This study shows a comparison of important parameters for dynamic simulation concerning the highrate and low-rate activated sludge tanks of several municipal wastewater treatment plants. The parameters for the dynamic simulation of the single-stage process are quite well known, but parameters for the high-ratellow-rate activated sludge process are still missi ng, although a considerable number of wastewater treatment plants are designed and operated that way. At present any attempt to simulate their operation is restricted to the second stage due to missing data concerning growth rate, decay rate, yield coefficient and others.
With the development of kinetic models and new design criteria for activated sludge systems, biomass determination becomes important. Various methods can be used to estimate the amount of biomass. Most of these methods are only applicable to pure culture studies. The activated sludge of wastewater treatment plants contains not only biomass, but also a high content of dead organic and inorganic material of unknown composition. Distinguishing between these sludge constituents is difficult. The best and most reproducible method for biomass estimation is often described as the determination of DNA content. This method includes the acid extraction of DNA, the quantitative determination of deoxyribose sugar by a colour reaction with diphenylamine, the calibration with standard DNA and the mathematical conversion into biomass. This study shows that the conventional method is strongly affected by unknown activated sludge constituents and in particular iron. The interference can be overcome by EDTA treatment. Inconsistencies in published calibration data are overcome.
This study shows results from four lab-scale wastewater treatment plants, which were installed behind the grit chamber of a municipal wastewater treatment plant. The lab-scale plants were fed with original wastewater, diluted with water from the final clarifier to give a constant concentration of 300 mg /l COD. The activated sludges were adapted to different sludge ages from 1.88 to 24.0 days. The steady-state behaviour was measured along with the decay rate, the yield coefficient, the oxygen demand, the C- and N- balance and the DNA of biomass XBH. The steady-state equations of Marais and Ekama were used to calculate the masses of active biomass, endogenous residue and inert VSS in the reactors. Measured parameter values were different for all sludge ages. They gave similar values for inert particulate VSS (Xi) of 7 to 9%. Parameter values of the IAWQ-Model No. 1 together with Xi-fitting could also be used to solve the equations, but in this case different Xi values for the different reactors had to be used for the same wastewater.
The objective of this study is to investigate to what extent the nitrification capacity of a pilot-plant fixed-film reactor changes during extensive periods of nutrient supply deficiency. The examined pilot-plant was an upflow reactor filled with swelling clay of medium grain size (6 to 8 mm). The experiments revealed that the maximum nitrification rate remained practically constant during the first weeks after the onset of unregulated ammonium supply. The capacity declined slowly, dropping to approximately 66% of the initial capacity after about ten weeks. Still ammonium peaks of up to 8 mg/l were readily nitrified throughout the entire period of the experiment. The reduction in nitrification capacity during the observation period did not result from decay processes of biomass but from the reactor becoming blocked and thus hampering transfer processes. It could be observed that the detached organisms attached again further up. This semi-industrial project demonstrated that a plug-flow fixed-film reactor can be used as effective means of tertiary nitrification.
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