EPA/625/7-90/005

June 1990

GUIDES TO POLLUTION PREVENTION:

The Paint Manufacturing Industry

RISK REDUCTION ENGINEERING LABORATORY

AND

CENTER FOR ENVIRONMENTAL RESEARCH INFORMATION

OFFICE OF RESEARCH AND DEVELOPMENT

U.S. ENVIRONMENTAL PROTECTION AGENCY

CINCINNATI, OHIO 45268
SECTION 3

WASTE MINIMIZATION OPTIONS FOR PAINT

MANUFACTURERS

Description of Techniques

This section discusses recommended waste minimization methods for paint manufacturers. These methods

come from accounts published in the open literature and

through industry contacts. The primary waste streams

associated with paint manufacturing are listed in Table 4

along with recommended control methods. In order of

occurrence at a facility, the waste streams are: equipment

cleaning wastes; spills and off spec paint; leftover inorganic pigment in bags and packages; pigment dust from

baghouses; filter cartridges; and obsolete products/customer returns.

The waste minimization methods listed in Table 4 can

be classified generally as source reduction, which can be

achieved through material substitution, process or equipment modification, or better operating practices; or as

recycling. An example of a source reduction method in the

table is the use of countercurrent rinsing to reduce the

volume of cleaning waste, while an example of recycling

is the working of spilled product back into the process.

Table 4. Waste Minimization Methods for the Paint Manufacturing Industry

Waste Stream Waste Minimization Methods

Equipment cleaning wastes

(rinsewater, solvent and sludge)

Use mechanical wipers on mix tanks.

Use high pressure wash systems.

install Teflon liners on mix tanks.

Use foam/plastic pigs to clean lines.

Reuse equipment cleaning wastes.

Schedule production to minimize need

for cleaning.

Clean equipment immediately.

Use countercurrent rinse methods.

Use alternative cleaning agents.

Increase spent rinse settling time.*

Use de-emulsifiers on spent rinses.*

Spills and off spec paint Increase use of automation.

Use appropriate clean up methods.

Recycle back into process. Implement

better operating practices.

Leftover inorganic pigment Use water soluble bags and liners.

in bags and packages Use recyclable/lined/dedicated

containers.

Air emissions, including pigment Modify bulk storage tanks.

dust Use paste pigments.

Install dedicated baghouse systems.

Filter cartridges Improve pigment dispersion.

Use bag or metal mesh filters.

Obsolete products/customer returns Blend into new products.

*These methods can only be viewed as waste minimization if they allow the continued use of spent cleaning solutions.

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Better operating practices are procedural or institutional policies that result in a reduction of waste. They

include:

l Waste stream segregation

l Personnel practices

- Management initiatives

- Employee training

- Employee incentives

l Procedural measures

- Documentation

- Material handling and storage

- Material tracking and inventory control

- Scheduling

l Loss prevention practices

- Spill prevention

- Preventive maintenance

- Emergency preparedness

l Accounting practices

- Apportion waste management costs to

departments that generate the waste

Better operating practices apply to all waste streams.

In addition, specific better operating practices that apply to

certain waste streams are identified in the appropriate

sections that follow.

EQUIPMENT CLEANING WASTES

Equipment cleaning generates most of the waste associated with paint manufacturing. Following production of

either solvent or water-based paints, considerable waste or

“clingage” remains affixed to the sides of the preparation

tanks. The three methods of tank cleaning used in the paint

industry are solvent washing for solvent-based paint,

caustic washing for either solvent or water-based paint,

and water washing for water-based paint.

Equipment used for preparation of solvent-based paint

is rinsed with solvent, which is then generally reused in the

following ways:

Collected and used in the next compatible batch

of paint as part of the formulation.

Collected and redistilled either on or off-site.

Collected and used with or without settling for

equipment cleaning, until spent. When the

solvent is finally spent, it is then drummed for

disposal.

In 1985, a survey conducted by the National Paint &

Coatings Association’s Manufacturing Management

Committee showed that over 82% of the respondents

recycled all of their solvent waste either on-site or off-site.

With current costs of disposal, onsite distillation of solvent

can be economically justified for as little as eight gallons

of solvent waste generated per day. Of all the solvent that

is recycled, 75 percent is recovered with the remaining

portion disposed of as sludge.

Caustic rinse is used for equipment cleaning of both

solvent and water-based paints, but more often with water-based paints. Water rinsing is usually insufficient in

removing paint that has dried in the mix tanks. Since

solvent rinsing can usually remove solvent-based paint

that has dried, the need for caustic is less.

There are two major types of caustic systems commonly used by the paint industry. In one type of system,

caustic is maintained in a holding tank (usually heated) and

is pumped into the tank to be cleaned. The caustic drains

to a floor drain or sump from which it is returned to the

holding tank. In the second type of system, a caustic

solution is prepared in the tank to be cleaned, and the tank

is soaked until it is clean. Most plants reuse the caustic

solution until it loses most of its cleaning ability. At that

time, the caustic is disposed of either as a solid waste or

wastewater with or without neutralization.

Water wash of equipment used in the production of

water-based paint is the source of considerable wastewater

volume, which is usually handled as follows:

Collected and used in the next compatible batch

of paint as part of the formulation.

 Collected and used with or without treatment

for cleaning until spent.

 Disposed with or without treatment as

wastewater or as a solid waste in drums.

Sludges from settling tanks are drummed and disposed of as solid waste. Spent recycle rinsewater is

drummed and disposed of as solid waste after the soluble

content prohibits further use.

The percentage of solvent-base and water-base paints

produced is the most important factor that affects the

volume of process wastewater generated and discharged at

paint plants. Due to their greater use of water-wash, plants

producing 90 percent or more water-base paint discharge

more wastewater than plants producing 90 percent or more

solvent-base paint. Additional factors influencing the

amount of wastewater produced include the pressure of the

rinse water, spray head design, and the existence or absence of floor drains. Where no troughs or floor drains

exist, equipment is often cleaned externally by hand with

rags; when wastewater drains are present, there is a greater

tendency to use hoses. Several plants have closed their

floor drains to force the use of dry clean-up methods and

discourage excessive water use.

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Waste associated with equipment cleaning represents

the largest source of waste in a paint facility. Methods that

reduce the need or frequency of tank cleaning or allow for

reuse of the cleaning solutions are the most effective.

Waste minimization methods considered include:

Use of mechanical devices such as rubber wipers. In

order to reduce the amount of paint left clinging to the walls

of a mix tank, rubber wipers are used to scrape the sides of

the tank. This operation requires manual labor and hence

the percentage of waste reduction is a function of the

operator. Since the benefits will be offset by increased

labor, mechanization/automation should be considered.

Many new mixers are available that are designed with

automatic wall scrapers (Weismantel and Guggilam 1985).

These mixers can be used with any cylindrical mix tank

(flat or conical bottom).

Use of high pressure spray heads and limiting wash/

rinse time. After scraping the tank walls, high pressure

spray hoses can be used in place of regular hoses to clean

water-based paint tanks. Based on studies (USEPA 1979),

high pressure wash systems can reduce water use by 80 to

90 percent. In addition, high pressure sprays can remove

partially dried-on paint so that the need for caustic is reduced. Tanks used for making solvent-based paints normally employ a built-in high pressure cleaning system. At

Lilly, in High Point, N.C., a high pressure cleaning system

was installed in several mix tanks. By continuously

pumping a fixed amount of solvent into a tank until it was

clean, the overall volume of solvent required for cleaning

was reduced (Kohl, Moses, and Triplett 1984).

Use of Teflon* lined tanks to reduce adhesion and

improve drainage. The reduced amount of “clingage” will

make dry cleaning more attractive. This method is probably applicable only to small batch tanks amenable to

manual cleaning.

Use of a plastic or foam “pig” to clean pipes. It was

reported that much of the industry is currently using plastic

or foam “pigs” (slugs) to clean paint from pipes. The “pig”

is forced through the pipe from the mixing tank to the

filling machine hopper. The “pig” pushes ahead paint left

clinging to the walls of the pipe. This, in turn, increases

yield and reduces the subsequent degree of pipe cleaning

required. Inert gas is used to propel the “pig” and minimize

drying of paint inside the pipe. The equipment (launcher

and catcher) must be carefully designed so as to prevent

spills, sprays, and potential injuries, and the piping runs

must be free of obstructions so that the “pig” does not

become stuck or lost in the system.

Better operating practices. At Desoto, in Greensboro, N.C., wash solvent from each solvent-based paint

batch is separately collected and stored. When the same

type of paint is going to be produced, waste solvent from

the previous batch is used in place of virgin solvent. In

1981, Desoto produced 25,000 gallons of waste mineral

spirits. In 1982, when the system was implemented, waste

solvent production amounted to 400 gallons. This same>

technique is currently being applied to their latex paint

production operation (Kohl, Moses and Triplett 1984).

In some cases, cleaning sludge can be recycled. One of the

audited facilities discussed in the DHS report (Calif. DHS

1987) recycles the sludge from alkaline cleaning of their

water-based paint mix tanks into a marketable product.

Other waste minimization measures based on good operating practices would be to schedule paint production for

long runs or to cycle from light to dark colors so that the

need for equipment cleaning would be reduced. For

facilities using small portable mix tanks for water-based

paints, immediate cleaning after use would reduce the

amount of paint drying in the tank and hence reduce the

need for caustic. Many times, dirty equipment is sent to a

central cleaning operation where it waits until a given shift

(usually night) to be cleaned. While tanks wait to be

cleaned, the residual paint dries up, often necessitating the

use of caustic solution for cleaning. By designing and

operating the cleaning operation to handle any peak load

continuously, all need for caustic should be eliminated or

drastically reduced.

For plants employing CIP (clean-in-place) and recycle

systems for wash/rinse operations, the inventory replacement frequency and waste volume can be minimized by

using these following waste reduction methods:

A countercurrent rinsing sequence. For facilities that

have additional storage space available, countercurrent

rinsing can be employed. This technique uses recycled

“dirty” solution to initially clean the tank. Following this

step, recycled “clean” solution is used to rinse the “dirty”

solution from the tank. Since the level of contamination

builds up more slowly in the recycled “clean” solution than

with a simple reuse system, solution life is greatly increased.

Countercurrentrinsing is morecommon with CIP systems,

but can be used with all systems.

Alternative cleaning agent. Many facilities use

caustic to clean their mixing equipment. When the buildup of solids and dissolved organics reaches a given concentration, the cleaning efficiency decreases and the solution

must be replaced. As reported by one of the audited

facilities, substituting a proprietary alkaline cleaning solution for their caustic solution cut the solution replacement

frequency in half and thereby reduced the volume of

cleaning solution requiring disposal.

*Registered trademark of E.I. Du Pont de Nemours & Co.

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Sludge dewatering by filtration or centrifugation.

The above three methods are useful in reducing the amount

of waste entering the environment provided they allow the

continued use of the cleaning solution. Dewatering only to

reduce sludge disposal volumes should not be viewed as

waste minimization.

Provision for adequate solid settling time in spent

rinse solution.

Use of de-emulsifiers in rinse water to promote

emulsion breakdown and organic phase separation.

OFF-SPECIFICATION PAINT

Most off-specification paint is produced by small

shops that deal in specialty paints. Since these paints cost

more to produce, and therefore sell at a premium price,

most off-spec paint is reworked into a salable product.

Since elimination of off-spec paint production has builtin economic incentives, the following techniques are widely

used:

Increased automation.

Better operating practices. Unless the sludge from

wet cleanup can be recycled into a marketable product, the

use of dry cleanup methods should be maximized wherever

possible. By closing floor drains and discouraging employees from routinely (i.e. needlessly) washing down

areas, some facilities have been able to achieve a large

decrease in wastewater volume (USEPA 1979). Other

effective ways to reduce water use include employing

volume-limiting hose nozzles, using recycled water for

cleanups, and actively involved supervision.

BAGS AND PACKAGES

Inorganic pigments, which may contain heavy metals

and therefore be classified as hazardous, are usually

shipped in 50 pound bags. After emptying the bag, an

ounce or two of pigment usually remains inside. Empty

containers of liquid raw materials that constitute hazardous

waste (e.g. solvents and resins) are typically cleaned or

recycled to the original raw material manufacturer or to a

local drum recycler. Empty liquid containers are excluded

from the following discussion. The following waste reduction techniques for bags and packages were noted:

Use of water soluble bags for toxic pigments and

compounds used in water-basedpaints. When empty, the

bags could be dissolved or mixed in with the paint. Such

a method is commonly used for handling mercury compounds and other paint fungicides. This method could not

be used, however, when producing high quality, smooth

finish paint since the presence of this material could affect

the paint’s film forming property or could increase the load

on the filters which would increase filter waste.

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Use of rinseable/recyclable drums with plastic liners

instead of paper bags.

Better operating practices. Through industry contacts, it

was established that the most effective way of reducing

hazardous waste associated with bags and packages (or any

other waste stream) was to segregate the hazardous materials

from the non-hazardous materials. As an example, empty

packages that contained hazardous materials should be

placed into plastic bags (so as to reduce or eliminate

dusting leading to non-hazardous material contamination)

and should be stored in a special container to await collection.

AIR EMISSIONS

The two major types of air emissions that occur in the

paint manufacturing process are volatile organic compounds and pigment dusts. Volatile organics may be

emitted from the bulk storage of resins and solvents and

from their use in open processing equipment such as mix

tanks. Since most existing equipment is of open design,

reducing or controlling organic emissions from process

equipment could require substantial expenditures in retrofit costs. Additional work on control methods appears to be

warranted in this area, and as a result, the following

measures only address bulk storage and pigment handling.

Control bulkstorage air emissions. Many methods are

available for reducing the amount of emissions resulting

from fixed roof storage tanks. Some of these methods

include use of conservation vents, conversion to floating

roof, use of nitrogen blanketing to suppress emissions and

reduce material oxidation, use of refrigerated condensers,

use of lean-oil or carbon absorbers, or use of vapor compressors. When dealing with volatile materials, employment of one or more of these methods can result in cost

savings to the facility by reducing raw material losses.

Some of the dusts generated during the handling,

grinding, and mixing of pigments can be hazardous.

Therefore, dust collection equipment (hoods, exhaust fans,

and baghouses) are provided to minimize a worker’s exposure to localized dusting and to filter ventilation air exhaust. The waste reduction methods considered consist of:

Use ofpigments in pasteform instead of dry powders.

Pigments in paste form are dry pigments that have been

wetted or mixed with resins. Since these pigments are wet,

less dust or no dust is generated when the package is

opened. In addition, most pigments in paste form are

supplied in drums (which can be recycled) and therefore

would eliminate the waste due to empty bags. While this

method would increase the amount of pigment handling

occurring at the supplier’s facility, it can be argued that the

overall number of handling/transfer points for dry powder

will be greatly reduced along with the probability of spills

and dust generation.
Dedicated baghouse system for pigment loading area.

At Daly-Herring Co., in Kinston, N.C., (while DalyHerring is engaged in the formulation of pesticides and not

paints, there are many material handling problems common

to both industries) dust streams from several different

production areas were handled by a single baghouse. Since

all of the streams were mixed, none of the waste could be

recycled to the process that generated them. By installing

separate dedicated baghouses for each production line, all

of the collected pesticide dust could be recycled (Huisingh

and Martin 1985). While this example is not intended to

imply that most of the dust generated by the paint industry

could be recycled, it does show the overall importance of

keeping waste streams segregated.

SPILLS

Spills are due to accidental or inadvertent discharges

usually occurring during transfer operations or equipment

failures (leaks). Spilled paint and the resulting clean up

wastes are usually discharged to the wastewater treatment

system or are directly drummed for disposal. If the plant

has floor drains, large quantities of water may be used to

clean up water-based paint spills. Dry cleaning methods

are employed for cleaning of solvent-containing spills or

for water-based spills where floor drains are not available.

Wastereduction methods similar to those for off-spec paint

include:

Increased automation.

Better operating practices. Unless the sludge from

wet cleanup can be recycled into a marketable product, the

use of dry cleanup methods should be maximized wherever

possible. By closing floor drains and discouraging employees from routinely (i.e. needlessly) washing down

areas, some facilities have been able to achieve a large

decrease in wastewater volume (USEPA 1979). Other

effective ways to reduce water use include employing

volume-limiting hose nozzles, using recycled water for

cleanups, and actively involved supervision.

FILTER CARTRIDGES

Spent filter cartridges are produced during the paint loading operation. These cartridges are designed to remove

undispersed pigment from the paint during loading and are

saturated with paint when removed. Hence, waste minimization and economy both call for as small a cartridge as

possible so as to reduce the amount of paint lost and the

capital spent for the filters. If frequent filter plugging is a

problem, then it should be first addressed from the standpoint of improving pigment dispersion, and not from the

standpoint of increasing filter area.

Viable alternatives to cartridge filters include bag filters

and metal mesh filters. Metal mesh filters are available in

very fine micron sizes and they can be cleaned and reused.

Since it is very important to minimize all wastes, the issue

of mesh filter cleaning waste reuse or recyling would need

to be addressed before switching to these filters.

OBSOLETE PRODUCTS/CUSTOMER RETURNS

Obsolete products and customer returns can be blended

into new batches of paint. Obsolete products result from

changes in customer demand, new superior products, and

expired shelf life. Marketing policies, such as discounting

older paints, can reduce the amount of obsolete products

requiring disposal.

References

Huisingh, D. and L. Martin. 1985. Proven Profit from

Pollution Prevention. Conference draft. The Institute

for Local Self-Reliance, Washington, D.C.

Kohl, J., P. Moses, and B. Triplett. 1984. Managing and

Recycling Solvents. North Carolina Practices,

Facilities, and Regulations. Raleigh, N.C.; North

Carolina State University.

USEPA 1979. U. S. Environmental Protection Agency,

Office of Water and Waste Management. Development

document for proposed effluent limitation guidelines,

new source performance standards, and pretreatment

standards for the paint formulating point source

category. EPA-440-1-79-049b. Washington, D.C.:

U.S. Environmental Protection Agency.

Weismantel, G., and S. Guggilam. 1984. Mixing and size

reduction (A chemical engineering special advertising

section). Chem. Eng. 92(13): 71-109.

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