The influence of the design of the mixing device on the efficiency of mass transfer during pneumo-mechanical aeration of wastewater

2020 ◽  
Author(s):  
А.Н. Григорьева ◽  
Р.Ш. Абиев
Keyword(s):  
Mass Transfer ◽  
Oxygen Transfer ◽  
Transfer Efficiency ◽  
Oxygen Transfer Efficiency ◽  
Aeration Efficiency ◽  
Mechanical Aeration

Аэрация при очистке сточных вод является самым энергоемким процессом. Затраты на обеспечение биологической очистки кислородом составляют около 60% в структуре себестоимости очистки. Таким образом, эффективность массообмена и снижение расхода воздуха является актуальной задачей для предприятий, которые стремятся повысить экономическую эффективность своей деятельности. Цель данной работы – определить эффективность пневмомеханической системы аэрации с использованием турбинной мешалки и разработанной авторами новой конической мешалки, а также сравнить эффективность диспергирования газа в пневматической и пневмомеханической системах аэрации. В качестве критерия для сравнения выбран показатель SOTE (Standard Oxygen Transfer Efficiency), который является основным технологическим параметром, позволяющим сравнивать эффективность различных аэрационных систем. Второй критерий эффективности – показатель SAE (Standard Aeration Efficiency) – отношение количества растворенного в жидкости кислорода к количеству используемой электроэнергии. В результате проведенных экспериментальных исследований установлено, что коническая мешалка по скорости насыщения воды кислородом работает также эффективно, как и турбинная, потребляя при этом гораздо меньше электроэнергии. С разработкой конического колеса вследствие низкого сопротивления лопастей перемешивание в системе «газ – жидкость» возможно в аппаратах больших размеров, что особенно актуально для аэротенков с небольшой глубиной при биологической очистке сточных вод в условиях, когда эффективность пневматической системы существенно снижается.

An assessment of oxygen transfer efficiency in a gas permeable hollow fibre membrane biological reactor

2010 ◽  
Vol 61 (5) ◽  
pp. 1165-1171 ◽  
Author(s):  
G. Soreanu ◽  
L. Lishman ◽  
S. Dunlop ◽  
H. Behmann ◽  
P. Seto
Keyword(s):  
Mass Transfer ◽  
Chemical Reaction ◽  
Oxygen Transfer ◽  
Membrane Surface ◽  
Treatment Plant ◽  
Hollow Fibre ◽  
Transfer Efficiency ◽  
Fine Bubble ◽  
Oxygen Transfer Efficiency ◽  
Bubble Diffusers

The clean water oxygen transfer efficiency (OTE) of a full scale non-porous hollow fibre gas permeable (GP) membrane (surface area of 500 m2) was evaluated at inlet air pressures of 1.2, 1.4, and 1.8 atm using two established testing methods. To form a basis of comparison with traditional aeration technologies, additional testing was done with conventional aerators (fine bubble and coarse bubble diffusers) replacing the GP membrane. OTE can be established based on the re-aeration of deoxygenated water or by monitoring the catalytic oxidation of a sodium sulphite (Na2SO3) solution. In this study, OTE values determined by sulphite oxidation (SOTES) were consistently higher than those established during re-aeration (SOTER) suggesting that the chemical reaction was enhancing the mass transfer. The chemical reaction was sufficiently fast in the case of the GP membrane, that the gas phase limited the mass transfer. The GP membrane operating at 1.2 atm had a SOTES of 70.6% and a SOTER of 52.2%. SOTER for the coarse bubble and fine bubble diffusers were 3.8% and 23.6%, respectively. This is comparable to the manufacturer's values, corrected for depth of 3.4% and 18.3%, respectively. Particularly, the derived OTE values were used to evaluate differences in energy consumption for a conventional treatment plant achieving carbon removal and nitrification. This analysis highlights the potential energy efficiency of GP membranes, which could be considered for the design of the membrane modules.

The Effect of Nozzle Type on Air Entrainment by Plunging Water Jets

2002 ◽  
Vol 37 (3) ◽  
pp. 599-612 ◽  
Author(s):  
Tamer Bagatur ◽  
Ahmet Baylar ◽  
Nusret Sekerdag
Keyword(s):  
Penetration Depth ◽  
Oxygen Transfer ◽  
Free Water ◽  
Air Entrainment ◽  
Water Jet ◽  
Transfer Efficiency ◽  
Entrainment Rate ◽  
Water Jets ◽  
Air Entrainment Rate ◽  
Oxygen Transfer Efficiency

Abstract In this study, for the plunging water jet aeration system using various inclined nozzle types, bubble penetration depth, air entrainment rate, water jet expansion, effect of water jet circumference at impact point, oxygen transfer coefficient and oxygen transfer efficiency which changed depending on the water jet velocity, were researched in an air-water system. Numerous studies were conducted with circular nozzles. The present study describes new experiments performed with different nozzle types. Three types of nozzles were examined, i.e., those with circular, ellipse and rectangle duct with rounded ends. Experimental results showed that water jets produced with ellipse and rectangle duct with rounded ends nozzles have very different flow characteristics, entrainment patterns on free water jet surface, and submerged water jet region within the receiving tank. Higher air entrainment rate and oxygen transfer efficiency was observed in the rectangle duct with rounded ends nozzle due to water jet expansion. Bubble penetration depth, however, is lower for the rectangle duct with rounded ends nozzle than for the other nozzles. The ellipse nozzle provided the highest bubble penetration depth. These results showed that it is appropriate to use ellipse nozzle in aeration of deep pool and rectangle duct with rounded ends nozzle in the applications where high bubble concentration is desirable.

Oxygen Transfer Efficiency Measurements Using Off-Gas Techniques

1989 ◽  
Vol 21 (10-11) ◽  
pp. 1295-1300 ◽  
Author(s):  
W. C. Boyle ◽  
B. G. Hellstrom ◽  
L. Ewing
Keyword(s):  
Oxygen Uptake ◽  
Uptake Rate ◽  
Oxygen Transfer ◽  
Oxygen Uptake Rate ◽  
Transfer Efficiency ◽  
Theoretical Development ◽  
Process Conditions ◽  
Uptake Rates ◽  
Oxygen Transfer Efficiency ◽  
On Line

The off-gas technique for measuring oxygen transfer efficiency in aeration tanks under process conditions was proposed as an accurate technique for calibrating or verifying on-line methods used to estimate oxygen uptake rates. The theoretical development of the off-gas technique was presented. Application of this technique in verifying or calibrating existing on-line methods for estimating oxygen uptake rate was presented. Direct application as an on-line method for estimating oxygen uptake rate was also discussed.

Experience with Ceramic Plate Diffusers in Large Activated Sludge Plants

1992 ◽  
Vol 25 (4-5) ◽  
pp. 127-134
Author(s):  
R. Warriner ◽  
T. C. Rooney
Keyword(s):  
Activated Sludge ◽  
Oxygen Transfer ◽  
Cost Effective ◽  
Transfer Efficiency ◽  
Ceramic Plate ◽  
Flat Plates ◽  
Higher Power ◽  
Oxygen Transfer Efficiency ◽  
Basin Floor ◽  
The Difference

Fine pore aeration systems were evaluated in a U.S.EPA sponsored study of oxygen transfer efficiency in 26 activated sludge plants. Two plants in the study, those of the Milwaukee Metropolitan Sewerage District, had aeration systems composed of flat plates grouted into containers placed flush with the basin floor. The remaining plants in the study had aeration systems utilizing various disk, dome, and tube devices that are now in far more widespread use than the flat plates. The District's aeration basins gave better oxygen transfer efficiency than the other ceramic diffuser systems studied. The difference may have been the result of the high tank area to diffuser area ratio and the low air flux rates associated with the plate systems. At one MMSD plant there were also four basins with recently installed ceramic disk diffuser systems. This provided an opportunity for side-by-side comparisons between the disks and the flat plates in containers. An analysis of diffuser system first costs and energy costs indicated that the ceramic plate system could be cost effective at higher power costs, but not at the prices presently paid by the District for power.

Study of Air Bubble Formation for Wastewater Treatment

2011 ◽  
Author(s):  
Bryan A. Miletta ◽  
R. S. Amano ◽  
Ammar A. T. Alkhalidi ◽  
Jin Li
Keyword(s):  
Wastewater Treatment ◽  
Oxygen Transfer ◽  
Surface Membrane ◽  
Bubble Formation ◽  
High Oxygen ◽  
Transfer Efficiency ◽  
Intimate Contact ◽  
Rubber Membrane ◽  
Unit Process ◽  
Oxygen Transfer Efficiency

Aeration, a unit process in which air and water are brought into intimate contact, is an extremely important step in the process of wastewater treatment. The two most common systems of aeration are subsurface and mechanical. A mechanical system agitates the wastewater by various means (e.g. paddles, blades, or propellers) to introduce air from the atmosphere. Subsurface aeration is the release of air, in the form of bubbles, within the tank of wastewater to supply the microorganisms with the required amount of oxygen they need to metabolize and break down the organic material suspended in the wastewater. The bubbles of Air are released from the bottom of the wastewater tank through diffusers. These diffusers have a surface membrane, usually made of punched rubber, to create the fine bubbles with high oxygen transfer efficiency from supplied air to the diffusers. Since the energy crisis in the early 1970’s, there has been increased interest in these systems due to its high oxygen transfer efficiency. This paper covers experimentation of different air diffuser membranes, varying in material, used in the aeration process of wastewater treatment. Rubber, EPDM rubber (ethylene-propylene-diene Monomer) and PTFE Polytetrafluoroethylene membranes coated membranes were tested. Experimental results showed that the rubber membrane produced the smallest bubble size against expectation. This could be a result of the coating being on the top surface only and the bubble starts from inside the punch.

An experimental study of nozzle diameters, aeration depths and angles on standard aeration efficiency (SAE) in a venturi aerator

2009 ◽  
Vol 4 (3) ◽  
Author(s):  
M.R. Ghomi ◽  
M. Sohrabnejad ◽  
M. R. Ovissipour
Keyword(s):  
Experimental Study ◽  
Oxygen Transfer ◽  
Air Entrainment ◽  
Nozzle Diameter ◽  
Venturi Tube ◽  
Water Pump ◽  
Significant Difference ◽  
Oxygen Transfer Efficiency ◽  
Aeration Efficiency ◽  
Nozzle Size

A 1.1 kW submersible water pump with a venturi air injector was used in this study to examine the effects of three factors including nozzle diameter (14, 17 and 20 mm), aeration depth (20, 40 and 60 cm), and aeration angle (0, 22.5 and 45°) on standard aeration efficiency (SAE). For maximum air entrainment, HT / DT ratio and DT / DN ratio were equal to zero and 2, respectively. Among the first factor experiments, 14 mm nozzle diameter showed the highest SAE value (P<0.05). Although, 60 cm aeration depth and 45° aeration angle had more SAE value among other depths and angles, but there was not a significant difference (P>0.05) in each aeration depths and angles. Only, the determination coefficient for effect of nozzle diameters on SAE value showed a good result (R2= 0.958). The greatest oxygen transfer efficiency in this study has been achieved with using 14 mm nozzle size, 60 cm depth of aeration, and 45° angle of venturi tube in water aeration that was 1.166 kgO2/ kWh. Venturi aerators are very inexpensive in comparison with other aerators and have some other advantages that can be considered as one of the best devices for water aeration.

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