JP2000202494A - Deodorant for dehydrated cake and deodorizing method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To effectively and continuously deodorize by using a deodorant containing nitrite, sulfite or hydrogen sulfite as a chemical for deodorizing dehydrated cake. SOLUTION: Raw water is introduced into a settler 1 to separate initially settled green sludge, the supernatant, in which a flocculant is added at need, is sent to an aeration tank 2 to be biologically treated and after the flocculant is added, the treated water is sent to a final settler 3 to separate sludge. In the separated sludge, a part is returned to the aeration tank 2 and the remainder is treated as excess sludge and sent with initially settled green sludge to a sludge concentrating tank 4 to be concentrated. The concentrated sludge is sent to a storage tank 5 and at this time, nitrite, sulfite or hydrogen sulfite is added in the sludge concentrating tank 4 or the sludge storage tank 5 and the sludge slurry is dehydrated by a dehydrator 6 to be carried out as the dehydrated cake.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a deodorizing agent and a method for deodorizing a dehydrated cake. More specifically, the present invention provides
The present invention relates to a deodorizing agent and a deodorizing method for a dewatered cake capable of effectively preventing odors derived from malodorous substances such as hydrogen sulfide and methyl mercaptan generated from a dewatered cake obtained by dewatering a sludge slurry in a sewage treatment plant.

[0002]

2. Description of the Related Art Sewage treatment plants, human waste treatment plants, food factories,
Various kinds of sludge are generated in a process of treating organic industrial wastewater such as a pulp and paper mill. For example, if the sewage is first solid-liquid separated in a sedimentation basin, primary sludge will be generated. If the supernatant water of the first sedimentation basin is treated by a floating organism method using an aeration tank or the like, the amount of activated sludge will increase. The water treated in the aeration tank or the like is guided to the final sedimentation basin, where the activated sludge is separated, a part of which is returned to the aeration tank or the like as returned sludge, and the remaining is sludge. The primary sludge and excess sludge are led to a sludge thickening tank, and then temporarily stored in a sludge storage tank. The sludge in the sludge storage tank is then dewatered by a dehydrator, and the resulting dewatered cake is carried out for landfill or incineration. From the sludge storage tank to the periphery of the dehydrator, the malodorous substances are volatilized from the sludge slurry, and the dewatered cake after dehydration generates odorous substances by rotting. Substances that are frequently detected as malodorous substances generated in sewage treatment plants include sulfur compounds such as hydrogen sulfide and methyl mercaptan, nitrogen compounds such as ammonia and trimethylamine, lower fatty acids such as valeric acid and isobutyric acid, and the sludge drying and incineration process. And aldehydes generated from methane. Among these, the amounts of hydrogen sulfide and methyl mercaptan generated from the sludge treatment process are particularly large. Most sludge storage tanks and dehydrators are closed systems, but the dewatered cake obtained by dehydration is transported in an open system,
Odor control is more important because it is often stored. In other words, conveyors and trucks are usually used to transport the dehydrated cake, and the deodorized cake, which is the source of the odor, moves. Therefore, it is difficult to treat the deodorized cake by a cover, suction of the odor, etc., and it is difficult to take measures against the odor. In addition, even at the final landfill site, the odor generated is diffused, causing discomfort to nearby residents and adversely affecting the environment. For this,
It is necessary to suppress the odor itself generated from the dehydrated cake, and various deodorizing methods have been conventionally proposed. For example, a deodorizing method using an active oxygen generating compound such as hydrogen peroxide, alkali persulfate, and chlorite has been adopted. The active oxygen-generating compound is characterized by its immediate effect and is effective, for example, a deodorizing effect can be obtained immediately after addition.
Since it is consumed by directly reacting with the reducing substance in the sludge, there is a disadvantage that the effect is lost in a short time. Japanese Patent Laid-Open No. 5-
No. 253599 discloses, as a deodorizing method capable of efficiently suppressing the odor generated from various dehydrated cakes, using a chlorite, a hypochlorite, and optionally a bacteriostat-based deodorant. A method for deodorizing a dehydrated cake has been proposed. Japanese Patent Publication No. 63-58640 discloses a method of deodorizing sewage sludge with an alkali metal or alkaline earth metal chlorite in a deodorizing method that completely deodorizes but does not completely kill bacteria. A method of treating at a temperature of ° C has been proposed. Since chlorite and hypochlorous acid have a short duration of the deodorizing effect, a method as late as possible after the sludge treatment step, for example, a method of adding immediately before dehydration has been adopted. The duration of the deodorizing effect of the cake is inadequate. JP-A-63-205197 proposes a method of deodorizing wastewater and sludge gas containing malodorous substances such as hydrogen sulfide, ammonia and methyl mercaptan by treating with zinc compounds such as zinc sulfate. Deodorizing treatment methods using compounds are also known. Zinc compounds and copper compounds have an immediate effect and have a large deodorizing effect on dewatered cakes. Is done. In addition, metal salts, particularly copper chloride, are highly corrosive, and there is a concern that they may adversely affect equipment. Furthermore, Japanese Patent Publication No. 1-60319 proposes a method for preventing the generation of hydrogen sulfide by sulfate-reducing bacteria under anaerobic conditions, in which nitrite ions are present in the growth environment of microorganisms. Nitrite is being considered for use in sludge slurries placed in closed systems such as in wastewater treatment equipment, but deodorizing means in the entire sewage treatment process including dewatered cakes stored in open systems Was not considered at all. In addition, Japanese Unexamined Patent Publication
Japanese Patent Application No. 0-105890 discloses a method of adding sulfite to sludge mainly composed of white bran generated from rice washing wastewater or a dewatered cake thereof to prevent propagation of various bacteria and spoilage. The method of deodorizing the sludge dewatered cake to be released has not been studied. JP-A-4-12659
No. 7 proposes a deodorizing method using an oxidizing agent-based deodorant and a bacteriostatic agent-based deodorizing agent as a method for efficiently suppressing the odor generated from the dehydrated cake. It has been known that the use of a bacteriostatic agent can provide a good effect by deodorizing the dehydrated cake for a long time, but the unit cost of the agent to be used is high and the treatment cost may be increased. From these situations,
A deodorizing agent and a deodorizing method that use chemicals that do not contain chlorine and metal, have no corrosiveness, are inexpensive, have low processing costs, have a long-lasting deodorizing effect, and are capable of deodorizing sludge slurry to dewatered cake. It has been demanded.

[0003]

DISCLOSURE OF THE INVENTION The present invention is directed to treating chlorine and nonmetallic odors derived from malodorous substances such as hydrogen sulfide and methyl mercaptan generated from sludge slurry and dewatered cake at sewage treatment plants and the like. An object of the present invention is to provide a deodorizing agent and a deodorizing method for a dehydrated cake which can be effectively prevented at low cost by using an agent.

[0004]

Means for Solving the Problems The present inventors have made intensive studies to solve the above-mentioned problems, and as a result, by using a deodorant containing nitrite, sulfite or bisulfite, an effective and effective method has been proposed. It has been found that continuous deodorization can be performed, and the present invention has been completed. Furthermore, the sludge dewatering equipment and the agent for deodorizing the dewatered cake are conventionally often added to the position immediately before the place to be deodorized or to the place to be deodorized, whereas nitrite, sulfite or It has been found that by adding bisulfite to the sludge slurry and dehydrating after a long period of time, effective and continuous deodorization can be performed. That is, the present invention provides (1) a deodorizing agent for a dehydrated cake containing nitrite, sulfite or bisulfite, and (2) adding nitrite, sulfite or bisulfite to a sludge slurry. (3) a method for deodorizing a dewatered cake, which is characterized in that dewatering is performed after dehydration.
After the addition of nitrite, sulfite or bisulfite to the sludge slurry, the time elapsed before dehydration is at least 15 minutes.
Item (3), wherein the deodorizing method of the dewatered cake according to item (2), and (4) the time elapsed from the addition of nitrite, sulfite or bisulfite to the sludge slurry until dehydration is 3 hours or more. And a method for deodorizing a dehydrated cake as described above.
Furthermore, as a preferred embodiment of the present invention, (5) the method for deodorizing a dehydrated cake according to (4), wherein the addition amount of nitrite, sulfite or bisulfite is 25 to 1,000 mg per liter of sludge slurry. Can be mentioned.

[0005]

BEST MODE FOR CARRYING OUT THE INVENTION The deodorizing agent for a dehydrated cake of the present invention comprises:
It contains nitrite, sulfite or bisulfite. The deodorizing method of the dewatered cake of the present invention is a method of adding a nitrite, a sulfite or a bisulfite to a sludge slurry and then dehydrating the same, and then adding a nitrite, a sulfite or a bisulfite to the sludge slurry, The elapsed time until the dehydration is preferably 15 minutes or more, more preferably 3 hours or more. In the present invention, the nitrite, the sulfite and the bisulfite can be used alone or in combination of two or more. There is no particular limitation on the nitrite used in the present invention. Examples thereof include nickel, copper nitrite, silver nitrite, zinc nitrite, and thallium nitrite. One of these nitrites can be used alone, or two or more can be used in combination. Among these, sodium nitrite and potassium nitrite can be used particularly preferably without adverse effects at the place of use even when the dehydrated cake is used secondarily.
The sulfite used in the present invention is not particularly limited, and examples thereof include ammonium sulfite, lithium sulfite, sodium sulfite, potassium sulfite, rubidium sulfite, cesium sulfite, and thallium sulfite. One of these sulfites can be used alone, or two or more thereof can be used in combination. Among these, sodium sulfite and potassium sulfite can be used particularly preferably without adverse effects at the place of use even when the dehydrated cake is used secondarily. The bisulfite used in the present invention is not particularly limited, and examples thereof include ammonium bisulfite, sodium bisulfite, potassium bisulfite, and calcium bisulfite.
In the present invention, bisulfite containing a large amount of disulfite as an impurity can also be used. One of these bisulfites can be used alone, or two or more can be used in combination. Among them, sodium bisulfite and potassium bisulfite can be particularly preferably used without any adverse effect at the place where the dehydrated cake is used secondarily.

There is no particular limitation on the sludge to which the present invention is applied.
For example, the present invention can be applied to various types of sludge generated in an organic industrial wastewater treatment process in a sewage treatment plant, a human waste treatment plant, a food factory, a pulp and paper factory, and the like. FIG. 1 is a process flow diagram of one embodiment of sewage treatment. Raw water is first guided to the sedimentation basin 1 to separate primary sludge. First, the supernatant water of the sedimentation basin is added to the aggregating agent if necessary, and then the aeration tank 2
And biological treatment is performed by the activated sludge method. The treated water in the aeration tank is fed to the final sedimentation basin 3 after adding a flocculant as needed, and the sludge is separated. Part of the separated sludge is returned to the aeration tank as return sludge, and the remainder is treated as excess sludge. The supernatant water of the final sedimentation basin is discharged as it is or after necessary treatment. The surplus sludge is sent to the sludge concentration tank 4 together with the primary sludge. The sludge concentrated in the sludge concentration tank is sent to the sludge storage tank 5. The sludge stored in the sludge storage tank is
It is dehydrated by the dehydrator 6 and carried out as a dehydrated cake. The supernatant water of the sludge thickening tank and the desorbed water from the dehydrator are returned to the raw water or discharged after being subjected to necessary treatment. In the method of the present invention, nitrite, sulfite or bisulfite is added to the sludge slurry and then dewatered. In this case, at least 15 minutes after the addition, more preferably 3 minutes
By dehydrating after a lapse of time or more, deodorization can be performed more effectively and continuously. Therefore, FIG.
In the case of taking the step shown in the above, a nitrite, a sulfite or a hydrogen sulfite is added in the sludge concentration tank 4 or the sludge storage tank 5, and a step where 15 minutes or more elapses before the sludge slurry is dehydrated in the dehydrator 6. It is preferable that the process be performed for 3 hours or more. When the treatment of sludge is carried out batchwise, the time interval between the addition of nitrite, sulfite or bisulfite and the dehydration can be determined directly from the operation time. When the sludge treatment is performed continuously, the time interval between the addition of the nitrite, the sulfite or the bisulfite and the dehydration can be calculated as the average residence time of the sludge slurry. By adding nitrite, sulfite or bisulfite to the sludge slurry and dewatering after 15 minutes or more, the generation of offensive odor components from the dewatered cake can be prevented for a longer time. Nitrite, sulfite, and bisulfite also have a deodorizing effect on sludge slurry, and the effect becomes remarkable when 15 minutes or more have passed after addition. Therefore, when the odor of a sludge treatment device such as a storage tank or a dehydrator becomes a problem, the sludge slurry reaches a device requiring deodorization1.
By adding the nitrite, sulfite or bisulfite 5 minutes or more before, not only the dehydrated cake but also the deodorization around these devices can be performed.

In the method of the present invention, the method of dewatering the sludge slurry after adding nitrite, sulfite or hydrogen sulfite is not particularly limited. For example, a centrifugal dehydrator, belt press dehydrator, screw press dehydrator, filter A press dehydrator, a vacuum dehydrator, or the like can be used. It is preferable that a dehydrating agent is added to the sludge slurry before or in the dehydrator, in order to improve the dehydration property. Examples of the dehydrating agent to be added include an anionic polymer flocculant, a cationic polymer flocculant, an amphoteric polymer flocculant, ferric chloride and slaked lime.
In the method of the present invention, the method of adding nitrite, sulfite or bisulfite is not particularly limited, and these salts can be added as an aqueous solution or can be added in a powder state. In the method of the present invention, the amount of nitrite, sulfite or bisulfite to be added to the sludge slurry is not particularly limited.
１1,000 mg, preferably 100-500 m
It is more preferably g. In particular, when dewatering is performed after 15 minutes or more after the addition to the sludge slurry, the deodorizing effect of the dewatered cake is maintained for a long time with a smaller amount of addition. The amount of nitrite, sulfite or bisulfite added is
If the amount is less than 25 mg per 1 liter of the sludge slurry, the deodorizing effect is insufficient, and a malodorous substance may be generated from the dewatered cake within a relatively short time after dewatering. The addition amount of nitrite, sulfite or bisulfite is 1,000 mg or less per 1 liter of the sludge slurry, so that a sufficient deodorizing effect can be obtained.
It is not necessary to add more than 00 mg of nitrite, sulfite or bisulfite. In the method of the present invention, if necessary, a bactericide such as zinc pyrithione can be used in combination.

From the sludge slurry, hydrogen sulfide is generated by the activity of sulfate-reducing bacteria, and sulfur-containing organic substances are decomposed by general microorganisms to generate hydrogen sulfide and methyl mercaptan. According to the method of the present invention, nitrite, sulfite or bisulfite is added to the sludge slurry to suppress the activity of sulfate-reducing bacteria and general microorganisms, suppress the generation of new malodorous components, and furthermore, after dehydration. Also, the activity of microorganisms in the dehydrated cake can be suppressed, and the generation of odor from the dehydrated cake can be prevented. According to the method of the present invention, nitrite,
By adding sulfite or bisulfite to the sludge slurry and then dewatering, the generation of malodorous substances from the dewatered cake can be suppressed for 24 hours or more, and in particular, by allowing 15 minutes or more after the addition to the sludge slurry. By adding a smaller amount, it is possible to suppress malodor for a longer time. Since nitrite, sulfite and bisulfite have low corrosiveness, they have little adverse effect on the secondary use of sludge and can be used safely. Nitrite, sulfite and bisulfite are less expensive than disinfectants, and can treat sludge at low cost. ADVANTAGE OF THE INVENTION According to the deodorizing agent and the deodorizing method of this invention, it is possible to process from sludge slurry to dewatered cake with one agent using a non-chlorine-based, non-metallic agent such as nitrite, sulfite or hydrogen sulfite. .

[0009]

EXAMPLES The present invention will be described in more detail with reference to the following Examples, which should not be construed as limiting the present invention. In Examples and Comparative Examples, the analysis of hydrogen sulfide was performed using a gas detector tube [Gastec 4M,
4L or 4LL] and the analysis of methyl mercaptan was carried out using a gas detection tube “Gastec 71H or 71.” The lower detection limit concentration was 0.25 ppm for both hydrogen sulfide and methyl mercaptan. Mixed raw sludge collected at the treatment plant [pH 4.8, SS17,
000 mg / liter] into a beaker having a capacity of 500 ml.
g was added, stirred 20 times with a spoonful to mix evenly, and the beaker was sealed with a polyethylene film. Immediately, when the air above the sludge slurry in the beaker was analyzed, the concentration of hydrogen sulfide was 100 ppm and the concentration of methyl mercaptan was 15 ppm. Subsequently, 25.0 g of a 0.2% by weight aqueous solution of a cationic dehydrating agent [Kurita Kogyo Co., Ltd., Crifix CP604] was added, and the mixture was stirred for 20 seconds at 500 rpm using a 2-blade stirrer. Was poured over a Buchner funnel lined with, and filtered. The sludge after filtration was dehydrated using a pressing machine to obtain a dewatered cake. 40 g of the obtained dehydrated cake is put into two fluororesin gas sampling bags, and the air is 1,000 m.
l, sealed and stored in a thermostat at 30 ° C.
After time and 48 hours, the air in the gas sampling bag was analyzed. After 24 hours, neither hydrogen sulfide nor methyl mercaptan was detected, and after 48 hours, the concentration of hydrogen sulfide was 800 ppm and the concentration of methyl mercaptan was 1
30 ppm. Comparative Example 1 400 ml of the mixed raw sludge used in Example 1 was put into a beaker having a capacity of 500 ml, and stirred 20 times with a spoon, the beaker was sealed with a polyethylene film, and the air above the sludge slurry in the beaker was analyzed. As a result, the concentration of hydrogen sulfide was 150 ppm, and the concentration of methyl mercaptan was 2
It was 0 ppm. Immediately, cationic dehydrating agent [Kurita Industries
25.0 g of a 0.2% by weight aqueous solution of Crifix CP604] was added to the mixture, and the mixture was stirred at 50 with a 2-blade stirrer.
After stirring at 0 rpm for 20 seconds, the mixture was poured on a Buchner funnel covered with a nylon filter cloth and filtered. The sludge after filtration was dehydrated using a pressing machine to obtain a dewatered cake. Each of the obtained dehydrated cakes is placed in three gas sampling bags for 40 times.
g, fill with 1,000 ml of air and seal tightly.
℃ 24 hours, 48 hours and 7 hours
Two hours later, the air in the gas sampling bag was analyzed. The concentration after 24 hours is 25 ppm of hydrogen sulfide,
The concentration after 48 hours was 900 ppm of hydrogen sulfide and 280 p of methyl mercaptan.
pm, the concentration after 72 hours is 600 ppm of hydrogen sulfide,
It was 100 ppm of methyl mercaptan.

Example 2 400 ml of the mixed raw sludge used in Example 1 was put into a beaker having a capacity of 500 ml, and 12.0 g of a 1.0% by weight aqueous sodium nitrite solution was added thereto. Mix and seal the beaker with a polyethylene film. After standing for 15 minutes, when the air above the sludge slurry in the beaker was analyzed, the concentration of hydrogen sulfide was 10 ppm,
The concentration of methyl mercaptan was 5 ppm. Immediately, a cationic dehydrating agent [Kurita Kogyo Co., Ltd., Crifix CP6
2], and the mixture was stirred at 500 rpm for 20 seconds using a two-blade stirrer, then poured on a Buchner funnel covered with a nylon filter cloth and filtered. The sludge after filtration was dehydrated using a pressing machine to obtain a dewatered cake. 40 g of the obtained dehydrated cake is put into each of three gas sampling bags, and the air is collected at 1,000 m.
l, sealed and stored in a thermostat at 30 ° C.
After hours, 48 hours and 72 hours, the air in the gas sampling bag was analyzed. After 24 hours, neither hydrogen sulfide nor methyl mercaptan was detected. The concentration after 48 hours was 15 ppm of hydrogen sulfide and 10 ppm of methyl mercaptan, and the concentration after 72 hours was 600 ppm of hydrogen sulfide and 70 ppm of methyl mercaptan. Example 3 The same operation as in Example 2 was repeated, except that the standing time after the addition of the 1.0% by weight aqueous sodium nitrite solution was 3 hours. Neither hydrogen sulfide nor methyl mercaptan was detected in the air above the sludge slurry in the beaker. In the air in the gas sampling bag, even after 24 hours,
Neither hydrogen sulfide nor methyl mercaptan was detected after 48 hours, and the concentration of hydrogen sulfide was 5 ppm and the concentration of methyl mercaptan was 20 ppm after 72 hours.

Example 4 400 ml of the mixed raw sludge used in Example 1 was placed in a 500 ml beaker, 4.0 g of a 1.0% by weight aqueous sodium nitrite solution was added, and the mixture was stirred 20 times with a spoon and uniformly. Mix and seal the beaker with a polyethylene film. After standing for 15 minutes, the air above the sludge slurry in the beaker was analyzed, and the hydrogen sulfide concentration was 105 pp.
m, the concentration of methyl mercaptan was 10 ppm. Immediately, 25.0 g of a 0.2% by weight aqueous solution of a cationic dehydrating agent [Kurita Kogyo Co., Ltd., Crifix CP604] was added.
After stirring at 500 rpm for 20 seconds using a stirrer with a single blade, the mixture was poured on a Buchner funnel covered with a nylon filter cloth and filtered. The sludge after filtration was dehydrated using a pressing machine to obtain a dewatered cake. 40 g of the obtained dehydrated cake was put in a gas sampling bag, filled with 1,000 ml of air and sealed, stored in a thermostat at 30 ° C., and after 24 hours, the air in the gas sampling bag was analyzed. Neither hydrogen sulfide nor methyl mercaptan was detected. Example 5 The addition amount of a 1.0% by weight aqueous sodium nitrite solution was 20.0%.
The same operation as in Example 1 was repeated, except that g was used. The concentration of hydrogen sulfide in the air above the sludge slurry in the beaker was 80 ppm, and the concentration of methyl mercaptan was 10 ppm.
In the air in the gas sampling bag, neither hydrogen sulfide nor methyl mercaptan was detected after 24 hours.
After 48 hours, the concentration of hydrogen sulfide was 600 ppm and the concentration of methyl mercaptan was 150 ppm. Example 6 The addition amount of a 1.0% by weight aqueous sodium nitrite solution was 20.0%.
The same operation as in Example 2 was repeated, except that g was used. 1
The concentration of hydrogen sulfide in the air above the sludge slurry in the beaker after standing for 5 minutes was 5 ppm, and methyl mercaptan was not detected. Neither hydrogen sulfide nor methyl mercaptan was detected in the air in the gas sampling bag after 24 hours or 48 hours. After 72 hours, no hydrogen sulfide was detected and the concentration of methyl mercaptan was 10 ppm. . Example 7 The same operation as in Example 6 was repeated, except that the standing time after the addition of the 1.0% by weight aqueous sodium nitrite solution was 3 hours. Neither hydrogen sulfide nor methyl mercaptan was detected in the air above the sludge slurry in the beaker. In the air in the gas sampling bag, after 24 hours, 4
After 8 hours and 72 hours, neither hydrogen sulfide nor methyl mercaptan was detected.

Example 8 400 ml of the mixed raw sludge used in Example 1 was placed in a beaker having a capacity of 500 ml, and 20.0 g of a 2.0% by weight aqueous sodium sulfite solution was added thereto. Then, the beaker was sealed with a polyethylene film. Immediately, when the air above the sludge slurry in the beaker was analyzed, the concentration of hydrogen sulfide was 120 ppm, and the concentration of methyl mercaptan was 10 ppm. Subsequently, a cationic dehydrating agent [Kurita Kogyo Co., Ltd., Crifix CP6]
2], and the mixture was stirred at 500 rpm for 20 seconds using a two-blade stirrer, then poured on a Buchner funnel covered with a nylon filter cloth and filtered. The sludge after filtration was dehydrated using a pressing machine to obtain a dewatered cake. 40 g of the obtained dehydrated cake was put in a gas sampling bag, filled with 1,000 ml of air and sealed, stored in a thermostat at 30 ° C., and analyzed for air in the gas sampling bag after 24 hours. ,
Hydrogen sulfide concentration 2.5 ppm, methyl mercaptan concentration 3
It was 8 ppm. Example 9 After adding a 2.0% by weight aqueous solution of sodium sulfite,
After standing for 3 hours, the air above the sludge slurry was analyzed, and the same operation as in Example 8 was repeated, except that the addition of a cationic dehydrating agent, filtration, and dehydration were subsequently performed. Concentration of hydrogen sulfide in air above sludge slurry in beaker 1
0 ppm, the concentration of methyl mercaptan 25 ppm, 24
In the air in the gas sampling bag after the time storage,
Neither hydrogen sulfide nor methyl mercaptan was detected. Example 10 The same operation as in Example 9 was repeated, except that 12.0 g of a 1.0% by weight aqueous sodium bisulfite solution was added instead of adding 20.0 g of a 2.0% by weight aqueous sodium sulfite solution. After standing for 3 hours, the concentrations of hydrogen sulfide and methyl mercaptan in the air above the sludge slurry in the beaker were both 30 ppm. Neither hydrogen sulfide nor methyl mercaptan was detected in the air in the gas sampling bag after storage for 24 hours. Comparative Example 2 Instead of adding 20.0 g of a 2.0 wt% aqueous sodium sulfite solution, a 1.0 wt% aqueous sodium chlorite solution 1
The same operation as in Example 8 was repeated, except that 2.0 g was added. In the air above the sludge slurry in the beaker,
Neither hydrogen sulfide nor methyl mercaptan was detected. After storage for 24 hours, the concentration of hydrogen sulfide in the air in the gas sampling bag was 850 ppm, and the concentration of methyl mercaptan was 60 ppm. Comparative Example 3 After adding a 1.0% by weight aqueous solution of sodium chlorite and allowing the mixture to stand for 3 hours, the air above the sludge slurry was analyzed, and then the addition, filtration and dehydration of a cationic dehydrating agent were performed. The same operation as in Comparative Example 2 was repeated. The concentration of hydrogen sulfide in the air above the sludge slurry in the beaker was 35 ppm, and the concentration of methyl mercaptan was 5 ppm. The hydrogen sulfide concentration in the air in the gas sampling bag after storage for 24 hours was 1,000 ppm, and the concentration of methyl mercaptan was 300 ppm. Table 1 shows the results of Examples 1 to 10 and Comparative Examples 1 to 3.

[0013]

[Table 1]

[Note] MM: methyl mercaptan, nd:
Not detected. As is clear from the results of Examples 1 to 10, nitrite,
When sulfites or bisulfites were added, no malodorous components were detected or reduced to a slight amount from the dehydrated cake 24 hours after the dehydration. In Examples 1 to 3 in which the addition amount of sodium nitrite was 300 mg / liter, the malodorous component in the air on the sludge slurry before filtration decreased with the passage of the standing time, and was not detected after standing for 3 hours. I have. That is, even when the sludge slurry needs to be deodorized, it is possible to deodorize the location by adding nitrite at least 15 minutes before reaching the location where deodorization is required. Further, in Example 3, in which the deodorized cake was allowed to stand for 3 hours after the addition of sodium nitrite, the malodorous component was not detected until after 48 hours, and the amount detected after 72 hours was slight. In Example 2 in which the standing time was 15 minutes and in Example 1 in which the standing time was not taken, no odor component was detected after 24 hours.
The detection amount of the offensive odor component after the time was 1 in Example 1 and 2 in Example 1.
It is 1/50 to 1/50 or less, and it is recognized that the deodorizing effect is significantly improved by taking a standing time after the addition of sodium nitrite. 300mg sodium nitrite
The results of Examples 2 and 3 in which the mixture was left for 15 minutes or 3 hours after the addition of 1 g / l were better than the results in Example 5 in which 500 mg / l of sodium nitrite was added and the standing time was not increased. Furthermore, even in the case where the amount of sodium nitrite added was 100 mg / liter, in Example 4 in which the mixture was left for 15 minutes after addition and then dehydrated, an odor component was detected in the dehydrated cake 24 hours after the dehydration. Absent. It can be seen that by adding sodium nitrite to the sludge slurry and dewatering after 15 minutes or more, the amount of sodium nitrite added can be reduced. In Examples 5 to 7 in which the addition amount of sodium nitrite was further increased to 500 mg / liter, the malodorous component in the air on the sludge slurry before filtration was further reduced. Further, in Example 5, in which the standing time after the addition of sodium nitrite was not taken, the malodor component of the dehydrated cake was not detected until after 24 hours, but the malodor component was detected after 48 hours. But,
In Example 7, which was left for 3 hours after adding sodium nitrite,
After 72 hours, it was not detected at all,
Even in Example 6, which was set to be minutes, no detection was made until after 48 hours.
The detection amount after 72 hours is also small. In Example 8 in which 1,000 mg / liter of sodium sulfite was added instead of sodium nitrite, the malodorous component was reduced. Further, Example 9 was left for 3 hours after the addition of sodium sulfite.
In Example 1, the concentration of the malodorous component in the air on the sludge slurry before filtration was low, and no malodorous component was detected from the dehydrated cake after 24 hours. In Example 10 in which 300 mg / liter of sodium bisulfite was added and dehydrated after 3 hours,
No odor component was detected after 24 hours. In comparison with Comparative Example 2 and Comparative Example 3 in which 300 mg / L of sodium chlorite conventionally known as a deodorant was added instead of sodium nitrite, it was found that Comparative Example 2 had just added sodium chlorite. No malodorous component was detected from the air on the sludge slurry, and no malodorous component was detected immediately after dehydration from the dewatered cake obtained by treating this sludge slurry. However, after 24 hours, a large amount of malodorous components is detected from the dehydrated cake. Further, in Comparative Example 3 in which the mixture was left for 3 hours after the addition of sodium chlorite, a malodorous component was detected from air on the sludge slurry before filtration,
The amount of the malodorous component detected from the dehydrated cake after 24 hours is also larger than that in Comparative Example 2. That is, when sodium chlorite is added, the malodor of the dehydrated cake after 24 hours cannot be prevented, and taking a standing time after the addition has an adverse effect on deodorization. From these results, taking a standing time after the addition of the drug, adding the drug to the sludge slurry and dewatering after 15 minutes or more, to exhibit good deodorizing properties, nitrite,
It turns out that it is a unique effect which sulfite and hydrogen sulfite have.

[0015]

According to the deodorizing agent and the deodorizing method of the present invention,
By using a non-chlorine-based or non-metal-based drug and adding a small amount of the drug, the deodorizing effect is maintained, and the generation of malodor of the dehydrated cake can be prevented for a long time.

[Brief description of the drawings]

FIG. 1 is a process flow diagram of one embodiment of sewage treatment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 First sedimentation tank 2 Aeration tank 3 Final sedimentation tank 4 Sludge concentration tank 5 Sludge storage tank 6 Dehydrator

Claims (4)

[Claims] 1. A deodorizing agent for a dehydrated cake, comprising a nitrite, a sulfite or a hydrogen sulfite. 2. A method according to claim 1, wherein the nitrite, sulfite or bisulfite is
A method for deodorizing a dewatered cake, comprising adding to a sludge slurry and then dewatering. 3. The method for deodorizing a dehydrated cake according to claim 2, wherein the elapsed time from the addition of the nitrite, the sulfite or the hydrogen sulfite to the sludge slurry until the dehydration is 15 minutes or more. 4. The method for deodorizing a dehydrated cake according to claim 3, wherein the elapsed time from the addition of the nitrite, the sulfite or the hydrogen sulfite to the sludge slurry until the dehydration is 3 hours or more.