JPH0866689A - Advanced treatment of organic sewage - Google Patents

Abstract

PURPOSE: To remove a phosphorus in a biologically treated water at high speed and to recover the phosphorus as resources by adding particulates of aluminum hydroxide or iron hydroxide to the biologically treated water of an org. sewage, then supplying the water to a filter layer. CONSTITUTION: The biologically treated water (raw water) containing SS and the phosphorus originated from a flowing water sludge and a stripped biological membrane passed through a biological treating process such as an activated sludge treatment of sewerage is flowed into a filter device 2 to remove the SS by a filter layer B. Then, particulates (phosphorus removing agent) 4 of the iron hydroxide or the aluminum hydroxide are injected from an injecting pipe 17 and the raw water injected with the particulates 4 is passed through a filter layer A by ascending stream to adsorption-remove the phosphorus. As a result, a washing waste water of the filter layer A containing in high concn. the phosphorus removing agent 4 on which the phosphorus is adsorbed is flowed into a washing waste water storage tank 7. NaOH aq. soln. 8 is added to the storage tank 7 and the soln. is stirred to adjust pH and the phosphorus is eluted from the phosphorus removing agent 4. In this way, the phosphorus in the raw water is removed at high speed and recovered as the resources.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention is a technology capable of highly purifying organic wastewater such as sewage and industrial wastewater.
In particular, it relates to a new technology capable of highly removing phosphorus and recovering phosphorus as a resource.

[0002]

2. Description of the Related Art A typical conventional phosphorus removal method is a coagulation sedimentation method. In this method, floc (SS between phosphorus and coagulant) is added to biologically treated water of wastewater by adding flocculant of any of aluminum sulfate, polyaluminum chloride, ferric chloride, and ferric polysulfate (polyiron). After the formation of the above, the flocs are removed by sedimentation, that is, phosphorus and SS are aggregated and removed. However, the coagulation-sedimentation method has the following major drawbacks. That is, a large amount of non-dewatering sludge with poor sedimentation is generated, making sludge treatment extremely difficult, and phosphorus cannot be recovered as a resource. Further, a flocculation filtration method is also known in which floc is formed by injecting a flocculant such as used in the flocculation-precipitation method while injecting raw water into a granular filter medium filtration layer such as anthracite, and flocs are filtered, which is bulky. Since a large amount of flocs are generated in the filtration layer, clogging of the filtration layer occurs in a short time, which is not practical. The coagulation filtration method also has a drawback that a large amount of non-dewatering sludge with poor sedimentation is generated and phosphorus cannot be recovered as a resource.

As a method of removing phosphorus from the treated water after biological treatment of organic wastewater, a method of passing treated water containing phosphorus through a packed bed of activated alumina is known. Since the saturated adsorption amount of phosphorus is small, frequent regeneration is necessary and maintenance is troublesome, and the running cost is high because activated alumina is expensive. In addition, the crystallization dephosphorization method in which raw water infused with slaked lime is passed through a packed bed of phosphate rock granules requires decarboxylation as a pretreatment, and maintenance work such as replacement work accompanying the expansion of phosphate rock is complicated. So it was not a practical method.

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to provide a novel phosphorus removal method in which hardly concentrated and dehydratable sludge is generated, and an advanced treatment method in which recovered phosphorus can be recovered as a resource. is there. Another object of the present invention is to provide an advanced treatment method capable of performing removal of phosphorus and filtration of the phosphorus removing agent in the same device at a high removal rate. Furthermore, an object of the present invention is to provide an advanced method for treating organic wastewater, in which maintenance and management of the treatment equipment is easy, running cost is low, and the equipment is compact.

[0005]

Means for Solving the Problems As a result of intensive research to solve the above problems, the present invention has been achieved by obtaining the following findings. That is, fine particles of aluminum hydroxide or iron hydroxide are treated as biologically treated water of organic wastewater (the biologically treated water of the present invention means that SS components derived from activated sludge and biological membranes are subjected to membrane separation, centrifugal concentration, precipitation, etc. After being added to the granular filter medium filtration layer, phosphorus in the biologically treated water can be removed at a high speed, long-term filtration is possible, and non-dehydrating sludge is not generated. Moreover, it was found that phosphorus can be recovered as a resource. In the present invention, iron hydroxide and aluminum hydroxide are iron oxides (Fe ₂ O ₃
・ NH ₂ O), aluminum oxide (Al ₂ O ₃・ nH ₂
It is also used to include O). Based on this finding, the object of the present invention can be achieved as follows. That is, iron hydroxide fine particles or aluminum hydroxide fine particles are added to biologically treated water of organic sewage to pass through a granular filter medium filter layer to remove phosphorus, and NaOH is added to the cleaning drainage of the filter layer to wash the drainage. After the phosphorus was eluted from the SS inside, solid-liquid separation was performed, and the phosphorus insolubilizing agent was added to the separated water to recover phosphorus as a solid matter, while the SS in which phosphorus was eluted was returned to the inflow water to the filtration layer. It is a high-level treatment method for organic wastewater, which is characterized by reused for phosphorus absorption.

In the present invention, the term "organic wastewater" refers to wastewater containing organic substances such as domestic sewage, human waste and industrial wastewater. In the present invention, treated water after biological treatment of the target organic wastewater, preferably after further removal of SS, is targeted.

The iron hydroxide and aluminum hydroxide fine particles having a large phosphorus adsorption force used in the present invention can be produced, for example, as follows. That is, alkaline M other than NaOH is added to an acidic aqueous solution of iron salt or aluminum salt.
If g salt or Ca salt is added to neutralize to pH 5 to 7, the reaction will proceed slowly, and iron hydroxide and water with good sedimentation, filterability, concentration, dehydration and high phosphorus adsorption will be obtained. Fine particles of aluminum oxide are obtained. In the present invention, the most preferable example of the means for producing fine particles of iron hydroxide or aluminum hydroxide having good phosphorus adsorption, filterability, concentration, and dehydration is iron or aluminum sulfate with magnesium hydroxide or carbonate. This is a method of neutralizing with an alkaline salt other than caustic soda, such as calcium or lime. Iron hydroxide and aluminum hydroxide produced by this method have an SVI value of 30.
While the fine particles are not more than the order of magnitude, the SVI value of the flocs produced by the conventional coagulation-sedimentation method and coagulation filtration method is usually 200 or more and bulky particles. Where S
The VI value (Sludge Volume Index) is a scale for evaluating the sedimentation concentration of the slurry, and is a value indicating the volume of sludge occupied by 1 g of solid matter after the slurry is filled in a graduated cylinder and allowed to stand for 30 minutes in milliliters. Indexed by.

The present invention is characterized by adding fine iron hydroxide and aluminum hydroxide fine particles having an SVI value of 30 or less as described above to biologically treated water and filtering.
The addition amount of iron hydroxide and aluminum hydroxide fine particles is about 5 to 20 mg, preferably 8 to 1 per 1 mg of phosphorus.
It is 5 mg. If it is less than this range, phosphorus cannot be sufficiently adsorbed, and if it is more than this range, the amount of precipitates becomes unnecessarily large. The iron hydroxide and aluminum hydroxide fine particles used in the present invention have the following advantages in addition to good concentration and dehydration properties. The phosphorus adsorption rate is significantly higher than that of a system in which a column is packed with a granular adsorbent such as activated alumina (particle size is about 2 to 4 mm). Since the particles are dense, the SS trapping capacity of the filtration layer is large.
Therefore, the filtration duration can be lengthened. On the other hand, in the conventional coagulation sedimentation method and coagulation filtration method, a flocculant is rapidly added to raw water (for example, activated sludge treated water of sewage) by adding a coagulant and stirring. The reaction proceeds, and bulky flocs of iron hydroxide, iron phosphate or aluminum hydroxide, and aluminum phosphate are generated, and a large amount of sludge having poor concentration / dehydration property is generated.

In the present invention, when the SS in the raw water is further reduced, SS separation means such as a filtration layer may be provided in two stages. At this time, the primary filtration layer and the secondary filtration layer may be separate devices or may be incorporated in the same device, but it is preferable that the device is compact as a whole. Then, it is preferable that the filtration layer is incorporated in the same device. At this time, the primary filtration for filtering the biologically treated water of the organic wastewater and the secondary filtration performed after adding the phosphorus removing agent to the primary filtered water are both
It is preferable to introduce the water to be treated from the lower part of the filtration layer and perform the filtration in an upward flow. When the upward flow is used, it becomes easy to wash solid substances such as SS attached to the filter medium when washing the filter layer. Further, at this time, it is rational that the primary filtration layer of the biologically treated water and the secondary filtration layer for removing phosphorus are arranged in the upper and lower parts in the same tank because the installation area can be reduced.

[0010]

The present invention has the above-described structure when treating the organic wastewater containing phosphorus, and therefore has the following effects. (i) First, biological treatment was performed, and phosphorus that was not removed by biological treatment was filtered together with biologically treated water containing SS derived from effluent activated sludge and exfoliated biofilm (primary filtration), and SS was first adjusted to several pp.
After removal to m or less, phosphorus is adsorbed and removed using a phosphorus removing agent. (SS in raw water hardly exists at the time of removing phosphorus.) (Ii) Since iron hydroxide and aluminum hydroxide fine particles having an SVI value of 30 or less are used as a phosphorus removing agent, bulky SS does not occur and therefore adsorption When SS is removed from the treated water by filtration (secondary filtration), the SS trapping capacity of the filtration layer is large and the filtration duration can be extended. (iii) Phosphorus can be desorbed from the SS of the secondary filtration having adsorbed phosphorus by addition of an alkaline agent, the phosphorus removing agent can be regenerated and reused, and the phosphorus can be recovered from the phosphorus desorption solution. Furthermore, the regenerated phosphorus removing agent can be added to the filtered water of the primary filtration layer and recycled for use.

The operation of the present invention will be described more specifically below with reference to the embodiment with reference to FIG. Treated water (raw water) containing SS and phosphorus derived from effluent activated sludge and exfoliated biofilm that has undergone a biological treatment process such as sewage activated sludge treatment
1 is flowed into the filtration device 2 to remove SS in the filtration layer B. After that, fine iron hydroxide or aluminum hydroxide fine particles 4 (a phosphorus removing agent obtained by neutralizing polyiron or aluminum sulfate with magnesium hydroxide) is injected through an injection pipe 17, and the treated water in which the fine particles 4 are injected is treated as above. Countercurrent filtration layer A
Through which the phosphorus is adsorbed and removed at a high speed in the process to obtain clear highly treated water 3.

If a granular urethane foam sponge or spherical expanded polystyrene is applied to the filter material of the filtration layers B and A, it has a large SS trapping capacity and is suitable. Other filter materials include polypropylene, anthracite,
Activated carbon etc. are mentioned. As the process continues,
Since the SS trapping amount of the filtration layer A reaches the limit and the filtration resistance reaches the limit value, the filtration layer A is washed at this point. The washing of the filtration layer A is effectively performed by stopping the raw water 1, opening the valve 6 while feeding air from under the filtration layer, and draining the water. The washing of the filtration layer B is performed after the washing of the filtration layer A is finished, and the valve 15 is opened while performing the air washing to remove the drain pipe 16
Just drain from.

As a result, the cleaning drainage of the filtration layer A containing a high concentration phosphorus removal agent for iron hydroxide fine particles or aluminum hydroxide fine particles adsorbing phosphorus flows into the cleaning drainage storage tank 7. When the aqueous NaOH solution 8 is added to this storage tank and stirred to adjust the pH to 11 or more, phosphorus is eluted from the phosphorus removing agent. After that, the stirring is stopped and the mixture is left to stand, and the phosphorus removing agent is usually precipitated for 3 to 4 hours by utilizing the time until the next washing.
The pH is preferably set to 11 to 13 in order to improve the efficiency of phosphorus elution. Then, the stirring is stopped and the mixture is left to stand to precipitate the phosphorus removing agent until the next washing (usually 12 to 24 hours). The settled sludge 9 has its phosphorus adsorption capacity regenerated (called phosphorus-eluting SS), and thus is returned to the biological treatment tank at the previous stage as a phosphorus removing agent (such as phosphorus-adsorbing fine particles) 4 and reused for phosphorus removal. Since the supernatant 10 contains a high concentration of phosphorus, phosphorus is produced as a precipitate of calcium phosphate, hydroxyapatite or magnesium phosphate, magnesium ammonium phosphate by adding and stirring the phosphorus insolubilizing agent 11 (Ca or Mg ion). To be done. This precipitate is separated by settling in a settling tank 12, and a phosphorus resource 13 is recovered as an insoluble phosphorus compound such as calcium phosphate or magnesium phosphate. The supernatant liquid 14 is returned to the biological treatment tank at the previous stage. By the above method, it becomes possible to remove SS and phosphorus from the biologically treated water of organic wastewater all at once and to a high degree. Further, according to the method of the present invention, the generated sludge has good dewatering property, is easy to treat, and can be reused, so that unnecessary sludge is not generated at all.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A concrete embodiment performed according to the flowchart of FIG. 1 will be described below. Example 1 Filtration layer B (layer containing sewage activated sludge treated water (containing 21 mg / liter of SS and 2.5 mg / liter of P in treated water) filled with polyurethane foam horny particles (particle size 5 × 10 × 10 mm) It was supplied at a filtration speed of 200 m / d. SS of outflow water from the filtration layer B was 2 mg / liter. When ferric polysulfate (polyiron) having an Fe content of 10% was diluted 10 times with water and magnesium hydroxide was added thereto to neutralize it to pH 5.5, it contained dense iron hydroxide fine particles of SVI15. Got a slurry. While adding 25 mg / liter of this slurry to the outflow water of the filtration layer B as a solid, it was passed through the filtration layer A (layer thickness 1 m) filled with expanded polystyrene having a particle diameter of 2 mm at a filtration speed of 200 m / d. As a result, the water quality of the treated water was SS 1.0 mg / liter, and P 0.09 mg / liter, which were favorable results. The filtration duration was 40 to 42 hours, and filtration was possible for a long time. NaOH was added to the washing wastewater of the filtration layer A to adjust the pH to 11, and the mixture was stirred for 30 minutes, phosphorus was eluted from the iron hydroxide, and then allowed to stand for 3 hours to precipitate the iron hydroxide SS. Sulfuric acid was added to this precipitated SS to adjust the pH to 6, and this was reused as phosphorus removing agent 4. On the other hand, 1200 mg / liter of calcium chloride as a phosphorus insolubilizing agent was added to the supernatant, and the mixture was stirred for 30 minutes in a stirring tank. As a result, a hydroxyapatite precipitate was formed. This was settled and separated in a settling tank and phosphorus was recovered as a resource.

Example 2 Magnesium hydroxide was added to an aqueous solution of aluminum sulfate (Al content 4%) to neutralize it to pH 6, and SVI1
A slurry containing 8 fine aluminum hydroxide particles was obtained. This was filtered while adding 30 mg / liter to the same raw water as in Experimental Example 1. The experimental conditions such as the configuration of the filtration layer and the filtration rate are the same as in Experimental Example 1. As a result, the treated water quality was SS 1.8 mg / liter and P 0.14 mg / liter, which were high quality. NaO for cleaning drainage of filter layer B
After adding H to adjust the pH to 11, SS was precipitated, and magnesium chloride and ammonium chloride were added to the supernatant, and p was added.
As a result of adjusting to H10, a crystalline precipitate of magnesium ammonium phosphate having a high fertilizer value was generated.

Comparative Example (Coagulation Filtration Method) Polyiron (150 m) was added to the same outflow water as in the first filtration layer B.
After adding g / l and passing water through the same filtration layer A as in Experimental Example 1 at a filtration rate of 200 m / d, the treated water quality was the same as in Experimental Examples 1 and 2, but the filtration duration was only 5 to 6 hours. I couldn't get it. It was confirmed that the cause was that when polyiron was added to the raw water at an injection rate necessary for phosphorus removal, a large amount of bulky flocs were generated, which blocked the filtration layer in a short time. The SS of the cleaning wastewater had a poor dewatering property, and 2% of the cationic polymer was added to the solid matter for dewatering with a belt press dewatering machine, but the water content of the dewatering cake was as high as 86%.

[0017]

INDUSTRIAL APPLICABILITY According to the present invention, by using fine particles of iron hydroxide or aluminum hydroxide having good filterability, sedimentation-concentration property, and dehydration property, phosphorus in biologically treated water of organic wastewater can be treated at high speed and always at a high level. Not only can phosphorus be removed, but phosphorus in wastewater can be recovered as a resource. Further, according to the present invention, since the fine particles of iron hydroxide or aluminum hydroxide are dense fine particles, sludge that is hardly dehydrated is not generated at all, and thus sludge treatment is extremely easy. Since bulky flocs do not occur, the filtration layer is not clogged and the filtration duration is long, and after phosphorus is eluted from iron hydroxide or aluminum hydroxide that has adsorbed phosphorus in the cleaning wastewater, it is returned to the biological treatment process. It can be reused for phosphorus removal. Further, according to the present invention, the maintenance of the processing apparatus is easy, the running cost is low, and the apparatus can be made compact.

[Brief description of drawings]

FIG. 1 is a flowchart of a process that is an embodiment of the present invention.

[Explanation of symbols]

 1 Raw water (biological treatment) 2 Filtration device 3 Highly-treated water 4 Phosphorus remover 5 Wash drainage 6 Valve 7 Wash drainage storage tank 8 NaOH aqueous solution 9 Precipitated sludge (phosphorus elution SS) 10 Supernatant 11 Phosphorus non-solvent 12 Precipitation tank 13 Recovered phosphorus 14 Supernatant 15 Valve 16 Drainage pipe 17 Injection pipe A Filtration layer B Filtration layer

Claims (1)

[Claims] 1. Iron hydroxide fine particles or aluminum hydroxide fine particles are added to biologically treated water of organic wastewater to pass through a granular filter medium filter layer to remove phosphorus, and NaOH is added to washing wastewater of the filter layer. After the phosphorus is eluted from the SS in the washing wastewater, solid-liquid separation is performed, and the phosphorus insolubilizer is added to the separated water to recover the phosphorus as a solid matter, while the SS in which the phosphorus is eluted flows into the filtration layer. An advanced method for treating organic wastewater, which comprises returning the wastewater to the factory and reusing it for phosphorus absorption.