JPH0771675B2 - Cleaning method of packing material layer in fixed bed type anaerobic reactor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention treats sewage containing relatively high concentration of organic impurities such as sewage and industrial wastewater by an anaerobic methane fermentation reaction. In a fixed-bed type anaerobic reaction tank in which a packing material having a large porosity is packed in layers to form a fixed bed, sewage is circulated and digested by the action of anaerobic microorganisms adhering to and growing on the packing material surface. , A cleaning method for removing excess microorganisms that cause clogging of a fixed bed from the surface of a packing material.

(Prior Art) The fixed bed type anaerobic reaction tank is large on an industrial scale and has a tank height and a tank diameter of about 10 m, and a fixed bed layer height of 6 to 11 m (JP-A-57-110392). No.). Therefore, it is necessary for the filler that forms the fixed bed to have a strength that can withstand the stacking weight and to have a relatively large surface without hindering the passage of water, gas, and sludge, and the porosity is about 95%. To do. Fillers of various materials and shapes such as plastic or ceramic corrugated sheet material, cage material, ring material, and flower material are generally used (No. 44-14682, No. 63-21316). No.).

When the treatment operation is performed for several tens of days while properly acclimatizing with seed sludge, anaerobic microorganisms adhere to the surface of the filling material and grow, which enables stable treatment, but good treatment results are obtained. It is empirically known that the porosity at 60 to 80%. However, if the treatment is continued for a long period of time, the microbial membrane that grows on the surface of the packing material gradually thickens as the wastewater is purified, and a part of the microbial membrane naturally flows out to the treated water system, but the microbial membrane as a whole does not Due to the proliferation, the porosity of the packing material is reduced, the fixed bed is clogged, and the treatment efficiency is deteriorated.

In this case, in order to detect the degree of clogging, measure the porosity in the fixed bed by a method such as introducing various tracers and measuring the residence time, and restore the porosity within a certain range at an appropriate time. The packing material layer is washed to forcibly peel off the microorganism adhesion film, and the sludge that has peeled off is discharged to the outside of the reaction layer.

As a method for cleaning a fixed bed of a large-sized fixed bed type anaerobic treatment tank of this type, backwashing with water, which is generally performed in a filter, requires a heavy load and is difficult to apply. Japanese Unexamined Patent Publication (Kokai) No. 57-110392 mentioned above discloses that methane gas generated in a tank is introduced under a fixed bed for gas cleaning. Since it is anaerobic, it is possible to perform gas cleaning using N ₂ gas.

(Problems to be Solved by the Invention) In the conventional methane and N ₂ gas scrubbing method, the scrubbing gas rising over the high bed height of the fixed bed repeats splitting each time it encounters each packing material, and thus spreads. Since it is considered that the gas flow rate will rise, it is thought that it is sufficient to distribute gas evenly under the fixed bed and blow it after backwashing water with air in the filter. m ³ /
It is said that sludge can be peeled off if the amount) is greater than the required backwash strength. This gas flow rate is considered to be about 0.15 to 0.2 m ³ / min · m ² although it varies depending on the individual application conditions.
However, it was found that there are many cases in which the porosity of the fixed bed does not recover at this gas flow rate in an industrial-scale actual device. On the other hand, in the measures that simply increase the gas flow rate,
A large-capacity fan and air-blowing equipment are required, resulting in excessively expensive equipment, and with the situation that adhered microorganisms are exfoliated excessively, the sewage treatment capacity is reduced and the quality of treated water deteriorates. It cannot be a solution.

Therefore, since the effectiveness of the gas cleaning method is questioned, various means for removing the microorganisms adhering to the filler, which are considered to have applicability other than gas cleaning, were investigated. As a result of this study, a method of vibrating the fixed bed filler using water in water, an ultrasonic cleaning method, and a method of lowering the water level in the reaction tank to sprinkle water from the upper part of the fixed bed were considered. Although it may have the effect of removing microorganisms, it requires large-scale equipment and excessive energy input due to the large fixed bed of industrial scale equipment and the enormous amount, number and bulk of packing materials. It takes a lot of time to set up, and the chemical cleaning method has a problem that the microorganisms remaining in the filling material have aftereffects and the activity is reduced, so that the removal of adhered microorganisms is effectively removed. It turned out that there was no viable way to do it to an appropriate degree and economically.

In accordance with the above, the present invention relates to the removal of adhered sludge from the filler layer of the fixed bed type anaerobic reaction tank by returning to the gas cleaning method, improving it developmentally, and applying it to an industrial scale apparatus. It is an object to establish a technical method that is effective for the proper removal of attached microorganisms and does not require a large facility cost.

(Means for Solving the Problem) The inventors of the present invention repeated the examination and experiment on this problem, and as a result, in an industrial scale fixed bed type anaerobic reaction tank, the clogging of the fixed bed may not occur uniformly over the entire area. However, since the fixed bed spreads widely, uneven distribution of sewage flow and channeling tend to occur locally, and the tracer detection means can detect local clogging. Is difficult, and the cleaning gas sucked into the water from the nozzle at the time of gas cleaning does not spread much because it uses a filler with a large porosity, rather it becomes a rod-like focused upflow of submerged bubbles and is fixed. Findings that do not exist in the prior art, such as a situation in which it passes through the floor, and therefore, the area where the detachment of the adhered microbial film can occur due to the cleaning action of the nozzle blown out from one nozzle is localized. Got

Based on these findings, the present invention effectively performs the exfoliation of the microbial membrane in the affected area by the cleaning action of the gas blown out from one nozzle and does not excessively exfoliate the microbial membrane in the fixed bed. If it is carried out sequentially over the entire area, recovery from clogging of the fixed bed will be achieved without fail, and the air volume for gas cleaning and the facility load on the piping system will be reduced, which will reduce the time and place of local movement. It was made based on the technical idea. Moreover, it has been found that, as a condition for enabling this, the cleaning gas flow rate per nozzle is determined and the nozzle arrangement pitch of the cleaning gas supply pipe system under the fixed bed is determined. As a result of experiments, it was confirmed that the nozzle pitch was selected to be in the range of 500 to 1100 mm and the cleaning gas air flow rate per nozzle was required to be 0.6 m ³ / min or more. Further, in response to this air volume, the cleaning gas piping system has lateral pipes arranged in parallel, nozzles are arranged in rows on the lateral pipes, and if gas cleaning is performed for each lateral pipe, the air volume required for a period of time can be met. It was confirmed that the Juan point can be kept to a reasonable limit.

Taking the above into consideration, the method for cleaning the filler layer in the fixed bed type anaerobic reaction tank of the present invention, as a configuration, removes impurities from wastewater such as industrial wastewater and sewage, so that the porosity in the closed tank is increased. In the anaerobic methane fermentation treatment in which the sewage is unidirectionally circulated and circulated through the fixed bed formed by packing the large packing material in a layered manner to bring it into contact with the anaerobic microorganisms adhering to the packing material, 500 below the fixed bed. Cleaning gas was blown into the water with a flow rate of at least 0.6 m ³ / min per nozzle from nozzle groups arranged with a pitch interval of ~ 1100 mm to recover from the clogging state through a gas upflow to a fixed bed in the water. It is characterized by

(Operation) Hereinafter, the operation of the method of the present invention will be described based on experimental results and the basis for limiting numerical values.

FIG. 1 shows a side view of the attached sludge peeling experiment device. Diameter
1700mm, 4000mm height tank (1) lower layer 3000mm height is filled with new filler to make a simulated layer (2), on top of which one layer of sludge adhered filler is placed and dimensioned as shown in Fig. 2. Then, the sample was sandwiched between the grids (3) and (3) to form a thin sample layer (4) and a new filler was filled on the sample layer (5) to form a dummy fixed bed (6) to form a dummy fixed bed (6). In the peeling experiment, the dummy fixed bed was immersed in water, and methane and air equivalent to N ₂ were blown from the blower (7) through the gas flow meter (8) through one nozzle (9) at the center under the fixed bed. After the time, 9 pieces of 300 mm square position, 16 pieces of 600 mm square position, 900 m of the sample layer (4)
Twelve sample fillings at the m-square position were taken out and weighed to calculate the sludge peeling rate (%).

According to the observation, the expansion range of the gas upflow (10) hardly changed even when the air volume was increased, and the diameter was about 400 mm, and it was found that an effective separation action can be expected only in this range. .

Fig. 3 shows the experimental results, where the gas flow rate per nozzle (m ³ /
(Min) and the sludge separation rate (%) on the vertical axis.

From now on, effective peeling will be performed at the 300 mm square position, but 600 mm
It is known that sufficient peeling is not performed at the positions of mm square and 900 mm square. If the sludge removal rate of 40 to 60% is a rough guideline,
The effective range is 0.6 to 1.1 m ³ / min per nozzle at 300 mm square position.

For comparison, as shown in Fig. 4, four nozzles were placed at 800 mm square corner positions, and the sample filler was placed on the upper side of each in a 300 mm square arrangement, and a peeling experiment was conducted with 1/4 of the above air volume per nozzle. It was found that the peeling rate was about 11 to 17% in all cases, and it was found that the peeling was not sufficiently effective even at a 300 mm square position with a small gas flow rate.

Next, in gas cleaning, the vertical liquid flow velocity induced by the upward flow of gas directly acts on sludge separation, so the liquid flow velocity distribution was confirmed using a small propeller rotating anemometer for confirmation. Examined. Figure 5 shows the results, with the gas flow rate per nozzle (m ³ / min) as a parameter, the radial distance from the nozzle position on the horizontal axis (mm) and the vertical liquid flow velocity on the vertical axis (cm / sec). (However, the apparent velocity is due to the gas-liquid mixed flow). From this, it was found that the air flow rate per nozzle was 0.68 and 1.13 m ³ / min, and the liquid flow velocity was sufficiently high at 25 to 32 cm / sec or more within a radius of 200 mm.

The reason why the ascending gas flow (10) is concentrated in the diameter range of 400 mm can be explained by the fact that the high-speed central flow has an effect of drawing the surrounding flow from the flow velocity distribution. And the effective stripping action range confirmed by these experiments is this diameter 400 mm range, but there is a spread of the influence action range around it, and it is not necessary to completely strip sludge, and in the actual device The upper limit of the nozzle pitch is 11 depending on the implementation results.
00mm. If the lower limit is less than 500 mm, it will be disadvantageous in terms of equipment cost.

Also, it is known from these experiments that the gas flow rate per nozzle needs to be higher than the lower limit of 0.6 m ³ / min, and there is no definite limit on the upper limit, but in terms of economy, excessive peeling does not occur. In order to do so, a reasonable gas flow rate known from experiments should be used.

(Example) FIG. 6 shows an example of the arrangement of a gas cleaning nozzle under a fixed bed of an industrial scale apparatus for carrying out the method of the present invention. In this pipe system, lateral tubes (11) are arranged in parallel, and nozzles (12) are arranged on each lateral tube (11) at a pitch of 500 to 1100 mm. It is desirable to set the pitch interval between the lateral tubes to this degree, but it was possible to sufficiently implement even if it was made slightly larger than this.

In the method of the present invention, the characteristic that sludge separation is locally performed in the affected area of the nozzle is utilized, and gas is supplied to one lateral pipe, and when the sludge separation by gas cleaning by the group of nozzles is completed, the valve is switched. It is possible to perform gas cleaning with the next lateral tube, and the gas flow rate required at one time is only the number of nozzles of that lateral tube, so it is not necessary to use a fan with a very large capacity and a high cost. I'm done.

In practice, the nozzle thickness loss ΔP (mm H ₂ O) is expressed by the following equation: ΔP = 0.34Q ^1.2・ d ^−3.0 [where Q: gas flow rate per nozzle (m ³ / sec) d: nozzle diameter (m )] If it is set to 80 mm H ₂ O or more, gas can be blown from each nozzle of the lateral tube with a uniform air flow.

Applying the method of the present invention to an industrial scale microbial contaminated adherent filler, there is an influence of the type of the filler, the property of the microbial sludge, the difference in the adhered amount, etc., but achieves a sludge peeling rate of 43.8 to 85.4%. I was able to.

(Effects of the Invention) As described above, according to the method of the present invention, even in an industrial scale fixed bed type anaerobic reaction tank, the sludge peeling removal for recovering the fixed bed from clogging can be reliably performed by gas cleaning. It is possible to realize the stable operation of the processing device and the improvement of the processing efficiency by carrying out the clogging detection timing or periodically, and at the same time, the facility does not require much cost.

[Brief description of drawings]

Fig. 1 is a vertical sectional side view of the attached sludge peeling experiment device, Fig. 2 is a plan view showing the arrangement of the sample filler in the sample tank, Fig. 3 is a table showing the peeling experiment results, and Fig. 4 is a sample. FIG. 5 is a plan view showing another arrangement of the packed bed, FIG. 5 is a chart showing the apparent liquid flow velocity distribution in the vertical direction, and FIG. 6 is a gas cleaning nozzle piping system under a fixed bed of an industrial scale apparatus for carrying out the method of the present invention. It is a top view shown. (1) ... Tank, (2) ... Simulated layer, (3) ... Grid, (4) ... Sample layer, (5) ... Presser simulated layer, (6)
…… Dummy fixed bed, (7) …… Blower, (8) …… Gas flow meter, (9) …… Nozzle, (10) …… Gas upflow,
(11) …… Lateral tube, (12) …… Nozzle.

Claims (1)

[Claims] 1. In order to remove impurities from sewage such as industrial wastewater and sewage, the sewage is unidirectionally circulated and circulated through a fixed bed formed by layering a packing material having a large porosity in a closed layer. In the anaerobic methane fermentation process in which anaerobic microorganisms adhering to the packing material are contacted,
The cleaning gas is blown into the water with an air flow of at least 0.6 m ³ / min per nozzle from a group of nozzles arranged with a pitch gap of 0 to 1100 mm so as to recover from a clogging state through a gas upward flow to a fixed bed in the water. A method for cleaning a packing material layer in a fixed bed type anaerobic reaction tank, characterized in that.