JP2000351000A - Deodorant for dewatered sludge cake and method for preventing generation of odor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the generation of odors from odorous substances such as hydrogen sulfide generated from sludge and dewatered cake in a sewage disposal plant, and the like, effectively by the use of a harmless, pollution-free chemical agent, by preparing a deodorant containing sorbic acid as an effective component. SOLUTION: In a sewage disposal plat, raw water is supplied to a first precipitation basin 1, and initial precipitation sludge is separated. The supernatant of the basin 1 is supplied to an aeration tank 2 for bio-treatment, and the treated water is supplied to a final precipitation basin 3, and sludge is separated. Excess sludge is supplied to a sludge concentration tank 4 together with the initial precipitation sludge, and the sludge is concentrated, sent to a sludge storage tank 5, stored, dewatered by a dewaterer 6, and carried out as dewatered cake. A deodorant to be added into the dewatered cake to prevent the generation of odors is prepared to contain solid sorbic acid as an effective component. Sorbit acid is preferably added immediately before a dewatering process.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an agent for preventing odor generation from sludge dewatered cake and a method for preventing odor generation. More specifically, the present invention provides a sludge dewatering method 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 such as a sewage treatment plant. The present invention relates to a cake odor generation inhibitor and a method for preventing odor generation.

[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 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 on the sludge slurry, such as being able to obtain a deodorizing effect immediately after being added, but is consumed by directly reacting with the reducing substance in the sludge. Therefore, there is a disadvantage that the effect is lost in a short time. JP-A-5-253599 discloses a deodorizing method capable of efficiently suppressing odors generated from various dehydrated cakes, which includes a chlorite and a hypochlorite, and optionally a bacteriostat-based deodorant. A method of deodorizing a dehydrated cake using both of them 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. ° 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-63-205
No. 197 proposes a method of deodorizing wastewater and sludge gas containing malodorous substances such as hydrogen sulfide, ammonia, and methyl mercaptan with a zinc compound such as zinc sulfate, and a deodorizing treatment using a copper compound. Methods are also known. Zinc compounds and copper compounds have an immediate effect and also have an effect of preventing odor generation of dehydrated cake, but when performing secondary use of dehydrated cake, such as cement materials and compost, there is a concern that adverse effects at the place of use, Use is avoided.
In addition, metal salts, particularly copper chloride, are highly corrosive, and there is a concern that they may adversely affect equipment. In addition, 1-6031
No. 9 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 environment in which microorganisms grow. 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. Also, JP-A-50-105890 discloses that
A method of adding sulfite to sludge mainly composed of white bran generated from rice washing wastewater or a dewatered cake thereof to prevent the propagation of various bacteria and preventing decay is described.How to deodorize a sludge dewatered cake that emits a strong odor Had not been considered. Japanese Patent Application Laid-Open No. 4-126597 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 used is high, which may lead to an increase in processing cost. Conventionally, dewatered cakes have been disposed of by landfill or incineration. In recent years, recycling such as utilization of soil improvement materials by composting and use of incinerated ash as a cement raw material has become popular. When used for compost and cement, in particular, the content of heavy metals must be avoided as much as possible, and it has become necessary for the odor control agent to be free of heavy metals. However, the chemicals used to deodorize conventional dehydrated cakes are not only metal salts,
As antibacterial agents, those containing metals such as zinc are often used, as represented by zinc pyrithione. A bacteriostatic agent containing a metal generally exhibits a large odor preventing effect due to a deodorizing effect of a metal and a rot preventing effect of the bacterium, but has a drawback of increasing the heavy metal concentration when used in a dewatered cake. Although iron salts are used for the purpose of preventing odor as a metal having little environmental impact, the effect is insufficient. Under the general circumstance that the more effective the bacteriostatic agent is, the higher the toxicity is, it is desired that the deodorized cake has a strong odor generation-preventing action and a low toxicity to the human body and the environment. Based on these circumstances, use drugs that do not contain heavy metals except chlorine and iron, and that are less toxic,
There is a need for an odor generation inhibitor and a method for preventing odor generation, which have a low treatment cost, maintain an odor generation prevention effect for a long time, and are capable of deodorizing sludge slurry to dewatered cake.

[0003]

DISCLOSURE OF THE INVENTION The present invention is intended to reduce the generation of odors originating from malodorous substances such as hydrogen sulfide and methyl mercaptan generated from sludge and dewatered cakes of sewage treatment plants and the like, by using chemicals that do not affect humans and the environment. It is an object of the present invention to provide an odor generation inhibitor and an odor generation prevention method for a sludge dewatered cake that can be effectively prevented by using the same.

[0004]

Means for Solving the Problems The present inventors have conducted intensive studies to solve the above-mentioned problems, and as a result, have noticed that sorbic acid, which is approved as a food additive, is particularly safe. As a result of intensive studies on the conditions for using this in a dewatered cake, they have found conditions in which the effect of preventing odor generation is excellent, and based on this finding, have completed the present invention. That is, the present invention includes the following items. (1) An odor generation inhibitor for a sludge dewatered cake, comprising a sorbic acid solid as an active ingredient. (2) A method for preventing odor generation of a sludge dewatered cake, comprising adding sorbic acid to a sludge slurry and then subjecting the sludge slurry to a dewatering step. (3) A sludge dewatering cake characterized by adding an oxidizing agent and at least one salt selected from nitrite, sulfite and hydrogen sulfite to a sludge slurry, and then adding sorbic acid to the sludge slurry. How to prevent odor generation. (4) A method for preventing odor generation in a sludge dewatered cake, comprising adding a ferric salt to a sludge slurry to lower the pH to less than 5, and adding sorbic acid and an amphoteric polymer coagulant to dewater the sludge.

[0005]

DETAILED DESCRIPTION OF THE INVENTION There is no particular limitation on the sludge to which the present invention is applied. It can be applied to sludge.
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 fed to the aeration tank 2 after adding a flocculant as needed, 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 dewatered by the dewatering machine 6 and carried out as a dewatered 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. The sorbic acid used in the present invention is a metal-free bacteriostatic agent and has a toxicity of LD50 (rat / rat).
It is characterized by a point of 10.50 ± 1.96 g / kg, which is significantly smaller than other drugs. For example, the toxicity is remarkably lower than that of zinc pyrithione, which is 331 mg / kg of LD50 (rat, diameter). Sorbic acid is a substance present in plants such as rowan and has biodegradability. The sorbic acid used in the present invention needs to be used in the form of powder or suspension, and water-soluble salts such as sodium salt and potassium salt are extremely ineffective.

[0006] The place where the sorbic acid of the present invention is added is not limited, but it is preferable to add it immediately before the dehydration step. The shorter the time from the addition to the flow into the dehydration step, the better, and it depends on the temperature conditions, but it is preferably within 15 minutes at room temperature, preferably within 3 minutes. Specifically, in consideration of mixing with the sludge slurry, it is desirable to add the same as the dehydrating agent shown in FIG. That is,
The sludge slurry discharged from the wastewater treatment process is stored in the sludge thickening tank, from which it is sent to a drawing pump, a drawing line, a storage tank, a mud pump, a mud sending line, a coagulation tank, and a dehydrator in that order to become a dewatered cake. In the process of a normal sludge slurry, it may be anywhere from after the mud pump to be sent out to the dehydrator to before the entrance of the dehydrator, for example, a mud feed line at the outlet of the mud pump, or a coagulation reaction immediately before dehydration. Can be added to the tank. The amount of the sorbic acid of the present invention is 50 to 3,000 mg per volume of the sludge slurry.
/ L can be added. The longer the amount of addition, the longer the duration of deodorization. In this way, by adding to sludge and dewatering immediately before the dehydration step, sorbic acid can be prevented from dissolving in water and flowing out into the dehydrated filtrate. As a result, it efficiently remains in the dehydrated cake and prevents generation of hydrogen sulfide and methyl mercaptan due to decomposition of sulfur-containing organic substances by microorganisms. Over time after the addition of sorbic acid, sorbic acid dissolves, flows out, or is consumed by other components, reducing the efficiency of the microbial bacteriostatic action of the dehydrated cake. In the present invention, an oxidizing agent and a nitrite, a sulfite or a bisulfite can be used together with sorbic acid. Further, by using a ferric salt in combination and setting the pH to less than 5, the effect is remarkably improved. The oxidizing agent used in combination with sorbic acid in the present invention includes chlorite, hydrogen peroxide, permanganate, iodate, hypochlorite, percarbonate, bromate, persulfate A known oxidizing agent such as a salt can be used. In particular, chlorite, hydrogen peroxide, permanganate, and iodate are preferred. Among these oxidizing agents, an oxidizing agent containing no heavy metal can be suitably used in combination.

The nitrite used in the present invention is not particularly limited in order to simply increase the deodorizing effect. Examples thereof include ammonium nitrite, sodium nitrite, potassium nitrite, rubidium nitrite, cesium nitrite, calcium nitrite, and calcium nitrite. Examples include strontium nitrate, magnesium nitrite, barium nitrite, nickel nitrite, 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, heavy metal salts such as nickel nitrite, copper nitrite, silver nitrite, zinc nitrite, thallium nitrite, etc., may cause adverse effects at the destination when secondary use of the dehydrated cake, and sorbic acid Although the addition amount can be reduced by the combined use with, it may not be desirable. In the present invention, sodium nitrite, potassium nitrite, ammonium nitrite, magnesium nitrite and the like can be suitably used. The sulfite or bisulfite used in the present invention is not particularly limited for its deodorizing effect. For example, ammonium, lithium, sodium, potassium, rubidium, cesium,
Thallium etc. can be mentioned. One of these sulfites and bisulfites can be used alone, or two or more can be used in combination. Among these sulfites or hydrogen sulfites, ammonium and sodium and potassium salts can be particularly preferably used without any adverse effect on the destination where the dehydrated cake is used secondarily. Examples of the ferric salt used in combination with sorbic acid in the present invention include ferric chloride, ferric sulfate, ferric polysulfate, and ferric nitrate. It is also recommended to use these ferric salts and acids in combination or to use a mixture of ferric salts and acids in order to promote the pH reduction of the sludge slurry.

In the method of the present invention, nitrite, sulfite or bisulfite is added to the sludge slurry and then dewatered. In this case, dehydration can be carried out more effectively and continuously by dewatering after 15 minutes or more, more preferably 2 hours or more after the addition. Therefore, when the process shown in FIG. 1 is taken, nitrite, sulfite or bisulfite is added in the sludge concentration tank 4 or the sludge storage tank 5 and the sludge slurry is dewatered in the dewatering machine 6 for 15 minutes or more. It is preferable that the process be performed after a lapse of more than two hours. 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. Add nitrite, sulfite or bisulfite to the sludge slurry and add
By performing dehydration after elapse of at least minutes, generation of malodorous components from the dehydrated cake can be prevented for a longer time. Nitrite, sulfite and bisulfite are:
The sludge slurry also has a deodorizing effect of the existing odor, and the effect becomes remarkable when 15 minutes or more have passed after the addition. Therefore, when the odor of a sludge treatment device such as a storage tank or a dehydrator becomes a problem, the nitrite, sulfite or bisulfite is added at least 15 minutes before the sludge slurry reaches the device requiring deodorization. Thereby, not only the dewatered cake but also the deodorization around these devices can be performed. The oxidizing agent used in combination with the present invention is not particularly limited in the timing of addition, but is preferably immediately before dehydration, and can be added usually at any time before the addition of sorbic acid. In the method of the present invention, the ferric salt is added so that the pH of the sludge slurry is less than 5. The effect of preventing the generation of odor of the sludge dewatered cake is greater as the pH is lowered. Therefore, it is economically advantageous to use a ferric salt and an acid together or a mixture thereof. The order of addition of the ferric salt and sorbic acid is not limited, but the shorter the time until the step of dehydrating sorbic acid, the better, and the deodorizing action of the existing odor of the ferric salt is preferably several tens of minutes. Therefore, it is preferable to add the ferric salt first. Specifically, it is added to the sludge supply pump outlet or the like on the way to the sludge storage tank 5 or the dehydrator 6 in FIG.

In the method of the present invention, there is no particular limitation on the method of dewatering the sludge slurry, and for example, a centrifugal dehydrator, a belt press dehydrator, a screw press dehydrator, a filter press dehydrator, a vacuum dehydrator and 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 added dehydrating agent include an anionic polymer flocculant, a cationic polymer flocculant, and an amphoteric polymer flocculant. However, when sorbic acid is used at a pH of less than 5 by adding a ferric salt, an amphoteric polymer coagulant having an anionic group and a cationic group in the same molecule shows a good coagulation / dehydration effect, In addition, a cationic polymer flocculant cannot be dehydrated. In the method of the present invention, the method of adding the oxidizing agent, nitrite, sulfite or bisulfite used in combination with sorbic acid is not particularly limited, and these may be added in the form of an aqueous solution or powder. In the method of the present invention, the oxidizing agent added to the sludge slurry is a sludge slurry 1 in terms of hydrogen peroxide.
Preferably, it is 25 to 2,000 mg per L.
It is more preferable that the amount be from 00 to 1,000 mg. In the present invention, the amount of the nitrite, sulfite or bisulfite used in combination is not particularly limited, but is preferably 25 to 1,000 mg, more preferably 100 to 500 mg. In particular, these salts may be added to the sludge slurry for 1
When dehydration is performed after 5 minutes or more, the deodorizing effect of the dehydrated cake is maintained for a long time with a smaller amount of addition. If the addition amount of nitrite, sulfite or bisulfite is less than 25 mg per liter of sludge slurry, the combined use of the deodorizing effect is insufficient. The addition amount of nitrite, sulfite or bisulfite is 1,000 mg or less per 1 L of the sludge slurry, so that a sufficient deodorizing effect can be obtained. Usually, nitrite, sulfite or hydrogen sulfite exceeding 1,000 mg per 1 L of the sludge slurry is obtained. No salt needs to be added.

In the method of the present invention, the amount of the ferric salt to be added is not limited, but the pH of the sludge after the addition is less than 5,
Preferably it is required to be between 3.5 and 4.5. The amount of the ferric salt required for this purpose is 2,000 to 5,000 mg / L for a ferric chloride solution (containing about 13% by weight of iron) and a ferric polysulfate solution (about 10% by weight). 2,500 ~
It is about 7,000 mg / L. If the alkalinity of the sludge is high, the amount of ferric salt added to be less than pH 5 increases, so it is economically advantageous to use an acid such as sulfuric acid in combination or by mixing it with ferric salt. . From the sludge slurry,
Hydrogen sulfide is generated by the activity of sulfate-reducing bacteria,
Sulfur-containing organic substances are decomposed by general microorganisms to generate hydrogen sulfide and methyl mercaptan. According to the method of the present invention, sorbic acid, optionally an oxidizing agent or nitrite, sulfite or bisulfite, or a ferric salt so as to have a pH of less than 5, is added to the sludge slurry to suppress the activity of microorganisms. Further, it is possible to suppress the generation of a new malodorous component, suppress the activity of microorganisms in the dehydrated cake even after dehydration, and prevent the generation of odor from the dehydrated cake.

[0011]

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 carried out by using a gas detection tube 4 manufactured by Gastec.
M, 4L, or 4LL was used to analyze methyl mercaptan using a gas detection tube 71H or 71 manufactured by Gastech. The lower detection limit concentration is 0.25 ppm for both hydrogen sulfide and methyl mercaptan. Examples 1 to 11 and Comparative Examples 1 to 7 Mixed raw sludge collected at A sewage treatment plant [pH: 4.8, SS
(Suspended substance: 17,000 mg / L) was placed in a beaker, the indicated drug was added, and the mixture was stirred 20 times with a spoonful. Next, a cationic polymer-based 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 pressed using a pressing machine to obtain a dewatered cake. This dehydrated cake is placed in a tetra bag, and the amount of dehydrated cake (28.1 to 3
0.2 g) of 25 times the volume of air, sealed,
Stored in a thermostat. The odorous substances in the bag, hydrogen sulfide (H ₂ S) and methyl mercaptan (MM), were measured every measurement time after the dehydrated cake was sealed in the tetra bag. When two kinds of drugs are used in combination, they were separately added so as to reach respective predetermined standing times. Sorbic acid was added by weighing the powdered drug. For hydrogen peroxide, sodium nitrite, sodium sulfite, and sodium bisulfite, aqueous solutions of the respective reagents were used. The amounts of addition are indicated in terms of weight of each pure product.

[0012]

[Table 1]

[0013]

[Table 2]

Comparative Example 1 is a blank test in which no drug was added. Examples 1 to 4 and Comparative Example 1 show that the deodorizing effect due to the addition of sorbic acid is remarkable, and that the duration of the deodorizing effect increases as the amount of sorbic acid increases. Examples 5 to 11, Example 1 and Comparative Example 2
The results of Nos. To 7 indicate that the combined use of sorbic acid and each drug improves the deodorizing effect. Examples 2 and 7
Indicates that the odor eliminating effect is reduced when sorbic acid is not added immediately before. Examples 12-18, Comparative Examples 8-11 and Reference Example 1 Mixed raw sludge collected at the B sewage treatment plant [pH: 6.1, SS
(Floating substance): 23,800 mg / L] 300 mL was placed in a beaker, and the odor generation suppressing effect was evaluated in the same manner as in Examples 1 to 11, except for the type of dehydrating agent and the amount added.

[0015]

[Table 3]

As the dehydrating agent, the cationic polymer type dehydrating agent CP604 was used in Comparative Examples 8 and 9 and Reference Example 1. When an iron salt was used in combination, an amphoteric polymer type dehydrating agent [Kurita Kogyo Co., Ltd., Chrisbest P358] It was used. In addition, iron salt was added and pH 5
In the sludge of less than 3, the flocculation floc was fine with the cationic polymer dehydrating agent and could not be dehydrated. Reference Example 1 to which 1,000 mg / L of sorbic acid was added had an odor control effect for 24 hours, but at 100 mg / L, the effect was improved, but the effect was insufficient. On the other hand, when the pH is adjusted to less than 5 by adding polyiron sulfate (PFS), 1
Odor generation of about 48 hours or more can be prevented at 00 mg / L, and this effect becomes more pronounced as the amount of iron salt added is increased and the pH is lowered. Comparative Examples 10 and 11 are cases where only the iron salt is used. Since the iron salt has an effect of fixing generated hydrogen sulfide, the amount of generated hydrogen sulfide is reduced. However, the effect of suppressing the generation of methyl mercaptan is small, and methyl mercaptan contributes more to malodor than hydrogen sulfide. Examples 19 to 22, Comparative Examples 12 to 13, and Reference Example 2 The same sludge as in Examples 12 to 18 was evaluated for the time and effect from sorbic acid powder addition to dewatering.

[0017]

[Table 4]

The potassium salt aqueous solution of Comparative Example 12 was 100 mg /
L, the odor could not be suppressed for 24 hours.
At 48 mg / L, an odor generation preventing effect of about 48 hours was obtained. This is when the sludge slurry is dewatered into a dewatered cake,
It is determined that 9/10 of the slurry amount was removed as the dehydrated filtrate, and at the same time, sorbic acid also flowed out into the filtrate at the same rate (9/10) and the amount remaining in the dehydrated cake was reduced to 1/10. Sorbic acid has a solubility in water of about 2,000mg
/ L, and the powder is gradually dissolved in water even when the powder is added. Therefore, when the time from the addition to the dehydration is as long as 180 minutes, the effect is almost the same as that of the aqueous potassium salt solution.
Therefore, the time of the addition-dehydration step is desirably about 15 minutes or less. Examples 23 to 25 and Comparative Examples 14 to 19 Example 12 (3,000 mg / L iron polysulfate, 100 mg / L sorbic acid added), Example 13 (5.00 ppm iron polysulfate)
0 mg / L, sorbic acid 100 mg / L) and Example 1
4 (7,000 mg / L iron polysulfate, 100 mg sorbic acid
/ L addition), an amphoteric polymer coagulant [Kurita Kogyo Co., Ltd., Kribest P358] cationic polymer coagulant [Kurita Kogyo Co., Ltd., Crifix CP604]
Alternatively, an anionic polymer flocculant [Kurita Kogyo Co., Ltd., Cliflock PA331] was added, and flocculation and dehydration tests were performed.
The amount of sludge collected was 200 mL, and a 0.2% by weight aqueous solution of a polymer flocculant was added to 60 mg / L, 80 mg / L, 100 mg / L,
After adding 120 mg / L, 140 mg / L or 160 mg / L and reacting, the whole amount was filtered using a 40-mesh filter cloth having a filtration area of 19.6 cm ² , and the filtrate amount after 20 seconds was measured.
The addition amount of the polymer flocculant and the filtrate amount after 20 seconds shown in Table 4 are values when the maximum filtrate amount was obtained. The cake obtained by the gravity filtration, from which the maximum amount of filtrate was obtained, was packed in a column having a diameter of 3 cm and a height of 1.75 cm, and dehydrated for 60 seconds at a pressure of 0.10 MPa through a filter cloth and a sponge vertically. The diameter of the dehydrated cake was measured, the peelability was visually determined, and the water content of the cake was measured. Further, the cake yield per unit area was determined from the dry weight of the cake and the diameter of the cake.
Three times the cake yield (mg / cm ² ) is the empirically estimated filtration rate (kg / m · H).

[0019]

[Table 5]

[0020]

[Table 6]

As can be seen from Table 4, only Examples 23 to 25 in which an amphoteric polymer flocculant was added were capable of flocculation filtration and dehydration, and were a cationic polymer flocculant or an anionic polymer flocculant. In Comparative Examples 14 to 19 in which was added, the coagulation and filtration properties were remarkably inferior, and the result was that dehydration was impossible.

[0022]

According to the present invention, the addition of sorbic acid can prevent the generation of odor from the dehydrated cake, and its effects are to increase the amount added, to use in combination with an oxidizing agent, to use nitrite and sulfite. Alternatively, by using it together with bisulfite or using it together with ferric salt and adjusting the pH to less than 5, the effect can be maintained for a long time. In addition, the sorbic acid and the concomitant drug used in the present invention are highly safe, have a small effect on the environment in the secondary use of the sludge dewatered cake, and are extremely toxic compared with the conventional odor generation prevention method using a bacteriostatic agent. With no adverse effects on the human body.

[Brief description of the drawings]

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

[Explanation of symbols]

 1 first sedimentation tank 2 aeration tank 3 final sedimentation tank 4 sludge concentration tank 5 sludge storage tank 6 dehydrator

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) // C09K 3/00 C09K 3/00 S (72) Inventor Shiro Arimura 3-chome Nishishinjuku, Shinjuku-ku, Tokyo No. 4 No. 7 Kurita Kogyo Co., Ltd. (72) Inventor Nobumi Maejima No. 4-7 Nishi Shinjuku 3-chome, Shinjuku-ku, Tokyo F-term inside Kurita Kogyo Co., Ltd. 4D059 AA04 AA05 BE08 BE16 BE26 BE38 BE53 BE56 BF12 BF16 BK02 DA22 DA23 DA24 DA33 DA44 DA45 DA70 DB08 EA01 EB05 EB11 EB16 4H011 AA02 BA06 BB06 BB18 DD01 DG03

Claims (4)

[Claims] An odor control agent for a sludge dewatered cake, comprising a solid sorbic acid as an active ingredient. 2. A method for preventing odor generation from a sludge dewatered cake, comprising adding sorbic acid to a sludge slurry and then subjecting the slurry to a dewatering step. 3. A sludge characterized by adding an oxidizing agent and at least one salt selected from nitrites, sulfites and bisulfites to a sludge slurry, and then adding sorbic acid to the sludge slurry. A method for preventing odor generation of dehydrated cake. 4. A sludge slurry having a pH of 5 by adding a ferric salt.
A method for preventing odor generation of a sludge dewatered cake, characterized in that the dewatering is carried out by adding sorbic acid and an amphoteric polymer flocculant.