JPS6210720B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for treating concentrated organic wastewater such as human waste, particularly biological denitrification, dephosphorization,
By organically combining BOD removal methods, physicochemical dephosphorization, BOD removal, and solid-liquid separation methods in a novel manner, concentrated organic wastewater such as human waste can be treated in the most rational manner. It concerns the method of processing. The main problem with conventional human waste treatment processes is that in biological treatment processes such as biological nitrification and denitrification methods and activated sludge methods, phosphoric acid (600%
~1000mg/) and chromaticity components can hardly be removed, so sulfuric acid, ferric chloride, or slaked lime act on phosphate ions and chromaticity components to form insoluble precipitates in biologically treated water. It is necessary to add and remove an inorganic flocculant that produces sulfuric acid, and for example, sulfuric acid soil requires a large amount of 500 to 1000 mg / 20 times diluted biologically treated water, and as a result, it is difficult to dewater. The amount of inorganic sludge generated has increased, and the treatment and disposal of the sludge has become a major problem.Moreover, even in composting, which has recently become popular, the mixing of inorganic sludge is undesirable. Conventional methods require 10 to 20 times more dilution water than human waste, so human waste treatment plants, which have difficulty securing dilution water sources, are suffering from a shortage of dilution water. As a natural result of trying to reduce the amount of inorganic sludge generated, the chromaticity of the treated water,
Phosphoric acid will increase. The present invention is an inorganic coagulation method that generates a large amount of inorganic sludge such as sulfuric acid chloride and ferric chloride, which was traditionally considered to be necessary for removing chromaticity and phosphoric acid. It is possible to achieve the seemingly contradictory effects of eliminating the need for the addition of additives or significantly reducing the amount of additives compared to conventional methods, and improving the chromaticity and removal rate of phosphoric acid compared to conventional methods. The purpose is to provide a possible method. That is, in the present invention, an anaerobic fermentation process is provided before the biological nitrification and denitrification process, and a flocculant containing at least a cationic polymer flocculant is added to the mixture of the effluent and excess sludge that has passed through these processes. It is characterized in that it is added and dehydrated, and the dehydrated separated liquid is further processed through a permeable membrane. Next, important points in the configuration of the present invention will be explained. First, the biological dephosphorization and nitrification/denitrification steps described below are operated at a dilution rate as low as possible, ideally in a non-diluted state. By doing this, it becomes realistically possible to treat all of the effluent from the biological dephosphorization, nitrification, and denitrification process using a permeable membrane and a dehydrator. When diluted 10 to 20 times and subjected to biological treatment, the amount of treated water becomes enormous.
Treatment using a permeable membrane requires a significantly large membrane area and operating power, making it difficult to apply in terms of running costs. In this way, the amount of water to be treated with the present invention is lower than that of the conventional method.
Since it is 1/10 to 1/20, it is easy to apply a permeable membrane, and most of the chromaticity components can be excessively removed by the permeable membrane without using an inorganic flocculant such as sulfuric acid. Therefore, a significant advantage is obtained that no inorganic sludge, which is difficult to dewater, is generated. However, since phosphoric acid removal is not complete with a permeable membrane, the present inventors initially thought that the application of membrane treatment was of little significance, but the present inventors worked diligently to resolve this contradiction. As a result of further investigation, we established an anaerobic fermentation process before the biological nitrification and denitrification method, and created a biological method in which the returned sludge is retained and the function of microorganisms to take in excess phosphorus in the liquid is enhanced. We arrived at the idea of applying a dephosphorization method, and were able to resolve the above-mentioned contradictions by using a new concept that could be called a combination process of biological dephosphorization process and permeable membrane. Furthermore, the chromaticity components in the liquid flowing into the permeable membrane,
As a result of studying methods to reduce the concentration of COD and BOD components and improve membrane flux, we decided to mix effluent from the nitrification and denitrification process, which includes biological dephosphorization, with excess sludge from the biological treatment process. We investigated a method of adding a cationic polymer flocculant to the slurry, allowing it to flow into a dehydrator, and separating it into a dehydrated cake and a dehydrated separated liquid, thereby incorporating the sludge treatment process into the water treatment process. (Traditionally, surplus sludge is treated in a system completely separate from the water treatment system.) As a result, cationic polymer flocculation, which has traditionally been used only for flocculation as a pretreatment for dewatering surplus sludge, Colloidal chromatic components, SS, BOD, COD, organic N, etc. in the liquid flowing out from biological dephosphorization and nitrification and denitrification processes coagulate with excess sludge and are discharged as a dehydrated cake. We discovered this phenomenon and established a method to significantly reduce the chromaticity components in the water flowing into the permeable membrane. Furthermore, by simply concentrating and separating the substances to be removed,
We have established a completely new method for disposing of concentrated liquid remaining on the membrane side, which is always a problem in membrane separation processes where solid matter is not removed, such as coagulation and sedimentation. In other words, the concentrated liquid of the permeable membrane was conventionally processed by evaporation,
This method has been disposed of by methods such as incineration, but this method results in extremely high fuel consumption and increases costs. Therefore, in the present invention, the permeable membrane side concentrated liquid is added to the mixed slurry liquid flowing into the dehydrator. A new method was developed in which the high molecular weight chromatic components in the concentrated liquid were co-agglomerated with the biological process surplus sludge and removed by adding a cationic polymer flocculant to the liquid. Adopted. As a result, it is no longer necessary to use methods that waste a large amount of thermal energy, such as evaporation or incineration, to dispose of the permeable membrane side concentrate, and the process has been significantly streamlined. The permeable membrane used in the present invention is a reverse osmosis membrane or a microporous membrane with low permselectivity, and an ultrafiltration membrane (UF membrane) or a microporous membrane is particularly preferred. Furthermore, one embodiment to which the new concept of the present invention is applied will be described with reference to FIG. First, concentrated organic wastewater 1 such as human waste is introduced into the anaerobic fermentation section 2. The sludge 4 is returned from the solid-liquid separation section 3 to the anaerobic fermentation section 2, where the raw water and activated sludge are brought into contact and retained under anaerobic conditions, so that the microorganisms in the activated sludge absorb excessive phosphorus. The subsequent nitrification section takes in excessive phosphorus from the liquid side under aerobic conditions. A biological denitrification unit 5 is arranged next to the anaerobic fermentation unit 2, and NO ₂ -N, NO ₃ -N in the circulating nitrification liquid 6 is
(abbreviated as NOx-N)), the denitrifying bacteria respires nitric acid while reducing the BOD in the stock solution.
NOx-N→N ₂ ↑ at high speed using the component as an organic carbon source
A reduction reaction takes place. Further, a nitrification unit 7 is provided following the denitrification unit 5, and the nitrification unit 7 is
NH ₄ --N and residual BOD are oxidized or removed to NOx --N, and phosphorus is excessively ingested. Although not shown in the drawings, it is of course possible to provide a second denitrification section and a reaeration section next to the nitrification section 7 if a high degree of nitrogen removal is desired. The biological nitrification and denitrification process is as follows:
In addition to the illustrated nitrification solution circulation method, it is also possible without any problem to adopt the so-called step method in which the stock solution is dispensed in a stepwise manner to the denitrification section in a process consisting of repeating the denitrification section and the nitrification section. It is of course possible to employ the so-called aerobic denitrification method in which weak aeration is performed in the denitrification section. Next, the solid-liquid separation unit 3 can adopt normal gravity precipitation, but in the case of a biological nitrification and denitrification process that incorporates a biological dephosphorization function, the solid-liquid separation unit 3 If the residence time is long, it tends to become anaerobic and phosphorus leaks into the treated water, so it is preferable to use a flotation separation method or a centrifugal concentration method that allows solid-liquid separation in a shorter time. Thus, a cationic polymer flocculant 11 is added to a mixed liquid 10 of separated water 8 and excess sludge 9 from the solid-liquid separation section 3, and a dehydrator 12 such as a centrifugal dehydrator or a roll press type dehydrator is used. Dehydrated cake 1
3 and a dehydrated separated liquid 14 are obtained. The dehydrated separated liquid 14 is
As mentioned above, the chromaticity of colloidal,
Since BOD, COD, organic N, etc. have been removed, and the fluid is considerably clear, it becomes easier to process with a permeable membrane, such as the UF membrane 15, and the flux is also improved. In most cases, the treated water can be discharged by this UF membrane 15 treatment, but if more advanced treatment is required, activated carbon adsorption may be performed after this. Note that some of the cationic polymer flocculant 11 added before the dehydrator 12 remains in the dehydrated separated liquid 14, but this residual polymer is completely removed by the UF membrane 15 and discharged. Another important advantage of the present invention is that there is no problem with the use of cationic polymers, which are no longer contained in water and are said to be highly toxic to fish. On the other hand, the concentrated liquid 16 of the UF membrane is recycled and mixed with the dehydrator inflow mixed liquid 10, is added with the cationic polymer flocculant 11 as described above, is flocculated, and then flows into the dehydrator 12. In this process,
The soluble components on the polymer side in the UF membrane concentrate 16 are:
As it undergoes co-aggregation and migrates into the dehydrated cake,
It has been confirmed that the concentration of the UF membrane concentrate 16 does not increase infinitely but remains balanced at a certain constant value. In addition, the separated liquid 8 of the solid-liquid separation section 3 in the biological dephosphorization, nitrification, and denitrification steps contains a small amount of phosphoric acid that could not be completely removed by biological dephosphorization. In order to remove this, inorganic flocculants such as sulfuric acid or ferric chloride are used in combination with the cationic polymer flocculant added before the dehydrator.
Another effective method is to add the inorganic flocculant 17 to the dehydrator separated liquid 14 to form a floc, and then directly treat it with the UF membrane 15. The amount of inorganic flocculant required to remove phosphoric acid is determined by the concentration of phosphoric acid, so whereas conventional methods require an extremely large amount (several thousand ppm) of inorganic flocculant to be injected, our method Since the invention combines biological dephosphorization with a physicochemical method using a flocculating UF membrane, the amount of inorganic flocculant required can be significantly reduced.
The treated water 18 of the UF membrane is discharged as is, or if necessary, it is further treated with ozone, activated carbon adsorption, etc. and then discharged. The present invention having the above configuration makes it possible to obtain the following industrially important benefits. Water quality that can be discharged without the need for dilution water can be obtained. By combining the biological dephosphorization process and the permeable membrane process, we achieved a clear separation of the functions of removing phosphorus and chromatic components, so that inorganic sludge that is difficult to dewater is not generated or is generated in a very small amount. Establish a rational disposal method for permeable membrane concentrate,
This makes it possible to apply membrane treatment without significantly increasing costs. The cationic polymer flocculant, which was conventionally used for dewatering excess sludge, can now also be used to clarify the liquid, improving the quality of raw water supplied to the permeable membrane and making it possible to increase flux. As a result of being able to use no dilution or a low dilution ratio close to that, it is possible to efficiently utilize the liquid temperature raising effect of the fermentation heat generated during biological dephosphorization, nitrification, and denitrification processes, and there is no need for external heating. Since the temperature inside the tank can be easily maintained at 30 to 35°C, the rate of phosphorus uptake and discharge by microorganisms, as well as the rate of nitrification and denitrification, is improved. As a result, the facility can be made more compact. If a high separation rate method such as pressure flotation or centrifugal concentration is used for solid-liquid separation in the biological dephosphorization process, the microorganisms that have taken up phosphorus will not be exposed to the anaerobic atmosphere, and the There is no risk of phosphorus leaking into the treated water as there is no discharge of phosphorus in the liquid separation section. Next, one embodiment of the present invention will be described based on experimental results. EXAMPLE An experiment was conducted based on the flow of the present invention shown in FIG. 1 using filtered human urine having the water quality as shown in Table 1 as a stock solution.

[Fronatsuk (product name)]

3 UF membrane treatment Molecular weight cut off: 6000 Membrane permeation water volume: 0.4m ³ /m ²・d (10Kgf/m ² ) Recovery rate: 95% or more. The water quality of the separated water in the solid-liquid separation section (pressurized flotation tank) of the phosphorus process was as shown in Table 2.

[Table] In this way, biological dephosphorization was performed with a removal rate of over 90% without using any chemicals. Also,
Naturally, the removal rates of BOD, COD, and nitrogen were extremely good. Next, cationic polymers are aggregated in a slurry liquid (10,000 to 12,000 mg/SS as SS), which is a mixture of pressurized flotation separated water, UF membrane concentrated recycle liquid, and excess sludge generated from biological dephosphorization, nitrification, and denitrification processes. A 1.5% to 2% SS solution (trade name of Flownatsuk) was added thereto, and the mixture was dehydrated using a decanter-type centrifugal dehydrator. As a result, a dehydrated cake with a cake moisture content of 79 to 81% and a dehydrated separated liquid having water quality as shown in Table 3 were obtained.

[Table] In the above process, as in the conventional method, sulfuric acid
It does not use inorganic flocculants such as ferric chloride that generate inorganic sludge that is difficult to dehydrate. Next, the dehydrated separated liquid having the water quality shown in Table 3 was UF
Overtreated with membrane. At this time, in order to remove the 75 mg of residual PO ₄ that could not be removed by biological dephosphorization, 300 mg of sulfuric acid was added and mixed.
After forming a floc, it was allowed to flow directly into the UF membrane. As a result, the UF membrane-treated water exhibited water quality as shown in Table 4, and extremely good water quality was obtained despite the non-diluted human urine treatment.

【table】 [Brief explanation of the drawing]

FIG. 1 is a system explanatory diagram showing one embodiment of the present invention. 1...Organic wastewater, 2...Anaerobic fermentation section, 3...Solid-liquid separation section, 4...Return sludge, 5...Biological denitrification section, 6
... Circulating nitrifying liquid, 7... Nitrification section, 8... Separated water, 9... Excess sludge, 10... Mixed liquid, 11... Cationic polymer flocculant, 12... Dehydrator, 13... Dehydrated cake, 14
...Dehydrated separation liquid, 15...UF membrane, 16...Concentrated liquid, 1
7... Inorganic flocculant, 18... Treated water, 19... Air.

Claims (1)

[Scope of Claims] 1. An anaerobic fermentation step is provided before the biological nitrification and denitrification step, and a flocculant containing at least a cationic polymer flocculant is added to the mixed liquid of the effluent that has passed through these steps and excess sludge. 1. A method for treating organic wastewater, the method comprising: dehydrating the organic wastewater by adding the following: and further treating the dehydrated separated liquid using a permeable membrane. 2. The method for treating organic wastewater according to claim 1, wherein the anaerobic fermentation step and the biological nitrification and denitrification step are carried out without dilution or in a near-undiluted state. 3. The organic wastewater treatment method according to claim 1 or 2, wherein the membrane-side residual concentrate obtained by the treatment with the permeable membrane is returned to the mixed liquid to be dehydrated. 4. The method for treating organic wastewater according to claim 1, 2 or 3, in which pressurized flotation or centrifugation is used as the solid-liquid separation means during the biological nitrification and denitrification process. 5. Claim 1, wherein a flocculant is further added to the dehydrated separated liquid and then treated with a permeable membrane.
The method for treating organic wastewater according to item 2, 3 or 4. 6 Claims 1, 2, and 3, wherein the permeable membrane is an ultrafiltration membrane or a microporous membrane.
The method for treating organic wastewater according to item 4 or 5.