JP7189744B2 - Water treatment method and water treatment equipment - Google Patents

Description

TECHNICAL FIELD The present invention relates to a water treatment method and a water treatment apparatus for treating water containing substances to be removed such as boron using a magnesium agent.

Wastewater discharged from various industries containing high concentrations of substances such as boron, fluorine, selenium, heavy metals, suspended solids, etc. must be treated to reduce these substances to below wastewater standards before being discharged. For example, in power generation equipment that burns coal to generate power, etc., desulfurization equipment is installed to purify the exhaust gas. Removes dust, etc. The water that has absorbed sulfur content, dust, etc. is appropriately discharged from the desulfurization facility as desulfurization effluent, treated to a level below the effluent standards, and discharged into the ocean or the like.

This desulfurization effluent usually contains boron, fluorine, selenium, heavy metals (iron, lead, copper, chromium, cadmium, mercury, zinc, arsenic, manganese, nickel, etc.) contained in coal and the like. Among them, boron may be contained at a high concentration as boric acid (H ₃ BO ₃ ) or the like, and may be present in the amount of about 200 to 500 mg-B/L.

In water treatment for boron and fluorine, magnesium oxide is added as a magnesium agent to make these substances insoluble, and solid-liquid separation of sludge containing insolubilized substances is performed to separate these substances from the water to be treated. A method is known (see Patent Document 1). However, the water treated by this method contains components with a slow sedimentation rate, such as fine particles of magnesium oxide, fine particles of insolubilized substances to be treated, and suspended solids originally contained in the wastewater. , turbidity components may remain in the supernatant water. Therefore, a coagulant is added to the treated water for the purpose of reducing the turbidity of the supernatant water.

JP 2005-001949 A

However, as a result of extensive research by the present inventor, the sludge containing the magnesium agent is relatively heavy, and especially the coarsened sludge has too high settling property, so even if it is stirred, it stays at the bottom of the flocculation tank. A problem was found in that it became difficult to discharge from the flocculation tank.

An object of the present invention is to provide a water treatment method and a water treatment apparatus capable of reducing turbidity of treated water and suppressing sludge retention in a flocculation step in water treatment using a magnesium agent.

The present invention comprises a reaction step of adding a magnesium agent to water to be treated containing a substance to be removed to generate an insolubilized substance of the substance to be removed, and adding a coagulant to the reaction water containing the insolubilized substance generated in the reaction step. and a solid-liquid separation step of solid-liquid separating the sludge generated in the aggregation step, wherein the flocculant has a colloid equivalent value of +0.5 meq/g or more and a weight average molecular weight in the range of 1 million to less than 10 million , and a copolymer of dimethylaminoethyl methacrylate methyl chloride quaternary salt and acrylamide, and a methyl chloride quaternary salt of dimethylaminoethyl acrylate. at least one of a copolymer of and acrylamide, a homopolymer of a methyl chloride quaternary salt of dimethylaminoethyl methacrylate, and a homopolymer of a methyl chloride quaternary salt of dimethylaminoethyl acrylate, and the pH in the reaction step is 8 or more, a water treatment method.

In the water treatment method, the magnesium agent preferably contains at least one of a compound containing magnesium and carbonic acid as main components, magnesium hydroxide, and baked products thereof.

In the water treatment method, the substance to be removed preferably contains at least one of boron, fluorine, selenium, and heavy metals.

Further, the present invention includes a reaction means for adding a magnesium agent to water to be treated containing a substance to be removed to generate an insolubilized substance of the substance to be removed, and agglomeration in the reaction water containing the insolubilized substance generated by the reaction means. a flocculation means for adding an agent to flocculate the insolubilized matter; and a solid-liquid separation means for solid-liquid separation of the sludge generated by the flocculation means, wherein the flocculant has a colloid equivalent value of +0.5 meq/g. above and having a weight average molecular weight in the range of 1 million to less than 10 million , and a copolymer of methyl chloride quaternary salt of dimethylaminoethyl methacrylate and acrylamide, methyl chloride 4 of dimethylaminoethyl acrylate At least one of a copolymer of a tertiary salt and acrylamide, a homopolymer of a methyl chloride quaternary salt of dimethylaminoethyl methacrylate, and a homopolymer of a methyl chloride quaternary salt of dimethylaminoethyl acrylate, in the reaction means A water treatment device having a pH of 8 or more .

In the water treatment apparatus, the magnesium agent preferably contains at least one of a compound containing magnesium and carbonic acid as main components, magnesium hydroxide, and baked products thereof.

Preferably, in the water treatment apparatus, the substance to be removed includes at least one of boron, fluorine, selenium, and heavy metals.

ADVANTAGE OF THE INVENTION According to this invention, in the water treatment using a magnesium agent, while reducing the turbidity of treated water, the water treatment method and water treatment apparatus which can suppress sludge retention in a flocculation process can be provided.

BRIEF DESCRIPTION OF THE DRAWINGS It is a schematic block diagram which shows an example of the continuous type water treatment apparatus which concerns on embodiment of this invention. BRIEF DESCRIPTION OF THE DRAWINGS It is a schematic block diagram which shows an example of the batch-type water treatment apparatus which concerns on embodiment of this invention.

An embodiment of the present invention will be described below. This embodiment is an example of implementing the present invention, and the present invention is not limited to this embodiment.

An outline of an example of a water treatment apparatus according to an embodiment of the present invention is shown in FIG. 1, and its configuration will be described.

FIG. 1 is a schematic diagram showing an example of the configuration of a continuous water treatment apparatus according to an embodiment of the present invention. The water treatment apparatus 1 of FIG. 1 includes a reactor 10 as a reaction means for adding a magnesium agent to water to be treated containing a substance to be removed to generate an insolubilized substance of the substance to be removed, and an insolubilized substance produced by the reactor 10. and a sedimentation tank 14 as a solid-liquid separation means for solid-liquid separation of the sludge generated in the flocculation device 12.

The reaction apparatus 10 includes a reaction vessel 16 and a magnesium agent addition line 18 . The reaction tank 16 is provided with a stirring device 20 which is a stirring means having a rotary driving means such as a motor and stirring blades.

The flocculation device 12 includes a flocculation tank 22 and a flocculant addition line 24 . The aggregation tank 22 is provided with a stirring device 26 which is a stirring means having a rotation driving means such as a motor and stirring blades.

In the water treatment apparatus 1 of FIG. 1, a water inflow line 28 is connected to the water inlet of the reaction tank 16 . A magnesium agent addition line 18 is connected to the agent inlet of the reaction tank 16 . One end of a reaction water discharge line 30 is connected to the reaction water outlet of the reaction tank 16 , and the other end of the reaction water discharge line 30 is connected to the reaction water inlet of the aggregation tank 22 . One end of a flocculated water discharge line 32 is connected to the flocculated water outlet of the flocculation tank 22 , and the other end of the flocculated water discharge line 32 is connected to the flocculated water inlet of the sedimentation tank 14 . A coagulant addition line 24 is connected to the chemical inlet of the coagulation tank 22 . A treated water discharge line 34 is connected to the treated water outlet of the sedimentation tank 14 . A sludge discharge line 36 is connected to the sludge outlet of the sedimentation tank 14 .

The operation of the water treatment method and the water treatment apparatus 1 according to this embodiment will be described.

The water to be treated containing the substance to be removed is supplied to the reaction tank 16 through the water-to-be-treated inflow line 28 , and the magnesium agent is supplied to the reaction tank 16 through the magnesium agent addition line 18 . In the reaction tank 16, the water to be treated and the magnesium agent are stirred by the stirring device 20, and the substances to be removed in the water to be treated are insolubilized by the magnesium agent to produce insolubilized substances (reaction step).

The reaction water containing the insolubilized substances in the reaction tank 16 is supplied to the flocculation tank 22 through the reaction water discharge line 30 , and the flocculant is supplied to the flocculation tank 22 through the flocculant addition line 24 . In the flocculation tank 22, the insolubilized substances and the flocculant are stirred by the stirring device 26, and the insolubilized substances in the reaction water are flocculated by the flocculant to produce sludge (flocculation step).

The flocculated water containing sludge in the flocculation tank 22 is supplied to the sedimentation tank 14 through the flocculated water discharge line 32 . In the sedimentation tank 14, solid-liquid separation is performed into treated water and sludge (solid-liquid separation step). The treated water that has undergone solid-liquid separation is discharged out of the system through a treated water discharge line 34 . The solid-liquid separated sludge is discharged out of the system through a sludge discharge line 36 .

The water treatment apparatus 1 shown in FIG. 1 has one reaction tank 16, but the number of reaction tanks is not limited to one, and two or more reaction tanks in series may be used. The water treatment apparatus 1 has one reaction tank 16 and one coagulation tank 22. In addition to the magnesium agent, a coagulant is added to the one reaction tank to insolubilize the substances to be removed and remove the insolubilized substances. The reaction vessel may also take on the role of flocculation.

FIG. 2 is a schematic diagram showing an example of the configuration of a batch-type water treatment apparatus according to an embodiment of the present invention. The water treatment apparatus 2 of FIG. 2 includes reaction means for adding a magnesium agent to the water to be treated containing the substance to be removed to generate an insolubilized substance of the substance to be removed, and adding a coagulant to the reaction water containing the generated insolubilized substance. , a batch-type reactor 40 is provided as aggregating means for aggregating insolubilized substances and solid-liquid separating means for solid-liquid separation of the generated sludge.

The batch reactor 40 includes a reaction tank 44 , a magnesium agent addition line 46 and a flocculant addition line 48 . The reaction tank 44 is provided with a stirring device 50 which is a stirring means having a rotary driving means such as a motor and stirring blades.

In the water treatment apparatus 2 of FIG. 2, a water inlet line 52 is connected to the water inlet of the reaction tank 44 . A magnesium agent addition line 46 and a coagulant addition line 48 are connected to the agent inlet of the reaction tank 44 . A treated water discharge line 54 is connected to the treated water outlet of the reaction tank 44, and a sludge discharge line 56 is connected to the sludge outlet.

The operation of the water treatment method and the water treatment device 2 according to this embodiment will be described.

After the water to be treated containing the substance to be removed is supplied to the reaction tank 44 through the water-to-be-treated inflow line 52 , the magnesium agent is supplied to the reaction tank 44 through the magnesium agent addition line 46 . In the reaction tank 44, the water to be treated and the magnesium agent are stirred by the stirring device 50, and the substances to be removed in the water to be treated are insolubilized by the magnesium agent to produce insolubilized substances (reaction step).

Flocculant is then supplied to reaction vessel 44 through flocculant addition line 48 . In the reaction tank 44, the insolubilized substances and the coagulant are stirred by the stirring device 50, and the insolubilized substances in the reaction water are coagulated by the coagulant to produce sludge (coagulation step).

Next, the stirring device 50 is stopped, and solid-liquid separation is performed into treated water and sludge in the reaction tank 44 (solid-liquid separation step). The solid-liquid separated sludge deposited on the bottom is discharged out of the system through the sludge discharge line 56 . After the sludge is discharged, the solid-liquid separated treated water in the reaction tank 44 is discharged out of the system through the treated water discharge line 54 .

Hereinafter, the magnesium agent and flocculant used in the water treatment method and water treatment apparatus according to the present embodiment will be described in detail.

The magnesium agent used in the water treatment apparatus 1 shown in FIG. 1 and the water treatment apparatus 2 shown in FIG. It contains at least one of magnesium oxide (Mg(OH) ₂ ) and sintered magnesium hydroxide.

Examples of compounds containing magnesium and carbonic acid as main components include basic magnesium carbonate ( _{mMgCO3.Mg (} OH) _2.nH2O ), magnesite (a mineral containing magnesium carbonate as a main component) and dolomite (carbonic acid). minerals containing calcium and magnesium carbonate as main components), and the like. Basic magnesium carbonate has m of 3 to 5 and n of 3 to 7 with respect to Mg(OH) ₂ . Magnesium hydroxide also includes minerals containing magnesium hydroxide as a main component, such as brucite.

When the magnesium agent used in the present embodiment is added to water, a portion of the magnesium agent dissolves to form magnesium ions and hydroxide ions, increasing the pH of the water to be treated. At this time, the substance coprecipitated by forming an insolubilized substance with the magnesium ion becomes a substance to be removed by the magnesium agent. In addition, the pH of the water to be treated increases, and magnesium ions and hydroxide ions form an insolubilized substance of magnesium hydroxide, and substances adsorbed to this insolubilized substance also become substances to be removed. That is, the substance to be removed contained in the water to be treated is not particularly limited as long as it forms an insolubilized substance with the magnesium agent or is insolubilized by being adsorbed on magnesium hydroxide. borate ion), fluorine (e.g., fluoride ion), selenium, and at least one of heavy metals (e.g., iron, lead, copper, chromium, cadmium, mercury, zinc, arsenic, manganese, nickel, etc.) Preferably, it contains at least one of boron, fluorine, selenium, and heavy metals.

In the water treatment using the magnesium agent of the present embodiment, the flocculant that can reduce the turbidity of the treated water and suppress sludge retention in the flocculation step has a colloid equivalent value of +0.5 meq / g or more, Moreover, it is a positively charged cationic polymer flocculant having a weight-average molecular weight in the range of 1,000,000 to less than 10,000,000. Among the cationic polymer flocculants, the colloid equivalent value is preferably in the range of +0.5 to +5.5 meq/g, more preferably in the range of +1.0 to +5.5 meq/g. A range of +1.8 to +5.5 meq/g is more preferred, and a range of +5.0 to +5.5 meq/g is particularly preferred. The weight average molecular weight is preferably in the range of 1 million to 10 million, more preferably in the range of 3 million to 9 million.

The colloid equivalent value is an index representing the strength of electric charge in a compound, and the larger the absolute value of the numerical value, the stronger the electric charge of the compound. A colloidal equivalent value is determined by the colloidal titration method. Specifically, when measuring the colloidal equivalent value of a cationic compound, an aqueous solution in which a drug is dispersed is titrated with a potassium polyvinyl sulfate solution. The pH of the solution during titration should be 4-10.

The weight-average molecular weight of the polymer flocculant can be measured by gel permeation chromatography using a high-performance liquid chromatography device (manufactured by Tosoh Corporation, HLC-8320GPC).

Examples of such cationic polymer flocculants include copolymers of methyl chloride quaternary salt of dimethylaminoethyl methacrylate and acrylamide, copolymers of methyl chloride quaternary salt of dimethylaminoethyl acrylate and acrylamide, Examples include homopolymers of quaternary methyl chloride salts of dimethylaminoethyl methacrylate, homopolymers of quaternary methyl chloride salts of dimethylaminoethyl acrylate, and polyamidines.

In water treatment using the magnesium agent of the present embodiment, if it is possible to reduce the turbidity of the treated water and suppress sludge retention in the flocculation step, in addition to the cationic polymer flocculant, an inorganic flocculant, an organic flocculation At least one of an agent, an anionic polymer flocculant, a nonionic polymer flocculant and an amphoteric polymer flocculant may be used in combination.

Examples of inorganic flocculants include iron-based inorganic flocculants such as ferric chloride and polyferric sulfate, and aluminum-based inorganic flocculants such as aluminum sulfate and polyaluminum chloride.

Examples of the organic coagulant include polyethyleneimine, dimethylamine/epichlorohydrin/ammonia condensate, dimethylamine/epichlorohydrin/ethylenediamine condensate, polydiallyldimethylammonium chloride, dicyandiamine/formaldehyde condensate, and the like. .

Examples of anionic polymer flocculants and nonionic polymer flocculants include polyacrylamide, sodium polyacrylate, and sodium acrylamide propanesulfonate.

The water treatment conditions and the like in the water treatment method and the water treatment apparatus according to this embodiment will be described below.

The water to be treated is not particularly limited as long as it contains at least one of the above substances to be removed. The water to be treated is water that is intended to be discharged into public water areas after treatment, or water that is intended to be reused after removal of soluble substances using purification means such as reverse osmosis membranes after use. You can also use fresh water. Examples of the former include desulfurization wastewater, plating wastewater, and glass manufacturing wastewater from coal-fired power plants. In the latter case, the water in the water recovery system in various industrial plants is targeted, and the water treatment method according to the present embodiment is performed in the preceding stage of the reverse osmosis membrane process to remove substances that cause blockage of the reverse osmosis membrane. The main purpose is to reduce In addition, since the magnesium agent used in the water treatment method according to the present embodiment can aggregate suspended solids in water, the water to be treated may contain suspended solids other than the substances to be removed.

The content of substances to be removed in the water to be treated is, for example, in the range of 0.01 to 75 mmol/L, and the content of suspended solids is in the range of, for example, 50 to 1,000 mg/L.

The content of boron in the water to be treated is, for example, in the range of 10 mg/L to 800 mg/L, preferably in the range of 20 mg/L to 500 mg/L, more preferably in the range of 100 mg/L to 500 mg/L. is. The content of fluorine in the water to be treated is, for example, in the range of 15 mg/L to 950 mg/L, preferably in the range of 20 mg/L to 100 mg/L. The content of selenium in the water to be treated is, for example, in the range of 0.1 mg/L to 10 mg/L, preferably in the range of 0.1 mg/L to 5 mg/L. The content of heavy metals in the water to be treated is, for example, in the range of 0.1 mg/L to 50 mg/L, preferably in the range of 0.1 mg/L to 10 mg/L.

The amount of the magnesium agent added in the reaction step varies depending on the type and concentration of the substance to be removed in the water to be treated, the required quality of the treated water (target substance removal rate), coexisting substances, etc., but is preferably 1 g/L or more. is 3 g/L or more, more preferably 5 g/L or more. In addition, although the pH of the water to be treated increases due to the addition of the magnesium agent, it is preferable to add the magnesium agent in such an amount that the pH of the water to be treated in the reaction step becomes, for example, 8 or more, preferably 9 or more, more preferably 10 or more. .

The reaction temperature in the reaction step may be, for example, as long as the water to be treated is 0° C. or higher and does not freeze, but the higher the temperature, the better the removal performance of the substance to be removed. It is in the range of 40°C.

The reaction time in the reaction step is not particularly limited as long as the substance to be removed is sufficiently insolubilized, but is, for example, in the range of 1 minute to 720 minutes, preferably in the range of 10 to 120 minutes.

The amount of the polymer flocculant added in the flocculation step is, for example, in the range of 0.1 mg/L to 10 mg/L, preferably in the range of 0.1 mg/L to 5 mg/L. If the amount of polymer flocculant added is less than 0.1 mg/L, flocculation may be insufficient, and if it exceeds 10 mg/L, sludge retention may occur in the flocculation step.

The aggregation temperature in the aggregation step is, for example, as long as the reaction water is 0°C or higher and does not freeze, preferably 15°C or higher, more preferably in the range of 20 to 40°C.

The aggregation time in the aggregation step is not particularly limited as long as the insolubilized material is sufficiently aggregated.

The stirring speed in the aggregation step is not particularly limited as long as the insolubilized material is sufficiently aggregated.

Sludge retention in the flocculation process is more likely to occur when the SS concentration in the tank is high, and the SS concentration is preferably 40,000 mg/L or less.

The solid-liquid separation method in the solid-liquid separation step is not particularly limited as long as it is a method capable of separating aggregates and treated water. In the case of continuous water treatment equipment, in addition to natural sedimentation using a sedimentation tank, forced sedimentation using a centrifugal separator, flotation using air bubbles, membrane filtration using microfiltration membranes, etc. It's okay. In the case of a batch-type water treatment apparatus, natural sedimentation treatment within a reaction tank is desirable.

In the treated water obtained by the water treatment method and water treatment apparatus according to the present embodiment, the content of substances to be removed is, for example, 25 mmol/L or less, and the content of suspended solids is, for example, 20 mg/L or less. can be

The contents of boron, fluorine, selenium, and heavy metals in the treated water can be, for example, 250 mg/L or less, 20 mg/L or less, 1 mg/L or less, and 0.5 mg/L or less.

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to examples and comparative examples, but the present invention is not limited to the following examples.

<Example 1>
Here, desulfurization effluent from a coal-fired power plant was used as the water to be treated, and the treatment was performed according to the following procedure. The desulfurization effluent contained suspended matter, boron, fluorine, selenium, calcium, magnesium, manganese, iron, zinc, cadmium and mercury. The contents of boron, fluorine, selenium, and heavy metals in the water to be treated were 700 mg/L, 30 mg/L, and 0.1 mg/L, respectively, and the contents of heavy metals (for example, manganese) were 10 mg/L. The content of boron is measured by azomethine H absorption spectrophotometry (JIS K 0102), fluorine by lanthanum-alizarin complexion absorption spectrophotometry (JIS K 0102), and selenium and heavy metals by ICP mass spectrometry (JIS K 0102). It was measured.

Put 300 mL of the desulfurization effluent in a glass beaker, add 5 g / L of commercially available magnesium oxide, which is a baked product of magnesium hydroxide (an amount that makes the pH of the water to be treated 9 or higher), and rotate at a rotation speed of 150 rpm. Stir for 10 minutes. After stirring, 1 mg/L of cationic polymer flocculant A, which is a homopolymer of methyl chloride quaternary salt of dimethylaminoethyl methacrylate having a colloid equivalent value of +5.0 meq/g and a weight average molecular weight of 3 million, is added to the treated water, The mixture was stirred at a rotation speed of 150 rpm for 1 minute and at a rotation speed of 40 rpm for 3 minutes. The degree of sludge dispersion was calculated from the following equation from the water surface height and sludge flow height during stirring at a rotation speed of 40 rpm. The higher the degree of sludge dispersibility, the better the sludge dispersibility and the easier it is to suppress sludge retention in the flocculation step. The water surface height is the height from the bottom of the glass beaker to the water surface, and the sludge flow height is the height from the bottom of the glass beaker to the interface where the sludge flows. After stirring, the treated water was allowed to stand for 5 minutes, and the turbidity of the treated water was measured. Turbidity was measured using a turbidity meter (Nippon Denshoku Co., Ltd., Water Analyzer 2000N). Table 1 shows the results.
Sludge dispersion degree (%) = sludge flow height ÷ water surface height × 100

The colloidal equivalent value of the flocculant was determined by colloidal titration using a polyvinyl potassium sulfate solution. Specifically, when measuring the colloid equivalent value of the cationic polymer flocculant, 1.67 g of the flocculant was collected in a 100 mL conical beaker, and 98.3 mL of pure water was added and stirred. Then, hydrochloric acid was added to adjust the pH to 4, and the mixture was stirred for 1 minute. After stirring, 2 to 3 drops of toluidine blue indicator (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., for colloidal titration) are added and stirred, and N/400 polyvinyl potassium sulfate (manufactured by Fujifilm Wako Purechemical Co., Ltd., for colloidal titration) is added. , molecular weight (162.21)n) solution. The end point was defined as a point at which the color of the sampled water changed from blue to reddish purple and was maintained for 10 seconds or more.

In addition, when measuring the colloid equivalent value of an anionic polymer flocculant, 95 mL of pure water in a 100 mL conical beaker and N / 200 methyl glycol chitosan (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., for colloidal titration, molecular weight ( 375.20)n) was added in 5 mL, 0.1N caustic soda solution was added and stirred for 1 minute. Then, 1.67 g of a flocculant was added and stirred for 5 minutes. After stirring, 2 to 3 drops of toluidine blue indicator were added and stirred, followed by titration with N/400 polyvinyl potassium sulfate solution in the same manner as above.

<Example 2>
Colloid equivalent value +3.2 meq / g, except for using a cationic polymer flocculant B which is a copolymer of acrylamide and a methyl chloride quaternary salt of dimethylaminoethyl methacrylate having a weight average molecular weight of 5 million. tested as well. Table 1 shows the results.

<Example 3>
Colloid equivalent value +1.8 meq / g, except for using a cationic polymer flocculant C which is a copolymer of acrylamide and a methyl chloride quaternary salt of dimethylaminoethyl methacrylate having a weight average molecular weight of 8 million. tested as well. Table 1 shows the results.

<Example 4>
Colloid equivalent value + 4.5 meq / g, except for using a cationic polymer flocculant D which is a copolymer of methyl chloride quaternary salt of dimethylaminoethyl acrylate and acrylamide having a weight average molecular weight of 8,500,000. tested as well. Table 1 shows the results.

<Comparative Example 1>
A test was conducted in the same manner as in Example 1, except that no polymer flocculant was added. Table 1 shows the results.

<Comparative Example 2>
The test was carried out in the same manner as in Example 1 except that the anionic polymer flocculant E having a colloid equivalent value of -1.4 meq/g and a weight average molecular weight of 17 million was used. Table 1 shows the results.

<Comparative Example 3>
The test was carried out in the same manner as in Example 1 except that an anionic polymer flocculant F having a colloid equivalent value of -5.1 meq/g and a weight average molecular weight of 18 million was used. Table 1 shows the results.

As shown in Table 1, the turbidity of the supernatant water of Examples 1, 2, 3 and 4 to which the cationic polymer flocculant was added was 21 degrees, 42 degrees, 39 degrees and 42 degrees, respectively. +5.0 meq/g of polymer flocculant A was the best. On the other hand, the supernatant water turbidity of Comparative Example 1, in which no polymer flocculant was added, was 95 degrees. From this result, it can be said that the cationic polymer flocculant is effective in reducing the turbidity of the treated water. Moreover, the degree of sludge dispersibility was 100% for all cationic polymer flocculants, and no sludge retention was observed.

On the other hand, the turbidity of the supernatant water of Comparative Examples 2 and 3 with the addition of an anionic polymer flocculant was 12 degrees and 20 degrees, respectively. there were. However, the sludge dispersibility was 22% and 33%, respectively, and sludge retention occurred in the flocculation process.

From the above results, it can be said that in water treatment using a magnesium agent, a cationic polymer flocculant capable of both reducing the turbidity of treated water and suppressing sludge retention in the flocculation process is suitable. Comparing the weight average molecular weights of the cationic polymer flocculant and the anionic polymer flocculant, the former was 3 million to 8.5 million, while the latter was 17 million to 18 million. Therefore, it can be said that high-molecular-weight flocculants tend to form highly precipitable sludge and are not suitable for water treatment using magnesium agents.

<Example 5>
12 g/L of magnesium oxide was added to 300 mL of the desulfurization waste water, and the mixture was stirred for 180 minutes at a rotational speed of 150 rpm. Subsequent tests were conducted in the same manner as in Example 1. Moreover, the content of boron in the treated water was measured by the method described above. Table 2 shows the results.

As shown in Table 2, the treated water to which magnesium oxide and polymer flocculant A were added had a supernatant water turbidity of 10 degrees, a sludge dispersion of 100%, and a boron content of 170 mg/L. From these results, it can be said that the method of the example can satisfactorily reduce the turbidity of the treated water, suppress the retention of sludge in the coagulation step, and can also satisfactorily treat boron.

Thus, according to the method of the example, in the water treatment using the magnesium agent, the turbidity of the treated water could be reduced, and sludge retention in the flocculation step could be suppressed.

1, 2 water treatment equipment, 10 reaction device, 12 flocculation device, 14 sedimentation tank, 16, 44 reaction tank, 18, 46 magnesium agent addition line, 20, 26, 50 stirring device, 22 flocculation tank, 24, 48 flocculant Addition line, 28, 52 treated water inflow line, 30 reaction water discharge line, 32 condensed water discharge line, 34, 54 treated water discharge line, 36, 56 sludge discharge line, 40 batch reactor.

Claims (6)

a reaction step of adding a magnesium agent to the water to be treated containing the substance to be removed to generate an insolubilized substance of the substance to be removed;
a flocculation step of adding a flocculating agent to the reaction water containing the insolubilized matter generated in the reaction step to flocculate the insolubilized matter;
A solid-liquid separation step for solid-liquid separation of the sludge generated in the aggregation step;
including
The flocculant has a colloid equivalent value of +0.5 meq/g or more, a weight average molecular weight in the range of 1 million to less than 10 million , and a methyl chloride quaternary salt of dimethylaminoethyl methacrylate and acrylamide. a copolymer of dimethylaminoethyl acrylate methyl chloride quaternary salt and acrylamide, a homopolymer of dimethylaminoethyl methacrylate methyl chloride quaternary salt, and a methyl chloride quaternary salt of dimethylaminoethyl acrylate comprising at least one of a homopolymer;
A water treatment method , wherein the pH in the reaction step is 8 or more . The water treatment method according to claim 1,
A water treatment method, wherein the magnesium agent contains at least one of a compound containing magnesium and carbonic acid as main components, magnesium hydroxide, and a calcined product thereof. The water treatment method according to claim 1 or 2,
The water treatment method according to claim 1, wherein the substance to be removed contains at least one of boron, fluorine, selenium, and heavy metals. a reaction means for adding a magnesium agent to water to be treated containing a substance to be removed to generate an insolubilized substance of the substance to be removed;
aggregating means for adding a flocculating agent to the reaction water containing the insolubilized matter generated by the reaction means to agglomerate the insolubilized matter;
Solid-liquid separation means for solid-liquid separation of the sludge generated by the aggregation means;
with
The flocculant has a colloid equivalent value of +0.5 meq/g or more, a weight average molecular weight in the range of 1 million to less than 10 million , and a methyl chloride quaternary salt of dimethylaminoethyl methacrylate and acrylamide. a copolymer of dimethylaminoethyl acrylate methyl chloride quaternary salt and acrylamide, a homopolymer of dimethylaminoethyl methacrylate methyl chloride quaternary salt, and a methyl chloride quaternary salt of dimethylaminoethyl acrylate comprising at least one of a homopolymer;
A water treatment apparatus , wherein the reaction means has a pH of 8 or higher . The water treatment device according to claim 4 ,
A water treatment apparatus, wherein the magnesium agent includes at least one of a compound containing magnesium and carbonic acid as main components, magnesium hydroxide, and a baked product thereof. The water treatment device according to claim 4 or 5 ,
A water treatment apparatus, wherein the substance to be removed includes at least one of boron, fluorine, selenium, and heavy metals.

Images