JPH02139099A - Treatment of organic sewage - Google Patents

Abstract

PURPOSE:To reduce running cost by adding calcium ion to a biological nitrification denitrification treatment stage and maintaining pH to 7.0 or more and solid-liquid separating activated sludge slurry contg. produced calcium phosphate ppt. and adding a prescribed inorganic flocculating agent to the separated water, flocculating and separating this water. CONSTITUTION:Organic sewage is treated by a biological nitrification denitrification treatment tank 2 and activated sludge slurry 3 is solidliquid separated by a UF membrane or an MF membrane solid-liquid separating stage 4. The separated water 6 is furthermore treated by a biological nitrification denitrification treatment tank 12. In this case, when calcium ion 14 is added to the treatment stage and pH is controlled to 7.0 or more, the producing reaction of calcium phosphate ppt. is caused and large parts of PO4<3-> in water to be treated are removed. The large parts of COD and color components are adsorbed on the interface of calcium phosphate ppt. and removed. Therefore the usage of an ironbased or aluminum-based inorganic flocculating agent 18 necessary to flocculate and precipitate the water 17 overflowed from a sedimentation basin 16 is made little and the treated water 20 treated at high degree is obtained.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention aims to rationally treat organic sewage containing large amounts of phosphorus and nitrogen, such as human waste, by a new process, and reduce the amount of inorganic flocculant used. The present invention relates to a method for treating organic sewage, which reduces wastewater, discharges sludge with good dewaterability, and consistently obtains highly treated water in a stable manner.

[Prior art]

The conventional and typical process for treating organic lη water containing phosphorus, nitrogen, and BOD, such as human waste water, consists of the process shown in the flow sheet in Figure 2. is called a high-load denitrification process and requires a large amount of iron-based or aluminum-based inorganic flocculants, so Fe (OH) s or AI!, which is difficult to dehydrate, is used. (
A large amount of coagulated and precipitated sludge of the OH)+ system is generated, and the equipment cost and running cost of the sludge treatment equipment are high, which is a serious drawback.

On the other hand, very recently, a new process for treating organic wastewater, as shown in the flow sheet of Figure 3, has been proposed and put into practical use in several places. This process is called the UP membrane (ultrafiltration membrane) separation phosphorus adsorption process, and its characteristics ensure solid-liquid separation and eliminate the need for a coagulation-sedimentation process. It also has the disadvantage of requiring the complicated work of disposing of the adsorbent regeneration waste liquid.
Moreover, since COD removal by coagulation and precipitation is omitted, there is a major drawback that the COO load flowing into the activated carbon is high and the running cost of activated carbon treatment is extremely high.

[Problem to be solved by the invention]

The present invention aims to appropriately eliminate the drawbacks of the conventional human waste treatment process described above, and specifically aims to solve the following problems.

(1) To eliminate the need for the phosphorus adsorption step that follows the OF membrane separation step, and to increase (reduce) the amount of iron-based or aluminum-based inorganic flocculant added for removing po, 3-ions.

(2) Improving the dewaterability of generated sludge.

(3) To improve the fertilizer value of sludge dewatering cake.

[Means to solve the problem]

The present invention performs solid-liquid separation of activated sludge slurry obtained by biological nitrification and denitrification treatment of organic wastewater using a UF membrane or liver membrane, and further performs biological nitrification and denitrification treatment of the permeated water through the membrane. adding calcium ions to the treatment step;
An organic method characterized by maintaining the pH at 7.0 or higher, separating the resulting activated sludge slurry containing calcium phosphate precipitate into solid-liquid, and adding an iron-based or aluminum-based inorganic flocculant to the separated water for flocculation separation. It is a method of treating sewage.

Note that liver membrane is an abbreviation for porous filtration membrane.

Below, the first part showing a flow sheet of one embodiment of the present invention is shown.
The present invention will be described in detail with reference to the figures.

The removed human waste 1 flows into a non-dilution type biological nitrification and denitrification treatment tank 2 (this will be referred to as the "main biological treatment tank"), where most of the waste is removed through biological nitrification and denitrification treatment. BOD
and nitrogen components are removed.

The activated sludge slurry 3 flowing out from the main biological treatment tank 2 is subjected to a solid-liquid separation process 4 using a tubular or flat membrane type IP membrane.
Complete solid-liquid separation is performed and separated into membrane-separated slurry 5 and membrane-permeated water 6 with zero SS.

The majority 7 of the membrane separation slurry 5 has an activated sludge MLSS concentration in the main biological reaction tank 2 of a predetermined value (usually MLSS 15,000).
■/! It is recycled to the main biological treatment tank 2 in order to maintain it at a certain level.

The remainder 8 of the membrane-separated slurry 5 is supplied as surplus sludge to a sludge dehydrator 9 such as a belt press centrifugal dehydrator, screw press, or filter press, and is separated into a dewatered cake 10 and dehydrated separated water 11.

Therefore, both the membrane permeated water 6 and the dehydrated separated water II are
Activated sludge MLSS flows into the second biological nitrification and denitrification treatment tank 12 (this is called the "byproduct treatment tank") maintained at 3000 to 5000 mg/42, and becomes membrane permeated water 6 and dehydrated separated water 11. A small amount of remaining BOD and nitrogen components (usually on the order of several tens of square meters/!) are removed. By-product treatment tank 1
2 is preferably provided with an injection device for a carbon source such as methanol in order to promote the action of activated sludge.

In addition, dehydrated separated water and miscellaneous sewage (vacuum car wash sewage, floor washing wastewater, etc.) generated during the operation of human waste treatment facilities.
13 is also preferably supplied to this by-product reaction tank 12 for treatment.

This is because when the dehydrated separated water If and miscellaneous wastewater 13 are allowed to flow into the main biological treatment tank 2, the amount of water to pass through the membrane in the IF membrane solid-liquid separation process 4 increases, and as a result, the pressure in the UF membrane solid-liquid separation process 4 increases. This is because, in addition to increasing the pump power cost, there are negative effects such as a decrease in the water temperature in the main biological treatment tank 2 and a decrease in the nitrification and denitrification reaction rate.

Calcium ions 14 are added to this by-product treatment tank 12, and the pH of the same type is adjusted to a weak alkali with a pH of 7.0 or more, for example, p
When adjusted to H7.5 to H8.5, calcium phosphate precipitates are produced, and at the same time most of the COD and chromaticity components are removed. As a calcium ion, C
aCl! , z or Ca (OH) 2 are preferably used.

Activated sludge slurry 15 in which activated sludge and calcium phosphate precipitate coexist flows out from by-product treatment tank 12 and enters settling tank 16, where the three substances are sedimented and separated. Separation here may also be by other means such as filtration.

The overflow water 17 from the settling pond 16 has COO, chromaticity, PO4
Most of 3-, for example, 80% or more, has been removed, and an iron-based or aluminum-based inorganic flocculant is added to this overflow water 17 for one day to form a coagulated sediment, which is then subjected to sedimentation, membrane separation, etc. In the solid-liquid separation step 19, the sludge is separated into coagulated and separated treated water 20 and separated sludge 21. In this solid-liquid separation step 19, dissolved COD in the overflow water 17, chromaticity,
A coagulated and separated treated water 20 in which PO4 is highly separated is obtained.

In the above solid-liquid separation step 4, a case is shown in which a UF membrane is used, but the same effect can be achieved even if a liver membrane is used.

As the iron-based or aluminum-based inorganic flocculant, second chloride
Use well-known materials such as iron and sulfuric acid.

[Effect]

In the present invention, since the target of treatment is organic wastewater with a high concentration of organic matter such as human waste wastewater, the organic wastewater is subjected to biological nitrification and denitrification treatment, and the activated sludge slurry is then passed through an OF membrane or liver. The water is separated by solid-liquid separation using a membrane, and the resulting membrane-separated water is further subjected to biological nitrification and denitrification treatment.

At that time, calcium ions are added to the treatment step to adjust the pH of the water to be treated to 7.0 or higher, for example 7.5 to 8.
．． 5 and slightly alkaline conditions, 5Ca
+OH-+3P043-+ Ca5(Of+)(PO=
) i↓ and other calcium phosphate precipitate formation reactions occur, and at the same time most of the po, 3- ions in the water to be treated are removed, and at the same time, most of the COD and chromaticity components are adsorbed to the interface of the calcium phosphate precipitate and removed. It was discovered that Its po, 3-1 COD, chromaticity removal rate is over 80% and 3
゜For this reason, the separated water obtained by solid-liquid separation of the generated activated sludge floc containing calcium phosphate is CO
The content of D, chromaticity, and PO43- has been significantly reduced, and the amount of iron-based or aluminum-based inorganic flocculant required for coagulation and precipitation is small, and the chromaticity of dissolved COO in separated water has been significantly reduced. , po, '- can be obtained from the treated water to a high degree.

〔Example〕

Hereinafter, the present invention will be specifically explained with reference to Examples. However, the present invention is not limited to this example.

Example 1 The results of processing in a processing apparatus according to the flow sheet according to an embodiment of the present invention shown in FIG. 1 will be described.

The removed human waste having the water quality shown in Table 1 was subjected to non-dilution type nitrified solution circulation biological nitrification and denitrification treatment in the main biological treatment tank. The operating conditions are shown in Table 2.

Table 1: Removal night soil water quality Note) T-N: Total nitrogen Note) Port: Capacity of main biological treatment tank Activated sludge slurry flowing out from the main biological treatment tank is collected by tubular type ultrafiltration membrane separation device 4 (molecular weight cut off: 50 .000)
When the membrane was injected using a pump at a pressure of 4 kg/cffl, membrane-permeated water having the quality shown in Table 3 was obtained.

In addition, the amount of excess sludge generated from the main biological treatment tank is 5.5 kg5S per 1 kft of human waste, and after adding a cationic polymer to it and coagulating it, it was dehydrated using a belt press type dehydrator. , the quality of the dehydrated separated water is S
Except for the high S content of 400 to 600 mg/l, the other components were equivalent to the values in Table 3.

The moisture content of the dehydrated cake was 78%.

Next, a mixed solution of membrane permeated water and dehydrated separated water was supplied to a by-product treatment tank, and while biological nitrification and denitrification treatment was performed, calcium ions were added to cause a calcium phosphate precipitate formation reaction. The operating conditions of the byproduct treatment tank were set as shown in Table 4.

Table 4 The operating conditions for the by-product treatment tank were approximately 177 to 178 in the conventional method (Figure 2).

Further, the amount of sludge generated in the coagulation and sedimentation step using FeCl 2 was 0.25 to 0.3 kg-557 kl-L urine, which was 178 in the conventional method (Figure 2).

The activated sludge slurry containing calcium phosphate precipitate from the by-product treatment tank enters the settling tank, where the activated sludge blocks are sedimented and separated. The quality of the overflow water flowing out from the settling tank is shown in Table 5, with PO43-1 chromaticity, COD
Most of them have been removed.

Next, FeCj2. 350mg/
I! .

After addition, coagulation and precipitation were performed under conditions of pH 4 and 5, and further sand filtration was performed. The quality of the obtained treated water was very good as shown in Table 6, and the same effect was obtained even when sulfuric acid was used as an added inorganic flocculant for FeClx.

〔Effect of the invention〕

The present invention has the following remarkable effects.

(1) The amount of iron-based or aluminum-based inorganic flocculants used is significantly reduced, and the amount of metal hydroxides that are difficult to dewater due to their use is also significantly reduced.

(2) In the by-product treatment tank, a sludge dewatering cake containing calcium phosphate is produced, which can be used as fertilizer.

(3) In order to treat sludge separated water and gray water in the second biological nitrification and denitrification treatment without flowing into the first biological nitrification and denitrification treatment, the first biological nitrification The pump power cost in the OF membrane or single membrane solid-liquid separation process following denitrification treatment can be significantly reduced compared to the conventional membrane separation method. Also, the required membrane area in the same process is reduced.

(4) Since calcium ions and iron-based or aluminum-based inorganic flocculants are combined using a new method, PO43
-Ions can be effectively removed, and the conventional PO41-adsorption step is no longer necessary, making maintenance easier.

[Brief explanation of the drawing]

FIG. 1 shows a flow sheet in one embodiment of the present invention, FIG. 2 shows a flow sheet for the most typical conventional organic sewage treatment process, and FIG.
A flow sheet of the membrane separation phosphorus adsorption process is shown. 1... Sludge removal human waste, 2... Biological nitrification and denitrification treatment tank, 3... Activated sludge slurry 4... IP membrane or single membrane solid-liquid separation process, Death... Membrane separation slurry 6. ...Membrane separated water, 12...Biological nitrification and denitrification treatment tank, 14...
Calcium ion, 15... activated sludge slurry containing calcium phosphate precipitate, 16... settling tank, 18.
...Iron-based or aluminum-based inorganic flocculant, 19...Solid-liquid separation step. Representative patent attorney (8107) Kiyotaka Sasaki. (3 others)

Claims (1)

[Claims] Activated sludge slurry obtained by biological nitrification and denitrification treatment of organic wastewater is subjected to solid-liquid separation using a UF membrane or MF membrane, and the water that permeates through the membrane is further subjected to biological nitrification and denitrification treatment. Add calcium ions and adjust the pH to 7.
0 or more, solid-liquid separation of the generated activated sludge slurry containing calcium phosphate precipitate, and coagulation separation by adding an iron-based or aluminum-based inorganic flocculant to the separated water. Processing method.