be  effectively  removed   from the
wastewater.  EPA examines the pore size of the filter  media  to ensure effective
filtration of wastewater.  For sludge filters, the pore size and  type relate  to
resistance to abrasion  and corrosion.
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2.6         References
Anonymous.  1985.  Feature report.  Wastewater treatment.  Chemical  Engineering
      92(18):71-72.

Grain, R.W.   1981.   Solids removal and concentration.   In  Third  Conference on
      Advanced Pollution  Control  for the Metal Finishing  Industry,  pp.  56-62.
      Cincinnati, Ohio:   U.S.  Environmental  Protection  Agency.

Eckenfelder,  W.W.,   Jr.,  Patoczka,  J.,  and  Watkins,  A.    1985.    Wastewater
      treatment.  Chemical  Engineering,  September 2,  1985.

Kirk-Othmer.  1980.   Encyclopedia of chemical  technology.  3rd ed. Vol. 10.  New
      York:  John Wiley and Sons.

Perry, R.H., and Chilton,  C.H.   1973.  Chemical engineers'  handbook.  5th ed.,
      Section 19.  New York:   McGraw Hill  Book Co.
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                     3.  HIGH TEMPERATURE METALS RECOVERY

3.1         Applicability

      High  temperature metals recovery  (HTMR)  is a  technology applicable to
wastes containing  metal  oxides and metal  salts  (including cadmium, chromium,
lead, nickel, and zinc compounds) at concentrations ranging from 10 percent to
over 70 percent with low levels (i.e., below 5 percent) of organics  and water in
the wastes.  There  are a number of different types of high temperature metals
recovery systems, which generally differ from one  another  in the source of energy
used and  the method of recovery.  These HTMR  systems include the rotary  kiln
process, the plasma arc reactor, the rotary hearth electric furnace system, the
molten slag reactor, and the flame reactor.

      HTMR  is  generally  not  used  for  mercury-containing  wastes  even though
mercury will volatilize readily at the process  temperatures present in the  high
temperature units.  The retorting process is normally  used for mercury recovery
because mercury  is  very volatile and lower operating  temperatures  can be used.
Thus, the  retorting process is more economical  than  HTMR for  mercury-bearing
wastes.  Retorting  is  discussed  in Section  II.B.5.

      The HTMR process has been demonstrated on wastes  such as baghouse dusts and
dewatered scrubber  sludge from the production of  steels and ferroalloys.  Zinc,
cadmium, and lead are the metals most frequently recovered.  The process  has not
been  extensively evaluated  for use with  metal   sulfides.    The  sulfides are
chemically  identical  to natural minerals  ordinarily  present  in  ores  used as
feedstocks  by  primary smelters.  Some  sulfide-bearing wastes from the chrome
pigments  industry  have  been  sent  to  such  primary  smelters.   However,   with
sulfides,  a  possibility exists for formation of either carbon disulfide  from
reaction with  carbon or sulfur dioxide  from reaction with oxygen in the  HTMR
processes.
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      Metal halide  salts  are  also  not directly used in HTMR processes.  They,
however,  may  be converted  to  oxides  or  hydroxides,  which  are  acceptable
feedstocks for HTMR processes.

3.2         Underlying Principles of  Operation

      The basic principle of operation for HTMR is that metal oxides  and salts
are separated from a waste through  a high temperature thermal  reduction  process
that uses carbon, limestone, and silica (sand)  as raw materials.  The carbon  acts
as a reducing agent and reacts with metal oxides to generate carbon dioxide and
free metal.   The silica and limestone serve  as fluxing  agents.   This  process
yields a metal product for reuse and reduces the concentration of metals in the
residuals and, hence,  the  amount of waste that needs to be land disposed.  An
example HTMR reaction  is the recovery of zinc, which proceeds as  follows:

                           ' 2  ZnO  + C •»  2 Zn  + C02 •

3.3         Description of High Temperature Metals Recovery Process

      The HTMR process consists of a mixing unit,  a  high temperature processing
unit (kiln,  furnace, etc.), a product collection system, and a residual  treatment
system.  A  schematic  diagram  for a high  temperature metals recovery  system is
shown in Figure  22.

      The mixing unit homogenizes  metal-bearing  wastes,  thus minimizing  feed
variations to the high temperature  processing  unit.  Before the  wastes  are fed
into the high temperature processing unit, fluxing  agents and carbon can be added
to  the  mixing unit and  mixed with  the wastes.    The fluxes  used  (sand  and
limestone)  are often  added to react with certain metal components,  preventing
their volatilization and resulting  in an  enhanced purity of the desired volatile
metals removed.
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                                                   AIR OR O,
                                                      1
EXHAUST AIR OR GAS
      TO THE
   ATMOSPHERE
ro
o
        I
WASTE INFLUENT ^
CARBON ^
(REDUCING AGENT)
FLUXES ^
/LIMESTONE. SANDI^
MIXING
UNIT
w
^
HIGH
TEMPERATURE
PROCESSING
UNIT
^.

PRODUCT
COLLECTION
UNIT
(CONDENSOR OR
CONDENSOR
AND BAGIIOUSE)
                                                                                             VOLATILE
                                                                                             METAL
                                                                                             PRODUCTS
                                                                                             TO REUSE
                                                                                             OR FURTHER
                                                                                             REFINEMENT
                                                                                             PRIOR TO
                                                                                             REUSE
                                                  RESIDUAL
                                                 COLLECTION
                                                (QUENCH TANK)
                                   NON-VOLATILE METAL PRODUCTS TO REUSE.
                                       FURTHER RECOVERY IN A FURNACE.
                                   STABILIZATION FOLLOWED BY LAND DIPOSAL.
                                        OR DIRECTLY TO LAND DISPOSAL
                                   Figure 22  High Temperature Metals Recovery System

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      The blended waste materials are fed to a furnace, where they are heated to
temperatures ranging  from 1100  to  1400*C  (2012 to 2552*F),  resulting in the
reduction  and   volatilization  of  the  desired  metals.    The  combination  of
temperature, residence time, and turbulence provided by rotation of the unit or
addition of an air or oxygen  stream  helps  ensure the maximum reduction and
volatilization of metal constituents.

      The product  collection system  can  consist  of  either a  condenser  or a
combination condenser  and baghouse.  The choice of a particular  system depends
on whether  the  metal  is to be collected in the metallic  form or as an oxide.
Recovery and collection are accomplished for the metallic form  by condensation
alone, and  for  the oxide by reoxidation, condensation,  and  subsequent collection
of the metal oxide particulates in a baghouse.   There  is no  difference  in these
two types of metal recovery and collection systems relative to the kinds  of waste
that can be treated;   the use of one system or the other simply reflects the
facility's preference relative to product purity. In the former case, the direct
condensation of metals allows  for the separation and  collection of individual
metals in a relatively uncontaminated  form; in the latter case,  the metals are
collected as a combination of several  metal oxides.

      The treated waste residual slag, containing  higher concentrations of the
less-volatile metals than the untreated waste,  is  sometimes cooled in  a quench
tank and (a) reused  directly as a  product  (e.g.,  a waste residual containing
mostly iron can be reused in steelmaking); (b) reused  after further processing
(e.g., a waste residual containing  oxides of iron, chromium,  and nickel can be
reduced  to  metallic  form and then recovered  for  use in  the  manufacture of
stainless   steel);  (c) stabilized  (material   has   no  recoverable  value)  to
immobilize  any  remaining  metal  constituents  and  then  land  disposed;  or
(d) directly land disposed as a  slag.
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3.4         Waste Characteristics Affecting Performance (WCAPs)

      In determining whether high temperature metals recovery will achieve the
same level of performance on an untested waste  that  it  achieved on a previously
tested waste and whether performance levels can be transferred,  EPA examines the
following waste characteristics:  (a) the concentrations of undesirable volatile
metals,   (b) the  metal   constituent   boiling   points,  and  (c) the  thermal
conductivity of the waste.

3.4.1       Concentration of Undesirable Volatile Metals

      Because HTMR is a  recovery process, the product must meet certain purity
requirements prior to reuse.  If the waste  contains  other  volatile metals, such
as arsenic or antimony,  which are difficult to separate from the desired metal
products and whose presence may affect the ability to reuse the product or refine
it for  subsequent reuse, HTMR may  not be  an appropriate  technology.   If the
concentration  of  undesirable  volatile  metals  in  the  untested  waste  is
significantly higher than that in the  tested waste, the system may not achieve
the same performance,  and other, more applicable treatment  technologies may need
to be considered for treatment of the  untested waste.

3.4.2       Metal Constituent Boiling  Points

      The greater the  ratio  of volatility  of the waste constituents,  the more
easily the separation of these constituents can proceed.  This ratio is called
relative volatility.   EPA recognizes,  however,  that the relative volatilities
cannot  be  measured  or  calculated  directly for the types  of wastes generally
treated by high temperature metals recovery.  This is because the wastes usually
consist of  a  myriad  of  components, all  with  different vapor pressure-versus-
temperature relationships.   However,   because the  volatility of components is
usually inversely proportional  to their boiling points  (i.e.,  the higher the
boiling point, the lower the  volatility),  EPA  uses the boiling point of waste
components as a surrogate waste characteristic  for  relative volatility.  If the


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differences  in  boiling  points  between  the more  volatile  and  less volatile
constituents are significantly smaller in the untested waste than  in  the tested
waste, the system may not achieve the same performance and other, more  applicable
treatment technologies may need to be considered for treatment of the untested
waste.

3.4.3       Thermal Conductivity of the Waste

      The ability to heat constituents within an HTMR process feed matrix is a
function of the heat transfer characteristics of the individual feed  components
(coke, limestone,  untreated waste, etc.).  The constituents being recovered from
the waste must be  heated  to near or above their boiling  points  in order for them
to be volatilized and recovered.   The  rate at which heat  will  be transferred to
the feed mixture is dependent «n the  mixture's thermal  conductivity, which is the
ratio  of the  conductive heat  flow  to  the  temperature gradient  across  the
material.    Thermal  conductivity  measurements,  as   part of a  treatability
comparison of two different  wastes  to be treated by  a  single HTMR system, are
most  meaningful  when  applied  to wastes  that are homogeneous  (i.e.,  uniform
throughout).   As wastes exhibit greater  degrees of  nonhomogeneity,  thermal
conductivity  becomes  less  accurate  in  predicting  treatability  because  the
measurement reflects heat flow through regions having the greatest conductivity
(i.e., the path of least resistance) and  not heat flow through all parts of the
waste.  Nevertheless, EPA believes that thermal conductivity may provide the best
measure  of  performance of heat transfer.   If the thermal conductivity of the
untested waste is significantly lower than that of the tested  waste,  the system
may  not achieve  the  same  performance and  other, more  applicable treatment
technologies may need  to be considered for  treatment of  the untested waste.

3.5         Design and Operating Parameters

       In  assessing  the effectiveness of  the design  and  operation  of  an HTMR
system, EPA examines the following parameters: (a) the HTMR temperature,  (b) the
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residence time,  (c)  the degree of mixing,  (d)  the carbon content of the feed, and
(e) the calcium-to-silica ratio of the feed.

3.5.1       HTMR Temperature

      Temperature provides an  indirect measure of the energy available (i.e.,
Btu/hr) to volatilize the metal  waste constituents.  The higher the temperature
in the high temperature processor, the more likely it is that the constituents
will react with  carbon to  form free metals and volatilize.  The temperature must
be equal  to or greater than the boiling point of the metals  being volatilized for
recovery.   However,  excessive  temperatures  could volatilize  less-volatile,
undesirable metals into the product, possibly inhibiting the  potential for reuse
of the product.   EPA monitors  the HTMR  processor temperature continuously, if
possible,  to  ensure that the  system is  operating at the  appropriate design
condition  (at  or  above  the  boiling point(s) of the metal  or  metals being
recovered, but not so high that it volatilizes other unwanted constituents) and
to diagnose operational  problems.

3.5.2       Residence Time

      The residence  time affects  the  amount of volatile metals volatilized and
recovered.  It  is  dependent  on the HTMR  processor temperature and the  thermal
conductivity of the feed blend.  EPA monitors the  residence  time to ensure that
sufficient time is provided  to effectively volatilize  the  volatile constituents
for recovery.

3.5.3       Degree of Nixing

      Effective mixing of the waste with coke, silica, and limestone is necessary
to produce a uniform feed blend to the system.  The quantifiable degree of mixing
is a complex assessment  that includes, among other things, the amount of energy
supplied, the length of time the  material  is mixed, and the related turbulence
effects of the specific size and shape of the tank  or vessel.  This is beyond the


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scope  of  simple measurement.   EPA, however,  evaluates the degree  of mixing
qualitatively by considering whether mixing is  provided  and whether the type of
mixing device  is  one  that could be expected to  achieve uniform mixing of the
waste.

3.5.4       Carbon Content of the Feed

      The  amount  of carbon  added  to the  waste  must be  sufficient  to ensure
complete reduction  of  the volatile metals being recovered.   EPA examines the
basis for calculation of the amount of carbon added  to the waste  to ensure that
sufficient carbon is being  used  in  the feed blend  to effectively reduce metal
compounds.

3.5.5       Calcium-to-Silica Ratio of the Feed

      The calcium-to-silica ratio in the feed blend  must be controlled to limit
precipitation of metallic iron in the high temperature processor.  The  iron forms
as solid calcium iron silicate,  which is very difficult  to subsequently process
into any useful material.  Aluminum oxide will  also  undergo reactions with lime
and silica to  form  calcium  aluminosilicates, which  will lower the density and
increase the volume of slag generated.

      Precipitates and modified slags affect the  reduction, volatilization, and
recovery of volatile metals by changing heat flow characteristics in the system
and by undergoing secondary,  high  temperature chemical  reactions  with metal
oxides in the feed, converting them to the previously noted inert metal silicates
or silicoaluminates.  The ratio of calcium to silica to  be used is dependent on
the waste composition.  Generally, a one-to-one silica-to-calcium oxide  ratio is
highly desired, so amounts of limestone and sand need to be adjusted based on the
calcium and silica content of the waste  to achieve  this  ratio.

      Excess lime may also be added to fix sulfur  in the feed as  calcium sulfate.
This will  prevent the  volatile  metals from reacting with sulfur to form metal


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sulfides, thereby  lowering the recovery of metals or oxides.   EPA monitors the
amounts  of  limestone   and   sand   added   to   the  waste  to  ensure  that  the
calcium-to-silica  ratio  selected  to  maximize  metal  or  oxide  recovery  is
maintained during  treatment.
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3.6         References


Center  for  Metals  Production.    1985.   Electric  arc  furnace  dust—disposal,
      recycle and recovery.  Pittsburgh, Pa.

Duby, P.  1980.  Extractive metallurgy.  In Kirk-Othmer encyclopedia of chemical
      technology.  3rd ed.  Vol.  9, p. 741.  New York:  John Wiley and Sons.

Lloyd,  T.   1980.    Zinc  compounds.     In  Kirk-Othmer encyclopedia  of  chemical
      technology.  3rd ed.  Vol.  24, p. 824.  New  York:  John  Wiley and Sons.

Maczek, H.,  and Kola,  R.   1980.  Recovery of zinc and lead from  electric furnace
      steelmaking dust at Berzelius.   Journal of Metals 32:53-58.

Price,  L.  1986.  Tensions mount  in EAF dust bowl.   Metal  Producing.   February
      1986.
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                               4.   ION EXCHANGE

4.1         Applicability

      Ion  exchange  is  a  treatment  technology  applicable  to  (a) metals  in
wastewaters where the metals are present as soluble ionic species (e.g., Cr*3 and
Cr04~2);  (b) nonmetalllc  anions  such  as  halides,   sulfates,   nitrates,   and
cyanides; and (c)  water-soluble, ionic organic compounds including (I) acids such
as carboxylics, sulfonics,  and some phenols, at  a pH sufficiently  alkaline to
yield ionic species, (2) amines, when the solution  acidity is  sufficiently  acid
to form the corresponding  acid  salt, and (3) quaternary amines  and alkysulfates.

4.2         Underlying  Principles of Operation

      Ion  exchange,  when  used  in  hazardous waste treatment,  is a  reversible
process  in  which  hazardous cations and/or  anions  are removed from  an  aqueous
solution and are replaced by nonhazardous cations and/or anions  such as  sodium,
hydrogen, chloride, or hydroxyl ions.  Ion exchange resins are cationic  if  they
exchange positive ions (cations)  and  anionic if  they  exchange negative  ions
(anions).  When the waste  stream to be treated is  brought into contact with a bed
of resin beads  (usually in  a packed column),  an  exchange  of hazardous ions for
nonhazardous  ions occurs  on the  surface of the  resin  beads.   Initially,  a
nonhazardous ion is loosely bound to the  surface  of the resin.  When a hazardous
ion is near the resin,  it  is preferentially  adsorbed to the surface of the resin
(based on the differences  in ionic  potential), releasing  the  nonhazardous  ion.

      Cation exchange resins contain mobile positive  ions,  such as hydrogen  (H*)
or sodium (Na*), which are attached to immobile functional acid  groups,  such as
sulfonic  (S03-) and  carboxylic  (COO")  groups.    Anion  exchange  resins  have
immobile basic  ions,  such as amine (NH2~),  to which the mobile  anions,  such as
hydroxyl (OH") or chloride  (Cl~),  are attached.
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      Ion exchange material is contacted with the solution containing the ion to
be removed  until  the active  sites  in the exchange  material  are partially  or
completely used up  ("exhausted")  by that  ion.   For example, a cation  exchange
resin (designated R") to which a mobile positive ion (N*) is attached reacts with
a solution of electrolyte  (M*X~)  as  shown  below:

                           MT + O* - R'M* + N* + X'

After exhaustion, the resin is then  contacted with  a  relatively low volume of a
very concentrated solution of the  exchange  ion to convert ("regenerate") it back
to its original form.  The regeneration reaction may be written  as  follows:

                   R~M* -i-  N*  (high concentration) -* R'N* + M*

For instance, in the case  of  a sodium-based resin, a strong solution of sodium
chloride is typically the  regenerant  solution.  The  regenerant  solution forces
the previously  removed  ions  back into  solution.   This  relatively low volume
solution, now highly concentrated with the contaminant ions, must then be treated
prior to  disposal   for  recovery  or removal  of the  hazardous  cation  or  anion
contaminants.  There will  continue to be a high concentration  of the regenerant
ion (sodium in the  above example)  in the used regenerant solution because excess
regenerant ion  is  necessary  to force the contaminant ions back  into solution.
The direction and extent of the completion of the exchange reaction depend upon
the equilibrium that is established between the ions in the solution (M*X~) and
those in the exchange material (R"N*).

4.3         Description of Ion Exchange Process

      Most ion exchange  operations are conducted in packed columns.  The aqueous
solution to be treated is  continuously fed to either the top or the bottom of the
column.   A  typical  fixed-bed  ion  exchange  column  consists  of  a  vertical
cylindrical pressure vessel with  corrosion-resistant linings.   If appropriate,
a filter is installed at  the  inlet  of the  column to  remove  suspended particles
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because they may plug the exchange resin.   Spargers  are  provided  at the top and
bottom  of  the  column  to  distribute  waste  flow.    Frequently,  a  separate
distributor is  used  for the regenerant solution to ensure  an  even flow.  The
resin bed, usually consisting  of  several  feet of ion  exchange resin beads, is
supported by a screen near the bottom distributor or by a support bed of inert
granular material. Externally, the unit has a valve manifold to permit downflow
operation, upflow backwashing  (to  remove any  suspended material), injection of
the regenerant solution, and rinsing of any excess regenerant.

      A typical  process  schematic  for a basic two-step  cation/anion  ion exchange
system  is presented  in Figure 23.   The  ion exchange  system  shown  in this
schematic includes a  series  treatment  with separate cation and  anion exchange
systems.  Some systems contain  both anion and cation exchange resins in the same
vessel'.  The pressure vessels used for ion exchange generally range  in size from
2 to 6 feet in diameter  for prepackaged modular  systems, which  typically handle
25- to 300-gpm flow rates, to a maximum custom  size of 12 feet in diameter, which
can handle  flow rates  up  to  1,150 gpm.   The height  of  these vessels varies
between 6  and  10  feet to provide  adequate  resin storage, distribution nozzle
layout, and freeboard capacity  for bed expansion during backwashing.  The nominal
surface loading area  of the ion  exchange vessels ranges  from  8  to 10 gpm per
square foot.

4.4         Waste Characteristics  Affecting Performance (WCAPs)

      In  determining whether  ion  exchange  will  achieve  the  same  level  of
performance on  an  untested waste  as on a  previously  tested waste and whether
performance  levels  can  be  transferred,  EPA  examines  the  following  waste
characteristics:  (a) the concentration and valence  of the contaminant, (b) the
concentration of competing ionic  species,  (c) the concentration  of interfering
inorganics and organics,  (d)  the concentrations of dissolved and suspended solids
and oil and grease, and  (e)  the corrosiveness relative to the  resin material.
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                     USED BACKFLUSH WATER
                         TO TREATMENT
     USED BACKFLUSH WATER
          TO TREATMENT
WASTEWATER
   INFLUENT
         BACKFLUSH  WATER
                                       RINSE WATER
                                       ACID REOENERANT
BACKFLUSH
    WATER'
                             CATION
                            EXCHANGE
                             SYSTEM
                  USED REGENERANT
                 SOLUTION AND RINSES
                    TO RECOVERY
                  AND/OR  TREATMENT
                       RINSE WATER
                       CAUSTIC
                       REGENERANT
              ANION
            EXCHANGE
             SYSTEM
  USED  REGENERANT
 SOLUTION AND RINSES
     TO  RECOVERY
  AND/OR TREATMENT
TREATED
EFFLUENT
TO FURTHER
TREATMENT
AND/OR DISPOSAL
                            Figure 23  Two-Step Cation/AnIon Ion Exchange System

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4.4.1       Concentration and Valence of the Contaminant

      As the  concentration  and valence  of adsorbable ions  In  the wastewater
Increase,  the size  of the  resin  bed  required  will  increase  as well,  or,
alternatively, the bed will become  exhausted more rapidly.   This is because a
given amount  of  ion exchange  resin has a  limited  number of sites  to adsorb
charged Ions.  If, for example, the valence is doubled or the concentration of
the adsorbed  ions  is doubled, the  sites  will  be exhausted  twice  as  quickly.
Hence,  very  high concentrations  of the  waste may  be inappropriate  for  ion
exchange because of rapid  site exhaustion, which could  conceivably require
regenerant volumes  to be  essentially  equal to  waste flow  volumes.    If  the
concentration and/or  the  valence of the  contaminant in an  untested  waste is
significantly higher than that of the tested waste, the system may not achieve
the same performance.  A larger exchange bed or more frequent regeneration may
be required  to  exchange higher  concentrations and/or higher valences  of the
contaminant and achieve the same treatment performance, or other, more applicable
treatment technologies may need to  be considered for treatment of the untested
waste.

4.4.2       Concentration of Competing Ionic Species

      The presence of other contaminants or ions in the wastewater can affect the
performance of the  ion exchange  unit  in  removing the hazardous contaminant of
concern.  Other  ions in the wastewater with the same charge as the contaminant
of concern will  compete  for exchange sites  on the resin.   Also,  ions with a
higher valence will  be preferentially adsorbed.  While a low concentration of the
contaminant  of   concern may  be  readily  removed  from a  solution  with  a  low
concentration of other similarly charged  ionic  species, the contaminant may not
be removed as efficiently  from solutions where  high concentrations of similarly
charged ions exist,  especially if those  ions have  a higher valence than that of
the contaminants.  If the  ions of concern  are removed  from a  solution with high
concentrations of other similarly charged ions, the resin will become exhausted
more rapidly because most  resins cannot  selectively adsorb one contaminant in a


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solution containing other similarly charged ionic species.  If the concentration
of competing ionic species in an untested waste is significantly higher than that
in the tested waste, the system may  not achieve  the  same  performance.  A larger
exchange bed or more  frequent  regeneration may  be required to exchange higher
concentrations  of  competing   ionic  species  and  achieve  the  same   treatment
performance, or other,  more applicable treatment technologies  may need to be
considered for treatment of the untested waste.

4.4.3       Concentration of Interfering Inorganics and Organics

      Interfering  inorganics,  such as  iron precipitates, can accumulate in the
pores of anion exchangers; these inorganics will physically break down or block
the resin  particles.   Some organic compounds,  particularly  aromatics,  can be
irreversibly adsorbed by the exchange  resins.  Also, some  ions tend to oxidize
after they are removed from solution.  For  instance,  Mn*2 (manganese) may oxidize
to the insoluble Mn*4  state, thereby permanently fouling  the exchange  sites and
requiring  the  premature replacement  of the  resin.   If the  concentration of
interfering inorganics and organics in  an untested waste is  significantly higher
than that  in the tested waste, the system may not achieve  the same performance
and other, more applicable treatment  technologies  may need  to be considered for
treatment of the untested waste.

4.4.4       Concentrations of  Dissolved and Suspended Solids and Oil  and
            Grease

      High concentrations of dissolved and suspended solids and oil and grease
can affect  the performance of ion exchange  sites.   Conventional   ion exchange
systems are usually downflow;  i.e.,  the wastewater flows  down through  the resin
bed.  Regeneration  is accomplished  in either the  downflow or upflow mode.  If
excessive concentrations of dissolved  and suspended solids and/or oil  and grease
are present in the wastewater,  the bed may clog and require  backwashing prior to
exhausting  its exchange capacity.   Backwashing may prove ineffective  in the
removal of some solids or oils.  If the concentration of dissolved and  suspended
solids and/or  oil   and grease in an untested waste is significantly higher than

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that in the tested waste,  the  system may not achieve the same performance and
other, more  applicable treatment technologies  may need to  be  considered for
treatment of the untested waste.

4.4.5       Corrosiveness

      Some wastewaters are extremely corrosive to  ion exchange resin materials,
reducing efficiency  or increasing downtime  for maintenance and  repair.   For
instance,  strong  solutions  of chromates may oxidize many  resins,  requiring
premature  replacement.    If  the  corrosiveness   of  the  untested  waste  is
significantly higher than that of the tested waste, the system may not achieve
the same performance and other, more  applicable treatment technologies may need
to be considered for treatment of the untested waste.

4.5         Design and Operating Parameters

      In assessing  the effectiveness  of the  design  and operation  of  an ion
exchange system, EPA examines the following parameters:  (a)  the  amount and type
of resin,  (b)  the amount  and  type  of regenerant  solution,  (c) the hydraulic
loading, and (d) the exchange  temperature.

      For  many hazardous  organic  constituents,   analytical  methods  are not
available or the constituent  cannot be analyzed in the waste matrix.  Therefore,
it would normally  be  impossible to measure the effectiveness  of the ion exchange
system.    In  these  cases  EPA  tries  to  identify  measurable  parameters  or
constituents that would act  as surrogates to  verify treatment.

      For organic constituents,  each compound contains a measurable amount of
total organic  carbon (TOC).    Removal  of TOC in the  ion  exchange system will
indicate removal of organic  constituents.  Hence, TOC  analysis  is likely to be
an adequate surrogate analysis  where the  specific  organic constituent cannot be
measured.   However, TOC analysis may not be able to adequately detect treatment
of specific organics in matrices that are heavily organic-laden (i.e., the TOC
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analysis may not be sensitive enough to detect changes at the milligrams/I Her
(mg/1)  level  in matrices where  total  organic concentrations  are hundreds or
thousands of mg/1).   In these cases other surrogate parameters should  be sought.
For example, if a specific analyzable constituent is expected to  be  treated as
well as the unanalyzable constituent, the analyzable constituent  concentration
should be monitored as a surrogate.

4.5.1       Amount and Type of Resin

      The main  design  parameter that affects the  performance of ion exchange
systems is  the  amount  and  type of resin used.   Numerous cationic and anionic
resins  are  commercially available.   The selection of  a resin  is  based on a
variety of  factors.  Different  resins have different exchange capacities, and
some have greater affinity than  others  for specific ions.   Certain  resins are
designed to tolerate  corrosive,  oxidizing, or high temperature  solutions, so
their exchange capacity does  not degrade as rapidly with  use.  Most resins  will
effectively remove contaminant ions from solution until  they  become  exhausted.
However,  if resin bed  exhaustion occurs  too frequently,   or if regeneration
requires excessive volumes of  the regenerant, the type and/or amount of resin
might need  to be changed.  In some instances, pretreatment  technologies may be
required prior  to  ion exchange.   For most metals  removal,  cation   resins are
usually  required.    However,  some metal  complexes,   such  as  copper cyanide
(Cu(CN)4~2),  chromates  (Cr04~2),  and arsenates  (As04~3), are  anionic and require
the use  of anion exchange resins.   EPA examines  the amount  and type  of ion
exchange resin in the treatment  system to ensure that a sufficient amount  of ion
exchange resin  is provided to effectively exchange  the metal  ions of concern.

4.5.2       Amount and Type of Regenerant Solution

      For hydrogen-based cation exchangers, acid regenerant  solutions are  used
(e.g., sulfuric, nitric, or hydrochloric acids).  For sodium-based cation resins,
sodium chloride is generally used.  For anion  exchange resins,  alkali (commonly
sodium hydroxide) is  used to regenerate hydroxide-based resins.  Sodium chloride
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is used for chloride-based  anion  resins.   EPA examines the amount and type of
regenerant solution used to  ensure that it is compatible with the resin and waste
treated and that  effective  removal  of the contaminant  ions from the exchange
resin is achieved.

4.5.3       Hydraulic Loading Rate

      The amount of time that the wastewater  contaminants are  in contact in the
ion  exchange  resin  (i.e.,  residence time)  impacts the  extent to  which ion
exchange occurs.  Higher residence times generally improve exchange performance,
but require larger  ion  exchange  beds to maintain the same overall throughput.
For a given size  ion exchange bed, the residence time can be determined by the
hydraulic loading rate.  Typical hydraulic loading rates for ion exchange systems
range from 600  to 15,000 gal/day-ft2.  EPA monitors the hydraulic loading rate
to ensure that sufficient time is provided to  effectively exchange contaminants.

4.5.4       Exchange Temperature

      High temperatures reduce resin  life, requiring premature replacement.  EPA
monitors the temperature in  an ion exchange column continuously, if possible, to
ensure that the system  is operating  at the appropriate design  condition and to
diagnose  operational  problems.   EPA  has information  showing  that  the high
temperature limit for anionic resins may  be approximately 60°C.
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4.6         References
De Renzo,  D.J.,  ed.  1978.  Unit operations for treatment of hazardous  industrial
      wastes.   Park Ridge, N.J.:  Noyes Data Corporation.

Dorfner, K.   1972.   Ion  exchangers:   properties and applications.  Ann Arbor,
      Mich.:  Ann Arbor Science Publishers, Inc.

Metcalf & Eddy,  Inc.  1979.  Wastewater engineering:  treatment disposal reuse.
      2nd ed.  New York:  McGraw-Hill  Book Co.

Patterson, J.W.  1985.  Industrial  waste treatment technology.  2nd ed.  Stoneham,
      Mass.:  Butterworth Publishers.

Perry, R.H.,  and Chilton,  C.H.   1973.   Chemical engineers' handbook.  5th  ed.
      New York:   McGraw-Hill Book Co.

Sundstrom, D.W., andKlei,  H.E.  1979.  Wastewater treatment.   Englewood Cliffs,
      N.J.:   Prentice-Hall,  Inc.

USEPA.  1982.  U.S. Environmental Protection Agency.  Development document  for
      the porcelain enameling point source category,  pp.  172-241.  Washington,
      D.C.: U.S. Environmental Protection Agency.

USEPA.  1983.    U.S.  Environmental Protection  Agency.   Treatabilitv manual:
      Vol. III.     Technology  for  control/removal  of   pollutants.  EPA-600/
      2-82-OOlc.  Washington, O.C.:  U.S. Environmental Protection Agency.

Wheaton, R.M.   1978.  Kirk-Othmer encyclopedia  of chemical technology. 3rd  ed.
      Vol. 13.  New York:  John Wiley  and Sons.
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                                 5.  RETORTING

5.1         Applicability

      Retorting  Is a  treatment  technology applicable  to  wastes  containing
elemental mercury,  as well  as  mercury present  in the  oxide,  hydroxide, and
sulflde forms, at levels above 100 parts per million, provided that the waste has
a low total  organic content (I.e.,  below  1 percent).   For  metals  other than
mercury, the typical retort operating temperatures (700 to  1000'F) are not high
enough to decompose the metal compounds. High temperature metals  recovery  (HTMR)
processes must be used to recover most  other metals when they  are not present in
the pure metal form.

      For most retorting processes, there  1s an additional  requirement that the
waste have a low  water content, preferably below 20 percent.  Dewatering reduces
energy consumption  by minimizing  the amount of water evaporated and precludes
problems  involving  the separation  of recovered metals  from large quantities of
water.

5.2         Underlying Principles  of Operation

      The basic principle of operation  for retorting is  a process similar to that
for high temperature metals recovery in that it provides for  recovery of  metals
from  wastes   primarily  by volatilization  and  subsequent  collection  and
condensation of the volatilized components.  Retorting yields a metal product for
reuse  and  significantly  reduces  the  concentration  of metals  in the  waste
residual, and, hence,  the amount of treated waste  that needs to be land disposed.
This technology is different from HTMR in that HTMR includes a  reduction reaction
involving the  use of carbon, while  retorting  does not  use  a reducing  agent.
Additionally,  this  process  differs with  regard  to the form and, possibly, the
Teachability of  the residue generated; HTMR generates a slag, while retorting
generates a granular solid  residue that may have  lower Teachability than  a slag
if mercury is  the only constituent of  concern present  in the  untreated waste.


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      The basic principle of operation of retorting is that sufficient heat must
be transferred to the waste to cause elemental  metals to  vaporize.   In the case
of mercury present as an oxide,  hydroxide,  or sulfide compound, sufficient heat
must  be  transferred  to the  waste to  first decompose  the compounds  to the
elemental form  and  then volatilize  the  mercury.   In mercury  wastes that are
wastewater treatment sludges, mercury is most often  present in the  form of the
sulfide  (HgS)  as a result  of the  use  of  sodium  hydrosulfide  treatment  of
mercury-bearing wastewaters.   In  a few instances, hydrazine  is  used to treat
these  same  wastewaters;  in  such   instances, a mercurous  hydroxide sludge is
generated.  This latter compound can be more easily  treated to yield  elemental
mercury because this reaction occurs more readily than the sulfide decomposition
at the temperatures  at which  the process is normally operated.   Preheated air is
provided  to  the retort  to supply  the  oxygen  necessary  for   the sulfide
decomposition and to enhance  the heat transfer to the waste.

      The equations  for decomposition of  both forms of  mercury are  presented
below:

      (a)  HgS + 02  - Hg + S02

      (b)  2Hg2(OH)2 - 4Hg + 2H20 + 02


5.3         Description of Retorting Process

      The retorting  process  generally consists of a  retort  (typically an oven,
i.e., multiple hearth  furnace or  rotary  kiln)  in which the waste  is  heated to
volatilize the metal constituents,  a condenser, a metals  collection system, and
an air pollution control system.  Figures 24  and 25 show a retort system without
and with a scrubber-type  air pollution control system.

      Trays of  wastes  are  placed  in the  retort,  where  they  are  heated, and
decomposition of mercury compounds  and volatilization  of the metallic mercury and
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                                                                                       EXHAUST AIR
                                                                                   TO THE  ATMOSPHERE
ro
   PREHEATED
       AIR
                   RETORT
           ~t
                      T
                                   COOLING
                                    WATER
                                                             I    AIR
                                                             1 POLLUTION
                                                               CONTROL
                                                                SYSTEM |
                                                                 STACK
                              METAL
                              COLLECTION
WASTE
INFLUENT
VOLATILE METALS
   TO REUSE
   TREATED  RESIDUAL WASTE TO STABILIZATION
            AND/OR LAND DISPOSAL
             Figure 24  Retorting Process  (Without a Scrubber and Subsequent  Wastewater Discharge)

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                                                WATER
                                                   VENTURI
                                                  SCRUBBER
ro
ro
       PREHEATED
           AIR
                        RETORT
                                                      DECANTER
                                        WASTE
                                        INFLUENT
                                                                            EXHAUST AIR
                                                                        TO  THE ATMOSPHERE
                     STACK
    WASTEWATER TO  TREATMENT
VOLATILE
METALS
TO REUSE
         TREATED  RESIDUAL  WASTE TO STABILIZATION
                  AND/OR  LAND DISPOSAL
                        Figure 25 Retorting Process (With a Scrubber and Subsequent Wastewater Discharge)

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other volatile elemental  metals  occur.  Although most commonly carried out  in an
oven, retorting can also be performed in a multiple hearth furnace.

      The vapor stream from the retort is cooled in a condenser. If  a scrubber
is not used  as  an air pollution control device,  an electrostatic precipitator is
provided after the condenser to remove any residual metal in the exhaust  vapor
stream, as well as to control other potential emissions such as sulfur dioxide
(S02), fly ash, and hydrogen chloride (HC1) vapors.  Condensed metal  is collected
for reuse before the electrostatic precipitator.

      Residual  solids  remaining  in  the  retort,   stripped  of  volatile   metal
contaminants,  are  collected  and  may  be  either  directly  land  disposed  or
stabilized,   to immobilize  any remaining  metal constituents,  and  then  land
disposed.

5.4         Waste Characteristics Affecting Performance fWCAPs)

      In determining whether retorting will  achieve  the same level  of performance
on an untested waste that it achieved on a previously tested waste and whether
performance  levels  can  be transferred,  EPA  examines  the following   waste
characteristics:  (a)  the concentration of  undesirable volatile constituents in
the waste and  (b) the thermal conductivity of the waste.

5.4.1       Concentration of Undesirable Volatile Constituents

      Because  retorting  is  a recovery process, its  product  must meet certain
purity  requirements prior  to  reuse.   If the  waste contains  other volatile
constituents with boiling points  equal  to  or below that of the metal(s)  to be
recovered, they will be volatilized and condensed along with the desired metal(s)
present in the waste.   These constituents may be difficult to separate from the
recovered product and may affect the ability to reuse the product metal or refine
it for subsequent  reuse.  Undesirable volatile constituents sometimes  present in
mercury-bearing wastes  include  (a) mercury chlorides, which distill  unchanged in
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the retorting process, and other volatile metal halides; (b) arsenic oxide and
arsenic  trichloride;  and (c) organomercury compounds,  such as phenylmercuric
acetate, which are not decomposed to elemental mercury by the retorting process.

      For wastes containing significant levels  (i.e., above  1 percent) of these
contaminants,  retorting  may  not  be  an   appropriate   technology.     If  the
concentration of  undesirable volatile  constituents  in  the  untested waste  is
significantly higher than that in the tested waste, the system may not  achieve
the same performance.  Chemical  pretreatment may be required to convert  mercury
chlorides  and organomercury  compounds  to  mercuric  sulfide  and/or  elemental
mercury and  achieve  the  same treatment  performance,  or  other,  more  applicable
treatment technologies may need to be considered for treatment of the untested
waste.

5.4.2       Thermal Conductivity of the Waste

      The ability to  heat constituents within a  waste matrix  is a function of the
heat  transfer  characteristics  of  the  waste   material.    Mercury  and other
recoverable metals in  the waste must  be heated to near  or above their  boiling
points in order to be volatilized and  recovered.  The rate at which  heat  will  be
transferred  to  the  waste  material   is  dependent on  the  material's  thermal
conductivity, which is the ratio of the  conductive heat  flow to the temperature
gradient across the material.  Thermal conductivity measurements, as part  of a
treatability comparison of two different wastes  to be treated by a single retort
system, are most meaningful when applied to wastes that are  homogeneous (i.e.,
uniform  throughout).   As  wastes exhibit  greater degrees  of nonhomogeneity,
thermal conductivity  becomes less accurate in predicting treatability because the
measurement reflects heat flow through regions  having the greatest conductivity
(i.e., the  path  of  least resistance)  and not  through all  parts of  the waste.
Nevertheless, EPA believes that thermal conductivity may provide the best  measure
of performance of heat transfer.   If  the thermal  conductivity of the untested
waste is significantly lower  than that of the tested waste,  the system  may not
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achieve the same performance and other, more applicable treatment technologies
may need to be considered for treatment of the untested waste.

5.5         Design and Operating Parameters

      In assessing the  effectiveness of the design  and  operation of a retort
system, EPA examines the following parameters:  (a) the retorting temperature and
(b) the residence time.

5.5.1       Retorting Temperature

      Temperature provides  an  indirect measure  of the energy available (i.e.,
Btu/hr) to  vaporize  the metal  of concern.  The  higher the temperature in  the
retort, the more likely it  is that the metal will volatilize.   The temperature
must be  equal  to or  greater than the  boiling  point of  the  metal.   However,
excessive  temperatures  could  volatilize  undesirable  constituents  into  the
product, possibly inhibiting its  potential reuse, and also could cause  sintering
of the feed material.  For mercury retorting, EPA monitors the retort temperature
to ensure  that the system is operating at the appropriate design condition  (a
temperature at least  equal  to the boiling point  of mercury (674*F)  but  below
1000'F) and to diagnose operational  problems.

5.5.2       Residence Time

      The  residence time  impacts the amount  of volatile metal  volatilized  and
recovered.    It   is   dependent   on   the  retort  temperature  and the thermal
conductivity of the waste.  Typical residence times in retort systems  for mercury
range from 4 hours to 20 hours.   EPA monitors  the  residence time to ensure that
sufficient time is provided to effectively volatilize all  of the mercury and/or
other metals to be removed  from  the  waste.
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5.6         References


Occidental Chemical Corp.  1987.  Delisting petition,  chloralkali plant, Muscle
      Shoals,  Alabama.    Submitted to  U.S.  Environmental  Protection  Agency,
      July 20, 1987.

Perry, R.A.  1984.  Mercury recovery from contaminated wastewaters and sludges.
      PB 238 600.

Sittig,  M.    1975.    Resource  recovery  and recycling  handbook of  industrial
      wastes.  Park Ridge, N.J.:   Noyes  Publications.

Versar.  1987.  Waste minimization audit  report  -  case studies  of minimization
      of mercury  bearing wastes  from chloralkali plants.   Prepared  for  U.S.
      Environmental  Protection Agency,  Office  of Research  and  Development,
      Hazardous Waste Engineering  Research  Laboratory  by  Versar Inc., Contract
      No. 68-01-7053.
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III.  TECHNOLOGIES APPLICABLE TO MIXED WASTE
           (RADIOACTIVE/HAZARDOUS)

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Introduction

      This section describes the treatment technologies applicable to mixed waste
(i.e., waste that  is both radioactive and  hazardous).  This introduction explains
what mixed wastes  are and how they are classified, where they are likely to be
generated, and how they  are regulated.  Following this introduction  are sections
discussing  (a) technologies  for  treating mixed wastes containing organics and
inorganics  other  than  metals,  (b)  technologies  for  treating mixed  wastes
containing metals, and (c) technologies for treating mixed wastes that cannot be
treated   by   technologies   determined  to  be   BOAT  for  the  corresponding
nonradioactive wastes (i.e., special mixed wastes treatability group).   Each of
these  three  sections  includes  subsections  describing  applicable treatment
technologies.

      Mixed wastes are  those wastes that  satisfy the definition of  radioactive
waste subject to  the  Atomic  Energy  Act  (AEA)  and that also contain waste that
either  is listed  as  a hazardous waste  in  Subpart  D  of 40 Code  of  Federal
Regulations (CFR)  Part 261 or exhibits any of the hazardous waste  characteristics
identified in Subpart C of 40 CFR Part 261.  Because they are hazardous, mixed
wastes  are  subject to the Resource Conservation  and Recovery  Act  (RCRA) Land
Disposal Restrictions.  All  promulgated  treatment standards  for  RCRA listed and
characteristic wastes apply to the RCRA mixed wastes unless EPA has specifically
established a separate treatability  group for a specific category of mixed waste
(see  following Section  C).   Although mixed wastes  are  regulated by EPA under
RCRA, the specific standards  for radioactive material  management  developed under
the AEA are administered by the Department of  Energy  (DOE) for government-owned
facilities and by the  Nuclear Regulatory Commission (NRC) for commercially owned
facilities. The majority of mixed wastes  can be divided into the  following three
categories  based  on  the  radioactive component  of the  waste:   (a) low-level
wastes,  (b)  transuranic (TRU) wastes,  and (c)  high-level  wastes.   Low-level
wastes  include  radioactive waste that   is not  classified  as  spent fuel  from
commercial nuclear power plants or as defense  high-level  radioactive waste from
the production of weapons.  TRU wastes are those wastes containing elements with
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an atomic number greater  than  92  (the atomic number for uranium).  TRU wastes
generally pose greater radioactivity hazards than  low-level wastes because they
contain long-lived  alpha  radiation  emitters.  However, commercial transuranic
waste is included as low-level  radioactive waste.   High-level mixed wastes have
high levels of radioactivity and are extremely dangerous to handle.  High-level
mixed wastes are generated  from the reprocessing  of irradiated fuel rods from
commercial and military nuclear reactors.

      Mixed low-level  wastes are generated principally from nuclear power plants,
the Department  of  Energy  (DOE), and  academic  and medical  institutions.   Some
examples of low-level mixed wastes  include  spent  solvents containing suspended
or dissolved radionuclides,  scintillation cocktails from diagnostic procedures,
spent Freon used for cleaning protective garments, acetone or solvents  used  for
cleaning pipes  or  other equipment,  and still bottoms from tha distillation  of
chlorofluorocarbon solvents  (CFCs).  Other wastes in this category include a wide
range of solid  materials  such  as spent ion-exchange resins (contaminated with
various metals), filters used in reclaiming CFCs,  adsorbents, residues  from  the
cleanup of  spills,  lead  shields,  lead-lined  containers,  welding  rods,   and
batteries.  Also, the production of military weapons produces large amounts  of
wastes that fall into the low-level and TRU  categories  of mixed waste.
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             A.   TECHNOLOGIES FOR MIXED WASTES CONTAINING ORGANICS
                       AND INORGANICS OTHER THAN METALS
      The  following  technologies  have  been determined  to be  applicable for
treating mixed waste.  These technologies were described in detail in previous
sections in this document for hazardous wastes that are not  mixed.  Technologies
for mixed waste operate under the same principles of operation  used for treating
nonmixed waste.  However,  with mixed waste these technologies typically separate
the hazardous waste components from the radioactive components, thereby reducing
the volume of the radioactive component requiring treatment, or immobilize the
waste (in the case of  stabilization technologies).  If the hazardous component
is  also  radioactive  (e.g.,  a  hazardous  solvent whose  structure  contains
radioactive  carbon),  that component may sometimes  be  removed from the waste,
leaving a less hazardous, less radioactive residual.

1.          Carbon Adsorption

      For organic low-level mixed wastes, carbon adsorption  may be used to remove
organics in wastewaters.  If the organic component is not  radioactive,  then this
treatment  reduces  the quantity of the hazardous  waste component  in the  mixed
waste.

2.          Distillation  Technologies

      A distillation technology such as batch distillation,  steam stripping,
fractionation, thin film evaporation, or thermal drying may  be applied to a  mixed
waste in that it can be used  to separate the mixed waste  into  the hazardous and
radioactive  waste  components,  as  long as the  hazardous  component  is not also
radioactive.  The separation can be made where the  volatility of the hazardous
components  is  significantly  different from  the  volatility of the radioactive
components.   The distillation  process  will  remove the  more  volatile organic
components,  leaving  the  less volatile constituents  in the  still bottoms.
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3.          Extraction Technologies

      As with  distillation,  extraction technologies (i.e., solvent extraction and
critical  fluid extraction)  may be  used to  separate  a  mixed waste  into  its
radioactive and hazardous components if  either the hazardous or the  radioactive
components can be  selectively extracted by the extracting solvent.
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              B.   TECHNOLOGIES FOR MIXED WASTES CONTAINING METALS

1.          Add Leaching

      Acid  leaching  may be  used to  extract  hazardous metals  (regardless of
whether  the metals  are radioactive)  from mixed  wastes,  principally soils,
separating the material  into its hazardous and radioactive components or removing
the hazardous and radioactive  component from the rest of the waste.  This process
may have greater  utility when combined with unit operations such as ion  exchange,
solvent extraction, chemical  precipitation, and filtration.

2.          Chemical Precipitation

      Chemical precipitation  may be applicable to mixed wastes for separating
hazardous metals  and/or hazardous metal radionuclides from other constituents in
wastewaters.  Specific conditions of pH,  temperature,  and  precipitating reagent
addition  are  required  to  selectively remove  part  or all  of the  radioactive
components  as  a  precipitate.

3.          Filtration

      Filtration technologies may be  used  following precipitation  and settling
processes to separate low-level  mixed  waste from high-level mixed waste. Hence,
filtration  may concentrate the  high-level  waste components  in the  filter  cake,
leaving a relatively low-level  filtrate.

4.          High Temperature  Metals Recovery

      The high temperature metals recovery (HTMR) process may be  applicable to
mixed  wastes  if  the  volatility  of   the  radioactive  metal   component is
significantly different from that of the nonradioactive portion.  This technology
is  similar  to distillation of  organics,  but  instead  "distills" more volatile
inorganic components from less  volatile  ones.


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5.          Ion Exchange

      Ion exchange  treatment  may be used  to  separate a mixed  waste into its
radioactive and hazardous constituents  if the  radioactive components  are ionic.
It will  also  concentrate the  radioactive  ionic species into  a small volume,
leaving a nonradioactive aqueous phase.  The principal mixed waste application
of this process is  to  recover metallic radionuclides from wastewaters or acid
leach liquors.   If more than  one  radionuclide exists in  solution,  it may be
necessary to use either a mixed bed ion exchange unit or different types of ion
exchange resins to recover all the radionuclides.

6.          Stabilization of Metals

      Stabilization  refers  to  a  broad  class  of  treatment   processes  that
immobilize  hazardous  constituents  in  a waste.    For treatment of  metals in
low-level mixed wastes and for some TRU wastes  containing low-level radioactive
components, stabilization  technologies  will   reduce  the  Teachability  of the
hazardous metal constituents (regardless of whether the metals are radioactive)
in nonwastewater  matrices.   However,  EPA  does not believe that stabilization
using cementitious binders is an appropriate treatment for high-level radioactive
mixed wastes  generated  during the  reprocessing  of  fuel   rods.    It does not
adequately  immobilize the high-level radioactive portion of the mixed wastes.
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       C.  TECHNOLOGIES FOR NIXED WASTES IN SPECIAL TREATABILITY GROUPS

1.          Amalgamation

      Amalgamation  is  applicable  to  radioactive wastes containing mercury and
particularly  to  wastes  containing  radioactive  mercury  isotopes.    Mercury
compounds are converted  into  a  solid mercury-zinc alloy, which is more easily
managed  and  less mobile  than  solutions containing radioactive  mercury.   The
process  can be  used directly  with radioactive wastes provided that additional
precautions are taken to prevent release of radioactive materials  and to protect
operations from  radioactive emissions.

      The Agency has established amalgamation  as a method of treatment  for mixed
wastes containing elemental mercury.   These types  of wastes  are typically found
in vacuum pumps  and  related manometers.  In the nuclear  industry, this form of
mercury  has  been  contaminated with radioactive  tritium  (a  radioisotope of
hydrogen).

      EPA  has  determined  that  amalgamation  not  only provides  a significant
reduction in air emissions of mercury but also  provides a change in mobility  from
liquid mercury  to  a paste-like  solid,  potentially reducing Teachability.  The
required method of treatment,  i.e., amalgamation,  may  be  performed using any of
the  following  elements:   zinc,  copper,  nickel,   gold,  and  sulfur.   Further
information on the  amalgamation process may be  found in  Section  I.B.I.

2.          Encapsulation

      Encapsulation  processes such as plastic and  asphalt encapsulation may be
used for the management of mixed wastes.  However,  the equipment used for mixing
of the wastes  with  molten  encapsulating  agents must be  of special  design to
protect workers from radioactive hazards.   Additional  precautions  may  be needed
to prevent generation of airborne particulates or vapors of radioactive material
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during the processing.   More  information  on  encapsulation may be found in the
encapsulation section (see Section I.B.3).

      The Agency  has established  a  treatment standard  of macroencapsulation
(encapsulating  an  entire  mass,  rather  than microencapsulation,  which coats
individual particles of a waste) as a method of treatment for radioactive lead
solids.  This treatment  standard applies to all forms of radioactive mixed waste
containing elemental lead  (including  discarded equipment containing elemental
lead that served as  personnel  or  equipment  shielding prior to becoming a RCRA
hazardous waste).   These lead solids do  not  include  treatment  residuals  such as
hydroxide sludges,  other wastewater treatment residuals,  or  incinerator ash,
which are usually amenable  to conventional pozzolanic stabilization, nor do they
include organolead materials that  can be incinerated and then stabilized as ash.

3.          Vitrification

      Vitrification  is   a  treatment  technology  that  will provide  effective
immobilization  of  the   inorganic  constituents  (i.e.,  both   radioactive  and
hazardous components) of a mixed waste.   Vitrification  has  been demonstrated to
be an effective treatment technology for high-level  mixed waste generated during
the  reprocessing  of  fuel  rods.   Since  vitrification  is  a  high-temperature
process,  small  quantities  of  organics that  may be  present will be volatilized
during the vitrification process.  If  there are gamma-emitting radionuclides
present,  the  gamma dose rate  will be reduced as a  result  of the increase in
density of the vitrified matrix (going from  the density of soil or  other solids
to the density  of glass).  If  radium is present, the radon  flux rate will also
be reduced because of the  change  in the density.  Both alpha  and beta  emitters
will  be  sealed in  the  glass  matrix.   More  information  on the vitrification
process may be  found in  the vitrification section (see Section I.B.5).
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4.          Incineration

      Incineration is a technology applicable to nonradioactive elemental mercury
(i.e., retorting)  waste containing high  levels  of organics.   The Agency has
determined   that   incineration   is   also  an   applicable   technology  for
mercury-containing   hydraulic  oil   contaminated  with  radioactive  material
(low-level mixed  waste) and has  set  incineration as  the  standard (method of
treatment)  for that  waste.    Incineration of  radioactive mercury  and other
volatile mixed waste components is likely to cause the mercury or other volatile
components to  volatilize.   Therefore, incinerators must  be equipped with air
pollution  control   devices  to ensure that  any  volatilized  hazardous   and/or
radioactive components are not released to  the atmosphere above permitted levels.
Incineration of  organic wastes containing concentrations of the radionuclides
tritium and carbon  14 will cause  the  escape of radioactive  compounds since the
combustion products of tritium  (radioactive hydrogen) and carbon  14 are steam and
carbon dioxide, respectively,  both of  which will usually escape conventional air
pollution control devices.
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References


U.S.  Congress,  Office  of  Technology Assessment.   1989.   Partnerships  under
      pressure: managing  commercial low-level  radioactive waste.  Washington,
      D.C.:  U.S. Government Printing Office.  OTA-0-426.

USEPA.  1990.  U.S. Environmental Protection Agency.   Federal  Register Notice,
      55 FR 22626, June 1, 1990.

U.S. General Accounting Office.  1989.  Fact sheet for the Chairman, Environment,
      Energy,  and  Natural  Resources  Subcommittee,  Committee  on  Government
      Operations,  House of Representatives;  Nuclear  Waste,  DOE's program  to
      prepare  high-level  radioactive waste  for final  disposal.    Washington,
      D.C.:  U.S. General Accounting Office.

U.S.  General Accounting Office.   1989.   Report  to the Chairman,  Committee  on
      Governmental Affairs, U.S.  Senate;  Nuclear Regulation,  the military would
      benefit from a comprehensive  waste  disposal  program.

Westinghouse Electric  Corp.   1983.   Waste technology  reprints:   Nuclear waste
      management  in the United States.
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                                    APPENDIX A
                                                             t

             LIST OF  BEST DEMONSTRATED  AVAILABLE TECHNOLOGY (BOAT)
                  BACKGROUND DOCUMENTS  AND ASSOCIATED BDAT(S)
f:\document\15254031.01.024

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      This appendix contains  a  list  of BOAT background documents prepared for
EPA's Office  of Solid Waste, Waste  Treatment  Branch, in  support  of the Land
Disposal  Restrictions.    (The specific  Third  under  which each  document was
prepared  is  also noted.)   This  appendix  is meant  to be  a  quick  reference,
however,  for  details on  a  specific waste  code  see  the  relevant  background
document for that waste code.  In summary, this  appendix presents  the  following:

      •  The waste codes,  industries,  or sources  of the waste associated with
         each background document.

      •  The treatment technologies on which the treatment  standards  were  based
         i.e., BOAT.  The BOAT associated with  each  background document  is also
         identified.   (Note  that BDAT(s) may  vary  for individual  waste  codes
         contained in a  background document.  For specific information on the
         BOAT applicable to a certain waste code,  see the applicable  background
         document.)

      •  The source of the treatment  data used to set the  treatment  standard and
         whether  the data were collected or  submitted  to EPA (actual data) or
         transferred from existing data.

      •  The category of waste treated  (i.e.,  organics, inorganics,  metals).
                                      A-l

f:\document\15254031.01.024

-------
                                                          LIST OF BOAT BACKGROUND DOCUMENTS AND ASSOCIATED BDAT(S)
 i
ro
Third
1/3
1/3
1/3
Waste Code/
(Background Document)
F001-FOOS (revised for
methylene chloride)
F006
K001
Industry or
Source of Uaste
Pharmaceutical
industry
Electroplating
operations
Wood preserving
industry
BDAT(s)
Steam stripping (wastewaters)
Stabilization (nonwastewaters)
Rotary kiln incineration,
Stabilization (nonwastewaters,
Actual Data
or Transferred
and
Origin of Data
Data/industry-subraitted
Data/ industry-submit ted
Data/EPA test.
transfer/FOOo
Types of
Wastes Regulated
Methylene chloride
Metals, cyanides
Organics, metals
           1/3   K01S
1/3   K016,  K01B,  K019,
      K020.  K030

1/3   K022
           1/3   K024
           1/3   K037
           1/3   K044, K045, K047
            1/3   K046 (nonreactives)
                                Distillation of  benzyl
                                chloride
Chlorinated organic*
production

Phenol/acetone
production

Phthalic anhydride
production

Disulfoton production
                                Manufacturing and
                                processing of
                                explosives

                                Lead-based initiating
                                compounds  production
wastewaters); chemical precipitation
(metals in wastewaters)

Liquid injection incineration
(nonwastewaters); chemical
precipitation (wastewaters)

Rotary kiln incineration
(nonwastewaters, wastewaters)

Fuel substitution, stabilization
(nonwastewaters)

Rotary kiln incineration
(nonwastewaters, wastewaters)

Rotary kiln incineration
(nonwastewaters, wastewaters)

Open burning/Open detonation,
incineration (nonwastewaters)
                         Stabilization (nonwastewaters)
                                                                  Transfer/KOI9
                                                                                                             Data/EPA test
Oata/industry-submitted,
transfer/FOOo

Data/EPA test
Data/EPA test


Data/000



Data/EPA test
Organics, metals



Organics


Organics, metals


Phthalic acid


Disulfoton, toluene


Reactive waste from
K044, K045. 1C047


Lead (metals)

-------
                                                         LIST OF BOAT BACKGROUND DOCUMENTS AND ASSOCIATED BOAT(S)
                      Waste Code/
         Third   (Background Document)
                                  Industry or
                                Source of Waste
                                 BOAT(s)
                                           Actual Data
                                          or Transferred
                                              and
                                         Origin of Data
                                      Types of
                                 Wastes Regulated
          1/3   K048-KOS2
 I
Co
1/3   K061



1/3   K062



1/3   K069


1/3   K071





1/3   K083


1/3   K086
                                Petrol refining
                                industry
                                          Primary steel
                                          production industry
Steel finishing from
Iron and steel
production

Secondary lead
smelting operations

Chlorine production
from the mercury
cell process
                                          Distillation bottoms
                                          from aniline production

                                          Solvent washes and
                                          sludges from the
                                          production of inks,
                                          pigments, soaps, and
                                          stabilizers
Solvent extraction, fluidiied bed
incineration, stabilization
(nonwastewaters); incineration,
chromium reduction, chemical
precipitation, and filtering
(wastewaters)

High temperature metal* recovery for
high zinc subcategory, stabilization
for low line subcategory

Chromium reduction, chemical
precipitation, settling, filtering
(nonwastewaters, wastewaters)

Recycling (noncalcium sulfate
category); (nonwastewaters)

Acid leaching, chemical oxidation
sludge dewatering/acid washing
(nonwastewaters), chemical
precipitation and filtering
(wastewaters)

Liquid injection incineration
(nonwastewaters, wastewaters)

Liquid injection incineration
(nonwastewaters, wastewaters);
chromium reduction, chemical
precipitation, settling,
filtering (wastewaters)
                                                                  Data/fndustry-subnitted
                                                                  Data/EPA test
                                                                                                            Data/EPA test
Data/industry-submitted
                                                                                                            Data/industry-submit ted
                                                                  Data/industry-submitted
                                                                  Data/EPA test,
                                                                  transfer/K062
                                 Organics, metals,
                                 inorganics
Metals



Metala



Metals


Mercury





Organics


Organics, metals
         t:\docuinani\1 5254031.01 O25

-------
                                                LIST OF BOAT BACKGROUND DOCUMENTS AND ASSOCIATED BDAT(S)
             Waste Code/
Third   (Background Document)
  Industry or
Source of Waste
        BDAT(s)
  Actual Data
 or Transferred
     and
Origin of Data
     Types of
Wastes Regulated
 1/3   K087
 1/3   K099
 1/3   K101. K102
 1/3   K103, KIM
 1/3   K106
 1/3   K004-K008, K021
       K02S, K036, K060.
       K100 (no document
       prepared)
Tar sludge from
coking operations
2,4-Dichlorophenoxy-
acetic acid (2,4-D)
production
Production of
veterinary
Pharmaceuticals from
arsenic

AniIine/ni trobenzene
production
Sludges from the
mercury cell process
in chlorine production

Pigments, fluoro-
methane, nitrobenzene,
disulfoton, coking
and lead production
Rotary kiln incineration
(nonwastewaters);
chromium reduction, chemical
precipitation, settling,
filtering (wastewaters)

Chemical oxidation (nonwastewaters,
Wastewaters)
Rotary kiln incineration
(nonwastewaters); chemical
precipitation, settling,
filtering (wastewaters)

Solvent extraction, steam stripping,
and activated carbon adsorption
followed by incineration of the
solvent stream from extraction
(nonwastewaters, wastewaters)

Thermal recovery (retorting)
(nonwastewaters)
Chromiun reduction, carbon
adsorption; chemical oxidation
and metal precipitation
(nonwastewaters, wastewaters)
                                         Data/EPA test,
                                         transfer/K062
                                         Data/EPA collected
Data/EPA test,
transfer/K062
Data/EPA test





Data/industry-subrtitted



Data/industry-submitted
                                 Organics, metals
2,4-Dichlorophenoxy-
aceticacid. chlorinated
dibenzo-p-dioxins,
chlorinated dibanzofurBns

Organics, metals
Organics, inorganics
(cyanides)
Mercury
Metals, organics
 2/3   F006-F012. F019
Electroplating, heat
treating operations
Alkaline chlorination,
stabilization (nonwastewaters),
alkaline chlorination, chemical
precipitation, settling,
filtering (wastewaters)
Oata/industry-submit ted
Cyanides, metals
f:\documont\15254031.01.025

-------
                                                          LIST OF BOAT BACKGROUND DOCUMENTS AND ASSOCIATED BOAT(S)
                       Waste Code/
          Third   (Background Document)
                                  Industry or
                                Source of Waste
                                                           BOAT(s)
                                           Actual Data
                                          or Transferred
                                              and
                                         Origin of Data
                                      Types of
                                 Wastes Regulated
 I
tn
           2/3   K011. K013. KOK
           2/3   Cyanide P wastes
                 (P013. P021. P029
                 P030, P063. P074, P098.
                 P099, P104, P106. P121)
           2/3   F024
2/3


2/3   K009, K010
Inorganic pigments
(K002-K008)
           2/3   K023, K093. K094
                 U028. U069, U088,
                 U102, U107. U190

           2/3   K027. Kill. K112
                 K113, IC1H. K115.
                 K116, K221, U223
           2/3   K028, K029, K095
                 1C 096
                                Acrylonitrile
                                production

                                Cyanide P wastes
                                Chlorinated aliphatics
                                production
                                           Pigments production
                                           Acetaldehyde production
                                Phthalic anhydride
                                production
                                Toluene diisocyanate
                                production
                                1,1,1,-trichloroethane
                                production
Rotary kiln incineration
(Nonwastewaters)

Electrolytic oxidation, alkaline
chtori nation,  stabilization
(nonuasteuaters), alkaline chlorination,
chemical precipitation, settling and
filtration (uastewaters)

Rotary kfIn.incineration
(nonuasteuaters); rotary kiln
incineration,  lime and sulfide
precipitation, vacuum filtering
(uasteuaters)

Not established under 2/3
rule; see 3/3

Rotary kiln incineration
(nonuasteuaters); steam stripping,
biological treatment (wasteuaters)

Rotary kiln incineration
(nonuasteuaters and uastewaters)
Incineration or fuel substitution
(nonuasteuaters); direct incineration,
or carbon adsorption followed by
incineration or fuel substitution,
stabilization (wasteuaters)

incineration, stabilization
(nonuasteuaters); lime and sulfide
precipitation (wasteuaters)
                                                                                            Data/EPA test
                                                                                            Data/industry-submitted,
                                                                                            transfer/F006-F012. F019
                                                                                            Data/industry-submit ted,
                                                                                            transfer/K062
See 3/3
                                                                                            Transfer/K019.
                                                                                            Transfer/data from
                                                                                              Office of Water

                                                                                            Transfer/K024
                                                                                            Transfer/KOIS, K086,
                                                                                            F006
                                                                                            Transfer/K019,
                                                                                            Transfer/K062
Acrylonitriles, cyanides


Cyanides, metals





Organics, metals





See 3/3


Organics



Organics



Organics. metals .





Organics. metals
          l:\documont\15254O31 Ol 025

-------
                                                LIST  OF  BOAT  BACKGROUND DOCUMENTS AND ASSOCIATED BDAT(S)
             Waste Code/
Third   (Background Document)
                            Industry or
                          Source of Waste
                                 BOAT(s)
                                           Actual Data
                                          or Transferred
                                              and
                                         Origin of Data
                                      Types of
                                 Wastes Regulated
 2/3   K036, K038, K039,
       K040, P039. P040,
       P041, P043, P044,
       P062, P07. P085.
       P089, P094, P097.
       P109, Pill, U058.
       U087. U235

 2/3   KOA3
 2/3
K069 (Calcium
sulfate)
 3/3   0001
 3/3   0002
 3/3   0003
                          Organophosphorous
                          pesticide production,
                          e.g.,  disulfoton,
                          phorates, and others
                          P and  U wastes
2,4-Dichlorophenol
production

Secondary lead
smelting industry
                          Wastes having the
                          characteristic of
                          ignitability

                          Wastes having the
                          characteristic of
                          corrosivity

                          Wastes having the
                          characteristic
                          of reactivity
                         Rotary kiln incineration
                         (nonwasteuaters);  biological
                         treatment;  carbon adsorption
                         incineration (wastewaters)
Incinerator (nonwastewaters,
wasteuaters)

Stabilization (nonwastewaters);
chromium reduction, chemical
precipitation, settling, and/or
filtering (yastewaters)

Deactivation*  to remove ignitability,
or incineration/fuel substitution.
recovery for high TOC D001

Deactivation*  to remove corrosivity
                         Deactivation* of cyanides; alkaline
                         except for cyanides;  alkaline
                         chlorination (cyanides)
                                         Transfer/K037.
                                         Data/industry-submitted
                                                                                           Data/industry-submitted
Transfer/FOOo
and K062
                                                                  Information references
                                                                  Information references
                                         Information references.
                                         Industry submitted data,
                                         transfer/Office of Water
                                 Organics, organophos-
                                 pSons coipords, dioxirs
                                 and furans
Phenols, dioxins,
and furans

Metals
                                 Waste having the
                                 characteristic
                                 of ignitability

                                 Waste having the
                                 characteristic
                                 of corrosivity

                                 Wastes having the
                                 characteristics
                                 of reactivity
l:\documontU 5254031.01.025

-------
                                                LIST OF BOAT BACKGROUND DOCUNENIS AND ASSOCIATED BOAT(S)
             Waste Code/
Third   (Background Document)
  Industry or
Source of Waste
        BOAT(s)
  Actual Data
 or Transferred
     and
Origin of Data
     Types of
Wastes Regulated
 3/3   Arsenic, selenium, (0004, characteristic and
       0010, K031, K084, K101,
       K102, P010, P011, P012,
       P036. P038, P103, P1U,
       P204, P205, U136)
 3/3   Barium (0005, P013)
Pill wastes 1 K wastes
for arsenic and
selenium and wastes
from veterinary
Pharmaceuticals
production

Characteristic and
P waste for barium
Vitrification (nonwastewaters);
chemical precipitation (wastewaters)
Stabilization (nonwastewaters);
chemical precipitation
settling, filtration (wastewatert)
Data/industry-submitted
transfer/Office of Water
Arsenic, metals,
inorganics
Data/Office of Water.
Data/industry-submitted
Barium
 3/3   Cadmium (0006)
 3/3   Chromium (0007, U032)
 3/3   Lead (0008, K069,
       K100, P110, UUA-UK6)
 3/3   Mercury (0009, K071,
       K106, P065, P092,
       U1S1)
 3/3   Silver (0011, P099,
       P104)
Characteristic waste
for cadmium
Characteristic and
U wastes for chromium
Characteristic and
U&P wastes for lead,
and K waste from
lead smelting
operations

Characteristic and
U&P wastes for
mercury and K waste
from chlorine
production
Characteristic wastes
for siIver, and P
silver wastes
Stabilization, thermal recovery
(cadmium batteries) (nonwastewaters);
chemical precipitation, filtration
(wastewaters)

Chrcvniin reduction, chemical
precipitation, settling, filtration,
dewatering of solids (nonwastewaters
and wastewaters)

Stabilization/vitrification (non-
wastewaters); chemical precipitation,
flocculation, clarification, filtration,
and sludge thickening (wastewaters)
Data/industry-submitted,
transfer F006, K062
Transfer/K062
Data/industry-submit ted
Thermal processing, incineration
acid leaching, roasting, retorting
amalgamation, stabilization
(nonwastewaters); chemical
precipitation, filtration,
incineration, ion exchange,
carbon adsorption (wastewaters)

Recovery, stabilization
(nonuastewaters);
chemical precipitation, filtration
(wastewaters)
Data/industry-submit ted,
transfer/K071
Cadmium
Chromium
Lead, organometalUc
compounds
Metals. organonetaUic
compounds
Data/industry-submitted,
and transfer/F006/
Office of Water
                                                                                                                                    Metals
f:\documontV1S254031.01.025

-------
                                                           LIST OF  BOAT  BACKGROUND DOCUMENTS  AND ASSOCIATED  BOAT(S)
                        Waste Code/
           Third   (Background Document)
  Industry or
Source of Waste
        BOAT(s)
  Actual Data
 or Transferred
     and
Origin of Data
     Types of
Wastes Regulated
 i
00
            3/3   Thallium (P113.  P1U.
                  P115. U2K. U215.
                  U216. U217)
            3/3   Vanadium (P119.  P120)
            3/3   F002. F005
            3/3   F006
            3/3   F019
            3/3   F024
            3/3   F025
            3/3   F039 and associated
                  U&P wastes (Vol. A-E)
U&P thallum
wastes
U&P vanadium
wastes
Spent halogenated and
nonhalogenated
solvents
Sludges from
electroplating
operation
Sludges from the
chemical conversion
coating of aluminum
Production of
chlorinated aliphatic
hydrocarbons

Wastes from production
of chlorinated
aliphatic hydrocarbons
having carbon chain
linkage

Hultisource leachate
and U&P wastes
Recovery, stabilization
(nonwastewaters);
chemical oxidation, chemical
precipitation settling, filtration
(wastewaters)

Stabilization (nonwastewaters);
recovery, chemical precipitation
(wastewaters)

Incineration (nonwastewaters);
biological treatment, steam (tripping,
carbon adsorption . w«t air
oxidation/chemical oxidation
liquid extraction (wastewaterc)

Stabilization (nonwastewaters);
alkaline chlorination, chromium
reduction, chemical precipitation
(wastewaters)

Alkaline chlorination, stabilization
(nonwastewaters); alkaline
chlorination, chromium reduction,
chemical precipitation
(wastewaters)

Stabilization, incineration
(nonwastewaters)
Incineration (nonwastewaters)
biotreatment, steam stripping,
carbon adsorption, liquid
extraction (wastewaters)
See Footnote b.
Data/industry-submitted
Data/industry-submitted
Transfer/EPA data from
various sources
Transfer/KOoZ
Transfer/F006-F012
Data/EPA test
Transfer/K019, K001,
F039 (Vol. A)
Data/transfer/EPA data
from various sources and
EPA test
Metals





Metals



Organics





Metals, cyanides




Metals, cyanides





Metals, organics



Organics
Metals, inorganics,
organics
           (AdocumanlM S254O31.01.02S

-------
                                                LIST OF BOAT BACKGROUND DOCUMENTS AND ASSOCIATED BOAT(S)
Waste Code/
Third (Background Document)
3/3 K001, U051 (addendum)
3/3 K002-K008
3/3 IC011, K013, KOU
3/3 K015
3/3 K017
Industry or
Source of Waste
Wood preserving
industry
Pigment industry
sludges
Acrylonitrite,
production
Still bottoms from
distillation of
benzyl chloride
Production of
epichlorohydrin
BOAT(s)
Incineration
(nonwastewaters, wastewaters)
Chemical precipitation, stabilization
(nonwastewaters); alkaline
chlorination followed by chromium
reduction (wastewaters)
Wet air oxidation (wastewaters)
Incineration, stabilization
(nonwastewaters)
Incineration (nonwastewaters);
biotreatment (wastewatert)
Actual Data
or Transferred
and
Origin of Data
Data/EPA test
Data/transfer/industry,
K062, transfer/FOOo
Data/industry-sutmitted
Transf«r/K048-52. K087.
transfer/F039 (Volume A)
Transf«r/F039,
(Vol. A and C)
Types of
Wastes Regulated
Organics, metals
Metals, inorganics
Metals, organics
Organics, metals
Organics
 3/3   K021
 3/3   K073
 3/3   K022
 3/3   K025
 3/3   K026
Aqueous antimony
catalyst front
fluoromethane
production

Chlorine production
Bottoms, tars
from production
of phenol/acetone

Distillation
bottoms from the
production of nitro-
benzene
Tails from the produc-
tion of methyl ethyl
pyridines
Incineration (nonwastewaters);
biotreatment, steam stripping,
lime conditioning, sedimentation,
Filtration (wastewaters)

Incineration (nonwastewaters);
biotreatment, steam stripping,
filtration (wastewaters)

Chemical precipitation, vacuum
filtration (wastewaters)
Incineration (nonwastewaters);
liquid-liquid extraction,
steam stripping, carbon adsorption,
incineration of spent carbon
(wastewaters)

Incineration (nonwastewaters,
wastewaters)
Transfer/K019. K048-52.
F039 (Vol. A)
Transfer/r019,
transfer/FOJ9 (Vol. A)
Transfer/F039 (Vol. A),
K062
Transfer/previous EPA
incineration tests,
transfer/Kl03-K104
T ransfer/prev i ous
incineration tests
Metals, organics




Organics



Metals, organics



Organics





Organics
I :\docum*nt\l 5 254O31.01.0 25

-------
                                                          LIST OF BOAT BACKGROUND DOCUMENTS AND ASSOCIATED BOAT(S)
                                                                                                               Actual Data
                                                                                                              or  Transferred
Third
Waste Code/
(Background Document)
Industry or
Source of Waste
BDAT(s)
and
Origin of Data
Types of
Wastes Regulated
 I
•—•
o
           3/3   K028, K029,
                 K09S, K096
           3/3   K032-K034, K041-K042.
                 K08S, K097, K098.
                 K10S. D012-D017
           3/3   K035
           3/3   K036
           3/3   K037
           3/3   K044, K045, K047
           3/3   KOA6 (reactives)
Wastes from
production of
1,1.1-trichloroethane
Natogenated pesticides
and chlorobenzene
waste
Uastewater treatment
sludges from the
production of
creosote

Still bottoms from
toluene reclamation
distillation in the
production of
disulfoton

Wasteuater treatment
Sludges from the
Production of
Disulfoton

Manufacturing
explosives and lead-
based initiating
compounds

Lead-based initiating
compounds
Stabilization (nonwasteuaters);
biotreatment, steam stripping
carbon adsorption,
filtration (wasteuaters)

Incineration (nonwasteuaters)
biotreatment, steam stripping,
carbon adsorption, liquid
extraction incineration/wet
air oxidation/chemical
oOxidation (wastewaters)

Incineration (nonwastewaterg);
biotreatment (wastewaters)
Incineration (nonwasteuaters for
disulfoton)
Biological treatment (wastewaters)
Deactivation. settling and filtration,
alkaline precipitation (wastewaters)
Deactivation by chemical treatment or
specialized incineration followed
by stabilization (nonwastewaters);
chemical deactivation followed by
alkaline precipitation, settling,
and filtrating (wastewaters)
Transfer/f039 (Vol. A),
transfer/F024
Transfer/EPA data
Transf«r/K087
Transfer/K037
Data/EPA test
Data/industry-subroitted,
EPA
Data/industry-submitted
Transfer/K062
Organics, metals
Various halogenated
pesticides, chlorinated
nonbornane   deriva-
tives,  other organics
Organics
Organics
Organics, organo-
phosphorus
pesticides
Reactive wastes
Lead
          f:\docum.nt\15254031.Or025

-------
                                                LIST Of BOAT BACKGROUND DOCUMENTS AND ASSOCIATED BDAT(S)
             Waste Code/
Third   (Background Document)
  Industry or
Source of Waste
        BDAT(s)
  Actual Data
 or Transferred
     and
Origin of Data
                                                                               Types of
                                                                          Wastes Regulated
 3/3   K048-K052
       (addendum)

 3/3   K060
 3/3   K061
 3/3   K083
 3/3   K086
Petroleum refining
industry

Ammonia still lime
sludge from coking
operations

Emission control
dust/sludge from the
primary production of
steel in electric
furnaces

Distillation bottoms
from the production
of aniline
Wastes from cleaning
equipment used in
formulation of ink
from pigments, driers,
soaps, and stabilizers
containing chromium
and lead
Incineration, solvent extraction
(nonuastewaters)

Incineration (nonwasteuaters)
biological treatment (wastewaters)
Chemical reduction, chemical
precipitation (wasteuaters)
Incineration, stabilization
(nonwastewaters); liquid-liquid
extraction, steam stripping,
carbon adsorption, biological
treatment (wastewaters)

Incineration, chromium reduction,
chemical precipitation, filtration,
stabilization (nonuastewaters),
incineration, wet air oxidation or
chemical oxidation,  carbon
adsorption, biological treatment,
or steam stripping
Data/industry-submit ted
Transfer/Office of Water,
transfer/K087
Transfer/K062.
industry data
                                         Transfer/previous EPA
                                         incineration test. Transfer/
                                         F039 (Vol.  A)
                                         Data/EPA test,
                                         transfer/F006-F012.
                                         transfer/F039 (Vol.  A)
                                                                          Organics, metals.
                                                                          inorganics

                                                                          Organics,  inorganics
                                                                          Metals
                                 Organics, metals
                                 Organics, cyanides
                                 (inorganic)
'The Agency has promulgated a treatment  standard of Deactivation for wastes  exhibiting  the characteristic of Ignitability (D001), Corrosivity (0002), or
Reactivity (D003).  As part of  the  land disposal restrictions, treaters of these above-mentioned wastes are required to use a deactivation technology that
will remove the characteristic  for which the waste is hazardous.  Technologies that are applicable and demonstrated for treating these characteristic wastes
are listed in 40 CFR Part 268,  Appendix 6.

bThe F039 background document (Volumes A  through  E) contains treatment performance data from various sources such as the BOAT program, the Office of Water's
Industrial Technology Division,  the  National  Pollutant  Discharge Elimination System,  the Hazardous Waste  Engineering Resource Laboratories,  and other
sources.  The F039 background document presents  numerous technologies  as  BOAT.  For further information,  refer  to the  F039 background document. Volumes A
through E.
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