IAWPRC Activated Sludge Model Research Articles

Performance optimization of an alternating oxidation ditch system by cycle timelength variation

Abstract This paper presents a methodology for the optimization of the operation of an alternating oxidation ditch system, performing carbon oxidation–nitrification, denitrification and settling, through the use of a mathematical model and pilot testing. Measurements have been made in a pilot plant located in the Sanitary Engineering Research and Development Center of E.Y.D.A.P at Metamorphosis-Athens. Also, a mathematical model consisting of 1-dimensional mass balance (convection–dispersion) equations, based on the IAWPRC activated sludge model No. 1 was used. After the calibration and verification of the model with the experimental data, the optimization of the system’s performance was achieved by testing operational cycles with different time lengths. Since carbon removal is way under the 91/271 E.U. directive’s upper limits and since the ditch system has not been designed for phosphorous removal, the limits for nitrogen removal have been used for comparison. In this work’s example, from the eight oper...

Modelling of an Intermittently Aerated Completely Mixed Activated Sludge Reactor

Mathematical models for description of dynamic behaviour of simultaneous nitrification and denitrification processes carried out in an intermittently aerated completely mixed activated sludge reactor (CMASR) are presented. The general IAWPRC activated sludge model has been extended with volatilisation process of wastewater impurity. The influence of wastewater composition on oxygen transport rate is also included. Different approaches for dissolved oxygen incorporation in biochemical reaction kinetics have been applied. Determination of some biokinetic parameter values by evaluating steady-state measurements of process variables is implied in one version of the proposed models. Experimental modelling of simultaneous nitrification and denitrification processes, carried out in an industrial Carrousel activated sludge reactor, was performed in the lab-scale intermittently aerated CMASR. Organic, ammonium, and heavy metal shock loads were applied in order to simulate transient behaviour of the lab-scale reactor and the influence of heavy metal on biochemical processes and biokinetic parameter values has been investigated. Dissolved oxygen concentration in activated sludge reactor, COD, ammonium, nitrate and biomass concentration responses of reactor were measured and evaluated. Good agreement between the observed data and calculated values by verified models has been achieved. Estimated values of biokinetic parameters, found by optimisation procedure, are close to those recommended for simulation of domestic wastewater treatment processes. The applicability of the IAWPRC kinetic and stoichiometric concept for dynamic behaviour description of an intermittently aerated CMASR reactor, including the above mentioned extension and modification, is demonstrated in the work.

Modelling of an alternating oxidation ditch system

This paper presents a mathematical model for an alternating oxidation ditch system, performing carbon oxidation-nitrification, denitrification and settling. The model consists of 1-dimensional mass balance (convection-dispersion) equations, based on the IAWPRC activated sludge model No 1. The data used for the calibration and the application of the model, are collected from a pilot plant. The present work consists of 3 parts. In the first part a brief description of the pilot plant is made. The second part deals with a short presentation of the basic equations and the boundary conditions of the model. The calibration and application of the model with the corresponding conclusions are contained in the third part. In the calibration, the values of the dispersion coefficient, E, and the correction factors α and β of the equation of the aeration equipment (rotors) have been determined equal to E=170000 m2 day−1, β=0.85 and α=0.3 and 0.825, for the operation of the rotors in the low and high speed, respectively. The application of the model shows that predicted effluent concentration values are in a very good agreement with experiments.

Modelling of oxidation ditches using an open channel flow 1-D advection-dispersion equation and ASM1 process description

A river water quality model is presented for the prediction of the concentration fields of the water quality variables in an oxidation ditch performing carbon oxidation, nitrification and denitrification. The model involves the one-dimensional convection-dispersion equations for all the variables, which are described in the IAWPRC Activated Sludge Model No 1. The model is applied to a typical oxidation ditch to show that all variables, with the exception of DO, are uniformly distributed in the ditch; thus permitting the characterisation of the oxidation ditch as a completely mixed reactor. The DO concentration, which controls the reaction rates of almost all the processes, shows a plug flow behaviour. The potential of the present model to be used to improve the DO control system of the ditch and to perform real time predictions is also demonstrated. All calculations have been performed with a PC.

Modelling of oxidation ditches using an open channel flow 1-D advection-dispersion equation and ASM1 process description

A river water quality model is presented for the prediction of the concentration fields of the water quality variables in an oxidation ditch performing carbon oxidation, nitrification and denitrification. The model involves the one-dimensional convection-dispersion equations for all the variables, which are described in the IAWPRC Activated Sludge Model No 1. The model is applied to a typical oxidation ditch to show that all variables, with the exception of DO, are uniformly distributed in the ditch; thus permitting the characterisation of the oxidation ditch as a completely mixed reactor. The DO concentration, which controls the reaction rates of almost all the processes, shows a plug flow behaviour. The potential of the present model to be used to improve the DO control system of the ditch and to perform real time predictions is also demonstrated. All calculations have been performed with a PC.

Parameter and state estimation of the activated sludge process—I. Model development

A new approach is introduced for combined state and parameter estimation, named Linearized Maximum Likelihood (LML). The LML method is motivated by the uncertain and nonlinear activated sludge dynamics. In this article, the theoretical background leading to the development of the LML method is presented, along with the resulting numerical algorithm. In a companion article (Kabouris and Georgakakos, 1996) the LML method is applied to the parameter and state estimation of a nitrifying activated sludge process, modelled by the IAWPRC Activated Sludge Model 1.

Parameter and state estimation of the activated sludge process—II. Applications

In a companion article (Kabouris and Georgakakos, 1996) the Linearized Maximum Likelihood (LML) method for the simultaneous estimation of activated sludge process states and parameters from noisy process measurements is presented. The present article describes the application of the LML method to the identification of a nitrifying activated sludge process, modelled by the IAWPRC Activated Sludge Model 1. It is concluded that identification of nine of the model parameters from process measurements is only possible when a sequential estimation scheme is applied and only influential measurements are considered.

SIMULATION OF THE OPERATING CONDITIONS OF THE MUNICIPAL WASTEWATER TREATMENT PLANT AT LOW TEMPERATURES USING A MODEL THAT INCLUDES THE IA WPRC ACTIVATED SLUDGE MODEL

There are some advantages to using the sewage system to transport and melt snow in snowy regions. Since this would cause a drop in sewage temperature, adequate methods of operating treatment plants at low temperatures should be addressed. First, calibration of the IA WPRC activated sludge model was done using pilot plant data from a 10°C experiment. Then, the temperature coefficients in the reaction rate equations were estimated using the data from operation at 5°C. Comparison of the simulation results with data gathered under other temperature conditions showed that the IA WPRC activated sludge model could be applied to low temperature conditions. A newly developed model of the full-seale plant was able to simulate not only the biological reaction in the aeration basin but also the perfonnance of primary and final clarifiers, and sludge thickening and dewatering processes. The sludge and cake production rates, MLSS, and nitrification perfonnance calculated by this model coincided with plant operation results at I2°C. Operation maps of the plant in Sapporo were drawn at presumed low temperatures, 4 and 8°C. They showed that if nitrifying bacteria were kept in the plant, an overload in the sludge treatment process would be unavoidable without augmenting the capacity of water or of the sludge-treatment system.

MODELING OXIDATION DITCHES USING THE IA WPRC ACTIVATED SLUDGE MODEL WITH HYDRODYNAMIC EFFECTS

A mathematical model is presented to predict the concentrations of the active heterotrophic biomass, the readily biodegradable substrate (soluble COD) and the dissolved oxygen (DO) in a completely aerobic oxidation ditch. The model involves the one-dimensional convection-dispersion equations for biomass, COD and DO. Hydrodynamic effects are represented in the model by the values of the average flow velocity and the dispersion coefficient. Biological processes are described in the model according to the IA WPRC activated sludge model, using typical values for the model parameters at 10°C. The equations are solved with the finite volume method. The application of the model leads to the following conclusions: (i) Steady state biomass concentrations are almost constant throughout the ditch. (ii) Steady state COD concentrations in the ditch are very low, and COD removal efficiency is practically independent of the values of the flow velocity and the dispersion coefficient. The distribution of the COD concentration in the ditch is less uniform, when small values of the dispersion coefficient are used. (iii) The distribution of the DO concentration in the ditch is very sensitive to the values of the flow velocity, the dispersion coefficient and to the capacity of the rotors. DO concentrations increase when the dispersion coefficient decreases or the flow velocity increases. (v) Daily sludge production, oxygen requirements and sludge age are calculated equal to 0.44 g (g COD removed)‒1, 0.56 g (g incoming COD)‒1 and 6.3 days, respectively.

Investigations into excess activated sludge accumulation at low temperatures

Low temperature operation has been reported to increase the yield of volatile suspended solids (VSS) but little quantitative data are available and an explanation for the reported phenomena is lacking. A laboratory study was initiated using two parallel 41. sequencing batch reactors operating at a sludge retention time (SRT) of approx. 10 days, and a hydraulic retention time (HRT) of approx. 1.25 days. An experimental design with two levels of temperatures (8 and 20°C) and two levels of influent volatile solid concentrations (approx. 15 and 70 mg/l) was selected. The experimental results verified the hypothesis that the observed yield (gΔ VSS/g Δ COD) increased at lower temperatures for both levels of influent suspended solids. As, experimentally, it was not possible to determine the relative composition of the accumulated volatile solids, the IAWPRC activated sludge model was adapted to estimate the fractions of: viable organisms, accumulated influent particulates and endogenous decay products. The simulations indicated that the actual concentration of viable organisms apparently decreased from approx. 52–63% of the MLVSS at 20°C to 29–47% at 8°C. Simulations were utilized to estimate the additional waste sludge production during cold weather at typical treatment plants. Increases of approx. 12–20% could result.

Calibration of an Activated Sludge Model Based on Human Expertise and on a Mathematical Optimization Technique – a Comparison

Two alternative methods, which both can be used to estimate some of the kinetic parameters of the IAWPRC Activated Sludge Model Nr. 1, are compared. By one method, which is based on professional experience and expertise, the unknown parameter values are determined one after the other by a sequential procedure. By the other method, the parameter values are determined simultaneously by use of a mathematical optimization technique. Both methods allow a good fit of a set of 25 experimental oxygen respiration rate time-series and yield accurate estimates of the model parameters. The sequential procedure can readily be employed for the evaluation of single experiments. The optimization technique is more suitable for the evaluation of larger data sets and allows for additional analysis of the data.

Optimizing Nitrogen Removal Reactor Configurations by On-Site Calibration of the IAWPRC Activated Sludge Model

This paper describes a modified version of the IAWPRC model and the techniques used to calibrate it on site. Growth rate of autotrophic bacteria and the inert wastewater fractions were measured by simple methods, both in laboratory pilots and on full scale. Model predictions were compared to full scale results in large plants (> 100 000 P E). Measured autotrophic growth rates ranged from 0.3 to 0.65 1/d, depending on wastewater toxicity. Most model constants compared well with original IAWPRC proposals, and several wastewater types were identified. Parameters to establish a suspended solids balance are given. Different configurations of plants for nitrogen removal were investigated, including conventional recirculation, sludge reaeration (RDN) and step feed alternate zone denitrification.

Designing Experiments to Determine the Coefficients of Activated Sludge Models by Identification Algorithms

A calibration technique comprised of an experimental procedure and a curve fitting mathematical method has been proposed in order to estimate the coefficients of the IAWPRC activated sludge model restricted to oxic reactions. A continuous activated sludge plant having two in-series biodegradation reactors is suggested for the experiment. This plant is operated by reducing, in steps, the first reactor volume. It was found that this experimental procedure enables scanning of a significant part of the kinetics contained in the model. The curve fitting mathematical method was an identification algorithm based on recursive non-linear Kaiman filter. In order to assess the validity of the calibration technique, simulated results of measurable variables, generated from presumed real coefficients, have been employed as real results by the identification algorithm. The effect of several erroneous initial estimates of the coefficients, which are required to start the identification, has been investigated. It was found that the proposed calibration technique gave rise to acceptable identifications of the real coefficients independent of the initial estimate used. The convergence rate for every coefficient, however, depends on the initial estimate. Those rates were properly related to the differences observed between the real results and the predictions obtained with the initial estimates for the measurable variables.

Computer Aided Design of Sequencing Batch Reactors Based on the IAWPRC Activated Sludge Model

A modified version of the IAWPRC activated sludge model was developed to describe the performance of laboratory and pilot scale Sequencing Batch Reactors (SBR). Changes of COD, ammonia and NOx during the SBR process cycle could be reliably predicted after the model parameters were adapted to SBR conditions. Most promising process strategies could be identified with the aid of a simulation program.