bluuebunny/crossref_metadata_2025 huggingface dataset:
Modelling of aeration systems at wastewater treatment plants
Authors: Rieger L. , Alex J. , Gujer W. , Siegrist H.
Published: July 2007

A model for the response time of aeration systems at WWTPs is proposed. It includes the delays caused by the air supply system (consisting of blowers, throttles and pipes), the rise time of the air bubbles and all control loops except the master DO controller. Beside a description of the required step-change experiments, different approaches for model calibration are given depending on the available data. Moreover, the parameters for the oxygen transfer and the response time of the aeration system model are not clearly identifiable. The model can be used for simulation studies which compare different types of controllers under changing loading and process conditions. The results from full-scale experiments at three different plants show that the response times of the aeration systems are in the range of 4–5 min. Taking all processes and time constants into account, some 30 min are needed to reach a new steady state after a step change of the airflow rate.
High-solids centrifuge is a boon and a curse for managing anaerobically digested biosolids
Authors: Murthy S. , Higgins M. , Chen Y.-C. , Peot C. , Toffey W.
Published: July 2007

High-solids centrifugation can reduce the cost of managing or disposing of anaerobically digested biosolids. High-solids centrifuges can increase relative cake solids by as much as 5% DS compared with other dewatering devices, such as belt filter presses, with a resulting 15–20% reduction in overall mass of hauled biosolids. Cost reductions can be similar (15–20%) or more, depending on the type of disposal or management involved. For example, the additional removal of water from the cake increases the energy content in the biosolids, thereby facilitating incineration or heat drying processes. For land application, the benefits are more mixed. As explained in this paper, increases in biosolids odours associated with high-solids centrifuges may increase digestion requirements and may compel producers to transport biosolids to more remote, distant sites, potentially increasing transportation costs. High-solids centrifuges shear anaerobically digested biosolids. The shear results in a net increase in labile protein, an odour precursor. Additionally, high-solids centrifugation also results in the inhibition of methanogenesis, a major mechanism for degradation of organosulphur odours. Therefore, the risks and benefits should both be weighed when considering high-solids centrifuges for land application of anaerobically digested biosolids.
Responsible development of nanotechnologies for water and wastewater treatment
Authors: Wiesner M.R.
Published: July 2007

Emerging technologies, including nanotechnologies, affect the social, economic, and environmental dimensions of our world, often in ways that are entirely unanticipated. There is considerable effort underway to explore uses of nanomaterials in applications such as membrane separations, catalysis, adsorption, and analysis with the goal of better protecting environmental quality. Along with the growth of a nanochemistry industry there is also the need to consider impacts of nanomaterials on environment and human health.
ICA and water in Korea – overview
Authors: Kim C. , Park T.-J. , Kim S.-H. , Hwang I. , Oh J.-E. , Ko J.
Published: July 2007

The natural water quality in Korea has improved significantly in the last 20 years since major collective national initiatives were implemented by governmental agencies, non-governmental organizations, and professionals among many others. Recently instrumentation, control, and automation (ICA) technology has become one of the most important technologies for carrying out this task. Korea has become especially well known with a strong reputation for information technology and international business with commercial products like semi-conductors, computers, mobile phones, computer games, and other electronic products. In this paper the background of Korean water quality is reviewed and several of the most significant national projects related to ICA are discussed. The major projects may include the Automatic Monitoring Network of River Water Quality and the Integrated Management System of Wastewater Treatment Plants in Upper Basin Area of Multi-purpose Dams.
Controlling the nitrite:ammonium ratio in a SHARON reactor in view of its coupling with an Anammox process
Authors: Volcke E.I.P. , van Loosdrecht M.C.M. , Vanrolleghem P.A.
Published: July 2007

The combined SHARON–Anammox process for treating wastewater streams with high ammonia load is the focus of this paper. In particular, partial nitritation in the SHARON reactor should be performed to such an extent that a nitrite:ammonium ratio is generated which is optimal for full conversion in an Anammox process. In the simulation studies performed in this contribution, the nitrite:ammonium ratio produced in a SHARON process with fixed volume, as well as its effect on the subsequent Anammox process, is examined for realistic influent conditions and considering both direct and indirect pH effects on the SHARON process. Several possible operating modes for the SHARON reactor, differing in control strategies for O2, pH and the produced nitrite:ammonium ratio and based on regulating the air flow rate and/or acid/base addition, are systematically evaluated. The results are quantified through an operating cost index. Best results are obtained by means of cascade feedback control of the SHARON effluent nitrite:ammonium ratio through setting an O2 set-point that is tracked by adjusting the air flow rate, combined with single loop pH control through acid/base addition.
On-line estimation of kinetic parameters in anaerobic digestion using observer-based estimators and multiwavelength fluorometry
Authors: Morel E. , Tartakovsky B. , Guiot S.R. , Perrier M.
Published: July 2007

Observer-based estimators (OBE) were used for estimation of state variables and kinetic parameters in an anaerobic digestion (AD) process. A simplified first-order model with time-varying kinetic parameters was used to design an OBE for kinetic parameter estimation. This approach was validated on a laboratory-scale anaerobic reactor equipped with a multiwavelength fluorometer for on-line measurements of COD and VFA concentrations in the reactor effluent. The proposed estimators provide continuous adjustment of kinetic parameters and can be used for predictions of state variables between samples acquisition and during sensor failure.
Influence of closed loop control on microbial diversity in a nitrification process
Authors: Bougard D. , Bernet N. , Dabert P. , Delgenes J.P. , Steyer J.P.
Published: July 2007

This paper compares two control strategies for a nitrification process. The objective is to achieve partial nitrification and thus to accumulate nitrite instead of nitrate. To this end, change in temperature setpoint and active control of oxygen and ammonia concentrations are evaluated in the long term. Evaluation is made on the control performances that are obtained, but also – and more importantly – on the microbial diversity. In particular, it is shown that the combined oxygen and ammonia control strategy is more appropriate since shift in the temperature setpoint strongly affects the composition of the microbial ecosystem present in the reactor whereas active control of oxygen and ammonia does not.
Modelling and control strategy testing of biological and chemical phosphorus removal at Avedøre WWTP
Authors: Ingildsen P. , Rosen C. , Gernaey K.V. , Nielsen M.K. , Guildal T. , Jacobsen B.N.
Published: July 2007

The biological phosphorus removal process is often implemented at plants by the construction of an anaerobic bio-p tank in front of the traditional N removing plant configuration. However, biological phosphorus removal is also observed in plant configurations constructed only for nitrogen removal and simultaneous or post-precipitation. The operational experience with this “accidental” biological phosphorus removal is often mixed with quite a lot of frustration, as the process seems to come and go and hence behaves quite uncontrollably. The aim of this work is to develop ways of intentionally exploiting the biological phosphorus process by the use of instrumentation, control and automation to reduce the consumption of precipitants. Means to this end are first to calibrate a modified ASM2d model to a full-scale wastewater treatment plant (WWTP), including both biological and chemical phosphorus removal and a model of the sedimentation process. Second, based on the calibrated model a benchmark model is developed and various control strategies for biological phosphorus removal are tested. Experiences and knowledge gained from the strategies presented and discussed in this paper are vital inputs for the full-scale implementation of a control strategy for biological phosphorus removal at Avedøre WWTP, which is described in another paper. The two papers hence show a way to bridge the gap from model to full implementation.
Introducing biological phosphorus removal in an alternating plant by means of control: a full scale study
Authors: Rosen C. , Ingildsen P. , Guildal T. , Nielsen T. Munk , Nielsen M.K. , Jacobsen B.N. , Thomsen H.A.
Published: July 2007

In this paper, a control strategy for introducing enhanced biological phosphorus removal (EBPR) in an alternating plant designed for enhanced biological nitrogen removal (EBNR) is presented. Alternating aerobic and anaerobic conditions to promote EBPR are provided by controlling the phases of the operational cycle, instead of a separate anaerobic volume. By utilising the control schemes already built in the STAR® control system for nitrogen removal, the control strategy is fully integrated in the system. The control system relies on on-line measurements of nitrogen (ammonia and/or nitrate) and orthophosphate. The control strategy has been implemented in full-scale operation at the Avedøre wastewater treatment plant in Denmark and the results show clear indications of success. The control strategy has operated robustly for several months with a 60% decrease in use of precipitation chemicals.
Full-cyclic control strategy of SBR for nitrogen removal in strong wastewater using common sensors
Authors: Poo K.M. , Im J.H. , Jun B.H. , Kim J.R. , Hwang I.S. , Choi K.S. , Kim C.W.
Published: July 2007

A full-cyclic automatic control strategy for sequencing batch reactors (SBR) was proposed using only common sensors such as ORP, DO and pH. The main objective was to develop a generally applicable and robust control strategy. To accomplish this, various control schemes found in the literature or suggested by authors were examined at diverse ammonia loads and SCOD/NH4+-N ratios. Advantages and constraints of each scheme were discussed and compared. Ammonia load was estimated with DO lag time during the aerobic stage, and then the influent pump was manipulated to meet the desired load at the next anoxic stage. A partial denitrification scheme was chosen for the anoxic stage period control, to save anoxic time and external carbon. For external carbon dosage control, intermittent feeding at each anoxic stage was concluded to be a suitable scheme. The anoxic stage period could be successfully controlled by the combination of pH increase and DO increase. Every suggested control scheme was incorporated into a full-cyclic control strategy and tested at 0.02, 0.035, 0.08 kg NH4+-N/m3/sub-cycle. From the results, it is expected to perform unmanned automatic SBR operation with this strategy.
Application of an automation system and a supervisory control and data acquisition (SCADA) system for the optimal operation of a membrane adsorption hybrid system
Authors: Smith P.J. , Vigneswaran S. , Ngo H.H. , Nguyen H.T. , Ben-Aim R.
Published: July 2007

The application of automation and supervisory control and data acquisition (SCADA) systems to municipal water and wastewater treatment plants is rapidly increasing. However, the application of these systems is less frequent in the research and development phases of emerging treatment technologies used in these industries. This study involved the implementation of automation and a SCADA system to the submerged membrane adsorption hybrid system for use in a semi-pilot scale research project. An incremental approach was used in the development of the automation and SCADA systems, leading to the development of two new control systems. The first system developed involved closed loop control of the backwash initiation, based upon a pressure increase, leading to productivity improvements as the backwash is only activated when required, not at a fixed time. This system resulted in a 40% reduction in the number of backwashes required and also enabled optimised operations under unsteady concentrations of wastewater. The second system developed involved closed loop control of the backwash duration, whereby the backwash was terminated when the pressure reached a steady state. This system resulted in a reduction of the duration of the backwash of up to 25% and enabled optimised operations as the foulant build-up within the reactor increased.
Supervisory control strategies for the new WWTP of Galindo-Bilbao: the long run from the conceptual design to the full-scale experimental validation
Authors: Ayesa E. , De la Sota A. , Grau P. , Sagarna J.M. , Salterain A. , Suescun J.
Published: July 2007

This paper presents the theoretical basis and the main results obtained during the development and full-scale experimental validation of the new supervisory control strategy designed for the Galindo-Bilbao wastewater treatment plant (WWTP). The different phases of the project have been carried out over the last 8 years, combining model simulations, pilot-plant experimentation and full-scale validation. The final control strategy combines three complementary control loops to optimise the nitrogen removal in pre-denitrifying activated sludge plants. The first controller was designed to maintain the average concentration of the ammonia in the effluent via the automatic selection of the most appropriate DO set point in the aerobic reactors. The second control loop optimises the use of the denitrification potential and finally, the third control loop maintains the selected amount of biomass in the biological reactors by automatic manipulation of the wastage rate. Mobile-averaged windows have been implemented to incorporate commonly used averaged values in the control objectives. The performance of the controllers has been successfully assessed through the full-scale experimental validation in one of the lines of the WWTP.
Estimating costs and benefits of advanced control for wastewater treatment plants – the MAgIC methodology
Authors: Devisscher M. , Ciacci G. , Fé L. , Benedetti L. , Bixio D. , Thoeye C. , De Gueldre G. , Marsili-Libelli S. , Vanrolleghem P.A.
Published: July 2007

This paper discusses a methodology to estimate the costs and benefits of advanced control for wastewater treatment plants. The methodology has been applied to four wastewater treatment plants, representing four standard types of plants built in Flanders, Belgium. The paper outlines the methodology and illustrated results from one of the four design cases. General results are shown and contrasted with full-scale experience. The methodology appears to give realistic results and will be used for further refinement of default control algorithms for certain types of plants. A preliminary analysis indicates that on-line control can become cost-effective for plant sizes above 50,000 population equivalents.
WWTP dynamic disturbance modelling–an essential module for long-term benchmarking development
Authors: Gernaey K.V. , Rosen C. , Jeppsson U.
Published: July 2007

Intensive use of the benchmark simulation model No. 1 (BSM1), a protocol for objective comparison of the effectiveness of control strategies in biological nitrogen removal activated sludge plants, has also revealed a number of limitations. Preliminary definitions of the long-term benchmark simulation model No. 1 (BSM1_LT) and the benchmark simulation model No. 2 (BSM2) have been made to extend BSM1 for evaluation of process monitoring methods and plant-wide control strategies, respectively. Influent-related disturbances for BSM1_LT/BSM2 are to be generated with a model, and this paper provides a general overview of the modelling methods used. Typical influent dynamic phenomena generated with the BSM1_LT/BSM2 influent disturbance model, including diurnal, weekend, seasonal and holiday effects, as well as rainfall, are illustrated with simulation results. As a result of the work described in this paper, a proposed influent model/file has been released to the benchmark developers for evaluation purposes. Pending this evaluation, a final BSM1_LT/BSM2 influent disturbance model definition is foreseen. Preliminary simulations with dynamic influent data generated by the influent disturbance model indicate that default BSM1 activated sludge plant control strategies will need extensions for BSM1_LT/BSM2 to efficiently handle 1 year of influent dynamics.
Cell-phone based assistance for waterworks/sewage plant maintenance
Authors: Kawada T. , Nakamichi K. , Hisano N. , Kitamura M. , Miyahara K.
Published: July 2007

Cell-phones are now incorporating the functions necessary for them to be used as mobile IT devices. In this paper, we present our results of the evaluation of cell-phones as the mobile IT device to assist workers in industrial plants. We use waterworks and sewage plants as examples. By employing techniques to squeeze the SCADA screen on CRT into a small cell-phone LCD, we have made it easier for a plant's field workers to access the information needed for effective maintenance, regardless of location. An idea to link SCADA information and the plant facility information on the cell-phone is also presented. Should an accident or emergency situation arise, these cell-phone-based IT systems can efficiently deliver the latest plant information, thus the worker out in the field can respond to and resolve the emergency.
Monitoring biodegradation of diesel fuel in bioventing processes using in situ respiration rate
Authors: Lee T.H. , Byun I.G. , Kim Y.O. , Hwang I.S. , Park T.J.
Published: July 2007

An in situ measuring system of respiration rate was applied for monitoring biodegradation of diesel fuel in a bioventing process for bioremediation of diesel contaminated soil. Two laboratory-scale soil columns were packed with 5 kg of soil that was artificially contaminated by diesel fuel as final TPH (total petroleum hydrocarbon) concentration of 8,000 mg/kg soil. Nutrient was added to make a relative concentration of C:N:P = 100:10:1. One soil column was operated with continuous venting mode, and the other one with intermittent (6 h venting/6 h rest) venting mode. On-line O2 and CO2 gas measuring system was applied to measure O2 utilisation and CO2 production during biodegradation of diesel for 5 months. Biodegradation rate of TPH was calculated from respiration rate measured by the on-line gas measuring system. There were no apparent differences between calculated biodegradation rates from two columns with different venting modes. The variation of biodegradation rates corresponded well with trend of the remaining TPH concentrations comparing other biodegradation indicators, such as C17/pristane and C18/phytane ratio, dehydrogenase activity, and the ratio of hydrocarbon utilising bacteria to total heterotrophic bacteria. These results suggested that the on-line measuring system of respiration rate would be applied to monitoring biodegradation rate and to determine the potential applicability of bioventing process for bioremediation of oil contaminated soil.
Automatic detection of exogenous respiration end-point using artificial neural network
Authors: Bisschops I. , Spanjers H. , Keesman K.
Published: July 2007

When aerobic bacteria receive a biodegradable material such as wastewater, then respiration changes from endogenous to exogenous. The reverse occurs when biodegradation is complete. When using respirometry a respirogram is recorded showing those changes in respiration, and for an expert it is not difficult to point the moments at which they occur. The area corresponding to the exogenous respiration phase is a measure of the easily biodegradable fraction of material, also called the short-term BOD or BODST. That value, in combination with a value for COD, can be used to determine the treatability of wastewater. Respirometry can also be applied on-line, e.g. for on-line monitoring of wastewater. However, automatic detection of the end-point of exogenous respiration is difficult. The first step towards on-line monitoring of wastewater treatability is to make automatic detection of this end-point possible. In this study the use of a neural network for detection of this end-point was investigated. Results are promising; after training the neural network is able to detect the correct end-point in the majority of the studied cases.
Improving oxygen concentration control in activated sludge process with estimation of respiration and scheduling control
Authors: Gerkšič S. , Vrečko D. , Hvala N.
Published: July 2007

The paper presents an efficient and simple model-based method of on-line estimation of respiration from the current values of dissolved oxygen concentration and airflow signals. Fast estimation of respiration is important because respiration appears as the most important disturbance signal in the control of dissolved oxygen concentration, and could therefore be used for improving control efficiency. A parameter scheduling PI (proportional and integral) control scheme is proposed, where the estimated respiration signal is used for scheduling of the PI controller parameters, by using local linearization of the process dynamics. The performance of the scheduling controller is compared to a conventional PI controller in simulation using the COST simulation benchmark, and experimentally on an activated sludge process pilot plant.
Knowledge-based fuzzy system for diagnosis and control of an integrated biological wastewater treatment process
Authors: Pires O.C. , Palma C. , Costa J.C. , Moita I. , Alves M.M. , Ferreira E.C.
Published: July 2007

A supervisory expert system based on fuzzy logic rules was developed for diagnosis and control of a laboratory- scale plant comprising anaerobic digestion and anoxic/aerobic modules for combined high rate biological N and C removal. The design and implementation of a computational environment in LabVIEW for data acquisition, plant operation and distributed equipment control is described. A step increase in ammonia concentration from 20 to 60 mg N/L was applied during a trial period of 73 h. Recycle flow rate from the aerobic to the anoxic module and bypass flow rate from the influent directly to the anoxic reactor were the output variables of the fuzzy system. They were automatically changed (from 34 to 111 L/day and from 8 to 13 L/day, respectively), when new plant conditions were recognised by the expert system. Denitrification efficiency higher than 85% was achieved 30 h after the disturbance and 15 h after the system response at an HRT as low as 1.5 h. Nitrification efficiency gradually increased from 12 to 50% at an HRT of 3 h. The system proved to react properly in order to set adequate operating conditions that led to timely and efficient recovery of N and C removal rates.
Decision algorithm based on data mining for coagulant type and dosage in water treatment systems
Authors: Bae H. , Kim S. , Kim Y.J.
Published: July 2007

Water shortages are gradually accelerating because higher standards of living are required and water resources are more heavily utilised. Therefore, effective water treatment is necessary in order to retain the required quality and amount of water. General treatment includes coagulation, flocculation, filtering and disinfection. Coagulation, flocculation and disinfection are major components of water treatment processes. In this paper, a new automatic decision algorithm is proposed for coagulation. The proposed method shows how to determine the coagulant type and amount using data mining techniques.
Extension of the IWA/COST simulation benchmark to include expert reasoning for system performance evaluation
Authors: Comas J. , Rodríguez-Roda I. , Poch M. , Gernaey K.V. , Rosen C. , Jeppsson U.
Published: July 2007

In this paper the development of an extension module to the IWA/COST simulation benchmark to include expert reasoning is presented. This module enables the detection of suitable conditions for the development of settling problems of biological origin (filamentous bulking, foaming and rising sludge) when applying activated sludge control strategies to the simulation benchmark. Firstly, a flow diagram is proposed for each settling problem, and secondly, the outcome of its application is shown. Results of the benchmark for two evaluated control strategies illustrate that, once applied to the simulation outputs, this module provides supplementary criteria for plant performance assessment. Therefore, simulated control strategies can be evaluated in a more realistic framework, and results can be recognised as more realistic and satisfactory from the point of view of operators and real facilities.
Biosensor-based control of nitrification inhibitor in municipal wastewater treatment plants
Authors: Okayasu Y. , Tanaka H. , Inui T. , Tanaka Y.
Published: July 2007

The effect of potassium cyanide (KCN) on nitrification processes in municipal wastewater treatment plants was studied by batch nitrification tests, which indicated that nitrification processes tend to be inhibited at a lower KCN concentration than the present discharge standard to sewerage. The experiment of the biosensor using nitrifying bacteria was also conducted for continuous monitoring of nitrification inhibitor in influent wastewater, and demonstrated that the biosensor can detect KCN at as low as EC10 of the abovementioned batch nitrification test. Moreover, to determine the effectiveness of application of the biosensor to avoid the impact of KCN due to an accidental spillage in a sewerage system, KCN was intentionally injected into the experimental models of activated sludge process equipped both with and without the biosensor. The model with the biosensor that could detect KCN could divert the wastewater including KCN to a refuge tank, which resulted in the avoidance of upset of the activated sludge process. On the other hand, the model without the biosensor was upset in the nitrification process due to KCN. Such differences demonstrate the effectiveness of the biosensor applied to countermeasures of an accidental spillage of toxic chemicals to avoid upset of nitrification in municipal wastewater treatment plants.
Efficient design and operation of a data acquisition system for pressurized pipeline systems
Authors: Kim S.
Published: July 2007

The unsteady flow analysis of pipeline systems provides useful guidelines for implementing data acquisition components such as data filtering ranges, sensor locations and sampling frequencies. A theoretical integration among hydraulics, free vibration analysis and signal processing is proposed for a comprehensive approach aiming at enhanced design and operation of data acquisition system. Transient analysis is performed to extract flow variation by a valve modulation in a pipeline system. Frequency transformation analysis is developed to convert pressure variations between time domain and frequency domain. Free vibration analysis provides spatial distribution of impedance characteristics and pressure variation for determining optimum sensor location. A real-time filter can be designed to secure valid signals of any particular unsteady event. Hypothetical and experimental applications show that the proposed method has potentials of the leakage detection of a pipeline system as well as an efficient design of data acquisition system.
New measurement techniques for secondary settlers: a review
Authors: Vanrolleghem P.A. , Clercq B.D. , Clercq J.D. , Devisscher M. , Kinnear D.J. , Nopens I.
Published: July 2007

In activated sludge wastewater treatment research, most of the attention has been devoted to the biodegradation process. However, in terms of effluent quality, the final settling and clarification processes are at least as important because any particle carried over the overflow weir brings with it not only COD, but also nitrogen and phosphorus. In recent years we see indeed increased attention on this separation step, and alternatives such as membrane separation are increasingly introduced. Still, a large installed base of settlers exists, whose operation could/should be optimised. The measurement techniques presented in this contribution each focus on one of the key processes in the secondary settler: hydrodynamics, particle aggregation and breakage, hindered settling and compression. For each technique, the measuring principle is explained and a typical data set shown.
Wastewater fingerprinting by UV-visible and synchronous fluorescence spectroscopy
Authors: Wu J. , Pons M.N. , Potier O.
Published: July 2007

Municipal wastewater samples have been collected in three different types of community and fingerprinted by optical methods combining UV-visible spectrometry, synchronous fluorescence spectrometry and turbidity. Correlations, whose slope depends on the sampling location, were obtained between absorbance at 254 nm and the synchronous fluorescence intensity of peaks P1 (I366/316), P2 (I430/380) and P3 (I520/470). The corresponding correlation coefficients are larger than 0.75. Although related to urine as ammonia, the fluorescence intensity of P1 does not exhibit a strong correlation with this substance (correlation coefficient of approximately 0.6). All the measured parameters exhibit diurnal variation patterns related to human activities.
On-line concentration measurements in wastewater using nonlinear deconvolution and partial least squares of spectrophotometric data
Authors: Vargas A. , Buitrón G.
Published: July 2007

A procedure for the on-line measurement of concentrations of toxins in wastewater using spectrophotometric data is proposed. The complete absorbance spectrum of a wastewater sample is used to predict the concentrations of all possible substances within. Two techniques are examined. In nonlinear spectral deconvolution, the spectrum is decomposed as a linear combination of base spectra and the coefficients of this deconvolution are used to nonlinearly estimate the concentrations. Under partial least squares analysis, the concentrations are directly estimated as a linear combination of the measured spectrum data. Both techniques show good results for estimating the kinetics of samples taken during the reaction phase in a laboratory anaerobic/aerobic SBR used for p-nitrophenol biodegradation.
A model of the redox measurement in aerated activated sludge
Authors: Cecil D. , Skou E.
Published: July 2007

A number of investigations have shown that pH, oxygen concentration, and the organic load affect the measured redox potential in aerated activated sludge. In this investigation, a model of the redox measurement is proposed. It is a kinetic model based on the necessary balance between the number of electrons accepted by and donated to a metal electrode in the sludge. The potential changes in order to maintain this balance. The model variables are pH, oxygen concentration, temperature and the activity of reduced compounds. Data from a wastewater treatment plant is analyzed using this model and it is shown that the model can be fitted to results from other published investigations. However we cannot as yet demonstrate a correlation between the activity of reduced compounds and the organic load on the sludge. The ultimate objective of this work is to extract more information from the redox measurement. This is a practical interest because the redox measurement is inexpensive and requires little maintenance.
Failure monitoring in water distribution networks
Authors: Misiunas D. , Vítkovský J. , Olsson G. , Lambert M. , Simpson A.
Published: July 2007

An algorithm for the burst detection and location in water distribution networks based on the continuous monitoring of the flow rate at the entry point of the network and the pressure at a number of points within the network is presented. The approach is designed for medium to large bursts with opening times in the order of a few minutes and is suitable for networks of relatively small size, such as district metered areas (DMAs). The burst-induced increase in the inlet flow rate is detected using the modified cumulative sum (CUSUM) change detection test. Based on parameters obtained from the CUSUM test, the burst is simulated at a number of burst candidate locations. The calculated changes in pressure at the pressure monitoring points are then compared to the measured values and the location resulting in the best fit is selected as the burst location. The EPANET steady-state hydraulic solver is utilised to simulate the flows and pressures in the network. A sensitivity-based sampling design procedure is introduced to find the optimal positions for pressure monitoring points. The proposed algorithm is tested on a case study example network and shows potential for burst detection and location in real water distribution systems.
Sensor validation and reconciliation for a partial nitrification process
Authors: Yoo C.K. , Villez K. , Lee I.B. , Van Hulle S. , Vanrolleghem P.A.
Published: July 2007

Wastewater treatment plants (WWTP) are notorious for poor data quality and sensor reliability due to the hostile environment in which the measurement equipment has to function. In this paper, a structured residual approach with maximum sensitivity (SRAMS) based on the redundancy of the measurements is used to detect, identify and reconstruct single and multiple sensor faults in a single reactor for high activity ammonia removal over nitrite (SHARON) process. SRAMS is based on inferences, which are insensitive to the faults in the sensor of interest and sensitive to faults in the other sensors. It is used for four types of sensor failure detection: bias, drift, complete failure and precision degradation. The application of sensor validation shows that single and multiple sensor faults can be detected and that the fault magnitude and fault type can be estimated by the reconstruction scheme. This sensor validation method is not limited by the type or application of the considered sensors. The methodology can thus easily be applied for sensor surveillance of other continuously measuring sensors and analysers.
Titrimetric monitoring of a completely autotrophic nitrogen removal process
Authors: Van Hulle S.W.H. , Zaher U. , Schelstraete G. , Vanrolleghem P.A.
Published: July 2007

Fully autotrophic nitrogen removal processes, such as the combined SHARON-Anammox process, help to improve the sustainability of wastewater treatment. Successful operation of such a completely autotrophic system is, among others, based on the strict control of the SHARON reactor in order to produce an Anammox-suited influent with a 1:1 ammonium:nitrite ratio. The high quality and high frequency measurements provided by a titrimetric set-up measuring the total ammonium (TAN) and total nitrite (TNO2) concentrations facilitate this control considerably. In this study, the use of a titrimetric set-up for monitoring the combined SHARON-Anammox process is investigated. The technique that interprets on-line collected titration curves was applied to a lab-scale system. Comparison with classic colorimetric results gave statistically indistinguishable results for TAN and TNO2 concentrations in the SHARON reactor. In the Anammox reactor, only TAN could be determined by the investigated method due to the very low TNO2 concentrations. Phosphate, a potential inhibitor of the Anammox process, is available as an additional measurement in the effluent of the SHARON reactor. Three measurements are thus combined in one single instrument. The proposed measuring technique holds different advantages over the other TAN and TNO2 measurement techniques such as on-site availability, easy automation, the absence of the need for high dilutions and cost reduction.
New intake control system based on river water quality
Authors: Furukawa S. , Morikawa A. , Masuda N. , Sakaguchi I.
Published: July 2007

The authors propose a new intake control system for water purification plants based on river water quality. In this system the intake flow rate of a plant will decrease while the river water is polluted, whereas it will increase after the water quality of the river has recovered. The purpose of this system is to reduce the operational costs of water purification while securing an adequate water supply. Simulation studies on the proposed system were conducted to investigate the reduced amount of coagulant dosage and waste sludge generated. Simulation results with 2-year, on-line turbidity data revealed that the reduction percentages of waste sludge for the first and second years were 5.8% and 8.5%, respectively. This remarkable effect suggests that the proposed system could also contribute to enlarging the capacity of landfill sites for incinerated sludge and to preserving the environment.
Sludge–sludge Interaction in the Enhanced Biological Phosphorus Removal Process
Authors: Ichihashi O. , Satoh H. , Mino T.
Published: July 2007

Metabolisms related to enhanced biological phosphorus removal (EBPR) were found to be affected when two activated sludges with different EBPR activities were mixed together. In the present study, two laboratory scale EBPR processes were operated in parallel, one of them with higher and another with lower EBPR activities. The activated sludges from the two reactors were mixed together at different mixing ratios. The supernatant was made the same for all mixing ratios, anaerobic–aerobic batch experiments were performed, and acetate uptake rate and phosphate release rate under anaerobic conditions and phosphate uptake rate under aerobic condition were determined. The metabolic rates measured were expected to be linear to the mixing ratios, as the supernatant was the same for all mixing ratios, whereas the metabolic rates were either promoted or inhibited by mixing of sludges. As an indicator for the sludge mixing effect on the metabolic rates, mixing effect intensity (MEI) was introduced. Chemical substances that are produced by microorganisms in activated sludge are proposed to be one of the possible causes of the sludge mixing effect.
Optimization of nitrogen and phosphorus limitation for better biodegradable plastic production and organic removal using single fed-batch mixed cultures and renewable resources
Authors: Md Din M.F. , Ujang Z. , van Loosdrecht M.C.M. , Ahmad A. , Sairan M.F.
Published: July 2007

The process for the production of biodegradable plastic material (polyhydroxyalkanoates, PHAs) from microbial cells by mixed-bacterial cultivation using readily available waste (renewable resources) is the main consideration nowadays. These observations have shown impressive results typically under high carbon fraction, COD/N and COD/P (usually described as nutrient-limiting conditions) and warmest temperature (moderate condition). Therefore, the aim of this work is predominantly to select mixed cultures under high storage responded by cultivation on a substrate – non limited in a single batch reactor with shortest period for feeding and to characterize their storage response by using specific and kinetics determination. In that case, the selected-fixed temperature is 30 °C to establish tropical conditions. During the accumulated steady-state period, the cell growth was inhibited by high PHA content within the cells because of the carbon reserve consumption. From the experiments, there is no doubt about the PHA accumulation even at high carbon fraction ratio. Apparently, the best accumulation occurred at carbon fraction, 160±7.97 g COD/g N (PHAmean=44.54% of dried cells). Unfortunately, the highest PHA productivity was achieved at the high carbon fraction, 560±1.62 g COD/g N (0.152±0.17 g/l. min). Overall results showed that with high carbon fraction induced to the cultivation, the PO4 and NO3 can remove up to 20% in single cultivation.
The effect of nitrite on aerobic phosphate uptake and denitrifying activity of phosphate-accumulating organisms
Authors: Yoshida Y. , Takahashi K. , Saito T. , Tanaka K.
Published: July 2007

An anaerobic/aerobic/anoxic/aerobic sequencing batch reactor (SBR) was operated with municipal wastewater to investigate the effect of nitrite on biological phosphorus removal (BPR). When nitrite accumulated, aerobic phosphate uptake activity significantly decreased and, in case of hard exposure to nitrite, BPR severely deteriorated. The interesting observation was that the relative anoxic activity of phosphate accumulating organisms (PAOs) increased after nitrite exposure. Moreover batch tests of aerobic phosphate uptake in the presence/absence of nitrite indicated that PAOs with the higher relative anoxic activity are less sensitive to nitrite exposure. From these results, we concluded that BPR is sensitive to nitrite exposure, but BPR containing PAOs with the higher relative anoxic activity is possibly more stable against nitrite than BPR containing PAOs with the lower relative anoxic activity.
Simultaneous treatment of sewage sludge and food waste by the unified high-rate anaerobic digestion system
Authors: Kim H.-W. , Han S.-K. , Shin H.-S.
Published: July 2007

This study aimed to evaluate the performance of the unified high-rate anaerobic digestion (UHAD) system treating co-substrate of sewage sludge and food waste. A 24-hr operating sequence consisted of four steps including fill, react, settle, and draw. The effects of co-substrate and organic loading rate (OLR) on the performance were investigated to verify the system applicability. In each OLR, the UHAD system showed higher CH4 recovery (>70%), CH4 yield (0.3 L CH4/g VSadded) and CH4 production rate (0.6 L CH4/L/d) than the control system. In the specific methanogenic activity (SMA) tests on thermophilic biomass of the UHAD system, the average SMA of acetate (102 mL CH4/gVSS/d) was much higher than those of butyrate (85 mL CH4/g SS/d) and propionate (42 mL CH4/gVSS/d). It was demonstrated that the UHAD system for co-digestion resulted in higher methane yield and methane production rate due to sequencing batch operation, thermophilic digestion, and co-digestion. The enhanced performance could be attributed to longer retention time of active biomass, faster hydrolysis, higher CH4 conversion rate, and balanced nutrient conditions of co-substrate in the UHAD system. Consequently, this optimized unification could be a viable option for the simultaneous treatment of two types of OFMSW with high stability.
Effective sludge solubilization treatment by simultaneous use of ultrasonic and electrochemical processes
Authors: Watanabe T. , Zeng D.-Y. , Cho K.-J. , Kuroda M.
Published: July 2007

Sludge disintegration treatment by using simultaneously ultrasonic irradiation and electrolysis was investigated experimentally. A lab-scale diaphragm cell irradiated with ultrasound at a constant oscillating frequency of 20 kHz was used as a reactor. The batch experiments were carried out under different conditions of electric outputs of the ultrasonic generator, electric current for the electrolysis and different initial SS concentrations. A simultaneous treatment in the cathodic compartment without any chemical doses considerably facilitated the sludge solubilization, compared to the sonication alone. An increase in the electric current up to 400 mA under a constant ultrasonic density decreased the specific energy by 55% within the experimental range. The specific energy consumption was also reduced when the initial SS concentration increased. In addition, before carrying out the simultaneous treatment, a brief electrolysis was effective for further reduction of the specific energy and the acceleration of soluble COD generation.
Dynamic analysis of coagulation of low turbidity water sources using Al- and Fe-based coagulants
Authors: Ebie K. , Kawaguchi T. , Yamaguchi D.
Published: July 2007

The direct filtration system is widely used in the treatment of source waters with low and stable turbidity. We have previously indicated the importance of optimizing agitation strength GR and time TR in rapid mixing tanks in order to decrease filter head loss and treated water turbidity in direct filtration. In the present study, we employ a batch-type coagulation experimental apparatus that incorporates a high-sensitivity particle counter, where the particulate concentrations are measured continuously after injection of coagulant, in order to clarify the fundamental coagulation and microfloc formation dynamics. Specifically, it is shown that, after injection of the coagulant, coagulation and microfloc formation occur through distinct periods: an agglomeration preparation period, followed by an agglomeration progression period, and then finally an agglomeration stabilization period, and that optimization of the GR value is the most important consideration, although both the coagulant concentration and GR influence the time at which agglomeration begins in the preparatory period, the time at which agglomeration stabilizes after the progression period, and the concentration of initial particles with diameters of 1–3 μm at completion of agglomeration.
Development of single-stage nitrogen removal using anammox and partial nitritation (SNAP) and its treatment performances
Authors: Furukawa K. , Lieu P.K. , Tokitoh H. , Fujii T.
Published: July 2007

Single-stage Nitrogen removal using Anammox and Partial nitritation (SNAP) process was newly developed as an economical nitrogen removal process for ammonium rich wastewaters. The experimental studies for the evaluation of SNAP process were carried out using a novel biofilm reactor, in which hydrophilic net-type acryl fiber biomass carrier was applied. This SNAP reactor was operated under operational conditions of pH 7.5–7.7, 35 °C and DO 2–3 mg/L, and 60 to 80% of influent NH4-N was removed under loading rate of 0.48 kg-N/m3/d. Through the DNA analysis of the attached sludge, it was made clear that ammonium oxidizing bacteria (AOB) and anammox bacteria coexisted in the attach-immobilized sludge on the acryl fiber biomass carrier. Favorable conditions for the growth of anammox bacteria were created inside attach-immobilized nitrifying sludge. Two kinds of anammox bacteria and two kinds of AOB were detected in the SNAP sludge. Existence ratios of anammox and AOB were estimated to be 15% and 8.7%, respectively, based on the obtained clone numbers. This coexisting condition was confirmed by the FISH image of SNAP sludge and its confocal laser scanning microscope.
Evaluation of sludge reduction and phosphorus recovery efficiencies in a new advanced wastewater treatment system using denitrifying polyphosphate accumulating organisms
Authors: Suzuki Y. , Kondo T. , Nakagawa K. , Tsuneda S. , Hirata A. , Shimizu Y. , Inamori Y.
Published: July 2007

A new biological nutrient removal process, anaerobic–oxic–anoxic (A/O/A) system using denitrifying polyphosphate-accumulating organisms (DNPAOs), was proposed. To attain excess sludge reduction and phosphorus recovery, the A/O/A system equipped with ozonation tank and phosphorus adsorption column was operated for 92 days, and water quality of the effluent, sludge reduction efficiency, and phosphorus recovery efficiency were evaluated. As a result, TOC, T-N and T-P removal efficiency were 85%, 70% and 85%, respectively, throughout the operating period. These slightly lower removal efficiencies than conventional anaerobic–anoxic–oxic (A/A/O) processes were due to the unexpected microbial population in this system where DNPAOs were not the dominant group but normal polyphosphate-accumulating organisms (PAOs) that could not utilize nitrate and nitrite as electron acceptor became dominant. However, it was successfully demonstrated that 34–127% of sludge reduction and around 80% of phosphorus recovery were attained. In conclusion, the A/O/A system equipped with ozonation and phosphorus adsorption systems is useful as a new advanced wastewater treatment plant (WWTP) to resolve the problems of increasing excess sludge and depleted phosphorus.