Metal Finishing Industry
Common Pollution Prevention Practices
Pollution prevention has emerged as an effective tool for companies to attain compliance with environmental requirements. As stated in the previous chapter, using pollution prevention as the primary technique for attaining compliance also can reduce operating costs and increase profits. Metal finishing firms have achieved widespread success in reducing pollution using everything from improved housekeeping to advanced technologies.
The primary goal of this manual is to describe the major pollution prevention techniques used in the metal finishing industry. Some of the technologies involve simple installations, for example, retrofitting pipes or drainboards. These methods are cost effective and can be implemented in house without outside consultation. Other methods such as metal removal from liquids and total recycling in a closed-loop system require large capital expenditures. Although EPA and the states do not mandate recycling or zero discharge, urging companies to plan new equipment purchases with these goals in mind should prove cost effective in the long run and help companies sustain environmental compliance and profitability.
This manual does not attempt to make blanket judgments as to the economic feasibility of the pollution prevention options that are presented. The conditions in each facility vary, and the characteristics and quantities of the platables are diverse. However, loss of raw materials in metal finishing can affect at least five distinct cost categories. Facilities should consider the following in any financial evaluation of pollution prevention options:
Assistance providers should take advantage of the expertise and knowledge of local conditions that a facility operator possesses when working with a firm. Assistance providers should also keep in mind that current practices are often the result of employee training. Employees might not know why the facility uses certain work practices. In some cases, the real reason for a practice no longer applies to the current situation.
The following sections present some of the overall strategies that a company should incorporate into a successful pollution prevention program including employee training, housekeeping, leak prevention, spill prevention, inventory management, chemical sample testing, and water quality monitoring.
Employee training can provide workers with the information necessary to minimize waste generation. Companies should train employees in the proper handling of chemicals and the reasons for implementing safer techniques. Employee training should also cover safety, rinsing techniques, and chemical hazards. For instance, only trained employees should be responsible for mixing bath solutions and setting flow levels.
Companies should realize that they might experience increased training costs to capture these benefits (APPU 1995). In general, this training produces a quick payback.
In addition, firms could consider designating specific employees to be responsible for specific tasks and properly training them in appropriate work practices so that they can do the job correctly. The tasks could include inspections of tanks, raw material distribution, and bath mixing. Properly trained employees are more likely to:
Although the benefits of improved housekeeping can be difficult to quantify, simple housekeeping improvements often can provide low-to-no-cost opportunities for reducing waste. Preventative maintenance and proper equipment and materials management can minimize leaks, spills, evaporative losses, and other releases of potentially toxic chemicals. A plant can reduce waste by developing inspection and maintenance schedules, controlling the purchasing and handling of raw materials, removing dropped parts quickly from baths, keeping filters and other process equipment in good working order, and authorizing a limited number of employees to accept and test samples from chemical suppliers (UNCE 1995).
Employees should quickly remove dropped parts and tools from process baths to reduce contamination of the bath. Firms can help speed up such removal by having rakes located in handy places. Shops also should coordinate maintenance schedules with inspection schedules to ensure that equipment is operating at optimal efficiency. Some of the benefits of improved housekeeping and preventative maintenance include:
Companies that have effective maintenance programs can see an increase in up-front labor costs, however, these costs usually are offset by decreased downtime (APPU 1995).
Inspecting tanks and pipes for leaks can lead to immediate reductions in waste at little or no cost. Firms should inspect production, storage, and waste treatment facilities regularly to identify leaks, improperly functioning equipment, and other items that could generate waste. Inspections can be as simple as walking by tanks and visually inspecting them or as complex as formal inspections that include checklists and a log of findings. Frequent inspections can identify problems before they become significant. Piping systems, filters, storage tanks, defective racks, air sparging systems, automated flow controls, and even operators' production procedures (including drain time and rinse methods) should be inspected regularly. Inspection routines could include setting up calibration schedules on all temperature, speed controls, and pH meters; instituting an employee training program; or implementing a computerized tracking system for preventative maintenance procedures (Cushnie 1994).
Spills can be reduced by training personnel in improved material handling and spill prevention methods. Training should include proper use of spouts, funnels, and drip pans during material transfer; design of drainboards to eliminate spills and reduce dragout; maintenance of liquid levels in tanks to reduce overflow spills; use of mops or pigs to clean up spills (as opposed to the use of an absorbent that must be treated or disposed of as a hazardous waste); and use of containment berms to contain spills. Training employees in proper spill prevention techniques can assist in reducing waste generation and disposal costs by eliminating spills and overflows (APPU 1995).
Controlling the purchasing and handling of materials can significantly reduce waste generation. Firms should purchase chemicals in the smallest possible quantities, reducing stockpiles of raw materials. Chemicals that are bought in bulk can be cheaper up front, but material remaining after the product has expired will require disposal. Companies should store materials in a locked space and limit access to a few designated employees. By controlling access to raw materials, operators will ensure that containers are completely empty before new containers are opened (Cushnie 1994).
Companies should label materials with shelf life dates to ensure that they have not degraded. Companies also should use a first-in, first-out policy. These practices will reduce the potential for spills, decrease the likelihood of mixing poor process baths, and minimize waste generated from the disposal of obsolete materials. Management also should establish standard operating procedures for inventory control and purchasing, working with suppliers to take back empty or off-spec containers (UNCE 1995).
In addition, firms should develop strict procedures for mixing chemicals. Mixing procedures should be designed to minimize spills, to provide correctly mixed baths, and to ensure that the baths are operated at the lowest possible concentration to reduce dragout loss.
Many suppliers provide metal finishers with a variety of process chemicals for testing. However, the material that the company does not use stockpiles at the site and must eventually be disposed of, increasing waste generation. If possible, metal finishers should stipulate that test samples will be accepted only if the supplier agrees to take back leftover samples. The unused portion of analytical samples taken from process baths should be returned to the process baths. Furthermore, using a bench test rather than implementing a full-scale test in a process bath will reduce waste generated by chemical testing (Cushnie 1994).
Surprisingly, few metal finishers scrutinize the quality of incoming water in their facility. Companies use water throughout the finishing process, in the cleaning process, and, most importantly, in the rinsing process. Water also is used as process bath makeup. Water quality can impact process efficiency and waste generation significantly. Whether a problem exists is based on many factors including the level of water cleanliness, the sensitivity of the plating chemistry, and the evaporation rate of the system. Hardness in the water decreases the ability of the water to rinse effectively and creates scales on heated surfaces. Some surface water contains high concentrations of calcium, magnesium, chloride, and other soluble contaminants that can build up in the bath and possibly reduce bath life and increase sludge generation. Companies should examine the quality of their incoming water to determine if some treatment of the water is required prior to use in the metal finishing process. For instance, in the Midwest the use of deionized water is more common mainly because of the presence of hard water. Companies can correct this problem by using water softeners that are relatively inexpensive or by deionizing their tap water (Gallerani 1990).
In many baths, the total dissolved solids content of the water tends to accumulate in the rinsing system and plating bath. For example, in closed-loop systems, impurities from many sources tend to build up in process baths. Common contaminants from tap water are calcium carbonate or bicarbonate and, to a lesser degree, chlorides or sulfates. Alkaline baths especially tend to absorb carbon dioxide from the air. Carbon dioxide combines with carbonate contamination in tap water and can cause carbonate levels in these baths to rise quickly. When a firm is not able to discharge bath as dragout, as is the case in closed-loop systems, the level of carbonates will tend to rise requiring additional treatment for the bath. In this case, normal procedures for sodium baths would be to chill a side stream from the bath to precipitate the carbonates and regain control.
Similar problems exist for almost all baths in one way or another. For example, metal impurities can build up from dropped parts or anode impurities. Organic additives combined with metals in the tap water can increase contamination. In each case, the question is the same: How can the bath be treated, and does the problem occur rapidly? In some cases, the problem might never occur or might occur so slowly that bath life is not a concern. For example, baths that degrade themselves, such as chromating baths, normally are changed frequently so that water quality problems never occur. As with all pollution prevention technologies, facilities have to examine their situation and determine whether they prefer using deionized water.
Arizona Pollution Prevention Unit (APPU). 1995. Metal Finishing in Arizona: Pollution Prevention Opportunities, Practices and Cost Benefits. Phoenix, Arizona: Arizona Department of Environmental Quality.
Cushnie, George. 1994. Pollution Prevention and Control Technology for Plating Operations. Ann Arbor, Michigan: National Center for Manufacturing Sciences.
EPA. 1994. Summary of Pollution Prevention Case Studies with Economic Data. Washington, DC: United States Environmental Protection Agency.
EPA. 1989a. Case Studies from the Pollution Prevention Information Clearinghouse: Electroplating. Washington, DC: United States Environmental Protection Agency.
EPA. 1989b. Pollution Prevention in Metal Manufacturing - Saving Money Through Pollution Prevention. Washington, DC: United States Environmental Protection Agency.
Gallerani, Peter A. 1990. Good Operating Practices in Electroplating Rinsewater and Waste Reduction. Boston, MA: Massachusetts Department of Environmental Protection.
University of Nebraska Cooperative Extension (UNCE). 1995. A Tool Kit for Metal Finishers. Lincoln, NE: University of Nebraska.