JP2869656B2 - Sewage purification method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for purifying sewage, and more particularly to a method for purifying sewage by purifying sewage by aerobic upward-flow fixed-bed biological treatment.

[Conventional technology]

Aerobic upflow fixed-bed biological treatment removes BOD in treated water by implanting microorganisms by introducing both treated water and air under the fixed bed and passing through the gap in the fixed bed by gas-liquid mixing. It is a way to do it. For the fixed bed, a porous granular substance is usually used so that microorganisms can be easily attached.

 This processing method has the following features.

That is, 1) the air becomes fine bubbles while passing through the fixed bed, so that the oxygen absorption efficiency is high.

2) Since the introduced air comes into contact with the water to be treated having a high BOD concentration first, the removal rate is extremely high.

3) Generally, cellulosic SS is different from soluble organic matter.
Although oxidative decomposition by biological treatment is difficult, SS is captured by the filtration function of the fixed bed, so that treated water that does not require precipitation separation can be obtained.

4) Compared to the conventional activated sludge method, the treatment time is shorter, and therefore, for the same treatment capacity, the volume, that is, the occupied area is much smaller.

5) When clogging occurs due to the filtration function,
Can be washed with water and air.

There are features such as.

However, in sewage treatment, generally, aerobic upflow fixed-bed biological treatment is not used, and the activated sludge method is exclusively used.

[Problems to be solved by the invention]

Looking at the recent treatment situation, the overcrowding in urban areas has become even more severe, and the amount of sewage to be treated has rapidly increased with this, and the current treatment facilities have fallen into a state where they cannot keep up with the increasing urban sewage. If this problem could be solved by the conventional activated sludge method, a vast site would be required to meet the future increase in sewage volume. However, since it is difficult to secure the density in the overcrowding, there is a demand for a treatment method that can provide sufficient facilities in existing premises and at the same time lower facility costs and running costs.

To solve this problem, the aerobic upflow fixed bed biological treatment is promising. However, municipal sewage contains cellulose-based suspended solids (SS) in total BOD (approximately 2
(00mg / l), it is 60-85% of the total. Therefore, if the aerobic upward fixed bed biological treatment is carried out, the SS adheres to the solid bed quickly and clogs in a few minutes. Can not. Therefore, although it has advantages, it is currently not generally used for sewage treatment.

Therefore, an object of the present invention is to provide a method for purifying sewage by making use of the advantages of aerobic upward-flow fixed-bed biological treatment.

[Means for solving the problem]

In order to solve the above problems, the present invention provides a method for purifying sewage, in which a coagulation and sedimentation treatment is performed in a first stage to reduce insoluble solids (SS) in sewage in advance by 75% or more, and then It is characterized by performing an aerobic upward flow fixed bed biological treatment.

The washing time of an aerobic upward fixed bed is usually about 15 to 30 minutes, but as the amount of insoluble solids (SS) contained in the water to be treated increases, the clogging pace increases and the number of washings increases. The greater the number of times, the more the operation is hindered. However, if the cleaning is performed at a rate of two to three days, the operation is not significantly affected. In order to keep this number of washings, it is desirable to remove insoluble solids (SS) that cause clogging as much as possible in the first-stage coagulation sedimentation treatment, and to keep the total BOD of the treated water at 80 mg / l or less. . In order to achieve this, it is necessary to remove at least 75% or more of insoluble solids (SS) contained in the sewage in the first-stage coagulation-sedimentation treatment. That is, based on a standard sewage having a total BOD of 200 mg / l, the SS content is 150 mg / l and the soluble BOD is
Contains 50mg / l. Therefore, if the removal rate of SS is set to 75% (this removal also removes 30% of the soluble BOD), the SS content remaining in the primary treated water is 150 × 0.25 = 38 mg / l, and the soluble BOD is removed.
Is 50 x 0.7 = 35 mg / l, and the total BOD of the primary treated water is 38 + 35
= 78 mg / l, achieving 80 mg / l or less.

In general, the coagulation-precipitation treatment includes a chemical coagulation method using a chemical agent and a biological coagulation method using a microorganism, and any of the present invention can be used. In chemical agglomeration, the amount of SS removed varies greatly depending on the combination and amount of coagulant,
If the addition amount is sufficient, a removal rate of about 95% can be expected,
It is not preferable to make it too large. First, the use amount of the chemical flocculant increases, and the running cost is affected. At the same time, the flocculant used needs to be treated as excess sludge, so that the treatment coverage increases. Therefore, the preferred removal range is
It is about 75-85%.

As the chemical flocculant, lime, iron chloride, polyaluminum chloride, water-soluble polymer and the like can be used. Further, in order to reduce the usage fee of the chemical flocculant, it is possible to reuse the excess sludge deposited in the settling tank. In this case, when a part of the excess sludge is returned to the coagulation tank to maintain the sludge concentration (MLSS) at 0.5 to 1 g / l, the amount of the chemical coagulant used can be minimized. In addition, if an inclined plate is provided above the precipitation tank, the amount of flocculant used can be reduced, and the SS removal rate can be improved.

On the other hand, when insoluble solids are removed by biocoagulation, air is blown from the bottom of the coagulation tank to maintain the oxidation-reduction potential (ORP) in the tank at about -50 mV to 0 mV, and at the same time, the excess discharged from the precipitation tank. A part of the sludge is returned to the flocculation tank to maintain the sludge concentration (MLSS) in the tank at about 1.5 g / l, the BOD volume load is ³ to 6 kg / m3 · day, and the sewage retention time is at least 40 minutes or more. It is desirable to process. By doing so, a removal rate of 75% is ensured, and the total BOD of the primary treated water can be reduced to 80 mg / l or less in the biocoagulation method as in the chemical coagulation method.

In the next step, aerobic upward flow fixed bed biological treatment, 1.
It is desirable to allow air to pass through the gaps of the fixed bed together with air from below the fixed bed in which porous particles having a diameter of 5 to 4 mm are stacked in a thickness of 2 to 3 m. As the porous particles, any particles may be used as long as they have a certain level of strength and microorganisms can easily adhere thereto. For example, sintered clay particles can be used. In this case, if the particle size is smaller than 1.5 mm, the head pressure increases, so the load of the feed pump for supplying the water to be treated becomes too large, which is inconvenient,
Exceeding m is not preferable because the capture of SS becomes insufficient.

The amount of process air blown with the primary treatment water is determined by the BOD to be treated and the concentration of ammoniacal nitrogen, and the efficiency of dissolving oxygen in the liquid. In the case of the present invention, the BOD is 80 mg / l
And ammonia nitrogen is about 15 mg / l, and the oxygen dissolution efficiency also depends on the water temperature. In the case of the present invention, since water and air are both gas-liquid mixed, a high efficiency of 20% to 40% is obtained. Hope,
A sufficient amount of air to be introduced is 1-2 Nm ³ per 1 m ^{3 of the} primary treated water. Undesirable the amount of air is not affected even treatment effect beyond the water 1 m ³ per 2 Nm ³ becomes a waste of energy.

The contact time is preferably at least about 12 minutes by adjusting the flow rate. If the superficial velocity is calculated assuming a contact time of 12 minutes and a fixed bed thickness of 2.7 m, the porosity of the fixed bed is approximately 50%, the volume occupied by air is approximately 3%, and the volume occupied by biofilm is approximately 2%. %, 2.7 x 0.45 x 60/12 = 6 m / hr.

Then, when the system is operated under such conditions for several days, a biofilm is formed on the surface of the fixed bed made of sintered clay particles. After a sufficient biofilm is formed, the total BOD of the incoming treated water is 80m
Since it is g / l or less, the BOD of the treated water is also treated to 20 mg / l or less. After about three days, the biofilm grows and becomes thicker, and the head pressure drop due to the fixed bed increases and the water flow decreases. At the same time, the air flow decreases and the fixed bed becomes clogged. Thereafter, the fixed bed is washed once every two to three days. Washing is carried out by introducing water temporarily storing treated water and washing air into the lower part of the fixed bed.At a flow rate of 10 to 15 m / hr that allows the porous particles to flow slightly, wash water and an appropriate amount of air are used. It can be restored by washing for 15-30 minutes. Since the wash water cannot be discharged as it is, it is returned to the raw water tank in front of the flocculation settling tank.

[Action]

The first-stage coagulating sedimentation tank and its associated equipment used in the present invention replace the first sedimentation tank used for general sewage treatment, and there is not so much difference in occupied area. However, the difference is very large in the second stage of biological treatment. For example, when treating sewage of 3,600 m ³ / day, if the superficial velocity is 5 m / hr and the contact time is 16 minutes, a biological treatment tank with a fixed bed thickness of 3 m and a cross-sectional area of 35 m ² will be required. , the activated sludge aeration apparatus normally method 500 to 700 m ²
In addition to the required area, about half the area of the aeration tank is required as the final sedimentation basin. Even if the raw water adjustment tank and other incidental facilities are taken into account, the present invention requires much less site area.

Also, as compared the amount of air, in the case of conventional activated sludge aeration apparatus, required air quantity of oxygen dissolution efficiency is 5-10% and is lower for the same raw water 1 m ³ per 4 to 8 m ³ is but, in the case of the present invention, since suffices treated water 1 m ³ per 1 to 2 nm ³ can reduce the power consumption required for the biological treatment almost 1/4. In addition, the running cost can be reduced to about 1/2 to 1/3 of the conventional cost even if necessary costs such as a chemical flocculant are included.

The concentrated sludge generated by the coagulation sedimentation process is digested,
It is dewatered and finally disposed of by incineration or landfill, but this is no substitute for the treatment of excess sludge in the ordinary activated sludge method. The purification method using a chemical flocculant has the disadvantage of increasing excess sludge, but has the advantage of easy dewatering of the sludge itself and is practical as such.
On the other hand, in the case of the purification method using biocoagulation, the amount of excess sludge generated is almost the same as that of the conventional method, but the disposal is easy because of good dehydration.

EXAMPLES Hereinafter, an aerobic upward-flow fixed-bed biological treatment plant having a processing capacity of 100 m ³ / day was designed and tested, and an example thereof will be specifically described with reference to the drawings. In the experiment, the coagulation sedimentation ability was higher than the above ability,
Part of the primary treated water was treated.

First, the apparatus used for the chemical flocculation and precipitation treatment will be described with reference to FIG. The illustrated raw water tank 1 has a capacity of 4 m ³ , and the raw water received here is almost quantitatively sent to the bottom of the chemical flocculation tank 3 by the raw water pump 2. The chemical flocculation tank 3 is a tank having a sectional area of 1 m ² and an effective height of 4.5 m, and a rectifying cylinder 4 having a diameter of 30 cm is provided therein in a non-contact state in order to make good contact with the chemical flocculant. . At the upper part of the cylinder 4, a stirrer 5 for generating an upward flow is installed.

The adjacent settling tank 6 has a sectional area of 1.6 m ² and an effective height of 4.5 m, and communicates with the chemical flocculation tank 3 at a position 2 m from the bottom. An inverted conical thickening section is formed at the bottom of the sedimentation tank 6 so that sludge can easily accumulate, and a sludge scraper 7 is disposed inside the thickening section. A discharge pipe 8 for discharging excess sludge is arranged at the bottom. An excess sludge pump 9 for discharging excess sludge to the outside of the system and a return pump 10 for returning a part of the sludge to the bottom of the chemical flocculation tank 3 are connected to the discharge pipe 8, and the sludge in the tank 6 is operated by the excess sludge pump 9 during operation. Is pulled out to a certain amount, and a part thereof is returned by the return pump 10. The amount returned is around 0.5% of the raw water flow. On the other hand, the inclined plates 11, which accelerate the precipitation of fine particles, are arranged at the upper part. Further, pipings 12a and 12b for charging the chemical flocculant are arranged above the chemical flocculation tank 3, and tanks 13a and 13b for storing the chemical flocculant are arranged at the starting point. And
The chemical flocculant stored here is supplied to the upper part of the chemical flocculation tank 3 at a constant ratio by a metering pump, not shown. The primary treated water that has passed through the overflow wall 14 of the settling tank 6 is sent to the aerobic upward-flow fixed-bed biological treatment described later.

Experiments were carried out using this apparatus with various combinations of coagulants and their amounts, and the results shown in Table 1 were obtained.
The flocculants used were iron chloride, polyaluminum chloride and anionic polymer flocculants. Each experimental data is 4
This is the average value of data taken for consecutive weeks.

Sludge concentrations of rotational speed 2rpm chemical flocculation tank 3 according sludge scraping machine combination and amount in Table 1 operating conditions the raw water flow rate 15~20m ³ / hr (350~700m ³ / day stirrer speed 150rpm chemical coagulants (MLSS) range 0.5-1 g / l Judging from these results, a desirable data example is Experiment No. 3 in consideration of the amount of excess sludge and the cost of the flocculant.

As a result, the conditions that can achieve SS removal rate of 75% or more and total treated water BOD of 80 mg / l or less are as follows: raw water flow rate is 15 to 20 m ³ / hr, polymer flocculant is 0.5 mg / l or more, and polyaluminum chloride is 10 mg / l. It was about 60 mg / l in the case of iron chloride.

Next, an apparatus used for the biocoagulation treatment will be described with reference to FIG. Since the apparatus itself is not much different from that used for chemical coagulation, the same parts are denoted by the same reference numerals, and only different parts will be described. The volumes of the raw water tank 1, the precipitation tank 6, and the biological flocculation tank 23 are the same as those used for the chemical flocculation treatment, and the sedimentation tank 6 adjacent to the biological flocculation tank 23 is located at the bottom of the biological flocculation tank 23. And the middle part of the settling tank 6. On the other hand, an air blowing nozzle 24 is disposed at the bottom of the biological flocculation tank 23 in place of the flow regulating tube 4. The start end of the nozzle 24 is connected to a compressor (not shown), and the oxidation-reduction potential of the biocoagulation tank 23 can be changed by changing the amount of air blown. A part of the sludge deposited at the bottom of the settling tank 6 and the sewage received by the raw water tank 2 are returned or supplied to the upper part of the biological flocculation tank 23 by the sludge return pump 10 and the raw water pump 2, respectively. It has become.

Also in this example, when an experiment was performed under the following conditions, the results shown in Table 2 were obtained. Each experimental data is the average of data taken for four consecutive weeks.

Operating condition the raw water flow rate 3~6m ³ / hr (70~140m ³ / day) Sludge concentration in the range -100 to + 100 mV biological flocculation tank redox potential of biological flocculation tank (ORP) (MLSS) 0.6~4g / l Residence time in the biocoagulation tank 50 min.Rotation speed of the sludge scraper 2 rpm As a result, the desirable conditions for achieving SS removal rate of 75% or more and total BOD of treated water of 80 mg / l or less are ORP −50 mV to 0 mV MLSS concentration 1 to 2.5 g / l residence time was found to be 40-60 minutes.

Next, an apparatus used for aerobic upward flow fixed bed biological treatment will be described with reference to FIG. The primary treatment water tank 31 is a tank for temporarily storing the primary treatment water treated in the previous stage, and has a capacity of 3
m is ^3. Then, the primary treated water stored here is supplied to the bottom of the aerobic upward-flow fixed-bed biological treatment tank 33 from the bottom of the tank using the primary treated water pump 32.

The aerobic upward-flow fixed-bed biological treatment tank 33 is a tank having a depth of about 5 m, and a filtration bed 34 is installed at a position about 1 m above the bottom,
A process air blowing nozzle 35 in contact with the upper part,
Nozzles 36, 37, which supply or jet water to be treated and washing water, and washing air, respectively, to the lower part of the filter bed 34.
38 are located. Air blow nozzle for process 35
The cleaning air nozzle 38 is connected to a compressor (not shown). The filter bed 34 is a partition through which water and air pass from below, but sand or porous particles do not pass from above. 20 at the top of filter bed 34
A 4-6mm diameter gravel is laid on the floor with a fixed floor of 3 cm.
9 are provided.

The fixed bed 39 has a sectional area of 0.5 m ² and a height of 2.7 m, and is filled with sintered clay particles having a diameter of 2 to 3 mm. An overflow wall 40 is provided at a position 1 m above the fixed floor 39, and the cross-sectional area of the overflow wall 40 is 1 m ² . The secondary treated water that has passed over the overflow wall 40 is sent to a treated water receiving tank 42 via a switching valve 41.
The switching valve 41 is normally directed toward the treated water receiving tank, but is switched to the raw water tank 1 when the fixed bed is clogged. The treated water receiving tank 42 functions as a tank for storing the washing water of the fixed bed 39, and therefore requires about twice the capacity of the aerobic upward flow fixed bed biological treatment tank 33. Therefore, the treated water receiving tank 42 has a capacity of 5 m ³ . An overflow wall 43 is provided at an upper portion thereof, and overflowed secondary treated water is discharged. On the other hand, the above-mentioned washing water nozzle 37 is connected to the bottom of the treated water receiving tank 42 via the washing pump 44.

When the primary treated water is treated by this apparatus, first, the switching valve 41 is switched to the treated water receiving tank 42 side, and then the primary treated water pump 32 and the process air nozzle 35 are operated. If clogging occurs, use the primary treated water pump.
32 and the process air nozzle 35 are stopped, the switching valve 41 is switched to the raw water tank 1 side, and then the cleaning pump 44 and the cleaning air nozzle 38 are operated. Washing for 15 to 30 minutes is sufficient.

When the primary treated water treated under the conditions of the preceding stage was purified using this apparatus under the following conditions, the results shown in Table 3 were obtained. In the table, the symbol C indicates a chemical flocculation treatment, and B indicates a biological flocculation treatment.

Operating conditions Treated water Primary treated water from which 75% or more of SS was removed in the preceding stage Treated water superficial tower speed 3-7 m / hr Contact time 10-25 min Air superficial tower speed 3-15 Nm / hr As a result, the total BOD was 20 mg / l or less. In addition, it was found that the condition that the operation period is long and the running cost is low is 1 to ² Nm ³ contact time 12 to 15 minutes per 1 m ^{3 of} air blown water.

[Effects of the Invention] As described above, according to the present invention, increasing sewage can be effectively treated using an aerobic upward-flow fixed-bed biological treatment that has not been conventionally used. In addition, the running cost can be reduced to 1/2 to 1/3 as compared with the conventional activated sludge method with the same processing capacity.

In addition, as a known example, there is an example using a downflow type in which the water to be treated descends, but the present invention is more advantageous than this. That is, in the downflow type, the SS is captured on the surface of the fixed bed and a large amount of biofilm is formed on the upper surface, so clogging is quick and the operation time is short, but in the upward flow, the SS is captured and bio- The operation time is long because the film is formed. Further, in the case of the downflow type, it is necessary to sufficiently perform aeration before the treatment, but in the case of the upward flow type, the gas-liquid mixture passes through the fixed bed, so that the oxygen absorption rate is high and the cost required for aeration can be reduced. .

[Brief description of the drawings]

1 to 3 show an apparatus used for carrying out the present invention. FIG. 1 is a schematic view of an apparatus used for chemical flocculation processing, and FIG. 2 is a schematic view of an apparatus used for biological flocculation processing. FIG. 2 is a schematic view of an apparatus used for aerobic upward-flow fixed-bed biological treatment. 1 ... raw water tank, 2,9,10,32,44 ... pump, 3 ... chemical flocculation tank,
4: Rectifying cylinder, 5: Stirrer, 6: Settling tank, 7: Sludge scraper, 8: Discharge pipe, 11: Inclined plate, 12a, 12b: Piping, 13a, 13b
… Chemical flocculant tank, 14,40,43… Overflow wall, 23… Biological flocculation tank,
24 ... air blowing nozzle, 31 ... primary treatment water tank, 33 ... aerobic upward flow fixed bed biological treatment tank, 34 ... filtration bed, 35 ... process air nozzle, 36 ... treated water nozzle, 37 ... washing nozzle, 38 ... Cleaning air nozzle, 39 ... Fixed floor, 41 ... Switching valve,
42… Treatment tank.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) C02F 3/06 C02F 1/52 C02F 9/00

Claims (1)

(57) [Claims] (1) In purifying sewage, a coagulation / sedimentation treatment is performed in a first stage to remove insoluble solids (SS) in the sewage in advance.
A method for purifying sewage, comprising subjecting a fixed-bed biological treatment to an aerobic upward flow after reducing the amount by 75% or more.