science, research, technology RUMBLES SEPTEMBER 2015 | 33 • In activated sludge, the desirable microorganisms are those that have the capability, under the right condi-tions, to clump and form a gelatinous floc that is heavy enough to settle. The formed floc or sludge can be then be characterized as having a sludge volume index. • The optimum pH range is between 7.0 and 7.4. Although growth can occur at pH values of 6 to 9, it does so at much reduced rates (see Figure 1 and Table 1). It is also quite likely that undesir-able forms of organisms will form at these ranges and cause bulking prob-lems. The optimal pH for nitrification is 8.0, with nitrification limited below pH 6.0. • Oxygen uptake is optimal at 7.0 to 7.4 pH. Biochemical oxygen demand removal efficiency also decreases as pH moves outside this optimum range. Mary Evans is a Regional Account Man-ager for Premier Magnesia, Flint, Texas. She is a Past President of the Water Environment Association of Texas and is the laboratory event coordinator of the WEF Operations Challenge Committee. Gary Sober is the Vice President of technol-ogy for Byo-Gon Inc., Chandler, Texas. Please Note: The information provided in this article is designed to be educational. It is not intended to provide any type of professional advice including without limitation legal, accounting, or engineer-ing. Your use of the information provided here is voluntary and should be based on your own evaluation and analysis of its accuracy, appropriateness for your use, and any potential risks of using the informa-tion. The Water Environment Federation (WEF), author and the publisher of this article assume no liability of any kind with respect to the accuracy or completeness of the contents and specifically disclaim any implied warranties of merchantability or fitness of use for a particular purpose. Any references included are provided for infor-mational purposes only and do not consti-tute endorsement of any sources. Table 1. Measurement of nitrification activity at a pH of 7.2 and lower. Source: EPA-625/4-73-004a, Revised Nitrification and Denitrification Facilities Wastewater Treatment, U.S. Environmental Protection Agency Technology Transfer Seminar.
RUMBLES - September 2015
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