Standard Oxygen Transfer Efficiency Research Articles

Predicting oxygen transfer of fine bubble diffused aeration systems—model issued from dimensional analysis

The standard oxygenation performances of fine bubble diffused aeration systems in clean water, measured in 12 cylindrical tanks (water depth from 2.4 to 6.1 m), were analysed using dimensional analysis. A relationship was established to estimate the scale-up factor for oxygen transfer, the transfer number ( N T ) N T = k L a 20 U G ( ν 2 g ) 1 / 3 = 7.77 × 1 0 - 5 ( S p S ) 0.24 ( S p S a ) - 0.15 ( D h ) 0.13 . The transfer number, which is written as a function of the oxygen transfer coefficient ( k L a 20 ) , the gas superficial velocity ( U G ) , the kinematic viscosity of water ( ν ) and the acceleration due to gravity ( g ) , has the same physical meaning as the specific oxygen transfer efficiency. N T only depends on the geometry of the tank/aeration system [the total surface of the perforated membrane ( S p ) , the surface of the tank ( S ) or its diameter ( D ) , the total surface of the zones covered by the diffusers (“aerated area”, S a ) and the submergence of the diffusers ( h ) ]. This analysis allowed to better describe the mass transfer in cylindrical tanks. Within the range of the parameters considered, the oxygen transfer coefficient ( k L a 20 ) is an increasing linear function of the air flow rate. For a given air flow rate and a given tank surface area, k L a 20 decreases with the water depth (submergence of the diffusers). For a given water depth, k L a 20 increases with the number of diffusers, and, for an equal number of diffusers, with the total area of the zones covered by the diffusers. The latter result evidences the superiority of the total floor coverage over an arrangement whereby the diffusers are placed on separate grids. The specific standard oxygen transfer efficiency is independent of the air flow rate and the water depth, the drop in the k L a 20 being offset by the increase of the saturation concentration. For a given tank area, the impact of the total surface of the perforated membrane ( S p ) and of the aerated area ( S a ) is the same as on the oxygen transfer coefficient.

Comparison of the efficiency of large-scale ceramic and membrane aeration systems with the dynamic off-gas method

The aeration systems of two full-scale activated sludge basins were compared over 2.5 years under the same operating conditions using dynamic off-gas testing. Only the material of the diffuser was different, membrane vs. ceramic tube diffusers. The experimental design took the complexity and dynamics of the system into consideration. The investigation has shown that, although the membrane diffusers have higher initial standard oxygen transfer efficiency (SOTE) and standard aeration efficiency (SAE), these decreased over time, while the SAE of the ceramic diffusers started lower, but increased slightly over the whole period. Measurement of air distribution in the basins along with dissolved oxygen concentration profiles have provided important information on improving process control and reducing energy costs. The results show that dynamic off-gas testing can effectively be used for monitoring the aeration system and to check design assumptions under operating conditions. The information can be used to improve the design of new aeration systems or in retro-fitting existing basins.

Comparison of Submerged Aerator Effectiveness

ABSTRACT The effectiveness of three different submerged aerators (diffusers), a membrane diffuser, a coarse bubble diffuser, and a soaker hose, is compared by analyzing their performance parameters at varying gas flow rates and water depths of up to 10 meters. The type of diffuser chosen for a specific application depends on aeration characteristics such as the total mass transfer coefficient, standard oxygen transfer rate (SOTR), standard oxygen transfer efficiency (SOTE), and standard aeration efficiency (SAE). From experimental data, the effects of the gas flow rate and submerged depth on the total mass transfer coefficient and SOTR are determined up to a 10 meter depth. As the flow rate and diffuser depth are increased, the mass transfer coefficient and the SOTR increase for all three diffusers. At low gas flow rates, the segment of soaker hose transfers oxygen at the highest rate. The coarse bubble diffuser transfers oxygen at a lesser rate than the soaker hose but is capable of performing at higher gas flow rates. The membrane diffuser performance resembles the high transfer of a soaker hose before approaching the transfer behavior of the coarse bubble diffuser at higher flow rates. Relationships are also defined for the SOTE and SAE. Non-dimensional parameter correlations quantify the dependence of the performance parameters on the gas flow rate and depth and provide a means of predicting diffuser behavior for specified system applications.

Deep Water Installation of a Diffused-Air Aeration System in a Shallow Pond

A 33-cm diameter air diffuser was installed in the bottom of a 3.28-m deep bore hole in the bottom of a 350-m2 pond. Water depth above the diffuser surface was 4.34 m. Air was supplied to the diffuser at 158 L/minute and a pressure of 4.86 m H20. The apparatus was highly effective in transferring oxygen to the water. Standard oxygen transfer efficiency was 28.7%, and the standard aeration efficiency, based on air delivered power, was 6.37 kg 02/kWµhr.

The effect of pore size on transfer capabilities, fouling tendencies, and cleaning of ceramic air diffusers

ABSTRACT: A study of the effect of fouling on the standard oxygen transfer efficiency (SOTE) of ceramic diffusers of four different pore sizes was conducted at the Monroe, Wis. wastewater treatment plant over a 2‐year period. Four pilot test headers were installed in the plant aeration tanks each containing four diffusers of one pore size. Only minor changes in SOTE, bubble release vacuum (BRV), and dynamic wet pressure (DWP) were observed indicating that the fouling phenomenon at Monroe was not progressive. The adverse effects of fouling with respect to back pressure and SOTE were found to be less than might have been predicted from the literature. The cleaning procedure used in the study, involving a combination of high pressure water spraying with liquid acid treatment, followed by additional spraying, resulted in nearly complete restoration of the diffusers' original characteristics.

Performance of packed column aerator at low hydraulic loading

A laboratory-scale packed column aerator filled with ceramic Raschig rings was tested for its performance with hydraulic loadings in the range of 16–86·3 m 3 m −2 h −1. Two columns of 0·19 m and 0·24 m inside diameter and packing sizes of 15, 25 and 36 mm were used. The system equation developed by previous workers for trickling filters in waste-water treatment was not generally applicable across the lower hydraulic loadings. The system coefficient incorporating the oxygen absorption coefficient (k La) was found to vary within the range of hydraulic loadings studied. The oxygen transfer rate equation developed for surface and submerged aerators was used for estimating standard oxygen transfer efficiency of the packed column aerator, which, in this case, ranged from 6·2 to 22·6 kg O 2 kWh −1.

Diffuser design for discharge to a stratified recipient : Poul Harremoës, Denmark

The standard oxygenation performances of fine bubble diffused aeration systems in clean water, measured in 12 cylindrical tanks (water depth from 2.4 to 6.1 m), were analysed using dimensional analysis. A relationship was established to estimate the scale-up factor for oxygen transfer, the transfer number (NT) The transfer number, which is written as a function of the oxygen transfer coefficient (kLa20), the gas superficial velocity (UG), the kinematic viscosity of water (ν) and the acceleration due to gravity (g), has the same physical meaning as the specific oxygen transfer efficiency. NT only depends on the geometry of the tank/aeration system [the total surface of the perforated membrane (Sp), the surface of the tank (S) or its diameter (D), the total surface of the zones covered by the diffusers (“aerated area”, Sa) and the submergence of the diffusers (h)].This analysis allowed to better describe the mass transfer in cylindrical tanks. Within the range of the parameters considered, the oxygen transfer coefficient (kLa20) is an increasing linear function of the air flow rate. For a given air flow rate and a given tank surface area, kLa20 decreases with the water depth (submergence of the diffusers). For a given water depth, kLa20 increases with the number of diffusers, and, for an equal number of diffusers, with the total area of the zones covered by the diffusers. The latter result evidences the superiority of the total floor coverage over an arrangement whereby the diffusers are placed on separate grids. The specific standard oxygen transfer efficiency is independent of the air flow rate and the water depth, the drop in the kLa20 being offset by the increase of the saturation concentration. For a given tank area, the impact of the total surface of the perforated membrane (Sp) and of the aerated area (Sa) is the same as on the oxygen transfer coefficient.