DE2212715A1 - Method and device for treating garbage or waste water with activated sludge - Google Patents

Description

Method and device for treating garbage "or Sewage with activated sludge

The invention relates to a method and a device for treating garbage or waste water with activated sludge, in particular discloses a method and apparatus wherein oxygenated aeration gas is effectively used got.

It is known that both household wastewater and industrial waste, where a biodegradable material is produced, prior to delivery to a receiving area or river for treatment be subjected. A number of methods and devices have become known for this purpose; one of the most famous is a method using activated sludge.

In the conventional method with activated sludge, the liquid waste to be cleaned is mixed with activated sludge,

2 0 9840/0767

so that a liquid mixture is created. This liquid mixture is aerated with an oxygen-containing gas so that the microorganisms consume and digest the waste as food. These living organisms need oxygen for their Maintain metabolic function, as well as to grow and reproduce, taking the organic waste rapidly consume. The microorganisms are relatively compact, so that they can subsequently be removed in a separating or clarifying agent. This effluent from the clarifier is largely cleaned, as most of it is organic Waste parts are removed by the microorganisms and the cleaned runoff can now go into the earth or into the water can be released without causing poisoning. Some of the clarified or settled microorganisms that are usually found referred to as activated sludge, are returned to an inlet end of the aeration or gas tank to to keep a desired amount of the microorganisms in the liquid mixture, making the biological process continuous is continued.

From this brief and simplified description of the activated sludge process, it can be seen that an adequate supply of oxygen is the critical point of the biological process. It has therefore long been known that the use of a ventilation gas with an oxygen content of more than 21 % oxygen in air is advantageous. The use of highly oxygenated air is described in U.S. Patents 2,684,941; 3,462,275; 3,236,766; 3,356,609. However, none of the known methods and devices has prevailed so far, for a wide variety of technical reasons, including high costs and unsuitable production and process conditions under which the high-oxygen gases are to be used. Recently, the cost of high purity oxygen has decreased significantly and devices such as those described in U.S. Patents 3,547,811 to 3,547,815 employ oxygen-rich gas

209840/0767

Suggested in closed air or aeration tanks. However, these devices require the entire tank to be closed, and the oxygen-containing gas that was originally used is let into this tank must be sufficient to meet the needs of the entire ventilation system.

In contrast to this, the present invention proposes that under certain "structural and procedural conditions The known advantages in the application of oxygen-rich gas are retained by the application of this gas a first area of the entire process is limited and thereby significant investment and operating costs the fact that free atmospheric air is used later in the process can be saved. In addition, the invention has further advantages in that the more effective Use of oxygen-rich gas is maximized in the first region of the method according to the invention.

It is therefore an important object of the present invention to provide an improved method and apparatus for treatment to propose activated sludge organic waste using oxygen-rich aeration gas in such a way that that all the benefits of using oxygen-rich gas are retained, while reducing the amount of it relatively expensive gas and cheaper air chambers are used.

The method according to the invention and the device for treating waste water with activated sludge initially comprises one closed aeration chamber in which a liquid mixture of aqueous waste and recirculated sludge in connection be brought with an oxygen-rich ventilation gas. The term "oxygen-rich ventilation gas" used here is defined as an oil vent gas having at least 35 and preferably 50 to 99 »9 volume percent oxygen. Min-

209840/0767

at least in a first area of the closed ventilation chamber the level of dissolved oxygen in the liquid mixture is between 5 and 15 p.p.m., and preferably between 5 and 10 p.p.m. After the ventilation time in the closed The chamber in contact with the oxygen-rich air gas becomes the Liquid mixture passed into one or more open air chambers, in which or in which a further treatment with atmospheric Air "at a relatively low level of the dissolved Oxygen takes place until the cleaning process has reached the desired level.

Other important features of the invention are presented in the following Embodiments explained in more detail, from which further important features emerge. It shows:

Fig. 1 schematically shows a side section through a device according to the invention;

2 and 3 also schematically show a side section by modified embodiments of the closed chamber of the activated chamber system according to the invention, and

4 shows, in the same way, a side section through a further modified embodiment of the activated one Chamber system of the device according to the invention.

1 shows a device 10 for treating waste water with activated sludge with a first closed aeration chamber or tank 12 and a subsequent open aeration chamber or tank 14. An inlet 16 is provided on tank 12, through the waste water, which is in a storage tank, not shown is pretreated or not pretreated, enters the closed tank 12. A clarification or settling tank 18 receives the (aerated) liquid mixture from the tank 14 through a line 20. The tank 18 operates in a known manner,

209840 / 0.7 67

by the sludge settles in the lower region and the purified effluent by a conventionally trained overflow _r element or other delivery element which is not shown, "emerges from the top of the tank 18th A part of the sludge is removed from the settling tank 18 and a line 22 is pumped back into the closed chamber 12 by a pump 24 for microorganisms to produce the activated sludge in the device 10. The remaining sludge is removed through a line 25 from the tank 18 for appropriate disposal.

The ventilation chamber 12 is a closed chamber with a · lower wall 28, upwardly directed side walls 30 and an end wall 32 which is closed by an upper wall 34 are. A front 7 / and element 36 hangs down from the wall 34 and a front wall element 38, which is directed upward from the wall 28, is arranged at a distance from the wall element 36 towards the front and opens at 40 slightly higher than the lower edge 42 of the wall element 36. The mouth 40 of the wall element 38 is below the level 44 of the liquid mixture 46, which contains the inflowed waste from inlet 16 and that from the tank .18 includes pumped back sludge. Thus, because part of the wall member 36 is below the liquid level 44, a closed chamber is formed and liquid flows from the tank 12 into the tank 14 via the upwardly directed wall element 38.

As already stated, the fluid mixture 46 contains the waste influence, and the pumped-back sludge is first Treated with building rich gas. Accordingly, the chamber 12 has a gas inlet 48 in the top wall 34 through which oxygen-rich vent gas enters the chamber above the level 44 of the liquid. The oxygen-free Before venting gas is taken from a source 51 and can be fed to the chamber 12 via a line 49. A circulation pump 50 with a suction end 53 is provided which is connected to the interior the chamber 12 is connected to the oxygen-rich ventilation

209840/0787

to bring gas from there over the liquid level 44. The gas is from the pump 50 through a line 54 to one or more Atomizers 56 out and bubbles arise in the liquid mixture. Stirring elements 58 are preferably provided, which stir the liquid mixture 46 so as to reduce the oxygen supply from the oxygen-rich air gas to the liquid mixture to convey effectively, but also to keep the solid matter in the waste slurried.

A ventilation opening with a tube 52 is provided in the wall 34, allowing gas to escape into the atmosphere. The gas pipe 52 has a control valve 55 with an oxygen analyzer 57, which determines the percentage of oxygen in the exiting gas, and by which the opening and Closing of the valve 55 is controlled so that a predetermined oxygen content is present in the admitted gas for reasons that will be explained in more detail below.

Preferably the oxygen-rich gas is passed through the source supplied under pressure such that the gas is supplied to the closed chamber as required. That is, when the gas pressure in the chamber 12 among those for the supply of oxygenated Gas set pressure drops because oxygen is released to the liquid mixture, it becomes more oxygen-rich Gas supplied through line 49 from source 51 *. The valve 55 remains closed until the analyzer 57 has an oxygen concentration notices below the desired level. Then the valve is opened to let more gas into the atmosphere submit. The suction pump 50 operates all the time, thereby supplying oxygen-rich gas to the nebulizer 56, so that oxygen bubbles form in the liquid mixture, which enriches it with oxygen.

After the treatment of the liquid mixture 46 in the closed chamber 12, which is described in more detail below, flows

209840 / 0.767

the liquid mixture via the wall 38 into the open chamber 14, where it further aerates in an atmospheric environment through a plurality of surface aeration elements 60 until the treated liquid mixture passes through the Line 20 flows into tank 18. Stirring elements 61 can below be provided on the surface in order to keep the solids in the solution and prevent them from settling in the chamber 14.

Figs. 2 and 3 show alternative embodiments for the closed one Ventilation chamber. The chamber 12 '(see. Fig. 2) has a bottom wall 28 ', side walls 30', an end wall 32 ', a top wall 34 'with a partial front wall member depending thereon 36 'and an upwardly directed front wall segment 38', which is spaced in front of the wall element 36 ', similar Fig. 1 is arranged. The chamber 12 'also has a first depending wall member 62 which extends from the top wall 34 to one level. 64 extends above the lower wall 28 'and defines a first sub-chamber 66. An upward-facing wall element 68 is spaced in front of the wall 62 and opens at 70 below the surface 44 'of the liquid. Walls 62 and cooperate with each other in such a way that they have a limited flow channel for the. Form liquid from sub-chamber 66.

A second depending wall 62 spaced in front of upward wall 68 extends to a plane 74 above the lower wall 28 'and defines second and third sub-chambers 76 and 78. One facing upwards Wall segment 80 is spaced from wall 72 in sub-chamber 78 and extends from lower wall 28 up to a plane 82 below the surface 44 'of the liquid mixture 46 ·. The wall 80 cooperates with the wall 72 in such a way that a limited flow channel for the liquid is formed by the sub-chamber 76 after the sub-chamber 78.

209840/0767

An inlet 49 'for the oxygen-rich air gas is in FIG first sub-chamber 66 is provided and a pipe 52 'with a control valve 55' and an oxygen analyzer 57 'is shown in FIG the third sub-chamber 78 is arranged.

A gas discharge opening 84 is provided in the sub-chamber 66, which is connected via a line 86 to a gas inlet 88 in the sub-chamber 76 is connected. A gas outlet opening 90 is via a line 92 with a gas inlet opening 94 in the sub-chamber 78 connected so that the gas flow within the chamber 12 'is graduated between the sub-chambers or sections 66, 76 μnd 78 runs. Before it exits through the dispensing opening 52 '. Agitation elements 58 'are preferably in each of the sub-chambers 66, 76 and 78 provided to keep the solids slurried in to keep the liquid mixture in the lower chimneys. Preferably Surface aeration elements 60 'are provided to facilitate the transfer of oxygen from the oxygen-rich air gas to promote the positive mixture effectively.

In the embodiment according to FIG. 2, both the liquid flow s mixture and the oxygen-rich air gas one after the other through the sub-chambers 66, 76 and 78. The oxygen-rich air gas, that from the source through inlet line 49 'to the Sub-chamber 66 is directed, may be similar to the embodiment 1 are introduced into the chamber 66 under pressure. Therefore, if the gas pressure within the chamber 12 is below the set pressure drops with which the oxygen-rich gas is supplied, additional oxygen-rich gas flows from the source through line 49 'to sub-chamber 66 in the chamber 12 '.

The gas control valve 55 'and analyzer 57' function in the same way as the valve 55 and analyzer 57 of FIG. 1. However, because the gas flow through the sub-chambers runs, the oxygen content of the ventilation gas can be regulated so that the oxygen content on a very

209840/0767

low * amount, "for example that of atmospheric air (ie 20.8 io oxygen) or any other oxygen concentration above or below that of air the oxygen content of the ventilation gas is 20.8 $ oxygen or less ", and the control valve '55 'closes as soon as the analyzer 57' detects an oxygen content greater than 20.8 $.

When the valve 55 'closes, the pressure within the chamber 12' tends to increase beyond the set amount at which oxygen-rich gas is introduced into the chamber 12 through the line 49 '. As a result, no further oxygen-rich air gas flows into the chamber 12 · "· While the chamber 12 'is closed in this way, the liquid 46' in each of the sub-chambers is ventilated by oxygen-rich air gas until enough oxygen is added to the liquid mixture so that the Gas pressure in the chamber 12 * is reduced and additional oxygen-rich air gas flows into the first chamber or so much oxygen is withdrawn from the gas in the sub-chamber 78 that a concentration of 20.8 % or less arises, in which case the valve 55 'opens and the oxygen-depleted gas is vented to the atmosphere When valve 55 'is opened, the gas pressure in chamber 12' decreases and additional oxygen-rich gas flows into the chamber through line 49 '.

It becomes clear here that the ventilation gas only flows out when the oxygen is mixed with the liquid mixture in such a way that the oxygen concentration in the ventilation section corresponds to that of air. In this case, the more expensive high-purity oxygen is fully and effectively used. In practice, however, it is not necessary and also not always desirable to enrich dps low-oxygen gas with an oxygen content of exactly 20.8 io , such as where a large part is, for example

209840/0 76 7

of the ventilation gas is carbon dioxide. It is therefore the object of the present invention to provide ventilation or enrichment to control the ventilation gas in such a way that the lowest possible oxygen concentration corresponds to the oxygen concentration the oxygen-rich gas and the particular composition and strength of the incoming gas to be treated Waste. However, it has been found that for most Waste types, especially those containing municipal sewage, maximum use of the oxygen-rich gas is achieved by the gas with a predetermined and controlled Oxygen content of 10-35t preferably less than 25, e.g. between 21 and 25 percent by volume of oxygen is enriched.

In Fig. 3, a closed ventilation chamber 12 ″ has a lower wall 28 ", side walls 30", end walls 32 "with depending front wall part 36 "and upwardly directed front wall segments 38", similar to the embodiments according to Pig. 1 and 2. Inside the closed chamber 12 "extends a partial wall segment 96 between the side walls 30" from a plane 98 above the surface level 44 "of the liquid mixture 46 "to a level 100 which is spaced above the bottom wall 28". An upward one partial wall segment 102 extending from bottom wall 28 "between walls 30" to a level 104 below surface level 44 "of the fluid mixture 46" extends, is arranged at a distance in front of the wall segment 96 and forms a limited flow channel in the liquid. A A second partial wall segment 106, similar to the wall segment 96, is provided, which is arranged at a distance in front of the wall segment 102 is. The wall segment 106 extends between the side walls 30 ″ and opens into planes 108 above the surface level of the liquid and 110 spaced from the bottom wall 28 ". A partial wall segment 112 extends from the lower wall 28 ″ and opens in a plane 114

209840/0767

below the liquid level and is under distance in front placed on wall 106, creating a restricted flow channel for the liquid is formed.

In the top wall 34 "is an inlet 49" for the oxygen-rich Gas and a gas pipe or gas slot 52 ″, a control valve 55 ″ and an analyzer 57 ″, similar to FIG. 1, are provided. Appropriate stirring elements 58 "can also be provided to keep the solids in a slurried state, further surface ventilation elements 60 ″ for aerating the liquid mixture. The closed chamber above the The level of the liquid 46 "is exposed to a uniform gas pressure similar to FIG. 1, while the liquid mixture 46" in "gradations through the individual sub-chambers through the chamber 12 "flows.

In Fig. 4, a method for treating wastewater using activated sludge is shown similar to Fig. 2, but 4 physically or spatially separate and closed ventilation chambers are used, between which the gas flow runs in individual stages.

e _r

In this embodiment takes a first closed ventilation chamber 120 the flowing sewage through a line 122 and the returning sludge from a clarification tank 124 through a line 126. A cleaning line 125 is provided for suitable removal of the sludge. The returned Sludge is pumped through line 126 with a pump 128. Oxygen-rich gas is supplied through line 130 as needed the closed chamber 120 is supplied, and both the liquid 132 and the venting gas flow from the first closed one Chamber 120 to a second closed chamber 134. The liquid flows through a suitable overflow 136 and the gas through line 138. Similarly, liquid and gas flow through suitable overflows or lines 142 and 146 into a third closed ventilation chamber 140.

209840/0767

From the chamber 140, the gas is released into the atmosphere through an exhaust line 148 which is passed through a control valve 150 and an oxygen analyzer 152 similar to FIG. 1 is controlled.

The liquid flows from the closed chamber 140 through an overflow 154 into an open chamber 156 for final aeration before entering the septic tank 124 through a line 158.

Suitable surface aeration elements 160 and agitation elements can be provided in each of the chambers 120, 134, 140 and 156.

It is thus clear that the closed chambers 120, 134 and 140 all act in a similar manner to the single chamber 12 ^f of FIG. 2, the chamber 12 'being divided into separate compartments by the walls 62, 68, 72 , 80, 36 ¹ and 38 '. The term "closed ventilation zone", as it is used here, therefore includes both a single chamber, with or without one or both of the liquid or gas chambers of FIGS. 1 to 3, and a large number of individual closed chambers (cf. . 4), all of which act like a single closed zone.

As already stated, the greatest oxygen demand in a process for treating wastewater using activated sludge is at the inlet end of the aeration tank when the incoming wastewater and the microorganisms in the recirculated sludge are mixed together for the first time, with the microorganisms in their maximum growth phase to find oneself. Therefore, in the present invention, the oxygen-rich gas is only used in the closed aeration zone, namely between $ 25 and $ 95, preferably 50 "/ o to 95 / £ of the total oxygen administered to the liquid mixture during the entire process,

209840/0767

while the remaining oxygen demand takes place by venting with air in a subsequent open aeration tank.

In a laboratory simulation of the process and the device according to the invention ran three experiments, which in the following Ta- ' Belle I are analyzed. Trials 1 and 2 were synthetic organic wastewater used from · a solution fön 256 parts of starch, 256 parts of glycine, 57 parts of aniline, 57 parts of baking soda, 11.4 parts of phenol, 28.2 parts Ammonium sulfate and 19 parts of phosphoric acid vestanden. Water was added to make a total of 3000 ml of one A stock or basic solution was created that has a chemical oxygen demand (GOD) of 215,000 mg / l. This basic solution was diluted with water until the chemical oxygen demand is reached which corresponded to the influx of tests 1 and 2.

The liquid mixture flowed successively through three containers with a capacity of twelve liters, the liquid level of which was kept at two thirds, to a clarification tank. Each container had an overflow so that the liquid mixture overflowed from the first container into the second container and liquid mixture from the second container into the third container and the overflow from the third container flowed into the clarification tank. In the clarification tank, the inflow from the aeration tank was able to settle and part of the sludge from the clarification tank was returned to the first tank. The synthetic organic waste water was pumped into the first container and whirled up by atomizing oxygen-enriched gas bubbles into the liquid mixture via an atomizer plate near the bottom of the container at a rate of 6 liters of gas per minute. The oxygen content of the gas bubbles in the first stage of the liquid mixture was measured so that an oxygen-rich gas was given. In the later stages the oxygen content of the gas bladders was reduced to less than 20.8 $> oxygen in order to demon-

2098A0 / Q767

-H-

strieren that a gas with an oxygen content accordingly that of atmospheric air or less can be used.

This underlines the adequacy in the use of atmospheric air or even low-oxygen air in the latter atmospheric stage of the device according to the invention, provided that in the first stage aeration with oxygen-rich Gas is made according to the teaching of the invention.

Experiment 3 was carried out similar to experiments 1 and 2, except that the first container was closed with a lid and had a return compressor to make the simulation of the first process stage more real. When trying 3 In addition, instead of synthetic organic waste water, as in experiments 1 and 2, real organic waste was created by one chemical industrial company used.

, Experiment 4 was carried out with a test installation according to the invention, the embodiment according to FIG. 4 being used. The sewage was taken from an urban sewer system. The four ventilation chambers used had a total liquid volume of about 335 liters. The process was carried out at an average temperature of 14 ^° C.

The results of the four experiments are summarized in Table I below.

209840/0767

TABLE I.

Summary of the operating conditions and results of a multi-stage Treatment process with oxygen-rich air and activated sludge

Returned sludge Holding time, per stage (hours) * Holding time, total (hours) * Inflow rate (liters / day) * COD, - inflow (mg / liter) BOD ₅ , inflow (mg / liter) COD, outflow (mg / Liter) BOD ₅ , drain (mg / liter) Remote COD (#) Remote BOD MLSS (mg / liter) ** MLVSS (mg / liter) ** TSS _SR (mg / liter) ** YSS _SR (mg / liter) **

_SR

(first stage) **

Attempt 1 31 Attempt 2 49 .38 attempt 37 1 3 Attempt 4 1 0.53 0 .13 1. 5 31 • α
VJI 1.58 1 3. 7th 0. I. 255, 313 103 1 1, 252 483 785 4,950 188 - 280 281 22nd 22nd 259 119 3-4 - 30th 130 91 95 67 15th 98 - 89 59 .880 .480 .450 87 2127 5 .345 9 .628 7th .332 3,800 VJl .986 8th .521 6th .400 3,200 24 .480 27 .741 .40 23 .000 2 14,500 23 1.65 24 2 20th 2 .; 12,200 5. .41 .66 , 7

TABLE I (Ports.) Attempt 1 Attempt 2 Attempt 3 Attempt

(total) ** 0.55 0.80 0.74 1.43

Holding time of the sludge in the clarification plant (hours) - 1.3 4.8 -

SVI (TSS) (ml / g) ** 94 78 100 72

dO ₂ / dt (first stage) (mg / l / h) 181 268 168 86

κ? dO ₂ / dt (second stage) (mg / l / h) 66 81 69 65

S dO ₂ / dt (third stage) (mg / l / h) 51 70 34 37 '

^ dO ₂ / dt (fourth level) (mg / l / h) - - - 38.5

ο ^ O ₂ in the gas (first stage) 50 63 80 68

ο ^ O ₂ in the gas (second stage) 12 14 10 39

Ot% 0 ₂ in the gas (third stage) 5 11 10 15

"** $ 0 ₂ in gas (fourth stage) - - 20.8

Dissolved oxygen (first stage) (p.p.m.) 10 10 30 11

Dissolved oxygen (second stage) (p.p.m.) 1-2 1-2 1-2 11

Dissolved oxygen (third stage) (p.p.m.) 1-2 1-2 1-2

Dissolved oxygen (fourth stage) (p.p.m.) -

Notes to TABLE I;

* - Operation of tests 1, 2 and 3 with a test duration of 22 hours a day; Hours per day were used for analytical procedures.

- need for biological oxygen

= floating solid particles in the mixed liquid

= suspended solid particles in the mixed liquid

= Total amount of suspended solids in recirculated sludge = volatilized suspended solids in recirculated sludge

ss ratio of supply: mass; calculated as the ratio of weight of oxygen equivalent to weight COD of the MLSS per 24 hours

SVI = sludge volume index

MLSS K> MLVSS 860 ^TSS SE O ^VSS SR O F (COD)
M.

- ie - 221f f 1S

It can be seen from Table I that the dissolved oxygen level of the first stage of Runs 1 and 2 was maintained at 10 ppm, the first stage of Run 3 at 30 ppm, and the first stage of Run 4 at 11 ppm when the oxygen content of the gas passed through the first container varies. The amount of oxygen-rich gas was $ 50 for experiment 1, $ 63 for experiment 2, and $ 80 for experiment 3 . In Run 4, 99.5% oxygen was added to provide a 68 % oxygen-rich gas above the liquid mixture in the first stage to maintain the observed level of dissolved oxygen.

From the determination of the amount of oxygen (mg) used per liter of liquid mixture per hour (dOp / dt), it becomes clear that in experiment 1 in all three stages the total amount of oxygen used per 3 liters per hour is 298 mg, of which 181 mg or about $ 61> were used in the first stage. In a similar way it becomes clear that in experiment 2 approx. 64 % oxygen and in experiment 3 approx. 62 ^c / o oxygen were used in each case in the first stage. In Experiment 4, a total of 226.5 mg of oxygen per four liters per hour were used for all four stages, of which 188 mg or 84 $ of the total oxygen in the closed ventilation zone, which consists of stages or chambers 1, 2 and 3.

It is also noteworthy that in experiment 4 the supply of oxygen was regulated as required, with the ventilation gas in the third closed chamber or stage being controlled by a valve that was manually throttled according to the oxygen content as soon as an oxygen analyzer determined this controls that the oxygen content of the air gas is 15 " . It also becomes clear how the oxygen content in the oxygen-rich gas varies from stage to stage as the oxygen in the gas is progressively used by the liquid mixture.

2 0 9 8 A 0 / 0.7 6 7

It is also important that all tests indicated a high percentage of chemical and biological oxygen demand degraded while maintaining an acceptable sludge index; this is a measure of the volume of liquid used by one gram of dried sludge. The results were also achieved when the oxygen-rich gas was used only in the first stage of experiments 1 to 3 and the first two stages of experiment 4 and even as an oxygen-poor gas in the last closed stage ( _with a lower oxygen content than atmospheric Air) was used. This underscores the adequacy of atmospheric air for use in the atmospheric stage of the invention and shows that oxygen-rich air gas is only required in the most critical phase of oxygen demand, namely the first mixing of wastewater and recycled sludge.

If, in the experiments described above, oxygen-rich gases with an oxygen concentration between 50 $ and 99 » 5 fo were used, it goes without saying that the preferred oxygen concentration of the oxygen-rich gas depends on the efficiency with which the oxygen atomizers work, ie on the submerged atomizers , the mixing elements and surface ventilation elements. However, the preferred oxygen concentration is also related to the composition or pollution of the inflowing wastewater and the level of dissolved oxygen that is to be kept in the liquid mixture. It has therefore been found that oxygen-rich gases with an oxygen concentration of only 35 percent by volume are sufficient for wastewater with low pollution, especially when highly effective atomizing devices are provided. It was also found that even when using 60 to 84 ° ß> of the total oxygen requirement in the closed ventilation zone in the experiments shown, wastewater with low pollution can nevertheless be successfully treated with the invention by only 25 # of the total

209840/0767

Oxygen demand through ventilation with the oxygen-rich gas and the remaining oxygen demand with atmospheric air is covered. In addition, the experiments described above showed, completely unexpectedly, that a high level of dissolved Oxygen at 10 p.p.m. or more in the first stage of the closed ventilation zone a significantly lower one Oxygen demand in the following stages of the overall system results, for example at 1-2 p.p.m. in the last Level of the ventilation zone. The liquid mixture is preferably ventilated at least in the first stage of the closed ventilation zone in such a way that an oxygen level of at least 3 p.p.m. and less than 15 p.p.m. is held.

Finally it was found that the volume of the liquid mixture in the closed ventilation zone after contact with oxygen-rich gas more than a third of the total volume of the liquid mixture in the whole system. Alternatively, the holding time of the liquid mixture should be in the closed, oxygen-rich zone last at least 20 minutes and preferably between 60 and 90 minutes or more if the waste is very heavy.

From the foregoing description it can be seen that the present invention provides substantial savings in amount required oxygen-rich gas, which is necessary to maintain the benefits of using oxygen-rich gases and at the same time lower the investment costs for the entire ventilation system.

209840/0767

Claims (1)

Claims 1.Process for treating biodegradable wastewater, ^ - with the wastewater with recirculated activated sludge is mixed and forms a liquid mixture that is aerated, removing the purified wastewater from the activated one Sludge is separated and the recovered activated sludge is recycled again, characterized in that that the liquid mixture (46) in a closed ventilation zone (12) for at least 20 minutes with oxygen-rich Gas is vented so that at least $ 25 of the total biological oxygen demand of the mixture is met and that the liquid mixture is in contact with atmospheric air in a subsequent ventilation zone (H) is brought so that the remaining needs of the liquid mixture is covered by biological oxygen. 2. The method according to claim 1, characterized in that the liquid mixture (46) in the closed ventilation zone (12) is ventilated for at least 60 to 90 minutes. 3. The method according to claim 1 or 2, characterized in that the liquid mixture (46) in the closed zone (12) is ventilated until between 50 and 95 $ of the total biological oxygen demand of the liquid mixture is covered. 4. The method according to claim 1, 2 or 3> characterized in that that the liquid mixture (46) is aerated in a first region (66) of the ventilation zone (12 '), so that a high level of dissolved oxygen arises that consequently the liquid mixture is aerated in a second area (76) of the closed zone (12 '), so that a 209840/0767 BATH ORIGINAL ZZ lower level of dissolved oxygen than is maintained in the first region, that the aeration gas further flows together with the plus mixture and that the mix of pleasantness finally with atmospheric Air is brought into contact to obtain an even lower level of dissolved oxygen. Method according to claim 4, characterized in that the area of the closed zone (12) has a plurality of discrete Stages (120, 134, 140, 156) and that the level of dissolved oxygen is lower in each stage is than in the next upstream stage. 6. The method according to claim 4 or 5 »characterized in that that the positive mixture (46) is aerated at least in a first area of the closed zone (12) in such a way, that the dissolved oxygen content is at least 3 p.p.m. but less than 15 p.p.m. amounts to. 7. The method according to claim 1 to 6, characterized in that the oxygen-rich gas in the closed zone (12) only ' ventilation is then carried out when the oxygen content of the ventilation gas is less than 25, preferably less than 20.8 Volume percent oxygen falls. 8. The method according to any one of claims 1 to 6, characterized in that that the oxygen-rich gas in the closed zone (12) is only ventilated when its oxygen content has dropped to substantially 21 percent by volume. 9. Device for treating biodegradable waste with activated sludge, characterized in that a closed ventilation area (12) and inlet elements (16, 22) for feeding in biodegradable waste and activated sludge provided in the closed zone (12) 209840 / Ο ·? 67 which form a liquid mixture (46) with one another, that an inlet opening (49) is provided for the supply of oxygen-rich gas into the closed ventilation zone (12), further ventilation elements (50, 53, 56, 58) for aerating the liquid mixture (46 ) are provided in the closed zone (12), whereby at least 25 ° / <> of the total requirement of the liquid mixture for biological oxygen is covered, that a second ventilation zone (14) is provided, which is in open connection with atmospheric air, that lines ( 40, 42) are provided through which the aerated liquid mixture is passed from the first closed zone (12) into the second aeration zone (14) as well as aeration elements (60, 62) which are used for the second aeration of the liquid mixture in the second zone (14) in connection with atmospheric air, so that the remaining biological oxygen demand of the liquid mixture (46) is covered. 10. The device according to claim 9, characterized in that controlled ventilation devices (52, 55 »57) are provided are to release the low-oxygen ventilation gas from the closed zone (12) only when the oxygen content , this range falls below a predetermined amount. 11. The device according to claim 10, characterized in that in the closed ventilation zone (12 ') partition walls (62, 68, 72, 80, 36 ^f , 38') are provided which form a series of closed stages for ventilation gases that Lines are provided through which the gas is successively conveyed from one stage to the next, that the inlet opening (16 ¹ ) for oxygen-rich gas is connected to the first of the stages (66), and that the controlled ventilation devices (52 ', .55 ', 57') are interconnected so that the low-oxygen ventilation gas can be removed from the last of the stages (78). 209840 / 0.7 67 12 »Door direction according to claim 9» 10 or 11, characterized in that that the liquid volume of the closed ventilation zone is greater than a third of the total volume the closed and open ventilation zones. tier patent attorney 20984Ü / Ö7S7