JPH03275193A - Treatment of waste water containing phosphorus compound - Google Patents

Abstract

PURPOSE:To efficiently treat waste water over a long period of time by adding at least one kind of metal ion such as Ba (II) ion to the waste water and subjecting this waste water to wet oxidation treatment at a specified temp. under a specified pressure while feeding an oxygen-contg. gas. CONSTITUTION:At least one kind of metal ion such as Ba (II) ion is added to waste water and this waste water is subjected to wet oxidation treatment at <370 deg.C under such a pressurization that the waste water keeps the liq. phase in a wet oxidation reactor 1 packed with a solid catalyst while feeding an oxygen-contg. gas. Since the added metal ion reacts with phosphate ion to form slightly soluble salt, the adsorption of phosphate ion on the catalyst can be inhibited and the catalyst is hardly affected by phosphorus as a catalyst poison. Stable catalytic activity can be maintained over a long period of time and stable treatment of waste water can be carried out.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a method for purifying wastewater containing phosphorus compounds by wet oxidation in the presence of a solid catalyst.

Specifically, when wastewater containing phosphorus compounds is subjected to wet oxidation treatment in the presence of a solid catalyst, the catalyst is made less susceptible to the effects of phosphorus catalyst poison, thereby enabling stable wastewater treatment over a long period of time. Regarding the method.

(Prior Art) Known wastewater treatment methods include a biochemical method called an activated sludge method and a wet oxidation method called a Zimmerman method.

In wet oxidation methods, methods using various oxidation catalysts have been proposed in order to speed up the reaction rate.

On the other hand, in recent years, eutrophication due to phosphates has progressed significantly in lakes and marshes around the country, and this has become a major problem. Legally, the wastewater standards for phosphorus have become extremely strict at around 8 ppm.
As countermeasures, coagulation-precipitation method, biological treatment method, crystallization method,
Various methods for removing phosphorus compounds, such as adsorption methods, have been proposed.

In addition, when wastewater containing phosphorus compounds is subjected to wet oxidation treatment in the presence of an oxidation catalyst, the treatment efficiency decreases over time because phosphorus is adsorbed onto the catalyst surface and covers the active sites, and eventually the catalyst is lost. There is the problem of phosphorus being a catalyst poison that can be activated.

In a human waste treatment method, a treatment technology has been proposed in which a magnesium ion supply agent is added to human waste as a pretreatment step prior to wet oxidation treatment, and phosphoric acid is separated and removed as a NH4MgPO4 precipitate, followed by wet oxidation (Unexamined Japanese Patent Publication No. Publication No. 63-97300> This technology is based on the fact that the phosphorus component is P.
Although it is an effective method for wastewater that exists in the form of ions such as phosphoric acid such as O43-, HPo, 2-, etc.,
Magnesium ions do not necessarily react with all phosphorus compounds. Furthermore, when wastewater containing solids such as surplus sludge is treated, it is difficult to separate and remove the phosphorus compounds as precipitates because the phosphorus compounds contained in the solids do not react with magnesium ions. Even if solids, etc. are separated in pre-treatment, it is not possible to treat the COD components present in excess sludge as solids at the same time. Therefore, secondary and tertiary treatments are additionally required, so separating and removing wastewater containing excess sludge and the like in a pretreatment process becomes extremely complicated and is also undesirable from a cost standpoint.

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

(Means for Solving the Problems) As a result of extensive research to solve the above-mentioned problems, the present inventors have found that when wet oxidation treatment of wastewater containing phosphorus compounds is carried out in the presence of an oxidation catalyst. Ba(II) ions, Ca(II) ions, Mg(II) ions, and 8A are added to the wastewater in advance.
(II[) ion, Fe(In) ion and Fe(
They have discovered that the following excellent effects can be obtained by adding at least one metal ion selected from the group consisting of II) ions.

That is, in the present invention, Ba(II) ions and Ca(II) ions are added to wastewater containing phosphorus compounds in advance.
ion, Mg(II) ion, octaβ(III) ion, Fe(III) ion, and Fe(II) ion, and then filled with a solid catalyst. 3 using an oxidation reactor
A method for treating wastewater, which is characterized by carrying out wet oxidation treatment at a temperature of less than 70° C. and under a pressure such that the wastewater maintains a liquid phase while supplying an oxygen-containing gas.

More specifically, by adding the above-mentioned metal ions, the phosphate ions undergo a reaction with these substances, for example, as shown in the following formula, forming a sparingly soluble salt.

3 Ca” +2 POaE−→Ca3(PO4)z3
Mg”+2 POn3- Mg+(PO4)z^(23
"10PO43-→ 1PO4 On the other hand, the reason why phosphate ions are adsorbed on the catalyst surface and the activity decreases is because the phosphorus component exists in an ionic state such as phosphoric acid such as PO4'-, 1PO4"2, etc. As mentioned above, if phosphate ions form a poorly soluble salt, they will pass through without being adsorbed onto the catalyst. Furthermore, even when treating wastewater containing solids such as sludge, the phosphorus compounds contained in the solids undergo a solubilization reaction under wet oxidation conditions to produce phosphate ions, but Ca(II) ions, Mg(
II) When ions and the like are allowed to exist in wastewater, the ions and phosphate ions form a sparingly soluble salt, which suppresses the adsorption of phosphorus onto the catalyst.

Therefore, by adding the above-mentioned metal ions to wastewater in advance, stable catalytic activity can be maintained over a long period of time.

Further, in the present invention, it is preferable that the metal ions added to the wastewater in advance be added before the wastewater is heated. The metal ions added to this wastewater include Ba(n) ions, Ca(
II) ion, Mg(I[) ion, A# (III
) ion, Fe(II[) ion, and Fe(II) ion. Among these, it is preferable to use Ca(H) ions, which have a fast production rate of poorly soluble salts, have a low solubility of the formed poorly soluble salts, and are inexpensive.

In addition, Ba(n) ions, Ca(II) added to wastewater
) ion, Mg(II) ion, AA(III) ion, Fe(II) ion, Fe(I[I) ion, the injection rate of metal ions depends on the phosphorus concentration in wastewater (including the concentration in solid content). to the equivalent ratio of 1 or more, preferably 1.1 to
It is recommended to set it to 5.

Furthermore, in the present invention, it is also preferable to add a flocculant to the liquid after wet oxidation treatment and then perform solid-liquid separation for the purpose of removing poorly soluble salts generated by addition of the ions according to the present invention.

The flocculants are selected as appropriate depending on the properties of the wastewater to be treated, but include - sulfuric acid used for boat fishing, PAC (polyaluminum chloride), calcium compounds, magnesium compounds, polymer flocculants, and cationic surfactants. Among these flocculants, inorganic flocculants are preferably used.

This makes it possible to remove poorly soluble salts of phosphorus from the treated water, making it possible to directly discharge or reuse the wastewater after treatment.

Catalysts according to the present invention include titania, silica, zirconia, alumina, activated carbon, which are generally used for wastewater treatment,
A carrier such as diatomaceous material can be used. In particular, since titania easily binds to phosphorus and is susceptible to phosphorus poisoning, the method according to the present invention is particularly effective for carriers containing titania. Furthermore, titania and titania-silica supports are preferable for use in this method because they have heat resistance.

Specifically, manganese, iron, cobalt,
Catalytically active elemental metals such as nickel, tungsten, copper, cerium, silver, gold, platinum, palladium, rhodium, ruthenium, and iridium, or their water-insoluble or sparingly soluble compounds, such as oxides, chlorides, and sulfides. The supported one is used.

The catalyst composition is 75 to 99.95% by weight of the carrier, preferably 85 to 99.9% by weight, and 0.05 to 25% by weight, preferably 0.05% to 25% by weight of the metal or its compound as the catalyst active component element. It ranges from 1 to 15% by weight. Preferably,
Among the catalyst active component elements, manganese, iron, cobalt, nickel, tungsten, copper, cerium, and silver are used in amounts of 0 to 15% by weight as compounds, and the amounts of platinum, palladium, rhodium, ruthenium, and iridium used are metals. as O to 5% by weight (however, the total amount of both is 0.1 to 15% by weight). Furthermore, a catalyst in which the above-mentioned platinum group metal is supported on a titania-zirconia carrier is preferable. In particular, in this catalyst titania 20-9
When a binary composite oxide or a mixture containing 0 mol % and 10 to 80 mol % of zirconia is used, it has excellent activity, hot water resistance, acid resistance, and durability.

Furthermore, the shape of the catalyst carrier may be pellet, spherical, honeycomb, ring, etc., but
Slightly soluble salts such as Ca5(PO4)z exist in wastewater,
Further, when dealing with wastewater containing suspended matter such as surplus sludge, a honeycomb shape is particularly preferable since clogging may occur in the catalyst layer due to solid matter, sedimentation, etc.

As the wet oxidation reactor according to the present invention, a commonly used single-tube cylindrical reactor, a multi-tube reactor, etc. are used depending on the wastewater to be treated.

Further, in order to maintain the liquid phase state of the wastewater, the reaction temperature is set to a temperature below 370° C. and a pressure higher than the pressure that maintains the liquid phase state at this temperature.

In the reaction, an oxygen-containing gas is used, but air is preferable since it is inexpensive, except in special cases such as when making the apparatus more compact.

Next, the present invention will be explained in more detail with reference to Examples.

Note that the present invention is not limited only to these Examples.

Example 1 FIG. 1 is a schematic diagram of an apparatus for treating wastewater containing phosphorus compounds according to the present invention. The inner diameter of the reactor 1 used is 50 mm, the tube length is 10 m, and the inside of the tube has a hole diameter (equivalent diameter of the through hole) of 4 tm and an opening ratio of 64%.
A honeycomb catalyst (PtO, 5 wt % supported on a titania-zirconia honeycomb carrier) was packed so that the catalyst layer length was 8 m.

Phosphorus compound (phosphoric acid equivalent 1) 3PO4900pplIl
) Pump calcium hydroxide solution into line 13 of waste water with a concentration of 40 g/It 4
It was added by

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

The wastewater treated in reactor 1 is discharged from line 15,
After being cooled in the heat exchanger 2, it was supplied to the gas-liquid separator 8, where it was separated into harmless gas and water. In this gas-liquid separator 8, a liquid level controller LC detects the liquid level and operates a liquid level control valve 9 to maintain a constant liquid level, and a pressure controller PC detects pressure and operates a pressure control valve 9. 10 to maintain a constant pressure.

Next, the treated liquid was led to a mixing tank 6, where an inorganic flocculant was added using a pump 5, and after solid-liquid separation in a coagulation-sedimentation tank 7, the supernatant liquid was directly discharged.

At this time, the processing conditions in the reactor 1 are as follows: reaction temperature 25
0°C and reaction pressure cuff 5kg/cJG, wastewater supply amount 30J/Hr, calcium hydroxide solution 9,000 ppm added to wastewater in advance, supply amount 5Il/Hr, air amount 4.8
00 Nβ/Hr. As a result, the COD reaction rate was 9
9%, and no decrease in the COD reaction rate was observed even during continuous operation for 2,000 hours under the above conditions.

Comparative Example 1 Using the same equipment used in Example 1, without adding metal ions in advance to wastewater with a concentration of 40 g/12 COD (Cr) containing phosphorus compounds (phosphoric acid equivalent H, PO4, 900 ppm), Continuous operation was carried out under the same treatment conditions.

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

1 2 Table 1 (Effects of the Invention) As described above, in the present invention, by adding metal ions in advance to wastewater containing phosphorus compounds, phosphate ions and metal ions react to form a sparingly soluble salt, and the phosphate ions This makes it possible to suppress the adsorption of phosphorus onto the catalyst, making it difficult for the catalyst to be poisoned by phosphorus. Furthermore, wet oxidation reaction conditions can also be applied to excess sludge, which is difficult to remove in the pretreatment process. Although phosphate ions are produced by the solubilization reaction of solids, adsorption of phosphate ions onto the catalyst is suppressed because they form poorly soluble salts with metal ions, etc., present in wastewater. .

That is, it is now possible to maintain stable catalytic activity over a long period of time for wastewater containing phosphorus compounds, and it has become possible to realize stable wastewater treatment over a long period of time.

[Brief explanation of drawings]

FIG. 1 is a flow sheet showing one embodiment of the present invention. l... Single tube cylindrical reactor 2... Heat exchanger 3... Waste water supply pump 4... Calcium hydroxide solution supply pump 5... Coagulant addition pump 6... Mixing tank 7. ... Coagulation sedimentation tank 8 ... Gas-liquid separator 9 ... Liquid level control valve 10 ... Pressure control valve 1) ... Compressor 12 ... Air supply line 13 ... Wastewater supply line 3 4 4...Calcium hydroxide solution supply line 5...Treatment liquid line 6...Flocculant supply line C...Pressure controller C...Liquid level controller run

Claims (3)

[Claims] (1) Ba(II) ions, Ca(II) ions, Mg(II) are added to the wastewater containing phosphorus compounds in advance.
ion, Al(III) ion, Fe(III) ion and F
At least one metal ion selected from the group consisting of e(II) ions is added and then a wet oxidation reactor packed with a solid catalyst is used at a temperature below 370°C and the wastewater maintains a liquid phase. A method for treating wastewater, characterized by carrying out wet oxidation treatment under pressure while supplying oxygen-containing gas. (2) The method for treating wastewater according to claim (1), wherein the solid catalyst is a catalyst whose carrier component is an oxide containing titania. (3) The method for treating wastewater according to claim (1), wherein a flocculant is added to the treated wastewater after the wastewater has been treated by wet oxidation, and hardly soluble salts are removed by solid-liquid separation.