United States
                   Environmental Protection
Hazardous Waste Engineering
Research Laboratory
Cincinnati OH 45268
                   Research and Development
EPA/600/S2-88/011  Mar. 1988
SEPA         Project Summary
                   Waste Minimization  Audit
                   Report:  Case  Studies of
                   Minimization of Mercury-
                   Bearing  Wastes  at  a  Mercury
                   Cell Chloralkali Plant
                   Marvin Drabkin and Edwin Rissmann
                    The U.S. Environmental Protection
                   Agency (EPA) is encouraging hazard-
                   ous waste generators to develop pro-
                   grams in order to reduce the generation
                   of hazardous waste. To foster such
                   programs, the  Agency's Office of
                   Research and Development Hazardous
                   Waste Engineering Research Labora-
                   tory (ORD/HWERL) is supporting the
                   development and evaluation of a model
                   hazardous waste minimization audit
                   (WMA) procedure using the EPA hier-
                   archy of  waste minimizations (WM)
                   options, with source reduction being
                   more desirable and recycle/reuse less
                   desirable. Treatment options, although
                   not considered WM, are evaluated if
                   neither of the former alternatives  is
                   available.  The WMA procedure was
                   tested initially in several facilities in
                   1986. WMAs were conducted at gener-
                   ators of a number of generic hazardous
                   wastes, including corrosives, heavy
                   metals, spent solvents, and cyanides.
                    In 1987, the HWERL WMA program
                   concentrated  on ORD's top priority
                   RCRA K and F waste list. Audits were
                   conducted at  generators of K071 and
                   K106 wastes (mercury cell Chloralkali
                   plants), K048-K052 wastes (sludges
                   and solids from petroleum refining),
                   F002-F004 wastes (spent  solvents),
                   and F006 wastes (wastewater treat-
                   ment sludges from electroplating oper-
                   ations). This Project Summary covers
                   WMAs carried out at two mercury cell
                   Chloralkali plants. These audits were
                   aimed at developing WM options for
K071 and K106 wastes generated at
these plants (referred to as Plant No.
1 and Plant No. 2 in this study).
  During the WMAs at Plant No. 1 and
Plant No. 2, the audit team determined
that the mercury level in  the high
volume K071  waste (brine treatment
sludge) was too low to permit economi-
cal recovery and recycle of this pollu-
tant to the process. However, retorting
of the K106 waste (mercury-bearing
wastewater treatment sludge) for
mercury recovery and recycle is tech-
nically feasible and may be  economi-
cally viable from Plant No. 2.
  A total of  six source reduction
options for K071 waste were studied
by the audit team at Plant No. 1. All
but one were  ruled out because of
technical and/or economic considera-
tions. Only one source reduction option
(replacement of mercury cells with the
newer  membrane cell  technology) is
technically feasible  and showed an
attractive  payback (approximately 2
years)  when applied at Plant No. 1.
However, this option is highly capital
intensive (requiring an  approximately
$20 million investment at Plant No. 1),
even though the K071  waste is elim-
inated if this option were implemented.
  Treatment options, while not consid-
ered WM, were considered by the audit
team for detoxification of K071 waste
at Plant No. 1. A total  of three treat-
ment options were considered, two of
which appeared to be both technically
and economically feasible. It is believed

that implementation of  these two
options would enable the treated waste
to be delisted with resulting saving in
disposal costs ranging from $325,000
to $380,000 and payback period rang-
ing from 2 to 2.3 years.  Plant No.  2
had already decided to install a treat-
ment option to detoxify K071 waste.
  This Project Summary  was devel-
oped by  EPA's Hazardous  Waste En-
gineering Research Laboratory, Cincin-
nati, OH. to announce key findings of
the research project that is fully doc-
umented in a separate report of the
same title (see Project Report ordering
information at back).

  The  national policy objectives estab-
lished  under the  1984  Hazardous and
Solid  Waste Amendments  to  the
Resource Conversation and Recovery Act
of 1976 include the goal of reducing or
eliminating hazardous waste as expedi-
tiously as  possible.  Further, the  EPA
Report to Congress on minimization of
hazardous waste  (issued in 1986) pro-
vided  recommendations  for private
industry   on  waste  minimization
approaches. To promote waste minimi-
zation activities, the HWERL of the EPA,
ORD, has undertaken a project to develop
and test  a  WMA procedure. It is envi-
sioned that such  a procedure would be
useful to generators of hazardous waste
as they search for waste  minimization
alternatives. The present HWERL project
expands on an audit procedure developed
and tested  in 1986 by conducting addi-
tional  WMAs in  cooperating industrial
and government facilities. This project is
one of several current audit efforts being
supported by HWERL.
  This study presents the elements of a
WM program, of which the audit proce-
dure is a central component and includes
details of the WMA  procedure, its
development, and its final recommended
form. A  case  study is presented  using
this WMA  procedure and  covers audits
performed at two mercury cell chloralkali
plants that generate listed wastes K071
and  K106.  Findings and  conclusions
resulting from these audits are presented

Description of the WMA
  The  function of the WMA procedure
is to force  the use of an  orderly step-
by-step  procedure  for  conducting an
audit at  a  host  site.  The initial WMA
procedure was developed in earlier work.
and  was  further  refined  during the
course of the present EPA-sponsored
audit effort. This procedure is applicable
to the development of both categories of
WM  options  (source reduction  and
recycling/reuse) as well as the develop-
ment of treatment options.
  The team employed in carrying out the
audit described in the full  report  was
composed entirely of  employees of an
outside consulting/engineering  firm.
Following  selection of the host facility
there  were  eight sequential  steps
executed by the audit team:

  1.  Preparation for the audit.

  2.  Host site pre-audit visit.

  3.  Waste stream  selection.

  4.  Host site waste minimization audit

  5.  Generation of WM options.

  6.  Preliminary WM options evaluation
     (including preparation of prelimi-
     nary cost estimates) and ranking of
     options in three  categories (effec-
     tiveness, extent of current use, and
     potential for future application).

  7.  Presentation, discussion, and joint
     review of  options with plant

  8.  Final report  preparation  and pres-
     entation to host site management.

This procedure was followed in carrying
out the WMAs summarized below.

Results  of the WMAs
Conducted at  Generators of
K071 Waste: Audits at Two
Mercury Cell Chloralkali Plants
  Mercury cell chloralkali plants produce
chlorine, with sodium  hydroxide (NaOH)
and  potassium  hydroxide (KOH) as co-
products depending on whether  sodium
chloride (NaCI) or  potassium chloride
(KCI) brine is used as feed  to the mercury
electrolytic cells employed in the process.
Listed  waste K071  generated by these
plants is defined  in 40CFR 261.32 as

 • K071: Brine purification muds from
   the mercury cell process in chlorine
   production, where separately prepur-
   ified brine is not used.
The results of the WMA on K071 waste
are presented below.

  The two mercury cell plants which
acted as the host sites in this case study
are both located  in the Southeast and
designated as Plant No. 1 and Plant No.
2. Plant No. 1 has a narnpplate capacity
of 138,000 metric tons of chlorine per
year. This  plant operates two  parallel
production lines—one producing  310
metric tons per day of  NaOH and the
other producing 246 metric tons per day
of KOH  as co-products. Louisiana rock
salt received by barge is the raw material
used. The plant generates approximately
5,000 tons per year of  K071  waste
(mercury-bearing  brine saturator  insol-
ubles and brine purification wastes). All
of these wastes are currently sent offsite
to a hazardous waste landfill. Figures 1
and 2 are typical schematics of the plant
and brine purification operations respec-
tively, for the NaCI-based process.
  Plant No. 2 has a nameplate capacity
of 116,000 metric  tons per year of
chlorine. The plant operates one produc-
tion line which also has a capacity of 354
metric tons per day of NaOH as a co-
product. Plant No. 2 uses Louisiana rock
salt as feedstock  for this process. This
plant generates  approximately 5,400
tons per year of K071  waste which  is
currently sent offsite to hazardous waste
  While K071 is a large-volume waste,
the audit team  determined that the
mercury  level (typically  in the 25  ppm
range) was too  low to permit economic
recovery and recycle of this pollutant
thus ruling out  recycle/reuse as a WM
option. Prepurification of the NaCI brine
feed to the electrolytic cells at Plant No.
1 (in order to eliminate the main  sources
of this waste—the brine saturator insol-
ubles and brine purification  sludge)
proved to be an  uneconomical  source
reduction option. A total of seven source
reduction options for this waste were
considered by the audit team. Six of these
had to be ruled out  because of unfavor-
able economics and/or unproven tech-
nical feasibility  of  the  process. The
seventh option (replacement  of the
mercury electrolytic cells with the newer
 This plant is currently undergoing a revamp in its
 brine purification operations in order to achieve a
 delistable K071 waste, i.e., reduce mercury levels
 in this waste low enough (as a result of the revised
 plant treatment) to attain a level of <12 ppb for
 this pollutant in EP-tox leachate thus enabling EPA
 to delist this waste.

                       NaCI (Rock Salt)-
                           Depleted NaCI Brine
      Sales •+—
                                                       Brine Area
Figure  1.    NaOH/chlorine production process.
                                                                            50% NaOH Solution
Figure 2.    NaCI brine treatment system.
                                                                    Brine Return
                                                                               Sludge Pads
                                                                                    K071 Sludge
                                                                                Brine Sludge
                                                                     C/2 to Processing
                                               C/2 Condensate    HCI
                                               from Chlorine
membrane cell technology—the  indus-
try's  process of  choice  currently)
appeared to have an attractive payback
period (approximately 2 years) primarily
due  to  significantly  more  economical
chlorine  production technology and to a
much smaller extent, due to elimination
of the K071  hazardous waste disposal
cost.  However, a retrofit of membrane
                        cell technology requires  Plant No. 1 to
                        invest  approximately  $20  million for
                        installation of this option. An investment
                        of this magnitude  is  unlikely  to  be
                        considered at this time because  of the
                        current depressed economics  of the
                        chloralkali industry.
                          While K071 waste treatment  is not
                        considered a WM option, the audit team
                                        determined that Plant No. 1  has several
                                        technically viable treatment options with
                                        reasonable payback periods available for
                                        K071 waste detoxification. One or more
                                        of these options, if implemented, has the
                                        potential for detoxifying the K071 waste
                                        thus allowing it to be delisted  by EPA
                                        with the  resulting  non-hazardous waste
                                        being able to be placed in a local sanitary

landfill. The  plant is  studying these
alternatives at the present time. Figures
3  and 4  depict two K071  treatment
options evaluated  by the  audit team
which  appear to be technically feasible
and have attractive payback periods (<3
  Table 1  summarizes  all of the K071
waste  reduction and treatment options
studied by the audit team for potential
application at Plant No. 1. One source
reduction option (highly capital intensive)
and  two  treatment  options meet the
criteria for  techniccal  and economic
feasibility  (at the preliminary evaluation
stage)  at this time. The plant  is giving
serious consideration to a  significant
revision  in  the present K071  waste
treatment and  disposal  operation  (as
must all of the 14 mercury cell chloralkali
plants  faced with this  problem) due to
the  pending  imposition of EPA Best
Demonstrated  Available Technology
(BOAT) requirements  for disposal in
hazardous waste landfills by the summer
of 1988.
                            Results of the WMA
                            Conducted at Generators of
                            K106 Waste: Audits at Two
                            Mercury Cell Chloralkali Plants
                              The two mercury cell chloralkali plants
                            that acted as host sites for WMAs on
                            minimization of  K071  waste,  were
                            audited for listed waste K106, defined
                            in 40CFR 261.32 as follows:

                            • K106:  Wastewater treatment sludge
                               from  the mercury cell process  in
                               chlorine production.

                            The results of the WMA on K106 waste
                            are presented below.

                              The K106 waste is a low volume waste
                            being generated at Plant No. 1 at the rate
                            of about 20 tons per year and at Plant
                            No. 2 at the rate of about 75 tons per
                            year.  This material (a wastewater  treat-
                            ment sludge in the form of a 0.5 to 1.5
                            percent  mercury  content filter cake) is
                            presently being sent offsite together with
                            K071 waste to hazardous waste landfills.
              The audit team determined that source
             reduction options were not available to
             reduce or eliminate the wastewaters that
             are  the source of this waste  since
             generation of these  wastewaters is
             unavoidable at mercury cell  chloralkali
             plants. A recycle/reuse option to recover
             and recycle the mercury pollutant from
             the wastewater is commercially proven
             but not economically feasible at  either
             of these plants. A recycle/reuse option
             is available to  recover  the  elemental
             mercury from the wastewater treatment
             sludge  using  a retorting process. This
             process is technically feasible and small-
             scale tests on Plant No. 1  filter cake have
             determined that the retorted residue is
             low  enough in mercury so that EP-tox
             leachate can pass EPA delisting require-
             ments. However, the cost of  recovering
             the relatively small amount of  mercury
             (<0.2 tons per year)  from Plant  No.  1
             K106 waste appears to make  this option
             economically unattractive. The  recover-
             able  mercury  from Plant  No.  2  K106
             waste (approximately  1.5 tons per year)
             may make the retorting option econom-
  Depleted Brine from
     Mercury Cells
                                         Treated. Purified
                                       Brine to Mercury Cells
                                 Brine Treatment
                                 and Clarification,
                                 Filter Backwash
                                Solids Clarification
                               ' Slurry
                                      '      '
                                      / Tank
                       |   | Existing Process
                             Proposed Process
   Clarifier '/A
'/Thickener '/\
, Underflow

/ 'Rotary /
'/, Filter^
Filter Cake IK071
To Hazardous
                                                                  Recycled Water
                                                                  from Wastewater
                                                                  Treatment System
, Horizontal Vacuum
 Belt Filter/Washer '
                                                                         Washed Non-Hazardous Filter
                                                                        Cake to Sanitary Landfill Disposal
Figure 3.
Proposed water washing process for NaCI saturator insolubles.

                                                        Wash Water
                                                       to Wastewater
                                                      Treatment System

   Depleted Brine
   from Mercury Cells
                                       Recycled Brine
Treated, Purified NaCI or
KCI Brine to Mercury Cells
                                              NaCI or KCI Brine Treatment Hot Process Treatment
                                                 and Clarification. Filter
                                                   Backwash Solids
     Solids (NaCI Brine Only)
                           NaCI Saturator Insolubles
                           (KCI Saturator Insolubles are
|    | Existing Process

r773 Proposed Process
\ZZA Modifications
                   To Water Washing
                                 Wash Water
                                 Waste water
                               ,  Treatment
                Washed Non-Hazardous Filter Cake
                to Sanitary Landfill Disposal
Figure 4.    Proposed sulfide precipitation option for removal of entrained mercury from the K071 brine purification wastes.
 Table 1.    Summary of Postulated Options for Minimization of Listed Waste K071 at Plant No. 1
Reduction of depleted
brine dissolved sulfate
level to minimize satura-
tor insolubles genera-
Use of prepurified salt
feed stock.
Use of solar salt as a feed
Remo val of mercury from
depleted brine prior to
brine resaturation, using
sulfide precipitation with
disposal of mercury sul-
fide waste.
Type of
Reduce generation rate ofsaturator
insolubles portion of K071 waste
by as much as one-third. Save
significant labor cost currently
involved in periodic cleanout of
Essentially complete elimination of
mercury-contaminated K071
waste generation in NaOH
Significant reduction of mercury-
contaminated K071 generation in
NaOH production.
Essentially complete elimination of
mercury-contaminated K071
waste generation in NaOH
Depleted brine side stream treatment
needed to reduce dissolved sulfate
results in excessive precipitant cost
as well as large additional generation
of mercury-contaminated wastes.
Unacceptable economics.
Unacceptable economics.
Commercially unproven process;
creation of another K071 waste;
unacceptable economics.

Table 1.    Continued
0(1 Kb)
Removal 'of mercury from
depleted brine prior to
brine resaturation using
sulfide precipitation, fol-
lowed by mercury retort-
ing and recovery from
mercuric sulfide waste.
Removal of mercury from
depleted brine prior to
brine resaturation using
ion exchange resin.
Conversion of mercury
electrolytic cells to mem-
brane electrolytic cells.
Type of
Same as D(1)fa).
Same as D(1)(a).
Complete elimination of all
mercury-bearing streams results in
elimination of K071 and K106
wastes; preliminary economics
indicate acceptable payback period
(~2 years). Membrane technology
commercially proven.
Commercially unproved process;
unacceptable economics.
No commercially available resin
available for handling harsh depleted
brine environment without extensive
pretreatment for chlorine removal;
limited resin capacity and allowable
brine flow rate require very large
resin beds (unacceptable eco-
Detailed feasibility study using defin-
itive base costs may show much
worse payback than preliminary
estimate. Space requirements for
auxiliary equipment may be

  (1)      Use of a washing process
          to reduce the level of
          mercury in the K071 sat-
          urated  insolubles below
          12  ppb,  enabling  this
          waste to be delisted.
Treatment   Simple, commercially proven pro-
            cess that would allow delisting of
            a large  portion of K071  waste.
            Favorable payback period (~2
            years). Space availability at plant is
            not a problem.
Potential delay in  achieving EPA
delisting because of lengthy proce-
dure involved.
  (2)      Same as (1) for saturator
          insolubles coupled with
          NaSH treatment process
          for brine purification
          muds, enabling delisting
          of the entire K071 waste
Treatment   Same as (1) for saturator insolu-
            bles; add/ton of process for brine
            muds still shows favorable payback
            period (2.3 years). Space availabil-
            ity at the plant for a combined
            treatment process is not a problem.
Sulfide  treatment  step  for brine
purification muds is  commercially
unproven. Lack of proven treatment
process could delay EPA delisting of
the entire stream until adequate body
of process data is available.
  (3)      Same as (1) for saturator
          insolubles coupled with
          Vulcan Treatment Pro-
          cess for brine purifica-
          tion  muds,  enabling
          delisting  of the  entire
          K071 waste stream.
Treatment   Same as (1) for saturator insolu-
            bles. Vulcan process is commer-
            cially proven and is expected to be
            BOAT for K071 waste. Space avail-
            ability at plant for combined treat-
            ment process is no problem.
Economics  of  Vulcan  process  for
combined NaCI and KCI brine stream
purification  muds appears unfavor-
able at this time. Vulcan process may
also generate higher TDS in effluent
from Plant  No. 1 than State will
ically feasible with  a payback period
(based  on a  preliminary estimate) of
about  3  years and  savings  of  about
$60,000 annually in waste disposal cost.
  While treatment is not considered as
WM, the audit team  studied  a treated
option (still in the experimental stage) for
solidification/stabilization of the K106
waste  at either Plant No. 1 or Plant No.
2 using lime  kiln or cement  kiln  dust.
Preliminary  results  of  tests on the
solidified  product  indicate that this
material may be able to pass the EPA
delisting requirement for mercury (<12
       ppb  in  the EP-tox  leachate). Payback
       period for the stabilization equipment
       involved would be less than 6 months
       and  savings  in  waste  disposal costs
       would be $4,500 and $55,000 per year
       for Plant No.  1  and  Plant No.  2,
         Table 2 summarizes the  K106 waste
       MW and treatment options evaluated by
       the audit team at Plant No. 1 and Plant
       No. 2. There appears to  be only one
       technically feasible WM option (recycle/
       reuse) for this waste involving retorting
       of the K106  filter cake for  elemental
    mercury recovery. This  option  appears
    uneconomical at Plant No. 1  and margi-
    nally economical at Plant No. 2 in terms
    of incremental investment  payback

Table 2.     Summary of Postulated Options for Minimization of Listed Waste K106 at Plants No. 1 and No. 2
 Type of
Extensive pretreatment of brine
required in order to safeguard resins
capacity to remove mercury. Unac-
ceptable economics.
  (a)      Ion exchange treatment
          of raw wastewater  for
          removal and recovery of
          mercury (applicable to
          both Plants No. 1 and No.
                          Recycle/     Process  demonstrated commer-
                          reuse        dally. Capable of achieving neces-
                                       sary mercury  level in effluent
                                       discharged under NPDES. Mercury
                                       can be recycled to mercury cell
                                       system in ionic form without having
                                       to reclaim the metal.
  (b)      Retorting of K106 waste
          to recover metallic mer-
          cury for recycle to mer-
          cury cells at Plant No. 1.
                          Recycle/     Process  demonstrated commer-
                          reuse        dally for hydrazine-based waste-
                                       water treatment sludge. Capable of
                                       producing residue  low enough in
                                       mercury to allow delisting by EPA.
                                       Metallic mercury recovered by
                                       retorting can be recycled to mer-
                                       cury cells.
                                                Unacceptable  economics unless
                                                recovery process throughput can be
                                                increased substantially. Plant No. 1
                                                is applying for conditional delisting
                                                of this  waste in  spite of negative
  (c)      Solidification/stabiliza-
          tion of K106 waste in an
          insoluble  matrix  fol-
          lowed by  disposal by
          Plant No.  1 as a  non-
          hazardous  waste (once
          delisted by EPA).
                          Treatment    Simple,  inexpensive  process to
                                       install and operate (favorable pay-
                                       back period). Once waste is delisted
                                       by EPA, can be placed in a nearby
                                       sanitary landfill.
                                                Process not  commercially proven.
                                                Will require a large body of opera-
                                                tional data to obtain EPA approval for
Same as (b) for Plant No.
Recycle/     Process has been in commercial
reuse        use in several mercury cell chlo-
             ralkali plants for sulfide-based
             wastewater treatment sludge. Rec-
             overed metallic mercury can  be
             recycled to mercury cells. Capable
             of producing residue low enough
             in mercury to allow delisting  by
             EPA.  Could have  favorable  eco-
             nomics (payback  period) due  to
             potentially high cost of K106 dis-
             posal once it cannot be combined
             with K071 waste (when  the latter
             is delisted at  Plant No. 2) lor
             shipment to the hazardous waste
                         May require extensive stack emis-
                         sions monitoring system for mercury
                         andSOi emissions.
Same as (c) for Plant No.
Treatment    Same as (c).
                         Same as (c).

     M. Drabkin andE. Rissmann are with Versar, Inc., Springfield, VA 22151.
     Harry F. Freeman is the EPA Project Officer (see below).
     The complete report, entitled "Waste Minimization Audit Report: Case Studies
       of Minimization of Mercury-Bearing Wastes at a  Mercury Cell Chloralkali
       Plant," (Order No. PB 88-166 798/AS; Cost: $19.95, subject to change) will
       be available only from:
            National Technical Information Service
            5285 Port Royal Road
            Springfield, VA 22161
            Telephone: 703-487-4650
     The EPA Project  Officer can be contacted at:
            Hazardous Waste Engineering Research Laboratory
            U.S. Environmental Protection Agency
            Cincinnati, OH 45268
United States
Environmental Protection
Center for Environmental Research
Cincinnati OH 45268
  PERMIT No G-35
Official Business
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