JPS6334799B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to improvements in nitrification and denitrification methods for human waste wastewater. The biological denitrification method uses nitrifying bacteria living in activated sludge to nitrify nitrogen (hereinafter referred to as NH ₃ ) to NOx (NO ₂ or/and NO ₃ ) under aerobic conditions. , which uses denitrifying bacteria to reduce and decompose NOx into _N2 gas, which is then released from the water. Biological denitrification methods using activated sludge are widely used to remove nitrogen from human wastewater, but the nitrification rate and denitrification rate of activated sludge are different from the activities of biological denitrification treatment equipment for other wastewater. Its characteristic is that it is much smaller than sludge, which is also a major drawback. The present invention eliminates the drawbacks of the conventional methods described above and improves the nitrification activity and denitrification activity of activated sludge in the biological denitrification treatment process of night soil wastewater, thereby making it possible to reduce the volume of the treatment equipment. The purpose is to provide an improved method. In other words, the present invention can collect human waste wastewater with a mesh opening of 1 mm.
After passing through the following sieves or screens, the superfluous water is nitrified and denitrified in the biological treatment process, and the activated sludge flowing out from the biological treatment process is concentrated using a centrifuge or pressure flotation concentrator. This is a nitrification and denitrification method for human waste wastewater, which is characterized in that the concentrated sludge is returned to the biological treatment process. Next, the process by which the present invention was conceived will be described. The present inventors extracted activated sludge from a human waste denitrification activated sludge device, used methanol as a hydrogen donor for denitrification, and selectively cultivated methanol-utilizing denitrifying bacteria in a temporary glass reaction tank. As a result, Hyphomicrobium; SP sprouted from the bacterial cells in about a week under conditions of water temperature 20℃ and pH 7.0.
discovered that this species has become the dominant species.
When we conducted a denitrification test using Hyphomicrobium, we found that the removal rate of NO ₃ -N was approximately 20 (mg) at 20°C.
NO ₃ -N removal/g・Hypho-microbium・h)
I found that. On the other hand, despite the addition of methanol during denitrification of the activated sludge used in this selective culture, the denitrification rate was 2.2%.
mg・NO ₃ -N/g・MLSS・h. In other words, it was found that there was a difference of about 10 times when considering the same weight of bacterial cells. The present inventors have determined that the main cause of this is that a large amount of SS that does not have denitrification activity contained in human waste flows into the biological treatment process and forms activated sludge. When the activated sludge was crushed and observed under a microscope, it was found that the activated sludge contained a large amount of fibers, plant fragments, and other things that did not appear to be bacterial cells. In this way, in order to use activated sludge that contains suspended matter in addition to microorganisms and has low denitrification activity per unit weight, the volume V (m ³ ) of the denitrification process equipment must be increased as shown in the following equation. This is extremely disadvantageous. V=Zn/Xs・Kn However, Zn: NOx-N flowing into the denitrification tank (Kg/day) Xa: Activated sludge concentration (Kg/m ³ ) Kn: Denitrification rate
(KgNOx - N/Kg・MLSS・day) Therefore, after passing the SS of human waste through a fine sieve, we conducted a treatment test on the human waste in a continuous activated sludge treatment equipment shown in the flow sheet in Figure 2. It was found that not only denitrification activity but also nitrification activity increased significantly. These results are shown in Tables 1 and 2.
Shown in the table. The results in this table were obtained from a batch test of sludge extracted from a continuous activated sludge treatment device.

【table】

【table】

[Table] Furthermore, the sludge during the above continuous operation was diluted with overflow water from the settling tank to equalize the concentration (adjusted to 100mg/).
After that, use a 100ml graduated cylinder for 30 minutes.
When SVI (Sludge Volume Index) was measured, the results were as shown in Figure 1.
It was found that the lower the SS concentration, the higher the SVI. On the other hand, even in continuous operation, when using human waste through a 1.0 mm screen, SS may begin to overflow from the settling tank, and the concentration of returned sludge decreases, resulting in a decrease in the MLSS of the nitrification and denitrification tank. Although the nitrification and denitrification activities of sludge increased, the nitrification and denitrification activities per unit volume of the tank did not improve.
It was not possible to increase the nitrogen load on the equipment.
Therefore, when the sludge with increased SVI was concentrated using a centrifuge and a pressure flotation device, solid-liquid separation was achieved extremely well, and the degree of concentration of the sludge could be increased. i.e. settling tube with stirring rake (diameter 60 mm, height 1200
In a sedimentation test using sludge (mm), sludge that was only concentrated to 3,300 mg in 6 hours was concentrated to 86,000 mg in a centrifuge.
mg/(2000G), and could be concentrated to 38000mg/each using a pressure flotation device. In this way, the present invention can treat human waste wastewater with a mesh size of 1.
By passing through a sieve or screen with a diameter of 1.5 mm or less, activated sludge with greatly improved denitrification and nitrification activities proliferates, and when such overtreated human waste wastewater is subjected to nitrification and denitrification treatment, Activated sludge flowing out from the treatment process has poor sedimentation properties, so sedimentation separators have poor concentration properties.A centrifugal separator or pressurized flotation equipment can accurately concentrate and separate the activated sludge. nitrification,
By returning to the denitrification tank, nitrification and
This is based on the knowledge that sludge with high denitrification activity can be easily and stably maintained at a high concentration and that human waste wastewater can be efficiently nitrified and denitrified. Next, one embodiment of the present invention will be explained based on FIG. 2. Human waste wastewater 1 that has been subjected to sand removal, impurity removal, crushing, etc. After the SS in the human waste sewage 1 is removed via the screen process 2 installed in the After the NOx in the nitrification solution 4 is denitrified by denitrifying bacteria using the BOD component of the human waste water 1 as a reductant, it flows into the nitrification process 6, where the NH ₃ of the human waste water 1 is nitrified to NOx, The BOD remaining in the first denitrification step 5 is oxidized and decomposed. A part of NOx is recycled to the first denitrification step 5,
The remainder flows into a second denitrification step 7, where it is denitrified with the addition of alcohol 8 such as methanol or without the addition of alcohol, and then solid-liquid separation is performed in a centrifugal concentrator 9, and the centrifuged water 10 is discharged or further agglomerated. It undergoes advanced treatments such as ozone oxidation and activated carbon treatment. The return sludge 3 can be concentrated to a concentration of 30,000 to 100,000 mg/cm, but if the return sludge pump (not shown) is one that can transfer high concentration sludge, for example, a screw pump such as Mono Pump (trade name) is used. Good, but concentration 60000-100000mg/
50% of the pump's maximum flow rate when transferring sludge.
It is desirable to operate at around %. The set flow rate varies greatly depending on the length of the suction and discharge pumps, so it is best to check in advance. If there is a process that can capture SS, such as coagulation sedimentation or coagulation pressurized flotation, after the centrifugal concentrator 9, the flow rate load of the centrifugal concentrator 9 can be increased and the centrifuged water 10
However, if the centrifuged water 10 is directly discharged, the SS of the centrifuged water can be reduced by reducing the flow rate load and sludge load. The opening of the screen in screen process 2 is as follows:
If it is less than 0.2 mm, the overspeed of human waste water will be extremely reduced due to clogging, so it is preferable to set the screen to 0.2 mm to 1 mm, rather than using a single screen with openings of 1 mm or less. For example, when combining three stages, the first stage is preferably 1 mm, the second stage is 0.7 mm, and the third stage is 0.4 mm. Furthermore, it is more effective to combine two or three stages of the same mesh size. As for the type of screen, a rotating drum type screen is preferable, and the mesh of the screen may be a bar screen, but a mesh type screen is more effective.
To prevent the screen SS from clogging,
It may be washed continuously or intermittently with high-pressure water. As described above, according to the present invention, activated sludge with high nitrification and denitrification activities can be maintained at a high concentration in the biological treatment process, and the volume of the biological treatment equipment can be significantly reduced, thereby reducing equipment construction costs. Significant savings can be made, and denitrification treatment of human waste wastewater can be performed even in areas where site area is limited.

[Brief explanation of the drawing]

FIG. 1 is a graph showing the results of basic experiments of the present invention, and FIG. 2 is a flow sheet showing one embodiment of the present invention. 1... Human waste sewage, 2... Screen process, 3... Returned sludge, 4... Circulating nitrification liquid, 5... First denitrification process, 6
...Nitrification process, 7...Second denitrification process, 8...Alcohol, 9...Centrifugal concentrator, 10...Centrifuged water.

Claims (1)

[Claims] 1 In a method of nitrifying and denitrifying human waste water using the activated sludge method, human waste water is treated with a mesh size of 1.
After passing through a sieve or screen with a diameter of less than mm, the filtrate is nitrified and denitrified in a biological treatment process, and the activated sludge flowing out from the biological treatment process is concentrated using a centrifuge or pressure flotation concentrator. and returning the concentrated sludge to the biological treatment process,
Denitrification method.