COST-EFFECTIVE WASTE MANAGEMENT FOR METAL FINISHING
FACILITIES: SELECTED CASE STUDIES
Gary E. Hunt, Environmental Engineer
Radian Corporation
Research Triangle Park, North Carolina 27709
Richard W. Walters, Assistant Professor
Department of Civil Engineering
University of Maryland
College Park, Maryland 20742
INTRODUCTION
Under current Federal regulations the metal finishing industry must control the wastewater and
hazardous wastes they generate. This can be accomplished through the use of cost-effective waste
management techniques. These range from simple water conservation techniques to more advanced
material recovery systems. All of these methods are based on readily available technologies, which
are simple and inexpensive to install, operate, and maintain. A systematic application of these methods can result in a significant reduction in the cost of wastewater treatment and hazardous waste
disposal. Yet, these techniques are not widely used within the metal finishing industry.
This paper presents some of the results of two studies into the application of these techniques to
metal finishing facilities within Maryland [1,2]. This work was sponsored by the Maryland Hazardous
Waste Facilities Siting Board. The Board recognized that many of the waste generators within the
State did not have the technical capabilities to develop cost-effective waste management strategies.
Thus, the Board investigated means by which industry could be provided with assistance on hazardous
waste management.
In these studies, selected metal finishing facilities were given detailed engineering and economic
evaluations of waste management techniques applicable to their facilities. The methods were selected
based on their cost and effectivenes in reducing wastewater and hazardous waste generation rates.
The selection was based on inplant process evaluations and, if necessary, bench scale treatability
studies.
In the following sections, an overview of the most important waste management techniques are
discussed along with examples from both the literature and the case studies. Additionally, a detailed
discussion of the results of four of the case studies is given.
WASTE MANAGEMENT TECHNIQUES
Water Conservation
The subject of water conservation has been widely discussed in the literature and the techniques
are simple, inexpensive, and well known [3-6]. Yet, none of the evaluated facilities had any significant
water reduction program. A 10 to 45% reduction in water usage could be realized by using proper
rinse tank design, mechanical flow controls, counter-current rinsing, and rinse water reuse.
Proper rinse tank design is the basic component of a water conservation program. Water flow
rates cannot be reduced if the rinse tanks do not provide adequate rinsing. The most important factor
in rinse tank design is to ensure that the rinse water is completely mixed. This will eliminate short
circuiting of the feed water and effectively use all of the tank's volume. As shown in Figure 1, a
rinse tank should include a feed water distribution line, air agitation, and a flow control valve. The
water feed line will evenly distribute the fresh water throughout the tank's volume. This line can
easily be constructed by drilling holes at 3-inch intervals into a PVC pipe and capping-off one end.
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