JPS63242397A - Treatment of waste water - Google Patents

Abstract

PURPOSE:To prevent filtration velocity from being reduced by mixing an inorganic flocculating agent with treatment water before separating sludge and allowing it to adsorb COD. CONSTITUTION:Organic waste water is subjected to biological treatment with activated sludge while aerating it in a biological treatment tank 30. Water to be treated which is deaerated in a deaeration tank 31 is sent to a flocculation tank 32 and an inorganic flocculating agent (e.g. aluminum sulfate and ferric chloride, etc.,) for flocculating activated sludge is mixed with the water to be treated. COD contained in the water to be treated is reduced by allowing the flock of flocculated activated sludge to adsorb COD. The water discharged from the flocculation tank 32 is separated from sludge and a part of the separated sludge is returned to the biological treatment tank 30, and the residual part is drawn out as excess sludge. Thereby filtration velocity can be enhanced.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention is directed to biologically treating organic wastewater with activated sludge, and separating the activated sludge from the treated water after the biological treatment by ultrafiltration to obtain purified water. Regarding processing method.

[Conventional technology]

Conventionally, in the above-mentioned wastewater treatment method, since most of the sludge can be separated from the treated water by ultrafiltration, the treated water after biological treatment was directly subjected to ultrafiltration.

[Problem that the invention seeks to solve]

However, as the sludge is separated, a gel layer tends to form on the surface of the ultrafiltration membrane (this has the disadvantage that this becomes a resistance when passing through the membrane and reduces the rate of permeation through the filtration membrane).

An object of the present invention is to prevent the rate of permeation of treated water through a filtration membrane from decreasing.

[Means for solving problems]

The present invention has led to the discovery that the less COD dissolved in the treated water, the more difficult it is to form a gel layer on the surface of the ultrafiltration membrane. The purpose is to mix a flocculant and cause COD in the treated water to be adsorbed to the activated sludge flocculated by the inorganic flocculant, and its effects are as follows.

[For production]

In other words, COD is added to activated sludge that is flocculated by an inorganic flocculant.
By adsorbing activated sludge flocs, the concentration polarized layer and gel layer formed on the surface of the ultrafiltration membrane are disturbed, and the thickness of the concentration polarized layer (St) and gel layer thickness (tg
) becomes thinner, for example, when sulfuric acid band is treated with AlzOz to 500%
When mg/l is added, the permeation flux of the treated water to the ultrafiltration membrane is 1.58rrr/m-day, and the permeation flux of the treated water when no sulfate is added is 0.92n? /
This is 1.71 times that in the case of m day, and the membrane permeation rate is greatly improved.

〔Effect of the invention〕

Therefore, it is possible to reduce the permeation rate of treated water through a filtration membrane by a method that has not been possible in the past, such as reducing the COD by adding an inorganic flocculant to treated water containing sludge before ultrafiltration. It has now become possible to efficiently obtain high-quality purified water over a long period of time.

〔Example〕

Next, embodiments of the present invention will be described based on the drawings.

As shown in Figure 1, the treatment process for organic wastewater such as human waste is biologically treated using activated sludge while aerating organic wastewater in a biological treatment tank (30).At this time, organic matter and nitrogen compounds in the wastewater are removed. As the sludge decomposes, some of the phosphate ions it contains are also adsorbed and removed by the activated sludge.Next, the treated water after biological treatment is degassed to remove air bubbles attached to the sludge in the degassing tank (31), and the treated water is coagulated. Sulfuric acid band (SO4) is sent to the tank (32) as an inorganic flocculant to flocculate the activated sludge.
3) Or ferric chloride (FeC13) or the like is mixed into the treated water.

Then, COD is adsorbed to the activated sludge flocs flocculated by these inorganic flocculants, thereby reducing COD in the treated water.

On the other hand, in the coagulation tank (32), ferric chloride (Fe
C13) or sulfuric acid band (Atz(so4)i), etc., can be added to the treated water to add orthorin (Il) to the treated water.
Phosphate ion (PO43), which is abundantly contained as zPOm)
) with insoluble phosphate (FePOa or AI
PO,) is generated.

After that, the unreacted flocculant (FeC1+
or the metal content (Fe3+ or A
The three Is are mixed with alkalis such as sodium hydroxide (NaOH) and calcium hydroxide (Ca (OH) z) in a coagulation tank (
3), the insoluble metal hydroxide (
Fe(OH)! or AI (OH) 3), and by mixing alkali into the treated water, the treated water becomes
Almost neutralized to pH 6-8.

The treated water discharged from the coagulation tank (32) is sent to the ultrafilter (33) by a pump (P), and from the treated water, sludge that has adsorbed COD and phosphates (FePO, or 81PO4) are extracted.
) and metal hydroxides (Fe (OH) 3) or AI (
The sludge containing OB)s is separated, a part of the separated sludge is returned to the biological treatment tank (30), and the remainder is extracted as surplus sludge.

Of the flocculated sludge returned to the biological treatment tank (1), metal hydroxide (Fe(OH)3 or AI(Oil)
s) reacts with phosphate ion (PO4''-) in the waste liquid as follows, Fe(Otl)z+HiPO4→FePO4+'HzO
Or AI(OR)3 +H:lPO4→AlPO4+HzO
, and exhibits the effect of removing phosphate ions (PO43-) from waste liquid.

Next, the relationship of the inorganic flocculant to the ultrafiltration membrane will be explained.

First, Table 1 below shows an example of water quality when human waste is treated with biological nitrification and denitrification. However, sulfuric acid and alkaline agents were not injected.

Table-1 (AhO3-free) (mg/ (1)
From Table 1 above, SS is 100% blocked by the ultrafiltration membrane,
N13. ”, NO□-, No:l-1PO4”-, CI
- almost 100% passes through the membrane, BOD is about 75%, CO
It can be seen that about 66% of D and about 56% of organic nitrogen are blocked by the film.

As the treated water passes through the ultrafiltration membrane, a polarized layer with a high concentration of molecules is generated near the membrane, and this becomes a gel layer on the membrane surface, providing resistance to the permeation rate.

Therefore, when we investigated the main factors that slow down the membrane permeation rate of treated water, we found that from Figure 2, the activated sludge concentration (MLSS 1 degree) of the human waste nitrification and denitrification treatment liquid has little effect on the membrane permeation flux (FLUX). It was found that the sulfuric acid band injection rate (Ah (h addition rate)) and membrane permeation flux (
From the graph of the relationship between the sulfuric acid band injection rate and the residual COD shown in Figure 4, it can be seen that COD is adsorbed to activated sludge flocs that coagulate due to the addition of sulfuric acid band, and the lower the COD in the treated water, the lower the COD in the treated water. It can be seen that the membrane permeation rate increases.

Therefore, human waste was treated with biological nitrification and denitrification method, and sulfuric acid band, an inorganic flocculant, was added as A1□03 at 500mg/
Table 2 below shows an example of water quality when ultrafiltration is performed with addition of
Shown below.

Table 2 (mg/j2) Comparing Table 2 and Table 1 above, the permeation flow rate when adding sulfuric acid band was 1.58r+? /m/m day, while the permeation flow rate when no addition was made was 1.58 0.92 m/m day, - = 1, the membrane permeation rate was improved by 71 times. I know that there is.

In addition, it can be seen that phosphate ion (PO4'-) is also reduced by the addition of sulfuric acid band.

[Another example]

As the inorganic flocculant, polyaluminum chloride may be used in addition to ferric chloride and aluminum sulfate.

Next, as an example of the apparatus for wastewater treatment of the present invention, the fifth
6 or 6, in FIG. 5, (1) is the human waste input pump, (2) is the aeration tank, and the circulation pump (3) is the aeration tank.
The mixed liquid is pumped to the gas-liquid contact pipe (14).

The gas-liquid contact tube (14) is provided with an air suction tube (13), which sucks atmospheric air through an ejector effect.

(11) is an air amount controller, and (12) is an air control valve. By adjusting the amount of air suction so that the DO in the aeration tank 1 is 0.1 to 1 mg/l, human waste is treated by biological nitrification and denitrification. (4) is a deaeration tank, which blows air to deaerate air bubbles attached to the sludge, pump (7) injects sulfuric acid, and pump (9) injects alkaline agent. ing. (8) is a storage tank for sulfuric acid band, and (10) is a storage tank for alkaline agent. (5) is an ultrafiltration pump, (6
) is an ultrafiltration device, and (16) is a return line for concentrated liquid.

(15) Outflow path for treated water.

The injection point for the sulfuric acid band and alkaline agent may be the aeration tank (2).

Next, in FIG. 6, (1) human waste input pump, (
20) is a denitrification tank, and (23) is a stirring pump.

(24) is a nitrification tank, and (25) is an aeration device with a blower (
B) It allows more air to be blown into it. (26) is a nitrification liquid circulation pump, which circulates the nitrification liquid to the denitrification tank (20) through the nitrification liquid circulation path (35).

The denitrification tank (20) is a tank for denitrifying NOx- and NOz- that have been circulated using BOD in human waste as a carbon source.

The treated liquid coming out of the nitrification tank (24) is led to a second denitrification tank (28), where No, -, and Not- denitrification is performed under Do-deficient conditions.

(27) is a stirring pump. (4) is a denitrification tank,
It is equipped with an aeration device (29), which blows air to remove air bubbles attached to the activated sludge. (7) is an injection pump for sulfuric acid, and (9) is an injection pump for alkaline agent.

(8) is a sulfuric acid band storage tank, and (10) is an alkali agent storage tank. (5) is an ultrafiltration pump, (6) is an ultrafiltration membrane device, and the concentrated liquid is passed through the pipe (16) to the denitrification tank (
20). (15) is an outflow pipe for treated water.

The injection points for sulfate band are the denitrification tank (20) and the nitrification tank (24).
), the second denitrification tank (28).

Note that (17) in the figure is a pipe for extracting excess sludge.

In Figure 5, the DO in the aeration tank (2) is 0.5 mg/l.
The amount below and 1 mg/1 or more may be produced alternately.

In FIGS. 5 and 6, a portion of the concentrated liquid may be returned to the degassing tank. However, it is not desirable to return the entire amount to the deaeration tank.

Furthermore, the injection point of the alkali agent may be placed not in the deaeration tank but in the return flow path of the concentrated liquid or the inlet of the activated sludge treatment tank.

In this case, there is an advantage that the pH value in the degassing tank is lowered, the dissolved organic matter concentration is lowered (preferably around PH5), and the permeation rate is further improved.

[Brief explanation of drawings]

The drawings show an embodiment of the wastewater treatment method according to the present invention.
The figures are schematic diagrams showing the processing process, Figures 2, 3, and 4.
5 and 6 are schematic diagrams of apparatus for carrying out the treatment process, respectively.

Claims (1)

[Claims] Organic wastewater is subjected to biological treatment using activated sludge, and purified water is obtained by separating activated sludge from the biologically treated treated water by ultrafiltration. A wastewater treatment method in which an inorganic flocculant is mixed into treated water before sludge separation, and COD in the treated water is adsorbed to activated sludge flocculated by the inorganic flocculant.