Identification and modelling of aerobic hydrolysis – application of optimal experimental design

Hydrolysis mechanism plays a dominant role in the delicate balance of electron donor/electron acceptor ratios in BNR and EBPR systems as an important carbon source. In this study, the surface‐saturation‐type hydrolysis kinetics was investigated based on respirometric measurements, within the context of the theoretical and the practical identifiability of mathematical models. The identifiable parameters of a selected model were derived from respirograms. In addition, the information from the experiments was evaluated on the basis of Optimal Experimental Design (OED) methodology for different initial conditions of the batch respirometric experiment. © 2003 Society of Chemical Industry     

Effect of biochemical storage on the denitrification potential of acetate in sequencing batch reactors.

This study evaluates the effect biochemical storage on the denitrification potential (N(DP)) of acetate. The fate of bacterial storage is evaluated in a sequencing batch reactor system operated in a sequence of anoxic/aerobic phases, fed with acetate as a pulse and continuously under anoxic conditions. N(DP) is defined based on system stoichiometry both for direct growth and storage on acetate. Experimental results do not support conceptual calculations based on system stoichiometry, yielding a higher denitrification potential, N(DP), for continuous feeding than the N(DP) obtained with pulse feeding, due to partial utilisation of the stored PHB within the anoxic phase. The nitrate, acetate and poly-beta-hydroxybutyrate (PHB) profiles obtained in the experimental studies were used in model calibrations for two different feeding patterns. Results of model simulations confirm the experimental results and evaluate the effects imposed on the denitrification potential by sludge age and the anoxic volume ratio.     

Estimating Components of Univariate Gaussian Mixtures Using Prony's Method

A new technique for estimating the component parameters of a mixture of univariate Gaussian distributions using the method of moments is presented. The method of moments basically involves equating the sample moments to the corresponding mixture moments expressed in terms of component parameters and solving these equations for the unknown parameters. These moment equations, however, are nonlinear in the unknown parameters, and heretofore, an analytic solution of these equations has been obtained only for two-component mixtures [2]. Numerical solutions also tend to be unreliable for more than two components, due to the large number of nonlinear equations and parameters to be solved for. In this correspondence, under the condition that the component distributions have equal variances or equal means, the nonlinear moment equations are transformed into a set of linear equations using Prony's method. The solution of these equations for the unknown parameters is analytically feasible and numerically reliable for mixtures with several components. Numerous examples using the proposed technique for two-, three-, and four-component mixtures are presented.     

Prioritization methodology of dangerous substances for water quality monitoring with scarce data

Monitoring and control of dangerous substances discharged into receiving waters have attracted more attention lately. Since it is not possible to analyze every single substance, a prioritization methodology is needed for the selection of those to be monitored. Existing well-developed models require significant amount of data for reliable outcomes. This paper presents a methodology to prioritize the dangerous substances having adverse effects on freshwaters in Turkey, where data are scarce. Such a methodology will also serve as a solid model for other countries with limited background data. The adopted methodology enabled the elimination of chemicals to generate a candidate list composed of 608 substances among more than 5000 substances. Further screening and prioritization were conducted using different assessment methods (i.e., Total Hazard Value, Total Impact Value, Combined Monitoring-based, and Modelling-based Priority Setting) to obtain a proposed Final Candidate Specific Pollutants List of 150 dangerous substances. The proposed Candidate National Pollutant List of Turkey was established by combining 45 priority pollutants of the European Union with a list of candidate specific pollutants. According to the outcomes of this study, monitoring and controlling of 195 dangerous substances in freshwaters are recommended. Further detailed studies should be conducted in order to observe the actual levels of these dangerous substances in freshwaters followed by a review of the monitoring list accordingly. Moreover, further revisions might be required in the proposed list due to some possible versatile conditions in terms of sampling points (i.e., change in the location of industries).     

Respirometric Assessment of Primary Sludge Fermentation Products

This study investigates the potential of primary sludge fermentation for the generation of readily biodegradable substrate. Experimental evaluation indicates that uncontrolled fermentation converted 22% of the initial volatile suspended solids in the sludge into soluble biodegradable chemical oxygen demand (COD). More than 85% of the soluble COD generated was associated with the formation of short chain volatile fatty acids (VFAs). The recoverable fraction of the fermented sludge supernatant may potentially increase the biodegradable COD content of the primary effluent by 5%. The VFA composition predominantly involved acetic and propionic acids as reported in the literature. Due to the high VFA content, activated sludge Model No. 1 could not predict the COD fractionation in the primary sludge; activated sludge Model No. 3 provided a better interpretation of the oxygen uptake profile through initial storage of the VFAs in the sludge.     

Producing NiCrAl alloy by the SHS method for use in thermal spray powder manufacturing

A series of Ni alloys containing 36.15–44.54 wt.% Cr and 2.0–13.50 wt.% Al was synthesized by Self-Propagating High-Temperature Synthesis (SHS) using a mixture of NiO, Cr₂O₃ and Al powders in order to obtain low-cost starting materials for thermal spray powder production. The experiments were carried out with the addition of an excess stoichiometric amount of Al between 0 % and 30 %. Additions of CaO and CaF₂ were also done to remove sulfur from the alloy and to investigate the effect on metal recovery. Thermochemical simulations of the SHS processes were examined with the FactSage program. The products were characterized by chemical analysis, X-ray diffraction (XRD), electron probe microanalysis (EPMA) and microhardness techniques.     

Simultaneous parameter estimation and segmentation of Gibbs randomfields using simulated annealing

An adaptive segmentation algorithm is developed which simultaneously estimates the parameters of the underlying Gibbs random field (GRF)and segments the noisy image corrupted by additive independent Gaussian noise. The algorithm, which aims at obtaining the maximum a posteriori (MAP) segmentation is a simulated annealing algorithm that is interrupted at regular intervals for estimating the GRF parameters. Maximum-likelihood (ML) estimates of the parameters based on the current segmentation are used to obtain the next segmentation. It is proven that the parameter estimates and the segmentations converge in distribution to the ML estimate of the parameters and the MAP segmentation with those parameter estimates, respectively. Due to computational difficulties, however, only an approximate version of the algorithm is implemented. The approximate algorithm is applied on several two- and four-region images with different noise levels and with first-order and second-order neighborhoods     

Implications of the task group model-I. The effect of initial substrate concentration

This paper explores the merit of the task group model to reflect the effect of the initial substrate concentration on the performance of microbial systems, assessed in terms of the effluent soluble COD. In this context, a structural modification is proposed to account for this effect, by incorporating mechanisms responsible for the generation of soluble microbial products, considered residual for the particular operating conditions of the activated sludge systems. Model simulations of a number of practically significant scenarios are performed and evaluated. Reasonably good agreement is depicted between the model outputs and experimental data from previous studies.