F. A. Havlik, P.E. Senior Application Engineer Infilco Degremont Inc. Richmond, Virginia

Transcription

1 PRETREATMENT AND RECYCLE AT WIRE ROPE MANUFACTURE H. U. Nash, P.E. Director. Technical Services Environmental Systems Service, Ltd. Culpeper, Virginia F. A. Havlik, P.E. Senior Application Engineer Infilco Degremont Inc. Richmond, Virginia INTRODUCTION To comply with limits on heavy metals discharged into the municipal sewer system, it became apparent that The Rochester Corporation would have to install effluent pretreatment equipment to precipitate the metals from their wire mill wastes prior to discharge. A comprehensive system was selected that would provide a high degree of treatment and produce finished water suitable for recycle and reuse in the manufacturing process. A significant reduction in city water consumption and sewer fees has been realized which reduces the capital and operating expense of the system. The purpose of this paper is to discuss the design, operation, and benefits of the system. WASTEWATER SOURCES The Rochester Corporation, located in Culpeper, Virginia, produces wire rope and electromechanical cable used in the oil and natural gas industry, in commercial fishing, oil well logging, power transmission, and undersea exploration. The in-house manufacture of high carbon steel wire for these cables requires the use of large quantities of rinse water which becomes contaminated with high concentrations of iron, lead, and zinc. The contaminated rinse water originates in the wire mill on the "patening" line which is a continuous process for finishing the wires before they are twisted into ropes and cables. The process begins when the wire is drawn to the desired diameter and stored on spools. The spooled wire is then passed through the "patening" line which consists of the following steps: 241

2 1. Caustic cleaning to remove wire-drawing lubricants 7 Caustic cleaner rinse. L. 3. Furnace (1800'F). 4. Molten lead quench tank to temper the wire. 5. Cooling tank (closed loop). 6. Hydrochloric acid pickling tank. *7. Pickling acid rinse. 8. Zinc phosphate (optional). *9. Zinc phosphate rinse (optional). 10. Borax flux (optional). 11. Molten zinc tank for hot-dip galvanizing (optional). *Sources of wastewater for treatment and locations for recycled water use. 2. Jar tes waste b machine The res ppm) tr turbidi residua signif 1 Approxi to brir 3. The slt by sett lime ai Figure which t Accelal unit, ( polyme! to ph with tl rate CI The major sources of contaminated rinse water are the pickling acid rinse which is contaminated with lead and the zinc phosphate rinse which is contaminated with zinc. The total flow from the "patening: line is approximately 100 gpm. LABORATORY BENCH STUDIES To determine the most effective treatment, 24-hour composite samples of both the acid and caustic streams were collected and sent to Tecsult Laboratories. Division of Infilco Degremont Inc., Richmond, Virginia, where complete analyses were run and treatment bench jar tests were made. These lab studies may be summarized as follows: Lime, ppm Target, ph Final, ph Lead, ppm Iron, ppm Zinc, ppm 1 The blended m proportioned 1. An acidic waste stream sample and a caustic waste stream sample were blended to simulate process effluent conditions. The blend yielded a mixture with a calculated metals content of 5.6 ppm for lead, 13.4 ppm for zinc, and 128 ppm for iron. 242

3 re-drawing lubricants. per the wire. ik. alvanizing (optional); and locations for 2. Jar tests were run on a 75% acid and 25% caustic waste blend, using liter beakers on a gang-stirring machine, on a 75% acid and 25% caustic waste blend. The results are shown in Table I. Hydrated lime (276 ppm) treatment to ph 10.3 yielded a supernatant with turbidity less than 2 NTU (visual estimate), and residuals for all three metals of interest, significantly below the desired maximum limits. Approximately 44 ppm of sulfuric acid was necessary to bring the supernatant back to a ph of The sludge-settling characteristics were determined by settling in a 1-liter graduate. Results for the lime are shown in Figure 1 and for the caustic in Figure 2. The sludge generated, settled at a rate which wou d allow a maximum rise rate in the R Accelator, Infilco Degremont Inc.'s solids-contact unit, of 0.5 gpm/ft2 even without the aid of a polymer. Treatment with sodium hydroxide (250 ppm) to ph 10.7, instead of lime, gave similar results, with the exception that the maximum allowable rise rate could be increased to 0.9 gpm/ft2. se water are the f with lead and the :d with zinc. The >proximately 100 gpm. TABLE I Jar Test Results Blend lent, 24-hour composite ams were collected and Infilco Degremont analyses were run and follows : nd a caustic waste imulate process yielded a mixture t of 5.6 ppm for lead, for iron. Lime, ppm Target, ph Final, ph Lead, ppm <0.1 <o. 1 <o. 1 (33 ppb) 5.6 Iron, ppm <0.05 <0.05 <0.05 (39 ppb) 128 Zinc, ppm (22 ppb) 13.4 The blended metals content is based on calculation for flow proportioned contribution. 243

4 TREATMENT PROCESS DESIGN with the completion of the lab work, it was now possible recommend the process, size. and types of equipment, as well control logic. The two streams, acid and caustic, would -e in the existing sump as always and then, by gravity, flow to the new treatment plant location where it enters (see Figure the 10-minute mixing and blending tank. The mixing is done b, air and the ph is adjusted with caustic. The flow then enter an upflow solids contact (Accelator) clarifier where the hea metals hydroxide reactions take place. Clear water leaves t unit at the top and accumulated sludge is discharged throu the concentrators at the bottom. The clarifier effluent t goes to the sand filter. The filter media is a single-size sand mm with a U.C. of 1.7 maximum designed for a combination airlwater backwash. The backwash water is recycl to the thickener and filtered water goes to a clearwell. Solution chemical feeders are furnished for feeding acid, caustic, and polymer. The sludge from the Accelator is transferred to a thickener with the overflow from the thickener returning to the mixing and blending tank and the thickened underflow to a filter press. The dried cake from the filter press is put in a dumpster and disposed of in a hazardous waste dump. With regard to control, the plant is designed for six-toeight-hour-per-day attendance and operates automatically. Tim acid and caustic feeders are driven by variable-speed DC motor8 which are ph controlled. The polymer feeder is manually controlled. The ph monitor on the influent also operates an air-actuated dump valve. In the event the caustic pump cannot keep the influent ph within the optimum range for pb on Zn precipitation, the dump valve is automatically opened and the influent is pumped to a 150,000-gallon emergency storage tank. The valve will also open during a power failure or control system failure. An annunciator panel located in the wire dl1 laboratory provides equipment status information and identifier system malfunctions. The new building which houses the wastewater treatment plant is big enough to accommodate additional equipment which could double the present rated capacity of 100 gpm. The plant building is 72'-0" x 40'-0" x 16'-0'' high with a 12'-0'' x 12'-0" access door to bring in future equipment. Bulk storage is provided for caustic in a 6,000-gallon F" tank. Acid is pumped direct from an acid carboy. Polymer Can be fed in either dry form, through a disperser, or liquid fom* 244

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6 PROCESS PERFORMANCE Soon after process start-up in January 1983, the system began to experience occasional upsets which would last from several hours to several days. A thorough review of the system was made by Environmental Systems Service, Ltd. (ESS) of Culpeper, Virginia. ESS was responsible for design and construction of the entire system and was under a one-year contract to operate the process. Their study determined that the process upsets were caused by overflows of high-strength industrial caustic cleaners containing dispersants and chelating agents. These cleaning chemicals, designed to remove wire-drawing lubricants from the wire prior to heat treating, were dispersing any floc formed in the Accelator and were disrupting the process. Since the caustic cleaners contained no lead or zinc contamination and required no treatment, the solution to the problem was the diversion of the caustic rinse waters directly to the city sewer. After caustic diversion, most process upsets have been eliminated. Another minor problem was the lack of adequate iron in the influent to generate a strong sludge blanket in the Accelator. The iron concentrations are low only after the mixing of a new batch of pickling acid in the wire mill. The solution to this problem was to install a small (2 gph) waste picking acid feed into the blend tank at the wire mill. Feeding small quantities of waste acid also reduced the cost of spent acid disposal. Occasional spills of acid and tank overflows still occur which can cause minor upsets, but the process can recover quickly (usually within two hours) without creating significant problems. Benefits from treated water recycle and reuse have been significant. Under present conditions, water and sewer rates for The Rochester Corporation have been reduced by approximately $5, per month because of their ability to recycle water. Operation and maintenance costs for the system average around $3,000.00/month. A tabulation of the overall system results is shown on Table 11. Date Mar Flow city GI - 5( 7: 7' 31 7, 41 6: 8: 6' 6( 9( 1: 5'

7 1983, the system :h would last from i review of the syst, Ltd. (ESS) of TABLE I1 Typical Monthly Results struction of the itract to operate the process upsets were itrial caustic Ling agents. These re-drawing lubricants 5 dispersing any floc ig the process. Sine zinc contamination ) the problem was the tctly to the city :ess upsets have been idequate iron in the ret in the Accelator. - the mixing of a new The solution to this ;te picking acid feed!ding small quantities!nt acid disposal. -flows still occur :ess can recover creating significant I Date Mar Flow To Gallons City Gal. Recycled GPD GPD , , ,820 36, ,380 74, , ,560 68, ,690 85, ,960 69, ,830 60, , ,200 73, ,420 59,120 41, ,540 60,390 Flow Recycled GPM Pb mg/l <0.01 <0.01 Zn mg/l Results Not Yet Tabulated 1 reuse have been ter and sewer rates duced by of their ability to costs for the system ion of the overall 247

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9 Rich8 DI U C' INTR T Intt wate conc that of 1 stan resu el ec chat been heav 1 an F litc dilt 1 der p re 1 el e( eff' BACl I whit In thr cat met a m 250 con

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