United States
Environmental Protection
Agency
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).
Introduction
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
below.
Description of the WMA
Procedure
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
visit.
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
personnel.
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
follows:
• 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
landfills.*
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)-
Vent
Depleted NaCI Brine
Sales •+—
Compression
Brine Area
Resaturated
NaCI
Brine
Cellroom
NaOH
50%
Boilers
Figure 1. NaOH/chlorine production process.
C/J
Gas
Chlorine
Liquiiaction
C/2
Liquid
Sales
Electricity
50% NaOH Solution
Sales
NaCI
NaCI
Saturators
K071
Sludge
NaOH
Figure 2. NaCI brine treatment system.
Brine Return
Reaction
Tank
NaCI
Sludge Pads
K071 Sludge
Brine Sludge
NaCI
Clarifier
Brine
Sludge
HCI
Filters
Vacuum
Dechlorination
C/2 to Processing
Depleted
Brine
Cellroom
C/2 Condensate HCI
from Chlorine
Processing
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
years).
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-
Dechlorinated
Depleted Brine from
Mercury Cells
Rock
Salt
Recycled
Brine
Brine
Saturators
Saturator
Insolubles
Solids
Water
Makeup
Treated. Purified
Brine to Mercury Cells
Brine Treatment
and Clarification,
Filter Backwash
Solids Clarification
Hot
Process
Treatment
Solids
Dilute
Brine
Recycle
' Slurry
Preparation
Tank
7/7777,
' '
Head
/ Tank
Underflow
Solids
LH1
Legend
| | Existing Process
Proposed Process
Modifications
Clarifier '/A
'/Thickener '/\
1
, Underflow
Solids
/ 'Rotary /
/Vacuum/
'/, Filter^
Filter Cake IK071
To Hazardous
Ll/acto
Recycled Water
from Wastewater
Treatment System
Landfill
Disposal
, Horizontal Vacuum
Belt Filter/Washer '
Washed Non-Hazardous Filter
Cake to Sanitary Landfill Disposal
Figure 3.
Rocks,
Trash
Proposed water washing process for NaCI saturator insolubles.
4
Wash Water
to Wastewater
Treatment System
-------
Dechlorinated
Depleted Brine
from Mercury Cells
Recycled Brine
Resaturated
Treated, Purified NaCI or
KCI Brine to Mercury Cells
NaCI or KCI Brine Treatment Hot Process Treatment
and Clarification. Filter
Backwash Solids
Clarification
Solids (NaCI Brine Only)
NaCI Saturator Insolubles
(KCI Saturator Insolubles are
Negligible)
Legend
| | Existing Process
r773 Proposed Process
\ZZA Modifications
To Water Washing
Process
Wash Water
to
Waste water
, Treatment
System
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
Option
A
B
C
D(1Xa)
Description
Reduction of depleted
brine dissolved sulfate
level to minimize satura-
tor insolubles genera-
tion.
Use of prepurified salt
feed stock.
Use of solar salt as a feed
stock.
Remo val of mercury from
depleted brine prior to
brine resaturation, using
sulfide precipitation with
disposal of mercury sul-
fide waste.
Type of
Option
Source
reduction
Source
reduction
Source
reduction
Source
reduction
Advantages
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
saturators.
Essentially complete elimination of
mercury-contaminated K071
waste generation in NaOH
production.
Significant reduction of mercury-
contaminated K071 generation in
NaOH production.
Essentially complete elimination of
mercury-contaminated K071
waste generation in NaOH
production.
Disadvantages
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.
Potential
Savings
l$/yr)
-------
Table 1. Continued
Option
0(1 Kb)
0(2)
E
Description
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
Option
Source
reduction
Source
reduciton
Source
reduction
Advantages
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.
Disadvantages
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-
nomics).
Detailed feasibility study using defin-
itive base costs may show much
worse payback than preliminary
estimate. Space requirements for
auxiliary equipment may be
unavailable.
Savings
($/yr)
600.00C
(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
stream.
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
allow.
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 $55,000 per year
for Plant No. 1 and Plant No. 2,
respectively.
Table 2 summarizes the K106 waste
MW and treatment options evaluated by
the audit team at Plant No. 1 and Plant
No. 2. There appears to be only one
technically feasible WM option (recycle/
reuse) for this waste involving retorting
of the K106 filter cake for elemental
mercury recovery. This option appears
uneconomical at Plant No. 1 and margi-
nally economical at Plant No. 2 in terms
of incremental investment payback
period.
-------
Table 2. Summary of Postulated Options for Minimization of Listed Waste K106 at Plants No. 1 and No. 2
Option
Description
Type of
Option
Advantages
Disadvantages
Extensive pretreatment of brine
required in order to safeguard resins
capacity to remove mercury. Unac-
ceptable economics.
Potential
Savings
<$/yr)
(a) Ion exchange treatment
of raw wastewater for
removal and recovery of
mercury (applicable to
both Plants No. 1 and No.
21.
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
economics.
(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
delisting.
4,500
Id)
Same as (b) for Plant No.
2.
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
landfill.
May require extensive stack emis-
sions monitoring system for mercury
andSOi emissions.
60.000
(e)
Same as (c) for Plant No.
2.
Treatment Same as (c).
Same as (c).
55,000
-------
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
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
BULK RATE
POSTAGE & FEES P/
EPA
PERMIT No G-35
Official Business
Penalty for Private Use $300
EPA/600/S2-88/011
0CQ1941 HWER GN
LIBRARY REGION V
230 S DEARBORN ST
CHICAGO
60604
•trU.S GOVERNMENT PRINTING OFFICE 1988-548-013/8
------- |