Liquid purification or separation – Processes – Liquid/liquid solvent or colloidal extraction or diffusing...
Reexamination Certificate
2000-07-20
2002-05-28
Fortuna, Ana (Department: 1723)
Liquid purification or separation
Processes
Liquid/liquid solvent or colloidal extraction or diffusing...
C210S636000, C210S170050, C210S195200, C210S257200, C210S333100
Reexamination Certificate
active
06395182
ABSTRACT:
The present invention relates to a method for purifying water, in particular ground water, under anaerobic conditions, using a membrane filtration unit. The present invention furthermore relates to a device for purifying water, in particular ground water, under anaerobic conditions, using a membrane filtration unit which is provided with the necessary valves, supply and discharge pipes and pumps, and to drinking water obtained by using such a method.
Netherlands patent application 82 00080, which is laid open to public inspection, relates to a method for obtaining water by using membrane filtration, whereby it is stated that the water to be filtrated must be prevented from coming into contact with air. If the water contains iron compounds, for example, said iron compounds will be converted into solid substances under the influence of the ambient air, which solid substances will then deposit on the membranes. In order to prevent contact with the ambient air, the mouth of the borehole to the aqueous liquid is sealed substantially gastight. In practice it has become apparent, however, that a considerable amount of flocks is formed when such a plant is started, which flocculation can be ascribed mainly to the presence of air in the supply pipes and to the membrane surface (which is still dry). Thus, said method is unsuitable for permanent filtration of water under anaerobic conditions.
From “Handbook of Water Purification”, 1981, Walter Lorch, page 307, it is known that ferrous ions in feed water oxidize into ferric ions under the influence of oxygen, which results in precipitation.
Japanese patent publication No. 58 133885 relates to a method for removing dissolved oxygen from liquids. Thus, the liquid is brought into continuous contact with gaseous nitrogen, after which the dissolved oxygen is removed together with gaseous nitrogen in a liquid tank. Then the liquid, from which the oxygen has been removed, is supplied to a membrane filtration unit of the reverse osmosis type.
Japanese patent No. 06 126299 relates to a water treatment plant which is successively provided with an active carbon filter, a de-aeration element, as well as a membrane filtration unit of the reverse osmosis type, whereby the water to be treated, which contains dissolved oxygen, is continuously passed through the de-aeration element.
Japanese patent publication No. 58 011091 relates to a method for de-aerating water, wherein first a flocculation agent and a auxiliary substance are injected into the liquid to be treated, which contains oxygen. Then the flow of water thus pre-treated is passed through a sand filter, after which the obtained filtrate is continuously passed through a de-aeration unit. The water thus obtained, from which the oxygen has been removed, is mixed with a reduction agent, for example a sulfite compound, and subsequently supplied to a membrane unit.
Japanese patent publication No. 61 050654 relates to a method for removing dissolved oxygen from washing water by injecting a deoxidizer into the washing water, and subsequently supplying said washing water to a de-aeration unit for the purpose of removing the dissolved oxygen and the carbon dioxide that remain, after which the washing water thus treated is supplied to a membrane filtration unit of the reverse osmosis type.
The above-discussed Japanese patent publications all relate to the continuous removal of oxygen from an oxygen-containing water flow, after which the water flow from which the oxygen has thus been removed is supplied to a membrane filtration unit. The objective of the present invention, on the other hand, is to clear the membrane filtration unit and the valves, pipes, pumps and the like connected thereto of oxygen, or at least to a considerable extent, during the starting phase, whereby the dissolved oxygen that may be present in the water to be purified is in particular not subjected to an additional treatment, so that the water to be purified comprising the dissolved oxygen that is inherently present therein is carried to a membrane filtration unit, in which anaerobic conditions have been created. After all, in practice mainly ground water will be used, which ground water is already contained in the ground under substantially anaerobic conditions, so that it is in particular desirable to maintain said anaerobic conditions during said membrane filtration rather than remove any remaining dissolved oxygen in advance from the aqueous flow to be purified, as the oxygen content thereof is too low to cause flocculation, which is harmful to the membrane filtration unit. The oxygen from the ambient air will cause flocculation, however, in particular the air which is present in pipes, pumps and in the membrane filtration unit.
Such a method for purifying water, using a membrane filtration unit, is also known from European patent application No. 0 655 418, for example. According to the method disclosed in said publication, the water to be purified is supplied to a reactor in which filter membranes are present. The reactor is furthermore provided with a pipe for discharging floating constituents, and with a pipe for discharging settled constituents. Such constituents are formed mainly by oxidation of metals, which oxidized metals are insoluble in the water. The water to be treated which is present in the reactor is injected with ozone so as to suppress the growth of biological constituents, which constituents have an adverse effect on the membrane filtration process. One drawback of such a method is the fact that contamination of the membranes occurs after some time, in spite of the fact that ozone is injected and that floating and settled constituents are discharged. Said contamination may be caused by the organic substances (macromolecules, biomolecules) and other organic substances (colloids, iron hydroxides, manganese hydroxides, calcium salts and the like) which are present in the water to be treated. In addition to that, also bacteria, algae and the like may cause contamination of the membrane surface.
Such contamination of the membrane surface may be of a reversible or of an irreversible nature. In the case of reversible contamination, the membrane surface can be cleaned by rinsing it with a special solution, for example a soap, acid or lye solution. From practice it is known, however, that frequent, that is, monthly cleaning may reduce the life of the membranes considerably, so that the cost of the plant may increase considerably. In the case of irreversible contamination, it is not possible to clean the membrane surface with the above-mentioned agents. The contamination cannot be removed at all and, depending on the rate of contamination, this may result in a very short life of the membranes, which is generally accompanied with a decrease in the productivity. Thus, the cost of the plant will increase considerably.
One way of preventing or strongly reducing contamination which is frequently used in practice is to subject the water to be purified to a pre-treatment. In the embodiment wherein ground water is purified, such a pre-treatment generally consists of an aeration step and one or more filtration steps. In the embodiment wherein surface water is purified, such a pre-treatment consists of a coagulation step, a flocculation step and a filtration step. In both filtration steps, which are carried out under aerobic conditions, suspended substances and iron and manganese flocks, which flocks are considered as iron and manganese hydroxides, are removed to a considerable degree from the starting material to be treated. Although the iron content and the manganese content can thus be reduced to <0.02 and <0.0005 mg/l respectively, the membranes must still be cleaned two to four times a year on average in order to maintain a reasonable water production per membrane element. One drawback of such a pre-treatment is the fact that additional plants must be built, so that the total cost will increase. Besides, such plants require the possible addition of further chemicals, which chemicals may have an adverse effect on the qual
Van Der Meer Walterus Gijsbertus Joseph
Van Winkelen Jacobus Cornelis
Barrett Enclosures, Inc.
Fortuna Ana
Seed Intellectual Property Law Group PLLC
LandOfFree
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