JPS5949073B2 - Wastewater treatment method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for treating wastewater with a high concentration of COD components.

A liquid phase oxidation method called the Zimmerman method is known as a method for treating wastewater containing COD components at a relatively high concentration.

This method blows air into wastewater under high temperature and high pressure to oxidize and decompose COD components, but the reaction rate is low, ammonia is not decomposed, and the organic nitrogen in the wastewater is converted to ammonia and the treated water is However, there are disadvantages such as increasing the ammonia concentration. The present inventor has conducted various experiments and research in view of the drawbacks of the liquid phase oxidation method of wastewater as described above, and has found that when performing liquid phase oxidation of wastewater using a gas with an oxygen concentration of 25% or more as an oxygen source, The decomposition reaction rate of COD components is significantly improved, and completely unexpectedly, the conversion of organic nitrogen in wastewater to ammonia is not only prevented, but also the ammonia originally contained in wastewater is reduced. It was discovered that even some of the components were decomposed and the ammonia concentration in the treated water decreased.

The present invention was completed based on these findings. According to the method of the present invention, various wastewaters, such as gas liquid by-produced in coke oven plants and coal gasification and liquefaction plants, wastewaters generated during gas purification in these plants, wet desulfurization towers, Wastewater from a wet desulfurization tower,
Oil-containing wastewater, activated sludge treated water, wastewater generated by thermal decomposition of municipal waste, settled activated sludge, chemical factory wastewater, petroleum refinery factory wastewater, liquor factory wastewater, human waste, sewage, sewage sludge, sewage sludge are treated using the Zimmerman method, etc. The target of the treatment is wastewater that is generated when subjected to a heat treatment method and that contains oxidizable organic and/or inorganic substances.

It is advantageous when treating wastewater from high temperature and/or high pressure systems, as the costs for heating and/or pressurization can be reduced. If wastewater contains an excessive amount of non-flammable suspended solids, they may adhere to the equipment that makes up the wastewater treatment equipment according to this method and reduce its efficiency, such as heat transfer on the surface of the heat exchanger. Depending on its concentration, composition, etc., it is preferable to remove all or part of it prior to treatment, since this may cause a decrease in the coefficient. Since the wastewater used in the method of the present invention has a diameter of 8 or more, depending on the type of wastewater, it is preferable to condition the wastewater in advance with an alkaline substance such as hydric soda, soda carbonate, or calcium hydroxide. The addition of alkaline substances to the wet reaction system is
It is sufficient to carry out the treatment in an amount necessary to keep the treated solution always within the range of about 5 to 8 ml at the necessary time.

As such an alkaline substance, the same substances as those used for the above-mentioned waste water preparation can be used. In the present invention, by performing wet oxidation of wastewater in the presence of titania particles and/or zirconia particles, carbon dioxide in wastewater is reduced.
The decomposition reactions of OD components and ammonia components can be significantly promoted.

In particular, when these particles are packed into a reaction tower and used as a fixed bed, the wastewater becomes a piston flow and moves inside the reaction tower, completely preventing untreated water from flowing out of the system and treating it. The quality of treated water will be further improved. The particles can be used in various forms such as spheres, pellets, cylinders, crushed pieces, powders, etc. In the case of a fixed bed, the filling volume of the reaction column is such that the space velocity of the liquid is 0.5 to 101/Hr (based on the empty column),
More preferably, it is 1 to 51/Hr (empty column standard). The particle size used in the fixed bed is usually about 3 to 50 mm, more preferably about 5 to 25 mm.
In the case of a fluidized bed, the amount of particles that can form a fluidized bed in the reaction column is usually 0.5 to 20% by weight, more preferably O. 5
~10% by weight is suspended as a slurry in waste water and used. In practical operations in a fluidized bed, particles are suspended in wastewater in the form of a slurry and then supplied to the reaction tower, and after the reaction is complete, the particles are sedimented, centrifuged, etc. from the treated wastewater discharged. Separate and recover using an appropriate method and use again. Therefore, considering the ease of particle separation from treated wastewater, the particle size of the particles used in the fluidized bed is preferably about 0.15 to about 0.5 mm. As the oxygen source in the present invention, a gas having an oxygen concentration of 25% or more is used.

Thus, compared to the case where air is used, the decomposition rate of COD components is greatly increased despite the reduction in the amount of gas blown, and moreover, the decomposition rate of COD components is significantly increased compared to when air is used. Decomposition is also performed. Gases with an oxygen concentration of 25% or more include oxygen-enriched air obtained by selective oxygen permeation membrane method, method of mixing pure oxygen with air, pressure swing adsorption method, etc., or pure gas obtained by vaporizing liquid oxygen. Examples include oxygen. The blown gas is passed through a selective oxygen permeable membrane made of polysiloxane, cellulose acetate, polypropylene, polyether, etc. under suction by a blower to reduce the oxygen concentration to 25-35.
In the case of using oxygen-enriched air of about 1.5%, it is very advantageous because the pressurized state by the blower can be used as is. In addition, the oxygen-containing gas may contain impurities such as hydrogen cyanide, hydrogen sulfide, ammonia, sulfur oxides, organic sulfur compounds, nitrogen oxides, and hydrocarbons, and these impurities can also be wet-oxidized. sometimes decomposed at the same time. The amount of these gases to be supplied is determined from the theoretical amount of oxygen required to oxidize and decompose organic and inorganic substances in wastewater (or wastewater and waste gas) into nitrogen, carbon dioxide, water, and the like. Generally, an amount of 1 to 1.5 times the theoretical amount of oxygen, more preferably 1.05 to 1.2 times, is used. The use of oxygen-containing waste gas has the great advantage that harmful components in the gas are also rendered harmless. The oxygen-containing gas may be supplied to the reaction tower in one stage or in two or more stages. In order to further increase the oxygen utilization efficiency, part or all of the gas discharged from the reaction column may be recycled if it is operationally and economically advantageous. The temperature during the reaction is usually 10
The temperature is 0 to 370°C, more preferably 200 to 300°C.

The higher the reaction temperature, the higher the removal rate of ammonia, organic and inorganic substances, and the shorter the residence time of wastewater in the reaction tower, but on the other hand, the equipment cost increases.
It should be determined by comprehensively considering the type of wastewater, the degree of treatment required, operating costs, construction costs, etc. Therefore, the pressure during the reaction may be any pressure that will keep the wastewater in a liquid phase at the minimum predetermined temperature. The present invention will be described in more detail below with reference to the accompanying drawings.

FIG. 1 is an example for explaining the present invention. In FIG. 1, wastewater is pumped up to a predetermined pressure by a pump 3 from a wastewater storage tank 1 through a line 2, and then a line 4 and a heated mixed with oxygen-containing gas via exchanger 5 and line 6;
A line 11 is filled with titania particles and/or zirconia particles and supplied to a reaction column 12 .

As mentioned above, depending on the type of wastewater, adjustment can be made by adding alkaline substances.
, line 11, or at two or more locations. If the wastewater contains a large amount of tar, etc., it is preferable to remove most or part of this in advance. The oxygen-containing gas having an oxygen concentration of 25% or more is pressurized by the compressor 7, passes through the line 8, the humidifier 9, and the line 10, mixes with waste water as described above, and is supplied from the line 11 to the reaction tower 12.

When using oxygen-enriched air with a concentration of about 25 to 35% as the oxygen-containing gas, the air passing through line 37 is sucked by blower 35 through line 32, selective oxygen permeable membrane 33, and line 34. The desired oxygen-enriched air may be obtained by feeding the air into the compressor 7 via the line 36.
In this case, since the pressurized state by the blower 35 can be utilized, the load on the compressor 7 can be reduced. The use of humidifier 9 is preferred, but not essential, since it prevents liquid evaporation inside reaction column 12 and improves heat recovery efficiency. However, when using oxygen-containing waste gas as an oxygen source, harmful components in the waste gas may migrate into the treated water, so it is usually not used. In order to improve the gas-liquid contact efficiency within the reaction tower 12 and increase the reaction rate, it is preferable to make the bubbles in the gas-liquid multiphase flow finer. Such a method for making bubbles finer is disclosed in, for example, Japanese Patent Application Laid-Open Nos. 49-49873 and 49-49874. Furthermore, the oxygen-containing gas may be added to the wastewater at the outlet side of the wastewater boost pump 3, or may be branched into one or more stages and fed to the reaction tower 12. If necessary, heating of the liquid may be carried out in line 6 or in the lower part of the reaction column 12. However, depending on the treated wastewater, there is no particular need to heat the liquid if the amount of heat required for heating can be supplied by the heat of reaction. In the case of heating, the wastewater may be heated by a heating furnace (not shown) on line 6 or by heat exchange with a heating medium on line 6, or by heating with a heating medium in the lower part of the reaction column 12. It may be heated by heat exchange. Inside the reaction tower 12, an alkaline substance is usually stored in the form of an aqueous solution in an alkaline substance storage tank 21. so that the flow rate of the liquid taken out of the reaction system from the line 13 is about 5 to 8. It is supplied via line 22, pump 23 and line 24.

After the waste water and oxygen in the gas react under predetermined conditions in the reaction tower 12, the treated water is taken out from the upper part of the reaction tower 12 through the line 13, and the gas and liquid are separated by the gas-liquid separator 14. separation is carried out.

The treated water that has exited the gas-liquid separator 14 enters the humidifier 9 through a line 15, and a portion of it is sent to the reaction tower 12 through lines 10 and 11 accompanied by oxygen-containing gas. Humidifier 9
The remaining treated water passing through line 6 is cooled in cooler 17, then reduced to atmospheric pressure and discharged through line 18. On the other hand, the gas phase component leaving the gas-liquid separator 14 is
The waste water is sent through line 19 to heat exchanger 5 where it is heated, then reduced to atmospheric pressure and discharged through line 20. After the gas-liquid mixture from above the reaction tower 12 is sent as it is to the heat exchanger 5, it is separated into gas and liquid by the gas-liquid separator 14, and if necessary, each may be cooled and discharged. .

In FIG. 2, features that are the same as in FIG. 1 are designated by the same numbers.

The wastewater is sent from the wastewater storage tank 1 to a mixing tank 30 where it is fed with titania and/or which is supplied via line 29 from the storage tank 28.
or mixed with zirconia particles to form a slurry. The slurry is pressurized to a predetermined pressure by the pump 3, and then supplied to the reaction tower 31 via the line 4, heat exchanger 5, line 6, and line 11 in the same manner as in FIG. The oxygen-containing gas may normally be supplied in the same manner as in FIG. 1, but in order to improve the fluidity of the slurry, it may be supplied to the reaction column 31 by branching from the line 10 in one or more stages. I can do it. Approximately 5-8 ml of liquid after wet oxidation treatment
As in the embodiment shown in FIG. It is supplied to the reaction column 31 via line 22, pump 23 and line 24.
The treated water containing titania and/or zirconia particles is passed through line 13, gas-liquid separator 14, line 15, and humidifier 9.
, line 16, cooler 17 and line 18, and enters the solid-liquid separator 25.

The liquid phase component is discharged through line 27, while the separated and collected particles are returned to particle storage tank 28 via line 26 and used for circulation. As in the case shown in FIG. 1, the humidifier 9 is normally not used when oxygen-containing waste gas is used as the oxygen source. In wastewater treated by the method of the present invention, the concentration of C0D components is significantly reduced, and the concentration of ammonia is also significantly reduced.

In addition, since the ratio of treated water is about 5 to 8, it can be discharged after dilution without the need for any particular neutralization treatment, or if necessary, it can be treated with a reverse osmosis device using the pressure within the system, for example. It is then subjected to higher-order processing such as introduction into the water and desalination treatment. Furthermore, the ammonia concentration and NOx concentration in the gas phase after gas-liquid separation are also extremely low. The method of the present invention has the following various advantages over the case where air is used as the oxygen source under the same conditions.

(1) High COD component removal rate.

(2) Organic nitrogen in wastewater is not converted to ammonia.

(3) The decomposition rate of ammonia components in wastewater is extremely high (
4) The concentration of ammonia and NOx in the exhaust gas as a gas phase is extremely low.

(5) Since the processing efficiency is high, processing costs are reduced due to reductions in construction costs due to downsizing of the equipment, reduction in operating costs, etc.

(6) By increasing the oxygen partial pressure, the same treatment effect as in the case of air blowing can be achieved even if the temperature and pressure are lowered.

Therefore, reductions in electricity costs, heating costs, etc., and cost reductions due to the simplification of each device are also significant. EXAMPLES The present invention will be explained in more detail with reference to Examples below.

Example 1 The method of the present invention was continuously carried out for 4000 hours according to the flow shown in FIG.

Gas liquid generated in coke oven (C0D6500m)
, total ammonia amount 3400 pvtn, total nitrogen amount 2900
ppn, Ttl 9.5) at a space velocity of 0.991 small r (empty column standard) is supplied to the bottom of a cylindrical reaction tower 12 made of stainless steel (SUS316L).

The mass velocity of the liquid is 3.45 t/m·hr. On the other hand, an oxygen-containing gas is supplied to the lower part of the stainless steel cylindrical reaction column at a space velocity of 50.81 lr (empty column basis, standard state conversion). The reaction chamber 12 is filled with titania particles having a diameter of 5 mm. The oxygen-enriched air is supplied through the compressor 7 with an oxygen concentration of 25% obtained by passing the air through a selective oxygen permeable membrane (first stage). The inside of the reaction column is maintained at a temperature of 250° C. and a pressure of 46 kg/CI]1 tG, and a 48% caustic soda solution is supplied so that the liquid state after wet oxidation is approximately 6.6.

After the reaction, the gas-liquid mixed phase is sequentially extracted from the upper part of the reaction tower and guided to a gas-liquid separator, and the separated gas and liquid phases are each indirectly cooled and then taken out of the system. The conditions of the liquid phase and gas phase after 4000 hours are as shown in Table 1 below.

By using titania particles, extremely high wastewater treatment effects have been obtained. After 4000 hours, the reaction tower was vertically divided into two parts, and the inner surface thereof was visually observed, but virtually no corrosion was observed.

Comparative Example 1 Wastewater is treated in the same manner as in Example 1, except that air is used instead of oxygen-enriched air with an oxygen concentration of 25%.

The results are shown in Table 1.

Examples 2-3 The present invention is implemented according to the flow shown in FIG.

Wastewater generated from pyrolysis treatment of municipal waste (1).
6) was adjusted to pH 9.5 in advance, and the space velocity was 0.99.
It is supplied to the lowest part of the high nickel steel cylindrical reaction tower 12 at a rate of 1/Hr (empty column standard).

On the other hand, oxygen-enriched air is supplied to the lower part of the reaction tower at a space velocity of 80.01/Hr (empty column standard, standard state conversion).
The reaction column is filled with zirconia particles having a diameter of 3 mm. The method for producing oxygen-enriched air and the oxygen concentration are as follows.

Example 2 Oxygen-enriched air with an oxygen concentration of 35% that has passed through a selective oxygen permeable membrane (two stages) is supplied to the compressor 7.

Example 3: Pressure swing adsorption in which four adsorption tanks containing synthetic zeolite as an adsorbent are used to alternately and repeatedly perform pressure adsorption and vacuum desorption of nitrogen, carbon dioxide, hydrocarbons, etc. in the air. Oxygen-enriched air with an oxygen concentration of 50γ obtained by the method is supplied to the compressor 7.

The inside of the reaction tower was heated at a temperature of 250°C and a pressure of 46 kg/CI [12
-G, and a 48% strength soda solution is supplied so that the liquid resistance after the wet oxidation reaction is about 6.5.

After the reaction, the gas-liquid mixed phase is sequentially extracted from the upper part of the reaction tower and guided to a gas-liquid separator, and the separated gas and liquid phases are each indirectly cooled and then taken out of the system. The results are shown in Table 2.

Comparative Example 2 Wastewater is treated in the same manner as in Example 2, except that air is used instead of oxygen-enriched air.

The results are shown in Table 2.

Example 4 Wastewater generated at a liquor factory (State 4.2, COD 940)
Processing operations are performed in the same manner as in Example 1, except that 0PIltnX7#I is adjusted in advance as shown in Table 3 below.

...The relationship between the value and the COD component concentration of the treated liquid (pH approximately 6.5) is as shown in Table 3.

[Brief explanation of drawings]

1 and 2 are flowcharts showing an embodiment of the method of the present invention. 1... Wastewater storage tank, 3... Pump, 5.
... Heat exchanger, 7 ... Compressor, 9 ...
...humidifier, 12,31...reaction tower, 14.
... Gas-liquid separator, 17 ... Cooler, 21
...Alkaline substance storage tank, 23...Pump, 25...Solid-liquid separator, 28...Titania and/or zirconia particle storage tank J, 30.・・・
...Mixing tank, 33...Selective oxygen permeable membrane, 3
5...Blower.

Claims (1)

[Claims] 1. While maintaining the wastewater at a temperature of 100 to 370°C and a pressure that maintains the liquid phase of the wastewater, add 1 to 1.5 times the theoretical amount necessary to decompose organic and inorganic substances in the wastewater. The wastewater is subjected to wet oxidation at a pH of 8 or more while supplying a gas having an oxygen concentration of 25% or more and in the presence of titania and/or zirconia particles, and the pH of the liquid after wet oxidation is about 5 to 8. A wastewater treatment method characterized by supplying an alkaline substance to a wet oxidation reaction system so as to achieve the following.