Conventional Aeration System Research Articles

Utilização de um gerador de bolhas ultrafinas para oxigenação de tanques de criação de tilápia do Nilo (Oreochromis niloticus) em sistema de recirculação

The objective of this work was to evaluate the use of an ultrafine bubble generator of own manufacture for oxygenation of Nile tilapia (Oreochromis niloticus) breeding tanks in a recirculating water system. The research was divided into two steps: 1) oxygen saturation test; 2) application of ultrafine bubble production technology for the breeding of Nile tilapia. In the first step, the water of a 2.0 m3 test tank was completely deoxygenated and the ultrafine bubble generator was turned on for 60 min. In the second step, the generator was connected to the water recirculating system for breeding of Nile tilapia to compare the overall performance of this system with other under conventional aeration system. The ultrafine bubble generator could reach 100% oxygen saturation in the test tank (27.8 °C) in approximately 21 min and, at the end of 60 min, the concentration was 21.8 mg L-1 (277.52% saturation). The results showed significant difference (p<0.05) between the mean dissolved oxygen concentration in the treatment with ultrafine bubbles (9.80 ± 3.68 mg L-1) and the treatment with conventional aeration (3.47 ± 0.88 mg L-1). No significant difference (p>0.05) was found for the zootechnical performance parameters evaluated. The conclusion was that the ultrafine bubble generator is more efficient to maintain a high dissolved oxygen concentration in the recirculating water in Nile tilapia breeding tanks than the conventional aeration system.

Simultaneous Stripping of Ammonia from Leachate: Experimental Insights and Key Microbial Players

Air stripping is commonly used to remove the ammonia in multistage treatment systems for municipal landfill leachate (LFL). This paper proposes a novel approach combining the process of stripping with biological removal of ammonia, based on simultaneous nitrification and denitrification (SND) in a single hybrid sequencing batch reactor (HSBR). To avoid the accumulation of free ammonia (N-FAN), the shallow aeration system was used for the treatment of raw LFL with N-TAN level of 1520 mg/L and pH 9.24. The mean N-FAN removal efficiency of 69% with the reaction rate of 55 mg L−1 h−1 and mean ammonium (N-NH4+) removal efficiency of 84% with the reaction rate of 44 mg L−1 h−1 were achieved within a month in such an HSBR (R1). The comparative HSBR (R2), with conventional aeration system maintaining the same concentration of dissolved oxygen (DO ≤ 1 mg/L), was removing only trace amounts of N-FAN and 48% of N-NH4+. The quantitative analysis of 16S rRNA genes indicated that the number of total bacteria, Actinobacteria, Bacteroidetes, Firmicutes, and Beta- and Gammaproteobacteria increased during the operation of both HSBRs, but was always higher in R1. Moreover, the bacterial community shift was observed since the beginning of the experiment; the relative abundance of Firmicutes, and Beta- and Gammaproteobacteria increased by 5.01, 3.25 and 9.67% respectively, whilst the abundance of Bacteroidetes and Actinobacteria decreased by 15.59 and 0.95%. All of the surveyed bacteria groups, except Gammaproteobacteria, correlated significantly negatively (p < 0.001) with the concentrations of N-NH4+ in the outflows from R1. The results allow us to suppose that simultaneous stripping and SND in a single reactor could be a promising, cost-effective and easy-to-operate solution for LFL treatment.

Study of Liquid Film Forming Apparatus (LFFA) Mechanisms in Terms of Oxygen Transfer and Bubble Hydrodynamic Parameters

Aeration system is extensively applied in aquaculture and waste water treatment. It provides oxygen for organism living and mixing while consumes colossal amounts of energy for operating. Hence, the improvement of aeration system is not only providing enough oxygen and mixing but also concerning to the energy saving. Liquid film forming apparatus (LFFA) is a simple equipment that itself does not consume any power. It can be installed in existing conventional aeration system without large-scale retrofitting. Laboratory scale experiment were performed in a 190-litre aeration tank. The different types of air diffuser providing different bubble aspects were installed at the bottom of the aeration tank as the conventional diffused aeration systems. The volumetric mass transfer coefficient (k_L a) of the aeration systems with LFFA are higher than the conventional systems notably. The mechanism of oxygen transfer in LFFA system can be summarized into 4 patterns: 1) Conventional mechanism, 2) Bubble collection mechanism, 3) Bubble recirculation mechanism and 4) Bubble-Liquid Foam mechanism. Then, the interfacial area (a) is improved comparing with the conventional diffused aeration system. The LFFA system should be operated with small bubble diameter generation ( 0.13 m/s) can be defined and provide a better understanding on oxygen transfer mechanism in LFFA system.

Effects of perfluorinated oxygen carrier application in yeast, fungi and plant cell suspension cultures

The growth of the yeast Saccharomyces cerevisiae, the fungus Rhizopus nigricans and Nicotiana tabacum cells with perfluorodecalin as an oxygen carrier has been studied. The volumetric mass transfer coefficient ( k L a) measured by the dynamic method was higher for the perfluorodecalin oxygenation system than for the conventional aeration system. The results show that perfluorocarbon can be successfully used as an efficient gas carrier, especially for the culture of delicate plant cells. The increase in yeast biomass in the suspension culture aerated by perfluorodecalin was as much as 110% higher than in the culture aerated by air. The fungus R. nigricans grew better when the conventional aeration system was used due to the fact that growth of the mycelium is limited by the transport of oxygen by diffusion in the pellets rather than by interfacial oxygen transport. In the case of isolated tobacco cells, an increase of over 350% in biomass growth was observed for the PFC aeration system.

Improvement of oxygen transfer efficiency in aerated ponds using liquid-film-assisted approach

In aerated ponds, oxygen is generally supplied through either diffused or mechanical aeration means. Surface transfer and bubble transfer both contribute significantly to oxygen transfer in a diffused aeration system. In the present study, a liquid-film-forming apparatus (LFFA) is successfully developed on a laboratory scale to improve considerably the surface transfer via the unique liquid film transfer technique. The experimental results show that the volumetric mass transfer coefficient for LFFA alone is found to be as much as 5.3 times higher than that for water surface and that the total volumetric mass transfer coefficient for the liquid film aeration system increases by 37% in comparison with a conventional aeration system. Additionally, by tuning finely the structural parameters of the LFFA, it can also lead to high dissolved oxygen (DO) water with the DO percent saturation greater than 90%. More importantly, this result is accomplished by simply offering a single-pass aeration at a depth as shallow as 26 cm. As a result, the objective of economical energy consumption in aerated ponds can be realized by lowering the aeration depth without sacrificing the aeration efficiency. It is noteworthy that the data presented in this study are acquired either numerically or experimentally.

Enhancement of Oxygen Transfer Efficiency in Diffused Aeration Systems using Liquid-Film-Forming Apparatus

Surface transfer and bubble transfer both contribute significantly to oxygen transfer in a diffused aeration system. In the present study, liquid-film-forming apparatus is successfully developed on a laboratory scale to improve considerably the surface transfer via the unique liquid film transfer technique. The experimental results show that the volumetric mass transfer coefficient for liquid-film-forming apparatus alone is found to be as much as 5.3 times higher than that for water surface and that the total volumetric mass transfer coefficient for liquid film aeration system increases by 37 % in comparison with conventional aeration system. Additionally, by tuning finely the structural parameters of the liquid-film-forming apparatus, it can also lead to high dissolved oxygen water with the dissolved oxygen percent saturation greater than 90 %. More importantly, this result is accomplished by simply offering a single-pass aeration at the depth as shallow as 26 cm. As a result, the objective of economical energy consumption in diffused aeration systems can be realized by lowering the aeration depth without sacrificing the aeration efficiency.

Development of High Efficient Oxygen Supply Method by Using Contacting Water-Liquid film with Air

Surface transfer and bubble transfer both contribute significantly to oxygen transfer in a conventional aeration system. However, bubble transfer plays the primary role of oxygen transfer. In the present study, the mere surface transfer is replaced by directly contacting liquid film designed elegantly with air. Liquid film aeration system is successfully developed on a laboratory scale. The experimental results from single-pass aeration mode show that the dissolved oxygen concentration in deoxygenate water reaches up to 95 % or higher, as compared with the saturation concentrations of the dissolved oxygen while using this novel aeration system. Meanwhile, an increase in oxygen mass transfer rate by 30% can be achieved in comparison with conventional aeration system. Moreover, the volumetric mass transfer coefficient for liquid film-forming apparatus (KLal) is found to be as much as 5 times higher than that for water surface in a conventional aeration test.

Development of a Water Purification System via Enhanced Aeration -1. Phenomenological Characteristics of the Aeration System.

River, lake and reservoir environments have been drastically deteriorated along with the economical and industrial developments of the country. The change of the human life style is also another important factor affecting on the pollution of water environments. One of the most effective and economical ways to conserve, improve and purify the water environment should be the enhancement of the dissolved oxygen concentration by aeration. An enhanced aeration system is developed to cope with low efficiency, scale-up difficulty and restricted versatility accompanied with conventional aeration systems. The developed aeration system utilises the centrifugal shear stress to generate an enormous number of fine air bubbles and to establish the high propagation performance of mixing energy. The pressure loss of the cyclone-like aerator is deduced from the dimensional analysis and experimental works, which serves to scale up the aeration system and to evaluate the energy consumption of the whole system. The performance of the aeration system is experimentally evaluated in terms of the maximum aeration rate and the dissolved oxygen transfer rate. The former is confirmed to take a remarkably higher value and the latter is expected to be much faster than those in conventional aeration systems.

Gas entrainment by plunging liquid jets

Abstract In this paper an extensive survey of the results of possibly all available experimental and theoretical studies on gas entrainment by plunging liquid jets has been presented. The following aspects of the phenomenon are thoroughly discussed: mechanisms, conditions of the onset of entrainment, amount of the entrained gas, characteristics of the resulting bubble dispersion (bubble size, depth of bubble penetration, gas holdup and bubble residence time) and mass transfer. Wherever possible, empirical correlations enabling estimation of the relevant quantities characterizing the entrainment phenomenon studied are given or recommended. Practical applications of the plunging jet aerator in waste treatment, fermentation and in the flotation industry are reviewed and its aeration (e.g. oxygenation) performance is compared with conventional aeration systems.

Application of gas permeable membranes for auxiliary oxygenation of sequencing batch reactors

In a Sequencing Batch Reactor (SBR) the substrate concentration is intended to increase during the fill phase to allow the heterotrophic bacteria to periodically enjoy maximum growth conditions. When growing at a maximum rate, however, the bacteria do also respire at a maximum rate, and it can be a problem, technically, to satisfy the oxygen demand thus generated. Use of conventional aeration systems to meet peak oxygen demands has proven unsatisfactory in some cases because of foam accumulation and volatilization of noxious substances.To satisfy the peak oxygen demand a membrane oxygenation system was developed and tested under field conditions. Silicone tubing was submerged in a Sequencing Batch Reactor, and loaded with pure oxygen whenever necessary. As demonstrated, oxygen penetrates through the wall of the tubing and contributes to a rapid increase of the oxygen concentration in the reactor. Long term experiments were conducted to study the applicability of this technique. Results are promising.

U-Tube Aeration Operating Characterization

A modification of U-Tube aeration, using low pressure air injection, was studied on a pilot scale. The pilot U-Tube system was made of four inch diameter pipe. Depths of 10 ft, 20 ft, 30 ft, and 40 ft were studied at flow rates up to about 300 gal per min. Air injection rates of 5%, 10%, 15%, and 20% at different depths were studied. The data were subjected to dimensional analysis and equations were derived for predicting prototype results. The effects of air injection depth, U-Tube depth and nominal water velocity on oxygen transfer economy were evaluated. The results show that water containing zero DO can be 100% saturated after one pass through a 40-ft deep U-Tube with 20% air injection. In the process of completely saturating water, the U-Tube oxygen transfer economy (#O 2 /HP-hr) is about the same as conventional aeration systems transferring oxygen to water with zero DO.