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Pollution Prevention and Control Technologies for Plating Operations
Section 6 - Wastewater Treatment
6.4 END-OF-PIPE TREATMENT SYSTEM DATA FROM THE USERS SURVEY
Exhibit 6-23 presents a summary of the end-of-pipe (EOP) treatment equipment purchased by the survey respondents. Most respondents purchased their EOP equipment in stages. Exhibit 6-23 shows the initial and final purchase dates (years) of equipment and the total capital cost of all equipment purchased. Also shown in Exhibit 6-23 are the types of treatment operations and processes that are present. Appendix B presents further details on these equipment purchases including the manufacturer of each major equipment item purchased (includes information on the initial system and up to three system additions), its cost and the shopís satisfaction level (shops were asked to rate on a scale of 1 to 5 their level of satisfaction with the equipment with 1 being the lowest satisfaction level and 5 being the highest).
For plating shops reporting treatment system costs, the average cost was $252,141 (purchased between 1967 and 1993). The following indicates the percentage of shops that reported the purchase of each type of unit operation:
- CN Cyanide Destruction 44.7%
- Cr Chromium Reduction 58.3%
- pH pH Adjustment 90.0%
- HP Hydroxide Precipitation 85.7%
- SP Sulfide Precipitation 0.0%
- PF Polishing Filter 19.3%
- EV Evaporation 3.7%
- FP Filter Press 75.0%
- SD Sludge Dryer 29.3%
- Oth Other (e.g., ion exchange) 2.7%
Exhibit 6-24 presents a summary of operating data submitted by the respondnents. Columns 1 and 2 show the shop code and the average electroplating wastewater flow rate. Columns 3, 4 and 5 provide treatment system labor information. Shown are the number of annual hours spent for system operation and maintenance, the hourly rate paid to the operators (in some cases the shops provided loaded rates that included overhead) and the total dollars spent annually for labor. Columns 6 and 7 show the annual costs for treatment chemicals and sludge disposal, and column 8 shows the sum of the reported annual operating costs (labor, treatment chemicals and sludge disposal). The final column indicates if a shop reported a compliance excursion (ìYesî) or not (ìNoî) or did not answer (ìNAî) that question on their survey form.
Exhibit 6-25 presents the chemical use data for survey respondents (not all shops were able to submit these data). Available wastestream characterization data for these shops are presented in Exhibit 6-26 (even fewer of the shops had characterization data). These data were used in developing the reagent use formulas in Section 6.3.2. As previously discussed, the data in Exhibits 6-25 and 6-26 indicate that actual reagent use is significantly higher than theoretical use. This is especially true for sulfuric acid. Higher than expected sulfuric acid usage rates are most common during the pH adjustment step in the chromium reduction process. This is most likely due to the buffering capacity of the wastestreams, which is not accounted for in commonly accepted models.