DK141868B - Process for Elimination of Organic and Inorganic Bonded Nitrogen from Household and Industrial Wastewater. - Google Patents

Description

(11) FREHLCESEUEliKRIFT 1U1868 DENMARK <") Intel. * C 02 F 3/30" (21) Application No. 57 ^ 7/72 (22) Filed on Jul 28, 1972 (23) Run Date Jul 28, 1972 ( 44) The application presented and submitted to the public was published on July 7 · JUNE · 19o0

DIRECTORATE OF

PATENT & TRADEMARKET ^ Priority begwet from Nov. 25; 1971j 17030/712 CH (71) CELLULOSE ATTISHOIZ AG, 4708 Luterbach, CH.

(72) Inventor: Max Dubach, In the Sun, CH — 4533 Riedholz, CH: Alfred £> cher * = clay, Laengacker, CH-4533 Riedholz, CH. "" (74) Clerk of the case:

International Patent Office. (84) Process for the elimination of organic and inorganically bound nitrogen from household and industrial wastewater.

The present invention relates to a process for eliminating organic and inorganically bound nitrogen from domestic and industrial wastewater.

A method for biological purification of wastewater by activated sludge is known, in which method, both the degradation of the contaminants by bacteria and partly the removal of the overgrown bacteria by bacteria-eating organisms is carried out in two completely separate steps. At the same time, the wastewater, possibly mechanically explained, is vented to the first stage to provide optimum living conditions for the bacteria in an aeration vessel, where the oxygen concentration is selected so that the clear effluent from a sediment pool connected to the aeration tank and the first stage to which the effluent is conducted after the aeration, after a certain residence time no longer contains free oxygen. This extracted oxygen-free wastewater extracted from the set basin is now vented again in the second stage of an aeration tank, and the sludge concentration is regulated so that the effluent from a second stage aeration tank connected to this stage has a oxygen content after a certain residence time. of at least 2 mg / l.

When diverting domestic and industrial wastewater to the natural streams, their content of ammonium and nitrate nitrogen compounds is constantly increased. The ammonium is a danger to the natural streams, as at higher pH levels it acts as poison to fish or upon entering nitrification can lead to an oxygen depletion in the stream. The nitrate, in turn, acts as a fertilizer and is one of the causes of the escalating eutrophication of the streams. In addition, the purification of these streams into drinking water is difficult or threatened, as nitrate in too high a concentration can harm the health of humans and animals. The high ammonium and nitrate content of natural streams may include: also be brought back to the inadequate elimination of these substances by the usual, known biological methods or wastewater treatment plants, incl. the previously mentioned method.

Therefore, there is a strong need for wastewater purification processes and plants which can eliminate as much as possible ammonium, nitrate and organically bound nitrogen from the associated wastewater. Various proposals are to nitrify the ammonium in an activated sludge process in a manner known per se and denitrify the nitrate-containing wastewater in a special step connected thereafter.

In the case of nitrification and denitrification, the following should be noted:

During nitrification in an activated sludge system, ammonium nitrogen is microbially oxygenated to nitrite and nitrate. Much of the organically bound nitrogen, which cannot be consumed by incarnation, is converted to ammonium nitrogen by ammonifying bacteria. The conversion of ammonium to nitrite takes place by means of Nitroso-monas bacteria and the conversion of nitrite to nitrate by Nitrobacter.

NH4_ ° 2. ^ NO "_ ° 2.", ». N0 ~

It is believed that the growth rate of Nitrosomonas is less than that of Nitrobacter, so that the former is a limiting factor for nitrification. Whether a nitrification is possible in an activated sludge plant depends on various factors, including of the temperature, aeration time, sludge concentration, sieve loading, oxygen content, inhibitors and pH.

In principle, nitrification is only possible when a certain sludge load is not exceeded under given conditions. At a sludge load exceeding 0.2 kg BOD ^ / kg sludge solids in the temperature range below 15 ° C, no or only very unsatisfactory nitrification occurs. At 20 ° C and a sludge load of up to 0.33 kg BOD ^ / kg sludge solids, complete nitrification can be achieved.

The abbreviation BOD, used in the specification. it denotes bioleg in spoon oxygen for 5 days.

The presence of various toxic substances in the wastewater can prevent nitrification. In particular, thioureas, cyanides, phenols, and heavy metal salts can inhibit the growth of nitrifying bacteria.

In denitrification, nitrite and nitrate are reduced to elemental nitrogen and nitrous oxide.

NO2, NO ”-» - N2, N20

The mechanism of denitrification has not yet been fully elucidated. In general, this process is perceived as a strict anaerobic process. In principle, hydrogen donors appear necessary for denitrification. In addition to the influence of oxygen content, pH and residence time also play a role during denitrification.

An interrelation between the pH and the influence of oxygen stress on the rate of denitrification was found. In the pH range above 7, denitrification is totally inhibited by the presence of oxygen.

In summary, in all studies it has been recognized that the association between sludge concentration and time as well as temperature and sludge load in nitrification. It is also recognized that, in principle, denitrification is possible.

Based on these findings, the present invention provides a method by which, so far as the usual wastewater treatment is carried out and at no significant additional expense, far-reaching elimination of ammonium, nitrate and organically bound nitrogen from household and industry can be achieved. -sewage. The invention aims to provide as favorable conditions as possible for all essential processes.

In the process according to the invention this is done in a biological wastewater treatment plant of the aforementioned kind, ie. with two consecutive and interconnected stages, each containing an aeration tank and a then connected basin, wherein the waste water in the first stage is aerated at a sludge load of 0.05-0.5, preferably 0.15 kg BOD . kg of sludge solids and then for deposition and for anaerobic formation of ammonium compounds (ammonification of the organic nitrogen compounds) is fed to the first basin from which it is withdrawn oxygen-free and conducted to the second stage where it is aerated at a sludge load of 0.01- 0.3, preferably 0.1, kg BOD, pr. and the process is characterized in that the ammonium-containing, oxygen-free, wastewater extracted from the first-stage seed pool is vented into the second-stage aeration vessel to maintain aerobic conditions in the second stage and for nitrification of ammonia. - that the nitrified wastewater thus conducted is directed to the second stage set basin and that part of the at least partially cleared wastewater is returned to the first stage where the wastewater denitrification takes place under the prevailing aerobic conditions, and that purified wastewater is subtracted from the second-stage pool in an amount corresponding to the inflow.

In the second step, a very low BOD ^ sludge load and a high sludge age are then taken into account for the low growth rate of Nitrobacter and especially for Nitrosomonas. In the first stage set basin, favorable conditions for denitrification are provided, whereby the low sludge load with the high conditional amount of sludge thereby conditioned at the same time gives protection to the nitrifying bacteria in the second stage, since toxicants for the most part in the the first step is partly adsorbed and partly biodegraded. At the same time, the ammonifying effect is enhanced in the reducing medium of the pool.

In this way, the plant is obtained without disturbance of the usual decomposition of the other pollutants and, using the conditions most favorable for ammonification and nitrification and denitrification respectively, an elimination of the total nitrogen content of the plant's wastewater up to 90¾ is obtained.

To optimize this elimination, advantageously, at least half of the nitrified wastewater from this basin fed to the second stage can be redirected back to the first stage within 24 hours and / or it can be ensured that a equal or greater amount of purified, nitrified water back to the first step, which at the same time, during 24 hours, this step is added to purified wastewater for purification.

For an installation with irregular wastewater supply, it is advantageous to work such that the hydraulic load of the system is kept constant, adjusted to the calculated peak load. With smaller amounts of wastewater, so much purified, nitrified water from the second stage set basin can be returned to the first stage that the hydraulic load of the first stage remains constant.

The water returned from the second stage denitrification tank for denitrification in the first stage can either be directed to the aeration tank or to the set basin. However, an advantageous and particularly thorough mixing of this recycled portion with the water from the first stage can also be achieved by passing the recycled water to the first stage through the connecting conduit between the aeration vessel and the basin.

In order to provide optimum conditions for the ammonification and denitrification in the first step, preferably a 0 "concentration of 0-2 mg O2 / I and a sludge concentration of 5-15 kg of sludge solids / m, and according to op. preferably, at least 2/3 of the amount of sludge present in the first stage is present in the set basin of this stage. The sludge load used in the process is calculated from the amount of sludge in kg of BOD *, which is fed with the wastewater to the first stage for every 24 hours, divided by the total sludge present in kg in the first stage. The sludge age obtained from the amount of sludge present throughout the first stage, divided by the daily amount of sludge increasing or discharged in kg, can be 5-30 days, preferably approx. 12 days. At the same time, according to the invention, it is preferably provided that the sludge delivered to the first stage basin is averaged after at least 1 hour and at most after 8 hours, preferably after 3 hours, to the associated aeration vessel where it is supplied with oxygen. This can be done according to the invention by an appropriate measurement of the amount of mud returned, so that this e.g. per. per hour is 1/5 to 1/2, preferably 1/4 of the contents of the set pool. As gas bubbles form during denitrification in the interior of the sludge flakes, a portion of the sludge floats on the surface of the basin. This sludge can be foamed off in a known manner and returned to the associated aeration tank or removed as excess sludge.

These measures provide particularly favorable conditions for the ammonification and denitrification, the oxygen starvation due to the long residence time of the sludge in the sediment pool becomes so large that the nitrate is reduced without detrimental effect on the elimination of the biodegradable organics. On the contrary, this elimination is promoted by the additional oxygen supply over the nitrate, thereby enabling an energy saving at the same time as the oxygen supply to the first stage aeration can be reduced.

To provide favorable conditions for the nitrification of the second step, preferably an oxygen concentration of 2-6 mg of O / l and 3 z of a sludge concentration of 0.5-4 kg of sludge solids / m is employed. The sludge age can be 5-30 days, preferably 12 days. At the same time, according to the invention, it is preferably provided that the sludge delivered to the set pool after 1/4 hour and at most after 4 hours, preferably after 1 hour, is returned to the associated aeration tank where it is supplied with oxygen. According to the invention, it is advantageous that at most half of the sludge present in the whole of the second stage is continuously found in the associated set basin. per hour is 1/5 to 1/2, preferably 1/4, of the contents of the set pool, consisting predominantly of the deposited sludge portion.

These measures provide particularly favorable conditions for the nitrification, especially at the low BOD sludge load, in the first stage, which is already largely purified wastewater and the high sludge age attained thereby. In particular, this avoids the occurrence of denitrification phenomena in the second stage, which can lead. to the known sludge swelling that can adversely affect the nitrification and degrade the quality of the drain.

In addition, it has been found that in addition to the decomposition of the organic contaminants and the elimination of the nitrate nitrogen, and without detrimental effect on these processes, an elimination of phosphates from the wastewater to be purified can be further carried out. This can be done by introducing known precipitating chemicals, e.g. aluminum or iron salts.

The method according to the invention is further illustrated in the following by means of the drawing, which schematically shows an example of a plant for carrying out the method.

The drawing shows a well-known two-stage biological wastewater treatment plant, which plant has a first aeration tank .1 and a set pool 3 connected thereafter by a conduit 2, which together forms the first stage of the plant. Through an overflow 4 and a conduit 5, the first stage set pool 3 is connected to a second aeration tank 6, which together with another set pool 7, which is connected over or over a line 8 after the second aeration container 6, forms the second stage of the plant. The aeration in the aeration vessels 1 and 6 is effected by suitable distributor means 9 and 10, which are connected to a common conduit 11.

The household or industrial wastewater to be purified and freed from ammonium and nitrate nitrogen is continuously, optionally explained, passed through a conduit 12 to the first stage aeration vessel 1 and then through the conduit 2 to the associated deposition stage with the clarification basin 3.

In this first step, in a known manner, aeration time is adjusted with air through the conduit 11 and the distributor 9 introducing the amount of oxygen and concentration of the biological sludge so that the clear drain through the conduit 5 from the first stage set basin 3 no longer contains free oxygen. The BOD ^ sludge load, attributed to the total amount of sludge in the aeration vessel 1 and the settling pool 3, amounts to 0.15 kg BOD ^ / kg sludge solids. 1/3 of this total amount of sludge is found in the aeration vessel 1, 2/3 in the basin 3. Through a conduit 13 for the return of sludge, so much sludge is pumped back into the aeration vessel 1 per hour, that amount corresponds to 1/4 of the contents of the set pool 3. The upwardly flowing sludge which accumulates in the water surface of the basin 3 is retained by a submerged partition 18 and is returned to the aeration tank 1 by means of a suitable means. Thereby, favorable conditions are provided for the denitrification of the nitrate and the ammonification.

7 141868

Oxygen-free wastewater containing the non-deposited equal portion of the sulfur and ammonium is withdrawn from the sink 3 through the overflow trench 4, and through the conduit 5 it is fed to the second stage aeration vessel 6 and then through the conduit 8 to the sediment pool 7. In the aeration vessel 6 is again adjusted in a manner known per se to aeration time with air through the conduit 11 and the distributor means 10 introduced oxygen quantity and sludge concentration such that the water flowing from the set pool 7 through a conduit 15 and a conduit 16 still contains at least 2 rags. / L, preferably 4 mg / l of free oxygen. The BOD ^ slurry load, attributed to the total amount of sludge in the aeration vessel 6 and the sediment pool 7, amounts to 0.1 kg BOD ^ / kg sludge solids. Ca. 2/3 of the total amount of sludge is permanently found in the aeration tank 6, 1/3 in the sediment pool 7. The amount of sludge transferred through a conduit 14 amounts to approx.

hour 1/4 of the volume of the set pool 7. This provides favorable conditions for the nitrification of the ammonium.

In the second step, for further elimination of phosphates from the wastewater to be purified, without interfering with the other processes occurring in this step, and especially without interfering with the nitrification, precipitating chemicals known per se, such as aluminum or iron salts, may also be added. , through a conduit 20, and the addition may advantageously occur before the water is fed into the set pool 7, e.g. in the aeration vessel 6.

Furthermore, it has been found that in certain cases it is advantageous to improve the sedimentation properties of the second step to further add organic and / or inorganic flocculants known in the art, e.g. ben-tonite, cellulose fibers or anionic, cationic or nonionic flocculation aids. Such aids in no way interfere with the desired nitrification.

For denitrification of the nitrified ammonium present in the second step, and thus to eliminate the nitrate nitrogen from the wastewater to be purified, only a portion, preferably at least 50¾, of that to the sediment pool within 24 hours is removed from the set basin 7, nitrified wastewater for recirculation to the first stage of the plant, where the favorable conditions for denitrification of nitrified nitrogen compounds are prevalent. Advantageously, the system is regulated so that an equal amount of water is fed to the first stage of denitrification from the set basin 7, which, during 24 hours, the step of uncleaned wastewater is fed through the line 12.

It has been found advantageous from the second stage set basin 7 to withdraw the water to be returned to the first stage at a depth of approx. 0.2-2 m, preferably from 0.8 m below the water level. The cut-out is shown in the drawing.

Claims (2)

Through a conduit 17 which returns the withdrawn water to the conduit 2, where a ground, mixing occurs, the water present in the first step is redone. According to a variant not shown, it would also be possible, instead of directing the fpa recirculation pool 7 for recirculated water to the first step through conduit 2 to pass it to the aeration vessel 1 or the recirculation pool 3. In denitrification in the first step, the sludge is more difficult to thicken due to the microbubble bubbles present in the sludge flakes. Therefore, it may be advantageous to degass the excess sludge extracted from this stage before being brought to sedimentation in a thicker of the usual kind. This can be done by stirring the sludge, prior to passing to the thickener, mechanically without air supply in a container for 1-7 hours, preferably for 3 hours, thereby removing most of the gas bubbles. Alternatively, the sludge can be cut off without the microbubbles acting too dry, consisting of the sludge instead of being sedimented in a known apparatus by flotation. Procedure Ten, 1 Elimination of Organic and Inorganic Bonded Nitrogen from Household and Industrial Wastewater in a Biological Wastewater Treatment Plant with Two Interconnected and Interconnected Steps, Each Containing an Aeration Container and a Submersible Sludge Recirculation Pool, the first stage is vented at a sludge load of 0.05-0, ¾ preferably 0.15, kg BOD, - per. kg of sludge solids and then for deposition and for anaerobic formation of ammonium compounds (ammonification of the organic nitrogen compounds) is passed to the first basin from which it is removed oxygen-free and conducted to the second stage where it is aerated at a sludge load of 0.01-0; 3, preferably 0.1, kg BOD kg of sludge solids and then passed to the second stage set pool, characterized in that the ammonium-containing, oxygen-free wastewater extracted from the first stage set pool (3) is vented into the second stage aeration tank (6) to maintain aerobic conditions in the second stage and to nitrification of the ammonium, so that the nitrified wastewater in this way is directed to the second stage set basin (7) and that part of the at least partially clarified wastewater is returned to the first stage where the wastewater denitrification takes place during the prevailing aerobic conditions, and that purified wastewater is subtracted from the second stage seed pool (7) in an amount corresponding to the inflow. · · Method according to claim 1, characterized in that at least 2/3 of the sludge present in the first stage is continuously present in the set pool of this stage.