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Oxygen is an important component of water quality and its ability to sustain life. Water aeration is the process of introducing air into a body of water to increase its oxygen saturation. Water aeration can be accomplished in a variety of ways, for instance, closed-conduit aeration. High-speed flow in a closed conduit involves air-water mixture flow. The air flow results from the subatmospheric pressure downstream of the gate. The air entrained by the high-speed flow is supplied by the air vent. The air entrained into the flow in the form of a large number of bubbles accelerates oxygen transfer and hence also increases aeration efficiency. In the present work, the optimum air-demand ratio for maximum aeration efficiency in high-head gated circular conduits was studied experimentally. Results showed that aeration efficiency increased with the air-demand ratio to a certain point and then aeration efficiency did not change with a further increase of the air-demand ratio. Thus, there was an optimum value for the air-demand ratio, depending on the Froude number, which provides maximum aeration efficiency. Furthermore, a design formula for aeration efficiency was presented relating aeration efficiency to the air-demand ratio and Froude number. [ABSTRACT FROM AUTHOR]

The primary purpose of water aeration is to increase the oxygen saturation of the water. This can be achieved by using hydraulic structures because of substantial air bubble entrainment at these structures. Closed conduit aeration is a particular instance of this. While there has been a great deal of research on air-demand ratio within closed conduit, very little research has specifically addressed aeration efficiency of closed conduit. In the present work an experimental study was conducted to investigate the aeration efficiency of high-head gated circular conduits. Results showed that highhead gated circular conduits were effective for oxygen transfer. The effects of Froude number and ratio of the water cross-sectional flow area to the conduit cross-sectional area on aeration efficiency were particularly significant, whereas the effect of conduit length was only moderate. Further, a design formula for the aeration efficiency was presented relating the aeration efficiency to ratio of water cross-sectional flow area to conduit cross-sectional area and Froude number. The obtained results will be useful in future modeling processes and aid the practicing engineer in predicting aeration efficiency for design purposes. [ABSTRACT FROM AUTHOR]

Hydrodynamic flow regulators are used in environmental engineering as a replacement for traditional flow throttling devices. They are extremely efficient, reliable and free from the common disadvantages of traditional devices. Recent research by the authors indicated that the atomization of a liquid by hydrodynamic flow regulators accelerates oxygenation and may be used for improving the quality of wastewater and stormwater. To date, an evaluation of the aeration capacity of a hydrodynamic flow regulator at the pilot scale or in a practical situation has not been presented in the literature. This study presents the experimental results of oxygen absorption tests for conventional and modified cylindrical hydrodynamic flow regulators (patent pending). These devices were tested in a closed-circuit experimental setup at the semi-commercial scale. The aeration efficiency of hydrodynamic flow regulators was assessed by means of the overall standard oxygen transfer coefficient (KLa(20), h-1) and standard oxygen transfer rate (SOTR, gO2/h) for a wide range of tested configurations. The effect of flow rate and discharge mode on the aeration capacity of flow regulators was investigated. The values of KLa(20) for cylindrical hydrodynamic flow regulators obtained in the experiments were between 2.62 and 15.57 h-1 while SOTR values ranged from 53 to 316 gO2/h. The modified discharge mode with two active outlets allowed for an increase in aeration efficiency of up to 15% compared to conventional designs. [ABSTRACT FROM AUTHOR]

Mathematical modeling has been a vital tool in the field of environmental engineering. Various models have been developed to simulate the level of aeration efficiency (AE) provided by different aerating structures to raise levels of dissolved oxygen (DO) in streams; one of which is the stepped cascade structure. Three models developed by Gameson et al. WRL, and Nakasone, in addition to Qual2k, a computer program for stream modeling, have been used in this research; values of AEs obtained have been compared to those computed using DO measured from a built model at a WWTP. A stepped cascade structure was installed with different heights to aerate five flowrates with different levels of COD. An adjustment has been made to the Nakasone model to test the effect of pollutant load on the amount of aeration that could be reached. Values of AEs computed using the Gameson model were 30%, 39.5%, and 40% for cascade heights (Hd) 45, 60, and 75 cm respectively for the five flowrates (q) that ranged from 21-66 m3/hr. Values of AEs from WRL model were 32.8%, 42%, and 43% consequently. Values of AEs from Nakasone model ranged from 4.6-7.5%, 6-10%, and 7.6-12% respectively. For the adjusted Nakasone model, values of AEs ranged from 3.2-4.9%, 3.3-5.3%, and 4.1-6.7% respectively. Finally, the AEs computed using the values of downstream DO generated by Qual2k ranged from 4-18%, 2-15%, and 2.5-5.1% correspondingly. Around 80% of the downstream DO values computed using the Nakasone and adjusted Nakasone model were closer to those measured in the field, thus more reliable in cascade design. [ABSTRACT FROM AUTHOR]

The carbon associated with wastewater and its treatment accounts for approximately 6% of the global carbon balance. Within the wastewater treatment industry, winery wastewater has a minor contribution, although it can have a major impact on wine-producing regions. Typically, winery wastewater is treated by biological processes, such as the activated sludge process. Biomass produced during treatment is usually disposed of directly, i.e. without digestion or other anaerobic processes. We applied our previously published model for carbon-footprint calculation to the areas worldwide producing yearly more than 106 m3 of wine (i.e., France, Italy, Spain, California, Argentina, Australia, China, and South Africa). Datasets on wine production from the Food and Agriculture Organisation were processed and wastewater flow rates calculated with assumptions based on our previous experience. Results show that the wine production, hence the calculated wastewater flow, is reported as fairly constant in the period 2005-2007. Nevertheless, treatment process efficiency and energy-conservation may play a significant role on the overall carbon-footprint. We performed a sensitivity analysis on the efficiency of the aeration process (αSOTE per unit depth, or αSOTE/Z) in the biological treatment operations and showed significant margin for improvement. Our results show that the carbon-footprint reduction via aeration efficiency improvement is in the range of 8.1 to 12.3%. [ABSTRACT FROM AUTHOR]

The efficiency of the aeration system in a full-scale activated sludge basin with 3 separately controlled aeration zones was improved for the low loading period in summer. The air flow rate to each aeration zone is currently regulated to hold a preset dissolved oxygen concentration (DO). Four different DO setpoint combinations were tested, each one for a one week period, using dynamic off-gas testing to measure the standardised oxygen transfer efficiency (αSOTE). As the DO setpoints were lowered, the total air flow rate to the basin decreased initially. A low DO in the first zones slowed biomass activity and pushed the load towards the end of the aeration basin. The relationship between αSOTE and the specific diffuser flow rate qD is different for each zone. In Zone 1 there was a strong decrease in αSOTE as qD increased, while Zones 2 and 3 were fairly independent of qD, Zone 2 at a higher level than Zone 3. Aeration costs were reduced by 15% for the most efficient combination. To achieve even more savings, a control strategy adjusting oxygen transfer rates over the aeration basin to the necessary oxygen transfer rates is suggested. It is based on changing the DO setpoints to reach the lowest total air flow rate while meeting the effluent requirements. [ABSTRACT FROM AUTHOR]