JPS6150680B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for biologically purifying sewage, industrial wastewater, and other organic wastewater using aerobic microorganisms. Conventional human waste treatment methods can be broadly classified into anaerobic digestion, aerobic digestion, and chemical treatment, but no matter which treatment technology is applied, biological oxidation treatment is used in the final step of treatment. The finishing touches are done according to the law. Typical biological oxidation treatment methods that are currently in practical use include fixed biofilm methods (sprinkle bed method, contact oxidation method, rotating disk method, etc.) and suspended organism methods (activated sludge method, etc.). In the field of human waste treatment, the activated sludge method is generally widely adopted because it enables high-grade treatment and is stable. However, even if so-called human waste wastewater, such as diluted human waste, undiluted human waste, diluted desorbed liquid, or undiluted desorbed liquid, is treated using the activated sludge method, the purification efficiency is not as high as initially expected based on experience in sewage treatment. Unable to do so.
There was a strong demand for an investigation into the cause. The present inventors have been working hard to investigate the cause for a long time, but it happened that a large amount of NO ₂ -N is contained in the activated sludge method treatment water of night soil wastewater (desorption liquid), and the concentration is low. Although it differs depending on the dilution ratio of syneresis, it was confirmed that the amount reached approximately 150 to 300 mg/. Furthermore, it has been experimentally confirmed that this NO ₂ -N is an extremely harmful substance to aerobic purification microorganisms, and if conditions are provided to prevent this NO ₂ -N from accumulating in the mixed culture solution, We learned that it is possible to achieve BOD removal efficiency equal to or higher than that of sewage even with human waste water. Human waste is naturally rich in NH ₄ -N (3000-5000mg/
), and the pH is alkaline (generally
7.5 to 8.8), and since it contains a high concentration of sulfide, if nitrifying bacteria live in activated sludge, the nitrification type will be stable as NO ₂ type. In other words, ammonia nitrogen, which is concentrated in human urine, is produced by Nitrobacter in the form of _NH3 .
robacter (nitrate bacteria)] activity. The higher the pH of the liquid, the more the reaction of NH ₄ OHNH ₃ +OH ^- proceeds in the right direction, so the toxicity of ammonia nitrogen becomes more pronounced in human waste. The nitrates that are concentrated in human waste are highly toxic to Nitrobacter (nitrate bacteria). For the above reasons, as mentioned above, when human waste wastewater is treated using the activated sludge method (other biological oxidation treatment), unless special conditions are regulated, the nitrification type is stable as the nitrite type. Such processing problems occur. NO ₂ -N is toxic to purified microorganisms;
If this concentration exceeds a certain level in the mixed culture solution, biological treatment will be affected. NO ₂ -N is toxic to concentrated crops, fish and shellfish, and therefore causes various pollution problems at the destination. The presence of NO ₂ -N increases the COD of the treated water, making it impossible to meet COD regulations when discharged into the sea. In addition, this is not just a matter of regulation; it actually consumes dissolved oxygen in rivers, which has a direct negative impact on river pollution. When performing ozone treatment on secondary treated water, ozone is consumed if NO ₂ -N is present. In order to solve the various problems in wastewater treatment caused by NO ₂ -N, it is necessary to treat the activated sludge treatment process (biological oxidation treatment process) under conditions where NO ₂ -N is not generated. At present, the following methods are available, but each of these countermeasures has a fatal flaw. That is, (i) the activated sludge process is operated at a sludge level such that nitrifying bacteria cannot exist in the treatment system; However, such a method not only increases the sludge load and deteriorates the quality of treated water, but also cannot necessarily completely stop nitrification. (ii) _NH4 −
If it is installed at a low level (continuously adjusted) according to the N concentration, the nitrification type will be NO ₃ -N type, and NO ₂
-The problem caused by N is solved, but the cost of chemicals for pH adjustment becomes excessive. Furthermore, even if the NO ₃ -N type nitrification type is adopted, scum trouble in the final settling tank cannot be avoided. There are other problems. The present invention aims to accurately eliminate these conventional drawbacks, and aims to solve the problem caused by NO ₂ -N, which is unavoidable in activated sludge treatment methods, by combining complete nitrification, partial denitrification, and solid-liquid separation by pressurized flotation. The purpose is to provide an effective and economical treatment method that can be solved by. Another object of the present invention is to convert NO ₂ -N, which is almost irresistibly produced when human waste water is treated by the activated sludge method, into NO ₃ through a special process.
-N, to perform extremely stable treatment and to provide a treatment method that is suitable for large-scale treatment and has simple operation management. The present invention allows human waste water to flow into an anaerobic tank either as it is or diluted to an appropriate concentration, while an appropriate amount of nitrification mixture is circulated from the aerobic tank, and the floated concentrated sludge is returned from a pressure flotation device. It is characterized by partially denitrifying the raw water by stirring and mixing it with the raw water and effectively utilizing the BOD source in the raw water. NH ₄ −
N is reduced to a significantly lower concentration or completely disappears, causing nitrobacterium (nitrobacterium) of _NH3 .
As a result, the toxicity of NO ₂ -N in conventional activated sludge treatment and other unfavorable effects on treatment can be completely eliminated, as the nitrification type is stabilized as NO ₃ -N. This means that it can be resolved. The amount of nitrogen that is partially removed depends on the amount of nitrification liquid being circulated, but in any case, it is
% cannot be removed. Therefore, there is a certain concentration of NO ₃ -N in the mixed liquid flowing out from the aerobic tank.
If this sludge flows directly into a conventional settling tank, a denitrification reaction will occur within the settling tank, making it impossible to separate and concentrate the activated sludge. Therefore, in order to make the process of the present invention perfect, it is essential to apply pressure flotation to separate and concentrate the activated sludge in the nitrification mixture. Next, an embodiment of the treatment method according to the present invention will be explained with reference to FIG. 2 in comparison with a conventional example (FIG. 1). Conventionally, as shown in FIG. The wastewater introduced into the sludge is mixed with air 3 and sludge returned from the sludge return pipe 5, subjected to biological treatment, and the effluent is separated by sedimentation in the sedimentation tank 4, and then led out as treated water from the discharge pipe 6. However, in the present invention, as shown in FIG.
Wastewater containing BOD, SS, and NH ₄ -N is collected from raw water inlet pipe 1.
It is introduced into the anaerobic tank 11 via. In the aerobic tank 2 that follows this anaerobic tank 11, a so-called nitrification mixed liquid is produced in which _NH4 -N in the raw water is oxidized to NOx due to the presence of activated sludge and the supply of oxygen such as air 3 from the blower 13. At least a portion of the water, for example 4 to 8 times the amount of inflow raw water, is circulated through the circulation pipe 12. The aerobic tank 2 is a pressurized flotation device 1
0, the treated mixed liquid is finally subjected to pressure flotation treatment to separate solid and liquid, and then is discharged from the discharge pipe 6 as treated water. The activated sludge separated and concentrated by the pressurized flotation device 10 is also returned to the anaerobic tank 11 through the sludge return pipe 5, and oxygen and the nitrification mixture are transferred to the anaerobic tank 1.
During the anaerobic stirring and mixing process in step 1, NOx is decomposed by denitrifying bacteria in the presence of a BOD source in the raw water. This partially denitrified raw water flows down to the subsequent aerobic tank 2 together with activated sludge, and the NH ₄ -N contained in the raw water is completely nitrified to NOx. As mentioned above, NH ₄ -N contained in raw water is reduced to an extremely low concentration or almost below the detection limit due to partial denitrification in the aerobic tank 11 and complete nitrification in the aerobic tank. Since the pH value at which equilibrium is reached is also relatively low, the inhibitory effect of NH ₃ on Nitrobacter is eliminated, and the nitrification type is completely stable as the nitric acid type. The nitrification mixture flowing out from the aerobic tank 2 contains residual substances that cannot be returned to the anaerobic tank 11 through circulation.
NOx (If it is circulated infinitely, all of the NOx generated in the aerobic tank can be returned to the anaerobic tank,
In order to reduce power costs, a nitrification mixture of 4 to 8 times the amount of normal raw water is circulated, and at this circulation rate NOx
The maximum return rate is approximately 80%. ) leaks into the treated water, so if activated sludge was separated using a conventional gravity settling device, the sludge would float to the surface due to the denitrification reaction in the settling tank, and scum would form, resulting in activated sludge treatment. It disappears. Therefore, a pressurized flotation device 10 is applied to forcibly separate activated sludge.
The activated sludge is concentrated, and an appropriate amount of the concentrated activated sludge is returned to the anaerobic tank 11 through the sludge return pipe 5 for treatment. on the other hand,
The treated water separated from activated sludge by the pressurized flotation device 10 is discharged into the natural water system via the discharge pipe 6. Next, examples of the present invention will be shown. The activated sludge treatment process, which is the basis of treatment, is the first
The process according to the present invention consists of an anaerobic tank, an aerobic tank, and a pressurized flotation tank as shown in the figure, and an appropriate amount of the nitrification mixture is circulated from the aerobic tank to the anaerobic tank. The specifications of each main device used in this experiment are that the anaerobic tank and aerobic tank both have a volume of 100, and the pressurized flotation tank has a volume of 50. The pressurization of the treated water in the pressurized flotation tank is 3.
Kg/cm ² , and the pressurized water amount was adjusted to be in the range of 150 to 200% (tank inflow water amount). Screened 10-fold diluted human urine was used as the sample urine, and its physicochemical properties are shown in Table 1.

[Table] As for the treatment conditions, the sample 10 times diluted human urine was supplied while adjusting the flow rate so that the supply amount was 100/day. The pressure of pressurized water in the pressurized flotation tank is 3Kg/
cm ² , the concentration of floated thickened sludge is average at 150% pressurized water volume.
25,000 mg/(20,000 to 30,000 mg/), and the return amount was adjusted so that the activated sludge concentration in the anaerobic tank and aerobic tank was 6,000 mg/day (35 to 45/day). Under these conditions, the BOD load on the activated sludge present in both the anaerobic and aerobic tanks is 0.07 to 0.1 Kg・BOD/
KgMLSS.day, and the quality of the treated water under these conditions is as shown in Table 1.
The solid-liquid separation was extremely good at ~25 mg/, and the BOD during treatment was extremely good in the range of 13-20 mg/. In contrast, in a treatment experiment using a conventional activated sludge treatment method as shown in Figure 1, the aeration tank volume was 200 and the activated sludge concentration was 6000 mg/cm (both the volume and sludge concentration were the same as in the process of the present invention). ), the BOD load on the activated sludge in the aeration tank is the same as the process of the present invention, and the treated water quality under the conditions of 0.07 to 0.1 Kg・BOD/KgMOSS.day is Table 1. As shown in Figure 2, scum was generated due to the denitrification phenomenon in the settling tank, and SS leaked into the treated water at a high concentration. In addition, we were able to maintain a return sludge concentration of around 10,000 mg/kg for a certain period from the beginning of the experiment, but that concentration gradually became diluted.
It became impossible to maintain activated sludge at 6000 mg/kg in the aeration tank, and activated sludge treatment was no longer possible. The process of the present invention uses a rational combination of an anaerobic process, an aerobic process, and a pressurized flotation process to eliminate various treatment problems caused by the NO ₂ -N that is inevitably produced in the activated sludge treatment of this type of wastewater. This method has the advantage of being able to completely eliminate the troubles of the above, and also being able to easily perform stable activated sludge treatment of nitrogen-containing organic wastewater, being suitable for large-scale treatment, and easy to manage.

[Brief explanation of the drawing]

FIG. 1 is a flow sheet of the conventional method, and FIG. 2 is a flow sheet of the present invention. 1... Raw water inflow pipe, 2... Aerobic tank, 3... Air, 4... Sedimentation tank, 5... Sludge return pipe, 6... Outflow pipe, 10... Pressure flotation device, 11... Anaerobic Sex tank, 12...Circulation pipe, 13...Blower.

Claims (1)

[Claims] 1. Organic wastewater containing concentrated ammonia nitrogen can be used as it is or after being diluted to an appropriate concentration,
The treated mixture is introduced into a treatment process consisting of an anaerobic process and an aerobic process, and an appropriate amount of the aerobic mixture is circulated from the aerobic process to the anaerobic process.Finally, the treated mixture is introduced into the pressure flotation process to form a solid-liquid. A biological treatment method for organic wastewater, characterized in that at least a part of the activated sludge separated and concentrated in the pressure flotation process is returned to the anaerobic process for treatment. 2. The biological treatment method according to claim 1, wherein the anaerobic step is performed by circulating the nitrification mixture from the aerobic step in an amount of 4 to 8 times the amount of inflow raw water. .