P2 Assessment at Truck Assembly Plant

By: Science Applications International Corporation
McLean, Virginia 22102

EPA Contract No. 68-C8-0061, WA 2-05
SAIC Project No. 1-832-03-200-33

Project Officer:
Mary Ann Curran
Pollution Prevention Research Branch
Risk Reduction Engineering Laboratory
Cincinnati, Ohio 45268

Risk Reduction Engineering Laboratory
Office of Research and Development
U.S. Environmental Protection Agency
Cincinnati, OH 45268

Abstract

The U.S. Environmental Protection Agency (EPA) has developed a systematic approach to identify, evaluate and implement options to reduce or eliminate hazardous waste. The approach is presented in a report entitled "Waste Minimization Opportunity Assessment Manual" (EPA/625/7- 88/003). To encourage use of this manual, EPA is conducting a series of assessment projects under the Waste Reduction Assessments Program (WRAP) -- surveys of waste practices and evaluations of waste reduction opportunities at selected sites.

The report summarized here describes the application of waste minimization procedures to a truck assembly facility. The focus of the assessment was on painting and related procedures. A systematic assessment of the facility identified seven possible options that would be of interest to this company and other companies involved in spray painting, solvent degreasing, zinc phosphating, and electro-coat painting. This facility volunteered to participate in the project and provided technical support during the study.

This Project Summary was developed by EPA's Risk Reduction Engineering Laboratory, Cincinnati, Ohio, to announce key findings of the research project that is fully documented in a separate report of the same title (see Project Report ordering information [provided in source document]).

Introduction

The purpose of this project was to demonstrate the application of EPA's Waste Minimization Opportunity Assessment Manual to a truck assembly facility. The manual provides a systematic, planned procedure for identifying ways to reduce or eliminate waste.

The facility produces trucks and specializes in custom paint colors and designs. This facility assembles five different models. The production processes are primarily related to assembly and painting while the majority of the components of the vehicles are manufactured at other sites.

Production is done on one main assembly line which begins with the chassis (frame rails) and ends with a ready-to-start truck. Associated assembly/finishing procedures such as cab painting, door assembly, phosphating of small parts, etc., are done on small assembly lines which incorporate their finished work into the main assembly line. The assembly line is continuously moving and tight schedule is required to produce the specified number of trucks in one 8-hour period. Production processes selected for this assessment include spray painting, degreasing and phosphating (E-Coat). The following wastestreams are produced at the facility:

• waste paint-liquid,
  
• waste paint-solid,
  
• detackified paint,
  
• paint booth water,
  
• degreasing solvent,
  
• rinse waters,
  
• spent process solutions (cleaner, activator and sealer), and
  
• phosphate bath and tank bottoms.

Procedure

The waste minimization assessment procedure is a systematic framework that can be used by a facility's own employees to identify waste minimization opportunities. As a structured program, it provides intermediate milestones and a step-by-step procedure to understand the facility's processes and wastes, to identify options for reducing waste, and to determine if the options are technically and economically feasible to justify implementation. These procedures consist of four major steps:

1. planning and organization;
   
2. assessment;
   
3. feasibility analysis; and
   
4. implementation.

The focus of the waste minimization assessment was on painting and related processes. The truck company staff participated in the surveys by providing background information and data about the facility, equipment, processes, operating procedures, waste generation, and waste minimization options. The personnel and management at the facility also provided ideas for waste minimization and input to the ranking criteria used for evaluating waste minimization options. This information was used later in the study to incorporate the facility's preferences in the evaluation process.

Results and Discussion

Seven options were identified that are potentially applicable to the facility:

Option 1. Paint Solids Dewatering and Water Recycle

Detackified paint that has accumulated in the paint booth reservoirs over a period of 4 to 6 weeks is pumped directly to a tank truck and hauled to a disposal site. The high water content of the detackified paint increases disposal costs, which are based solely on volume. Dewatering this detackified paint can significantly reduce disposal costs by reducing the volume of waste sent to disposal. Further, recycling the paint booth water will reduce water use and extend the period between required draining and cleaning of the booths; thus both the production downtime and the chemicals needed to maintain the quality of the paint booth water can be reduced.

The detackified paint can be dewatered with the use of a belt filter. The belt filter is an automatic gravity filtration system that typically uses a disposable fabric as the filter media. The detackified paint will be pumped from the paint booth to the belt filter. The fabric media filters out the paint solids and other debris while the water passing through is recycled to the paint booth reservoir. The detackified paint is rolled off of the filter into a drum for disposal.

Option 2. Improve Painting Transfer Efficiency

Transfer efficiency refers to the percentage of paint that leaves the paint gun and is actually deposited on the partūs surface. Two types of spray painting equipment having high transfer efficiencies are high volume-low pressure (HVLP) and electrostatic. The facility currently uses HVLP in their chassis paint booth and achieves a transfer efficiency of approximately 50%. Electrostatic spray painting may further increase chassis painting efficiency; some preliminary tests at the plant have achieved positive results.

The cab painting equipment has been modified and the operating pressure was reduced from 60 psi to 40 psi. Although transfer efficiency is approximately 35%, it is unclear whether further increases in efficiency are technically feasible for cab painting.

Option 3. Procedural and Small-Equipment Changes

The facility is currently investigating a variety of procedural and small-equipment changes to improve their waste minimization efforts for the spray painting operations. The following is a discussion of each change.

• Shipping Unused Paint With the Finished Truck Small volumes (<1 gal) of unused paint are left over from the cab painting operation. Many of the cabs are custom painted, and the unused paint that is not immediately reusable is discarded. The proposed change involves packaging the unused paint in a suitable container and shipping it with the truck for later use by the customer for needed touch-ups. Before implementation, regulatory constraints governing this option will be evaluated.

• Adjusting the Production Schedules to Reduce Color Changes After painting each truck cab, the painting system must be cleaned out unless the same color is used to paint the next truck. Although the painting sequence is presently considered when the overall production schedule is developed, improvement is still possible. The painting sequence should receive still greater consideration because the waste generated from painting is so closely tied to the number of clean-outs.

• Installation of Control and Monitoring Devices and Alarms on Painting Systems The transfer efficiencies of the spray painting operations are operator dependent and are partly related to the air pressures used. High pressures generally reduce the transfer efficiency and therefore increase waste generation. Operators often use higher-than-necessary air pressures because the higher pressures reduce painting time. Reducing air pressure levels involves the use of air pressure controls on the painting system, digital displays of the air pressure that are visible by the foremen, and high pressure alarms. Another device that could be used is a microprocessor control for paint flow; these devices closely control the flow rate of paint and can be expected to increase transfer efficiency.

• Painting Details Over Background Colors Many of the trucks produced at the facility are custom painted. The painting designs often include details such as stripes. Currently, when stripes are ordered, the cab is entirely painted with the color of the stripe. The stripe is then masked, and the cab is repainted with the general or "background" color. This procedure is used because it requires less masking, which is labor intensive. Changing this procedure by reversing the sequence would significantly reduce the volume of paint sprayed and therefore the waste produced by overspray. The higher masking costs may be justified when both the costs for paint and the disposal costs for related wastes are considered.

Option 4. Reduce Paint Mix Volume

Paints for cab painting are custom mixed with the use of an automated device in the paint mix room. The volume of paint mixed is recorded in a computer data base, with the volume depending on the truck model and the type of paint. After painting, the painters return the unused paint to the mix room where it is discharged into drums. The unused volume is recorded in the data base. By reviewing this data base, the facility is able to minimize waste.

Option 4 involves more extensive use of the painting data base to reduce the volumes of paint mixed and paint wasted. The computer software can generate statistical analyses of paint mixed and wasted for different truck models and paint types. Implementing this option is expected to reduce raw material costs (paint) and waste disposal costs (unused paint).

Option 5. Minimize Contamination of Degreasing Solvent

During the wiping process used to degrease the chassis, operators currently use solvent- soaked rags, which are rinsed and stored in a bucket. When the solvent in the bucket becomes overly contaminated with oil, grease, and dirt, it is discarded into a drum to await disposal. This option involves a minor equipment and a procedural change to prevent the contamination of solvent.

To reduce the volume of discarded solvent, the solvent bucket should be eliminated. Instead, a container that delivers fresh solvent by hand pumping should be used to soak the wiping rags. This container should have a secure lid to prevent the operators from rinsing rags in the fresh solvent. Dirty rags should be wrung-out over a waste solvent container.

This option may require that the rags be changed more frequently because the rinsing step currently used would no longer be available. Because these rags are currently recycled through an industrial laundry, additional wastes are not expected from this practice.

Option 6. Ion Exchange With Recycle of Rinse Waters

On the zinc phosphate/E-Coat line, which consists of several processing and rinsing steps, there are three rinse tanks: hot rinse, ambient temperature rinse, and distilled water rinse. The rinse tanks are fed on a continuous basis and discharged to a sewer line that conveys the wastewater to the pretreatment system where it is combined with paint booth waters and then chemically treated. The resultant sludge is considered a listed hazardous waste.

This option involves the use of an ion exchange recycle system to treat the rinse waters, after which they would be recycled to the phosphating line on a continuous basis. The system would reduce water usage and may also reduce the volume of sludge generated by the pretreatment system. Currently, the pretreatment process includes the use of ferric chloride in the flocculation/precipitation system; this results in high sludge volumes. The ion exchange system may reduce the use of ferric chloride by breaking the phosphate complex and by reducing the hydraulic loading of the pretreatment system. The heavy metals, such as zinc, would be retained on the cation column, and the anions, such as phosphate, would be retained on the anion column. The regenerant from the cation column would contain regulated metals and would require pretreatment before discharge. The regenerant from the anion column may not contain any regulated pollutants, and it may be possible to discharge it following simple neutralization, thus eliminating it from the treatment process.

Before implementing this option, the facility should conduct tests to select the optimal ion exchange resins and to determine its effect on the ferric chloride requirements.

Option 7. E-Coat Line Bath Maintenance

The spent process solutions (cleaner, activator and sealer) are discarded approximately every 2 weeks and reformulated with fresh chemicals. The discarded solutions are drained to the treatment system. Concentrated wastewaters such as these require a significant volume of chemical reagents for treatment and result in high sludge volumes. This option involves the use of filtration devices to remove undissolved contaminants and to maintain the solution in working condition for an extended time period.

Conclusions and Recommendations

The assessment phase of the waste minimization procedure included:

• collecting the data,
  
• selecting the target areas,
  
• reviewing the data, and
  
• generating and screening options.

• state of the technology,
  
• availability of equipment,
  
• performance specifications,
  
• testing,
  
• space and utilities,
  
• production effects, and
  
• training.

NOTE: The investment and projected savings for the procedural/small-equipment changes (Option 3) were not determined during the feasibility analysis phase. However, the majority of minimization techniques which make up this option are expected to be implemented by the facility.

The relative comparison used in this study indicates that the three best options are:

1. Option 4 reducing paint mix volumes through closer control,
   
2. Option 5 minimizing solvent contamination by using a different working container and procedures, and
   
3. Option 2 improving transfer efficiency by installing electrostatic painting in the chassis booth.

1. Option 1 dewatering paint solids and recycling the booth waters and chemicals, and
   
2. Option 6 using ion exchange to recycle the phosphate/E-coat rinse water.

Some testing is needed before implementing several of the options.

• For Option 1, testing should focus on determining if recycle can significantly reduce booth chemical use. A conservative assumption was made during the analysis that a 10% reduction is possible.

• For Option 2, the facility should contact electrostatic paint equipment suppliers and request an onsite demonstration.

• For Option 6, bench-scale testing and possibly pilot-scale testing is needed to determine the most suitable ion exchange resins.

The full report was submitted in fulfillment of Contract No. 68-C8-0061, WA2-05 by Science Applications International Corporation under the sponsorship of the U.S. Environmental Protection Agency.

This Project Summary was prepared by staff of Science Applications International Corporation, McLean, VA 22102.

Mary Ann Curran is the EPA Project Officer (see below). The complete report, entitled "Waste Minimization Opportunity Assessment: A Truck Assembly Plant." (Order No. PB_________; Cost: _______, subject to change), will be available only from:

National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
Telephone: 703-487-4650

The EPA Project Officer can be contacted at:

Risk Reduction Engineering Laboratory
U.S. Environmental Protection Agency
Cincinnati, Ohio 45268