JPH0880488A - Complete treatment of organic sewage - Google Patents

Abstract

PURPOSE: To avoid the production of a sludge difficult to concentrate and dehydrate and utilize the recovered phosphorus as resources after biologically treating an org. sewage contg. phosphorus, adding an aluminum-base flocculant to the filtered water to remove phosphorus and recovering the phosphorus. CONSTITUTION: An org. sewage 1 is biologically treated and then passed through a filtration tank 2 to remove the SS such as effluent sludge. An aluminum-base flocculant 4 is then added to the filtered water from a tank 2 to form a floc contg. phosphorus in a stirred tank 5, a high molecular flocculant 6 is further added to increase the diameter of the floc in a settling tank 7, and the floc is settled as a sludge 9. An alkaline agent 10 (e.g. sodium hydroxide) is then added to the sludge 9 obtained by settling the floc to dissolve the flocculated sludge 9 in a stirred tank 11. A calcium compd. 12 is added to the soln. to recover phosphorus as hydroxyapatite, etc., in a settling tank 13.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technology capable of highly purifying phosphorus-containing organic wastewater such as sewage, and more particularly to a new technology capable of recovering phosphorus as a resource.

[0002]

2. Description of the Related Art A typical conventional phosphorus removal method is a coagulation sedimentation method. This method uses SS such as activated sludge treated water of sewage, biological treated water containing phosphorus and aluminum sulfate,
After adding aluminum-based or iron-based aggregating agents such as polyaluminum chloride, ferric chloride, and ferric polysulfate (polyiron) to form flocs (SS of phosphorus and aggregating agent),
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 hardly dehydratable sludge with poor sedimentation is generated, which makes treatment of the hardly dehydratable sludge extremely difficult, and the removed phosphorus cannot be recovered as a resource. In the conventional coagulation-sedimentation method, sludge with poor filterability, concentration-sedimentation property, and dewatering property is likely to be generated. Probably, the coagulant is added to the raw water (eg, sewage activated sludge treated water) and stirred. It is considered that this is because the reaction of the raw water with hydroxide ions and phosphate ions rapidly progresses, and bulky flocs of iron hydroxide, iron phosphate, aluminum hydroxide and aluminum phosphate are generated.

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 processing method in which the processing apparatus is easy to maintain and manage, the running cost is low, and the apparatus is compact. Furthermore, the object of the present invention is to
It is to provide an advanced processing method capable of removing phosphorus at a high speed.

[0005]

As a result of intensive studies for solving the above-mentioned problems, it was found that the problems can be solved by the advanced method for treating organic wastewater of the present invention. That is,
An aluminum-based coagulant is added to the biologically treated water of the organic wastewater to separate and remove phosphorus from the biologically treated water as sludge, and alkali is added to the separated sludge to dissolve the sludge, and phosphorus ions are added to the solution. An organic wastewater characterized by adding an insolubilizing chemical to recover phosphorus, separating phosphorus, and then adding the solution together with a newly supplied aluminum-based coagulant to inflow water to the coagulation-separation step. It is an advanced processing method.

In the present invention, the term "organic sewage" refers to sewage from households, sewage containing organic substances such as human waste. In the present invention, the target organic sewage is biologically treated to further remove SS. Further, in order to remove SS, it is preferable to apply the filtration method rather than the precipitation method.

[0007]

The present invention will be described below with reference to FIG. FIG. 1 is a diagram showing one embodiment of the method of the present invention. FIG.
The processing steps of the present invention are roughly classified as follows. After biologically treating the organic sewage 1, a step of removing SS such as activated sludge flowing out from the biologically treated water through the filtration tank 2, an aluminum-based coagulant 4 is added to the filtered water 3 from the filtration tank 2, and phosphorus is added in the stirring tank 5. A flocculating step of forming flocs containing, adding a polymer flocculant 6 to increase the floc diameter in the settling tank 7, and separating and separating flocs as flocculated sludge 9; The agent 10 is added, and the aggregated sludge 9 is dissolved in the stirring tank 11. The calcium compound 12 is added to this, and the precipitation tank 1
4 in which phosphorus is recovered as hydroxyapatite 15 and the like.

Each of the above steps will be described in more detail with reference to FIG. Step of removing SS: The amount of SS such as effluent activated sludge and biofilm contained in the biologically treated water 1 is, for example, 2
Although as small as about 5 mg / liter, in order to recover and reuse phosphorus, these residual SS are completely removed by filtering through the filtration tank 2. The filter tank 2 is filled with a filter medium, for example, as a fixed filter bed to form a packed filtration layer. Examples of the filter medium to be filled in the fixed filter bed include an inorganic filter medium such as anthracite and chamotte, and a filter medium made of porous organic polymer particles such as polyurethane sponge particles.

Phosphorus removal step for sedimentation and separation of flocs: Aluminum-based flocculant 4 is added to filtered treated water 3 from which SS has been completely removed in the above-mentioned filtration step, and agitation tank 5 (2
Stirring (~ 3 minutes) forms flocs containing phosphorus. Suitable examples of the aluminum-based flocculant 4 include aluminum sulfate and polyaluminum chloride (PAC). The amount of addition is, for example, 10
The concentration is in the range of mg / liter to 200 mg / liter, and varies depending on the condition of the concentration of phosphorus contained in the treated water. The flocs containing phosphorus are sent to the settling tank 7 together with the treated water, and a polymer flocculant 6 (hereinafter abbreviated as a polymer) is added in order to grow the flocs on the way.
Here, the polymer coagulant 6 is preferably an anionic polymer, but is not limited thereto. The flocs having a larger diameter and easily settled by adding the polymer are poured into the settling tank 7 from the central feed well together with the treated water.
The flocs rapidly settle in the settling tank 7 to form aggregated sludge 9. On the other hand, the supernatant water enters the overflow weir at the upper part of the settling tank 7 and flows out of the system as highly treated water 8 from there.

Phosphorus recovery step: The aggregated sludge 9 settled and deposited in the precipitation tank 7 enters the phosphorus recovery step, and first, while being transferred from the precipitation tank 7 to the stirring tank 11, an alkaline agent 10, for example, NaOH, KOH. , Slaked lime, quick lime, etc.
Is added to adjust the pH to 11 or more. 1-2 in the stirring tank 11
Stir for about an hour to dissolve aluminum hydroxide, aluminum phosphate and the like. Calcium compound 12, for example, calcium chloride, quick lime, calcium hydroxide, etc., is added to the outflow water from the stirring tank 11, and the water is added to the precipitation tank 13 (1
Allow the sludge containing phosphorus (calcium phosphate 14) to settle for 0 to 24 hours. However, the alkaline agent 10
When slaked lime or quick lime is used as the above, the calcium compound 12 may not be added at this stage. The calcium phosphate 14 that has settled in the settling tank 13 is discharged as mud, and is further subjected to solid-liquid separation by centrifugation or the like, and then used as a fertilizer-producing raw material or as it is as a fertilizer.

Since the alkaline supernatant liquid 15 in the settling tank 13 and the dehydrated separated liquid in the sludge 14 contain aluminate ions, when they are refluxed in the stirring tank 5, they are diluted with the filtered water 3 and neutralized. At the same time, aluminum hydroxide precipitates. At this time, it is extremely important to add a small amount of fresh aluminum-based coagulant. Otherwise, it was observed that the phosphorus removal rate gradually deteriorates as the operation is continued for a long time. In order to adjust the pH in the stirring tank 5 to the optimum pH value for phosphorus removal of 5 to 6,
It is preferable to add the acid 16 when refluxing from the settling tank 13.

In the present invention, the SS of activated sludge flocs is used without the filtration step 2 for removing SS in the biologically treated water 1.
When the aluminum-based coagulant 4 is directly added to the biologically treated water 1 containing a relatively large amount of SS, a considerable amount of activated sludge flocs SS is mixed into the calcium phosphate 14 settling in the settling tank 13, which is disadvantageous in phosphorus recovery. Therefore, it is preferable to provide the filtration step 2. By the above action, the discharge to the outside of the system is well dehydrated, and is a valuable calcium phosphate as a resource, and the remarkable effect that gelation of aluminum hydroxide, which is difficult to dehydrate, and aluminum phosphate does not occur. is there.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The following is a concrete embodiment carried out according to the flow chart of FIG. Example 1 Sewage activated sludge treated water (SS 18 mg / liter and P2.1 mg / liter is contained in the treated water) was sent to a filtration tank 2, and polyurethane foam angular particles (particle size 5 × 10 5) in the filtration tank 2 were sent. Water was passed through a filter medium-packed layer (layer thickness 1 m) filled with (× 10 mm) at a filtration rate of 120 m / d. The SS of outflow water from the packed bed was 2-3 mg / liter. 100 ml of polyaluminum chloride is added to 1 m ^{3 of} this filtered water.
mg / liter was added, and flocs were aggregated at pH 6. While the floc suspension water was being transferred to the settling tank 7, 1 mg / l of an anion polymer (Ebagros A120) was added and poured into the settling tank 7 to cause sedimentation and separation as aggregated sludge. The average water quality of the highly treated water flowing out from the settling tank 7 was SS 2 mg / liter and P 0.11 mg / liter, and phosphorus was highly removed.

A 3% aqueous solution of caustic soda was added to the total amount (2.5 liters by volume) of the settled sludge (concentration of solid matter: 9 g / liter), the pH was adjusted to 12, and the mixture was stirred for 1 hour to dissolve most of the settled sludge. Then it became liquid. 7 g of 20% calcium chloride aqueous solution as calcium
When added, an insoluble compound of calcium phosphate, which is valuable as a fertilizer, was deposited, so this was precipitated, and the supernatant liquid (aluminum content 4.5 g) was added to the filtered water 1
It was added to m ^3, and adjusted to pH6 by addition of sulfuric acid, further 1 volume of 10mg of the original 10 minutes polyaluminum chloride
/ Liter was added. As a result, the phosphorus content of the treated water from the sedimentation tank was 0.10 to 0.13 mg / liter. The amount of calcium phosphate produced was about 9 g as a solid and 0.22 liter as a volume. On the other hand, in the case of the coagulation-sedimentation method to which the present invention is not applied, the amount of sedimentation sludge generated was 2.5 liters in volume, so the amount of sludge production of the present invention was about one tenth, which was very small. Further, when calcium phosphate sludge was dehydrated by a centrifugal dehydrator, dehydration was easy and a dehydrated cake having a water content of 77% was obtained.

[0015]

INDUSTRIAL APPLICABILITY In the present invention, after the organic wastewater containing phosphorus is biologically treated, aluminum-based coagulant is added to the filtered water obtained by filtration to remove phosphorus, and phosphorus is recovered. Phosphorus in the wastewater can be effectively removed and can be recovered as a phosphorus resource. In addition, since the amount of coagulated sludge generated is reduced, sludge treatment is significantly rationalized. Furthermore, since the inorganic coagulant for phosphorus removal can be reused, the amount of the inorganic coagulant used can be reduced.

[Brief description of drawings]

FIG. 1 is a process drawing showing an example of a method for treating organic wastewater of the present invention.

[Explanation of symbols]

 1 Biological treated water 2 Filtration tank 3 Filtration treated water 4 Aluminum flocculant 5 Stirring tank 6 Polymer 7 Precipitation tank 8 Highly treated water 9 Aggregated sludge 10 Caustic soda 11 Stirring tank 12 Calcium compound 13 Precipitation tank 14 Calcium phosphate 15 Alkaline supernatant 16 acid

Claims (1)

[Claims] 1. An aluminum coagulant is added to biologically treated water of organic wastewater to separate and remove phosphorus from the biologically treated water as sludge, and alkali is added to the separated sludge to dissolve sludge, It is characterized in that a chemical that insolubilizes phosphorus ions is added to the solution to recover phosphorus, and after the phosphorus is separated, the solution is added to the inflow water to the aggregating and separating step together with the aluminum-based aggregating agent newly supplied. Advanced treatment method for organic sewage.