KR19990076100A - Sedimentation and Removal of Salts in Contaminated Water Using Alumina Cement, Quicklime, and Sulfate - Google Patents

Abstract

The present invention provides a method for the precipitation of nitrates, nitrites, sulfates, hydrochlorides, phosphates and the like present in groundwater, sewage or wastewater through mixed stirring of alumina cement, quicklime and sulfate compounds, and a continuous process method accordingly.

Description

Sedimentation and Removal of Salts in Contaminated Water Using Alumina Cement, Quicklime, and Sulfate

The present invention is a method for controlling the reaction rate by adding a sulfate compound in the precipitation removal of salts such as nitrates, nitrites, sulfates, chlorine salts, phosphates, etc. present in groundwater, surface water or wastewater using alumina cement and quicklime; To a continuous process thereof.

Many of the substances contained in groundwater, wastewater or sewage have insufficient purification effect in general treatment operations and processes. Various inorganic materials including inorganic salts and complex organic synthetic materials are the main culprit, and various wastewater advanced treatments are required. Among them, compounds containing nitrogen and phosphorus have been studied since the 1960's, which causes eutrophication by accelerating plant growth, and especially nitric acid, which causes blue cyanosis of infants.

In general, high nitric acid concentrations can be lowered by dilution with low nitric acid sources. However, when it is difficult to use a low nitric acid source, a nitric acid removal reaction is required. Techniques that have been used to remove nitric acid include ion exchange resins, biological nitrification and denitrification, chemical reduction, reverse osmosis, and electrodialysis. Among them, the most practical and available processes for large-scale water purification are ion exchange resin and biological denitrification.

However, both processes have very serious disadvantages. Among them, the ion exchange resin method is the best in terms of cost, but it is limited to the treatment of concentrated by-products and is therefore only possible in coastal areas or areas where there is no possibility of eutrophication. In addition, since a large amount of salt must be added, the operating cost is high, and the water quality itself has a large corrosive property. In general, biological denitrification is known to be the most economical by-products without worrying about by-products, but there are also many problems to be solved, such as post-treatment, causing problems with carbon sources, or sensitive control.

Ion exchange resins are basically physicochemical processes that require regeneration of cyclic resins. Periodic regeneration of the consumed resin may be performed using sodium chloride or sodium bicarbonate, but as a result must be reprocessed or discarded with high concentrations of nitric acid, sodium chloride, sodium bicarbonate. However, ever-increasing environmental concerns and regulations have made it difficult to dispose of reclaimed materials in recent years, making widespread application of this process difficult. Another problem is that the groundwater contains many anions in addition to nitric acid, making it difficult to remove the selective nitrate. For example, when sulfate ions, chlorine ions, etc., together with nitrate ions are present at the same time, removal of only nitrate ions is difficult and the removal efficiency is lowered. In addition, sulfuric acid and nitrate ions are exchanged with the chlorine ions of the resin, which increases the amount of chlorine in the water that can cause corrosion of the pipe and also exceeds the threshold of chlorine content available for drinking water (200 mg / L). The problem is that you can. In addition, the amount of NaCl used for the regeneration of the ion exchange resin is increased, which may cause another environmental problem, and the risk of nitric acid being released as it is during the regeneration of the resin cannot be overlooked.

Chemical removal of nitric acid using iron hydroxide has been studied mainly in the United States. It is known that ferrous sulfate forms are the most economical among various reducing materials. Reduction of nitric acid using ferrous metals requires the use of 1 to 5 ppm of copper or silver catalysts, the best results being obtained at pH 8.0. These conditions can be adjusted using lime or soda. About 70% of the reactants are usually obtained as a gas of nitrogen or nitrogen oxides and the rest is reduced to ammonia. This reaction has the disadvantage that it is difficult to reduce to a complete nitrogen gas and the use of ferrous metal is too large.

Biological denitrification is most widely used for the purification of waste water and septic tank effluents. Denitrifying bacteria reduce nitric acid to nitrogen gas when organic substrates are present. The most widely used substrates include methanol, which is inexpensive and effective. Biological denitrification using various types of filtration tanks with bacterial supports has been studied. In particular, the time required for the growth of bacteria and the temperature of the reaction tank have a great effect on the efficiency, and there are control difficulties such as careful supply of methanol for sufficient consumption, and the blockage caused by the growth of microorganisms is periodic. Can occur.

In addition, although precipitation methods using aluminum and calcium have been disclosed for the removal of nitrate ions, the methods up to now are not able to control the precipitation reaction rate and the reaction rate is very fast, so that the reactants are administered in large quantities, which is why the continuous process This was impossible. That is, if the reaction rate of the reactant alumina cement or calcium aluminate and calcium oxide proceeds too fast, excessive calcined calcium aluminate or alumina cement is hydrated at a rapid rate compared to the nitrate ions to be treated to further remove precipitates. By not being able to carry out the reaction and adding additional reactants, the reactants were abused in excess of the quantity to be treated, accompanied by the generation of large amounts of sludge, which in turn increased the operating costs of this treatment process, thereby actually removing wastewater. Or it was difficult to apply to contaminated water. Therefore, in order for the precipitation removal reaction of nitrate ions to be practical, the control of the hydration reaction rate and the concentration utilization technology of the sludge should be preceded, and thus, it may be competitive in ion exchange resin method or biological treatment method.

On the other hand, main causes of phosphorus generation include domestic wastewater and agricultural return water. Phosphorus promotes the growth of aquatic plants, resulting in eutrophication. Phosphorus in wastewater can be removed by 10% from conventional biological treatment as primary treatment, but for further treatment, chemical precipitation using lime, alum, iron (III) chloride and iron (III) sulfate can be insoluble. Only possible through However, such drug additions result in an increase in dissolved solids. On the other hand, ion exchange resin method, reverse osmosis method, ultrafiltration method, and electrodialysis method are spotlighted as treatments with high selectivity while suppressing the generation of sludge by existing flocculation or precipitation. However, in most cases, pretreatment such as primary and secondary treatments and adsorption of activated carbon should be preceded and costly and careful consideration should be made.

Various salts present in groundwater, sewage, and wastewater can be controlled faster and more economically than conventional physicochemical or biological methods, while controlling the reaction rate, thereby making it practical for groundwater, sewage and wastewater. It is an object of the present invention to provide a simple, effective and inexpensive water treatment process which makes it possible and allows such a precipitation reaction to be carried out in a continuous process.

1 is a continuous process diagram of a salt removal reaction of a salt using a tubular reactor and a precipitation filtration tank according to the present invention.

2 is a continuous process chart of the precipitation removal reaction of salt using a tubular reactor, a secondary stirring tank and a precipitation filtration tank according to the present invention.

Explanation of symbols for the main parts of the drawings

1: powder feeder 2: agitator

3: double tubular reactor 4: settling tank

5: flat filtration membrane device 6: sludge discharge valve

7: contaminated water 8: treated water

9: reactant (alumina cement, quicklime) 10: backwash device

11: secondary stirring tank

This object of the present invention was achieved by adding a sulfate compound at the beginning or the middle of the reaction to control the reaction rate based on the precipitation method of nitric acid using aluminum and calcium, and providing a continuous process thereof.

The present invention consists of alumina cement or commercially available alumina cement, which is determined to be defective in the calcining process, is mixed with quicklime in a fixed ratio and administered in wastewater or sewage, and a salt compound is added to remove salts in the contaminated water. .

In the process method of the present invention, the water-soluble sulfate is appropriately added at the beginning or the middle of the hydration reaction of alumina cement to control the reaction rate of the hydration reaction, that is, by delaying the hydration reaction according to the nitrate ion in the contaminated water detected in a small amount. For example, alumina cement and quicklime can be used more efficiently. Therefore, it is possible to reduce the amount of alumina cement and quicklime and the amount of sludge produced thereby.

As the sulfate compound, any sulfate compound dissolved in water and present as a sulfate can be used. Preferably, calcium sulfate (CaSO ₄ ), potassium sulfate (K ₂ SO ₄ ), sodium sulfate (Na ₂ SO ₄ ), One selected from the group consisting of ferrous sulfate (FeSO ₄ .7H ₂ O), ferric sulfate (Fe ₂ (SO ₄ ) ₃ .5H ₂ O), and combinations thereof.

The amount of sulfate used will vary depending on the process, but if the amount is too small, the reaction rate control effect will be reduced and the reactant will have to be added in excess. If the amount is too large, the delay rate will be too large, resulting in high process efficiency. Will fall. Therefore, the sulfate is preferably added at a concentration of 0.001 to 0.01 M.

As shown in FIG. 1, a specific reaction process of the present invention is composed of a double tubular reactor 3 and a filtration membrane settling tank 4 and 5 to perform continuous removal of salts in a minimal process for the reaction. Can be. Here, the filtration membrane-embedded sedimentation tank may be mounted separately from the sedimentation tank and the filtration tank. In the reaction process of the present invention, a powder supply device (1) rather than a solution is required to prevent pre-hydration of the alumina cement. The contaminated water to be treated, alumina cement and quicklime enter the reactor (3) and are mixed and stirred at a constant rate to proceed the precipitation reaction of the salt component in the contaminated water and the hydration reaction of the alumina cement, and the sulfate appropriately at the beginning or the middle of the reaction. Is added to control the reaction rate. In this way, the insoluble compound and the sludge produced in the reactor 3 are transferred to the filtration membrane built-in settling tanks 4 and 5 as shown in FIG. 1 to precipitate the insoluble compound and the sludge. In the process of the present invention, the filtration membrane-containing sedimentation tanks 4 and 5 periodically back-permeate the sludge deposited on the filtration membrane 5 with natural precipitation and precipitate it again, so that efficient precipitation and filtration can be achieved in one unit process.

Another process of the present invention, as shown in Figure 2, consists of additionally installing a secondary stirring tank 11 together with the tubular reactor, in this secondary stirring tank 11 to concentrate the sludge exiting the tubular reactor Afterwards, the mixture was re-reacted with secondary mixing and stirring with contaminated water, so that even a small amount of the reactant caused effective salt precipitation.

In addition, in the process of the present invention, calcium ions and aluminum ions eluted after the reaction are precipitated by addition of carbonates, respectively, and precipitated by neutralization. More specifically, the residual calcium ions in the treated water were precipitated with calcium carbonate by adding carbonates such as slaked lime, sodium carbonate and potassium carbonate, and then the treated water in a basic state was neutralized with an acid such as sulfuric acid or hydrochloric acid and treated in the treated water. Residual aluminum ions are precipitated off with aluminum hydroxide. Here, the carbonate is added in an amount such that sufficient precipitation reaction with calcium ions can occur, and an acid is added to the treated water in a basic state after that in an amount such that the final pH is close to neutral, and the final treated water Can be discharged. As such, the method of precipitating and removing calcium ions with carbonate is easier and more economical than conventional treatment with CO ₂ .

Such a continuous process method of the present invention controls the hydration reaction rate of the alumina cement using sulfate, and at the same time the influent is continuously introduced to allow the precipitation reaction to occur, so that the alumina cement in the contaminated water in the reactor By causing a sufficient precipitation reaction with nitrate ions and the like and minimizing the hydration reaction with water, the amount of alumina cement used is greatly reduced compared to the batch reaction.

The precipitation removal method of the present invention can be applied to ions such as sulfuric acid, hydrochloric acid, phosphoric acid and nitrous acid in addition to nitric acid, and can be widely used for removing salts in various wastewaters. In addition, in the case of high concentration of contaminated water, a multistage settling reaction is also possible in order to finally treat it at a low concentration below the water quality standard.

This process method of the present invention can reduce problems such as the use of additional salts or corrosion due to the presence of salts in the treated water compared to the conventional ion exchange resin method, and reduces the enormous construction cost due to low reaction rate such as biological denitrification The burden on the treatment process can be reduced. In addition, even in the presence of a salt concentration of 1000 ppm or more, it is possible to treat at a large reaction rate without dilution, so that it can be effectively used for removing salt in general industrial wastewater. It can also be used as a nitric acid removal process for toxic wastewater, where biological denitrification is not possible.

The sludge obtained in the precipitation process of the present invention contains a large amount of nitric acid, which can be applied as a sustained-release fertilizer for acidic soil reforming, or can be restored to cement or reused as a reactant in the treatment process of the present invention through a calcination process. You can reduce the burden as much as possible.

In the following, the present invention has been described in more detail with reference to Examples. This embodiment is only intended to illustrate the invention, but the invention is not limited thereto.

Example 1

Removal of Nitrate Using Alumina Cement and Calcium Oxide

Alumina cements sold in Korea are classified into dry weight ratio of 50%, 70%, and 80% alumina cement, depending on the components of alumina. Each manufacturing process and firing conditions are very different, with 50% and 70% alumina cement being produced by firing and 80% alumina cement being obtained by melting. Therefore, there is a big difference in the rate of reaction with water and the resultant, which also affects precipitation of nitrate by hydration reaction. As shown in Table 1 below, nitrate removal experiments were performed by mixing alumina of these alumina cements having different alumina contents with calcium oxide in a constant molar ratio (Al / NO ₃ mole ratio: 6.41, Ca / NO ₃ mole ratio: 9). It was.

As a result of this experiment, 50% alumina cement with low alumina content showed the best removal efficiency and removal rate of nitrate, so that the concentration of nitrate rapidly decreased from the initial 1059 ppm to 205 ppm about 60 minutes at the start of the reaction. Indicated. On the other hand, in the case of 80% alumina cement, even after 90 minutes from the start of the reaction, the reduction of nitrate was only 200 ppm, resulting in a removal efficiency of 19.7%. This indicates that differences in the firing process and the resulting hydrate form affect the formation of insoluble nitrate compounds. In addition, when alumina alone was used, no precipitation of nitric acid was found, indicating that only calcined compounds of alumina and calcium oxide could be insolubilized into new compounds including nitrates through a hydration reaction.

Alumina 80% Alumina Cement 70% Alumina Cement 50% Alumina Cement Initial Nitrate Concentration (mg / L) 1025 1047 1040 1060 Alumina Cement Volume (mg / L) 5253 6550 7500 10480 Quicklime Volume (M) 0.144 0.11 0.12 0.075 Mol of Al / NO ₃ 6.4 6.4 6.4 6.4 Mo of Ca / NO ₃ 9 9 9 9 Final processing time (minutes) 90 90 90 60 Nitrate Concentration After Treatment (mg / L) 1025 839 287 205 % Removal 0 20 72 80

Example 2

Reaction Rate Control of Precipitation Removal by Addition of Calcium Sulfate

Based on the reaction result of Example 1, nitric acid was used in the same manner as in Example 1 except that 50% alumina cement was used to remove calcium sulfate at the initial stage of the reaction using a good removal rate of 50% alumina cement. Precipitation removal reaction of the ion was performed. In each case, the amount of CaSO ₄ was added differently to observe the change in reaction rate. CaSO ₄ was injected at 0 M (not added), 0.005 M, 0.008 M, and 0.01 M, respectively.

As shown in the following Table 2, the results of each experiment indicate that the reaction time taken for the removal rate to be about 75% is about 15 minutes after the start of the reaction when CaSO ₄ is not added and for 0.005 M CaSO ₄ . It was about 60 minutes after the start of the reaction, and about 240 minutes after the start of the reaction for 0.008 M CaSO ₄ , and about 960 minutes after the start of the reaction for the 0.01 M CaSO ₄ . With this result, delay the hydration reaction of calcium sulfate takes place on the alumina cement, and serves to reduce the precipitation rate, CaSO ₄ is than 0.005 M CaSO reaction time look the same removal rate of about 8 when injecting ₄ if no You can see that it doubles. As a result, it can be seen that the reaction time can be adjusted without lowering the removal rate through the addition of CaSO ₄ .

Minutes Nitrate Concentration (mg / L) 0 M CaSO ₄ (none) 0.001 M CaSO ₄ 0.005 M CaSO ₄ 0.008 M CaSO ₄ 0.01 M CaSO ₄ 0 1060 1030 1010 1091 1040 15 272 301 816 1050 1076 30 236 229 560 1039 1030 60 208 211 290 742 979 120 190 211 441 747 240 173 181 273 583 300 163 170 256 780 480 208 390 720 326 960 272

Example 3

Control of Precipitation Removal Reaction Rate by Addition of Other Sulfates

The precipitation removal reaction of nitrate was carried out in the same manner as in Example 2, except that 0.01 M potassium sulfate and 0.01 M ferrous sulfate were used instead of calcium sulfate.

As a result of measuring the concentration of nitrate with time, potassium sulfate became 1041 mg / L to 341 mg / L at about 480 minutes after the start of the reaction. In the case of ferrous sulfate, the concentration of nitrate was 1148 mg / L. It took about 300 minutes to reach 254 mg / L (Table 3). This result, as in Example 2, it can be seen that potassium sulfate and ferrous sulfate can delay the hydration reaction of the alumina cement.

Minutes Nitrate Concentration (mg / L) 0.01 MK ₂ SO ₄ 0.01 M FeSO ₄ 0 1053 1148 15 1046 1013 30 1013 856 60 873 755 90 612 410 120 526 321 180 447 287 300 346 254 480 341

Example 4

Nitrate removal process through multi-step reaction

Experimental results of Example 1 it can be seen that the nitrate removal rate by the precipitation reaction does not exceed 85% for most precipitation reactions. Treatment of high concentrations of contaminated water requires multiple stages of precipitation to meet water quality standards. Two step nitrate removal experiments were carried out as shown in Table 4 to determine the treatability of high concentrations of nitrates through a multi-step reaction. As alumina cement, 50% alumina cement was used. First, the filtrate obtained by the precipitation experiment using 50% alumina cement and quicklime was subjected to the same treatment again in this step to examine the treatment efficiency.

As a result, it was confirmed that the concentration of nitrate, which had reached the initial 1015 ppm, was reduced to 205 ppm at the first 15 minutes of the reaction, and in the two-stage reaction, it was also reduced to the same yield to precipitate out at 30 ppm. Could know. In addition, in the case of 5000 ppm or 10000 ppm, when the precipitation reaction having a removal rate of 80% was performed in multiple stages using 50% alumina cement in this manner, the result could be lowered below the drinking water quality standard.

Stage 1 2 steps Initial Nitrate Concentration (mg / L) 1015 176 Alumina Cement Volume (mg / L) 10480 10480 Quicklime Volume (M) 0.075 0.075 Molar ratio of Al / NO ₃ 6.4 6.4 Molar ratio of Ca / NO ₃ 9 9 Final processing time (minutes) 30 15 Nitrate Concentration After Treatment (mg / L) 176 30 Removal rate (%) 82.6 80.4

Example 5

Precipitation removal effect on other anions

Sulfate (SO ₄ ^2- ), phosphate (HPO ₄ ^2- ), and chlorine (Cl ⁻ ) ions, etc., were precipitated to other ions other than nitric acid present in groundwater, sewage, and wastewater. The reaction was carried out under the same conditions as using 50% alumina cement. Almost everything was removed at 945 mg / L after 1 hour for sulfate (SO ₄ ^2- ) and 6 mg / L at 998 mg / L after 1 hour for phosphate (HPO ₄ ^2- ) Was removed from 970 mg / L to 309 mg / L in about an hour and a half (Table 5). Through these results, it can be seen that other salts can be removed through the precipitation process according to the present invention. The difference in the removal rate of each salt is judged to be due to the effect of ionic strength, that is, sulfates, phosphates and nitrates with high ionization tend to have higher precipitation than hydrochlorides with relatively low ionization tendency. It is considered that ion diffusion due to ionization tends to influence the removal of various anions by hydration of alumina cement.

SO ₄ HPO ₄ Cl Initial Salt Concentration (mg / L) 946 998 981 Alumina Cement Volume (mg / L) 10480 10480 10480 Quicklime Volume (M) 0.075 0.075 0.075 Final processing time (minutes) 60 60 90 Salt concentration after treatment (mg / L) 0 6 309 Removal rate (%) 100 99 68

Example 6

Removal of Eluted Aluminum and Calcium Ions

As a result of detecting aluminum ions or calcium ions in the treated water after the precipitation reaction according to Example 1, eluted aluminum and calcium ions reached 56.5 mg / L and 133 mg / L, respectively. The calcium ions were removed by precipitation with calcium carbonate using soda ash, and aluminum ions were precipitated and removed with aluminum hydroxide in the process of neutralizing the treated water in the base state. As a result, 93-99% of calcium ions precipitated into calcium carbonate after soda ash was injected into the treated water, and the remaining calcium ions in the water were 10 mg / L. Was added to be 7.0 so that 99% of the aluminum ions precipitated with aluminum hydroxide, the aluminum ions remaining in the water was lowered to 0.1 mg / L to meet the drinking water standards.

Example 7

Continuous Salt Removal Process Using Tubular Reactor and Filtration Membrane Precipitation Tank

Continuous process experiments for nitrate removal by precipitation reaction were performed. As shown in FIG. 1, the process consists of a tubular reactor and a settling tank, and the size of the reactor consists of an inner tubular with a radius of 10 cm and a height of 27 cm and an outer tubular with a radius of 15 cm and a height of 30 cm. lost. The reactor separated the inflow and outflow into the double tube to fully hydrate the newly supplemented alumina cement. The operation volume was 3 L and the influent flowed in at a flow rate of 50 mL / min. In addition, the size of the sedimentation tank is 25 cm in width, 25 cm in length and 30 cm in height. The operating volume is 18 L. The treated water flowing from the reactor is adjusted to the height and introduced into the sedimentation tank by potential energy. Was flowed out at a flow rate of 50 mL / min. At this time, water contaminated with nitrate was continuously sent to the reactor, and alumina cement and quicklime were continuously injected. 5 g / L of alumina cement, 0.001 M of calcium sulfate and 0.075 M of quicklime were injected into the reactor. In the reactor, the nitrate precipitate formed as an insoluble compound by the hydration reaction of alumina cement was precipitated in the precipitation tank, and passed through a filtration membrane to obtain final treated water. The experimental results are shown in the following Table 6. The removal of nitrate in the reactor during the process showed a constant removal rate of about 68% for about 6 hours, but the treated water that passed through the filtration membrane in this process was about 75%. The removal rate is shown. This is considered to increase the removal rate of nitrate in the final water passed through the filter membrane by the reaction of unreacted sludge in the settling tank.

Through these results, it can be seen that by the continuous process of the present invention, even more effective removal rate enhancement effect can be obtained with a smaller amount of reactants.

Time (min) Final treatment Nitrate Concentration (mg / L) Yield (%) 0 989 0 10 326 67 40 253 74 70 280 72 100 289 70.8 160 293 70.4 250 250 74.7 310 263 73.4 370 279 71.8

Example 8

Except that the amount of alumina cement was reduced to 2.5 g / L was carried out in the same manner as in Example 7. The experimental results are shown in the following Table 7, and the initial 1017 mg / L nitrate ions fell to 734 mg / L 50 minutes after the start of the reaction, after about 260 minutes it was shown to maintain a 50% removal rate.

Time (min) Final treatment Nitrate Concentration (mg / L) Yield (%) 0 1017 0 40 851 16 50 734 27.8 80 732 27.9 110 703 31 140 726 29 170 654 36 200 558 45 230 514 49.5 260 507 50 310 505 50 390 502 50 420 505 50 540 504 50

Example 9

Continuous Salt Removal Process Using Tubular Reactor, Secondary Stirring Tank, and Precipitation Tank with Filtration Membrane

As shown in FIG. 2, a secondary stirring tank was installed between the tubular reactor and the filtration membrane-containing precipitation tank in the process of Example 7. The appearance of the secondary agitator tank is the same as that of the sedimentation tank without a built-in filtration membrane, and the stirrer is installed at the inlet part. Operation was carried out for continuous process experiments for nitrate removal by precipitation reaction in the sludge concentration.

Specifically, the flow rate was 100 mL / min, and the stirring was stopped for 5 hours after the start of the reaction to fully concentrate the sludge, and then stirring was started. Injecting 2.5 g / L of alumina cement, 0.001 M of calcium sulfate, and 0.075 M of quicklime into the reactor, the initial 1100 mg / L of nitrate ions dropped to 370 mg / L 380 minutes after the start of the reaction, followed by 1050 minutes. The removal rate was maintained above 65% (Tables 8a and 8b).

This result, it can be seen that the nitrate removal rate in the case of the secondary stirring tank was increased by about 15% compared with the above Example 8 consisting of the tubular reaction tank and the filtration membrane settling tank without the secondary stirring tank. Therefore, it can be seen that through effective concentration and agitation of the sludge in the secondary agitation tank, a more effective continuous process can be performed with a smaller amount of reactants.

Time (min) Final treatment Nitrate Concentration (mg / L) Yield (%) 0 1105 0 110 706 36 140 711 35.6 170 719 34.8 200 709 35.8 230 706 36.1 260 699 36.7 290 702 36.4 320 694 37.1 350 523 52.6 380 369 66.6 445 375 66 475 346 68.7 505 344 68.8 535 382 65.4 565 420 62 595 402 63.6 655 413 62.6

Time (min) Final treatment Nitrate Concentration (mg / L) Yield (%) 715 405 63.3 775 393 64.4 835 385 65.1 865 397 64.1 925 392 64.5 985 354 67.9 1045 388 64.8

Based on the chemical precipitation method, the present invention can reduce problems such as the use of additional salts and corrosion due to the presence of salts in the treated water, compared to the conventional ion exchange resin method, and the enormous maintenance cost required for expensive resin replacement. At the same time, it can be designed in small size and overcomes the very low processing speed in biological denitrification, post-treatment problems of microorganisms, and limitation of groundwater application. In addition, it is possible to control the reaction rate by the sulphate, and it is possible to carry out more effective salt removal through the continuous process of this precipitation reaction, and further increase its efficiency by concentrating and stirring the reactant sludge during the continuous process. .

Claims (9)

A method of precipitating and removing salts present in groundwater, sewage or wastewater by alumina cement and quicklime, wherein the reaction rate is controlled by adding sulfate. The method of claim 1 wherein said sulfate is selected from the group consisting of calcium sulfate, potassium sulfate, sodium sulfate, ferrous sulfate, ferric sulfate, and combinations thereof. The method according to claim 1, wherein the sulfate is added at a concentration of 0.001 to 0.01 M. The method according to claim 1, wherein after the precipitation reaction, the residual calcium ions are precipitated by addition of carbonate, followed by precipitation treatment of the residual aluminum ions by neutralization with acid. The method of claim 4 wherein said carbonate is selected from the group consisting of slaked lime, potassium carbonate and sodium carbonate. The method according to claim 1, wherein the precipitation reaction is carried out by mixing and stirring salts present in groundwater, sewage or wastewater in a double tubular reactor consisting of inner and outer tubular phases with alumina cement, quicklime and sulfate to generate an insoluble precipitate. A continuous process method comprising the precipitation of this in a settling tank. 7. The method of claim 6, wherein a filtration membrane is mounted in the settling tank. 7. A method according to claim 6, wherein the reactor is equipped with a secondary agitation tank. The method according to claim 8, wherein after the sludge concentration in the secondary stirring tank, stirring is started.