JPH0135715B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention generates a microbial film to purify sewage, human waste, industrial wastewater, and other organic wastewater containing ammonia to remove nitrogen, organic substances, and suspended substances in the wastewater. This relates to biological treatment methods that purify wastewater by removing [Prior Art] Various methods have recently been studied for purifying organic wastewater by attaching microorganisms to the surface of granular fillers such as sand, anthracite, activated carbon, and plastic materials. Among them, a method in which wastewater is brought into contact with air or oxygen in a granular filler packed bed in a fixed bed state, and the packed bed is washed intermittently to discharge the sludge outside the system, can be treated without circulating the sludge. Advantages include: no bulking occurs, sludge clogging can be prevented, no sedimentation and separation section is required due to overaction, and only the amount of air needed to remove BOD is required since no agitation is expected. It is attracting attention. [Problem to be solved by the invention] However, in the biofilm filtration method,
Although very high treatment effects can be obtained for the removal of BOD and SS or the nitrification of ammonia, it has been difficult to actively remove nitrogen at the same time. In order to remove this nitrogen, it is necessary to separately provide denitrification equipment, which inevitably complicates the processing flow and complicates operation management. Meanwhile, as a result of many years of research into the biofilm filtration method, the inventor discovered an important characteristic. In other words, we repeatedly investigated the dissolved oxygen (DO) distribution in the packed bed using the biofilm filtration method, in which wastewater is passed downward through a bed of granular filler and air or oxygen is supplied from the bottom of the bed. However, the DO at the bottom of the packed bed is the highest, gradually decreases from the bottom to the top, and reaches the lowest value at the top of the packed bed. This tendency is a universal phenomenon, regardless of the amount of air supplied and the type of wastewater.Also, this phenomenon is caused by the fact that the substrate concentration is higher in the upper part of the packed bed than in the lower part. This also agrees with the qualitative judgment that there are many microorganisms attached to the surface and their activity is high. The present invention focuses on the DO distribution characteristics of the biofilm filtration method, and simultaneously removes nitrogen, organic substances, and suspended solids (SS) from ammonia-containing organic wastewater in the same packed bed, simplifying the treatment flow. ,
The purpose is to provide an energy-saving, efficient, and simple wastewater treatment method that facilitates operational management. [Means for Solving the Problems] The present invention achieves biological decomposition by passing organic wastewater in a downward flow through a packed bed filled with a granular filler for attaching microorganisms and performing aeration from the bottom of the packed bed. When purifying by action and overaction, the aeration amount is controlled so that the upper part of the packed bed is maintained in an anaerobic state and at least the middle to lower part of the packed bed is maintained in an aerobic state, and the amount of air diffused is This is a biological treatment method characterized by circulating a portion of it to the upper part of a packed bed for treatment. [Function] The present invention actively utilizes the universal DO distribution characteristics in the packed bed, and specifically controls the DO in the middle part of the packed bed to 0.5 to 1.0 mg/ The upper part is maintained in an anaerobic state, and the middle part to the lower part is maintained in an aerobic state, and the organic wastewater is passed downward and a part of the runoff water is circulated to the upper part of the packed bed. Biological denitrification and removal of organic substances in the anaerobic section, biological oxidation of organic substances and biological nitrification of ammonia in the lower aerobic section, and biofilm attached to the granular packing material throughout the packed bed. This causes an overeffect. The filling layer thickness in the present invention is suitably 1500 mm or more, preferably 2000 mm or more. This is because when the packed bed thickness is less than 1500 mm and the water is classified into anaerobic and aerobic parts, the linear velocity of water decreases and SS in the raw water is trapped only in the upper part of the packed bed, resulting in an increase in the frequency of backwashing. This is because the processing efficiency is reduced. Further, the middle part of the packed bed preferably means that the anaerobic state in the packed bed changes to the aerobic state. However, it is difficult to compartmentalize because there is a gradual change from an anaerobic state to an aerobic state, and there are changes in treatment conditions such as the properties of wastewater, circulating water volume ratio, and water flow linear velocity. Therefore, in actual equipment, the properties of the wastewater to be treated, especially the nitrogen components of organic nitrogen, ammonia nitrogen, nitrate nitrogen, and nitrite nitrogen, and BOD
Clarify the concentration, determine the denitrification rate, BOD removal rate, and nitrification rate in advance, and change from anaerobic state (denitrification region) to aerobic state (BOD oxidation region and nitrification region)
Find the point at which the change should occur and determine the DO detection point. That is, the position of the DO detection section differs depending on the raw water, but it is preferable to position it between 1/5 and 4/5 of the height of the packed bed. Next, the control range of DO is the DO in the middle of the packed bed.
It is desirable that the amount is 0.5 to 1.0 mg/. Generally, denitrification occurs efficiently when DO is 0.5 mg/or less, and hardly progresses when DO is 1 mg/or more. On the other hand, the nitrification phenomenon progresses efficiently when DO is 2 mg/or more, so it is better to take this point into account when adjusting the amount of aeration. For example, if the DO in the middle part of the packed bed is set to 0.5 mg/or less, the DO in the upper part of the packed bed will almost disappear, which is convenient for denitrification, but the DO in the lower part of the packed bed will be
is difficult to exceed 2mg/, which is inconvenient for nitrification. Conversely, if the DO in the middle part of the packed bed is set to 1 mg/or more, the DO in the lower part of the packed bed will be 2 mg/ or more, which is favorable for nitrification, but the DO in the upper part of the packed bed will be
It is difficult for the amount to fall below 0.5mg/, which is inconvenient for denitrification. In this way, by controlling the DO in the packed bed as described above, ammonia in the wastewater is biologically nitrified at the bottom of the packed bed, and the nitrified runoff water returns to the top of the packed bed as circulating water. , biologically denitrified at the top of the packed bed. BOD is used as a hydrogen donor during denitrification in the upper part of the packed bed, and residual BOD is removed by aerobic biodegradation in the middle part of the packed bed. Here, the amount of circulating water is determined by the nitrogen removal rate, and is preferably 3 to 6 times the amount of normal raw water. Furthermore, to explain one embodiment of the present invention with reference to the drawings, raw water 1 which is ammonia-containing organic wastewater such as sewage, human waste, industrial wastewater, etc. enters a raw water tank 2; Circulating water 17, which is a part of the treated water 10 that flows out, also flows into the raw water 1.
and circulating water 17 are mixed. Regarding this mixing method, it is sufficient to simply bring the raw water 1 and the circulating water 17 into contact with each other, and if necessary, a stirrer may be provided, or stirring may be performed using a diversion plate. Then, the mixed raw water 3 of the raw water 1 and the circulating water 17 is guided by the mixed raw water pump 4 to the upper part of the treatment tank 5 filled with granular filler 6, and is passed in a downward flow. In the treatment tank 5, a packed bed 7 consisting of a granular filler 6 such as sand, anthracite, activated carbon, or plastic material is immersed, and the mixed raw water 3 is gradually absorbed by the microbial film attached to the surface of the granular filler 6. undergoes biological decomposition and overaction, passes through a support layer 9 made of gravel 8, and flows out as treated water 10 into a distribution tank 1.
It reaches 1. Note that it is also possible to provide a perforated plate below the filling layer 7 and omit the support layer 9. On the other hand, a pipe 13 guided by a blower 12 is embedded in the support layer 9, and is configured to uniformly supply air to the packed layer 7. In addition, in the packed bed 7, a DO detector 1 is installed in the middle part of the packed bed.
4, the air supply amount is adjusted by adjusting the opening of the automatic valve 15 so that the DO in the middle part of the packed bed is 0.5 to 1.0 mg/. Moreover, if a turbo blower is used as the blower 12 and the amount of air supplied is adjusted, it is also possible to further save energy. The treated water 10 that has reached the distribution tank 11 is divided into a treated water tank 16 and a raw water tank 2 as circulating water 17. is discharged. If this type of treatment continues for a long time, the raw water will
Since the packed bed 7 is clogged due to proliferation of SS or microorganisms, the mixed raw water pump 4 is periodically stopped, the backwash pump 19 is operated, and the inside of the treatment tank 5 is backwashed with the treated water 10. By discharging the water from the drainage pipe 20 as washing water 21, it is possible to return to overtreatment. [Example] Next, Table 1 shows an example in which primary treated sewage water was treated using a treatment tank with a diameter of 400 mm and a height of 4000 mm.

【table】

〔Effect of the invention〕

As described above, according to the present invention, not only organic substances and suspended solids can be removed in the same packed bed, but also nitrogen can be actively removed at the same time without changing the basic structure of the conventional biofilm filtration device. Because it can be done,
The treatment flow is extremely simplified, and maintenance and inspection, etc., are also easier.Also, the characteristics of the conventional biofilm treatment method, which removes organic substances and suspended solids at the same time, are utilized, making it possible to reduce consumption. In terms of power, there is no waste at all, and in terms of installation space, it only takes up about the same area despite nitrogen removal, making it extremely useful and enabling energy-saving and efficient processing.

[Brief explanation of drawings]

The drawing is a flow sheet showing one embodiment of the invention. 1...Raw water, 2...Raw water tank, 3...Mixed raw water,
4... Mixed raw water pump, 5... Treatment tank, 6... Granular filler, 7... Filled bed, 8... Gravel, 9... Support layer, 10... Treated water, 11... Distribution tank, 12 …
...Blower, 13...Piping, 14...DO detector,
15... Automatic valve, 16... Processing water tank, 17... Circulating water, 18... Piping, 19... Backwash pump, 20
...Piping, 21...Backwash drainage.

Claims (1)

[Scope of Claims] 1 Organic wastewater is passed downward through a packed bed filled with granular filler for microbial adhesion and air is diffused from the bottom of the packed bed to purify it through biological decomposition and overaction. At the same time, the amount of aeration is controlled so as to maintain the upper part of the packed bed in an anaerobic state and at least the middle to lower part of the packed bed in an aerobic state, and also direct some of the runoff water to the packed bed. A biological treatment method characterized by circulation in the upper part. 2 The air diffusion amount control reduces the layer thickness of the packed bed to 1.5
m or more, and the dissolved oxygen in the middle of the packed bed is 0.5~
The method according to claim 1, wherein the treatment is carried out while maintaining the concentration at 1.0 mg/. 3. The method according to claim 1 or 2, wherein the amount of circulation of the effluent water is 3 to 6 times the amount of organic wastewater flowing.