JPH02135190A - Treatment of waste water containing phosphorus - Google Patents

Abstract

PURPOSE:To efficiently remove phosphorus compds. in waste water and to also remove iron ions by adding a phosphorus compd. fixing agent to the waste water under acidic conditions to make the phosphorus compds. insoluble, separating the compds., neutralizing the remaining waste water and carrying out filtration with a membrane. CONSTITUTION:A phosphorus compd. fixing agent 3 such as ferric sulfate or iron chloride is added to waste water 1 contg. phosphorus such as night soil or waste water discharged by processing marine products under acidic conditions to make phosphorus compds. insoluble. The raw water is then sent to a settling and separating vessel 8, where the insoluble compds. are settled and separated. The remaining raw water is neutralized by adding NaOH 5 in a neutralizing vessel 13 to deposit iron ions as iron hydroxide. The raw water is further sent to a separating apparatus 15 provided with a membrane. In the apparatus 15, suspended solids (SS) having a division mol.wt. or above are filtered off and treated water 22 is separated from a concd. liq. The COD and BOD of the waste water contg. phosphorus are reduced, SS, phosphorus compds., etc., are removed at a high rate and the waste water is treated at a low running cost because no iron ions flow out.

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention relates to a method for advanced purification of wastewater containing phosphorus compounds, such as human waste, fishery processing wastewater, domestic wastewater, sewage, or industrial wastewater, and in particular, to It has a high removal rate of oxygen demand (hereinafter referred to as COD), biological oxygen demand 1i (hereinafter referred to as BOD), suspended solids (hereinafter referred to as SS), phosphoric acid, etc. The present invention relates to a treatment method that substantially eliminates the outflow of iron ions.

<Prior art and its problems> Conventionally, as a method for treating wastewater highly contaminated with organic matter, etc., the method has been to dilute it with water and then treat it by an activated sludge method. Furthermore, advanced wastewater treatment technology has been developed due to the need to reuse sewage and industrial wastewater.

There are two types of advanced treatment technologies for sewage and wastewater. This is a method that combines precipitation generation and precipitation removal using an inorganic flocculant such as slaked lime or ferrous chloride. Physicochemical treatment methods can process various substances to be treated and can perform advanced treatment, but they require complicated treatment steps and increase the size of the equipment, and they do not necessarily remove substances to low concentrations. There are some objects to be processed that are not necessary and it may not be economical.

For this reason, methods are being considered that combine various treatment methods depending on the wastewater to be treated.

To process human waste, after diluting it, we perform the nitrification and denitrification activated sludge method, which is a biological treatment method, to remove BOD and nitrogen, and then add sulfuric acid bread soil to the treated water to remove the remaining phosphorus and carbon.
Methods are being used to remove OD, chromaticity, and SS.

However, flocculation treatment using sulfuric acid bread soil consumes a large amount of flocculant, and disposal of the flocculated sludge that is generated also poses a major problem.

In addition, in recent years, the presence of phosphoric acid has become a major cause of eutrophication, and the eutrophication of lake and river waters has resulted in water quality becoming foul-smelling, and the discharge of phosphoric acid-containing wastewater into closed sea areas has become a cause of red tide. Such phosphoric acid can be removed by advanced treatment using a reverse osmosis membrane, but this requires equipment costs and expenses. For this reason, the mainstream methods of dephosphorization in human waste, sewage, and industrial wastewater treatment methods include adding ferrous salts in the aeration stage to precipitate phosphoric acid as iron salts, and adding ferrous salts in the aeration stage to precipitate phosphoric acid as iron salts. A method of precipitation treatment by adding a ferrous salt and a method of using an aluminum salt in place of the iron salt are known.

The present inventors treated waste water by coagulating and precipitating phosphoric acid with FeCl3 and then performing solid-liquid separation through membrane filtration. In this method, phosphoric acid can be efficiently removed simply by carrying out the aggregation reaction at pH 4 to 5, followed by membrane treatment, and furthermore, COD
It was also found that the operating cost of the active adsorption tower in the final step could be reduced as well.

However, with this method, iron ions added as a flocculant and ferrous ions generated during the flocculation process are not removed, resulting in a decrease in membrane permeation flow rate (hereinafter sometimes referred to as flux) during membrane treatment.
The problem was that it was not stable.

<Problems to be Solved by the Invention> The purpose of the present invention is to solve the problems of the prior art, to not only efficiently remove phosphorus compounds, but also to sufficiently remove iron ions and further improve the quality of treated water. An object of the present invention is to provide a method for treating phosphorus-containing wastewater that causes less decrease in flux during membrane filtration.

<Means for Solving the Problem> That is, the present invention is a method for treating wastewater containing phosphorus compounds, the method comprising the following steps (a) to (d). I will provide a.

(a) A step of adding a phosphorus compound fixing agent under acidic conditions to produce a phosphorus compound as an insoluble substance.

(b) A step of separating the insoluble matter.

(C) Neutralizing the liquid from which the insoluble substances have been separated and removed.

(d) A step of separating the neutralized liquid into a concentrated liquid and treated water by membrane filtration.

Here, a method for treating phosphorus-containing wastewater in which the acidic conditions in step (a) are pH 3 to 5 is preferred.

Further, a method for treating phosphorus-containing wastewater in which the wastewater containing phosphorus compounds has undergone a biological treatment process as a pretreatment is preferable.

Furthermore, a method for treating phosphorus-containing wastewater in which at least a portion of the concentrate membrane-filtered in step (d) is returned to the insoluble matter generation step in step (a) is preferable.

Furthermore, it is preferable to decolorize the treated water obtained in step (d) using activated carbon.

The present invention will be explained in detail below.

The wastewater to which the method of the present invention is applied is not particularly limited as long as it contains phosphorus compounds, but it is wastewater containing organic substances such as human waste, fishery processing wastewater, food wastewater, sewage, and factory wastewater. The wastewater is subjected to biological treatment if necessary, and then the following steps (a) to (d) are performed. In biological treatment, microorganisms such as anaerobic bacteria, aerobic bacteria, and suitable anaerobic bacteria are introduced into wastewater together with activated sludge, and appropriate treatments such as aeration and stirring are performed.

- Step (a): A step of adding a phosphorus compound fixing agent under acidic conditions to produce a phosphorus compound as an insoluble substance.

The process of making phosphorus compounds insoluble is to immobilize them by adsorption or chemical reaction by adding contact particles, powder, or precipitate to the phosphorus compounds in the wastewater. In some cases, it is prevented from flowing out of the system, and in other cases, a compound is added and reacted with a phosphorus compound to form an insoluble precipitate. The phosphorus compound fixing agent to be used is not particularly limited as long as the phosphorus compound is an insoluble phosphorus-containing material, but powders and granules such as phosphate rock, apatite, bone char, alumina, (ac12. aluminate, F
Examples include chemical substances such as e-salts, Fe salts are preferred, and ferric salts are particularly preferred, especially pesO4 and FeCl3. The concentration of the phosphorus compound fixing agent is F with respect to the total phosphorus concentration.
The concentration of metals such as e, AI, Ca, etc.
a)/total phosphorus = 1.5 to 3 molar ratio is preferable.

The acidic conditions are preferably pH 3 to 5, more preferably 4 to 4.5.

When FeCl3 is used as a phosphorus compound fixing agent, acidic conditions are adjusted by adding an alkali such as caustic soda or caustic potash, but in some cases, an acid such as nitric acid, hydrochloric acid, or sulfuric acid is added as necessary. You may.

The apparatus for carrying out step (a) may be either a batch type or a continuous type, but a mixing tank 5 equipped with an agitator 6 illustrated in FIG. 1 is preferable.

The time and temperature for carrying out step (a) vary depending on the type and degree of pollution of the wastewater to be treated and are not limited. Preferably, the temperature is 10 to 120 minutes and 15 to 50°C.

Step (b); step of separating the insoluble matter obtained in step (a).

Step (b) involves separating the insoluble phosphorus-containing precipitate obtained in step (a) and removing it from the system (not particularly limited as long as it is a step. Pressure separation method, ultrafiltration separation method, filtration separation method) Preferably, a gravity separation tank 7 equipped with a stirrer as shown in FIG. and discharged from the system through the discharge line 13.

The supernatant obtained in step (b) is COD.

It is preferable to set it to 80ff1g72 or less, SS, and 90■/Q or less. The residence time in the separation tank 7 varies depending on the type of wastewater used, but is preferably 2 to 10 hours.

If necessary, a flocculation aid such as an anionic or nonionic polymer may be added to improve the flocculation of insoluble materials, but in the method of the present invention, sufficient precipitation separation can be achieved without the use of any flocculation aid. One of its characteristics is what it can do.

Step (C): a step of neutralizing the supernatant liquid from which insoluble matter has been separated and removed in step (b).

An alkaline neutralizing agent such as NaOH or KOH is added to the liquid obtained in step (b) to make it neutral to pH 6-8.

The treatment temperature is preferably 15 to 70°C. Preferably, the chest 1
A neutralization tank 9 illustrated in the figure is used.

In the method of the present invention, step (a) is carried out under acidic conditions, and as a result of the redox reaction between ferric ions, which conventionally precipitated as ferric hydroxide under neutral conditions, and COD, ferrous iron is produced. Ions are generated, but since the process involves a neutralization process, the solubility is high and the concentration of Fe2° is reduced, allowing advanced treatment wastewater to be replaced without containing ferrous ions.

Step (d): A step of filtering the liquid neutralized in step (C) through a membrane to separate it into a concentrated liquid and treated water.

Membrane filtration is performed using a permeable membrane having a molecular weight cut-off of 10.000 to 100.000 under pressure conditions of 1.0 to 5.0 kg/am'. As the material of the permeable membrane that can be used, resins such as aromatic polyamide, polysulfone, polybenzimidazole, nitrile, polyvinyl halide, and polyvinylidene halide are used, and preferably polyacrylonitrile, polyvinylidene halide, etc. Polyvinylidene fluoride is good.

The format of the membrane filtration device is not particularly limited, but a rod-type membrane module, a tube-type membrane module, a hollow-tube membrane module, a winding membrane module, a hollow fiber membrane module, a flat membrane module, etc. are used. However, tubular and hollow tubular membrane modules are preferred because they are easy to physically clean. More preferably, a flat membrane type module illustrated in FIG. 1 is preferred.

Since the method of the present invention has step (b), step (d)
The rate of decrease in flux during membrane filtration is small (even if wastewater is continuously treated, a value of 2001/rr?hr or higher can be maintained for more than two weeks.

Furthermore, at least a portion of the concentrated liquid separated from the treated water in step (d) is preferably returned to step (a) and/or step (C).

This return process can reduce the amount of neutralizing agent required in the neutralization process (c).

The treated water treated by the method of the present invention described above may be further subjected to adsorption treatment if necessary. The adsorption treatment can be performed using an organic adsorption resin or an inorganic adsorbent such as activated carbon, zeolite, diatomaceous earth, or acid clay.

One of the preferred embodiments of the present invention will be described with reference to FIG.

°The flowchart shown in FIG. 1 shows that a mixing tank 6 equipped with an agitator 7, a sedimentation separation tank 8 equipped with scraping blades 9, a neutralization tank 13, and a membrane separation device 15 are arranged in this order to form a conveyor line. The processing line for phosphorus-containing compounds, which is continuously connected at 14, is installed. Separately, a raw water tank 2, a ferric chloride tank 3, and a caustic soda tank 4 are provided, and each of these has a carry-in line 26 equipped with a pump 25, and the carry-in line 26 is connected to the mixing tank 6.
The raw water 1, ferric chloride, and caustic soda can be supplied to the mixing tank 6, respectively.

Further, if necessary, a caustic soda tank 5 is provided, and the caustic soda tank 5 has a carry-in line 26 similarly equipped with a pump 25, and is arranged so as to be able to supply caustic soda to the neutralization tank 13. Caustic soda may be supplied to the neutralization tank 13 from the caustic soda tank 4 without providing the caustic soda tank 5.

Raw water 1 is introduced into a raw water tank 2, and in the raw water tank 2, the water level of the raw water is kept constant by a float 21.

The raw water 1 in the raw water tank 2 is transferred to the carry-in line 2 by the pump 25.
6 and enters the bottom of the mixing tank 6.

Separately, ferric chloride and caustic soda are appropriately supplied into the mixing tank 6 from the ferric chloride tank 3 and the caustic soda tank 4, respectively.

Raw water, ferric chloride, and caustic soda are stirred and mixed by a stirrer 7 in a mixing tank 6, and are supplied while being adjusted to maintain a predetermined pH value. In the mixing tank 6, the phosphorus compound contained in the raw water reacts with ferric chloride to become an insoluble substance.

The raw water that has been mixed in the mixing tank 6 for a certain period of time and contains phosphorus compounds as insoluble substances is spilled into the sedimentation separation tank 8 via the conveyance line 14. In the raw water left still in the sedimentation tank 8, insoluble substances are precipitated and separated by gravity, and the insoluble substances accumulate at the bottom of the sedimentation separation tank 8.

If insoluble matter sticks to the bottom of the sedimentation tank 8, it is difficult to separate and remove it, so the scraping blade 9 scrapes off the insoluble matter stuck to the bottom and guides the insoluble matter to the discharge bottom of the sedimentation tank 8. The bottom of the sedimentation separation tank 8 is connected to a discharge line 11 and a valve 10.
through valve 1 to remove insoluble matter accumulated at the bottom.
0 is opened and the concentrated liquid 12 is discharged out of the system through the discharge line 11.

Insoluble substances include SS aggregates and the like in addition to insoluble phosphorus compounds.

The raw water from which the precipitate has been separated is conveyed to the neutralization tank 13, where it is neutralized to a predetermined pH with caustic soda introduced from the caustic soda tank 5. Through the neutralization treatment, iron ions are precipitated as iron hydroxide.

The neutralized raw water is sent to the membrane separation device 15 via the pump 25 by the conveyance line 14. Raw water is membrane separator 1
By passing through the separation membrane in 5, substances exceeding the molecular weight cutoff are filtered out and become treated water 22, which is conveyed to the outside of the yarn through a treated water line 19.

A flow meter 20 is provided in the treated water line 19, and the amount of permeated liquid from the membrane separator 15 can be read at all times.

Further, the permeated liquid from the membrane separation device 15 exceeding the amount of liquid flowing into the neutralization tank 13 from the conveyance line 14 is returned to the neutralization tank 13 via the float 21 provided in the neutralization tank 13.
The liquid level is kept constant.

The membrane separator concentrate separated from the treated water 22 by the membrane separator 15 passes through the return line 16 and partially enters the neutralization tank return line 17 and is returned to the neutralization tank 13.
It enters the mixing tank return line 18 and is returned to the mixing tank 6. By returning this high pH liquid, the amount of caustic soda used in the entire system can be saved.

<Example> The present invention will be specifically explained below using Examples.

The invention is not limited to the examples.

(Example 1) Raw water having the water quality shown in Table 1 was treated using the apparatus shown in FIG.

The test conditions and measurement conditions were as follows. The molecular weight (atomic weight) of the compound used was calculated using the following value.

P H30,97F e CR3; 162.2F
e; 55.85 F e (OR) 3; 1o
tiJC2H35,5F e PO4; 150.82
0; 16 NaOH; 40■, Test conditions 1/1 Raw water raw water feed amount 37.8-51.6 Q/h standard value 4
5.02/h 1.2 Mixing tank volume 50Q Residence time 1.11h Operational pH control at pH 4°0 to 4.5 is 682g of flaked caustic soda
Dissolved in tap water 2012, 0.48-0.68g/h
Quantitative feed was carried out.

Ferric chloride feed amount Total phosphorus content (hereinafter sometimes abbreviated as total P) in raw water is 90
2/I2 and ferric chloride was fed at a Fe/total 2 molar ratio of 2. Ferric chloride is 38% product (40'Be') 2,
785 g was diluted with 202 g of tap water and used.

Total phosphorus feed amount; 45 x 9 (1/30.97-
13G, 8+*mo 'j /hFe/total P molar ratio;
2.0 FeCQ3 feed amount; 130.8 x 2.0S2
6L, 5mmo2/h=42.4g-FeC
23/h -111,6g-38%FeCR3/h1.3 Sedimentation tank cross-sectional area 0.29fi volume (1,253m' Area load 45X 10-310.297=(1,15
2m”/n? -h depth 3.64cm/day Residence time 0.235x 103/45-5.62h Scraping blade rotation speed 1.15rphOuter diameter 600■ Tip peripheral speed 2.16m/h Inlet suspended solids Concentration Concentrated liquid Suspended solid concentration Concentrated liquid withdrawal amount Suspended solid concentration Removal rate Outlet suspended solid concentration 1.4 Neutralization tank pH was targeted at 6.5 to 7.5. pH of coagulation mixing tank
The control was carried out by dissolving 40 g of caustic soda flakes in tap water 102 and feeding the solution at a rate of 0.27 to 0.75 I2/h.

Inlet suspended solids concentration concentration magnification Neutralization tank Suspended solids concentration Return amount to mixing tank Hold up 5 Membrane separator flat membrane type module; UFP-102S2P O, 22
Ia 3■72 10 times 730mg/R 4,82/h 730■/2 12.000mg/Q 2,812/h 90% 73■/2 Between surfaces 3. Om EFT frame dicoint operating conditions; pressure, inlet 2.4kg/cm' outlet 1.
6kg/cnl" Linear velocity 2.5m/s Membrane; IRIS-3065 manufactured by Loos-Boulin (Material polyvinyritine fluoride) Molecular weight cut off 40.000 and 70.0002, Analysis method 2.1 Total phosphorus content Ammonium molybdate method (Based on Sewage Testing Law) 2.2
C0D 100°C potassium permanganate method (JIS K-01
2.3 Total Fe amount 0-phenanthroline method (based on JIS K-0102)
2.4 Suspended solids (SS) concentration ■ 500 mg/Q-acofloc A100 in sedimentation separation tank treated water sample 500-
1- was added thereto, and flocculation treatment was carried out for 10ml1n under weak stirring. This was analyzed based on J[SK-010214.1 suspended solids. The filter material is Toyo Roshi Glass Filter G520
It was used.

■ Sedimentation separation tank Take a sample of concentrated liquid 20- to a 50-centrifuge tube and spin at 3,000 rpm, 2
The mixture was centrifuged at 0 mL of water, the supernatant was decanted, and the precipitate was resuspended in 30 mL of distilled water. After that, it was centrifuged again, dried at 105℃ for a day and night, and then weighed.
It was a minute.

■ 500mg/2-Acofloc A to sedimentation tank sample 500+nff
1001- was added and flocculated for 10 min under weak stirring. After standing for 10ml, the supernatant was decanted and the precipitate was transferred to a 50-centrifuge tube. After this, SS was measured by the same operation as in Section 0.

■ Mixing tank The same operation as in section ■ was performed, but quantitative measurements were difficult due to floating flocs and poor formation. Therefore, the theoretical value was calculated by calculation. The calculation formula is shown below.

CFLII (0 cho-ρX 150.28) I (
QFε-QT-P)X 106.8+ +(Cup
X QHi+)/ (QRir+ (b+u)CFL
; Mixing tank suspended solids concentration (■/l2)Cup; Neutralizing tank suspended solids concentration (mg/Q) Kano-ρ; Total phosphorus feed amount (m+1off/h) QFe; Ferric chloride feed amount (!Q/ h) Qpv ; Amount of raw water fed (!2/h) QHw ; Amount returned to the mixing tank (2/h) 2.5 Using a chromaticity absorption photometer, measuring wavelength 410 nm, cell 10 mm
Measured at

(Comparative example) As a comparison, the sedimentation separation tank 8 and the neutralization tank 13 (which have a concentration tank 27 with the same capacity as the neutralization tank, and the mixing tank return line 18 from the membrane separation device 15 to the mixing tank 6) The same process as in Example 1 was carried out using the apparatus shown in FIG. 2, which is the same apparatus as in FIG. 1 except for the following conditions.

Raw water quality: Total phosphorus concentration 80mg/12COD LQ
Omg/R FeCI2a/total phosphorus=1. Total phosphide 1aOH/FeC23 = 1.5 mol P O,
114mo St /hFe C230,17mo
Q/h=a27.7g/hN ao H0,25?
+*o2/h-1o, 3g/h permeable membrane outflow 2
002/*2.h or more The outflow at each location and the measured suspended solids (SS) concentration are shown in Figure 2.

3. Test results and considerations 3.1 Raw water quality The raw water quality during the test period varied depending on the operating conditions. p
Table 1 shows the highest, lowest, and average H, COD, total phosphorus content, and chromaticity.

Table 1 Raw water quality 3.2 Amount of caustic soda added to the mixed layer The amount of caustic soda added to the mixed layer varied depending on the mixing tank pH 1 raw water QH and Fe/total 2 molar ratio. The relationship between raw water pH and NaOH/Fe molar ratio was measured, and the results are shown in FIG.

The results in Figure 4 are shown by the following formula, and the average pH of the mixing tank is 4.2.
0, a high correlation with a correlation coefficient r=0.908 was obtained.

NaOH/Fe (molar ratio')-O, 334X raw water pH
+4.2L6rlIQ, 90g 3.3 Average area load during the settling tank test period 4.17m/day.

Under conditions of an average residence time of 4.94 h, an average removal rate of suspended solids concentration of 89.14% was obtained.

In addition, the average suspended solids concentration of the sedimentation separation tank concentrate is tz, o
It was 3omg/Q. The concentrated liquid was easy to handle, and no problems such as sedimentation, solidification, or blockage of pipes were observed.

3.4 Neutralization tank The temperature of the neutralization tank was not controlled. Therefore 15.4~
It fluctuated at 42.1°C, with an average temperature of 32.2°C. The temperature dependence coefficients were el and o24 in the following equation, which were almost the same values as in the pure water system.

FIUX"-FIUXt2x (1+(tL-t2)X
klK-0,024 From the above results, it is believed that higher flux levels can be obtained by operating at higher temperatures.

Amount of Caustic Soda Added for pHX Adjustment The required amount of caustic soda to adjust pH 4 of the treated water from the sedimentation separation tank to pH 7 was 44.7 mmoR/h on average.

This amount corresponded to about 10% of the amount added in the mixing tank.

The total amount of caustic soda added in the mixing tank and neutralization tank is changed to NaOH/
The Fe molar ratio is shown in Fig. 5.

From Figure 5, NaO
The H/Fe molar ratio was approximately 2.1.

In addition, the following relational expression is obtained from FIG. 5, and the correlation coefficient r-0
,876.

Total NaOH/Total Fe = -0,270X raw water pH H+
3.9543.5 Membrane separator/UF flux A flux of 200 Q/rd, h or more was stably obtained for 16 days or more. The measurement results of the flux amount are shown in Figure 3.

The film deposits, which cause a decrease in flux, are easily peeled off, and a significant flux recovery was observed by temporarily stopping module operation. Intermittent operation using level control of the neutralization tank was considered effective in improving flux. In the test, the system was paused once in the morning and once in the afternoon.

Flux change over time for each membrane grade IRIS-3065, molecular weight cutoff 40.000 and 70,
Figure 6 shows the flux change over time for the 000 membrane. In this data, the molecular weight cut off is 40.000 on the high pressure side, and 70.000 on the high pressure side.
．． Goo is the low pressure side.

The large variation in the initial stage of the test in FIG. 6 is due to the fact that the plate flux was measured before and after the temporary stop operation.

From this result, a membrane with a molecular weight cutoff of 40,000 has To, 0
It was found that higher flux was obtained compared to 00.

However, after washing with the chemical solution, almost no difference was observed.

The chemical cleaning module was cleaned with a chemical solution. The washing conditions are as follows.

Water used: Treated water treated with the device of the present invention Pressure during cleaning: Inlet 0.5kg/c; Outlet 0.3kg/c++? Flow rate: 4.8m”/h LVJ, 4m/h
Pressure during s flux measurement: Inlet 2.3kg/am' Outlet 1.7kg#/Flow rate: 8.5m'/h LVx2.5m
/5(1)0.1mo2/Q-Hydrochloric Acid Cleaning It was assumed that the cause of the decrease in flux was the deposition of ferric hydroxide, so cleaning with 0.1moQ/2-HCl was performed. However, the flux after cleaning was 4527h (205Ω/m2
．． Almost no effect was observed in h).

(2) 600cm/9-Sodium hypochlorite washing After replacing the hydrochloric acid cleaning solution, 600cm 151-Sodium hypochlorite washing was performed. Since the pH of the washing water after replacement was approximately 4, the concentration of the washing solution was determined from the amount required to bring the pH to 8.

7lux after cleaning is 125ff/h (568Q/m2
．． It recovered to h). From this, it was found that the cause of the decrease in flux was organic matter such as residual COD.

(3) Cleaning with 600mg/Q-sodium hypochlorite alone Based on the above results, a cleaning test with 600mg/R-sodium hypochlorite alone was conducted. As a result, the flux after cleaning was 85 Q/h (386 fl/m2.h). Compared to when it was used in combination with hydrochloric acid, the decrease was 32%, but the initial flux in the demonstration was almost unchanged.

(4) With the UF membrane (7) Based on the cleaning result that exceeds the COD rejection rate, we believe that COD inhibition is occurring with the UF membrane, and measure the COD of the sedimentation tank treated water, neutralization tank concentrate, and membrane separation device treated water. did.

The results are shown in Table 2.

Table 2 COD inhibition rate of UF membrane As shown in Table 2, an average of 12.8% COD inhibition was observed with the UF membrane. The molecular weight cutoff of IRIS-3065 used was 40,000 to 70,000, which is presumed to be due to the precoat effect since it is a flox coexisting system.

From the above cleaning test results, it was found that the cause of the decrease in UF flux was largely due to the COD components contained in the sedimentation separation tank treated water. Therefore, if the amount returned from the neutralization tank to the mixing tank is increased from 1/10 to about 115, an improvement in furanoges can be expected.

In addition, it is possible to maintain a flux of 200127n (, h) or more with chemical cleaning once or twice a month and open cleaning once every three months.

3.6 Good treated water quality was maintained throughout the treated water quality test period. However, there were times when the pH of the mixing tank increased and the COD reached 65 .mu./Q. The results are shown in Table 3.

Table 3 Treated water quality (Example) Average value: 40+ng/2 to 29+ng/ff
It declined to . This seems to be due to the effect of increasing the Fe/T-P molar ratio in the mixing tank from 2.0 to 2.4, but the inclusion of a neutralization tank with a residence time of 5 hours creates a buffering effect that improves the quality of the treated water. was considered to be more stable.

Total phosphorus concentration T-P, total iron concentration T-Fe is 0.1
An analysis value of +ng/R or less is within the analysis error range and can be safely ignored if the mixing tank pH and neutralization tank pH are properly controlled with a controller or the like.

On the other hand, in the comparative example, 2mg/
1 of dissolved iron remained.

In the comparative example, the SSa degree in the neutralization tank 13 is 20.000@
/ Q: There was no margin for the design value of UF Flavux 200ff/rd, h. In the example, S in the neutralization tank 13
The S concentration was 1.000 mg/12, which had sufficient margin for the designed value of UF flux 200 Q/d, h.

3.7 Activated Carbon Adsorption Characteristics We requested Takeda Pharmaceutical Co., Ltd.'s Chemical Products Research Laboratory to collect crosstalk data such as activated carbon adsorption of the treated water obtained in Example 1 and Comparative Example. The activated carbon grade used was W5 C-873.
It is 2.

Figure 7 shows the activated carbon adsorption isotherm data of the treated water obtained in the comparative example. From the results in Figure 7, Takeda W3C-8/32
The COD equilibrium adsorption amount is less than 1/2 compared to the Hokuetsu carbon data of 240g-COD/kg-AC used as conventional design data (7) 110g-COD/kg-ACa
t was 110 mg/12 COD.

The activated carbon adsorption isotherm data of the treated water obtained in the example is shown in FIG. As shown in Figure 8, the treated water obtained in the example had an equilibrium COD adsorption amount of 230g-COD/kg even at a low setting of 25mg/2 compared to the average COD29/Q.
-The values were almost the same as the AC and Hokuetsu carbon data.

This indicates that the activated carbon COD adsorption capacity is improved by the treatment method including the neutralization step of the present invention. Therefore, the running cost of activated carbon in the method of the present invention was reduced by the amount that the COD inlet concentration was reduced to 1/3 compared to the comparative example.

In addition, nitrogen components and the like were measured in the treated water obtained in the comparative example, the treated water obtained in the example, and the treated water obtained in the example that was further treated with activated carbon.

The results are shown in Table 4.

Table 4 shows that among the nitrogen components, evening aircraft nitrogen was 59.
0%, and 97.3% was removed by activated carbon treatment. However, it can be seen that there was almost no change in nitrate nitrogen.

・The total phosphorus concentration increased from 0.08 mg/12 to 0.20 μ/2 due to activated carbon treatment, but this is a measured value near the lower limit of analysis and cannot be described as a clear phenomenon.

The chromaticity of the activated carbon-treated water was 17 deg.

Visually, it is almost zero.

<Effect of the invention> The method for treating phosphorus-containing wastewater of the present invention is COD.

BOD, 33. The removal rate of phosphorus compounds, etc. is high (and there is virtually no outflow of iron ions, so high-level purification of wastewater containing phosphorus compounds can be performed at low running costs).

[Brief explanation of the drawing]

FIG. 1 is a flowchart illustrating the processing method of the present invention. FIG. 2 is a flowchart illustrating the conventional processing method used in the comparative example. FIG. 3 is a graph showing the change over time in the permeation flow rate (flux) of the membrane separation device obtained in the example.・Figure 4 shows the raw water pH and mixing tank NaOH used in the example.
It is a graph showing the relationship between the amounts added. FIG. 5 is a graph showing the relationship between the pH of the raw water used in the examples and the total amount of caustic soda added. FIG. 6 is a graph showing changes over time in permeation flow rate (flux) for each membrane grade obtained in Examples. FIG. 7 is a graph showing adsorption crosstalk during activated carbon adsorption treatment of treated water obtained in a comparative example. FIG. 8 is a graph showing adsorption isotherms during activated carbon adsorption treatment of treated water obtained in Examples. Explanation of symbols 1... Raw water (drainage) 2... Raw water tank 3... Ferric chloride tank 4.5... Caustic soda tank... Mixing tank... Stirrer... Precipitation separation tank ...Scraping blade...Valve...Discharge line...Insoluble matter (concentrated liquid)...Neutralization tank...Transportation line...Membrane separation device...Return line...Medium Wash tank return line...Mixing tank return line...Treated water line...Flow meter...Float...Treated water...Pump...Carry-in line...Concentrator tank UF Flu ux (1 /m”-h at 35°C) 40 tanks NaOH/FeC-+L>) Full force seindar °/Total f loss (Monoshi term 2,) FIG. ylZ$1. Example “A'rLj'L! ”4 quotient 3IL degree O
D (mg/I) F lux (1/m”-hat 35°C) F f G. 3 Lives of Husband #L Example [Accessory Calyx Al Whale- Co D; 34.2 (mg/I) COD (mg/
l

Claims (5)

[Claims] (1) A method for treating wastewater containing phosphorus compounds,
A method for treating phosphorus-containing wastewater, comprising the following steps (a) to (d). (a) A step of adding a phosphorus compound fixing agent under acidic conditions to produce a phosphorus compound as an insoluble substance. (b) A step of separating the insoluble matter. (c) Neutralizing the liquid from which the insoluble substances have been separated and removed. (d) A step of separating the neutralized liquid into a concentrated liquid and treated water by membrane filtration. (2) The method for treating phosphorus-containing wastewater according to claim 1, wherein the acidic conditions in step (a) are pH 3 to 5. (3) The method for treating phosphorus-containing wastewater according to claim 1 or 2, wherein the wastewater containing the phosphorus compound has undergone a biological treatment process as a pretreatment. (4) The method for treating phosphorus-containing wastewater according to any one of claims 1 to 3, wherein at least a part of the concentrate membrane-filtered in the step (d) is returned to the insoluble matter generation step in the step (a). . (5) The method for treating phosphorus-containing wastewater according to any one of claims 1 to 4, wherein the treated water obtained in step (d) is further decolorized using activated carbon.