JPS6325840B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for treating wastewater containing a large amount of solids, such as sewage.

In the method generally applied to treat wastewater containing a large amount of solids, large solids in the wastewater are removed using a coarse screen, impurities are crushed using a comminuator, and then biochemical treatment, For example, a process of applying sessile biological treatment or activated sludge treatment is adopted. In this method, solids are mixed into the activated sludge, so in order to keep the amount of activated sludge constant, it is necessary to maintain a huge MLSS, which requires the use of extra stirring power or the use of large volumes. It becomes necessary to use an additional aeration tank, and the amount of surplus sludge generated increases. Furthermore, solid matter decomposes while remaining in the form of sludge for a long period of time, which creates a load for biodegradation, increasing the overall load and increasing power consumption to maintain the aeration tank in an aerobic state. do.

This invention was made in order to solve the above-mentioned problems, and it is possible to effectively capture and separate solids in wastewater sequentially in two stages, increasing the concentration of the captured solids. The purpose of the present invention is to provide a wastewater treatment method that allows anaerobic digestion of captured solids to be performed in a small volume and eliminates the inconveniences associated with increased MLSS.

An embodiment of the present invention will be described below with reference to the drawings. The coarse screen indicated by reference numeral 1 in Fig. 1 is for separating large-sized solids contained in the wastewater to be treated. After undergoing separation of small solids by passing through screen 2, it is introduced into aeration tank 3 for biochemical treatment. Inside this aeration tank 3,
Normal biochemical oxidation using activated sludge is carried out, and the liquid that has undergone a predetermined amount of aeration is supplied to the next settling tank 4. A part of the activated sludge that has been sedimented and separated in the settling tank 4 is returned to the aeration tank 3 as return sludge, and the remainder is sent to the screen sludge treatment tank 5 together with the screen slag separated from the wastewater by the fine screen 2. Sent.

Therefore, the coarse screen 1 is used in the first stage separation process to capture and separate large solids in the wastewater, and the fine screen 2 is used in the second stage to further capture and separate small residual solids in the wastewater that has passed through the coarse screen 1. Separation step: The aeration tank 3 is a step in which the sewage that has passed through the fine screen 2 and the supernatant liquid produced in the screen slag treatment tank 5 are introduced to perform biochemical treatment using activated sludge. ing.

In addition, if the screen slag captured by the fine screen 2 is in a dehydrated state, the screen slag is conveyed to the screen slag treatment tank 5 by a screw conveyor, or excess sludge etc. is poured into the screen slag. They may be mixed and conveyed with fluidity.

An example of a specific configuration of the screen slag treatment tank 5 is shown in FIG. 2. This screen slag treatment tank 5 is provided with a cylinder body 13 disposed almost vertically inside a tank main body 12 having an odor port 11, and a pipe 14 extending through the cylinder body 13. One end of this pipe 14 communicates with the fine mesh screen 2 and the settling tank 4 in order to introduce the screen slag and excess sludge into the tank body 12.

The cylindrical body 13 is for forming an annular precipitation chamber 15 having a predetermined volume between it and the outer peripheral surface of the pipe 14, and this precipitation chamber 15 has a large number of small holes 14a formed in the pipe 14. It communicates with the inside of the pipe 14 through the pipe 14, and also communicates with an anaerobic digestion chamber 16 formed within the tank body 12 at the lower end. Also, cylinder body 1
A pipe 17 connected to the upper end of the pipe 17 is for taking out the liquid that has reached above the opening from the settling chamber 15 to the outside of the screen slag treatment tank 5 by overflow, and the taken out liquid is transferred to the aeration tank 3. sent to.

The screen slag and excess sludge sent from the fine screen 2 and settling tank 4 flow into the anaerobic digestion chamber 16 through the pipe 14, and in this process,
Moisture moves into the precipitation chamber 15 through the small holes 14a. In this settling chamber 15, solid matter contained in the liquid transferred from the pipe 14 is sedimented and separated, and the separated solid matter is passed into the anaerobic digestion chamber 16 through an opening formed at the lower end of the cylinder body 13. sedimentation. Further, the supernatant liquid generated in the settling chamber 15 flows out from the pipe 17 in accordance with the rise in the liquid level due to the inflow of new liquid. Therefore, the solids contained in the screen slag and excess sludge are collected at a high concentration in the anaerobic digestion chamber 16, where they are biochemically decomposed by anaerobic bacteria. By this decomposition, the solid matter is liquefied or gasified, the liquid rises in the tank body 12 and is sent to the aeration tank 3 through the pipe 17, and the gas is discharged from the odor port 11 after being separated from the liquid. The scum generated in the anaerobic digestion chamber 16 is removed by the scum inflow prevention plate 14.
b prevents it from flowing into the precipitation chamber 15.

FIG. 3 shows a screen sludge treatment tank 5 of another form. In this example, a settling chamber 1 is provided within the tank body 12.
5, a partition wall 18 that forms a precipitation chamber 15 with the side wall of the tank body 12 is used in place of the cylindrical body 13 used in the example of FIG. The lower end of this partition wall 18 reaches a position where it faces a protrusion 12a provided on the side wall of the tank body 12 at a predetermined interval, and this interval forms a passage through which solids flow from the settling chamber 15 into the anaerobic digestion chamber 16. do. In addition,
In this example, the pipe 14 has no small holes.

The method of the invention can also be applied to systems in which denitrification and nitrification are carried out as biochemical treatment of wastewater. That is, as shown in FIG. 4, the liquid that has passed through the fine screen 2 is supplied to a treatment tank 21 for denitrification. As shown in FIG. 5, for example, the treatment tank 21 has a structure in which the inside of a tank body 22 is divided into a denitrification chamber 24 and a precipitation chamber 25 by a partition wall 23, and the wastewater to be treated is stored in the denitrification chamber 24. will be introduced in The liquid that has been denitrified by denitrifying bacteria passes through the passage formed between the tank body 22 and the partition wall 23 to the precipitation chamber 2.
5, where solid matter is sedimented and separated, and the supernatant liquid is taken out by overflow.

The supernatant liquid flowing out of the settling chamber 25 of the treatment tank 21 flows into the next nitrification tank 26, where it is nitrified according to a conventional method, and then sent to the settling tank 27. During this process, a part of the nitrification liquid is returned to the treatment tank 21 for denitrification.

The screen slag treatment tank 5 has a fine mesh screen 2
Screen slag separated from wastewater and sedimentation tank 2
The surplus sludge sedimented and separated in step 7 is subjected to anaerobic digestion treatment as shown in the example of FIG. 2, and the resulting supernatant liquid is supplied to the treatment tank 21. The supernatant obtained by anaerobic digestion of the screen slag contains a large amount of organic acids, and is therefore optimal as a carbon source necessary for the action of denitrifying bacteria in the denitrifying chamber 24. , which helps improve the denitrification effect.

Further, in the example shown in FIG. 6, the wastewater that has passed through the fine screen 2 is denitrified in a denitrification tank 31, then nitrified in a nitrification tank 32, and then treated in a settling tank 33.
be accommodated in. A part of the nitrified liquid is returned to the denitrification tank 31 for denitrification treatment. In addition, some of the sludge that has been sedimented and separated in the settling tank 33 is transferred to the denitrification tank 33.
The remaining surplus sludge is returned to the screen sludge treatment tank 5 together with the screen sludge captured by the fine screen 2. The supernatant liquid obtained in the screen slag treatment tank 5 is mainly supplied to the denitrification tank 34 in the latter stage, and a portion is also supplied to the denitrification tank 31 in the former stage as necessary. Since this supernatant liquid contains a large amount of organic acid as described above, it becomes an effective carbon source during denitrification. In particular, when performing two-stage denitrification as in this example, most of the organic matter is removed through the first stage of denitrification, followed by nitrification, and sedimentation separation, so the second stage of denitrification removes the carbon source. It is said that there is a shortage of organic substances such as methanol, and that it is necessary to add organic substances such as methanol from the outside. However, in this invention, since the supernatant liquid rich in organic acids obtained in the screen sludge treatment tank 5 is supplied to the subsequent denitrification tank 34, there is no need to supply a carbon source from the outside, which is economically advantageous. Become.

As described above, according to the present invention, large solids in wastewater are first captured and separated by the coarse screen in the previous stage, and small solids that were not captured by the coarse screen are captured in the fine screen in the next stage. As a result, the moisture content of the trapped solids is significantly reduced, the concentration of the solids becomes extremely high, and the thermal efficiency is improved, and the highly concentrated solids (screen slag) are introduced into the screen slag treatment tank. Since the anaerobic digestion treatment and precipitation treatment are carried out using the anaerobic digestion treatment, these treatments can be carried out efficiently.Furthermore, due to the improvement in thermal efficiency, it is possible to reduce the volume of the screen slag treatment tank, and the screen slag The processing tank can be made smaller.

In particular, by using the above-mentioned fine-mesh screen to reliably capture and remove even the finest solids in wastewater,
The wastewater that passes through the fine screen and is sent to the next biochemical treatment process contains almost no solids, so the load caused by the solids is significantly reduced in the biochemical treatment process. , the efficiency of wastewater treatment using activated sludge is greatly improved. Therefore,
For example, when aerating wastewater that contains a large amount of SS solids, such as sewage, the solids are converted into soluble substances and the BOD value rises from the initial level, resulting in a rise in the BOD value. However, with this method, the amount of SS solids in the aerated liquid is extremely small, so the BOD value can be reduced immediately during aeration. This results in a significant reduction in processing time and power costs.

Furthermore, if the screen sludge captured by the fine screen is left as it is, it will be troublesome to dispose of it and it will be unhygienic.However, according to this invention, the screen sludge is treated with anaerobic digestion, making it hygienic. There is no odor problem, and the amount of sludge that is disposed of is significantly smaller. Furthermore, since biological treatment can be performed mainly on soluble substances, less energy is required, and maintenance of mechanical equipment is easy, making it particularly suitable for small-scale sewage treatment systems. Furthermore, the gas generated during anaerobic digestion in the screen treatment tank contains methane gas and the like, so it can be used as fuel and energy can also be recovered.

[Brief explanation of drawings]

Fig. 1 is a flowchart showing one embodiment of the sewage treatment method of the present invention, Fig. 2 is a longitudinal cross-sectional view of the digestion tank used in the example of Fig. 1, and Fig. 3 is a longitudinal cross-section of another digestion tank. 4 is a flowchart showing another embodiment of the present invention, FIG. 5 is a longitudinal sectional view of the processing tank used in the example of FIG. 4, and FIG. 6 is a flowchart showing another embodiment of the invention. This is a flowchart showing the following. 1... Coarse screen, 2... Fine screen, 3... Aeration tank, 4... Sedimentation tank, 5... Screen slag treatment tank, 12... Tank body, 13... Cylindrical body,
14... Pipe, 14a... Small hole, 15... Sedimentation chamber, 16... Anaerobic digestion chamber, 17... Pipe, 2
1... Processing tank, 22... Tank body, 23... Partition wall,
24... Denitrification chamber, 25... Sedimentation chamber, 26... Nitrification tank, 27... Sedimentation tank, 31... Denitrification tank, 32...
Nitrification tank, 33... Sedimentation tank, 34... Denitrification tank, 35
...Sedimentation tank.

Claims (1)

[Claims] 1. A preliminary separation step in which large solids in the wastewater to be treated are captured and separated by a coarse screen, and residual solids in the wastewater that have passed through the coarse screen are further captured and separated by a fine screen. The screen slag captured and separated by the fine-mesh screen is introduced into a screen sludge treatment tank, which is divided into a settling chamber and a digestion chamber that communicates with the bottom of the settling chamber. A sewage treatment method comprising a step of performing a digestion treatment and a precipitation treatment, and a step of introducing the sewage that has passed through the fine screen and the supernatant liquid generated in the screen slag treatment tank and performing biochemical treatment. 2 The above-mentioned screen sludge treatment tank introduces the excess activated sludge returned from the above-mentioned biochemical treatment process and performs anaerobic digestion treatment together with the screen sludge introduced from the above-mentioned fine screen, and removes the excess activated sludge generated in the above-mentioned settling chamber. 2. The wastewater treatment method according to claim 1, wherein the clear liquid is sent to the biochemical treatment step. 3. The wastewater treatment method according to claim 1, wherein the biochemical treatment step comprises an aeration treatment means or a denitrification treatment means.