Approaching Zero Discharge in Surface Finishing
A capsule report…
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This guide was prepared by Peter A. Gallerani, Integrated Technologies, Inc., and
Kevin Klink, CH2M Hill. Douglas Grosse, U.S. Environmental Protection
Agency (USEPA), Office of Research and Development, National Risk Management
Research Laboratory (NRMRL), served as the project officer, co-author, and provided editorial assistance. Dave Ferguson, U.S.EPA, NRMRL, served as the technical advisor.
The following people provided technical review, editorial assistance and graphic design: Dr. David Szlag, U.S.EPA, NRMRL; Paul Shapiro, U.S.EPA, Office of Research and Development; Joseph Leonhardt, Leonhardt Plating Co.; Dr. John Dietz, University of Central Florida; Carol Legg, U.S.EPA, NRMRL; and John McCready, U.S.EPA, NRMRL.
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The following is a synopsis of EPA document EPA/625/R-99/008. The complete document is posted on PF Online with permission from David Grosse of the U.S. EPA National Risk Management Research Laboratory. You can also check out other current EPA publications and information from EPA's Office of Research and Development's Center for Environmental Research Information at its Technology Transfer Highlights Homepage at http://www.epa.gov/ttbnrmrl/.
This document provides technical guidance to surface finishers, environmental managers and decision makers on control technologies and process changes for approaching zero discharge (AZD). AZD is one of the key themes underlying the Strategic Goals Program (SGP), a cooperative effort among the U.S. Environmental Protection Agency (EPA), the American Electroplaters and Surface Finishers Society, the National Association of Metal Finishers, and the Metal Finishing Suppliers Association to test and promote innovative ideas for improved environmental management within the metal finishing industry. For more information on this program, see http://www.strategicgoals.org.
In its broadest sense, "zero discharge" means no discharge to any media. More commonly, zero discharge focuses on zero wastewater discharge. This report presents information and strategies for approaching zero discharge for concentrated process fluids and associated rinse waters from surface finishing manufacturing. This focus is intended to minimize discharges of spent and/or underused process fluids. Specific SGP goals addressed in this report are:
- Improved use of process chemistry (SGP goal is 98% metals utilization on product);
- Water use reduction (SGP goal is 50% reduction); and
- Hazardous waste emissions reduction (SGP goal is 50% reduction in metals emissions to air and water, and 50% reduction in hazardous waste sludge disposal).
The following list provides a section-by-section overview of this report:
Section 2: Systematic AZD Planning Section 3: Process Solution Purification and Recovery Technologies Section 4: Rinse Purification or Concentrate Recovery Technologies Section 5: Alternative Surface Finishing Processes and Coatings Section 6: Improving Existing Process Conditions and Practices Section 7: Conclusions Section 8: References Appendix A: Systematic Approach for Developing AZD Alternatives Appendix B: Installed Costs Systematic AZD Planning 1. Is the AZD target a fixed endpoint or an optimization point? 2. What tradeoffs are there between point source and more combined reduction strategies?
3. What tradeoffs are there between up-the-pipe pollution prevention and end-of-pipe pollution control? 4. What combination of technology, technique and substitution would provide the best overall solution? 5. What future production and facility scenarios should be considered? 6. Are AZD solutions well defined? 7. How does the surface finishing process chemistry change with production? Changes in process chemistry can necessitate the need to purchase fresh or make-up process bath chemicals. Similarly, the increased volume of waste process baths and rinses requiring treatment results in more waste treatment chemicals and corresponding increases in waste generated.
This section and related Appendix A provide key considerations for planning through implementation of any AZD project. Without systematic planning and appropriate implementation, an AZD project can fail or fall short of overall potential. The techniques and technologies presented in Sections 3-6 should be pursued within a systematic framework. Specific approaches within these general categories may be used independently or in combination to meet specific AZD goals.
This section presents technologies for in-plant purification and maintenance of surface finishing process solutions and rinses. Pursuing this approach results in reduced discharges through improved use of process solutions.
This section presents technologies for purification of rinses for recycling to surface finishing processes. Pursuing this approach can result in a combination of improved use of process solutions and water.
Section 5 advances alternative surface finishing processes and coatings. Most of the alternative surface finishing processes and coatings can result in substantial reductions in discharges compared to traditional processes.
This section presents techniques for modifying existing process operations and plant practices. Reduced discharges can result in modifications that provide for better process optimization.
This is a supplement to Section 2 that presents a systematic method to guide the identification, development, and implementation of AZD actions.
This appendix provides installed cost information.
Systematic AZD solutions can be developed by integrating holistic source reduction planning, including considerations for multiple sources, composite solutions and life cycle process and facility optimization. Nine key considerations for systematic AZD planning are:
The type of AZD target frames the overall AZD options and the planning approach. A fixed endpoint could be below or beyond the most cost-effective (optimal) AZD target. For example, assume that for a particular wastewater stream, the most cost-effective (life cycle) approach would be to use single-stage reverse osmosis to recycle water and reduce wastewater by 80%. A less-than-optimal AZD target might be to pursue a 50% reduction goal, and a beyond-optimal AZD target might be to pursue a 90% or 100% wastewater reduction goal. These endpoint goals may be based on specific drivers or constraints, such as cost. As zero discharge is approached, the costs for incremental discharge reductions can increase significantly in proportion to the benefits achieved.
Point source AZD strategies involve the use of bath or rinse purification systems for individual tanks or sources. Alternative strategies might include combining compatible streams from different processes for purification/recovery. This could include use of single fixed location recovery systems (e.g., centralized reverse osmosis/ion exchange for recycling rinse waters from several process lines). Another combined strategy would be to use a mobile system to perform intermittent purification/recovery of several point sources. For example, a single mobile diffusion dialysis system might be used to purify/recycle several different acid baths. Combined strategies may be more cost-effective, due to economy of scale, unless there are substantially increased plant interface requirements. Point source systems may offer more flexibility, redundancy and reliability.
Up-the-pipe systems can reduce end-of-pipe system requirements. For example, bath purification and water recycling can combine to reduce wastewater treatment system contaminant loading and hydraulic sizing. In-plant systems may also produce byproducts requiring waste treatment or management.
Sections 3, 4, 5 and 6 present a range of technologies, techniques and process substitution strategies for AZD. Integrated approaches should be considered as potential improvements over single-approach solutions. These sections cover diffusion dialysis, microfiltration, membrane electrolysis, acid sorption, electrowinning, ion exchange, reverse osmosis, vacuum evaporation, atmospheric evaporation and alternative processes.
AZD solutions should consider overall life cycle and future production and facility needs. Potential future requirements may lead to modified AZD alternatives, or more allowances for change. Defining future scenarios may lead to specific phased implementation plans or decisions to accelerate/delay plans for facility renovation.
Whether dealing with a single-point source, multi-process or overall facility alternatives, all significant impacts should be identified and implemented to define requirements for a comprehensive AZD solution. Those include process byproducts, cross-media impacts, plant interface and utility requirements, operations and maintenance requirements. A particular approach may be able to meet the primary AZD performance requirement (e.g., 90% acid reuse) but may present implementation problems caused by other aspects (air discharge requiring ventilation system, permitting, etc). Comprehensive definition of AZD alternatives is important to identify barriers to implementation.
One key dimension is understanding the chemistry for each process step and how the chemistry changes during production cycles, including:
8. What opportunities are there to use existing systems? New systems?
Enhancements to existing systems may produce significant benefits at low cost and overall effort. Additional capital for new systems may result in overall net beneficial gains in capacity, productivity, reduced wastes, automation and space. Beneficial process changes may also result from eliminating or consolidating processes.
