一种振荡射流充气混合设备

为克服喷射充气设备对流扩散能力不足的缺点,研制可形成间歇脉冲射流和交变剪切流场的设备。利用数学物理原理证明了射流沿程卷吸的必然性,并通过水气混合体中混合击波的机理阐明了气体被推入水体的现象。最后介绍在生产中的实际应用。     

Reduction of aeration costs by tuning a multi-set point on/off controller: A case study

The objective of this work was to select the best configuration for a dissolved oxygen multi-set point on/off controller of a full-scale wastewater treatment plant to ensure the best dissolved oxygen concentration set-point values. The optimal set point values should allow the attainment of a good quality of effluent wastewater and minimise the operational costs related to the aeration process. To achieve this goal, simulation and optimisation software and off-line optimisation techniques were used. As a result of the optimisation of the dissolved oxygen controller, a more stable system was obtained. Because of the stability of the system, the quality of the effluent and activated sludge and the operating life of the aeration equipment was increased. Moreover, the aeration costs were reduced by approximately 17%.     

Experimental Study of Air Entrainment Rates due to Inclined Liquid Jets

The air entrainment rate due to inclined liquid jet plunging into a pool was investigated experimentally. Three types of fluids with varying physical properties in terms of viscosity and surface tension were utilized. For the impinging jet test section, nozzles with different inner diameters were selected. The inclination angles and liquid jet velocities at the nozzle outlet were varied and the entrained air rate was measured by the soap meniscus method. Taking the falling velocity of the liquid jet as a characteristic velocity, it was found that the air entrainment rate under the present experimental condition largely depended on the Weber number. From the obtained database, a new empirical model dependent on the Weber number and Laplace length scale is proposed which is capable of predicting the air entrainment flow rate at a mean absolute relative deviation of 21.7 %.     

Experimental study on improving the separation performance of liquid-solid fluidized bed using flotation reagent and newly designed aeration unit

In the study, a pilot-scale liquid-solid fluidized bed (LSFB) apparatus was modified by adding an aeration unit, which enabled us to test the effect of air addition on LSFB separation performance for fine coal (0.25 ~ 1.00 mm). Upward water flow velocity, aeration volume and flotation reagent (Kerosene and 2-Caprylic alcohol) dosage varied throughout the experiment. The optimum results from the three experimental conditions (without aeration, with aeration only, with aeration and reagent) were compared by their respective probable error (Ep) values. The Ep values of the three experimental conditions were 0.109, 0.08 and 0.07, respectively. The results indicated that the addition of air obviously enhanced LSFB performance, while the addition of flotation reagent further improved the separation result.     

Biodrying performance and bacterial community structure under variable and constant aeration regimes during sewage sludge biodrying

This study investigated biodrying performance under variable and constant aerations. The matrix-related properties, air-related parameters, and bacterial community were assessed. Under variable aeration, the velocity and temperature of the air above the pile surface were high; bacterial diversity indicated that the biodrying was achieved during an established period; Proteobacteria was dominant throughout the biodrying; and there was better performance of the biodrying product intended for direct incineration or for postcuring land use. Different aeration conditions led different biomass percentages, but the dominant phyla were similar.     

Chute Aerators: Steep Deflectors and Cavity Subpressure

Chute aerators are applied to high-velocity spillways to entrain air into the flow so that cavitation damage is avoided. Air entrainment occurs locally at the aerator, whereas further downstream the flow is deaerated. This process is relevant because it defines the influence range of an aerator. A preliminary study investigated the effect of the aerator geometry and of the approach flow conditions on the streamwise bottom and average air concentration characteristics. Two aspects were excluded, namely, the effect of (1) steep deflectors, which operate more efficiently regarding air entrainment yet with simultaneously poor flow features; and (2) cavity subpressure effect on the streamwise air concentration field. A cavity subpressure reduces, in particular, the streamwise bottom air concentrations or it provokes aerator choking so that the cavitation protection is not ensured. Physical model tests indicate that optimum aerator performance results at deflector angles around 10°, i.e., a slope of 1∶5 relative to the chute bottom with acceptable shock wave formation, spray generation, and jet height.     

CFD study to determine the optimal configuration of aerators in a full-scale waste stabilization pond

Aerated lagoons (ALs) are important variants of the pond wastewater treatment technology that have not received much attention in the literature. The hydraulic behaviour of ALs and especially the Facultative aerated lagoons (FALs) is very complex since the aeration in these systems is designed for oxygen transfer but not necessarily to create complete mixing. In this work, the energy expenditure of the aerators was studied by means of a scenario analysis. 3D CFD models (one phase and multiphase) of a 3 ha FAL in a waste stabilization pond system in Cuenca (Ecuador) were built for different configurations of aerators. The thrust produced by the aerators was modelled by an external momentum source applied as velocity vectors into the pond fluid. The predictions of a single phase model were in satisfactory agreement with experimental results. Subsequently, a scenario analysis assessing several aeration schemes with different numbers of aerators in operation were tested with respect to velocity profiles and residence time distribution (RTD) curves. This analysis showed that the aeration scheme with all 10 aerators switched on produces a similar hydraulic behaviour compared to using only 6 or 8 aerators. The current operational schemes comprise of switching off some aerators during the peak hours of the day and operating all 10 aerators during night. This current practice could be economically replaced by continuously operating 4 or 6 aerators without significantly affecting the overall mixing. Furthermore, a continuous mixing regime minimises the sediment oxygen demand enhancing the oxygen levels in the pond.     

Potential for autumn aeration of stored rough rice and the potential number of generations of Sitophilus zeamais Motschulsky in milled rice in Japan

Historical weather data from 84 sites in Japan were used to estimate the number of hours 15°C from 1 September to 31 October, based on the individual years from 1994 to1999, to evaluate the potential for using aeration at a threshold level of 15°C to cool rough rice stored during autumn. The number of hours 15°C in September and October ranged from 68±21 in Kyushu to 1067±27 h in northern Hokkaido. At an airflow rate of 0.0013 m³/s/m³, the time required to cool a storage silo containing rough rice to 15°C ranged from 85 days in southern Japan to 5 days in northern Japan. Weather data for the same sites were also used to estimate the number of hours below 15°C from 1 May to 30 September, to evaluate the potential of Sitophilus zeamais Motschulsky, the maize weevil, to infest bagged milled rice at ambient or uncontrolled temperatures. The number of hours 15°C from 1 May to 30 September ranged from 33±15 h in Kyushu to 2392±130 h on the northeastern coast of Hokkaido. As temperature decreased, there was a predicted increase in the number of days required to complete a generation, and as relative humidity increased, a predicted increase in the number of generations that could be produced. These simulation studies show how historical weather data can be used to develop risk management models for storage of bulk rough rice and bagged milled rice in Japan. Aeration during autumn could be used to cool large-bulk storage silos containing rough rice, while the simulations for development of Sitophilus zeamais populations on bagged milled rice emphasize the importance of insect management strategies for value-added products.     

Development of microbubble aerator for waste water treatment using aerobic activated sludge

In large-scale waste water treatment plants, the aerobic biochemical reactor is the most important process, where the oxygen supply into the microorganisms often limits the overall waste water treatment rate. On the other hand, several kinds of microbubble distributors have been developed to enrich the oxygen dissolution in water. Therefore, the application of microbubbles for a waste water treatment system was investigated in this study.The oxygen absorption performance of typical microbubble generators was compared with typical bubble generators. To evaluate each bubble generator, the liquid-phase volumetric oxygen transfer coefficient, gas hold-up and power consumption per unit liquid volume were measured in a bubble column attached to each bubble generator. All the microbubble generators allowed the oxygen to dissolve faster than the typical aerators. The spiral liquid flow type microbubble generator had the highest oxygen transfer coefficient even at a low air flow rate although it used more energy than the typical distributors.To improve an industrial waste water treatment system, a novel aeration system utilizing a spiral liquid flow type microbubble generator was proposed in this study. The present system has some advantages such as compact size, portability and fast oxygen dissolution rate. To ensure the performance for organic waste water treatment, the effects of the aeration rate, dissolved oxygen concentration and device properties on the specific consumption rate of model organic waste were investigated. For the novel aeration system, the most suitable conditions to treat organic waste were found.     

Quasi-static bubble formation on submerged orifices

The static formation of air bubbles emanating from a submerged orifice was analyzed based on the principles of force balance. The analysis was corroborated by experiments using a shadow imaging technique. The influence of the Young contact angle of the three material components was investigated by identifying two modes of formation, corresponding to bubble formation at the orifice rim and spreading of the bubble base on the horizontal surface around the bubble. The characteristics of the formation process such as shape, height and volume of the bubble and the non-dimensional pressure difference at the orifice are given for both modes up to the critical equilibrium, defined by the maximum bubble volume, at which the bubble releases dynamically.