FR2551049A1 - Continuous aerobic biological treatment - Google Patents

Abstract

Process for the performance of submerged aerobic biological reactions uses a cylinder container which is divided by a bell into an aeration space and a settling space which communicate through an annular gap. The raw effluents are distributed together with the necessary nutrients in the aeration space in concentric circles. Not more than 1.1 times the admitted liquid is circulated from the centre of the aeration space to the settling space. The deposited microorganisms are recycled to the aeration space and the surplus sludge with them is entrained with the liquid outflow from the centre of the container. The cylindrical container is divided by a bell into an aeration space and a settling space. The air is introduced through open-ended tubes from the pipe. Microorganisms, deposited in the settling space return to the aeration space through the gap. Influent liq. passes from pipe to a distributor chamber and concentric rings. Controlled flow passes through an air lift to distributor chamber and through pipes to the settling space. Surplus sludge goes through pipe to a sludge treatment. Purified liquid leaves through an overflow, and the gases are extracted through pipe.

Description

 The present invention relates to a method and an apparatus for carrying out submerged aerobic biological processes. More particularly, it relates to the continuous realization of aerobic microbiological processes> submerged - for example, the biological treatment of residual water, carried out with an activated sludge - and the circulation and the exit of the required microorganisms and also an apparatus for implementing this process.

 Dissolved organic substances are first of all decomposed by aerobic microorganisms, according to known methods of treatment of residual water carried out using activated sludge. In accordance with known methods, the supply of oxygen to the microorganisms and its distribution in the residual waters are obtained with various means of surface aeration. These methods can be used economically to purify poorly contaminated waste water, for example municipal sewage.

 However, the purification of industrial waste water rich in organic substances - as well as those which come from fermentation processes on an industrial scale - requires the use of a greater mass of microorganisms (activated sludge), so that the oxygen supply and the need for agitation are also increased.

In the case where surface aeration means are used for the purification of highly contaminated residual water, the specific energy consumption of the oxygen supply becomes significantly higher than that which is necessary for municipal sewage and the large volumes to be treated also increase the costs of the treatment. As an example of the above, we note that then the specific energy consumption of a surface aeration is from 0.45 to 0.55 kWh / kg O2 for the purification of slightly contaminated sewage only, it reaches 0.7 - 0.8 kWh / kg O2 for highly contaminated industrial waste water. As the volume of oxygen also increases, the aeration costs become even higher
A surface aeration has another disadvantage in that it is suitable for achieving uniform aeration of basins having only a limited depth of water (not exceeding 3 - 4 m) and for this reason, the structure used for performing the purification offers a large base area. It has other disadvantages, such as a strong foul odor, formation of mist and sprayed liquid and a risk of freezing.

The use of the so-called "deep aeration" system (BAYER TURMBIOLOGIE; HOECHST BlOHOCH REAKTOR) has become important1 to eliminate the above drawbacks of surface aerators, in the purification of highly contaminated industrial waste water. As the water depth is much greater, we can have in these processes, a notable saving of species and simultaneously, the duration of stay of the air bubbles becomes longer and therefore the quantity of dissolved oxygen increases. These processes are carried out in carbon steel tanks which are less expensive and can be more simply constructed than the reinforced concrete structure and at the same time they allow the implementation of modern methods for establishing phase surfaces and to stir the liquid in the tank / Hydrocarbon
Proc. 191-195 (1980); Chem. Ing. Tech. 52, 930 - 932 (198Q7
As a result, the specific energy consumption in deep aeration tanks amounts to 0.25 - 0.40 kwh / kg 02, which is much more favorable than that obtained in surface aerators, although the air introduced must be compressed at a rate which depends on the depth of the water / Chem. Ing. Tech. 52, 330 - 331 (1980) 7.

 Another characteristic aspect of deep-ventilation tanks is that the sludge settling space, which is an essential part of the biological activated sludge equipment, is constructed with the tank and arranged concentrically at the upper external part of that -this, in order to save space and use the position energy of the water already mounted. On the periphery of the decantation space, a certain number of conical or pyramidal "sections" are formed for the outlet of the mud or else a larger compartment equipped with inclined deflection plates, promoting the sliding of the mud, to ensure a uniform output from it. These two implementations result in the formation of dead spaces, increase the investment costs and make the operation random.

 During the treatment of residual water carried out with an activated sludge, the water purified by microorganisms delivers a mass of microorganisms from the aeration space, the quantity of this mass corresponding to the flow rate and to the concentration of the sludge. The quantity of the mass of microorganisms thus delivered is several times greater than that which is formed in the biological purification of the residual waters in circulation and therefore, to maintain the concentration of the aerator mud, it is necessary to recycle in the aerator part of the sludge separated in the settling space - with the exception of the excess sludge formed -. The stream of recycled sludge is added to the stream of fresh residual water and for this reason, it is preferable to recirculate the mass of sludge required from the settling space, with a minimum stream of water. that the concentration of the mud in the settling space is increased by 1.5 to 2.5 times compared to the initial value, by carrying out a sedimentation. In practice, an additional recycling of 0.8 to 2 times of sludge is used - compared to the fresh residual water introduced - depending on the characteristic properties of the sludge.

 According to known methods of activated sludge, large settling volumes and a suitable pumping capacity are used and operated in order to obtain a thicker sludge if possible.

 In accordance with an essential aspect of the method of the present invention at the end of the aerobic microbiological procedure, no more than 1.1 times of current of liquid to be treated and to be introduced onto the mantle of the aeration space is introduced. symmetrical in a circle, at the axis of the aeration space, in a concentric decantation space arranged above and outside of and communicating with the aeration space. The microorganisms separated by free settling ( not prevented) from this space, are recirculated in the aeration space along the lower periphery, the stream of purified liquid overflows at the top of the decantation space, while during this time, microorganisms formed continuously in the aerated space (excess sludge) are eliminated using the liquid stream leaving the axis of the aerated space and are concentrated separately. Thanks to this process, the concentration of the mud in the aeration space can be maintained in a simple manner using a stream of liquid representing at most 15% of the volume of liquid to be treated. the amount of treated liquid stream leaving the settling space and excess sludge leaving is always the same as the amount of liquid stream to be treated and introduced into the system.

Thus, the volume of liquid representing at most 1.1 volume, sent into the settling space is 10% greater than the sum of the volume introduced and the amount of excess mud stream compared to the overflowing treated liquid stream. at the top of the settling area. This excess liquid being at most 15% of the liquid introduced returns to the aeration space at the bottom of the decantation space with the diluted sludge and it is always sufficient to maintain the hydraulic balance of the system. Consequently, there should be no thickening of the mud at the bottom of the space
decantation and at the same time, the mass of sludge separated from the treated liquid can easily be passed through the aeration space at the cost of a pumping performance significantly less than that which is usually required.

 According to the process of the present invention, the stream of raw fluid to be treated, the nutrients and auxiliary agents can be introduced into the microbiological process in the vicinity of the mantle of the aerated tank or along other concentric circles. In this way, the concentration gradient formed during the radial flow can be achieved. The concentration gradient can also be changed by grouping the gas streams introduced into the space in concentric circles and by regulating the gas supply of each group as well.

 Air or a gas having an increased oxygen content can be used in the various aerobic microbiological processes. The gas can be heated or cooled before it enters the system or appliance, much like liquids. The position energy of the gases introduced into the aeration space at the bottom of the tank, generally through concentric distribution conduits, can be exploited to agitate the contents of the tank according to the "rising air" principle. . At the same time, the gas streams introduced are dispersed or, if desired, subjected to a pulsation, in order to obtain oxygen transfer and suitable contact.

 It is often necessary not to release gases used in aerobic microbiological processes directly to the open air, for reasons of unpleasant odor and risk of infection, but to collect and eliminate them, if desired , after post-purification. For this reason, in some cases a firm ventilation space is used.

 By means of concentric deflection cylinders arranged in the closed aeration tank and going below the level of the liquid, the gases can be directed, parallel or against the current with respect to the current of liquid going in the radial direction; in this way the gases leaving the liquid space are introduced into the consecutive space section, using an intermediate operating machine. This coupling is particularly advantageous when using oxygen-enriched gases and in procedures in which the oxygen demand changes greatly over time.

 It often happens in aerobic microbiological procedures that the mass of microorganisms cannot be easily separated from the liquid. In the case of purification of water by activated sludge, such a phenomenon is the "swelling" of the sludge, resulting from various maneuvers of overload and slight poisoning. To overcome this difficulty and facilitate separation, various additives are used in accordance with the present invention - for example, coagulants and polyelectrolytes.

The advantages of the present invention can be summarized as follows
- microorganisms entrained with the treated liquid sent through the aeration space, can be recycled by the use of a small volume of liquid in the aeration space and distributed uniformly along the periphery of the equipment in a simple way;
- the sedimentation of the mass of microorganisms does not require the presence of thickening agent of the mud and thus of the volume can be gained
- the mass of microorganisms formed continuously (excess sludge) can be concentrated under favorable conditions from a small portion of the liquid which does not represent more than one tenth of the volume introduced
- the active sludge is quickly recycled in the aeration space, making it possible to avoid anaerobic procedures
- the mass of microorganisms recycled from the decantation space in the aeration space, can preferably be aerated before being mixed with the liquid to be treated
- the ventilated space can function either as a stirred tank reactor or as a flow-through reactor or a combination of these
- the concentration gradient of the liquid moving in the aeration space in the radial direction, can be simply regulated by the introduction of liquid and air.

 The process according to the present invention is particularly suitable for the biological treatment with activated sludge of highly contaminated residual water and for the production on an industrial scale of continuous fermentation technologies.

 The vertical section of the apparatus suitable for carrying out the method of the present invention is shown in Figures 1 and 2.

 Fig. 1 illustrates a characteristic aspect of the equipment, while FIG. 2 shows a specific implementation thereof. It should be noted that the invention encompasses a certain number of implementations within the framework thereof.

 The apparatus is described with reference to FIG. 1. The cylindrical and conical tank 10 is divided by the cylindrical and conical air chamber 11 of separation, into two sections communicating with each other by the slot 5 which extends along the periphery. The aerobic microbiological process is carried out in the space 12, located below the air chamber 11. The air or the oxygen-enriched gas is preferably introduced into tubes 13 and 13a which are open at the same time. their upper and lower ends. These tubes are arranged in groups according to the desired goal. The microorganisms are separated from the treated liquid in the space 19, around the air chamber 11. The separated microorganisms are recycled in the space 12 through the slot 5.

 The liquid to be treated is introduced continuously into the aeration space 12 through the duct 1, the distribution plates and the junction circuits 9 and / or 9a along one or more concentric circles. The liquid to be treated is mixed at the entry points with the contents of the tank using air or oxygen-enriched gas introduced into the stirring and contact tubes 13. The liquid to be treated is supplied with the quantity of oxygen required for aerobic microbiological procedures with radial flow. The gas necessary for the microbiological procedure and for stirring is introduced through the pipe 2 of the frame and its quantity can be controlled using supply valves 2, preferably arranged along concentric circles in each series of tubes. The current of liquid introduced into the conduits 9 crosses the tank while being agitated, in the radial direction towards the axis of this tank, in which a measured quantity 3 of liquid containing microorganisms is led onto the distributor plate 15 using the air rise 14 or some other convenient means, after which it is sent through conduits 16 and inlet tubes 17 into the settling space surrounded by walls 10 and 11 arranged concentrically with respect to the ventilation space.

 The microorganisms leaving the decantation space are directed, while the sedimentation is left free (not prevented), through the slot 5, directly in the aeration space in which the microorganisms can be activated if necessary, using the series of tubes 13a closest to the mantle, before coming into contact with the raw liquid. The microorganisms (excess sludge) being continuously formed in the microbiological process, are preferably distributed in stream 3, sent through the conduit 6, to the sludge thickener 20 which operates in known manner. The stream of liquid 4 clarified in the decantation space of the device is eliminated via the overflow channel 18. The gases leaving the microbiological process are combined and eliminated through line 7 and purified, if it is necessary.

 According to FIG. 2, the gas space of the device is divided into sections by concentric cylindrical envelopes 22, arranged in the ventilation space 12 and immersed in the liquid. The gases leaving the separate gas spaces are transported in the contact section with consequent agitation in the radial direction inward or outward and thus the gases pass in a current parallel or counter-current to the radial flow of the liquid.

In addition to the foregoing provisions, the invention also comprises other provisions, which will emerge from
the description which follows.

 The invention will be better understood with the aid of the additional description which follows, which refers to an example of implementation of the method which is the subject of the present invention.

 It should be clearly understood, however, that this exemplary implementation is given solely by way of illustration of the object of the invention, of which it does not in any way constitute a limitation.

EXAMPLE
Equipment has been established with a volume of 1720 cm3 and a water depth of 7.5 m to carry out the purification of residual water by an activated sludge. This equipment is divided by an air chamber 11 into an aeration space (1380 cm) and a decantation space (340 cm3). Sixty contact tubes with angel are built in the aeration space. The liquid aeration space conteru is agitated by means of these tubes, by the exploitation of the position energy of the gas introduced at the bottom, while the oxygen necessary for the microbiological procedure is dissolved in the waste water and takes part in the purification process.

The biologically purified residual water is sent to the decantation space by means of the air rise 14, through eighteen inlet tubes arranged uniformly on the periphery of the decantation space 19.

 The residual water to be treated consists of 54 m3 / h of raw residual water from various pesticide manufacturing technologies. The raw residual water is first neutralized, qualitatively balanced and supplied with nutrients, then introduced into the aeration space of the equipment, through the conduit 9 along the mantle. The average degree of contamination of residual water is 5700 g / m; COD chemical oxygen demand), and this is eliminated with an average efficiency of 90%.

3750 m / h of air are introduced under a pressure of 1.85 bar into the aeration space, distributed by three concentric reinforcing conduits. The average concentration of mud in the aerated space is 4.5 kg / m and the yield of excess mud is 26 kg / h.

 54 m3 / h of water containing mud are led to the air from the air rise 14, from the ventilated space to the discharge space, from which 47-48 m m3 / h of purified water freed from mud, via the overflow channel.

The excess sludge formed in the biological process is also eliminated using the air rise 14 by means of a water current of 6 - 7 m3 / h, depending on the concentration of the sludge. The mud is decanted and concentrated in a small apparatus according to known methods. The mud (about 260 kg / h) precipitating from the purified water leaving the overflow, passes along the mantle of the device with a current of 6 - 7 m3 / h of water and is re-introduced into the ventilation space through the slot 5. This downward flow of liquid is sufficient to maintain the hydraulic balance of the system.

For comparison, here is the volume of material of aeration space and the sedimentation unit of known processes
- entry of residual water into the aeration space 54 m3 / h;
- water flow required to recycle the concentrated sludge at 9 ka /, 3 from the settling space: 48 m3 / h,
- water flow required to remove excess sludge: 3 - 3.5 m3 / h
- volume of the concentration decantation space 3 400 m
The comparison clearly demonstrates the following advantages of the process of the present invention
- it is not necessary to thicken the activated sludge which settles, before recycling it in the aeration space, thus, one can save approximately 15% of the volume of the decantation space
- the recycling of the sludge from the settling space is simple and the volume of the liquid stream represents only 15% of that used in the known processes, so that the required pumping capacity is smaller in proportion .

 The volume of the apparatus required for decanting and thickening the excess sludge is small, in proportion to the amount of excess silt; at the same time, the separate settling space allows the use of these technologies and these additives in the settling of excess sludge, which have a favorable effect on the thickening process.

 As is apparent from the above, the invention is in no way limited to those of its embodiments of implementation and application which have just been described more explicitly; on the contrary, it embraces all the variants which may come to the mind of the technician in the matter, without departing from the framework, or the scope, of the present invention.

Claims (8)

 1.- Continuous process for carrying out submerged aerobic biological processes, in a tank for the aeration of microorganisms, this tank having a vertical axis and a circular cross section and in a decantation space located outside this tank, along its upper periphery, characterized in that the stream of raw liquid to be treated, the nutrients and auxiliary agents are introduced into the tank in the vicinity of or on the mantle of the aerated tank and qu 'they are distributed along other concentric circles, while the liquid containing the microorganisms is stirred and brought into contact with currents possibly subjected to pulsations of air or oxygen-enriched gas distributed at the bottom of the tank; Is introduced from the liquid containing the microorganisms, a volume not exceeding 1.1 volume of the liquid stream (s) sent into the system, to the axis of the aerated tank, this introduction being carried out along from the periphery of the tank in the settling zone; the microorganisms separated from the liquid are recycled during free sedimentation (not prevented) at the bottom of the decantation space in the aerated space, while the flow of liquid free of microorganisms at the top of the space overflows decantation, the microorganisms formed are continuously eliminated in the aerated space (excess sludge) outside the system, using the stream of liquid entrained at the axis of the tank and these are separated. this liquid.  2.- Method according to claim 1, characterized in that the gas streams introduced into the tank are disposed separately along concentric circles and that the gas supply of the separate groups is regulated separately.  3.- Method according to any one of claims 1 or 2, characterized in that the liquid and / or gases are heated or cooled before ~ introducing them into the process.  4.- A method according to any one of claims 1 to 3, characterized in that directs the gases against the current or in parallel with the current of liquid passing through the air space, dividing the air space pre regency in several sections and introduce the gases leaving the first liquid space in the next section and repeat this procedure  , - Method according to any one of claims 1 to 4, characterized in that an additive is used for the separation of microorganisms from the liquid.  6. Apparatus for carrying out the method according to claim 1, having a circular cross section and a vertical axis, characterized in that a tank (10) is divided into two sections by an air chamber (11) arranged concentrically, namely the ventilation space (12) and the settling space (19), which are connected by a chamber (15) dc upper distribution arranged in the center, with conduits (16) and which common between them by gravitation at the bottom of the air chamber and a liquid outlet section (6) joins the distribution chamber (15) and a outlet section Water line (4) joins the decantation space (19) via a collecting channel (18).  7.- Apparatus according to claim 6, characterized in that an air rise (14) or a submerged pump or a pump disposed outside the apparatus, is connected to the distribution chamber (15) serving liquid outlet from the ventilation space (12).  8.- Apparatus according to claim 6 or 7, charac terized in that tubes (9) and (9a) dipping into the aeration space (12) and leaving the distribution chamber (8) disposed in the axis of symmetry of the device and placed in one or more concentric circles, serve as an inlet for the stream of raw liquid to be treated.  9. Apparatus according to any one of claims 6 to 8, characterized in that it comprises a number of inlet tubes (17) in the settling space of the apparatus, preferably distributed uniformly along from the periphery of the decantation space, to introduce the liquid withdrawn from the aeration space by a force current and containing microorganisms.  10.- Apparatus according to any one of claims 6 to 9, characterized in that the ventilation space of the apparatus is closed at the top and comprises a section (8) for the outlet of gases leaving the system.