625582018
vvEPA
United States
Environmental Protection
Agency
Industrial Environmental Research
Laboratory
Cincinnati OH 45268
            Technology Transfer
Environmental Pollution
Control Alternatives:

Sludge  Handling,
Dewatering, and Disposal
Alternatives for the
Metal Finishing  Industry

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Technology Transfer                        EPA 625/5-82-0?F
Environmental Pollution
Control Alternatives:

Sludge  Handling,
Dewatering,  and Disposal
Alternatives for the
Metal Finishing Industry
October 1982
                   U.S. Environmental Protection Agency
                   Region V. '/v-.ry
                   230 South Doaibcrn Street
                   Chicago, Illinois  60604
Technical content of this report was provided by the
Industrial Environmental Research Laboratory
Cincinnati OH 45268

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                     This alternatives report was prepared by Centec Corporation of Reston VA for
                     the Industrial Environmental  Research Laboratory's Nonferrous Metals
                     and  Minerals Branch in Cincinnati OH. The EPA Project Officer is
                     Alfred B. Craig, Jr.

                     EPA thanks the following companies and organizations for providing
                     information and assistance: Barrett Centrifugals, Chemical Waste Manage-
                     ment, Inc., Industrial Filter and Pump Manufacturing Company, Komline-
                     Sanderson, Lenser America, Inc., SCA Services Company, and William  R.
                     Perrin Company.

                     Photographs were provided by Aqualogic® Inc., Industrial Filter and Pump
                     Manufacturing Company,  Komline-Sanderson, and D. R. Sperry & Co.

                     The  contact for further information is:

                     Nonferrous Metals and Minerals Branch
                     Industrial  Environmental  Research Laboratory
                     U.S. Environmental Protection Agency
                     Cincinnati OH  45268
                     This report has been reviewed in accordance with the U.S. Environmental
                     Protection Agency's peer and administrative review policies and approved for
                     presentation and publication.
                     COVER PHOTOGRAPH: Recessed plate filter press with in-ground bin
                     to receive discharged cake
U,S.  Environmental  Protsction Agency

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Contents                       1 • Overview	   1

                                   2. Resource Conservation and Recovery Act	   4
                                       Regulatory Framework	   4
                                       Exclusion from RCRA	   6
                                           Reducing the Waste Generation Rate	   6
                                           Seeking Nonhazardous Status	   6
                                       Regulatory Requirements	   6
                                           Transporters of Hazardous Wastes	   6
                                           Treatment,  Storage, and  Disposal Facilities	   7

                                   3. Hazardous Waste Disposal Sites	   8
                                       Landfill Design	   8
                                       Waste Identification Procedure  	   8
                                       Disposal Cost Factors	   8
                                       Pretreatment Capabilities	  10

                                   4. Reducing Sludge  Generation and Cost of Disposal	  11
                                       Reducing Sludge Generation	  11
                                           Waste Composition	  11
                                           Water Use	  12
                                           Treatment Processes	  12
                                       Sludge Dewatering	  14
                                       Sludge Segregation	  16

                                   5. Sludge  Dewatering Equipment	  18
                                       Filter  Presses	  19
                                           The Equipment	  19
                                           Determining Applicability	  20
                                           Costs	  21
                                       Vacuum Filters	  22
                                           The Equipment	  22
                                           Determining Applicability	  24
                                           Costs	  25
                                       Basket Centrifuges	  26
                                           The Equipment	  26
                                           Determining Applicability	  27
                                           Costs	  27
                                       Pressure Belt Filters	  29
                                           The Equipment	  29
                                           Determining Applicability	  30
                                           Costs	  30
                                       Evaluating the Cost for Sludge Dewatering Alternatives	  33

                                   References	  35
                                                                                                    in

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Illustrations                   Figures
                                    1. Hazardous Wastes from Electroplating Operations	     5
                                    2. Influence of Wastewater Heavy Metal  Concentration on Sludge
                                       Volume	    11
                                    3. Sludge Generation Factors for Alternative Chromium Reduction
                                       Processes	    13
                                    4. Sludge Volume versus Solids  Concentration	    14
                                    5. Recessed Plate Filter Press: (a) Unit and Auxiliaries Needed for
                                       Sludge Dewatering and  (b) Annual Sludge Disposal Cost	    15
                                    6. Plate-and-Frame Filter Press	    20
                                    7. Recessed Plate Filter Presses: Unit Prices	    20
                                    8. Filter Press Dewatering Systems: Annual Sludge Disposal Costs ...    21
                                    9. Rotary Vacuum Filter: (a) Basic Principle of Continuous Rotary
                                       Filtration, (b) Filter Cake Capacity and  Cake Dryness (from  Filter
                                       Leaf Test), and (c) Scale-Up Performance	    23
                                   10. Rotary Vacuum Filters: Unit Prices and Power Requirement. ...    24
                                   11. Rotary Vacuum Filters: Annual Sludge  Disposal Costs	    25
                                   12. Basket Centrifuge	    26
                                   13. Basket Centrifuges: (a) Large Unit Price and Hydraulic Drive Horse-
                                       power and (b) Small Unit Price	    27
                                   14. Basket Centrifuge Systems: (a) Dewatering System with Auxiliary
                                       Equipment and (b) Annual Sludge  Disposal Costs	    28
                                   1 5. Pressure  Belt Filter	    29
                                   16. Pressure  Belt Filter: Unit Price and Power Requirements	    30
                                   1 7. Pressure  Belt Filter System: Annual Sludge Disposal Cost	    31

                                   Tables
                                    1. Structure of  RCRA Subtitle C  Regulations	     4
                                    2. Four Hazardous Waste Characteristics	     5
                                    3. Extraction Procedure Toxicity  Limits	     6
                                    4. Typical Secure Chemical Landfill Sites: Summary of Costs	     9
                                    5. Sludge Generated and Sludge  Disposal  Volume for Electroplating
                                       Waste Treatment System	    12
                                    6. Dewatering  Equipment for Electroplating Sludge:  Typical  Per-
                                       formance Characteristics	    18
                                    7. Performance  of Dewatering Equipmentfor Electroplating Sludge ...    19
                                    8. Comparative Total  Investment and Annual Operating Costs for
                                       Sludge Dewatering	    32
                                    9. Economic Evaluation of Precoat Rotary Vacuum Filter Sludge Dis-
                                       posal  Alternative	    33
                                   10. Sludge Disposal Under Four Dewatering Alternatives: Analysis of
                                       Annual Costs	    34
IV

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1.  Overview
Under regulations implementing the
Clean Water Act of 1977 (Public
Law 95-217) metal finishing facil-
ities may be required to treat
spent process wastewaters to
remove regulated pollutants before
the wastewaters are discharged.
Treatment for heavy metal pollutants
generally consists  of reducing the
solubility of the metals, then
separating the resulting precipitants
from the wastewater. Consequently,
the treatment yields a solid waste,
or sludge, containing a high con-
centration of potentially harm-
ful or toxic substances. This sludge
must be disposed  of in a manner
that ensures that the pollutants,
once removed from the wastewater,
will not pose a threat to the
environment.

Recognizing the increased rate of
solid waste generation and the need
for environmentally safe disposal,
the U.S. Congress included provisions
for solid waste disposal in the Re-
source Conservation and Recovery
Act (RCRA) of 1976 (Public Law
94-580). Subtitle C of RCRA contains
provisions for hazardous waste
management. It directs the U.S. En-
vironmental Protection  Agency
(EPA) to identify those  wastes that
are hazardous, and to establish
national standards for generators and
transporters of hazardous wastes
and for operators of hazardous waste
management facilities involved
in the treatment, storage, and dis-
posal of these wastes.

The EPA has classified the following
metal finishing wastes as hazard-
ous materials:1

• Plating baths and the sludge
  accumulated in these baths
• Stripping and cleaning solutions
• Sludge resulting from wastewater
  treatment

Metal finishing shops disposing
of any of these wastes are regulated
by the RCRA standards. Under
RCRA, EPA holds waste generators
responsible for the ultimate safe
disposal of their wastes. Waste gen-
erators are also required to keep
records, use proper labels and
containers, and keep a manifest sys-
tem to document proper disposal.

The more stringent control of
hazardous waste disposal  means
that plating shops may have difficulty
in finding licensed disposal facili-
ties, and may incur higher prices for
hauling and disposal than  if their
wastes were nonhazardous.

Hauling costs depend on the distance
to the disposal site and the size of
the load. Haulers typically use
trucks designed for loads of 40,000
Ib (18,000 kg), or 5,000 gal (19,000 L);
they can transport liquids  or solids.
A partial  load would be charged
the same price as a full load.  Prices
for long hauls  are in the order
of $3 to $5 per loaded mile for the
5,000-gal (19,000-L) load, based on
the distance one way.3 A 300-mi
(480-km) trip,  therefore, would cost
$0.18/gal to $0.30/gal of  waste,
assuming the truck had a full load.
Because there are so few  dis-
posal sites, long-distance  hauling  is
becoming the rule, not the exception.

Disposal facilities operating state-
of-the-art secure chemical landfills
charge according to volume, type
of waste, and  type of container.
Disposal of drum quantities is by far
the most expensive. Fees at disposal
sites range from $25 to $50 for
each drum that requires burial in the
site. The equivalent cost per
gallon would be $0.60 to  $1.20,
based on 42-gal (159-L) drum capac-
ity. Adding drum and hauling costs
could bring the total disposal
cost to $100 per drum.

Bulk liquids, which include dilute
sludges and spent process  baths, are
less expensive to dispose  of than
drum quantities; however,  the
disposal cost includes the cost for
solidifying the waste before it
is placed in the landfill site. Costs
range from $0.25/gal to $0.75/gal.
                                                                       "All costs in this report are in 1981 dollars.

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Elevated installation of recessed plate filter press
For dewatered sludge, which is
placed untreated in the landfill site,
disposal cost ranges from $0.20/gal
to $0.50/gal.

The hazardous waste generator
has two alternatives for reducing the
cost of disposal. One approach
is to seek relief from the RCRA regu-
latory requirements; the other is to
reduce the volume of waste.

The generator can avoid the regula-
tory requirements of RCRA by
having the waste classified  as non-
hazardous. The EPA has established
a procedure  that provides a means
of petitioning the Agency to ex-
clude from regulatory control a waste
that is generally classified as
hazardous.1'2 Obtaining such an
exclusion for a wastewater sludge
usually entails proving that the
sludge does not leach hazardous sub-
stances at harmful concentrations
into the ground water. If such
proof is to be established, the waste
must be subjected to the Extraction
Procedure, a test developed to
simulate the aggressive leaching
that occurs in a municipal codisposal
landfill.

An exclusion from many of the RCRA
requirements has  been allowed
for generators producing less than
2,200 Ib/mo  (1,000 kg/mo) of
hazardous waste.1  The waste must
still be disposed of safely, but many of
the associated record-keeping  and
reporting responsibilities are not
required of generators of small
quantities of  waste.

There are several means of lowering
the cost for waste hauling and
disposal. The generator can reduce
the amount of metals, chemical
compounds, and wastewater that
must be treated by the waste
treatment process. The solids can be
concentrated with dewatering
equipment to reduce the volume of
water contained in the sludge.3
Minimizing wastes,  implementing
recycle and recovery modifications
where possible, and using processes
and reagents that generate less
sludge can  significantly reduce the
amount of sludge solids requiring de-
watering. The remaining solids
can be dewatered for final off-site
disposal for a further reduction
in volume of  more than 90 percent.

The high cost of sludge disposal
justifies purchase of dewatering equip-
ment for all but those plants gen-
erating very small volumes of sludge.

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The properties of individual sludges
vary widely, however, and some
form of pilot testing  is needed to
determine whether a particular
type of dewatering equipment is
suitable.

Of the types of equipment available,
filter presses are usually the least
expensive to install.  Filter presses
have further advantages in their
mechanical simplicity and in their
ability to achieve higher cake solids
concentrations than other de-
watering equipment types. Good
performance with a filter press
requires a sludge with good filtration
characteristics. Sludges that have
highly compressible,  delicate
particles or that tend to blind the
media are not well suited for equip-
ment of this type.

Poor-filtering sludges can be
dewatered by centrifuges,  pressure
belt filters, or vacuum filters that
use a precoat filter aid. These
devices are more mechanically
sophisticated than filter presses and
usually cost  more. Their automa-
tion, however, often reduces the need
for operating labor.

This report is provided to aid the
metal finisher in assessing waste gen-
eration alternatives and developing
a cost-effective means of compliance
with the regulatory requirements.
The section that follows constitutes
an overview of the regulatory
framework developed for hazardous
waste disposal. Section 3 reviews
the disposal methods and associated
costs of commercially operated
secure chemical landfills. Section 4
reviews factors influencing waste
generation and describes what
can be done to reduce waste
volume and the cost of disposal. The
main emphasis of the report is the
final section, which evaluates
the types  of dewatering equipment
available and their cost and
performance.

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2.   Resource
Conservation and
Recovery Act
On May 19, 1980, EPA issued regu-
lations under RCRA as a basis for
a national hazardous waste manage-
ment program. The regulations
came as a result of 1976 Congres-
sional legislation that directed EPA to:

• Identify those wastes  that are
   hazardous
• Establish national standards for
   generators and transporters of
   hazardous wastes and for
   operators of hazardous waste man-
   agement facilities involved
   in the storage or disposal of
   these wastes

Hazardous wastes are  regulated
from the time they are created to the
time of their disposal.  This cradle-
to-grave monitoring is achieved
by a manifest system.4"6  Any
waste that is transported off site for
treatment, storage, or disposal
must be accompanied  by a manifest
that:

• Identifies who generated the waste
• Provides a full  description of the
   contents and quantity of the waste
• Designates the facility to which
   the waste must be shipped

Under RCRA, EPA holds the generator
of a waste responsible for the ulti-
mate safe disposal of that waste.
Strict civil penalties can be imposed
for any violations of the regulations.
In addition, regulations governing
the transportation of hazardous
materials over public roads were pub-
lished on May 22, 1980, by the
U.S. Department of Transportation
(DOT).7
                                                                         Regulatory Framework

                                                                         Table 1 gives the structure of
                                                                         the RCRA regulations. Part 261 of
                                                                         Subtitle C defines four characteristics
                                                                         of wastes that would present an
                                                                         environmental threat if disposed of
                                                                         improperly (Table 2). A solid waste is
                                                                         hazardous if it exhibits any of these
                                                                         four characteristics, or if it is spe-
                                                                         cifically listed in Part 261  as haz-
                                                                         ardous.1 In the latter case, EPA
                                                                         evaluated the hazard associated with
                                                                         unregulated disposal of wastes
                                                                         for which adequate information was
                                                                         available. Then, if the findings so
                                                                         warranted, the Agency made a
                                                                         general determination that a given
                                                                         waste is hazardous. Figure 1 shows
                                                                         the four common plating shop
                                                                         wastes that are generally classified
                                                                         as hazardous. All four wastes
                                                                         were determined to be toxic; plating
                                                                         baths, sludge from plating baths,
                                                                         and stripping and cleaning solutions
                                                                         may exhibit reactive properties
                                                                         as well.

                                                                         RCRA standards for solid waste
                                                                         generators such as plating shops are
                                                                         defined in Part 262 of Subtitle C.4
                                                                         They include provisions for record
                                                                         keeping,  reporting, implementing a
                                                                         manifest  system, and obtaining
                                                                         an EPA identification number.
                                    Table 1.

                                    Structure of RCRA Subtitle C Regulations
                                                          Description
                                                         Part (40 CFR)
                                    General provisions and definitions	
                                    Identification and listing of hazardous waste
                                    Standards applicable to:
                                        Generators storing wastes <90 d 	
                                        Transporters	
                                        Permitted treatment, storage, and disposal facilities  .  . .
                                    Interim status standards applicable to treatment, storage, and
                                      disposal facilities	
                                    Permits for treatment, storage, and disposal facilities	
                                    Guidelines for State hazardous waste programs ,	
                                                      260
                                                      261

                                                      262, Sec. 262.34
                                                      263 (and Pts. 171-179
                                                        of 49 CFR)
                                                      264

                                                      265
                                                      122, 124
                                                      123
                                    SOURCE: U.S. Environmental Protection Agency, "Hazardous Waste Management System:
                                    General," Federal Register 45(98).33067, May 19, 1980.

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 Table 2.

 Four Hazardous Waste Characteristics
      Characteristic
                                             Description
 Ignitabihty. .
 Corrosivity	

 Reactivity	
The waste is capable of causing fires during routine transportation
  to storage and disposal, or of burning so vigorously as to
  create a hazard.
The waste is aqueous and has a pH <2 or >12.5 or corrodes
  steel at a rate >0.25 m/yr.
The waste is extremely unstable and tends to react violently or
  explode, thus posing a problem at all stages of waste
  management.

When the waste is subjected to a specified leaching procedure,
  the leachate fraction  contains certain contaminants in a
  concentration >100 times that specified in the National
  Interim Drinking Water Standards.
SOURCE: U S Environmental Protection Agency, "Hazardous Waste Management System:
Identification and Listing of Hazardous Wastes," Federal Register 45(98):331 21 -33122, May 1 9,
1980.
 Extraction Procedure
  toxicity	
   Workflow
                                                                   Product
         Stripping and
         cleaning solutions
         (F009)
                                        Wastewater treatment
           EPA hazardous
           waste no.
        Hazardous waste
                               Hazard code
           F006

           F007
           F008

           F009
  Wastewater treatment sludge     Toxic
    from electroplating operations
  Spent plating solutions         Reactive, toxic
  Spent plating bath and sludges   Reactive, toxic
    from bottom of bath
  Spent stripping and cleaning     Reactive, toxic
    solutions
   SOURCE: U S. Environmental Protection Agency, "Hazardous Waste Management System:
   Identification and Listing of Hazardous Waste," Federal Register 45(98):33123, May 19,
   1980
Figure 1.

Hazardous Wastes from Electroplating Operations
 If a  hazardous waste is transported
 off site for treatment, storage,
 or disposal, the  generator must pre-
 pare a manifest.4'5 The manifest
 designates the treatment, storage,
 or disposal facility to which the
 waste is being transported; in the
 event an emergency prevents delivery
 to this facility, an alternate receiv-
 ing facility is designated. The
 manifest must contain a full descrip-
 tion of the waste being shipped
 in terms of contents and quantity,
 and it must identify the generator and
 transporter. Sufficient copies of
 the manifest are needed to provide
 a  copy for the records  of the gen-
 erator, each transporter, and
 the receiving facility, as well as a
 copy to  be returned to the generator
 after disposal of the waste.

 The EPA considers that a  generator
 storing hazardous waste on site
 for more than 90 days is an operator
 of a storage facility, and therefore
 must have applied for a facility
 permit before November 19,1980, to
 continue such operations.6 Storage
 for less  than 90 days does not
 require a permit,  but certain standards
 must be  met. Regulations specify:

 • Provisions for inspection of
   containers
 • Precautions for ignitable or reac-
   tive waste containers
 • Personnel training
 • Contingency plans and emergency
   procedures for dealing with
   the release of hazardous wastes
   from their containers or tanks

The hazardous waste management
 regulations issued on May  19, 1980,
 specified that plants operating
a waste  treatment system regulated
 by the Clean Water Act still had to
comply with the RCRA standards for
 hazardous waste treatment and
storage facilities. After reviewing
comments on the regulations,
EPA decided to  award operators of
wastewater treatment and neutraliza-
tion units a permit-by-rule if they
comply with certain  specified
standards. Accordingly, plants with
waste treatment facilities do not
have to apply for a treatment and stor-

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age facility permit or comply with
the interim status standards for
those facilities. (Some State agencies
administering the RCRA Program,
however, have not adopted the
permit-by-rule exclusion.) Details
of this Wastewater Treatment
Tank Exclusion were published on
November 17, 1980.8


Exclusion from RCRA

Costs related to RCRA compliance
can be lowered in one of two
ways. The rate at which hazardous
waste is generated can be reduced to
below 2,200 Ib/mo (1,000  kg/mo),
or the generator can have the
waste declared nonhazardous.1

Reducing the Waste Generation
Rate. An exclusion from many
of the RCRA requirements has been
allowed for generators producing
less than 2,200 Ib/mo (1,000 kg/mo)
of hazardous waste (small genera-
tors). This upper limit applies to
the total mass of waste and includes
water and other  nonhazardous
constituents. The waste must  still
be disposed of either in authorized
hazardous waste management
facilities or in facilities approved
by a State agency for municipal or
industrial waste disposal. The
associated record keeping, reporting,
and waste manifest are not required
of the small generator. Lacking an
EPA identification number and
waste manifest, however, the  gen-
erator may have  more difficulty in
finding  a disposal facility that
will accept metal finishing  wastes.
Moreover, within 2 to 5 yr, EPA
may initiate rules to include in the
RCRA requirements small gen-
erators  producing more than 220
Ib/mo (100 kg/mo) of hazardous
waste.

Seeking Nonhazardous Status.
For some plating shops, having the
waste declared nonhazardous
(delisted) is effective in  reducing
RCRA-related costs.1'2 The  EPA has
established an appeals procedure
that provides a generator with a
means of petitioning the Agency to
exclude from the regulatory controls
a waste that is usually classified
as hazardous. The Agency has
authority to grant a temporary exclu-
sion on the grounds of significant
likelihood that the appeal will
be successful.

A plating shop seeking to have its
waste delisted must prove its waste
nonhazardous, which means
proving that the waste does not ex-
hibit toxic or reactive characteristics.
Proving the waste nonreactive
generally requires testing to verify
a low level of cyanide. Proving  the
waste nontoxic requires subjecting
the waste to the Extraction Pro-
cedure and proving that the sludge
could not leach hazardous sub-
stances at harmful concentrations
into ground water. The Extraction
Procedure is designed to sim-
ulate the aggressive leaching that
occurs in municipal codisposal land-
fills. A sample of the waste is
extracted and analyzed to determine
whether it possesses any toxic
contaminants identified  in the
National Interim Primary Drinking
Water Standards (NIPDWS) and, if so,
at what levels. The waste will be
considered hazardous if it contains
concentrations of contaminants
100 times greater than those speci-
fied in the NIPDWS (Table  3). In
addition, a complete chemical assay
of the waste must be included  in
the delisting petition.

If a  waste is to be delisted, it must be
tested for each characteristic that
is assumed to be  present. Sufficient
tests (at least four)  of each type
must be conducted to ensure repre-
sentative results.  Costs to perform
the testing should range between
$300 and $1,000. The test results are
an essential step  in the appeals
procedure. Every reason for a waste
being judged hazardous must be
refuted. Even if a  waste passes
the Extraction Procedure, however,
EPA may rule that sufficient hazard
exists to warrant denying the appeal.
Table 3.
Extraction Procedure Toxicity Limits
      Contaminant
  Maximum
concentration
   (mg/L)
Arsenic.
Barium
Cadmium
Chromium
Lead.
Mercury
Selenium
Silver
     5
   100
     1
     5
     5
     02
     1
     5
SOURCE U S  Environmental Protection
Agency, "Hazardous Waste Management
System" Identification and Listing of
Hazardous Wastes," Federal Register 45(98).
33122, May 19, 1980
Cadmium, chromium, and lead are
the only common plating com-
pounds included in the Extraction
Procedure toxicity  limits (Table 3).
These  contaminants usually
result from only a few point sources
within  a plating facility. Therefore,
segregating these  wastes from
the rest of the plant's waste streams
can result in the major waste stream
exhibiting nontoxic character-
istics during the Extraction Proce-
dure testing.


Regulatory Requirements

Transporters of Hazardous Wastes.
Under RCRA, the role of  the  haz-
ardous waste transporter is simply
to supply transportation to the
generator. The transporter delivers
the waste to the hazardous waste
management facility that the genera-
tor designates on the manifest. Any
person transporting hazardous
waste  within the United States must
obtain an EPA identification number,
and must comply with EPA and DOT
regulations for transporters of
hazardous wastes.5 7 The EPA regu-
lations are adopted from  the regula-
tions developed by  DOT. They include
vehicle specifications, requirements
for reporting hazardous material
incidents, and requirements
for handling, loading, unloading,
and segregating hazardous materials.

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The requirements for transporters
apply to both inter- and intrastate
transportation and are enforceable by
EPA or DOT.

A transporter may not accept a
hazardous waste from a generator
unless both parties have an EPA
identification number and the
waste  is accompanied by a signed
manifest. The transporter must sign
the manifest and return  a copy to
the generator before leaving the gen-
erator's property. When  the ship-
ment is transferred to another
transporter or to the designated
hazardous waste management facil-
ity, the original transporter must
obtain  the signature of the next party
on the manifest and keep one
copy. The second transporter re-
tains one copy  of the manifest and
transmits the remaining  copies
to the  next party. The designated
treatment, storage, or disposal
facility is required to send one copy,
with all the signatures, back to the
generator. Special requirements
exist for bulk shipments by rail
or water.

Treatment, Storage, and Disposal
Facilities. Facilities that treat, store,
or dispose of hazardous  wastes
are also regulated under RCRA.6  In-
terim operating permit status has
been granted to all such facilities pro-
vided they:

• Had been in operation or under
   construction before November 19,
   1980
• Had notified EPA of their haz-
   ardous waste activities by
   August 18, 1980
• Had applied for a permit by No-
   vember 19, 1980

Requirements for disposal sites cover

• General facility standards
• Emergency precautions and actions
• The manifest system
• Record keeping and reporting

Requirements forfacilities on interim
status cover:
   Reactive, ignitable, and incom-
   patible wastes
   Closure and postclosure care
   Containers and tanks
   Surface impoundment, waste piles,
   land treatment, and landfills
   Incinerators
   Underground injection
   Thermal, chemical, physical,
   and biological treatment
   Financial responsibility and
   liability
For the foreseeable future, disposal
in a landfill is the only feasible method
of  disposing of many hazardous
wastes. The regulations are intended
to provide long-term protection of
ground water and human  health.
They specify monitoring require-
ments; failure to monitor the
land treatment facility is a viola-
tion of the regulations. They include
requirements for controlling and
monitoring water run-on and run-off,
as well as general requirements for
ignitable, reactive, and incompat-
ible wastes. Owners and operators
must consider specific factors
and methods in addressing closure
and postclosure  requirements.
Also, record keeping and  surveying
are required so that the exact loca-
tion and contents of each waste
cell will be known.

EPA has proposed financial require-
ments intended to ensure that
funds will be available for closure
of treatment, storage, and disposal
facilities, and for postclosure
monitoring and maintenance  at
disposal facilities.9 The proposed
requirements also include liability
coverage for injuries resulting
from operation of a hazardous waste
management facility. These pro-
posals allow a number of  ways
to provide financial insurance.

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3.   Hazardous  Waste
Disposal Sites
The secure chemical landfill is the
state of the art for disposal of metal
finishing waste treatment sludges.10'11
It is designed to preclude the risk
of ground water contamination
by toxic heavy metals that would
leach through the soil and into the
ground water unless prevented from
doing so. The secure chemical
landfill provides a means by which
toxic wastes can be buried in an
environmentally acceptable manner.


Landfill Design

There are  basically two  designs
for a secure chemical landfill.
The first takes advantage of natural
geological barriers created by imper-
meable clays.  The second adds a
flexible elastomer liner as further pro-
tection against leaching of pollut-
ants into the ground water. In both
cases, disposal involves direct
burial of wastes in cells designed
to avoid contaminating the surround-
ing environment.

The wastes to be buried are classified
and segregated, and their positions
within a burial cell are recorded.
Bulk liquid wastes are solidified with
lime or cement dust before burial;
bulk solids are buried directly.
Drums of wastes are surrounded
by sufficient sorbent material to ab-
sorb the entire contents  of the drum,
thereby eliminating the  presence
of any free liquids in the cell. Only
compatible wastes are placed in
a given disposal cell. When a cell is
full, a compacted clay cover is placed
over the top to prevent precipitation
from filtering into the cell, thereby
minimizing the formation of leachate
and preventing its migration from
damaged drums.

A piping system for leachate collec-
tion is buried  in a permeable bot-
tom layer at the center  of each
cell. All leachate  is recovered and
is periodicalty pumped out of the cell
through a standpipe connected to
the piping system.  The  recovered
leachate is solidified, then buried in
the landfill. A monitoring-well
system is placed  outside the
landfill cells for early detection
of any leachate that may leak out
of the area. A properly operated
secure chemical landfill does not
usually experience leachate in
its monitoring wells.


Waste Identification Procedure

Before a  hazardous waste disposal
site will accept a waste for disposal, it
will require the generator to submit
a completed waste identification
profile. The procedure includes an
analysis of a sample of the waste
to be landfilled. The analysis includes,
for example, pH, flash point, and
heavy metals content. From the pro-
file and analysis, the disposal
facility can determine whether
the waste is compatible with the
landfill disposal methods and
operating permits. (Many secure
chemical landfills do not accept re-
active wastes containing cyanides.)
If the waste is acceptable, the gen-
erator prepares a shipping manifest
that identifies the  waste origin
(generator), destination  (disposal
facility), hazard class and material
identification number, EPA haz-
ardous waste number, and weight.
The manifest is carried by all
transporters and is presented to
the disposal facility when the waste
is delivered. Appropriate copies of
the manifest are returned to the
transporter and the generator.

When the waste is received at
the landfill site, a  representative
sample is taken and analyzed to en-
sure that the waste material received
is the same  as  that identified by
the waste profile documents. If the
waste is  accepted, it can then be
landfilled. If rejected, it is usually re-
turned to the generator.


Disposal Cost Factors

The total  cost for disposing of sludge
wastes consists of the costs for
hauling, for disposal  site pre-
treatment, and for landfilling. These
costs depend on the physical
nature and chemical  composition
of the wastes, and on the distance be-

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Table 4.
Typical Secure Chemical Landfill Sites: Summary of Costs

Company and site
Chemical Waste Management 	
Emelle AL



Rollins Environmental Services .
Baton Rouge LA
U.S. Pollution Control, Inc 	
Lone Mountain OK

SCA Services Inc
Pinewood SC



Nuclear Engineering Co 	
Louisville KY


Description
	 Clay base 500-700 ft thick, permeability
<10~8cm/s Liquid waste solidified
with lime or cement dust. Leachate
collection system in segregated
cells, sampling wells.
. . . Clay base, elastomer-lined cells
Leachate-monitoring wells.
Clay liner, permeability <10~8 cm/s.
Leachate-samplmg wells.

Fuller's earth base 10 ft thick, permeability
<10~8 cm/s, elastomer liner over
5 ft compacted clay, 2 ft clay over liner.
Leachate collection system, leachate-
monitonng wells, segregated cells
. . . Impermeable clay base Leachate-
monitoring system

d
Disposal
$25-$35/drum
$0.25/gal liquid
$0.025-$0.03/lb
for dewatered
sludge
$0.03/lb for de-
watered sludge
$44/drum
$003/lb bulk waste

$26-$31/drum
$0.065/lb bulk
liquid
$0.04/lb for de-
watered sludge
$0055-$0.10/lb
for dewatered
sludge
3Sta
Haulmgb
$2.96/loaded mi




NS


$0.42/1 00 Ib at 20 mi
$5/100 Ib at 700 mi)
$099/100 Ib bulk
liquid (<100 mi)
$320/100 Ib bulk
(>100 mi)

$2/loaded mi


a1981 dollars

b40,000-lb truckloads

Note —NS = data not supplied

SOURCE- Secure chemical landfill companies
tween generator and disposal site.
Table 4 summarizes information
on transportation and landfilling costs
for a number of hazardous waste
management facilities.15

The cost for burying a  sludge waste
depends on whether the waste is
delivered as a bulk liquid, as a
bulk solid,  or in drums. Sludge is
generally considered a liquid if it is
pumpable.  Drum disposal is usu-
ally the most expensive—ranging
from $25 to $50 for a 42-gal (1 59-L)
drum—because considerably more
handling is needed. Moreover, the
value of the drum  container is lost.

Sludge disposal in bulk liquid quan-
tities is the next most  expensive,
ranging from $0.25/gal to $0.75/gal.
Although bulk liquid is more easily
handled than drums, the liquid waste
must be solidified  before  burial. In
bChemical Waste Management and SCA
 Services, Inc., personal communica-
 tions to Peter Crampton.
Dewatered sludge discharged from centrifuge
                                    this step, the liquid is usually mixed   Disposal of bulk solid quantities of
with lime, cement dust, or clay,
and the cost of the solidification
material becomes part of the total
disposal cost.
waste sludge is the least costly,
typically ranging from $0.025/lb to
$0.05/lb ($0.20/gal to $0.50/gal). A
bulk solid needs no special treat-
ment before burial if it contains

-------
no free liquid. Also, the overall cost
of disposal is lower per unit of dry
solids because of the smaller volume
of the water associated with the
waste. In general, the average
disposal costs for all bulk loads of
sludge are approximately $0.25/gal
(see Table 4). Unfortunately, some
disposal sites do not have the
material-handling capabilities to
dispose of nonpumpable  wastes. It
is important, therefore, to determine
the local disposal conditions before
developing a waste disposal
strategy.

The cost for hauling sludge wastes
depends on three significant factors:

• Load size
• Distance hauled
• Fuel costs
A typical bulk load of sludge is hauled
by a truck with a 40,000-lb (18,000-
kg) capacity. A load that is less
than full will incur the same haul-
ing cost as a full load. From Table 4,
the average hauling cost is $3 per
loaded mile in bulk loads. Therefore,
if a bulk load of sludge is  hauled
300 mi (480 km), the average hauling
cost is about $0.18/gal. When
sludges are hauled to distant
disposal sites, it is common for a
number of small generators to com-
bine and thus make full use of the
hauling capacity of a truck. To
maintain proper responsibility for
the individual waste volumes,
the wastes are segregated in sepa-
rate hoppers  or drums.

Pretreatment Capabilities

In general, the  hazardous  waste
management facility does  not
pretreat or process sludge wastes
on site except to mix liquid waste with
solidification materials. Physical or
chemical treatment—such as de-
watering, drying, orpH adjustment—
is not performed on site. Some of
the large chemical waste disposal
companies do have or are planning to
have facilities that offer a wide
range of treatment capabilities. For
example, RCRA does not allow land-
fill disposal of sludges containing
reactive materials such as cyanide.
The disposal facility would therefore
increase its potential market by
providing  chemical treatment for
cyanide oxidation, making these
wastes compatible for landfill
disposal. As an alternative to
solidifying dilute sludges, sludge
dewatering could also be done at
the treatment facilities.
 10

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4.   Reducing Sludge
Generation  and  Cost of
Disposal
Sludge handling and disposal costs
normally depend heavily on sludge
volume. The high cost of disposal
provides a strong incentive for modi-
fying plating procedures to reduce
this volume. A program to mini-
mize chemical losses and water con-
sumption can reduce sludge gener-
ation significantly.12"14 After
wastewater treatment, the dilute
sludge can be dewatered mechani-
cally to reduce the volume by 90
to 95 percent.

Many factors contribute to the
formation of insoluble solids
during wastewater treament; major
factors are:

•  Concentration of heavy metals
   and other dissolved solids that pre-
   cipitate during treatment
•  Volume of water to be treated
•  Reagents, conditioners, and unit
   processes used  in treatment

Incremental reductions in the amount
of hazardous waste generated will
lower disposal costs. Reducing
the waste generation rate to below
2,200 Ib/mo (1,000 kg/mo) will
 exempt the plant from reporting re-
 quirements defined in RCRA for
 hazardous waste generators.
 Eliminating toxic materials (cad-
 mium, lead, chromium) from the
 waste stream will result in a sludge
 that would prove nonhazardous
 if analyzed according to the Extrac-
 tion Procedure.


 Reducing Sludge Generation

 Waste Composition.  The concen-
tration of heavy metals in  the
wastewater will influence  the
amount of solids generated in the
neutralization-precipitation proc-
ess.14-15 Particularly with systems
using lime  as the neutralizing
reagent, however, metal hydroxides
will usually constitute less than
25 percent of the solids. The rest
will be calcium salts (carbonates, phos-
phates, sulfates) and other insoluble
compounds that  are formed by re-
actions with the  lime.

Figure 2 shows the sludge volume
resulting from lime neutralization of
electroplating wastewater  over a
                                      o
                                     Q
                                     D
                                         30 i-
                                         20
                                         10
                                                                                     O
                                                              O
                                             o
                                                            o
                                                       I
                                                                  I
                                                                             I
                                                                                       I
                                                      100        200        300        400

                                                        HEAVY METAL CONCENTRATION (mg/L)
                                                              500
                                     "Volume of sludge per volume of wastewater treated after 1 h settling Treatment consists of
                                      lime neutralization.

                                     SOURCE: Robinson, A K., and J. C. Sum. "Sulfide Precipitation of Heavy Metals," prepared
                                     for U S. Environmental Protection Agency under EPA Grant No. 5805413, Seattle WA,
                                     Boeing Corporation, undated
                                  Figure 2.

                                  Influence of Wastewater Heavy Metal Concentration on Sludge Volume
                                                                                                     11

-------
range of heavy metal concentrations.
Based on the relationship shown,
lime neutralization of 1,000 gal
(3,800 L) of wastewater containing
100 mg/L of heavy metals would
yield, after  1 h of settling, 90 gal
(340 L) of sludge. Although the data
do not define the suspended solids
concentration of the sludge, metal hy-
droxide sludges will typically
gravity settle to between 1 and 5
percent solids by weight.

Reducing chemical losses, therefore,
will reduce sludge generation rates
as well as chemical replacement
and wastewater treatment costs.
The  m-plant modifications that
can reduce chemical losses are
well-documented16"18  and include
such  procedures as:

 • Dragout recovery and recycle
 • Maximum use  of stripping and
   cleaning solutions before they are
   discarded
 • Drip trays and splash guards
   to direct losses back to the bath
 • A good  housekeeping and
   maintenance program to permit
   rapid finding and repair of
   leaks in tanks, valves, and pump
   seals

 Table 5 gives the amount of metal
 hydroxide  solids  precipitated
during treatment for various metals
in the raw wastewater, as well
as the associated sludge volume
at 3 percent and 25 percent solids by
weight.  Loss of 1 Ib (0.45 kg) of
nickel into the wastewater will result
in 6.1 gal (23.1 L) of sludge at 3 per-
cent solids by weight. The cost of
disposing of this volume of sludge will
usually be greater than the original
cost of the nickel salt.

Water Use. The  amount of sludge
generated is also affected by the
volume of water needing treatment.15
In areas of hard  water, precipitation
of natural water  contaminants,
such as carbonates and phosphates,
can generate a sludge volume
exceeding that associated with
chemicals discharged to the waste
stream. Moreover, consumption
of many treatment reagents and chem-
ical conditioners used in waste-
water treatment  depends on the vol-
ume of water treated. These com-
pounds frequently end up in the
sludge and increase  its volume.

Several steps can be taken to
reduce water use.16'18 The major
water requirement is for rinsing;
multiple stage counterflow rinse sys-
tems and adequate agitation in the
rinse tank will significantly reduce the
amount of  rinse water needed. For
 Table 5.
 Sludge Generated and Sludge Disposal Volume for Electroplating Waste
 Treatment System
Sludge (gal/lb metal

Waste metal components

Aluminum 	
Cadmium 	 .
Chromium . 	
Copper . . 	
Iron . . 	
Nickel 	
Zinc . . . .
Dry solids
(Ib/lb metal
precipitated)3

2.89
1.3
1 98
1.53
1 61
1 58
1 52
precipit
Generated
(at 3% solids
by weight)
11 2
5
7.7
5.9
62
6 1
59
ated)
Dewatered
(to 25% solids
by weight)
1 14
0.51
079
0.6
063
0.62
0.6
 'Using sodium hydroxide

 SOURCE U S Environmental Protection Agency, Environmental Pollution Control Alternatives-
 Economics of Wastewater Treatment Alternatives for the Electroplating Industry, EPA 625/5-79-
 016, June 1979
automated plating lines, flow restric-
tors on the rinse water feed can be
used to control fresh water additions
at the minimum required for good
rinsing.  Rinse tank conductivity
meters can do the same for inter-
mittent plating operations.  Reusing
spent rinses or treated effluent
for less  critical water requirements
will reduce water consumption.

The benefits of reducing water use
go far beyond decreasing the amount
of sludge generated, but the impact
on sludge disposal should  not be
ignored in cost-benefit evaluation of
potential modifications.

Pretreating the water to reduce its
hardness level can reduce the
contribution of naturally occurring
water contaminants to sludge gen-
eration. Water softeners using ion
exchange resins or reverse osmosis
systems can remove calcium and
magnesium from water supplies.

Treatment Processes. The reagents,
conditioners, and unit  processes
employed in wastewater treatment
should be evaluated in terms of
their effect on sludge generation
rates. For example, lime and caustic
soda  are the two alkali neutraliz-
ing agents used most  frequently.15
Lime has advantages over caustic
soda  in that it costs less per unit
of neutralizing capacity, produces
sludge that settles and dewaters more
readily, and can reduce the solubil-
ity of metals to lower  levels in
some applications (primarily
because of the complex-breaking
capabilities of the calcium ions).
Lime has disadvantages, however, in
that it requires a  higher investment
in the reagent feed system, takes
longer to react in the wastewater, and,
depending on the chemical compo-
sition of the wastewater, can produce
as much as 10 times the dry weight
of sludge produced by caustic soda.

Coagulating agents commonly
used to improve floe formation before
clarification also can contribute to
sludge generation.12 Alum and ferric
12

-------
 chloride are widely used, and ulti-
 mately both are converted to
 hydroxides and add to the amount
 of sludge for disposal. Although
 polyelectrolyte conditioners are more
 expensive than inorganic coagu-
 lants, they do not add to the quantity
 of sludge and have provided effective
 solids-settling rates. Their actual
 cost may therefore be lower.

 The significance of treatment
 process selection can be appreciated
 when the different systems used
 to reduce chromium are  consid-
 ered.14'15 Three types have been
 demonstrated:

 • Chemical reduction using a sulfur
   compound — sulfur dioxide (S02)
   or sodium bisulfite (NaHS03)
 • Electrochemical reduction using
   sacrificial iron electrodes
 • Reduction using a slurry of in-
   soluble ferrous sulfide (FeS)

 Using  sulfur dioxide or sodium
 bisulfite  has an advantage because,
 exceptfor the chromium, no insoluble
 byproducts are formed in the re-
 duction reaction:

 3S02 + 2H2Cr04 + 3H20  -*
  Cr2(S04)3 + 5H20

 In electrochemical reduction units,
 an electric current is  used to gen-
 erate ferrous ions that react with the
 hexavalent chromium ions:
  3Fe+3 + Cr+3 + 8Or-T

The ferric ions generated by the
reduction will precipitate at a neutral
pH  and add to the sludge volume.

Similarly,  using ferrous sulfide as
the reducing reagent will generate
ferric  ions and sulfur, both of
which will add to the sludge volume:

H2Cr04 + FeS+4H20 —
  Cr(OH)3 + Fe(OH)3 + S + 2H20

It would appear that the electro-
chemical  and ferrous sulfide reduc-
tion processes would be unfavorable,
at least in  terms of sludge generation
rates;  however, there is an addi-
tional factor to consider. Reduction
using sulfur dioxide or sodium
bisulfite requires a wastewater pH
between 2 and 3. Consequently, a
significant amount of acid may be
needed to lower the pH, then a signif-
icant amount of base would be
needed to raise it back to neutral
to precipitate the chromium as
chromic hydroxide [Cr(OH)3].
Electrochemical and ferrous sulfide
reduction systems can operate at
neutral pH. Particularly in sulfur
dioxide and bisulfite reduction sys-
        tems employing sulfuric acid and
        lime, the amount of calcium salts pre-
        cipitated can exceed the amount of
        precipitants resulting from the
        ferric ions and sulfur generated in
        the alternative reduction processes.

        Figure 3 shows the sludge generation
        rates of the three reduction sys-
        tems over a range of hexavalent
        chromium concentrations.14-15 The
        electrochemical  and ferrous  sulfide
        processes actually generate  less
        sludge solids at chromium concen-
         15
         12
   08
   tn o
   sl
                      Legend:
ferrous sulfide reduction
electrochemical reduction
sulfur dioxide reduction
                         50           100           150

                           HEXAVALENT CHROMIUM  (mg/L)
                                                                 200
   SOURCES: U.S. Environmental Protection Agency, Control and Treatment Technology for
   the Metal Finishing Industry: Sulfide Precipitation, EPA 625/8-80-003, Apr. 1980.
   U.S. Environmental Protection Agency, Economics of Wastewater Treatment Alternatives
   for the Electroplating Industry, EPA 626/5-79-016, June 1979.
Figure 3.

Sludge Generation Factors for Alternative Chromium Reduction  Processes
                                                                                                         13

-------
trations below 75 mg/L It is im-
portant to remember that the solids
generation rates are based on
assumptions regarding the initial pH
of the wastewater and the neutral-
izing reagent employed. Any
firm conducting a similar analysis
for its treatment system should test
to determine how much sludge is
generated by each of the differ-
ent treatment alternatives.

To reduce sludge disposal costs,
it is necessary to select the waste
treatment techniques that generate
the least amount of waste sludge.12-13
Although some of the newer treat-
ment techniques produce an effluent
of high quality, they generate much
more sludge than the conven-
tional approaches they replace.
The high cost of waste disposal re-
quires that the foregoing sludge
generation factors influence the selec-
tion of wastewater treatment
systems.


Sludge Dewatering

Although the volume of sludge can
be reduced significantly by modifica-
tions that reduce the pollutant and
wastewater loadings on the treatment
system, a sludge residue will
result from wastewater treatment.
The cost to dispose of this residue
will depend primarily on volume. The
volume of sludge can be reduced
significantly by mechanical de-
watering equipment. Figure 4 shows
the reductions possible when
sludge is dewatered from 1  percent
solids by weight to different solids
concentrations.

Normally the clarifier underflow
will contain between 0.5 and 3 per-
cent solids by weight. Allowing
the clarifier underflow to settle in a
thickener tank will  increase  the
solids content to between 2 and 5
percent by weight.  Using the curve
in Figure 4, 1,000 gal (3,800 L)
      1,000
        500
   _
   o
        100
        50
         10
                   I
                          I
                                  I
                                                         I
                   5       10       15      20     25      30

                       SOLIDS CONCENTRATION (% by weight)
                                                                35
  Note —Initial conditions, 1,000 gal at 1% by weight
Figure 4.

Sludge Volume versus Solids Concentration
of sludge at 1 percent solids by weight
would be reduced to 330 gal
(1,250 L) when thickened to 3 per-
cent solids by weight. A mechanical
dewatering device will achieve
anywhere from  10 to 50 percent
solids by weight, depending on
the type of equipment and the
dewatering properties of the sludge.
Assuming  dewatering to 25 per-
cent solids by weight, the sludge vol-
ume would be reduced to 40 gal
(150 L)—4 percent of the original
clarifier underflow volume.
Vacuum filters, filter presses, pressure
leaf filters, belt filters, and centri-
fuges have been applied successfully
for mechanical dewatering of metal
hydroxide sludges. The properties
of individual sludges vary widely,
however, and some pilot evaluations
are  necessary to determine whether
a particular type of dewatering
equipment is suitable. As a rule, equip-
ment vendors will provide testing
if supplied with a sample of the sludge.
14

-------
Four features are common to sludge
dewatering systems (Figure 5a):

•  A solids collection sump
•  One or more feed pumps
•  Elevation of the dewatering device
•  Filtrate return upstream

The solids collection sump receives
the dilute clarifier underflow and
provides a reservoir of feed solution
so that the mechanical dewatering
device can be fed continuously.

The feed pump delivers the sludge
to the dewatering device. Pump
type depends on the physical
properties and viscosity of the sludge,
and on the type of  dewatering
device. Specially designed centrifu-
gal, diaphragm, and progressive
cavity pumps are suitable for
handling slurries.

Elevating the dewatering device
facilitates handling dewatered sludge.
Ideally, the dewatered sludge
should be discharged  directly into
a hopper—the transport medium to
the disposal site. If this approach
is  impractical, a straight run of
conveyors can be used to transport
the sludge to a point overthe hopper.

Filtrate is returned  to the clarifier
or other  upstream process vessel.
Usually the level of suspended
solids is too high to allow direct
discharge.

The basic premise  in the design  of
sludge-handling systems is to
prevent the flow path from becoming
plugged  with sludge or debris.
Plugging is usually caused either by
buildup of debris behind an obstruc-
tion in the flow path, or by solids
settling in the pipes. To minimize the
chance that such occurrences
will interrupt operation, the system
should use valves,  instrumenta-
tion, and so forth, that do not obstruct
flow through pipes, and should
include provisions for  flushing out
clogged  lines.
           Filtrate to clanfiei
                                                   Filter press
   Clarifier underflow i
   SOURCE: U.S. Environmental Protection Agency, Environmental Regulations and
   Technology: The Electroplating Industry, EPA 625/10-80-001, Aug. 1980.
  (b)
   8
   03
   O
   o
   O
   a.
   03
   D
125 r
        100  -
         75  -
                                                 at 3% solids by weight
                                                 at 20% solids by weight
                                 80         120

                           CLARIFIER UNDERFLOW (gal/h)
                                                      160
                                                         200
   aAt $0.50/gal.
Figure 5.

Recessed Plate Filter Press: (a) Unit and Auxiliaries Needed for Sludge
Dewatering and (b) Annual Sludge Disposal Cost
                                                                                                          15

-------
Basket centrifuge discharging centrate
Determining the capacity needed in
the dewatering system requires
testing. If a treatment system is
already in place, capacity can be de-
termined easily by measurement
of the clarifier underflow volume  and
suspended  solids concentration.
Lacking a treatment system, a
representative wastewater sample
should be treated in a manner
similar to the manner employed in
the proposed treatment system.
After treatment and settling, the vol-
ume of sludge generated per unit
volume of water treated  can be
determined visually. A sample of the
settled sludge can be analyzed
for suspended solids content.
The high cost of sludge disposal will
justify purchase of dewatering
systems for all plants except those
generating very small volumes
of sludge. As a further incentive, if
dewatering reduces the mass to
below 2,200 Ib/mo (1,000 kg/mo),
the generator is excluded from many
of the regulatory requirements of
RCRA.  Before evaluating the
benefits of sludge dewatering,
however, the capability of local dis-
posal sites to handle nonpumpable
sludges should be ascertained.

Consider, for example, the installation
of a recessed plate filter press to
dewater a dilute clarifier underflow
from 3 percent to 20 percent
solids by weight. Figure 5b com-
pares the annual cost of disposal, at
$0.50/gal of sludge, for the two
concentrations. At 20 percent
solids by weight, the figure shows
the disposal cost with as well
as without the annual cost to operate
the filter press. Even with its cost
included, the filter press reduces an-
nual  disposal  costs at underflow
rates exceeding 8 gal/h (30 L/h).

Thus, mechanical dewatering
is usually cost effective, except for
plants generating very small sludge
volumes. Under RCRA requirements,
sludge must be dewatered or
solidified before it is used in land
application. Modern disposal
facilities that accept industrial solid
waste are likely to have some
means of dewatering or solidifying
the waste.  Plants generating
small sludge volumes may find  it
more cost effective to use the
dewatering capabilities at a central
disposal facility.


Sludge Segregation

A mixture of hazardous and non-
hazardous waste is considered
a hazardous waste. Segregating
wastes will reduce the volume of haz-
ardous waste considerably and,
therefore, the cost of treatment and
disposal.2'19 The sources of toxic
contaminants in plating are usually
limited to a few operations. Cadmium,
16

-------
lead, and chromium are the only      The segregated sludge containing    Toxic substances can also be
common plating materials on         toxic substances must be disposed of  eliminated from a plant's waste by
the EPA list of toxic substances. If    in a manner acceptable for haz-      recovery and recycle of the toxic
toxic wastes are separated from      ardous wastes; however, the volume  contaminants.  Dragout from
the rest of the waste stream, the treat-   should be considerably less than     cadmium, lead, and chromium
ment residue from the nontoxic       the total amount of waste generated,  plating operations has been recov-
waste streams should be able to pass   The generator will avoid the report-  ered by recovery systems. The
the Extraction Procedure and be      ing and manifest  requirements       combined benefits of material recov-
judged nonhazardous by EPA.        if the hazardous waste amounts to   ery, waste treatment cost reduction,
Disposal of a waste that is judged    less than 2,200 Ib/mo (1,000 kg/mo),  and producing a nonhazardous
nonhazardous should be less costly.                                     sludge can provide significant
                                                                     returns on the investment in
                                                                     recovery equipment.
                                                                                                   17

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5.  Sludge  Dewatering
Equipment
Mechanical dewatering devices are
used to achieve a higher sludge
solids concentration than can be ob-
tained  by gravity thickening. Weak
attractive forces bind much of
the water contained in a sludge to
the solid particles; when the bonds
are subjected to  mechanical
force, much of the water remaining
in the sludge after gravity thickening
can be removed. The following
types of equipment can be  used for
mechanical dewatering of electro-
plating sludges:

• Pressure filters
• Vacuum filters
• Centrifuges
• Compression filters

When  pressure filters are employed,
the dilute sludge is pumped into
the filter; the solids are retained
on the filter membrane and the
filtrate is discharged. Recessed plate
filter presses  use this method.
They can dewater sludge to high
solids content owing to the large pres-
sure gradient they can apply across
the sludge cake.

Vacuum filters dewater sludge
by applying a vacuum on one side
of a water permeable membrane that
has a sludge  layer or suspension
on  the other side.  In response
to the pressure gradient, the water
passes through the membrane.
Rotary drum and vacuum belt
filters  use this principle.
Centrifuges dewater sludge similarly
to gravity thickening, but by rapidly
rotating the sludge, they create a
centrifugal force thousands of
times more powerful than normal
gravity. The strong centrifugal
force greatly speeds up the settling
process and magnifies the com-
paction  effect. This dewatering
mechanism makes centrifuges most
suitable for compressive sludges
that settle well.

Compression filters dewater
sludge by squeezing it between
water permeable membranes.
They have proven effective mainly
for dewatering highly compressive
sludges typical of those  resulting
from polyelectrolyte conditioning.

Criteria for  selecting one of the
foregoing devices for a specific ap-
plication include:

• Sludge properties (solids
   concentration, particle size,
   compressibility)
• Volume of sludge to be dewatered
• Local disposal requirements

Table 6 compares  some of the
characteristics of the different equip-
ment types. Table  7 summarizes
the performance of different
dewatering systems for metal
finishing sludges in industrial appli-
cations.

The data in Table 7 indicate that
centrifugation will  normally achieve
                                    Table 6.
                                    Dewatering Equipment for Electroplating Sludge: Typical Performance
                                    Characteristics


Equipment
Filter press 	

Precoat vacuum filter 	

Pressure belt filter 	
Fee

Rate
(gal/mm)
2-250
1 -250
1-250
2-60
5-200
id

Solids
(% by
weight)
1-5
3-10
05-3
2-5
2-6
Solids

(%by
weight)3
95-99
50-99
95-99
50-95
90-95


concentration
(% by weight)
20-50
15-40
20-50
5-25
20-40
Installed

cost
($1,000)b
20-200
30-150
30-150
20-175
40-200
                                    "Feed solids in sludge cake

                                    b1981 dollars. Includes auxiliary equipment
 18

-------
Table 7.

Performance of Dewatering Equipment for Electroplating Sludge
Equipment type and unit size
Recessed plate filter press.
8.5-ft3 sludge-holding capacity . . .
10-ft3 sludge-holding capacity ...

12.5-ft3 sludge-holding capacity . . .

21 -ft3 sludge-holding capacity




260-ft3 sludge-holding capacity. . . .

Vacuum filter3

Rotary precoat vacuum filter:
9.4-ft2 filtration area 	
37.7-ft2 filtration area

Basket centrifuge:
1-gal bowl capacity 	


4-gal bowl capacity 	
Pressure belt filter 9.8-ft-wide sludge-
holding capacity . . 	

Sludge
feed
rate
(gal/h)

95
300

NA

825




1 2,000

NA


100-150
330


120


120-150

800

Solids (% by
weight)
Feed

3
1-2

NA

5




3-6

3-5


NA
1-5


3


5

2-6

Cake

30
30

40

35-40




30

70-75


15
30


12-20


18

NA

Comment

NA
Plastic-plating lime
sludge
Chromium hydrox-
ide dewatermg
Operation attention
2-h shift, unit
cleaned every 6-8
wk with recircu-
lated 50% HCI
Heat-treated zinc
hydroxide sludge
Metal oxide waste
treatment sludge

Low maintenance
Cloth life 1 yr;
repairs <$200/yr

Satisfactory per-
formance; low
maintenance
High maintenance

Aluminum hydrox-
ide sludge
"Unit size not available

Note —NA — not available
solids concentration in the range
of 12 to 20 percent by weight.
Both precoat vacuum filtration and
pressure filtration can achieve
30 percent cake solids by weight
if the sludge has good filtration
properties.

The one data point given for vacuum
filtration (without precoat) shows
that the equipment achieved  70
to 75 percent cake solids by weight.
This high cake concentration resulted
because the sludge was composed
of metal oxides rather than metal
hydroxides. The metal oxide precipi-
tants can  be dewatered to  higher
solids content than can hydroxides
because, unlike hydroxides, they
do not have water chemically
bound to the metal oxide molecule.
Also, the metal oxide solids are
much less compressible and they
filter better. It is possible to generate
metal oxide sludge, but the waste-
water treatment is significantly
different from that of conventional
hydroxide precipitation systems.

Only one data point is given for
a belt filter press; this equipment has
been used to a limited degree for
metal finishing  waste sludge.
Its higher cost  usually restricts its
use to applications where other
equipment types cannot operate
satisfactorily.


Filter Presses

The Equipment. Filter presses come
in two basic types: recessed plate
and plate and frame. In both cases,
the press is a series of parallel
plates pressed together by a hydraulic
 ram, with cavities between the
 plates. The plates are recessed on
 each side to form the cavities
 in the recessed plate press. A frame
 of equal dimension is placed between
 flat  plates  in the plate-and-frame
 press (Figure 6). The plates come  in
 a variety of materials; originally
 they were fashioned from wood, later
 from steel  or ductile  iron. Plates in
 predominant use today are made
 of light weight, chemically durable
 polypropylene  or fiber-reinforced
 polyester.

 A filter press is a batch unit. At
 the start of the cycle, slurry is pumped
 into the cavities through a port that
 runs through the bank of  plates.
 When the cavities are full, the
 pressure forces the filtrate through
 the filter media, along the drain-
 age  surface of  the plates, into
 orifices that are located in the cor-
 ners of the plates and connected
 to the filtrate port. The process con-
 tinues until the cake solids in the
 cavities thicken to a degree
 such that, at the pressure limit of
 the press, only a small volume
 of filtrate is being produced. The
 pump is shut off at this point, the ram
 is withdrawn, and each cavity
 is emptied individually. The press
 is then closed  and the cycle begins
 again. Usually the filter cakes are
 dropped into a  hopper under the
 press or are transported to a hopper
 by a screw conveyor, which also
 breaks up the cakes.

 The  filter press has a number of
 advantages over other filtration equip-
 ment.  Filter presses can operate
 well at variable or low feed  solids
 conditions. They can  produce a
 very dry cake because of the high
 pressure differential they can exert
 on the sludge.  Some  commercial
 units are designed with a  pressure
 limit of 225 Ib/in2 gauge (1,653
 kPa), and produce sludge cakes with
 solids content  in the range of 50
to 70 percent by weight. Filter
 presses are mechanically reliable;
the hydraulic ram and the plate-
shifting mechanism (which facilitates
cake discharge  on the larger units)
                                                                                                       19

-------
                                Plate
                                                Frame
                      Fixed
                                                           Movable head
                                                                            Closing device
      Filtrate
   Sludge fee
   under pres:
                                            • Filter cloth
Figure 6.

Plate-and-Frame Filter Press
are the only moving parts. Power
consumption is low; the only
significant power use is for feed
pump operation [2  to 20 hp (1.5 to
15 kW)].

The disadvantages  of the filter
press include its batch  operating
cycle, the labor associated with re-
moving the cakes from the press, and
the downtime  associated with find-
ing and replacing worn or dam-
aged filter cloths. At the end of each
filtration cycle, about 30 min of
operator labor  will  normally be
needed to empty the press and  start
a  new cycle. A filter press is usually
sized to operate on a 4- to 8-h cycle.

Determining Applicability. The most
reliable way to test whether a fil-
ter press  is applicable  is to obtain a
small bench-scale  unit from a
press manufacturer. Several design
specifications  can  be determined
by bench-scale testing:

 • Press filter cake volume
 • Press filtration area
 • Pressure limit
 • Optimum cycle time
cake solids concentration and fil-
tration cycle  time.

Press filtration area actually relates
to the  optimum cake thickness
between the  plates in the press. Re-
cesses between plates in filter
presses range from 1 in (2.5 cm) to
as much as 3 in (7.6 cm). The
wider the spacing, the  less expen-
sive the filter press per unit of
cake volume, but the lower the filtra-
tion capacity (gallons of filtrate
per hour)  per unit of cake volume.
        80
        60
        40
        20
                                   Legend:
                                   MM**
    automatic plate shift, hydraulic ram
    manual plate shift, manual closure
                 10
                        20
                               30
                                      40
                                             50
                                                     60
                                                            70
                                                                   80
                             FILTER  CAKE VOLUME" (ft3
   'Includes carbon steel frame, polypropylene plates, and filter cloths.

   bBased on sludge cakes 1.25 in thick

   SOURCE- Equipment vendors
 Press filter cake volume relates to the  Figure 7.
 solids loading rate and the expected
                                     Recessed Plate Filter Presses: Unit Prices
20

-------
Feed solids concentration and filter-
ability  of the sludge affect the
choice of spacing.

Pressure limit relates to the solids
content of the sludge cake versus the
applied pressure.

Optimum  cycle time is determined
by the press volume and filtration area
specified. The longer the  cycle
time, the  lower the labor  require-
ments, because  cake discharge and
restarting occur  less frequently.
A longer cycle time  will require a
larger unit, which of course will
cost more.

Testing with  a bench-scale filter
press,  however,  can be costly
and time consuming. The applicabil-
ity of a filter press, or of any filtration
technique, can be determined
more simply  by use  of a filter leaf
test apparatus.20 Several factors can
be evaluated, for example, filter-
ability, medium fouling, and cake
release from  the medium. Vendors
of filter press  equipment can scale up
filter leaf test data to determine
the required  size of a filter press.

As an alternative to testing, filter
press vendors need  only a sludge
sample and the volumetric rate and
solids content of the press feed
to determine the required size and
cost of the unit.

Costs.  Figure 7 shows the relation-
ship of filter  press purchase price
to the  volume of cake solids for
a press with a 1.25-in (3.2-cm)  cake
recess and an operating pressure
of 100 Ib/in2 gauge  (790  kPa).  The
cost covers only the purchase price of
the press; auxiliary equipment
needed includes:

•  High pressure feed pump or pumps
•  Sludge feed storage
•  Filtrate return to the clarifier
•  Cake solids handling and discharge

The cost of auxiliaries can be
considerable, but fortunately
there are alternatives that can elim-
inate some of the expense. Sludge
feed piping, filter, and filtrate
discharge piping can be designed
as a closed hydraulic system. This ap-
proach enables the sludge feed
pump  to provide the pressure
head needed to return the filtrate  to
the clarifier, thus eliminating the
need for a filtrate receiving tank and
return  pump in applications where
gravity flow return is not feasible.

Handling and disposal of the cake
solids  can be simplified by elevation
of the  press, enabling the filter
cake to be discharged directly into
the disposal hopper. This approach
will eliminate the need for solids
conveying systems and reduce
the amount of operator attention
associated with discharge"of
the cake solids.

Owing to the batch  operation
of the  filter press, storage volume
                                 is needed for the sludge feed.
                                 Normally, a sump to receive the
                                 clarifier underflow will provide the
                                 necessary storage volume. If the
                                 solids retention time in a clarifier is
                                 high, the clarifier can be used as
                                 the storage chamber; otherwise a
                                 holding tank will be required to
                                 provide adequate sludge storage.

                                 Operational costs associated with the
                                 press are for power to operate the
                                 feed pumps and labor to turn the
                                 press around at the end of each cycle.
                                 Minor operational costs are asso-
                                 ciated with maintaining the filter
                                 media in good condition. These
                                 costs include replacement of dam-
                                 aged or  worn filter cloths and
                                 periodic cleaning to control  media
                                 blinding.

                                 In Figure 8, the cost associated
                                 with using a filter press for sludge
       140
       120
       100
    I   80
    o
CO
g   60
CO
Q
3
Z

<
    40
        20
                                 Legend:
                                        including annual cost of filter press
                                        disposal only
                                                     20-ft3
                                                     filter capacity
                          10-ft3
                          filter capacity
               5-ft3 filter
               capaci
                            120       180      240       300

                          CLARIFIER UNDERFLOW6 (gal/h)



     aAt $0.43/gal. Sludge dewatered to 25% solids by weight.

     bAt 3% sohds by weight.

     Note.—4,800-h/yr operation.
                                                                 360
Figure 8.

Filter Press Dewatering Systems: Annual Sludge Disposal Costs
                                                                                                         21

-------
Rotary vacuum filter with belt discharge for enhanced cake-medium separation
dewatering is shown as a function of
the clarifier underflow rate, including
costs for transporting and dispos-
ing of the sludge at a secure chemical
landfill as well as costs associated
with the filter press. It  is assumed
that  the clarifier underflow is
dewatered from 3 to 25 percent
solids by weight. Disposal is assumed
at $0.43/gal ($0.25 for disposal
and $0.18 for hauling), representing
the average cost for a bulk load of
40,000 Ib (18,000 kg)  shipped
300  mi (480 km) to the landfill. Cost
for the filter assumes a unit  sized
to operate on a 4-h cycle.

For example, with a clarifier (or
thickener) underflow rate of 100 gal/h
(380 L/h) at 3 percent  solids by
weight, the annual disposal cost
would  be $39,000: $21,000 for
transporting and disposing of the de-
watered sludge and $18,000 for
depreciation and operation of a press
with 10ft3 (0.3 m3) of filter capacity.
If the same volume of sludge were
disposed of without dewatering,
the annual disposal cost would
be $200,000. Based on the assump-
tions in Figure 8,  the filter press
installation saves $161,000 peryear.

The economic benefits of  installing
dewatering equipment are also
realized for plants generating small
volumes of sludge. The filter press
achieves a net disposal cost reduc-
tion where clarifier underflow
rates exceed 5  gal/h (19 L/h).

The rate of return  on the investment
associated with a recessed plate
filter press is a function of the
volume of sludge and the cost of
sludge disposal.  For a plant dispos-
ing of its sludge at $0.43/gal, the
investment in a filter press with a 5-ft3
(0.15-m3) filter capacity yields a 30-
percent after-tax return when the
feed rate exceeds 12 gal/h (45 L/h).
The cost of the press would be
$19,000; installation with the re-
quired auxiliaries should bring
the total to $29,000.


Vacuum Filters

The Equipment. The rotary drum (Fig-
ure 9a) is the most common type of
vacuum filter. The drum is positioned
horizontally and rotates partly
submerged in a vat filled with a slurry.
22

-------
                                                Dewatenng zone
                                                (cake drying)
                                                         Rotation
                                                          Discharged
                                                          filter cake
   (b)
12
             10
         >
         \-
         (J
         Q-
                                              Cake
                                                    Filtering zone
                                                         30
                                                        25
                                                        in
                                                        20
                                                        15
                0123

                              CYCLE (min/r)

         Note —At 3% feed solids by weight
   (C)   25
   (fi
   Q
   _i
   O
        20
        15
                   100      200      300      400

                               FEED RATE (gal/h)
                                                      500      600
   Note —At 3% feed solids by weight
Figure 9.

Rotary Vacuum Filter: (a) Basic Principle of Continuous Rotary Filtration,
(b) Filter Cake Capacity and Cake Dryness (from Filter Leaf Test), and
(c) Scale-Up Performance
The surface of the drum, which is
covered by a filter medium, consists
of a series of horizontal panels.
Vacuum is applied independently
to each panel by pipes inside
the drum; the pipes connect to a
common vacuum source, usually pro-
vided by a vacuum pump.

The filter  has three basic operating
zones: filtering,  cake drying (de-
watering), and cake discharge.
In the first zone, vacuum is applied
as a section of the drum submerges in
the slurry. A cake forms on the filter
medium as the solids are captured,
and the filtrate is drawn to the
vacuum source. The vacuum is main-
tained as  the drum section rotates
out of the slurry into the second
zone. The vacuum removes additional
water and draws air through the
cake to promote further drying. In
the last zone, the discharge of
the cake  is accomplished when the
vacuum is replaced with a  blast of
air that separates the cake from
the medium.

Other means have been developed
to facilitate discharge of the filter
cake. In one variation, a  series
of parallel strings, tied around the
drum, separate from the  drum in
a tangential plane at the discharge
point, lifting the filter cake from
the medium. The strings pass around
a roller and the  cake separates from
the strings and  is discharged. In
another variation, the medium is sep-
arated from the  drum, passes over a
roller where the cake is discharged,
and is washed before being di-
rected back to the filter drum by an-
other roller. These variations
were developed to make the rotary
filter more versatile—able to handle
slurries forming gelatinous cakes
that are difficult to discharge  and,
consequently, that foul the filter
medium.

A third variation of the rotary drum
filter uses a precoat, usually diatoma-
ceous earth, that acts as the filter
                                                                                                       23

-------
medium. As the drum rotates past a
scraper, a thin portion of the precoat
cake is removed along with the
collected solids, resulting in a clean,
unfouled surface each time a sec-
tion of the drum enters the slurry.
Precoat filtration provides excellent
filtrate quality and can remove
slimy solids that are difficult to filter
and that would  rapidly foul a per-
manent filter medium.

Precoat filtration is generally used to
dewater dilute sludges  because it
offers a high filtration rate per
unit of filter area. Precoat consump-
tion usually ranges from 5 to 20 Ib
(5 to  20 kg) for each 100 Ib
(100  kg) of sludge  solids ($0.50-
$2/100 Ib sludge solids). The  pre-
coat does add to the quantity  of
solids for disposal, but often precoat
filtration yields  a cake with
higher solids  content than does
standard vacuum filtration.

Determining Applicability. The filter
leaf test20 is the common proce-
dure for evaluating the  applicability
of vacuum filtration  and determin-
ing required unit size. The filter
leaf is a small disk with drainage
grids similar to production filters. Fil-
ter cloths of different materials
and weaves can be attached to
the disk for evaluation.

The leaf is submerged in the agitated
slurry for a specified time, then re-
moved. After the vacuum has
been allowed to dry the cake  for
a set period of time, quantity of filter
cake, cake solids percentage,  and
filtrate volume are determined.
The test is repeated with different fil-
tration and drying times to determine
the most effective operating con-
ditions.  The two key factors are
dry solids capacity  in pounds  per
 hour per square foot (kilograms
 per hour per square meter) of filter
 area, and cake  solids concentration.
 Varying the test cycle time is equiv-
   o
   o
   o
        70
        60
        50
   LLJ    40
   a
        30
        20
        10
                           Legend'
                                                          -  20
                                                          -  15
                                                                  a
                                                                  DC
                                                                  a:
                                                                  o
                                                                  Q-
                                                             10
                          40      60      80

                            FILTER AREA (ft2)
                                                  100
                                                          120
  aSkid-mounted unit complete with vacuum pump, separator, filtrate removal pump, and
   internal piping

  blncludes power for vacuum and filtrate pumps and for belt drives

  SOURCE  Equipment vendors
Figure 10.

Rotary Vacuum Filters: Unit Prices and  Power Requirement
alent to varying the revolution
speed on thefilterdrum. Aftera num-
ber of runs, curves similar to those
in Figure 9b can be developed.
The figure shows that slowing the
drum revolution speed increases cake
solids concentration and reduces
filter capacity.

The curves can be used to predict
the performance of a full size
filter as a function of filtration area. As
the solids loading rate (or feed rate)
for a particular application is set,
the cake solids concentration
will depend on filtration area (Fig-
ure 9c). A disposal cost analysis
is needed for different filter sizes to
determine the optimum filter size
for a given application. The analysis
will require defining the disposal
cost of the sludge as a function
of solids concentration and obtaining
equipment and operating costs for
the filters.

It  is also important in pilot testing
to determine how easily the cake re-
leases from the medium at the end of
each run. To determine the poten-
tial effect of  cloth blinding, the
filter leaf test can be repeated a num-
ber of times  while the different
variables  are held constant. If the
collected filtrate is measured
after each run, any deterioration
 24

-------
       120 r-
       100  -
   =-    80  -
   U)
   O
   u
   U)
   O
   Q.
        60  -
        40  -
        20  -
                                         includes annual cost of vacuum filter
                                         disposal only
                        100            200          300

                          CLARIFIER UNDERFLOW11 (gal/h)
                                                                 400
   aAt $043/gal for bulk 40,000-lb truckload shipped 300 mi to landfill Sludge dewatered
    to 25% solids by weight.

   bAt 3% solids by weight.

   Note —4,800-h/yr operation.
Figure 11.

Rotary Vacuum Filters: Annual Sludge Disposal Costs
in filtration rate caused by medium
fouling can be observed. Selecting a
suitable filter cloth fabric and
weave can often reduce cloth blinding.

As a rule, rotary drum vacuum filters
perform best with feed solids
ranging from 3 to 5 percent by weight.
A thickener should be installed to
concentrate dilute sludge from
a clarifier. Precoating the filter is
an effective means of dewatering
dilute sludges. Without precoat, good
filtration rates and trouble-free cake
release are usually realized with a
sludge having solids that are  not
too sticky or compressible. Chemical
and thermal conditioning or pre-
coat body feeding will often improve
sludge filtration characteristics.
Such conditioning can become eco-
nomically attractive  in reducing
equipment size and improving
performance.

Vendors of filters, filter cloths,
filter aids, and sludge  conditioners
will provide guidance  in test pro-
cedures and supply product samples
to aid the potential customer in
evaluating the applicability of vacuum
filtration to a given sludge disposal
situation.

Costs. Figure  10 shows the unit
cost and power requirement for a
rotary vacuum filter as a function of
filter area. The cost is for a prepiped,
skid-mounted unit that includes
the filter, the vacuum pump and asso-
ciated vacuum lines, a vapor-liquid
separator, and a filtrate removal
pump. No costs are included
for handling the discharged sludge
cake. The major cost of operating
a vacuum filter is associated with
the power supplied to the vacuum and
filtrate pumps and the  drum agitator
drives. The unit operates continuously
and should only require operator
attention for maintenance and
repairs. As with most membrane
filters, the filter medium requires peri-
odic cleaning  with an  acid or alka-
line solution to remove fouling
agents. Regular filter cloth replace-
ment is also necessary, but should
not constitute a major expense.

Figure 11  shows the annual disposal
cost for sludge dewatered using
a rotary vacuum precoat filter
as a function of the clarifier underflow
rate. Total disposal cost includes
the cost of operating the filter
as well as that of hauling and land-
fill disposal. A typical  precoat
filtration rate of 12 gal/h/ft2 (489
L7h/m2) was used to determine
                                                                                                         25

-------
the necessary filtration area. It is
assumed that the filter dewaters the
underflow from 3 to 25 percent
solids by weight. Using the cost
components indicated, the vacuum
filter realizes a cost reduction
compared with sludge disposal at
3 percent solids by weight when
the underflow exceeds approximately
10 gal/h (38 L/h)—even though at
that feed rate the smallest commer-
cial unit available would have
considerable excess capacity.

The savings in hauling and disposal
cost justify investment in the
equipment. For a plant disposing
of its sludge at $0.43/gal, the
installation of a vacuum filter with a
19-ft2 (1.8-m2) filter area  yields
a 30 percent after-tax return on in-
vestment when the feed rate exceeds
approximately 30 gal/h (113 L/h).
The investment required for installa-
tion of a 19-ft2 (1.8-m2) filter would
total $73,000.


Basket Centrifuges

The Equipment. Centrifuges dewater
sludge in a manner similar to gravity
thickening, but by rapidly rotating
the sludge they create an apparent
gravity thousands of times more
powerful than normal. The centrifugal
force thus created speeds up
settling and magnifies the compac-
tion effect, making centrifuges
most suitable for compressive sludges
that settle well. Several centrifuge
types are available commercially, in-
cluding basket, scroll, and disk
centrifuges. Only the basket centri-
                             Motor
   Basket
                                                           Polymer
                                                           feed pipe
                                                           Sight glass
                                                           Ce'ntrate
                                                           discharge
                                              Feed inlet
fuge is used to any degree to
dewater plating sludge.

The basket centrifuge (Figure 12)
is a vertical rotating bowl that
has a lip extending inward at the top.
Sludge is introduced into the
bottom of the unit and the solids,
owing to their greater density,
are thrown against the inner wall of
the basket. When  the basket
becomes full, clarified liquid (or
centrate) is decanted over the inner
lip and removed from the unit.

The rotating basket comprises two
zones: against the outer wall of
the basket is the solids retention
zone, which contains the accumulated
sludge solids; the  rest of the basket
constitutes the clarification zone,
which separates the solids from
the incoming feed. As the cycle con-
tinues, the volume of accumulated
solids increases and consequently re-
duces the capacity of the clarifica-
tion zone until the residence
time of the fresh feed in  the clari-
fication zone is insufficient to settle
out the suspended solids. At this
point, the level of  solids  in the
centrate increases dramatically.
This change, or "breakover," is
detected by a monitor. The feed is
cut off and a skimmer is run into the
basket to remove excess water
from the cake surface. The basket
then decelerates from operating
speed (anywhere from  1,000
to 3,000 r/min) to approximately
75 r/min. A plow enters the basket
and pushes the cake out at the
bottom of the centrifuge. As the plow
retracts, the basket is accelerated
and the feed is resumed.

The time required  for the phases
of the operating cycle when the unit
is not receiving feed usually varies
from 6 to 8 min. A unit of this
type has a feed rate up to  60 gal/min
(225 L/min), with solids recovery
of 50 to 95 percent. It can produce
a sludge cake ranging from 10
to 25 percent solids concentration.
 Figure 12.

 Basket Centrifuge
26

-------
 Determining Applicability. Centri-
 fuges are effective for dewater-
 mg sludges that contain solids of an
 apparent density greater than
 water, that is to say, solids that want
 to settle. Usually the  feed is treated
 with polymer conditioning agents
 to improve the settling character-
 istics of the solids. Centrifuges,
 unlike some filters, are well suited
 for dewatermg compressible sludges.
 They are also attractive because
 of their compact size and automated
 operation.

 Cake solid  concentration obtainable
 with a given sludge can be deter-
 mined by testing the  sludge on
 a bench-scale centrifuge. Most ven-
 dors have a number of these units
 and will perform field tests or
 do the work in their own laboratories
 if a feed sample is supplied.

 The pilot test procedure determines
 the required size and  performance
 of a solid bowl centrifuge for a
 particular sludge. Tests are per-
 formed to determine whether polymer
 conditioning is needed and, if so,
 the optimum dose. The  unit's
 performance is evaluated at the
 optimum dose with varying feed  ca-
 pacities. Normally, the cake solids
 concentration decreases with
 increasing feed rate, as does solids
 recovery (the percentage of feed
 solids contained in the filter cake).

There is a disadvantage, however,
 in  many centrifuge applications;
 owing to high rotation speed,
 if rotating elements are not well
 maintained, frequent breakdown can
 occur. This problem is particularly
 likely with sludges containing
abrasive solids. Moreover, consider-
able power is required to operate
the unit. New low-speed units,
capable of operating with improved
 power efficiency, are being marketed.

 Costs. Figure 1 3 shows  the unit
cost for the two available classes of
 basket centrifuge. These units
typically use 75 percent of the avail-
able power during the feed-and-skim
stage of the cycle. Figure 13a
  (a)
   60
?  40

cc
cc
         20
     cc
     Q
                                                       Legend/
                                                   -i 110
                                                            100   §
                                                                 L>
                                                                 CC
                                                                 Q_

                                                            90
                                                            80
                                  10

                           BASKET VOLUME (ft3)
                                              15
                                                         20
     SOURCE  Equipment vendors
               (b)    ^   15r
                         10
                          0
                                 I
                                       I
                           0123

                           BASKET VOLUME (gal)

                     SOURCE Equipment vendors
Figure 13.

Basket Centrifuges: (a) Large Unit Price and Hydraulic Drive Horsepower and
(b) Small Unit Price
includes the horsepower rating of
the unit drive for the large centrifuge.
Large units are available with basket
volumes between 8 and  16  ft3
(0.23 and 0.45 m3).

Small units, which are not automati-
cally cycled, are available with
basket volumes of 1 to 2 gal (3.8 to
7.5 L). Small units have minimum
                               installation requirements, and
                               their unit price (Figure 13b) is
                               markedly lower than that of the large
                               units. They are well suited for
                               small operations disposing of drum-
                               load quantities of sludge. The de-
                               watered sludge  can be discharged
                               directly into the drum. The 2-gal
                               (7.5-L) unit can  handle as much as
                               100 gal/h (378  L/h) of sludge
                               feed. Solids recovery,  however.
                                                                                                       27

-------
   (a)
                         Sludge feed sump
   (b)
               150 i-
               125  -
           8
           o
           =.  100  -
           o
           Q_

           55
           Q
                50  —
                25  -
                                                                      Note —PD = positive displacement.
                                                                       Legend:
          Includes annual cost of centrifuge

          Hauling and disposal only
                                              I
                                                        I
                   0       100      200      300      400




                        CLARIFIER UNDERFLOW* (gal/h)
"At $0.43/gal. Sludge dewatered to 20% solids

 by weight.


bAt 3% solids by weight.



Note.—4,800-h/yr operation.
Figure 14.


Basket Centrifuge Systems: (a) Dewatenng System with Auxiliary Equipment and (b) Annual Sludge Disposal Costs
28

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tends to deteriorate at the higher
flow rates.

The unit costs in Figure 13 include
the centrifuge and drive system
and the control hardware  needed to
cycle the unit properly. Other
associated costs are for site prepa-
ration, feed pump, centrate removal,
and piping. Operating cost will be
primarily for power to operate
the unit and for polymer conditioning
agents, which are commonly used
to improve the performance of
the unit and increase its processing
capacity. The small manual units
will also require operating labor to
cycle the unit. The large units
are automated and should require
minimum operator attention.

The small units are reasonable in
cost, but the operating labor required
                                  is excessive for dewatering systems
                                  with average feed rates over 15
                                  gal/h (57 17h). As an example,
                                  a 2-gal (7.5-L) basket centrifuge
                                  dewatering sludge from 3 to 20 per-
                                  cent solids by weight could proc-
                                  ess approximately 13 gal (50 Lj
                                  of sludge feed per cycle. Where the
                                  sludge feed rate is 50 gal/h (190 L/h),
                                  the unit would have to be cycled four
                                  times per hour. Each cycle requires
                                  operator control, so labor cost
                                  would be excessive compared with
                                  that of other equipment.

                                  Figure 14a is  a flow diagram of
                                  a typical basket centrifuge sludge
                                  dewatering system. Figure 14b shows
                                  the annual cost, based on clarifier
                                  underflow rate, of disposal of
                                  sludge dewatered in a basket centri-
                                  fuge. Based on the assumptions
                                  in Figure  14b, at underflow rates
exceeding 1 8 gal/h (68 L/h) the cen-
trifuge system nets a reduction in
annual disposal cost compared
with disposal of sludge without de-
watering. At a disposal  cost of
$0.43/gal,  installing a 2-gal (7.5-L)
basket centrifuge will generate
a reasonable after-tax return on in-
vestment (over 30 percent) for a
clarifier underflow greater than 1 8
gal/h (68
Pressure Belt Filters

The Equipment. The pressure belt
filter (Figure 1 5) is finding increased
application because it offers
certain advantages over other
commonly used dewatering devices.
This filter is especially suitable for
dewatering the large, highly
compressible particle floe char-
                                          Gravity drainage
                                          stage
                                                                       Sludge dumps
                                                                       to new belt:
                                                                       internal water
                                                                       released
                                                                                               Dewatered
                                                                                               cake
   Flocculated
   sludge
Sludge dumps
to new belt:
internal water,
released
   Low pressure
   stage
                                                                                           High pressure
                                                                                           stage
                           Medium pressure
                           stage
Figure 15.

Pressure Belt Filter
                                                                                                       29

-------
acteristic of polymer-treated
sludges. A common problem with
such sludges is that, when subjected
to a pressure gradient, the solid
particles collapse against the filter
medium and block the transport
of water through the medium.
The belt press eliminates this prob-
lem by using gravity to remove
most of the  water. Then,  as the belt
travels through successive regions, a
gradual increase in pressure forces
additional water from  the sludge.

In the first stage of unit operation,
the polymer-dosed sludge is spread
over a slow-moving filter cloth
belt and any free water drains off.
To be suitable for further processing,
the sludge should form a cohesive,
continuous  blanket in this region.
The sludge  blanket leaves the
drainage section and  enters the
mild compression zone.  It is com-
pressed between water permeable
membranes, more water is forced out,
and the sludge layer becomes a
more nearly solid mass. The more
cohesive the sludge layer becomes,
the more  compressive force it can
adsorb without extruding through the
filter medium  or being forced from
between the belts. The compressive
force gradually increases as the
sludge layer travels through the unit—
some models have compressive
limits as high as 100 Ib/in2 (680
kPa). Sludge properties,  cake
thickness, time under compression,
and the magnitude of the compres-
sive force all influence the cake
dryness.

The capacity of a belt press is
determined by belt width and belt
speed. Belt width depends on
the model selected, and ranges
from 1 to 10 ft (0.3 to 3 m). Belt speed
sets the time  the sludge will travel
through the press. Unit capacity
can  be increased by adjustment to
the belt speed to compensate for
a higher feed rate, but only to a
limited degree. The major criterion
for good filter operation is formation
of a cohesive, solid sludge blanket
in the gravity drainage zone.
When feed rate increases, the belt
speed will normally be lowered
to allow additional drainage time;
however, as with other filtration
equipment, cake dryness will usually
fall off as feed rate increases. For
greater  flexibility  in meeting chang-
ing feed conditions, some units
have separate filter belts and
speed controls for the gravity de-
watering and compression zones.
This design also permits the use in
each zone of a filter medium designed
specifically for that zone.

Determining Applicability. Pressure
belt filters are suitable for polymer-
treated  sludge that drains well
and forms a cohesive, compressible
sludge cake when dewatered.
                             The best way to determine their
                             performance on a specific sludge is
                             to have a press manufacturer perform
                             pilot tests with a bench-scale unit.

                             The pilot testing will determine
                             the performance of the filter in terms
                             of cake  dryness and solids capture
                             efficiency at varying polymer
                             dose rates, thus establishing the
                             optimum polymer dose. Once
                             the optimum dose is known, the
                             performance of the unit as a function
                             of feed  rate can  be determined.
                             From these relationships, the size
                             and performance of full-size units can
                             be estimated.

                             Costs. Figure 16 shows the cost
                             and power requirement of a high-
                             pressure belt filter package unit
                             as a function of belt width. The pack-
                             age unit comes complete with a
                                              Legend
   o
   o
   o
       140 r~
120
       100
        80
        60
                                                         T 50
                                                            40
                                                            30
                                                            20
                                                          f-
                                                                 O
                                                                 O
                                                                 Q.
                                                            10
                           4       6

                            BELT WIDTH (ft)
                                                  10
                                                          12
   ''Skid-mounted unit complete with polymer feed pump and dilution tank, flash mix chamber,
   sludge feed, and wash water pump

   ^Includes power for press drives, conditioning tank drive, polymer feed pump, polymer tank
   mixer, and belt wash pump (if needed)

   SOURCE Equipment vendors
                                    Figure  16.

                                    Pressure Belt Filter: Unit Price and Power Requirement
30

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polymer-mixing and feed system,
and includes belt-washing auxiliaries.
The necessary piping and valves
are preassembled and the unit
is skid mounted. The cost range
shown is representative for high-
pressure units; however, prices vary
among the different systems
marketed, mainly because of varia-
tion in belt configuration and degree
of compression achieved.

Belt presses have a major advantage
over centrifuges and vacuum filters
in that they consume consider-
ably less power. Depending on the
size and manufacturer of the belt
press system, total power consump-
tion ranges from 5 to 30 hp (4 to
22 kW). Centrifuges  and vacuum
filters, sized to accomplish the same
service, consume between 15
and 100 hp (11 and  75 kW).

Other associated operating costs
include chemicals for polymer
conditioning and wash water for
continuous cleaning of the filter be It.
Polymer cost can be significant in
the operation of belt filters; for
some sludges, optimum polymer dose
per ton (megagram) of dry solids
can be as high as 200 Ib (100  kg).
Polymer dose rates generally
range from 10 to 50 Ib/ton (5 to 25
kg/Mg), at a cost of $30/ton to
$150/ton of dry solids.  Rates for
wash water to clean the filter belt of
fouling agents vary from 10 gal/
min (38 L/min) for small  units to 100
gal/min (380 L/min) for larger
models. The wastewater load asso-
ciated with the belt wash water
has been reduced significantly by
use of the filtrate from the gravity de-
watering zone of the press to
supply part, if not all, of the wash
water.

In Figure 17, the annual cost  of
sludge disposal associated with
pressure belt filtration is shown as
a function of clarifier underflow
rate, assuming dewatering to 20 per-
cent solids by weight. The pressure
                                    Legend:
                                           includes annual cost of belt filter
                                           disposal only
o
Q_

5
_j
D

Z
<
       120
       100
        80
        60
        40
        20
                     J_
           0          50         100        150        200

                          CLARIFIER UNDERFLOW" (gal/h)


   dAt $0 43/gal Sludge dewatered to 20% solids by weight

   bAt 3% solids by weight

   Note —4,800-h/yr operation
                                                            250
Figure 17.

Pressure Belt System: Annual Sludge Disposal Cost
belt unit size used in the cost
analysis was determined by assum-
ing a maximum hourly feed rate of
approximately 300 gal/ft (37 L/cm) of
belt width. At this feed  rate, a unit
with a  belt 1 ft (30 cm) wide (the
smallest size available) could
process about 75 Ib (34 kg) of dry
solids per hour. Based on the
disposal cost formula used in Figure
17, the pressure belt filter yields
                                a cost reduction compared with dis-
                                posal at 3 percent solids when
                                the underflow rate exceeds 10 gal/h
                                (38 L/h)—despite the unit's high
                                initial cost and its low utilization at
                                that feed rate.

                                For a  plant disposing of its sludge
                                at $0.43/gal, the pressure belt
                                                                                                        31

-------
Pressure belt filter

 Table 8.
 Comparative Total Investment and Annual Operating Costs for Sludge Dewatering
Costs ($)
Feed
sludge
volume3
(gal/h|
50 	
100
1 50 	
200 . . .
250 	
300 	

Filter
press
Installed c
h Annual
investment
. . 29,900
. . 39,100
.. . 39,100
. . 51,700
	 51,700
. .. 51,700

23,000
37,000
51,000
63,000
76,000
89,000
Precoat
vacuum
Installed
investment6
73,000
73,000
73,000
78,000
78,000
78,000
rotary
filter
Annual0
24,000
39,000
55,000
68,000
80,000
93,000
Basket
Installed
investment
34,000
34,000
48,000
1 74,000
1 74,000
1 74,000
centrifuge
b Annual0
37,000
70,000
85,000
89,000
102,000
115,000
Pressure
Installed
investment11
1 04,400
1 04,400
1 04,400
1 04,400
104,400
125,000
belt filter
Annual0
31,000
50,000
69,400
88,000
107,000
1 26,000
 aAssumed at 3% solids by weight.
 blncludes all system auxiliaries.
 "Includes equipment operating, fixed, and sludge disposal costs
 Note.—1981  dollars.
32

-------
filter installation with a belt 1 ft (30
cm) wide would have a reasonable
rate of return (30 percent return
on  investment after taxes) at feed
rates  exceeding 50 gal/h (190  L/h).
Table 9.
Economic Evaluation of Precoat Rotary Vacuum Filter Sludge Disposal
Alternative
                                                                     Item
                                                                                                           Cost
Evaluating the Cost for Sludge       Installation of modifications ($)•"
Dewatering Alternatives                 E—^	     45000
                                              Auxiliary equipment	     11,500
The foregoing sections have de-                                                                         	
scribed the operation, cost, and per-        Total equipment cost	      56,500
formance of equipment types             installation	      4-500
commonly used for sludge dewater-                                                                      „ „„„
     ..       ...     ...                       Total cost including installation	     61,000
ing. Vacuum filters, filter presses.         Contingency, 20% of total mcludmg installation	     12,200
centrifuges, and belt presses                                                                            	
have all found application  for de-           Total installed cost	      73,200
watering sludge from metal finishing                                                                      "
waste treatment.  It is not usually      Annual costs ($/yr).b
necessary, however, to evaluate each      Flxed costs
alternative before selecting a de-             Depreciation on equipment	      7,300
                          °                   Taxes and insurance	       1,600
watering system. Some general              Cost of capltal	        NA
guidelines follow.                                                                                       	
                                            Total fixed costs	       8,900
If disposal costs  are less than
$15,000/yr, it is  unlikely that de-         ^"^^
watering equipment would be justi-              Power at $o.o5/kWh (io hp at 0.75 kWh/hp)	       500
fied economically. Many landfill                  Precoat chemicals at $0.1 o/ib	       700
Sites can solidify or dewater dilute                Operating labor, at $10/h (0.5 h/8 h operation)	       700
sludge, and their capabilities                     Maintenance	      1.000
should be used.                            Total equipment opera,,ng cos,	      2,90o
                                          Sludge disposal fee, at 25% solids and $043/gal	     12,380
The lowest cost alternatives in                                                                          —
terms of capital investment are filter        Total annual operating cost  	     15,280

presses and Small manual  basket           Total annual cost including fixed cost  	     24,180
centrifuges. Minimum  size versions
of both systems can be  installed      ,            .
      A   (tin r\nr>                     Investment justification:
for under $3O,000.                       Current disposal cost at 3% solids ($/yr)	    103,000
                                          Reduction from current cost ($/yr)	     	      78,820
The Small  filter press System,             Average return on investment (%)d	         59
although equal in COSt to the Centri-      Investment payback (yr)e   		K5
fuge. will usually have more capacity.   aElevated Insta,,atlon of precoat rotary vacuum ,,,ter wlth 19.ft2 fllter area.
At  low feed rates, the  cost per unit
of capacity is  lowest for the filter      Based on  1 -050 h/vr of f"ter °Pera"on-
press. The lOW capacity per cycle Of   C4,800 h/yr and 22% operating factor.
the basket centrifuge will require      d($78,820X0.55)/$73,200 (0.55 based on a 45% tax rate).
significant operating labor at          =$73,2oo/[($78,820 x 0.55) + 7,300],
flow  rates above  10 to 15 gal/h
(38 to 57  L/h)                         Note.—1981 dollars. Dewatering 50 gal/h from 3% to 20% solids by weight. NA = not applicable.
Poor-filtering sludges can usually
be dewatered by precoat vacuum fil-
tration. With polyelectrolyte con-
ditioning, most sludges can be
dewatered effectively with a centri-
fuge or belt filter.

Table 8 compares the investment
and annual operating costs of
the four equipment alternatives for
flows ranging from 50 to 300
gal/h (190 to 1,135 L/h). At all levels,
the filter press  was least costly in
general; however, at the higher
range of flows the cost advantage
was less significant. Table 9 gives the
cost factors included in the analysis,
using the example of a precoat
vacuum filter dewatering  50 gal/h
(190 L/h) of clarifier underflow. The
investment had an excellent return,
with payback after only 1.5 yr.
                                                                                                              33

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Table 10.

Sludge Disposal Under Four Dewatering Alternatives: Analysis of Annual Costs
With installed modifications

Item

Disposal solids concentration (% by weight) ....
Cost of modifications ($) 	 	
Annual cost of modifications ($}.
Fixed 	
Operating 	 	

Total annual cost ($) 	
Annual savings ($) 	
Average return on investment (%)' . .
Investment payback (yr)9
Present
conditions Filter
press8
... 3 25
.... — 29 900

— 3 100
. . — 7,600
1 03 000 1 2 300
103,000 23,000
— 80,000
— 147
	 — 06
Precoat
rotary
vacuum
filterb
25
73 200

8 900
2,900
12 300
24,100
78,900
59
1.5

Basket
centrifuge0
20
34 000

4 000
1 6,400e
16 600
37.000
60,200
97
09

Pressure
belt
filterd
20
104 400

12 500
2,500
16 000
31,000
68,200
36
22
"5-ft  filter capacity, 4-h cycle time

b19-ft2 filter area

°Batch solid bowl centrifuge with 2-gal basket

d1-ft-wide belt

eDoes not include cost of polymer treatment, which may be required.

'(Annual savings X 0 55)/total investment (0 55 based on a 45% tax rate).

9Total mvestment/[(annual savings X 0.55) + depreciation].

Note—1981 dollars  50 gal/h clanfier underflow.
Comparing the vacuum filter with
the other equipment types (Table 10),
however, shows that equipment
payback ranges from 0.6 yr for a filter
press to 2.2 yr for a  belt filter press.
The filter press proves the best
choice, mainly because of the low
investment and manpower require-
ments. The 5-ft3 (0.14-m3) cake
volume of the press would only need
dumping every 6 h. A larger press
could be selected to reduce labor, but
the investment would be greater.
Of course, if pilot testing indicated a
sludge with poor filtration proper-
ties, either the properties would
have to be modified or different equip-
ment would have  to  be selected.
34

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References
'U.S. Environmental Protection
 Agency. "Hazardous Waste Man-
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 and Listing of Hazardous Wastes."
 Federal Register 45(98):33084-
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2National Association of Manufac-
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 Small Business. Washington DC,
 NAM, Oct. 1980.

3Richard W. Grain. "Solids Removal
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 Environmental Protection Agency
 and American Electroplaters'
 Society (cosponsors).  Third Con-
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 Feb.  1981.

4U.S. Environmental Protection
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5U.S. Environmental Protection
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6U.S. Environmental Protection
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 May 1 9, 1 980.

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12Roy, Clarence. "Methods and
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  Sludges." In U.S. Environmental
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  600/8-79-014. NTIS No. PB
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13Steward, F. A., and Leslie E. Lancy.
  "Minimizing the Generation of
  Metal-Containing Waste Sludges."
  In U.S. Environmental  Protection
  Agency and American  Electro-
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  Annual Conference on Advanced
  Pollution Control for the Metal
  Finishing Industry.  NTIS No.
  PB 282443. Jan. 1978.

14U.S. Environmental Protection
  Agency. Environmental Pollution
  Control Alternatives: Economics of
  Wastewater Treatment Alter-
  natives for the Electroplating Indus-
  try. EPA 625/5-79-01 6.
  June 1979.

15U.S. Environmental Protection
  Agency. Control and Treatment
  Technology for the Metal Finishing
  Industry: Sulfide Precipitation.
  EPA 625/8-80-003. Apr. 1980.
                                                                                                 35

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16U.S. Environmental Protection       18U.S. Environmental Protection     19Crampton, Peter. "Sludge Handling
 Agency. Control and Treatment      Agency. In-Process Pollution         and Disposal." Paper presented at
 Technology for the Metal Finishing    Abatement: Upgrading Metal-       U.S. Environmental Agency
 Industry: In-Plant Changes.          Finishing Facilities to Reduce Pol- '   Seminar on Handling Electro-
 EPA 625/8-82-008. Jan. 1982.      lution. EPA 625/3-73-002. NTIS     plating Wastes, Philadelphia PA,
                                   No. PB 260546. July 1973.         Sept. 30, 1980.
17Kushner, Joseph B. Water and
 Waste Control for the Plating Shop.                                    20Liptak, B. G. (ed.) Environmental
 Cincinnati OH, Gardner Publi-                                          Engineers Handbook. Vol 1.
 cations, 1976.                                                       Radnor PA,  Chilton Book Co.,
                                                                     1974. P. 905.
                     U.S. Environmental  Protection  Agency
                     Region v   'JV^'V
                     230 3o i-cn Do-vbo-n  Street   -'
                     Chicago, Illinois   60504
 36
                                                                                  Tfr U S G PO -1982 - 561- 644

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