JPS6254079B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for advanced treatment of wastewater, and more particularly, to a method for advanced treatment of treated water obtained by treating wastewater by biological nitrification and denitrification. Conventionally, in advanced treatment of wastewater, it has been required to reduce BOD, COD, chromaticity, nitrogen, phosphorus, etc. in the final treated water as much as possible due to environmental problems at the destination. By the way, sewage with a high concentration of BOD components is first subjected to biological treatment, but if the nitrogen contained in this sewage must also be removed, it is customary to treat it using biological nitrification and denitrification methods. be. For example, when human waste is treated as wastewater without dilution using the biological nitrification and denitrification method, the nitrogen content can be removed to a nearly satisfactory level, but other components require more advanced treatment. The present invention meets these demands and aims to provide a method for efficiently removing impurities from wastewater. That is, the present invention provides a method for advanced treatment of treated water obtained by treating wastewater in a biological nitrification and denitrification process, in which an oxidizing agent and After adding a metal ion dissociation substance and reacting under acidic conditions, it is separated into concentrated sludge and concentrated separated water in a concentration step, and the concentrated sludge is dehydrated in a dehydration step to be separated into dehydrated separated water and dehydrated cake. In addition, after adding powdered activated carbon to the concentrated separated water or the concentrated separated water and the dehydrated separated water and stirring them together, the supernatant water is led to at least a granular activated carbon treatment step. If one embodiment of the present invention is described based on the drawings, human waste 1 is first treated in a biological nitrification and denitrification process 2. In order to adjust the sludge concentration in this denitrification process 2 to a constant concentration, a part of the sludge in the biological treatment tank flows into the centrifuge 3 and is separated into thickened sludge 4 and separated water 5, and the thickened sludge 4 is denitrified. Returned to nitrogen process 2. Meanwhile, the separated water 5 is mixed into the effluent slurry 6 from the denitrification step 2. This effluent slurry 6 does not mean supernatant water from which activated sludge has been separated in a final settling tank as in the conventional activated sludge method, but rather a slurry containing excess sludge. Thus, an oxidizing agent 8 such as hydrogen peroxide is added to the mixed slurry 7 which is a mixture of the separated water 5 and the effluent slurry 6.
and metal ion dissociation substance 9 are added, and stirred for a predetermined time in a reaction tank 10 under acidic conditions of pH 3 to 4. The reaction liquid from the reaction tank 10 is neutralized with a neutralizing agent such as magnesium hydroxide, slaked lime, or caustic soda, if necessary, and then separated into a concentrated sludge 13 and concentrated separated water 12 in a concentration tank 11. Powdered activated carbon 18 is added to the concentrated separated water 12 separated by the concentration tank 11 and stirred for a predetermined time in the contact tank 17. If necessary, a flocculant 20 is added to the powdered activated carbon treated water 19, and the mixture is stirred in the settling tank 21. The powdered activated carbon is separated, and the supernatant water 22 is treated in the subsequent granular activated carbon tower 25 and discharged to the outside of the system as highly treated water 26. On the other hand, the concentrated sludge 13 is separated into dehydrated separated water 15 and dehydrated cake 16 in the dehydration step 14, and the dehydrated separated water 15 is flowed into a contact tank 17 if necessary, and is subjected to contact stirring treatment with the concentrated separated water 12 using powdered activated carbon 18. If it is not necessary, it is mixed with the supernatant water 22 of the sedimentation tank 21 and subjected to subsequent treatment. Note that, for convenience of explanation, the chemical oxidation treatment in the reaction tank 10 will be abbreviated as Fenton treatment below. In this way, in the reaction tank 10, the purification of the biologically treated water from the denitrification process 2 and the reforming of sludge for sludge dewatering are simultaneously achieved using the same chemical, and the sludge dewatering process is completed as before. There is an advantage that there is no need to separately add a dehydration aid for use and a flocculant for coagulation and precipitation. That is, the present invention adds an oxidizing agent 8 and a metal ion dissociative substance 9 to the mixed slurry 7 to achieve a pH of 3 to 4.
This method takes advantage of the fact that when stirred while maintaining a constant temperature, the Fuenton reaction occurs, which purifies the biologically treated water and reforms the sludge. In the present invention, the metal ion dissociating substance 9 is preferably an iron ion dissociating substance, and any of ferric chloride, ferric sulfate, ferrous sulfate, and polyferrous sulfate can be used, but ferrous sulfate is the most effective. In addition, substances that dissociate Al ions and Cu ions can also be used, and salts, oxides, hydroxides, and single metals of Fe, Al, and Cu can be used alone or in combination. On the other hand, as the oxidizing agent 8, ozone can be used in addition to hydrogen peroxide, and these may be used in combination. The concentrated sludge 13 obtained from the concentrated liquid 11 is dehydrated in a dehydration step 14, but in order to improve the dewatering properties of the sludge, it is necessary to add a large amount of oxidizing agent 8 to reform the sludge. On the other hand, if the amount of oxidizing agent 8 is large, BOD and COD as impurities incorporated in the sludge will be eluted and have a negative impact on the subsequent advanced treatment process. Therefore, the amount of the oxidizing agent 8 to be added is determined depending on the desired moisture content of the dehydrated sludge cake 16.
~3000mg/, hydrogen peroxide 500~1000mg/, the moisture content of the dehydrated cake 16 is 60~65%,
Concentrated separated water 12 in concentration tank 11 after Fuenton treatment
The water quality is BOD40~50mg/, SS10~30mg/,
COD was 50 to 130 mg/, and chromaticity was 50 to 100 degrees. Thus, in advanced treatment of human waste, a key point is how to economically reduce COD components. In the present invention, the reason why it was decided to treat concentrated separated water 12 in granular activated carbon column 25 after contacting and stirring powdered activated carbon 18 for a predetermined period of time is as follows. That is, conventionally, a granular activated carbon column was directly used to remove the contaminants remaining in the concentrated separated water, but the present inventors
This is because, after intensive research into methods for treating COD components, it was found that it is effective to perform the powdered activated carbon treatment described above before directly treating the concentrated separated water in the granular activated carbon tower. That is, as shown in Figure 2, when looking at the equilibrium adsorption amount of activated carbon for concentrated separated water, when the raw water concentration (Co) is COD 100 to 130 mg/, the equilibrium adsorption amount X/M is approximately 0.20 g・COD/g・Although the value of c is quite high, the slope of the curve is steep, and COD
It can be seen that a large amount of activated carbon is required to reduce the amount of carbon to 20-30mg/. This is due to the presence of a mixture of easily adsorbable organic matter and poorly adsorbable organic matter in water, and the COD reduction curve (Co89
mg/) also shows this. That is, from FIG. 3, powdered activated carbon was prepared under the conditions shown in Examples below.
By adding 200 to 400 mg of easily adsorbable substances and then treating it in a granular activated carbon tower, the life of the granular activated carbon tower is greatly extended, and the total cost of powdered activated carbon processing and granular activated carbon processing cost can be reduced compared to the conventional direct treatment cost. It was found that the cost can be significantly reduced compared to the case of granular activated carbon treatment. The granular activated carbon treatment step is for removing contaminants remaining in the supernatant water 22 of the sedimentation tank 21, and as for the adsorption method of this activated carbon treatment step as a polisher, a normal fixed bed type is sufficient. The inflow water of the activated carbon tower is supplied from the top of the tower, passed through the activated carbon packed tank in a downward flow, and the treated water is extracted from the bottom of the tower.
If a so-called reverse moving bed adsorption system is applied in which activated carbon is moved in the opposite direction to the water flow direction, the interior of the column will be backwashed every time it is filled, resulting in a more dynamic adsorption system. By the way, the COD component in concentrated separated water can be reduced to the target COD value by subsequent powdered activated carbon treatment and granular activated carbon treatment as a polisher, but where the amount of BOD components in concentrated separated water is a problem, the subsequent Since the amount that can be removed by the physical adsorption effect of activated carbon is small, as shown in FIG.
It is best to process it with In addition, 24 in FIG. 1 is biologically treated water. This biological treatment step 23 can be carried out using a biological treatment device using a normal aeration method, biofilm method, etc., but the granular activated carbon treatment step is a two-stage method, and the first stage treatment is performed using an activated carbon tower. It is also possible to pass the supernatant water 22 in a downward flow while continuously introducing air from the bottom of the tower to mainly remove BOD components, and perform normal activated carbon treatment in the second stage of treatment. . In addition, in the dehydrated separated water 15 from the dehydration step 14,
If the amount of COD components is a problem, it may be treated via the contact tank 17. As described above, according to the present invention, advanced treatment of wastewater can be carried out rationally and efficiently.
This method has the advantage of providing extremely high quality highly treated water with low BOD, COD, etc. Next, examples of the present invention will be described. Example In accordance with the flow sheet cited in the description of the embodiment, human waste having the properties shown in the attached table was treated without dilution at a treatment rate of 0.5 m ³ /day. The processing conditions for each step are as follows. 1 Biological nitrification and denitrification process (1) Residence time 1st denitrification tank 1 day Nitrification tank 2 days 2nd denitrification tank 1 day (2) Other water temperature 27-35℃ MLSS 15000-20000mg/Nitrification liquid circulation Sludge return method: 10 to 30 times Centrifugal separator 2 Fuenton treatment process Ferrous sulfate 2000 to 3000 mg/ Hydrogen peroxide 500 to 1000 mg/ Neutralizing agent Slaked lime 3 Concentration process Gravity thickener Solid load 50 Kg/m ² days 4 Dehydration process Fully automatic filter press 5 Powdered activated carbon treatment process Powdered activated carbon 200-400mg/residence time 5-15 minutes 6 Granular activated carbon treatment process (two-stage treatment method) Column size 5.0〓 _cn × 200 ^L _cn flow rate SV; 0.5 ~1.5 Activated carbon amount 2 First, human waste was treated in a biological nitrification and denitrification process. Next, a mixed slurry (SS concentration of approximately 10,000 ~
Add 2000-3000mg/of ferrous sulfate and 500-1000mg/hydrogen peroxide to 12000mg/), stir for 3-5 hours under PH3-4 conditions, and then adjust the pH with slaked lime.
5.5, and then solid-liquid separation was performed using a gravity thickener to obtain concentrated sludge and concentrated separated water of 18,000 to 20,000 mg/ml. This concentrated sludge was dehydrated using a fully automatic filter press, resulting in a dehydrated cake with a water content of 60-65%. On the other hand, 200 to 400 mg of powdered activated carbon/
After contact stirring for 5 to 15 minutes, the mixture was introduced into a settling basin, and 3 to 5 mg of anionic polymer was added thereto to precipitate the powdered activated carbon and SS, which was then used as the inflow water of the granular activated carbon tower. A small amount of air is continuously introduced into the first stage granular activated carbon tower from the bottom of the tower, and the supernatant clear water of the settling tank is passed in a downward direction.
The concentration was maintained at a level of 1 mg/mg or more. Thereafter, the water was passed in a downward flow to a conventional activated carbon tower. (Fig. 1, 2
(See Figures and Figure 3) The properties and quality of the concentrated separated water, powdered activated carbon treated water, and granular activated carbon treated water as the final treated water are as shown in the table below. 【table】

[Brief explanation of the drawing]

FIG. 1 is a system explanatory diagram showing one embodiment of the present invention, FIG. 2 is a diagram showing the equilibrium adsorption amount of activated carbon, and FIG. 3 is a COD reduction curve for powdered activated carbon. 1... human waste, 2... denitrification process, 3... centrifugal separator,
4...Thickened sludge, 5...Separated water, 6...Outflow slurry,
7... Mixed slurry, 8... Oxidizing agent, 9... Metal ion dissociated substance, 10... Reaction tank, 11... Concentrate, 12...
Concentrated separated water, 13... Concentrated sludge, 14... Dehydration step, 15... Dehydrated separated water, 16... Dehydrated cake, 17
... Contact tank, 18 ... Powdered activated carbon, 19 ... Powdered activated carbon treated water, 20 ... Coagulant, 21 ... Sedimentation tank, 22 ... Supernatant water, 23 ... Biological treatment process, 24 ... Biological treatment water,
25... Granular activated carbon tank, 26... Highly treated water.

Claims (1)

[Scope of Claims] 1. A method for advanced treatment of treated water obtained by treating wastewater in a biological nitrification and denitrification process, wherein an oxidizing agent is added to a mixed slurry of the treated water from the biological nitrification and denitrification process and excess sludge. After adding a metal ion dissociated substance and reacting under acidic conditions, the concentrated sludge is separated into concentrated sludge and concentrated separated water in a concentration step, and the concentrated sludge is dehydrated in a dehydration step to be separated into dehydrated separated water and dehydrated cake. At the same time, powdered activated carbon is added to the concentrated separated water or the concentrated separated water and the dehydrated separated water, and after contact stirring, solid-liquid separation is carried out, and the resulting supernatant water is led to a post-treatment process including a granular activated carbon treatment process. Features: Advanced wastewater treatment method. 2. The method according to claim 1, wherein the post-treatment step comprises a biological treatment step as a first stage and the granular activated carbon treatment step as a second stage. 3. The method according to claim 2, wherein the biological treatment step after the powdered activated carbon treatment is performed by introducing air into a bed filled with granular activated carbon. 4. The method according to claim 1, 2 or 3, wherein an iron salt is used as the metal ion dissociation substance.