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: equipmentcleaning 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 beachieved 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.

9Better 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 WASTESEquipment 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-basedpaint 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 bothsolvent 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 therinse 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.

1 0Waste 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 removepartially 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” willmake 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 recyclesystems 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 usecaustic 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 auditedfacilities, 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.

11Sludge 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 whereverpossible. 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 excludedfrom 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. Sucha 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.

12 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 thepaint 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 processequipment 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 whereverpossible. 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 CARTRIDGESSpent 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 aproblem, 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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