Highest Aeration Efficiency Research Articles

Experimental investigation on oxygenation efficiency of an effective aeration system for ponds

Dissolved oxygen (DO) concentration in water is one of the most important water quality parameters in rivers, lakes, and reservoirs. The most effective way to increase DO concentration in water is aeration. Conduits with high aeration performance are predicted to significantly increase aeration efficiency. Based on this prediction, the physical parameters affecting the aeration efficiency (E20) of the conduit aeration system were experimentally investigated. The effect of different jet plunge angles, flow rates, hydrostatic levels, Froude numbers, and gate opening rates was investigated to optimize the system for the best ventilation efficiency. As a result, the aeration efficiency (E20) improves with increasing air intake performance at low gate openings, high Froude numbers, and hydrostatic levels. The increase in jet plunge angles and hydrostatic level directly increases the aeration efficiency. The study showed that conduit systems can be an important alternative for pond aeration due to initial investment and operating costs, low energy cost, and high aeration efficiency.

Modelling the biological treatment process aeration efficiency: application of the artificial neural network algorithm.

The biological treatment process (BTP) is responsible for removing chemical oxygen demand (COD) and ammonia using microorganisms present in wastewater. The BTP consumes large quantities of energy due to the transfer of oxygen using air pumps/blowers. Energy consumption in the BTP is due to low solubility of oxygen, which results in low aeration efficiency (AE). The aim of the study was to develop an AE model that can be used to monitor the performance of the BTP. Multilayer perceptron artificial neural network (MLP ANN) algorithm was used to model AE in the BTP. The performance of the AE model was evaluated using R2, mean square error (MSE), and root mean square error (RMSE). Sensitivity analysis was performed on the AE model to determine variables that drive AE. The results of the study showed that MLP ANN algorithm was able to model AE. R2, MSE, and RMSE results were 0.939, 0.0025, and 0.05, respectively, during testing phase. Sensitivity analysis results showed that temperature (34.6%), COD (21%), airflow rate (19.1%), and OTR/KLa (15.7%) drive AE. At high temperatures, the viscosity of wastewater is low which enables oxygen to penetrate the wastewater, resulting in high AE. The AE model can be used to predict the performance of the BTP, which will assist in minimizing energy consumption.

Application of MABR in upgrading and reconstruction of a wastwater treatment station

MABR membrane aeration biofilm reactor process was adopted for the reconstruction of a sewage treatment station in North China. MABR membrane components were added to the original CAST process and a new secondary sedimentation tank was built to reconstruct the original biochemical system. In the meanwhile, an advanced treatment system with new high-density tanks and V-shaped filters were built to ensure the quality of the final effluent. In the establishment of the MABR membrane aeration biofilm reactor process, only new aeration membrane components were added and no new equipment and civil works were needed in the original biochemical tank. No new blowers were needed due to the high aeration efficiency and low energy consumption of the biofilm system. The one-off investment is about 850 yuan·m−3 and the reconstruction period was about 15 days, indicating its advantages of short reconstruction period and low operational cost. For the new membrane aeration biofilm reactor process, the mean value of ammonia nitrogen in the inflow was 39 mg·L−1 and its mean value in the effluent was 3 mg·L−1, i.e. the average removal rate was 92%. The mean value of total nitrogen (TN) in the inflow was 63 mg·L−1 and the mean value in the effluent was 11 mg·L−1, making an average removal rate of 83%. The mean value of total phosphorus (TP) in the inflow was 7.5 mg·L−1 and the mean value in the effluent was 0.9 mg·L−1, thus the average removal rate was 88%. The TP concentration in the effluent could be kept below 0.4 mg·L−1 by chemical phosphorus removal by the follow-up advanced treatment section. The mean value of COD in the inflow was 367 mg·L−1 and the mean value of effluent was 35 mg·L−1, i.e. the average removal rate was 90%. After the reconstruction of the treatment process, the effluent quality of the sewage treatment station stably reached the Class 1A level of tHe Discharge Standard of Pollutants for Municipal Wastewater Treatment Plant (GB 18918-2002).

A comparative study of impeller aerators configurations

This paper presents a comparative experimental study of different configurations of mechanical surface aerators used in wastewater treatment plants. A laboratory scale tank equipped with different configurations for aeration process was installed to compare the standard aeration efficiency and power consumption of curved blade impellers with 3, 6, 9, and 12 blades. Different parameters thought to have significant effects on standard aeration efficiency (SAE) and power consumption, such as submergence depth and rotating speed were studied. Results show that an optimum configuration (9 blades) has the highest aeration efficiency (2.60 Kg. O2/KW.hr) at 500 rpm. Also, a submersion depth ratio of 0.35 was optimum, giving the highest standard aeration efficiency, as increasing submergence depth ratio above this value causes drop in standard aeration efficiency as a result of inevitable increase in input power consumption in this case.

Comparative study of local gas-liquid hydrodynamics and mass transfer between conventional and modified airlift reactors

Modified airlift reactor (MALR) was developed for improving the oxygen transfer coefficient (KLa) by installing the slanted baffles in the riser compartment. MALR can enhance KLa value up to 97% compared to a regular reactor. However, insufficient analysis of the hydrodynamics and other oxygen transfer parameters of this new reactor has been performed to date. Therefore, this paper aims to analyse local gas-liquid dynamics and evaluate the oxygen transfer performance in MALR compared to regular reactors using clean water as a liquid phase. Air bubble distribution was employed in terms of bubble diameter, rising velocity, and interfacial area. Slanted baffles maintained the bubble size between 3.88 and 4.63 mm for the studied superficial gas velocity (Ug), which is smaller than that in airlift reactor (ALR) by approximately 0.2 mm. Bubble rising velocity (UB) is relatively increased with Ug, regardless of reactor classes. New reactor could extend the bubble residence in the water by lengthening the bubble stream path of the slanted baffles leading to decrease UB values about 39% and 52% compared to bubble column reactor (BCR) and ALR, respectively. These performances consequently resulted in an interfacial area almost two times higher than in regular reactors. Oxygen transfer improved in MALR with an extra amount of oxygen transfer efficiency of 1.57% and 0.63% over BCR and ALR, respectively. This resulted in the highest aeration efficiency (AE) compared to other examined reactors, following a trendline expression of AE ˜ 0.046 Ug−0.6. Insertion of slanted baffles produced 5% and 12.8% more dead zone volume than ALR and BCR, respectively. In conclusion, MALR can significantly enhance oxygen transfer performance due to the ability to maintain bubble size and extend the gas-liquid transfer period.

Numerical Investigation on the Hydraulic Properties of the Skimming Flow over Pooled Stepped Spillway

Pooled stepped spillway is known for high aeration efficiency and energy dissipation, but the understanding for the effects of pool weir configuration on the flow properties and energy loss is relatively limited, so RNG k − ε εturbulence model with VOF method was employed to simulate the hydraulic characteristics of the stepped spillways with four types of pool weirs. The calculated results suggested the flow in the stepped spillway with staggered configuration of` two-sided pooled and central pooled steps (TP-CP) was highly three dimensional and created more flow instabilities and vortex structures, leading to 1.5 times higher energy dissipation rate than the fully pooled configuration (FP-FP). In FP-FP configuration, the stepped spillway with fully pooled and two-sided pooled steps (FP-TP) and the spillway with fully pooled and central pooled steps (FP-CP), the pressure on the horizontal step surfaces presented U-shaped variation, and TP-CP showed the greatest pressure fluctuation. For FP-TP and FP-CP, the vortex development in the transverse direction presented the opposite phenomenon, and the maximum vortex intensity in TP-CP occurred at Z/W = 0.25, while FP-FP illustrated no significant change in the transverse direction. The overlaying flow velocity distribution in the spanwise direction demonstrated no obvious difference among FP-FP, FP-TP, and FP-CP, while the velocity in TP-CP increased from the axial plane to the sidewalls, but the maximum velocity for all cases were approximately the same.

The Effect of Shape and Arrangement of End Sill Stepped Cascade Weirs on Water Quality

Hydraulic structures can be accepted as the key components in improving aeration efficiency because of the strong turbulent mixing associated with substantial air bubble entrainment at these structures. Different hydraulic structures have been designed to enhance aeration such as stepped cascades. A laboratory model of stepped cascade weir with five different shapes of end sill (normal, triangle, rectangle1, rectangle2 and rectangle3) have been installed at Al- Mustansiriya University, College of Engineering to evaluate treatment system and reduced pollutants in marginal water for different flow rates (35,60 and 80 L/min). Results indicate that high removal efficiency of all pollutants parameter (Cu, Cr, Mo, Br, Fe, Mn, Zn, PO4, Cl-, ClO2, Hardness as CaCO3, NH3, NO2, Toxic matter) is for rectangle1 shape at Q=60L/min. High aeration efficiency is 45.7% for rectangle1 shape at Q=80L/min. High removal efficiency for BOD5 and COD are 48% and 47% respectively for rectangle 1 at Q=80 L/min.

Hydraulic Structures in Water Aeration Processes

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. This paper reviewed the literature on hydraulic structures used in water aeration processes. The hydraulic structures were divided into two groups as the high-head flow systems and the free-surface flow systems. The high-head flow systems were circular and venturi nozzles, pipe with venturi tube, and high-head conduit, and the free-surface flow systems were weir, stepped cascade, and free-surface conduit. Air/water flow ratio and aeration efficiency in circular nozzles with air holes and venturi nozzles were significantly high. Pipes with venturi tubes showed high aeration efficiency although they had low air/water flow ratio. In high-head and free-surface conduits, almost full oxygen transfer, up to the saturation value, occurred. Forty-five degrees triangular sharp-crested weir had significantly better air/water flow ratio and aeration efficiency than other sharp-crested weir shapes. Stepped cascades, in particular nappe flow regime, were very efficient means of aeration.

Aerobic thermophilic treatment of sewage sludge at pilot plant scale. 2. Technical solutions and process design

The performance of the ATS process depends essentially on the oxygen transfer efficiency. Improvement of the mass transfer capacity of a bioreactor allowed to reduce the incubation time necessary to attain sludge stabilization. It is important to use equipment with a high aeration efficiency such as an injector aeration system. The ratio between the total oxygen consumption and the organic matter degradation (ΔCOD) ranged between 0.4 and 0.8 in the pilot plant, whereas 1.23 was found in completely mixed bioreactors (Bomio, 1990). No significant improvement of the bacterial degradation efficiency was attained with a specific power input exceeding 6–8 kW m −3. A mean residence time of less than 1 d allowed organic matter removals up to 40% with specific power consumption of 10 kWh kg −1 COD oxidized. The sludge hygienization is one of the objectives and benefits of the thermophilic treatment: not only temperature but also the total solids content were important factors affecting inactivation of pathogens. The inactivation rate was promoted by the increase of temperature, while the residual colony forming units decreased with reducing the total solids content of sewage sludge. It is concluded that continuous operation mode would not affect the quality of the hygienization but could display the high degradation potential of the aerobic system.

Effect of oxygen on ethanol production by a recombinant ethanologenic E. coli.

Escherichia coli strain B, bearing the pet plasmid pLO1297, and the wild-type culture, lacking the plasmid, responded to aeration of the complex medium by an approximate three- and fourfold increase in both growth rate and growth yield with glucose and xylose, respectively. At a relatively low oxygen transfer rate (8 mmol O2/L/h), the sugar-to-ethanol conversion efficiency exhibited by the recombinant strain decreased 40% and 30% for glucose and xylose, respectively. At a high aeration efficiency (100 mmol O2/L/h), the ethanol yield with respect to xylose was 0.15 g/g for the recombinant and 0.25 g/g for the culture lacking the plasmid. These observations suggest that oxygen reduces the ethanologenic efficiency of recombinant E. coli by diverting carbon to growth and end products other than ethanol. Previous observations, by others, on the effect of oxygen on ethanologenic recombinant E. coli were made with different strains bearing different plasmids. In addition to the possibility of strain and plasmid specificity, the results of this study suggest that previous conclusions were influenced by the particular environmental conditions imposed on the culture, including poor aeration efficiency and lack of pH control.