JP3871749B2 - Treatment method of flue gas desulfurization waste water - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for treating flue gas desulfurization waste water. More specifically, the present invention is excellent in the recovery rate of membrane performance by washing and reduces the frequency of membrane replacement in the treatment of flue gas desulfurization effluent from a coal-fired power plant with a solid-liquid separation and concentration step using a membrane. More particularly, the present invention relates to a method for treating flue gas desulfurization wastewater, and a method for treating flue gas desulfurization wastewater that can eliminate the treatment of the washing waste liquid itself generated by washing.
[0002]
[Prior art]
Flue gas desulfurization drainage is drainage generated when smoke, desulfurization treatment is performed on flue gas generated when fuel such as oil and coal is burned. Ions such as sulfate ion, sulfite ion, calcium ion and gypsum In addition to COD components derived from suspensions and fuels, etc., metals such as iron, aluminum, manganese and other heavy metals, fluorine, silica and the like are contained.
When treating flue gas desulfurization waste water containing such pollutants, the pollutants in the waste water are first agglomerated and separated from water as solids as possible. Some COD components that are not solidified but dissolved in water and ions to be removed are removed by an adsorption step, an ion removal step, a decomposition treatment step, and the like. Further, an oxidizing step is provided in order to remove reducing substances that are subject to COD, such as sulfite ions and manganese ions.
The waste water that has passed through the oxidation process and the aggregation process separates flocs generated by the aggregation with a membrane. The membrane used in the membrane separation step is contaminated by the continuation of processing, and the amount of permeated water (flux) decreases. For this reason, when the amount of permeated water is reduced, back-flow cleaning for backflowing the treated water from the permeated water side and chemical cleaning for cleaning the membrane with a liquid containing a cleaning agent are performed.
Conventionally, general chemical cleaning is generally performed using an alkali solution or an acid solution, or using these solutions in combination. When polyaluminum chloride (PAC), sulfuric acid band, magnesium hydroxide, ferric chloride, slaked lime, etc. are used for coagulation neutralization of the effluent, suspended matter (SS) generated during concentration is dissolved by alkali or mineral acid Is possible. Therefore, conventionally, chemical cleaning of the membrane has been performed using an alkali such as sodium hydroxide or a mineral acid such as hydrochloric acid. Sodium hydroxide is heated to 40-60 ° C. to dissolve the silica, and the mineral acid is heated to room temperature or heated to contact other membranes to dissolve other metals.
However, for membranes applied to flue gas desulfurization wastewater, the cleaning effect with alkali or acid is not sufficient, and if washing with sodium hydroxide, hydrochloric acid or sulfuric acid, which is often used, is repeated every fixed period of time, the membrane is washed. There was a problem that the recovery rate was not sufficient, the membrane performance gradually decreased, and the membrane replacement frequency increased. In addition, the flux lowering speed during normal operation is fast, the chemical cleaning period is also shortened, the apparatus operating rate is lowered, and the amount of cleaning chemicals is increased. Further, when chemical cleaning is performed, cleaning waste liquid is generated, and it is necessary to separately process the cleaning waste liquid, which causes problems such as equipment costs and chemical costs.
[0003]
[Problems to be solved by the invention]
The present invention, when treating flue gas desulfurization wastewater by oxidation, agglomeration, membrane separation, increase the membrane cleaning recovery rate, extend the period of chemical cleaning, can reduce the frequency of membrane replacement, Further, it is an object of the present invention to provide a method for treating flue gas desulfurization effluent that can easily treat the waste liquid for washing the membrane.
[0004]
[Means for Solving the Problems]
As a result of intensive studies to solve the above-mentioned problems, the present inventors have greatly affected the performance recovery of the membrane in the contamination of the membrane surface when the flue gas desulfurization wastewater is oxidized, aggregated, and membrane separated. It is clarified that the contaminating component is manganese dioxide, and manganese dioxide deposited on the film surface can be removed by washing with a cleaning solution containing oxalic acid, and the cleaning waste liquid containing oxalic acid used for cleaning is The present inventors have found that it can be easily treated by returning it and mixing it with flue gas desulfurization effluent, and based on this finding, the present invention has been completed.
That is, the present invention
(1) In a method for treating flue gas desulfurization effluent by passing the flue gas desulfurization effluent through an oxidation process, an agglomeration process, and a membrane separation process, an aqueous solution containing oxalic acid and a mineral acid method of processing waste water of flue gas desulfurization, wherein the washing with washing in combination with an aqueous solution or mixed aqueous solution of oxalic acid and a mineral acid and,
(2) Washing the contaminated membrane with a cleaning solution containing oxalic acid and a mineral acid aqueous solution or cleaning with a mixed aqueous solution of oxalic acid and mineral acid , returning the waste wastewater to flue gas desulfurization A method for treating flue gas desulfurization waste water as described in (1),
Is to provide.
Furthermore, as a preferred embodiment of the present invention,
(3) The method for treating flue gas desulfurization waste water according to (1) or (2), wherein a microfiltration membrane (MF membrane) is used in the membrane separation step,
( 4 ) The method for treating flue gas desulfurization waste water according to (1) to (3), wherein the cleaning liquid is a mixed aqueous solution containing 0.05 to 1% by weight of oxalic acid and 3 to 15% by weight of mineral acid,
( 5 ) A method for treating flue gas desulfurization waste water according to any one of (1) to (3), wherein the oxalic acid aqueous solution having a concentration of 0.05 to 1% by weight and the mineral acid aqueous solution having a concentration of 3 to 15% by weight are washed together. ,
( 6 ) The method for treating flue gas desulfurization waste water according to (1) to ( 5 ), wherein the contaminated membrane and a cleaning liquid containing oxalic acid are brought into contact at room temperature to 80 ° C. for 1 to several tens hours.
( 7 ) The method for treating flue gas desulfurization waste water according to (1) to ( 6 ), wherein the contaminated membrane is further washed with alkali,
Can be mentioned.
[0005]
DETAILED DESCRIPTION OF THE INVENTION
The method of the present invention can be applied to a process in which flue gas desulfurization effluent discharged from a flue gas desulfurization apparatus such as a thermal power plant is passed through an oxidation process, an aggregation process, and a membrane separation process. FIG. 1 is a process flow diagram of one embodiment of the method for treating flue gas desulfurization waste water of the present invention.
In the method of the present invention, the oxidation step 1 is mainly intended to oxidize manganese ions contained in the flue gas desulfurization waste water to form insoluble manganese dioxide. The oxidation means is not particularly limited, and can be performed by, for example, air aeration or addition of permanganate, ozone, a chlorine-based oxidant, or the like. In FIG. 1, the oxidation step is provided in front of the agglomeration reaction tank 2, but it is also possible to add an oxidizing agent to the agglomeration reaction tank and simultaneously perform the oxidation step and the agglomeration step.
Moreover, regardless of the removal of manganese ions, for example, when a step of air aeration to oxidize sulfite ions in waste water is included, manganese dioxide is produced as a result. Similarly, manganese dioxide is generated when air stirring is used for stirring in the aggregation step. The oxidation step in the present invention may be an oxidation step not aimed at removing manganese dioxide as described above.
In the method of the present invention, the water to be treated that has finished the oxidation step is sent to the agglomeration reaction tank 2. In the agglomeration step in the agglomeration reaction tank, a pH adjuster, a flocculant, and the like are added to the water to be treated to agglomerate suspensions, fluorine ions, metal ions, a part of COD components, and the like in the water to be treated. The aggregation reaction tank is preferably provided with a pH meter 3. By adding a pH adjuster, the pH can be adjusted to be suitable for agglomeration of the suspension in the water to be treated or the pH at which ions dissolved in the water to be treated are insolubilized. There is no restriction | limiting in particular in the pH adjuster to be used, For example, alkalis, such as sodium hydroxide and slaked lime, and acids, such as hydrochloric acid and a sulfuric acid, can be used. There are no particular restrictions on the flocculant used, for example, aluminum compounds such as aluminum sulfate, polyaluminum chloride and aluminum oxide, iron salts such as iron chloride, iron sulfate and polyiron, hydroxides such as slaked lime and magnesium hydroxide Polyacrylamide, its hydrolyzate, cation-modified product, and polymer flocculant such as polyacrylic acid can be appropriately selected and used according to the properties of the suspension. The amount of the flocculant added can be set according to the amount and properties of the removal target in the water to be treated.
[0006]
In the method of the present invention, the water to be treated that has finished the aggregation step in the reaction aggregation tank is sent to the circulation tank 4. The water to be treated in the circulation tank is sent to the membrane separation device 6 using the circulation pump 5, and the aggregated flocs generated in the aggregation process by membrane separation are separated from the water. The separation membrane to be used is not particularly limited. For example, microfiltration membrane (MF membrane), ultrafiltration membrane (UF membrane), reverse osmosis membrane (RO membrane), nanofilter membrane (NF membrane), etc. Although it can select and use suitably according to a property, in many cases, a microfiltration membrane and an ultrafiltration membrane can be used conveniently. There is no restriction | limiting in particular in the form of a membrane element, For example, a planar membrane clamping type | mold, a planar membrane spiral winding type | mold, a tubular membrane, a hollow fiber membrane etc. can be used. There is no restriction | limiting in particular also in the format of a membrane separator, For example, an external pressure type, an internal pressure type, a pressurization type, a pressure reduction type etc. can be selected suitably, and can be used.
The water sent from the circulation tank to the membrane module by a circulation pump and permeated through the film is discharged as treated water as it is or once after being put into the treated water tank 7 and further subjected to necessary treatment such as pH adjustment. Part of the water to be treated concentrated in the membrane module is circulated to the agglomeration reaction tank and the remainder to the circulation tank. By circulating the water to be treated concentrated in the agglomeration reaction tank, the returned sludge becomes a seed crystal for the agglomeration reaction, and a large floc having good separability is formed. The treated water circulated to the circulation tank is supplied again to the membrane module, and solid-liquid separation by the membrane is repeated. By the membrane separation, the water to be treated in the coagulation reaction tank usually containing several tens to several hundred mg / liter of SS is concentrated until the SS component of the sludge in the circulation tank is about 2% by weight. The SS in the permeated treated water is 1 mg / liter or less.
[0007]
In the method of the present invention, when the membrane is contaminated by use of the membrane and the amount of permeated water is reduced, the membrane is washed. The membrane is cleaned by back-flow cleaning and chemical cleaning. Backflow cleaning is usually performed about once every 5 minutes to 5 hours. For example, pressurized air is sent from the compressor 8 to the treated water tank 7 to pressurize the treated water and from the membrane permeate side to the raw water side. Back flow cleaning can be performed. Backflow cleaning cannot completely remove the dirt on the membrane surface, and the amount of permeated water gradually decreases, so chemical cleaning is performed.
In the method of the present invention, chemical cleaning is performed with a cleaning liquid containing oxalic acid. There is no particular limitation on the chemical cleaning method using the cleaning liquid containing oxalic acid. For example, cleaning can be performed using an aqueous oxalic acid solution having a concentration of 1 to 10% by weight, and an aqueous oxalic acid solution having a concentration of 0.05 to 1% by weight. And a mineral acid aqueous solution having a concentration of 3 to 15% by weight, or a mixed aqueous solution containing 0.05 to 1% by weight of oxalic acid and 3 to 15% by weight of a mineral acid. Can do. When using an oxalic acid aqueous solution and a mineral acid aqueous solution in combination, there is no restriction on the order of washing, and after washing with an oxalic acid aqueous solution, it can be washed with a mineral acid aqueous solution, or conversely, after washing with a mineral acid aqueous solution, oxalic acid It can be washed with an aqueous solution. When only the oxalic acid aqueous solution is used, the cleaning effect is small when the oxalic acid concentration is less than 1% by weight, and when the oxalic acid concentration exceeds 10% by weight, the cleaning effect is not improved in accordance with the increase in concentration. When using an oxalic acid aqueous solution and a mineral acid aqueous solution together or when using a mixed aqueous solution of oxalic acid and mineral acid, if the oxalic acid concentration is less than 0.05% by weight, the cleaning effect is small, and the oxalic acid concentration is 1% by weight. If exceeded, the cleaning effect will not improve in proportion to the increase in concentration. When the concentration of the mineral acid aqueous solution used in combination with the oxalic acid aqueous solution and the concentration of the mineral acid in the mixed aqueous solution of oxalic acid and mineral acid is less than 3% by weight, the cleaning effect is small. It does not improve in proportion to the rise in The SS component adhering to the film usually contains a component soluble in the oxalic acid aqueous solution and a component soluble in the mineral acid aqueous solution, so oxalic acid and mineral acid are mixed as a cleaning agent, A high cleaning effect can be obtained by making both act simultaneously, which is preferable.
[0008]
In the method of the present invention, chemical cleaning of the membrane can be performed by filling the raw water side of the membrane with an aqueous oxalic acid solution or a mixed aqueous solution of oxalic acid and mineral acid. The temperature at the time of contact between the membrane and the aqueous oxalic acid solution or the mixed aqueous solution of oxalic acid and mineral acid is preferably from room temperature to 80 ° C. There is no particular advantage even if the temperature at the time of contact is lower than room temperature by cooling, and the cleaning effect may be rather reduced. Generally, increasing the temperature at the time of contact between the membrane and an aqueous solution of oxalic acid or a mixed aqueous solution of oxalic acid and mineral acid improves the cleaning effect, but it is not necessary to set the temperature above 80 ° C., and rather the deterioration of the membrane may be stopped. There is. The contact time between the membrane and the oxalic acid aqueous solution or the mixed aqueous solution of oxalic acid and mineral acid is preferably 1 to several tens of hours. If the contact time is less than 1 hour, the membrane may not be sufficiently cleaned. A contact time of several tens of hours is sufficient, and even if the contact time exceeds several tens of hours, the cleaning effect is usually not improved.
In the method of the present invention, alkali cleaning can be performed in addition to acid cleaning. Alkaline washing is effective for removing silica-based scales, and can be suitably carried out when there is a lot of silica as a membrane contaminant. There is no restriction | limiting in particular in the alkali washing liquid to be used, For example, sodium hydroxide aqueous solution, potassium hydroxide aqueous solution, etc. can be used. The concentration of the alkaline cleaning liquid is preferably 4 to 15% by weight. The alkaline cleaning liquid is preferably brought into contact with the membrane while filling or circulating the membrane for several hours at room temperature or in a heated state. In the method of the present invention, the order of washing may be alkali washing after acid washing, or may be acid washing after alkali washing, and the order is not particularly limited.
In the example shown in FIG. 1, the alkali cleaning liquid is prepared in the alkali storage tank 9, and the mixed acid cleaning liquid of mineral acid and oxalic acid is prepared in the acid storage tank 10. In cleaning, first, the pump 11 is driven to supply the alkaline cleaning liquid in the alkaline storage tank 9 to the permeate side of the membrane separation device 6 and return to the alkaline storage tank 9 through a pipe, and the alkaline cleaning liquid is circulated for a predetermined time. Next, the alkaline cleaning liquid is added to the concentrated water side and circulated. Thereafter, the cleaning liquid is switched to the acid cleaning liquid, and the acid cleaning liquid in the acid storage tank 10 is similarly circulated between the acid storage tank 10 and the membrane separation device 6 to clean the membrane. Washing in this way removes membrane contaminants unique to flue gas desulfurization effluent and restores membrane performance.
And the washing | cleaning waste liquid generate | occur | produced by the film | membrane washing | cleaning of this invention method can be processed without providing a waste-liquid processing apparatus separately by utilizing the process process of flue gas desulfurization waste_water | drain. In the example of FIG. 1, the cleaning waste liquid generated by cleaning the membrane module stores the alkaline cleaning waste liquid separately in the alkaline storage tank 9 and the acidic cleaning waste liquid in the acid storage tank 10. The alkaline cleaning waste liquid contains sodium hydroxide, potassium hydroxide and the like used for cleaning. The acidic cleaning waste liquid contains oxalic acid or oxalic acid and mineral acid. The washing waste liquid is returned directly to the flue gas desulfurization effluent by the pump 11 or to the coagulation reaction tank, and is mixed with the flue gas desulfurization effluent at a certain ratio. The amount of cleaning waste liquid returned depends on the frequency of cleaning the membrane module and the amount of cleaning liquid used for one cleaning, but is usually one-tenth of the amount of flue gas desulfurization wastewater. The cleaning waste liquid can be returned without reducing the operation efficiency of the treatment process. The flue gas desulfurization wastewater usually contains enough calcium ions to convert the oxalic acid in the returned cleaning waste liquid into insoluble calcium oxalate, but a method such as using slaked lime to adjust the pH if necessary Thus, calcium ions can be supplied to the water to be treated. Oxalic acid in the washing waste liquid is neutralized in the treatment process of flue gas desulfurization wastewater, becomes water-insoluble calcium oxalate, and is removed by the membrane separator together with the floc floc. The cleaning waste liquid is treated at the same time as the flue gas desulfurization effluent. Moreover, the flux is rather stabilized by mixing the washing waste liquid with the flue gas desulfurization waste water. Although this mechanism of action is not clear, it is considered that SS particles produced by mixing the cleaning waste liquid are suitable for membrane treatment.
In the method of the present invention, as the treatment process of the flue gas desulfurization waste water, any treatment process other than the oxidation process, the aggregation process and the membrane separation can be added to any stage as necessary. For example, an adsorption tower filled with an adsorbent resin, activated carbon, ion exchange resin, or the like can be provided to remove an ionic COD component that cannot be removed in the aggregation step. Further, depending on the required water quality, a fluorine adsorption tower can be provided in order to improve the fluorine removal rate, and a heavy metal fixing agent can be used in combination in the agglomeration step in order to increase the heavy metal removal effect.
[0009]
【Example】
Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples.
Example 1
Thermal power plant desulfurization effluent was treated with a polypropylene tubular microfiltration membrane (inner diameter 5.5 mm, pore diameter 0.2 μm). The pure water flux of this microfiltration membrane is 22.4 m ³ / m ² · day (at 0.5 kg / cm ² · 25 ° C.). The water quality of the wastewater was pH 7.2, COD _Mn 20 mg / liter, SS 41 mg / liter, fluorine 20 mg / liter, manganese 3.6 mg / liter.
After raw water was oxidized with air at pH 8.5 in the oxidation step, polyaluminum chloride and potassium permanganate were added in the agglomeration reaction tank to carry out an agglomeration reaction and sent to the circulation tank. The solution was sent from the circulation tank to the membrane module using a circulation pump, and the membrane permeated water was discharged as treated water. The membrane separation conditions were: membrane surface flow rate 2 m / s, water temperature 30-40 ° C., circulating water inlet pressure approximately 1 kgf / cm ² , circulating water outlet pressure approximately 0.6 kgf / cm ² , membrane permeate water volume 5 m ³ / m ² · day. (Constant flow rate).
The water quality of the treated water was pH 6.9, COD _Mn 18 mg / liter, SS 1 mg / liter or less, fluorine 4.1 mg / liter, manganese 0.1 mg / liter or less. Further, the sludge in the circulation tank was concentrated to about 2% by weight of the SS component.
The membrane operated for one month under these conditions had a pure water flux of 9.0 m ³ / m ² · day. The membrane was washed with an 8 wt% aqueous sodium hydroxide solution at 60 ° C. for 2 hours, followed by washing with 7 wt% hydrochloric acid in which 0.1 wt% oxalic acid was dissolved at 25 ° C. for 2 hours. The pure water flux of the membrane was 21.6 m ³ / m ² · day, and the membrane recovery rate was 96.4%.
Example 2
Using a microfiltration membrane under the same conditions as those used in Example 1, washing with hydrochloric acid and washing with an oxalic acid aqueous solution were sequentially performed.
The membrane having a pure water flux of 9.0 m ³ / m ² · day after one month of operation was washed with an 8 wt% aqueous sodium hydroxide solution at 60 ° C. for 2 hours, followed by 7 wt% hydrochloric acid. The plate was washed at 25 ° C. for 2 hours, and further washed with a 0.5 wt% aqueous oxalic acid solution at 25 ° C. for 2 hours. The pure water flux of the membrane was 22.1 m ³ / m ² · day, and the membrane recovery rate was 98.7%.
Reference Example Using a microfiltration membrane under the same conditions as those used in Example 1, washing with an oxalic acid aqueous solution was performed.
The membrane with a pure water flux of 9.0 m ³ / m ² · day after one month of operation was washed for 2 hours at 60 ° C. with an 8 wt% aqueous sodium hydroxide solution, followed by a 5 wt% oxalic acid aqueous solution. And washed at 25 ° C. for 2 hours. The pure water flux of the membrane was 21.1 m ³ / m ² · day, and the membrane recovery rate was 94.2%.
Comparative Example 1
Using a microfiltration membrane under the same conditions as those used in Example 1, only washing with hydrochloric acid was performed without using oxalic acid.
The membrane having a pure water flux of 9.0 m ³ / m ² · day after one month of operation was washed for 2 hours at 60 ° C. with an 8 wt% aqueous sodium hydroxide solution, followed by 7.5 wt% hydrochloric acid. And washed at 25 ° C. for 2 hours. The pure water flux of the membrane was 19.6 m ³ / m ² · day, and the membrane recovery rate was 87.5%.
According to the cleaning using the cleaning liquid containing oxalic acid in Examples 1 and 2 and the reference example , the recovery rate of the pure water flux of the microfiltration membrane is high, and the contamination of the membrane is efficiently removed. In Comparative Example 1 in which no is used, the recovery rate of the pure water flux of the microfiltration membrane is low.
Example 4
Thermal power plant desulfurization effluent was treated with a polypropylene tubular microfiltration membrane (inner diameter 5.5 mm, pore diameter 0.2 μm, membrane area 0.036 m ² ). The flux of this microfiltration membrane is 12.0 m ³ / m ² · d (0.5 kgf / cm ² , converted to 25 ° C.). The water quality of the wastewater was pH 6.5, COD _Mn 25 mg / liter, SS 150 mg / liter, fluorine 25 mg / liter, manganese 3.0 mg / liter, calcium 1,500 mg / liter.
After the waste water is oxidized in the air in the oxidation process, 2,000 mg / liter of polyaluminum chloride and 6.0 mg / liter of potassium permanganate are added in the reaction tank, and the pH is adjusted to 6.5 with sodium hydroxide to cause agglomeration reaction. And sent to the circulation tank. The solution was sent from the circulation tank to the membrane module using a circulation pump, and the membrane permeated water was discharged as treated water. Membrane separation conditions were as follows: membrane surface flow rate 2 m / s, water temperature 30-40 ° C., circulating water inlet pressure 1.0 kgf / cm ² , circulating water outlet pressure 0.8 kgf / cm ² , membrane permeate flow rate 5 m ³ / m ² · d (Constant flow rate). The membrane was backwashed with treated water for 10 seconds once every 15 minutes.
When operating for one month under these conditions, the water quality of the treated water was COD _Mn 19 mg / liter, SS 0 mg / liter, fluorine 7.5 mg / liter, and manganese 0.2 mg / liter. In addition, the sludge in a circulation tank was concentrated to about 2 weight% of SS components. The flux was 6.0 m ³ / m ² · d, and the flux reduction rate per day was 0.20 m ³ / m ² · d ² (0.5 kgf / cm ² , converted to 25 ° C.).
The membrane was washed with an 8 wt% aqueous sodium hydroxide solution at 60 ° C. for 5 hours, replaced with pure water, and then washed with 7 wt% hydrochloric acid in which 0.1 wt% oxalic acid was dissolved at 25 ° C. for 2 hours. Washed. The flux of the film recovered to 12.0 m ³ / m ² · d by washing. The COD _{Mn of} the cleaning waste liquid generated during this cleaning was 85 mg / liter.
While this washing waste liquid was uniformly added to the flue gas desulfurization effluent at a rate of 5% by volume, the coagulation reaction and membrane separation in the reaction tank were continued. When treated under the same conditions as the first month, the quality of the treated water is COD _Mn 19 mg / liter, SS 0 mg / liter, fluorine 7.5 mg / liter, manganese 0.2 mg / liter. The water quality was exactly the same. Further, after 40 days, the flux was 6.0 m ³ / m ² · d, and the flux reduction rate per day during this period was 0.15 m ³ / m ² · d ² . That is, the rate of flux reduction per day is less than the first month.
From the above results, even when the membrane cleaning waste liquid containing oxalic acid is added to the flue gas desulfurization wastewater and treated, there is no change to the treated water quality when the membrane cleaning waste liquid is not added, and the rate of flux reduction is suppressed, It was found that the flux was stable and the cleaning frequency was reduced.
[0010]
【The invention's effect】
According to the method of the present invention, it is possible to maintain a high performance recovery rate in the membrane cleaning of flue gas desulfurization wastewater containing SS that is sparingly soluble in mineral acids such as manganese dioxide. There is an effect of lowering the cost. Furthermore, by mixing the membrane cleaning waste liquid with the flue gas desulfurization waste water, the membrane cleaning waste liquid and the waste water can be treated at the same time, the processing of the cleaning waste liquid itself can be omitted, and the operation efficiency of the entire apparatus can be improved. Furthermore, the flux of the membrane is stabilized by mixing the waste cleaning liquid with the waste water.
[Brief description of the drawings]
FIG. 1 is a process flow diagram of one embodiment of a method for treating flue gas desulfurization waste water of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Oxidation process 2 Coagulation reaction tank 3 pH meter 4 Circulation tank 5 Circulation pump 6 Membrane separation device 7 Treated water tank 8 Compressor 9 Alkali storage tank 10 Acid storage tank 11 Pump

Claims (2)

In a method for treating flue gas desulfurization wastewater that passes through an oxidation process, agglomeration process, and a membrane separation process, the flue gas desulfurization wastewater is treated with an aqueous solution containing oxalic acid and an aqueous mineral acid solution. method of processing waste water of flue gas desulfurization, which comprises washing with a mixed aqueous solution of combination with cleaning or oxalic acid and a mineral acid. Wash the contaminated membrane with a cleaning solution containing oxalic acid and an aqueous mineral acid solution, or return the cleaning wastewater generated by cleaning with a mixed aqueous solution of oxalic acid and mineral acid and mix it with the flue gas desulfurization effluent. The processing method of the flue gas desulfurization waste water of Claim 1.

Images