Akira Ohkawa

Permeation of wet CO2/CH4 mixed gas through a liquid membrane supported on surface of a hydrophobic microporous membrane

A double-layer liquid membrane was proposed where a supported liquid membrane of diglycolamine (DGA) or triethylene glycol (TEG) was supported on the surface of another microporus membrane, a Durapel membrane(Millipore), by its hydrophobicity. This surface supported liquid membrane was used for the separation of CO2 from a wet CO2/CH4 mixed gas. The liquid membrane of this construction is durable up to a transmembrane pressure of 250 kPa. That is, the liquid membrane is applicable for the vacuum mode permeation and pressurized permeation mode. Permeation experiments through the DGA liquid membrane with a 25 μm thickness shows that the CO2 permeability was 30–100 Barrer with a CO2/CH4 separation factor of 40–100. The CO2 permeability was comparable to polymer membranes. The partial pressure dependency of the CO2 permeability may imply the existence of facilitated transport during the vacuum mode permeation. A comparison of the dry feed and wet feed experiments using the TEG liquid membrane showed that there was no large effect of the water vapor in the feed on the selectivity and permeabilities.

Some flow characteristics of a vertical liquid jet system having downcomers

Abstract The flow characteristics and performance of a vertical liquid jet system having downcomers in an air-water system have been studied in relation to those having no downcomer. In order to obtain the basic data which are necessary for comparing the characteristics between the two systems with and without the downcomer, flow characteristics such as the bubble penetration depth and the gas entrainment rate which change depending on variables such as the nozzle diameter, the jet velocity and the nozzle height were first investigated experimentally. After evaluating the effects of these operating variables on such flow characteristics, empirical equations which may be used to predict the bubble penetration depth and the gas entrainment rate over the range of conditions tested in this ordinary liquid jet system were obtained. For the jet system having the downcomer, the effects of operating variables such as the nozzle diameter, the jet velocity, the downcomer diameter and height, etc. on the flow behaviour or on flow characteristics such as the bubble penetration depth, the gas entrainment rate, the gas holdup, etc. were then investigated, and the empirical correlations useful for predicting the boundary of flow regions, the gas entrainment rate, the gas holdup, etc. in this downcomer device were also presented. Furthermore, a comparison of flow characteristics such as the bubble penetration depth and the gas entrainment rate, which are the factors of importance as indices to evaluate the performance of plunging jet systems, between the two liquid jet systems with and without the downcomer was carried out, based on the results obtained above. As a result, it was ascertained that inserting a downcomer of small size in the gas entrainment region has the effect of markedly increasing the penetration depth of the entrained bubbles compared to that under corresponding conditions in the ordinary liquid jet system having no downcomer without any anxiety over a decrease in performance of gas entrainment and it also produces a much longer gas-liquid contacting section.

Separation of propylene/propane mixture by a supported liquid membrane containing triethylene glycol and a silver salt

Abstract A double-layer liquid membrane was used for the separation of propylene/propane mixed gas. The double-layer membrane was constructed such that a supported liquid membrane consisting of a hydrophilic and non-volatile liquid was supported on the surface of another hydrophobic microporous membrane. This construction enabled the liquid membrane to be used in the permeation mode of vacuum pressure on the permeate side. In the experiment, the feed gas was saturated by water vapor in order to swell the liquid membrane and ionize the silver salt in it. A liquid membrane of a triethylene glycol (TEG) and silver salt, AgBF4, mixture showed selective permeation for propylene. The silver salt acts as facilitating agent of the olefin in the triethylene glycol liquid membrane. Water vapor in the process enhanced the permeation rate and separation factor of the liquid membrane.

Effect of gas sparger type on operational characteristics of a bubble column under mechanical foam control

The effects of gas sparger types on the operational characteristics of a bubble column (BC) with a rotating-disk mechanical foam-breaker (MFRD), such as foam-breaking, foaming, flow and mass transfer characteristics, were studied. The required critical disk rotational speed, N c , and liquid hold-up in the foam, Φ L , reflected the foam-breaking behaviour of the MFRD and the foaming behaviour of the BC respectively, which changed depending on the gas sparger type. The dependence of the gas sparger type on the gas hold-up, e g , was similar to that observed for the volumetric mass transfer coefficient, k L a. A comparative investigation of k L a with various gas spargers, in terms of the specific power input, also demonstrated the usefulness of the porous sintered glass bead filter as a gas sparger.

Simultaneous removal of carbonaceous and nitrogenous pollutants by a plunging liquid jet bioreactor with crossflow filtration operated under intermittent aeration

Abstract Simultaneous removal of total organic carbon (TOC) and nitrogen (T-N) by a plunging liquid jet bioreactor was investigated for small-scale treatment of domestic wastewater. The bioreactor was operated under suspended growth and attached growth conditions and intermittent aeration to carry out both nitrification and denitrification processes in one vessel. In the suspended growth system, TOC removal efficiency was about 90% but nitrogen removal was about 50%. The nitrogen removal was not sufficient because nitrification was a rate-limiting step. To overcome this limitation, a biomass carrier was inserted in the reactor. In the attached growth system, nitrification proceeded almost completely and, hence, nitrogen removal was increased. TOC and nitrogen removal efficiency was 97% (effluent TOC concentration was about 3·0 mg/l) and 84% (effluent T-N concentration was about 2·0 mg/l) in the oxic periods, respectively, and those were 93% (TOC concentration was about 5·5 mg/l) and 90% (T-N concentration was about 1·2 mg/l) in the anoxic periods. This effluent T-N concentration satisfies the severest target value for T-N discharge concentration in small-scale domestic wastewater treatment in Japan. The bioreactor system with the biomass carrier operated under intermittent aeration was judged to be excellent for simultaneous removal of TOC and nitrogen in small-scale treatment of domestic wastewater.

Activated sludge treatment of small-scale wastewater by a plunging liquid jet bioreactor with cross-flow filtration

Abstract A new energy-saving membrane bioreactor was developed and applied to biological treatment of wastewater. The reactor used air entrainment by a plunging liquid jet for aeration and membrane filtration for solid-liquid separation. The major feature of the bioreactor was that the membrane module was incorporated into the liquid circulation line for the formation of the liquid jet so that the operations of aeration and membrane separation could both be accomplished using only one pump. Air entrainment and oxygen transfer characteristics of the reactor were investigated. Wastewater treatment by the bioreactor was carried out successfully with the TOC removal efficiency above 97%. The TOC removal efficiency of the cake layer deposit on the ceramic microfilter was comparable to that of the suspended microorganisms in the aeration tank. The role of the cake layer was evaluated in terms of facility of operation. The results obtained show that the bioreactor system has considerable potential for the biological treatment of small-scale agricultural or domestic wastewater discharged in rural or sparsely populated areas.

LIQUID FLOW IN IMPELLER REGION OF AN UNBAFFLED AGITATED VESSEL WITH UNSTEADILY FORWARD-REVERSE ROTATING IMPELLER

For an unbaffled agitated vessel with an unsteadily forward-reverse rotating impeller whose rotation proceeds with repeated acceleration, deceleration, and stop-reverse processes, the liquid flow in the impeller region was studied based on photographs showing path lines of tracer particles. An image series taken during one cycle of the forward-reverse rotation was analyzed to characterize the internal stream inside the impeller rotational region and the discharge stream outside its region when a disk turbine impeller with six flat blades was rotated unsteadily. Because of the unsteady flow generated inside the impeller rotational region, the velocity vector of outflow from its region fluctuated periodically with the change of the impeller rotation rate. The circumferential velocity was almost in phase with the impeller rotation rate, oscillating periodically. The radial velocity exhibited larger values in the process for the impeller from decelerating to stopping and reversal. The radial flow, whose velocity decreased downstream outside the impeller rotational region, was clarified to be transformed into upward and downward axial flows that are almost uniform in the circumferential direction throughout the region near the vessel wall.

Ethanol production by encapsulated and immobilized yeast

Immobilized yeast was encapsulated with cell-free calciumalginate gel by two-step preparation procedure. The volume of coated film decreased with increasing cell concentration. The encapsulation did not affect ethanol production and could prevent cell leakage from the gels.

Relation between mechanical foam-breaking difficulty and the foaming characteristics of solutions

Abstract Using a small foaming apparatus, liquid foaming characteristics such as liquid holdup in foamate flow ( φ t ), rate of liquid drainage from foam (ν), foam velocity ( u f ) and foam size ( d f ) were examined for various liquids. A parameter φ f , incorporating φ t , ν and u f , was obtained. The relationship among φ f , d f and the liquid holdup in foam, φ b , in the actual gas-bubbling systems under foam control was expressed in the form of φ b ∞ φ f d f 1.83 , regardless of the type of foaming liquid or its concentration. This relationship was useful for the prediction of φ b as related to mechanical foam-breaking difficulty.

Performance evaluation of a plunging liquid jet bioreactor with crossflow filtration for small-scale treatment of domestic wastewater

Abstract Activated sludge treatment of wastewater was successfully carried out by a plunging liquid jet bioreactor with crossflow filtration. The TOC removal efficiency was above 95% in the continuous treatment in which influent BOD concentration was increased in steps from 150 to 1200 g/m 3 . Removal function of cake layer largely contributed to the overall treatment performance and stability of the bioreactor system. Cake layer was found to act as a dynamically formed ultrafiltration membrane. The observed rejection of poly(ethylene glycol) having a molecular weight of 20 000 by the cake layer was about 40%. The removal function of cake layer was explained by both biodegradation in and solute rejection by the cake layer. The rejection by the cake layer played a major role in the removal function of cake layer. Performance of the bioreactor system was simulated based on a mathematical model. A case study for the treatment of small-scale gray-water was carried out using the model. The required working volume was reduced to about one half compared to that of the conventional activated sludge process when the cake layer had an observed rejection of only 20%. The cake layer also contributed to treatment performance and operation. Design and operational considerations were also discussed. It was concluded that the bioreactor system has a high potential for small-scale treatment of domestic wastewater.