By David Chew and Jessie Nelson

When printed wiring board manufacturers increase capacity and/or replace outdated water treatment equipment, wastewater recycling and metal recovery becomes an attractive alternative to traditional water purification, use, treatment and discharge. A case study of a typical recycling/recovery system is analyzed here including goals, operating conditions, problems encountered and operational costs.

Multek Inc. (Irvine, CA) produces multilayered PWBs. In the spring of 1995, Multek purchased a water recycling and copper recovery system for its innerlayer processing facility. Wet processes include pre-clean/scrub, develop/etch/strip, and oxide treatment of all innerlayers.

The project goals included: 1) replace an outdated system, 2) recover copper from the processes listed above, and 3) recycle all copper bearing rinse water as deionized water. Copper, from the rinse water and from process solutions, is electrolytically recovered to eliminate the production of copper hydroxide waste. Non-metal bearing rinses are neutralized and discharged. There is no flow-through precipitation equipment required.

The other option available to Multek was to increase both the capacity of the deionized water production and the capacity of the wastewater treatment system. The recycling option compared favorably because, for the same capital cost, the recycling system treats the wastewater and produces deionized water, while significantly reducing the amount of fresh water required from the city.

In this case, the equipment will recycle up to 30 gpm of copper bearing rinse water and recover up to 25 pounds of copper per day; there is approximately 25 gpm of non-metal bearing rinse water discharged to the local POTW. The design also includes a 10 gpm reverse osmosis (RO) system, which provides water to those non-metal bearing rinses which are not recycled, but require RO quality water. The RO system also provides make-up water to the water recycling system to account for regeneration and evaporation losses (approximately 5 percent of the recycled water).

The equipment was installed and became operational in the summer of 1995.

The metal bearing rinses are treated through carbon and cartridge filtration prior to a patented three-step ion exchange process. The first step is cation exchange for copper removal. Other cations such as sodium and potassium are removed in the second cation step, while anions are removed in the third and final ion exchange process (U.S. Patent #4,863,612). The deionized water is stored and recycled back to the same metal-bearing rinse tanks.

The regenerations from the first cation are collected for copper recovery. Regenerations from the second cation and anion are neutralized and discharged with no further treatment.

Segregating copper by utilizing two cations in series increases the copper concentration in the subsequent electrolytic recovery, which increases its plating efficiency.

The electrolytic recovery consists of a unique combination of electrowinning and ion exchange. The acidic copper solution is sent through a selective ion exchange column as it is cycled through the electrowinner. Effluent copper concentrations from the ion exchange column are below 1.0 mg/l, when discharged to the sewer.

The entire system is monitored and controlled via a computer interface, which shows real time data on a graphic interface, and logs extensive data into a spreadsheet every five minutes.

Steady state operation reveals an average inlet conductivity to the recycling system of 700 mhos/cm. Because of the acidic pH, this corresponds to approximately 300 mg/l total dissolved solids (TDS) as CaCO3. This is primarily sodium, copper, hydrogen (ion), sulfate, and chloride. The average effluent water quality from the recycling system is five mhos/cm (0.20 megohm-cm).

There is an average of 39,000 gallons of deionized water produced per day by the recycling system. The system uses 30 gallons of 50 percent H2SO4, 55 gallons of 30 percent HCl, and 54 gallons of 30 percent NaOH, while discharging 3,250 gallons per day of regeneration waste.

The electrolytic recovery system recovers fifteen pounds per day of copper. This represents an elimination of 239 pounds of copper hydroxide/dithiocarbamate sludge (at 30 percent solids) per day produced at Multek. This unit requires 50 kW-hr per day to reduce the copper and transfer solution.

As one might expect, issues were encountered during the first year of operation. These ranged from rinse tank plumbing errors to inadequate pH adjustment.

Upon start-up, there were some oversights in drain and feed water plumbing in the manufacturing area, which caused hard city water to be continuously fed into the recycling system. This caused two problems. First, the water in the Los Angeles area is very high in TDS, which added to the regeneration frequency of the recycling system. Second, the hardness precipitated as calcium and magnesium sulfate during regeneration of the first cation. The city water actually caused hardness fouling and silica fouling in the ion exchange resin. Once the hard water was found and eliminated, the fouling problems disappeared.

During the year, Multek switched to a different oxide chemistry, which contained a silicated cleaner; this cleaner had the potential to foul the ion exchange equipment. Because the rinse contained very little copper, it was removed from the recycling system and was sent to final neutralization.

There were pH adjustment problems associated with the electrolytic recovery system. These problems were solved by adding a secondary caustic addition to the cycle.

As mentioned previously, the second cation and anion regenerations were to be sent directly to final neutralization. An intermediate equalization tank was added to collect these regenerations before sending them to final neutralization. This was added for two reasons. First, it provided some self-neutralization of acid and caustic, which saved chemistry in final neutralization. Second, it provided a staging area so operators could check copper concentration prior to discharge into final neutralization.

Table 1 lists the actual costs associated with all water and water treatment for innerlayer production. In order to compare this with more traditional water purification, use, treatment and discharge, we have compiled a similar cost breakdown for that type of equipment. The costs are based on operations at Multek’s adjacent building, where they use microfiltration for heavy metal precipitation prior to discharge. The costs are summarized in Table 2.

One can see that there has been significant savings versus traditional, once-through treatment. Annual savings are $226,700; the cost per board square foot has been cut in half from 30 down to fifteen cents at Multek. A closer look shows that most of the cost savings are from two areas: recycling expensive deionized water and eliminating the need for a precipitation system.

The chemical requirements for an ion exchange system are a direct function of the influent TDS. The rinse water used in the production of innerlayers typically runs high because of the disproportionate amount of horizontal equipment used. Horizontal processing equipment traditionally uses less water per panel than vertical, open rinse tank equipment. Oxide is the only process which is not a horizontal, conveyerized operation.

This explains the relatively high influent TDS into the recycling system compared to other, similar installations which treat a combination of inner- and outerlayer wastewater. However, even considering the high TDS of the rinse water, it is still significantly lower than the TDS of the available city water!

There are several points that become important when installing recycling equipment. Obviously, housekeeping becomes even more important. Everything added to the rinse tanks must be removed, since the rinse water returns to the process. Maintenance departments need to pay close attention to conveyorized equipment, and ensure that rollers and other dragout-limiting devices are operational and installed correctly.

Pipe labeling is critical. Labels help to remind operators and maintenance personnel that drains are segregated for important reasons, not to mention the obvious safety implications.

Automatic data logging has been proven an invaluable resource that leads directly to a successful system such as this. Trends and other specific information leads to quick and efficient troubleshooting. It is the opinion of both Kinetico and Multek that automation data has provided the greatest contribution to our mutual success in implementing this system.

The recycling system has proven to be a cost-effective strategy for reducing water use and operating costs at Multek’s innerlayer facility.

Jessie Nelson is responsible for regulatory compliance for Multek’s facility in Irvine, Calif., and Roseville, Minn. He is a graduate of Golden West College in California in organic, inorganic chemistry. Nelson holds several technical certifications including hazardous material/waste management and waste minimization/reduction of industrial waste.

David Chew is responsible for the design and installation of equipment for water recycling and metal recovery applications at the Engineered Systems Division of Kinetico Incorporated. Chew is a graduate of the University of Wisconsin-Madison with a bachelor’s degree in Chemical Engineering. He is currently working towards an MBA at the University of California-Berkeley.

Multek Testimonial

"In one year, Kinetico saved Multek 13.8 million gallons of water ($226,700) and cut waste treatment costs by 50 percent.

"We researched the companies providing wastewater recycling systems, looking for the best solution. Our goals were to replace an outdated system, recover copper from various processes and recycle copper bearing rinse water as deionized water. For the same capital investment, Kinetico’s counter current ion exchange and electrowinning designs provided us with solutions that met our primary environmental goals and provided us with significant cost benefits. The integrated water recycling and copper recovery system treats the wastewater and dumps, produces deionized water and reduces industrial water use. Kinetico understood our objectives and delivered results."

Jessie Nelson, Manager of Environmental Programs. Multek Incorporated, Irvine, California