JP4538706B2 - Cleaning method for water treatment equipment - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for cleaning a water treatment apparatus. More specifically, the present invention is a water treatment apparatus for reducing impurities in water by passing water through a packed bed of iron metal particles, and the contaminants adhered to the surface of the iron metal with the minimum required washing water and washing time. It is related with the washing | cleaning method of the water treatment apparatus which can remove reliably.
[0002]
[Prior art]
The flue gas desulfurization effluent discharged from the flue gas desulfurization process for treating coal or petroleum combustion exhaust gas contains various impurities such as heavy metals and non-metals, so it is necessary to remove these impurities from the flue gas desulfurization effluent. There is. The water quality of the flue gas desulfurization wastewater varies depending on the fuel used and the flue gas desulfurization method, and a method for treating the flue gas desulfurization wastewater corresponding to the change in water quality is required.
When the wastewater contains peroxosulfuric acid, iodic acid, selenic acid, etc., the wastewater can be passed through a packed bed of iron metal particles to reduce impurities in the water. When the pH of the wastewater is adjusted to 5 or less and brought into contact with ferrous metal, divalent iron ions are eluted from the ferrous metal according to the following formula.
Fe + 2H ⁺ → Fe ²⁺ + H ₂
Peroxosulfuric acid, iodic acid and selenic acid contained in the waste water react with divalent iron ions according to the following formulas, respectively, and are reduced.
S ₂ O ₈ ^2- + 2Fe ²⁺ → 2SO ₄ ^2- + 2Fe ³⁺
2IO ₃ ⁻ + 10Fe ²⁺ + 12H ⁺ → I ₂ + 10Fe ³⁺ + 6H ₂ O
SeO ₄ ²⁻ + 6Fe ²⁺ + 8H ⁺ → Se ⁰ + 6Fe ³⁺ + 4H ₂ O
Further, when the oxidation-reduction potential is −400 to −100 mV, a reaction between iron metal and selenic acid occurs according to the following formula.
SeO ₄ ²⁻ + 3Fe + 8H ⁺ → Se ⁰ + 3Fe ²⁺ + 4H ₂ O
After reducing the impurities contained in the waste water by bringing them into contact with the iron metal in this way and adding an alkaline agent to the reduced treated water so that the pH is 7 or more, the iron ions in the water can be expressed, for example, by the following formula: In this way, water-insoluble iron hydroxide is formed to form floc.
Fe ²⁺ + 2NaOH → Fe (OH) ₂ + 2Na ⁺
Fe ³⁺ + 3NaOH → Fe (OH) ₃ + 3Na ⁺
At this time, in addition to the reduced selenium, heavy metals, suspended substances, fluorine, COD components, etc. contained in the waste water can also be coagulated, settled and separated at the same time.
FIG. 1 is an explanatory diagram of an example of a water treatment device that reduces water impurities by passing water through a packed bed of iron metal particles. The water treatment apparatus shown in the figure has a drainage, washing water and air inlet 2 at the bottom of a cylindrical column 1 and a water discharge port 3 for reducing treatment water and washing drainage at the top. A porous plate 4 is attached to the lower part of the column, and iron metal particles are filled thereon to form a packed layer 5 of iron metal particles. A perforated plate 6 is attached to the upper part of the column to prevent particles from flowing out when the packed bed is washed.
If drainage of water is continued through the packed bed of iron metal particles, the pollutants contained in the drainage and pollutants generated during the reduction process adhere to the iron metal particles, and the packed bed of iron metal particles is clogged. Etc. occur. The main components of such pollutants are iron oxide, iron hydroxide, FeO (OH) and the like produced by oxidation of part of the eluted divalent iron, and the amount generated varies depending on the quality of the wastewater. In other words, if a large amount of oxidizing substances are included in the wastewater, including coexisting oxidizing substances other than the oxidizing substances to be treated, the amount of pollutants generated will increase even with the same divalent iron elution amount. . Therefore, when there is a change in water quality, over-cleaning or insufficient cleaning may occur in a certain cleaning time. In particular, the influence of coexisting oxidizing substances other than the oxidizing substances to be treated is significant. In the case of insufficient cleaning, the iron metal particles are combined to form a large lump, resulting in a decrease in processing performance. Once a lump is formed, it is difficult to unravel and eventually it is impossible to pass water. Therefore, normally, an excessive cleaning time is set with a margin so as not to cause insufficient cleaning. However, if an excessive cleaning time is set, there is a problem that the cleaning water is wasted.
[0003]
[Problems to be solved by the invention]
The present invention reliably removes contaminants adhering to the surface of iron metal with a minimum amount of cleaning water and cleaning time in a water treatment device that reduces impurities in the water by passing water through a packed bed of iron metal particles. The object of the present invention is to provide a cleaning method for a water treatment apparatus that can be used.
[0004]
[Means for Solving the Problems]
As a result of intensive studies to solve the above-mentioned problems, the present inventors have conducted a cleaning process for exhausting water from a packed bed in a water treatment apparatus for reducing impurities in water by passing water through the packed bed of iron metal particles. By measuring the concentration of pollutants in the waste water and controlling the supply time of the mixed fluid of cleaning water and gas supplied to the packed bed, the contamination adhered to the surface of ferrous metal with the minimum required cleaning water and cleaning time. It has been found that substances can be removed reliably, and the present invention has been completed based on this finding.
That is, the present invention
(1) A cleaning method for a water treatment apparatus for reducing impurities in water by passing water through a packed bed of iron metal particles, and temporarily stopping the flow of waste water to be reduced into the packed bed of iron metal particles After supplying air to the packed bed of iron metal particles and loosening the packed iron metal layer, supply cleaning water while continuing to supply air, and then stop supplying air and supply only cleaning water. and passed through, by measuring the suspended solids concentration in the wash waste water discharged from the packed bed, suspended after the substance concentration was continued washing until the 200 mg / L, water flow of wastewater reduction treatment water flow A method of cleaning a water treatment device, characterized by switching to
(2) The method for cleaning a water treatment apparatus according to item 1 , wherein the cleaning time with only cleaning water is 0.5 to 3 minutes , and
(3) The method for cleaning a water treatment apparatus according to item 1 or 2, wherein the suspended solids concentration is measured by a sensor provided in a cleaning drain pipe or a bypass of the cleaning drain pipe,
Is to provide.
[0005]
DETAILED DESCRIPTION OF THE INVENTION
A cleaning method for a water treatment apparatus according to the present invention is a cleaning method for a water treatment apparatus for reducing impurities in water by passing water through a packed bed of iron metal particles, and a mixed fluid of cleaning water and gas in the packed bed When the pollutant in the packed bed is removed by supplying, the concentration of the pollutant in the washing wastewater discharged from the packed bed is measured to control the supply time of the mixed fluid. Although there is no restriction | limiting in particular in the contaminant density | concentration of the washing waste_water | drain to measure, It is preferable that it is a suspended substance density | concentration or turbidity. The suspended substance concentration and turbidity can be measured easily and continuously using a commercially available measuring instrument.
The method of the present invention is a cleaning of a water treatment apparatus in which wastewater containing an oxidizing substance such as peroxosulfuric acid, iodic acid, and selenic acid as impurities is passed through a packed bed of iron metal particles, and the impurities in the wastewater are reduced. Can be applied to. When the pH of the wastewater is adjusted to 5 or less and brought into contact with iron metal, divalent iron ions are eluted in the water, and the oxidizing substances contained in the wastewater are reduced by reacting with the divalent iron ions. The Furthermore, when the oxidation-reduction potential is −400 to −100 mV, selenic acid reacts with iron metal and is reduced. In this way, after reducing impurities by contacting impurities contained in the wastewater with iron metal, when an alkaline agent is added to the reduction-treated water and the pH is set to 7 or more, the iron ions in the water become water-insoluble water. It becomes iron oxide and forms floc. At this time, in addition to the reduced selenium and the like, heavy metals, suspended substances, fluorine, COD components and the like contained in the waste water can also coagulate at the same time and be removed by solid-liquid separation.
Examples of the iron metal particles that are brought into contact with the wastewater whose pH is adjusted to 5 or less include particles of pure iron, crude steel, alloy steel, and other iron alloys. When the iron metal is an iron alloy, the iron content is preferably 85% by weight or more.
[0006]
The contact between the waste water and the iron metal particles can be efficiently performed by passing the waste water through a column filled with the iron metal particles. However, if drainage of water is continued through the packed bed of iron metal particles, contaminants adhere to the surface of the iron metal particles, and the packed bed of iron metal particles becomes clogged, resulting in the removal efficiency of impurities in the drainage. Gradually decreases. Examples of such pollutants include iron oxide, iron carbide, iron sulfide generated by the reaction of iron metal or iron ions, suspended substances in waste water, and the like.
In the method of the present invention, drainage is passed through the packed bed of iron metal particles, and after reducing impurities, the drainage of drainage is stopped, and a mixed fluid of washing water and gas is passed through the packed bed of iron metal particles. To remove and remove the contaminants adhering to the surface of the iron metal particles, or to remove the contaminants that clog the packed bed of iron metal particles. In the method of the present invention, after stopping the water flow of the waste water, before supplying the mixed fluid of the cleaning water and the gas, the cleaning metal can be passed to wash the iron metal particles, or only the gas Can be supplied to loosen the packed bed of iron metal particles. Washing water containing no divalent or trivalent iron ions present in the packed bed of iron metal particles is washed by passing washing water through the packed bed of iron metal particles. Can be substituted. When only the gas is supplied and the packed bed is loosened, the packed bed can be loosened without generating washing waste water since no washing water is supplied during that time. In the method of the present invention, the gas that forms the mixed fluid with the washing water is not particularly limited, and examples thereof include air and nitrogen gas. Usually, air can be preferably used.
[0007]
The drainage water whose pH is adjusted to 5 or less is usually performed in an upward flow because hydrogen gas is generated. In addition, it is preferable to supply the mixed fluid of cleaning water and gas in an upward flow. By supplying a mixed fluid of washing water and gas as an upward flow, the packed bed of iron metal particles expands and fluidizes, and is vigorously stirred by the mixed fluid containing bubbles and contaminated from the surface of the iron metal particles. The material is stripped and discharged along with the water stream along with the clogging pollutants. In cleaning with only cleaning water, even if the packed bed of iron metal particles is expanded, the effect of removing contaminants is small, and even if a large amount of cleaning water is consumed, the cleaning effect does not increase.
In the method of the present invention, the flow rate of the cleaning water for forming a mixed fluid of cleaning water and gas is preferably LV = 30 to 150 m / h. The flow rate of the wash water can be selected according to the size of the iron metal particles, etc., but when the mixed fluid of wash water and gas is supplied, the packed bed of the iron metal particles is developed by 10 to 50%. It is preferable to make it to the extent to do. When the water flow rate of the washing water is less than 30 m / h, there is little development of the packed bed of iron metal particles, and there is a possibility that the contaminants adhering to the surface of the iron metal particles are not sufficiently separated. If the flow rate of the wash water exceeds 150 m / h, the amount of wash water consumed increases and iron metal particles may flow out.
In the method of the present invention, the supply amount of gas for forming a mixed fluid of washing water and gas may be 0.1 to 10 times the volume per minute with respect to the packed bed of iron metal particles. preferable. If the supply amount of the gas is less than 0.1 times the volume per minute with respect to the packed bed of iron metal particles, the stirring force may be weak and the cleaning effect may not be sufficiently improved. The amount of gas supply is usually 10 times the volume per minute of the packed bed of iron metal particles, and even if more gas is supplied, cleaning is performed in accordance with the increase in gas supply amount. The effect is not improved.
[0008]
In the method of the present invention, the concentration of contaminants in the cleaning wastewater discharged from the packed bed of iron metal particles is measured to control the supply time of the mixed fluid of cleaning water and gas. There are no particular restrictions on the location of the sensor that measures the concentration of contaminants, and it can be installed at any location in contact with the cleaning wastewater. When cleaning with a mixed fluid of gas and gas, a sensor can be installed by providing a bypass pipe in a pipe used as a cleaning drain pipe, or a sensor can be installed directly in a pipe used as a cleaning drain pipe. Most of the gas contained in the mixed fluid separates into gas and liquid and escapes to the gas phase above the packed bed of iron metal particles, but part of the gas may be contained in the cleaning waste water. By providing a bypass pipe in the pipe used as the washing drain pipe and installing the sensor, it is possible to prevent the measurement error due to the bubbles so that the washing drainage in contact with the sensor does not contain bubbles. In the method of the present invention, when the concentration of contaminants in the cleaning wastewater reaches a predetermined control value, it is preferable to stop the supply of gas and end the cleaning with the mixed fluid. The control value of the contaminant concentration when the cleaning with the mixed fluid is finished can be set experimentally. After draining the wastewater through a packed bed of iron metal particles for a certain period of time and reducing it, the mixed bed of washing water and gas is supplied to the packed bed of contaminated iron metal particles to clean the packed bed, The pollutant concentration is measured and the relationship between the cleaning time and the pollutant concentration is shown in a graph.
FIG. 2 is an example of a graph showing the relationship between washing time and suspended solids concentration. Even if wastewater is discharged from the same discharge source, the quality of the wastewater varies with time, so the amount of pollutants generated in the packed bed of iron metal particles varies greatly. As shown in FIG. 2, it is preferable to repeatedly determine the relationship between the cleaning time and the pollutant concentration when processing wastewater discharged from the same discharge source, and to set the pollutant concentration when stopping the cleaning. . For example, in the relationship shown in FIG. 2, it is preferable to stop the cleaning when the concentration of suspended solids in the cleaning wastewater reaches 200 mg / L, and it is more preferable to stop the cleaning when it reaches 100 mg / L or less. preferable. By measuring the concentration of contaminants in the cleaning wastewater discharged from the packed bed of iron metal particles and controlling the supply time of the mixed fluid of cleaning water and gas, lumps of iron metal particles are generated due to insufficient cleaning. Therefore, the processing performance of the packed bed of iron metal particles can be stably maintained without excessive cleaning and waste of cleaning water and cleaning time.
[0009]
In the method of the present invention, it is preferable to supply the mixed fluid of the cleaning water and the gas and finish the cleaning, and then stop the supply of the gas and perform the cleaning only with the cleaning water. By washing with only washing water, it is possible to wash away the polluted substances separated by the mixed fluid of washing water and gas, and to expel air bubbles from the packed bed of iron metal particles. It can be formed uniformly.
In the method of the present invention, it is preferable that the cleaning with only the cleaning water after the supply of the mixed fluid of the cleaning water and the gas is performed for 0.5 to 3 minutes. If the cleaning time with only the cleaning water is less than 0.5 minutes, there is a possibility that washing away the polluted contaminants and expelling bubbles will be insufficient. Cleaning with only cleaning water is usually sufficient for 3 minutes or less, and even if cleaning with only cleaning water is continued, the cleaning effect is not improved. After the cleaning with only the cleaning water is completed, the supply of the cleaning water is stopped and settled to form the packed bed of iron metal particles again.
In the method of the present invention, there is no particular limitation on the timing of starting the cleaning of the packed bed of iron metal particles. For example, when a predetermined time has elapsed since the previous cleaning, when the reduction treatment of a predetermined amount of wastewater is completed, When the differential pressure of the packed bed of particles reaches a predetermined value, it can be arbitrarily set.
[0010]
Drawing 3 is an explanatory view of one mode of the washing method of the water treatment equipment of the present invention. In this embodiment, wastewater containing an oxidizing substance as an impurity is adjusted to pH 5 or lower and then supplied to the iron metal particle packed tower 7. The reduced water whose impurities have been reduced through the packed bed of iron metal particles is sent to the agglomeration tank 9 via the reduced water discharge pipe 8. An alkaline agent is added to the reduced treated water in a coagulation tank, adjusted to be alkaline and iron hydroxide is aggregated, and treated water is obtained by solid-liquid separation. After drainage is passed for a certain period of time, the valve 10 is closed to stop the supply of drainage, the valve 11 is opened and air is sent to the packed bed of iron metal particles to loosen the packed bed. Next, the valve 12 is opened while the air continues to be fed, the washing water is fed by the pump 13 and fed into the packed bed of iron metal particles as a mixed fluid of the washing water and air.
The cleaning waste water discharged from the packed bed of iron metal particles is sent to the pollutant concentration measuring device 15 via the bypass pipe 14 from the reduced treated water discharge pipe 8 used as the cleaning drain pipe. When the pollutant concentration in the cleaning wastewater is lowered to the set value, a signal is sent from the control device 16 to the valve 11 to stop the supply of air and cleaning with only cleaning water is performed. After the cleaning with only the cleaning water is performed for a predetermined time, a signal is sent from the control device 16 to the valve 12 or the valve 12 and the pump 13, the supply of the cleaning water is stopped, and the cleaning of the packed bed of iron metal particles is finished. Next, the valve 10 is opened again, and the reduction treatment of the waste water is resumed.
In the past, contaminants were removed by supplying a mixed fluid of cleaning water and gas to the packed bed of iron metal particles for a certain period of time, but in actual wastewater treatment, the quality of wastewater fluctuates, It was difficult to set the optimal cleaning time because the degree of contaminants adhering to the surface of the iron metal particles was different. According to the method of the present invention, by measuring the concentration of pollutants in the washing wastewater and controlling the supply time of the mixed fluid, it is possible to reliably carry out washing with the minimum amount of washing water, and stably over a long period of time. Impurities in the waste water can be removed.
[0011]
【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
The flue gas desulfurization effluent from a coal-fired power plant was passed through a packed bed of iron metal particles for reduction treatment.
The selenium (VI) concentration in the wastewater is 0.5 mg / L. A column with an inner diameter of 30 mm was filled with 500 mL of spherical iron metal particles having an average particle diameter of 0.6 mm to form an iron metal particle packed layer, and a water treatment apparatus whose process is shown in FIG. 3 was produced. An SS densitometer [Electrochemical Meter Co., Ltd., SSD-10] was used as the pollutant concentration measuring device.
Hydrochloric acid is added to the waste water so that the elution amount of divalent iron ions is 75 mg / L, heated to 70 ° C., and upward flow at a flow rate of 7.5 L / h (LV = 10.6 m / h). I passed water.
Water flow was stopped once every 12 hours, air was supplied at 85 L / h for 20 seconds, the iron metal particle packed bed was loosened, and industrial water was then supplied as washing water with LV = 90 m / Water was passed for 900 seconds at h. Next, the supply of air was stopped, and only cleaning water was passed for 60 seconds. During this time, the suspended solids concentration in the washing waste water was measured. In this way, the packed bed of iron metal particles was washed six times.
Of the obtained 6 washing time-suspended substance concentration curves, the curve with the highest suspended substance concentration and the curve with the lowest suspended substance concentration are shown in FIG. From these curves, it was judged that it was appropriate to continue washing until the suspended solids concentration in the washing wastewater reached 200 mg / L.
Example 2
The same selenium (VI) concentration 0.5 mg / L wastewater as in Example 1 was passed through a packed bed of iron metal particles and reduced in the same manner as in Example 1.
Water flow was stopped every 12 hours, and washing was continued under the same conditions as in Example 1 until the concentration of suspended solids in the washing wastewater reached 200 mg / L. When the suspended solid concentration of the washing wastewater reached 200 mg / L, the air supply was stopped and only the washing water was passed for 60 seconds. Subsequently, the reduction treatment was resumed by switching to drainage water flow.
Reduced treated water flowing out from the packed bed of iron metal particles is led to a coagulation tank, and adjusted to pH 9.5 by adding an aqueous sodium hydroxide solution to coagulate and precipitate iron oxide and the like to obtain treated water. It was.
As a result of performing the reduction process by drainage water flow and the washing process with the mixed fluid of washing water and air for 500 hours, the selenium concentration in the treated water is always 0.1 mg / L or less, and the average value is 0.03 mg. / L. In addition, the average time per washing with the mixed fluid was 280 seconds.
Comparative Example 1
From the data in FIG. 2, for safety, the cleaning time with the mixed fluid of cleaning water and air was set to a constant value of 600 seconds per time, and the drainage water flow was performed in the same manner as in Example 2. A reduction process and a cleaning process using a mixed fluid of cleaning water and air were performed for 500 hours. The selenium concentration in the treated water was always 0.1 mg / L or less, and the average value was 0.03 mg / L.
Comparative Example 2
Reduction treatment by drainage water flow in the same manner as in Example 2 except that the cleaning time with the mixed fluid of cleaning water and air is set to a constant value of 280 seconds, which is the average cleaning time of Example 2 for one time. And the washing | cleaning process by the mixed fluid of washing water and air was performed for 500 hours. The selenium concentration in the treated water reached a maximum of 0.2 mg / L, and the average value was 0.08 mg / L.
[0012]
【The invention's effect】
According to the method of the present invention, when the wastewater containing an oxidizing substance such as peroxosulfuric acid, iodic acid, and selenic acid as impurities is passed through the packed bed of iron metal particles for reduction treatment, Washing can be performed efficiently with an appropriate amount of washing water against fluctuations in the quality of the wastewater, and wastewater treatment can be performed stably over a long period of time.
[Brief description of the drawings]
FIG. 1 is an explanatory diagram of an example of a water treatment apparatus.
FIG. 2 is an example of a graph showing the relationship between washing time and suspended solids concentration.
FIG. 3 is an explanatory view of one aspect of a cleaning method for a water treatment apparatus of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Column 2 Inlet 3 Outlet 4 Porous plate 5 Packing layer 6 of iron metal particles Porous plate 7 Iron metal particle packed tower 8 Reduction treatment water discharge pipe 9 Coagulation tank 10 Valve 11 Valve 12 Valve 13 Pump 14 Bypass pipe 15 Contaminant Concentration measuring device 16 Control device

Claims (3)

A cleaning method of a water treatment apparatus for reducing impurities in water by passing water through a packed bed of iron metal particles, and temporarily stopping the water flow of wastewater to be reduced to the packed bed of iron metal particles, After supplying air to the packed bed of metal particles and loosening the ferrous metal packed bed, supply cleaning water while continuing to supply air, then stop supplying air and allow only cleaning water to flow. After measuring the suspended solids concentration in the wastewater discharged from the packed bed and continuing the washing until the suspended solids concentration reaches 200 mg / L, switch to the drainage water for reduction treatment. A method for cleaning a water treatment apparatus. The cleaning method for a water treatment apparatus according to claim 1 , wherein the cleaning time with only the cleaning water is 0.5 to 3 minutes . The water treatment apparatus cleaning method according to claim 1 or 2, wherein the suspended substance concentration is measured by a sensor provided in a cleaning drain pipe or a bypass of the cleaning drain pipe.

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