Step Feed Research Articles

Modeling and Control of Oxygen Transfer in High Purity Oxygen Activated Sludge Process

A dynamic mathematical model for the high purity oxygen activated sludge process, which incorporates structured biomass, gas–liquid interactions and control systems, was developed. The model was calibrated using pilot plant data associated with the development of the West Point Treatment Plant near Seattle, Wash. The calibrated model was used to simulate oxygen transfer rates for various operating conditions. Simulations showed that an optimal control system can reduce aerator power by 33% as compared to a conventional design, and reduce average oxygen feed gas by as much as 18%. Vent gas purity control dramatically reduced the peak aerator horsepower required to maintain set point dissolved oxygen concentration during high loadings. Step feed operation reduced the stag-to-stage variation in aerator horsepower and also reduced the required peak power. Predicted power savings for a 605,000 m³/day plant were $500,000 per year at current power costs.

ECONOMIC BENEFITS OF CHEMICALLY-ASSISTED PRIMARY TREATMENT, STEP FEED, AND ANOXIC ZONES

ECONOMIC BENEFITS OF CHEMICALLY-ASSISTED PRIMARY TREATMENT, STEP FEED, AND ANOXIC ZONESA project to expand the City of Garland Duck Creek Wastewater Treatment Plant from 20- to 40-mgd (average daily flow) was initiated in 2002 to provide for future growth and planned diversion of flow from the City's other treatment plant. The selected expansion configuration provides a new stand-alone activated sludge system (aeration basins and final clarifiers) that will operate in parallel with...Author(s)Gerald W. FoessPaul JarrettBrian G. WilliamsSourceProceedings of the Water Environment FederationSubjectSession 3 - Municipal Wastewater Treatment Processes: Process Optimization and Biological ModelingDocument typeConference PaperPublisherWater Environment FederationPrint publication date Jan, 2003ISSN1938-6478SICI1938-6478(20030101)2003:12L.313;1-DOI10.2175/193864703784755346Volume / Issue2003 / 12Content sourceWEFTECFirst / last page(s)313 - 323Copyright2003Word count227

2911 粗粒ダイヤモンド砥石による炭化けい素の超平滑研削条件の検討

In the previous report, the possibility of ultra-smooth grinding of fine ceramics with # 140 mesh metal bond diamond wheel was ascertained. In this paper, the effect of step feed parallel to grinding direction on surface roughness of ground silicon carbide ceramic (HPSC) is examined. It is found that the parallel step feed has large effect on the surface roughness. In addition, the surface roughness of silicon carbide ceramic formed by using suitable grinding conditions can attain to below within 22nm (Rz).

Evaluation of Alternative DO Control Strategies for High Rate BNR Processes

Evaluation of Alternative DO Control Strategies for High Rate BNR ProcessesAssessment of the level of DO control necessary to meet nutrient removal performance targets and contain energy costs is critical in large wastewater treatment plants. An additional challenge for high rate, step feed BNR processes are the changing DO demands, due to both the diurnal variation and the process' step feed pattern. A comprehensive evaluation using dynamic process simulation showed...Author(s)Keith MahoneyJames MuellerChris VillariDimitrios KatehisEileen ProffittSourceProceedings of the Water Environment FederationSubjectSession 75 Municipal Wastewater Treatment Processes: Advances in Aeration SystemsDocument typeConference PaperPublisherWater Environment FederationPrint publication date Jan, 2003ISSN1938-6478SICI1938-6478(20030101)2003:5L.264;1-DOI10.2175/193864703784606963Volume / Issue2003 / 5Content sourceWEFTECFirst / last page(s)264 - 271Copyright2003Word count198

Improving the predictions of ASM2d through modelling in practice

The paper presents the adjustments carried out on the structure and in some default values of the kinetic coefficients of the ASM2d model in order to get an improved prediction for the experimental results obtained in pilot scale plants studies with different activated sludge treatment processes for carbon, nitrogen and phosphorous removal. In order to predict the high effluent filtered COD experimentally observed in high rate processes for carbon removal, a new model structure has been proposed, incorporating into the carbon model a soluble fraction of the slowly biodegradable substrate. Studies with the step feed and the alternating processes showed simultaneous nitrification-denitrification in aerated reactors which was predicted with increased values in the oxygen saturation coefficients for heterotrophic and autotrophic biomass. Both processes also showed loss of the denitrification capacity under unfavourable conditions, such us rains and low anoxic fraction, which required a very large decrease in the value of the reduction factor for denitrification so as to improve the predictions for effluent nitrate experimental results. Regarding phosphorus removal, the ASM2d model showed a satisfactory predictive capacity. For improved predictions of phosphorus release in anaerobic conditions, high values of the rate constant for storage of X(PHA) and low values of the anaerobic hydrolysis reduction factor were used. For phosphorus uptake in aerobic and anoxic conditions satisfactory predictions were obtained using the default values.

Alternative Supplemental Carbon Sources for the Step Feed BNR Process

Alternative Supplemental Carbon Sources for the Step Feed BNR Process

スクイーズ空気膜による非接触位置決め特性の基礎的研究 ステップ応答の数値的解析と実験的検証

The aim of this study is to consider positioning characteristics of floating object suspended by steady-state squeeze air films. For the columned thrust squeeze air bearing model, the numerical analysis technique based on Lees' difference approximation method is applied to solve the Reynolds equations. The piezo-driven oscillating pad generates the steady-state squeeze air film and step motion for shifting the floating object. The numerical results for the step response of the object position and air film pressure extremely agreed with the experimental ones. The step response showed the strong nonlinearity of dynamic air film characteristics. The phase lag between squeeze motion and step feed motion has a great influence on the step response. Because the squeeze motion is sinusoidal oscillation, the acceleration which acts on floating object affects with phase lag. Therefore minimizing the acceleration by controlling the phase lag can decrease the overshoot. The numerical results are shown in case of single air film generation on lower side and in case of dual air films on upper and lower sides. As a result, the operation with dual air films increases the damping characteristic and is effective to decrease the overshoot especially for the large step width.

Characterization of Denitrification and Nitrification in a Step‐Feed Alternating Anoxic–Oxic Sequencing Batch Reactor

This study was conducted to characterize the denitrification and nitrification in a bench-scale sequencing batch reactor operating with a three-stage, alternating anoxic-oxic sequence and step feed (SAOSBR) for treating synthetic wastewater. The results of long-term operation and dynamic studies showed that the SAOSBR increased the availability of organic matter in wastewater for exogenous denitrification in anoxic periods, and subsequently allowed nitrification to occur under a lower organic loading in oxic periods. Comparatively high kinetic rates of 1.2 to 6.6 mg nitrate/g mixed liquor suspended solids (MLSS) x h for denitrification and 1.0 to 2.8 mg nitrogen/g MLSS x h for nitrification were found in dynamic studies. With sufficient influent organics and alkalinity, complete denitrification and full nitrification could be achieved sequentially in the alternating anoxic and oxic periods, resulting in an average total nitrogen removal efficiency up to approximately 90%. Alkalinity recovery because of exogenous denitrification was experienced, and a minimum influent alkalinity to total Kjeldahl nitrogen (TKN) ratio of 2.4 was required to reach complete TKN removal. The pH value would be a better parameter other than oxidation-reduction potential or dissolved oxgyen to determine the completeness of nitrification and denitrification in the SAOSBR.

CO2 recovery from flue gas by PSA process using activated carbon

An experimental study was performed for the recovery of CO2 from flue gas of the electric power plant by pressure swing adsorption process. Activated carbon was used as an adsorbent. The equilibrium adsorption isotherms of pure component and breakthrough curves of their mixture (CO2 : N2 : O2=17 : 79 : 4 vol%) were measured. Pressure equalization step and product purge step were added to basic 4-step PSA for the recovery of strong adsorbates. Through investigation of the effects of each step and total feed rate, highly concentrated CO2 could be obtained by increasing the adsorption time, product purge time, and evacuation time simultaneously with full pressure-equalization. Based on the basic results, the 3-bed, 8-step PSA cycle with the pressure equalization and product purge step was organized. Maximum product purity of CO2 was 99.8% and recovery was 34%.

Control and Stabilisation of Odorous Sludge from Fleetwood Sewage‐Treatment Works

AbstractFollowing completion of the construction of Fleetwood sewage‐treatment works in 1996, the sludge (from the plant) was causing health and safety problems for the workforce and there were complaints of odour from the local community. Problems arose due to overloading of the biological‐treatment units, resulting in little or no dissolved oxygen in parts of the process. There was a need to stabilise the sludge in the short term, culminating in the need for chemical conditioning, and an investigation into operational procedures to stabilise the sludge in the long term. The sludge was successfully stabilised using ferric chloride and sodium hydroxide. The long‐term stability of the sludge was further improved using operational changes (such as the inclusion of step feeding and by demonstrating the effect of load removal upstream from the existing biological process) via pilot‐plant studies.

Effect of Step Feed Ratio and Temperature on Nitrogen Removal in an Anoxic-Oxic Activated Sludge Process.

『大阪大学大学院工学研究科環境工学専攻生物圏・水環境工学研究室 研究活動報告』, Vol.12(2000.4.1～2001.3.31), pp.105-113, 大阪大学大学院工学研究科環境工学専攻生物圏・水環境工学研究室, 2001.5 に掲載

Ultraprecision Positioning by Preload Change of Lead Screws

Ultraprecision positioning is examined for a fine feed system utilizing the elastic deformation of lead screws accompanying the change in the preload in a double nut. The nonlinear deformation due to Hertzian contact of the ball screw can be ignored within a feed of 1μm under an dequate initial preload. No effect of table load on nanometer-order displacement is observed in the range from 10 to 50 kg. The table displacement obtained under an increase in the preload coincides well with the result under a decrease in the preload. Feed control with preload change based on a one-to-one correspondence of preload change and displacement is effective for avoiding the hysterisis phenomenon of the piezoelectric acturator adopted as a deformable spacing part in a double nut. In addition, the preload can be used as a measure to detect the table displacement in place of a position sensor which sometimes shows unreliability owing to unstable performance in the nanometer region. The minimum step feed deduced from preload change is 1nm for a sliding screw and 5nm for a ball screw.

Development and verification of design and operation criteria for the step feed process with nitrogen removal

The step feed process with three stages of denitrification-nitrification reactors has been studied using simulations in order to develop criteria for the optimum selection of the design parameters and to propose efficient operational strategies. To verify the simulation results experimental studies in a pilot plant of 1100 litres were carried out. The simulation studies showed that the optimum influent flow distribution to the three anoxic reactors is in the range of 40-40-20% and 33-33-34% depending on the wastewater characteristics and effluent requirements. These two latter conditions and in turn the influent flow distribution determine the anoxic and aerobic reactor volumes. The reduction of the dissolved oxygen in the two first aerobic reactors and the use of facultative zones in the final D-N stage are proposed as operational strategy. The experimental results proved the validity of the criteria developed for design and operation. A high capacity of the IAWQ activated sludge model No. 1 to predict the performance of the step feed process was observed.

The use of dynamic BNR and two-dimensional clarifier modelling to investigate nitrogen removal at Eastern Treatment Plant, Melbourne, Australia

The use of process and two-dimensional clarifier modelling to investigate the implications of upgrading Melbourne Water's Eastern Treatment Plant to a nitrification/denitrification process is discussed. Results indicate that the existing clarification capacity is sufficient for the increased solids loading arising from operation at a nitrifying sludge age but that the existing diffuser system may need to be replaced in order to achieve the required oxygen transfer rate. The impact of step feeding into unaerated zones to reduce the aeration tank suspended solids concentration and to achieve denitrification is discussed and the installation of baffles to improve the performance of peripheral feed clarifiers is suggested.

An NMR Study of the Effect of Polymerization Methods on Segmented Sequence Distributions of Poly(butylene terephthalate)/Poly(tetramethylene glycol) Block Copolymers

Sequence distributions and microstructures of block copolymers of poly(butylene terephthalate) and poly(tetramethylene glycol) (PBT/PTMG) were investigated by NMR spectroscopy. The two block copolymers that had same chemical compositions, but were expected to have different sequence distributions were synthesized by two different polymerization methods differing in feeding time of PTMG (sample I, one step feeding; sample 2, two step feeding). To figure out the small differences in microstructures of the two copolymers using NMR, the choice of solvents, the NMR experimental conditions, the 1H and 13C, peak assignments and the methods of extracting sequence distributions were closely reexamined. Using phenol-d6/tetrachloroethane (TCE) as NMR solvent, various kinds of controlled 1D and 2D experiments were carried out for peak assignment and close quantification of the peaks. Next, the various parameters relating to the sequence distributions were calculated and those were compared for two samples. As the results, the sample that was made with one step feeding of PTMG was found to have nearly the same sequence distributions as expected by feed ratio. Though there were slight variations in microstructures of two samples, detailed statistical treatment (error analysis) of 10 independent data showed that there were not significant differences in sequence distributions. In the end of this report, the differences in the status of terminal groups of two samples were discussed by manifest 1H signals.

Ultraprecision Positioning by Preload Change of Lead Serews. Characteristics of Fine Feed.

The ultraprecision positioning is examined against the fine feed system utilized the elastic deformation of lead screws accompanying preload change in double nuts. The nonlinear deformation due to Hertzian contact of ball screw can ignore within a feed of 1 μm under adequate initial preload. The influence of load on table displacement of nanometer order is not observed in the range from 10 to 50 kg. The displacement obtained under increase in preload coincide well with the result under decrease in preload also. Feed control with preload change based on one to one correspondence of preload change and displacement is effective to avoid the hysteresis phenomenon of PZT actuator adopted as deformable spacing part between double nuts. Further, preload can use as a measure to detect table displacement in place of position sensor which sometimes shows unreliability owing to unstable situation in nanometer region. The minimum step feed deduced from preload change is 1 nm for sliding screw and 5 nm for ball screw.

Fine Feed by Preload Change of Lead Screws. Application to Ultraprecision Positioning.

In the preloaded double nuts of lead screw, the nuts displace slightly in the axial direction with the preload change because of the deformations of threads and screw, nut body. To apply this small displacement to the fine feed in ultraprecision positioning, the nut displacement characteristics accompanying preload change are examined against ball and sliding screws. Theoretical displacement is the order of nanometer with preload change of 1N and less displacement is easy to obtain under low spacing part stiffness. The experimental results obtained by the feed units show the step feed of from nanometer to submicron and the range of fine feed comes to several microns. The feed drive equipped with preload control lead screw has the advantage of high resolution positioning over a long traverse path by using it in combination with coarse positioning of screw rotation and fine positioning of preload control.

Simulation of the operational conditions of the full-scale municipal wastewater treatment plant to improve the performance of nutrient removal

Simulation analysis based on a mathematical model is one of the powerful tools for determining the operational conditions for a full scale biological nutrient removal plant. The model that included the Activated Sludge Model No.2 was developed for simulating the performance of the plant in Sapporo City. The investigated plant has the biological reaction basin which consists of the four zones, anaerobic-aerobic-anoxic-aerobic phases with the step feed of the primary effluent to the anaerobic and anoxic zones. We performed three experiments to calibrate and verify our model: (i) Characterization of organic matters in the influent of the reaction basin with the OUR measurement method; (ii) Measurement of COD and nutrient concentration at the plant; (iii) Lab-scale batch experiments with the anaerobic-aerobic-anoxic-aerobic phases. The calibrating process of the model showed that no modification of parameter values was required to evaluate the performance of the plant and population of the activated sludge. Simulated results showed that the choice of the sewage step feed ratio did not affect the nitrogen removal and that the denitrification rate in the anoxic zone was controlled by the hydrolysis rate of the slowly biodegradable organic matters. The results of the lab-scale experiment and simulation results showed that the addition of the readily biodegradable organic matters like fermentation products of the primary settler sludge was effective to improve the performance of nitrogen removal.

Simulation of the operational conditions of the full-scale municipal wastewater treatment plant to improve the performance of nutrient removal

Simulation analysis based on a mathematical model is one of the powerful tools for determining the operational conditions for a full scale biological nutrient removal plant. The model that included the Activated Sludge Model No.2 was developed for simulating the performance of the plant in Sapporo City. The investigated plant has the biological reaction basin which consists of the four zones, anaerobic-aerobic-anoxic-aerobic phases with the step feed of the primary effluent to the anaerobic and anoxic zones. We performed three experiments to calibrate and verify our model: (i) Characterization of organic matters in the influent of the reaction basin with the OUR measurement method; (ii) Measurement of COD and nutrient concentration at the plant; (iii) Lab-scale batch experiments with the anaerobic-aerobic-anoxic-aerobic phases. The calibrating process of the model showed that no modification of parameter values was required to evaluate the performance of the plant and population of the activated sludge. Simulated results showed that the choice of the sewage step feed ratio did not affect the nitrogen removal and that the denitrification rate in the anoxic zone was controlled by the hydrolysis rate of the slowly biodegradable organic matters. The results of the lab-scale experiment and simulation results showed that the addition of the readily biodegradable organic matters like fermentation products of the primary settler sludge was effective to improve the performance of nitrogen removal.

Nitrogen removal upgrade of a wastewater treatment plant within existing reactor volumes: A simulation supported scenario analysis

A simulation supported scenario analysis for the upgrading of a municipal WWTP Hoogstraten (Belgium) with nitrogen removal is presented. The most cost-effective solution is to create optimal aerobic and anoxic conditions within the existing reactor volumes. The IAWQ-model No. 1 was used for the simulation of the biological reactor. A measuring campaign and some specific respirometric tests provided the necessary information for calibration and verification of the biological model. The study consisted of two parts: 1) increase of the denitrification capacity, and 2) optimisation of operation. First, the impact of three measures, i.e. creation of anoxic zones, implementation of step feeding and introduction of internal recirculation, was evaluated by means of simulation. For this purpose a standard time variant influent was defined based on the measuring campaign. This approach made it easy to compare the different scenarios. In the second part of the study some specific problems were handled. To avoid high nitrate concentrations during weekends three possible control actions were simulated. The simulation study also evaluated the usefulness of the primary clarifier in the upgraded design and the effect on the biological process of first flush during intensive rainfall.