JP2010089023A - Method for volume-reducing waste sludge - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for volume-reducing waste sludge efficiently while dispensing with large equipment without causing an increase in the running cost. <P>SOLUTION: The method for volume-reducing waste sludge, which is generated when organic matter is treated with an aerobic microbe, comprises: a pretreatment step of adding one or a plurality of pretreating agents selected from the group consisting of inorganic acids, organic acids and alcohols to the waste sludge to be treated to decrease the adhesion force of microbes in the waste sludge, thin the epidermis of each microbe and lower the pH of the waste sludge and separating water from the waste sludge to concentrate the waste sludge; and a post-treatment step of volume-reducing the waste sludge concentrated at the pretreatment step. The volume reduction of the waste sludge is preferably attained by performing a hydrothermal reaction in a subcritical state. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a method for reducing the volume of excess sludge, and particularly to a method capable of reducing the amount efficiently by concentrating excess sludge in advance without requiring a large amount of equipment and incurring high running costs.

  Biological treatment methods are the most common organic wastewater treatment methods, and among them, methods using aerobic microorganisms are often employed. One of the problems with the treatment method using aerobic microorganisms is that the microorganisms grow as the organic matter is digested by the microorganisms, and this becomes new waste as excess sludge.

  Excess sludge contains a large amount of water and requires a large amount of cost for its disposal. Pretreatment such as agglomeration, dehydration, and drying is performed, and after volume reduction, it is incinerated or landfilled as industrial waste. However, the present situation is that a large amount of cost is required for the volume reduction of the excess sludge and the treatment as industrial waste, and a new environmental problem is derived.

  For example, when treating factory wastewater, as shown in FIG. 2, the aerobic microorganism digests and absorbs the pollutant load substance in the aeration tank 10, but the aerobic microorganism repeatedly grows during the treatment, and the microorganism The number of individuals increases, and most of them become surplus. This surplus microorganism is called surplus sludge and is generated in large quantities, so it is necessary to remove it from the process.

  Conventionally, a sedimentation tank 11 is provided after the aeration tank 10 and separation is performed using the difference in specific gravity. A part of the separated excess sludge is returned to the aeration tank 10 and reused in the process, but most of the sludge is removed from the process. Will be disposed of. Disposal of surplus sludge is generally processed as industrial waste, but in the state of specific gravity separation, it contains a large amount of water, so it is large in volume, difficult to transport and store, and the cost required for processing is also high. Become enormous.

  Therefore, a method is adopted in which excess sludge is stored in the sludge storage tank 13 and the volume is reduced by dehydration or weight reduction. For example, flocs are formed in sludge using a chemical such as a flocculant, and separation from moisture is performed by giving a specific gravity difference. The concentration tank 13 is separated by natural sedimentation and filtered using a dehydrator, or dehydrated using a centrifuge, and the resulting cake is disposed of.

  However, the cost required for these operations is enormous, and not only the processing cost becomes high, but also bad smell is generated due to the decay of excess sludge during the volume reduction process and storage, and the factory environment is deteriorated.

  On the other hand, various methods for dewatering, drying and reducing excess sludge have been proposed without incurring high costs and new environmental problems. For example, a method of digesting and reducing excess sludge using supercritical or subcritical is known (Patent Literature 1, Patent Literature 2, Patent Literature 3, Patent Literature 4, Patent Literature 5, Patent Literature 6).

JP 2000-218295 A JP 2007-111673 A Japanese Patent Laid-Open No. 2002-159999 Japanese Patent Laid-Open No. 2003-236593 JP 2003-117597 A JP 2003-19490 A

  However, each of the methods described in Patent Documents 1 to 6 requires a large amount of equipment and running cost, and has a difficulty in practical use.

  In view of such problems, the present invention provides a volume reduction method for excess sludge that can efficiently reduce excess sludge without requiring a large amount of equipment and incurring high running costs. And

  Therefore, the method for reducing the volume of excess sludge according to the present invention is used to reduce the volume of excess sludge generated by organic matter treatment with aerobic microorganisms, and one or a plurality of previous sludges selected from the group of inorganic acids, organic acids and alcohols. By adding the treatment agent to the excess sludge to be treated, the adhesive strength of the microorganisms in the excess sludge is reduced, the skin of the microorganisms is thinned, and the pH of the excess sludge is reduced, thereby separating the excess sludge moisture. And a post-treatment step for concentrating excess sludge and a post-treatment step for reducing the amount of excess sludge concentrated by the pre-treatment.

  One of the features of the present invention resides in that one or more pretreatment agents selected from the group of inorganic acids, organic acids and alcohols are added to the excess sludge before reducing the excess sludge. When these pretreatment agents are added to excess sludge, the adhesive strength of microorganisms is reduced and the microbial epidermis is acid-corroded to form a thin film. Furthermore, since the pH of the excess sludge is lowered to the acidic range, the emulsification of microorganisms and moisture is impaired, and the moisture contained in the excess sludge is easily separated as supernatant water or precipitated water, and the excess sludge is concentrated. be able to.

  As a result, the agglomerated surplus sludge is dispersed, the activity of microorganisms is reduced, and moisture can be easily separated, so that excess sludge can be reduced in weight, for example, at a critical point of 374 ° C., supercritical or critical exceeding 22 MPa. Weight loss by hydrothermal reaction of subcritical high-temperature high-pressure water below the point can be performed efficiently.

  Moreover, since the water | moisture content of the excess sludge was isolate | separated efficiently beforehand and concentrated before the weight reduction process, digestion weight loss by a hydrothermal reaction can be performed with little energy. Therefore, the above-described operation can be referred to as pretreatment or primary treatment of the hydrothermal reaction.

  In addition, the water that floats or settles by separation has a low water pollution load, and can be easily reprocessed in the conventional process even if it is returned to the raw water.

  Furthermore, as a result of surplus sludge dispersed by the above-mentioned operation being able to concentrate to about 1/2 to 1/4 as compared with the amount before pretreatment, the surplus sludge concentrated by this method is a prior art. The amount can be further reduced by a dehydration method.

  In addition, the hydrogen ion concentration (“pH”) can be lowered by the action of the inorganic acid, organic acid and / or alcohol used in the above-described operation, and when it is lowered to the acidic range, the growth of aerobic microorganisms can be suppressed. At the same time, it is possible to suppress the decay of excess sludge and to improve the problem of malodor.

  Moreover, since the amount of excess sludge is concentrated to 1/2 to 1/4 by the pretreatment, the energy cost required for heating in the hydrothermal reaction can be reduced to 1/2 to 1/4.

  Furthermore, the hydrothermal reaction temperature can be lowered for the following reasons. That is, in the reaction apparatus of the same capacity, the reaction treatment time can be extended by 2 to 4 times, so that the hydrothermal reaction temperature can be lowered.

  On the other hand, aerobic microorganisms weaken not only the biological membrane but also the shell material itself due to the action of inorganic acid, organic acid and / or alcohol, so the excess sludge can be reduced by low-temperature and long-term hydrothermal reaction. It is possible to provide a novel volume reduction method that can be performed. According to this method, it is possible to reduce the volume of excess sludge at a treatment temperature of less than 140 ° C., which has been considered difficult in the past.

  Furthermore, the treatment liquid treated by the method of the present invention can be easily separated and the supernatant is less contaminated, and can be returned to the raw water as it is or after simple treatment, and then reprocessed.

Specifically, the following effects can be obtained.
1. The sludge treatment amount of the hydrothermal reaction becomes 1/2 to 1/4, and the energy cost required for heating can be reduced.
2. By reducing the amount of sludge treated by the hydrothermal reaction, the reaction time can be easily extended, and the energy cost can be reduced or the equipment cost can be reduced by lowering the treatment temperature or downsizing the apparatus.
3. Furthermore, since the hydrogen ion concentration is reduced at the same reaction temperature, the hydrolysis reaction, which is the main reaction in the same treatment, can be promoted.
4). Combined with the action of inorganic acid, organic acid and / or alcohol in the pretreatment, the concentrated and reduced sludge obtained by the method of the present invention is sterilized or sterilized, and is used in the subsequent dehydration process, storage and disposal. Can improve pollution problems such as odor and pollution.
5). Furthermore, the method according to the present invention does not require a large amount of energy, such as agglomeration by a drug, dehydration by electric power, and drying by heat, according to a conventional method, and is an environmentally friendly inorganic acid, organic acid and / or It is possible to provide a method in which the volume of excess sludge is reduced with less energy by using alcohol to efficiently separate the moisture of the excess sludge in advance and concentrating the excess sludge.

  Here, examples of the inorganic acid include hydrochloric acid, nitric acid, phosphoric acid, sulfuric acid and the like. Examples of the organic acid include formic acid, oxalic acid, acetic acid, citric acid and the like. Examples of the alcohol include ethanol and methanol.

  Hereinafter, the present invention will be described in detail based on examples.

  FIG. 1 schematically shows a method for reducing excess sludge according to the present invention. In the figure, 20 is an aeration tank for treating organic substances with aerobic microorganisms, 21 is a sedimentation tank for separating liquid and sludge from treated liquids due to a difference in specific gravity, 22 is a sludge storage tank for storing separated sludge, and 25 is a surplus. A pretreatment device for pre-treating sludge according to the present invention, 26 is a hydrothermal reaction treatment device for digesting and reducing excess sludge with high-temperature and high-pressure water, and 23 is for concentrating excess sludge after hydrothermal reaction treatment. The concentrator 24 is a dehydrator. Hereinafter, the processing in the preprocessing device 25 will be mainly described.

  The effect of treatment in the pretreatment device 25 is evaluated by measuring the soluble biochemical oxygen demand of sludge (hereinafter referred to as “BOD”), the amount of suspended activated sludge (hereinafter referred to as “MLSS”), and pH. did. The measurement was performed as follows.

  In addition, as a quick evaluation method of sludge reduction effect in each operation at the time of implementation, measure the amount of sludge after standing for a certain time using a graduated cylinder, divide by the total volume before operation, the ratio is the concentration rate or reduction rate It was. In addition, as a method for evaluating the strength of odor, strength values were compared using commercially available odor sensors.

[BOD]
The measurement was performed according to the method specified in the Japanese Industrial Standards Standard Water Quality Analysis Method (JISK 0102-21.2.32.3).
[MLSS]
It was measured according to the method specified in the Japanese Industrial Standards Standard Water Quality Analysis Method (Sewage Test Method).
[PH]
It measured according to the method prescribed | regulated to the standard water quality analysis method (JISK 0102-122.3) of a Japanese industrial standard.
[Concentration rate or weight loss rate]
The concentration rate or weight loss rate was evaluated by the following rapid evaluation method of the sludge settling part. That is, 100 ml of the sample after completion of each operation was put into a 100 ml graduated cylinder, and the amount of sediment after standing at room temperature for 2 hours was measured. Evaluation expression is
[100 ml-precipitation amount ml) * 100/100 ml
And expressed as a concentration rate or weight loss rate%.
[Odor]
The difference by the sensor display numerical value by commercially available "odor sensor" XP-329S (for hydrogen sulfide measurement) made by New Cosmos Electric Co. was comparatively expressed. In the operation method, a 200 ml sample was placed in a 500 ml glass container with a lid, and measurement was performed after shuffling. As a blank, a sample-free product was prepared and measured in the same container, and the sensor value was adjusted to zero.

As the sludge to be treated, the sludge of the sludge reservoir in the wastewater treatment process of the food manufacturing factory was collected, and specimens having the following characteristic values were used as the stock solution samples.
[MLSS] 7.800 mg / l
[BOD] 40 mg / l
[PH] 7

300 ml of the above sludge sample was transferred to a 500 ml beaker and subjected to a predetermined pretreatment. In the pretreatment method, the following pretreatment agent was added while the sludge was stirred and adjusted to pH 4, then transferred to a 100 ml graduated cylinder, and the concentration rate was evaluated.
1) No treatment (blank) 2). Nitric acid 3). Sulfuric acid 4). Hydrochloric acid 5). Formic acid 6). Succinic acid 7). Phosphoric acid 8). Acetic acid

  The sludge sample after the above pretreatment was transferred to a 100 ml capacity graduated cylinder and the sedimentation rate of sludge after 2 hours was measured. The results are shown in Table 1.

The sludge similar to Example 1 was used as the to-be-treated sludge. A 300 ml sludge sample was transferred to a 300 ml beaker, adjusted to pH 4 using formic acid and employing the following stirring method, then transferred to a 100 ml graduated cylinder, the concentration rate was evaluated, and the results are shown in Table 2.
1). Stirring with a 15 ° C (room temperature) turbine agitator (blank) 2). Stirring with a 40 ° C (warming) turbine stirrer 3). Stirring with a 60 ° C (warming) turbine stirrer 4). Ultrasonic irradiation at 15 ° C (normal temperature) 5). Ultrasonic irradiation at 40 ° C (heating) 6). Ultrasonic irradiation at 60 ° C (heating)

  It was confirmed that the excess sludge generated from the current wastewater treatment equipment could be concentrated, and the amount of dewatered cake by the dehydrator of the final equipment could be reduced to about 1/10. Further, the hydrothermal reaction device 26 is configured by a treatment for preventing the decay of activated sludge or a sealed structure, and can reduce harmful and odorous substances such as methane gas generated from the activated sludge wastewater treatment device. Furthermore, since the hydrothermal reaction device 26 is operated under sterilization or sterilization conditions, there is little or no harmful microorganisms in the waste liquid / sludge discharged from the pretreatment device 25 of this example, and in the sterilization or sterilization state. In addition, it is safe in the subsequent storage, transportation, and reuse for fermenting compost and the like, and since it produces almost no odor, it is effective in terms of the environment.

The same sludge as in Example 2 was used as the treated sludge. Transfer 1000ml of sludge sample to a 1L beaker, adjust the temperature to 40 ° C respectively, add citric acid and alcohol, stir and disperse, put into 1000ml graduated cylinder, and inject air from below with aerator. Then, aeration was carried out for 10 minutes each, and the floating sludge was collected and removed, and the floated and settled portions were separated, separated into separated water and sludge, and the weight loss rate evaluation and characteristic values were analyzed. Concentration rate was determined by the following formula by subtracting the obtained separated water (ml) from 1000 ml of the stock solution and using the rest as sludge.
1000 ml-separated water (ml) = sludge (ml)
(1000ml-sludge ml) * 100 / 1000ml
The concentration rate was defined as%. The results are shown in Table 3.

  In Examples 1 and 2 above, the effect of the sludge sedimentation method due to the difference in the performance of various acid species and the stirring contact method was confirmed. It is a method commonly used in the treatment process, and it has been confirmed that the sludge and separated water can be separated more effectively by using the citric acid and alcohol by examining the acid species and their effects. It was.

As the sludge to be treated, the sediment sludge from the sedimentation tank of the wastewater treatment plant of the food manufacturing plant was collected, and specimens having the following characteristic values were used as stock solution samples.
[MLSS] 7.400 mg / l
[BOD] 10 mg / l
[PH] 7

  The above sludge sample was transferred to a 300 ml beaker, heated to 40 ° C. with formic acid and added, adjusted to pH 4, and then stirred using ultrasonic waves. Using 300 ml of sedimented sludge obtained by this method as a sample, hydrothermal reaction treatment was performed in a lab reactor (Model: TVS-N2-500, manufactured by Pressure Glass Co., Ltd.). The results are shown in Table 4.

  The sludge concentration rate of 67% is obtained by pretreatment of the sludge, and the hydrothermal reaction for the concentrated sludge can be further reduced by extending the treatment to a low temperature temperature of 130 ° C and a reaction time of 120 minutes. In total, it was found that the volume of raw sludge can be reduced to about 90%.

According to the present invention, industrial waste can be reduced, processing costs can be reduced, equipment can be downsized, energy can be reduced, and environmental problems such as odor and CO ₂ can be reduced. , Its practicality is great.

It is a figure which shows typically the volume reduction method of the excess sludge which concerns on this invention. It is a figure which shows the conventional volume reduction method of the excess sludge typically.

Claims (3)

In reducing the volume of excess sludge generated by organic matter treatment by aerobic microorganisms,
By adding one or more pretreatment agents selected from the group of inorganic acids, organic acids and alcohols to the excess sludge to be treated, the adhesion of microorganisms in the excess sludge is reduced and the skin of the microorganisms is made thin. A pretreatment step of separating the excess sludge by reducing the pH of the excess sludge and concentrating the excess sludge;
A post-treatment process for reducing the amount of excess sludge concentrated by the pre-treatment;
A method for reducing the volume of excess sludge, comprising:   The method for reducing the volume of excess sludge according to claim 1, wherein the excess sludge is reduced by a hydrothermal reaction.   The surplus sludge according to claim 1, wherein the surplus sludge is irradiated with ultrasonic waves or aerated when or after adding one or more pretreatment agents selected from the inorganic acids, organic acids and alcohols. Volume reduction method.

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