JPS643558B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a denitrification treatment method for economically efficient and stable treatment of organic wastewater containing biodegradable organic matter, ammonia nitrogen (hereinafter referred to as NH ₄ ⁺ -N), and nitrogen-containing organic matter. Regarding the denitrification treatment of organic waste liquid, many actual devices are already in operation for BOD and human waste with high nitrogen concentration, and among them, the nitrification liquid circulation method is the mainstream. Ammonia ions (NH ₄ ⁺ ) in organic wastewater and NH ₄ ⁺ generated from nitrogen-containing organic compounds are converted to nitrite ions (NO ₂ ^- ) by nitrite bacteria in the first aerobic aeration tank for nitrification. NH ₄ ⁺ +1.5O ₂ →NO ₂ ^- +H ₂ O+H ⁺ NO ₂ ^- is oxidized to nitrate ions (NO ₃ ^- ) by nitric acid bacteria. NO ₂ ^- +0.5O ₂ →NO ₃ ^- In the anaerobic stirring tank for denitrification, denitrifying bacteria
It performs the following respiratory activities using NO ₂ ^- or NO ₃ ^- as a hydrogen acceptor. Respiration using NO ₂ ^- 2HO ₂ ^- +6 (H) → N ₂ +2OH ^- +2H ₂ O Respiration using NO ₃ ^- 2NO ₃ ^- +10 (H) → N ₂ +2OH ^- +4H ₂ O Advantages of the nitrified fluid circulation method The NO ₂ ^- NO ₃ ^- generated in the first aerobic aeration tank is circulated to the first anaerobic stirring tank installed in front of this tank, and used as a hydrogen donor to reduce NO ₂ ^- and NO ₃ ^- . BOD in feed organic waste liquid
It consists in using the ingredients. This results in a cycle
BOD in feed organic wastewater commensurate with NO ₂ ^- , NO ₃ ^-
Since the BOD is removed in the first anaerobic stirring tank into which it first flows, the amount of BOD removed in the subsequent first aerobic aeration tank is reduced, and the amount of oxygen supplied can also be reduced. Furthermore, the amount of new organic matter supplied as a hydrogen donor in the second anaerobic stirring tank following the first aerobic aeration tank can be reduced. Further, in the aerobic first aeration tank, an alkaline agent is supplied to prevent the pH from decreasing due to nitrification, but the alkali is liberated again by being circulated to the anaerobic first stirring tank and denitrified, so the amount of alkali supplied also decreases. Neutralization due to nitrification NH ₄ OH + 2O ₂ +NaOH→NaNO ₃ +3H ₂ O Release of alkali due to denitrification 2NaNO ₃ +5(H ₂ )→N ₂ +2NaOH+4H ₂ O However, until now, aerobic primary and Since the second aeration tank uses an open air aeration system, it has the following drawbacks. In other words, even if most of the BOD in the organic waste liquid is removed in the first anaerobic stirring tank, the amount of oxygen required to remove 1g of BOD is approximately 1g, but the following formula: NH ₄ ⁺ +40→NO ₃ ^- +H ₂ O + 2H ⁺ The required amount of oxygen per 1g of NH ₄ -H is 4.6g. For example, for human waste, BOD: T - KN = 12000
mg/: 4500 mg/ (T-KN refers to the sum of organic nitrogen and NH ₄ -N), nitrification alone will require about 1.5 times the amount of oxygen required for BOD removal alone. Therefore, in high-load processing, oxygen supply becomes rate-limiting, and stable processing cannot be expected, especially for waste liquid with large load fluctuations, and the tank volume becomes large, requiring a large amount of construction cost. Furthermore, nitrifying bacteria are considered to be more highly aerobic than BOD oxidizing bacteria, so when only BOD removal is being performed, the oxygen concentration (hereinafter referred to as DO) in the aeration tank is usually 0.5.
mg/or more is sufficient, but generally for nitrification
Since it is necessary to maintain DO at 2 mg/ or more and the required amount of supplied air increases, stable processing cannot be expected in high-load processing when load fluctuations are taken into account as described above. In addition, in the case of nitrogen removal during human waste treatment, the Ministry of Health and Welfare's ``Structural Guidelines'' states that a 10-fold dilution process is standard, but in order to save water for dilution, even lower dilution or no-dilution processes are currently being considered. In low dilution treatment, the specific gravity of the liquid becomes high, and due to the influence of dissolved substances, the increase in the amount of aeration air associated with high loads will lead to deterioration of treated water quality due to destruction of sludge flocs, and maintenance management such as increasing the amount of defoaming water to prevent foaming in the tank. This makes processing complicated and makes it difficult to perform stable processing in response to load fluctuations. In general, the activity of bacteria decreases as the temperature decreases, but the growth rate of nitrifying bacteria is particularly slow compared to other aerobic bacteria (BOD oxidizing bacteria) and denitrifying bacteria, so the activity of nitrifying bacteria in winter is favorable. This will control the volume of the first aeration tank. Conventional air aeration methods use open aeration tanks, which dissipate a large amount of heat, and lower water temperatures in winter reduce treatment efficiency, resulting in larger tank volumes and higher construction costs. It is an object of the present invention to improve the above-mentioned conventional drawbacks and to provide a method for treating organic waste liquid that can stably obtain good treated water quality using economically inexpensive equipment. That is, in the present invention, the organic waste liquid is constructed in the order of an anaerobic first stirring tank, an aerobic first aeration tank, an anaerobic second stirring tank, and an aerobic second aeration tank,
Furthermore, when a part of the liquid mixture flowing out from the first aerobic aeration tank is processed by a device that circulates it to the first anaerobic stirring tank, the first aerobic aeration tank and the second aerobic aeration tank are closed tanks. A method for denitrifying organic waste liquid, characterized in that oxygen-enriched gas is supplied from a first aerobic aeration tank, and the exhaust gas is reused and treated in a second aerobic aeration tank. The present invention is particularly effectively used for organic waste liquids that are rich in BOD, organic nitrogen, and ammonia nitrogen, such as human waste, chemical industrial wastewater, and surplus sludge thermally decomposed liquid. The organic waste liquid 6 to be treated is divided into a first anaerobic stirring tank 1, a first aerobic aeration tank 2, a second anaerobic stirring tank 3,
The separated liquid in the solid-liquid separation tank 5 is discharged as treated water through a treatment process consisting of the second aerobic aeration tank 4 and the solid-liquid separation tank 5 in this order. The first aerobic aeration tank 2 and the second aerobic aeration tank 4 are of a closed type, and the gas phase portions of both tanks are communicated through an aerobic tank communication pipe 11, and a sludge return path 9 is connected to the first anaerobic stirring tank 1. The oxygen source for the aerobic aeration tank, which returns the separated sludge to the solid-liquid separation tank and circulates the mixed liquid in the first aerobic aeration tank through the mixed liquid circulation path 8 to contact and mix it with the organic waste liquid in an anaerobic atmosphere. Oxygen-enriched gas with an oxygen concentration of 50% or more is supplied to the first aerobic aeration tank, and this exhaust gas is supplied to the second aerobic aeration tank through the aforementioned piping and reused as an oxygen source there. The oxygen concentration of the aerobic first aeration tank exhaust gas is
The dissolved oxygen concentration in the tank is maintained at 21% or more, preferably 30% or more, and the dissolved oxygen concentration in the tank is 6 mg/ or more. This is important from the viewpoints of efficient use of supplied oxygen-enriched gas, stability of treatment against load fluctuations, reduction of excess sludge, improvement of sludge settling properties, and efficiency of aeration. Further, for the purpose of dilution and defoaming, industrial water or well water is supplied as dilution water 12 to the first aerobic aeration tank, and methanol, ethanol, acetic acid, etc. are used as hydrogen donors for denitrification in the second anaerobic stirring tank. An inexpensively available nitrogen-free organic compound is supplied from the nitrogen-free organic material supply pipe 7. Furthermore, it is ideal for nitrification in the aerobic first aeration tank.
Alkaline agents may be supplied to maintain the pH range. This varies depending on the T-KN, BOD concentration, PH buffering property, load, etc. of the waste liquid to be treated, but in the case of human waste treatment using the method of the present invention, the use of alkaline agents is unnecessary, or even if used, the amount is extremely small. be. The present invention eliminates the following drawbacks of the conventional method and makes it possible to stably obtain good treated water quality using economically inexpensive equipment. By making the first aerobic aeration tank a closed type and supplying oxygen-enriched gas, a higher DO can be maintained more stably and more easily than with conventional methods. Oxygen penetrates into the inside of the activated sludge flocs without becoming rate-limiting in oxygen supply during treatment. However, since aerobic conditions are maintained, processing efficiency is increased, high-load processing is possible, and stable processing is possible even with load fluctuations. For the same reason, since a high activated sludge concentration can be maintained, the treatment efficiency per tank volume increases. By using oxygen-enriched gas, the gas phase oxygen concentration is higher than in the conventional method, which increases the driving force for oxygen dissolution into the mixed liquid in the tank, reducing the amount of gas supplied and the power required for aeration. It is possible to prevent the destruction of sludge flocs even under high loads, and to prevent foaming in cases of low dilution treatment of human waste. In the nitrification solution circulation method, BOD oxidizing bacteria, nitrifying bacteria, and denitrifying bacteria circulate in each tank as a mixed system. The denitrifying bacteria cultivated in this method are facultative anaerobic bacteria, but since most of the BOD components in the waste liquid to be treated are removed in the anaerobic first stirring tank, the denitrifying bacteria are facultative anaerobic bacteria. In the 1 aeration tank, the high DO region is passed through with a very low load, so aerobic digestion progresses. Since the growth rate of denitrifying bacteria is higher than that of nitrifying bacteria, a decrease in denitrifying bacteria increases the ratio of nitrifying bacteria in the system, which is advantageous for this method in which the nitrification rate is rate-limiting. This gives rise to the advantage of reduction. The second aerobic aeration tank is installed for the purpose of promoting sedimentation and removing residual BOD by degassing the _N2 gas generated during denitrification treatment in the second anaerobic stirring tank, but it maintains a high DO. It is known that this further improves sedimentation properties. According to the present invention, a high DO can be easily maintained by using the aerobic first stirring tank exhaust gas with an oxygen concentration of 21% or more, so it is economical to reduce tank volume, improve sedimentation, and stabilize water quality compared to conventional methods. can be achieved. Next, the present invention will be explained in more detail with reference to Examples. Examples and Comparative Examples Table 1 shows examples and comparative examples of human waste as a representative organic waste liquid that is rich in BOD, organic nitrogen, and _NH4 -N and has large load fluctuations. In both Examples and Comparative Examples, the human waste to be supplied is approximately 450 mg/kg of human waste removed by a drum screen using T-KN.
It was prepared and supplied. In the example, pure oxygen was supplied to the first and second aerobic aeration tanks and the DO was adjusted to 10mg/, and the MLSS in the tank was approximately 6000.
mg/The amount of urine circulated from the first aerobic aeration tank to the first anaerobic stirring tank was 5 times the amount of urine supplied. The volume ratio of each tank is the volume ratio confirmed to be the most efficient in the method according to the present invention, that is, the first anaerobic stirring tank: the first aerobic aeration tank: the second anaerobic stirring tank = 1 :2:1 was adopted. In the comparative example, the tank volumes shown in Table 1 were adopted as the most common tank volume ratios compared to the conventional air aeration method. DO was approximately 3 mg/in the first aerobic aeration tank and approximately 5 mg/in the second aerobic aeration tank. Inside the tank
The MLSS was approximately 4000 mg/, and the circulating amount of the aerobic first aeration tank mixture was 5 times the amount of supplied urine. In addition, in both Examples and Comparative Examples, nitrite nitrogen (NO ₂ ^- -N) flowing into the anaerobic second stirring tank and nitrate nitrogen (NO ₃ ^- -
Methanol was supplied as a hydrogen donor in an amount three times the amount of methanol (N). PH control of the first aerobic aeration tank was not performed in each case. Also, the experimental temperature was the same for each example.
The temperature was controlled at 25°C. In each experiment, the tank volume and MLSS were kept constant, the urine volume was increased stepwise at regular intervals, and the treated water was analyzed. The values shown in Table 1 indicate the best conditions and results under which the treated water BOD is 30 mg/or less and the denitrification treatment is carried out stably. The BOD volume load of the first anaerobic stirring tank is 8.2 Kg BOD/m for ³ days in the example, which is about 6 times higher than that of the comparative example of 1.25 Kg BOD/m ^{for 3} days. The T-KN volume load in the first aerobic aeration tank was 1.2KgT-KN/m in the example and 0.4Kg in the comparative example in ³ days.
T-KN/m Achieves approximately 3 times higher load processing than ³ days. The second anaerobic stirring tank has a somewhat generous size in each example, but the tank volume in the example is half that of the comparative example. In the aerobic second aeration tank, the Example exhibits the same or better effect even with a residence time that is a fraction of that of the Comparative Example. The MLSS is low at about 6000 mg/in the example and about 4000 mg/in the comparative example because the sedimentation properties of activated sludge are poor, and if the concentration is higher than this, sludge overflows in the solid-liquid separation tank and the concentration of returned sludge decreases. This is due to a decrease in the concentration in each tank. In the example, activated sludge with good sedimentation properties is obtained because high DO treatment is performed during oxygen aeration in an aerobic aeration tank, and a high MLSS concentration can be maintained. This result is a factor in the high-load processing in the embodiments described above. As described above, it is clear that according to the method of the present invention, the treatment is stable and good treated water quality can be obtained. In other words, since the quality of supplied human waste water is almost constant in each case, the total volume of each tank per supplied human waste is: total volume/supplied human urine amount = 12.3/16 = 0.77 in the example, and total volume/supplied in the comparative example. The amount of human waste = 18.5/5 = 3.7, which means that in the example, treated water of the same or higher quality can be obtained with a total volume of about 1/5 of that of the comparative example.

【table】

【table】 [Brief explanation of drawings]

The drawing is an explanatory diagram showing an example of a processing method according to the present invention. 1...Anaerobic first stirring tank, 2...Aerobic first aeration tank, 3...Anaerobic second stirring tank, 4...Aerobic second aeration tank, 5...Solid-liquid separation tank, 6... ... Organic waste liquid, 7 ... Nitrogen-free organic material supply pipe, 8 ... Mixed liquid circulation path, 9 ... Sludge return path, 10 ... Oxygen enriched gas, 11 ... Aerobic tank communication pipe, 12 ... diluted water.

Claims (1)

[Claims] 1 Organic waste liquid is transferred to the anaerobic first stirring tank and the aerobic first stirring tank.
It is composed of an aeration tank, an anaerobic second stirring tank, and an aerobic second aeration tank in this order, and is further treated with a device that circulates a part of the liquid mixture flowing out from the aerobic first aeration tank to the anaerobic first stirring tank. At this time, the first aerobic aeration tank and the second aerobic aeration tank are sealed tanks, and oxygen-enriched gas is supplied from the first aerobic aeration tank, and the exhaust gas is reused and treated in the second aerobic aeration tank. A method for denitrifying organic waste liquid, characterized by: