KR100413203B1 - No wasting activated sludge process - Google Patents

Abstract

The present invention is a series of biological wastewater treatment methods consisting of anaerobic or anoxic tank, aeration tank and sedimentation tank, wastewater treatment to remove heavy metals and phosphorus and improve nitrogen removal ability by adding inorganic or organic flocculant and / or particulate inorganic minerals to the treatment tank. It is about a method. According to the method of the present invention, the solid residence time can be increased to reduce the amount of sludge produced by 1/4 to 1/10, and a small amount of sludge generated can be recycled to 100% by regenerating the particulate inorganic mineral.

Description

Wastewater treatment method with improved nitrogen and phosphorus removal ability {NO WASTING ACTIVATED SLUDGE PROCESS}

The present invention relates to a wastewater treatment method, and more particularly, to a biological treatment method of a new wastewater that can effectively remove nitrogen and phosphorus in wastewater causing water eutrophication, and recycle sludge, thereby producing no sludge. will be.

Conventionally, most of the sewage treatment plants have a standard activated sludge process, but this process mainly removes organic matter and cannot remove nitrogen and phosphorus in waste water. Treated water without nitrogen and phosphorus is introduced into rivers and coastal waters, causing eutrophication. Therefore, in the United States and Europe, since the 1970s, efforts have been made to remove nitrogen and phosphorus in wastewater with organic matter by combining biological nitrogen and phosphorus removal processes or biological nitrogen removal processes and chemical removal processes. Against this backdrop, new processes have emerged to replace the activated sludge process, and the simultaneous removal of biological nitrogen and phosphorus is applied in the United States, and the representative processes are A ² O method, AO method and Bardenpho method. , Sequencing batch reactor (SBR), UCT process, and postrip method. On the other hand, we found that phosphorus had the greatest impact on eutrophication in Europe and argued that the concentration of phosphorus in wastewater should be maintained at 0.02 mg / l to suppress eutrophication. In addition, the simultaneous removal process of biological nitrogen and phosphorus has a limit (0.8 mg / ℓ) for phosphorus removal, and in order to suppress eutrophication, it is judged that the coagulation process, which is one of chemical treatment processes, is suitable. It is applied to minimize the concentration of phosphorus in the treated water.

Nitrogen contained in the waste water is present in the form of NO ₂ ^-- N _, NO ₃ ^-- N, NH ₄ ⁺ -N or organic matter, most of the general sewage in the form of NH ₄ ⁺ -N. Nitrogen in these waste waters is oxidized to NO ₃ ⁻ by microorganisms such as nitrobacters (nitrification reaction) and then removed by N ₂ (denitrification reaction) by various kinds of denitrification bacteria. Therefore, the nitrogen of this type must be oxidized to NO ₃ ⁻ in order to remove nitrogen in the waste water. However, the nitrification reaction is very sensitive to environmental changes, unlike denitrification, and can be easily suppressed by changes in external conditions. These external conditions include temperature, pH, BOD / TKN ratio of influent, hardly decomposable compounds, heavy metals, etc. Of these, it is almost impossible to control the influence of temperature in the actual process.

On the other hand, phosphorus in the waste water can be removed using anaerobic and aerobic conditions in the biological removal process. That is, phosphorus is released under anaerobic conditions, and excess phosphorus is ingested by the microorganisms under aerobic conditions at a later stage. The phosphorus is then removed by discarding the microorganisms (sludge) ingesting excess phosphorus in the reactor. As such, the biological removal process is very complex for application in a full scale treatment plant, and phosphorus release under anaerobic conditions or excess phosphorus intake conditions under aerobic conditions are easily suppressed by external conditions. In addition, in the biological removal process, phosphorus is removed by sludge disposal, so that a large amount of sludge is generated compared to other processes, and the sludge treatment cost is high and the global trend to reduce sludge generation is violated.

On the other hand, many biological treatment processes, including activated sludge processes, can economically treat organics and nitrogen, but generate sludge as a byproduct. These by-products are finally subjected to a treatment step such as landfill or incineration, and in the case of landfill, there are problems such as odor, generation of pests, and groundwater contamination. In particular, countries with small land areas, such as Korea, are not suitable for landfilling, and most of the sludge is incinerated in Japan and France, which have a similar environment. Against this backdrop, domestic landfilling of sewage from sewage treatment plants has been banned since 2001, and only incineration or ocean dumping are allowed. In addition, it has been attempted to reuse the sludge generated in the sewage treatment plant elsewhere, such as compost, but the situation is not widely applied because the process conditions are difficult and uneconomical.

On the other hand, in the 1970s, a study was conducted to remove nitrogen by using the excellent ammonium ion exchange ability of natural zeolite. Semmons proposed that the zeolite could be filled in a column and then passed through wastewater to remove nitrogen. However, since the ammonium removal mechanism of zeolite is an ion exchange reaction (a kind of substitution reaction), regeneration is necessary when the ion exchange capacity of the zeolite runs out. As a regeneration method, a regeneration method using NaCl salt, a regeneration method using deaeration, or a biological regeneration method are used, of which biological regeneration is known to be the most economical. J. Olah also found that nitrification and removal of organics could be enhanced by injecting zeolites into activated sludge aeration tanks. As such, many studies have been conducted to remove nitrogen and phosphorus by injecting zeolite into a biological reactor. In Korea, the characteristics of zeolites were recognized in the 1990s, and research results for wastewater treatment using them (Korean Patent Publication Nos. 97-2624, 97-9650, 97-11327, 97-11330, 97 -0042279, 98-073764, 99-0050101, 99-0050182, 99-0073117, 99-0074576, 2000-0000806, and the like. Most of these results are related to zeolite column reactors in which a zeolite regeneration tank is installed separately, and on the other hand, a method for simultaneously removing nitrogen and phosphorus by directly adding zeolite to a biological reactor is mentioned. However, since the above patents use a zeolite column, there is an additional cost for the blockage of the column and an installation and maintenance cost for regeneration. The process of injecting zeolite into the biological reactor to remove nitrogen and phosphorus simultaneously, as mentioned above, Due to the large amount of sludge produced, the government's policy to prohibit sludge landfilling from sewage treatment plants has not been met since 2001, and it can never satisfy the phosphorus concentration in the effluent that can suppress eutrophication, and the burden of continuously injecting zeolite have.

The present invention is to solve the above problems, it is possible to effectively remove the nitrogen and phosphorus in the waste water that causes the water enrichment to improve the phosphorus concentration that can suppress eutrophication as well as the water quality requirements for nitrogen and phosphorus. It relates to a treatment method for satisfying. In addition, the method according to the present invention can maintain the SRT (Solids Retention Time) of 50 days or more to reduce the amount of sludge generated to 1/4 to 1/10 of the existing treatment plant, and also by incineration of the small amount of sludge generated by the inorganic particles By regenerating the mineral and recycling the sludge 100%, it provides a new method of biological treatment of the waste water which does not generate any sludge.

1 is a view showing the process flow of the wastewater treatment plant system of the present invention.

The present invention refers to inorganic or organic flocculants and / or particulate inorganic minerals (wherein inorganic minerals refer to zeolites, clays, glasses, diatomaceous earths, pozzolanes, fly ashes, bentonites, which comprise 50 to 80% of SiO ₂ by weight). It is added to the treatment tank to remove heavy metals, hardly decomposable substances and phosphorus, and to increase the nitrogen removal ability consists of removing nitrogen and phosphorus simultaneously in one reactor.

Generally, the treatment tank is composed of an anaerobic tank or anoxic tank located at the front end and an aeration tank immediately located at the rear end, and a sedimentation tank which precipitates sludge generated in the aeration tank. The location of the anoxic tank and the aeration tank may be changed by the characteristics of the raw water. In addition, when the nitrogen concentration of the raw water is high, the anaerobic tank and the aeration tank can be reinstalled in the existing system. In this case, the system flow chart may be configured as an anaerobic tank or an anaerobic tank-aeration tank-anoxic tank or anaerobic tank-aeration tank-sedimentation tank. On the other hand, the treatment rate can be increased by using a circulation system for returning the sludge in the aeration tank or the settling tank back to the anaerobic tank, anoxic tank and aeration tank to remove nitrogen and maintain sludge concentration in the reactor.

The flocculant injected in the present invention may be injected at any stage of the system consisting of an anaerobic tank or an anaerobic tank, aeration tank, and settling tank, but the aeration tank end or near the settling tank inlet is most suitable. As the flocculant, an inorganic flocculant or an organic flocculant can be used. The inorganic flocculant used in the present invention is alumina sulfate, FeSO ₄ nH ₂ O, FeCl ₂ nH ₂ O, FeCl ₃ nH, represented by Al ₂ (SO ₄ ) ₃ nH ₂ O (o ≦ n ≦ 50). ₂ a divalent iron salt such as an inorganic flocculant, and the Ca ²⁺ and Mg ²⁺ such as O and the like metal salts. In addition, inorganic polymer flocculants such as poly aluminum chloride (PAC), poly aluminum sulfate silicate (PAS), poly aluminum chloride silicate (PACS), poly aluminum chloride calcium (PACC), poly ferric chloride (PAC), and poly aluminum sulfate (PAS) Can also be used.

PAM (polyacrylamide), PEI (polyethylenimine), polyamine, etc. can be used as an organic flocculant. Among these flocculants, alumina sulfate and iron salt coagulant are preferable in view of phosphorus removal rate and economic efficiency.

Inorganic minerals introduced in the treatment method of the present invention may be injected at any stage of the process as in the flocculant, but are preferably injected into the conveying sludge line or the aeration tank front end. In particular, among such inorganic minerals, it is most preferable to add clinoptilolite having a high ammonium ion exchange capacity. Generally, a powdery inorganic mineral having a diameter in the range of 10 to 5000 μm is used. In particular, in the case of clinopthinolite, it is effective that the diameter is in the range of 10 to 20 μm.

Further, the treatment method of the present invention includes dewatering the sludge, then drying or incineration and reusing the residual oil product into media. In the treatment method of the present invention, the sludge can be dewatered using a general dehydration method such as pressurized dehydration, centrifugal dehydration, belt compression dehydration, and the like. Inorganic minerals and flocculants may reduce the amount of polymer injected as a dehydration pretreatment material by more than half. Sludge drying and incineration temperature is 100-1200 degreeC, and 400-800 degreeC is preferable.

Referring to the present invention in more detail based on the accompanying drawings as follows.

The treated water passed through the primary settling tank is introduced into the anaerobic tank or anoxic tank (1). The treated water is transferred to the aeration tank 2 through an anaerobic tank or an anaerobic tank, organic matter is removed from the aeration tank and nitrified, and finally sludge is precipitated and removed in the secondary settling tank 3 to obtain final treated water. Nitrified treated water and sludge in the secondary settling tank (3) and the aeration tank (2) are returned to the anaerobic or anoxic tank through a certain amount through the conveying line (9) to remove nitrogen. Such conveying amount is 100 to 400% in the aeration tank, respectively. In secondary sedimentation tanks, 30 to 150% is suitable. Between the settling tank 3 and the denitrification tank 2 may be provided with an internal conveying line 10 to be returned to the denitrification tank 1 treated water in the aeration tank (2).

In the present invention, the inorganic mineral is injected into the conveying sludge line or the aeration tank front end. Inorganic minerals, especially Clinoptilolite, perform ion exchange reactions with ammonium ions in water. These ion exchanged zeolites provide a rich source of nitrogen to nitrifying bacteria such as nitrobacter or nitrosomonas to promote nitrification. Let's do it. In other words, inorganic minerals promote the nitrification reaction by supplying a rich source of nitrogen to nitrifying bacteria while providing surface area. However, the pore size of inorganic minerals is very small, which limits the surface area for nitrifying microorganisms.

The mixed injection of the flocculant according to the present invention is very economical and effective since it can remove phosphorus while providing surface area to microorganisms. In the presence of suspended nitrifying bacteria in the system and nitrifying bacteria attached to inorganic minerals, both are electrically negative at pH 5-9. At this time, when the flocculant is injected, the cationic component and the macromolecular component of the flocculant together with phosphorus aggregate the floating microorganisms to form a giant floc. The formed floc is formed with a channel through which water and nutrients can move, and a void through which bacteria of several micrometers to several tens of micrometers can attach and grow. In other words, flocculants provide poor pores for inorganic minerals and provide surface area for microorganisms that remove organic matter, including nitrifying bacteria, to maintain high concentrations of microorganisms and to remove phosphorus.

Inorganic minerals are added in an anaerobic or anaerobic tank and aeration tank to maintain a concentration of 500 to 20000 mg / l, preferably 1000 to 8000 mg / l. If the inorganic mineral concentration is higher than 8000 mg / l, it is uneconomical due to the increase in the amount of use. If the concentration is lower than 500 mg / l, the effect by the inorganic particles cannot be obtained more than expected. Inorganic minerals are disposed of together with the waste sludge and must be replenished by the amount of waste. The amount of flocculant varies depending on the characteristics of the influent, and is generally added at 10 to 1000 mg / l with respect to the influent flow rate, and preferably 10 to 200 mg / l.

In general, the solids retention time (SRT) is the time the sludge stays in the system, and the larger the amount of sludge discarded from the settler, the shorter the SRT. In general, SRTs are maintained for 5 to 15 days in biological processes, including activated sludge processes. The sludge generation can be reduced by maintaining the SRT for a long time, but when the SRT is increased, the flocculation phenomenon is reduced and streaked, so that a small sized pin flop is generated and is not removed from the settling tank and flows out along the flow of the effluent. This happens. In addition, a certain amount of sludge should be discarded because microorganisms grow and sludge generation increases due to carbon components in the wastewater. Therefore, the conventional method could not make the SRT long enough.

However, since the microbial flocs produced in the present invention are large in size and hard due to inorganic minerals and flocculants, pin flocs are not generated even when the SRT is sufficiently long, and the precipitation is excellent. In addition, it is possible to maintain a sufficiently long SRT because the low carbon source in the wastewater flowing into most domestic sewage treatment plants. That is, according to the method for treating wastewater according to the present invention, the SRT can be sufficiently long (20 to 100 days), and as a result, the amount of sludge generated can be reduced to the existing 1/4 to 1/10.

Hereinafter, preferred embodiments of the present invention have been described, but the present invention is not limited thereto.

Comparative Example 1

The artificial wastewater was treated by a general standard activated sludge process consisting of aeration tank and sedimentation tank. At this time, the residence time (HRT) in the aeration tank was 6 hours and the SRT was 10 days. The water quality of the treated water thus treated was analyzed, and the results are shown in Tables 1, 2, and 3.

Organic matter treatment rate Influent Concentration [mg / L] Treated water concentration [mg / L] Throughput [%] BOD ₅ BOD ₅ BOD ₅ Standard activated sludge method 458 120 74

Nitrification rate Influent Concentration [mg / L] Treated water concentration [mg / L] Nitrification rate [%] T-N NO ₃ ^-- N T-N NO ₃ ^-- N Standard activated sludge method 124 0 120 28 22

Phosphorus Removal Rate Influent Concentration [mg / L] Treated water concentration [mg / L] Throughput [%] T-P T-P T-P Standard activated sludge method 5.2 4.29 18

Example 1

The same artificial wastewater used in Comparative Example 1 was treated as follows in three wastewater treatment apparatuses consisting of an aeration tank and a sedimentation tank. In one treatment apparatus, the anodic tank was injected with a concentration of 4000 mg / l of clinoptilolite having a particle size of 10 to 20 µm. The other treatment device was injected with alumina sulfate as a flocculant at 50 mg / l with respect to the influent flow rate. Another treatment device was simultaneously infused with clinoptilolite and alumina sulfate as described above. The quality of the treated water treated by the three treatment apparatuses was analyzed, respectively, and the results are shown in Tables 4, 5, and 6.

Organic matter treatment rate Influent Concentration [mg / L] Treated water concentration [mg / L] Throughput [%] BOD ₅ BOD ₅ BOD ₅ Clinoptilolite injection 45 90 Alumina Sulfate Injection 32 93 Clinoptilolite and Alumina Sulfate Injection 18 96

Nitrification efficiency Influent Concentration [mg / L] Treated water concentration [mg / L] Nitrification Efficiency [%] T-N NO ₃ ^-- N T-N NO ₃ ^-- N Clinofytilolite addition 128 One 120 99 83 Alumina sulfate addition 0 128 51 40 Add Clinoptilolite and Alumina Sulfate 0 121 118 98

Phosphorus Removal Efficiency Influent Concentration [mg / L] Treated water concentration [mg / L] Removal efficiency [%] T-P T-P Clinofytilolite addition 5 3.9 22 Alumina sulfate addition 1.2 76 Add clinoptilolite and alumina sulfate 0.92 82

Example 2

The sedimentation of the sludge obtained in the experiments of Comparative Example 1 and Example 1 was evaluated by measuring the average SVI (Sludge Volume Index, capacity indicator of the sludge). The results are shown in Table 7.

Sedimentation Rate and SVI According to SRT SRT SVI [mℓ / g] Standard Activated Sludge Clinoftilolite addition Sulfate Addition Add clinoptilolite and alumina sulfate 40 258 85 92 74 80 * 142 128 92 100 * 285 156 81

In the results of Table 7, the result of the simultaneous injection of clinoptilolite, alumina sulfate, and clinoptilolite and alumina sulfate and treatment of wastewater, the sedimentation rate of the produced sludge was determined by the standard activated sludge method. It can be seen that the increase significantly compared to the settling rate. In general, when the SVI is 100 or less, the sludge settling property is excellent, and when the SVI is 200 or more, the sludge settling property is inferior. At more than 80 days, it was confirmed that the sludge settling property is reduced. However, when injecting clinoptilolite and alumina at the same time, it can be seen that the sludge settling property is excellent even at SRT 100 days.

Example 3

The same artificial wastewater as in Example 1 was composed of an aeration tank and a sedimentation tank, and a denitrification tank was formed at the front end of the aeration tank and treated in three identical treatment apparatuses equipped with a circulating nitrification denitrification system. At this time, Clinoptilolite having a particle size of 10 to 20 µm was injected into the aeration tank of one treatment device, and 80 mg / l of alumina sulfate was injected into the other treatment device, and Clinoptilillo was added to the other treatment device. Light and alumina sulfate were injected in the same manner as above. In the denitrification tank and in the nitrification tank, the experiment was carried out with HRT of 2 hours and 4 hours, respectively, and SRT of 40 days. And when the quantity of inflow was set to 1Q, the conveyed amount of sludge was 1Q and the internal conveyed quantity was 3Q. The nitrogen removal rate of the treated water thus treated was compared with the nitrogen removal rate obtained in Comparative Example 1, and the results are shown in Tables 8 and 9.

Influent Concentration [mg / L] Treated water concentration [mg / L] Nitrogen removal rate [%] T-N T-N Clinoptilolite injection 102 30.6 70 Alumina Sulfate Injection 102 53 48 Clinoptilolite and Alumina Sulfate Injection 108 15 86

Influent Concentration [mg / L] Treated water concentration [mg / L] Phosphorus Removal Rate [%] T-P T-P Clinoptilolite injection 8.30 6.95 16 Alumina Sulfate Injection 8.15 0.62 93 Clinoptilolite and Alumina Sulfate Injection 8.52 0.47 95

From the results of Example 6, as shown in the present invention, respectively, simultaneously and simultaneously injecting clinoptilolite and alumina sulfate were applied to the cyclic nitrification denitrification process. The removal rate of 48% was obtained, and 86% of nitrogen removal rate was obtained by injecting clinoptilolite and alumina at the same time. This nitrogen removal rate is 16% higher than the clinoptilolite nitrogen removal rate and can be confirmed that 38% higher than alumina sulfate. In the case of phosphorus, clinoptilolite injection showed a very low phosphorus removal rate of 16%, and alumina sulfate showed a high phosphorus removal rate of 93% due to the flocculant. However, the simultaneous injection of clinoptilolite and alumina sulfate showed the highest phosphorus removal rate of 95% due to phosphorus removal of coagulant and high concentration of microorganisms due to coagulant and clinoptilolite.

Example 4

The same artificial wastewater treatment as in Example 1 was treated in two identical treatment apparatuses comprising an aeration tank and a sedimentation tank, and having a circulating nitrification denitrification system having a denitrification tank at the front of the aeration tank. In one of the treatment apparatuses, alumina sulfate was injected at 50 mg / l while maintaining clinoptilolite at 4000 mg / l in the aeration tank, and the sludge produced was dried and crushed at 500 ° C., and then reinjected into the aeration tank. The sludge was reused. In another treatment apparatus, clinoptilolite and alumina sulfate were injected in the same manner as above. The HRT in the denitrification tank and the nitrification tank was tested for 2 hours and 4 hours, respectively, and the SRT for 40 days. When the amount of influent water was set to 1 Q, the sludge conveyance amount was 1 Q and the internal conveyance amount was 3 Q. The removal rates of nitrogen and phosphorus were compared and the results are shown in Table 10 and Table 11.

Influent Concentration [mg / L] Treated water concentration [mg / L] Nitrogen removal rate [%] T-N T-N Sludge reuse 102 30.6 70 New Clinoptilolite Injection 102 29 71

Influent Concentration [mg / L] Treated water concentration [mg / L] Phosphorus Removal Rate [%] T-P T-P Sludge reuse 8.30 2.98 88 New Clinoptilolite Injection 8.15 2.90 88

As shown in Tables 10 and 11, there was little effect on nitrogen and phosphorus removal rates when sludge was reused and when fresh clinoptilolite was injected. That is, when the sludge is dried and reused, there is no effect on the nitrogen and phosphorus removal rate.

Example 5

In order to test the treatment efficiency according to the particle size of clinoptilolite, the same artificial wastewater as in Comparative Example 1 was treated in three wastewater treatment apparatuses consisting of an aeration tank and a sedimentation tank as follows. In one treatment apparatus, clinoptilolite having a particle size of 10 to 20 µm was injected into the aeration tank so as to have a concentration of 4000 mg / l. Another treatment apparatus was injected with clinoptilolite having a particle size of 30 to 100 µm, and another treatment apparatus was injected with clinoptilolite having a particle size of 200 to 1000 µm as described above. The water quality of the treated water treated by the three treatment apparatuses was analyzed, respectively, and the results are shown in Table 12, Table 13, and Table 14.

Organic matter treatment rate according to the particle size of clinoptilolite Influent Concentration [mg / L] Treated water concentration [mg / L] Throughput [%] Particle size distribution BOD5 BOD5 BOD5 10 ~ 20 ㎛ 450 22 95 30 ~ 100 ㎛ 25 95 200 ~ 1000 ㎛ 32 93

Nitrification Efficiency According to the Size of Clinoftilolite Influent Concentration [mg / L] Treated water concentration [mg / L] Nitrification Efficiency [%] Particle size distribution T-N NO3--N T-N NO3--N 10 ~ 20 ㎛ 128 One 120 120 94 30 ~ 100 ㎛ 0 128 98 86 200 ~ 1000 ㎛ 0 121 98 86

Phosphorus Removal Efficiency According to Clinoptilolite Particle Size Influent Concentration [mg / L] Treated water concentration [mg / L] Removal efficiency [%] Particle size distribution T-P T-P 10 ~ 20 ㎛ 5 3.5 30 30 ~ 100 ㎛ 3.5 30 200 ~ 1000 ㎛ 3.7 29

As described above, the removal rate of organic matter and phosphorus according to the particle size of clinoptilolite did not have a significant effect. However, in the case of nitrification rate, the highest nitrification rate was 94% when the particle diameter was 10 to 20 μm. In order to obtain a high nitrification rate from this, it may be most preferable to apply clinoptilolite having a particle diameter of 10 to 20 μm.

The wastewater treatment method of the present invention can effectively remove nitrogen and phosphorus in wastewater by nitrification and phosphorus adsorption by adding inorganic mineral and flocculant, and reduce sludge generation amount to 1/4 to 1/10 than before. It is a biological treatment method of wastewater that can not only satisfy the water quality requirements for nitrogen and phosphorus by reusing a small amount of sludge generated, but also reduce the overall cost of sludge removal.

In addition, the microbial flocs produced in the present invention are relatively large in size and hard because they are produced using the particulate inorganic material as a seed, and do not generate a pin flop even when the SRT is set long. Therefore, it is possible to set the SRT long enough to reduce the amount of sludge generated, and because the microbial flocs produced in the present invention have a high specific gravity, they are settled at a higher speed than sludge produced by the conventional method. Wastewater can be treated at high speed without In addition, about 2 to 5 times higher concentrations of microorganisms are maintained in the aeration tank, so organic removal and nitrification rates may be 2 to 5 times faster.

Claims (6)

delete delete delete delete In the method for treating wastewater in a treatment tank consisting of an anaerobic or anoxic tank, aeration tank and sedimentation tank, the treatment tank is selected from zeolite, clay, glass, diatomaceous earth, pozzolane, fly ash, bentonite or clinoptilolite, and has a thickness of 10 to 5000 µm. A particulate inorganic mineral having a diameter in the range was injected at a rate maintaining a concentration of 500 to 20000 mg / l, and an inorganic coagulant such as alumina sulfate, iron salt inorganic coagulant, divalent metal salt or polyaluminum chloride, polyaluminum sulfate silicate, A flocculant selected from organic coagulants such as polyamine is injected at a rate of 10 to 1000 mg / l with respect to the inflow flow rate, the solid retention period is maintained at 20 to 100 days, and the sludge generated is dried at 100 to 1200 ° C after dehydration and incinerated. And reusing the residue into the media, where the flocculant is aerated in the treatment tank. It is injected in the vicinity of the inlet end or the settling tank, the waste water treatment method that inorganic mineral is injected into the conveying line or the front end of the aeration tanks. The wastewater treatment method of claim 5, wherein the sludge is dried and incinerated at 400 to 800 ° C. after dewatering the sludge.