CS196358B2 - Process for growth of fibrous biomase inhibiting in activated sludge system - Google Patents

Description

The invention relates to improvements in the treatment of urban sewage and / or industrial wastewater by the activated sludge process. In particular, it relates to the control of operating conditions to enhance the selective production and maintenance of highly active biomass, which is substantially free of fibrous growth, in the system, the sludge obtained having advantageous settling properties and being able to substantially remove phosphates from the incoming waste water.

The activated sludge process has been used for many years to remove biological oxygen demand (BOD) from wastewater. This process consists in keeping the aeration tank in which the wastewater is supplied to the microorganism suspension to form a mixture. The mixture is aerated to supply oxygen to breathe biomass that attracts, assimilates, and metabolizes the biological consumption of wastewater oxygen.

After a suitable aeration period, the mixture is introduced into a clarifier in which the biomass settles and the treated effluent flows into the watercourse. The main part of the seeded biomass, which concentrates at the bottom of the clarifier, is returned to the aeration tank and a minor portion is cleaned to maintain a constant supply of bio-substances in the system.

Despite the multifunctionality and efficiency of fiber biomass in the activated process system and its many modifications, the main problem remains. It is the simultaneous growth of those species of organisms that have a high specific surface area and / or are fibrous, such as spheroids, which do not settle appropriately in the clarifier. The corrugated biotoase results in the inability to release biomass from the treated waste water.

Another problem is the efficacy of phosphate removal from wastewater. The causes of such removal are unclear and the process is incapable of extrapolating to wastewater treatment plants on a biological scale in general. So far, there are no reliable or satisfactory ways in which removal control would be. phosphates by the biological action generally established. *

Several modifications have already been made to the activated sludge base process in avoiding the growth of filamentous species and / or high surface area organisms, resulting in a phenomenon called "scaling". One way is to divide the effluent effluent into different sections of the aeration tank to cover the oxygen consumption. Furthermore, the burden of biological oxygen consumption on the aeration tank should be reduced. A third way is to add poisons to the system to selectively destroy or196358 filamentous and high surface area ganisms.

Another way is to temporarily create a completely anaerobic system, and to talk about the destruction of fibrous biomass, which is made up largely of the necessary aerobes. Another way is to maintain a high dissolved oxygen content and a high steady state bioavailability (oxygen in the initial; liquid phase or its hydraulic equivalent) to promote the selective growth of active non-fibrous biomass that will outgrow or prevent the development of fibrous species of higher specific surface area.

Numerous technologies have been proposed in recent years to modify the activated sludge process used to improve the removal of nitrogen and / or phosphorus. Among the various methods disclosed are those that include nitrification-denitrification systems, one form of which is described by J, L. Barnard in Watelr and Was. te Engineering (1974) 33.

In this Bardenpho process, four mixed sludge pools are operated in series, followed by a clarifier from which sludge returns to the first tank. The first and third tank work behind. non-oxidizing conditions and receive a mixture containing nitrates and nitrites (NO _X -) from the second and fourth tanks in series, which are aerated. While the periodic good removal of phosphorus and nitrogen in the pilot plant is reported when operating at sufficiently high residence times, the production of dense, readily filterable sludge is not achieved.

None of the methods proposed hitherto are able to avoid biomass growth and efficient phosphate removal. '

The above-mentioned drawbacks eliminate the method of preventing the growth of fibrous biomass in the activated sludge system, which consists in mixing activated sludge in the initial contact zone with waste water flowing with biological oxygen consumption and optionally containing phosphates and ammonia, the initial contact zone maintains under anaerobic conditions, for example by contacting the mixture with an oxygen-free gas, at a nitrate and / or nitrite concentration of less than 0.3 ppm and a dissolved oxygen content of less than 0.7 ppm, to produce non-fibrous microorganisms the oxygen uptake, with or without treatment in the intermediate zone, which may optionally be maintained under non-oxidizing conditions, the biological oxidation is allowed to proceed in the oxidation zone in a mixture by contact with the gaseous oxygen which enters the oxidation zone, zone dissolved oxygen content in the range. 1 ppm to 20 (ppm, the oxidized mixture is transferred from the oxidation zone to the settling zone, where the purified top liquid is separated from the settled sludge and a portion of the settled sludge is returned to the initial contact zone to mix the activated sludge in this zone with the effluent .

The process of the invention produces an active dense biomass that is easily concentrated during secondary clarification.

1 is a schematic side view of a simplified system according to the invention, and FIG. 2 is a similar drawing of the modified embodiments.

It has now been found that the desired selective production of species of organisms that are capable of removing phosphates and creating the necessary biomass population from highly active metallurgical species, and rapidly settling microorganisms, can be supported and maintained by strictly maintaining anaerobic conditions at the beginning of mixing incoming waste water and returned sludge from secondary clarification. The result is that

1. there is no growth of undesirable micro-organisms with a high specific surface area, such as sphaerotilus;

2, substantial amounts of the incoming biological oxygen demand are drawn from the incoming waste water by microorganisms having the ability to do this under anaerobic conditions.

It is believed that the energy for the active transport of the biological oxygen demand to the cell walls is derived from the hydrolysis of polyphosphates and that those species that are most capable of storing polyphosphates will grow under these conditions.

The initial anaerobic zone according to one embodiment is followed by an oxidative aerobic zone, where the bonded food in the aerobic zone is oxidized and where any remaining biological oxygen demand is bound and oxidized. During this aerobic state, the energy lost by the hydrolysis of the polyphosphates is compensated and the polyphosphate is re-formed and stored in aerated biomass and the phosphates are removed from the mixture.

According to a further embodiment, as hereinafter described, a non-oxidizing zone for performing denitrification is arranged between the anaerobic and oxidizing aerobic zones.

The nature of the phosphorus deposition in the biomass is such that there is little return of phosphates, thereby allowing the phosphorus to be eliminated from the waste activated sludge system.

Fig. 1 shows a modified treatment plant using activated sludge, which is equipped with a conventional waste water inlet 11 to be treated. Usually, the waste water from the sewage sludge is from the primary settling tank or clarifier (not shown) but primary sedimentation is not necessary. The effluent initially enters the anaerobic mixing zone A, in which it is mixed with recycled sludge deposited in the settling tank or clarifier 12 and returned to zone A via line 13. Part of the settled sludge from clarifier 12 is removed through line 14, while the cleaned up excess liquid does. Dispatches to watercourses or containers with or without further treatment as necessary.

As noted, zone A is maintained under strict anaerobic conditions. The terms 'anaerobic' and 'non-oxidative' are not clearly and consistently defined in the literature in which these terms are used. For the purpose of this application, the term "anaerobic" is defined as the condition existing within the wastewater treatment zone that is substantially free of NO _X "(i.e., less than 0.3 ppm and preferably less than 0.2 ppm, expressed as an elememtarium). nitrogen], wherein the conditions are such that the dissolved oxygen concentration (RKJ is less than 0.7 ppm and preferably less than 0.4 ppm.

The term "non-oxidizing" as used in this application is defined as an existing state within a wastewater treatment zone where. The biological oxygen demand is metabolysed with nitrates and / or nitrites at an initial total concentration greater than about 0.5 ppm, expressed as nitrogen, and the dissolved oxygen is contained in an amount of less than 0.7 ppm, preferably less than 0 ppm. , 4 ppm. /..· 'Feather · ensuring that. zone A was maintained under anaerobic conditions; can. "To follow any one or more of the following steps." The container forming zone A can. be provided with a layer of nitrogen, carbon dioxide or other inert gas on the surface of the liquid to prevent atmospheric air from entering the liquid; or a lightly placed cover on or above the liquid surface may be provided, or a rigid cover may be provided above the liquid surface. ·

Instead, or in addition to this, nitrogen purge gas can be supplied to the screen and bubbled through the mixture in zone A to displace any oxygen present. This last choice is shown in FIG. 1 by a line 15 introducing nitrogen into the bottom of zone A.

Wastewater normally contains little or no NO _x due to the reducing action ^_ biological oxygen in the presence of microorganisms in the incoming waste water. A potential source of NOX is ^_ back the returned sludge from the secondary clarifier and returned back from a mixture of aerobic conditioning zone nitrifikaičních biological systems, i.e. those which cause the oxidation of ammonia spořeby NOX- oxygen.

The NOv concentration in the initial anaerohe zone where the recycled sludge is mixed with the incoming waste water is maintained less than 0.3 and preferably less than 0.2 ppm NO _X - expressed as elemental nitrogen by avoiding nitrification introducing the aerobic zone mixture. · í system, and management 'NO _X ^-. content in the recycled sludge from the underflow of the clarifier, Ni, O _x ~ concentration in the recycled slurry can be controlled by creating a sufficient residence time in the clarifier and the sludge recirculation system to enable adequate reduction of NO _X ^_ to elementary nitrogen by means of the biological oxygen demand of the biomass in reflux sludge . .

Although not necessary, zone A is preferably divided into two or more treatment sections of the liquid to allow the flow of liquid through the anaerobic zone to be inhibited. It has been found that the formation of mass-divided sections or their hydraulic equivalent better achieves the desired release from the growth of filamentous organisms, thereby obtaining the development of dense sludge under otherwise unfavorable conditions.

Such adverse conditions include, for example, operation at low concentrations of biological oxygen consumption, where biomass with a large specific surface area would have the advantage of competing in absorbing poor food intake. By liquid distribution, the bypass of the untreated biological oxygen demand from the anaerobic zone is excluded.

In the embodiment shown in FIG. 1, zone A is plotted as divided into two sections, or chambers 16 and 17, each equipped with agitation means 19. The liquid passes through an almost closed stream through several sections of zone A and is discharged into the oxidation zone designated B. While Zone A has two separate sections 16 and 17, it will be appreciated that multiple sections may be formed in this way. . ...

Zones A and B may be separate bonded containers or may be a single tank of any desired design, provided by suitable means to separate zone A from zone B while allowing indirect fluid flow from zone A to zone B without back-mixing. .

The liquid is aerated in oxidation zone B in a known manner.

As shown, the compressed air may be released to the bottom of the oxidation zone in the manifold 20. Instead, if necessary. additionally or in addition to the distributors, the oxidation zone may be provided with mechanical aerators. Instead of air, oxygen may be supplied to zone B of any desired element, in which case suitable means may be provided to cover all or part of the zone.

In operation, the dissolved oxygen content in zone B should be maintained above about 1 ppm and preferably above 2 ppm to ensure an adequate presence of oxygen for the metabolism of biological oxygen consumption and for the removal of phosphates.

As shown in FIG. 1, zone B is divided into 2 liquid treatment sections 26 and 27, although it will be appreciated that a plurality of such sections may be used if necessary. One reason for the partition is that the removal of phosphates, as found, is the first order with respect to the concentration of soluble phosphates; such low values, the phosphate content of the.

196338 is best obtained by creating a restrained flow.

In carrying out the system illustrated in FIG. 1, it should be emphasized that the initial zone of contact and mixing of incoming waste water with recycled sludge must be maintained under anaerobic conditions. It has been found, unexpectedly, that under such conditions selective production of microorganism species that is not only able to remove phosphates, but that the biomass obtained is essentially constituted, occurs. non-fibrous organisms that form highly active dense and rapidly settling sludge.

• The production of filamentous microorganisms, which are essential aerobes, is sealed because their growth is only allowed under aerobic conditions. Under anaerobic conditions maintained there, it is promoted. selective production and growth of species of microorganisms that are able to accumulate unusually high amounts of polyphosphates in their cell walls. This is due to allowing the following species, which are capable of hydrolyzing poles, phosphates to generate energy for active transport, do so, and thus have beneficial access to biological oxygen consumption of effluent:

In contrast, those species that would normally bind food by active transport, in which energy is derived from aerobic oxidation · biological oxygen demand, are relatively unable to compete in this case.

The resulting effect is to promote the growth of those species that can accumulate polyphosphates during oxidation and hydrolyze polyphosphates during anaerobic supply. The conditions which favor such microorganisms also promote the formation of relatively low-volume sludge (Mohlmann) and relatively high settling rate in the zone (ZUR). The species that assimilate and oxidize biological oxygen consumption most effectively outweigh the biomass population.

Thus, the method of the present invention promotes the development of active non-fibrous phosphorus-accumulating species at a competitive disadvantage for others. These species are capable of binding high levels of phosphorus and growing the system to such an extent that it has been found in the sludge that it contains 6% phosphates, expressed as elemental phosphorus in the dry matter. from the anaerobic phase mixture as described above and further described that polyphosphorates are hydrolyzed as evident by the release of soluble phosphate into the anaerobic zone mixture.

After initial anaerobic contact, the mixture is subjected to aeration in zone B to oxidize the bound biological oxygen demand and to completely remove and oxidize any remaining biological oxygen demand. During this aeration period, the oxidation energy is partly utilized for cell growth and partly utilized to energetically increase the content of soluble phosphates in the mixture relative to deposited polyphosphates in biomass cells.

This phenomenon. is detected in this aeration zone, in which the concentration of soluble phosphates decreases rapidly. After the aerobic stage, which results in removal. as phosphates, talk biological oxygen consumption and stabilization, the mixture can be discharged into the secondary clarifier, whereby pure sludge is discharged either for further treatment or directly into watercourses.

In the embodiment shown in FIG. 2, denitrification measures are provided. while maintaining the desired production of non-fibrous metallurgical sludge with associated phosphate removal and without excessively prolonging the total treatment time required.

In the illustrated embodiment, three separate treatment zones are formed: anaerobic zone C followed by a non-oxidizing zone D and an aerobic oxidation zone E, such as, in the previously described embodiment, the biological oxygen demand effluent to be treated enters a modified activated system. The sludge of FIG. 2 through line 31, being mixed in the initial treatment tank or vessel 34 with recycled activated sludge returned from the settler or clarifier 32. The vessel 34 is maintained under anaerobic conditions as previously discussed; that is, measures have been taken to maintain the initial treatment stage in zone C in the substantially complete absence of dissolved oxygen as in zone A.

That is, the dissolved oxygen concentration is below 0.7 ppm and preferably below 0.4 ppm. ^;

In the vessel or tank 34, the mixture is stirred under strictly anaerobic conditions, thereby allowing, as stated in the embodiment described above, the incorporation of biological oxygen demand by organisms that are provided by recycled activated sludge to deliver those kinds of organism. which may affect this transfer 'advantageous opportunities to obtain food and thus exclude the growth of other species.

The conversion energy is obtained by hydrolyzing the polyphosphates contained in the recycled sludge biomass. This method promotes the growth of species that preferentially accumulate phosphates, as previously provided sufficient absence of dissolved oxygen by covering the vessel 34 or otherwise preventing contact with atmospheric "oxygen" and / or displacing oxygen from the mixture by bubbling nitrogen gas as indicated. 38.

As shown in FIG. 2, an almost impeded flow is maintained in the vessel 34, by splitting this stage liquid flow vessel by two or more mass separated or hydraulically separated stages.

From the vessel or chamber 34, the mixture passes to a non-oxidizing treatment zone, designated D

Β

35. Το can be separate, container or part of a continuous pool. suitably separated from the preceding zone C to allow a simultaneous one-shift liquid flow without back-mixing. Dissolution of dissolved oxygen in zone D may occur. as previously described for zone C.

In FIG. 2, nitrogen gas is introduced into zone-C through line 38 to deprive the mixture of any dissolved oxygen and prevent oxygen from entering the atmosphere.

From zone D, the mixture then flows into and through the aerobic oxidation zone E, in which it is aerated to oxidize the biological oxygen demand including ammonia and remove phosphates. The oxidized mixture from zone E flows to clarifier 32 where pure sludge water is separated from the sediment sludge and a portion of the sediment. the sludge is returned in a controlled amount to the vessel 34 via line 33.

In the non-oxidation zone D, nitrates and nitrites (NO,) are taken up in concentrations higher than 2 ppm, expressed as elemental nitrogen and reduced to elemental nitrogen and thus discharged. To produce this effect, part of the mixture from oxidation zone E is returned to zone E via line 40. These nitrates and nitrites are formed in zone E by oxidation of nitrogen-containing substances (considered as ammonia) contained in the incoming waste water entering the system management 31.

In the oxidation zone E, the equilibrium of biological oxygen consumption changes and ammonia is oxidized to nitrites and ultimately at least partly to nitrates.

The oxidized mixtures from the last stage of zone E return to the initial stage of zone D, where the nitrate and nitrite content is brought into contact with the incoming biological oxygen demand. Care must be taken to avoid the introduction of NO _X 'into the anaerobic zone C.

In the embodiment shown in FIG. 2 not only selectively produces non-fibrous biomass with the desired phosphate removal as in FIG. 1, but also substantially removes nitrogenous nutrients. In addition, substantial removal of the crude protein is achieved without substantially prolonging the overall treatment time.

The amount of mixture returned from the oxidation zone E to the non-oxidation zone D can be in practical operation 100 to 400 percent of the feed volume entering the line system 31. The amount of sludge recycled by line 33 as in line 13 (Fig. 1) can be of the order of about 10 to 50%, preferably 20 to 30%, of the feedstock.

The oxidation zone E is controlled in substantially the same manner as zone B previously described. The treated mixture passes from the oxidation zone (B or E) to the clarifier. The aeration zone should be provided to ensure good removal of biological oxygen consumption and effective nitrification. in operation at minimum concentration of 358,

of 1 oxygen and preferably greater than 2 ppm. ·. ·

When higher dissolved oxygen levels are required at the outlet end of the oxidation zone, they can be formed without adversely affecting the system. ,

In the practice of the invention, the mixture is passed through an approximately enclosed stream through the entire conditioning system consisting of zones A and B of the embodiment of Figure 1 or zones C, D and E of the embodiment of Figure 5. It has been found that the degree of denitrification varies directly to a concentration of NO _X - where this concentration is below about 2 ppm and hence the flow inhibition is advantageous to achieve low NO _X values - in the outflow from zone D. In addition, preferably each of these zones C, D and E is arranged in a split liquid design, each treatment zone being divided into two or more separate treatment stages or their hydraulic equivalents as determined by the distribution of residence times by trace experiments (see Levenspiel, "Chemical Réaction Engineering", John Miley and Sons, New York, 1962, pp. 242-306. The need to include a non-oxidation zone to remove nitrogen in the system will either e depend on the ammonia content of the incoming waste water and on the limits established for the permissible nitrogen content of the treated effluent which is discharged. As a rule, which is not necessarily followed, the introduction of a non-oxidizing intermediate zone is generally recommended whenever the input effluent contains an excess of about 10 ppm of ammonia nitrogen, expressed as elemental nitrogen. Example 1

The system based on the embodiment of Fig. 1 has been tested for several months in the treatment of urban sewage from Allentown, Penrisylvania.

The system utilized an anaerobic, 6 L zone, which was divided into bulkheads

5. the same stages (1.2 liters each), followed by a 10-liter oxidation zone divided by partitions into 5 equal stages (· 2 liters) into which air was dispersed. Nitrogen gas was distributed in the anaerobic zone, which was equipped with a loosely sealed cover. From the last stage of aeration, the oxidized mixture was passed to a clarifier from which a portion of the settled sludge was returned to the initial anaerobic stage in an amount of about 20% by volume of the incoming waste water. The results shown in Table 1 are mean values over a 10-day operation.

From the results shown in Table 1, it was apparent that the desired sludge volume index indicating a dense, easily settled sludge was maintained, with more than 901% phosphate removal achieved. Elimination of biological oxygen consumption was on average 95% or higher.

188356

The residence time of the sludge in a sludge recirculation člřiči .Approximately was 1.7 hours, corresponding to an effective reduction of NO _X ^_ F 11.26 ppm as .is estimated from the effluent from the clarifier to 0.18 ppm in the recirculating sludge.

The nitrate and nitrite content (measured as NO _x ^_ nitrogen) in the 5 sections of the anaerobic zone remained below 0.16 mg per liter. The phosphate concentrations expressed as mg of phosphorus per liter in 10 Sections were as follows: 9.35, 12.87, 13.55, 13.63, 13.07, 6.64, 3.65, 1.78, 1.05 and 0.72. These values indicate phosphate release in the first 5 anaerobic sections and exponential phosphate removal in the last 5 aerobic sections.

TABLE 1

MLVSS mg / l 4082 COD (filtered) inlet, mg / l 286 COD (Filtered) Outflow mg / L 48.88 BOD5 (filtered) inlet, · mg / l 127.4. BODs (filtered) mg / L discharge 5.72 inlet time, hours 2.86 recirculated sludge,% inflow ' 20.73 nominal residence time anaerobic zone hr. 0.89 aerobic zone 1.48 phosphorus (as P) mg / l NHs (as N) mg / l NO _X - (as N), mg / l zone settling speed 196.42 cm / hour SVI, ml / g TSS 69 ’/ tot. scattering, acid. in anaerob. 0,29—0,32 zone, mg / l belk; scattering of acid. in aerobic 6.41 zone, mg / l tot. scattering of acid. in aerobic 6.16 zone, mg / l Relevant abbreviations used in of this table .and in the description have the following meanings:

". BODs - biological oxygen consumption,

MLVSS - Mlxed Liquor Volatile Suspended. Sol-ids - only those suspended substances that are volatile and are present in the mixture,

COD -t Chemical Oxygen Demand

SVI - Sludge Volume Index

TSS - Total Suspended Solide. amount of suspended substances,

RK - dissolved oxygen.

Example 2

The system operating according to the flow chart in Fig. 2 was used to treat urban wastewater from Allentoiwn, Pennsylvania. The system contained three separate vessels forming an 7.2 liter anaerobic zone (I) divided by baffles into 3 equal 2.4-liter chambers; non-oxidizing zone (II) with a capacity of 3.6 liters divided by partitions into 3 equal chambers

1.2 liters; and an oxidation zone 3 having a content of 12

In fresh. flow In recirculation. In cleaned sludge liquid

6.1 3.85 0.44

18.35 0.82 '0.43

0.08 0.18 11.216 liters divided into 4 chambers of 1.2, 2.4, 3.6 and 4.8 liters.

Nitrogen gas was introduced into each chamber of the anaerobic and non-oxidizing zones to maintain substantially the absence of oxygen. The mixture from the last chamber of the aeration vessel (III) flowed into the clarifier from which the purified liquid was withdrawn, while a portion of the settled sludge was recirculated to the I chamber of the anaerobic zone in which it was contacted and mixed with the incoming waste water.

The mixture thus passed sequentially through the closed flow system and in the established liquid order in each zone. Part of the mixture from the last chamber of the oxidation zone (III) was collected and recycled to the 1st chamber of the non-oxidation zone (II).

Oxygen was introduced into the oxidation zone by dispersing air into the mixture.

The operating conditions and results are shown in Table 2, based on average values during weekly operation.

The residence time of the sludge in the clarifier and recycle was about 1.4 hours, which corresponds to "the effective reduction of NO _X from ^_ 4.85 ppm as is. the clarifier effluent to about 0.07 ppm in recirculated sludge.

TABLE 2

In fresh inlet In the sludge cycle In purified liquid ^: MLVSS 3399 GOD (in-fiber) inflow, mg / l 258.5 COD (fiber) inlet, mg / l · 155.0 BODs (fiber) inlet (avg.), 42.24 • mg / l BODs (fiber) inlet (avg.), 2.07 mg / l recirlkulov. sludge,% inflow 30.5 · 2 · in, recycle, III to II,% inflow  182.9 runoff delay time, throw. 2.95 phosphates such as P, mg / l, 86.48 3.33 4.13 0.45 % removal ammoniacal nitrogen like- N, 97.03 43.51 2.34 0.40 · mg / l,% removal NO _X - nitrogen as N, mg / l, 01.34 0.7 0.07 4,85 ' '% removal SVI. (avg), ml / g TSS 154.0 SVI, stirred, ml / g 51.79 zónová sed. speed, cm / hr 134.2 MLVSS 3399 COD (in-fiber) inflow, mg / l 258.5 COD (fiber) inlet, mg / l 155.0 BODs (fiber) inlet (avg.), 42.24 ^: Mg / 1 BODs (fiber) inlet (avg.), 2.07 mg / l - recirlkulov. sludge,% inflow 30.52 in, recycle, III to II,% inflow 182.9 / -. _t inlet time, hours 2.95 phosphates such as P, mg / l, 86.48 1.39 15.34 8.19 % removal ammonia nitrogen such as · N, 97.03 0.69 8.58 4.88 mg / l,% removal NO _X - nitrogen as N, mg / l, 61.34 5,51 '· 0.06 1.29

% removal

SVI (avg), ml / g TSS 154.0

SVI, stirred, ml / g 51.79 zone sett. speed, m / h 134.2

TABLE 3

Zone I

Section 1 2 3 NO /, mg / l 0.05 0.05. 0.06 NHs-N, mg / l 10.43 10,04 8.58 PO3- ³ -I P, mg / l · 10.46 14.11 15.34 RK, mg / l 0.14 0.12 0.13 Z ó na I I Section 4 , -5 6 NO /, mg / l 2.1 1.69 1.29 NH3 — n, mig / 1 5.32 5,05 4.88 PO / ³ —P, mg / l ' 10.24 - 8.49 8.19 - RK, mg / l 0.43 0.35 . 0.43 Z ó n a 11 I Section - 7 · 8 9 10 NO _X , mg / l 2.23. 3.71 5.21 5,51 NHs-N, mg / 1 ' 3.92 2.44 1.16 0.69 PO / ³ —P, mg / l 6.33 '4,5.3 • 2.60 1.39 RK, mg / l 7,47- 7.14 5.29 3.54

198338

Table 3 shows the nitrogen and phosphorus concentrations in each of the sections of the system shown in Table 2, together with dissolved oxygen concentrations.

The system provides better economy not only because of the lower cost of chemicals that it otherwise requires to induce the desired phosphate removal, but also in terms of higher waste water throughput per unit volume of liquid, with excellent removal of biological oxygen demand and COD. Thus, even in cases or circumstances in which the phosphate content of the wastewater flowing does not create a problem, the system according to the invention offers important economic advantages due to the high performance. The embodiment shown in Figures 1 and 2 shows excellent results when working with typical urban wastewater at a residence time of the order of about 3 hours at about 20 ° C.

A somewhat higher flow retention time may be required for industrial wastewater where the soluble biological oxygen demand is in excess of about 150 ppm. Existing activated sludge systems can be easily, well. modified at low cost to operate in accordance with any of these embodiments.

In addition, the economic advantages of the systems operating in accordance with the present invention include the advantage of high clarifier bottom liquid density, which is a good indicator of good settling rate and the actual absence of fibrous biomass (ascertained by microscopic observation). Thus, the solids concentration in the lower clarifier content of 3.6% volatile suspended solids (VSS) was found in operation according to the invention, while conventional systems operate at about or below 1% VSS in the lower clarifier stream.

The densified bottom stream and high zone settling speeds thus create cost benefits even in areas where neither phosphorus removal or nitrification is required. In addition, the systems of the present invention achieve a reduction of phosphates (such as phosphorus) in the effluent to 1 ppm or less, a reduction in the inlet biological oxygen demand of less than 10 ppm, with complete removal of ammonia and a reduction in total nitrogen (such as N). 25% of the inlet content.

The system described in FIG. 2 may be. also useful where phosphate removal is not required; nor nitrification due to the good properties of the obtained sludge. Another factor contributing to the benefits of saving oxygen requirements where nitrification is required because oxygen in the NO _X ^_ causes the metabolism of biological oxygen demand in non-oxidizing zone. Further, reducing the NO _x content in the mixture entering the clarifier minimizes the release of nitrogen from this point of view. Thus, the "floating, sludge" induced by the release of nitrogen in the clarifier, which is generally the case with nitrification effluents, does not occur.

The systems described in Figures 1 and 2 also have the advantage of producing a biomass containing up to 6% or more phosphorus (by weight percent). Thus, a process is provided in which a high phosphorus content can be obtained. This may be advantageous for industrial use. The application increases the fertilizer quality of the waste biomass.

Claims (10)

1. A method for inhibiting the growth of fibrous biomass in an activated sludge system, characterized in that in the initial contact zone, the activated sludge is mixed with the incoming wastewater with biological oxygen consumption and optionally a phosphate and ammonia content, maintaining the initial contact zone under anaerobic conditions, e.g. by contacting the mixture with an oxygen-free gas, at a nitrate and / or nitrite concentration of less than 0.3 ppm and a dissolved oxygen content of less than 0.7 ppm, to produce non-fibrous microorganisms that bind, biological oxygen consumption, with or without treatment in the intermediate zone, which may optionally be maintained under non-oxidizing conditions, the oxidation zone is allowed to undergo biological oxidation in admixture by contact with oxygen gas which is injected into the oxidation zone, maintaining a dissolved oxygen content of 1 ppm in the oxidation zoneup to 20 ppm, oxidized. The mixture is transferred from the oxidation zone to the settling zone, where the purified top liquid is separated from the settled sludge and a portion of the settled VYNALEZU. the sludge returns to the initial contact zone for mixing activated! sludge in this wastewater flow zone. 2. A method according to claim 1, characterized in that a series of at least two hydraulically separated sections in a co-current are formed in the initial contact zone. liquid flow contact. 3. The process of claim 1 wherein the dissolved oxygen content in the initial contact zone is maintained less than 0.4 ppm. 4. A method according to claim 1, characterized in that a series of at least two hydraulically separated sections is formed in the oxidation zone in a co-current liquid jet contact. 5. A method according to claim 1, characterized in that nitrogen gas is contacted in the initial contact zone with the mixture to maintain anaerobic conditions in the zone. 6. The process of claim 1, wherein the mixture formed in the initial contact zone of the waste water with biological oxygen consumption and containing ammonia or phosphates is treated in a non-oxidizing zone. 15 18 before being discharged into the oxidation zone, wherein the dissolved oxygen content in the non-oxidation zone does not exceed 0.7 ppm and nitrates and / or nitrites are introduced into the zone by internally converting the nitrate and / or nitrite mixture from an oxidation zone wherein the mixture has a nitrate and / or nitrite concentration in the range of 2 ppm to 20 ppm, expressed as elemental nitrogen. 7. The method of claim 6, wherein the mixture transferred from the oxidation zone to the non-oxidation zone constitutes 100 to 400% of the volume of fresh wastewater inflow entering the initial contact zone. 8. A process according to claim 1, characterized in that the sludge to be circulated into the initial contact zone constitutes 10 to 50% by volume of the inflow of fresh waste water introduced into the initial contact zone. 9. A method according to claim 6, wherein at least two fluid jet contact sections are formed in the non-oxidation zone. ^! 10. The method of claim 6, wherein the total inlet time in the initial anaerobic contact zone; the non-oxidation zone and the oxidation zone are at most 5 hours. l sheet shakes