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John C Little - One of the best experts on this subject based on the ideXlab platform.

  • predicting oxygen transfer and water flow rate in airlift Aerators
    Water Research, 2002
    Co-Authors: Vickie L Burris, Daniel Frank Mcginnis, John C Little
    Abstract:

    Water flow rate, gas-phase holdup, and dissolved oxygen (DO) profiles are measured in a full-scale airlift aerator as a function of applied air flow rate. A model that predicts oxygen transfer based on discrete-bubble principles is applied. The riser DO profiles are used to calculate the initial bubble size. The range of calculated bubble diameters obtained using the model is 2.3–3.1 mm. The Sauter-mean diameter of bubbles measured in the laboratory ranged from 2.7 to 3.9 mm. The riser and downcomer DO profiles and gas holdups predicted by the model are in close agreement with the experimental results. A model that predicts water flow rate based on an energy balance is used to calculate Kt, the frictional loss coefficient for the air–water separator. Excluding the data at the very lowest air flow rate, the range of calculated values for Kt (3–8) is close to a literature value of 5.5 proposed for hydrodynamically similar external airlift bioreactors. The models should prove useful in the design and optimization of airlift Aerators.

H N Chang - One of the best experts on this subject based on the ideXlab platform.

  • steady state analysis of the coupling aerator and secondary settling tank in activated sludge process
    Water Research, 1996
    Co-Authors: H N Chang
    Abstract:

    Abstract The steady state analysis of coupling the function of aerator and secondary settling tank in activated sludge process for wastewater treatment is carried out to obtain appropriate responses of output variables and to decide optimum operating parameters. To consider the effect of the secondary settling tank, limit flux theory is applied and the aerator is assumed to be a continuous flow stirred tank reactor. By using sludge recycle ratio and sludge waste ratio as the operating parameters, the responses of the output variables—biomass concentration in aerator, dissolved pollutant and solid concentration in effluent—are represented as response surfaces and isoresponse curves. Acceptable operating zone can be obtained from the curves and optimum parameters can be determined. Coupling the function of aerator and secondary settling tank is important to consider the appropriate control of an activated sludge process.

Willi H Hager - One of the best experts on this subject based on the ideXlab platform.

  • closure of chute Aerators i air transport characteristics
    Journal of Hydraulic Engineering, 2012
    Co-Authors: Michael Pfister, Willi H Hager
    Abstract:

    Keywords: Chute Aerators Note: [849] Reference EPFL-ARTICLE-180342doi:10.1061/(ASCE)HY.1943-7900.0000189View record in Web of Science Record created on 2012-07-29, modified on 2016-08-09

  • chute Aerators ii hydraulic design
    Journal of Hydraulic Engineering, 2010
    Co-Authors: Michael Pfister, Willi H Hager
    Abstract:

    Chute Aerators are applied if cavitation damage on spillways is expected or observed. The aerator efficiency is usually described with the ratio of the air discharge entrained through the air supply ducts and the water discharge, which does however not account for the resulting air concentration distribution within the flow or for air detrainment. The present study investigates the streamwise development of the air transport along the flow downstream of chute Aerators. Based on an extensive test program in which six governing parameters were systematically varied, the development of the average and the bottom air concentrations is provided up to the self- aeration point. Based on this information, an optimization of Aerators in terms of increased air entrainment and reduced detrainment rates is possible, by assuming minimum required air concentrations. The main parameters influencing the air transport downstream of Aerators are the approach flow Froude number, the deflector angle and the chute bottom angle.

  • chute Aerators i air transport characteristics
    Journal of Hydraulic Engineering, 2010
    Co-Authors: Michael Pfister, Willi H Hager
    Abstract:

    Chutes with flow velocities in excess of some 20 to 30 m/s are usually prone to cavitation damage. Therefore, these flows are aerated using chute Aerators. The current literature describes the aerator efficiency mainly in terms of the air entrainment coefficient as the ratio of the entrained air and the water discharges. However, this global coefficient neither specifies the air distribution nor its detrainment rate. The present investigation focuses on the flow structure and the air transport downstream of chute Aerators. Systematic hydraulic model tests were conducted including a data analysis of the spatial air concentration distribution in both the near and the far aerator fields. Based on these, three flow zones were introduced, namely: 1 jet zone; 2 reattachment and spray zone; and 3 far-field zone. It was further found that Aerators have primarily an effect on the average air concentration, whereas the increase of the bottom air concentration is typically small.

  • development of air concentration on chute spillways
    Journal of Hydraulic Engineering, 2006
    Co-Authors: Kristian Kramer, Willi H Hager, Hanserwin Minor
    Abstract:

    To protect hydraulic structures such as spillways, chutes, and bottom outlets against cavitation damage, air is normally added by means of Aerators in regions where the cavitation number falls below a critical value. Although Aerators have been investigated for more than 30 years, the current design methods for aerator spacing are not reliable. The detrainment process was not previously investigated in detail because of limited laboratory instrumentation. The research presented in this paper provides new model data for hydraulic chutes of variable bottom slope. An advanced remote-controlled, fiber-optical instrumentation was employed to investigate the streamwise development of air concentration contours, velocity contours, and air bubble size along a 14-m model chute. The main hydraulic parameters such as bottom slope, inflow Froude number, inflow depth, and two distinctly different air supply devices for air-water flow generation were employed. Results enable prediction of the reduction of bottom and average air concentration, depending on the inflow air concentration and the chute slope. The minimum air concentration is proven to be a function of the streamwise Froude number. The point of minimum air concentration is constrained by the point of air inception. Downstream of this point the air concentration increases from the surface aeration, depending on the chute slope.

Feng Zhang - One of the best experts on this subject based on the ideXlab platform.

  • the oxygen transfer efficiency and economic cost analysis of aeration system in municipal wastewater treatment plant
    Energy Procedia, 2011
    Co-Authors: Changqing Liu, Feng Zhang
    Abstract:

    Abstract This paper mainly discussed the oxygen transfer efficiency and economic cost of aeration system in one of Wastewater Treatment Plant (WWTP) in Shandong province. The Standard Oxygen Transfer Rate (SOTR) of new and old aerator of aeration system in this WWTP was studied in this paper firstly. The results show that the SOTR of the older aerator were reduced obviously, and the reason of this phenomenon is that the micro-porous in the membrane has damaged and blocked. The cost analysis of the aeration system combining with the actual operation of this WWTP was also studied, conclusions were got that 0.9 million Yuan can be saved each year after replace the old aerator which has already run more than 10 years. Furthermore, this replacement can recovery its cost after only 14 months.

Vickie L Burris - One of the best experts on this subject based on the ideXlab platform.

  • predicting oxygen transfer and water flow rate in airlift Aerators
    Water Research, 2002
    Co-Authors: Vickie L Burris, Daniel Frank Mcginnis, John C Little
    Abstract:

    Water flow rate, gas-phase holdup, and dissolved oxygen (DO) profiles are measured in a full-scale airlift aerator as a function of applied air flow rate. A model that predicts oxygen transfer based on discrete-bubble principles is applied. The riser DO profiles are used to calculate the initial bubble size. The range of calculated bubble diameters obtained using the model is 2.3–3.1 mm. The Sauter-mean diameter of bubbles measured in the laboratory ranged from 2.7 to 3.9 mm. The riser and downcomer DO profiles and gas holdups predicted by the model are in close agreement with the experimental results. A model that predicts water flow rate based on an energy balance is used to calculate Kt, the frictional loss coefficient for the air–water separator. Excluding the data at the very lowest air flow rate, the range of calculated values for Kt (3–8) is close to a literature value of 5.5 proposed for hydrodynamically similar external airlift bioreactors. The models should prove useful in the design and optimization of airlift Aerators.