JP2547269B2 - Treatment of wastewater containing phosphorus compounds - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for purifying waste water containing a phosphorus compound by wet oxidation in the presence of a solid catalyst. Specifically, a treatment that enables stable long-term wastewater treatment by making the catalyst less susceptible to the action of phosphorus catalyst poisons during wet oxidation treatment of wastewater containing phosphorus compounds in the presence of a solid catalyst. Concerning the law.

(Prior Art) As a wastewater treatment method, a biochemical method called an activated sludge method and a wet oxidation method called a Chimmerman method are known.

As the wet oxidation method, a method using various oxidation catalysts to increase the reaction rate has been proposed.

On the other hand, in recent years, eutrophication due to phosphate has progressed remarkably in lakes and marshes, which has become a big problem. The legally strict drainage standard for phosphorus is about 8 ppm, and as a countermeasure for this, various phosphorus compound removal methods such as coagulation sedimentation method, biological treatment method, crystallization method and adsorption method have been proposed. There is.

Further, when the wastewater containing a phosphorus compound is subjected to wet oxidation treatment in the presence of an oxidation catalyst, the treatment efficiency decreases with time because phosphorus covers the active sites adsorbed on the catalyst surface, and finally the catalyst is There is the problem of phosphorus poisoning that it will be deactivated.

Prior to the wet oxidation treatment in the human waste treatment method, a treatment technology has been proposed in which magnesium ion supplying agent is added as a pretreatment step to human urine, and phosphoric acid is separated and removed as NH ₄ MgPO ₄ precipitate and then wet oxidized. (JP-A-63-97
No. 300 bulletin). This technology is an effective means for wastewater in which phosphoric acid exists in the state of ions such as phosphorylation such as PO ₄ ³⁻ and HPO ₄ ²⁻ , but magnesium ions can be converted into all phosphorus compounds. It does not always react. Further, when treating wastewater containing solids such as excess sludge, the phosphorus compounds contained in the solids do not react with magnesium ions, so it is difficult to separate and remove the phosphorus compounds as precipitates. Even if solid matter is separated by pretreatment, it is not possible to treat the COD component in the excess sludge that is present at the same time as the solid matter, and when treating this COD component, only for this treatment. Since secondary and tertiary treatments are further required, separation and removal of wastewater containing excess sludge and the like by pretreatment becomes very complicated in the process and is not preferable in terms of cost.

(Problems to be Solved by the Invention) Accordingly, an object of the present invention is to provide a method for efficiently treating wastewater containing a phosphorus compound for a long period of time using a wet oxidation reactor filled with a solid catalyst.

(Means for Solving the Problems) As a result of intensive studies to solve the above-mentioned problems, the present inventors have found that when waste water containing a phosphorus compound is subjected to wet oxidation treatment in the presence of an oxidation catalyst. It has been found that the following excellent effects can be obtained by previously adding metal ions of Na (I) ions and / or K (I) ions to the wastewater.

That is, according to the present invention, when treating wastewater containing a phosphorus compound, metal ions of Na (I) ions and / or K (I) ions are added to the wastewater containing a phosphorus compound in advance, and then the wet catalyst is filled with a solid catalyst. A method for treating wastewater, which comprises performing a wet oxidation treatment using an oxidation reactor at a humidity of less than 370 ° C. and under a pressure at which the wastewater holds a liquid phase while supplying a gas containing oxygen.

More specifically, the addition of the above metal ions causes the phosphate ions to react with these substances, for example, as shown in the following formula.

3Na ⁺ ＋ PO ₄ ³ → → Na ₃ PO ₄ 3K ⁺ ＋ 2PO ₄ ³ → → K ₃ PO ₄ On the other hand, phosphate ions are adsorbed on the catalyst surface and cause a decrease in activity because the phosphorus component is PO ₄ ^3- , HPO. _This is a phenomenon that occurs when existing in the ionic state of phosphoric acid such as ₄ ^2- . The former reaction, that is, the affinity between the metal ion and the phosphate ion is stronger than the adhesion reaction of the latter, that is, the affinity between the carrier and the phosphate ion, so that the carrier reaction causes the carrier phosphate ion to be attached. It has the effect of preventing and further removing phosphate ions adhering to the carrier. Therefore, the catalyst passes through without being adsorbed. Further, when treating wastewater containing solid matter such as sludge, the phosphorus compound contained in the solid matter undergoes a solubilization reaction under wet oxidation conditions to produce phosphate ion, but Na (I) ion, K ( I) When ions or the like are allowed to exist in the waste water, the adsorption of phosphorus on the catalyst is suppressed by the effect of the ions.

Therefore, by adding the metal ion described above to the wastewater in advance, it is possible to maintain stable catalytic activity for a long period of time.

Further, in the present invention, it is preferable that the metal ions added to the wastewater in advance are added before the temperature of the wastewater is raised.

Examples of the Na (I) ion and / or K (I) ion to be added include sodium hydroxide, sodium nitrate, sodium nitrite, sodium carbonate, sodium hydrogen carbonate,
Any of water-soluble salts of potassium hydroxide, potassium nitrate, potassium nitrite, potassium carbonate, and potassium hydrogen carbonate may be used, but sodium hydroxide and potassium hydroxide are preferably used.

The injection rate of metal ions of Na (I) ions and / or K (I) ions to be added to the wastewater is 1 or more in an equivalent ratio with respect to the phosphorus concentration in the wastewater (including the concentration in the solid content). , Preferably 1.1 to 5.

As the catalyst according to the present invention, carriers such as titania, silica, zirconia, alumina, activated carbon, and diatomaceous earth which are generally used for wastewater treatment can be used. In particular, since titania easily binds to phosphorus and is easily affected by phosphorus poisoning, the method according to the present invention is particularly effective for a carrier containing titania. Alternatively, the titania and titania-silica carriers have heat resistance and are therefore preferable for use in the present method.

Specifically, titania, titania-silica, titania-zirconia, and other carriers, manganese, iron, cobalt, nickel, tungsten, copper, cerium, silver, gold,
A metal which is a catalytically active element such as platinum, palladium, rhodium, ruthenium and iridium or a compound thereof insoluble or sparingly soluble in water, for example, an oxide, chloride or sulfide supported thereon is used.

The catalyst composition is 75 to 99.95% by weight, preferably 85 to 99.9% by weight of the carrier, and 0.05 to 25% by weight, preferably 0.1 to 15% by weight of the metal of the catalytically active component or a compound thereof.
It is in the range of% by weight. Of the catalytically active component elements, manganese, iron, cobalt, nickel, tungsten, copper, cerium and silver are preferably used as compounds of 0.
-15% by weight, and the amount of platinum, palladium, rhodium, ruthenium, and iridium used is 0-5
% By weight (however, the total amount of both is 0.1 to 15% by weight). Further preferred is a catalyst comprising the platinum group metal supported on a titania-zirconia carrier. In particular, 20 to 90 mol% of titania and zirconia
When a binary composite oxide or a mixture of 10 to 80 mol% is used, the activity and the hot water resistance, acid resistance and durability are excellent.

In addition, the shape of the catalyst carrier, pellet, spherical,
Honeycomb-like, ring-like, etc. can be used, but when treating wastewater containing suspended matter such as excess sludge, solids, sedimentation and the like may cause blockage in the catalyst layer, Honeycomb is particularly preferred.

As the wet oxidation reactor according to the present invention, a normally used single-tube cylindrical reactor, depending on the wastewater to be treated,
A multitubular reactor is used.

Further, in order to maintain the liquid state of the waste water, the reaction temperature is set to a temperature lower than 370 ° C. and at a pressure higher than the pressure for maintaining the liquid state at the temperature.

Oxygen-containing gas is used in the reaction, but inexpensive air is preferable except for special cases such as downsizing of the apparatus.

 Next, the present invention will be described in more detail with reference to examples.

The present invention is not limited to these examples unless it goes against the spirit of the present invention.

Example 1 FIG. 1 is a schematic diagram of an apparatus for treating wastewater containing a phosphorus compound according to the present invention. Reactor 1 used
The inner diameter of the tube is 50 mm and the tube length is 10 m.
A 6 mm long pellet catalyst (pt 0.5 wt% supported on a titania-zirconia carrier) was packed to a catalyst layer length of 8 m.

COD (C that contains phosphorus compounds (phosphoric acid equivalent H ₃ PO ₄ 600ppm))
r) A sodium hydroxide solution was added by a pump 4 to a wastewater line 10 through which a wastewater having a concentration of 40 g / l flows.

On the other hand, air was pressurized by the compressor 9, mixed with wastewater supplied from the wastewater supply pump 3, preheated by the heat exchanger 2, and then supplied to the reactor 1.

The wastewater treated in reactor 1 is discharged from line 12,
After being cooled by the heat exchanger 2, the gas was supplied to the gas-liquid separator 5, where it was separated into harmless gas and water. In the gas-liquid separator 5, the liquid level controller LC detects the liquid level and operates the liquid level control valve 6 to maintain a constant liquid level, and the pressure controller PC detects the pressure to detect the pressure level. 7 is operated to maintain a constant pressure.

At this time, the processing conditions in the reactor 1 are as follows.
0 ℃ and reaction pressure 75kg / cm ² G, wastewater supply 30l / Hr
The amount of sodium hydroxide solution added to the wastewater in advance was 6,500 ppm, the supply amount was 5 l / Hr, and the air amount was 4,800 Nl / Hr. As a result, the COD reaction rate was 99%, and no decrease in the COD reaction rate was observed even after continuous operation at 2,000 hours.

Comparative Example 1 COD (C which contains phosphorous compound (phosphoric acid equivalent H ₃ PO ₄ 600ppm))
r) Continuous operation was carried out under the same treatment conditions using the same apparatus used in Example 1 without adding metal ions to the wastewater having a concentration of 40 g / l in advance.

 Table 1 shows the change over time in the COD reaction rate.

Example 2 Phosphorus compound (phosphoric acid equivalent H ₃ PO ₄ 600 pp according to Example 1)
m) COD (Cr) containing 40g / l flowing wastewater line 10
The potassium hydroxide solution was added to pump 4.

Continuous operation was carried out under the same treatment conditions except that the concentration of the potassium hydroxide solution was 9,200 ppm and the supply amount was 5 l / Hr.

Under these conditions, the COD conversion was 99%, and no decrease in COD conversion was observed even in continuous operation at 2,000 Hr.

(Effect of the invention) As described above, according to the present invention, the affinity between phosphate ions and the carrier is suppressed by adding metal ions to the wastewater containing the phosphorus compound in advance, and the phosphate ions adhere to the carrier. It is also possible to prevent this, and to remove the phosphate ions attached to the carrier.

Therefore, it is possible to realize stable wastewater treatment for a long time with respect to wastewater containing a phosphorus compound.

[Brief description of drawings]

FIG. 1 is a flow sheet showing an embodiment of the present invention. 1 …… Single tube cylindrical reactor 2 …… Heat exchanger 3 …… Waste water supply pump 4 …… Sodium hydroxide solution supply pump 5 …… Gas-liquid separator 6 …… Liquid level control valve 7 …… Pressure 〃8 …… Air supply line 9 …… Compressor 10 …… Waste water supply line 11 …… Sodium hydroxide solution supply line 12 …… Treatment liquid line

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Kunio Sano Inventor, Kunio Sano 1 992 Nishi-oki, Kinohama, Aboshi-ku, Himeji-shi, Hyogo Pref.

Claims (2)

(57) [Claims] 1. When treating wastewater containing a phosphorus compound,
Using a wet oxidation reactor in which metal ions of Na (I) ions and / or K (I) ions were added to the wastewater containing phosphorus compounds in advance, and then a solid catalyst was used for the temperature less than 370 ° C.,
A method of treating wastewater, which comprises subjecting the wastewater to a wet oxidation treatment under a pressure that maintains a liquid phase while supplying a gas containing oxygen. 2. The method for treating wastewater according to claim 1, wherein the solid catalyst is a catalyst containing an oxide containing titania as a carrier component.