Integrated solutions for total industrial water management. SEVEN GOOD REASONS TO RECIRCULATE YOUR RINSE WATER Introduction Across the country and around the world, the printed circuit board industry is facing one challenge after another. The industry is faced with ever increasing water, sewer, and especially wastewater treatment and disposal costs, while confronted with strict enforcement of lower, ever decreasing discharge limits. Extremely high fines and liabilities for non-compliance, plus bad publicity are other motivating factors. These challenges demand that we re-examine how and why we use water, and sometimes, the conclusions we reach are surprising. We often hear the term "zero discharge", and most of us wonder if there really is such a thing. The approach to zero discharge, by definition, means you have to recycle your water. How and why are circuit board manufacturers recycling water today? This article illustrates this by describing several systems installed during the last five years, that typify seven reasons why water recycling makes sense, and one or two where it doesn't. To begin with, the goal of zero discharge, isn't the real reason to recirculate rinses; the reasons are much more fundamental. Table 1 shows seven reasons why it might make sense to recycle water in PCB manufacturing operations. The first reason, saving money, seems obvious, but around the country, combined water and sewer costs vary from less than $2.00 to over $5.00 per thousand gallons. In some parts of Europe the total cost for water is over $10.00 per thousand gallons. If you are blessed with an abundant supply of relatively cheap good quality water, you may not think that this applies to you, however, do you know what it costs you to treat wastewater? Often this is not accurately known, and it is probably much higher than most people expect. Typical treatment and sludge disposal costs add another $3.00 - $12.00 per thousand gallons, depending upon the size and complexity of the treatment system. This combined cost of $5.00 - $15.00 per thousand gallons can provide a powerful incentive to recycle water. The first example is a new, printed circuit board plating line. The plant has a water and sewer cost of just over $5.00 per thousand gallons. At full production, it would use 60 gpm of rinse water, 24 hours per day, 6-7 days per week. Without water recirculation, the annual cost for water would be over $150,000, plus there were "capacity" changes in the sewer rate schedule for each gpm of peak flow. Figure 2 shows schematically how water use will be slashed 89%, saving over $130,000 per year. Thanks to simple process chemistries and only one metal, copper, being present, this facility requires no other wastewater treatment equipment, and produces no F006 sludge! This also illustrates how water recycling contributes to reason numbers three and six, in Table 1. The cost of this equipment is approximately $250,000, which is not much more than the cost for a conventional treatment system for the same flow. Another printed circuit board manufacturer faced a mandatory 25% water use reduction, and was expecting business to significantly increase in the coming year. They had two choices: either build a new plant somewhere else, or find a way to expand in the same location and use less water. Analysis of all the rinses showed a good potential for water recycling; approximately 70% of the rinse water could be easily recycled, and a large portion of this was deionized water, which was used once and then waste treated. The cost of this deionized water was approximately $10.00/1,000 gallons, which made recycling even more attractive. In this case, two separate water recycling systems were selected, one for dilute, copper containing rinses, and a second system for dilute rinses, which contained lead. Separate systems were recommended in this case to avoid lead sulfate precipitation, which would occur if the rinses were combined. In this case, 30% of the rinses are still sent to conventional treatment because it didn't make economic sense to go further. The real benefit is that in addition to complying with water usage requirements, this manufacturer can now expand without additional investment in wastewater treatment equipment (Reasons one, two and four). An example of how water recycling can be used to segregate regulated from non-regulated waste and also create a zero discharge facility is at a large aerospace facility in Colorado. This is a huge, multi-building complex with one central wastewater treatment plant designed for several hundred gallons per minute. Like many aerospace companies, they manufacture a large variety of parts and have both regulated and unregulated flow going to the same treatment system. Because of two 10-20 gpm flows which contained regulated metals, all of the sludge produced from a 700 gpm treatment system had to be managed as hazardous waste! Since they used a lime precipitation system, this was several tons of sludge per day! Recycling the regulated rinse waters and hauling away the wastes could allow delisting of the wastewater treatment sludge, which could already pass the TCLP test. The preferred solution was to totally isolate the regulated, metal containing flows. Ion exchange was used to recirculate the rinses, and all regenerations and dumps of spent treatment solutions were evaporated down to the point where solids began to precipitate, and then hauled away by a licensed waste hauler. In this case, zero discharge means no continuous flow to drain, not zero waste. How close to true zero discharge did they get? What had been a regulated flow of up to 40,000 gallons per day, is now 200-300 gallons per day of concentrated waste. That's 99% plus of the way to true zero discharge. How does this example relate to your operations? Do you have rinses which are non-hazardous and non-regulated mixed in with wastes you are required to treat? If you do, how difficult would it be to separate them? Sometimes by segregating out a regulated material, it can be recovered in pure enough form to be of value to a recycler, whereas mixed metal wastes have essentially no value. An example from another industry exemplifies reason number five, is shown in Figure 1. A company decided to locate a new plant, which makes stainless steel fittings in western Pennsylvania. The only wet operations consisted of alkaline cleaning, nitric acid passivation and their rinses. There were ony a few problems with the site that was chosen; there were no floor drains in the plant; the only place to discharge to was a small creek, and if they had to get a discharge permit, it would delay the start-up of the whole plant. Due to TDS limits, toxicity testing requirements and metal limits in the ppb range, as well as wanting to get the plant operating as soon as possible, it was decided to make this operation zero discharge. Much like the previous example, all the rinses were recycled using ion exchange, and all regenerations and solution dumps are sent to an atmospheric evaporator for volume reduction. In addition to this, an oil separator was used to remove free oil from the cleaner. What might have been a 4-6 gpm flow to a conventional wastewater treatment system, resulted in less than three drums of waste in the first six months of operation and now at full production is <1 drum of waste per month. In addition to this, there are no wastewater monitoring reports to fill out, no toxicity tests, and no liabilities which would be present if there were a discharge. Due to the cleanliness of the parts being treated and the tiny amount of metal that is dissolved, this is virtually a zero discharge plant. Another "zero discharge" facility example is a circuit board assembler who previously had no wet processing. The switch away from freon for final cleaning after soldering, however, required aqueous cleaning with hot DI water. Not wanting to deal with discharge regulations, and low operating costs for the 6 gpm of DI water at 130oF, were the factors which made this facility decide to install a closed-loop rinse recirculation system, as illustrated in Figure 4. The operating costs for 6 gpm of hot DI water for a two-shift operation would have been over $34,000 per year ($4,750 for water and sewer, $8,640 for deionization, and $20,800 for electric heat)! The operating cost for the recirculating system is less than $3,000 per year and the waste disposal cost for the neutralized regenerations is less than $2,000 per year. Again, the potential hassles with permits and reports and discharge limits were entirely avoided (Refer to Figure 3). Table 2 lists several features common to all of the water recycling system users. Not every facility should recycle water. The decision must be made in the context of several important variables which vary considerably from place to place (These are shown on Table 3). In particular, discharge limits and the quality of water required can have a strong influence on the choices. The technology used for water recycling is also an important choice as well as the decision to recycle at the source or after conventional treatment. Recycling after conventional treatment may seem attractive, since it is a simple addition to existing equipment. On the other hand, it doesn't reduce the costs for conventional treatment, nor does it reduce the sludge volume produced by it. Two examples where the decision not to recycle water show how these factors can influence the decision. The first example is a small prototype circuit board manufacturer. Production volumes were very low at this shop, water was cheap and of good quality, further, the discharge limits were at the maximum allowed under federal guidelines. At this location, grab samples of the effluent were often below the discharge limits without treatment. The goals at this facility were to achieve strict compliance at low capital cost and, especially, low labor requirements. Figure 4 shows how this was accomplished. An ion exchange system which selectively removes copper and lets other ions pass through was used on the copper rinses which were segregated from other rinses. The other rinses are sent directly to final pH adjustment. Process solution dumps are either batch treated or sent to a 10 sq. ft. electrowinner. Ion exchange regenerations of <50 gallons every two weeks are also sent to the electrowinner. In this case, water recycling would have generated several hundred gallons per day of waste and required nearly full time operation of the batch treatment system, instead of infrequent operation with the chosen system. A final example is another new facility, which doesn't plan to recycle any water and believes that this is the best decision. This operation plates copper alloy lead frames. The solutions used include ammonium persulfate, MSA, an MSA tin/lead plating bath and an ammonium bifluoride stripper. The primary goal of this facility is to get as close as possible to zero hazardous waste, not zero discharge. This facility also has ammonia, fluoride and TDS limits, in addition to metals limits. Calculations show that these three non-metal limits will be met in the combined rinses, but cannot be met if the flow of water is reduced by recycling. The only way to meet the primary goal in this case is not to recycle the water. The copper, tin and lead are recoverable by electrowinning to produce recyclable by-products rather than sludge. If the TDS and fluoride were above the allowable limits, the only ways to bring them down would also make solid and/or liquid wastes, which are much less desirable. These two examples show that water recycling may not be the best solution for everyone. There are many good reasons to recycle water, and once in a while, a few good reasons not to. Along the way there are many choices to be made. Hopefully, this article will stimulate interest and help make those choices easier. Table 1: Seven Reasons To Recycle Water 1. To save money on water, sewer and wastewater treatment. 2. To comply with mandatory water use restrictions, while maintaining or increasing production output. 3. To recover and/or reuse valuable materials. 4. To reduce hydraulic loading on wastewater treatment equipment. 5. To meet discharge limits which are beyond the capability of conventional or even advanced treatment technology. 6. To reduce or eliminate sludge produced by conventional treatment, or to segregate hazardous from non-regulated wastes. 7. To produce high purity water at very low cost for spot-free, ionic contamination free products. Figure 1: Zero Discharge Stainless Clean and Passivate No pix Figure 2: Printed Circuit Board Plating Line No pix Figure 3: Zero Discharge for Final Circuit Board Cleaning After Assembly No pix Table 2: Common Features 1. All had discharge limits which would have required technology beyond simple neutralization and clarification, or had a payback for water recycling of less than four years. 2. All made serious efforts to reduce dragout before adding water recycling equipment. 3. All of them installed equipment to minimize any solution dumps and treatments. 4. All of them still make some waste, but much less than conventional treatment. 5. All of them decided to recirculate water at the source, rather than at the end of the treatment system. 6. All of them used deionized water for bath make-up to minimize contaminants, and extend the bath life between dumps or treatments. 7. All of them use as much or more water in their rinses than they did before recirculating their rinse water, resulting in cleaner parts and less contamination of subsequent process solutions. 8. Every one of them thinks they made a better choice than simply installing a conventional treatment system with no water recycling. Table 3: Important Variables to Water Recycling Decisions 1. Available Water Supply, Cost & Quality 2. Quality of Water Needed 3. Cost of Wastewater Treatment 4. Discharge Regulations 5. Process Chemistries Used 6. Source or End-of-Pipe 7. What Technologies Can Be Used To Recycle Water