'

Two are the parameters characterizing hydrolysis of slowly biodegradable substrate, kh and Kx. The third is the parameter describing ammonification, ka. These parameters can be evaluated with data collected with the CSTR receiving feed conforming to a daily cyclic square wave pattern.19 This is done by nonlinear curve fitting of ASM No. 1 to the OUR data collected during one feed cycle. All other parameter values are known or assumed. The OUR pattern for such a bioreactor was shown in Figure 8.7. The plateau in the OUR after feed cessation is due to degradation of organic substrate released by hydrolysis of slowly biodegradable substrate. The existence of a sustained plateau is evidence that the biomass is saturated and that hydrolysis is occurring at the maximum rate, thereby allowing evaluation of kh. Operation of the bioreactor at an SRT of two days ensures that this condition will exist. The pattern by which OUR declines with time is determined by Kx. The best

way to estimate kh and Kx is by curve-fitting techniques to match the OUR response of the model to the OUR pattern in Figure 8.7. Because of the short SRT involved, nitrification will not be occurring. Furthermore, since the bioreactor is fully aerobic, denitrification need not be considered. Thus, a simplified form of the model may be used. Since all of the other parameters have been selected, the only unknowns for the curve-fit are kh and Kx, In addition, because nitrification is excluded from the bioreactor, ammonia will build up as ammonification occurs. Consequently, estimation of ka can be based on the release of ammonia during the nonfeed period. 19

8.6 USING TRADITIONAL MEASUREMENTS TO APPROXIMATE WASTEWATER CHARACTERISTICS FOR MODELING

As seen in the preceding section, characterization of a complex wastewater in a manner suitable for use with ASM No. 1 is quite involved and represents a significant investment of time and money. Consequently, such characterizations are not ordinarily done as part of the routine measurements made at wastewater treatment plants. Rather, in the United States, wastewaters are normally characterized in terms of the concentrations of TSS, VSS, five-day biochemical oxygen demand (BOD5), ammonia-N, total Kjeldahl nitrogen (TKN), and alkalinity. Total COD is also commonly measured, but the frequency is usually less than that of the other characteristics, although it is increasing. Furthermore, distinction is seldom made between soluble and particulate phases during measurements of BOD5, COD, and TKN. Because there are circumstances in which it would be advantageous to conduct preliminary modeling studies prior to conducting detailed treatability studies, it would be very useful to be able to translate the traditional data available in the records of wastewater treatment plants into a form that can be used with the models presented herein. Luckily, with a few simplifying assumptions, this can be done for domestic wastewaters. Such translations cannot be made for industrial wastewaters, however, because each is unique.