JPS6322200B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a biological denitrification method for organic wastewater, and more specifically, to a biological denitrification method for organic wastewater such as night soil wastewater, food wastewater, special factory wastewater, etc. using a nitrification solution circulation method. The biological denitrification method of organic wastewater using a nitrification liquid circulation method is well known and widely used because of its advantages such as high equipment efficiency and low running cost. This is a method in which wastewater is supplied to a denitrification tank and then to a nitrification tank, and a large amount of nitrified liquid that has passed through the nitrification tank is circulated to the denitrification tank for treatment. The biological denitrification method is divided into two stages: the nitrification process carried out under aerobic conditions and the denitrification process carried out under anaerobic conditions _. ⁺ −N) to nitrite nitrogen (NO ₂ ⁻ −N) and nitrate nitrogen (NO ₃ ⁻ −N)
Finally, it is reduced and decomposed to nitrogen gas. Recently, in this nitrification solution circulation denitrification treatment method, the efficiency of the equipment has been improved by increasing the sludge concentration and increasing the oxygen supply efficiency, but the biological In order to perform denitrification at a high load, it is necessary to maintain a high MLSS concentration, but in conventional solid-liquid separation using gravity sedimentation, there are limits to the sedimentation rate and concentration of sludge, and it is difficult to maintain a high MLSS concentration. When performing high-load processing, if air is used as an oxygen source,
There were drawbacks such as a huge amount of air required and a significant increase in energy consumption. For this reason, the present inventors first applied a flow as shown in FIG. 1 to a high concentration (for example,
An attempt was made to supply gases 5 and 7 containing oxygen (at least 50% by volume) and to separate the mixed liquid from the reaeration tank into thickened sludge 3 and separated liquid 13 using a centrifugal separator 12. This process has the advantage that it is possible to perform high-load processing, and at the same time, it is possible to maintain dissolved oxygen in the nitrification tank, and the amount of gas is small and there is no problem of foaming. However, even with the process shown in FIG. 1, the following problems remain unsolved. 1 Biodegradation of organic matter in human waste (first denitrification tank 4)
The carbon dioxide gas generated is dissolved in the liquid phase, and the liquid phase carbon dioxide gas is diffused into the gas phase in the closed nitrification tank 6 and reaeration tank 9, so the gas phase oxygen concentration decreases and the oxygen utilization efficiency decreases. descend. 2 The SS in the separated liquid 13 of the centrifugal thickener 12 is lighter than the SS in the thickened sludge 3, and the flocs have been crushed, so even if the sediment is separated as it is, high-concentration precipitated sludge cannot be obtained. , and there is a large amount of SS in the treated water, so a flocculant is required to form flocs when performing coagulation and sedimentation. 3 SS in the separated liquid 13 from the centrifugal concentrator 12 is
200mg/l or more, usually about 2000mg/l, so if the BOD in the inflowing wastewater 1 is about 5000mg/l or less, the specified value in the nitrification tank 6
It becomes impossible to maintain the MLSS concentration. The main purpose of the present invention is to increase oxygen utilization efficiency in biological denitrification of organic wastewater as described above,
The objective is to realize an efficient processing method that enables high-load processing and reduces the consumption of power and coagulant. According to the present invention, there is provided a biological denitrification method for organic sewage using a nitrification solution circulation method, which method includes supplying a gas containing at least 50% by volume of oxygen to a sealed nitrification tank. The whole amount of the mixed liquid from the nitrification tank, or from the second denitrification tank if a second denitrification tank is provided after the nitrification tank, is separated into concentrated sludge and separated liquid by a centrifugal thickener. The method is characterized in that at least a portion of the thickened sludge is returned to the first denitrification tank, and the separated liquid is guided to the reaeration tank. Hereinafter, the method of the present invention will be specifically explained with reference to the accompanying drawings. FIG. 1 is a flowchart schematically showing the process considered in arriving at the present invention. Second,
3 and 4 are flowcharts schematically showing an example of the method of the present invention, respectively. In these examples, organic sewage (e.g. human waste) 1, together with thickened sludge 3 from centrifugal thickener 12 and optionally return sludge 21 from settling tank 18, and circulating nitrified liquid 2 from nitrification tank 6, It is introduced into the first denitrification tank 4 under anaerobic conditions, and the circulating nitrification liquid 2 is
NO ₂ ^- and NO ₃ ^- are N ₂ due to the BOD component in wastewater 1.
It is reduced and decomposed into gas. On the other hand, NH ₄ ⁺ in wastewater 1
passes through the first denitrification tank 4 as it is and is led to the nitrification tank 6 under aerobic conditions where it is nitrified to NO ₂ ^- and NO ₃ ^- , and a part of this nitrification mixture is transferred to the circulating nitrification solution 2.
The remaining part is sent to the second denitrification tank 8, which is the next step. The nitrification tank 6 is of a closed type, and a gas 5 containing at least 50% by volume of oxygen is supplied at its inlet, and the exhaust gas 7 from the nitrification tank 6 is sent to a re-aeration tank 9 to re-evaluate the treated liquid. Used for aeration to remove residual BOD components. but,
As shown in FIG. 3, a gas 5' containing at least 50% by volume of oxygen is supplied to the reaeration tank 9, and the exhaust gas from the reaeration tank 9 is supplied to the nitrification tank 6 as the supply gas 5. Good too. However, in this case, the exhaust gas from the reaeration tank 9, that is, the gas supplied to the nitrification tank 6, must contain at least 50% by volume of oxygen. Further, as shown in FIG. 4, the exhaust gas 7 from the nitrification tank 6 is
It may be discharged as it is outside the system; in this case, the reaeration tank 9 is separately supplied with a gas 5' containing at least 50% by volume of oxygen. As shown in FIG. 1, in the method previously developed by the present inventors, the treated liquid that has been further denitrified in the second denitrification tank 8 is then sent to the re-aeration tank 9 to remove residual BOD. Then, this treated liquid 11 is sent to a centrifugal concentrator 12. Part or all of the concentrated sludge 3 separated here is returned to the first denitrification tank 4, and the separated liquid 13 is sent to the mixing tank 1 for the next process.
Sent to 4. However, the second to fourth aspects of the present invention
In the method shown in the figure, the treated liquid 11' from the second denitrification tank 8 is first sent to the centrifugal concentrator 12. Part or all of the concentrated sludge 3 separated by the centrifugal concentrator 12 is returned to the first denitrification tank 4, and if there is a remainder, it is discharged outside the system, and the separated liquid 13
is sent to the next step, the reaeration tank 9. The treated liquid 22 from which residual BOD has been removed in the reaeration tank 9 is then led to a mixing tank 14, where it is mixed with an inorganic flocculant 16, and then led to a flocculation tank 15 where it is mixed with a polymer flocculant 1.
7 and then led to a settling tank 18. Here, the supernatant liquid is discharged as treated water 19, and if desired, part of the settled sludge 20 is returned to the sludge 21.
The sludge is returned to the first denitrification tank 4, and the remainder is removed as surplus sludge. In addition, in the method of the present invention, among the steps explained above, the steps of the second denitrification tank 8, mixing tank 14, flocculation tank 15, and settling tank 18 are each desired steps, and may be omitted if necessary. Can be done. According to the method of the present invention having the configuration as described above, the following surprising advantages can be obtained. B. Since a centrifugal concentrator is used before the reaeration tank, carbon dioxide gas is dissipated and the pH of the separated liquid flowing into the reaeration tank is increased. Therefore,
Carbon dioxide in the exhaust gas from the nitrification tank is redissolved in the liquid phase in the reaeration tank, and the gas phase oxygen concentration is restored.
Therefore, oxygen utilization efficiency is improved and aeration power is also saved. (b) Since the separated liquid from the centrifugal concentrator is subjected to aerobic treatment in the reaeration tank, floc formation progresses and sedimentation properties are improved. Therefore, when carrying out coagulation precipitation, the consumption of flocculant is reduced. C. In the reaeration tank, the treated water does not contain returned sludge and the SS concentration is low, so power for stirring and aeration can be saved. D. Since the precipitated sludge can be made to have a high concentration, if the BOD concentration in flowing wastewater is low, it can be returned, and the MLSS concentration in the nitrification tank can be maintained. The present invention will be further explained below with reference to Examples. Example Human waste was diluted approximately 1.5 times and subjected to biological nitrification and denitrification treatment under the conditions shown in the table below. In the table, the comparison example is a case where the process was performed as shown in FIG. 1, and Experiment 1, Experiment 2, and Experiment 3 were cases where the process was performed as shown in FIGS. 2, 3, and 4, respectively. The obtained results are also listed in the table. From these results, according to the method of the present invention, the oxygen concentration in exhaust gas and oxygen utilization efficiency are improved, the treated water quality is improved despite the low flocculant addition rate, and the settled sludge concentration is increased. It is clear that there are.

【table】

【table】 [Brief explanation of drawings]

FIG. 1 is a flowchart schematically showing the process considered by the inventors while arriving at the present invention. Figures 2, 3 and 4 are
Each is a flowchart schematically showing an example of the method of the present invention. 1... Supply sewage, 2... Circulating nitrification liquid, 3... Thickened sludge, 4... First denitrification tank, 5,5'... Supply gas, 6... Nitrification tank, 8... Second denitrification tank, 9...Reaeration tank, 12...Centrifugal concentrator, 14...Mixing tank,
15... flocculation tank, 18... sedimentation tank.

Claims (1)

[Claims] 1. In a biological denitrification method for organic wastewater using a nitrification solution circulation system, at least
A gas containing 50% by volume of oxygen is supplied, and the entire amount of the mixed liquid from the nitrification tank, or from the second denitrification tank if a second denitrification tank is provided after the nitrification tank, is centrifugally concentrated. Biological desorption of organic sewage characterized by separating thickened sludge and separated liquid by a machine, returning at least a part of the thickened sludge to a first denitrification tank, and guiding the separated liquid to a reaeration tank. Nitrogen method. 2. The denitrification method according to claim 1, wherein exhaust gas from the nitrification tank is supplied to the reaeration tank. 3. Claim 1, wherein a gas containing at least 50% by volume of oxygen is separately supplied to the reaeration tank.
Denitrification method described in section. 4. The denitrification method according to claim 1, wherein the gas supplied to the nitrification tank is exhaust gas from the reaeration tank.