JPS641200B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention deals with organic matter such as sewage, human waste, industrial wastewater, etc.
This relates to advanced treatment of wastewater containing nitrogen and phosphorus. Conventionally, advanced treatment methods for sewage, human waste, industrial wastewater, etc. have added Ca(OH) ₂ to the treated water of the activated sludge method.
Forms poorly soluble substances such as CaCO ₃ and Ca ₅ (OH) (PO ₄ ) ₃ ,
Coagulation precipitation methods have been used to coprecipitate colloidal substances. However, the following points are listed as drawbacks of this conventional method. (1) In order to speed up the formation of poorly soluble substances, it is necessary to add a large amount of Ca(OH) ₂ to adjust the pH of the water to be treated to PH0-12.
The amount of sludge created by (OH) ₂ is enormous, making it difficult to treat and dispose of the sludge. (2) When discharging treated water, a large amount of mineral acid is required because the pH of the treated water, which has a pH of 10 to 12, needs to be brought to around neutrality. (3) In addition to the sedimentation tank in the biological treatment process, Ca
In order to separate the sludge caused by the addition of (OH) ₂ , it is necessary to install a coagulation and sedimentation tank of the same size as the biological treatment process. The present invention is a method for solving the above-mentioned drawbacks of the conventional flocculation-precipitation method. The present invention processes wastewater containing organic matter, nitrogen, and phosphorus through a first step consisting of a biological treatment step and a solid-liquid separation step, and an alkali agent having hydroxyl groups (OH ^- ) is applied to the effluent of the first step. When processing in the second step of solid-liquid separation after addition, the effluent from the first step is subjected to the biological treatment step in a substantially neutral state (preferably pH 7.5 to 8.2), and calcium ions are added to the biological treatment step. A readily soluble calcium compound is added as calcium ions 1 to 5 times the amount of phosphate ions flowing into the first step so that the phosphate ions remain in the effluent at a molar concentration higher than that of the phosphate ions in the effluent, and the pH of the second step is 8. Hydroxyl group (OH ^- ) so that ~10
It is characterized by adding an alkaline agent having the following properties. Next, an embodiment of the present invention is shown in FIG. 1, and a detailed explanation of the present invention will be given. First, to explain the first step of the present invention,
Raw water containing BOD or ammonia nitrogen is
From the inlet 1, the easily soluble calcium compound is in liquid or powder form and flows from the medicine inlet 2 to the biological reaction tank 11.
The activated sludge in the reaction tank and the return sludge 7 returned from the solid-liquid separator 12, which will be described later, are mixed together. In the biological reaction tank 11, easily soluble calcium compounds react with CO ₃ ^-- , HCO ₃ ^- , PO ₄ ^3- in the inflowing raw water, or CO ₂ generated from the decomposition process of BOD in the raw water. and calcium carbonate (CaCO ₃ ) hydroxyapatite (Ca(OH)
(PO ₄ ) ₃ ) and other poorly soluble compounds are produced at the same time.
Colloidal substances, which are components of chromaticity, COD, etc., also aggregate and become hardly soluble flocs. The easily soluble calcium compounds added in the first step include calcium chloride (CaCl ₂ 2H ₂ O),
There are slaked lime (Ca(OH) ₂ ), quicklime (CaO), calcium peroxide (CaO ₂ ), etc., and these are conveniently in liquid or powder form. Further, the addition position may be anywhere as long as it is the first step, and for example, when performing biological nitrification and denitrification, it may be added to either the nitrification tank or the denitrification tank. Furthermore, the amount of addition shall be such that calcium ions remain in the effluent of the first step, but the amount as calcium ions shall be 1 to 5 times the amount of phosphate ions in the raw wastewater introduced into the biological reaction tank 11. . This is because the production of hydroxyapatite and calcium carbonate is within the range in which biological activity per unit sludge is not inhibited. The sludge generated in the biological reaction tank 11 is then supplied to the solid-liquid separator 12 through the conduit 3.
The sludge generated in the biological reaction tank 11 includes activated sludge grown due to organic matter decomposition, calcium carbonate (CaCO ₃ ) and hydroxyapatite (Ca(OH)).
Mixed with poorly soluble compounds such as (PO ₄ ) ₃ ). When using a settling tank as a solid-liquid separation device, the size of the settling tank is determined by the sedimentation rate of sludge.
Conventionally, in the case of MLSS 3000mg/, the separation speed in the sedimentation tank was 6 to 10mm/min, but in the present invention, since poorly soluble compounds are mixed with the sludge,
Even with MLSS6000mg/, the upward flow rate in the sedimentation tank is 20 to 30
A rising flow rate of mm/min is possible. Therefore, according to the present invention, the capacity of the settling tank can be reduced to 1/2 to 1/5 of the conventional one. The above is the explanation of the first step of the present invention. Next, the second step of the present invention will be explained. The supernatant water from the solid-liquid separator 12 in the first step is stirred and mixed in the alkali mixing tank 13 through the conduit 4 and the alkali agent through the chemical inlet 9. Although unreacted calcium ions remain in the supernatant water supplied from the conduit 4, there are almost no anions as hydroxyl groups (OH ^- ) are consumed in the first step. Therefore, in order to further remove PO ₄ ^3- , SS, chromaticity, and COD components that could not be removed in the first step in the second step, an alkaline agent having a hydroxyl group (OH ^- ) is added to reduce the activity. It is necessary to generate a high amount of Ca(OH) ₂ . Therefore, by adding an alkaline agent with hydroxyl group (OH ^- ) to the second step, highly active Ca
(OH) ₂ is generated in the alkali mixing tank 13,
Utilizing this Ca(OH) ₂ , the PO ₄ ^3- , SS, chromaticity, and COD components remaining in the supernatant are converted into hydroxyapatite (Ca ₅ (OH) (PO ₄ ) ₃ ) through an aggregation reaction.
Agglomerated flocs such as these are formed and removed. The amount of alkali agent having a hydroxyl group (OH ^- ) to be injected is such that the pH of the alkali mixing tank is PH8 to 10. In addition, the alkaline agents of the present invention include NaOH,
Highly soluble materials such as KOH and Ca(OH) ₂ are preferred. In the alkali mixing tank 13, the colloidal substances that are components of PO ₄ ^3- , SS, chromaticity, and COD remaining in the supernatant water supplied from the conduit 4 undergo a coagulation reaction to form flocs. The flocs formed in the alkali mixing tank are introduced into the solid-liquid separation tank 14 through the conduit 5, where they are separated into solid and liquid, and the separated water is obtained as treated water. The sludge consisting of flocs separated in the solid-liquid separation tank 14 is returned to the biological reaction tank 11 through the conduit 8. The advantage of the present invention is that by adding a readily soluble calcium compound so that calcium ions remain in the effluent water of the first step, CO ₃ ^-- , HCO ₃ ^-- in the raw water is removed in the biological reaction tank 11 of the first step. , PO ₄ ^3- , etc., react with easily soluble calcium to form calcium carbonate (CaCO ₃ ), hydroxyapatite (Ca ₅ (OH)
At the same time, the production of poorly soluble compounds such as (PO ₄ ) takes place without inhibiting the biological activity per unit sludge, and at the same time colloidal substances, which are chromatic and COD components, are also aggregated and solidified into poorly soluble flocs. It can be separated by the liquid separator 12. Also, the PH of treated water 6 is PH=
The pH value is around 9, and the pH does not reach 10 to 12, unlike water treated by the conventional method using Ca(OH) ₂ , and the amount of acid required to adjust the pH when discharging the treated water is 0 compared to the conventional method. It only takes ~10%. Furthermore, since most of the substances have been removed in the first step, the flocs separated in the solid-liquid separation tank 14 contain PO ₄ ^3- , SS, chromaticity, and COD remaining in the supernatant water of the first step. Since it only contains colloidal substances as ingredients, the amount of alkaline agent added is small, and unlike conventional methods that use large amounts of Ca(OH) ₂ , there is no undissolved chemical that becomes sludge. In the second step, highly active Ca
(OH) ₂ is produced, and the amount of sludge produced by flocculation is also very small. Therefore, the solid-liquid separation tank 14 can be not only a sedimentation tank but also a device with a high solid-liquid separation rate, such as a multilayer sand filter made of anthracite, sand, and gravel. If the sludge 8 is directly sent from the solid-liquid separation tank 14 to the biological reaction tank 11, it will pass through the biological reaction tank 11 in the first step and then be transferred to the first stage in the solid-liquid separation device 12.
It also becomes possible to treat it together with process sludge. As mentioned above, the present invention improves the conventional Ca
(OH) ₂ improves the quality of treated water by coagulating sedimentation method.
It has the advantage of reducing the size of processing equipment and reducing the amount of chemicals used. Next, examples will be shown. Example 1 The first step of the present invention, that is, the biological treatment process, is provided with an aeration tank and a settling tank, and the second step is provided with an alkali mixing tank, a sand filter tank, and a PH adjustment tank. The origin was as follows. i.e. aeration tank 16
, sedimentation tank 12, alkali mixing tank 5, sand filter tank
12, PH adjustment tank 10 was used, and the activated sludge concentration in each tank in the first step was adjusted to about 2000 mg/. Experiments were conducted using groundwater from a certain group with the chemical properties shown in Table 1 as raw water. The amount of raw water treated was 64/day, and the amount of sludge returned from the settling tank in the first step was 20/day. Calcium chloride was used as the easily soluble calcium compound, and the addition rate was set to be 0.2 g per influent sewage (2.5 times the amount of phosphate ions in the raw water as calcium ions). Next, the treated water (supernatant water) from the first step was introduced into the alkali mixing tank of the second step, and 20 mg of caustic potash was added as an alkali agent, and the mixture was mixed and stirred to adjust the pH to 8.5. Next, water was passed from the alkaline mixing tank to a multilayer sand filter tower made of anthracite, sand, and gravel at a linear velocity of LV = 180 m/day to perform solid-liquid separation. The results of Example 1 are shown in Table 1. On the other hand, as a comparative example, conventional Ca(OH) ₂ flocculation and precipitation,
The results of the sand filtration method are shown in Table 2 as a comparative example. As is clear from these tables, by simply adding a small amount of caustic soda to the treated water in the first step, the present invention can stably obtain higher quality treated water than the conventional coagulation-sedimentation method. The amount of sludge generated,
It has also been found that the amount of chemicals used in the present invention is much lower.

【table】

【table】

[Table] Example 2 The first step of the present invention, that is, the biological treatment process, uses a biological nitrogen method with a nitrifying solution circulation method, and the second step uses an alkali mixing tank, sand filter tank, and PH adjustment. A tank was installed, and the specifications of each device were as follows. That is, the first denitrification tank 150, the nitrification tank 200, the second denitrification tank 100, the reaeration tank 50, the first settling tank 40,
Alkali mixing tank 20, sand filter tank 12, PH adjustment tank 10
The activated sludge concentration in each tank in the first step is approximately 8000.
It was adjusted to be mg/. In addition, the chemical properties of the sieve waste, which is the liquid to be treated in this case, are as shown in Table 3.
/day, dilution water 90/day circulation nitrification liquid amount 600-700
Denitrification treatment was carried out under the conditions of /day. In addition, methanol (CH ₃ OH/NO ₃ -N=2.5/
1) was added to perform denitrification by external respiration, and the addition rate of slaked lime to the nitrification tank was set at a rate of 5 g per 1 sieve residue night urine. Next, residual calcium ions are present in the treated water (supernatant water, that is, denitrified water) in the first step.
230mg/contains. This denitrified water is transferred to a second
Introduced into the alkaline mixing tank in the process and used as an alkaline agent
After adding 50 mg of NaOH and adjusting the pH to 8.6 to perform coagulation, water was passed through a sand filter tower made of anthracite, sand, and gravel at a linear velocity of LV = 180 m/day to perform solid-liquid separation. . The results are shown in Table-3. On the other hand, as a comparative example, Table 4 shows the results of a treatment combining biological nitrification and denitrification method and coagulation sedimentation sand filtration method in parallel with the treatment according to the present invention. As shown in these tables, when comparing the present invention and the comparative example, it is clear that the present invention not only generates less sludge and uses less chemicals, but also has a higher quality of treated water than the comparative example.

【table】

【table】 [Brief explanation of the drawing]

FIG. 1 is a system explanatory diagram showing an embodiment of the present invention. 1... Raw water inlet, 2... Medicine inlet, 3... Conduit, 4...
Conduit, 5... Conduit, 6... Treated water, 7... Return sludge, 8
... Return sludge, 9 ... Alkaline agent inlet, 11 ... Biological reaction tank, 12 ... Solid-liquid separation device, 13 ... Alkali mixing tank, 14 ... Solid-liquid separation tank, 15 ... Stirrer.

Claims (1)

[Scope of Claims] 1 Wastewater containing organic matter, nitrogen, and phosphorus is subjected to a first step consisting of a biological treatment step and a solid-liquid separation step, and the effluent of this first step is treated with hydroxyl groups (OH ^- ).
In the second step of solid-liquid separation after addition of an alkaline agent having a Easily soluble calcium compounds are first added as calcium ions so that they remain at a molar concentration greater than or equal to phosphate ions.
A high level of wastewater characterized by adding 1 to 5 times the amount of phosphate ions flowing into the process, and adding an alkaline agent with hydroxyl groups (OH ^- ) so that the pH of the second process is 8 to 10. Processing method. 2. The advanced wastewater treatment method according to claim 1, wherein sand filtration is used for solid-liquid separation in the second step. 3. The advanced wastewater treatment method according to claim 1 or 2, wherein the sludge generated during solid-liquid separation in the second step is returned to the first step.