JPH0773706B2 - Wastewater treatment method - Google Patents

Description

TECHNICAL FIELD The present invention relates to activated sludge treatment of sewage and industrial wastewater (hereinafter abbreviated as sewage wastewater), and more specifically, high efficiency in activated sludge treatment of sewage wastewater. The present invention relates to a method for treating activated sludge in the above.

(Prior Art) Generally, activated sludge treatment of sewage wastewater is performed as follows.

First, in the case of sewage, the sewage collected at the sewage treatment plant is
First, after removing most of the sediment and coarse suspended solids with a sedimentation basin, sedimentation basin, etc., activated sludge treatment in an aeration tank decomposes sewage pollutants, and then in the final sedimentation basin. The activated sludge is separated by sedimentation, and the supernatant water is sterilized by chlorine and then discharged. On the other hand, the activated sludge settled in the final settling tank is returned to the aeration tank as return sludge, and part of it is withdrawn as excess sludge, and is disposed of after methane fermentation, incineration, etc.

Further, in the case of treating industrial wastewater such as ammonium hydroxide, a part of ammonium compounds is removed by a distillation method or the like, and then diluted with seawater and / or fresh water to 2 to 6 times to obtain inorganic phosphorus as a nutrient source of activated sludge. About 1 part by weight (as phosphorus) of an acid compound was added to 100 parts by weight of biological oxygen demand (BOD) to perform activated sludge treatment, and the activated sludge was settled and separated in a sedimentation tank, and then the supernatant was discharged. To do. On the other hand, the settled activated sludge is disposed of in the same way as municipal sewage.

However, the conventional activated sludge treatment methods have the following problems.

First, the problems in the activated sludge treatment method of sewage will be described. For example, this activated sludge for sewage treatment has a high SVI (Sludge Volume Index), which is an index of sedimentation, and a sedimentation sludge with good compaction can be obtained and separated in the final settling pond. If treatments with large fluctuations are performed or filamentous fungi are generated in the activated sludge, the activated sludge becomes in a bulking state, resulting in poor sedimentation. Therefore, in the conventional activated sludge treatment of sewage, it is difficult to maintain the activated sludge in the aeration tank at a high concentration, and therefore, there is a limit to the improvement of treatment efficiency such as reduction of treatment time and compaction of treatment equipment. Yes, and when bulking occurs, activated sludge flows down from the sludge settling tank, and the quality of treated water tends to deteriorate. In addition to this, there are many problems in the sludge dewatering process, the methane fermentation process, and the sludge treatment process after meta-fermentation, etc., even in the treatment process of the surplus sludge that is not returned to the aeration tank among the sludges that have been settled and separated. Existing.

For this reason, the conventional activated sludge treatment method requires a large site when constructing a sewage treatment plant, and since it is difficult to simplify the treatment process and compact the treatment equipment, the construction of a sewage treatment plant is expensive. is necessary.

Next, the problems in the activated sludge treatment method of industrial wastewater will be described. In this case as well, there are many problems similar to the activated sludge treatment method for municipal sewage. For example, wastewater generated from coal liquefaction plant, coal gasification plant, etc.
It contains a substance that inhibits the function of activated sludge, such as cyanide compounds and / or sulfides, in a fairly high concentration.
If the load fluctuates or a large treatment is carried out, the activated sludge easily becomes a bulking state, resulting in poor sedimentation, and the treatment performance deteriorates. Therefore, even in the activated sludge treatment of industrial wastewater, it is difficult to maintain the activated sludge in the aeration tank at a high level, and there is a limit in shortening the treatment time and compacting the treatment equipment. Therefore, in the conventional activated sludge treatment of waste water, when the pollutant load amount increases, it is inevitable to install additional equipment, which requires a large site and a high cost.

Therefore, development of a highly efficient activated sludge treatment technology is demanded as one means for solving the problem of such wastewater treatment.

As a method to perform activated sludge treatment of conventional wastewater with high efficiency,
There is a method of maintaining a high concentration of activated sludge in the aeration tank, and there are a fluidized bed method and a fixed bed method in this method.

In the fluidized bed system, activated sludge is added to the aeration tank with fine particles of earth and sand such as diatomaceous earth and sand, or particles of activated carbon or particles of a porous organic polymer compound, and these particles are aerated to aerate the inside of the aeration tank. It is a method of flowing and adhering activated sludge to this to improve the sedimentation of the activated sludge and maintain the activated sludge at a high concentration.

The fixed bed method is a method in which a honeycomb tube made of an organic polymer compound or a multi-layer plate is immersed in an aeration tank, and activated sludge is adhered to this to fix it.

However, these methods also have many problems.

First, the fluidized bed method using fine particles of sediment such as diatomaceous earth and sand requires a long time for the activated sludge to adhere stably because the affinity between the activated sludge and these inorganic fine particles is not sufficient. . Moreover, the method of treating the activated sludge adhering to this carrier as surplus sludge has not been fully established. Further, in the case of a fluidized bed system using powdered activated carbon and particles of an organic polymer compound, the affinity between these particles and activated sludge is very good, and the activated sludge adheres stably. However, when surplus sludge treated by this method is treated by a methane fermentation method, a technique for reusing these particles after methane fermentation has not been sufficiently established. When incinerating surplus sludge, these carrier particles are higher in cost than inorganic carrier particles, and if they cannot be reused, they increase the cost of sewage treatment.

On the other hand, in the case of a fixed bed system using a fixed bed type carrier of activated sludge, such as a honeycomb tube made of an organic polymer compound, a laminated plate, etc., the activated sludge has a good affinity with these carriers, and thus the propagated activated sludge is It is likely that the particles will adhere to the carrier and cause clogging of the carrier. Therefore, it is necessary to take out these carriers from the aeration tank and frequently wash them with water to regenerate them. However, the activated sludge attached to these fixed bed type carriers has a complicated fixed bed structure, and since the affinity between the carrier and the activated sludge is high, it is difficult to regenerate by simple water washing, and regeneration is complicated. Requires processing. As described above, conventional carriers for immobilizing activated sludge have problems in compatibility with activated sludge, reusability, handleability, cost, etc., and are not suitable for application to large-scale activated sludge such as sewage. Is suitable

(Problems to be Solved by the Invention) In order to solve the problems of the carrier for immobilization of activated sludge used in the conventional activated sludge treatment of sewage, the inventors of the present invention have performed blast furnace granulation. A patent has been filed for a highly efficient method for treating activated sludge as a carrier for immobilizing activated sludge. (Japanese Patent Application No. 61-184934) However, in the conventional aeration method centered on air, there is a limit to the oxygen supply to the activated sludge, and even with the above-mentioned patent application invention, the activated sludge concentration in the aeration tank is high. There is a limit to conversion. Therefore, it was found that sufficient oxygen should be supplied to the densified activated sludge in order to further improve the efficiency by making the most of the characteristics of the activated sludge treatment method using granulated blast furnace as an immobilized carrier. .

It is an object of the present invention to solve the above-mentioned problems in the activated sludge treatment of the conventional wastewater, and to provide an activated sludge treatment method capable of treating with higher efficiency while making the most of the features of the invention of the prior application. .

(Means and Actions for Solving Problems) The present invention relates to activated sludge treatment of sewage and industrial wastewater,
In the aerobic fluidized bed aeration tank, granulated blast furnace with a particle size of 0.02 to 0.2 mm was used as a carrier for immobilizing activated sludge, and the oxidation-reduction potential (ORP) of the aeration tank was compared with that of gold or an alloy of gold and antimony. The characteristic feature is that 30 to 95% oxygen-enriched air is supplied to the aeration tank so that the measured value of the composite electrode composed of silver and silver chloride as the reference electrode falls within +50 to +150 mV.

As the method for supplying the oxygen-containing air, oxygen-enriched air may be used alone, or may be mixed with normal air to be supplied, or the oxygen concentration of the air supplied to the aeration tank may be 30 to 95. Oxygen-enriched air and normal air are supplied to the aeration tank at the same time so that the concentration becomes%.

The present inventors, in the process of studying the activated sludge treatment method of the sewage wastewater, blast furnace slag produced by quenching the slag generated as a by-product from the blast furnace of the steel mill with water is structurally and compositionally As a result of research focusing on the fact that activated sludge easily adheres, the result is that the settling property of activated sludge is improved and it has a remarkable effect on increasing the concentration, making it the most suitable carrier for immobilizing activated sludge. I found a thing.

Furthermore, it was found that the addition of blast furnace slag to the aeration tank as a carrier for immobilization of activated sludge has another effect of maintaining the pH of the aeration tank within a range suitable for activated sludge. Therefore, by using the slag of the blast furnace, it is possible to suppress the malfunction of the activated sludge treatment due to the pH change and to perform the stable treatment.

Further, a method of blowing pure oxygen or oxygen-enriched air instead of air into the conventional activated sludge treatment is a known technique, but this technique is combined with an activated sludge treatment method using granulated blast furnace as a fixed carrier. And, it was found that the concentration of activated sludge can be remarkably promoted, and the efficiency can be improved not seen in the past.

Hereinafter, the present invention will be described in detail.

Blast furnace slag is 100 to 3 per ton of pig iron from a blast furnace at an iron mill.
It is manufactured by quenching slag generated by 00 kg with high pressure water. The blast furnace slag has a vitrification rate of about 90% or more,
It is also porous. As shown in Table 1 for the composition, the main components are CaO, SiO ₂ and Al ₂ O ₃ , and FeO and MgO
Etc. are included. The activated sludge is likely to adhere to the slag of the blast furnace due to its porous nature and composition.

Hereinafter, the relationship between the composition of the slag of blast furnace and the adhesion of activated sludge will be described.

In general, activated sludge treatment tends to lower the pH of the aeration tank due to nitrite compounds, nitric compounds produced by nitrification reaction of ammonia compounds, or fatty acids produced by decomposition of organic pollutants. . If the pH is outside the range suitable for the activated sludge to inhabit, bulking of the activated sludge, poor decomposition of pollutants, etc. will likely occur, resulting in poor treatment.
If blast furnace slag is added to the aeration tank for activated sludge treatment, CaO in the blast furnace slag will dissolve even if the pH of the aeration tank drops, suppressing the decrease in pH and making it ideal for inhabiting activated sludge. It is maintained in a wide pH range and is extremely effective in stabilizing activated sludge treatment and improving the quality of treated water. At this time, the dissolution of CaO in the slag of the blast furnace does not occur rapidly but gradually. This is because the vitrification rate of the slag of blast furnace is about 90% or more, which suppresses the rapid dissolution of CaO, so that the pH does not rise rapidly. In addition to reacting with dissolved CaO, nitric acid compounds, nitrite compounds and fatty acids, it also reacts with carbon dioxide gas generated by the respiratory action of activated sludge to form calcium carbonate. The calcium carbonate thus generated is fine particles, and activated sludge easily adheres to this. Furthermore, the blast furnace slag in which CaO is dissolved becomes more and more porous, and the activated sludge tends to adhere to it. Activated sludge requires a trace amount of metals such as iron and magnesium in addition to phosphorus and nitrogen as nutrient sources. The blast furnace slag contains FeO and MgO respectively, and the activated sludge contains iron,
Since it takes in nutrients such as magnesium, it easily attaches to the slag of blast furnace.

As described above, the blast furnace water slag is porous, and the composition of activated sludge easily adheres to the blast furnace slag, which has the effect of suppressing treatment problems such as bulking of activated sludge and poor decomposition of pollutants. Although it is a carrier, it has been clarified that it has superior properties to commonly used inorganic immobilization carriers such as diatomaceous earth and sand.

Next, when the blast furnace water slag is used as a carrier for immobilizing activated sludge, the blast furnace water slag may be pulverized to 0.5 mm or less and added in an amount of 10 to 50 kg per 1 m ^{3 of} the aeration tank. The relationship between the particle size of the blast furnace slag and the adhesion of the activated sludge is that the finer the blast furnace slag, the easier the activated sludge adheres, but the finer the blast furnace slag, the easier the blast furnace slag flows from the sludge settling tank into the treated water. From this point, the particle size is preferably 0.02 mm or more. The relationship between the particle size of the blast furnace slag and the dispersibility in the aeration tank is that the particle size of the blast furnace slag is 0.5 mm.
If it exceeds, the dispersibility is not sufficient and it is difficult to disperse it uniformly in the aeration tank. Therefore, taking these things into consideration, the particle size of the blast furnace slag added to the aeration tank is 0.02 to 0.
The optimum range is 5 mm.

According to the present invention, in addition to the fact that the blast furnace slag is excellent as a carrier for immobilizing activated sludge in this manner, by aerating oxygen-enriched air as described above, the activated sludge treatment is significantly improved. We have completed a method that enables highly efficient processing.

Hereinafter, description will be given with reference to the flow chart shown in FIG.

In FIG. 1, 1 is a sewage pump for supplying sewage wastewater, 2 is an oxygen-enriched air production device, 3 is a diffuser pipe, 4 is an aeration tank, and is produced by the oxygen-enriched air production device 2 described above. The oxygen-enriched air can be aerated by the air diffuser 3 provided at the bottom of the aeration tank 4. Reference numeral 5 is a sludge settling tank, and a return sludge pump 8 is arranged between the settling tank 5 and the aeration tank 4 so that the sludge in the settling tank 5 can be returned to the aeration tank 4. An ORP meter 6 is installed in the aeration tank 4 and
Oxygen-enriched air supplied to the aeration tank 4 by operating the oxygen-enriched air production apparatus 2 via the ORP value control device 7 based on the redox potential (abbreviated as ORP below) measured by the total 6. You can control the amount. Reference numeral 9 is a rake provided in the sludge settling tank 5.

In FIG. 1, artificial sewage is sent from the sewage pump 1 and oxygen concentration of 30 to 30
95% oxygen enriched air is supplied. The aeration tank 4 has no grain size.
Water-granulated blast furnace in the range of 02~0.5mm is per aeration tank 1m ^3, 10~50
Kg is added. The concentration of oxygen-enriched air blown into the aeration tank is 30
If it is less than%, the effect of increasing the dissolved oxygen concentration of the sewage wastewater is poor, and promotion of efficiency cannot be promoted, resulting in a high cost. On the other hand, when the oxygen-enriched concentration is 95% or more, it is very difficult to obtain oxygen-enriched air having an oxygen concentration of more than 95% due to the technical limitation of the oxygen-enriched air manufacturing apparatus.

In the present invention, oxygen-enriched air having an oxygen concentration of 30 to 95% is used, and such air can be obtained by, for example, a selective oxygen-permeable membrane or a precession swing absorption method (PAS). However, a cost-effective method may be selected.

The next-generation activated sludge treatment performance is closely related to the oxidation-reduction potential of the aeration tank, and it is effective to control the amount of aeration using ORP as an index, but sometimes blast furnace water sludge is used as an immobilization carrier and ORP is also used. If oxygen-enriched air with an oxygen concentration of 30% or more is supplied and managed as an index, the decomposition of pollutants will proceed remarkably well, and there will be a significant effect on the suppression of nitrification reaction, activated sludge bulking, etc. Found out. For activated sludge treatment of sewage, the appropriate ORP range is 0 to +100 mV
(Measured with gold, or gold-antimony alloy / silver / silver chloride composite electrode; hereinafter, ORP value represents the measured value of this electrode).

When sewage activated sludge treatment is performed, there is a considerable correlation between the aeration tank ORP value and the aeration amount.
The aeration amount may be controlled in accordance with ORP, but in the present invention, the aeration amount corresponding to ORP + 50 mV or less is required to uniformly disperse the blast furnace water sludge with a particle size of 0.02 to 0.5 mm in the aeration tank. Run out. Therefore, in the present invention, OR
It is necessary to set the target of P to +50 mV or more to supply the aeration amount of oxygen-enriched air required to maintain this ORP.

On the other hand, the upper limit of ORP can be up to +150 mV due to the adhesion of activated sludge to the slag of blast furnace. That is, in the case of the conventional method without adding slag of blast furnace, nitrification reaction remarkably occurs at ORP + 100 mV or more, and sludge floats and flows out due to pH drop in the aeration tank and denitrification reaction in the sludge settling tank, resulting in deterioration of treated water quality. Invite. However, when adding slag of blast furnace,
When ORP + 100 mV or more, nitrification reaction is increased as in the conventional method, but pH drop, sludge floating and outflow, etc. do not occur, treated water quality is good, and there is no problem in treatment performance. However, when ORP exceeds +150 mV, activated sludge is fragmented due to aeration, and it tends to be difficult to adhere to the slag of blast furnace. From these, considering the dispersibility of the slag of blast furnace and the adherence of activated sludge, it is optimal to maintain the ORP of the aeration tank within the range of +50 to 150 mV.

In the case of performing activated sludge treatment of industrial wastewater, for example, in the case of activated sludge treatment of cheap water, the difference between the ORP in the aeration tank and the COD of the treated water and the amount of nitrogen oxides generated in the aeration tank is described. Have a close relationship with.

First, regarding the relationship between the biodegradability of organic pollutants and ORP, the COD value of treated water becomes lower as ORP becomes on the oxidation side up to +200 mV. Furthermore, phenol, which is relatively easily decomposed by activated sludge, decomposes even at about -100 mV to 0 mV, but the decomposition rate of cresol and rhodan compounds decreases at 0 mV or less, but +50 mV or more, or +100 mV or more. Almost decomposes.

On the other hand, the nitrification reaction in activated sludge does not produce nitrogen oxides at ORP + 100 mV or less as in the case of municipal sewage, but even if blast furnace granulation is added, the production of nitrogen oxides is gradually recognized from about +150 mV, +200 to 250 mV. In the above case, nitrogen oxides are rapidly generated, and sludge floats and flows out in the settling tank, and at the same time, the COD of the treated water increases because the nitrogen oxides themselves are COD components.

Therefore, also in the activated sludge treatment of industrial wastewater, considering the degradability of pollutants and the dispersibility of blast furnace water sludge, the ORP of the aeration tank is maintained in the range of +50 to 150 mV, similar to the activated sludge treatment of municipal wastewater. Is the best.

(Example) Next, the Example of this invention is described.

Example 1 (Example of treatment of municipal sewage) The particle size was set in the aeration tank 4 of the ORP-controlled activated sludge treatment device in which the ORP of the aeration tank (volume 20) shown in Fig. 1 is controlled to +100 mV.
600 g of 0.02 to 0.2 mm blast furnace water slag (corresponding to 30 kg per 1 m ^{3 of the} aeration tank, 2% by weight / volume) was added, and a high concentration artificial sewage having the composition and properties shown in Table 2 was treated.

Table 3 shows the relationship between treatment conditions and treated water quality. Oxygen-enriched air is produced by a selective oxygen permeable membrane and has an oxygen concentration of 33-
35%.

Table 4 shows changes with time in the properties of the activated sludge in the case of the present invention to which oxygen-enriched air was supplied, together with the comparative example to which ordinary air was supplied.

From the results of Table 3, the blast furnace slag addition activated sludge treatment (RUN / C) using the oxygen-enriched air of the present invention was performed under a high load condition of BOD volume load of 1.9 kg-BOD / m ³ -day. , BOD ₅ is 5mg
/ Below (removal rate 98% or more), COD _Mn is 10 mg / below (removal rate 95% or more) and SS is 5 to 10 mg /, and blast furnace slag is used as a carrier for immobilization of activated sludge and replaced with air. It was revealed that a better treated water quality can be obtained by supplying oxygen-enriched air.

Table 4 shows the changes over time in the properties of activated sludge added with blast furnace water slag after oxygen-enriched air was supplied. MLVS before the addition of blast furnace water slag
S (volatile matter of sludge) is 907 mg /, but it becomes 2,200-3,200 mg / 10-30 days after addition of blast furnace slag, and it increases to 3500-6,000 mg / when the air is changed to oxygen-enriched air. . However, SVI, which is an index of sedimentation of activated sludge,
Is stable around 20 with oxygen-enriched air supply, MLVS
Sedimentability does not decrease even if S increases.

As described above, when the slag of the blast furnace is added to the aeration tank of the activated sludge treatment device to perform the treatment by supplying the oxygen-enriched air, the treatment efficiency, treated water quality, activated sludge properties and the like are remarkably improved. At the same time, it was clarified that the treatment performance was extremely stable due to the oxygen-enriched air.

Example 2 (Example of treatment of urban sewage) Treatment was carried out using actual sewage (diversion type) of a large city whose properties are shown in Table 5 under the conditions of Example 1. Table 6 shows the relationship between treatment time and treated water quality.

From the results in Table 6, the treatment time was changed from the standard 8-hour treatment to 4 hours and 2 hours, but the BOD of treated water was 5 mg / or less (removal rate 74-94% or more) in any case, COD Is 7.2-1
3.1 mg /, TOC is 3.2-10.1 mg /.

For this reason, when blast furnace slag was used as a carrier for immobilizing activated sludge and oxygen-enriched air was supplied, the treatment efficiency was quadrupled, and the treatment equipment could be made compact.

Example 3 (Industrial wastewater) Under the conditions of Example 1, the treatment of the low water generated from the coke oven of the steel mill having the properties shown in Table 7 was performed. Table 8 shows the relationship between treatment conditions and treated water quality.

From the results of Table-8, in the activated sludge treatment method according to the present invention using oxygen-enriched air, the COD volume load is 5 kg-COD / m ³
The quality of the treated water was good without bulking even under heavy load conditions. In particular, the COD removal rate was 95% or more, and the effect of the present invention in which blast furnace water granulation was added and oxygen-enriched air was supplied was clarified as compared with air aeration.

(Effects of the invention) The method of the present invention for supplying oxygen-enriched air having an oxygen concentration of 30 to 95% to an aeration tank while using blast furnace slag as a carrier for immobilizing activated sludge is It is remarkably effective for improving properties such as sedimentation of activated sludge and controlling bulking of activated sludge. Furthermore, the method of the present invention can reduce the treatment time by about 75% of the standard activated sludge treatment without addition of blast furnace water slag without impairing the treatment performance, resulting in improved treatment efficiency and treatment equipment. It has become possible to make it compact.

[Brief description of drawings]

FIG. 1 is a flow chart showing an embodiment of the method for treating wastewater according to the present invention. 1 ... Sewer pump, 2 ... Oxygen-enriched air production device, 3 ...
… Air diffuser, 4 …… Aeration tank, 5 …… Sludge settling tank, 6 …… OR
P meter, 7 ... ORP control device, 8 ... Return sludge pump, 9 ...
…rake,

Claims (1)

[Claims] 1. In the treatment of activated sludge of sewage and industrial wastewater, blast furnace granules having a particle size of 0.02 to 0.2 mm are used as a carrier for immobilizing activated sludge in an aerobic fluidized bed type aeration tank,
Set the redox potential (ORP) of the aeration tank so that the measured value of the composite electrode consisting of gold or an alloy of gold and antimony and silver / silver chloride as the reference electrode is within +50 to +150 mV.
A method for treating wastewater, comprising supplying oxygen-enriched air having an oxygen concentration of 30 to 95 ° C to an aeration tank.