Liquid purification or separation – Processes – Treatment by living organism
Reexamination Certificate
2000-06-15
2002-05-28
Upton, Christopher (Department: 1724)
Liquid purification or separation
Processes
Treatment by living organism
C210S626000, C210S627000, C210S631000, C210S638000, C210S760000, C210S192000, C210S195200, C210S195300, C210S196000
Reexamination Certificate
active
06395177
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a method for decoloring liquids, in particular ground water. The present invention furthermore relates to a device for decoloring liquids, in particular ground water, by using such a method, as well as to decolored ground water which has been obtained by using the method according to the present invention.
In practice a number of processes for decoloring ground water exist, namely adsorption on active carbon and membrane filtration. The process of adsorption on active carbon comprises a bed of active carbon, through which the water to be decolored is passed with a residence time of about 10-30 minutes, after which a product flow is obtained from which the colour has been removed. One drawback of such a process is the fact that in practice the filter bed of active carbon is already saturated within a month. The saturated active carbon must then be removed from the filter bed and be returned to the supplier, where the saturated bed material is regenerated by means of steam into active carbon, which can be reused in the filter bed. Since the application of such necessary regeneration operations interferes with a continuous operation, it is usual in practice to connect a number of filter beds in series, so that a continuous operation is ensured. Another drawback of decoloring ground water by using active carbon is the fact that the ground water generally contains certain organic-substances which, if they bond to active carbon, form an ideal seed-bed for bacteria and higher organisms, for example worms. As a result of this luxuriant growth, especially the bacteriological quality of the ground water leaving the filter bed of active carbon will decrease. In addition, the presence of said higher organisms in the distribution network may lead to problems.
Another process for decoloring ground water consists of membrane filtration. The advantage of such membrane filtration on a nano filtration scale (pore size: 0.01-0.001 micron) is the fact that in addition to the removal of the colour, also substances such as iron and manganese can be removed. One drawback of such membrane filtration is the high energy consumption, namely about 0.5 kWh per m
3
of purified water. Another major drawback is the fact that 10-20% of the ground water to be decolored leaves the process in the form of a waste flow (concentrate flow). In connection with the possible scarcity of ground in the future it is desirable, therefore, not to waste any ground water.
SUMMARY OF THE INVENTION
The object of the present invention is to avoid the aforesaid problems of the known processes for decoloring ground water.
In addition to that it is desirable that a method be developed which is capable of processing, in a continuous manner, ground water of varying composition, in particular of a varying colour intensity, into decolored ground water which also has a high bacteriological quality, that is, which is in principle free from bacteria and viruses.
Another object of the invention is to provide a device for decoloring liquids which requires small capital investments and which enables a high production rate of decolored liquids.
The method as referred to in the introduction is according to the present invention characterized in that the following steps are carried out:
i) subjecting the ground water to a biological treatment in a bioreactor;
ii) feeding the effluent from the bioreactor of step i) to a membrane filtration unit, in which membrane filtration unit a separation between biomass and decolored ground water takes place; followed by
iii) feeding back the biomass from step ii) to the bioreactor;
whereby the ground water is subjected to an oxidation treatment in an oxidation reactor prior to carrying out step i).
Although the term ground water will consistently be used in the description below, it should be understood that besides ground water, also surface water, process water and industrial water can be processed by using the method according to the present invention.
Such a method for biologically purifying waste water, whereby the waste water to be purified is biologically treated in a reactor and the effluent from the reactor is fed to a membrane unit connected after said reactor, is known per se from German Offenlegungsschrift 195 27 295. According to the method described therein, a propellant is fed to the membrane unit, as a result of which the concentrate is fed back to the reactor and the filtrate is withdrawn from the membrane unit by means of a vacuum. Such a method requires a complicated plant consisting of a reactor, a membrane filtration unit, a propellant compressor and a vacuum pump. In addition, the plant is unsuitable for processing waste water flows of considerably different compositions.
Although an aerobic biological reactor connected to ultrafilters is known from the article “Membrane biological reactor system for treatment of oily wastewater”, Knobloc et al., Water Environment Research, 66 (1994) March/April, edition 2, Apr. 3, 1994, pages 133-139, it is not known from said publication to decolor liquids, in particular ground water, by using a method wherein an oxidation treatment, a biological treatment and a membrane filtration separation are successively carried out.
By subjecting the ground water to a biological treatment in a bioreactor, the organic substances present in the ground water will be converted into water and carbon dioxide by bacteria, after which the ground water that has been treated in the bioreactor and the bacteria present therein are carried to a membrane filtration unit. The pore size of the membrane filtration unit is selected such that the biomass, that is, the bacteria, do not pass through the membrane, whilst the ground water treated in the bioreactor will diffuse through the membrane of the membrane filtration unit. Then the biomass is withdrawn from the membrane filtration unit and returned to the bioreactor. According to such a method conversion of organic substances takes place in the bioreactor, after which the suspension of biomass and biologically treated ground water is separated into decolored ground water and biomass in the membrane filtration unit. In particular embodiments it is preferred to discharge a part of the amount of biomass to be returned to the bioreactor. Since the liquid to be treated has in principle been freed from bacteria and viruses already by the membrane filtration unit, a liquid having a high biological quality is thus obtained.
The determination of the colour intensity takes place in accordance with Dutch standard NEN 6413, which document may be considered to be incorporated herein. According to this document, the colour intensity of water is indicated by the number of mg of platinum which must be added in the form of potassium chloroplatinate to 1 liter of colourless water in order to give said water the same colour intensity as the water to be examined. A content of less than 5 mg of Pt/Co/1 is indicated as colourless.
The present applicants have carried out extensive research with regard to the colour intensity of water, and they have found that the presence of humic acids or humic acid compounds has a significant influence thereon. Consequently, they propose the following theory, whereby it should be understood that they are by no means bound thereby. Said research has shown that the colour of the ground water is mainly caused by the presence of humic acids or humic acid compounds. The term humic acid is understood to mean organic compounds having complex structures built up of several benzene-like six-membered nuclei having a molecular weight of at least 1000 Dalton or higher. Although the bacteria present in the bioreactor are capable of decomposing such humic acids or humic acid compounds into smaller organic compounds, eventually water and CO
2
, such a conversion will take place slowly in practice. By first subjecting the ground water to an oxidation treatment in accordance with the method according to the present invention, the humic acids or humic acid compounds pre
Van Der Meer Walterus Gijsbertus Joseph
Van Winkelen Jacobus Cornelis
N.V. Waterleiding Friesland
Seed Intellectual Property Law Group PLLC
Upton Christopher
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