DE2339557A1 - METHOD AND DEVICE FOR REMOVING NITROGEN FROM ORGANIC WATER CONTAINING NITROGEN COMPOUNDS - Google Patents

Description

The invention relates to improvements in the treatment of waste water, and more particularly relates to one Method and apparatus for removing nitrogen from organic compounds containing nitrogenous compounds Wastewater, the wastewater containing the nitrogenous compounds in dissolved and / or suspended form included · The invention also relates to the Treatment of organic waste water that contains phosphates in addition to nitrogenous compounds, to remove nitrogen and phosphates from this waste water,

The methods and devices that have hitherto been used for this purpose have many disadvantages.

It is the object of the invention to overcome these disadvantages.

This object is achieved by the invention specified in claims and 20,

409808/0894

Although the biological denitrification occurring in the first and third stages is not yet fully understood, it is generally believed that a significant number of facultatively anaerobic bacteria found in normal activated sludge have electrons in the respiratory chain on nitrites and nitrates rather than oxygen transmitted when the oxygen tension is low enough. Mi-fc in other words: The! Titrates and nitrites replace the oxygen as the last electron acceptors in the respiratory chain as soon as the oxygen tension drops sufficiently.The nitrates and nitrites are _{reduced to nitrogen gas, N 2} O-GaS and other forms of nitrogen-containing gases.

Since here the electron path down to the last electron transfer from the cytochromes to the last Acceptor is the same as in normal breathing under _ aerobic conditions, it is believed that all substrates commonly used by the cells for respiration also for the reduction of nitrates and nitrites as Can serve hydrogen donors.

It is therefore assumed that the cell mass changes only slightly under low oxygen tension Cell mass differs under aerobic conditions and the substrate degradation rates are not disadvantageous «Therefore it can be assumed that the cell growth rates are those of aerobic Similar to processes

4098 08/0894

In denitrification processes, wastewater containing nitrates must therefore be contaminated with bacteria * under anaerobic conditions. brought into contact or mixed, whereby the bacteria have to breathe fast enough for the denitrification to effect in a reasonable time. The bacteria can be suspended and grow on underwater substances or be present in some other way

When a denitrification process under anaerobic Conditions are carried out and not enough oxygen, nitrates and nitrites are supplied can cause a Sulphate reduction and anaerobic fermentation occur

The first and third stages of the invention must therefore expediently be operated under conditions where nitrates and nitrites are the last electron acceptors in the respiratory chain of the optional anaerobic bacteria are used, but in which neither a suIf at reduction nor anaerobic fermentation occur. Such conditions are called "oxygen-free conditions" in the further course of the description.

If, therefore, in the process according to the invention, the conditions in the first stage become so anaerobic, that a sulfate reduction or anaerobic fermentation occurs, sufficient oxygen can be supplied, in order to rule out these undesirable side effects without reducing the nitrates and nitrites excessively would be disturbed.

4Q9808 / Ö894

As far as the first stage is concerned, the inflowing, organic wastewater is the source of carbon for the facultative anaerobic bacteria in the activated sludge returned to the first stage, to ensure denitrification the effect of nitrates and nitrites

The denitrification capacity of the third stage is determined by the breathability of the second to the third stage of reaching sludge determined

In certain cases, it may be necessary to operate the first and third stages under oxygen-free conditions It may be necessary to prevent air from entering these steps by making these steps essentially airtight be completed·

It is known that biological processes are adversely affected when ^{the temperature drops below approx. 30 ° C.}

The reduced breathability in the first stage is of little importance if the temperature is not significant drops below 20 ° C, because due to the recycled active sludge a sufficiently high concentration of Facultative anaerobic bacteria to be found in the first stage is and 'the incoming organic waste water provide enough carbon

However, if the temperature drops below approx. 15 ° C, The slowed breathing in the third stage can lead to insufficient denitrification in the case of the invention Conduct proceedings.

409 8 0 8/0894

In this regard, however, the airtight sealing of the first and third stages can be used for containment contribute to heat loss «However, this measure can only be used for this purpose Be of reduced effectiveness

To a large extent, therefore, insufficient denitrification in the third stage as a result of too low a temperature To avoid this, it may be necessary »to increase the capacity of the third stage to such an extent that denitrification can proceed as completely as possible under all possible temperature conditions.

The one for increasing the capacity of the third Level required costs can, however, especially »if the seasonal temperature fluctuations are very tall, be very tall

Any alternative or additional measure to the most extensive Avoidance of insufficient denitrification in the third stage could, if necessary, be a suitable one in the third stage Carbon source must be provided

A further feature of the invention can thus in the third stage a suitable carbon source Be provided to improve breathing when below that for maintaining denitrification level required during the procedure drops

409808/0894

When applying the invention, by comparing the for increasing the capacity of the third tier required cost with the cost of periodically placing a carbon source in the third stage, the more cost-effective procedure can be determined for a specific location.

As a carbon source, peelers can use suitable carbon donors without nitrogen content, e.g. methanol, can be used

As for the second stage, the ecology autotrophic, nitrifying bacteria is not yet fully known · It has been found, however, that plants are operated with activated sludge such könnenj that above a temperature of approx · 1O ⁰ C nitrification of nitrogen compounds incessantly and takes place reliably.

Palis the oxygen tension is high enough to transform the nitrifying agents present in the activated sludge Bacteria convert the nitrogenous compounds into nitrates. Hence, ammonia turns into nitrates and nitrites and nitrites into Nitrates transformed.

There seems to be a difficulty factor in converting ammonia into nitrites, because nitrites are quickly and easily converted into nitrates. The end result of nitrification is therefore nitrates

409808/0894

The second stage of the process according to the invention is therefore operated under aerobic conditions, i.e. with ventilation, in order to remove the dissolved nitrogenous compounds to oxidize biologically to nitrates

The second stage can be ventilated by any suitable means by surface aeration means or by underwater lift means be ventilated.

The surface ventilation means can, for example be provided in the form of ventilation discs. The underwater ventilation can for example be achieved by using air, pure oxygen or a mixture is blown from air and oxygen into the mixed water in the second stage.

Surface ventilation has the disadvantage that it cools down when the outside temperature is low can lead. In addition, their use is limited by the depth of the aerated liquid · Uhterwasser aeration can be as a result of the fact that the compressed air or the compressed oxygen is below the surface of the to be ventilated Liquid is blown in, lead to a beneficial heating effect. This should be noted if the outside temperature plays a role.

The concentration of dissolved oxygen must be high be enough to maintain aerobic conditions · however, it should not be too high because then at the

409808/0894

Return of the mixed water from the second to the first stage and when the mixed water is supplied from the second Too much oxygen is carried into the third stage, which has an adverse effect on denitrification in the first and third stage has »

The concentration of dissolved oxygen in the second stage can, for example, be between approx. 0.5 and approx. 4 mg / l · The dissolved oxygen concentration can preferably be between approx. 0.5 and approx. 2 mg / l. It should be the lowest Value that still results in good nitrification can be selected »This value can be higher in winter than in summer _e

The dissolved oxygen concentration in the second stage should therefore be measured periodically and the Ventilation means can be adjusted accordingly. The dissolved oxygen concentration can, however, also through automatically working devices can be measured and dosed.

In the second stage, the solids residence time is important because it should be long enough to prevent excessive loss of nitrifying organisms
to avoid. The residence time is determined by a
the size of the second stage and / or the concentration of the suspended solids in the mixed water

Λ09808 / 0894

The nitrifying organisms are temperature dependent · Using the test _{results of Downing (Downing, AL, Painter, Η β} Α. And Knowles, G. “Nitrification in the activated sludge process ¹¹ ) - journal“ Proceedings of the Institute for Sewage Purification "(work reports of the Institute for Wastewater Treatment), Part 2, page 130 (1964)) Regarding the relationship between the temperature and the growth rate of these microorganisms, the minimum residence time of the solids or the sludge age to ensure the nitrification can be calculated according to FIG. 1 of the drawings 1 shows the temperature in ⁰ C along the abscissa, the sludge age in days along the left ordinate and the growth rate in km / day along the right ordinate The relationship between sludge age and temperature is shown as a solid line and the growth rate as a dashed line.

The proportion of the mixed water recirculated from the second to the first stage can preferably be corresponding the incoming fresh throughput and the concentration of nitrogenous compounds in the inflowing, organic wastewater can be controlled in order to achieve a considerably high denitrification in the first stage

409803/0894

The recirculated portion is expediently controlled so that such a reduction of nitrates and nitrites in the first stage takes place that the breathability of the bacteria in the third stage for coping the nitrates from the second to the third stage are sufficient.

The proportion of the mixed water recirculation throughput from the second to the first stage depends on the fresh throughput of organic waste water, the concentration of nitrogenous compounds in the influence, the in the third stage reducible amount of nitrate and the residence time in the first stage.

The Miachwasser-Hüokführung Durchaatz portion can can therefore be easily calculated by determining the amount of nitrate reducible in the third stage. This Recirculation throughput rate can be controlled so that the nitrate level in the second stage does not match the level that can be reduced in the third stage.

If the proportion of the mixed water return flow is too small, more nitrates are carried from the second to the third stage than in the third stage can be reduced, which would then result in an insufficient nitrate content in the discharge.

Is the proportion of the mixed water recirculation throughput too high, the capacity of the system would also have to be increased to cope with the greater throughput

409808/0894

be, -which, the economy and the efficiency of the procedure would decrease.

The volume ratio of recirculation throughput to hairdressing throughput can expediently at least be about 2 ': 1 ". For example, it can be between about 2: 1 and about 10: 1.

"Preferably the proportion of active sludge management throughput controlled in such a way that a suitable concentration of solids is achieved in the various stages of the plant prevails and thus also a sufficient number of bacteria to ensure denitrification and litrification in the process

For maximum nitrification and denitrification, especially during the colder months, there is a high concentration of suspended solids in the mixed water he wishes. If the concentration is above the optimum value, it forces the system to have too high a capacity again

Semasa is an embodiment of the invention the proportion of the active sludge recirculation throughput is controlled in such a way that a solids concentration in the mixed water of preferably at least approx. 2,000 mg / l prevails «

In the method according to the invention, a small Share of active sludge from the solids separation stage returned to the second stage if the number

A09808 / 0894

the bacteria in the second stage are too small. These However, the measure should only be allowed under exceptional conditions to be required·

The notifying party has determined that in processes in which only nitrification is carried out, the pH value sometimes drops significantly · This has an unfavorable influence on the nitrification and the pH value must therefore be discontinued.

The applicant has found that the inventive Process in which both denitrification and nitrification are carried out, the pH does not sink. In tests that were carried out with unbuffered wastewater, there was even an increase the pH value is observed.

Tails however the pH of the inflow is too low it is advisable to raise the pH value in the course of pre-treatment in order to achieve optimal nitrification. * The pH value should expediently be raised to at least approx. 6.2. The optimal pH is at about 8.2.

In the method, he third stage agitation means may be provided respectively, Mild agitation to the water for the purpose of mixing in the first and in d ^N.

4098O8 / QS94

The pesticide separation stage can be designed in any way · It can be in the form of a clarification stage, a flotation stage or a sedimentation stage, for example are provided.

In the method according to the invention, between the third stage and the solids separation stage, a fourth stage in the form of an aeration stage can be provided. The purpose of the fourth stage is to allow any gas bubbles that might impede the separation of solids to escape and stabilize the sludge to facilitate solids separation. The fourth stage can be called a filtration stage be designed to nitrify ammonia that was released in the third stage.

The process can also be used to remove phosphates when the organic wastewater Contain phosphates. This aspect will be described later. As an alternative or additional measure, therefore, according to a further feature of the invention, the organic waste water in a further process step treated with suitable chemicals to remove phosphates from it

ι This phosphate removal can be suitable for anyone Time to be made during the inventive method.

40980870894

Any chemical that is suitable for phosphate removal and thereby nitrogen removal can be used for this , not adversely affected, can be used. It can chemicals such as alum, aluminate or iron salts are used.

The invention also relates to a device for carrying out the method according to the invention. These The device has a first stage in the form of a denitrification stage for taking up organic substances Wastewater containing nitrogenous compounds; a second stage in 3? form of a hit ication stage ej a third stage in the form of a denitrification stage j a pesticide separation stage to produce the clarified Outflow and an active sludge j mixed water recirculation means for the return of mixed water from the second stage to the first stage, and active sludge return means for recycling at least part of the active sludge produced by the solids separation stage to the first stage.

The mixed water return means may be provided in the form of a pump capable of the Recirculate mixed water with a volume throughput required to carry out the process

The active sludge return means can also be provided in the form of a pump capable of to recycle the active sludge with a certain volume throughput.

Λ09808 / 0894

The device can also have supply means, the mixed water under the action of gravity from the first to the second, from the second to the third and convey from the third to the solids separation stage.

The supply means between the first and second stages can be arranged in such a way that the from the first stage overflowing mixed water at one point is introduced into the second stage below the liquid level. The one between the second and the third Feeding means located on the level can work in the same way

The mixed water management means between the second and the first stage promote mixed water from the second stage back into the first stage so that short circuits in the first and the second stage largely avoided will·-

The second stage takes the form of a nitrification stage is provided, the device has ventilation means for ventilation of the second stage.

The ventilation means can be in the form of surface ventilation means or be provided by underwater ventilation means

If surface ventilation means are provided, these can, for example, in the form of one or more Ventilation disks may be provided, which are for the purpose of air transport in the one located in the second stage Mixed water are set in rotation.

409808 / Ö894

If underwater ventilation means are provided, these can for example in the form of air or Oxygen supply means can be provided with which Compressed air or compressed oxygen fed into the second ■ stage and there at an underwater point is released.

The device can have stirring means in its first and third stage, the gentle stirring for mixing purposes only.

So that the first, and the third stage under sour ■ can be operated in low-substance conditions, the device can have covering means to the first and to cover the third tier.

These covering means can be designed as desired. In one embodiment of the invention exist the covering means, for example, from lids made of foamed plastic

When the outside temperature is low, so can the second stage are covered in order to reduce the heat losses as much as possible.

The device can furthermore if necessary Have means for feeding a suitable source of nitrogen-free carbon into the third stage.

Furthermore, between the third stage and the solids separation stage, a fourth stage in the form of a Ventilation stage should be provided in the grass vesicles,

4 09 808/0894

which could hinder the solids separation in the solids separation stage, can escape, and in which the Sludge is stabilized in order to separate the solids to facilitate.

The fourth stage can take the form of a nitrification stage are operated in which, if necessary, released in the course of the procedure in the third stage Ammonia is nitrified.

When the gate direction has a fourth stage, the feeding means described above between the third stage and the solids separation stage by feeding means between the third and fourth stages and feeding means between the fourth stage and the solids separation stage replaced. This supply means can also be a gravity drive, as above has been described.

The solids separation stage can be designed as desired »So aie can, for example, be in the form of a clarification stage, a flotation stage or a sedimentation stage be provided.

Depending on the target capacity of the device, on economic considerations regarding the construction of the device, of a possible increase in the capacity of the device, etc. can be any suitable containers are provided for the four stages of the device

409808/0894

Palls, for example, approx. 25 · ΟΟΟ m_organische Wastewater must be treated daily in the 'device, the second and fourth stages in the form endless, annular channels are provided, the denitrification stages within the range of the endless, ring-shaped channels enclosed areas are arranged

In the event that the system is enlarged, enough floor space could be kept available to build another device of the same capacity

However, if the available area is limited and excavation work does not pose any major difficulties You can also prepare the different levels in the form of recessed in the ground and arranged side by side Containers can be provided · With this arrangement, the depth of the various containers can be approx. 9 »14 m and more, which considerably reduces the floor space requirement

The stepped containers of the device can be made of any suitable material. So they can for example made of concrete, prefabricated concrete slabs or the like.

If the device has to have a capacity of more than approx.20,000 m of organic waste water per day, economic considerations usually lead to a

8/0834

Construction method in which the soil to a depth of approx. 9 »14 m or more is excavated and the four steps side by side be placed in the excavated pit.

Since the inventive method with the associated Device is to be used together with physicochemical units for water recovery if necessary, a flow equalization can be provided.

This could be done in that the first stage is built large enough to compensate for the flow and denitrification to be able to serve. The mixed water could then be conveyed from the first to the second stage with constant throughput. The repatriation of hit rates from the second stage to the first stage when the mixed water is returned largely prevents it from becoming Pauline in the first stage.

While the present invention relates generally to the treatment of organic nitrogenous In particular, it can be used in the treatment of sewage in the form of sewers. The cloaca can be in its raw state or already discontinued

In the drawings showing several embodiments of the invention:

1? Ig. 1 is a graphical representation of Downing's test results for determining the Minimum residence time or the sludge age, through which a hitrification is ensured;

4Ü98GS / O894

FIG. 2 shows a schematic current diagram of an inventive Device for carrying out the method according to the invention, in which Organic wastewater in the form of settled cesspools are treated to make nitrogenous from them Remove links;

Fig. 3 is a schematic plan view of an embodiment of the device for performing the inventive method;

4 shows a schematic plan view of a further exemplary embodiment of the implementation device of the method according to the invention;

Fig. 5 is a schematic plan view of another Embodiment of the device for carrying out the method according to the invention;

Fig. 6 is a graph showing the results for nitrogen and phosphorus in operation the device according to FIG. 2 in the form of an experimental installation and for a period of twenty Days, and

7 shows a graph of the chemical oxygen demand in mg / l and the phosphates in mg phosphorus / l in the outflow when operating the test facility for a period of time of six weeks to achieve phosphate removal.

409808/0894

]? ig. 2 illustrates on the basis of a current diagram the method according to the invention and the device, with the help of which organic wastewater in the form of settled cloaca can be treated to .from them and / or remove suspended nitrogenous compounds.

The device 10 has supply means 12 for the supply of settled waste water.

Raw wastewater is usually sieved and, after settling, passes over the under the action of gravity Feed means 12 into the device 10.

The device 10 consists of a first stage 14 in the form of a biological denitrification stage, a second stage 16 in the form of a biological nitrification stage, a third stage 18 in the form of a biological denitrification stage, a fourth stage 20 in the form an aeration stage and a solids separation stage 22 for generating a clarified effluent flowing out of the device 10 at 24 and an active sludge, which flows out of the solids separation stage 22 at 26,

The device 10 has a drain line 28 for discharging waste sludge from the device 10 and furthermore sludge return means 30 with a pump 31 for returning part of the active sludge to the first stage 14.

409808/089

7339557

The device 10 also has a return line 32 for mixed water and a pump 34 for return From mixed water from the second stage 16 to the first Level 14.

The device 10 also has feed means 14 »1, 16.1, 18.1 and 20.1 to use gravity the mixed water from the first to the second, from the second to the third, from the third to the fourth stage and from the fourth stage to lead to solids separation stage 22.

The supply means between the stages are provided in such a way that the overflowing mixed water from the the previous stage flows into the following stage under the action of gravity below

The return line 32 for the mixed water takes this from the second stage 16 in addition to the supply means 16.1, so that a short circuit in the second stage 16 is largely avoided. This mixed water is in in the vicinity of the supply means 12 is returned to the first stage, so that here, too, a short circuit between the recycled mixed water and the mixed water discharged from the first stage 14 by means of the feed means 14.1 is largely avoided.

In the first stage 14 and the third stage 18 stirring means 36 are provided to gently stir the mixed water for mixing.

The first stage 14 and the third stage 18 are operated with the exclusion of oxygen.

^ 09808/0894

~ ^23v ~ 7339557

The second stage 16 and the fourth stage 20 are with ventilation means !! 38 provided under aerobic Conditions operated aerobic stages, thus in the second stage 16 as well as in the fourth stage 20, if ammonia released by the third stage 18 is present there, nitrification can take place. The fourth stage 20 also serves to allow grass bubbles to escape, which impede the separation of the solids and stabilize the sludge to facilitate the separation of solids.

The aeration of the second stage 16 is controlled so that the concentration of dissolved oxygen is high enough to allow nitrification to take place, but not so high that excessive dissolved oxygen via the supply means 16 · 1 from the second ¹ stage - 16 can pass into the third stage 18 and via the return line 32 for the mixed water from the second stage 16 into the first stage 14

In tests that have been carried out, it has been found that the ventilation is readily controlled in this way it can be that in the second stage 16 a concentration of dissolved oxygen of between approx. 2 mg / l and approx. 0.5 mg / l prevails.

In 'Fig. 3 denotes 10.3 an exemplary embodiment a device for carrying out the method according to the invention

409808/08 9 4

A device according to this embodiment would then be used if the device 10.3 The area occupied by the installation site is not a critical size and does not represent the required capacity is less than approx. 25,000 m of organic waste water per day.

The device 10.3 has feed means 12.3 for feeding organic waste water into the device 10.3.

The device 10.3 also has a first stage 14.3 in the form of a denitrification stage, a second stage 16.3 in the form of a nitrification stage, a third stage 18.3 in the form of a denitrification stage, a fourth stage 20.3 in the form of an aeration stage and a solids separation stage 22.3 for generating one at 24.3 the device 10.3 flowing clarified effluent and an active sludge flowing out of the solids separation stage 22 _e 3 at 26.3.

The device 10.3 has a discharge line 28.3 for discharging waste sludge from the device 10.3 and sludge return means 30.3 with a pump 31 * 3 for Returning at least part of the active sludge to the first stage 14.3. The device 10.3 also has a return line 32.3 for mixed water and a return pump 34 * 3 for returning the mixed water from the second Step 16.3 to the first step 14.3.

409808/0894

7339557

The device 10, 3 also has feed means 54, 56, 58 and 60 in order to convey the mixed water successively through all stages up to the solids separation stage.

In the first stage 14 * 3 and the third stage 18.3 stirring means 36 x 3 are provided to gently stir the mixed water for mixing.

The first stage will be 14.3 and the third stage will be 18.3 operated in the absence of oxygen. In them nitrites and nitrates become nitrogen gas, nitrogen oxide and other smaller proportions of nitrogenous gases are reduced.

! all in the first stage 14.3 and the third stage 18.3 the concentration of the dissolved oxygen If the influence of air is adversely affected, these two levels can be covered with suitable covering material « The covering means can expediently be lids made of foamed plastic.

The second stage 16.3 and the fourth stage 20.3 are aerobic stages. Hence, each of them has ventilation means 38.3 for ventilation.

The second step 16.3 and 20.3 the fourth stage are formed in the form of endless, annular channels concentrically disposed and within which the first stage and the third stage 14.3 1-8 * 5 are arranged ·

409808/0894

7339557

Since stages 16.3 and 20.3 are usually kept so flat that effective surface ventilation . can take place, the ventilation means are 38.3 ia Eorm from Surface ventilation means shown.

In the exemplary embodiment shown in FIG. 3, the ventilation means 38.3 consist of four ventilation systems, two of which are diametrically opposite each other.

Each ventilation system has a motor 40 which drives a rotatably mounted shaft 42. Each shaft 42 has several ventilation disks attached to it 44

Each ventilation disk 44 is provided with a plurality of holes or elevations, of which in the steps 16.3 and 20.3 during the rotation of the shaft 42 air in the mixed water is introduced.

The ventilation means 38.3 thus serve both to ventilate the mixed water and to transport the Mixed water along stages 16.3 and 20.3

The device 10.3 can have automatic test devices (not shown) that monitor the concentration of the dissolved oxygen in stages 16.3 and 2Ο · 3 and the aeration means 38.3 accordingly control that the desired concentrations are maintained.

409808/0894

In Pig * 4, 10.4 denotes a further embodiment a device for carrying out the method according to the invention.

According to its "structural design, the in Pig. 4 shown device for the same purposes as the device according to Pig. 3 suitable.

The device 10.4 is generally similar to the device

10.3 and has supply means 12.4 for supplying organic waste water in the device 10.4.

The device 10.4 also has a first stage 14 * 4 in the form of a denitrification stage, a second stage 16.4 in the form of a uitrification stage, a third stage 18 · 4 in the form of a denitrification stage, a fourth stage 20.4 in the form of an aeration stage and a pesticide separation stage 22.4 to generate a clarified effluent flowing out of the device 10.4 at 24 »4, and to generate it an active sludge that is removed from the pesticide separation stage at 26.4 22.4 flows on.

The device 10.4 also has a drainage line

28.4 for removing waste sludge from the device 10. · 4 and sludge return means 30.4 with a pump 31 «4 for returning at least part of the active sludge to the first level 14 * 4.

The device 10.4 also has a return line 32.4 for mixed water and a return pump 34 * 4 for returning the mixed water from the second stage 16.4

in the first stage 14 4

4Ö9808 / Ö894

The device 10.4 also has feed means 54 · 4 » 56.4, 58.4 and 60.4 to view the mixed water under the influence of visual force guide through the various stages of the device

In the first stage 14.4 and in the third stage 18.4 Agitation means 36.4 are again provided in order to slightly stir the mixed water for the purpose of mixing.

The second stage 16.4 and the fourth stage 20 * 4 are ■ again aerobic stages and have ventilation means 38.4 for ventilating these two stages. The ventilation means are in turn surface ventilation means and consist of rotatably mounted ventilation rotors, the for the purpose of aeration of the mixed water and its conveyance along the steps 16.4 and 20.4 are set in rotation can.

In contrast to the device according to FIG. 3, the device 10.4 according to Pig. 4 only the second stage 16.4 the shape of an endless, ring-shaped channel on

In FIG. 5, 10.5 denotes a further exemplary embodiment of a device for carrying out the invention. according to the procedure.

According to its structural design, the one shown in Fig. shown device 10.5 intended for cases in which the area occupied by the device of Is important or where underwater ventilation takes place «

409806/0894

The device 10 * 5 also has feed means 12.5 in order to feed organic waste water to the device.

The device 10.5 also has a first stage 14 * 5 a second stage 16.5 in the form of a denitrification stage in the form of a nitrification stage, a third stage 18 x 5 in the form of a denitrification stage, a fourth stage 20.5 in the form of an aeration stage, and a solids separation stage 22.5 for generating a clarified outflow that flows out of the device 10.5 at 24.5, and for Generation of an active sludge, which at 26.5 the solids separation stage 22.5 leaves on.

The device 10.5 also has a drain line 28.5 for discharging waste sludge from the device 10.5 and sludge return means 30.5 with a pump 31 * 5 for Returning at least part of the active sludge to the first stage 14 · 5 ·

The device 10.5 also has a return line 32.5 for mixed water and a pump 34 * 5 for return of the mixed water from the second stage 16.5 to the first stage 14.5.

The device 10.5 also has feed means 54.5, 56.5 »58 * 5 and 60.5 to get the mixed water through the different stages of the device 10.5 to promote.

409808/0894

The feed means can also be operated with gravity in this device the first stage should also serve to compensate throughput, the supply means 54.5 can consist of a pump.

In the first stage 14 x 5 and the third stage 18 x 5 agitation means 36 * 5 are again provided

The second and fourth stages are also aerobic here Steps and have ventilation means 38.5 aur ventilation of these two levels on

In this embodiment, underwater ventilation is provided when the depth of the various Steps for surface ventilation -too large. The ventilation means 38 * 5 are in the form of ventilation lines provided, through which compressed air or pure oxygen is directed into underwater areas of levels 16.5 and 20.5.

The device 10.5 is particularly suitable for cases where there is sweep of more than 20,000 m of wastewater per day. If the capacity to be handled by the device is much greater than this amount, the system can consist of several units, each of which corresponds to the device 10 * 5

When building the device 10.5 could be a pit with The depth of this pit could be approximately 9.14 m or more, and the various stages 14.5, 16.5, 18.5 and 20.5 could be in this pit will be built in

409808/0894

In the drawings, the devices 10.3, 10.4 and 10.3 shown approximately to scale for a pail in which the residence times of the wastewater are based on the average duration in dry weather, approx. 4 hours in the first stage, approx. 4 hours in the third stage, approx. 15 hours in the second stage and about 2 hours in the fourth stage. These dwell times apply to average throughputs in dry weather and do not take into account the amounts of the reflux flow rates of the mixed water and the active sludge

The arrangement shown in Pig * 5 is special economically. The arrangement and the design of the various stages can be changed as required.

With a device according to Pig.2 were numerous Experiments carried out in a laboratory mass rod. The average

Results of these various tests are given in Table I. summarized.

The tests were carried out at operating temperatures of between 20 and 23 ^° C., the throughput of settled wastewater being approx. 1 l / hour. The pesticide separation stage consisted of a sewage treatment plant, which is mentioned in Table I.

409808/0894

The residence times observed in the experiments for the various stages were as follows:

First level 14: approx. 2 hours; Second stage 16: approx. 6 hours; Third level 18: about 6 hours, and fourth level 20: about 2 hours.

The residence times mentioned above are not the actual residence times, because these are determined by the Return of the mixed water from the second to the first stage and the return of the active sludge determined. For example, if the volume ratio of recycle flow - from the second to the first stage - to Irish flow 2: 1, and, provided that the return flow rate of the mixed water from the second to the first Stage taken into account when the volume ratio of the return flow rate of the active sludge from the

409808 / Ö894

Solids separation stage 22 back to the first stage 14 to fresh throughput is 1 ί 1, the actual residence time in the first stage 14 is approx. 30 minutes. The actual residence times in the other stages were accordingly about 1 1/2 hours in the second stage, about 3 hours in the third stage and about 1 hour in the fourth stage. ,.

The first column of Table I gives the volume ratios of active sludge recycle throughput to fresh throughput of settled wastewater, while the second column shows the volume ratios of Idischwasser recirculation throughput - from the second stage 16 to the first stage 14 - to fresh throughput on settled Indicating sewage.

Columns 4 and 5 of Table I give the concentration of dissolved oxygen required for oxidation in mg / l in the wastewater at the inlet and outlet. Columns 6 to 10 give the total nitrogen content according to Kjeldahl in mg / l, while the Columns 11 to 14 show the nitrate concentration in mg nitrogen Specify per liter.

£ 09808/0894

Table I.

return 2 3 Chera. sow
erstoffbe
allowed
(mg / 1) 5 - 6th Total nitrogen content
according to Kjeldahl (mg / 1) 8th 9 10 NO ₁ 11 -N (mg / 1) 13th 14th Stick
material-
removed
voltage (%) i'lish-
water
the end
second
step date 4th the end
flow A
flow 7th step
2 step
3 step
4th step
1 12th step
3 step
4th 15th O
CD
CO
Cw) mud
the end
Clarification
fe 9/2 A
flow 30th 58 step
1 2.6 - 2.2 1.6 step
2 3.0 8.2 2: 1 13/2
14/2 310 40
38 86
89 15.6 2.2
1.8 3.6
3.0 2.0
1.6 4.8
0.8 17.0 10.0
7.4 15.4
10.8 82.4 09
to 1: 1 16/2 470
460 40 75 18.6
18.4 1.6 3.0 1.4 0.6 > 20
23.5 3.0 6.6 81.5
86.0. 17/2 500 42 90 17.4 2.4 4.0 1.4 2.4 20.0 1.0 4.6 89.5 4: 1 18/2
19/2 560 42
30 · 81
71 11, 0 1.6
1.8 3.4
2.4 1.6
1.8 0.8
1.0 15.2 0.8
0 _f 8 3.4
2.8 _f
93.4 1: 1 20/2 340
280 34 68 13.0
10.2 1.8 2.4 1.8 2.2 15.0
12, 2 1.0 2.8 93.8
93.2 270 9.8 13.2 93.2

From the test results in Table I it can be seen that that in the second and fourth stages practically complete Hltrification was achieved. This goes out the low total nitrogen content according to Kjeldahl emerged. It can also be seen that there is practically complete denitrification in the first and third stages took place, which can be seen from the low nitrate levels. The total nitrogen levels became 'too over 93 # away.

The residence times were determined quite arbitrarily in the experiments carried out. It is quite possible that other residence times are even more suitable. This will be done later using a concrete example explained.

In carrying out the above-mentioned experiments, the nitrates in each Imt stage and the dissolved oxygen concentrations in the second and fourth stages were observed and the process was controlled accordingly. It has also been found that checking the ammonia concentration in the discharge is useful. This is particularly true when the clarified effluent from the device is to be chlorinated ("breakpoint chlorination").

As previously stated, the addition of limited amounts will effect methanol or other carbon sources for the third stage an increase in activity

409808/0894

this level at times of low activity. This allows the size of the third stage are kept shorter than usual, excessive dwell times in the third stage can lead to an increase in the ammonia content, thereby reducing the efficiency of the procedure is largely reduced

Several further tests were carried out with a device according to FIG. 2 in the form of a so-called test installation carried out.

The test plant was fed with a constant throughput of 100 nr settled wastewater per day, which was taken from the wastewater supplied to a municipal wastewater treatment plant «

The settled wastewater was withdrawn with a constant throughput, so that the daily fluctuations the degree of pollution of the wastewater, but not the daily. Throughput fluctuations were taken into account.

The average oxygen demand of the incoming settled wastewater fluctuated per day between 300 mg / l in rainy periods and 700 mg / l during long periods of drought. The total nitrogen content According to Kjeldahl at the entrance to the test facility, nitrogen fluctuated between 30 and 40 mg / l. Based on the throughput of settled wastewater were the residence times used in the operation of the plant 2 hours in the first stage, 6 hours in the second

^ 09808/0894

Stage, 4 hours in the third stage and 1 hour in the fourth stage

The volume ratio of sludge recirculation throughput to fresh throughput of settled wastewater was 1.! 1, and the volume ratio of the mixed water recirculation flow rate from the second to the first stage to the fresh flow rate of settled wastewater was 3 i 1

An automatic sampler was used to take effluent samples every two hours. The in Results compiled in the diagram of FIG. 6 are the mean values of the outflow parameters over the course of the course several weeks of uninterrupted operation «.

In Fig. 6, the ordinate axis shows the concentration in mg / l and the days of operation are recorded along the abscissa

The meaning of the different curves is as follows:

(a) White circles ι Kjeldahl nitrogen content in

Influence in mg nitrogen / l.

(b) Black triangles: phosphorus content of the influence

in mg phosphorus / l.

(c) White triangles: phosphorus content in the discharge

in mg phosphorus / l.

(d) White squares: total nitrogen content in the discharge

in mg nitrogen / l.

409808/0894

(e) Black circles: nitrate nitrogen in the discharge

in mg nitrogen / l.

. (f) Black squares s ammonia nitrogen in the discharge

in mg nitrogen / l.

From the results shown in Figure 6, it can be seen that substantial nitrogen removal is achieved became. 33's total nitrogen content in all of its Forming was about 4 to 5 mg nitrogen / l in the discharge.

It was also found that the level of phosphate in the discharge was quite low. During the first half the operating time it was determined that the phosphate content was approximately or slightly less than 1 mg phosphorus / l The phosphate content in the outflow then increased steadily to an average of 3 to 4 mg / l · During this period Time it was found that the concentration of suspended solids in the mixed water up to values of approx. 5,000 mg / l rose and there was sludge in the sewage treatment plant accumulated. No sludge was removed during this period.

Since, as just mentioned, no sludge was removed during the test period, precipitated phosphates remained with the exception of the portion that left the system in the clarified discharge, in the sludge and thus in the system.

In view of the reasonably low phosphate levels in the cleared effluent, the procedure was modified to achieve improved phosphate removal.

409808/0894

The invention therefore also extends to the method already described, in which a fourth Stage is designed as a ventilation stage and is then used when the organic waste water phosphates contain. In this variant, the fourth stage is ventilated in order to have one for the precipitation of the phosphates To obtain a sufficiently high concentration of dissolved oxygen, and also activated sludge from the solids separation stage discharged to remove phosphates from organic waste water

To a concentration of at least approx * 3 mg dissolved To maintain oxygen per liter, the fourth stage should be vented. By means of a suitable In the fourth stage, aeration can easily achieve a concentration of at least about 4 mg of dissolved oxygen per liter can be maintained.

To remove the phosphates can be done on a regular basis Active sludge can be removed at intervals or continuously.

In the process, the active sludge recirculation throughput from the solids separation stage can be controlled in such a way that the residence time of the sludge _{in the solids separation stage and thus also the development of GO 2} in the solids separation stage is limited.

The development of COp increases with the residence time of the sludge in the solids separation stage. this leads to cause precipitated phosphates to settle in the cleared discharge

409808/0894

dissolve whatever has the effect of the phosphate concentration increases in the clarified discharge "

The sludge recycling rate should therefore controlled so that the phosphate concentration in the clarified effluent is kept within acceptable levels remain.

Bs has been found that when the volume ratio of slurry to transit Rückführungsdurehsatz ^1-average fresh throughput in dry weather between 1: 1 and 2: 1, the phosphate concentration in the clarified effluent generally remains within acceptable limits.

The method can include a further method step in which the sludge from the solids separation stage is subjected to a sludge treatment process to obtain a phosphate-containing effluent.

Such a phosphate-containing discharge would be relatively small and concentrated. It could therefore be on the floor trickled or treated by means of a suitable device in such a way that its phosphate content is removed and it is then fed back into the process · For example, it could be with lime or another suitable Phosphate precipitants are treated, whereupon the precipitated phosphates are removed and the so treated The effluent is fed back into the process.

409808/0894

7339557

Treating this concentrate with lime is more economical than treating the organic ones Wastewater with lime, because the volume is smaller and the phosphate concentration is greater.

The lime treatment has the further advantage that the pH of the treated effluent is raised will. If the treated stream is fed back into the process, the increased pH has a beneficial effect on nitrification and denitrification.

Both the sludge to be returned and the sludge removed, or both, can be subjected to the sludge treatment process be subjected.

In the treatment of the sludge to be returned can this can be passed through an anaerobic pool before being returned to the first stage

The anaerobic basin can be of any known type. For example, it can be in the form of a Thickening tanks are provided in which a separation of solids and liquids takes place and the Phosphates dissolve.

If the discharged sludge is to be subjected to the sludge treatment process, known ones can be used for this Procedures such as anaerobic or aerobic digestion, heat treatment or dehydration, before his Combustion can be used.

4098 08/0894

To apply the invention to phosphate removal To explain further, reference is now made to further tests carried out, for example. These further tests corresponded to the tests shown and evaluated in FIG. 6 Active sludge is removed regularly and the fourth stage is ventilated more vigorously than before, so that there is concentration in it Maintained dissolved oxygen of approx. 4 mg / l and finally sludge was prevented from accumulating in the solids separation stage.

These attempts resulted in phosphate concentrations in the discharge as shown in the diagram of the Pig. 7 shown are.

In FIG. 7, the number of the operating position is along the abscissa and the number of the operating position along the upper part of the ordinate Chemical oxygen requirement in the outflow in mg / l and the phosphate concentration along the lower part of the ordinate entered in the outflow in mg P / l.

During the first phase of the experiment, the sludge recycle pump experienced mechanical difficulties as a result of which higher phosphate concentration values were measured in the discharge during this time · The phosphate concentration the influence was approx. 12 mg / l, so that the efficiency of the phosphate removal was over 90 #.

409808/0894

In the diagram of the long. 7 becomes the average the phosphate concentrations in the form of phosphorus in the discharge are indicated by a dashed line. This average value was 0.7 mg / l. The average chemical oxygen demand in the discharge is also determined by means of a Indicated by a dashed line and amounted to 39 »4 mg / l.

From the tests carried out in connection with the present invention it was found that between the extent of nitrate removal in the first Stage and the residence time in the first stage is related. Calculated on the basis of when dry Weather average inflowing throughput should a certain minimum residence time in the first stage must be observed.

If the dwell time in the first stage is shorter than this minimum time, the extent of the ritual distance increases with increasing mixed water recirculation throughput from the second to the first stage. It is believed, that this is related to the fact that the chemical oxygen content decreases with increasing recirculation throughput of the mixed water in the first stage a minimum is diluted. This assumption is confirmed by the fact that the required minimum residence time is affected by the temperature, i.e. the required minimum dwell time increases with increasing Temperature decreases,

409808/0894

"44- 7339557

Palls over the dwell time in the first stage
the minimum time, the extent of nitrate removal in the first stage increases with increasing mixed water recirculation throughput from the second to the first stage.

The first stage should therefore be designed so that the residence time is above the required minimum residence time lies.

There are two ways to comply with this condition:

The first possibility is that the capacity of the first stage in a pilot plant with the help of separation stages is gradually increased and the nitrate removal is measured in the first stage. The capacity the first stage can be increased in this way up to the point in time at which an increase in the mixed water recirculation throughput from the second to the first stage to an increase in the extent of nitrate removal in. the first stage leads.

The second option is to use several separate pools, each pool a certain volume of recirculated active sludge with another certain volume of incoming sludge organic wastewater according to the throughput ratios to be used in the process of incoming Wastewater is mixed into recycled active sludge,

409808/0894

-45- 7339557

This · volume ratios can later by adding additional "volumes of recycled Mixed water in the different basins can be changed according to further throughput ratios · The The respective nitrate removal values in the various basins can then be determined. In this way can adjust the extent of nitrate removal in the first stage for each residence time and for each proportion of the mixed water recycle flow rate to be determined

On the basis of the tests carried out, it could be determined that the minimum residence time required for the first stage should be at least about 2 1/2 hours.

This minimum dwell time is important when the outside temperature is below 20 ° C. This fact is confirmed by the fact that in the experiments described above, the residence time in the first stage was about 2 hours for each attempt.

If in the present description the dwell time is only due to the inflowing throughput (fresh throughput) is calculated, it is identified by the character t, which means only the capacity is marked. When calculating the actual Residence time, the return flow rates of the mixed water and the active sludge must be taken into account, and this administration time is indicated by the sign t.

409808/08 9.4

To the construction of a device to carry out of the method according to the invention and the context Explaining the variables for obtaining optimal results will now be an embodiment of FIG Invention described.

Form the basis for the construction of a device for carrying out the method according to the invention the following data:

1. The expected reduction S in chemical oxygen demand in mg / l or the difference in chemical oxygen demand between influence and discharge.

2. The solids yield Y removed from the plant

in kg of solids per kg of chemical oxygen demand. This yield can also be expressed in kg solids per kg removed "BOD ₁ -" (five-day biological oxygen demand in mg / l) or per kg removed "TOC" (total organic carbon in mg / l).

3. The rate of endogenous decomposition of the biological solid · k. as a proportion of the total of the solids biodegradable per day. This speed depends on the temperature, and this dependency should be in either mathematical or graphical form.

4-. The denitrification speed DN ₁ in the first tank and the denitrification speed DN in the third tank and their temperature dependency must also be known

409808/0694

5. The expected minimum temperature of the liquid in the pool must be known in ⁰ C, because this influences the nitrification and denitrification speeds ·

6. The highest proportion X to be maintained in mg / l of suspended pesticides in the mixed water and the return flow rate necessary to maintain this proportion R must be determined.

7. The total amount of nitrogen entering the system according to Kjeldahl (TKN) in mg / l must be determined.

8. The minimum solids residence time (SRT) in the second tank for nitrification at the lowest temperature must be established. .

9. The minimum dwell time in the first stage, which leads to a " higher nitrate reduction must be measured.

It is believed that the temperature dependence of the rate of denitrification and the rate of endogenous decomposition of biodegradable solids can be expressed by the modified Arrhenius equation as follows:
(T) = DN ₁ (20) O ₁ ( ^T

₅ (T) = DN ₃ (20) O ₁ ( ^T k _b (T) = k _b (20) O ₂ < ^T where T and 20 are values for the temperature in ⁰ C.

409808/089

It is assumed that the following values for the variables listed in the equations above apply:

S _r (COD) = 400 mg / 1 TKN, = 40 mg / l Y = 0.48 kg pesticides removed / kg

chemical oxygen demand = 0.1 per day at 20 ⁰ C = 5 mg NO ^ -N / g pesticides / hour ₂ = 1.25 mg NO ^ -N / g solids / hour

O ₁ = 1.09 Q ₂ = 1.08 T = 14 ⁰ C SRT '= 12 days X,' = 5,000 mg / 1

R = 1 times the average throughput

in dry weather

The above assumed values are based on the intended results on obtained from the literature Information based on calculations made on the basis of the test results obtained by the applicant and on the previous experience of the applicant.

The system consists of four basins arranged one behind the other in a row, the first of which is basin is operated with the exclusion of oxygen, i.e. no air is supplied, so that the nitrates are reduced.

/.09808/0894

These nitrates come from the second basin, from which a waste water stream was returned. The rest on Nitrates, i.e. the portion not reduced in the first tank, must be in the third, with the exclusion of oxygen operated pools are reduced. The fourth basin is used for re-ventilation when one is on the basis residence time of approx. 1 hour based on the average throughput in dry weather.

Ss should therefore begin with the design of the third, operated under the exclusion of oxygen according to which the remaining proportion of nitrates can be calculated in order to determine the size of the first Basin and the mixed water return flow rate from the second to the first basin.

Assuming that the residence time t (3) in the third basin, calculated on the basis of the average Dry weather throughput (adwf) is 2 hours, the actual residence time is therefore:

t = t _q (3) / (1 + R)
* 2/2 m 1 hour

The denitrification rate in the third

Basin is:

(14-20) (H ⁰ G) = 1.25 χ (1.09)

0.74 mg NQ ₅ -Vg solids / hour

409808/0894

For X = 5,000 mg / l, the one removed from this basin is Amount of nitrate 0.74 χ 5 x 1 = 3 »70 mg / l ·

However, approximately 1 mg / L dissolved oxygen is also directed into the third basin. The corresponding nitrate ^{content is 1} / 2.9 = 0.345 mg / l. Hence the nitrate nitrogen concentration is in the third basin

Cn = 3.70-0.35
= 3.35 mg / l

The nitrate concentration in the second tank should therefore do not exceed the value of 3.7 mg / l. The ammonia in the Influence is not adversely affected by the first basin, but it becomes almost completely in the second basin nitrified. A certain part of the total amount of nitrogen flowing into the system remains in that from the Device flowing mud. A small part of ammonia is not nitrified, and some are non-degradable, Organic substances in the solution contain nitrogen.

About $ 10 of the going into the plant Total nitrogen will not appear as nitrates in the process. The total amount of the nitrogen to be nitrified is therefore:

Cn ₀ = 0.9 x TKH
= 0.9 χ 40
= 36 mg / l based on the "adwf".

4098 08/0894

• Assuming that there is a unit flow rate and a state of equilibrium with regard to the influence and outflow of nitrates in the second basin, the following equation results for the mixed water recirculation flow rate B in the first basin: Γ 1 + R + R _x J. Cn = Cn _Q

R = ^Gn o - 1 - R

35 - 2

- 10.7 - 2nd

* 8.7
₁ (H ⁰ C) = 5 x (1.09) ¹⁴ " ²⁰

= 2.96 mg NO, -N / g solids / hour With a mixed water return flow rate that corresponds to 8.7 times the fresh flow rate, and with a sludge recirculation throughput, which corresponds to the fresh throughput corresponds, the nitrate concentration at the entrance of the first basin is Cn = 3 »35 mg / l. It is believed, that 1 mg / l dissolved oxygen is returned to the first tank, which corresponds to 0.35 mg / l ΝΟ, -Ν. To calculate the residence time in the first basin, the ■ corresponding to a nitrate concentration of Cn = 3 »70 mg / l« Recirculation throughput can be calculated. The actual dwell time is

χ 1 _{= Oj25} hours «5

409808/0894

Based on the primary throughput, the dwell time is 0.25 x 10.7 = 2.675 hours.

This dwell time is longer than the minimum dwell time already mentioned.

The residence time in the first basin is longer than that in the third basin. A solution is sought where the pool dimensions are as small as possible. Another calculation is carried out in which a dwell time of 2.4 hours for the third basin is assumed due to the fresh throughput.

C _n = 0.74 χ 5 x 1.2
- 4.44 mg / l

₁ Ji _x Z

4.44

⁼ 8.2 ~ 2
= 6.2 mg / l.
The actual dwell time is

iiii χ 1 = 0.30 hours. 2.96 5

The residence time due to the fresh throughput is 2.46 hours. Therefore, the pool must have dimensions which allow a residence time of 2.5 hours, so that a recycle throughput ratio of approx. 6: 1 is required is. This ratio could of course be reduced in summer because there are more nitrates in the third tank were reduced. Nor should it be in winter

4 0 9 8 0 8/0894

required to have the nitrates completely removed and a value of, for example, 2 mg / l in the discharge is still acceptable, gives eich. for the last example Cn = 4.44 + 2 = '6.42,

= 5.6-2 = 3.6.

Therefore, a return rate of 4 times the fresh throughput is sufficient. The one on the The retention time in the first basin based on the throughput is:

VD-. _χ £ _β 2.42 hours. Therefore, the residence times in the first and third pool amount irrespective of the proportion of the recycle flow rate or from the allowable liitratpegel in the effluent in each case approximately 2 ^1/2 hours.

The second pool must meet the requirements of the nitrification be designed, whereby the residence time of the solids in this basin is longer than that for the The minimum dwell time required should be nitrification. The pool size must be determined empirically.

The size is designed, for example, so that the dwell time t (2) for the fresh throughput is 6 hours. The total dwell time for the entire system is the sum of the residence times in the four basins:

4Q9808 / Ö8Q4

2.5 + 6.0 + 2.5 + 1.0 = 12 hours

The aforementioned residence time of 6 hours for the second basin has been determined empirically and according to selected based on the experience of the applicant. The same applies to the residence time of 1 hour for the fourth basin.

The daily sludge load can be calculated from the equation of Barnard et al. be determined (Barnard, J.L, et al "Design Optimization for activated sludge and extended aeration plants", lecture at the 6th International IAWPE conference in Jerusalem)

ΔΛ. s, Y, S _r - k _b «X» X · t ^

where ΔΧ = daily sludge accumulation per waste water volume

in mg / l and
X = biodegradable part of the biological

Solids in the basin is «.

The value X results from the following equation: = YS + k _b .Xt - \ / US _r + k _b , Xt} - 3.08 YS _r .k _b .X, t

The factor k _fe is temperature dependent as follows: k _b (H ° C) = 0.1 χ {1, O8) ^(U ~ ^2O)

■ 0.063
It follows:

YS "+ k," Xt = 0.48 χ 400 each 0.063 x 5,000 χ 12 ^{r D} * 24

= 192 + 158

= 350

4098G8 / Ö894

X = 350 -VI22 «500 - 3.08 χ 192 χ 158

2 χ 158

= 0.56
ΔΧ »192 - 158 χ 0.56

= 103 mg / l

The residence time for the solids in the second basin is therefore

SRT = 5,000 χ 6 = 12.1 days 103 χ 24

and is sufficient for nitrification.

The total dwell time is therefore 12 hours, of which 2.5 hours in the first pool, 6 hours in the second pool, 2.5 hours in the third pool and 1 hour in the fourth and last basin. Since this was assumed for a calculation, it would have to be suspended in the mixed water Solids content 5,000 mg / l and the ratio of mixed water recirculation throughput to fresh throughput between 4: 1 and 8: 1, depending on the requirements on the The composition of the discharge, i.e. the treated wastewater, is dependent.

METHANOL ADDED TO THIRD BASIN

To support denitrification at low temperatures, the one in the third basin can be used Mixing water methanol can be added. The amount of methanol depends on the required degree of denitrification.

/ ♦ 09808/0894

Since most of the nitrates have been removed in the first basin, the amount of methanol is less than a fifth of the amount required for total denitrification. The addition of methanol would only be necessary during the colder months of the year. According to McCarty, PL et al. "Biological denitrification of wastewaters by addition of organic materials ¹¹ , published on the occasion of the 24th conference on industrial waste at Purdue University, the addition of methanol is about 3%. The removal of an additional 4 mg / l nitrate nitrogen in the third basin therefore requires an addition of 12 mg methanol / l. The chemical oxygen demand of the methanol must be added to the total oxygen demand distance in the system if the minimum residence time for Solids for the purpose of nitrification is calculated.

The chemical oxygen demand (COD) of methanol can be calculated from the following equation:

2 OH ₃ OH + 3O ₂ = 2 CO ₂ + 4H ₂ O

1 mg methanol / l has a chemical oxygen demand of 1.4 mg / l · Therefore, the addition of 12 mg brings Methanol / l entails an additional chemical oxygen demand of approx. 17 mg / l.

409808/0894

The actual amount of methanol required depends on the temperature and the design of the plant. The most economical solution must be sought. The cost of providing an additional tank volume for denitrification and the cost of pumping must be compared to the cost of the methanol.

If, in the above example, the residence times in the first and third basins are 2 hours each, and if the volume ratio of recirculation throughput to fresh throughput is 3 ι 1, the outflowing nitrate nitrogen concentration can be calculated as follows.

The nitrate concentration in the third basin is diluted five times because of the recirculated mixed water and the recirculated sludge. The ITitratkonzentration is then ^56/5 = 7.2 mg / 1, if a complete denitrification in the first basin takes place. The denitrification rate in the first tank is 2.96 χ 5 «15 mg / l / hour · The residence time is

t ^{(1) = 2/5 =} 0.4 hours. The maximum denitrification is »15 χ 0.4 = s 6 mg / l.

Hit recycle throughput: Average throughput = 3: 1 this would result in a removal of 6x3 = 18 mg / L, In this way only 18 mg nitrate / l would be removed.,

409808/0894

so that another 18 mg / l can be removed by means of methanol or by increasing the proportion of recirculation in the throughput would be. Since the amount of methanol to be added about three times as large as the ifitrate to be removed sticks off about 54 mg methanol / l would have to be added to the third tank in order to add the remaining nitrogen remove. These costs would therefore have to be matched by the enlargement of the basin for denitrification and / or additional caused by the increase in the throughput rate of the recycled mixed water Costs are compared to determine the most cost-effective solution

In the exemplary embodiment just described, the respective steps have been designated as "basins" ·

From the explanations of this exemplary embodiment it can be seen that the method is suitable for the respective purpose can be adjusted

409808/0894

Claims (1)

Claims Process for removing nitrogen from organic waste water containing nitrogenous compounds, characterized in that the organic waste water through a first stage (14), in the form of a biological denitrification stage, a second stage (16) in the form of a biological nitrification stage, a third stage (18) in the form a biological denitrification stage and a solids separation stage (22) to produce a clarified Wastewater and an active sludge are passed, with mixed water from the second stage (16) to the first stage (14) and at least parts of the active sludge are returned to the first stage (14). 2. The method according to claim 1, characterized in that the denitrification stages (14, 18) with exclusion of oxygen operate. 3. The method according to claim 1 or 2, characterized in that that the aeration of the second stage (16) is controlled so that the concentration of dissolved oxygen in this level is kept between approx. 0.5 and approx. 4 mg / l. 4. The method according to claim 3, characterized in that the concentration of dissolved oxygen between about 0.5 and about 2 mg / 1 is maintained. 409808/0894 5. The method according to any one of the preceding claims, characterized in that a suitable carbon source is provided in the third stage (18) in order to increase the breathing rate to improve optional anaerobic bacteria in the activated sludge of the third stage (18). 6. The method according to claim 5, characterized in that the carbon source in proportion to the decrease in breathing rate the facultative anaerobic bacteria is seen. 7. The method according to any one of the preceding claims, characterized in that the proportion of the mixed water recirculation flow rate from the second stage (16) to the first Stage (14) is controlled so that the greater part of the nitrates in the first stage (14) and the smaller part of the nitrates is reduced in the third stage (18), 8. The method according to claim 7, characterized in that the proportion of the mixed water recirculation throughput in the Relation to the breathability of the bacteria in the third stage (18) is controlled such that nitrates, which are of the second stage (16) to reach the third stage (18) in which third stage can be significantly reduced. 9. The method according to claim 7 or 8 _f, characterized in that the proportion of the mixed water recirculation throughput is controlled such that the nitrate level at the entrance to the third stage (18) is kept below the nitrate proportion which is reduced in the third stage (18) can. 409808/0894 10. The method according to any one of claims 7 to 9, characterized in that the volume ratio of mixed water recirculation throughput to feed throughput of organic Wastewater is at least 2: 1. 11. The method according to any one of the preceding claims, characterized in that the active sludge return flow rate is controlled in such a way that one is sufficient for denitrification and nitrification in the three stages (14,16,18) high number of bacteria is present. 12. The method according to claim 11, characterized in that that the active sludge recirculation throughput is controlled in such a way that the proportion of suspended solids in the mixed water in the nitrification and denitrification stages (16,14,18) of the process is at least 2,000 mg / l. 13. The method according to any one of the preceding claims, characterized in that between the third stage (18) and the solids separation stage (22) a fourth stage (20) is provided in the form of an aeration stage to remove gas bubbles, which a solids separation in the solids separation stage (22) would make it difficult to escape and to stabilize the sludge to facilitate the separation of solids. 409808/0894 14. The method according to claim 13, characterized in that that with a given phosphate content the organic waste • water the fourth stage (20) is aerated to a concentration dissolved oxygen of at least 3 mg / 1 in the fourth stage (20) and a phosphate precipitation to achieve, and that from the solids separation stage (22) is regularly discharged active sludge to phosphates to be removed from organic waste water. 15. The method according to claim 14, characterized in that that the fourth stage (20) is vented to maintain a dissolved oxygen concentration of at least 4 mg / 1 in it . 16. The method according to claim 14 or 15, characterized in that that the active sludge recirculation throughput of the solids separation stage (22) is controlled by the residence time of the active sludge and thus the development of carbon dioxide in the solids separation stage (22). 17. The method according to any one of claims 14 to 16, characterized characterized in that the sludge from the solids separation stage (22) is subjected to a sludge treatment process to obtain a phosphate-containing effluent stream. 18. The method according to claim 17, characterized in that that the effluent is treated with suitable chemicals to remove phosphates from it, 409808/0894 • 19th Method according to one of the preceding claims, characterized in that if the organic wastewater "contains phosphates, this organic wastewater with suitable Chemicals are treated to remove phosphates from sewage. 20. Device for performing the method according to Claim 1, characterized in that it a first stage (14,14.3,14.4,14.5) in the form of a biological denitrification stage for the uptake of organic, nitrogenous Wastewater containing compounds; a second stage (16,16.3,16.4,16.5) in the form of a biological Nitrification stage;
a third stage (18,18.3,18.4,18.5) in the form of a biological denitrification stage; a solids separation stage (22,22,3,22,4,22,5) to produce one .cleared wastewater and an activated sludge; Feeding funds (14.1,16.1,18,1,54,56,58,54.4,56,4,58.4,54.5, 56.5,58,5) for the purpose of supplying mixed water from the first stage (14,14,3,14,4,14.5) to the second stage (16,16,3,16,4,16.5), from the second stage to the third stage (18,18.3,18,4,18.5) and from the third stage to the solids separation stage (22,22.3, 22.4,22.5); Mixed water return lines (32,32.3,32.4,32.5) for return of Misxihwasser from the second stage (16,16.3,16.4,16.5) for first stage (14,14.3,14.4,14.5) and Sludge return agent (30,30.3,30.4,30.5) for the return of active sludge from the solids separation stage (22,22,3,22.4,22.5) to the first stage (14,14.3,14,4,14.5). 409808/0894 7339557 ' 21. The device according to claim 20, characterized in that that adjustable ventilation means (38,38,3,38.4,38.5) for ventilation the second stage (16,16.3,16.4,16.5) are provided. 22. The apparatus of claim 20 or 21, characterized in that in the first stage (14,14.3,14.4,14.5) and in the third stage (18,18,3,18.4,18.5) stirring means (36,36,3, 36.4,36.5) are provided to mix the mixed water in these stages. 23. Device according to one of claims 20 to 22, characterized in that between the third stage (18,18.3,18.4,18.5) and the solids separation stage (22,22.3,22.4,22.5) a fourth stage (20,20,3,20.4,20.5) is provided in the form of an aeration stage, in which gas bubbles which separate solids in the solids separation stage (22,22,3,22,4,22.5) could hinder, escape, and in which the sludge is stabilized around the Facilitate separation of solids, 24. The device according to claim 23, characterized in that that the fourth stage (20,20.3,20.4,20.5) ventilation means (38,38,3,38.4,38,5) for the purpose of phosphate precipitation dissolved a concentration from the mixed water in the fourth stage (20,20.3,20.4,20.-5) in this stage Maintain oxygen of at least 3 mg / 1. 4Q9808 / 089A 25. Device according to one of claims 20 to 24, characterized in that the feed means
(14,1,16.1,18.1,54,56,58,54.4,56,4,58,4,5.4.5,56.5,58.5) _r the mixed water return lines (32,32.3,32.4,32.5)
and the sludge return means (30,30.3,30,4,30.5) are arranged in such a way that short circuits are avoided in the individual stages of the device. 409808/0894