Chemical Engineering

Biological phosphorus removal Off-line calibration Pilot plant study a b s t r a c t This paper presents the results of an experimental study for the modelling and calibration of denitrifying activity of polyphosphate accumulating organisms (PAOs) in full-scale WWTPs that incorporate simultaneous nitrogen and phosphorus removal. The convenience of using different yields under aerobic and anoxic conditions for modelling biological phosphorus removal processes with the ASM2d has been demonstrated. Thus, parameter h PAO in the model is given a physical meaning and represents the fraction of PAOs that are able to follow the DPAO metabolism. Using stoichiometric relationships, which are based on assumed biochemical pathways, the anoxic yields considered in the extended ASM2d can be obtained as a function of their respective aerobic yields. Thus, this modification does not mean an extra calibration effort to obtain the new parameters. In this work, an off-line calibration methodology has been applied to validate the model, where general relationships among stoichiometric parameters are proposed to avoid increasing the number of parameters to calibrate. The results have been validated through a UCT scheme pilot plant that is fed with municipal wastewater. The good concordance obtained between experimental and simulated values validates the use of anoxic yields as well as the calibration methodology. Deterministic modelling approaches, together with off-line calibration methodologies, are proposed to assist in decision-making about further process optimization in biological phosphate removal, since parameter values obtained by off-line calibration give valuable information about the activated sludge process such as the amount of DPAOs in the system. ª (J. Ribes), [email protected] (J. Ferrer), aurora.seco@uv. es (A. Seco). A v a i l a b l e a t w w w . s c i e n c e d i r e c t . c o m j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / w a t r e s w a t e r r e s e a r c h 4 4 ( 2 0 1 0 ) 5 2 8 4 e5 2 9 7 0043-1354/$ e see front matter ª

This paper is focused on the evaluation of the applicability of low-cost sensors (pH and ORP) versus nutrient analysers for controlling biological nitrogen removal in WWTPs. A nutrient removal pilot plant located in Carraixet WWTP (Valencia, Spain) that is equipped with a significant number of nutrient analysers and low-cost sensors was used. The relations between reliable, cheap on-line sensors such as pH and ORP (located in anaerobic, anoxic and aerobic zones) and the nitrification/denitrification processes are provided. The nitrification process can be evaluated by measuring the pH difference between the first and last aerobic zones. The denitrification process can be evaluated by measuring the pH difference between the first and last anoxic zones and the ORP in the last anoxic zone. Furthermore, when WWTPs include an anaerobic reactor, the ORP in the anaerobic zone can also be used. With all these factors in mind, these sensors give valuable information for applying advanced control systems such as fuzzy logic-based controllers. Also, low-cost sensors involve lower investment, maintenance and operational costs and lower energy consumption derived from aeration and pumping than nutrient analysers. Thus, low-cost sensors can be successfully used as an attractive alternative to nutrient analysers to control biological nitrogen removal in WWTPs. Key words | monitoring, nitrogen biological removal (NBR), nutrient analysers, ORP sensors, pH sensors, process control M. V. Ruano et al. | Low cost-sensors as alternative to on-line N analysers Water Science & Technology-WST | 60.12 | 2009

In this paper, we evaluate the application of a sensitivity analysis to help fine-tuning a fuzzy controller for a biological nitrogen and phosphorus removal (BNPR) plant. The Morris Screening method is proposed and evaluated as a prior step to obtain the parameter significance ranking. First, an iterative procedure has been performed in order to find out the proper repetition number of the elementary effects (r) of the method. The optimal repetition number found in this study (r ¼ 60) is in direct contrast to previous applications of the Morris method, which usually use low repetition number, e.g. r ¼ 10 ∼ 20. Working with a non-proper repetition number (r) could lead to Type I error (identifying a not-important factor as significant (false positive)) as well as Type II error (identifying an important factor as not significant (false negative)), hence emphasizing the importance of finding the optimal repetition number for each study in question. With the proper r found, the Morris Screening helped identify the parameter significance ranking, thereby facilitating the calibration of fuzzy controllers, which contain many parameters that need to be adjusted for different wastewater treatment plant (WWTP) applications.

In this paper, a model-based algorithm for optimizing the primary sludge fermentation process design and operation is described and evaluated. This is a recently used method to obtain the volatile fatty acid ͑VFA͒, needed for the enhanced biological phosphorus removal process, directly from raw wastewater. The proposed algorithm consists of a heuristic reasoning algorithm based on the expert knowledge of the process. Only effluent VFA and the sludge blanket height have to be set as design criteria, and the optimization algorithm obtains the minimum return sludge and waste sludge flow rates which fulfill those design criteria. It has been evaluated by simulating different temperature and sludge volume index ͑SVI͒ influent conditions in order to evaluate the algorithm performance under different conditions, as well as its sensitivity with respect to temperature and SVI, which are the most important parameters in these systems. The same tendencies observed by simulation were observed afterward in pilot plant experiments.

Many bacteria have been observed to stop growing below a certain substrate threshold concentration. In this study, a modification of the Monod kinetics expression has been proposed to take into account this substrate threshold concentration observed in bacterial growth. Besides the threshold concentration no additional parameters have been added to the kinetic expression and so, only the substrate threshold concentration and the half-saturation constant have to be estimated for model calibration purposes. Furthermore, for parameter estimation purposes, practical identifiability of this new function has been studied and the results have been satisfactory. The new model has been applied, as an example, to a simple anaerobic model to simulate the competition for hydrogen between sulphate reducers and methanogens in a thermophilic methanol-fed bioreactor. Oscillatory behaviour and mathematical instabilities have been avoided by using the proposed model. Parameter sensitivities have also been calculated along the simulation period in order to investigate the importance of hydrogen threshold concentration parameters. r