WO1997029994A1

WO1997029994A1 - Plant for purification of contaminated water

Info

Publication number: WO1997029994A1
Application number: PCT/DK1997/000063
Authority: WO
Inventors: Povl Kaas
Original assignee: AQUA SYSTEM AS
Current assignee: AQUA SYSTEM AS
Priority date: 1996-02-12
Filing date: 1997-02-11
Publication date: 1997-08-21
Anticipated expiration: 1998-08-12
Also published as: AU1719097A

Abstract

A plant (1) serving the purpose of purification of contaminated waste water (14), the solid substances being removed mechanically, and particular and/or dissolved substances are removed by precipitation. The plant comprises one, mainly U-shaped, flow duct (12) for the water, a number of endless bandpass filters (15, 16, 17) placed in the duct for successively removal of solid substances and precipitated particular and/or dissolved substances. After the bandpass filters there is in the duct placed an ozone purification unit (5) especially for removal of organic substances and a UV-section (6) for succeedingly photochemical treatment of the water. In the duct there is next placed a ion exchange section (7) for removal of nitrates and an ion exchange section (8) for removal of salts. The purified water has a quality of drinking water. For many purposes it is possible to take out purified water, which has not gone through the whole process. The water is purified in the plant so quickly that there is no time for secondary reactions to emerge, which undesired might develop for example ammonia, phosphorus compounds and hydrogen sulphides. Furthermore, the plant takes up remarkably little ground space, which is only a fraction of the space for a conventional plant.

Description

Plant for purification of contaminated water

The invention concerns a plant for purification of contamina¬ ted water, where solid substances mechanically are removed and particular and/or dissolved substances are removed by precipitation.

Purification of sewage from, for example, industries and households will normally take place in plants where the water runs through a number of process steps, which typically can comprise an initial mechanical purification in grates and/or sand traps, a preliminary treatment by precipitation, chemical precipitation or biosorption, a treatment in one or more acti¬ ve sludge plants and a finishing treatment by filtration and successive precipitation.

It is wellknown that such conventional plants are expensive to build and run, and that they take up a lot of space. The capa¬ city of the plants is furthermore limited by the fact, that quite many of the processes require rather long time of resi¬ dence of the sewage in great tanks or basins. During this long time of residence a secondary reaction will normally take pla¬ ce, whereby undesired products are developed, such as ammonia, phosphorus compounds and hydrogen sulphides.

The object of the invention is to provide a plant of the type mentioned in the opening paragraph, which is cheap to produce and with a modest need for space is capable of, quicker and more efficient than previously known, treating rather large amounts of sewage without simultaneous secondary reactions.

The new and unique, whereby this is obtained according to the invention, is that the plant comprises a passage duct for the water, a number of endless bandpass filters placed in the duct for successively removal of solid substances and precipitated particular and/or dissolved substances, and one UV-section placed in the duct after the bandpass filters with at least one UV-lamp for photochemical treatment of the water.

Opposite to the abovementioned conventional units, where par¬ ticular and precipitated solids use a long time, e.g. in a sedimentation tank, to sink to the bottom and create sludge, it is now the flowing water itself, that quickly and securely leads the particular or preticipated substances to the cloth of the bandpass filter, which thereby continuously removes the substances, while the purified water flows along in the duct via the meshes of the filter. The very short time of treatment in the plant results in the fact that it with a compact construction can have a large capacity, and that secondary reactions not really will find the time to start.

The construction of the bandpass filters used is described in details by the applicant's Danish Patent Application No. 0145/96, to which there is referred as a reference.

It will be expedient to use several, e.g. three successively following filter sections with equally finer bandpass cloths. The first section can thus be adapted to remove the more coar¬ se impurities. In the second section can particular substan¬ ces, which are precipitated with a polymer, be removed. In the third section a removal of the remaining particular substan¬ ces, which are preticipated with a polymer, and dissolved sub¬ stances which are preticipated with chemicals, can take place.

In dependance of the quality of the sewage, there can be ap¬ plied fewer or more filter sections than the abovementioned three. The decisive point is, that the filter sections combi¬ ned is capable of purifying the water to such a degree, that the water in the UV-sections only will contain dissolved sub¬ stances and/or microparticles. Otherwise, the translucency of the water will be reduced and consequently the light from the UV-lamps will not efficiently be able to penetrate and perform the photochemical processes as presumed.

The lamps in the UV-section can advantageously be constructed in such a way that there in the UV-section is used light with wavelengths, which can decompose or convert those substances, which at this step are in the sewage in question.

The light from low pressure lamps in the UV-area 150 - 200 nm will thus be able to decompose hydrogen peroxide. The light from low pressure lamps in the UV-area 200 - 280 nm will be able to decompose ozone and reduce bacterias, vira, amoebas and microfungi. Medium pressure lamps in the UV-area 200 - 315 nm will primarily be able to convert nitrite and ammonia substances to nitrate and at the same time contribute to a reduction of bacteria, vira, amoebas and microfungi. Finally, the highpressure lamps in the UV-area 200 - 400 nm will partly be able to convert hydrogen peroxide and ozone to OH-radicals, partly be able to decompose the remaining hydrogen peroxide and ozone.

If the sewage does not contain salts, as e.g. chlorides, it can now, after passing the UV-section, be used for watering of agricultural soil or parks in the cities. If the water, on the other hand, is to be led out into a natural recipient, it is necessary first to remove the contents of nitrate, if any. According to the invention the nitrate and the salts can be removed in each their ion exchange unit which has been placed in the duct after the UV-section. If both processes is needed, the ion exchange unit for nitrate is placed first. For the ion exchanging process each ion exchange section will use a ion exchange mass, which is placed in an ion exchange area before an endless bandpass filter to keep the ion exchan¬ ge mass fixed in the duct and continuously lead a part of the mass up to a regeneration basin with a regeneration mean, which typically is an aqueous solution of sodium chloride. The regenerated ion exchange mass can be recirculated to the ion exchange area by means of an air ejector or similar device.

By a particular preferred embodiment an ozone purification section can be inserted,before the UV-section, in the duct for removing especially organic substances, chemical solvents and colour residues, which might remain in the sewage after the treatment in the previous filtering sections. It is therefore of great importance to the effective function of the UV-secti¬ on, that the light from the lamps will not have to penetrate turbid and coloured water.

The ozone section can be adapted in the way, which is descri¬ bed in the applicant's Danish Patent Application No. 145/96, to which is referred as a reference.

An ozone generator produces ozone, which under a high pressure is pumped into a reaction container with water. In the contai¬ ner a supersaturated aqueous solution of ozone is created with an enormous amount of very fine, suspended ozone bubbles, which are driven into the sewage of the section, via a set of nozzles. At a distance from these nozzles a second ozonecon- taining current of water is driven into the sewage via a se¬ cond sets of nozzles, whereby coarse ozone bubbles are created in the water. The ozone in the fine and the coarse bubbles are decomposing the said impurities, and the reaction products flocculate in collaboration between the two types of bubbles, then the floes are removed by means of a bandpass filter, which is placed in the duct.

The plant can be build on the basis of one long duct, which is produced on the spot, where it is used and can be made of e.g. concrete. In many cases the individual sections can, however, advantageously be produced as prefabricated elements, which are assembled to a complete plant on the spot, where it is used. The elements can be assembled in a row or placed on top of each other to save space.

The invention will be explained more fully by the following description of embodiments which just serve as examples, with reference to the drawing, where

Fig. 1 schematically shows a first embodiment of a plant ac¬ cording to the invention with sections build together in a long row,

Fig. 2 shows a section after the line 11 - 11 in fig. l, Fig. 3 schematically shows a second embodiment of a plant ac¬ cording to the invention with sections build on top of each other.

Fig. 4 schematically shows an ozone purification section cor¬ responding to the plant shown in fig. 1 or 2, and

₅ Fig. 5 schematically shows an ion exchange section correspon¬ ding to the plant shown in fig. l or 2.

The plant in fig. 1 is in full indicated with the reference number l. The plant comprises in the embodiment shown a first filter section 2, a second filter section 3, a third filter section 4, a ozone purification section 5, a UV-section 6, a first ion exchange section 7 and a second ion exchance section 8. The different sections are build together in a long row.

10 The sewage to be purified, is led in the direction of the ar¬ row through an inlet 9 by means of a pump 11, and the purifi- cated water is led in the direction of the arrow out of the plant via an outlet 10.

The whole plant is based on one long duct 12, in which the sewage 14 flows, while it step by step is purified from impu¬ rities. As shown in the cross section in fig. 2, the duct is mainly Ushaped. In practice the duct furthermore can have a cover 13 for protection against wind and weather and for let¬

15 ting the plant be presented with an outlook, which even in a housing quarter will blend in with the surroundings.

The said construction according to the invention is unique, because it functions without the many pumps, valves and pipe connections, which it is necessary to use by conventional pu¬ rification plants. The investment in such a plant is therefore already for this reason substantially smaller than normal.

20 In the filter sections 2, 3, 4 of the plant bandpass filters 15, 16, 17 are placed , respectively. The first filter section 2's bandpass filter 15 is shown in fig. 21, and as shown it extends from side to side in the duct 12 and from its bottom to some place above the surface. The sewage therefore is for¬ ced to pass the filter cloths of the bandpass filters when passing the duct. In this process the bandpass filters will by means of mesh widths, being smaller section by section, remove finer and finer particles from the water.

_?f. In the first section 2 the bandpass filter 15's mesh width thus dependant of the quality of the sewage can be for example approximately between 0,5 and 5 mm. In this section coarse impurities, which are carried in the sewage, are removed. In the second section 3 the bandpass filter 16's mesh width can for example be approximately between 60 and 280. In the section a polymer is now used to flocculate fine particles, which then in floes are removed by the bandpass filter 16.

In the third section 4 the bandpass filter 17's mesh width can for example be approximately between 30 and 120. Chemicals are added to react with dissolved substances, microparticles, bac¬ teria and vira in order to create primary particles. Further¬ more a polymer is added to flocculate the primary particles, which then in floes are removed by the bandpass filter 17.

The floes from the sections 3 and 4 will in the direction of the arrows be taken out of the plant and in the shape of slud¬ ge go to sludge treatment by, e.g. pressing and digestion.

When the sewage leaves the last of the three filter sections 2, 3, 4 it will normally continue to have a contents of for example organic substances, chemical solutions and colour re¬ sidues, which it, in many cases, will be necessary to remove. In the plant shown in fig. 1 this takes place in the succe¬ eding ozone section, which in principle is shown in fig. 4.

The ozone is produced by an ozone generator 21 and pumped by a pressure pump 22 under a high pressure into a reaction contai¬ ner 23 containing water which, in the case shown, is a part of the sewage of the section, and which with a pump 24 also is pumped into a reaction container 23 under a high pressure.

In the reaction container a supersaturated aqueous solution of ozone with an endless number of very small fine bubbles with free ozone is thereby created, and this aqueous solution is driven via a first set of nozzles 25 into the section 4 close to the bottom 12 of the duct, whereby an area around the nozzles are filled with fine bubbles, which are manifested as a white fog in the waste water.

In a cycle 27 the sewage is led from section 4 and back again via a second set of nozzles 26 by means of a pump 28 with a lower operation pressure than the pressure in the reaction container 23. The cycle 27 is, as shown, connected to the ozo¬ ne source 21, and it consequently leads an aqueous solution of ozone in through the nozzles 26, where the ozone as a result of the loss of pressure is released in the sewage in the form of, in this case, rather large bubbles.

The ozone in both the finer and the coarse bubbles are for example decomposing organic substances, chemical solutions and colour residues, which might be in the sewage at this stage. The ozone in the fine bubbles will react immediately and effi¬ ciently with the impurities due to the joint exceedingly large tangent surface of the fine bubbles with the impurities. The fine bubbles, which now each has been provided with a surroun¬ ding shell af reaction products, are caught by the rising large bubbles, whereby the reaction products gradually are formed into floes, which by the flowing waste water are led to the cloth of a bandpass filter 18, which takes the floes out of the ozone section. In some cases it will furthermore be of advantage to add hydrogen peroxide to this section. The hydro¬ gen peroxide can convert hydrogen sulphides to sulphuric acid. Furthermore, an addition of hydrogen peroxide and/of free ozo¬ ne serve to ensure that sufficient oxidations means for the succeeding photochemical process are provided.

After passeing the ozone cleaning section the sewage is now so clear that it advantageously can be submitted to a photochemi¬ cal treatment in a succeeding UV-section with UV-lamps 39 in a composition which is adapted to the quality of the sewage at this stage.

If a high quality of the purificated sewage is required, a combination of lamps with light in wavelength areas, each one being especially effective to treat certain forms of impuri¬ ties, could be used.

Light with wavelengths from 150 to 200 nm will thus be capable of decomposing hydrogen peroxide. Light with wavelengths from 200 to 280 nm will be capable of decomposing ozone and reduce of bacteria, vira, amoebas and microfungi. Light with wave¬ lengths from 200 to 400 nm will furthermore be capable of con¬ vert hydrogen peroxide and ozone to OH-radicals and decompose remaining hydrogen peroxide and ozone, if any.

If the purified waste water does not contain salts, it is, after the UV-section, ready to be used for watering of, for example crops within the agriculture. If the purified sewage is to be led out to a natural recipient, it must, however, first has to be releaved from nitrates.

This takes place in the ion exchange section 7, shown in fig. 1, and, in more detailes,in fig. 5. In this section a bandpass filter 19 is placed, and before this the sewage is filled with ion exchange mass 31. Purified water from the other side of the bandpass filters 19 are via a cycle 32 with a pump 33 led, via a number o nozzles 34, to flow in below the ion exchange mass 31, which thereby will be creating a fluid bed in the sewage.

The bandpass filter 19 is stopping the ion exchange mass from being carried away with the flow in t e duct. At the same time the bandpass filter is bringing a par of the ion exchange mass up to a regeneration basin 35 with a aqueous solution of sodium chloride to regenerate the ion exchange mass. At the bottom of the regeneration basin 35 a grating 36 is placed, through which the sodium chloride runs to, after passing the ion exchange mass, be destructed or deposited. An air ejector 37 serves the purpose of via a pipeline 38 to recirculate the regenerated ion exchange mass to the fluid bed area before the bandpass filter 19. During this process the ion exchange mass will at the same time be freed from water with sodium chloride residues.

Salts are removed in a succeeding ion exchange section 8 with a bandpass filter 20. The adaption of this section is similar to the construction shown in fig. 5, and will therefore not be described further here. Instead of sodium chloride for regene¬ ration of the ion exchange mass is sodium hydroxide used.

When the water has gone through all the abovementioned purifi¬ cation processes it will have a quality, which in fairness can be described as drinking water.

The plant shown schematically in fig. 1 is build of a row of prefabricated elements, which have been transported to the spot, where the plant is to be used and then assembled in a row. Each element contains one of the sections 2 - 8 of the plant. These elements can, however, also be placed on top of each other, as shown in fig. 2. In this case the sewage is, by mean of the pump 11, pumped up to the first section 2, which is placed at the top of the plant. From here the sewage runs successively through the other sections under the influence of the gravity force via pipelines 40, which, as shown, extend between two sections placed on top of each other.

By using the purification plant according to the invention it is now possible to purify sewage efficiently in such a short time that no secondary reaction, being undesired development of for example ammonia, phosphorus compounds and hydrogen sulphides, will have time to emerge,.

The plant will furthermore be capable of purifying sewage to a very high quality. To this can be added, that water with a satisfactory quality for many purposes can be discharged wit¬ hout necessarily having been exposed to all of the process steps.

A particular remarkable quality of the plant is, that even with a very high capacity, it takes up negligible little space.

In order to demonstrate this fact can be mentioned, that a typical conventional plant for purification of 4.000 m pr. hour occupie an area of approximately 60.000 m². A fully built-up plant according to the invention will for a compari¬ son take up an area of approximately 4.000 m² when its secti¬ ons are placed in a row, as shown in fig. 1. When the sections are placed on top of each other, as shown in fig. 2, it will only take op an area of approximately 400 m .

The plant according to the invention is suitable for purifica¬ tion of the sewage from households in cities and in rural areas, and from many different kinds of industries, a.o for example chemical factories, drug companies, food companies, industrial painting factories, and textile dyeworks. Opposite to the conventional plants this plant can furthermore operate perfectly even in geographical areas with frequently low tem¬ peratures, under which cercumstanees the bacteria cultures in the conventional plants to a greater or smaller degree will stop their activity.

The plant is furthermore suitable for working up for example brackish and fresh water to be used as process water within the industry and in foodstuff companies. As examples can be mentioned, cold storage plants, desulphurizing plants, green¬ house and fish farms.

Claims

1. A plant for purification of contaminated water, where so¬ lid substances are mechanically removed and particular and/or dissolved substances are removed by precipitation, c h a r a c t e r i z e d in that the plant comprises a flow duct for the water, a number of endless bandpass filters for successively removal of solid substances and precipitated particular and/or dissolved substances placed in the duct, and one UV-section placed in the duct after the bandpass filters having at least one UV-la p for photochemical treatment of the water.

2. A plant according to claim 1, c h a r a c t e r i z e d in that the UV-section comprises at least one low pressure lamp in the UV- area 200-280 nm and at least one medium pressure lamp in the UV- area 200-315 nm.

10 3. A plant according to claim i or 2,c h a r a c t e r i z e d in that the UV-section comprises at least one low pressure lamp in the UV- area 200-280 nm, at least one medium pressure lamp in the UV- area 200-315 nm and at least one high pressure lamp in the UV- area 200-400 nm.

4. A plant according to claim 1, 2 or 3, c h a r a c t e r i ¬ z e d in that the UV-section comprises at least one low pres¬ sure lamp in the UV- area 200-280 nm, at least one medium pressure lamp in the UV- area 200-315 nm, at least one high

_ m. pressure lamp in the UV- area 200-400 nm and at least one low pressure lamp 150-200 in UV nm.

5. A plant according to each of the claims 1 - 3, c h a r a c¬ t e r i z e d in that it comprises at least one ion exchange section placed in the duct after the UV-section mainly for removing nitrate from the water with a ion exchange mass in an ion exchange area in the duct.

6. A plant according to each of the claims 1 - 5, c h a r a c¬

20 t e r i z e d in that it comprises at least a second ion ex¬ change section in the duct placed after the first ion exchange section for the main purpose of removing salts from the water with a ion exchange mass in an ion exchange area in the duct.

7.A plant according to claim 5 or 6, c h a r a c t e r i z e d in that the ion exchange section comprises an endless bandpass filter to keep the ion exchange mass in its place at an ion exchange area before the filter and continuously transport a part of the mass up to a regeneration basin with a regenerati¬

25 on mean.

8. A plant according to claim 7, c h a r a c t e r i z e d in that the plant furthermore comprises an air ejector or similar unit for taking the regenerated mass back to the ion exchange area.

9. A plant according to each of the claims 1 - 8, c h a r a c¬ t e r i z e d in that it comprises an ozone purification sec¬ tion for removal of especially organic substances.

10. A plant according to each of the claims l 9, c h a r a c¬ t e r i z e d in that the plant is assembled by a number of separate sections with preferably the same exterior dimen¬ sions.