Liquid purification or separation – Processes – Including geographic feature
Patent
1996-02-09
1998-02-03
Nessler, Cynthia L.
Liquid purification or separation
Processes
Including geographic feature
210793, 210798, 210807, 210170, 210274, 210275, 210285, 210286, B01D 2410, B01D 3502
Patent
active
057140774
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
FIELD OF THE INVENTION
This invention relates to a liquid filtration system for industrial effluent discharges and particularly, though not exclusively, to a filtration system incorporated in a drain for a waste landfill sate.
A waste landfill site ma be defined as an excavated trench in which waste material is disposed and covered by the removed soil and by a suitable capping.
Leachate emanating from waste landfill site, or other effluent discharge requires discharging in a controlled manner. Known systems for draining the leachate, which is usually in the form of an aqueous suspension, include equipment such as pipes, valves and pumps for transporting the leachate away from the storage area, and they exhibit only finite lifetime.
Suitable filter material, are normally included in the drainage systems to restrict the maximum size of solid particles in the discharge of flowing through the system to prevent blockage of the drain. However, the filter material slowly becomes blocked by the particles removed from the discharge. Facilities for cleaning the filter may be provided, most commonly by backwashing or by other mechanical means. Such filter cleaning methods require action by an operator to instigate and control the filter cleaning procedure.
It is obviously a disadvantage of the above-mentioned systems that a large amount of maintenance is required to ensure that efficient filtration and drainage of the discharge can be effected over a long period of time.
SUMMARY OF THE INVENTION
According to the invention in a first aspect we provide a method of filtering a liquid suspension, said method comprising the steps of passing the liquid suspension through a granular filter material so as to remove solid particles from said suspension to produce a filtrate, halting the flow of liquid suspension through the filter material thereby relieving the pressure in the system and facilitating particulate matter to settle down the filter, and causing a reverse flow of the filtrate through the filter material, whereby said particles retained by the filter material are further encouraged to settle to a lower region thereof.
Prior to the step of causing a reverse flow of the filtrate, an airstream may be passed though the filter material so as to agitate the filter material granules, thereby facilitating further settlement of the filtered particles.
The liquid suspension ma comprise a discharge or seepage from a landfill site for storage, burial or disposal of waste material. The waste material may include hazardous material such as toxid or radioactive waste material. For example the waster material may include heavy metals such as nickel, zinc, cadmium, copper, cobalt, mercury, lead or low level radioactive waste which is defined in the United Kingdom as Waste containing radioactive materials other than those acceptable for dustbin disposal, but not exceeding 4 GBq/te alpha or 12 GBq/te beta/gamma. Where contaminants may have dissolved in the liquid suspension these may be removed therefrom by another chemical or biochemical treatment process as will be apparent to those skilled in the art.
According to a further aspect of the invention we provide apparatus for filtering a liquid suspension in accordance with the above method according to the first aspect, said apparatus comprising a passage having an inlet end and an outlet end, the inlet end being at a higher position than said outlet end, wherein the passage between said inlet and outlet ends is formed in a substantially sinuous path, and wherein a granular filter material is located in at least a portion of said sinuous path.
Preferably the said passage comprises a series of intercommunicating substantially vertical and substantially horizontal sections.
In one embodiment the passage includes a first vertical section, the upper end of which provides the inlet end of the passage, a first horizontal section communicating with a lower end of said first vertical section, a second vertical section communicating at its lower end with the
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Brown David John
Higson Stephen Geoffrey
British Nuclear Fuels PLC
Nessler Cynthia L.
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