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a <br />11, <br />17 <br />11 <br />filter press hydraulic system - checked monthly (lab) <br />filter plate mating surfaces - cleaned prior to use (lab) <br />filter press oil level in hydraulic reservoir - checked monthly (lab) <br />filter press oil in hydraulic reservoir - replaced annually (maint.) <br />filter press filter media and gaskets - replaced every 4 years (maint.) <br />ii. pH neutralization system <br />mixer - checked monthly (lab) <br />mixer - serviced annually (maint.) <br />PH probes - standardized daily, calibrated weekly <br />PH probes - calibrated quarterly by outside service <br />tank - cleaned out quarterly ( maint.) <br />5. Pretreatment system periodic checklist(s) - See Appendix A <br />6. Description of each specific routine batch process. <br />Chromium treatment unit <br />The chromium treatment unit is operated as a batch treatment system. <br />Conversion coating rinse water undergoes pH neutralization, if necessary, <br />prior to being treated to reduce soluble hexavalent chromium (Cr +6) to <br />trivalent chromium ions (Cr +3), which form insoluble salt precipitates. A <br />coagulant is used to flocculate and absorb these precipitates to cause their <br />settling and removal from the water. An anionic polymer is used to <br />enhance the flocculation. The clarified water will be discharged, and the <br />sludge will be de -watered by the filter press and stored before off-site <br />disposal. <br />r The chromium treatment unit consists of a 1,300 gallon batch treatment <br />tank for chromium reduction, precipitation and settling of the solids, a <br />sludge de -watering unit (filter press), associated pumping and nixing <br />equipment and piping systems. <br />7. Treatment and disposal method for the chromium treatment unit <br />Turn on mixer at full speed. Adjust to pH of 6.0. Actuate chemical feed <br />pump and allow to feed MR -1 to —110 mV. Adjust pH to maintain a pH of <br />6.0. Mix for 1 hour. Add 2.0-2.5 gallons of SWT -732 and mix for 15 <br />minutes. Adjust pH to 8.5-9.0. Add freshly made polymer and mix for 30 <br />minutes. Slow to "0" speed and mix for 20 minutes. Turn off the mixer <br />and wait for 20 to 30 minutes for the floc to settle. Take a sample of the <br />supernatant to measure for hexavalent chromium with the test kit or for <br />total chromium with the AA unit in the laboratory. Record the result and <br />measure the pH. Record the pH prior to discharge. <br />-W—�/fo <br />