A model for the activated sludge process which considers wastewater characteristics, floc behavior, and microbial population

Benefield, Larry D.; Molz, Fred J.

doi:10.1002/bit.260260410

Cited by 35 publications

(16 citation statements)

References 2 publications

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“…Diffusion of substrates through activated sludge flocs is a well‐established phenomenon ( Atkinson and Davies, 1974 ; Bakti, 1992 ; Benefield and Molz, 1984 ; Kossen, 1979 ; Matson and Characklis, 1976 ). This phenomenon is accounted for in the popular International Water Association (IWA) (London) activated sludge models (ASMs), as a result of the half‐saturation constants in the Monod functions used in the microorganism growth rate expressions for heterotrophs for dissolved oxygen and nitrate ( O'Shaugnessey et al, 1998 ).…”

Section: Introductionmentioning

confidence: 99%

Diffusion of Oxygen Through Activated Sludge Flocs: Experimental Measurement, Modeling, and Implications for Simultaneous Nitrification and Denitrification

Daigger

Adams

Steller

2007

Water Environment Research

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Diffusion of dissolved oxygen through activated sludge flocs was studied, as it represents a potential mechanism for simultaneous nitrification and denitrification in activated sludge systems. Dissolved oxygen profiles through six floc particles collected at different times from a full‐scale activated sludge plant demonstrated that that the dissolved oxygen concentration declines through all floc particles. For larger floc particles (2‐mm diameter and greater), the dissolved oxygen concentration reached near‐zero values at depths depending on process operating conditions. A mathematical model based on diffusion of dissolved oxygen, organic substrate (methanol), ammonia, nitrite, and nitrate through a spherical floc and consumption of dissolved oxygen by heterotrophs and autotrophs accurately predicted the dissolved oxygen profile and required adjustment of only one model parameter—the concentration of heterotrophs. A different dissolved oxygen decline pattern was exhibited for the smaller floc particles characterized, with the dissolved oxygen reaching a non‐zero plateau toward the center of the floc. This pattern was not reproduced with the mathematical model developed and suggests that additional mechanisms are responsible for the transport of dissolved oxygen into the center of these flocs. Implications of these results regarding the occurrence of simultaneous nitrification and denitrification include consideration of the factors that affect floc size and distribution (simultaneous nitrification and denitrification is maximized with larger floc particles), coupling of the International Water Association (London) activated models to predict activated sludge composition with diffusion models to consider intrafloc effects, and the effects of substrate diffusion on the apparent half‐saturation constant for various substrates in activated sludge systems.

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Section: Introductionmentioning

confidence: 99%

Diffusion of Oxygen Through Activated Sludge Flocs: Experimental Measurement, Modeling, and Implications for Simultaneous Nitrification and Denitrification

Daigger

Adams

Steller

2007

Water Environment Research

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“…The existence of these intraparticle zones was proposed, but not experimentally observed, by several researchers (Benefield and Molz, 1984;Bakti and Dick, 1992;Scuras, et. al., 1998;Pochana and Keller, 1999;Daigger and Littleton, 2000).…”

Section: Resultsmentioning

confidence: 90%

Characterization of the Floc Micro-Environment in Dispersed Growth Systems

Kaempfer¹,

Adams²

2000

proc water environ fed

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The phenomenon of nitrogen and phosphorus removal in aerated biological reactors where no formal anoxic or anaerobic zones are present is referred to as simultaneous biological nutrient removal (SBNR). One possible mechanism for SBNR is the development of anoxic/anaerobic zones within floc particles (designated the floc microenvironment). A better understanding of the mechanisms of SBNR can provide a basis for the rational design of dispersed growth systems optimized for SBNR. In this research, a bench-scale CSTR was used to simulate an activated sludge system and maintain typical conditions observed at treatment plants for in situ microprobe measurements of floc particles. Microprobes were used to obtain pH and dissolved oxygen (DO) profiles through floc particles. The results show that anoxic zones exist within floc particles of sufficient diameter. Profiles of pH were also taken and found to remain relatively constant through a floc particle. Initial results suggest that time of floc growth and floc sizes have direct effects on the size of the intraparticle anoxic zone. Shearing of the floc, or reducing the floc size, is believed to be detrimental to the presence of intraparticle anoxic zones.

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“…The concentration of influent substrate concentration determines the performance of the plant. Benefield and Molz [17] showed that although substrate treatment would not likely be affected until a very low DO was reached, a distinction between excess and low DO was made since nitrification can be limiting at DO concentrations less than 2 mg L −1 .…”

Section: Effect Of Influent Substrate Concentrationmentioning

confidence: 99%

Heterogeneous Modeling, Identification and Simulation of Activated Sludge Processes

Mustafa¹,

Ibrahim²,

Elkamel³

et al. 2009

American J. of Environmental Sciences

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Problem statement:The activated sludge system is a complex dynamic process and must account for a large number of reactions between large numbers of components. There is necessity for simulation models which describe the dynamic behavior of the activated sludge process. The application of the models in most treatment plants is limited due to lack of appropriate data acquisition and parameters identification studies. To realize this, an improvement of the operating strategies of Waste-Water Treatment Plants (WWTP) is required. The objectives of this study were to: (i) To build a process model considering mass transfer limitations and simulate an existing plant (Helwan WWTP) and validate the results using data from another existing plant with (Zenine WWTP). (ii) To adjust the model kinetic parameters of the biochemical reactions under the effect of mass transfer conditions to be prepared for simulation purposes. (iii) Study the effect of the operating conditions on the removal efficiency of both substrate and ammonia. Approach: A process model of the process was built considering mass transfer limitations and the three growth processes: Carbon oxidation, nitrification and denitrification. Helwan WWTP was used in order to extract the suitable stoichiometric and kinetic parameters to be used for the simulation. Helwan WWTP was used through the simulation results of the substrate (BOD) and ammonia. Egyptian Zenine WWTP was used for the testing and validation of the process model through predicting the response of substrate. Results: The average error of the removal efficiency in Helwan WWTP reached 3.3% for the substrate and 12.5% for the ammonia while the average error of the removal efficiency in Zenine WWTP of substrate reached 4.6%. The effects of recycle ratio, flow rate and influent substrate concentrations on the removal efficiency of the aeration tank were studied. It was found that the removal efficiency of substrate and ammonia was increased by increasing the recycle ratio, influent substrate concentrations and also increased by decreasing influent flow rates. It was found also that the sludge age increased by increasing the recycle ratio and decreased by decreasing the influent flow rates. Conclusion: The heterogeneous process model was able to describe the characteristics and reflects the real phenomena existing in activated sludge processes.

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A model for the activated sludge process which considers wastewater characteristics, floc behavior, and microbial population

Cited by 35 publications

References 2 publications

Diffusion of Oxygen Through Activated Sludge Flocs: Experimental Measurement, Modeling, and Implications for Simultaneous Nitrification and Denitrification

Diffusion of Oxygen Through Activated Sludge Flocs: Experimental Measurement, Modeling, and Implications for Simultaneous Nitrification and Denitrification

Characterization of the Floc Micro-Environment in Dispersed Growth Systems

Heterogeneous Modeling, Identification and Simulation of Activated Sludge Processes

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