WO1987000162A1

WO1987000162A1 - Process and apparatus for treatment of water

Info

Publication number: WO1987000162A1
Application number: PCT/FI1986/000073
Authority: WO
Inventors: Esko MÄLKKI
Original assignee: Maelkki Esko
Priority date: 1985-07-11
Filing date: 1986-07-04
Publication date: 1987-01-15
Also published as: FI852741A0; FI852741L; EP0266352A1

Abstract

A process and apparatus for the treatment of water, especially iron and manganese containing phreatic water, wherein water is flowed through a substantially coarse-grained filter or under and/or over flow barriers in a low filter vessel (1, 10, 13, 15) having a small, e.g. 5:1 cross-sectional surface area relative to that of the body of water. The water to be treated is set to flow in horizontal direction along a coarse-grained (o/ >= 1mm) filter stuff or flow barrier located on the interface of air and water.

Description

Process and apparatus for treatment of water.

The present invention relates to a process and appara¬ tus for the treatment of water, particularly for the deironing and demanganization of phreatic water.

A particular objective has been the deironing and de¬ manganization effected in small units, which is one of the problems areas in water treatment.

Iron and manganese are quite common ingredients in phreatic water. For example, when phreatic water is exposed to air, e.g. upon bringing the water out of its natural environment, these substances will be readily oxidized and turned into solid form. This causes considerable operating trouble, e.g. due to precipitate formation.

In natural phreatic waters, iron and manganese are present as a variety of compounds, sometimes bound e.g. to humus, with varying possibilities of separat¬ ing them (by precipitation) . Especially the deiron¬ ing can sometimes be effected by simple aeration and filtration, sometimes it requires considerably more effective processes. Demanganization is generally more difficult than deironing. Generally speaking, the quality spectrum of phreatic water is quite ex¬ tensive, which is why the water treatment require¬ ments and possibilities vary to a great degree.

In addition to iron and manganese, a requirement for treatment may be caused, among others, by reduced nitrogen compounds ( H-- and N0₂-ions) , detrimental gases (methane, hydrogen sulphide, radon etc.) dis¬ solved in water, a low pH and a high C0₂-concentrat- ion (metal tube corroding properties and lack of oxygen) .

The prior art, generally factory-made small water- treatment equipment, whose operating principle ranges from simple aeration and filtration all the way to chemical water treatment, does cover subdomains of water treatment but there are considerable deficien¬ cies. The most effective processes are capable of producing good results, but at the cost of consider¬ able expenses. Another problem is maintenance of the equipment and a short maintenance interval. Especial- ly with high iron contents (> 10 mg Fe 1 ) , the pre¬ cipitate formation is abundant and the purifying equipment comprising fine granular masses is quickly clogged. Nearly all commercially available assemblies are based on pressurized systems, which have their limitations e.g. in view of the removal of detrimental gases. It is hard to find an apparatus which fulfils all purifying requirements and, especially, is readily maintainable.

Even in deironing and demanganization alone, the ground- water or phreatic water treatment equipment is required to have very good capability with different water qual¬ ities taken into consideration. Such capability is generally attained at reasonable costs only with water¬ works and applied biological methods. Biological water treatment plants (pure water) comprise generally on- ground aeration ladders and rubble filters as pretreat¬ ment units, the primary treatment unit comprising a slow filter, which is made of sandy soil types and can be a man-made reservoir or an absorption basin, drain¬ ing waters into the ground-water zone.

The use of such bulky constructions is out of the ques¬ tion especially in small-scale water treatment, wherein the equipment should be placeable in household facil¬ ities. Especially in winter operation, it would also be beneficial for waterworks to make the total area/ output of a plant smaller than at present, in which case such plants could be economically covered. In known slow filtration plants or the like, this ratio is generally such that for each cubic meter of water

2 pprroodduucceedd tthhee:re is needed a surface area of 1-2 m or even larger.

It has been possible to reduce this drawback by using an invention disclosed in the Finnish Patent applic¬ ation No. 842094, wherein water is flowed in vertical direction in chamber pairs, whose bottom ends are in flow communication with each other, said chambers be¬ ing provided with a filter layer in close proximity to the water level and, if necessary, with other filter materials. By using an apparatus of this invention, it has been possible to reduce the surface area of a filter unit many times over relative to the produced amount of water, if compared to slow filtration plants.

When studying even more effective water treatment possibilities, in vertical chamber filters set out in Patent application 842094, the water flow was closed in a space below of the surface filter layer of a pair of chambers and conditions were otherwise arranged in a manner that the water to be treated only flowed along a filter stuff located on the air and water interface and adjacent thereto. The purification pro¬ cess was still found to proceed effectively despite the lack of. lower water circulation in chambers and the lenghtywater retention time causedbythe circulation....

This experiment has opened a new possibility of apply- ing biological treatment, since e.g. in an assembly of the same size as before, the flow capacity can be sub¬ stantially increased; even more than ten times over with respect to an apparatus set out in Patent applic¬ ation 842094. It is true, howver, that the purificat¬ ion result obtained by this improved mechanism is achieved with respect to the invention disclosed in the above-cited application at the cost that the amount of iron precipitate retained in a filter stuff will be greater, i.e. the clogging thereof occurs within a shorter period of time. However, this drawback can be eliminated e.g. by using a prior known backwash tech¬ nique, a possibility offered by the new application process.

An improved biological water treatment of the present invention can be effected (a) by a process, wherein water is flowed in a horizontal direction along a coarse-grained (grain size >_^ 1 m) filter stuff placed on the interface or separating surface of air and water. Application of the process is feasible (b) by using an apparatus characterized by comprising:

1) one or a plurality of parallel and/or superimposed vessels provided with suitable guide flanges or support structures;

2) vessels used as such or placed in a suitable con¬ tainer and provided with

a) filter stuffs promoting biological activity, placed especially in close proximity to water level or

b) these and further with water-flow controlling partitions or filter cassettes having permeable walls, as well as

c) an overflow chamber, placed inside the vessel and provided with a screen, structure and aeration ladder, said chamber controlling the water level.

Other characterizing features of the invention are set forth in annexed claims.

The basic unit of a treatment apparatus comprises a low filter vessel, having a small cross-section with respect to its surface area, e.g. 5:1, said vessel being partly filled with water and water flowing from one vessel end to the other or in circle; all in all in a horizontal direction. When flowing in a coarse¬ grained stuff placed in the vessel, the molecular groups of water, through the action of mechanical hydrodynamic dispersion, are distributed on either side of the in¬ dividual grain and, thus, at least some of those groups find their way repeatedly to the interface of air and water. By means of said flow barriers placed in the vessel, water is furthermore set to flow in a wavelike path adjacent to the interface of air and water and, thus, it is also repeatedly brought into contact with said interface.

In addition to water being thus aerated, various pH- and oxidation-reduction conditions are formed in the portion of filter stuff on the interface of air and water, thus creating favourable facilities for various bacterial activities. On the other hand, the filter cassettes placed in the vessel allow the use of vari¬ ous mineral masses favourable to e.g. biological act¬ ivity, nutrients containing such masses as well as the use of alkalizing masses; as readily exchangeable units. The design and operating principle of filter vessels are significant in. view of both small-scale purificat¬ ion plants and waterworks applications.

By placing filter vessels fitted with guide flanges on top of each other, it is possible to assemble a com¬ pact, effective biological oxidation reactor having a suitable vertical height and which can be dimensioned according to difficulties encountered in water treat¬ ment. The height (thickness) of filter vessels can be varied in several ways during the manufacturing, whereby the above-mentioned flow phases, which are important in view of the purification process and take place in close proximity to the interface of air and water, can be multiplied in the same space by reducing the vessel thickness but by increasing the number of vessels.

The apparatus can be used both as an open treatment plant, the treated water being passed into a suitable container, and as a pressurized unit by placing the reactor in a suitable vessel designed as a pressure tank. The separate vessels of a reactor itself can be assembled as a compact package by means of guide flanges and suitable link rods, which facilitates e.g. backwash technique. ' ^'■

In addition to a superimposed series-connected set of vessels, a waterworks application offers a possi¬ bility of designing a filter vessel so extensive that the desired purification process is achieved in a single filter vessel, several of which can be connect¬ ed in parallel. Thus, the system can be designed e.g. in a manner that filter vessels, provided e.g. with slide beds ("rollers"), are placed on top of each other upon support frames, said frames - being of simple and inexpensive design - being responsible for the stabil- ity of the entire structure. The use of support structures offers .the advantages that (a) filter vessels, even in large sizes, can be manufactured inexpensively from light materials and even from metals in lightweight structures, (b) their assembly and maintenance is easy and (c) a support structure construction allows the use and flexible testing of most versatile combinations of vessels.

The_. inflow and outflow of water will be adapted to various modes of operation.

All the above-mentioned embodiments of basic unit and apparatus can be fitted with (a) a preaeration unit, (b) a dry filter unit as well as (c) an after-filter unit/units, which fit in the same set of vessels and serve to improve the reliability of water purification especially in difficult water quality conditions.

On the basis of results obtained with small purific¬ ation pilot units it can be concluded that a 4 x 4 x 4 size package is capable of treating the amounts of wwaatteerr iinn tthhee oorrddeerr ooff 550000 ttoo 1000 m 3 d-1 ; depending on the quality of raw water.

Operation of the apparatus is further based on the following.

— natural phreatic waters contain iron and manganese bacteria which, together with physico-chemical react¬ ions involved in purification, have a crucial effect on a purification process

The apparatus can also be inoculated with a suitable strain of bacteria and transplant it e.g. in filter cassettes together, with its mineral masses

- apparatus is dimensioned so that, water retention time (stepless adjustment possible) is appropriate with respect to. raw water quality

- for best possible biological activity, contact mater¬ ial lies both above and below water level. Contact materials may comprise materials both lighter and heavier than water, the latter even as filters on the surface of water only by means of pierced or perfor¬ ated carrier grains

- apparatus construction allows the use of various filter materials and combinations thereof

- in addition to deironing and demanganization, the treatment offers other advantages as well, effecting partly on removal of said substances. Due to effect¬ ive oxidation, water flowing into distribution system is highly aerated. Its phosphor and carbon dioxide contents decrease and pH increases, thus reducing or totally eliminating metal pipings corroding properties of water. Eventual reduced nitrogen compounds turn into more harmless nitrate form. Detrimental gases dissolved in water escape

- volume of various chamber units can be adjusted as required by water quality conditions

- the permeable wall sections of partitions and filter cassettes are designed in a manner that portions the size of an opening (slit) are deflected to form vertical lamellae extending parallel to flow. Accord¬ ing to operating experiences, such a design allows a large opening area and is nevertheless stable and least susceptible to iron precipitate cloggings as the flow-resisting or antiflow surface area is as small as possible and vertical disposition of open¬ ings prevents iron precipitate from settling on lamellar surfaces.

It should further be noted:

- there is nothing to prevent the use of this process and apparatus even in major waterworks

- apparatus or its components can be manufactured in¬ dustrially and it is very simple in design. In.add¬ ition to metal structures, it is possible to use plastics (including support frame constructions) even in large-scale filter vessels

- treating apparatus is an entity, wherein unit systems provide facilities for most versatile process arrange¬ ments and regulation thereof as well as facilities for economical embodiment of purification or treat¬ ment system.

The invention will now be described in more detail with reference made to the accompanying drawings, in which

fig. 1 shows a basic unit I for the filter vessel in an apparatus of the invention.

Fig. 2 is a cross-section along line II-II in fig. 1.

Fig. 3 shows a circular vessel for basic unit I.

Fig. 4 is a cross-section along line IV-IV in fig. 3.

Fig. 5 shows another basic unit II for a filter vessel. Fig. 6 is a cross-section along line VI-VI in fig. 5.

Fig. 7 shows a third basic unit III for a filter vessel.

Figs. 8, 9 and 10 are cross-sections along lines VIII, IX and X in fig. 7, respectively.

Fig. 11 shows an apparatus assembled from the vessels of basic unit I and connected to an after- filter.

Fig. 12 is a schematic view of the filter vessels of basic unit I mounted on a support frame for parallel operation.

Referring to fig. 1, a basic unit I comprises a filter vessel 1, provided with a raw water supply pipe 0, filter stuff 2 and an overflow chamber4 fitted with a screen section 5 and, as shown in fig. 2, an aeration ladder 6 and a water outlet 7. The vessel may also be provided with a flush water outlet pipe 9 and a lid 22 with its ventilation duct 23 (fig. 11).

Water to be treated is passed from the raw water supply pipe to the other end of the vessel, from where it flows in overall horizontal direction but doing a little zigzag due to the action of flow-dividing hydrodynamic dispersion. Thus, at least some of the water molecules come repeatedly into contact with the stuff on the interface of air and water; the more abundantly the lower a vessel is in cross-section and the longer the flowing distance. Finally, water flows into an overflow chamber regulating its level 3, dis¬ charging through out of the filter vessel thorugh out¬ let 7 by way of its screen section and aeration ladder. In a circular vessel embodiment 10 of basic unit I (figs. 3, 4), provided with a solid wall 11, water circulates in a circumferential path, the microflow phenomena and other features being as described above. The vessel has an empty central space 12 which can be used for designing flushing systems.

A basic unit II (figs. 5 and 6) comprises a filter vessel 13, provided with a raw water supply pipe 0, filter stuff 2, partially solid walls 14, an overflow chamber 4 fitted with a screen section 5, an aeration ladder 6 as well as with a water outlet 7. The vessel may also be provided with a flush water outlet pipe 9 and a lid 22 with its ventilation duct 23 (fig. 11).

Water to be treated is passed from the raw water supply pipe to the other end of the vessel, from where it flows, deflected by partitions in a wavelike pattern, along said filter stuff and is repeatedly directed onto the interface 3 of air and water. The action of flow further produces the above-mentioned microflow phenom¬ ena and contact actions associated therewith. Water discharges out of the filter vessel as in basic unit I.

A basic unit III (figs. 7-10). comprises a filter vessel 15, provided with a raw water supply pipe 0, filter stuff 2 containing filter cassettes 16 fitted with guide flanges/grooves 18 and partially permeable wall sections 17 (figs. 9, 10); with another filter stuff 2 in a space between cassettes, permeable floors 19 with its brackets 20 (fig. 8) as well as with an overflow chamber 4 , fitted with a screen section 5, an aerat¬ ion ladder 6 and a water outlet 7. The vessel may also be provided with a flush water outlet pipe 9 and a lid 22 with its ventilation duct 23 (fig. 11). The raw water to be treated is passed from the supply pipe to a first filter cassette located at the other end of the vessel, flowing therethrough and discharging from the cassette through a permeable wall section into the space between cassettes, flowing on to the next filter cassette and finally out of the vessel by way of the overflow chamber, as in the preceding basic units. During the flow, water assumes a wavelike pattern due to the action of filter cassettes and, as a result of this and the dispersion phenomena taking place in the stuff in a space between said cassettes, the travelling path of the body of water/its molecules is repeatedly directed into the contact with the inter¬ face of air and water.

A set of filter vessels designed from basic unit I (a compact oxidation reactor) connected to an after- filter (fig. 11).

The water supplied into a top vessel 1 , fitted with a lid 22 and a ventilation duct 23 associated there¬ with as well as with a flush water outlet pipe 9, flows by way of an overflow chamber 4 into a second filter vessel mounted therebelow by means of guide flanges 8. Thus, in a circular embodiment of basic unit I, the second vessel is disposed in a manner that water coming out of the overflow chamber of the pre¬ ceding vessel will be directed at the same location as the raw water inflow in the vessel above.

Water flows through the set of vessels into an after- filter 24, wherein the water flowing through a mass of sand is collected by means of a collecting pipe 25 and passed by way of a pure water take-up pipe 28 into a water supply...Inorder to eliminate siphon effect, the pipe is fitted with an aeration pipe 26, a flush water inlet pipe 27 and an outlet pipe 29.

During the operation, valves 0, 23, 26 and 28 are open. Flush water drains by way of collecting pipe 25 through a mass of sand in after-filter 24 and further upwards from one filter vessel to another by way of overflow chambers 4 and finally runs out by way of a flush water outlet pipe 9.

In a set of vessels, designed from basic unit I and mounted on a support frame 30 (fig. 12), water to be treated is simultaneously passed into parallel-linked filter vessels according to basic unit I, flowing there¬ from by way of take-up pipes 28 into a collecting pipe 31. From there onwards to an appropriate after-filter or into a water supply. Each vessel is provided with a separate flushing system depending on the basic unit constructio .

Claims

1. A process for the treatment of water, especially iron and manganese containing phreatic water, wherein water is flowed through a substantially coarse-grained filter stuff or under and/or over flow barriers in a low filter vessel (1, 10, 13, 15) having a small, e.g. 5:1 cross-sectional surface area relative to that of the body of water, c h a r a c t e r i z e d in that the water to be treated is set to flow in substantial¬ ly horizontal direction along a coarse-grained { >_ 1 mm) filter stuff or flow barrier located on the interface of air and water.

2. A process as set forth in claim 1, c h a r a c t e r i z e d in that water is set to flow in repeated contact with the interface of air and water as a result of flow- dividing mechanical hydrodynamic dispersion and wavelike motion produced by said flow barriers.

3. An apparatus for the application of a process as set in claim 1, comprising one or a plurality of filter vessels (1, 10, 13, 15), connected in parallel or in series, at least partially filled with water and fitted with a filter stuff (2) , at least some of the latter being above the water level; and/or appropriately alternately below or above open/permeable walls (14); c h a r a c t e r i z e d in that said filter vessel

(1, 10, 13, 15) is low and its cross-sectional surface area is small with respect to that of the body of water, the ratio being preferably 1:5.

4. An apparatus as set forth in claim 3, c h a r a c t e r i z e d in that said filter vessel (1, 10, 13, 15) is provided with an in-built overflow chamber (4) , including a screen section (5) and an aeration ladder (6) .

5. An apparatus as set forth in claim 4, c h a r a c t e r i z e d in that the apparatus is provided with separate filter cassettes (16), mounted on by means of guide flanges/grooves (18) and fitted with partially permeable wall sections (17).

6. An apparatus as set forth in claim 5, c h a r a c t e r i z e d in that said partially per¬ meable wall sections (17) are vertical lamellae ex¬ tending parallel to flow.

7. An apparatus as set forth in claim 5, c h a r a c t e r i z e d in that filter stuff (2) and perforated.floors (19) can be fitted in spaces between filter cassettes (16).

8. An apparatus as set forth in claims 3 - 5, c h a r a c t e r i z e d in that a number of filter vessels (1, 10, 13, 15) are fitted together on top of each other by means of guide flanges (8) .

9. An apparatus as set fort in any of the preceding claims, c h a r a c t e r i z e d in that the apparatus output can be regulated by varying the number of filter vessels (1, 10, 13, 15).

10. An apparatus as set forth in any of the preceding claims, c h a r a c t e r i z e d in that in a unit having the same volume, the flow proceeding along the interface of water and air can be increased by making said filter vessels (1, 10, 13, 15) thinner or vice versa.

11. An apparatus as set forth in any of the preceding claims, c h a r a c t e r i z e d in that the filter or contact materials comprise volcanic pumice-stone, iron-magnesium or magnesium cargonate, peat charcoal or apatite.

12. An apparatus as set forth in claim 3 - 5, c h a r a c t e r i z e d in that a number of filter vessels (1, 10, 13, 15) can be mounted on a support¬ ing carrier frame (30) .