Section 10. PLATING WASTES

Transcription

1 Section 10. PLATING WASTES

2 I Y 0 4. Tank 4 4 Nickel plating tank containing nickel solution 5. Tank #5 Rinse tank containing well water only Likewise as shown in Figure 1, wastewaters generated from the copper plating line involved parts dipping into the contents of the following six tanks: 1. Tank #6 Caustic cleaners consisting of sodium hydroxide 2. Tank #7 Rinse tank containing well water only 3. Tznk #8 Sulfuric acid tank 4. Tank #9 Rinse tank containing well water only 5. Tank #10 Copper plating tank containing copper cyanide solution 6. Tank #I1 Rinse tank containing well water only Analysis of the above list of tank constituents suggests that pollutant types should be in the categories of aciditylalkalinity, suspended solids. dissolved metals, and cyanide. The preceding paragraphs serve as an introduction to Paul s Chrome Plating, Incorporatedits characteristics of operaticin and potential sources of pollution. The following discussion will concentrate only on the considerations given to industrial waste treatment and no further mention will be made of the sanitary wastewaters. BASIS FOR FACILITY DESIGN Data was required to design the wastewater treatment system properly. To obtain the needed information concerning wastewater composition, samples from the rinse tanks and lagoon discharge were collected. In addition, flow rates were determined for each source of water in the plating shop. The wastewater samples, the analysis of which are presented in Table I. were collected during plant operation. Table I. Analytical Results of Raw Wastewaters Prior to Treatebllity Studies Sampling Point NickeVChrome Lagoon Effluent Copper Rinse Rinse PH Parameter 4 0 ) (mg/l). Flgure 1. Sbematlc of original waslewnter treatment system. The chrome/nickel wastewaters were generated from dipping operations related to the followin8 e tanks : 1. Tank I1 Caustic strip tank consisting of sodium hydroxide 2., Tank U2 Chrome tank containing chromium solution 3.. Tank #3 Rinse tank containing well water only. Alkalinity to Methyl Orange, CaCO, Acidity to Methyl Orange, CaCO, Suspended Solids PhosphorusTotal as P PhosphorusOrtho as P Ammonia, as N C 22 Color, PtCo IronTotal Manganese Oil and Grease Phenol CO c Cyanide Aluminum co.01 co.01 co.01 Copper Nickel ChromiumTotal ChromiumDissolved 0.34 co.01 I.40 ChromiumHexavalent 2.23 Zinc bad <0.01 <0.01 co

3 ~ ~~ ~ The data presented indicated that the copper rinse line was a source of cyanide with concentrations ranging from mg/l. A comparison of the concentration of cyanide in copper rinse wastewaters and lagoon effluent indicated little difference. With rinsewaters from the nickel/chrome plating line diluting copper rinsewaters at about 3:1 ratio (12 gpm:4 gpmsee Table II), the expected concentration of cyanide in the discharge from the copper plating line rinsewaters should have approximated a minimum concentration of 2.0 mg/l, neglecting dilution from runoff and rainfall. However, the lower cyanide concentrations in the lagoon effluent indicated that: (I) the copper plating line was not being used as frequently as normal for the data sampled; or (2) the use of the nickevchrome line was greater than normal. The copper concentrations of 0.45 mg/l and 0.44 mg/l. respectively, for copper rinsewaters and lagoon effluent supported this conclusion. In fact, with the exception of zinc, the same was concluded when comparisons of all metal concentrations were made. Using similar methods of comparison, Table I suggests that the nickevchrome line *as being used more frequently than normal. Analysis of nickel and total and dissolved chromium concentrations for both the nickel/chrome rinsewaters and lagoon ef*ent indicated that a 300% dilution of copper plating line rinsewaters by nickel/chrome rinses would not result in concentrations as low as those appearing in the lagoon. The concentrations of nickel, total chromium, and dissolved chromium of 4.10 mg/l, 1.74 mg/l. and I.40 mga indicated that the nickel/chromium rinsewaters were a source of metallic pollution. The concentration of hexavalent chromium of 2.23 mg/i verified that the ickel/chrome rinsewaters were a significant source of metallic pollution. Table 111 presents the applicable discharge standards for which treatment was designed. Ccmparthe data for the lagoon effluent in Table I with the requirements in Table 111, only cyanide and 'iromium exceeded recommended limits. Based on the analysis of lagoon effluent. treatment procedures emphasized reduction of chromium and cyanide in the discharge. Table IV illustrated the results of the treatability studies. Since metals and cyanide were the expected pollutants, treatment concentrated on these items. For the treated wastewaters from the nickel/chrome plating line, the cyanide and total chromium were reduced to ~0.01 and 0.3 mg/l respectively. Again. assuming equal dilution from both waste streams, the anticipated average effluent concentrations were projected as shown in Table V. These projected concentrations and the analyses presented in Table I indicated that the treated discharge should not contain any pollutants exceeding allowable values. As indicated previously. Table I1 presented actual flow rates and proposed reduced flow rates for 'he wastewater treatment facilities. Although #5 and #I 1 rinse tanks were not in use, flow allotments re made for possible future expansion. 3 recommendations were proposed in Table 11. The first was that the samll parts rinse be rc to an average flow of 2 gpm from the measured 8 gpm. The second was that flows to all rinse IhC be reduced to 2 gpm. These recommendations were necessary to minimize capital required for wastewater treatment. Table 11. Rinsewater Flow Rates Measured Actual Proposed Reduced Source Flow Rates (gpm) Flow Rates (gpm) \+ kel/chrome Rinse Line Small Parts Rinse 8 2 (w.1 #3 Rinse Tank (Chrome Rinse) 4 2 (max.) #5 Rinse Tank (Nickel Rinse) 0 2 (max.) rotal 12 6 hpper Plating Line RI Rinse Tank (Cleaner Rinse) 4 2 (max.) #9 Ripe Tank (Sulfuric Rinse) Nil 2 (max.) #I t%nse Tank (Copper Cyanide Rinse) 0 2 (max.) 'otal. 4 6 AC? Parameter Table 111. Design Discharge Slandards Minimum Maximum PH Average Concentration (mg/l) Maximum Concentration (mg/l) Suspended Solids Oil end Grease IS 30 Phenol Cyanide Zinc 1.o 2.o Copper 1.o 2.0 Nickel 1.o 2.0 Manganese 1.o 2.0 Lead 0.05 Chromium, Total o Chromium, Hexavalent 0.05 Iron Table IV. Analytieal Results of Rinsewaters After Treatability Studies Parameter Copper Rinse (mg/l) Nickel/Chrome Rinse (mgfl) Nickel Copper Zinc 0.04 <0.01 Iron Chromium, Total < Chromium. Hexavalent <0.01 Cyanide <0.01 Parameter Table V. Projected Effluent Concentrations Anticipated Average Effluent Concentrations (mg/l) Copper 0.08 Nickel 0.14 Chromium, Total 0.15 Chromium, Hexavalent <0.01 Iron 0.a Cyanide <0.01 DESCRIPTION OF TREATMENT PROCESS As discussed in prior paragraphs, wastewaters were generated from copper and nickevchrome plating and collected in separate concrete pits. The designed treatment process continued to maintain this segregation because the Wastewaters from ezch plating line were intercepted, collected. and chemically treated in separate batch tanks after each operating day (see Figure 2). The following summarizes the chemical treatment required to produce an acceptable effluent for each plating lint:

4 After supernatant was completely decanted, concentrated sludge was discharged to the sludge storage tank. Copper Wastewaters i Similarly to nickelkhrome, the wastewaters generated during the day were collected in a separate batch treatment tank. The ph was increased to 10.5 with caustic soda. Hypochlorite was added to chemically destroy the cyanide. After a minimum holding time of onehalf hour. the ph of the solution was decreased to 8.5 to 10.0 with sulfuric acid. Polyelectrolyte was added to induce settling. The treated wastewaters separated into phases. The supernatant was decanted to the ph adjustment tank for continuous ph adjustment to with sulfuric acid (H2S04). The contents of the ph adjustment tank was then discharged to Breakneck Creek. When the supernatant was completely decanted, concentrated sludge was discharged to the storage tank. After analyzing the flow schematic and the above treatment methodologies, several similarities can be noticed; however, the chemical treatment for each line is significantly different. Therefore, it was absolutely essential that the above treatment scheme be carefully followed to insure proper wastewater treatment. OPERATING RESULTS Table VI presents data obtained after installation of the wastewater treatment system. The procedures used for treatment have been described in the preceding section. As is illustrated in Table VI, all parameters are within the guidelines prescribed for this facility (see Table 111). An interesting comparison can be made between the values presented in Tables I and VI. The samples obtained for the Table I analyses were collected just after Paul's Chrome Plating began operation; the samples on which the results in Table VI were based, were recently collected. In between these sampling periods, considerable expansion of the business occurred. This increase in business activity is reflected in greater concentrations of wastewater contamination. In particular, metals and cyanide increased approximately ten to twenty times while the other contaminants, Le., suspended solids, oil and grease, and phenol, remained constant between the two periods of sampling. Apparently, electroplating activity has increased in greater proportion to business volume than the cleaning operations. Table VI. Results After Treatment of Plant Wastewaters Lei/Cbrome Wastewaters Figure 2. Schematic of existing wastewater treatment system The segregated wastewaters generated for the entire operating day were collected in the batch eatment tanks. Sulfuric acid was added to the wastewaters to depress the ph to 2.5. Sodium bisulfite (NaHSO,) was added to obtain complete reduction of hexavalent chromium. After about one hour of agitation, the ph of batch treatment tank contents was increased to.510.jpwith caustic soda (NaOH) to precipitate metals as metallic hydroxides. Polyelectrolyte was added and after thorough mixing, phase separation occurred. Supernatant was decanted to ph adjustment tank for continuous ph adjustment to with iifuric acid (H2SO4). ph idjustment tank contents were discharged to Breakneck Creek. Concentration (mn/l) Parameter Before Treatment After Treatment Nickel Copper Zinc Iron Chromium, Total Chromium, Hexavalent Cyanide Lead Manganese Suspended Solids Oil and Grease Phenol ? < M <0.01 <O.oOl <O.oOl

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