Metal Finishing Guide Book

2013

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waste or regulated waste. Finally, in the rinsing process there is the cost of water in purchasing, sewer charges, and treatment and testing costs before disposal to sewer. Original Rinse Water Treatment Process and Associated Costs. Company XYZ's original rinse water treatment to remove dissolved metals was with electro-precipitation. (Electro-precipitation is a technology using a combination of oxygen from air and electrochemical reactions at the anode and cathode that causes dissolved metals to precipitate out of solution and form a sludge.) The process does not require chemical additives, unlike other methods of treating dissolved metals. Company XYZ would recirculate the treated water back through their rinsing system and their scrubber until sufficient salts built up in the water to cause rinsing problems. The system used significant amounts of compressed air to oxygenate the water and significant electricity—both for pumpFigure 2. Reverse Osmosis System, 3,200ing water through the system and for gallon per-day output at Company XYZ. the precipitation electrodes. This system also treated the scrubber water from the chrome exhaust system in the same way. Chrome mist from the chrome plating tanks was captured by the scrubber water. This scrubber water required treatment in the same electro-precipitation system to remove the chromium. The total energy consumption of the electro-precipitation water treatment was 192,196 kWh per year at a total electricity cost of $16,041 per year. The annual cost for disposal of the hazardous sludge from the electro-precipitation process was approximately $7,900. Another cost was scrubber ball disposal twice a year due to biofouling associated with high mineral and organic content of the recirculated electroprecipitation water. The electro-precipitation process cannot remove organics and the acid and alkaline rinses produce salts, which also cannot be removed by this process. The cost of scrubber cleanout labor, scrubber ball replacement, and scrubber ball disposal as hazardous waste was approximately $22,400 per year. Therefore, the total costs associated with the electro-precipitation process were $46,341 per year. The original electro-precipitation treatment process had the following electricity consuming components, which ran 24 hours a day and 7 days per week: • • • • • 674 (3) 1 HP Water Circulation Pumps (1) 2 HP Water Circulation Pump (1) 1 HP Reactor Pump (1) 1 HP Filter Pump (1) 5.8 HP Sludge Blower

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