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We summarized the experience from three decades of oxygen transfer testing and aeration research at the Technical University of Darmstadt to validate the oxygen transfer efficiency of modern fine-bubble diffusers. A total of 306 oxygen transfer tests in clean water of 65 different fine-bubble diffusers, carried out in the same test tank under identical test conditions, were analysed and compared with previous results. As a result, we could show that the performance of fine-bubble aeration systems has increased by 17% over the last three decades. Therefore, modern well-designed and operated aeration systems can achieve specific standard oxygen transfer efficiency (SSOTE) values between 8.5 and 9.8% · m−1. Additionally, a comparison of various diffuser types and diffuser densities was done. Based on the new results, an exemplary cost/benefit analysis for a 100,000 PE WWTP shows the calculation of an optimized diffuser density with respect to investment and operating costs.

In conventional activated sludge (CAS) systems and membrane bioreactors (MBR), aeration, mixing and filtration are affected by various properties of activated sludge (AS) and especially viscosity and morphological properties of flocs. The aim of the present study was to understand the relationship between hydrodynamic conditions and AS floc size properties. Floc size distribution (FSD) measurements were performed in four systems showing different hydrodynamics: (i) a standard stirred reactor (SR), (ii) a pilot bubble column (BC), (iii) a full-scale aeration zone equipped with fine bubble diffusers, (iv) a full-scale filtration zone equipped with coarse bubble diffusers. The measurements were carried out on-site, using the mixed liquor from a full-scale MBR. The FSD of the given activated sludge mainly depends on the average shear rate ( γ ) and on the circulation time in the SR. To a lesser extent, local properties, such as maximal shear rate, also influence the FSD. In the same way, the main operating parameter governing the FSD in the BC was γ . For a similar γ , the flocs were slightly larger in the BC than in the SR. In addition, in the full-scale systems, for a similar γ estimated, the FSD characteristic diameters were lower in the filtration zone (with coarse bubbles) than in the aeration zone (with fine bubbles). The FSD in the aeration zone was well correlated with the FSD in the BC whereas the flocs were slightly smaller in the filtration zone than in the BC.

La aireación es el principal consumidor de electricidad en el tratamiento de las aguas residuales municipales, presente en ciertos procesos biológicos, como los lodos activados, los cuales demandan entre el 50-70% de los costos de la energía necesaria para tratamiento del agua residual. Por consiguiente, para lograr una alta eficiencia de la transferencia de oxígeno en los tratamientos biológicos aeróbicos, son usados comúnmente los difusores de burbuja fina. El desempeño de las membranas de los difusores de burbuja fina es afectado por el ensuciamiento que comprende la acumulación de sustancias suspendidas o disueltas sobre su superficie y/o dentro de sus poros, ocasionando el incremento de los costos de operación, asociados a los sistemas de aireación. Con el propósito de mitigar el ensuciamiento en la industria del tratamiento de aguas residuales, son usadas diferentes técnicas de limpieza convencionales que traen consigo desventajas. El presente trabajo evalúa la técnica de limpieza convencional mediante la adición de agentes químicos y la limpieza con ultrasonido, siendo esta ultima una técnica novedosa para remover el ensuciamiento en difusores de burbuja fina; desde el punto de vista de la presión de descarga, costos de operación, eficiencia y transferencia de oxígeno en condiciones estándar. Los resultados muestran que la aplicación de las técnicas de limpieza recupera parcialmente la transferencia de oxígeno en las membranas difusoras y a la reducen los costos operativos.Concluyendo que, entre las tres técnicas de limpieza evaluadas, el ultrasonido es el que presenta los mejores resultados. 1. GLOSARIO ...................................................................................................................... 10 2. RESUMEN........................................................................................................................ 13 3. INTRODUCCIÓN ............................................................................................................ 14 4. PLANTEAMIENTO DEL PROBLEMA ......................................................................... 16 5. DELIMITACIÓN.............................................................................................................. 18 5.1 Conceptual....................................................................................................................................18 5.2 Geográfica ....................................................................................................................................18 6. OBJETIVOS ..................................................................................................................... 20 6.1 Objetivo general...........................................................................................................................20 6.2 Objetivos específicos ..................................................................................................................20 7. ANTECEDENTES............................................................................................................ 21 8. JUSTIFICACIÓN ............................................................................................................. 24 9. MARCO TEÓRICO.......................................................................................................... 25 9.1 Difusores empleados en el tratamiento de aguas.....................................................................26 9.1.1 Difusores de burbuja gruesa:............................................................................................. 26 9.1.2 Difusores de burbuja fina:................................................................................................. 27 9.2 Ensuciamiento de los difusores .................................................................................................28 9.3 Limpieza de difusores de membrana utilizadas en la industria del agua .............................30 9.4 Tratamientos de limpieza de membrana en difusores de burbuja fina .................................31 9.4.1 Limpieza física:................................................................................................................. 31 9.4.2 Limpieza química:............................................................................................................. 31 9.5 Limpieza de membranas con ultrasonido.................................................................................32 9.5.1 Antecedentes de limpieza de membranas con ultrasonido................................................ 32 10. METODOLOGÍA ............................................................................................................. 35 11. RESULTADOS Y ANÁLISIS DE RESULTADOS ........................................................ 43 11.1 Análisis de las técnicas de limpieza en difusores de burbuja fina a escala 1:33.................43 11.1.1 Evaluación de la transferencia de oxígeno:....................................................................... 44 11.1.2 Evaluación de la presión de descarga (DWP):.................................................................. 46 11.1.3 Costos de operación – Banco de pruebas:......................................................................... 47 11.2 Simulación de limpieza a diferentes configuraciones de procesos de lodos activados......49 11.2.1 Evaluación de la transferencia de oxígeno:....................................................................... 49 11.2.2 Evaluación de los costos de operación.............................................................................. 52 12. CONCLUSIONES ............................................................................................................ 54 13. REFERENCIAS BIBLIOGRÁFICAS.............................................................................. 56 14. ANEXOS .......................................................................................................................... 61 A. Implementación de limpieza de membranas de ultra y microfiltración con ultrasonido. ..61 B. Tipos de difusores empleados en el tratamiento de agua residual ........................................63 C. Características de difusores disponibles en el mercado por diferentes fabricantes............64 D. Limpieza química en difusores de membrana tubulares (Jiang et al., 2020).......................65 E. Ecuaciones de aireación..............................................................................................................66 F. Estructuración de difusores de burbuja fina a escala 1:33 .....................................................67 G. Hoja de cálculo de la aplicación de resultados a diferentes configuraciones de procesos de lodos activados.............................................................................................................................67 Aeration is the main consumer of electricity in municipal wastewater treatment, present in certain biological processes, such as activated sludge, which demand between 50-70% of the energy costs necessary for wastewater treatment. Therefore, in order to achieve high efficiency of oxygen transfer in the Aerobic biological treatments, fine bubble diffusers are commonly used. The performance of fine bubble diffuser membranes is affected by fouling, which comprises the accumulation of suspended or dissolved substances on their surface and / or within their pores, causing increased operating costs associated with air conditioning systems. aeration. In order to mitigate fouling in the industry of the wastewater treatment, different conventional cleaning techniques are used that bring with them disadvantages. The present work evaluates the conventional cleaning technique by adding chemical agents and cleaning with ultrasound, the latter being a novel technique to remove dirt in fine bubble diffusers; from the point of view of discharge pressure, operating costs, efficiency and oxygen transfer under standard conditions. The Results show that the application of cleaning techniques partially recovers the oxygen transfer in the diffuser membranes and reduces operating costs, concluding that, among the three cleaning techniques evaluated, ultrasound is the one that presents the best results. Pregrado

The operation of membrane bioreactors (MBRs) at higher than usual mixed liquor suspended solids (MLSS) concentrations may enhance the loading rate treatment capacity while minimizing even further the system's footprint. This requires operating the MBR at the highest possible MLSS concentration and biomass activity (e.g., at high loading rates and low solid retention times (SRTs)). Both a negative effect of the MLSS concentrations and a positive effect of the SRT on the oxygen transfer have been reported when using conventional fine bubble diffusers. However, most of the evaluations have been carried out either at extremely high SRTs or at low MLSS concentrations eventually underestimating the effects of the MLSS concentration on the oxygen transfer. This research evaluated the current limitations imposed by fine bubble diffusers in the context of the high-loaded MBR (HL-MBR) (i.e., high MLSS and short SRT-the latter emulated by concentrating municipal sludge from a wastewater treatment plant (WWTP) operated at a short SRT of approximately 5 days). The high MLSS concentrations and the short SRT of the original municipal sludge induced a large fraction of mixed liquor volatile suspended solids (MLVSS) in the sludge, promoting a large amount of sludge flocs that eventually accumulated on the surface of the bubbles and reduced the free water content of the suspension. Moreover, the short SRTs at which the original municipal sludge was obtained eventually appear to have promoted the accumulation of surfactants in the sludge mixture. This combination exhibited a detrimental effect on the oxygen transfer. Fine bubble diffusers limit the maximum MLSS concentration for a HL-MBR at 30 g L-1 ; beyond that point is either not technically or not economically feasible to operate ; an optimum MLSS concentration of 20 g L-1 is suggested to maximize the treatment capacity while minimizing the system's footprint.

Achieving energy neutrality has shifted focus towards aeration system optimization, due to the high energy consumption of aeration processes in modern advanced wastewater treatment plants. A study on fine bubble diffuser fouling and mitigation, quantified by dynamic wet pressure (DWP), oxygen transfer efficiency and alpha was carried out in Blue Plains, Washington, DC. Four polyurethane fine bubble diffusers were installed in a pilot reactor column fed with high rate activated sludge from a full scale system. A mechanical cleaning method, reverse flexing (RF), was used to treat two diffusers (RF1, RF2), while two diffusers were kept as a control (i.e., no reverse flexing). There was a 45% increase in DWP of the control diffuser after 17 months of operation, an indication of fouling. RF treated diffusers (RF1 and RF2) did not show significant increase in DWP, and in comparison to the control diffuser prevented about 35% increase in DWP. Hence, reverse flexing potentially saves blower energy, by reducing the pressure burden on the air blower which increases blower energy requirement. However, no significant impact of the RF treatment in preventing a decrease in alpha-fouling (αF) of the fine pore diffusers, over time in operation was observed.

Oxygen transfer in wastewater treatment is significantly influenced by the mixed liquor suspended solids (MLSS). The effect is more pronounced at MLSS concentrations higher than 20 g L−1 when supplying air by conventional diffused aeration systems. The oxygen transfer performance of a supersaturated oxygenation technology (i.e., the supersaturated dissolved oxygen (SDOX) system) was evaluated in clean water and in activated sludge with MLSS concentrations from 4 to 40 g L−1 as a promising technology for uncapping such limitation. The evaluation was carried out at the laboratory facilities of the faculty of food technology and biotechnology at the University of Zagreb. The sludge was collected from a full-scale conventional activated sludge (CAS) wastewater treatment plant (WWTP) operated at a solid retention time (SRT) of approximately 5 days. The evaluation was carried out using a laboratory-scale setup consisting of a bench-scale SDOX system (2.75 L) supplying pure oxygen to a 5 L biological reactor. The SDOX exhibited oxygen mass transfer rate coefficient (KLa) values (2.6 h−1) in clean water lower than for fine bubble diffusers (11 h−1). However, higher oxygen transfer rate (OTR) values and alpha factors (mass transfer ratio of process-water to clean-water) as a function of the MLSS concentration were observed. A standard oxygen transfer efficiency (SOTE) of approximately 100 % in clean water was reported. The SDOX technology can be presented as a promising alternative for supplying dissolved oxygen (DO) into mixed liquor solutions; particularly, at the high MLSS concentrations required by high-loaded membrane bioreactor (HL-MBR) systems and aerobic digesters.

The effects of aeration and alkalinity on water quality and product quality of Nile tilapia ( Oreochrmis niloticus ) were determined for simulated commercial hauling conditions. Three types of aeration were tested: pure oxygen aeration with a fine bubble diffuser (Oxygen), air aeration with medium bubble diffusers (Air), and a combination of both pure oxygen aeration with a fine bubble diffuser and air aeration with a medium bubble diffuser (Mixed). Simulated transport hauls were conducted at two initial alkalinities: 1.74 ± 0.11 meq/L (Low) and 8.84 ± 0.55 meq/L (High). The Air treatments resulted in the lowest carbon dioxide concentration, and the highest pH and un-ionized ammonia concentrations. At high alkalinities, the Air treatments were unable to maintain adequate dissolved oxygen levels. The Mixed treatment resulted in reduced carbon dioxide and dissolved oxygen concentrations. The Oxygen treatment resulted the highest dissolved oxygen, highest carbon dioxide, and lowest pH and un-ionized ammonia. Un-ionized ammonia concentrations were higher with the High Alkalinity treatments because of higher pH. Significant mortality was observed in the Air treatments in both the Low- and High-Alkalinity treatments. Mortality in the Oxygen and Mixed treatments for both low and high alkalinities were comparable to that observed in commercial tilapia transport using fine bubble diffusers and pure oxygen. These results indicate that mortality due directly to hauling water quality will not be increased at high alkalinity, if pure oxygen aeration is used. The potential effects of water quality during hauling on survival and product quality may be less than the impact from (a) physical damage from loading and un-loading and (b) physiological problems resulting from pH and temperature shock during the transfer from the hauling tanks to retail holding systems, especially for fish of reduced fitness.

The oxygen flow rate was studied for carbon stone and ceramic plate diffusers, two types of diffusers that are commonly used in hauling applications. New diffusers were used in all experiments. It was found that oxygen flow was largest for dry diffusers operated in air and reduced for diffusers started in air and then placed in water and further reduced for diffusers soaked in water prior to use. The coefficient of variation for the two types of diffusers ranged from 7 to 18% for new units. If individual flow adjustment is not provided for each diffuser in a manifold distribution system (one oxygen source, several diffusers), small differences in pressure losses between diffusers can result in significant differences in oxygen flows. The initial oxygen flow during the loading of fish may be depressed until accumulated water in the hose and diffuser is expelled. Under some conditions, the oxygen flow rate can increase by 2–4 times over a 6–8 h period. Decreases in oxygen flow due to prior history may make it difficult to achieve the needed operating flows in a timely manner without exceeding the diffuser's pressure rating. This problem is likely to become more important due to aging and clogging of the diffusers.

The objective of this experimental study was to collect and to interpret data in order to better understand the oxygen mass transfer phenomena occurring in full-scale aeration tanks equipped with fine bubble diffusers and slow speed mixers (inducing horizontal liquid flows). Bubble size, local depth and oxygen mass transfer coefficient were measured in situ for a given air flow rate (1555 N m3 h−1) and for two different axial liquid velocities. The increase in the global oxygen transfer coefficient is of 29% when the mean axial liquid velocity varies from 0 to 0.42 m s−1. The small influence of the liquid velocity on the local bubble Sauter diameter (about −4%) cannot explain the increase in kLa20. This increase in kLa20 with the axial liquid velocity is mainly due to the attenuation of the vertical liquid circulation induced by the gas injection.

Many activated sludge plants (ASP) use fine bubble diffused air as their source of oxygen. Blowers are attached to air pipework, which distributes air to a network of diffusers installed on the floor of the ASP tank. Modern diffusers are made from a rubber membrane which flexes to allow fine bubbles of air to pass through holes in the diffusers which then pass into the mixed liquors in the tank. The diffusers come as circular discs, tubes and more recently mats or panels. Yorkshire Water is in the process of building new ASP at some of their biggest sewage treatment works to meet new final effluent consent standards associated with the freshwater fisheries directive (FFD). These new works will treat sewage from a combined population of over two million people in the Yorkshire area. Black & Veatch is involved in some of the first works to have a new type of fine bubble diffuser installed in the ASP basins. These diffusers resemble a mat or panel and are fixed to the floor of the tank as opposed to circular and tubular diffusers which as fixed above the floor. Oxygen transfer testing has been carried out to show the efficiency of these aeration systems, which may offer significant savings in operating costs to water operators. This paper examines the results from the tests and compares them with other tests carried out in the United States and tests that have been carried out on other types of diffusers. The paper will discuss the results of the oxygen transfer tests and present capital and net present costs (NPC) for various diffuser installations.

The aim of this paper is the theoretic and experimental study of the hydrodynamics and mass transfer of the swarm of bubbles generated by fine bubble diffusers (FBD) made from ceramics. Thus the hydrodynamic parameters of the dispersed air-water system (pressure loss on FBD, bubble size distribution, global gas hold up) were experimentally determined. Regarding mass transfer, the volumetric mass transfer coefficient Kla, standard oxygen transfer rate (SOTR) and standard aeration efficiency (SAE) were also determined. The results showed that Kla increases with air flow rate and there is an optimum air flow rate (120 180 l/h) that gives maximum aeration efficiency. The maximum value of SAE (4.25 kgO2/kWh) was obtained for Q = 150 l/h, in homogeneous regime. Comparing the ceramic FBD with a sintered glass FBD issued that an increase of 35% of the mass transfer can be obtained by using glass FBD. Still, SAE accomplished by the two types of FBD tested is in the range given by literature or even greater.

Fine bubble diffusers have largely replaced coarse bubble diffusers and mechanical aerators when it comes to treating sewage and wastewater. But what role does energy efficiency play? Adrian Ovezea explains how efficient use of this technology can save energy in treatment plants and looks at the different options available.

In order to optimize aeration in the activated sludge processes, an experimentally validated numerical tool, based on computational fluid dynamics and able to predict flow and oxygen transfer characteristics in aeration tanks equipped with fine bubble diffusers and axial slow speed mixers, is proposed. For four different aeration tanks (1;1493;8191 and 29, 313 m 3 ), this tool allows to precisely reproduce experimental results in terms of axial liquid velocities, local gas hold-ups. Predicted oxygen transfer coefficients are within ±5% of experimental results for different operating conditions (varying pumping flow rates of the mixers and air flow rates). The actual bubble size must be known with precision in order to have a reliable estimation of the oxygen transfer coefficients. 2007 Elsevier Ltd. All rights reserved.

The technology of rapid ozone mass transfer followed by degasification, the GDT™ Process, was first introduced in 1995 by Mazzei et al. At the time of introduction, municipal ozone installations utilized a low concentration, air-fed ozone gas as a disinfectant in atmospheric contact basins fitted with fine bubble diffusers (FBD). Over the past decade, air- fed ozone has given way to highly concentrated, oxygen-fed ozone. The change to concentrated oxygen feed gas has increased concerns about the corrosive effects of high finished water dissolved oxygen (DO). Water treatment plants using oxygen fed ozone have reported finished water DO levels in excess of 20 mg/L, with some plants resorting to air sparging at the back end of the contact basin to restore finished water to atmospheric gas levels. However, the evolution to oxygen feed gas has also produced significant cost benefits. Operating an ozone generator on oxygen increases its ozone production; reducing the size and capital cost of the generator neede...

Causes for the increase of the pressure loss of fine bubble diffusers made of elastomers were investigated. Methods are described for removing clogging material from membrane diffusers and/or attenuating or even avoiding the formation of clogging deposits. On the basis of some practical examples the procedure is discussed and obtained reductions of pressure losses are specified.

A contributor to success in managing membrane operations is to be able to identify suitable engineering design approaches to slow down the membrane fouling rate. Two such approaches were discussed in this study, namely: (1) offsite chemical and mechanical cleaning, and (2) air scouring. A longer subsequent operation time was observed after a membrane was cleaned chemically compared with mechanically. For air scouring during membrane operation, the investigation aimed at determining the crossflow velocity induced by coarse and fine bubble diffusers. Higher crossflow velocities were obtained with the latter. Uniformly distributed fine air bubbling might possibly have caused less uplift resistance and induced higher crossflow velocities. Such air scouring, at critical aeration intensity, was able to prolong the membrane operation for up to 8 months without needing chemical or mechanical cleaning.

Aeration tanks of wastewater treatment plants (WWTP) are a potential source of atmospheric aerosol particles. Several groups of organic compounds (sterols, polycyclic aromatic hydrocarbons, estrogens) were analyzed in aerosol particles sampled at a municipal WWTP, and the particle size distribution was measured directly with optical particle counters. Aerosol emissions from an activated treatment tank equipped with fine bubble diffusers were low; however, at the preaeration tank equipped with coarse bubble diffusers, sterol concentrations up to 14 ng m(-3) were measured. Directly next to the tank, sterols were associated mainly to particles with aerodynamic diameter >1.35 microm. The results suggest that coprostanol could be a useful tracer for monitoring the emission of aerosol particles from WWTPs. Moreover, wastewater treatment could contribute substantially to the atmospheric concentrations of cholesterol and 24-ethylcholesterol. Aeration tanks with fine bubble diffusers are no major source of atmospheric aerosol particles, whereas coarse bubbling devices seem to emit considerable amounts of aerosol particles.

International audience; The effect of air flow rate on oxygen transfer efficiency was examined in clean water and under process conditions in an oxidation ditch equipped with fine bubble membrane diffusers and large blade slow speed mixers. Under process conditions, an increase in the air flow rate resulted in a decrease of the oxygen transfer efficiency similar to that observed in clean water. Consequently, the value of the alpha factor was in the order of 0.58 independently of the air flow rate (between 45 and 110 m(3) h(-1) per m(2) of membrane). The combined influence of the air flow rate and of the horizontal liquid velocity on the oxygen transfer efficiency was studied. Results have evidenced that regrouping the diffuser grids and applying an horizontal flow could lead to a significant limitation in the impact of the air flow rate on the oxygen transfer efficiency. Finally, the use of the off gas method to determine the oxygen transfer efficiency of an aeration system at a given air flow rate led to the definition of a relationship, that enabled the evaluation of the system oxygenation capacities at air flow rates different from the one at which the measurements were initially performed.; L'effet du débit d'air sur le rendement d'oxygénation a été examiné en eau claire et en boues dans un chenal d'aération équipé de diffuseurs d'air en fines bulles et d'agitateurs à grandes pales fonctionnant à vitesse lente. En boues, une augmentation du débit d'air entraîne une diminution de rendement d'oxygénation similaire à celle observée en eau claire : en conséquence, la valeur du facteur alpha était de l'ordre de 0,58, indépendamment du débit d'air (compris entre 45 et 110 m3h-1 par m2 de membrane). L'influence combinée du débit d'air et de la vitesse horizontale du liquide sur le rendement d'oxygénation a été étudiée. Les résultats ont montré que le regroupement des modules de diffuseurs et l'application d'une vitesse horizontale au liquide pouvait réduire l'impact du débit d'air sur le rendement. Enfin, l'utilisation de la méthode des bilans gazeux pour déterminer le rendement d'oxygénation à un débit d'air donné conduit à la définition d'une relation permettant d'évaluer la capacité d'oxygénation du même système à des débits d'air différents de celui de la mesure.

Diffusion of odourous air into activated sludge basins is an effective and economical approach for odour control at wastewater treatment plants. Over 30 facilities in North America practice this technique. Most of these applications are for dilute or moderate strength air streams with relatively low hydrogen sulfide (H2S) levels. Unfortunately, the lack of data documenting the effectiveness of the process and concerns for blower corrosion have limited its acceptance as a method for controlling odour emissions. This paper presents a compilation and review of wastewater treatment facilities that are currently using activated sludge diffusion. Performance data are tabulated, and information on operation and maintenance of the blower/diffuser systems are summarized. New data are presented that compare the effectiveness of coarse vs. fine bubble diffusers for treatment of a high strength, high-H2S air stream from sludge holding tanks at Concord, NH. Designand performance information is presented on a dedicated odour control system installed at Phoenixville, Pennsylvania in 1996 that collects high-H2S air streams from an influent chamber and primary clarifiers and diffuses it into a mechanically-aerated activated sludge basin. A cost-effectiveness analysis is presented for a blower/diffuser system installed exclusively for odour control. Methods used to overcome initial operational problems are discussed.

The alpha correction factor (KLa process water/KLa clean water; where KLa is the volumetric oxygen mass transfer coefficient) was evaluated for 4 kinds of static aerators and 2 kinds of fine bubble diffusers used in municipal facultative aerated lagoons. For this purpose, a 40 m3 steel tank was filled (3.1 m side water depth) with clean or process water. The process water consisted of “mixed liquor” from a municipal facultative aerated lagoon divided into a cascade of four identical basins that were 3.5 m deep. Results showed that in the last three basins, the alpha correction factors were relatively high, being between 0.85 to 0.95 for any type of aeration device. In the first lagoon, however, the alpha correction factors were between 0.70 and 0.90 for static aerators and about 0.70 for fine bubble diffusers. Furthermore, at the inlet of the first basin, the alpha factor was as low as 0.59 for a static aerator and 0.26 for a fine bubble diffuser, due to the composition of the “mixed liquor”. It was shown that the alpha correction factor that should be used for the design of aeration systems for facultative aerated lagoons should be lower in the first basin of a series of basins and could be higher than 0.85 for the downstream basins.

The bulk of the operating costs for biological aerated filters are associated with aeration, accordingly, any efficiency improvements which may be made to this aspect of the process could result in significant savings operationally. This study used off-gas analysis to determine the effects on oxygen transfer efficiency of variations to the air flow and substrate loading rates to two pilot scale granular media biological aerated filters (BAFs) treating primary settled sewage. The columns provided a good representation of full scale units, providing up to 99% ammonia reduction. Incremental increases in the mass transfer coefficient (KLa) were observed, as reported elsewhere and attributed to direct interfacial transfer between the bubbles and the biofilm. The OTE varied with flow rate but was far more sensitive at the lower end of the experimental range, rising sharply for air flow rates below 5 to 10 m/h. Increasing the organic loading rate also improved the OTE. The use of fine bubble diffusers did not improve the OTE, however, probably as a result of the packing media used.

A broad weir-aeration model was derived to predict downstream dissolved oxygen (DO) over a wide range of upstream DO concentrations and fall heights. This model was then used to construct a three-dimensional (3D) surface of downstream DO for a range of upstream DO concentrations and fall heights. A 3D surface for kWs˙hr per ton of DO absorbed was constructed for a range of upstream DO concentrations and fall heights. This shows the asymptotic rise in energy per ton of DO absorbed as higher downstream DO concentrations are realized. The energy consumption per ton of DO absorbed for weir aeration is below that for surface aeration and above that for fine bubble diffusers, for downstream DO concentrations of 0–8 mg/L.

The objective of this work is to decrease energy consumption of the aeration system at a mid-size conventional wastewater treatment plant in the south of Sweden where aeration consumes 44% of the total energy consumption of the plant. By designing an energy optimised aeration system (with aeration grids, blowers, controlling valves) and then operating it with a new aeration control system (dissolved oxygen cascade control and most open valve logic) one can save energy. The concept has been tested in full scale by comparing two treatment lines: a reference line (consisting of old fine bubble tube diffusers, old lobe blowers, simple DO control) with a test line (consisting of new Sanitaire Silver Series Low Pressure fine bubble diffusers, a new screw blower and the Flygt aeration control system). Energy savings with the new aeration system measured as Aeration Efficiency was 65%. Furthermore, 13% of the total energy consumption of the whole plant, or 21 000 €/year, could be saved when the tested line was operated with the new aeration system.

Experiments in a 1400 m³ annular ditch fitted with 2 mixers and fine bubble diffusers demonstrated and quantified the improved oxygen transfer resulting from the horizontal rotation of the water. Compared with no horizontal flow, oxygen mass transfer in clean water increased 40-50 per cent for a horizontal flow of 0.4-0.5 m per second. This was relatively independent of diffuser air flow ; there was no advantage in exceeding this horizontal flow. The improvement arose from prolongation of hair bubble contact time, air bubble deformation and especially from the decrease in the diameter of the nascent bubbles. Shearing, elimination of air bubble coalescence and the renewal of the liquid layer around the air bubbles were all insignificant factors., La mise en rotation horizontale de l'eau dans un chenal d'oxydation par une agitation séparée améliore le transfert d'oxygène d'un système d'aération à insufflation d'air. Ceci peut s'expliquer par les modifications, dues à l'écoulement horizontal, de plusieurs paramètres qui jouent un rôle dans le transfert d'oxygène. Une étude expérimentale a été menée sur un chenal annulaire de 1400m3 équipé de diffuseurs fines bulles et d'agitateurs pour quantifier cette connaissance empirique. Les conclusions préliminaires de cette recherche sont présentées.

International audience; Mixing and aeration characteristics obtained on three full scale loop reactors for 28 configurations (different mixers' location and rotation speed, air flow rates and diffuser grids' location) were analyzed. The propellers' thrust was measured in situ. Observed values vary with the tank geometry, the location of the mixers and the induced axial velocity. In situ thrust values are lower than the nominal ones obtained during shop tests, by 10 to 30 %. For the nominal rotation speed of the propellers, observed thrust-to-power ratios are comprised between 685 and 875 N kW-1. In agreement with previous results, an increase in the oxygen transfer rate with the axial velocity was observed, due to a partial neutralization of the spiral flows formed at the edge of the aerated zones. Aeration efficiency is not decreased, as the additional power consumption due to mixing is offset by the oxygen transfer enhancement. SAE values are comprised between 2.0 and 2.6 kg O2 kWh-1. Such on site results are especially important to be used as input and output data in CFD models.

A bench-scale experiment was conducted in a 701, tank of tap water to examine the effect of three design variables on oxygen transfer in a coarse bubble diffused aeration system. The experiment used non-steady state gas transfer methodology to examine the effect of orifice diameter, air flow rate and reduced tank surface area on the overall oxygen transfer coefficient (KLa20, h−1); standard oxygen transfer rate (OTs, g O2 h−1); energy efficiency (Ep, g O2 kW h−1) and oxygen transfer efficiency (Eo, %). The experiments demonstrated that KLa20 and OTs increased 122% when air flow rate was doubled (9.4–18.81 min−1), while Eo and EP increased approx. 12%. A reduction in orifice diameter from 3175 μm (3.2 mm) to 1588 μm (1.6 mm) to 794 μm (0.8 mm) to 397 μm (0.4 mm) significantly increased KLa20, OTs, EP and Eo. The presence of a floating surface cover had no effect on KLa20 and OTg, and a marginal decrease in EP and Eo. The mean bubble sizes produced by the 397, 794, 1588 and 3175 μm diffusers were 4.7, 6.6, 7.7 and 7.2 mm dia, respectively. There was no significant effect of air flow rate on bubble size within the range of air flow rates used in this experiment. A comparison of this study's coarse bubble results with a concurrent study on fine pore (fine bubble) aeration reveals that KLa, OTs, EP and Eo continue to increase as orifice diameter is decreased to the 40–140 μm (i.e. fine pore) diameter range. The most efficient coarse bubble diffuser (i.e. 397 μm) was approx. 68% as efficient as the 140 μm fine pore diffuser. A classification system using existing EPA bubble size criterion for coarse and fine bubble diffusers, and the aeration systems' operational response of EP and Eo to increased air flow rates is recommended for differentiating coarse and fine bubble diffused aeration systems.

Following a promising study at pilot scale a new aeration control law has been implemented at a full scale wastewater treatment plant displaying a conventional activated sludge process. The new control law is based on the direct measurements of ammonium and nitrate concentration in the biological tank by ion selective electrodes. This control law features a cascade of two Predictive Function Controls and calculates an optimal air flow rate to be provided to the biomass through fine bubble diffusers. The results obtained at the full scale plant confirmed the high performance of this control strategy allowing to substantially reduce the amount of diffused air while providing an easy means to manage the effluent quality to the plant operator.

The Mexican petrochemical industry, Morelos S.A. de C.V., is one of the biggest and more important petroleum industries in Mexico and Latin America. It has an activated sludge system to treat its wastewater flow, which is approximately 7,000 m3/d. The wastewater contains volatile organic carbon substances classified as toxics. The old surface aeration system was changed for fine bubble diffusers; however, one major drawback of the new aeration system is that the temperature in the bioreactor has increased due to the compression of the air, which at the compressor exit reaches 85 degrees C. This effect results in the temperature in the bioreactor attaining 32 degrees C during the fall, whereas in the spring and summer, the bioreactor temperature reaches higher values than 40 degrees C. The high temperatures reduce the microorganism activity and cause a higher volatilisation rate of volatile compounds, among other effects, which affect the performance of the biological treatment. This work was performed to obtain a better modelling of the wastewater treatment from the petrochemical industry. The model describes the effect of the temperature on the performance of the biological treatment. The model was obtained from tests that were carried out in laboratory reactors with 14 L capacity, which were operated at different temperatures (from 30 to 45 degrees C), with the same wastewater and conditions as the actual system.

The bubble and surface volumetric mass transfer coefficients for oxygen, k L a b and k L a s , are separately determined for 179 aeration tests, with diffuser depths ranging from 2.25 to 32 m, using the DeMoyer et al. [2003. Impact of bubble and free surface oxygen transfer on diffused aeration systems. Water Res 37, 1890–1904] mass transfer model. Two empirical characterization equations are developed for k L a b and k L a s , correlating the coefficients to air flow, Q a , diffuser depth, h d , cross-sectional area, A cs , and volume, V . The characterization equations indicate that the bubble transfer coefficient, k L a b , increases with increasing gas flow rate and depth, and decreases with increasing water volume. For fine bubble diffusers, k L a b is approximately six times greater than k L a b for coarse bubble diffusers. The surface transfer coefficient, k L A s , increases with increasing gas flow rate and diffuser depth. The characterization equations make it possible to predict the gas transfer that will occur across bubble interfaces and across the free surface with a bubble plume at depths up to 32 m and with variable air discharge in deep tanks and reservoirs.

The standard oxygenation performances of fine bubble diffused aeration systems in clean water, measured in 24 full scale annular ditches, were interpreted using dimensional analysis. Two relationships have been developed between the oxygen transfer efficiency per meter of submergence (SOTEs) and the parameters affecting oxygen transfer: air flow rate (QG), depth of submergence (h), surface area (S), membrane surface (Sp), aerated surface (Sa), width of the basin (W), angle between mixers and diffusers (Ang) and horizontal velocity (UC). These relationships differentiate annular ditches according to the diffuser placement: tank coverage higher than 50 % of the surface area (Type I) or at the maximum 50 % of the area (Type II). They can be used to predict oxygen transfer performances, at a design stage.; Les performances d`oxygénation standard en eau claire des systèmes d`insufflation d`air en fines bulles équipant 24 chenaux d`aération annulaires ont été interprétées à l`aide de l`analyse dimensionnelle. Deux relations ont été développées entre le rendement d`oxygénation spécifique standard (SOTEs) et les paramètres influençant le transfert d`oxygène : le débit d`air (QG), la hauteur d`immersion des diffuseurs (h), la surface du bassin (S), la surface totale de membrane perforée (Sp), la surface totale des zones occupées par les diffuseurs (Sa), la largeur du chenal (W), l`angle entre les agitateurs et la première rampe de diffuseurs (Ang) et la vitesse horizontale de circulation (UC). Ces relations différencient les chenaux selon la disposition des diffuseurs : surface de bassin couverte supérieure à 50 % du radier (Type I) ou au plus 50 % du radier (Type II). Elles peuvent être utilisées pour prédire les performances d`oxygénation du couple chenal d`aération/système d`aération, au moment du dimensionnement de l`installation.

[Departement_IRSTEA]GMA [TR1_IRSTEA]21 - TECHNEAU / EPURE; On the basis of full-scale data from 58 clean water tests performed in 26 activated sludge tanks equipped with fine bubble diffusers and of a theoretical approach, it can be stated that fine bubble aeration systems with total floor coverage arrangement provide higher k(L) values and the lowest spiral liquid circulation. An efficiency criterion for oxygen transfer (N(T)) was defined on the basis of the dimensional analysis. The transfer number N(T) allows to take account of the impact of vertical liquid circulation movements on oxygen transfer. The values of N(T) calculated from the results of full scale nonsteady-state clean water tests vary from 5.3 10(-5) to 9.1 10(-5) and are directly dependent upon the arrangement of air diffusers. It has been evidenced that the highest transfer numbers corresponded to the total floor coverage arrangement and the average calculated N(T) values is 7.7 10(-5), independently of the diffuser density and of the gas velocity, over the ranges studied. The lowest transfer numbers are obtained when the diffusers are located in separate grids, and the transfer number is reduced with increasing air flow rate.; A partir des résultats de 58 mesures de performances d'oxygénation de systèmes d'insufflation d'air en fines bulles effectuées sur 26 sites réels et d'une approche théorique, il a été montré que les couvertures plancher de diffuseurs conduisent aux kLa les plus élevés et aux vitesses de circulation verticales du liquide les plus faibles. Un critère d'efficacité du transfert d'oxygène (N(T)) a été défini à partir de l'analyse dimensionnelle. Le nombre de transfert N(T) permet de rendre compte de l'impact des mouvements de circulation liquide verticale sur le transfert d'oxygène. Les valeurs de N(T) calculées à partir des résultats des essais de réoxygénation varient de 5.3 10(-5) à 9.1 10(-5) et dépendent directement de la disposition des diffuseurs. Il a été montré que les nombres de transfert les plus élevés correspondaient aux couverture plancher et la moyenne des N(T) calculés est de 7.7 10(-5), indépendamment de la densité de diffuseurs et des vitesses de gaz dans les gammes étudiées. Les nombres de transfert les plus faibles sont obtenus pour des configurations modulaires et sont d'autant plus faibles que le débit d'air est élevé.

The MAC3D numerical model, a three dimensional flow solver initially developed for reservoir hydrodynamics, has been extended to account for the flow and gas transfer induced by bubble plumes. The latter are represented as buoyant columns in which dissolved gas is transferred to or from surrounding water. The local transfer rate is proportional to the dissolved gas concentration, and the resulting flow and gas transport are computed by solving discrete equations for the conservation of mass and momentum. The upward force imposed by a bubble column is directly proportional to the airflow rate through the associated bubble diffuser, and inversely proportional to the local depth and the bubble rise velocity. Gas transfer coefficients are empirical quantities that have to be inferred from laboratory experiments, but eddy viscosity and diffusivity are obtained directly from a k-E turbulence model. In the numerical solution of the governing equations, the explicit MacCormack scheme has been replaced by an implicit upwind scheme that improves stability and reduces execution time by a factor of five to ten. In this report, the model is validated for unstratified or weakly stratified water bodies by comparing predicted velocities and gas transfer rates with data from laboratory experiments and field tests using coarse and fine bubble diffusers.

The off-gas method was used to study oxygen transfer efficiency in a long, narrow activated sludge basin. The basin was equipped with square, ceramic, fine pore diffuser plates arranged in a uniform longitudinal pattern at a depth of 4.3 m. Oxygen transfer efficiency, at 20°C and zero dissolved oxygen concentration, during the second and third years following diffuser cleaning, was between 15 and 17%. A uniform distribution of air to the tank was compared with a tapered air supply (more air at the inlet end and less at the outlet). The tapered air supply gave lower dissolved oxygen at the outlet and did not increase overall oxygen transfer. With a 3 to 5-fold variation in air flow, at either the inlet or outlet zone of the basin, the oxygen transfer efficiency, adjusted for zero dissolved oxygen, stayed constant.

This paper reviews the current stateofunderstanding of biological fouling of fine bubble diffusers. Results of a survey conducted in the United Kingdom and United States which implicates biological...

Water pollution control by effluent treatment becomes increasingly expensive as the degree of treatment is increased. As has previously been demonstrated, instream aeration provides an economical alternative for the higher degrees of treatment. For large, deep, navigable rivers, another alternative may be still more economical, namely, mobile oxygenating craft, using fine bubble diffusers. The propellors in the craft plus its mobility would give important advantages in dispersing the oxygenated water; and one craft could replace a multiplicity of static aeration sites.

Aeration is an energy-intensive process of aerobic biological treatment in wastewater treatment plants (WWTP). Two-stage processes enable energy-efficient operation, but oxygen transfer has not been studied in depth before. In this study, α-factors were determined with long-term ex situ steady-state off-gas measurements in pilot-scale test reactors (5.8 m height, 8.3 m3) coupled to full-scale activated sludge basins. A two-stage WWTP with more than 1 Mio population equivalent was studied over 13 months including rain and dry weather conditions. Operating data, surfactant concentrations throughout the two-stage process, and the effect of reverse flexing on pressure loss of diffusers were examined. The values of αmean, αmin, and αmax for design load cases of aeration systems were determined as 0.45, 0.33, and 0.54 in the first high-rate carbon removal stage and as 0.80, 0.69, and 0.91 in the second nitrification stage, respectively. The first stage is characterized by a distinct diurnal variation and decrease in α-factor during stormwater treatment. Surfactants and the majority of the total organic carbon (TOC) load are effectively removed in the first stage; hence, α-factors in the second stage are higher and have a more consistent diurnal pattern. Proposed α-factors enable more accurate aeration system design of two-stage WWTPs. Fouling-induced diffuser pressure loss can be restored effectively with reverse flexing in both treatment stages.