Method for purifying water

A method for purification of water with a water purifier. The water purifier includes an anode and a cathode as electrodes in such a way that a gap remains between the anode and the cathode. In the method, an electric field is generated between the anode and the cathode, water for purification is conveyed to the gap and an additive enhancing floc formation is introduced to water for purification or to purified water in an amount of less than 50 g and at least 1 g, measured as dry matter, per each cubic metre of water for purification. Floc material manufactured with the method, when water for purification is municipal wastewater. The use of the floc material produced in this way as a soil conditioner or for manufacturing a soil conditioner.

TECHNICAL FIELD

The aspects of the disclosed embodiments are related to water purifiers and methods for purification of water. The aspect of the disclosed embodiments are related to water purifiers based on electroflotation and purification of water by means of electroflotation. The aspects of the disclosed embodiments are related to purification of wastewater produced in small real estates, mines, factories or communities. The aspect of the disclosed embodiments are also related to material produced during electroflotation, as well as to the use of such material.

BACKGROUND

Purification of water is important as regards human activity and environmental protection, firstly, to produce drinking water and secondly, to control environmental load. For example, purification of water, such as wastewater, is needed in the industry, such as the paper, mining and chemical industries, and for purification of service waters, such as greywater (various cleaning waters) or blackwater (toilet wastewater) used in communities (e.g., residential areas) or vessels (e.g., ships).

A solution for purification of such waters is based on electroflotation. In electroflotation, the purification of water takes place by means of electric current. Electric current is passed to two electrodes: an anode, to which a voltage is applied, and a cathode, to which a voltage negative with respect to said anode is applied. Therefore, it is possible to say that a positive voltage is applied to the anode, although the absolute level of voltages in relation to ground potential, for example, is not relevant as such. Water for purification is arranged between said electrodes; thus, the water for purification functions as an electrolyte. A suitable metal electrode is typically used as the anode.

Due to said electric current, electrolytic reactions take place in the cell, as a result of which ions are dissolved in the electrolyte from the anode and hydrogen gas is reduced at the cathode. According to Archimedes' principle, hydrogen gas naturally goes up in the cell carrying precipitated impurities along with it to the surface. In this way, impurities can be separated from the surface of purified water in the top part of the cell assembly. Impurities precipitated on the surface are generally called flocs. A water purifier based on electroflotation and the cell reactions occurring in it are proposed in patent FI115904B.

Purification of water in an economical manner to the purity level required by the application is one of the challenges of electroflotation. In an overall economical solution, it is necessary to minimise electrode wear and electricity consumption in proportion to the quantity of water for purification and taking into account the target purity level of water. To achieve a better purity level with a particular consumption of electricity, it is known to add certain additives to the process, for example, to the water for purification, before electrodes. In addition, a problem in the prior art is the disposal of floc material generating as a side product, which increases the costs of water purification.

BRIEF SUMMARY

The aspects of the disclosed embodiments are directed to providing a process for purification of water to a purity level according to the application in an economical way. In addition, the use of the floc material produced is provided, by means of which the costs of the process notably decrease or even change into profit. It has been noted that by adding an additive that enhances floc formation to water for purification or to purified water, it is possible to achieve the purity level according to the application with a lower energy consumption and lower anode wear compared to a situation where such material is not supplied to the process. It has also been noted that an efficient purification effect is already achieved with a small amount of additive, such as at least 1 g and less than 50 g measured as dry matter per each cubic metre of water for purification. Since the additive costs, a small quantity of additive influences the overall economy of the process.

DESCRIPTION OF THE EMBODIMENTS

In this application, the term “generalized cylindrical shell” means the plane that a line segment forms when passing along a closed curve. Advantageously, generalized cylindrical shell refers to the shell of a cylinder with a circular bottom, i.e., the shell of a cylinder. An example of a generalized cylindrical shell, which is simultaneously a shell of a cylinder, is the longitudinal section of a pipe with a circular cross-section. Said longitudinal direction is denoted with symbol z0in the drawings.

In this application, symbol z1means the upward direction. During use, the above-mentioned longitudinal direction z0may be oriented essentially in the vertical direction as described below. The transverse direction means any direction perpendicular to the longitudinal direction. Some transverse directions perpendicular to each other are denoted with symbols x and y. For example, the longitudinal direction may mean the longitudinal direction z0or the vertical direction z1.

The apparatus according to the examples is called water purifier10or equipment10for purification of water. Equipment10for purification of water is equipment that is suitable for purifying water. A water purifier10, in addition to being suitable for purifying water, is also arranged to purify water.

Referring toFIGS. 2a-4b, an equipment for purifying water comprises a cathode20and an anode30as electrodes. The cathode20is an electrode that does not wear during electrolysis and the anode30is an electrode that wears during electrolysis. Electrolysis is provided using a power source50. The power source50is arranged to provide a primary voltage V1and a secondary voltage V2, of which the primary voltage is higher than the secondary voltage (V1>V2). It is possible that one of these voltages (V1, V2) is ground potential.

Said primary voltage V1is passed to the anode30via a first electric cord52. Said secondary voltage V2is passed to the cathode20by means of a secondary electric cord54. As a result of a voltage difference, cell reactions known as such start at the electrode pair (20,30), specifically in the gap25between them, as is described above in context with the prior art technique. As a result of the reactions, impurities rise to the top in the inner part12of the water purifier as floc material90, from where they can be removed, for example, via an opening83, such as the end of a discharge pipe82(FIGS. 1 and 6). Correspondingly, purified water can be removed lower in the equipment via a discharge pipe84for purified water.

Floc material90can be removed via the opening83at least when the flow of purified water in the pipe84is suitably restricted. Such restriction can be performed with a valve85, for example. Advantageously, the flow is restricted by utilising at least hydrostatic pressure of purified water.

InFIGS. 2aand 2b, the cathode20has a plate-like shape. The anode30also has a plate-like shape. In the arrangement shown inFIGS. 2aand 2b, there are at least two cathodes and at least two anodes. Correspondingly, the water purifier has at least two or at least three gaps25for purifying water. The plane of a plate-like electrode defines two perpendicular directions, of which one can be called the longitudinal direction of the electrode. The length of the electrode in said longitudinal direction can be smaller than the width, or it can be larger than the width. Said longitudinal direction +z0is advantageously arranged essentially vertical during the use of the water purifier. Such positioning facilitates the control of the water flow in the water purifier10and the collection of floc material in the top part of the water purifier. The longitudinal direction of the electrode20,30is essentially vertical, when said longitudinal direction +z0forms an angle of a maximum of 30 degrees with the upward vertical direction +z1(or such angle is not formed; i.e., it is zero). Such a situation is shown inFIG. 6. Advantageously, said angle is below 10 degrees or below 5 degrees. The cathode20may be arranged inside an outer casing11.

Water for purification is advantageously arranged to flow from the bottom to the top, as inFIGS. 2a-4b, or in another direction, such as the horizontal direction. Nevertheless, floc material essentially rises upwards, possibly slightly in the horizontal direction together with the flow. As regards the supply of an additive, it is advantageous that water for purification is arranged to flow from the bottom to the top.

The cathode20comprises a suitable electrically conductive material. An electrically conductive material means material whose resistivity is at most 10−2└m at a temperature of 20° C. The cathode may be composed of such material. More advantageously, the resistivity of the material in question is at most 10−5└m at least in one direction at this temperature; the direction may be relevant, since the material can be anisotropic. Advantageously, the cathode20comprises at least one of the following: steel, acid-proof steel, stainless steel and graphite. Most suitably, the cathode comprises steel, such as acid-proof steel, since the treatment and connection to other constructions of such material is easy to carry out by welding or forcing, for example. Furthermore, steel is a relatively inexpensive material. The dimensioning of the cathode20can be selected as needed. For example, the cathode20can be made of a plate with its thickness ranging between 0.5 mm and 5 mm, such as 1 mm-3 mm, for example, approximately 2 mm. The length of the cathode20can be selected as needed. For example, the length can be at least 30 cm-5 m, 50 cm-2 m, or 75 cm-1.5 m.

The anode30comprises an electrically conductive material. Advantageously, the anode30comprises such electrically conductive material whose resistivity is at most 10−2└m, more advantageously at most 10−5└m, at a temperature of 20° C. Specifically, the electrically conductive material of the cathode20is not in contact with the electrically conductive material of the anode30. In the electrode pair (20,30) formed by the anode30and the cathode20, a gap25remains between the anode30and the cathode20in said transverse direction. In the gap25, firstly, said water can be purified by means of electrolysis and secondly, water can be transferred in said longitudinal direction +z0from the bottom to the top, for example. The gap25causes that the electrically conductive materials of the electrodes (20,30) are not in galvanic contact with each other. Thus, an electric voltage difference V1−V2(i.e., potential difference) may be present between them, by means of which electrolysis that purifies water operates. As is known, for example, from patent FI115904B, the material typically used as the cathode is more electronegative than the material used as the anode.

The anode30can be essentially as long as the cathode20or it can be shorter than the cathode. Most suitably, the length of the anode30is between 75% and 110%, more preferably between 85% and 100% of the length of the cathode20.

InFIGS. 3aand 3b, the cathode20is in the form of a generalized cylindrical shell, preferably a cylinder. This embodiment of the water purifier is proposed in the Finnish patent application FI20150258 and in the corresponding PCT application, which were not yet published at the time of preparation of this application. The outer surface of a component with a form of a generalized cylindrical shell comprises in each of its points a vector +z0oriented in the same longitudinal direction +z0of the cathode20. Thus, the cathode is in the form of a profile extending in its longitudinal direction +z0, whose cross section in the perpendicular plane toward the longitudinal direction forms a closed curve (or a closed path without an end), preferably a circle. The longitudinal direction z0is advantageously essentially vertical during use, in the way described above.

In this embodiment, the cathode20preferably has a form of a cylinder, or a shell of a cylinder with a circular bottom. This facilitates the manufacture of the cathode20. The cathode20can be made from a pipe with its wall thickness ranging between 0.5 mm and 5 mm, such as 1 mm-3 mm, such as approximately 2 mm. The outer diameter of said pipe may range, for example, between 50 mm and 150 mm, such as 60 mm-100 mm, such as approximately 75 mm. The length of the cathode20can be selected as needed. Most suitably, the length is larger than the diameter. For example, the length can be at least 30 cm-5 m, 50 cm-2 m, or 75 cm-1.5 m.

The anode30is also in the form of a generalized cylindrical shell, preferably a cylinder. InFIGS. 3aand 3b, the anode30remains within said cathode20in the perpendicular direction transverse to said longitudinal direction +z0. The transverse direction means any direction perpendicular to the longitudinal direction +z0. The longitudinal direction of the anode is essentially the same as the longitudinal direction +z0of the cathode. This is the case when the cathode30is not in contact with the anode20although within it. Advantageously, the cathode20is in the form of a cylinder, the anode30is in the form of a cylinder and has a smaller diameter, and the longitudinal directions and the longitudinal centre axes of these cylinders are the same.

For preventing a water flow inside the anode30, the support40for the anode is solid in one embodiment. An embodiment comprises a plug44or equivalent, with which water flow to the inside of the anode support40is prevented (seeFIG. 3b).

As regards purification of water, it is not relevant whether the anode30remains inside the cathode20or the cathode20inside the anode30in the perpendicular transverse direction toward the longitudinal direction +z0. Instead, this arrangement may be relevant in another way, for example, regarding the maintenance of the equipment10, as is described in application FI20150258. If the water purifier10comprises more than one electrode pair, as inFIGS. 5aand 5b, the anode can be the inner-most electrode in some of them and the cathode can be the inner-most electrode in others. InFIGS. 5aand 5b, only cathodes20a,20b,20are shown, and an anode remains within each of these in these embodiments (not shown inFIGS. 5aand 5b).

Advantageously, the anode30has a similar cross-section to that of the cathode20, most advantageously a cylinder. The outer diameter of the anode30is selected suitable considering the inner diameter of the cathode20and the width d of the gap25remaining between the electrodes, which will be discussed in more detail later. As the anode30wears during use, it can have a certain thickness in the transverse direction before use, such as between 5 mm and 35 mm, more preferably between 10 mm and 25 mm, such as approximately 20 mm.

Referring toFIGS. 1-6, the water purifier10advantageously comprises an outer casing11, which limits the inner part12of the water purifier. The outer casing11is not absolutely necessary; however, it improves electrical safety of the water purifier. InFIG. 6, electrode pairs remaining in the inner part12are illustrated using reference numbers20a,20band20c.

As the anode30must be replaced from time to time, it is advantageous that the anode30is easy to replace. Therefore, the water purifier10ofFIGS. 3a-4bcomprises a support40extending in said longitudinal direction +z0(seeFIGS. 3band 4b), of which at least a part is arranged inside the anode30in said transverse direction. The support advantageously extends in the longitudinal direction +z0throughout the entire anode30inside the electrode; that is, inside the anode30in said transverse direction. With this, the benefit is achieved that the anode30can be lifted from the upper part of the support40, although the anode30would be composed of separate parts. Disposed in the bottom part of the anode support40, there are means for supporting the anode30in its bottom part upwards in said vertical direction +z1. InFIGS. 3a-4b, arranged in the bottom part of the anode support40, there is a first projection42extending in the transverse direction from the frame of the anode support40, such as a first flange42, a bar42, or a cross formed by two crossing bars. The first projection42is arranged to support the anode30in its bottom part upwards in said vertical direction +z1. According to the drawing, the first flange42is arranged to support the anode30below it, upwards in said vertical direction +z1. Consequently, the anode30can be replaced, for example, by lifting it using the anode support40and replacing the anode30or its parts. In an embodiment, the anode support40comprises means41for fastening a lifting device, such as a link or a hook41, by which the support40and the anode30can be lifted. As will be described below, the anode30preferably comprises at least two parts; therefore, the lifting of the anode30might not be successful without said support40. Lifting by the top part would only lift parts that are fixedly and solidly connected to the lifting point. The effect of the support40proposed is that an upwards +z1force can be easily applied to the anode30, below it or in its bottom part (such as the lower-most separate part) for lifting the anode30.

Since different anode materials remove different impurities from water, in prior art solutions it is necessary to use at least two different water purifiers successively (i.e., in a cascade), using different materials in the anodes. Such an arrangement is rather large.

In the embodiments shown inFIGS. 3a-4b, the anode30comprises at least a first anode material32and a second anode material34. These first32and second34anode materials are different from each other. Thus, it is possible to purify several types of impurities with a single anode30. The anode20can naturally also comprise a third anode material and even further anode materials according to preference. Specifically, the anode30comprises both the first anode material32and the second anode material34on its outer surface; on that of its outer surfaces that is pointed towards the cathode. Thus, both anode materials32,34are in contact with water running in the gap25, and electrolysis that purifies water takes place effected by both anode materials32,34.

Specifically, according toFIGS. 3band 4b, the anode30comprises a first area32′ or first areas (32a,32b) comprising a first anode material32, and a second area34′ or second areas (34a,34b) comprising a second anode material34. In addition, said first area32′ is separate from said second area34′; in other words, the areas do not comprise the same part of the outer surface of the anode30that is pointed towards the cathode20. Said first area or first areas may consist of said first anode material32. Said second area or second areas may consist of said first anode material34.

Suitable anode materials include multivalent metals, excluding mercury and any other metals that is/are in a liquid form at normal operating temperatures. With normal operating temperatures, the temperatures ranging between +0° C. . . . +95° C., most typically between +10° C. . . . +55° C., are meant.

For example, one of the following can be used as the first anode material: aluminium (Al), iron (Fe), magnesium (Mg), carbon (C), chromium (Cr), copper (Cu), manganese (Mn), tin (Sn), lead (Pb) and bismuth (Bi). As the second anode material, when such is used, another suitable material included in this list can be used. Advantageously, the first anode material comprises aluminium (Al) and the second anode material comprises iron (Fe). Advantageously, aluminium (Al) is used as the first anode material and iron (Fe) as the second anode material.

Advantageously, the first anode material32and the second anode material34are arranged in the anode30subsequently in said longitudinal direction +z0, whereat water for purification flows in the gap25beside both the first32and the second34anode material. Thus, water to be purified during the purification process is in contact with both the first32and the second34anode material. InFIGS. 3band 4b, water for purification first flows beside the second anode material34, after which water for purification flows beside the first anode material32. It has been noted that when the first anode material comprises aluminium (Al) and the second anode material comprises iron (Fe), the part of the anode30containing iron (34′,34a,34b) is arranged on the upstream side in the flow direction of water for purification relative to the part (32′,32a,32b) of the anode20that contains aluminium. Since the flow direction of water inFIGS. 3band 4bis from the bottom to the top, the iron electrode34is arranged below the aluminium electrode32in the height direction. Such an arrangement has shown to provide a good purification result. In addition, since the iron electrode is the first electrode contacting water, its wear increases. Nevertheless, iron is less expensive than aluminium, which is why such an electrode arrangement also contributes to keeping the operating costs low.

Arranged between the first32and the second34anode material, there may be spikes or equivalent for conducting electricity between different anode materials. Thus, various parts of the anode have the same electrical voltage. It has been noted, however, that in such a configuration electrodes usually wear unevenly, which increases the need of maintenance.

Referring toFIGS. 4aand 4b, if the anode30comprises more than one anode material, a different voltage is advantageously applied to different materials. For example, when the anode30comprises a first32and a second34anode material, a first primary voltage V1acan be applied to the first anode material32and a second primary voltage V1bdeviating from the first primary voltage V1acan be applied to the second anode material34(i.e., V1a≠V1b). Both the first V1aand the second primary voltage V1bare higher than the secondary voltage V2. The voltage difference (V1a−V2) created by the first primary voltage can deviate from the voltage difference (V1b−V2) created by the second primary voltage, for example, at least by 5%, at least by 10%, or at least by 20%.

Electrically insulating material36is arranged between the first32and the second34anode material to be able to maintain a voltage difference. Electrically insulating material means material whose resistivity is at least 1 └m at a temperature of 20° C. For example, referring toFIGS. 4aand 4b, a mutually equal voltage (V1a, V1c, V1a=V1c) can be applied to parts32a,32bof the anode30comprising the first electrode material32and a mutually equal voltage (V1b, V1d, V1b=V1d) can be applied to parts34a,34bof the anode30comprising the second electrode material34in such a way that a voltage applied to the first anode material32is different from that applied to the second anode material34(V1a≠V1b, for example, in the way described above).

Correspondingly, the equipment comprises a power source arrangement50, which is arranged to generate a voltage, such as ground potential, for the cathode20; said first primary voltage V1aand said second primary voltage V1b. In addition, the equipment10comprises a first power cord52afor applying the first primary voltage V1ato the area of the anode (32′,32a), which comprises the first anode material32. In addition, the equipment10comprises a second power cord52bfor applying the second primary voltage V1bto the area of the anode (34′,34a), which comprises the second anode material34.

When using the water purifier, the first anode material32is consumed in an amount of a first quantity m1per unit volume of water for purification and the second anode material34is consumed in an amount of a second quantity m2per unit volume of water for purification. The quantity (m1, m2) means here the mass consumed (in grams, for example) or the thickness consumed (in millimetres, for example). In addition, the consumption naturally depends on the quantity of water for purification. For example, electrode material(s) may be consumed in an amount ranging between approximately 5 g and 100 g per cubic metre for purification depending on the purification need. In turn, the purification need is influenced by pre-screening, among other things.

Voltages (V1a, V1b) are advantageously controlled in such a way that said first quantity m1is in the same order of magnitude with or approximately equal to the second quantity m2. More specifically, voltages (V1a, V1b) are advantageously controlled in such a way that the ratio (m1/m2) of the first quantity m1to the second quantity m2is between 0.1 and 10, more preferably between 0.25 and 4, and most preferably between 0.5 and 2. When the anode has only two parts, this is advantageously valid for the quantity referring to the mass. If the anode has more parts, these values advantageously refer to the total wear of the mass of different materials. In other words, voltages can be controlled in such a way that both materials are consumed in an amount that is in the same order of magnitude in total for different parts of the electrode in the sense mentioned above. For example, parts32aand32bmay consume aluminium in total, for example, in an amount of a quantity m1and parts34aand34may consume iron in total, for example, in an amount of a quantity m2. When voltages are controlled in this way, the first primary voltage V1ais typically applied to the first anode material32and the second primary voltage V1bdeviating from the first primary voltage V1ais applied to the second anode material34(i.e., V1a≠V1b). In this case, sufficient purification is typically ensured.

Referring toFIGS. 4aand 4b, if the anode30comprises at least two areas (32a,32b) that are electrically isolated from each other, both comprising the first anode material32, mutually different voltages (V1a, V1c, where V1c≠V1a) can be applied to the different areas32a,32bfor optimising purification of water and/or wear of electrode parts. If the anode comprises at least two electric areas (34a,34b) that are electrically isolated from each other, both comprising the second anode material34, mutually different voltages (V1b, V1d, V1b≠V1d) can be applied to the different areas34a,34bfor optimising purification of water and/or wear of electrode parts. For example, in the latter parts of the electrode pair in the flow direction of water, a voltage lower than that applied to the first parts in the flow direction of water can be applied, since water has already been partly purified in the later parts. This type of control can additionally ensure that electrode wear in the different areas (32a,32b,34a,34b) is relatively even in the sense described above.

FIG. 4ashows a power source arrangement50, which comprises one or more power sources. The power source arrangement50is additionally arranged to form a third primary voltage V1cand a fourth primary voltage V1d. Furthermore, the equipment10comprises a third power cord52cfor applying the third primary voltage V1cto the area of the anode32′ comprising the first anode material32, to a part32bthat has been isolated from said area32a. Furthermore, the equipment10comprises a fourth power cord52dfor applying the fourth primary voltage V1cto the area of the anode34′ that comprises the second anode material34, to a part34bthat has been isolated from said area34a.

When using the equipment10, the first anode material32is consumed in an amount of a primary first quantity m11per unit volume of water in the primary first area32aand in an amount of a secondary first quantity m21in the secondary first area32b. In addition, the first anode material34is consumed in an amount of a primary second quantity m12per unit volume of water in the primary second area34aand in an amount of a secondary second quantity m22in the secondary second area32b. As above, the quantity may refer to mass or thickness.

Voltages (V1a, V1b, V1c, V1d) are advantageously controlled in such a way that said quantities m11, m21, m12and m22are in the same order of magnitude or approximately equal. More precisely, voltages (V1a, V1b, V1c, V1d) are advantageously controlled in such a way that the ratio of the smallest of the following: m11, m12, m21, m22to the largest of the following: m11, m12, m21, m22is between 0.1 and 1, more preferably between 0.25 and 1, and most preferably between 0.5 and 1. Specifically, when consumption refers to a change of thickness, uniform consumption ensures uniform wear of the different parts of the electrode.

Advantageously, the first anode material32is arranged in the anode30as one or more cylindrical rings and the second anode material34is arranged in the anode30as one or more cylindrical rings. Cylindrical rings mentioned inFIG. 3bare piled on top of each other to form the anode30in such a way that the first anode material32touches the second anode material34in the longitudinal direction +z0. Cylindrical rings mentioned inFIG. 4bare piled on top of each other to form the anode30in such a way that electrical insulation36remains between said cylindrical rings. Advantageously, the ring made from the first anode material32remains between two rings made from the second anode material34in the longitudinal direction +z0. Said rings can be equally high or their heights can be varied according to water for purification and/or control voltages.

When the parts of the anode are electrically insulated from each other by means of insulation36, the anode comprises at least two parts that are electrically insulated from each other. In an embodiment, the anode comprises at least three parts that are electrically insulated from each other. In an embodiment, the anode comprises at least four (exactly four inFIGS. 3band 4b) parts that are electrically insulated from each other.

The width d of the gap25is adapted according to the application. The width d of the gap25may depend on the point of observation, for example, if the electrodes20,30are not completely parallel and/or completely of equal shape. The point of observation means here (a) a point on the plane of the anode30facing towards the cathode20, or (b) a point on the plane of the cathode20facing towards the anode30. Such a point of observation limits the gap25. When viewed from this point of observation, the width d of the gap25means either(a, when the point of observation is on the surface of the anode30) the shortest transverse distance to the cathode20, i.e., to its inner surface, or(b, when the point of observation is on the surface of the cathode20) the shortest transverse distance to the anode30, i.e., to its outer surface.

Typically such shortest distance is oriented from said point of observation to the direction of the normal of the surface of the point of observation.

On one hand, the suitable width d of the gap25is limited by the composition of dirty water. Dirty water is typically pre-filtered using at least a screen70or equivalent. Most typically, the mesh size is approximately 8 mm in such screening. With a gap width d slightly larger than this, the operation is also ensured in cases where water for purification comprises impurities of this size. The water purifier10may comprise said screen70(FIG. 5). A smaller mesh size prior to the purification based on electroflotation reduces the need of electrical purification. Advantageously, the mesh size can be smaller, such as 2 mm or 5 mm. It is also possible to use screens of several sizes successively in such a way that the mesh size decreases in the flow direction.

In some embodiments, the width d of the gap25, at least in some of the above-mentioned points of observation, is at least 2 mm, at least 5 mm, at least 8 mm, or at least 10 mm. In some embodiments, the width d of the gap25, in all of the above-mentioned points of observation, is at least 2 mm, at least 5 mm, at least 8 mm, or at least 10 mm. In some embodiments, the average width d of the gap25, calculated over all of the points of observation, is at least 2 mm, at least 5 mm, at least 8 mm, or at least 10 mm. If the water purifier comprises a screen with its holes having a mesh size, the width d of the gap25can be at least equal to said mesh size in all of the above-mentioned points of observation. With such dimensioning, blocking of the gap25is avoided, although water to be purified would contain even large impurity particles.

On the other hand, the suitable width of the gap25is limited by the operating voltage. The gap25must be sufficiently narrow in order that low operating voltages can be used and high electrical powers are avoided. In addition, a low operating voltage is advantageous in terms of operational safety.

In some embodiments, the width d of the gap25, in all of the above-mentioned points of observation, is at most 25 mm, at most 20 mm, or at most 15 mm. In some embodiments, the average width d of the gap25, calculated over all of the above-mentioned points of observation, is at most 25 mm, at most 20 mm, or at most 15 mm. Advantageous widths for the gap25are such where the average gap width, calculated over all of the above-mentioned points of observation, is between 2 mm and 25 mm, such as between 5 mm and 20 mm, particularly advantageously between 8 mm and 15 mm. Advantageous widths also include such where the width d of the gap in all of the points of observation is between 2 mm and 25 mm, such as between 5 mm and 20 mm, particularly advantageously between 8 mm and 15 mm.

The magnitude of the required voltage difference V1−V2may depend on the purification need. The purification capacity is also influenced by the magnitude of electrical current passing through the electrodes, which naturally depends on the voltage difference. The magnitude of the purification need depends, among other things, on the flow of water for purification (magnitude of flow, e.g., m3/h) through the equipment10. Therefore, the water purifier10comprises means56(seeFIGS. 1 and 5), such as a pump56aand/or a valve56b, for controlling the flow of water for purification (i.e., magnitude of flow). The pump56acan be used, if the pressure of water for purification is not otherwise sufficient to provide a suitable flow. If, on the other hand, the pressure of water for purification is high, the flow can be restricted with the valve56b, for example. In addition, it is possible to use a slightly over-dimensioned pump56aand restrict the flow with the valve56b.

Said power source50or power source arrangement50is arranged to provide voltages V1(such as V1a, V1b, V1cand V1d) and V2, or the operating voltage V1−V2of the electrode pair (20,30) (or operating voltages V1a−V2and V1b−V2; or V1a−V2, V1b−V2, V1c−V2and V1d−V2). In an embodiment, said power source50is arranged to produce said primary voltage V1, which is higher than said secondary voltage V2by 1 V-200 V, such as 2 V-100 V. As the anode30wears, the width d of the gap25slightly increases. Due to this, it may be necessary to increase the operating voltage V1−V2during use. In an embodiment, the power source50is arranged to increase the voltage difference (V1−V2) between the electrodes20,30during the purification of water. An increase in the voltage difference can be controlled by a control unit60, for example (seeFIGS. 2a, 3a, 4a).

It has been noted that a sufficiently strong electric field in the electrode pair (20,30) over the gap25causes that microbes, such as viruses and bacteria in the water for purification, are killed. In addition, electric current also disintegrates other harmful substances, such as drugs and hormones, the residuals of which often occur in municipal wastewaters. It has been noted that in some cases the voltage difference sufficient for this purpose is approximately 1 V/m (or more). It has been noted that in some cases the electric field strength sufficient for this purpose (or voltage difference (V1−V2) divided by the width d of the gap25is approximately 100 V/m (or more); i.e., for example, 1 V, if the width d of the gap25is 10 mm. Here, the width d of the gap refers to the average width d of the gap calculated over all of the points of observation. When municipal wastewater, for example, has been processed with such an electric field, active microorganisms or other harmful substances will not appear in the floc material90(FIGS. 1 and 5). More advantageously, the electric field strength is 200 V/m-20 kV/m, such as 300 V/m-15 kV/m. In addition or alternatively, the voltage difference V1−V2is advantageously between 1.5 V and 100 V, such as between 2 V and 50 V. If there are more than one different voltages V1a, V1b, said voltage and electric field strength apply to at least one part of the electrode pair; advantageously, said voltage and electric field strength apply to all parts of the electrode pair.

Since the floc material is sanitised in this way, it can be used as a soil conditioner, for example. It has been noted that such floc material comprises a great amount of nitrogen and/or phosphorous among others, both of which, in turn, work well as a soil conditioner. The amounts of nitrogen and/or phosphorous may even be such that it is not necessary to dilute the floc material when used as a soil conditioner. Therefore, floc material can be mixed with material that is poorer in nitrogen and/or phosphorous content, such as peat, before using it for soil conditioning. Alternatively, floc material can be used for manufacturing a soil conditioner, in which case a soil conditioner manufactured from this floc material can be used at a later stage. Floc material can be mixed with material poorer in nitrogen and/or phosphor content in a mass ratio of 1:50-1:1, such as in a mass ratio of 1:20-1:4. Thus, the concentration of floc material (percent by mass, later m/m) in a ready-to-use soil conditioner may range, for example, between 2 m/m and 50 m/m, such as between 5 m/m and 25 m/m. Said nutrient-poorer material may comprise at least one of the following: earth, peat, sand and clay.

Purified water can be used, according toFIG. 6, for flushing the electrodes20,30. For example, transverse openings may have been arranged in the outer electrode for cleaning. Thus, water can be pumped from the inner part12of the water purifier to the gaps25through said openings in the electrodes for flushing the electrodes. InFIG. 6, such a pump and a corresponding pipe are illustrated using reference numbers58and57respectively. For example, with a small pressure difference, it is possible to prevent water from flowing in a wrong direction through the openings in the outer electrode. According to preference, a container for purified water can also be used to ensure sufficiency of purified water for the above-mentioned cleaning purpose.

Alternatively, the pump58can be used to recirculate purified water through the gaps25. By using a flow that is notably larger than during normal water purification, electrodes (20,30) can be flushed in this way with purified water. This is illustrated inFIG. 5, where purified water can be conveyed along the pipe59into the gaps25of the electrode pairs. According to preference, a container for purified water can also be used to ensure sufficiency of purified water for the above-mentioned cleaning purpose.

By cleaning the electrode pair (20,30) from time to time it is ensured that the purification result is sufficient. This, in turn, contributes to maintaining a low consumption of additive and/or electricity.

Furthermore, the water purifier10can comprise a valve72for draining water from the water purifier10. By opening the valve72it is possible to remove the heavy matter accumulated on the bottom of the equipment. This heavy matter may originate from a dissolving electrode, for example. In an embodiment, the water purifier10is drained at intervals.

Referring toFIGS. 1 and 6, in the invention, an additive enhancing floc formation is supplied to purified water or to water for purification. With this, it is effected that water is purified more efficiently than without an additive. Correspondingly, the water purifier10comprises means65for supplying an additive to water for purification or to purified water. InFIG. 1, an additive is supplied to water for purification (i.e., in the flow direction on the upstream side relative to the electrode pair). InFIG. 6, an additive is supplied to purified water with the equipment10(i.e., in the flow direction on the downstream side relative to the electrode pair). The means65may comprise, for example, a container64and a pump66. As an additive, an agent enhancing floc formation can be used; for example, to increase its tendency to form flocs. This improves the purification process in such a way that the electricity demand decreases and anode wear is reduced compared to a situation without an additive.

The additive can comprise a polymer. The additive can comprise a water-soluble polymer. The additive can comprise polyacrylamide (PAM). Dry polyacrylamide can be used as an additive. For example, such an agent is known under the trademark Superfloc®. The charge of polyacrylamide may be cationic, anionic or neutral.

It has been noted that the required quantity of the additive depends on its supply point. Advantageously, the additive is supplied, according toFIG. 6, in the flow direction of water for purification, after the electrode pair20,30. Advantageously, the additive is supplied, according toFIG. 6, in the vertical direction, above the electrode pair20,30. Thus, the vertical direction of electrodes is essentially upright in the sense described above, and water for purification is conveyed to the gap25from below.

It has also been noted that the required quantity of the additive depends on its supply method. The additive is advantageously supplied as a water solution. Referring toFIG. 1, the additive is advantageously supplied dissolved in purified water. InFIG. 1, purified water is brought to a container64along a channel68. The supply of an additive to the container64is illustrated with the arrow69. Referring toFIG. 6, an additive is most advantageously supplied dissolved in water that has been purified with the same equipment10, which is used to purify water and to which the additive is supplied as a water solution. InFIG. 6, water purified with the equipment10is conveyed along the channel68to the container64, where a suitable quantity of said additive is mixed with it. When added to the container64, the additive can be dry. The supply of the additive is illustrated with the arrow69. The water solution formed in the container64is introduced to purified water or to water for purification (preferably to purified water). The water solution formed in the container64is supplied to the equipment10, from where water is conveyed to the container64.

It has been noted that in arrangements and purification methods of this kind, quite a small amount of additive is sufficient, such as at least 1 g measured as dry matter per each cubic metre of water for purification. A suitable amount of additive measured as dry matter of additive is below 50 g per each cubic metre of water for purification, such as 5 g-49 g per each cubic metre of water for purification, and, for example, 10 g-40 g per each cubic metre of water for purification.

For example, a dry additive can be mixed in the container64with purified water, such as with water purified with the equipment10, in an amount of 100 g-20 kg per each cubic metre of water brought to the container64. Furthermore, this solution can be mixed with water for purification (FIG. 1) or with purified water (FIG. 6) in such a way that the amount of the additive used in the process remains within the above-mentioned limits. The pump66can be used to adjust the amount of the additive solution supplied.

Referring toFIGS. 1 and 2, a water purifier according to an embodiment comprises a control unit60, which is arranged to control at least one, preferably all of the following: (a) said means56for controlling the flow of water for purification, (b) a power source arrangement50, and/or (c) a pump66for supplying an additive solution. By controlling the power source arrangement50, it is possible to control the operating voltage V1−V2, such as operating voltages (V2, V1a, V1b), such as operating voltages (V2, V1a, V1b, V1c, V1d).

Depending on the purification need and the size class, the water purifier10may comprise only one electrode pair (20,30), as inFIGS. 3a-4b, or more than one electrode pair, as inFIG. 2. Electrode pairs according toFIGS. 3a-4bcan be arranged several in parallel to increase the purification capacity.

It has been noted that the separation of floc material90from purified water takes some time. Referring toFIG. 6, floc material is advantageously separated from purified water in such a way that in the equipment, in a point h1in the vertical direction, water from which floc material has not been separated is allowed to flow upwards inside the equipment10, and in the same point h1in the vertical direction but in a different point in the horizontal direction, water from which floc material has been separated is allowed to flow downwards inside the equipment10. For example, in the internal pipe82bdepicted inFIG. 6, at height h1, a mixture of purified water and floc material flows upwards. Correspondingly, inside the outer casing82abut outside the internal pipe82b, at height h1, purified water, from which floc material has been removed, flows downwards.

Advantageously, the equipment10is dimensioned in such a way that the flowing of purified water from the upper edge of the electrode pair20,30to the point at which purified water is removed from the equipment (e.g., the point at which the discharge pipe84of purified water is connected to the equipment10) takes at least 3 seconds, such as 5 s-200 s, more preferably 6 s-30 s, such as 8 s-15 s, such as approximately 10 s. This also ensures a sufficient exposure time for the additive to form flocs.

As described above, the water purifier10can be used, for example, in the mining industry, in the paper industry or for purification of municipal wastewaters. The water purifier10is particularly suitable for purification of municipal wastewaters. An arrangement comprises a residential building and a water purifier10according to any of the embodiments described.

It has been also noted that floc material produced particularly during purification of municipal wastewaters has an economically viable use as a soil conditioner and/or for manufacturing a soil conditioner, as described above. The use of floc material for soil conditioning is a method for improving soil. The use of floc material for manufacturing a soil conditioner is a manufacturing method of a soil conditioner. In such a method, floc material manufactured by purifying municipal wastewater using any of the methods described above for manufacturing floc material90is received (e.g., by purchasing). In addition, soil is improved with floc material90, or a soil conditioner is manufactured using floc material90. Optionally, floc material90is manufactured in such a method by purifying municipal wastewater using any of the methods described above. In addition, soil is improved with floc material90or a soil conditioner is manufactured using floc material90. It is possible to purify water, during which floc material90is produced, and to use at least part of the floc material for own use for soil conditioning and/or sell at least part of the floc material to another party. It is possible to manufacture the first floc material by oneself, purchase a further amount (i.e., receive) of another floc material and improve soil with both the first and the second floc material, or produce a soil conditioner from these floc materials.

The following examples are related to the embodiments described above.

1. A method for purification of water with a water purifier (10), wherein

the water purifier (10) comprises an anode (30) and a cathode (20) as electrodes in such a way that a gap (25) remains between the anode (30) and the cathode (20),a primary voltage (V1) is applied to the anode (30),a secondary voltage (V2) is applied to the cathode (20), where the primary voltage is higher than the secondary voltage (V1>V2),water for purification is conveyed to the gap (25), andan additive enhancing floc formation is introduced to water for purification or to purified water in an amount of at least 1 g and less than 50 g, measured as dry matter, per each cubic metre of water for purification.
2. A method according to Example 1, whereinthe additive comprises a polymer, such as polyacrylamide, for example, cationic, anionic or neutral polyacrylamide.
3. A method according to Example 1 or 2, whereinthe primary voltage (V1) and the secondary voltage (V2) create a voltage difference (V1−V2) and an electric field over the gap (25), andthe voltage difference (V1−V2) is at least 1 V or the electric field strength ((V1−V2)/d) is at least 100 V/m;advantageouslythe strength of said electric field is 100 V/m-20 kV/m, or the voltage is 1 V100 V.
4. A method according to any of Examples 1 to 3, whereinthe anode (30) comprises a first anode material (32) and a second anode material (34), the second anode material (34) being different from said first anode material (32), andwater for purification flows in the gap (25) beside both the first (32) and the second (34) anode material;advantageouslysaid first anode material (32) is aluminium andsaid second anode material (34) is iron;
most advantageouslyin the anode (30), aluminium (32) is arranged in the flow direction of water for purification on the downstream side relative to iron (34).
5. A method according to Example 4, whereina first primary voltage (V1a) is applied to the first anode material (32), anda second primary voltage (V1b) is applied to the second anode material (32), whichsecond primary voltage (V1b) is unequal to the first primary voltage (V1a); for examplesaid voltages (V1a, V1b) are controlled in such a way thatthe first anode material (32) is consumed in an amount of a first quantity (m1) per unit volume of water for purification,the second anode material (34) is consumed in an amount of a second quantity (m2) per unit volume of water for purification, andthe ratio (m1/m2) between the first quantity (m1) and the second quantity (m2) is between 0.1-10, preferably between 0.25-4, and more preferably between 0.5-2.
6. A method for improving soil or for manufacturing a soil conditioner, whereinmunicipal wastewater is purified with a method according to any of Examples 1 to 5 for manufacturing floc material (90),floc material (90) produced is collected andsoil is improved or a soil conditioner is manufactured using floc material (90).
7. A method according to any of Examples 1 to 6, whereinsaid additive is supplied as a water solution;
advantageouslya dry additive is mixed with clean water for forming said water solution;
most advantageouslya dry additive is mixed with water purified with said water purifier (10) for forming said water solution.
8. A method according to any of Examples 1 to 7, whereinsaid additive is supplied to a point located after the cathode (30) in the flow direction of purified water;
for examplean additive is supplied to a location that is higher than the top part of the cathode (30).
9. Floc material (90) manufactured in such a way thatmunicipal wastewater is purified with a method according to any of Examples 1 to 8, whereatimpurities contained in municipal wastewater for purification rise to the top of the water purifier (10) as floc material (90), from where said floc material (90) can be removed.
10. Use of the floc material according to Example 9 as a soil conditioner or for manufacturing a soil conditioner.
11. A method for improving soil or for manufacturing a soil conditioner, whereinfloc material manufactured by purifying municipal wastewater with a method according to any of Examples 1 to 8 for forming floc material (90) is received, andsoil is improved or a soil conditioner is manufactured using floc material90.