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52 <br />• so that information can be fed back to the input so that <br />proper adjustments can be made to improve the process. The <br />classic process engineering diagram shown in Figure 11 <br />summarizes these principles. <br />The requirements on monitoring for effective feedback <br />are: <br />1. That the measured properties respond rapidly to <br />changes in the input parameters. <br />2. That the measured properties accurately reflect <br />the key reactions that occur in the chemical process. <br />3. That the properties be easily and rapidly measured <br />even to the point of automated readings. <br />In processes involving water, pH and conductivity <br />usually are the most reliable feedback monitors. Since the <br />key reaction in most effluent treatment processes is neutrali- <br />zation of the acid water with an appropriate base, monitoring <br />pH to provide input feedback is obviously essential. Moni- <br />toring the conductivity will provide information on whether <br />too much base has been added. In addition, both pH and <br />conductivity can be easily measured and readily automated. <br />This is especially true for conductivity where the equipment <br />is typically easier to maintain than pH meters. Again, <br />complete chemical analyses of the output stream are necessary <br />to better understand the water treatment process. But again, <br />once the process is understood and under control, routine <br />monitoring can be accomplished with conductivity and pH and <br />0