JP2003010889A - Odor preventing method for sludge dehydration cake - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an odor preventing method of a sludge dehydration cake capable of effectively preventing the odor derived from hydrogen sulfide, methylmercaptane, ammonia and an amine generated from the sludge hydration cake at a sewage treating plant, a excretion treating plant for a long period of time. SOLUTION: In the odor preventing method for a sludge dehydration cake, dry ice and an anti-fungi agent are co-existed at the sludge dehydration cake.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for preventing odor generation of a sludge dewatering cake. More specifically, the present invention is a sewage treatment plant, hydrogen sulfide generated from sludge dewatering cake such as human waste treatment plant, methyl mercaptan, ammonia,
The present invention relates to a method for preventing odor generation in a sludge dewatering cake, which can effectively prevent odors derived from amines and the like for a long time.

[0002]

2. Description of the Related Art Sewage treatment plants, human waste treatment plants, food factories,
Various sludges are generated in the process of treating organic industrial wastewater such as pulp and paper factories. For example, solid-liquid separation of sewage in a first settling basin produces first settling sludge, and treatment of the supernatant of the first settling basin using an aeration tank or the like by a floating organism method increases the amount of activated sludge. The water treated in the aeration tank etc. is guided to the final settling basin, the activated sludge is separated, part of it is returned to the aeration tank etc. as return sludge, and the rest is made into excess sludge. The initial sludge and excess sludge are guided to a sludge thickening tank, and then temporarily stored in a sludge storage tank. The sludge in the sludge storage tank is then dehydrated by a dehydrator, and the obtained sludge dehydrated cake is carried out for landfill or incineration. The sludge dewatered cake after dewatering produces a malodorous substance due to decay. Substances often detected as malodorous substances generated in sewage treatment plants are hydrogen sulfide, sulfur compounds such as methyl mercaptan, nitrogen compounds such as ammonia and trimethylamine, and lower fatty acids such as valeric acid and isobutyric acid. Among these, the amounts of hydrogen sulfide and methyl mercaptan are particularly large. Many sludge storage tanks and dehydrators are closed systems, but sludge dewatering cakes obtained by dehydration are often transported and stored in an open system, so odor control is important. That is, a conveyor or a truck is usually used to convey the sludge dewatering cake, and the sludge dewatering cake, which is an odor generating source, moves. Therefore, it is difficult to perform processing such as covering with a lid or sucking the odor, and it is difficult to take measures against the odor. In addition, even in the final landfill, the generated odor diffuses, causing unpleasant sensation to nearby residents, which adversely affects the environment. For this reason, it is necessary to suppress the odor itself generated from the sludge dewatering cake, and various deodorizing methods have been conventionally proposed. We have added 2 mL of water to 100 mL of water at 25 ° C for sludge dewatering cake, such as nitrite.
A method for preventing odor generation of sludge dewatering cake by adding a bacteriostatic agent that dissolves 0 g or more was previously proposed. According to this method, the odor generation of the sludge dewatering cake can be effectively prevented, but the odor control of the sludge dewatering cake is limited to 48 hours, and depending on the sludge property or the like, or in the summer, In some cases, it was difficult to control the odor over time. For this reason, there has been a demand for a method for preventing the generation of odors in sludge dewatering cakes, which can prevent the generation of odors for a longer period of time.

[0003]

DISCLOSURE OF THE INVENTION The present invention effectively prevents odor derived from hydrogen sulfide, methyl mercaptan, ammonia, amine, etc. generated from sludge dewatering cake in sewage treatment plants, night soil treatment plants, etc. for a long time. The present invention has been made for the purpose of providing a method for preventing the generation of odor in a sludge dehydrated cake.

[0004]

Means for Solving the Problems As a result of intensive studies to solve the above problems, the present inventors have found that the coexistence of dry ice and a bacteriostatic agent in a sludge dewatering cake has the effect of preventing odor generation. The inventors have found that they can be stably maintained for a long time, and have completed the present invention based on this finding. That is, the present invention provides (1) a method for preventing odor generation from a sludge dewatering cake, characterized by allowing dry ice and a bacteriostatic agent to coexist in the sludge dewatering cake, and (2) the average particle size of the dry ice is 0. The method for preventing odor generation of a sludge dewatering cake according to claim 1, which is .1 to 10 cm, (3) The method for preventing odor generation of a sludge dewatering cake according to claim 1, wherein dry ice is supplied to the hopper of the sludge dewatering cake, 4) Dry ice is supplied to the hopper of the sludge dewatering cake, and then the inside of the hopper is shielded from the atmosphere. The method for preventing odor generation of the sludge dewatering cake according to claim 3, and (5) the bacteriostatic agent is nitrite. A method for preventing odor generation of a sludge dewatering cake according to item 1,
Is provided.

[0005]

BEST MODE FOR CARRYING OUT THE INVENTION In the method for preventing odor generation of a sludge dewatering cake according to the present invention, dry ice and a bacteriostatic agent are allowed to coexist in the sludge dewatering cake. Usually, in order to dehydrate sludge, the sludge slurry is supplied from a sludge storage tank to a dehydrator, and the dehydrated sludge dewatering cake is transferred by a conveyor or the like to the hopper of the sludge dewatering cake and temporarily stored. The stored sludge dehydrated cake is regularly carried out and disposed. In many cases, the sludge is dehydrated continuously during the day, for example, from 9 to 16 o'clock, and the sludge dewatering cake is unloaded.
The next day or the day after the next day. While the sludge is being dehydrated, the sludge dewatering cake produced by dehydration is continuously supplied to the hopper. By coexisting dry ice and a bacteriostatic agent in the sludge dewatering cake, the synergistic effect of dry ice and a bacteriostatic agent is remarkably exhibited, and the odor generation preventing effect is stably maintained for a long time. In the method of the present invention,
There is no particular limitation on the size of dry ice supplied to the sludge dewatering cake, and crushed dry ice can be crushed to use a crushed product of any size, but with an average particle size of 0.1 to 10 cm. It is preferably, and more preferably 1 to 5 cm. The particle size of the dry ice is a particle size obtained as a virtual spherical shape by measuring the weight of the crushed dry ice and dividing it by the density of 1.56 g / cm ³ to obtain the volume. If the average particle size of dry ice is less than 0.1 mm,
The vaporization of dry ice may be too fast and the duration of the odor prevention effect may be shortened. If the average particle size of dry ice exceeds 10 cm, it may be difficult to uniformly mix it with the sludge dewatering cake.

In the method of the present invention, dry ice is preferably supplied to the hopper of the sludge dewatering cake. There is no particular limitation on the method for supplying dry ice to the hopper of the sludge dewatering cake, for example, dry ice can be directly supplied to the hopper of the sludge dewatering cake, or
It is also possible to add dry ice to the sludge dewatering cake that is transferred from the dewatering machine to the hopper by a conveyor or the like, and supply it to the hopper together with the sludge dewatering cake. The dry ice can be continuously supplied while the sludge dewatering cake is being supplied to the hopper, or can be intermittently supplied. When the supply of the sludge dewatering cake to the hopper is completed, shut off the inside of the hopper from the atmosphere,
It is preferable to reduce the escape of carbon dioxide generated by vaporization of dry ice. In the method of the present invention, the supply amount of dry ice to the sludge dewatering cake is not particularly limited, but is preferably 10 to 100 g per 1 kg of the sludge dewatering cake, and 20 to 50 g per 1 kg of the sludge dewatering cake.
Is more preferable. The supply amount of dry ice is
If it is less than 10 g per 1 kg of sludge dewatering cake, the effect of preventing odor generation may be insufficient. Even if the amount of dry ice supplied exceeds 100 g per 1 kg of sludge dewatering cake, the purpose of preventing odor generation can be achieved, but it may be economically disadvantageous.

In the method of the present invention, the bacteriostatic agent is an agent which inhibits the growth or proliferation of bacteria. In the method of the present invention, a drug generally called a bactericidal agent can also be used as a bacteriostatic agent by exhibiting a bacteriostatic action by using it at a low concentration. Examples of the bacteriostatic agent used in the method of the present invention include nitrite, hypochlorite, quaternary ammonium salt, ethanol, formaldehyde, pyrithione (2-pyridinethiol-1-oxide), its sodium salt and zinc salt. , Derivatives such as dimers, and sorbic acid. These bacteriostatic agents may be used alone or in combination of two or more. Among these, nitrite can be preferably used, for example, ammonium nitrite, lithium nitrite, sodium nitrite, potassium nitrite, cesium nitrite, magnesium nitrite, calcium nitrite, strontium nitrite, barium nitrite. , Nickel nitrite, lead nitrite and the like. Among these, sodium nitrite, potassium nitrite, and calcium nitrite are easy to handle and obtain, and do not hinder the secondary use of the sludge dewatering cake, and thus can be particularly preferably used.

In the method of the present invention, there is no particular limitation on the method for allowing the bacteriostatic agent to be present in the sludge dewatering cake. For example, the bacteriostatic agent can be added to the sludge slurry before dehydration, or the sludge after dehydration can be added. It is also possible to add a bacteriostatic agent to the dehydrated cake. When the bacteriostatic agent is a water-insoluble or sparingly soluble compound, the bacteriostatic agent can be uniformly dispersed in the sludge dehydrated cake by adding the bacteriostatic agent to the sludge slurry before dehydration. Further, even if the water-insoluble or sparingly soluble bacteriostatic agent is added to the sludge slurry, the ratio of being lost in the filtered water in the dehydration step is small. When the bacteriostatic agent is a water-soluble compound, the bacteriostatic agent is added to the sludge dewatering cake as it is or after preparing an aqueous solution of the bacteriostatic agent, and the mixture is stirred to form the bacteriostatic agent in the sludge dewatering cake. It can exist almost uniformly. Alternatively, the bacteriostatic agent can be made into a high-concentration aqueous solution, and can be sprayed, for example, with a sprayer on the sludge dewatering cake conveyor, the outlet to the cake hopper, and the like. Alternatively, even a readily water-soluble bacteriostatic agent can be added to the sludge slurry before dehydration. When the bacteriostatic agent is added to the sludge dehydrated cake as an aqueous solution, a large dilution ratio results in addition of a large amount of water, which increases the water content of the cake. Therefore, the concentration of the aqueous solution is preferably 20% by weight or more, and more preferably 30% by weight or more.

In the method of the present invention, when dry ice and a bacteriostatic agent are allowed to coexist in the sludge dewatering cake, a synergistic effect between the two is remarkably exhibited, and the reason why the odor generation preventing effect lasts for a long time is not clear. It is estimated that the mechanism is as follows. In the hopper of the sludge dewatering cake,
A bacteriostatic agent such as nitrite ion suppresses the microbial activity involved in decay of sulfur-containing proteins and the like, and this effect prevents the generation of odorous substances such as hydrogen sulfide and methyl mercaptan, which are their decomposition products. . However, nitrite ions and the like are decomposed by the microorganisms in the sludge dewatering cake, eventually disappearing, and then odor is rapidly generated. Decomposition such as nitrite ion is more likely to proceed as the temperature is higher and the pH is higher. In the hopper of the sludge dewatering cake, the temperature rises due to microbial activity, the pH rises due to ammonia generated by the proteolysis of the sludge, and further the nitrite ion over time increases in order to accelerate the decomposition rate of nitrite ions. Ion decomposition proceeds at an accelerated rate. When oxygen is driven out by carbon dioxide generated by vaporization of dry ice in the sludge dewatering cake layer, the oxidation reaction of organic matter in the cake, which has a large heating value, due to oxygen does not occur. Less likely to occur. In addition, carbon dioxide itself suppresses the microbial activity, and the microbial activity associated with the decomposition of nitrite ions is also suppressed. Furthermore, the vaporization of dry ice reduces the temperature inside the hopper even slightly,
Suppress microbial activity. By adding 20 g of dry ice per 1 kg of sludge dewatering cake, a temperature decrease of about 3 ° C is expected. By these actions, the temperature, which is an element that promotes the decomposition of bacteriostatic agents such as nitrite ions, and the activity of degrading microorganisms are led not to be degraded, and the activity of odor-producing microorganisms is also led to not acting. Also,
Even at several degrees Celsius, it is considered that the introduction time of the initiation of microbial activity is delayed due to the initial cooling and drastic environmental changes in the carbon dioxide atmosphere.

[0010] Conventionally used bacteriostatic agents such as pyrithione are said to be difficult to decompose into microorganisms, but even if such bacteriostatic agents are used, it is very difficult to prevent odor generation for 48 hours or more. Met. According to the method for preventing odor generation of sludge dewatering cake of the present invention, by coexisting dry ice and a bacteriostatic agent in the sludge dewatering cake, a strong synergistic effect of dry ice and a bacteriostatic agent is exerted, and the cake is maintained for 72 hours or more. It is possible to prevent the generation of odor from. The method of the present invention can prevent odor generation by a simple operation of coexisting a bacteriostatic agent and dry ice conventionally used in a sludge dewatering cake, and does not require complicated equipment for supplying dry ice. Also, since the supply of dry ice can be started or stopped at any time, for example, in accordance with the cake unloading schedule of the sludge dewatering cake from the hopper, the method of the present invention is carried out only when necessary, and sludge dewatering is economically performed. Generation of odor from the cake can be prevented.

[0011]

The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples. In addition, in the examples and comparative examples, the analysis of hydrogen sulfide was carried out by using the gas detector tube 4 manufactured by Gastec
The analysis of methyl mercaptan was carried out using Gas Detector Tube 71H or 71 manufactured by Gastec Co. using M, 4L or 4LL. The detection lower limit concentrations of hydrogen sulfide and methyl mercaptan are both 0.25 ppm (volume ratio). Example 1 Mixed raw sludge from a sewage treatment plant (pH 5.2, suspended matter concentration 2.1)
% By weight), 120 mg of dehydrating agent [Kurita Kogyo Co., Ltd., Cliffix CP604, cationic polymer] per liter of sludge
Was added to agglomerate and then dehydrated by a batch type belt press dehydrator. The average water content of the obtained sludge dewatering cake is 7
It was 5.2% by weight, and the sludge concentration was about 12 times concentrated. 40 kg of the obtained sludge dewatering cake is 100 L in volume.
Into the dilite tank of No. 1, 126 g of 38 wt% sodium nitrite aqueous solution and 1,200 g of dry ice crushed to a particle size of 0.1 to 2 cm were added and mixed, and the cake was lightly compressed. Sludge dewatering cake occupied about half of the volume of the dilite tank. Seal the opening of the die light tank with vinyl chloride sheet and adhesive tape,
Stored in a thermostatic chamber. 24 hours later, 48 hours later and 72 hours
After a lapse of time, the gas in the die light tank was sampled in a tetra bag and analyzed. Hydrogen sulfide and methyl mercaptan were not detected in either case. Example 2 Instead of adding the sodium nitrite aqueous solution to the sludge dewatering cake, sodium nitrite was added to the sludge slurry before dewatering at a ratio of 1,800 mg of sodium nitrite per 1 kg of the sludge dewatering cake. The same operation as in 1 was performed to analyze the gas in the die light tank. Example 3 Instead of sodium nitrite, the same operation as in Example 1 was performed except that sodium pyrithione was added to the sludge slurry before dehydration at a ratio of 120 mg of sodium pyrithione (Na pyrithione) per 1 kg of the sludge dehydrated cake, The gas in the dilite tank was analyzed. Example 4 Instead of sodium nitrite, the same operation as in Example 1 was carried out except that pyrithione zinc was added to the sludge slurry before dehydration at a ratio of 120 mg of pyrithione zinc (Zn pyrithione) per 1 kg of sludge dehydrated cake, The gas in the dilite tank was analyzed. Example 5 Example 1 was repeated except that 16.0 g of sorbic acid was added instead of 126 g of 38 wt% sodium nitrite aqueous solution.
The same operation as the above was performed to analyze the gas in the die light tank.

Comparative Example 1 40 kg of sludge dewatering cake obtained in the same manner as in Example 1
Was charged into a 100 L volume dilite tank, 126 g of 38 wt% sodium nitrite aqueous solution was added and mixed, and the cake was lightly compressed. Block the opening of the die light tank with a vinyl chloride sheet and adhesive tape, and
It was stored in a constant temperature room at ℃. After 24 hours, the gas in the die light tank was sampled in a tetra bag and analyzed. Hydrogen sulfide and methyl mercaptan were not detected. 48
After a lapse of time, when the same analysis was carried out, hydrogen sulfide was 1
50 ppm and methyl mercaptan were 100 ppm. Furthermore, after 72 hours, hydrogen sulfide was 600 ppm and methyl mercaptan was 1,200 ppm. Comparative Examples 2 to 5 The same operation as in Examples 2 to 5 was carried out except that dry ice was not added, and the gas in the die light tank was analyzed. Comparative Example 6 The gas in the dilite tank was analyzed by performing the same operation as in Example 1 except that only dry ice was added without adding the sodium nitrite aqueous solution. Comparative Example 7 The same operation as in Example 1 was carried out except that neither the sodium nitrite aqueous solution nor the dry ice was added, and the gas in the dilite tank was analyzed. Table 1 shows the types of the bacteriostatic agents used in Examples 1 to 5 and Comparative Examples 1 to 7, the addition place and the addition amount, and the addition amount of dry ice, after 24 hours,
Table 2 shows the odorous component concentrations in the gas after 48 hours and 72 hours.

[0013]

[Table 1]

[0014]

[Table 2]

As shown in Table 2, in Examples 1 to 5 in which the dry ice and the bacteriostatic agent were coexisted in the sludge dehydrated cake, the concentration of the odorous component was several tens ppm or less even after 72 hours, The effect of preventing odor generation continues for a long time. Particularly, in Example 1 in which the sodium nitrite aqueous solution and dry ice were added to the sludge dewatering cake, even after 72 hours,
Hydrogen sulfide and methyl mercaptan are not generated at all.
On the other hand, in Comparative Examples 1 to 5 in which only the bacteriostatic agent was added without adding dry ice, the concentration of the odorous component became almost 100 ppm or more after 48 hours, and odor was generated by the addition of the bacteriostatic agent alone. Prevention is limited to 48 hours.
Further, comparing Comparative Example 6 in which only dry ice was added with Comparative Example 7 in which neither dry ice nor a bacteriostatic agent was added,
The odor component generation amount of Comparative Example 6 may be larger, and dry ice alone does not have an odor generation prevention effect, or dry ice slightly promotes odor generation. It can be seen that by using dry ice alone, which has no odor generation preventing effect, a remarkable synergistic effect is exhibited with the bacteriostatic agent, and the generation of odor components is suppressed for a long time.

[0016]

According to the method for preventing odor generation of sludge dewatering cake of the present invention, the coexistence of dry ice and a bacteriostatic agent in the sludge dewatering cake exerts a strong synergistic effect of dry ice and a bacteriostatic agent, Generation of odor from the sludge dewatering cake can be prevented for 72 hours or more.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Kojima Eijun             Kurita, 3-4-3 Nishi-Shinjuku, Shinjuku-ku, Tokyo             Industry Co., Ltd. F-term (reference) 4D059 AA01 AA03 BE10 BE15 BE57                       BK01 DA37 DA41 DA45 DA70                       DB01 DB02

Claims (5)

[Claims] 1. A method for preventing odor generation in a sludge dewatering cake, which comprises allowing dry ice and a bacteriostatic agent to coexist in the sludge dewatering cake. 2. Dry ice has an average particle size of 0.1 to 10 c.
The method for preventing odor generation of a sludge dewatering cake according to claim 1, wherein m is m. 3. The method for preventing odor generation of a sludge dewatering cake according to claim 1, wherein dry ice is supplied to the hopper of the sludge dewatering cake. 4. The method for preventing odor generation of a sludge dewatering cake according to claim 3, wherein after supplying dry ice to the hopper of the sludge dewatering cake, the inside of the hopper is shut off from the atmosphere. 5. The method for preventing odor generation of a sludge dewatering cake according to claim 1, wherein the bacteriostatic agent is nitrite.