Review of Folklore in Design and Operation of Secondary Clarifiers

Parker, Denny; Kinnear, Dj; Wahlberg, Eric J.

doi:10.1061/(asce)0733-9372(2001)127:6(476)

Cited by 40 publications

(14 citation statements)

References 7 publications

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“…Under critical loading conditions, i.e., at j410 kg?m À3 , simulation results obtained for X TSS,Eff using the Taká cs model are significantly lower than those obtained with the Pló sz model. Under moderate and low loading, i.e., at jo10 kg m À3 , Parker et al (2001) show that proper activated sludge system operation with good SST design results in average X TSS,Eff around 10 g m À3 . X TSS,Eff values obtained with the Taká cs model at jo10 kg m À3 thus suggest an overestimation of a properly designed and functioning SST effluent quality.…”

Section: Scenario Simulationsmentioning

confidence: 97%

“…The main reason for this discrepancy is that the two conical SSTs have a 0.5-1m shallower centre-depth than the other flat bottom clarifiers studied. Parker et al (2001) show that, in a conical SST compared to a flat-bottom reactor, higher sludge blankets can develop because of (i) the development of the compressive blanket beginning from a higher elevation; (ii) sludge conveyance inefficiencies; (iii) less storage volume for the same depth in the centre.…”

Section: Scenario Simulationsmentioning

confidence: 98%

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Shall we upgrade one-dimensional secondary settler models used in WWTP simulators? – An assessment of model structure uncertainty and its propagation

Plósz

Clercq

Benedetti

et al. 2011

Water Science and Technology

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In WWTP models, the accurate assessment of solids inventory in bioreactors equipped with solid-liquid separators, mostly described using one-dimensional (1-D) secondary settling tank (SST) models, is the most fundamental requirement of any calibration procedure. Scientific knowledge on characterising particulate organics in wastewater and on bacteria growth is well-established, whereas 1-D SST models and their impact on biomass concentration predictions are still poorly understood. A rigorous assessment of two 1-DSST models is thus presented: one based on hyperbolic (the widely used Takács-model) and one based on parabolic (the more recently presented Plósz-model) partial differential equations. The former model, using numerical approximation to yield realistic behaviour, is currently the most widely used by wastewater treatment process modellers. The latter is a convection-dispersion model that is solved in a numerically sound way. First, the explicit dispersion in the convection-dispersion model and the numerical dispersion for both SST models are calculated. Second, simulation results of effluent suspended solids concentration (XTSS,Eff), sludge recirculation stream (XTSS,RAS) and sludge blanket height (SBH) are used to demonstrate the distinct behaviour of the models. A thorough scenario analysis is carried out using SST feed flow rate, solids concentration, and overflow rate as degrees of freedom, spanning a broad loading spectrum. A comparison between the measurements and the simulation results demonstrates a considerably improved 1-D model realism using the convection-dispersion model in terms of SBH, XTSS,RAS and XTSS,Eff. Third, to assess the propagation of uncertainty derived from settler model structure to the biokinetic model, the impact of the SST model as sub-model in a plant-wide model on the general model performance is evaluated. A long-term simulation of a bulking event is conducted that spans temperature evolution throughout a summer/winter sequence. The model prediction in terms of nitrogen removal, solids inventory in the bioreactors and solids retention time as a function of the solids settling behaviour is investigated. It is found that the settler behaviour, simulated by the hyperbolic model, can introduce significant errors into the approximation of the solids retention time and thus solids inventory of the system. We demonstrate that these impacts can potentially cause deterioration of the predictive power of the biokinetic model, evidenced by an evaluation of the system's nitrogen removal efficiency. The convection-dispersion model exhibits superior behaviour, and the use of this type of model thus is highly recommended, especially bearing in mind future challenges, e.g., the explicit representation of uncertainty in WWTP models.

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Section: Scenario Simulationsmentioning

confidence: 97%

Section: Scenario Simulationsmentioning

confidence: 98%

Shall we upgrade one-dimensional secondary settler models used in WWTP simulators? – An assessment of model structure uncertainty and its propagation

Plósz

Clercq

Benedetti

et al. 2011

Water Science and Technology

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“…The foam formed a stable and brown layer, which stayed in the tank for several weeks, and sometimes 90% surface of aeration was covered by foaming. The height of foaming is usually more than 10 cm and SVI value closed to 350 mL g −1 (SVI values above 150 mL g −1 are typically associated with filamentous growth [19]). Bulking and foaming seldom occurred in summer and autumn, and the SVI was less than 100 mL g −1 .…”

Section: Plant Performance and Controlsmentioning

confidence: 99%

Cause and pre-alarm control of bulking and foaming by Microthrix parvicella—A case study in triple oxidation ditch at a wastewater treatment plant

Xie

Dai

Ya-tong

2007

Journal of Hazardous Materials

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“…With well designed clarifiers, low concentrations of effluent suspended solids (, 10 mg/L average) can be obtained (Parker et al 1996(Parker et al , 2001. Mü ller & Krauth (1998) report on an automatic control strategy to limit the storm water inflow to the aeration tank according to the actual treatment capacity, with the ammonia concentration in the nitrification zone and the sludge blanket level in the secondary clarifiers as control parameters.…”

Section: Introductionmentioning

confidence: 99%

Utilization of activated sludge plants for enhanced treatment of combined sewage

Nikolavcic

Svardal

Wandl

et al. 2008

Water Science and Technology

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A process is introduced which utilizes secondary clarifiers for the treatment of combined sewage. Under storm water conditions, surplus sewage bypasses the aeration tanks after primary treatment and is directly introduced into the secondary clarifiers. The hydraulic capacity of existing activated sludge plants can be increased without additional tank volume. Particulate matter as well as dissolved compounds are removed to a high extent. Investigations on a full scale treatment plant (100,000 p.e.) show that the effluent quality is comparable with full biological treatment, even if the hydraulic loading is increased by 50%.

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Review of Folklore in Design and Operation of Secondary Clarifiers

Cited by 40 publications

References 7 publications

Shall we upgrade one-dimensional secondary settler models used in WWTP simulators? – An assessment of model structure uncertainty and its propagation

Shall we upgrade one-dimensional secondary settler models used in WWTP simulators? – An assessment of model structure uncertainty and its propagation

Cause and pre-alarm control of bulking and foaming by Microthrix parvicella—A case study in triple oxidation ditch at a wastewater treatment plant

Utilization of activated sludge plants for enhanced treatment of combined sewage

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