JPS6055199B2 - Sewage treatment method and equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method and apparatus for treating sewage, and more specifically, to a method and apparatus for treating sewage, and more specifically, for treating sewage by aerobically decomposing organic components in sewage and separating the resulting nitrates into their elements. The present invention relates to a method and an apparatus for carrying out the method.

Activated sludge processes remove particulate materials, colloidal materials, and organic compounds that remain after large-sized, heavy materials in wastewater are removed by screening and/or gravity settling. These residual materials generally include carbohydrates, cellulose and its derivatives, proteins, amines, ammonia, minerals, and the microorganisms and protozoa that sustain life by feeding on these materials. When such sewage is oxygenated by agitation in the presence of oxygen or air that causes chemical and/or biological reactions, the sewage particles form sludge aggregates due to the reaction, and these agglomerates The material precipitates easily and allows microbial life and other microscopic organic life to grow and reproduce. The sludge agglomerates thus actively absorb and oxidize the organic substances contained in the wastewater, thereby decomposing them into carbon dioxide, soluble products, and easily precipitated products. Similarly, if this treatment is carried out for a sufficient amount of time, the ammonia content in the wastewater will be decomposed into nitrates and hydrogen ions. Additionally, as the flocs settle, almost all of the solids suspended in the wastewater and most of the colloidal solids settle with the flocs. This activated sludge is continuously maintained by returning a portion of the recovered sludge to the wastewater to be treated. By separating this activated sludge and returning it to the wastewater to be newly treated and further aeration treatment, the wastewater can be continuously purified, and the biochemical oxygen demand (B .O.D) is removed. The water that remains after the activated flocculated waste settles can be safely discharged into adjacent rivers and irrigation canals. For a detailed description of this activated sludge process and equipment for carrying out the process, reference may be made to US Pat. No. 2,684,941, issued July 24, 1959. However, it should be noted that the wastewater discharged after purification treatment still contains soluble nitrogen compounds (resulting from the decomposition of ammonia) and phosphates. Discharging these substances into lakes and rivers promotes the growth of algae and other aquatic plants, which in turn causes undesirable phenomena such as lowering the oxygen content in rivers and causing water pollution. . Removal of nitrogen compounds is generally absent from existing activated sludge processes. However, when attempting to remove such potential contaminants, activated sludge is generally kept in an oxygen-deficient atmosphere and the microorganisms present in this sludge decompose the nitrates, thereby There has been reliance on the use of external denitrification tanks that consume the oxygen produced. However, such methods are space- and time-consuming, expensive, and inefficient, and account for only 50-60% of the nitrate produced by this activated sludge method.
only it will be removed. In view of the above, the first object of the present invention is to provide an improved method for purifying sewage. The second objective is to provide a unique denitrification technology (removal of nitrogen compounds).

A third objective is to utilize this denitrification technology in conjunction with activated sludge methods for wastewater purification.

The fourth purpose is to combine and continuously perform aerobic decomposition and denitrification of a filth-containing liquid.

A fifth objective is to substantially eliminate the polluting effects of activated sludge effluent.

In accordance with the above objectives, the present inventors have developed a highly efficient method which eliminates most of the contaminating effects of the effluent produced by the purification process and also eliminates most of the difficulties inherent in conventional denitrification techniques. We discovered a purification and denitrification treatment method.

Accordingly, the denitrification process of the present invention involves adding the raw wastewater to be treated to a waste-containing liquid storage tank in which aerobic decomposition has been completed and which is substantially anoxic. The microorganisms in the activated sludge-containing liquid have other organic matter that reacts with them in this way but require oxygen. To meet their own oxygen needs, the microorganisms act on nitrate compounds dissolved in the filth-containing liquid and consume the oxygen produced by the decomposition of these compounds. When this treatment is carried out continuously to remove solid substances from the filth-containing liquid, the content of the nitrate compounds produced by aerobic decomposition of ammonia in the filtrate-containing liquid in the resulting effluent is approximately 10 % or less. The apparatus provided for carrying out the treatment method described above comprises an aeration storage tank provided with intake means, at least one stirring means and removal means. In constructing this device, it is essential that the intake means be located sufficiently isolated from the agitation means, thereby achieving aerobic decomposition of the filthy liquid and a substantial reduction in the oxygen content. Give yourself enough time to do it. Similarly, the intake means should be located sufficiently isolated from the next aeration point;
It must be possible to subject the dirt-containing liquid to significant denitrification before it is subjected to fresh aeration. To achieve the above, the present invention is defined in the opening claims;
The present invention also proposes a wastewater treatment method and apparatus as described in detail in this specification, which will be described below with reference to the accompanying drawings.

Referring to FIG. 2, a typical apparatus for use in the present invention is illustrated with an aeration reservoir 1 fitted with an intake means 12.
Contains 0. This aeration storage tank 10 is divided into two sections 16 and 18 by a partition wall 14. (In the figure, these two sections are divided into the same size, but this does not necessarily have to be the case.) These two sections are divided into areas 20 and 2.
It communicates with 2. A stirring means 24 is attached to the aeration reservoir and is generally in communication with the area 20. This agitation means 24 supplies air or oxygen above the surface of the filth-containing liquid into the liquid while strongly agitating it, and performs aeration treatment on the liquid, while at the same time, the filth-containing liquid in the aeration storage tank is heated so that almost no sludge sedimentation occurs. The role is to keep the body in a state of motion so that it does not become erect. Such agitation means are well known to those skilled in the art, and those who actually design and construct the device understand whether it is a horizontal type or not.
You can choose the most suitable stirring device for your particular system, even if it is vertical. The stirring speed and depth of the stirring means in the dirt-containing liquid can also be varied to achieve optimal aeration conditions.

Furthermore, the vertically arranged stirring means can be converted into a mixer and propulsion means by simply reducing the rotational speed and reducing the immersion depth of the stirring propeller. The position of the intake means 12 in the storage tank 10 is essentially the relative distance between the intake means 12 and the stirring means 24 .

The distance between the agitation means 24 and the intake means 12 in the direction of flow therefore allows for substantial aerobic decomposition of the filth-containing liquid and at the same time the oxygen content of the filth-containing liquid is almost reduced. It must be sufficient to continue the aerobic decomposition until Similarly, the distance between the intake means 12 and the agitation means 24 within the section of the storage tank 10 where the denitrification process takes place is sufficient to allow a substantial amount of the denitrification process to take place before the next aeration operation begins. There must be. To achieve the objects of the invention, the distance between the intake means 12 and the agitation means 24 should be at least 10% of the distance through which the waste water flows at the end of a continuous aeration cycle in said means 24, i.e. If so, it must be at least 10% of the sum of (a) the distance between stirring means 24/intake means 12 and (b) the distance between intake means 12/stirring means 12, viewed from the direction of flow. Although the position of the intake means 12 relative to the withdrawal means 26 is of minor importance, it may be arranged at a position other than immediately before or adjacent to the withdrawal means 26 in order to avoid process abnormalities resulting from the discharge of untreated wastewater. is preferred. In fact, other locations within the reservoir 10 may be used as long as they satisfy the distance requirements defined between the intake means 12 and the agitation means 24. Communication area 22 may be equipped with a liquid flow regulator septum 28 to control the direction of liquid flow and flow uniformity, if desired.

The removal means 26 communicate with the settling device 30 above or below the surface of the circulating dirt-containing liquid.

The settling device 30 may include first and second settling tanks, a sludge shaker, a surplus sludge thickener, and the like. The activated sludge obtained from the wastewater settles by gravity in the settling device 30, while the purified water overflows from the outlet end of the settling device 30 and is discharged directly into an adjacent stream, or It is further chemically treated, purified and sterilized in a second settling tank (not shown). At the bottom of the settler 30 with sludge in suspended solids. All or most of the sediment may be withdrawn, or all or most of it may be refluxed via line 34 back to the reservoir 10 to mix with the dirt-containing liquid contained therein. The excess sludge flows via the groove 32 to the excess sludge thickener 36, after which it is removed. Relating the treatment process described with respect to Figure 1 to the apparatus shown in Figure 2, it is possible to combine the raw, untreated filth-containing liquid, i.e., the filth and water that remains after the heavier materials in the wastewater have been removed. The mixture flows into the aeration reservoir 10 via the intake means 12.

The filth-containing liquid is maintained in horizontal motion within the storage tank and subsequently brought into contact with the agitation means 24, whereby the liquid is aerated and continues to move horizontally within the storage tank. . The ensuing aerobic decomposition involves breaking down the organic compounds contained in the wastewater into soluble solids, precipitable solids, water, and carbon dioxide. This aspect of the process serves to provide a primary energy source for additional microbial growth. Subsequent treatment with microorganisms converts the ammonia content into nitrates, which remain in the filth-containing liquid as dissolved nitrogen compounds. The microorganisms used in the above-mentioned treatments attach to the sludge aggregates resulting from almost all the solids suspended in the liquid. In the settling device 30, these aggregates settle as sludge and are pumped back to the storage tank 10, thereby supplying microorganisms with an average age of 30 to 40 days. The aerobic decomposition is continued until the oxygen content in the aerated filth-containing liquid is almost exhausted.

From the intake means 12, untreated filth-containing liquid is newly introduced into the filth-containing liquid in motion,
Start the denitrification process. In this way, the conditions in the reservoir at the time of new addition of filth-containing liquid, i.e. the presence of additional organic matter and the substantial absence of oxygen, are determined by the aerated filth-containing liquid as described above. It is ideal for microorganisms in liquids, satisfying their oxygen requirements by decomposing the nitrate compounds in the liquid into their respective elemental components. Disassembly. The oxygen produced is consumed by microorganisms for aerobic decomposition of the newly introduced filth-containing liquid. It should also be noted that a more effective denitrification process is obtained by maintaining the water temperature above about 45°F. The cycles of aerobic decomposition and denitrification proceed in succession, such that in each cycle there is a decrease in the amount of organic matter, a conversion of ammonia to nitrate in oxygen-rich areas within the reservoir, and a decrease in the oxygen content of the reservoir. Nitrate removal occurs in deficient areas.

The average length of time that the dirt-containing liquid remains in the reservoir depends on the volume of the reservoir and the amount of newly added dirt-containing liquid that enters and leaves the reservoir. The actual decomposition and denitrification process takes about 24 hours! This can be achieved if the residence time is between 1 and 2, but the residence time may be longer or shorter than this at the discretion of the person actually performing the treatment. For example, in the case of a storage tank with a sewage outflow capacity of 2 Sf, if additional sewage flows into the storage tank, an average capacity of approximately 2 Sf of treated liquid will be discharged. During this period, the sewage will accumulate between 50 and 1
About 00 cycles of aerobic decomposition and denitrification are completed. Furthermore, the amount and proportion of the filthy liquid discharged generally corresponds to the quantity and proportion of newly introduced filthy liquid. It should be noted that the effluent liquid discharged generally contains The ammonia in the liquid removed by the treatment method of the present invention contains at least about 90% of the nitrate concentration produced by aerobic decomposition.

While additional nitrate is produced each time newly added filthy liquid is aerated, the amount of such newly added filthy liquid increases the total amount of filthy liquid present in the reservoir. The fact that it is small compared to
In both cases, it is ensured that the nitrate content in the effluent liquid does not exceed about 10% of the initial nitrate content produced in the liquid. Another notable advantage of the method of the present invention is that since no nitric acid is produced, there is no decrease in PH levels that typically accompanies denitrification. Therefore, the formation of soluble calcium phosphate complexes occurring at acidic pH levels is minimized in the device according to the invention, so that a greater amount of phosphate is present in the sludge than in the effluent liquid. This becomes certain. This distribution of phosphates is desirable because the absence of phosphates in the effluent reduces the polluting effects of the effluent. Therefore, more phosphates and colloidal solids are available for removal during the post-sterilization step, which is accomplished by adding iron salts, chlorides, or other flocculants to the secondary precipitator, and the storage tank There is no need to return secondary sludge to the A modified version of the apparatus of FIG. 2 is shown in FIG.

In this variant, the mixing and propulsion means 3 are provided in the interfacial zone 22.
The structure of the device is exactly the same as that of FIG. 2, except that 8 is attached. The propulsion means 38 mixes the wastewater already flowing in the storage tank 10 and the newly introduced wastewater,
Moreover, the sludge in the storage tank hardly settles, and
It serves to maintain the liquid in motion without aerating the liquid containing dirt. Since the propulsion means 38 is not an additional source of aeration, the relative distance between the intake means 12 and the agitation means 24 is the same as described with respect to the apparatus of FIG. The propulsion means 38 may be replaced by secondary stirring means equivalent to the stirring means 24, thereby providing a device with two stirring means 24, 38 and one intake means 12.

Therefore, during one revolution in the storage tank 10, the wastewater encounters two aerobic decomposition zones and one denitrification zone. When additional aeration is provided, the distance between this second aeration point 38 and the intake means 12 is sufficient to substantially decompose the filth-containing liquid and provide oxygen depletion. On the other hand, the distance between the intake means 12 and the stirring means 24 must be sufficient to allow adequate denitration of the dirt-containing liquid, i.e. at least the distance between the stirring means 28 and the stirring means 24. 10% is essential. Furthermore, one or both of these stirring means are modifiable units that can act alternately as a propulsion/mixing means and as an aeration means, according to the wishes of the practitioner. be. Another modification of the device of the invention is shown in FIG. This device includes a storage tank 40,
bulkhead 42 defining sections 44, 46 communicating with zones 48, 50, removal means 60 and sludge return pipe 6;
4 and a settling device 62 with a surplus sludge channel 66.
The basic difference of this device is that there are two intake means 52, 5.
4, and two stirring means 56, 58, which are arranged relative to each other so as to show the dimensional relationship described above. Thus, the distance between the agitation means 56 and the intake means 54 and the distance between the agitation means 58 and the intake means 52 respectively allow for substantial aerobic decomposition and substantial oxygen depletion of the sewage. It is sufficient for Similarly, the distance between the intake means 54 and the agitation means 58 and the distance between the intake means 52 and the agitation means 56, respectively, are such that the distance between the intake means 54 and the agitation means 58 and the distance between the intake means 52 and the agitation means 56 are such that the filth-containing liquid is substantially denitrified prior to being further aerated. is sufficient to enable it to be carried out. The latter distance is, respectively, the stirring means 56.
and 58. As described for the apparatus shown in Figure 4, the method of this invention consists of two processes: aerobic decomposition and denitrification for one rotation of the filth-containing liquid.
It consists of cycles.

The sewage thus enters through the intake means 54, is kept in motion by the agitation means 58, is aerated, undergoes aerobic decomposition and oxygen depletion in the storage area between the agitation means 58 and the intake means 52, and is further It mixes with raw additional wastewater introduced at the intake means 52, undergoes denitration treatment in the area between the intake means 52 and the stirring means 56, is further aerated at the stirring means 56, and is further aerated at the stirring means 56 and the intake means 54. In between, it is further subjected to aerobic decomposition, mixed with the raw wastewater introduced by the intake means 54, and further subjected to denitrification treatment. This cycle progresses continuously. Discharge of treated wastewater is started at an appropriate time during the overall treatment.
Of course, other variations can also be made with the apparatus of the invention described above.

For example, a tank with no partitions and a unidirectional flow of liquid may be used in place of the preferred partitioned storage tank. Similarly, a storage tank divided into multiple sections or a number of aeration storage tanks connected in series may be used instead of an aeration storage tank with a single dual-purpose section. The aeration storage tank can be equipped with an arbitrary number of stirring and propulsion means that can be placed at different positions within the storage tank, and an arbitrary number of intake means and extraction means. Only the distance required for decomposition and denitrification processes must be maintained. Furthermore, the intake means may be arranged to inject untreated liquid in the direction of flow of said aerated dirt-containing liquid. In this way, a large motivating force is provided for the movement of the dirt-containing liquid within the reservoir. On the other hand, injection against the direction of flow has the effect of stirring the raw wastewater in the circulating liquid more efficiently and mixing it more quickly. Baffles may also be installed in the reservoir adjacent to the agitation means and/or in areas communicating with the partitioned section to increase the amount of aeration of the filth-containing liquid and to assist in its flow movement and direction. )
may be placed. Additionally, the reservoir may be equipped with a heater and/or an insulating cover to increase processing speed and maintain adequate speed when operating at cooler temperatures. In accordance with a particular example of using the apparatus shown in FIG. 3 to carry out the process of this invention, a filth-containing liquid is transported in a single horizontal, 750 foot closed annular passageway, provided with agitation means and a propulsion means. , and a minimum speed of 0.8 to 1.
It was introduced into a reservoir configured to move at 0 ft/sec.

The aeration equipment supplied oxygen at an amount of about 2 to 4 bonds per horsepower into the waste water with strong agitation. It was found that the oxygen supplied by the aeration device was substantially consumed by the microorganisms in the liquid in 8 to 12 minutes. When the oxygen was almost exhausted, additional dirt-containing liquid was introduced to carry out the denitrification reaction. This filth-containing liquid was then mixed and subjected to continuous motion by a mixing and propulsion device. The time that this filth-containing liquid remains in the storage tank where it is continuously subjected to aerobic decomposition and denitrification processing is estimated to be 24 Tf on average. Analysis of the effluent liquid after settling and refluxing approximately 50% of the solid substances removed from the filth-containing liquid revealed that approximately 90% or more of the nitrate compound content generated in the filtrate-containing liquid was generated during the treatment process. was shown to be removed. In summary, the present invention provides an efficient wastewater treatment method that can be operated continuously, decomposes organic substances in wastewater to the highest degree, and removes potential pollutants that are normally discharged into rivers, etc. The purpose of this invention is to provide a device that can eliminate most of the

Although this invention has been described above with respect to specific aspects,
It is clear that various modifications can be made without departing from the spirit and scope of the invention.

[Brief explanation of the drawing]

FIG. 1 is a flow sheet showing the path that treated wastewater follows and the treatment steps encountered in accordance with the present invention; FIGS. 2, 3, and 4 are typical schematic plan views for use with the present invention; FIG. This shows its constituent elements and their interrelationships. In the drawing, 10, 40 are storage tanks for aeration, 12, 52, 54 are intake means, 14, 42 are partition walls, 20, 48 are communication areas, 22, 50 are communication areas, 24, 56, 58 are stirring means, 26 , 60 is a take-out means, 28 is a baffle, 30, 6
2 is a sedimentation device, 32, 66 is an excess sludge groove, 34, 6
4 is a sludge return pipe, and 38 is a stirring/propelling means.

Claims (1)

Claims: 1. Injecting a raw filth-containing liquid into a reservoir with a single horizontal closed ringway and circulating the liquid through said passageway at a speed of at least about 24 cm/sec to suspend it. The liquid is aerated in the passageway to promote aerobic decomposition of the wastewater and the formation of nitrate compounds in the liquid, and the aerated liquid is removed from the liquid. The liquid containing nitrate compounds and raw waste is circulated around the passageway for a first distance during which the decomposition proceeds until the liquid is substantially oxygen-deficient at the time the liquid is injected. circulating the treated liquid a second distance around said passageway over which denitrification proceeds in said liquid until reaching a next aeration treatment point in said passageway, said treated liquid being in an amount approximating the injection volume of raw filth-containing liquid; to purify the circulating liquid contained therein and settle the sludge,
draining the resulting clarified effluent and returning at least a portion of the settled sludge, the second distance being at least about 10% of the sum of the first and second distances, and A method for treating wastewater using continuously activated sludge, wherein the average residence time of the liquid in the storage tank is at least about 24 hours. 2 At least two tubes having intake means for introducing the filth-containing liquid to be treated and divided in the longitudinal direction by a partition wall.
a communication area forming a section and communicating with the section divided by the partition wall for circulating the liquid; and a communication section arranged sufficiently partitioned from the intake means for keeping the liquid in motion and aerating it. a storage tank for aeration treatment of the liquid, which is provided with at least one stirring means; a take-out means provided in a part of the aeration storage tank; a sludge settling device communicating with the take-out means; a surplus sludge thickener communicating with the sludge channel by a sludge groove, and sludge return means for returning a portion of the surplus sludge into the circulating filth-containing liquid, the distance in the direction of flow from the intake means to the agitation means; 2. A continuous sewage treatment apparatus, characterized in that the distance traveled by the filth-containing liquid to be treated is at least about 10% of the total distance traveled.