United States Environmental Protection Agency National Risk Management Research Laboratory Cincinnati, OH 45268 Research and Development EPA/600/SR-95/087 August 1995 vvEPA Project Summary Chromate Recovery from Chromating Rinsewater in the Metal-Finishing Industry Arun R. Gavaskar, Robert F. Olfenbuttel, and Eric H. Drescher The recovery system evaluated in this study combines various aspects of vacuum evaporation and flash distilla- tion. It provides a continuous supply of good quality rinsewater to the chromating line at the Quality Rolling and Dehurring Co. (QRD). Recircula- tion prevents nearly 450,000 gal of wa- ter from going to waste every year. Contaminants removed from the circu- lating water include chromium, zinc, and other dissolved solids. Contami- nants are concentrated in a tiny waste stream (one 55-gal drum) and disposed of. Because QRD uses three different chromate formulations on a single chromating line, this concentrate could not be reused. At plants that use a single formulation, reuse should be possible. Because wastewater (requir- ing treatment) is not generated, the re- covery system reduces operating costs. At QRD, the return on investment was sufficient for the initial capital outlay to be recovered in approximately 4 yr. This Project Summary was developed by EPA's National Risk Management Research Laboratory, Cincinnati, OH, to announce key findings of the re- search project that is fully documented in a separate report of the same title (see Project Report ordering informa- tion at back). Introduction The goal of the U.S. Environmental Pro- tection Agency's (EPA) 33/50 Program is to promote voluntary reductions in the re- lease of hazardous chemicals by 33% by the end of 1992 and by 50% by the end of 1995. One objective of the EPA 33/50 Program is to evaluate, in a typical work- place environment, examples of prototype or innovative commercial technologies that have potential for pollution prevention. Support for this program also was pro- vided by the Connecticut Hazardous Waste Management Service (CHWMS). The goal of this study was to evaluate the techni- cal, pollution prevention, and economic issues involved in using a recovery sys- tem to recover the rinsewater from the chromating line in a metal finishing plant. Chromium is a hazardous metal targeted for early reduction under the EPA's 33/50 Program. The recovery unit tested was manufactured and provided by Cellini Pu- rification Systems, Inc.1 Similar units with varying capabilities may be available from other vendors. The site for the testing was QRD Co., a medium-size metal finishing plant, in Thomaston, CT. QRD has operated the chromating line with the recovery system for about 1 yr. The recovery system con- figuration at QRD is shown in Figure! QRD uses three different chromate for- mulations — blue, clear, and yellow — on the chromating line. The chromating line receives a variety of parts (from QRD's customers) that first are zinc-plated and then chromated. Contamination accumulates mainly in the Rinse 1 Tank, which functions as a Mention of trade names or commercial products does not constitute endorsement or recommendation for use. ------- From Zn Electroplating From Mechanical Zn Plating Still Bottoms Rinse 1 Rinse 2 "Ciear'A \Water Chromate Tank Purge Water | Recapture i Sump \---*--' Tank Cooling \ 500 gal Tower Sample Port Water Recycle Line Figure 1. Chromating rinsewater recovery system. (Sampling locations marked by an asterisk.) ------- dragout rinse. This contaminated water is processed through the recovery unit at an average rate of 1 gal/min. The water is first drawn into the recovery unit still. The contents of the still are recirculated through a steam heat exchanger and a spray nozzle back into the column of the still. The water is heated to 110°F before it goes through the spray nozzle and is flash- distilled under vacuum. In the column, the down-flowing liquid returns to the bottom of the still and the distillate vapor rises upward and is later condensed by a wa- ter-cooled condenser. The condensate is stored in a small side tank, from which it is returned periodically by level control to the Rinse 2 Tank, which is the clean, final rinse. The recovery system is fully auto- mated and integrated into the chromating line and requires very little operator atten- tion. The chromating line operates for 1 shift/ day, but the recovery unit remains on 24 hr/day so that the rinsewater gets ad- ditional cleaning after the contaminant con- tribution from the chromating line stops. Approximately 50 gal/day of fresh tap wa- ter is added into the Rinse 2 Tank to make up for evaporative losses. Once ev- ery 3 or 4 wk, the still bottoms are evacu- ated into the sump tank. The sump tank also stores the rinsate generated when the chromate lines are purged before a formulation switch. When the sump tank is full, QRD plans to process its contents through the recovery unit and concentrate it down to around 55 gal. This 55 gal of concentrate containing chromates can be either reused or disposed of as hazard- ous waste. QRD does not reuse it be- cause it contains a mixture of three differ- ent chromate formulations. Other plants that use only a single formulation may be able to reuse the concentrate. Testing was conducted over one shift (6 hr of continuous chromating line opera- tion) and on the following morning before the next day's shift. Samples were col- lected periodically from the locations shown by asterisks in Figure 1. Product Quality Evaluation Rinsewater quality was monitored throughout the shift, and the results are shown in Table 1. Water quality in Rinse 1 continues to deteriorate as the contribu- tion from the dragout increases. Contami- nation in the Rinse 2 Tank is maintained at very low levels by the periodic influx of clean processed water from the recovery unit. As the Rinse 2 Tank gets full, some water is transferred manually into Rinse 1 to simulate a countercurrent flow through the rinses. Overnight processing, while the chromating line is not operating, helps to reduce contamination further, as observed in the 8:00 a.m. sample collected the next morning. Plants that operate the chromating line three shifts per day will not have the benefit of this additional over- night processing, and contaminants may accumulate to levels slightly higher than those shown for Rinse 2 in Table 1, until an equilibrium state is reached. Processed water coming out of the re- covery unit (before it reaches the Rinse 2 Tank) was also sampled and analyzed (Table 2). A tap water sample was col- lected and analyzed for comparison. The recovery unit reduced contamination of chromium and zinc in the processed wa- ter to levels slightly above levels in the fresh (tap) water supply. Because tap wa- ter at QRD normally is high in dissolved solids, the recovery unit was able to re- duce the total dissolved solids (TDS) level to below that in the tap water. Small amounts of acidic components in the chro- mate solution transfer over into the distil- late as seen from the low pH of the processed water. This, in turn, progres- sively reduces the pH in the Rinse 2 Tank (Table 1). The low pH is not a concern in this operation. Table 3 shows the characterization of the still bottoms and the chromate solu- tions. The contaminants that are removed from the rinsewater can be noticed accu- mulating in the still bottoms. From this table, it can be seen that if the still bot- toms materials is concentrated further, the chromate concentrations would ultimately reach those in the chromate tanks. If only one formulation were being used, the final concentrate could have been returned to the chromate tanks. Zinc and dissolved solids levels in the still bottoms are still relatively low to be of concern during re- use. Pollution Prevention Evaluation Without the recovery system, QRD would maintain a continuous 5 gal/min flow of fresh water to Rinse 2 (clean final rinse). The overspray in Rinse 2 would be collected and sprayed in Rinse 1 (dragout). After Rinse 1, the water would be taken to the on-site wastewater treatment plant. For one 6-hr shift/day, 5 days/wk, 50 wk/ yr operation, 450,000 gal of wastewater Table 1. Water Quality in Rinse Tanks Sample No. Rinse 1 Tank W-R1-1 W-R1-2 W-R1-3 W-R1-4 W-R1-5 W-R1-6 Rinse 2 Tank W-R2-1 W-R2-2 W-R2-3 W-R2-4 W-R2-5 W-R2-6 Time 9:30 a.m. 11:00 a.m. 12:30 p.m. 2:00 p.m. 3:30 p.m. 8:00 a.m.? 9:30 a.m. 11:00 a.m. 12:30 p.m. 2:00 p.m. 3:30 p.m. 8:00 a.m.? Cr mg/L 2.57 12.0 29.5 14.6 24.7 8.91 0.21 0.435 0.589 0.843 1.35 0.593 Zn mg/L 4.5 23.5 61.0 32.5 53.2 26.1 0.4 1.15 1.50 3.28 3.97 2.42 TDS* mg/L 48 162 372 273 374 196 42220 174 141 119 88 28 Cond. nmhos/cm 60 200 475 340 450 312 190 180 160 130 55 pH 4.39 4.20 4.08 4.30 4.14 4.46 280 6.47 7.11 6.85 5.22 4.56 3.90 * Total dissolved solids. Next day. ------- Table 2. Processed Water Quality Sample No. W-PW-1 W-PW-2 W-PW-3 W-PW-4 W-PW-5 W-TW-lt Time 9:30 a.m. 11:00 a.m. 12:30 p.m. 2:00 p.m. 3:30 p.m. 12:30 p.m. Cr mg/L 0.235 0.348 0.437 0.445 0.482 0.079 Zn mg/L 0.338 0.592 0.793 0.796 0.870 0.291 TDS* mg/L 30 32 42 31 9 250 Cond. ^mhos/cm 55 60 80 80 80 400 pH 3.88 3.76 3.63 3.68 3.71 6.39 * Total dissolved solids. Field blank consisting of tap water supply at QRD. Table 3. Characterization of Distillation Still Bottoms and Chromate Tanks Sample No. Still Bottoms C-SB-1 C-SB-2 C-SB-3 C-SB-4 Chromate Tanks Blue Yellow Clear Time 9:30 a.m. 12:30 p.m. 3:30 p.m. 8:00 a.m.? 2:00 p.m. 2:00 p.m. 2:00 p.m. Cr mg/L 162 168 216 224 1,254 1,471 3,860 Zn mg/L 258 277 385 420 1,739 15 0.743 TDS* mg/L 2,280 2,240 3,170 3,610 16,740 3,590 25,110 Cond. ^mhos/cm 2,700 2,500 3,200 4,000 12,000 15,000 28,000 pH 3.52 3.59 3.80 3.95 2.57 1.55 2.87 Next day. Total dissolved solids. (requiring treatment) would be generated annually. Not only would QRD have to accommodate this new influx of wastewa- ter; the sludge generated in their treat- ment plant would have to be handled and disposed of as hazardous waste because of the presence of chromium. By using the recovery system, QRD not only saves nearly 450,000 gal of water, but also pre- vents the creation of a large, new, haz- ardous waste stream. Instead, it generates only about four drums of still bottoms con- centrate that has to be disposed of. This waste concentrate can be avoided through reuse by plants that use only one formula- tion. QRD adds approximately 50 gal of fresh water to the Rinse 2 Tank daily to make up for evaporative losses in the system. Economic Evaluation Table 4 lists the major costs of operat- ing with and without the recovery system. The recovery unit provides a savings in annual operating costs of $23,082. QRD's recovery unit cost $78,000 with an addi- tional $9,000 cost for installation and aux- iliary equipment (such as cooling tower, piping, etc.). A payback period of 4 yrwas estimated at QRD for the investment. Conclusions The recovery system at QRD prevents the generation of large volumes of waste- water and hazardous sludge that other- wise would result from the chromating operation. Further pollution prevention would be possible at plants that use only one formulation, through potential reuse of the chromium contained in the still bot- toms concentrate. Rinsewater quality is maintained at acceptable levels through- out the shift without adding large volumes of fresh water. By eliminating wastewater treatment costs, considerable savings are realized at QRD that result in a reason- able payback period. This system has potential for use in many applications that generate waste- water. One concern is the relatively high energy (steam) consumption of the recov- ery unit. Future versions of this system are focusing on reducing this energy re- quirement. The full report was submitted in fulfill- ment of Contract No. 68-CO-0003, Work Assignment No. 3-36, by Battelle under the sponsorship of the U.S. Environmen- tal Protection Agency. ------- Table 4. Major Operation Costs Comparison Item Annual Amount Without Recovery System Water (rinse) Wastewater treatment 450,000 gal 450,000 gal With Recovery System Water (rinse, makeup) Water (cooling, makeup) Waste disposal Energy - electricity - steam Maintenance Labor 12,500 gal 12,500 gal 55 gal 60,950 kW hr 3,000,000 Ib 100hr Unit Cost, $ Annual Cost, $ 4.65/1,000 gal 88.00/1,000 gal TOTAL 4.65/1,000 gal 4.65/1,000 gal 350.00/55 gal 0.068/kW hr 0.004/lb 8.00/hr TOTAL 2,093 39,600 41,693 58 58 350 4,145 12,000 1,200 800 18,611 ------- Arun R. Gavaskar, Robert F. Olfenbuttel, and Eric H. Drescher are with Battelle, Columbus, OH 43201. Lisa Brown is the EPA Project Officer (see below). The complete report, entitled "Chromate Recovery from Chromating Rinsewaterin the Metal-Finishing Industry,"(OrderNo. PB95-243044; Cost: $17.50, subject to change) will be available only from: National Technical Information Service 5285 Port Royal Road Springfield, VA22161 Telephone: 703-487-4650 The EPA Project Officer can be contacted at: National Risk Management Research Laboratory U.S. Environmental Protection Agency Cincinnati, OH 45268 United States Environmental Protection Agency National Risk Management Research Laboratory (G-72) Cincinnati, OH 45268 Official Business Penalty for Private Use $300 BULK RATE POSTAGE & FEES PAID EPA PERMIT No. G-35 EPA/600/SR-95/087 ------- |