Liquid purification or separation – Processes – Treatment by living organism
Patent
1996-05-01
1998-06-09
McCarthy, Neil
Liquid purification or separation
Processes
Treatment by living organism
210792, 210796, 210189, 210270, 210274, C02F 304, B01D 2444, B01D 2446
Patent
active
057628017
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a method and to an apparatus for purifying sewage water or drinking water biologically in a filter bed comprised of a granular filter medium, wherein the filter medium is transported by air from the bottom to the top of the filter bed, to obtain a continuously working filter.
When treating sewage water or drinking water biologically in a continuously working filter that includes a granular filter medium, there is used a bacteria strain which has been cultured particularly for the nature of the treatment concerned. These treatments typically involve nitrification and denitrification processes, which are concerned with removing nitrogen from the water. In order to utilize a filter bed optimally, it is necessary that the bed always contains a sufficiently large bacteria culture to effect the process concerned.
An example of a continuously working filter that includes a granular filter medium is found described and illustrated in Swedish Patent Specification 7602999-0 where the filter bed can consist of two or more modules. The suspension to be treated is taken in at the bottom of the filter bed and flows upwardly through the bed and exits from the upper surface of the bed as a finally treated liquid, at least for the moment. The granular filter medium, for instance sand, is transported from the bottom of the filter bed by means of an air-lift pump and is delivered to an apparatus for extracting suspended material and from there back to the upper side of the filter bed. The filter medium therewith passes slowly down through the filter bed and meets suspension under treatment.
It is this transportation in the air-lift pump from the bottom of the bed to the upper side thereof that can create a critical situation with regard to the bacteria strain. Under certain conditions, the bacteria strain can be so decimated during this transportation as to noticeably decrease the reactivity in the filter bed.
An object of the present invention is to achieve this transportation in the air-lift pump in a manner which will prevent the bacteria strain from being decimated to an extent which will appreciably affect the effectiveness of the water purification process. This object is achieved by using two or more transport tubes in parallel. As a result, the flow conditions in the transport tubes or pipes will not have a negative effect on the reactivity of the filter bed caused by excessive losses of the bacteria strain.
The invention and the problem fundamental to the invention will now be described in more detail.
An air-lift pump is used beneficially to transport vertically a suspension comprised of particles of varying sizes. The air used to operate the air-lift pump is introduced at an adapted overpressure into the transport tube of the pump immediately above the bottom orifice of the tube. The air rises up through the tube and entrains by suction medium located in the proximity of the bottom tube orifice. The air flow introduced into a transport tube of given diameter determines the amount of filter medium that can be transported per unit of time, although only to a certain limit for a given transport tube. The transport tube is unable to transport larger quantities of filter medium when this limit is reached. When wishing to increase the transport capacity, it is necessary to increase the diameter of the transport tube. With large tube diameters or large volumes of air per unit of time, the transportation conditions in the tube become violent, in other words greater turbulence is generated.
It is possible to see in an electron microscope the direct consequence of excessively strong turbulence in the tube transporting the bacteria strain. The convex surfaces of the filter particles, or granules, are completely free of bacteria. These bacteria are found in existing pores and to a greatly reduced extent in concavities or hollows. The observations made in the microscope can, in many instances, be verified by analyzing adosine triphosphate and measuring the oxygen consumption (grams COD per kilo
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Hagrot Magnus
Jonsson Kurt
Lenvik Lennart
Oskarsson Jonas
McCarthy Neil
Nordic Water Products AB
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