JP3442205B2 - Treatment method for phosphorus-containing wastewater - Google Patents

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a new technology for biologically treating phosphorus-containing organic wastewater such as sewage,
In particular, it relates to a new technology that can recover phosphorus from wastewater as a fertilizer resource and significantly reduce the amount of excess sludge generated.

[0002]

2. Description of the Related Art The "coagulant-added activated sludge method" in which an aluminum-based or iron-based inorganic coagulant is added to an aeration tank of the activated sludge method to simultaneously perform biological treatment and phosphorus removal is known. However, the "coagulant-added activated sludge method" can only remove phosphorus, but cannot recover the removed phosphorus as a resource, resulting in generation of hard-to-dehydrated coagulated sludge and an increase in excess sludge generation. As a result, in this method, in addition to biological sludge, non-dewatering coagulated sludge such as aluminum phosphate sludge and iron phosphate sludge is generated, and sludge treatment is difficult, and a solution to that problem has been desired.

[0003]

The present invention adds a new idea to the conventional "coagulant-added activated sludge method" and recovers phosphorus as a resource from phosphorus-containing organic sewage such as sewage and at the same time generates sludge. The challenge is to significantly reduce it.

[0004]

The above-mentioned problems of the present invention are as follows.
(1) In the biological treatment step, first, an iron-based or aluminum-based phosphorus removing agent is added to phosphorus-containing organic wastewater to adsorb and remove phosphorus from the wastewater into the phosphorus removing agent, and then the phosphorus removing agent from the biological treatment step. The effluent containing
A part of the settled sludge is returned to the biological treatment step, and the sludge extracted from the other part of the settled sludge or the biological treatment tank is subjected to ozone oxidation under alkaline conditions for solid-liquid separation, and calcium ion or magnesium is added to the separated liquid. A method for treating phosphorus-containing wastewater, comprising adding ions to remove phosphorus and returning the solid-liquid separated ozone-oxidizing sludge to the biological treatment step. (2) The biological treatment step is a nitrification denitrification treatment method or a biological dephosphorization method, and the separated liquid after the ozone oxidation is returned to an anaerobic denitrification tank or an anaerobic phosphorus discharge step. The method for treating phosphorus-containing wastewater according to 1).

[0005]

BEST MODE FOR CARRYING OUT THE INVENTION FIG. 1 shows the flow of the process for treating phosphorus-containing wastewater of the present invention described in (1) above.

In FIG. 1, phosphorus-containing organic sewage such as sewage is supplied as raw water 2 to a biological treatment step 1 such as an aeration tank of an activated sludge method for biological treatment. The iron-based phosphorus removing agent 4 or the aluminum-based phosphorus removing agent is added to the aeration tank of the biological treatment step 1 or a slurry 3 (slurry phosphorus-containing activated sludge, which may be hereinafter referred to as slurry) flowing out from the aeration tank. Then, phosphorus in the raw water 2 is removed by aggregation and adsorption. In the following description, an iron-based phosphorus removing agent is used in order to avoid complication, but the same action occurs even when an aluminum-based phosphorus removing agent is used. Here, as the iron-based phosphorus removing agent, polyiron, secondary chloride
Examples of the aluminum-based phosphorus removing agent include iron and iron hydroxide, and aluminum sulfate, PAC, aluminum hydroxide, activated alumina and the like.

The slurry 3 is subjected to solid-liquid separation in the settling tank 5 to obtain treated water 6 from which phosphorus, BOD and SS are highly removed, and the treated water 6 is discharged out of the system. On the other hand, the biological sludge, the settled sludge 7 from the settling tank 5 in which iron phosphate and iron hydroxide coexist, together with the extracted sludge 10 extracted from the aeration tank (biological treatment process 1), most of the sludge 8 is biological. Return to processing step 1. In the present invention, at this time, an MLSS automatic measuring device is installed in the aeration tank (biological treatment process 1) to control the amount of the returned sludge 8 so that the MLSS in a predetermined concentration range is always maintained in the biological treatment process 1. . The control range of the concentration of MLSS in this biological treatment process 1 is usually 3000 to 4000.
mg / liter. In this way, by constantly controlling the concentration of MLSS in the biological treatment process 1 within the control range and transferring only the excess sludge to the ozone oxidation tank 10 of the next process, only the minimum transfer sludge 9 is ozone-removed. Oxidation and solubilization of sludge make ozone consumption economical.

Transfer sludge 9 transferred to the ozone oxidation tank 10.
The settled sludge 7 and the drawn sludge 10 extracted from the aeration tank minus the returned sludge 8 are ozone-oxidized in the ozone oxidation tank 11 under alkaline conditions. The pH of the system is adjusted by adding caustic soda, and the pH is preferably in the range of 10-12. The change that the transferred sludge 9 undergoes by the addition of ozone in the ozone oxidation tank 11 under alkaline conditions is that SS, which is difficult to be biooxidized such as biological cells in the sludge, is solubilized to be a soluble organic matter (BOD), and iron-based phosphorus is removed. The phosphate group adsorbed to the agent is desorbed as phosphate ion by the following ionic reaction with the hydroxyl ion coexisting with the agent.

[0009]

[Equation 1]

Here, the necessary amount of ozone added to solubilize SS in sludge is 10 to 20 of SS in sludge.
Weight percent is preferred. If the amount of ozone is too small, sludge solubilization will not proceed sufficiently, and if it is excessive, ozone will be wasted and the cost will increase.

As described above, by carrying out ozone oxidation of the transferred sludge 9 in the ozone oxidation tank 10 under alkaline conditions, desorption of phosphorus from iron hydroxide adsorbed phosphoric acid, solubilization of sludge and promotion of ozone oxidation can be achieved. A combined effect is obtained. Heating at this time can further promote solubilization.
Solid-liquid separation unit 1 equipped with sedimentation, centrifugation or membrane separation of solubilized sludge that has been subjected to ozone oxidation in ozone oxidation tank 10.
Solid-liquid separation is performed in 2. Calcium phosphate (magnesium ammonium phosphate) is precipitated by adding calcium salt 13 (or magnesium salt) to the separated liquid 16 (containing phosphorus at a high concentration). These precipitates are easily dehydratable precipitates and can be easily solid-liquid separated, and the separated solid components are composed of phosphorus compound 14 which is highly valuable as a fertilizer. The precipitation reaction of the phosphorus compound 14 is a fast reaction,
10 to 30 minutes is enough. Calcium ion or magnesium ion to be added is 1-2 with respect to the molar concentration of phosphorus.
The same amount is enough.

One of the features of the process for treating phosphorus-containing wastewater of the present invention shown in FIG. 1 is that the iron-based phosphorus removing agent and the aluminum-based phosphorus removing agent can be recovered. That is, since the solubilized sludge 15 from the solid-liquid separation section 12 contains iron hydroxide in which phosphorus is desorbed under the alkaline condition and the phosphorus adsorption power is regenerated, when returned to the biological treatment step 1, The phosphorus in the raw water 2 can be adsorbed and removed again. Therefore, the addition amount of the fresh iron-based phosphorus removing agent 4 can be greatly reduced, and the addition becomes unnecessary in some cases.

As explained above, in the method of the present invention,
For phosphorus-containing organic wastewater such as sewage, the BOD component is first decomposed in the biological treatment step 1 and is ozone-oxidized in the ozone oxidation tank 10 under alkaline conditions, so that phosphorus is desorbed, and biological cells such as biological cells are not easily oxidized. Are solubilized.
Therefore, when the solubilized sludge is subjected to solid-liquid separation, phosphorus is present as ions in the separated liquid, and as described above, it is recycled as an excellent fertilizer such as calcium phosphate. In addition, since the solid sludge after ozone oxidation has improved biodegradability, it is further biologically decomposed by being returned to the biological treatment step 1, and the phosphorus removing agent can also be recycled and used. There is almost nothing that turns into something.

As another method of the present invention, a biological nitrification denitrification method or a biological dephosphorization method by an anaerobic aerobic method can be adopted in the biological treatment step. When the biological nitrification denitrification method is applied to the biological treatment process, a part of the sludge circulating between the denitrification tank and the nitrification tank is transferred to the alkaline ozone oxidation tank,
Anaerobic oxidation of ozone under alkaline conditions to solubilize the transferred sludge, followed by solid-liquid separation of the solubilized sludge, and the separated sludge contains iron hydroxide whose phosphorus adsorption power has been regenerated Returned to the tank. On the other hand, phosphorus is deposited as calcium phosphate or the like from the separated liquid containing free phosphorus, and the deposit is recycled as an excellent fertilizer. The phosphorus-removed liquid, which still contains BOD, is returned to the anaerobic tank for use as an organic carbon source for denitrifying bacteria. When applying the biological dephosphorization method by the anaerobic aerobic method to the biological treatment step, as in the case of the biological nitrification denitrification method, the raw water and sludge containing phosphorus are separated between the anaerobic tank and the aerobic tank. Circulating, in the step of removing phosphorus from the raw water, from the circulating sludge, a part of the sludge is transferred from the aerobic tank to the alkaline ozone oxidation tank, in the same manner as in the case of the biological nitrification denitrification method below, Treatment of phosphorus-containing wastewater of the present invention while recycling phosphorus, circulating phosphorus adsorbent by returning solubilized sludge, and promoting phosphorus discharge action of dephosphorization bacteria by returning the separated liquid containing BOD to an anaerobic tank Is advantageously implemented.

[0015]

EXAMPLE Based on the process of FIG. 1, targeting sewage,
The phosphorus-containing wastewater of the present invention was treated. Example 1 Table 1 shows the water quality of the sewage used for the treatment. Table 1 Water temperature: 21 ° C. SS: 110 mg / l BOD: 95 mg / l Phosphorus: 3.8 mg / l The volume of biological treatment tank (aeration tank), MLSS and sewage supply are as shown in Table 2. . Table 2 Aeration tank volume: 6 liters Aeration tank MLSS: 3200 mg / liter Sewage supply amount: 24 liters / day When transferring biological treatment sludge from the aeration tank to the sedimentation tank, ferric chloride Add the aqueous solution. The ferric chloride aqueous solution is added at a rate of 120 mg per liter of biologically treated sludge at the beginning of the operation, and is 30 mg per liter of biologically treated sludge in the steady state.

Most of the sludge settled in the aeration tank and the sludge settled in the settling tank are returned to the aeration tank. The amount returned was measured by controlling the amount of MLSS in the aeration tank with an MLSS automatic measuring device provided in the aeration tank. As a result, the amount of sludge returned to the aeration tank is 2 without ozone oxidation treatment.
It was 0 liter / day. On the other hand, the amount of sludge transferred for performing alkaline ozone oxidation is 1.3 to 1.5 in this treatment.
g · ss / day. The conditions for alkaline ozone oxidation are shown in Table 3. Table 3 Alkaline ozone oxidation tank volume: 1 liter Alkaline ozone oxidation tank pH: 11 Ozone addition amount: 15% (Inflow SS
Hit)

The solubilized sludge subjected to alkaline ozone oxidation was subjected to solid-liquid separation by a precipitation method. The solid sludge was returned to the aeration tank. On the other hand, the separated liquid is transferred to a phosphorus recovery tank, where calcium salt (calcium chloride) is added in an amount of 20 per liter of the separated liquid.
00 to 3000 mg was added. As a result of treatment for 1 year under the above conditions, the quality of treated water is shown in Table 4. Table 4 SS: 5 mg / liter BOD: 6 mg / liter Phosphorus: 0.23 mg / liter The amount of excess sludge generated is 12 g · ss per 1 m ³ of sewage.
I was very sorry.

Comparative Example 1 The quality of the sewage used for the treatment was the same as that shown in Table 1 of the above-mentioned Example, and the sewage was subjected to solubilization of sludge by alkaline ozone oxidation, solid-liquid separation and phosphorus recovery. A comparative test was performed under the same conditions as shown in Table 2 based on the process of FIG. 1 except that the process was removed. As a result, the quality of treated water was similar to that shown in Table 4, but
The required iron injection rate is always 1 per liter of biological sludge.
A proportion of 20 mg was required, a significantly higher injection rate than that of the examples of the invention.

[0019]

EFFECTS OF THE INVENTION As a result of subjecting phosphorus-containing wastewater such as sewage to biological treatment and alkaline ozone oxidation solubilization treatment according to the present invention, (1) surplus biological sludge is hardly generated from the treatment step. (2) Since the addition amount of the iron- or aluminum-based phosphorus removing agent for removing phosphorus can be significantly reduced,
Almost no hardly dehydratable inorganic sludge is generated. (3) Due to the effects of the present invention described in (1) and (2) above, the sludge treatment process is significantly simplified. (4) The recovered phosphorus can be used as an excellent phosphorus fertilizer.

[Brief description of drawings]

FIG. 1 is a flow chart 1 of biological treatment of phosphorus-containing wastewater of the present invention.
It is explanatory drawing which shows an example.

[Explanation of symbols]

1 biological treatment tank 2 Raw water 3 slurry 4 Iron-based phosphorus remover 5 settling tank 6 treated water 7 Settled sludge 8 Return sludge 9 Transfer sludge 10 Extracted sludge 11 Ozone oxidation tank 12 Solid-liquid separation section 13 Calcium 14 Phosphorus compounds 15 sludge 16 Separation liquid 17 Separation liquid after phosphorus recovery

─────────────────────────────────────────────────── ─── Continuation of front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) C02F 3/12 C02F 3/28-3/34 C02F 11/00-11/20

Claims (2)

(57) [Claims] 1. In the biological treatment step, first, an iron-based or aluminum-based phosphorus removing material is added to phosphorus-containing organic wastewater to adsorb and remove phosphorus from the wastewater into the phosphorus removing agent,
The effluent containing the phosphorus removing agent from the biological treatment step is separated by sedimentation, a part of the precipitated sludge is returned to the biological treatment step, and the sludge extracted from the other part of the sludge or the biological treatment tank is under alkaline conditions. It is characterized in that it is subjected to ozone oxidation with solid-liquid separation by means of, and calcium ions or magnesium ions are added to the separated liquid to remove phosphorus, and returned to the biological treatment step together with the solid-liquid separated ozone-oxidizing sludge. Treatment method of phosphorus-containing wastewater. 2. The biological treatment step is a nitrification denitrification treatment method or a biological dephosphorization method, and the separated liquid after ozone oxidation is returned to an anaerobic denitrification tank or an anaerobic phosphorus discharge step. The method for treating phosphorus-containing wastewater according to claim 1.