Cleaning and liquid contact with solids – Processes – Using sequentially applied treating agents
Reexamination Certificate
1999-03-19
2001-08-21
Gray, Linda (Department: 1734)
Cleaning and liquid contact with solids
Processes
Using sequentially applied treating agents
C134S002000, C134S003000, C134S026000, C134S029000, C134S041000, C134S076000, C210S636000, C210S791000, C210S321690
Reexamination Certificate
active
06277209
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to techniques for regenerating filtration membrane cartridges used in solid-liquid separators for high-concentration activated sludge and, in particular, to method and apparatus of regenerating filtration membrane cartridges for activated sludge with which filtration membrane cartridges employing filtration membranes composed of an organic flat membrane are readily regenerated at low cost.
BACKGROUND OF THE INVENTION
In activated sludge treatment facilities to perform solid-liquid separation of high-concentration activated sludge, an air diffuser disposed in a tankblows out aeration air to supply oxygen to activated sludge in the tank and the organic matter and nitrogen in raw water is treated with the activated sludge, and a mixed liquor in the tank, which is a mixture of water treated and the activated sludge, is subjected to solid-liquid separation by a membrane separator immersed in an aeration tank.
The above membrane separator has a plurality of filtration membrane cartridges and filters a mixed liquid by using a head within the tank as a driving pressure. The air diffuser is disposed beneath the membrane separator and blows out aeration air upwardly. Updraft caused by air lift action of the bubbles of the aeration air flows along the membrane surfaces of filtration membrane cartridges to clean these membrane surfaces. This cleaning suppresses a reduction in the separation function of the filtration membrane cartridges, thereby preventing the membrane separator from resulting in malfunction.
In the above filtration membrane cartridge, a filtration membrane composed of an organic flat membrane, such as ultrafiltration membrane or microfiltration membrane, is provided on the surface of a filter plate and the periphery of the filtration membrane is secured to the filter plate by welding. Its lifetime is generally between two and five years. When this filtration membrane cartridge is put into service, however, its periphery is flapped by updraft to deteriorate the strength of a welded part, which may result in a shorter lifetime than the normal lifetime as described. On the other hand, filtration membranes used in the filtration membrane cartridges are prepared by coating an organic macromolecular membrane material on both sides of a non-woven fabric serving as a substrate. Since such filtration membranes have durability, little or no breakage takes place, however, contamination due to activated sludge progresses with age, leading to a reduction in flux.
Accordingly, it is a primary object of the invention to provide method and apparatus of regenerating filtration membrane cartridges for activated sludge which effect recovery of the filtration function of contaminated filtration membrane cartridges, remedy of broken parts, and replacement of filtration membranes, with ease and at low cost.
DISCLOSURE OF THE INVENTION
A method of regenerating a filtration membrane cartridge for activated sludge according to the invention, the filtration membrane cartridge being used in solid-liquid separation for activated sludge and prepared by covering the surface of a filter plate with a filtration membrane made of an organic flat membrane, comprises subjecting the filtration membrane cartridge to the steps in the order named: cleaning with sodium hypochlorite; rinsing with water; cleaning with oxalic acid; and giving hydrophilic property with a hydrophilic agent.
In the step of cleaning with sodium hypochlorite, the filtration membrane cartridge is immersed in a washing tank storing a solution of sodium hypochlorite, to decompose and remove organic contaminants clogging the pores of the filtration membrane by oxidation of the sodium hypochlorite.
In the step of rinsing with water, the filtration cartridge is immersed in a washing tank storing a rinsing water, to wash away the sodium hypochlorite attached to the filtration membrane with the rinsing water. This prevents sodium hypochlorite and oxalic acid from reacting with each other to evolve chlorine gas.
In the step of cleaning with oxalic acid, the filtration membrane cartridge is immersed in a washing tank storing a solution of oxalic acid, to clean and remove the ferrous substances attached to the filtration membrane with the oxalic acid.
In the step of giving hydrophilic property with a hydrophilic agent, the filtration membrane cartridge is immersed in a washing tank storing a solution of saccharide, as an example of hydrophilic agents, thereby applying the hydrophilic agent to the filtration membrane in preparation for dry lay-up.
According to one preferred embodiment, the filtration membrane cartridge is subjected to washing with water or a hydrophilic agent prior to the step of washing with sodium hypochlorite. That is, the filtration membrane cartridge is immersed in a washing tank storing a solution of water or a hydrophilic agent, to clean and remove the activated sludge attached to the filtration membrane with the water or hydrophilic agent.
According to other preferred embodiment, the filtration membrane cartridge is subjected to washing with sodium hypochlorite, followed by washing with caustic soda. When the filtration membrane cartridges is used in a drainage containing a considerable amount of aluminum composition, they are immersed in a washing tank storing a solution of caustic soda, to decompose and remove a difficultly soluble alumina attached to the external surface and pores of the filtration membrane by the caustic soda.
According to other preferred embodiment, the filtration membrane cartridge is subjected to washing with oxalic acid, followed by washing with hydrochloric acid. When Ca composition in drainage is attached to the filtration membrane cartridge in the form of a difficultly soluble CaCo
3
, the filtration membrane cartridge is immersed in a washing tank storing a solution of hydrochloric acid, to decompose and remove the CaCo
3
attached to the filtration membrane by the hydrochloric acid.
A method of regenerating filtration membrane cartridge for activated sludge according to the invention, the filtration membrane cartridge having a filtration membrane of an organic flat membrane which is disposed so as to cover the surface of a filter plate made of a resin, a welded part serving to seal which is formed along the periphery of the filtration membrane by securing the filtration membrane to the filter plate by welding with ultrasonic wave, and a region surrounded by the welded part which is defined as an effective filtration region, comprises the step of applying an adhesive agent to the periphery of the filtration membrane along the welded part, such as to bond the periphery of the filtration membrane to the filter plate by the adhesive agent.
This method is effective for the case where the damage to the filtration membrane cartridge is due to deterioration in the sealing property of the welded part which is caused by the filtration membrane coming off from the filter plate at a portion of the welded part. The presence of a bonding part between the filtration membrane and the filter plate, which is formed on both sides of the welded part by an adhesive agent, permits to remedy the sealing property in the periphery of the filtration membrane.
According to one preferred embodiment, an organic reinforcing filtration membrane of strip form is disposed along a welded part between a filtration membrane and a filter plate so as to cover the periphery of the filtration membrane, and an adhesive agent is applied to the reinforcing filtration membrane, whereby the filtration membrane and the reinforcing filtration membrane are integrally bonded to the filter plate by the adhesive agent.
This method is effective for the case where the damage to the filtration membrane cartridge is due to deterioration in the sealing property of the welded part which is caused by the filtration membrane being broken at a portion of the welded part. That is, the sealing property is remedied in such a manner that a reinforcing filtration membrane is secured by adhesive agent so a
Izumi Kiyoshi
Kubota Kenji
Nigara Yoshio
Yamada Yutaka
Gray Linda
Kubota Corporation
Tung & Associates
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