WO1987003574A1

WO1987003574A1 - Process and plant for purifying waste water

Info

Publication number: WO1987003574A1
Application number: PCT/EP1986/000715
Authority: WO
Inventors: Peter Kunz
Original assignee: Fraunhofer-Gesellschaft Zur Förderung Der Angewand
Priority date: 1985-12-09
Filing date: 1986-12-06
Publication date: 1987-06-18
Also published as: EP0265442A1; DE3543432A1; AU6840387A

Abstract

To purify waste water a process is proposed in which, in addition to physical pre-clarification (5) with the formation of a biological primary sludge, a biological pre-treatment (8) is envisaged in which conversion of the material is controlled in order to adjust the loading in the following treatment stages. The sludge accruing in the biological pre-treatment is separated by filters (23) from the waste water and fed to the primary sludge. As a result of the biological pre-treatment, suspended inorganic and organic matter is removed from the waste water, as well as easily convertible and dissolved organic compounds, so that they do not overload the subsequent processing stages. By controlling the conversion of material it is possible to vary in a specific manner the loading of the subsquent processing stages, for example to hold it constant irrespective of the inflow conditions in the pre-clarification stage. If a biological post-treatment is effected, it is possible to adjust the balance of nutrients in the post-clarification stage by controlling the conversion of material in the pre-clarification stage.

Description

Process and plant for cleaning wastewater

The invention relates to a process for the purification of waste water with at least one primary sludge, the physical preliminary clarification, a highly loaded biological pretreatment and a subsequent biological and / or physical aftertreatment, in which mainly dissolved waste water ingredients are converted into a secondary sludge.

The majority of wastewater treatment plants and practically all municipal wastewater treatment plants have rake and sand trap systems at the inlet for the mechanical-physical separation of coarse and speci¬ fically heavy particles, which are followed by a preliminary treatment in which the settable particles are separated by sedimentation. The primary clarification takes place in mostly elongated tanks, over the bottom of which a conveyor is guided, which transports the sedated primary sludge into a sludge collection trough, from which it is finally drawn off and fed to a digestion process. The sedimentation rate in the pre-clarifier decreases exponentially with increasing residence time. whereby suspended matter can hardly be separated. You get into the aftertreatment with the waste water.

As an aftertreatment, for example, an activated sludge process is possible in which microorganisms, namely the so-called destructors, find optimal conditions with regard to nutrient supply and oxygen supply. The destructors convert dissolved organic substance into the body's own substance, multiply and grow into solid structures, which are in turn accessible to physical separation processes. The separation - usually by sedimentation, more rarely by flotation - takes place in the secondary clarifier, in which the biomass is obtained as secondary sludge. The secondary sludge is partly returned to the activated sludge stage and partly removed as excess sludge. The necessary oxygen is provided by direct introduction of air or by circulating the wastewater. In the trickling filter process, on the other hand, the pre-clarified wastewater is sprinkled on the surface via rotary sprinklers, from where it seeps through the trickling filter material. The destructors sitting on the surface of the trickling filter material convert the biodegradable wastewater ingredients into sludge. The disc immersion process works in a similar way, in which the destructors sit on rotating discs which are immersed in the pre-treated waste water. During the diving process, the destructors absorb the wastewater ingredients and supply themselves with atmospheric oxygen when they emerge. If the vegetation has a certain thickness in the trickling filter and disc immersion method, it is entrained with the wastewater flow due to anaero decomposition processes and the repeated hydraulic stress. These particles can then also be sedimented. Finally, flotation processes are also used for post-treatment, in which non-sedimenting suspended matter and chemically precipitated wastewater ingredients are dispersed by means of precipitants and flocculants. However, practice has shown that such a post-flotation can hardly be carried out economically.

In the processes and systems for wastewater treatment used today, there is in particular no optimization in the aftertreatment downstream of the primary clarification, be it biological and / or chemical-physical. This means that, for example, the biological aftertreatment is operated with an underload. the installed parts of the system are not optimally adapted to the requirements and the process runs uncontrolled, as a result of which the secondary sludges generated, for example, are difficult to dewater.

In the known process mentioned at the outset (DE-A 1-31 41 889), attempts have been made to optimize a pond aeration system which operates according to the activated sludge process by preceded by a highly stressed biological pretreatment in the form of a trickling filter system, where appropriate between Tropf¬ body system and ventilation pond an adsorption pool is turned on. This measure is intended to reduce the organic pollution of the aeration tanks, either to make them smaller or to increase the amount of waste water supplied to them. The biomass accumulating in the trickling filter system or in the absorption basin is not separated separately, but is fed to the aeration ponds and sedimented there. The primary sludge obtained by preliminary clarification is therefore added to the secondary sludge settling in the aeration ponds. The sludge drawn from the ventilation ponds is made up of all wastewater ingredients that were separated in the course of the clarification process. What is more serious, however, is that part of the existing and formed solids is mineralized with oxygen consumption, so that water-eutrophic substances (nitrate, phosphate) are generated in the sewage treatment plant.

The invention is based on the object of proposing a method and a plant for the purification of waste water which enables optimum operation in the treatment stage downstream of the preliminary clarification, regardless of whether this treatment stage is operated biologically, chemically or physically or in mixed operation .

This object is achieved according to the invention in that the sludge obtained in the biological pretreatment is separated from the waste water and added to the primary sludge, and in that the substance used in the biological pretreatment is controlled to adjust the load in the aftertreatment.

In the process according to the invention, not only the sedimentable particles are separated off in the preliminary clarification stage, but also organic suspended matter and easily degradable dissolved organic wastewater constituents are converted into biomass and filtered out of the wastewater. The biomass formed in this way is added to the primary sludge, so that the sludge load in the biological or biological-chemical-physical aftertreatment is reduced and the mineralization in the secondary sludge is limited. The load in the post-treatment stage can thus be adjusted to optimal microbiological conditions by controlling the rate of metabolism in the biological pre-treatment. This is possible without difficulty by controlling the oxygen and / or the nutrient supply in the biological pretreatment. With the biological pretreatment, the feed conditions for the aftertreatment stage can be controlled, for example, as a function of the feed quantity or the feed concentration of biodegradable substances.

The effect of the post-treatment stage on the daily as well as the weather-dependent inflow amount can be equalized by the fact that at times of peak loads. the metabolic rate in the biological clarification stage is increased. In the same way operational peak loads caused by industrial wastewater can be compensated. While the aforementioned measures aim to equalize the inlet conditions in the post-treatment stage, i.e. to keep the load in the post-treatment stage constant, the biological pre-treatment can also be controlled in such a way that the load in the post-treatment stage is increased or decreased in a targeted manner, for example for a to receive biological aftertreatment alternating with nutrient-rich or nutrient-poor phases in order to influence the type of microorganisms and / or to be able to select the microorganisms in a way that is adapted to the ingredients of the incoming wastewater.

The preliminary clarification according to the invention has a particularly favorable effect on all subsequent activation processes which are operated with growth areas because the silting up of these areas is considerably reduced and a constant inflow concentration leads to uniform, highly active growth on these areas. Furthermore, the use of chemicals can be reduced in the case of chemical-physical aftertreatment with precipitants and flocculants, because the losses caused by unnecessary reactions with suspended solids and solid matter and bacterial mass are avoided - - CT / EP86 / 00715

become. Because of the reduction in the amount of secondary sludge, post-flotation can also be carried out economically. Finally, the invention has the advantage that the primary-secondary sludge ratio is shifted in favor of larger amounts of primary sludge. The primary sludge obtained according to the invention contains a considerably higher proportion of organic substances than the conventional only physical preliminary clarification, which give the primary sludge a higher usable energy content during digestion and combustion.

It is therefore advantageous to sludge accumulated in the biological pre-treatment together with the sedimented primary sludge anaerobically and then dewatered.

With this measure according to the invention, sludge treatment can be separated into a primary sludge treatment and a secondary sludge treatment. For primary sludge, sludge digestion is possible with less energy input and better energy yield in the form of usable digestion gas. The increased retention of heavy metals, poorly biodegradable undissolved organic substances or even toxic compounds in the pre-clarification stage through biological conversion or - through filtering leads to an accumulation of pollutants in the primary sludge, but has the advantage that a pollutant-free or low-pollutant secondary sludge is obtained in the post-treatment stage which is then in any case accessible for agricultural use. Since this sludge is largely mineralized, it is no longer decayed, but only hygienized and z. B. stabilized with lime. In addition, the biocoenosis is protected against pollution in the biological post-treatment stage, which is particularly susceptible to faults. On the other hand, there is an impairment of the anaerobic biocoenosis in the digestive process due to the higher concentration of pollutants, since hydrogen sulfide is practically always produced by sulfate reduction in anaerobic fermentation and this hydrogen sulfide reacts with most heavy metals to form poorly soluble metal sulfides.

To control the metabolic rate in the biological pretreatment, it can also be advantageous if wastewater containing nitrates is returned from the aftertreatment to the biological pretreatment.

To carry out the method, the invention is based on the known plant (DE-Al-31 41 889) mentioned at the outset, which has at least one primary clarifier with a primary sludge outlet that receives the incoming wastewater, a device with growth areas for biological pretreatment of the wastewater and one or has more downstream basins for biological and / or chemical-physical post-treatment of the wastewater. This plant is characterized according to the invention in that the device for biological pretreatment has a sedimentation basin which is connected on the sludge side to the primary sludge discharge from the preliminary clarification basin and on the filtrate side to the downstream basin for post-treatment, and has means for controlling the loading of the growth areas.

The sedimentation basin for the biological pretreatment can be arranged between the pretreatment basin and the post-treatment basin, particularly in the case of new plants. However, the pre-clarification tank itself preferably serves as the sedimentation tank for the biological pretreatment. This has the particular advantage that the biological pre-clarification stage can be retrofitted into the pre-clarification tank of existing sewage treatment plants at low cost. In a preferred embodiment it is provided that a filter is arranged on the outlet side in the sedimentation basin of the biological pretreatment. This filter can also be installed at any time in existing pre-clarification tanks on the drain side.

According to one embodiment of the invention, the filter can also form the growth areas for the biological pretreatment by immersing only part of its area in the waste water. The filter can be designed as a circumferential immersion filter (drum filter, disc filter or the like) in order to provide the necessary oxygen supply to the residue that forms on the filter. The oxygen supply can be controlled by controlling the circulation speed, the immersion depth or, if necessary, additional aeration, and also by controlling the filter cake starch, which at the same time controls the material conversion in the biological pre-clarification stage.

Instead, it is also possible to use fixed filter surfaces, which are then flushed with compressed air. The filter cake thickness can be regulated by rotating scrapers for rotating filters, and by rotating scrapers for fixed filters.

Instead of the above-mentioned designs, it is also possible for the growth areas for the biological pretreatment to be formed by rotating immersion bodies, the filter then being connected downstream of the immersion bodies. The immersion bodies can be designed as immersion trickling bodies, as disc immersion bodies or as material fill.

The sludge peeling off from the immersion body and / or retained by the filter is - when used in the - pre-clarification basin - detected by the sludge conveyor there and conveyed together with the primary sludge into the sludge collecting trough. The filtrate accumulating behind the filter (mechanically and biologically pre-treated wastewater) reaches the biological and / or chemical-physical post-treatment stage.

The invention is described below on the basis of some exemplary embodiments schematically shown in the drawing. The drawing shows:

Figure 1 is a flow diagram of an overall sewage treatment plant with a built-in biological pre-treatment stage;

FIG. 2 shows a plan view of a preliminary clarification tank with a biological preliminary clarification stage;

Figure 3 shows a section III-III of Figure 2;

Figure 4 shows a section IV-IV according to Figure 2;

FIG. 5 shows a partial section through a round basin with a biological preliminary clarification stage;

FIG. 6 shows a section of a further embodiment of the primary clarifier with a biological primary clarifier and

FIG. 7 shows a further embodiment of the clarifier compared to FIG. 6. The wastewater treatment plant shown schematically in the flow diagram in FIG. 1, which has only an exemplary character, has a lifting unit 2 at the wastewater inlet 1 and then, as the first separating device, a rake 3 which separates the large-sized cargo from the wastewater. The wastewater then passes into a sand trap 4 and from there into a pre-clarification basin 5, in which particles and suspended matter are sedimented with a predetermined dwell time. A clearing device 6 is arranged in the primary clarifier 5, which conveys the sediment to the sludge collecting trough 7. Furthermore, in this exemplary embodiment, a device 8 for biological pretreatment of the wastewater is arranged in the primary clarifier 6, which will be described in detail later. The particles separated off there also reach the area of the clearing device 6 by sedimentation and are also transported by the latter into the collecting trough 7. This primary sludge is drawn off from the collecting trough and fed to a digester. In the exemplary embodiment shown in the drawing, the pre-clarified wastewater flows from the pre-clarification tank 5 into an activation tank 11, which is supplied with oxygen via a compressed air device, the wastewater being circulated at the same time. In the exemplary embodiment shown, the activation tank 11 is followed by a flotation tank 12 in which further wastewater constituents are converted into particles by means of precipitating and flocculating agents and are either deposited on the bottom or made to float. From the flotation basin 12, the cleaned waste water arrives at 13 in the receiving water. The flotate and the sediment are withdrawn as secondary sludge from the flotation basin 12 via 14 and 15, a part of the flotate can be returned to the activation tank 11 via 16, while the sediment withdrawn via 15 and the excess secondary sludge running off via 17 18 treated, e.g. B. be mixed with lime to finally get into a drainage system 19, in which the digester 10 leaving the sludge is dewatered. FIGS. 2 to 4 show a first embodiment for a combined physical-biological preliminary clarification in a single preliminary clarification basin 5. One follows the sludge collecting trough arranged on the inlet side

Sedimentation section 20 with a clearing device 6 in the form of a clearing chain 21, which runs with its lower run 22 above the bottom of the primary clarifier 5 and transports the sedimented sludge into the collecting trough 7. On the discharge side, the primary clarifier has the device 8 for biological pretreatment, which is designed as a highly loaded biological stage. In the exemplary embodiment shown, the device has two disc-shaped filters 23 arranged next to one another, each of which sits on a shaft 24, is rotated by means of a drive (not shown) and to which fixed wipers 25 are also assigned. The shaft 24 can be mounted in the outlet-side wall of the primary clarifier 5, on the other hand on a diving wall 26 crossing the primary clarifier ... Below the disc-shaped filter 23, the primary clarifier 5 has a base 27 which separates the sedimentation section 20 from the one behind Separates the drain chamber 28 lying in the filter 23 by enclosing the disk-shaped filters 23, as can be seen in FIG. 4, on the lower part of their circumference. A pump 29 is installed in the discharge chamber 28 and conveys the filtrate to the next clarification stage.

The disk-shaped filters 23, which are designed as immersion disks, run with part of their surface area in the ambient air, absorb oxygen there and transport it below the water level. In this way, the filters 23 also form the growth areas for the microorganisms. The filter resistance is increased as it grows up, so that there is a lowering of the level in the drainage chamber 28. The biomass that forms on the filters 23 is released by the hydraulic stress and sinks over the base 27 into the sedimentation path 20 in order to be gripped there by the lower run 22 of the clearing chain 21 and to be transported into the collecting trough 7. If necessary, the filter resistance can be checked by checking the; Growth, e.g. B. od. The like can be controlled. The filter 23 not only removes organic and inorganic suspended solids from the waste water, but also converts easily dissolved organic compounds into biomass. By the strength of the filter cake and by controlling the speed of the filter 23, the remaining load of the waste water in the outlet chamber 28 and thus the load of the subsequent clarification stages can be controlled. The circulating speed of the filter disks or the distance or pressure from wipers or a filter rinsing which may also be possible can be controlled in such a way that a certain limit water level is not exceeded in the pre-clarifier on sedimentation section 20. Likewise, the differential pressure between the sedimentation section 20 and the outlet chamber 28 can be influenced by controlling the pump 29.

Another embodiment is shown in FIG. 5, in which the primary clarifier 5 is formed by the inner chamber of a two-chamber circular clarifier 30, while the outer chamber 31 forms the biological secondary clarifier. The primary clarifier 5 is connected to the activation tank 31 via an overflow 32. A scraper bridge 33 runs on the circular clarification tank 30, on which a compressed air supply 34 is laid, which ensures the necessary supply of oxygen in the activation tank 31.

A filter 23 is again inserted in the primary clarifier 5, which in this case is designed to be stationary again and in turn forms growth areas for the microorganisms. The filter 23 is also on the inlet side Assigned scraper 35, which sits on the scraper bridge 33 and ensures constant growth on the filter 23 as it rotates. Furthermore, the filter resistance can be influenced or the filter 23 can be cleaned via a branch line 36 of the compressed air supply 34.

FIG. 6 shows a pre-settling tank 5 with a sedimentation section 20, which is shown in the drawing in a shortened form, and a biological pre-settling stage 8 arranged on the discharge side the biological pre-clarification stage 8 extends. In this case, the device for biological pretreatment has a plurality of immersion drip bodies 37 arranged one behind the other, which are seated on a shaft 38 which is driven at variable speeds, of which several can optionally be arranged parallel to one another. These immersion droplets form the growth surface for the microorganisms. They run with the majority of their surfaces in the ambient air and only dip into the wastewater with their lower third. They are separated from the sedimentation section 20 by an upper weir 39, so that the wastewater behind it is calmed. On the outlet side, a filter 23 in the form of a drum filter is arranged in the primary settling tank 5, but in this case it is designed exclusively as a mechanical filter, extends over the entire width of the primary settling tank and on the inside is provided with a wastewater drain 40 leading into the subsequent tanks is. The filter cake settling on the filter can be sucked off via a suction box 43 by means of a level-controlled pump 41 and can be returned via a line 44 to the inlet of the primary settling tank in order to be at least partially settled on the sedimentation section 20. The embodiment according to FIG. 7 essentially corresponds to that according to FIG. 6. It differs from this only in that the biological growth areas in the preliminary clarification stage 8 are formed by disc immersion bodies 42, which are placed in a packet-like manner on transverse drive shafts 43.

In the aforementioned embodiments, a further pump (not shown) can also be provided in the area of the biological pretreatment to control the immersion depth of the growth areas. Finally, a line for returning nitrate-containing waste water into the biological pretreatment can be provided for denitrification between a downstream settling tank and the inlet of the primary clarifier 5.

Claims

1. Process for the purification of wastewater with at least one physical, a primary sludge preliminary clarification, a biological pretreatment and a subsequent biological and / or chemical-physical aftertreatment, in which mainly dissolved wastewater ingredients are converted to a secondary sludge , characterized in that the sludge obtained in the biological pretreatment is separated from the waste water and added to the primary sludge and in that the metabolic rate in the biological pretreatment is controlled to adjust the load in the aftertreatment.

2. The method according to claim 1, characterized in that the sludge obtained in the biological pretreatment is separated from the waste water by filtering.

3. The method according to claim 1 or 2, characterized gekennzeich¬ net that the metabolism in the biological pretreatment is controlled in the sense of keeping the load constant in the aftertreatment. - ^j - -

4. The method according to claim 1, characterized in that the metabolism in the biological pretreatment is controlled in the sense of a targeted change in nutrient load in the aftertreatment.

5. The method according to any one of claims 1 to 4, characterized in that the metabolic rate in the biological pretreatment is controlled via the oxygen supply.

6. The method according to any one of claims 1 to 5, characterized in that the metabolic rate in the biological pretreatment is controlled via the nutrient supply.

7. The method according to any one of claims 1 to 6, characterized in that the sludge obtained in the biological pre-treatment together with the primary sludge is digested anaerobically and then dewatered.

8. The method according to any one of claims 1 to 7, characterized in that nitrate-containing waste water from the aftertreatment is returned to the biological pretreatment for denitrification.

9. Plant for carrying out the method according to one of claims 1 to 8, consisting of at least one primary sewage tank receiving the incoming wastewater with a primary sludge discharge, a device with growth areas for biological pretreatment of the wastewater and one or more downstream tanks for biological and / or chemical physical aftertreatment of the wastewater, characterized in that the device (8) for the biological pretreatment comprises a sedimentation basin which is connected to the sludge on the - τ

Primary sludge discharge (9) from the primary settling tank (5) and on the filtrate side is connected to the downstream tanks (11, 13) for the aftertreatment, and has means (35, 36) for controlling the loading of the growth areas (23, 37, 42).

10. Plant according to claim 9, characterized in that in the sedimentation basin (5) of the biological pretreatment (8) on the outlet side a filter (23) is angeord¬ net.

11. Plant according to claim 9 or 10, characterized in that the sedimentation basin for the biological pretreatment serves the primary clarifier (5) and that the filter (23) is arranged in the region of the waste water drain of the primary clarifier.

12. Plant according to one of claims 9 to 11, characterized in that the filter (23) also forms the growth areas for the biological pretreatment.

13. Plant according to one of claims 9 to 12, characterized in that the filter (23) dips with a part of its area in the waste water.

14. Plant according to one of claims 9 to 13, characterized in that the filter (23) is designed as a circulation filter.

15. Plant according to one of claims 9 to 13, characterized in that the filter (23) is fixed. 16. Plant according to one of claims 9 to 11, characterized in that the growth areas for the biological pretreatment of rotating immersion bodies

(37, 42) are formed and that the filter (23) is connected downstream of the immersion bodies.

17. Plant according to claim 16, characterized in that the immersion bodies are designed as immersion drips (37) or as disc diving bodies (42).

18. Plant according to claim 16, characterized in that the immersion body has a bed of material.

19. Plant according to one of claims 9 to 18, characterized in that the means for controlling the application of the growth areas have a pump for changing the water level in the sedimentation basin (5).

20. Plant according to one of claims 9 to 14 and 16 to 18, characterized in that the means for controlling the application of the growth puddles have speed-controllable drive motors for the circulation filter (23) or the rotating immersion bodies (37, 42).

21. Plant according to one of claims 9 to 20, characterized in that the means for controlling the application of the growth areas have a controllable ventilation device for the sedimentation basin (5).

2.2. Plant according to one of claims 9 to 21, characterized in that the means for controlling the loading of the growth areas has a quantity control for the nitrate-containing waste water returned from the aftertreatment.