KR20090103621A - Method and Apparatus for removal of ammonia from waste water - Google Patents

Abstract

PURPOSE: A method for removing ammonia in wastewater and an apparatus therefor are provided to simplify ammonia removal processes by minimizing biological processing processes for denitrification and nitrification. CONSTITUTION: A method for removing ammonia in wastewater includes the following steps of: collecting the wastewater in which ammonia component is contained and Coke Oven Gas condensed water in a first pH adjusting tank(10); basifying the wastewater with an alkaline solution; separating the gasified wastewater to ammonia gas and effluent trough a stripping process; transferring the separated ammonia gas to a sintering exhaust gas processing facility; and performing a biological processing process of the wastewater in a second pH adjusting tank(50).

Description

Method and Apparatus for Removing Ammonia from Wastewater {Method and Apparatus for removal of ammonia from waste water}

The present invention relates to a method and apparatus for removing ammonia from wastewater, and more particularly, to minimize complex and costly nitrification and denitrification biological treatment processes for ammonia by using ammonia stripping and sintered flue gas treatment. It relates to a method and apparatus for removing ammonia from wastewater which simplifies or eliminates ammonia removal.

Industrial wastewater generated from factories includes organic substances, nitrogen components and various pollutants, and nitrogen components contained in wastewater adversely affect ecosystems such as eutrophication of seawater during discharge.

Nitrogen components in various industrial wastewater exist in the form of organic nitrogen and inorganic nitrogen, which are referred to as total nitrogen. Mineral nitrogen is again divided into ammonia and nitrate nitrogen (NOx-N).

Mineral nitrogen causes color and odors in industrial wastewater, and causes harmful gases and eutrophication, which is a direct cause of increased chemical oxygen demand (COD) and biochemical oxygen demand (BOD). .

1 is a block diagram illustrating a method for removing ammonia from wastewater according to the prior art.

As shown, conventionally, since wastewater quality standards were limited only to organic matter, a method of treating only organic matter was used. This method neutralizes high pH wastewater in the pH adjustment tank, removes most of heavy metals and toxic substances by flocculation sedimentation method, and then removes organic matter by biological treatment using activated sludge. High concentration of inorganic nitrogen was hardly treated.

In recent years, biological nitrogen removal processes are applied to remove both organic nitrogen and inorganic nitrogen as water quality standards of treated water are strengthened and nitrogen is mandatoryly required. Biological nitrogen removal processes include algae culture, aquatic plant cultivation, and microbial nitriding.

 However, such biological nitrogen removal process is difficult to treat due to the toxicity of various poly aromatic hydrocarbons (PAH) or heavy metals contained in industrial wastewater. In particular, nitrifying microorganisms that convert ammonia to nitrate are denitrified and aerobic. Unlike microorganisms, it is very sensitive to toxicity and is a major cause of failure of biological nitrogen treatment.

In addition, in the biological nitrogen removal process, the nitrogen component introduced into the industrial wastewater is treated as a two-stage process of nitrification and denitrification. For the denitrification, a process of returning a flow rate of about 3 to 7 times the original wastewater is selected. Therefore, it consumes a lot of energy and economically, such as having to inject external carbon sources such as methanol.

In the inorganic nitrogen, ammonia is released as it remains in the waste water at a high concentration. Therefore, in order to comply with legal emission limits in industrial wastewater treatment, the removal of inorganic nitrogen from the total nitrogen content in the wastewater, in particular the removal of ammonia, is key.

As a method for removing ammonia, there is an ammonia stripping method using physical properties of ammonia. The ammonia stripping method is a method of removing wastewater by spraying it through an injection nozzle and by discharging air into the atmosphere by crossing air with wastewater by a fan. Ammonia in water is mostly in ionic form (NH ₄ ⁺ ) at neutral and room temperature conditions, but only 20% at pH 10, 6.3% at 10.5, and only 2% at 11, and the rest is free ammonia (NH _3). Exist). Ammonia, which is in the form of free ammonia (NH ₃ ), is easily separated from water and released into the atmosphere through contact with air.

However, since the ammonia stripping method is regulated as a substance causing air pollution, distilled ammonia has a disadvantage in that gas ammonia needs to be additionally removed according to atmospheric regulations even if ammonia is removed through stripping in water.

Paradoxically, since most of the processes for removing atmospheric ammonia are scrubber methods using water, there is a problem in that the ammonia stripping method is negatively recognized when removing ammonia from the wastewater and there are limitations in using it directly on site.

Here, the scrubber method is a series of processes in which a gas is brought into contact with a liquid and a soluble component in the gas is dissolved in a liquid phase as opposed to stripping.

The present invention is to solve the conventional problems as described above, the object of the present invention is to remove the ammonia in the waste water by the stripping method, the gaseous secondary pollutants generated at this time and other air pollution facilities present in the process In conjunction with the treatment, the problem arising from the removal of biological nitrogen, as well as providing a method for removing ammonia from the waste water to reuse the distilled ammonia.

The present invention is to solve the conventional problems as described above, the present invention is to collect the waste water and COG (Coke Oven Gas) condensed water containing ammonia in the first pH adjustment tank, the agent for supplying and alkaline solution Step 1; A second step of introducing the waste water basified in the first step into a stripper to separate the ammonia gas and the waste water through a stripping process; A third step of sucking the ammonia gas separated in the second step at a vacuum negative pressure and transferring the ammonia gas to the sintered flue gas treatment facility; And a fourth step of neutralizing the second pH adjustment tank after conducting the wastewater separated in the second step to the lower portion of the stripper 20 and collecting it in the discharge tank and performing a biological treatment process.

The ammonia gas transferred to the sintered flue gas treatment facility in the second step is injected to remove NOx.

The ammonia gas transferred to the sintered flue gas treatment facility in the second step is injected into ammonia water through a concentration process to remove NOx.

In the first step, the basicization of the first pH adjustment tank is maintained by measuring the hydrogen ion index of the wastewater and supplying the alkaline solution to maintain the alkaline hydrogen ion index.

In the fourth step, neutralization of the second pH adjustment tank is maintained by measuring the hydrogen ion index of the wastewater and supplying an acidic solution to maintain the neutral hydrogen ion index.

A first pH adjusting tank for collecting wastewater containing ammonia and supplying an alkaline solution for basifying the collected wastewater; A stripper in which the wastewater collected in the first pH adjusting tank is introduced together with air introduced from the outside and separated into ammonia gas and wastewater; A sintered flue gas treatment facility connected to the stripper and used to remove ammonia nitrogen (NOx) by sucking ammonia gas in the stripper; A second pH adjusting tank disposed below the stripper and collecting basicized wastewater and supplied with an acidic solution for neutralizing the basicized wastewater; And a microbial reaction tank connected to the second pH adjusting tank to collect wastewater discharged from the second pH adjusting tank and removing organic matter in the collected wastewater through a biological reaction.

The present invention removes the ammonia in the wastewater by the stripping method, but the ammonia generated at this time is transferred to the sintered flue gas treatment facility to be used to remove NOx in the flue gas, thereby preventing environmental pollution by the release of conventional ammonia gas, and at a low cost. Providing ammonia in the sinter flue-gas process reduces the cost of removing NOx.

The present invention also eliminates ammonia as well as various volatile contaminants that are toxic to microorganisms in the stripping process. Thus is enhanced the activity of the microorganisms during biological treatment processes during thio cyanide (thiocyanide, SNC ^-) has the effect that can be increased to up to 6 times the removal efficiency.

That is, the biological treatment process for removing ammonia from wastewater can be minimized, and the biological treatment process can be stably carried out, thus reducing the need for post-treatment processes. can do.

1 is a block diagram showing a method for removing ammonia from wastewater according to the prior art.

2 is a block diagram showing a method for removing ammonia from wastewater according to the present invention.

Figure 3 is a schematic diagram showing the configuration of a removal device for realizing a method for removing ammonia of wastewater according to the present invention.

Explanation of symbols on the main parts of the drawings

10: 1st pH adjustment tank 11: Alkaline solution tank

12: Agitator 13: Supply pipe

15: supply pump 17: ion index measuring instrument

19: control valve 20: stripper

21: discharge pipe 23: blower

25: gas flow regulator 27: air inlet pipe

30: sintered flue gas treatment facility 40: discharge tank

50: second pH adjusting tank 60: microbial reaction tank

Hereinafter, a preferred embodiment of the method and apparatus for removing ammonia from wastewater according to the present invention will be described in detail.

FIG. 2 is a block diagram showing a method for removing ammonia from wastewater according to the present invention, and FIG. 3 is a schematic diagram showing a configuration of a removal apparatus for realizing a method for removing ammonia from wastewater according to the present invention.

The present invention comprises a first step of basifying the waste water and COG (Coke Oven Gas) condensate generated during the steelmaking process to pH 11 or more; Performing a stripping process on the basified wastewater after the first stage to separate ammonia into ammonia gas and wastewater; The ammonia gas separated in the second step is transferred to the sintered flue gas treatment facility for sintered gas treatment through the discharge pipe and used in the third step of removing NOx.

Then, the wastewater separated after the second step is adjusted to neutral by lowering the pH, and further performing a fourth step of removing the remaining thiocyanide (SNC ⁻ ) and organics using a biological treatment method.

In general, contaminants present in wastewater are:

Ammonia (mg / L) Phenol (mg / L) SCN (mg / L) Total CN (mg / L) Oil / Grease (mg / L) SS (mg / L) 100-2000 100-1200 100-700 20-400 1000-4000 300-1500 Naphtalene (µg / L) Acenaphtalene (µg / L) 9H-Fluorene (µg / L) Phenanthrene (µg / L) Anthracene (µg / L) Fluoranthene (µg / L) To 560 To 120 60-62 210-230 70-100 260-280

(Source: Yoon Video and Park Dong Hee, 2006)

As shown in Table 1, it is important to remove the ammonia in the wastewater because its content is approximately 100-2000 mg per liter of wastewater.

Ammonia in the wastewater is balanced by the following equation.

_{NH 3 + H 2 O ↔ NH} 4 + + OH -

The equilibrium equation for ammonia shifts this equilibrium to the left when the pH is above 7. Therefore, when the pH of the wastewater is sufficiently increased to 11 or more, ammonium ions (NH ₄ ⁺ ) are converted into free ammonia (NH 3), so that the ammonia gas and the waste water are easily separated. In particular, at pH 11 only 2% is present in ionic form and the remainder is free ammonia (NH ₃ ).

Based on this principle, the wastewater and COG (Coke Oven Gas) condensate generated during the steelmaking process are collected in the first pH adjusting tank 10 and an alkaline solution is injected through the supply pipe 13 to basify the wastewater to pH 11 or more. In addition, the basic wastewater is supplied into the stripper 20 through the supply pump 15 to perform the stripping process.

The first pH adjustment tank 10 preferably has a structure in which a partition is installed to divide the site where the wastewater is supplied and discharged to both sides to increase the residence time so that the alkaline solution is evenly mixed with the wastewater.

After supplying the alkaline solution into the first pH adjusting tank 10, the alkaline solution and the wastewater in the first pH adjusting tank 10 are stirred using the stirrer 12 so as to rapidly and evenly mix.

The supply of the alkaline solution is connected to the alkaline solution tank 11 filled with the alkaline solution, the alkaline solution tank 11 and the first pH adjusting tank 10 to supply the alkali solution feed passage 13 and the supply pipe 13. It is made by a control valve 19 arranged to open and close the supply pipe 13 in accordance with the hydrogen ion index measured from the ion index measuring device (17).

The alkaline solution may use sodium hydroxide (NaOH) and sodium hydrogen carbonate (NaHCO 3) or slaked lime (Ca (OH) ₂ ), but is not limited thereto.

The pH is measured by an ion index measurer 17 which measures the hydrogen ion index of the wastewater. The higher the pH, the higher the ammonia removal rate. However, if the pH is adjusted to 11 or more, the cost is high and the pH should be adjusted between 11 and 13 because the elevated pH should be lowered for the subsequent biological treatment.

In the stripping process, wastewater is sprayed into the stripper 20 through an injection nozzle (not shown), and air is crossed with wastewater by a fan to separate ammonia in the wastewater into ammonia gas. Ammonia in the form of free ammonia (NH ₃ ) is easily separated from the water through contact with air, so the ammonia in the waste water is easily separated.

The ammonia gas separated from the waste water is transferred to the sintered flue gas treatment facility 30 through the discharge pipe 21 connected to one side of the stripper 20. At this time, the separated ammonia gas is guided to one side of the stripper 20 by suction at the vacuum negative pressure of the blower 23 and is transferred to the sintered flue gas treatment facility 30 through the discharge pipe 21.

The blower 23 is disposed in the discharge pipe 21 and has a function of maintaining the pressure inside the stripper 20 at a vacuum negative pressure. The gas flow regulator 25 is provided in the discharge pipe 21 to control the discharge flow rate of the ammonia gas. It may be further provided.

The wastewater from which the ammonia gas is separated is led to the lower portion of the stripper 20 and collected in the discharge tank 40. The wastewater collected in the discharge tank 40 is transferred to the second pH adjusting tank 50 connected to the microbial reactor 60 for the biological treatment process.

Wastewater collected into the discharge tank 40 is simultaneously removed in the stripping process, as well as ammonia, high volatile organic substances such as phenol and naphthalene (acenaphtalene), such as toxic to microorganisms.

Meanwhile, the ammonia transferred to the sintered flue gas treatment facility 30 is used to remove NOx, which is nitrate nitrogen, in the flue gas generated in the sintering process.

Flue gas generated during the sintering process contains air pollutants such as dust SOx, NOx and dioxins. As air pollution regulations are tightened, recently, selective catalytic reduction (SCR) or activated carbon processes have been used to deal with this. Ammonia is used in this process to remove NOx.

SCR is a method that reduces NOx to 80 ~ 95% by selectively reacting NOx with ammonia on the catalyst and reducing it to N ₂ and H ₂ O. It is the most commercialized technology. As the catalyst, a catalyst obtained by mixing V ₂ O ₅ with TiO ₄ may be used.

The reaction formula for NOx removal using ammonia in SCR is shown below.

4NO + 4NH ₃ + O ₂ → 4N ₂ + 6H ₂ O

2NO ₂ +4 NH ₃ + O ₂ ≧ 3N ₂ + 6H ₂ O (where NO ₂ accounts for approximately 5% of the total NOx)

At this time, the gaseous ammonia is concentrated and supplied in the form of a liquid, and sprayed with air to increase contact with NOx. However, the ammonia generated in the stripping process may be introduced into the process of treating NOx such as SCR or activated carbon process to remove NOx, omitting other concentration processes.

In addition, since NH3 / NOx in the exhaust gas can obtain high NOx removal efficiency when the molar ratio is 1: 1, the NOx removal process supplies ammonia in consideration of the ratio of NOx. The supply of ammonia is adjustable by the gas flow controller 25 provided in the discharge pipe 21. Of course, a separate reservoir and a flow controller may be provided to control the supply of ammonia.

In the second step, a biological treatment step of wastewater from which ammonia gas has been removed is carried out. That is, the pH of the wastewater from which the ammonia has been removed is adjusted to neutral by lowering the pH in the second pH adjusting tank 50, and after the neutral wastewater is introduced into the microbial reaction tank 60, nitrogen is added using the activated sludge method. Decompose to ₂ Activated sludge is a method of removing nitrogen through respiration and growth by feeding pollutants (organic matter, BOD).

In addition to the activated sludge process, the biological treatment process may include nitrification and denitrification, algae culture, aquatic plant cultivation, and microbial nitriding. Nitrification and denitrification can be minimized or omitted because ammonia is removed from the wastewater.

The biological treatment process is performed in a state in which various contaminants that are toxic to the microorganism are removed through the stripping process, thereby increasing the activity of the microorganism. Accordingly, the removal efficiency of thiocyanide (SNC ⁻ ) can be increased up to 6 times. That is, the stripping process may improve the efficiency of the biological nitrogen removal process beyond the ammonia removal effect.

For reference, reference numeral 16 is a wastewater supply pipe for supplying wastewater to the first pH adjustment tank 10, and reference numeral 18 is a wastewater inflow pipe for introducing wastewater into the stripper 20.

Hereinafter, it will be described through examples to help understand the present invention.

( Example)

1. pH adjustment step

The ammonia-containing waste water and COG (Coke Oven Gas) condensate are collected in the first pH adjusting tank 10, and an alkaline solution is supplied so that the pH of the waste water is 11 or more to convert the ammonia ions into free ammonia form.

At this time, the basicization of the first pH adjustment tank is maintained by measuring the hydrogen ion index of the wastewater, supplying an alkaline solution and maintaining the alkaline hydrogen ion index.

2. Stripping process

The wastewater basicized in the first pH adjusting tank 10 is introduced into the stripper 20 through the supply pump 15, and at the same time, air is introduced through the air inlet pipe 27 to convert the wastewater into ammonia gas and wastewater. Separate. The separated ammonia gas is transferred to the sintered flue gas treatment facility 30 by the vacuum negative pressure of the blower 23, and the wastewater from which the ammonia gas is removed is led to the lower portion of the stripper 20 and collected in the discharge tank 40.

3. NOx removal process

The ammonia gas transferred to the sintered flue gas treatment facility 30 is made into a liquid state through a concentration process to remove NOx by spraying the flue gas with air during the selective catalytic reduction (SCR) process.

In addition, ammonia may be removed in the exhaust gas during the selective catalytic reduction (SCR) process to remove other concentrations and skip other concentration processes.

4. pH adjustment step

In the stripping process, the wastewater collected in the discharge tank 40 is collected in the second pH adjusting tank 50, and neutralized by supplying an acidic solution so that the pH of the wastewater is 7-8. As the acidic solution, aluminum sulfate, caustic soda may be used.

At this time, the neutralization of the second pH adjustment tank may be maintained by measuring the hydrogen ion index of the wastewater and supplying an acidic solution to maintain the neutral hydrogen ion index.

5. Biological treatment process

Wastewater neutralized in the second pH adjusting tank 50 is introduced into the microbial reaction tank 60 to decompose nitrogen into N ₂ using activated sludge and discharge it to the outside.

Within the scope of the basic technical idea of the present invention, many other modifications are possible to those skilled in the art, and the scope of the present invention should be interpreted based on the appended claims. will be.

Claims (6)

A first step of collecting the ammonia-containing waste water and COG (Coke Oven Gas) condensed water into a first pH adjusting tank and supplying an alkaline solution to make it basic; A second step of introducing the waste water basified in the first step into a stripper to separate the ammonia gas and the waste water through a stripping process; A third step of sucking the ammonia gas separated in the second step at a vacuum negative pressure and transferring the ammonia gas to the sintered flue gas treatment facility; A fourth step of conducting the wastewater separated in the second step to the lower portion of the stripper 20 and collecting it in the discharge tank and then neutralizing it in the second pH adjusting tank and performing a biological treatment process. How to remove ammonia. The method of claim 1, The ammonia removal method of the wastewater, characterized in that the ammonia gas transferred to the sinter exhaust gas treatment facility in the second step is injected to remove NOx. The method of claim 1, The ammonia gas transported to the sintering flue gas treatment plant in the second step is injected into ammonia water through a concentration process to remove NOx, characterized in that for removing waste water. The method of claim 1, The basicization of the first pH adjustment tank in the first step is maintained by measuring the hydrogen ion index of the wastewater and supplying an alkaline solution to maintain the alkaline hydrogen ion index, the ammonia removal method of the wastewater. The method of claim 1, The neutralization of the second pH adjustment tank in the fourth step is maintained by measuring the hydrogen ion index of the wastewater and supplying an acidic solution to maintain the neutral hydrogen ion index. A first pH adjusting tank for collecting wastewater containing ammonia and supplying an alkaline solution for basifying the collected wastewater; A stripper in which the wastewater collected in the first pH adjusting tank is introduced together with air introduced from the outside and separated into ammonia gas and wastewater; A sintered flue gas treatment facility connected to the stripper and used to remove ammonia nitrogen (NOx) by sucking ammonia gas in the stripper; A second pH adjusting tank disposed below the stripper and collecting basicized wastewater and supplied with an acidic solution for neutralizing the basicized wastewater; A microbial reaction tank connected to the second pH adjusting tank for collecting wastewater discharged from the second pH adjusting tank and removing organic matter in the collected waste water through a biological reaction; .