JPS5933438B2 - Anaerobic biological treatment method and device for wastewater - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an anaerobic biological treatment method and apparatus for wastewater, and more specifically, the present invention relates to an anaerobic biological treatment method for wastewater and an apparatus thereof, and more specifically, the present invention relates to an anaerobic biological treatment method for wastewater introduced in a downward flow using a combination of a fluidized bed of microorganism-supported particles and a transport bed. The present invention relates to a method and apparatus for doing so.

Wastewater to which anaerobic biological treatment is applied usually includes wastewater containing molasses or alcohol, wastewater with an extremely high concentration of organic matter, such as human waste, and surplus activated sludge discharged by activated sludge methods. Gas is recovered by methane fermentation.

Anaerobic fermentation of organic wastewater and sludge usually involves two stages of fermentation: acidic fermentation and methane fermentation. In the former fermentation, acid-producing bacteria convert organic substances such as carbohydrates, fats, and proteins into organic acids, alcohol, etc. In the latter fermentation, methane bacteria convert organic acids, alcohol, etc. into methane and carbon dioxide gas.

In anaerobic fermentation, there is a very close relationship between fermentation temperature and residence time. Taking the case of fermentation of activated sludge as an example, with medium temperature fermentation (27-38°C), residence time is 30-24 days, and with high-temperature fermentation (27-38°C). 43-54°C) for 26-14 days.

In this way, although the residence time in anaerobic fermentation is shortened in high-temperature fermentation, a very long residence time is required.
The scale of the fruiting device becomes extremely large.

However, anaerobic treatment of wastewater containing a high concentration of organic matter is an energy-saving wastewater treatment method that allows the recovery of methane gas. For example, it can be used as an energy-saving wastewater treatment device for organic wastewater with medium to low concentration.

The present inventors have discovered that in order to enable methane fermentation treatment of not only high-concentration but also medium-low concentration organic wastewater and to significantly improve conventional methods, it is necessary to increase the concentration of microorganisms in the biological treatment tank. Considering this to be the most important factor, we use granular material with a specific gravity of 1 or less and the ability to float on water as a microbial carrier, and fill a methane fermentation tank with microorganisms attached to the surface and drain the wastewater. They developed a method and device for biologically treating wastewater by introducing it as a downward flow and circulating it.

That is, firstly, the present invention is to fill the powder with microorganisms attached to the surface, which has a specific gravity smaller than that of water, and which floats on the water, and to pass the powder and granular material slightly below the water surface above the powder. The wastewater is introduced as a downward flow into the anaerobic biological treatment section, which is a plate material that prevents floating and is equipped with a distributor for the passage of wastewater, and the gas generated by the anaerobic biological reaction in the treatment section is collected. In an anaerobic biological treatment method in which the water in the biological treatment tank is circulated and supplied as a circulating flow, the powder and granules are made into a fluidized bed and purified by contacting with wastewater. A granular material circulation section that communicates with the lower part of the anaerobic biological treatment section is released, and the powdered rice bodies leaving the anaerobic biological processing section are made to pass through a circulating flow starting section and the granular material circulation section. This is a method for anaerobic biological treatment of wastewater, characterized in that the wastewater is returned to the anaerobic biological treatment section.
) A circulating flow starting part that collects and circulates gases generated by anaerobic biological reactions, and starts and raises waste water as an upward flow; The medulla is filled with floating medulla, and above it, and slightly below the outer surface, is a plate material that prevents the passage and levitation of the powder and granules, and is equipped with a distributor for the passage of waste water. , an anaerobic biological treatment section that brings wastewater flowing in a downward flow into contact with the granular material in a fluidized bed state, and (C) an upper part of the distributor and a lower part of the anaerobic biological treatment section that communicates with each other. Anaerobic biological treatment of wastewater, characterized in that it is formed from a granular material circulation section, and is equipped with a tank in which each section is connected upwardly and downwardly, a pipe for introducing wastewater into the nuclide, and a pipe for extracting treated water from the nuclide. It is a device.

As described above, in carrying out anaerobic biological treatment of wastewater, the present invention fills water with microorganisms attached to its surface with buoyant powder, and also deposits the powder above the water and slightly below the water surface. The anaerobic biological treatment section has a plate-shaped distributor that prevents the passage and floating of particles and is equipped with a distributor for the passage of wastewater, and the gas generated by the anaerobic biological reaction is collected and the water in the biological treatment tank is In addition to the circulating flow starting section which is provided to circulate and fluidize the powder and granular material, the floating powder and granular material flowing out from the anaerobic biological treatment section is passed through the gas supply section and then re-circulated. In order to introduce the material into the anaerobic biological treatment section, a fluidized bed and a transport bed are provided in the biological treatment tank by providing a particulate circulation section that communicates the upper part of the distributor with the lower part of the anaerobic biological treatment section. It is unique in that it is formed by combining the two.

In a downward flow fluidized bed using floating powder, even if the downward flow rate of wastewater is kept constant, the specific gravity of the powder changes depending on the amount or thickness of microorganisms attached to the surface of the powder. changes, and the expansion rate of the fluidized bed often differs.

The thickness of microorganisms attached to the powder is determined by the temperature of the outside air and wastewater, the concentration of organic matter in the wastewater, the quality of the organic matter, etc., but in any case, the fluidized bed must be maintained at a constant expansion rate for a long period of time. is extremely difficult.

Such an increase in the rate of expansion and excessive adhesion of microorganisms to some of the powder and granules inevitably causes some of the powder and granules to detach and flow out from the anaerobic biological treatment section.

Then, the separated powder and granules are lifted by gas and float to the water surface above the distributor located in the upper part of the anaerobic biological treatment section.

If such a phenomenon continues, the volume of powder and granular material in the anaerobic biological treatment section may decrease, making normal operation impossible.

However, since the present invention is configured as described above, anaerobic biological treatment can be carried out stably over a long period of time without causing such troubles.

The powder or granules serving as microorganism carriers used in the present invention may have a specific gravity of 1 or less and have the property of floating on water, and the particle size is not particularly limited, but is generally 0.5 to 20 mm.
The appropriate specific gravity is 0.2 to 0.95 in a dry state.

Synthetic resin is generally used as the material for powder and granules, but
As a result of many years of experiments by the present inventors, it has been found that it is difficult for microorganisms to fully adhere to synthetic resin particles with smooth surfaces, and that synthetic resin foam with a roughened surface is suitable for microorganisms. It has been found to be desirable as a carrier.

Calcium carbonate,
An example of this is blending an inorganic substance such as Merck, barium sulfate, etc. into a synthetic resin, and by this means it is possible to simultaneously adjust the specific gravity and increase the hydrophilicity of the powder.

Next, the method of the invention will be explained with reference to detailed drawings.

1 and 2 are explanatory diagrams showing embodiments of the device of the present invention, with FIG. 1 showing a circular device and FIG. 2 showing a square device.

3 and 4 are plan views of the respective devices.

The apparatus is mainly composed of an anaerobic biological treatment section 1, a waste water circulation starting section 2, and a granular material circulation section 3.

Wastewater to be treated, that is, raw water, is introduced into the apparatus through a raw water introduction pipe 4.

The anaerobic biological treatment section 1 is filled with floating powder in water with microorganisms attached to its surface, and uses wastewater introduced as a downward flow and gas generated by the anaerobic biological reaction as a starting source. The recycled wastewater is fluidized to form a fluidized bed.

That is, the gas generated in the sealed tank is collected and supplied to the wastewater circulation flow starting section 2, where the wastewater is lifted up to create an upward flow, and is poured into the upper part of the anaerobic biological treatment section 1. The flow is averaged by the distributor 6, and the raw water flows in the anaerobic treatment section 1 as a downward flow.

Note that mechanical means such as an impeller and a pump may be provided in the waste water circulation starting section 2 and used together, or these mechanical means may be used alone.

When the raw water passes through the anaerobic biological treatment section 1 as a downward flow, it comes into contact with powder particles on the surface of which anaerobic or facultative anaerobic microorganisms are attached, causing an anaerobic or facultative anaerobic microbial reaction (main In the invention, anaerobic means both anaerobic and facultative anaerobic).

That is, the organic matter contained in the raw water is decomposed and gasified (methane fermentation of the organic matter or nitrogen gasification by denitrification of nitric acid and nitrite), and the generated gas is released into the wastewater in the form of bubbles.

Note that due to the adhesion of the generated gas, the apparent specific gravity of the powder particles decreases, and the floating property increases.

Therefore, the fluidized bed formed by the downward flow of wastewater is in better condition.

(The raw water is purified and taken out from the bottom T of the device,
The treated water is discharged from the system as treated water through the treated water outlet pipe 8.

On the other hand, some of the treated water and raw water pass through the powder circulation section 3 and flow into the anaerobic biological treatment section 1 .

At this time, the powder and granules separated from the processing section are transferred to the circulating flow starting section 2.
, further passes above the distributor 6, enters the powder circulation section 3, and returns to the anaerobic biological treatment section 1 again.

This circulation of the granular material A is actually carried out continuously, and a transport bed is formed.

When the granular material passes through the circulating flow starting section 2, some of the attached microorganisms are detached and remain on the water surface above the distributor, but the apparent specific gravity of the granular material at this time is due to the detachment of the microbial film. Because of this, it becomes smaller.

Therefore, in order to reintroduce this powder into the anaerobic biological treatment section 1, the flow rate must be higher than that required to form a fluidized bed.
To be more precise, a velocity higher than the terminal velocity of the particles is required.

Therefore, using an apparatus as shown in FIG. 6 (depth 1001000) and using air as gas, the flow velocity of the water flow in each part of the apparatus was investigated, and the following results were obtained.

As is clear from this result, the flow velocity in the part (2) furthest from the aeration section is the second highest after the water surface velocity in (2).

Furthermore, the flow velocity in each part is not constant. In the present invention, as a method for introducing powder into the anaerobic biological treatment section by utilizing the phenomenon of obtaining different flow rates, as described above, the powder connecting the upper part of the distributor and the anaerobic biological treatment section is introduced. A granule circulation section is provided.

In this way, the granular material reaches the remote part due to the water surface flow flowing at high velocity, and then the granular material can be easily introduced into the anaerobic biological treatment section at the flow rate of the remote part.

The device of the present invention has the lower end of the partition wall that partitions the inside of the processing tank placed above the bottom of the tank, and the upper end placed below the top of the tank to connect each part of the tank, and furthermore, the entire tank is brought into contact with outside air. It is a closed type to prevent it from happening.

For details inside the device, first refer to distributor 6.
It is desirable that the distance between the water surface 11 and the water surface 11 be 50 mm or more.

There is no particular limit on the maximum distance, but considering the ease of cleaning the surface of the distributor 6, it is approximately 500 m.
It is appropriate to set it to less than m.

The preferred distance for normal practice is 100-300 mm.

The aperture ratio of the distributor 6, that is, the ratio of the aperture area to the total area of the distributor, is in the range of 0.5% to 15%, preferably 2 to 8%.

There is no particular restriction on the type of distributor, and for example, a single or double perforated plate as shown in FIG. 5 may be used.

Next, the upper end 10 of the powder circulation section 3 is approximately 50 mm above the water surface 11.
By setting the position at a distance of ~100 mm, it is possible to efficiently take in and circulate the powder floating on the water surface.

On the other hand, the lower end of the granular material circulation section 3 may be placed in the fluidized bed in the anaerobic biological treatment section 1, or may be directed toward the lower part of the fluidized bed or the bottom of the tank.

In the former case, there is an advantage that the circulating water undergoes anaerobic decomposition, while in the latter case, it cannot undergo anaerobic decomposition, but if solids such as sludge are deposited at the bottom of the tank, stirring It is effective in floating these objects and preventing them from depositing.

Note that the desirable area of the granular material circulation section is within 20% of the area of the distributor openings.

In order to collect the gas generated by the anaerobic reaction, a hood 12 is provided at the top of the device to seal the device.

As mentioned above, a part of the generated gas passes through the pipe 14 and is returned to the diffuser 5 in the apparatus by the compressor 13 for starting the circulating flow.

Other generated gases are extracted from the pipe 15, and if the gas can be effectively used, it is stored in a storage tank or the like for use.

Note that although it is possible to perform methane fermentation etc. with one device of the present invention, two or more devices can be used in combination if desired.

According to the method and apparatus of the present invention, anaerobic biological treatment of wastewater can be carried out in a stable manner over a long period of time.

Next, the present invention will be explained in detail with reference to examples.

EXAMPLE Using the apparatus shown in FIG. 2, anaerobic biological treatment of wastewater at the outlet of a human waste septic tank was carried out.

The outline of the device and its constituent materials as well as the experimental conditions are as shown below.

Anaerobic biological treatment equipment: Made of polyvinyl chloride resin, sealed square tank equipment Total volume: 330 (L) x 100 (W) x 40
0(H)213.21 Fluidized bed volume: 250(L) x 100(W) x 25
0 (H) = 6.25A Powder filling amount = 3.51 Powder filling amount Foamed polypropylene containing 10% talc with rough surface Powder shape: 2.5 (φ) x 3 (L) Powder specific gravity: 0.75 (dry), 0.88 (wet) Distributor hole diameter: 10 mm Number of distributor holes = 16 Distributor hole total area: 12.56cyy'
c Powder circulation part area: 1.23ffl (1/2B pipe)
Generated gas was also supplied to start the circulating flow.

The amount of gas supplied was adjusted so that the expansion of the fluidized bed was 1.5 times the height of the static bed.

Activated sludge was used as a seed culture for anaerobic microorganisms to be attached to the powder surface.

The temperature was controlled at 20°C during the entire experiment.

The experimental results are shown below. It was two months after the start of the experiment that the gas generation reached a nearly steady state.

As can be seen from the experimental results, the anaerobic microbial treatment of the present invention exhibits high BOD removal efficiency and gas generation at high BOD loads.

In addition, the fluidized bed volume in the example is 6.254, and the inflow raw water amount is 12 to 21/hr, and the residence time is 30 minutes to 3 hours.

Considering that the residence time of ordinary anaerobic methane fermentation is several days to several tens of days, it will be understood that the method and apparatus of the present invention are extremely superior.

The composition of the generated gas was on average 66.8% methane, 27.8% carbon dioxide, 2.1% nitrogen gas, 2.7% hydrogen, etc.

[Brief explanation of the drawing]

1 and 2 are explanatory diagrams of embodiments of the device of the present invention, with FIG. 1 showing a circular device and FIG. 2 showing a square device. FIGS. 3a and 3b and 4a and 4b are plan views, respectively. Figure 5 a, b. C is an explanatory diagram showing an aspect of the distributor. FIG. 6 is an explanatory diagram of an experimental aeration tank. 1...
Anaerobic biological treatment section, 2... Circulating flow starting section, 3.
... Powder circulation section, 4 ... Raw water conduit, 5
... Diffusion device, 6 ... Distributor 18 ... Treated water discharge pipe, A ...
・Powder material.

Claims (1)

[Claims] 1. The specific gravity of the microorganisms attached to the surface is lower than that of water;
The anaerobic system is filled with powder and granules that float on water, and above which is installed a distributor for wastewater, which is a board that prevents the powder and granules from passing through and floating slightly below the water surface. By introducing the wastewater into the biological treatment section as a downward flow, and collecting and circulating the gas generated by the anaerobic biological reaction in the treatment section, the water in the biological treatment tank is made into a circulating flow. In an anaerobic biological treatment method for purifying granular material by making it into a fluidized bed and bringing it into contact with wastewater, a granular material circulation section is provided that communicates the upper part of the distributor with the lower part of the anaerobic biological treatment section, An anaerobic biological treatment method for wastewater, characterized in that the granular material leaving the anaerobic biological treatment section is returned to the anaerobic biological treatment section by passing through a circulating flow starting section and the granular material circulation section. 2 The inside of a closed tank for anaerobic biological treatment of wastewater (a
) A circulating flow starting part that collects and circulates gases generated by anaerobic biological reactions and starts the wastewater as an upward flow; It is filled with floating powder and granules, and above it, and slightly below the water surface, is installed a distributor, which is a plate material that prevents the powder and granules from passing through and floating, and which allows wastewater to pass through. an anaerobic biological treatment section that brings the wastewater flowing in a downward flow into contact with the granular material in a fluidized bed state; A wastewater wastewater system, characterized in that it is formed of a communicating part for circulating powder and granules, and is equipped with a tank in which each part is connected upwardly and downwardly, a pipe for introducing wastewater into the tank, and a pipe for extracting treated water from the tank. Anaerobic biological treatment equipment. 3. The device according to claim 2, which employs mechanical means as a means for forming a circulating flow in the water in the tank. 4 The lower end of the partition wall that partitions each part of the tank is located above the tank bottom, and the upper end is located below the top of the tank, thereby making the various parts of the tank communicate with each other. Device.