WO1987005593A1

WO1987005593A1 - System for biological purification of water

Info

Publication number: WO1987005593A1
Application number: PCT/SE1987/000125
Authority: WO
Inventors: Lars A^oke Hans GUNNARSSON; Björn Hubert ROSÉN; Malte Ernst LÖNEGA^oRD
Original assignee: Purac Aktiebolag
Priority date: 1986-03-19
Filing date: 1987-03-12
Publication date: 1987-09-24
Also published as: SE8601279L; SE456421B; SE8601279D0; AU7164287A

Abstract

A system and a method of purifying water in a biological way by means of a two-step process, at which the water to be purified is supplied into the treatment container or reactor (1) distributed uniformly across the bottom surface. The water supplied into the container (1) is caused to pass through a first biological filter consisting of suspended biological mass (11), in which gas is generated and at the same time the organic impurities in the water are decomposed. The water treated in the first treatment step thereafter is caused to pass through one or several stationary biological filters (13), where additional biological purification takes place at the same time as a sludge rich in bacteria grows on the carrier bodies of the biological filters. The stationary biological filters (13) are cleaned by means of the gas generated in the first treatment step, which gas is collected in the upper portion of the container (1) and recovered while the purified water rising to the upper portion of the container is drained off.

Description

System for biological purification of water

This invention relates to a system for the biological purific¬ ation of water, comprising a closed container or reactor, at the bottom part of which an inlet for water to be purif¬ ied is located, and in which container one or several zones with carrier material for the retaining of microbal biomass are arranged, and at the upper portion of the container an outlet for gas generated at the purification process and an outlet for purified water are located.

It is known since long that water containing solved organic impurities can be purified efficiently in a biological way. At a purification process of this kind the water to be purified is treated in a closed or open container, in that a suitable bacteria culture is added to the water and S3-c ui_fcaneously conditions suitable for the biological activity, for example a suitable temperature, are maint¬ ained. The added bacteria while considerably increasing in number feed on said organic impurities, which are broken down and converted. Substances insoluble in water together with consumed and living bacteria form a sludge rich in bacteria, a so-called activated sludge, which can be used for further biological treatment.

It is known since long to carry out a biological treatment of the kind here referred to in a closed system without air acess, a so-called anaerobic treatment. The anaerobic treatment has the advantage, that gas rich in energy is generated. The method, however, has the disadvantage that the treatment time is relatively long, which implies that the building volume of the installations for a certain treatment capacity is great and thereby involves high investment costs. One way of rendering the anaerobic treat¬ ment more efficient is the introduction of so-called biological filters for the retaining of microbal biomass, which filters yield an efficient combined treatment, which also is space-saving. One inconvenience with known biolog¬ ical filters, however, is that the sludge layer so much increases in thickness that the filters are clogged and obstruct an effective water flow. Such cloggings, of course, drastically reduce the efficiency of the biological filters, and the installation must be switched off in order to clean the biological filter from excess sludge by flushing or other cleaning action. This inconvenience is avoided by the system and method according to the invention, the characterizing features of which are apparent from the attached claims.

One embodiment of the invention is described in the follow¬ ing with reference to the accompanying schematic drawing, in which Fig. 1 is a section through a system according to the invention, Fig. 2 is a cross-section of Fig. 1 along the intersecting line A-A, Fig. 3 shows an embodiment of the biological filter consisting of inclined plates, and Fig. is a cross-section showing foam pockets of the system.

The system shown in Fig. 1 comprises a container or reactor 1, which in principle is a closed vessel. The cross-section of the container 1 can be circular, but may also be, as shown here, polygonal. In the container 1 a drive shaft 2 driven by a motor 3 is mounted. The drive shaft 2 is provided at its lower portion 4 with a distribution device 5 for the water supplied so that the water is distributed uniformly across the bottom surface of the container 1. The said distribution device 5 consists of a number (at the embodiment shown four) of tubular distribution arms 6, which are conn¬ ected to a distribution chamber 7, into which a stationary supply pipe 8 opens. Each of the tubular distribution arms 6 is provided with outlet nozzles 9, which are substantially uniformly distributed along the length of the arms 6 and so adjustable, that the amount of water flowing through can be adjusted. The outlet nozzles 9 can be directed down¬ wards or to the side. As mentioned above, the distribution device 5 for the water to be purified is attached rigidly on the lower portion 4 of the drive shaft 2. This implies that the distribution device 5 with its distribution arms 6 will be caused to rotate immediately above the bottom portion of the container 1. When simultaneously water is supplied into the distribution chamber 7 of the distrib¬ ution device 5 via the stationary pipe 8, the mouth portion of which is mounted sealingly in the rotary distribution chamber 7. the water" supplied will be led into the distrib¬ ution arms 6 and pressed out through the outlet nozzles 9_ while the distribution arms 6 at their movement sweep over the bottom portion of the container 1, whereby a very good distribution of the water supplied is obtained across the surface of the bottom portion.

The water supplied to be purified is led into the first cleaning portion 10 of the container or reactor 1 and will contact a biologically activated sludge 11 suspended in water. Said sludge constitutes a biological mass. The sludge particles, which per se are heavier than water, are maintained floating in the water, due to the fact that the water in the container 1 has an upward flow move¬ ment while simultaneously a gas generation, which is described below, maintains a flow of rising gas bubbles through the suspended bilogical filter 11.When the water containing solved organic impurities gets into contact with the suspended biological mass 11 in the container portion 10, the impurities are broken down whereby methane gas, carbon dioxide and a sludge containing bacteria are formed. For rendering it possible that the biological decomposition process takes place in an efficient way, the said activated biological mass 11 is required to contain bacteria of a suitable type. The methane-forming bacteria constitute in this respect an important part of the bacteria population, it is. further necessary that the external prerequisite conditions, such as temperature and acidity of the water, are maintained on a level suit¬ able for the biological process, and it may be sometimes necessary, therefore, to heat the water in the container 1 or to adjust its pH value. The decomposition of the impur¬ ities of the water which takes place in the container portion 10 can be said to be a first treatment in a first sludge system. As a result of the treatment, methane gas is formed which develops as small bubbles, which owing to being lighter than water rise upward in the container 1. In order to render the biological treatment of the water more efficient, an agitator 12 is provided in the container 1. As appears from Fig. 1, the agitator 12 consists of a plurality of wings or blades, which are fixed on the drive shaft 2.

The water, which has passed through the first sludge system in the first biological cleaning in the portion 10 of the container 1 is not treated completely, because the treat¬ ment time for the passage of the water through said first sludge system is relatively short. The water, however, flows slowly upward in the reactor, because purified water is drained off from the upper portion of the container 1, which water is passed through one or several biological filters 13, which are arranged in the container 1 and comprise a solid material, on and/or in which a sludge layer can grow. In Fig. 1 an arrangement is shown, in which two biological filters 11 are placed one above the other and built-up on a support 14 pervious for water or perforated (for_^ example a net or a grating) which constitutes the bottom for the biological filters 13. The said material, when required, can be prevented from moving upward by means of a device similar to the device 14. The biological filters 13 in most cases consist of a great number of bodies of plastic or similar material, which are designed so that their surface is large in relation to their volume. The biological filters 13 are arranged_. so in the container 1, that they fill entirely the cross-sectional area of the container, which implies that the water passing through the container is forced to pass through the biological filters 13. The said rigid bodies constituting the biological filters 13 are carriers of a sludge containing bacteria, and at the passage of the water an additional biological treatment takes place in a second sludge system where the sludge is not in suspended state but is supported by a carrier material.

The said bodies, which are the carrier material for the biologically activated mass of the biological filters 13, together form a great number of labyrinth flow passages for the water caused to pass through the biological filters 13, which implies that the water in an effective way comes into contact with the biological activated material, whereby impurities remaining in the water are effectively broken down. At the biological treatment, as decomposition product a sludge is formed which forms a sludge layer on the carrier bodies of the biological filters 13. This sludge layer increases in thickness for finally possibly being capable to block the flow passages for the water through the biological filters.

As mentioned above, at the biologicak purification process methane gas is formed, and the gas, which was formed in the first sludge system 11 during the first purification process in the portion 10 of the container 1, will rise to the biological filters 13 and pass therethrough. It was found, however, that the small bubbles of methane gas adhere to the sludge in the biological filters and that an ever increasing number of gas bubbles combine to greater bubbles with increased lifting power. When the lifting power of the combined bubbles has increased sufficiently, the bubbles detach themselves and make their way through the flow paths of the biological filters at the same time as possible blocking sludge masses are removed and released. The flow of these large gas bubbles has an effective cleaning influence on the biological filters, the flow passages of which automatically are maintained open. The released sludge drops down through the bottom 14 of the biological filters 13 and finally fall into the container portion 10 and participate in

along the plates 24 and finally sinks down in the suspended biological mass 11 in the portion 10 of the container 1. It was found, that the combination of two-step cleaning with biological filter purification by means of gas bubbles generated in the first cleaning step and the use of plates 24 in the stationary biological filters in the second cleaning step yields a good purification effect and a safe operation of the plant without risk of shutdowns owing to clogged biological filters.

It was also found, that by a plant of the kind here described a good biological purification effect can be achieved in a relatively short treatment time and a separate external sludge recycling system can be avoided, which implies reduced investments in the plant, and that with the plant a good purification effect and high operation reliability are obtained owing to the self-cleaning effect of the biological filters obtained by the methane gas generated in the first cleaning step. The process, further, has the advantages characteristic of an anaerobic biological purification process, viz. that the process is economic because a gas rich in energy is generated. No energy, therefore, must be supplied to the process for its funct¬ ioning, but the process, instead, generates useful energy.

The invention is not restricted to the embodiment shown, but can be varied within the scope of the invention idea.

Claims

1. A system for biological purification of water, com¬ prising a closed container provided with an inlet for water to be purified at the upper portion of the container, an outlet for gas generated at the purification process and an outlet for purified water, which inlet consists of a rotary device comprising a plurality of substantially horizontally projecting tubular arms (6) for the water supplied, which arms are coupled to a drive shaft (2), c h a r a c t e r i z e d i n that the water is supplied at the bottom of the container (1) through a conduit (8) connected to a distribution chamber (7), from which the water is passed through the tubular arms (β), which are provided with outlet nozzles (9), so that the water supplied is distributed uniformly across the bottom surface of the container (1), and that in the container (l) at a chosen level above its bottom at least one stationary biological filter (13) is located which extends over the greater part of the cross-section of the container and rests on a water pervious surface (l4).

2. A system as defined in claim 1, c h a r a c t e r ¬ i z e d i n that the biological filter (13) consists of bodies, which are arranged on a grating or screening plate and have a large surface in relation to their volume, on which bodies the sludge can grow.

3. A system as defined in claim 2, c h a r a c t e r ¬ i z e d i n that above the biological filter (13) a perforated plate, for example screening plate or wire, for retaining the bodies in the filter is located.

4. A system as defined in claim 1, c h a r a c t e r ¬ i z e d i that the biological filter (13) consists of a plurality of inclined plates (24).

5. A system as defined in claim 1, c h a r a c t e r ¬ i z e d i n that it comprises an agitator (12) attached to the drive shaft (2) for agitating the water in the area between sludge treatment at the bottom portion (10) of. the container (1) and the biological filter (13).

6. A system as defined in claim 1, c h a r a c t e r ¬ i z e d i n that it comprises a scraper attached to the shaft (2) for removing possible floating sludge or foam (18) on the water surface through sludge pockets (23).