JPH03137990A - High level treatment of sewage to be treated - Google Patents

Abstract

PURPOSE:To make sewage as high quality treated water by adding a catalyst to an effluent of a secondary treatment process from a sewage treatment facility, recovering the catalyst while treating the effluent with ozone, and filtering the resulting effluent after adding a flocculant. CONSTITUTION:Flowing water to be treated is led to the secondary treatment process 8 such as an activated sludge process, and a suspension catalyst (e.g. iron oxide catalyst) 9 is added to the treated water flowing out from the secondary treatment process. Then, it is led to ozone treatment process 10 and while carring out the ozone treatment, the suspension catalyst 9 is recovered and recycled. Further, after a flocculant 11 is added to the ozone treated water flowing out from the ozone treatment process 10 and adding a trace of the suspension catalyst 9, treated water is obtained through a sand filtration process 12. Periodically cleaned water in the sand filtration process 12 is sent to a sludge treating process 13.

Description

DETAILED DESCRIPTION OF THE INVENTION [Purpose of the Invention (Field of Industrial Application) The present invention relates to an advanced treatment method for treated sewage water in which secondary treated water flowing out from a sewage treatment plant is treated with ozone.

(Prior Art) Conventionally, the oxidizing power of ozone has been used to treat contaminated water. For example, in Europe, 19
Treatment has been carried out for the purpose of sterilizing tap water since 2006, and in Japan it has been used throughout the country for the purpose of decolorizing wastewater treatment at human waste treatment facilities. It has also been used for the oxidation treatment of organic matter in industrial wastewater and special purpose water.

On the other hand, in recent years, the demand for water, such as industrial water and tap water, has increased rapidly with the development of industry and the improvement of living standards, but it is becoming difficult to secure water due to the decrease in groundwater and the pollution of river water. In addition, due to development accompanying urbanization and river culverts, etc.
Nature such as greenery and waterfronts, which provide a comfortable and peaceful living environment, are being destroyed.

Therefore, in order to solve these problems, there is a movement to perform advanced treatment of secondary treated water flowing out from sewage treatment plants with ozone and use it effectively as water for miscellaneous purposes such as toilet water, amenity water, and sewerage (landscape water). However, various aspects are being considered.

Tertiary treatment technology (sand filtration equipment) is already becoming established for secondary treated water flowing out from sewage treatment plants, but the current quality standards for effluent water are BOD of 10 ppm or less, coloring, deaeration, etc. 1; it is at a level that does not cause discomfort, and it is expected that further improvements in water quality will be made in the future in order to expand the effective use of treated water as described above.

By the way, as a conventional advanced treatment method for sewage treated water of this kind, for example, as shown in Figure 2, inflowing treated water is passed through a secondary treatment process 1 such as an activated sludge method, and the secondary treatment water is In order to remove the contained phosphorus, nitrogen, etc., a flocculant such as PAC was mixed in, and the water was then passed through a sand filtration process 3, and the tertiary treated water was passed through an ozone treatment process 4, where it was decolorized, deodorized, and defoamed. We are trying to get treated water. Note that the washing water periodically washed in the sand filtration process 3 is sent to the sludge treatment process 5.

In this case, ozone is produced by silent discharge against air or oxygen and is obtained as an ozone-containing gas. For water treatment, gas-liquid contact with the water to be treated is carried out using aeration pipes and injector-packed towers. Gas-liquid contact using air diffusers and injectors introduces fine ozone-containing gas from the bottom into a continuous layer of water to be treated, and the ozone in the bubbles rising through the water oxidizes pollutants in the water to be treated. Have it washed. Ozone gas dissolves into water from air bubbles and is used to oxidize dissolved organic matter. In particular, the reaction of unsaturated bonds such as decolorizing components is fast, and the decolorizing effect is extremely high. However, the reduction in COD etc. depended only on the amount of reacted oxygen atoms, and no significant effect was seen on dissolved organic matter that does not have unsaturated bonds.

Therefore, the present inventors investigated ways to improve these problems and discovered that ozone treatment can be effectively carried out by dispersing suspended catalysts that promote ozone oxidation reactions in water. Upon investigation, it was found that iron oxide significantly accelerates the ozone oxidation reaction. Below, an example of an experiment in a laboratory will be shown.

(Experimental Example I) Ozone treatment was performed using malonic acid CH2(COOH)2 as a dissolved organic substance. Add malonic acid aqueous solution (C
OD 38 mg/D: water temperature 25℃) 250
mJ7 installed, ozonized air (ozone concentration 15mg/Ω)
was diffused at a rate of 0.5 g per minute, and the change in COD over time was determined. A in FIG. 3 shows the result in this case.

Next, 2.0 g of ferric oxide was suspended in the same malonic acid aqueous solution and ozone treatment was performed in the same manner. B in FIG. 3 shows the results in this case.

From the results of these two experiments, the COD removal rate of the suspension containing iron oxide increased from 13.2% to 57.9% after 30 minutes compared to the suspension containing no iron oxide.
After some time, the concentration rose from 15.8% to 87.4%, indicating that iron oxide promotes the ozone oxidation reaction.

(Experiment example n) Next, actual sewage wastewater was subjected to ozone treatment.

In this case, the actual raw water is mainly domestic wastewater, which is treated with secondary sewage treatment using the activated sludge method.
Tertiary treated water was used which was injected with 9 mg/Ω of polyaluminum chloride as a coagulant and filtered through sand.

As for the experimental method, all other experimental conditions were the same except that the malonic acid aqueous solution in Experimental Example I was replaced with tertiary treated sewage water. A in Figure 4 shows the results when the test was carried out without mixing ferric oxide, and B in Figure 4 shows the results when the test was carried out with ferric oxide suspended. .

From these two experimental results, as in the case of experimental example ■,
The COD removal rate is 20.0% after 30 minutes, but it is 48.0%.
%, and after 1 hour, the reaction efficiency rose from 28.0% to 56.0%, and an improvement in the reaction efficiency in treated sewage water was also observed.

Therefore, recently, as shown in Figure 5, inflowing water to be treated is passed through a secondary treatment process 1 such as activated sludge method, and in order to remove phosphorus, nitrogen, etc. contained in the secondary treatment water, PA is used.
A treatment method has been proposed in which a coagulant 2 such as C is mixed in, the water is passed through a sand filtration step 3, a catalyst 6 is mixed into the tertiary treated water treated in the sand filtration step 3, and ozone treatment is performed in an ozone treatment step 4. ing.

From the above, as an advanced treatment method for sewage treatment water,
In the ozone treatment process, the treatment effect is improved by mixing a suspended catalyst into the treated water. However, when using e.g. iron oxide as suspended catalyst, the particle size is 0.2 μm.
It is extremely fine and most of it can be recovered by precipitation, but
It is thought that some of the iron oxide may mix into the supernatant and flow out as treated water, and if iron oxide is contained in the treated water, it will appear brown, which is not preferable in ozone treatment for the purpose of decolorization.

Therefore, in order to remove the catalyst, a filtration device or the like must be additionally provided, and as a result, the overall equipment becomes complicated.

(Problem to be solved by the invention) As described above, in the conventional advanced treatment method for sewage treatment,
When ozone treatment is performed using a catalyst to obtain highly treated water, there is a problem in that a filtration device or the like must be used.

An object of the present invention is to provide an advanced treatment method for sewage treatment water that can perform ozone treatment using a catalyst and obtain highly treated water without using a filtration device or the like to remove the catalyst. It is in.

[Structure of the Invention] (Means for Solving the Problem) In order to achieve the above object, the present invention mixes a catalyst into the treated water flowing out from the secondary treatment process of a sewage treatment plant, and then performs the ozone treatment process. The catalyst is recovered while performing ozone treatment through the ozonation process, and then a flocculant is added to the ozonated water containing a trace amount of catalyst flowing out from the ozonation process, and then the treated water is obtained by passing it through a sand filtration process. ing.

(Function) Therefore, in the advanced treatment method for sewage treated water of the present invention, the sewage flowing into the sewage treatment plant is subjected to secondary treatment such as activated sludge method in the secondary treatment step, and the secondary treatment water is catalyzed. Decolorization and deodorization are achieved through ozone treatment in the ozone treatment process.

Defoaming and COD are reduced. A flocculant is added to the ozonated water flowing out from the ozone treatment process, and by passing it through the sand filtration process, 88% of the phosphorus and nitrogen contained in the secondary treatment water and a trace amount flow out during catalyst recovery. The catalyst will be removed at the same time and highly treated water will be obtained.

(Example) Hereinafter, an example of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a process diagram showing an example of the overall configuration of the advanced treatment method for treated sewage water according to the present invention. That is, in the advanced treatment method for sewage treated water of this embodiment, the inflowing water to be treated is first passed through a secondary treatment process 8 such as an activated sludge method, and a suspended catalyst is added to the treated water flowing out from the secondary treatment process 8. (For example, iron oxide catalyst) 9 is mixed.

Next, this is passed through an ozone treatment step 10 to perform ozone treatment, while the suspended catalyst 9 is collected and recycled.

Next, a flocculant 11 is added to the ozonated water containing a small amount of suspended catalyst 9 flowing out from the ozonation process 10, and then passed through a sand filtration process 12 to obtain treated water.

In addition, the washing water regularly washed in sand filtration step 12 is
The sludge is sent to the sludge treatment process 13.

In the advanced treatment method for sewage treatment water of this embodiment, an iron oxide catalyst is mixed as a suspended catalyst 9 into the secondary treatment water that has been subjected to secondary treatment such as an activated sludge method in the secondary treatment step 8. This also promotes the treatment of dissolved organic matter that does not have unsaturated bonds, making it possible to increase the ozone reaction efficiency. In addition, the ozonated water flowing out from the ozonation process 10 has a property that the 88 minutes contained in the secondary treatment water tends to coagulate, and the flocculant 11 added to the ozonated water flowing out from the ozonation process 10 also Only a small amount is required. Furthermore, the ozonated water flowing out from the ozonation process 10 contains a small amount of suspended catalyst 9.
However, by adding a flocculant 11 to the water and passing it through the sand filtration step 12, all the solids, including phosphorus and nitrogen contained in the secondary treatment water, are removed. Highly treated water can be obtained.

As mentioned above, in the advanced treatment method for sewage treated water of this embodiment, the inflowing water to be treated is passed through the secondary treatment step 8, and a suspended catalyst 9 is added to the treated water flowing out from the secondary treatment step 8. An iron oxide catalyst is mixed in, and then it is passed through an ozonation process 10 for ozonation, while the suspended catalyst 9 is collected and recycled, and then a trace amount of suspended catalyst 9 flows out from the ozonation process 10. A flocculant 11 is added to the ozone-treated water containing ozonated water, which is then passed through a sand filtration step 12 to obtain treated water.

Therefore, by suspending an iron oxide catalyst in the ozone treatment step 10, organic substances are added to the surface of iron oxide, making it more susceptible to ozone oxidation, or iron oxide becomes peroxide due to the reaction between ozone and organic substances. Since the oxide accelerates the decomposition of intermediate products such as hydrogen peroxide, it becomes possible to accelerate the ozone reaction and significantly increase the reaction efficiency. In addition, the ozone treatment in this example is an ozone treatment using an inexpensive iron oxide catalyst, and a small amount of flocculant 11 is used to remove the 88 minutes and the suspended catalyst 9 that flows out in small amounts due to the ozone treatment. Since the suspended catalyst 9 can be removed at the same time as the addition, there is no need for any special filtration equipment or the like for removing the suspended catalyst 9, and the overall equipment can be simplified accordingly.

In addition, in the above embodiment, the case where iron oxide is used as the suspension catalyst 9 has been explained as an example, but the invention is not limited to this in any way, and the case where secondary iron oxide is used as the suspension catalyst 9 is explained. The present invention can also be similarly applied to obtain similar effects.

[Effects of the Invention] As explained above, according to the present invention, a catalyst is mixed into the treated water flowing out from the secondary treatment process of a sewage treatment plant, and then the catalyst is mixed into the treated water flowing out from the secondary treatment process of a sewage treatment plant, and then the catalyst is added while performing ozone treatment through the ozone treatment process. A flocculant was added to the ozonated water containing a small amount of catalyst that flows out from the ozonation process, and then passed through a sand filtration process to obtain treated water. It is possible to provide an advanced treatment method for sewage treated water that can perform ozone treatment using a catalyst to obtain highly treated water without using any equipment or the like.

[Brief explanation of the drawing]

Figure 1 is a process diagram showing an example of the advanced treatment method for sewage treatment water according to the present invention, Figure 2 is a process diagram showing an example of the conventional advanced treatment method for sewage treatment water, and Figure 3 is a malonic acid aqueous solution. Figure 4 shows an example of the change in COD over time when sewage water was placed in an air washing bottle and subjected to experimental ozone treatment. FIG. 5 is a process chart showing another example of the conventional advanced treatment method for sewage treated water. 8... Secondary treatment step, 9... Suspension catalyst, 10...
Ozone treatment process, 11... flocculant, 12... sand filtration process, 13... sludge treatment process. Figure 1 Figure 2

Claims (2)

[Claims] (1) A catalyst is mixed into the treated water flowing out from the secondary treatment process of a sewage treatment plant, and then passed through an ozone treatment process to recover the catalyst while performing ozone treatment, and then a trace amount flows out from the ozone treatment process. An advanced treatment method for sewage treated water, characterized in that a flocculant is added to ozonated water containing a catalyst, and then the treated water is obtained through a sand filtration process. (2) The advanced treatment method for treated sewage water according to claim (1), wherein an iron oxide catalyst is used as the catalyst.