JP5282767B2 - Odor generation prevention method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an odor prevention method which effectively prevents occurrence of odor in the whole sludge treatment process after a sludge thickener tank, specifically prevents odor problems of hydrogen sulfide, methyl mercaptan, etc., corrosion of electric facility due to hydrogen sulfide, corrosion of an apparatus due to sulfuric acid generated by biological oxidation of hydrogen sulfide, which are generated in each process from the occurrence of sludge slurries (outlet of the sludge thickener tank) in a sewage treatment plant etc. to a sludge storage tank, a sludge dehydrator, and dehydrated cake conveyance-storage equipment. <P>SOLUTION: In the method for adding nitrite to the sludge in the sludge storage tank to prevent the occurrence of odor from the sludge, the adding amount of the nitrite is varied so as to intensively add nitrite several times a day. Therefore, remaining nitrite ion concentration of the sludge in the sludge storage when an hour passes after the time of completion of each intensive addition is kept to be &ge;20 mg/L. <P>COPYRIGHT: (C)2011,JPO&amp;INPIT

Description

  The present invention relates to a method for preventing odor generation in the entire sludge treatment process after the sludge concentration tank, and more specifically, from generation of sludge slurry (sludge concentration tank outlet) in a sewage treatment plant to a sludge storage tank, a sludge dehydrator, Effective prevention of malodorous problems such as hydrogen sulfide and methyl mercaptan generated in each process leading to the transport and storage facilities of dehydrated cake, as well as corrosion of electrical equipment caused by hydrogen sulfide and equipment corrosion caused by sulfuric acid produced by the biological oxidation of hydrogen sulfide The present invention relates to a method for preventing odor generation.

Various types of sludge are generated during the treatment of organic wastewater from sewage treatment plants, human waste treatment plants, food and pulp and paper mills, etc., and in these sludge treatment processes, problems caused by the generation of odors as shown below have occurred. Yes.
In each process from the outlet of the sludge concentration tank to the sludge storage tank and the sludge dewatering machine, malodorous substances mainly composed of hydrogen sulfide present in the sludge are volatilized (dissipated), and the working environment is deteriorated. At the same time, corrosion of electrical equipment due to volatilized hydrogen sulfide, and equipment corrosion due to sulfuric acid produced by biooxidation of hydrogen sulfide also occur.
Furthermore, in the process leading to the dewatered cake transport / storage facility, the rot progresses during storage and storage, and malodorous substances, mainly methyl mercaptan, are generated by the decomposition of the sulfur-containing protein.

  Therefore, the present applicant (etc.) has applied sludge on the basis of a method for preventing the generation of hydrogen sulfide based on microorganisms by making nitrite ions present in the growth environment of the microorganisms (Japanese Patent Laid-Open No. 57-187099). Various technical proposals such as a method (Japanese Patent Application No. 12-215640) in which the effect is remarkably enhanced by finding a method to be used as a treatment odor prevention and further adjusting pH and the like have been made.

Japanese Patent Laid-Open No. 57-187099 Japanese Patent Application No. 12-215640

  Many of the above proposals are methods for adding nitrite to a sludge storage tank to prevent the generation of odors such as hydrogen sulfide and methyl mercaptan in the storage tank and the sludge dehydration process. Although it was able to obtain good results, it faced the problem that its effect gradually decreased during continuous use of nitrite. For this reason, in order to maintain the effect of preventing odor generation, the amount of nitrite added may need to be increased to more than twice the initial amount of nitrite application, but the effect of preventing odor generation is still insufficient. was there.

  The present inventors fundamentally reviewed the method of “adding a drug proportionally or continuously in accordance with the inflow of sludge”, which is a conventional and natural drug addition method, By adding intensively several times a day, an increase in the decomposition rate due to sludge of nitrite used as a drug is prevented and further reduced, resulting in an extremely excellent odor generation preventing effect, It came to discover the effective addition method which can also reduce the amount of chemicals used.

According to the knowledge obtained after intensive studies by the present inventors, it has been found that the above-mentioned problem is based on the following phenomenon.
When nitrite is added to the sludge, the nitrite becomes nitrite ions in the sludge. First, the reducing substance in the sludge reacts with the nitrite ions, and the nitrite ions are consumed rapidly. Along with this reaction, reducing substances in the sludge are also consumed, and the reducing substances are almost completely consumed in about one hour. Thereafter, nitrite ions are gradually degraded by microorganisms. Although it depends on the type of sludge, the consumption rate of nitrite ions by the reducing substance is about 50 mg / L · hr, and is hardly consumed after the first hour. The consumption rate of nitrite ions due to microbial activity is about 10 to 20 mg / L · hr. However, when a small amount of nitrite is continuously supplied, the nitrite ion decomposition ability of the sludge increases with time, and a so-called habituation phenomenon occurs. This is presumably because microorganisms in the sludge have increased resistance to nitrite ions, or microorganism species with particularly high nitrite ion resolution and high resistance have proliferated. Due to such a habituation phenomenon, the consumption rate of nitrite ions by microorganisms gradually increases, exceeding 30 mg / L · hr and sometimes exceeding 50 mg / L · hr. Such an increase in the consumption rate of nitrite ions occurs remarkably when the average sludge residence time is as long as about 24 hr, and it is unclear when the sludge average residence time is as short as about 6 hr, suggesting the above-mentioned inference.

  Therefore, as described above, when nitrite is intensively added several times a day, microorganisms in the sludge are temporarily exposed to high concentrations of nitrite ions, so the microorganisms are damaged, The decomposition rate of nitrite ions can be greatly reduced. After this, even if the addition of nitrite is stopped or the amount added is reduced, the amount of decomposition is small, so that nitrite ions are likely to remain in the sludge, making it a virtuous cycle for odor prevention treatment. . Therefore, the concentration of nitrite during intensive addition so that the consumption rate after 1 hour after nitrite addition of nitrite ion is low (less than 10 mg / L · hr, preferably less than 2 to 8 mg / L · hr). It is necessary to adjust the addition, and this manages that the residual nitrite ion concentration in the sludge in the sludge storage tank is kept at a high level (20 mg / L or more) after 1 hour from the end of each concentrated addition. Is achieved by doing

That is, the present invention provides novel whereas the sludge is turned more than once a day, the sludge of the sludge reservoir sludge replaced by sludge staying is discharged sent to a dehydrator, the residence time of the sludge Is a method for preventing the generation of odor from sludge by adding nitrite by an addition process corresponding to the above, and the consumption rate after 1 hour of nitrite ion addition due to microbial activity is 10 mg / L · hr In order to maintain the concentration below, the concentrated addition of nitrite to the sludge is 2 to 2 per day so that the residual nitrite ion concentration of the sludge in the sludge storage tank after 1 hour from the end of the addition becomes 20 mg / L or more . Odor generation prevention method characterized by intermittently repeating a state of a predetermined addition rate at the time of concentrated addition and a state where the addition rate at the end of addition is 0 in a range of 12 times ,
Is to provide.
Addition corresponding to the sludge retention time to sludge in the sludge storage tank where new sludge is introduced at least twice a day, while the sludge staying in the sludge is sent to the dehydrator and discharged. A method of adding nitrite according to the process to prevent the generation of odor from sludge, and maintaining the consumption rate of nitrite ions due to microbial activity after less than 10 mg / L · hr after the end of nitrite addition. Therefore, concentrated addition of nitrite to sludge in the range of 2 to 12 times per day so that the residual nitrite ion concentration of the sludge in the sludge storage tank after 1 hour from the end of the addition is 20 mg / L or more A high addition step of intermittently repeating a state of a predetermined addition rate at the intensive addition and a state where the addition rate is zero at the end of addition, and addition at the end of addition in the high addition step The speed is 0 A low addition step of adding nitrite so as to fill the state, and the sum of the daily addition amount of nitrite of the high addition step is 2 of the sum of the daily addition amount of nitrite of the low addition step Odor generation prevention method characterized by being more than doubled,
Also provide
As a preferred mode for carrying out this,
Odor generation prevention method characterized in that the ratio of the sum of the amount of nitrite added per day in the high addition step and the amount of total nitrite added per day is 2/3 to 1,
It is good.
Furthermore, as a method for preventing odor generation of sludge conditioned by nitrite ions,
Odor generation prevention method characterized by performing any of the above after suspending the addition of nitrite for 1/2 or more of the average residence time of sludge in the sludge storage tank,
Can also be provided.

  Although nitrite is added by the conventional method of adding chemicals in proportion to the amount of inflow of sludge in a proportional or continuous manner, initial effects are obtained, but gradually. Although the amount of nitrite required increases and becomes inappropriate, the odor generation prevention method of the present invention performs addition of nitrite intermittently or stepwisely, and after 1 hour has elapsed. By controlling the residual nitrite ion concentration, even if the total amount of nitrite added remains the same or reduced, the effect of preventing the generation of hydrogen sulfide and methyl mercaptan can be demonstrated stably, and the odor problem caused by these , And electrical equipment corrosion due to hydrogen sulfide, and equipment corrosion due to sulfuric acid generated by biological oxidation of hydrogen sulfide can be effectively prevented.

  In addition, in sludge treatment systems where the required amount of nitrite has increased and the effect of preventing odor generation has declined, the addition of nitrite has been suspended after suspending the addition of nitrite for 1/2 or more of the sludge retention time in the sludge storage tank. By carrying out the addition, the effect of preventing odor generation can be quickly recovered.

(A) It shows typically the addition pattern of nitrite in this invention, Comprising: It is the graph which shows an example of the intermittent injection | pouring in this invention, (b) The graph which shows an example of the level | step difference injection | pouring in this invention. (A) Experimental flow of Comparative Examples 1 to 3 in the laboratory test 1 in the example, (b) Experimental flow of Examples 1 to 3. It is the schematic which shows the experimental apparatus of the laboratory test 2 in an Example.

The specific injection pattern of nitrite is not the method of continuous addition, which is common sense of general chemical injection, or the method of adding proportionally to the inflow of sludge, which is the object to be treated. As in the invention, the total daily addition amount is intermittently injected, for example, 1 to 12 times, or step injection is performed in which the high addition step (concentrated addition) and the low addition step are alternately repeated.
The intermittent injection is a method in which, for example, as shown in FIG. 1 (a), the state of the addition rate A at the concentrated addition and the state of the addition rate 0 at the stop are alternately repeated.
The step injection is a method in which, for example, as shown in FIG. 1B, the state of the addition rate A in the high addition step and the state of the addition rate B in the low addition step (0 <B) are alternately repeated.
In FIG. 1, the addition rate A and the interval during concentrated addition are constant, but this may vary. However, it is desirable to perform it periodically from the viewpoint of control and management, and such control can be easily performed by using a timer.

The number of concentrated additions (per day) is better from the characteristics of nitrite. However, if the number is low, there will be a time zone in which nitrite ions disappear and odor is generated. .
In practice, it is preferable to reduce the number of additions when the average residence time of the sludge storage tank to which nitrite is added is long, and increase the number of additions when the average residence time is short. However, if the number of times of addition is excessive, the amount of one addition is reduced by that amount, which is inadequate because it is an approximation of the conventional method (continuous and proportional addition).
The number of specific concentrated additions per day is 1 to 12, and more desirably varies depending on the average residence time of the sludge storage tank, chemical pumping capacity, sludge properties, sludge inflow, sludge extraction pattern, etc. When sludge extraction is continuous for 24 hours with an average residence time of 24 hours, about 2 to 5 times are preferable. When the average residence time is 12 hours, it is preferably 2 to 10 times per day.

  The concentration of nitrite once (addition rate x time) should be such that the concentration of residual nitrite ions can be maintained at 20 mg / L or more in the sludge storage tank after 1 hour from the end of the addition. is important. As a result, sludge, more precisely sludge microorganisms, are damaged and the decomposition rate of nitrite ions is reduced, and as a result, generation of hydrogen sulfide and methyl mercaptan can be reliably prevented.

  If the residual nitrite ion concentration after 1 hour from the end of one concentrated addition is well above 20 mg / L, the amount of nitrite added once can be reduced, and the total amount used (total amount added) Can also be reduced. However, if the amount added is too low, the decomposition rate of nitrite ions will increase this time, the residual nitrite ion concentration will be lower than 20 mg / L, and the concentration may further decrease sequentially. Therefore, it is necessary to confirm this tendency and adjust the amount added once so that the residual nitrite ion concentration does not fall below 20 mg / L.

  Further, in the step injection, the high addition step and the low addition step are alternately repeated, but the ratio of the sum of the daily addition amount of the high addition step to the total addition amount of nitrite per day is 2/3. It is preferable to set to -1.

In order to change or adjust the nitrite intermittent injection or step injection in the present invention automatically and in accordance with the sludge treatment status and odor treatment effect, any addition device and control mechanism are used in combination. However, the simplest device and mechanism include, for example, a method of turning on and off the medicinal pump using a timer.
In addition, the nitrite addition place in the present invention is generally injected directly into the sludge storage tank, but it may be a process prior to the sludge storage tank, such as a sludge pump pipe to the sludge storage tank. It is not limited. Further, the adding means may be performed by a chemical injection pump, or may be a batch injection manually or a combination of a pump and manual injection, and is not particularly limited. Further, the interval of addition or stoppage of addition is set according to the operation of the treatment system, but can be simply set at equal intervals.

According to the present invention described above, the amount of nitrite used can be reduced and the effect of preventing odor generation can be stabilized, but the state of the target sludge microorganisms is likely to change, and the sludge treatment state is always difficult to be constant. For this reason, sometimes, microorganisms having high resistance to nitrite and high decomposition ability increase in the sludge storage tank (acclimation phenomenon).
In such a case, although the method of increasing the amount of nitrite added once can be dealt with, the most effective method is 1/2 or more of the average residence time of sludge, preferably 1 to 3 times the average residence time. Stop nitrite addition for a period of time, replace the acclimated sludge in the sludge storage tank with sludge that is not resistant to nitrite ions, and then implement intermittent injection of nitrite or step injection to quickly prevent odor generation Can be recovered.

  In the present invention, any known odor generation preventing method may be used in combination. For example, the pH of the sludge may be adjusted, or sulfite, bisulfite, sorbic acid, or an organic bacteriostatic agent may be used in combination with nitrite.

1) Laboratory test 1
1-1) Sludge A first-stage gravity-concentrated sludge and excess centrifugally-concentrated sludge (average residence time 24 hr) at the sewage treatment plant are collected separately, and after measuring the total solids concentration (TS), the water is more accurate with Atsugi City water. TS was adjusted to 2.5%, and this was mixed at 50:50 to obtain a test sludge. Since the test was conducted for 14 days, each sludge adjusted to 2.5% was stored and used in a refrigerator at 5 ° C. for 7 days, and fresh sludge was collected for the latter 7 days and adjusted in the same manner.

1-2) Test method 10 L of sludge was put in a container with a stirrer, and Comparative Examples 1 to 3 were continuously added with nitrite (continuous injection) as shown in the experimental flow of FIG. As in the experimental flow shown in b), Examples 1 and 2 were batch-added (intermittent injection), and Example 3 was added using both batch addition and continuous injection (step injection). 12 hours after the start, half of the sludge, 5 L, was replaced with new sludge, and this was repeated for 14 days. Sodium nitrite was used as the nitrite, and the detailed addition method is shown in Table 1.

1-3) Evaluation method Evaluation was performed on the 3rd, 7th and 14th days.
The test items are the following four items.
1) The concentration of residual nitrite ions (NO ₂ ⁻ ) in the sludge in the container after 1 hour had passed after sludge replacement (after batch addition of nitrite after sludge replacement in intermittent injection). The measurement results are shown in Table 1 as “+1 hrNO ₂ ⁻ ”.
2) Remove 50 mL of sludge from the sludge before replacement of sludge in a 600 cc container, and use hydrogen sulfide (H ₂ S) and methyl mercaptan (MM) in the gas phase after sufficiently permeating for 1 minute in the gas detector tube. Measured. The measurement results are shown in Table 1 as “odor”.
Concentration was determined ^- 3) residual NO ₂ in the sludge replacement before the sludge. The measurement results are shown in Table 1 as “residual NO ₂ ⁻ ”.
4) 3 sludge) residual NO ₂ ^- The sample concentration is less than 30 mg / L, add so that the nitrite 30 mg / L, 1 hour stirrer remaining after stirring NO ₂ ^- was measured concentration , NO ₂ thereof than 1 hour ^- it was calculated consumption. The results are shown in Table 1 as “consumption rates”.

1-4) Results

表２より、１日目終了後のＮＯ₂ ^-の消費速度は１６ｍｇ／Ｌ・ｈｒで、まだ高く、臭気もあったが、２日目には、ほぼ実施例１のＮＯ₂ ^-の消費速度に近い５ｍｇ／Ｌ・ｈｒになり、臭気も０ｐｐｍになった。 From Table 1, in Examples 1, 2 and 3 were intermittently injected or stepped infusion of nitrite, odor is 0ppm both H ₂ S, MM, 14 day NO ₂ ^- consumption rate each 3,5 and It was confirmed to be as small as 5 mg / L · hr.
In Comparative Examples 1 and 2 contrast, the day 14 NO ₂ ^- consumption rate is more than 30, and 20 mg / L · hr and becomes 4-10 times of Examples 1 to 3, the habituation is advancing Was confirmed. In Comparative Example 1, 200 and 80 ppm of H ₂ S and MM are generated, respectively. In Comparative Example 2, H ₂ S and MM of 5-2 ppm are generated regardless of the amount of nitrite added twice that of Example 1. did.
Thus, the clear difference between Examples 1 to 3 which are intermittent injection or step injection and Comparative Examples 1 and 2 which are continuous injections is that the consumption rate of NO ₂ ⁻ does not change with time in Examples 1 to 3. Or, while it gradually decreases, in Comparative Examples 1 and 2, it clearly increases, and the amount of odor generation increases with time.
Although Comparative Example 3 is the intermittent injection, remaining 1 hour after adding a nitrite NO ₂ ^- is a 12 mg / L at maximum (day 7), defined in the present invention the concentration 20mg / Since the absolute amount of nitrite to be added was insufficient, the predetermined effect could not be obtained.
It should be noted that ½ of the sludge after the 14-day test in Comparative Example 1 where the acclimatization progressed and the NO ₂ ⁻ effect declined was replaced with new sludge and left for half a day. It processed again by the nitrate injection method (intermittent injection) (Example 4). The results are shown in Table 2.

From Table 2, the consumption rate of NO ₂ ⁻ after the end of the first day was 16 mg / L · hr, which was still high and had odor, but on the second day, the consumption rate of NO ₂ ⁻ of Example 1 was almost the same. 5 mg / L · hr close to 0, and the odor was also 0 ppm.

2) Laboratory test 2
2-1) Sludge First-stage gravity-concentrated sludge and excess centrifugally-concentrated sludge from the A sewage treatment plant are collected separately, and after measuring the total solids concentration (TS), the water is accurately adjusted to 2.5% by Atsugi City water. This was adjusted, mixed at 50:50, and used in the same manner as in the laboratory test 1.

2-2) Test method It was determined how to set the nitrite addition time and the addition stop period in intermittent injection.
10 L of sludge was taken in a container with a stirrer, and as shown in FIG. 3, the new sludge was charged at 3 L / hr for 20 minutes every hour using a timer. The amount of new sludge input at one time is 1 L, and 24 L of new sludge is input per day, so the average residence time is 10 hours for a container capacity of 10 L.
In Comparative Example 4, nitrite was added at the same time (20 minutes) at a concentration of 120 mg / L with respect to the new sludge in accordance with the input amount and time of the new sludge. In Comparative Example 5, nitrite was added twice at a concentration of 180 mg / L for the same time (20 minutes) with respect to the input of new sludge, and nitrite was not added once thereafter. The cycle was repeated. In Examples 5 to 7, nitrite was added at 960, 480, and 240 mg / L for 20 minutes every 8 times, 4 times, and once every 2 times. In Examples 5 to 7 and Comparative Examples 4 and 5, the total daily addition amount of nitrite is 2880 mg. Sodium nitrite was used as the nitrite.

2-3) Evaluation method Evaluation was performed for 14 days, and on days 3, 7, and 14, sludge immediately before nitrite was added was collected, and the odors of H ₂ S and MM (Table 3) were measured.
Further, residual after 1 hour after completion of NO ₂ ^- was measured concentration (Table 4).
Further, NO ₂ for sludge just before new sludge charged ^- was also measured consumption rate (Table 5). The measuring method is the same as in the laboratory test 1.

2-4) Results

As apparent from Table 3, immediately before nitrite was added, in Examples 5 and 6, both H ₂ S and MM were 0 ppm. Moreover, in Example 7, it became 0 ppm on the 7th and 14th day.
On the other hand, in Comparative Examples 4 and 5, all H ₂ S and MM were generated, and the values increased with each passing day.
Further, as apparent from Table 4, in Examples 5 to 7, the concentration of nitrous acid after 1 hour from the end of nitrite addition was 20 mg / L or more (7 days and 14 days in Example 7). In Examples 4 and 5 (40 minutes after the end of addition of new sludge from the nitrite addition interval), it was 6 mg / L or less.
Further, Table 5 from apparent in the day 14 NO ₂ ^- consumption rate of, with respect to more than about 5 mg / L · hr Examples 5-7, Comparative Examples 4 and 5 20 mg / L · hr approximately There was a difference of 4 times or more.

3) Actual equipment confirmation test At B sewage treatment plant, sodium nitrite is applied to prevent odor generation in the sludge storage tank and to prevent odor generation in the dehydrator supplied with sludge from the storage tank. However, since a decrease in the effect was observed after about half a month after the start of application, the sodium nitrite addition rate was gradually increased, and the initial average sodium nitrite addition rate of 100 mg / L was 2 Although the addition rate of 250 mg / L is 5 times, the prevention of H ₂ S and MM generation was still insufficient.
Therefore, the intermittent injection method of the example was tested at this treatment plant.

3-1) sludge storage tank of the conventional continuous injection method B sewage sludge always 300 meters ³ are stored, the amount of sludge supplied to the dehydrator (belt press) and pull from here to 1 day at 300 meters ³ The average residence time is 24 hours. The amount of stored sludge in the sludge storage tank is controlled in water level, and once every hour, 12.5 m ³ of concentrated sludge is charged at a rate of about 60 m ³ / hr for about 12 minutes.
Prior to the demonstration of the present invention, the sodium nitrite solution was continuously added to the sludge storage tank at a rate of 3.2 kg / hr as a nitrite for 24 hours. The total amount added per day was 76.8 kg / day, and the average amount of nitrous acid added to 300 m ³ of sludge was 256 mg / L.

3-2) Intermittent injection method of the present invention First, the addition of nitrite was stopped for 16 hours (0 day 16: 00 to 1 day 8:00) which is 2/3 of the average residence time. From 8:00 to 12:00, confirm that the nitrite concentration was increased to 56 mg / L (12:00) by adding nitrite at an addition rate of 12.8 kg / hr that was four times higher than before, Thereafter, the addition was stopped.
On the 2nd and 3rd day, 3 hours from 8:00 to 11:00 and 3 hours from 20:00 to 23:00, 6 hours in total, 12.8 kg / hr, 4 times the conventional addition rate Nitrite was added. The total amount of nitrite added per day at this time is 76.8 kg / day, which is the same as before.
Furthermore, from the 4th to the 15th day, the addition of nitrite was set to 8:00 to 10:00 and 20:00 to 22:00 for a total of 4 hours. At this time, the total daily addition amount of nitrite is 51.2 kg / day, which is 2/3 of the conventional amount.

3-3) Evaluation method Sludge collected 1 hour after completion of nitrite addition and 7:30, 16:00 sludge are collected, 1) generation amount of H ₂ S and MM, 2) residual NO ₂ ⁻ concentration, 3) NO ₂ ^- was measured consumption rate. The evaluation method is the same as in the room test 1. At the same time, the concentrations of H ₂ S and MM on the coagulated sludge supply section of the belt press dehydrator were measured. The measurement results are shown in Table 6.

3-4) Results

As is clear from Table 6, in the conventional continuous injection method on Day 0, H ₂ S and MM are constantly generated in both the storage tank sludge and the belt press dehydrator, and the average of 256 mg / L in the storage tank sludge. Despite the addition of nitrite, the measured residual NO ₂ ^- concentration was 0 mg / L. Further, the consumption rate of NO ₂ ⁻ was very large at 50 mg / L · hr or more.
1 day, by the conventional 4-speed of the addition of nitrite 4 hours, the residual NO ₂ to the end of the addition time of 12:00 as described above ^- increasing to a concentration 56 mg / L, the 1 hour lapse after (13:00) the residual NO ₂ ^- concentration 32 mg / L was detected. Although temporary some, H ₂ S in the reservoir the sludge and dewatering machine, the MM could be 0 ppm. However, the consumption rate of NO ₂ ⁻ was still as high as about 20 mg / L, and residual NO ₂ ⁻ disappeared in about 4 hours (16:00).
On the second day, but there was a rate of addition of the same nitrite as 1 day residual NO ₂ ^- concentration rises early, 1 day to 3 hours the addition, the completion of the addition time of (11:00) residual NO ₂ exceeds ^- concentration 84 mg / L is detected, the 1 hour after a lapse of 12:00 residual NO ₂ ^- concentration 72 mg / L was detected. The consumption rate was also less than 10 mg / L · hr. As a result, H ₂ S during the day, at the same time could be a 0ppm the MM, most residual NO ₂ ^- even 7:30 the next day 3 concentration is reduced, H ₂ S, the occurrence of MM was slightly .
The effect was further improved on the third day than on the second day, and residual NO ₂ ⁻ was detected (16 mg / L) for the first time at 7:30 on the fourth day, and completely H ₂ S over the entire 24 hours. It was determined that the occurrence of MM could be prevented.
From the 4th day onwards, the addition time of nitrite was set to 2 hours, and the addition time and the total addition amount were reduced to 2/3 of the 2nd day and the 3rd day. In the meantime, the result that it was judged that H ₂ S and MM could be 0 ppm was obtained.

  As described above, the addition of nitrite by the method of “adding proportionally or continuously in accordance with the inflow of sludge”, which is a conventional general chemical addition method, has a predetermined effect at the beginning. Although it is obtained, the amount of necessary nitrite gradually increases and becomes inappropriate, but the method of preventing odor generation of the present invention performs addition of nitrite intermittently or stepwise, By controlling the residual nitrite ion concentration after 1 hour, even if the total amount of nitrite added is unchanged or reduced, the effect of preventing hydrogen sulfide and methyl mercaptan can be stably exhibited. It is possible to effectively prevent the bad odor problem caused by the above, the electrical equipment corrosion due to hydrogen sulfide, and the equipment corrosion due to sulfuric acid generated by the biological oxidation of hydrogen sulfide.

  In addition, in sludge treatment systems where the required amount of nitrite has increased and the effect of preventing odor generation has declined, the addition of nitrite has been suspended after suspending the addition of nitrite for 1/2 or more of the sludge retention time in the sludge storage tank. By carrying out the addition, the effect of preventing odor generation can be quickly recovered.

Claims (2)

While new sludge is turned more than once a day, the sludge of the sludge reservoir sludge replaced by sludge staying is discharged sent to a dehydrator, the adding step corresponding to the residence time of the sludge A method for preventing the generation of odor from sludge by adding nitrite, in order to maintain the consumption rate of nitrite ions due to microbial activity after 1 hour after addition of nitrite to less than 10 mg / L · hr The concentration of nitrite to the sludge is in the range of 2 to 12 times per day so that the residual nitrite ion concentration of the sludge in the sludge storage tank after 1 hour from the end of the addition is 20 mg / L or more , An odor generation preventing method characterized by intermittently repeating a state of a predetermined addition rate at the time of concentrated addition and a state where the addition rate at the end of addition is zero . New sludge is added at least twice a day, while the sludge staying in the sludge is sent to the dehydrator and discharged to replace the sludge in the sludge storage tank. A method for preventing the generation of odor from sludge by adding nitrite,
Residual nitrite ion in sludge in sludge storage tank after 1 hour from the end of addition in order to maintain the consumption rate after 1 hour after nitrite addition of nitrite ion due to microbial activity to less than 10 mg / L · hr Concentrated addition of nitrite to sludge in a range of 2 to 12 times per day so that the concentration is 20 mg / L or more, the state of the predetermined addition rate at the concentration addition and the addition rate at the end of the addition are 0 A high addition step of intermittently repeating a certain state alternately;
A low addition step of adding nitrite so as to fill a state where the addition rate at the end of addition in the high addition step is 0,
A method for preventing odor generation, wherein the sum of the amount of nitrite added per day in the high addition step is at least twice the sum of the amount of nitrite added per day in the low addition step.

Images