Original Date: 06/02/1997
Revision Date: 01/18/2007
Best Practice : Source Reduction and Water Reuse
Committed to reducing waste in all aspects of its business, Sharretts’ primary goal is optimizing water usage while minimizing waste. Sharretts has identified and implemented several innovative ideas in these areas, resulting in mutually beneficial results for the company and the environment. Several techniques and process modifications have also been established to further reduce the amount of water used in process operations.
After significant analysis and investigation, Sharretts determined that the effluent from the plant’s treatment system (Figure 2-2) was sufficiently clean for reuse in other areas of the plant. After treating the plant’s process water, the water reuse system captures the water in a water reuse tank and recirculates it through the various processes. Excess water is then discharged to the publicly-owned Treatment Works. Sharretts is also using a filter press to reduce the water content in the sludge produced during the waste water treatment process. The filtered water is adjusted to the proper pH level and then redistributed through the water reuse system for replenishment of process water.
Sharretts implemented cascading rinses for the running rinse tanks in all of its major plating lines. This countercurrent rinse technique provides improved rinse quality with less water. Primary modifications for this improvement were the installation of baffling and some piping changes. In addition, Sharretts has installed restrictors in its running rinse lines. The restrictors manage and control the amount of water used at each location, while still providing sufficient water quantities to maintain product quality.
Another technique used at Sharretts is drag-out control. Contaminants can be carried (dragged out) from the previous processing tank to the next bath. By increasing the dwell time over the previous processing tank after the parts are removed, contaminants dragged to the next bath are minimized. This technique reduces the water quantity needed for rinsing and increases the lifespan of the baths. Sharretts has optimized its dwell times while still allowing for maximum productivity and through-put on each of its lines.
Sharretts has also installed evaporators on the still rinse tanks after the zinc-plating baths. The rinses are processed through a filtration system to remove contaminants and are then pumped through an evaporator. After the water is evaporated, the remaining concentrated liquid is pumped into the plating bath as a chloride addition, which reduces the amount of input materials required for the bath. Additional benefits include decreased water quantities to be processed through the plant treatment system, reduction of the volume of water purchased for plant operations, reduced hazardous waste generation, increased material savings, and the elimination of chlorides from the waste treatment system. Sharretts uses a similar system on the still rinse tanks after the cleaner stages on two of its production lines.
By initiating these improvements, Sharretts estimates that its hazardous waste production has decreased from 240,000 pounds per year in 1994 to 130,000 pounds per year in 1997. In addition, the company has decreased its chemical costs for waste water treatment from $35,000 to $21,000 over the same timeframe.
Figure 2-2. Emigsville Waste Water Treatment Plant
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