Patent Application
20060049092
1. Field of the Invention
This invention relates to a membrane bioreactor, more particularly to a membrane bioreactor that includes a porous pre-filtering element, a membrane module and a turbulent flow-forming unit.
2. Description of the Related Art
Up to now, secondary treatment of municipal wastewater is commonly conducted by activated sludge treatment (AST). Although the conventional AST has been utilized for many years, it requires control of sludge concentration and relatively large space for separation of suspended solids, and has drawbacks including a slow reaction rate and unstable quality of permeate after treatment. In addition, the conventional AST is uneconomical because expensive landfill is required to dispose the sludge produced therefrom.
Recently, membrane bioreactor (MBR) has superseded the conventional AST in wastewater secondary treatment. The membrane bioreactor combines bio-treatment techniques and membrane separation techniques, and includes a bio-membrane module, which is classified into external type and internal type, in a reaction tank of the conventional AST. Particularly, wastewater contacts micro-organisms that exist in the sludge in the reaction tank so as to conduct a decomposition reaction. The mixture obtained after the decomposition reaction is driven by a sufficient differential pressure so as to pass through a biomembrane of the biomembrane module. The water thus treated is discharged from the biomembrane module, and the sludge thus formed is left in the react-ion tank. The membrane bioreactor functions to decompose organic materials and to separate the sludge from the treated water. As such, the membrane bioreactor can be used as a substitute for the secondary sedimentation and the gravity sedimentation in the conventional AST.
The membrane bioreactor is suitable for treating sludge with a high concentration range, achieving an effective solid-liquid separation, and minimizing the reaction tank volume and the amount of sludge formed in the reaction tank. Thus, the problem encountered in the conventional activated sludge treatment, i.e. the quality of discharging water cannot be further improved, can be solved by using the membrane bioreactor so as to meet stringent environmental requirements for discharging water. A variety of commercial membrane bioreactors have been developed since 1980, such as hollow fiber membranes adopted by ZENON company, Canada, which have a relatively large interceptive surface area per unit volume, and flat sheet membranes adopted by KUBOTA company, Japan.
In view of the foregoing, current hollow fiber membranes or flat sheet membranes still have the following drawbacks, which mandate further improvement:
1. Membranes tend to get fouled because of adhesion of a mass of microorganisms and phlegmatic materials.
2. Maintenance cost is high. Since the membranes have a tendency to get fouled, more membrane modules are required to increase the surface area of the membranes so as to increase wastewater flux through the membranes.
3. Cleaning of the membranes, such as the hollow fiber membranes, is laborious.
In addition, the membrane bioreactor can be classified into two major types pursuant to disposition, i.e. the external type (or the branched type) and the internal type (or the submerged type) As shown in
In practice, the external type membrane bioreactor 1 occupies a relatively large space, and consumes a large amount of energy due to the use of positive differential pressure and cross-flow operation. In addition, the membrane module 102 is required to be cleaned frequently because the membrane is susceptible to fouling under a relatively high flux of wastewater. Thus, the operational cost is relatively high. On the other hand, the internal type membrane bioreactor 2 is space-saving because the membrane module 202 is submerged in the reaction tank 201, and is energy-saving because the membrane of the membrane module 202 has a relatively large surface area. However, the wastewater flux of the membrane module 202 is relatively low as compared to that of the external type membrane module 1. Besides, the membrane module 202 cannot be cleaned conveniently because the membrane module 202 is required to be removed from the membrane bioreactor 2. Apparently, the external type and the internal type membrane bioreactors 1, 2 both have their own disadvantages that require further improvement. The focus of current research for improving the membrane bioreactor is on how to increase the wastewater flux. However, these improvements normally result in a high operation cost. Therefore, there is a need in the art to provide an apparatus capable of minimizing membrane fouling under a high wastewater flux so as to prolong the service life of the membrane module.
According to one aspect of the present invention, a membrane bioreactor includes: a tank adapted to receive wastewater therein; a porous pre-filtering element mounted in the tank for conducting a primary filtration of the wastewater; a membrane module mounted in the tank and disposed downstream of the porous pre-filtering element for conducting a secondary filtration of the wastewater pretreated by the porous pre-filtering element, the membrane module cooperating with the porous pre-filtering element to define a compartment therebetween for receiving the wastewater pretreated by the porous pre-filtering element; and a turbulent flow-forming unit associated with the compartment for generating turbulent flow in the compartment.
According to another aspect of the present invention, a membrane bioreactor includes a porous pre-filtering unit adapted to receive wastewater for conducting a primary filtration of the wastewater; a membrane filtering unit disposed downstream of the porous pre-filtering unit for conducting a secondary filtration of the wastewater pretreated by the porous pre-filtering unit, the membrane filtering unit including first and second membrane modules that cooperatively define a compartment therebetween for receiving the wastewater pretreated by the porous pre-filtering unit; and a turbulent flow-forming unit associated with the compartment for generating turbulent flow in the compartment.
Other features and advantages of the present invention will become apparent in the following detailed description of the preferred embodiments of the invention, with reference to the accompanying drawings. In the drawings:
Referring to
The tank 10 defines an inner space 11 therein, and has a bottom wall 12. The inner space 11 is adapted to receive wastewater, and is divided into first and second compartments 111, 112 that are in fluid communication with each other. In the first compartment 111, suspended solids in the wastewater are removed. The detailed descriptions regarding the operations conducted in the first compartment 111 are omitted herein since these are not pertinent to the technical features of the present invention and can be readily appreciated by those skilled in the art.
The porous pre-filtering element 20, the membrane module 30 and the turbulent flow-forming unit 40 are disposed in the second compartment 112. The primary filtration of the wastewater is conducted through the porous pre-filtering element 20. The membrane module 30 is disposed downstream of the porous pre-filtering element 20 for conducting a secondary filtration of the wastewater pretreated by the porous pre-filtering element 20. The membrane module 30 cooperates with the porous pre-filtering element 20 to define a third compartment 113 therebetween for receiving the wastewater pretreated by the porous pre-filtering element 20. The turbulent flow-forming unit 40 is associated with the third compartment 113 for generating turbulent flow in the third compartment 113. In this embodiment, the turbulent flow-forming unit 40 is disposed in the third compartment 113.
The bottom wall 12 of the tank 10 is formed with an inlet 121 under the turbulent flow-forming unit 40, and an outlet 122 in fluid communication with the membrane module 30.
Preferably, the porous pre-filtering element 20 is mounted removably in the second compartment 112 of the tank 10, and has a plurality of pores 21. The porous pre-filtering element 20 may be made from a material selected from the group consisting of sponge and non-woven fabric materials. Preferably, the pores 21 of the porous pre-filtering element 20 have a pore size ranging from 50 μm to 500 μm.
The membrane module 30 includes an outer porous membrane 31 that permits growth of microorganisms thereon, and an inner supporting mesh 32 that is enclosed by the outer porous membrane 31. The outer porous membrane 31 has a plurality of pores 33. Preferably, the outer porous membrane 31 is an ultra-filtration membrane made from polyvinylidene fluoride (PVDF). The pores 33 of the outer porous membrane 31 preferably have a pore size smaller than that of the pores 21 of the porous pre-filtering element 20. Preferably, the pore size of the pores 33 of the outer porous membrane 31 ranges from 0.01 to 0.4 μm. The membrane module 30 has an outlet 34 connected to the outlet 122 of the bottom wall 12 of the tank 10 so as to discharge the wastewater after treatment.
As shown in
The supporting frame of the turbulent flow-forming unit 40 further includes a bottom plate that is formed with bottom holes 43 that are registered with the inlet 121 of the bottom wall 12 of the tank 10. The turbulent flow-forming unit 40 further includes a gas-supplying member for supplying gas into the third compartment 113 through the inlet 121 of the tank 10 and the bottom holes 43 in the bottom plate of the supporting frame. The baffles 42 of the flow-dividing member are arranged in such a manner to permit the gas supplied into the third compartment 113 to flow in a meandering manner along the vertical direction.
Referring to
The porous pre-filtering unit includes a filtering tank 10′ that defines an inner space 11′ therein. A porous pre-filtering element 20, which has a structure similar to that of the porous pre-filtering element 20 shown in
The membrane filtering unit 50 includes a membrane tank 51 and first and second membrane modules 52 that are disposed in the membrane tank 51 and that cooperatively define a third compartment 113′ therebetween for receiving the wastewater pretreated by the porous pre-filtering element 20, and a turbulent flow-forming unit 53 associated with the third compartment 113′ for generating turbulent flow in the third compartment 113′. In this embodiment, the turbulent flow-forming unit 53 is disposed in the third compartment 113′.
The membrane tank 51 has an inlet 511 for receiving the wastewater pretreated by the porous pre-filtering unit and stored in the second compartment 112′, and two outlets 512. Each of the first and second membrane modules 52 has a discharging outlet 524 that is registered and that is in fluid communication with a respective one of the outlets 512 of the membrane tank 51 so as to permit discharging of the wastewater therefrom.
The turbulent flow-forming unit 53 includes a flow-dividing member that is mounted in the third compartment 113′ in the membrane tank 51. The flow-dividing member has a structure similar to that of the flow-dividing member of the turbulent flow-forming unit 40 shown in
Each of the first and second membrane modules 52 has a structure similar to that of the membrane module 30 shown in
Referring to
Preferably, in this embodiment, each of the baffles 42 has a V-shaped cross-section.
In view of the foregoing, the suspended solids having a relatively large particle size in the wastewater are removed by passing through the porous pre-filtering element 20. Then, the pretreated wastewater flows into the third compartment 113 (113′), and is subsequently pumped out of the membrane bioreactor. Strong turbulent flow is generated in the third compartment 113 (113′) by virtue of the turbulent flow-forming unit 40 (52), and acts on the outer porous membrane 31 (521) so as to minimize fouling of the membrane module 30 (52). Therefore, the cleaning frequency of the membrane module 30 (52) is significantly decreased, and the operational life of the membrane module 30 (52) is prolonged.
In addition, in the first and third embodiments, the wastewater turbulent flow formed in the compartment 113 also acts on the porous pre-filtering element 20 so as to avoid fouling of the porous pre-filtering element 20. Therefore, the cleaning frequency of the porous pre-filtering element 20 is also decreased, and the operational life of the porous pre-filtering element 20 is prolonged. Furthermore, the porous pre-filtering element 20 is made from inexpensive materials, such as sponge or non-woven fabric materials, and can be replaced periodically.
While the present invention has been described in connection with what is considered the most practical and preferred embodiments, it is understood that this invention is not limited to the disclosed embodiments but is intended to cover various arrangements included within the spirit and scope of the broadest interpretations and equivalent arrangements.
