Effect of air flow rate on oxygen transfer in an oxidation ditch equipped with fine bubble diffusers and slow speed mixers

2000 ◽  
Vol 34 (5) ◽  
pp. 1756-1762 ◽  
Author(s):  
S Gillot
Keyword(s):  
Flow Rate ◽  
Oxygen Transfer ◽  
Air Flow ◽  
Oxidation Ditch ◽  
Air Flow Rate ◽  
Slow Speed ◽  
Fine Bubble ◽  
Bubble Diffusers

Optimization of oxygen transfer in clean water by fine bubble diffused air system and separate mixing in aeration ditches

1998 ◽  
Vol 38 (3) ◽  
pp. 35-42 ◽  
Author(s):  
G. Déronzier ◽  
Ph. Duchène ◽  
A. Héduit
Keyword(s):  
Water Flow ◽  
Flow Rate ◽  
Oxygen Transfer ◽  
Contact Time ◽  
Air Flow ◽  
Interfacial Area ◽  
Design Parameters ◽  
Air Bubbles ◽  
Air Flow Rate ◽  
Fine Bubble

The influence of design parameters on the transfer of oxygen was studied in different ring ditches equipped with fine bubble membrane air diffusers and separate mixing. The results produced evidence that the oxygen transfer efficiency (OTE) decreases when the air flow rate per diffuser increases. OTE increases asymptotically with the horizontal water flow (50% for velocity up to 0.5 m/sec). It increases also when the diffuser modules are brought closer together. Theoretical analysis enabled ranking of the impact of the design parameters on which the oxygen transfer is dependent, namely the interfacial area (a) and the oxygen transfer coefficient (Kl). The increase in the air flow rate per diffuser essentially reduces the interfacial area by an increase in the diameter of the initial air bubbles and by a reduction of the contact time due to an acceleration of the “spiral flows” (vertical rotation of water flow). The horizontal rotation of water increases the interfacial area most probably by decreasing the diameter of the initial air bubbles and by a lengthening of the contact time resulting from a reduction in the large spiral flows. Bringing the diffuser modules closer together makes longer the contact time by a reduction in the large spiral flows.

Oxygen transfer and aeration efficiency - influence of diffuser submergence, diffuser density, and blower type

1998 ◽  
Vol 38 (3) ◽  
pp. 1-6 ◽  
Author(s):  
Martin R. Wagner ◽  
H. Johannes Pöpel
Keyword(s):  
Wastewater Treatment ◽  
Energy Consumption ◽  
Flow Rate ◽  
Oxygen Transfer ◽  
Wastewater Treatment Plants ◽  
Air Flow ◽  
Oxygen Absorption ◽  
Air Flow Rate ◽  
Fine Bubble ◽  
Aeration Efficiency

The main factors of fine bubble aeration systems in uniform arrangement in clean water are the air flow rate, the depth of submergence of the diffusers, and the diffuser density. While the influence of the air flow rate on the oxygen transfer parameters is known, knowledge of the influence of the depth of submergence and the diffuser density on the specific oxygen transfer efficiency SOTE [%/m] and on the specific oxygen absorption SOA [g/m3·m at STP] is very limited. Both parameters are of great importance in dimensioning fine bubble aeration systems. Therefore, a literature review was conducted to show the influence of the diffuser submergence and density and the type of blower on oxygen transfer and aeration efficiency. The main review results are, that higher values of specific oxygen absorption can be obtained at higher diffuser density; secondly, the volumetric oxygen transfer rate VOTR [g/m3·h] is higher with increasing depth of submergence at the same air flow rate. Also it can be stated that with greater depth of submergence the specific oxygen absorption [g/m3·m at STP] is reduced. Dependent on the air flow rate and the pressure head, the energy consumption [Wh/m3·m at STP] of the blowers used in wastewater treatment plants is different. For example, the energy consumption varies from 4.3 [Wh/m3·m at STP] (positive displacement blower) to 3.0 [Wh/m3·m at STP] (turbo-compressors) at a pressure of 10 m and an air flow rate of 5,000 m3/h at STP. From the results of the literature review the following conclusions can be drawn: (1) High specific oxygen absorption values (SOA) [g/m3·m at STP] can be achieved applying shallow tanks, high diffuser densities and low specific air flow rates; (2) High aeration efficiencies (AE) [kg/kWh] can be obtained by applying high volumetric oxygen transfer rates and adequate selection of the blowers used at the wastewater treatment plants.

A control strategy for reducing aeration costs during low loading periods

2004 ◽  
Vol 50 (7) ◽  
pp. 61-68 ◽  
Author(s):  
C. Sahlmann ◽  
J.A. Libra ◽  
A. Schuchardt ◽  
U. Wiesmann ◽  
R. Gnirss
Keyword(s):  
Flow Rate ◽  
Control Strategy ◽  
Oxygen Transfer ◽  
Air Flow ◽  
Air Flow Rate ◽  
Transfer Rates ◽  
Diffuser Flow ◽  
Aeration System ◽  
Oxygen Transfer Efficiency ◽  
Biomass Activity

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.

Air Injection by Self-Aspirating Impeller in Aerobic Fermentation

1975 ◽  
Vol 38 (2) ◽  
pp. 94-99 ◽  
Author(s):  
F. A. AZI ◽  
A. G. MEIERING ◽  
C. L. DUITSCHAEVER ◽  
A. E. READE
Keyword(s):  
Flow Pattern ◽  
Flow Rate ◽  
Oxygen Transfer ◽  
Draft Tube ◽  
Air Flow ◽  
Air Injection ◽  
Vertical Flow ◽  
Rotor Speed ◽  
Air Flow Rate ◽  
Biological Tests

A novel fermentor is described in which aeration is achieved by air induction through a hollow impeller system: no air pump is required. Air flow into the vessel increased with rotor speed, impeller diameter and height of liquid above the impeller. Although longer impellers increased the air flow rate. oxygen transfer was favored by shorter impellers. The presence of a draft tube in the vessel creates a vertical flow pattern in the medium which increases gas hold-up and, therefore, oxygen transfer. Biological tests on the system using a mold and a yeast showed that performance compared favorably to conventional fermentor systems using separate aerators and agitators.

Prediction of alpha factor values for fine pore aeration systems

2008 ◽  
Vol 57 (8) ◽  
pp. 1265-1269 ◽  
Author(s):  
S. Gillot ◽  
A. Héduit
Keyword(s):  
Flow Rate ◽  
Oxygen Transfer ◽  
Air Flow ◽  
Domestic Wastewater ◽  
Aeration Tank ◽  
Air Flow Rate ◽  
Factors Affecting ◽  
Domestic Wastewater Treatment ◽  
Alpha Factor ◽  
The Impact

The objective of this work was to analyse the impact of different geometric and operating parameters on the alpha factor value for fine bubble aeration systems equipped with EPDM membrane diffusers. Measurements have been performed on nitrifying plants operating under extended aeration and treating mainly domestic wastewater. Measurements performed on 14 nitrifying plants showed that, for domestic wastewater treatment under very low F/M ratios, the alpha factor is comprised between 0.44 and 0.98. A new composite variable (the Equivalent Contact Time, ECT) has been defined and makes it possible for a given aeration tank, knowing the MCRT, the clean water oxygen transfer coefficient and the supplied air flow rate, to predict the alpha factor value. ECT combines the effect on mass transfer of all generally accepted factors affecting oxygen transfer performances (air flow rate, diffuser submergence, horizontal flow).

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