FI70566C - TVAOSTEGS AKTIVSLAMFOERFARANDE FOER RENING AV AVLOPPSVATTEN - Google Patents

Description

ΓΒ1 classified ad.su 70566 • $ 3n? (11) utlAggningsskrift / uood C Patent ay3r ::: etty

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(51) Kv.ik. * / Lnt.ci. * c 02 F 3/12, 3/30 FINLAND —FINLAND (21) Patent application - Patentansökning 772657 (22) Application date - Ansökningsdag 07.09.77 (F ») (23) Start date - Giltighetsdag 07-09-77 (41) Made public - Blivit offentlig 1 1. 03.78

National Board of Patents and Registration Date of publication and publication. -

Patent and registration authorities Ansökan utlagd och utl.skriften publicerad (86) Kv. application - Int. ansökan (32) (33) (31) Privilege claimed - Begärd priority 10.09-76

Germany 1i i tt Republic - Förbundsrepubl iken Ty sk! and (DE) P 26 * 40875.3 (71) Mach inefabriek W. Hubert ε Co. BV, Franekervaart 1, Sneek, Netherlands-Nederländerna (NL) (72) Rotho Böhnke, Aachen, Bernd Diering, Aachen, Germany 1-Förbundsrepubl iken Tyskland (DE) (7 * 0 Berggren Oy Ab (5 * 0 Two-stage active effluent treatment) - Tvästegs aktivs 1 amförfarande för rening av av 1oppsvatten

The invention relates to a two-stage activated sludge process for the treatment of waste water.

Activated sludge methods form a special form of biological wastewater treatment. Wastewater from residential and industrial facilities has previously been either allowed to drain into the ground, used to irrigate crops, or fed to local waters either mechanically treated or untreated. Wastewater treatment plants have only recently been expanded with a biological phase. The purpose of waste water treatment is to minimize the risks to human and animal health and life associated with inadequate treatment. In the treatment of wastewater by the activated sludge method, the steps of biological self-treatment of natural water bodies have been concentrated to a minimum, which considerably shortens their schedule. Due to the artificial aeration in the aeration tanks and the simultaneous action of the activated sludge (recoverable sludge), the initially colloidally dissolved 2,70566 substances partially agglomerate partly around the organic and partly inorganic suspended matter and optionally around any precipitating substance to form flakes. However, partly due to aeration, coagulation and flocculation of dissolved and semi-dissolved substances occur, whereby these substances form a good nutrient for bacteria and microorganisms. It is assumed that due to the strong action of bacteria and microorganisms, dissolved and colloidal organic contaminants in wastewater are subject to a kind of suction effect that can be called biogenic adsorption. The biological cleaning effect is thus obtained due to the interaction between the surface function of the flakes and the oxidation of the substances adsorbed through said organisms by means of enzymes in the presence of oxygen. The water flowing from the aeration tank together with the activated sludge is separated from the sludge in another precipitation basin, after which it flows in the usual way as biologically purified water to the sewer, i.e. to a natural or artificial waterway. Part of the sludge must be returned as reversible sludge to the aeration tank, where it will complete the digestion of the decomposing organic matter in the effluent. The residual sludge is either stabilized in the digestion tank, mixed with the pre-clarification sludge or fed to the sludge removal plant if it happens to be a stabilized sludge. The contents of the basin must be constantly rotated so that said flakes cannot settle to the bottom of the aeration basin, where they would die in the absence of oxygen.

It is already known to use single- or two-stage activated sludge plants to carry out the activated sludge process. The operating principle of the simplest form of such a plant is the pre-precipitation of the effluent and the subsequent one-stage efficient aeration. However, this method is very sensitive to sudden, sharp increases in wastewater volume and the effects of industrial wastewater, as all biologically treated wastewater is fed to the aeration tank so that any activated sludge can be destroyed. Increases in wastewater volumes and the effects of industrial wastewater can only be managed more reliably in single-stage activation plants with lower sludge loads and longer residence times.

In an effort to make the activated sludge method less sensitive and at the same time, however. methods that include two-stage aeration have had to be developed to reduce aeration time.

Il 70566 3

It is known to carry out the separation of biokenosis in two steps (DE-A-2 321 722 and US-A-3 764 524). However, it is a method in which ambient air is not used, but the various steps are treated with a gas containing at least 50% by volume of oxygen. Excess sludge is removed immediately from the sludge cycle without recycling from the second treatment stage where the sludge load is in the range of 0.15 kg BOD / kg dry matter and day. However, this known separation of biokenoses is a method which does not differ substantially from methods in which no separation of biokenoses takes place. In this prior art biokenosis separation, the energy consumption is also not reduced, since here too the biodegradation of all impurities takes place and the high molecular weight impurities or their removal do not bind adsorptively in the first treatment step.

4 70566

Based on the latest observations, such a two-step biological method achieves optimal results by the following procedure: the activated sludge of the first biological step is used to perform all the separate processes required for biological digestion. These processes include e.g. adsorption of dissolved organic substances to sludge flakes, their diffusion into the cell and substrate, and optionally endogenous respiration. In a highly active state, the sludge is fed into partially purified wastewater mixed with an intermediate treatment system. After sludge separation, the partially treated wastewater is directed to a second biological stage, which is used with a lower volume and sludge load. The main purpose of this step is to remove the remaining organic matter by means of a long residence time and a large amount of acid fed. In addition, the biomass content decreases significantly due to self-absorption. This is followed by conventional process steps such as second precipitation, etc. The following are important process parameters: B0D5 sludge load 0.5-1.0 kg BODr / kg TS in the first biological stage and low 3 3 BOD ^ volume load less than 0.5 kg / m / day and at the same time low sludge load approx. 0.05 kg BOD ^ / kg TS. Using these parameters and utilizing the biological activity of the second stage sludge by feeding the sludge to the first activation stage, a high BOD ^ digestion efficiency of more than 85% is achieved in both biological stages to achieve a removal concentration of less than 40 mg BOD ^ / l.

The disadvantage of the known methods mentioned above is the very considerable energy consumption. The degrees of purity obtained are consistently unsatisfactory because the activated sludge can be very easily contaminated due to the underloading of the second stage and the return of the second stage residual sludge to the first stage. It is also to be feared that the known methods will not meet future water protection regulations, which are becoming increasingly stringent.

The object of the invention is therefore to provide a two-stage activated sludge process for the treatment of waste water, whereby the process achieves even better and more stable degrees of purity. At the same time, energy costs are significantly reduced, so that the cost of capital does not rise as much as in a corresponding conventional sludge activation plant.

li 5 70566 This object is solved according to the invention in that all wastewater is fed to the first aerated activation stage, which is used as a peak load stage with a volume load Br of about 10 kg BOD ^ / m / day and a sludge load BTS of at least 2 kg BOD5 / kg dry matter / day . The intermediate precipitation of the waste-water-slurry mixture removed from the first stage ensures an accurate separation of the biokenoses of the two activation stages, whereby sufficient residual sludge is removed from the intermediate precipitation stage so that the age of the slurry is kept low. Finally, the intermediate precipitated wastewater is fed to a second aerated activation stage, which is used as a low loading stage.

A further feature of the process according to the invention is that, in comparison with known two-stage activation methods, it is not necessary to feed the second activation stage biochenose to the untreated effluent bypass, since polar, readily rotting organic compounds are sufficiently fed to the second activation stage.

The term wastewater is used in the context of the present invention in its broadest sense. In general, it is an aqueous system in which organic substances are dispersed also in the presence of dissolved or suspended inorganic substances. The particles of the dispersed phase may actually be dissolved, emulsified in colloidal and / or suspended form. The degree of dispersion of the particles to be separated is usually not very important. Nor does the implementation of the method of the present invention depend on whether or not the substances precipitate. For example, sand and sludge precipitate, while solutes and colloids that make wastewater turbid do not precipitate. The fact that wastewater often contains both non-rotting and rotting substances is also generally not important for the implementation of the method.

The following are several embodiments of the method according to the invention, which do not limit the invention. The method can therefore be used in households for washing, rinsing and bathing, as well as for the treatment of wastewater generated in W.Cs, municipal wastewater treatment, which also includes rainwater from roads, roofs and yards, and purely industrial wastewater treatment. The method according to the present invention is particularly important in connection with the treatment of industrial wastewater. The method according to the invention is also suitable for combination with other purification methods, in which case it must be adapted according to the case in question.

6 70566

The two activation steps of the process according to the invention are aerated either by means of compressed air or by breaking or spraying the surface of the water by means of rapidly rotating rod rollers, e.g. Kessener brushes, or Simplex centrifuges, Vortair mixers, Simcar fans or other known surface fans. Different aeration means can also be combined with each other if necessary.

One skilled in the art can also, based on the guidelines provided by the invention, select the most suitable aeration tank to perform the method. The following are just a few examples of aeration tanks, and the list can be expanded as needed. For example, compressed air pools have been found to be advantageous. Advantageously, the so-called Haworth ducts, which are aerated by impellers that simultaneously move the water forward. Kessener pools, mixing pools and pools operating according to Simplex, Inca and Aero-Accelerator methods can also be used.

The aeration and aeration tanks do not have to be of the same quality in the first and second activation or aeration stages of the method according to the invention. Therefore, it is particularly advantageous, for example, if the first activation stage (peak load stage) comprises aeration with large bubbles, while fine bubbles are used for aeration of the second activation stage. Particularly good results can also be obtained if the second activation stage is carried out with a thoroughly mixed drainage system which is not dependent on the structure of the aeration basin of the first activation stage. Such a system represents a minor modification of the Haworth channel. Air and / or oxygen are supplied, for example, by means of rotors. High efficiency is usually achieved, for example, with low-load oxidation barriers (circulating plants). An additional advantage is that the construction costs of such plants are about 30% lower than in known plants with a corresponding digestion capacity.

Pre-precipitation of wastewater is usually not required. Only when the wastewater contains difficult materials such as fibers, etc., can the pre-removal of the sludge be necessary and even then it is not time consuming (time äo, 5 h). Intermediate and final precipitation are performed by conventional methods.

Termination of the process of the invention by a filtration or flocculation filtration process may be necessary to further reduce the BOD 2 value. This reduction can be more than 50%. If such filtration is performed, the final precipitation system can be made smaller, deviating from the ATV instructions, because the filtration process retains any different sludge particles. Given the smaller final precipitation system, filtration does not incur significant additional construction costs. Compared to a conventional wastewater treatment plant (BTS = 0.15), the present method is even cheaper and has a much higher efficiency.

The sludge from the intermediate and final precipitation steps must be partially returned as recovery slurry to the respective activation steps, while the rest of the sludge is transported as residual sludge to the sludge digestion tank, e.g. through a thickener. In the case of such recovery sludges, it must be ensured that they have undergone an initial separation. This results in a favorable separation of the biokenoses of the two activation steps and further ensures that no operational difficulties occur immediately after a short time, as is the case with known methods.

One skilled in the art can, without departing from the scope of the invention, modify the method according to the invention by carrying out, before, after or in between, conventional measures according to activated sludge technology. For example, the adsorption of the first activation step can thus be improved by the addition of a flocculant, while the overall stabilization of the system can be achieved by means of polyelectrolytes.

The addition of certain enzymes to the second activation step may be advantageous, in which case the enzymes must be adapted to the particular type of effluent.

The basic technological relationships of the method according to the invention are explained in more detail below.

Initially, it can be assumed that readily adsorbable substances have a higher affinity for the adsorbent than for solvents, in the present case 707066 water. This means that less water-soluble, i.e. higher molecular weight, i.e. less rotting substances are retained in the first activation or peak loading step, while readily water-soluble and thus easily rotting substances are fed to the second activation step, where they are biologically digested.

The successful and reliable use of the method according to the invention is essentially based on the knowledge that the slurry of the peak loading phase must be kept continuously in the so-called in the insertion step where respiration of the substrate begins. This slurry is fine-grained in structure and has a very high specific surface area that is important for adsorption activity. The sludge index is usually low. The reactions that take place in the first activation step are mainly of a physicochemical nature, whereas in the known methods the biological processes in the foreground are in this background. Despite the high cleaning effect (over 60%), oxygen consumption and thus energy requirements are relatively low.

However, when carrying out the method according to the invention, it is necessary to ensure good thorough mixing and a high sludge load, as well as a low sludge age in the first activation step. In this case, it has been found that a volume load BR of about 10 kg BOD ^ / m / day and a sludge load BTg of at least 2 kg BOD ^ / kg TS / day guarantee the desired technical result.

The method according to the invention differs from known purification methods in that experiments have shown that although no precipitating or neutralizing agents are added to the first peak loading activation step, in the second activation step the high pH value decreases and the conductivity decreases to a level safe for biocoenoses.

The method according to the invention also differs from the known methods to a certain extent in terms of the order of the purification steps. In current conventional biological treatment methods, the entire sludge load fed to biological processes is converted to a biologically high degree of activated sludge. The following purification sequence is followed: 9 70566 a) adhesion (adsorption) of higher molecular weight compounds to flakes and digestion of lower molecular weight (more easily rotting) compounds, b) digestion into higher molecular weight compounds after absorption of energy, and the separation of metabolites.

In contrast, a large proportion of the higher molecular weight compounds do not rot in the peak / low load phase of the present invention. Instead, they are removed after a short time after the adsorption of the peak loading step with the young slurry, so that they no longer burden the purification process of lower molecular weight and especially polar compounds in the second activation step. This results in significant energy savings. This can be seen by comparing the oxygen consumption of the method according to the invention and the known methods. For this purpose, the formula for oxygen demand OVR = 0,5n.BR + 0,1 l TSR / g 02 / m3 d? where the different symbols have the following meanings: OVR oxygen demand η cleaning power, ie amount of decaying substance, B organic volume load / m3 / day κ λ TSD% reversible substances / m x \

Taking into account the respiration of the substrate and the soil as well as the oxygen demand of the nitrification and denitrification steps, the following table is concluded: 10 70566

Stabi- Nitrifi- Residual BOD ^ Residual BOD ^ cation 20 mg / l 30 mg / l BTS 0.05 0.15 0.30 0.60

Soil and

substrate 0.42 0.56 0.78 1.18 OVR

respiratory

Nitrification and denitrification 0.05 0.23 0.34 0.26 cation

0VV0VR

OVR 0.47 0.79 1.12 1.44 + Ni + Den.

Soil and substrate nitrification and de— -ιλ-ίο. -i increase in respiration due to α „mtrification x Den. = denitrification

The energy consumption K is functionally related to the oxygen demand OV ^ according to the following equation:

m · OJ

K = -? k where k is the amount of oxygen supplied per kWh that is 1800 g C ^ a in aeration with medium-sized bubbles.

The actual total power consumption KG = + K ^ m including the auxiliary equipment is obtained from the following table by applying the ATV instructions: BTS 0.05 0.15 0.30 0.60 1.0 TS 5 3.3 3.3 3.3 3 .3 g / l

K 21 15 11 9 8 kWH / T

X ♦ et I = inhabitant Here energy consumption is given in kilowatt hours per inhabitant and per year.

The total energy consumption associated with the OV value can be

R

get from the following formula: · ,! 7 0 5 6 6 a KG = KN + 0,1014 · m · η · a + 0,0203 · m · $ BTg whose new symbols have the following meanings: Special energy requirements of KN auxiliary equipment, air plant B ^ g = 0, 05 - KN = 2,5 kWh / I * a, air plant BTg 0.10 - KN = 3,0 kWh / I * a, m additional consumption due to nitrification and denitrification η amount of biological purification rate, β purification of organic matter, and a specific load of organic putrefactive material g BOD ^ / I-day.

The factors for the different activation steps can be obtained, for example, from the following table: BTS 0.05 0.15 0.30 0.60 1.00 Dim.

m 1.12 1.41 1.44 1.22 1.10 n 96 94 91 86 81% a 57 48 45 42 42 g /]. · D 8 0.50 0.60 0.60 0.70 0.70 BOD5 (dec,) 10 15 20 30 40 mg / 1 On the basis of these calculations, the following results are obtained for the two-stage activated sludge method according to the invention (without filter): KN = 3 .00 kWh / Ι * a KH = (1.10 + 0.09) = 1.19 kWh / I · a

Ks = (2.27 + 2.16) = 4.43 kWh / 1-a KN means the energy consumption of the auxiliary equipment. KH means the energy consumption of the peak load phase implemented according to the invention and Kg the energy consumption of the low load phase, whereby the total energy consumption of the two activation phases is 8.6 kWh / Ia.

Assuming that both the one-step comparison method with BTS = 0fl5 and the method according to the invention operate at a final stage with a BTg of 0.15, the energy savings I = (15.0 to 8.6 =) are 6.4 kWh / I * a ( without filter) 12 705 6 6

The conventional method, which eventually operates with a Bm of 0.15, gives an average BOD5 residue of 15 mg / l. The same result is obtained by the method according to the invention. If a filtration station is used in the process according to the invention, the BOD 2 value decreases to 8-10 mg / l. The sum of 300,000 I and IE (number of inhabitants / residents) is thus given the following values:

Method In fact, the living time used is the volume of time in hours

Ideal volume used *

O

Conventional 77,000 m ° 14 BTS = 0.15 80,000 m3

According to the invention, 60,300 m 2 3 9fl

Without filter station 68,300 m o

56,000 m 7.6 according to the invention

With filter station 74,500 m + filter χ The ideal volume used was determined by relating the usable volume of each treatment unit to a unit price of DM 300 .- / m3. The ideal volumes thus also represent the estimated cost comparison of the main units of the wastewater treatment plant.

The conventional method operates with a low loading step followed by final precipitation. The method according to the invention has a peak loading step, a low loading step, intermediate precipitation and final precipitation, whereby the process can be terminated by a filtration step, if desired.

As can be deduced from the above calculations, the method according to the invention is a considerable step forward in this field, in particular in terms of power consumption and space utilization, while the cleaning power is as good or better than in the known methods.

The invention has the advantage that the method according to it can be used in plants which can be used with much lower energy consumption than plants used by conventional methods, but the construction costs are not adversely affected. In fact, the space requirement of the plant used by the method according to the invention is much smaller than in known plants. Finally, the process according to the invention, in combination with the filtration step, achieves very high purification efficiencies (BOD = <10 mg / l). The plants used by the method according to the invention are not at all sensitive to sudden and sharp increases in the amount of wastewater. Another important advantage is that the invention can be used to expand older or congested wastewater treatment plants. By pre-connecting the peak load plant to be built and converting the pre-precipitation system to an intermediate precipitation system, the load of the already existing activation phase can be significantly reduced. In addition, the final precipitation system also needs to be expanded. It should be noted, however, that when using the idea of the invention, the old parts of the wastewater treatment plant can be used continuously.

An embodiment of the method according to the invention will be explained in more detail below with reference to the accompanying drawing.

The wastewater enters the plant via the inlet line 1 and is fed by means of a pump 2 via a pipe 11 to the sludge pre-discharge device 3.

Once the difficult components, such as fibers, etc., have been removed, the waste water passes through the pipe 12 to the first aeration tank, i.e. to the first activation stage 4, which is run as a peak loading stage. The aerated material then enters the intermediate precipitation device 5 via the pipe 13. The clarified phase is led through the pipe 14 to the second aeration tank, i.e. to the second activation stage 6, which is used as a low loading stage. Sludge is removed from device 5 for intermediate precipitation. This sludge is fed through a pipe 22 and a pump 23 to the pipes 24 and 25. The purpose of the pipe 24 is to return the sludge to the first stage, while the purpose of the pipe 25 is to remove residual sludge from the system, e.g. by a thickener. The same goes for the original slurry removed through pipe 27. At the end of the biological digestion in the device 6, the aqueous phase enters the final precipitator 7, from which the sludge is removed via a pipe 18 and a pump 19. This sludge is either returned by the pipe 20 to the second stage as a recovery sludge or removed from the system as a residual sludge by the pipe 21. The clarified aqueous phase is fed by means of a pipe 16, a pump 8 and a pipe 26 to a quick filter 9, from which the clarified water is led through the outlet pipe 10 to the water system. The rinsing water can be supplied by means of pipes 28 and 27 from the quick melt effervescent 9 to the second stage system.

Claims (11)

70566 14 A two-stage activated sludge treatment method for treating wastewater, wherein the effluent is fed to a first activation stage (4), and the treated effluent is precipitated (5) to remove residual sludge (25) and return sludge (24) to be returned to the first activation stage, followed by to the activation step (6), and that the water treated therein is passed to a further precipitation step (7) from which the residual sludge (21) and the recovery sludge (20) to be returned to the second activation step are removed, the purified water being removed from the first precipitation step and discharged from the system. (4) is used as a substantially biogenic flocculation and adsorption step utilizing air treatment and a volume load BR = about 10 kg BHK ^ / m and a day and a sludge load B ^ = more than 2 kg BHK ^ / kg dry matter and a day that the first activation step receivable j separating and precipitating the mixture of effluent and sludge in said first precipitation step (5) until the purity of the effluent is at least 60%, keeping the biochenoses of both activation steps (4, 6) separate and removing sufficient residual sludge from the first precipitation step (5); The second stage of activation (6), which is essentially a biological purification step with a load of about 0.15 kg BHK / kg dry matter and day, is subjected to a biocenosis stage. to keep water of the above purity from the first-mentioned precipitation step (5). A method according to claim 1, characterized in that a flocculant or precipitant is added to the peak loading step to promote adsorption. Method according to one of Claims 1 to 2, characterized in that large bubbles are used in the aeration of the first activation stage (4). 70566 15 Method according to one of Claims 1 to 3, characterized in that final filtration or flocculation and filtration are used after the last precipitation step. Method according to Claim 4, characterized in that the filter rinsing slurry is returned only to the second stage. Method according to one of Claims 1 to 5, characterized in that the second activation step is carried out in ring channels. Method according to one of Claims 1 to 6, characterized by a pre-precipitation step before the first activation step. Method according to one of Claims 1 to 7, characterized in that the wastewater with a very high degree of contamination is treated. Method according to one of Claims 1 to 8, characterized in that the waste water is mainly contaminated with organic substances. Method according to one of Claims 1 to 9, characterized in that the aeration of the second activation step takes place with fine bubbles. Process according to one of Claims 1 to 10, characterized in that enzymes are added to the low loading step in order to promote biological digestion. ie 70566 TT ------------