JPS6253238B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention performs primary treatment of wastewater containing high concentrations of BOD and nitrogen compounds using photosynthetic bacteria (mainly purple non-sulfur bacteria) without dilution, and activates the primary treated water without solid-liquid separation. Using chemical sludge 2
The present invention relates to a wastewater treatment method that highly efficiently and highly removes BOD and nitrogen compounds in the wastewater by purifying the wastewater through a combination of secondary and tertiary treatments. BOD and nitrogen compounds in wastewater containing high concentrations of BOD and nitrogen compounds (hereinafter simply referred to as raw wastewater), such as human waste, livestock wastewater, and industrial wastewater from fish processing, tanneries, and silk byproducts. Conventionally, the activated sludge method, trickling filter method, rotating disk method, etc., have been applied to remove raw wastewater by diluting it. In other words, raw wastewater, for example, the BOD of human waste is
10000~13000ppm, nitrogen compounds 3000~
Since the concentration is extremely high (5000 ppm), the conventional method for treatment was to dilute it approximately 20 times with fresh water. However, such conventional treatment methods by dilution require fresh water for dilution, and the increase in water volume due to dilution not only increases the size of treatment equipment, but also requires secondary treatment (BOD) in the case of dilution treatment. Because almost no nitrogen compounds are removed during the removal process (removal process), the tertiary treatment (nitrogen compound removal process) equipment must be installed based on the nitrogen compounds in the raw wastewater, so the treatment equipment in particular becomes extremely large. In addition, it has many drawbacks, such as problems due to regulations on the total amount of wastewater and the recent need for resource conservation and energy conservation. In order to solve the above-mentioned drawbacks of the prior art, the present inventors have conducted research on a non-dilution treatment method for BOD-concentrated wastewater using photosynthetic bacteria (mainly purple non-sulfur bacteria), and have previously published Japanese Patent Application No. 143,650/1989. ``Method for treating human waste'', Patent Application No. 154849, 1982 ``Method for treating wastewater''
As described in Japanese Patent Application No. 53-9406 ``Method of Treating Wastewater'', the objective of highly efficient removal of BOD by non-dilution treatment using photosynthetic bacteria was achieved, and in addition to BOD, nitrogen compounds were also removed in the same way. For information on how to efficiently and highly remove
As described in No. 92863, "Wastewater treatment method," the objective was achieved to a certain extent, but after further intensive study on a method for efficiently removing BOD and nitrogen compounds using photosynthetic bacteria and activated sludge, the present invention was reached. The gist of it is as follows:
Wastewater containing a high concentration of BOD and nitrogen compounds is first treated without dilution using photosynthetic bacteria, and then the first treatment water is subjected to a second treatment using activated sludge to mainly remove BOD, and a second treatment to mainly remove nitrogen compounds. In performing the next treatment and purification, in the above-mentioned secondary and tertiary treatment using activated sludge, the primary treated water is transferred to the denitrification tank A without solid-liquid separation, and the primary treated water in the denitrification tank A is The liquid in the nitrification tank and the activated sludge in the settling tank in the final process are both returned and added to the process, and then the treated water is sent to the nitrification tank, denitrification tank B, reaeration tank, and settling tank in the next process. It consists in a method of treating wastewater, which is characterized by sequential transfer and treatment. The wastewater treatment method of the present invention is carried out through the following eight steps, as shown in the process diagram of the process example in FIG. (1) Raw wastewater is first put into the solubilization adjustment tank shown in Step 1 in Figure 1 without dilution, and the water volume and BOD concentration are made uniform, and at the same time, air aeration is usually performed for about 24 hours to increase the concentration. Reduce molecular weight of molecular substances (for example, organic oxidation). If the raw wastewater is human waste, at this stage the BOD is over 5000ppm and the nitrogen compounds are
It is 2000ppm or more. (2) Next, if the wastewater obtained by the above treatment is not neutral, it is neutralized with acid or alkali in the neutralization tank shown in Step 2 of Figure 1. (3) The neutralized wastewater is transferred without dilution to the photosynthetic bacteria treatment tank shown in step 3 in Figure 1, where it is inoculated with photosynthetic bacteria and subjected to air aeration for primary treatment to remove BOD and nitrogen compounds. I do. (4) The primary treated water treated with the photosynthetic bacteria described above can be directly processed in step 4 of Figure 1 without solid-liquid separation.
The process is transferred to the combined process of secondary and tertiary treatment shown below, but first, the circulating liquid is transferred to the first denitrification tank A, and then the circulating liquid circulated from the nitrification tank shown in step 5 of Figure 1, and the process 8 of Figure 1. It is mixed with the return sludge returned from the final settling tank shown. In this case, mixing is performed by mechanical stirring or gas stirring using generated gases such as nitrogen gas and carbon dioxide gas, and mainly nitrate nitrogen in the circulating liquid is reduced to nitrogen gas by the action of denitrifying bacteria in an anaerobic state. The organic carbon source necessary for this denitrification is
Using BOD, BOD is removed at the same time as denitrification. (5) The treated water in denitrification tank A is transferred to the nitrification tank shown in step 5 in Figure 1, and the ammonia nitrogen still present from the primary treated water is mainly converted to nitrate nitrogen by the action of nitrifying bacteria in activated sludge. The BOD that has been oxidized to 100% and still remains from the treatment in denitrification tank A is removed here. In this case, sufficient aeration is usually performed while mixing by air aeration. Most of the nitrate nitrogen in the nitrification tank treated water is circulated to the denitrification tank A together with the circulating fluid, and the rest is transferred to the denitrification tank B shown in step 6 in FIG. (6) The nitrification tank treated water is transferred to the denitrification tank B shown in step 6 in Figure 1, and kept in an anaerobic state as in the case of the denitrification tank A in step 4 to remove the nitric acid contained in the nitrification tank treated water. Reduces nitrogen to nitrogenous gas. In this case, it becomes an organic carbon source for denitrification.
Since BOD is hardly contained in the nitrification tank treated water, methanol etc. are added as an organic carbon source. (7) The treated water in denitrification tank B is transferred to the re-aeration tank shown in step 7 in Figure 1 and aerated with normal air.
Mainly, the residual BOD of the organic carbon source, such as methanol, added in step 6 for denitrification is removed, the sludge generated in the denitrification tank B to which nitrogen gas has adhered is deaerated, and the sludge is activated. (8) The treated water from the reaeration tank is transferred to the final settling tank shown in Step 8 in Figure 1, where it is separated into sludge and supernatant water, the supernatant water is discharged, and the sedimented and separated sludge is returned to denitrification tank A. At the same time, the surplus will be extracted and disposed of. The effluent from the final settling tank usually has a BOD of
20ppm or less, and nitrogen compounds are 10ppm or less. That is, in the wastewater treatment method of the present invention
Regarding the method for removing BOD and nitrogen compounds, 1.
In order to remove 5% or more of BOD and 40% or more of nitrogen compounds in the raw wastewater in the next treatment step 3, denitrification tank A in step 4, nitrification tank B in step 5, and denitrification tank B in step 6 are all used. It can be made very small.
Furthermore, the alkaline agent that was conventionally necessary for denitrification treatment is not required, and in denitrification tank A, BOD in the primary treatment water can be used as an organic carbon source necessary for denitrification. And as mentioned above, a large amount of nitrogen compounds are removed in denitrification tank A, which can use BOD for denitrification, and a small amount of nitrogen compounds should be removed in denitrification tank B, so denitrification tank B contains almost no BOD. The amount of organic carbon source, such as methanol, required for denitrification can be significantly reduced. Therefore, the wastewater treatment method of the present invention, combined with the effect of non-dilution treatment using photosynthetic bacteria, provides a total system with very low equipment costs and
The system has low operating costs. To explain in more detail the combined step of secondary and tertiary treatment in the treatment method of the present invention, in step 4 of FIG. 1, the secondary treatment mainly removes BOD from the primary treatment water, and step 5 of FIG. The conditions required for the denitrification tank A include the following:
Adjusting the tank volume and pH to satisfy formula (1) below,
Securing the organic carbon source necessary for denitrification treatment;
Since the denitrification reaction is usually carried out by denitrifying bacteria under anaerobic conditions, it is necessary to perform mechanical stirring or aeration stirring by gas blowing so that the dissolved oxygen is 0.1 ppm or less. Moreover, in the case of the treatment method of the present invention, BOD in the primary treatment water can be removed by effectively using it as an organic carbon source for denitrification treatment, so there is no need to add an organic carbon source in denitrification tank A. The amount of circulating fluid that circulates from the nitrification tank to the denitrification tank A should be large in order to increase the amount of denitrification in the denitrification tank A, but it is usually 50% of the original wastewater volume in proportion to the amount of nitrogen compounds to be removed. Set to a range of ~600%. Below 50%, a sufficient denitrification effect cannot be obtained, while above 600%, the denitrification effect improves, but the amount of circulating fluid becomes excessive and the amount of power increases, and the nitrification tank This is because a large amount of dissolved oxygen flows into the denitrification tank A, reducing the circulation efficiency and making it impractical. The treated water in denitrification tank A is then transferred to the nitrification tank in step 5 in Figure 1 for treatment, thereby converting ammonia nitrogen in the primary treated water to nitrifying bacteria (nitrite bacteria, nitrate bacteria) in the activated sludge. Due to its action, it is mainly oxidized to nitrate nitrogen, and it still remains in denitrification tank A.
Remove BOD here. The conditions required for such nitrification tank treatment include adjusting the tank volume and pH (6.5 to 6.5 to
9.0) and to supply the oxygen necessary for nitrification, it is usually necessary to perform air aeration so that the dissolved oxygen is 2 ppm or more. Furthermore, in step 6 in Figure 1, the conditions required for denitrification tank B are the same as those for denitrification tank A in order to reduce and remove nitrogen compounds mainly consisting of nitrate nitrogen in the nitrification tank treated water to nitrogen gas. the below described
In addition to adjusting the tank volume and pH to satisfy equation (1) and creating an anaerobic state, for example, methanol is added as an organic carbon source for denitrification since there is almost no organic carbon source in the nitrification tank treated water. is necessary. The conditional expressions (1) and (2) regarding the volumes of the denitrification tank and nitrification tank and the reaction equations for nitrification and denitrification are as follows. △N/VdXs<Kn...(1) △N: Amount of nitrate nitrogen to be denitrified (Kg day ^-1 ) Vd: Denitrification tank capacity ( ^m3 ) Xs: Sludge concentration in the denitrification tank (Kgm ^-3 ) Kn: Denitrification rate (day ^-1 ) 1/Q=△Xs/VnXs<μ...(2) Q: Sludge age (days) △Xs: Sludge discharge amount (Kg day ^-1 ) Vn: Nitrification process capacity _（ ^{m 3 ） _} _{_} ^_ _{_ _} ^_ ) 2NO ₂ ^- +O ₂ →2NO ^- ₃ ...(4) NH ₄ ⁺ +2O ₂ →NO ^- ₃ +H ₂ O+2H ⁺ ...(5) Denitrification reaction: 3NO ^- ₃ +CH ₃ OH→3NO ^- ₂ +CO ₂ +2H ₂ O ......(6) 2NO ^- ₂ +CH ₃ OH→N ₂ +CO ₂ +H ₂ O+2HO ^- ...(7) 6NO ^- ₃ +5CH ₃ OH→3N ₂ +5CO ₂ +7H ₂ O +6OH ^- ...(8) Thus, In the treatment method of the present invention, the amount of nitrogen compounds removed in the primary treatment step 3 is large, and the primary treated water has a high free alkalinity, and as can be seen from the above reaction equations (3) to (8). In the nitrification reaction, H ⁺
Hydroxyl ions are generated in the denitrification reaction, but the nitrification tank and denitrification tank A are always well mixed by the circulating fluid, and the pH of both tanks is maintained at the optimal state for the nitrification reaction and denitrification reaction, respectively. Therefore, there is no need to add an alkaline agent. In addition, the activated sludge concentration in each tank of denitrification tank A, nitrification tank, and denitrification tank B is
Set between 1000ppm and 10000ppm. this is,
Below 1,000 ppm, it is difficult to secure sufficient nitrifying bacteria and denitrifying bacteria, resulting in poor treatment efficiency.On the other hand, above 10,000 ppm, there is no problem in terms of removing BOD and nitrogen compounds, but it is especially difficult to remove highly concentrated activated sludge from nitrification tanks. In order to maintain dissolved oxygen at 2ppm or higher, the power cost for aeration becomes excessive, and in order to maintain this activated sludge concentration, activated sludge from the final settling tank in step 8 in Figure 1 must be removed. This is because the amount of returned supply becomes excessive, making it impractical in terms of maintaining activated sludge in the nitrification tank, denitrification tank A, and denitrification tank B. As detailed above, in the wastewater treatment method of the present invention, wastewater containing a high concentration of BOD and nitrogen compounds is treated without dilution using photosynthetic bacteria, and the primary treated water is used as it is for secondary and tertiary treatment. Activated sludge treatment, which also serves as treatment, not only makes it easy to remove BOD and nitrogen compounds to a high degree, but the size of each tank used in the combined secondary and tertiary treatment process is much smaller than before. Furthermore, an alkaline agent is not required, and the organic carbon source for denitrification is significantly less than conventional methods. It has many advantages such as no need for chemicals such as flocculants, and can significantly reduce equipment costs and operating costs compared to conventional methods, and its industrial value is great. If dephosphorization equipment is further added to the treatment method of the present invention, it will become an excellent system that can efficiently treat wastewater containing high concentrations of BOD, nitrogen compounds, and phosphorus without dilution. Next, the present invention will be explained in more detail with reference to Examples and Comparative Examples. Example 1 and Comparative Example 1 Human waste obtained by crushing large impurities using a crushing pump
After removing impurities with a 30-mesh screen and solubilizing it in a solubilization tank with air aeration for 24 hours, the photosynthetic bacteria are added to 20% of the human waste volume without dilution.
A considerable amount of the water is inoculated and treated with photosynthetic bacteria, and then the primary treated water flowing out from the photosynthetic bacteria treatment tank is treated without solid-liquid separation according to the treatment method of the present invention shown in Figure 1 to remove BOD and nitrogen compounds. was removed, and the results shown in Table 1 below were obtained. In the above-mentioned treatment method of the present invention, the retention period in the denitrification tank A was set to 1.5 days, the nitrification tank was set to 5 days, and the denitrification tank B was set to 0.5 days. In addition, the amount of circulating fluid from the nitrification tank to the denitrification tank A is 600% of the raw drainage volume.
The ratio was set to %. On the other hand, the amount of sludge returned and supplied from the final settling tank to denitrification tank A was controlled at a ratio of 30 to 100% while monitoring the amount of surplus sludge generated and the activated sludge concentration in the settling layer. Further, air aeration was performed so that the amount of dissolved oxygen in the nitrification tank was 2 to 3 ppm, and mechanical stirring was performed so that the amount of dissolved oxygen in denitrification tanks A and B was 0.1 ppm or less. Separately, for comparison, the treatment data and tank volume when the treatment method of Comparative Example 1 shown in Fig. 2 obtained a treatment effect equivalent to that of the treatment method of the present invention of Example 1 are shown in Table 2 below. . The difference between the treatment method of Comparative Example 1 in Fig. 2 and the treatment method of the present invention is that photosynthetic bacteria treatment is not performed in the primary treatment, and the raw wastewater is diluted 10 times with fresh water.
Activated sludge treatment was performed as is. In addition, in the treatment method of the present invention of Example 1 shown in FIG. 1 and the treatment method of Comparative Example 1 shown in FIG. 2, methanol was used as the organic carbon source added to the denitrification tank B. Table 3 below shows comparative data on the amount of methanol added between the treatment method of the present invention and the treatment method of Comparative Example 1.

【table】

【table】

【table】

[Table] As is clear from the results in Tables 1, 2 and 3,
Compared to the treatment method of the present invention, in the treatment method of Comparative Example 1, the tank volume is 2.2 times or more, and the amount of methanol added is 5.4 times. In other words, in the treatment method of the present invention, the tank volume and amount of methanol added are significantly smaller than in the treatment method of Comparative Example 1, and dilution water is not required, and BOD and nitrogen compounds can be removed efficiently and to a high degree. I understand.

[Brief explanation of the drawing]

FIG. 1 is a process example of the treatment method of the present invention, and FIG. 2 is a process diagram of a process example of the treatment method of Comparative Example 1.

Claims (1)

[Claims] 1 Firstly treat wastewater containing high concentrations of BOD and nitrogen compounds without dilution using photosynthetic bacteria, then use activated sludge to treat the firstly treated water mainly as BOD.
When performing purification by combining secondary treatment to remove nitrogen compounds and tertiary treatment to mainly remove nitrogen compounds,
In the secondary and tertiary treatment using the above activated sludge,
The primary treated water is transferred to the denitrification tank A without solid-liquid separation, and the liquid in the nitrification tank and the activated sludge in the settling tank in the final step are returned to the primary treated water in the denitrification tank A. A method for treating wastewater, characterized in that the treated water is treated while being added, and then the treated water is sequentially transferred to the next step of a nitrification tank, a denitrification tank B, a reaeration tank, and a settling tank.