KR100556686B1 - The method of nitrogen removal in plating wastewater - Google Patents

Abstract

The present invention relates to a method for simultaneously removing cyanide, ammonia nitrogen and nitrogen nitrate contained in plating wastewater in one reactor. The present invention relates to a method for reducing chromium contained in plating wastewater and removing heavy metals. A pretreatment step of flocculating pressure flotation and an electrolytic device having a positive electrode and a negative electrode metal electrode, and the electrolyte of sodium chloride and metals such as zinc, tin, copper, lead, iron, antimony, aluminum, etc. An electrolysis step of simultaneously decomposing cyan, ammonia nitrogen and nitrate nitrogen contained in the waste water by injecting a single or multiple liquid catalyst including the liquid catalyst and the unreacted liquid catalyst in the electrolyzed waste water; and And a post-treatment step of flocculating pressure flotation to remove untreated heavy metals. To, toxic heavy metals and the content is to remove the nitrogen of the high plating wastewater, and in particular a cyanide (CN), ammonium nitrogen contained in the wastewater (NH ₃ -N) and nitrate (NO ₃ ^- -N or NO ₂ ^- the -N) can be efficiently removed at the same time in a single reactor.

Plating wastewater, nitrogen nitrate, ammonia nitrogen, electrolysis, oxidation, reduction, liquid catalyst

Description

The method of nitrogen removal in plating wastewater

1 is a schematic view showing an apparatus for removing nitrogen from the plating wastewater according to an embodiment of the present invention,

2 is a flow chart showing a nitrogen removal method of the plating wastewater according to an embodiment of the present invention.

3 is a graph showing the nitrogen removal efficiency of the plating wastewater according to an embodiment of the present invention,

Figure 4 is a graph showing the treatment efficiency according to each metal of the liquid catalyst according to an embodiment of the present invention.

** Explanation of symbols for main parts of drawings **

10: chromium reduction tank 20,50: flocculation pressure injury tank

30: electrolytic cell 31: electrolytic device

32: electrolyte storage tank 33: liquid catalyst storage tank

The present invention relates to a method for removing nitrogen components of plating wastewater, and more particularly, to a method for simultaneously removing cyanide, nitrate nitrogen and ammonia nitrogen contained in plating wastewater in one reactor. .

Recently, as the industrial advancement progresses, the kinds of pollutants contained in the discharged wastewater are diversified.In particular, the plating process is used in a large amount of acid, aqueous alkali solution and cyanide compound, and these compounds are discharged to the outside after plating. have. Effluents such as cyan, ammonia, ammonium, nitrite, nitrate, and organic nitrogen such as urea and amino acids Nitrogen, which is present in the form of, causes a deficiency of dissolved oxygen in the water, causing eutrophication, red tide, etc., which is a major cause of environmental pollution.

Therefore, in order to prevent environmental pollution by wastewater, the government regulates the total nitrogen emission of wastewater, and companies have been developing various wastewater purification treatment devices and methods to reduce the nitrogen content of wastewater. Various wastewater treatment methods such as biological treatment using microorganisms and chemical treatment using chemicals have been developed as wastewater purification treatments.

In the wastewater purification treatment method, a chemical treatment method is a method of inducing reduction of nitrate by adding a chemical to the wastewater. For example, US Pat. No. 6,030,520 voluntarily oxidizes a metal to reduce nitrate to nitrite. There is disclosed a chemical treatment method of nitrate waste which reduces nitrite to nitrogen gas. However, when using such a chemical method takes a long time for the reduction reaction, it is difficult to obtain the reduction efficiency as desired, there is a fear that the total nitrogen content in the water rather increases by the unreacted reaction of the added amide. In addition, there is a problem that secondary environmental pollution occurs due to the use of a large amount of chemicals.

In order to solve this problem, recently, biological treatment methods for decomposing nitrates in wastewater using eco-friendly and economical microorganisms have been widely used. According to the biological treatment method, organic nitrogen, ammonia Chemistry, nitrite screen, while passing through the nitrification step nitrite-nitrogen is nitrogen gas (N ₂₎ nitrite denitrification (Denitrification) process or the nitrate is converted into nitrogen gas (N ₂₎ Nitrogen is removed from wastewater by denitratification process. This biological treatment method requires expensive equipment that occupies a large installation space, and it is pointed out that the treatment efficiency is low compared to such an economic investment.

Particularly, in the case of plating wastewater, it is very difficult to apply biological treatment methods because it contains a large amount of biotoxic components such as cyanide, residual chlorine, and heavy metals. In order to apply the biological treatment method, the cyan concentration should be pretreated at 0.5mg / l or less, so the cost of chemical treatment is very expensive, and the treatment becomes more difficult in the case of forming a heavy metal and a complex compound (Metal-CN). . In addition, most of the plating wastewater has low BOD (Biochemical Oxygen Demand), so even after the cyan pretreatment, carbon sources such as methanol should be injected as a nutrient for microorganisms. In this case, the C / N ratio is usually 10: 1 to 15: 1. Therefore, it becomes a very uneconomical treatment method, there is a problem that is almost impossible to apply in the case of industrial wastewater, such as plating wastewater.

The present invention has been proposed to solve the above problems, it is possible to remove nitrogen in the plating wastewater with high toxicity and heavy metal content by using electrochemical oxidation and reduction reaction, in particular cyanide (CN) contained in the wastewater, ammonia-nitrogen (NH ₃ -N) and nitrate nitrogen to (NO ₃ ^{- -} -N or NO ₂ -N) for its object to provide a method of removing nitrogen a plating waste water that can be removed at the same time in the reactor.

In addition, an object of the present invention is to add a catalyst in the form of a liquid in the electrolytic device to increase the efficiency of nitrogen removal, and to further apply a post-treatment process to provide a nitrogen removal method of the plating wastewater to eliminate the possibility of further contamination.

In order to achieve the above object, the purification treatment method of the plating wastewater of the present invention includes a pretreatment step of reducing chromium contained in the plating wastewater and cohesive pressure flotation of the wastewater to remove heavy metals, and a metal electrode of the positive electrode and the negative electrode. It is equipped with an electrolytic device having an electrolyte of sodium chloride (NaCl) and zinc (Zn), tin (Sn), copper (Cu), lead (Pb), iron (Fe), antimony (Sb) in the electrolyzer into which the wastewater is introduced ), An electrolysis step of simultaneously decomposing cyan, ammonia nitrogen, and nitrate nitrogen contained in the wastewater by injecting a single or multiple liquid catalyst including any one of aluminum (Al) and the electricity. And a post-treatment step of flocculating pressure flotation to remove the unreacted liquid catalyst and untreated heavy metal in the decomposed wastewater.

In addition, the liquid catalyst may use the metal in the form of a compound of any one of Mx (SO ₄ ) y, Mx (Cl) y, Mx (CO ₃ ) y, Mx (OH) y or dissolve the element in hydrochloric acid or sulfuric acid. Characterized in that it is a liquid catalyst to be used.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

1 schematically shows a nitrogen removal apparatus for plating wastewater according to an embodiment of the present invention, and FIG. 2 is a flowchart illustrating a nitrogen removal method for plating wastewater according to an embodiment of the present invention.

As shown in FIG. 1, the apparatus for removing plating wastewater includes a chromium reduction tank 10 for reducing chromium contained in the plating wastewater, and a method for removing various heavy metals contained in the plating wastewater using a cohesive pressure flotation method. Electrolyzer 30 for electrolysis of the plating waste water, comprising a first floatation tank 20 for pretreatment, an electrolytic device 31 having metal electrodes of positive and negative electrodes, an electrolyte storage tank 32, and a liquid catalyst storage tank 33. ), The second supply tank for post-treatment for removing the unreacted liquid catalyst and the untreated heavy metal in the wastewater electrolyzed in the electrolytic cell by using the cohesive pressure flotation method. 50.

The nitrogen removal method of the plating wastewater of the present invention having such a configuration will be described with reference to FIG. 2, and before the process of removing nitrogen, the chromium contained in the plating wastewater is reduced (S11) and the heavy metal is removed (S12). And a pretreatment step (S10) of flocculation and flotation of the plated wastewater, and an electrolytic device having a metal electrode of the anode and the cathode, injecting the electrolyte for oxidation reaction (S21) and reducing the electrolyte into the electrolyzer into which the wastewater is introduced. Injecting the liquid catalyst for the reaction (S22), the electrolysis step (S20) for simultaneously electrochemically decomposing cyan, ammonia nitrogen and nitrate nitrogen contained in the plating wastewater and unreacted in the electrolyzed wastewater It is made of a post-treatment step (S30) to flocculate the pressure flotation to remove the liquid catalyst and the untreated heavy metal.

In more detail, in order to efficiently remove nitrogen components contained in the wastewater generated after plating, a pretreatment step (S10) is first performed to remove heavy metals such as chromium contained in the plating wastewater. In general, the plating waste water has a low acidity (pH 2 to pH 3) at the first inflow, and therefore, it is first to reduce the chromium (Cr ⁶⁺ ) (S11) to increase the acidity to pH 7 to pH 8 and perform electrolytic treatment. Economically advantageous.

In addition, since the reduced plating wastewater contains various heavy metals having toxicities, the heavy metals are removed (S12) by using a dissolved air flotation method (S12).

Wastewater from which chromium is reduced and heavy metals are removed through the pretreatment step (S10) is introduced into an electrolytic cell to proceed to an electrolysis step (S20) in which nitrogen contained in the wastewater is removed by an electrochemical oxidation and reduction reaction.

If you look briefly at the electrolysis (hereinafter referred to as 'electrolysis') technology, it has been used in various fields recently. Especially, it is an electrolytic technology applied to waste water purification treatment. In the case of ChemDen technology developed at the Los Alamos National Laboratory, the cathode for reduction By using zinc plate as an electrode and sulfamic acid (NH ₂ SO ₃ H) as a reducing agent, a technology was developed to reduce nitrate nitrogen to nitrogen gas. However, this technique is applicable only to the removal of nitrate nitrogen, which may lead to an increase in ammonia nitrogen concentration by sulfamic acid, and is widely used due to the possibility of zinc particles being discharged from the zinc plate, which is the cathode electrode, in continuous operation. I can't.

Electrolytic device for the electrolysis step according to an embodiment of the present invention is provided with an electrode of the anode (Anode) and the cathode (Cathode), respectively, the anode performs an oxidation reaction by cyanide (CN) and ammonia nitrogen (NH _3- removing the N), and the cathode is to be carried out a reduction reaction nitrate nitrogen (NO ₃ ^- the removal of -N) ^- -N or NO _2.

Electrolytic For this case of the positive electrode (Anode) of the device using an insoluble electrode (DSA, Demensional Stable Anode), and, in addition to the direct oxidation reaction due to the positive electrode by injection of sodium chloride (NaCl) as an electrolyte hypochlorous acid ions (ClO ^-) to produce Thus, cyanide (CN) and ammonia nitrogen (NH ₃ -N) can be more efficiently removed through indirect oxidation by hypochlorite ions.

In general, the cathode of the electrolytic apparatus directly performs a reduction reaction, and thus it is not possible to use an indirect reduction reaction by the electrolyte, so that the reduction efficiency is only about half that of the oxidation efficiency. In order to solve this problem, a reducing electrode using a metal oxide-based material having excellent reduction reaction such as zirconium (Zr), iridium (Ir), zinc (Zn), and iron (Fe) has been developed. In the case of waste water, the untreated heavy metal component is attached to the electrode in the pretreatment step, and thus cannot perform its function.

Therefore, the nitrogen removal method of the plating wastewater according to the embodiment of the present invention can increase the efficiency of the reduction reaction by the cathode electrode by directly injecting the catalytic material of the metal ion component having excellent reduction performance into the liquid phase into the electrolytic cell into which the plating wastewater flows. Make sure In an embodiment of the present invention, zinc (Zn) is used as a metal component having excellent reduction reaction, and injected into the electrolyzer in the form of ZnSO ₄ or ZnCl ₂ to inject it in the liquid form.

In the case of ZnCl ₂ , chlorine ions (Cl ⁻ ) act as an electrolyte, which can significantly reduce the treatment cost. Zinc ion in the waste water of the electrolytic cell (Zn ²⁺⁾ is electron (e ^-) generated from the cathode reacts with nitrate and with the generation of nitrogen gas (N _2), is reduced with Zn metal and also attached to the cathode . In addition to the Zn-based liquid catalyst, tin (Sn), copper (Cu), lead (Pb), iron (Fe), antimony (Sb), and aluminum (Al) -based metals may be used. It is also possible to use more than two hybrid liquid catalysts.

In addition, in order to ionize these metals into a liquid phase, Mx (SO ₄ ) y, Mx (Cl) y, Mx (CO ₃ ) y, Mx (OH) y compounds may be used, or the elements may be dissolved in hydrochloric acid or sulfuric acid. Can be used. In this case, when the liquid catalyst is a compound of the form of Mx (Cl) y, dissociated Cl ^- ions in the waste water act as an electrolyte, thereby increasing the efficiency of the oxidation reaction and thus not injecting a separate electrolyte. , Sn, Cu, Pb, Fe, Sb, Al is a metal, x, y represents an integer of 2 or more according to the bonding of each compound.)

As described above, the efficiency of the liquid catalyst for each metal and the treatment efficiency of nitrate nitrogen according to the nitrogen removal method of each plating wastewater are shown in the graphs of FIGS. 3 and 4, respectively.

Referring to FIG. 3, in the metal used as the liquid catalyst, the efficiency according to each metal was found in the order of Zn> Sn> Cu> Pb> Fe> Sb> Al.

Figure 4 shows the case of using a common electrode and a liquid catalyst of ZnCl ₂ , the case of using a reduction electrode coated with ZnO ₂ or IrO ₂ , the case of using both a liquid catalyst and an electrolyte as the nitrogen removal method of the plating waste water In the case of using both the liquid catalyst and the electrolyte as in the embodiment of the present invention, it can be seen that the removal efficiency of nitrate nitrogen is most excellent.

As described above, the plating wastewater subjected to the electrolysis step is mostly free of cyanide, ammonia nitrogen, and nitrate nitrogen, but there may be heavy catalysts which are not completely treated in the liquid catalyst or pretreatment stage. In order to completely remove the remaining liquid catalyst and heavy metals, the post-treatment step is performed again to remove the liquid catalyst and heavy metals by a dissolved air flotation method. When the flocculation pressure flotation method is used, the hydraulic retention time (HRT) can be reduced to 20 ~ 30% compared to the general precipitation method, so that the change of acidity (pH) or the coagulated heavy metal due to the delay of treatment time can be reused. Can be prevented.

As described above, the plating wastewater which has undergone the pretreatment step, the electrolysis step, and the post-treatment step is finally removed from various heavy metals and nitrogen. In particular, the concentration of total nitrogen can satisfy the environmental regulation value of 60 mg / l or less.

Although the present invention has been described in detail through specific embodiments above, the present invention is not limited to the above-described examples and should be made by those skilled in the art to which the present invention pertains, within the scope of the technical idea of the present invention. Various changes may be made.

As described above, according to the nitrogen removal method for plating wastewater of the present invention, nitrogen of plating wastewater having high toxicity and heavy metal content can be removed by using electrochemical oxidation and reduction reactions, and particularly, cyanide (CN) contained in the wastewater. , ammonia nitrogen (NH ₃ -N) and nitrate nitrogen to (NO ₃ ^{- -} -N or NO ₂ -N) can be removed from one reactor at the same time. In addition, the present invention improves the efficiency of nitrogen removal by adding a catalyst in the form of a liquid in the electrolytic device, and applies a pretreatment process and a post-treatment process by the flocculation pressure flotation method, so that heavy metals and total Nitrogen can be removed.

Claims (6)

In the purification treatment method of plating wastewater, A pretreatment step of reducing chromium to increase acidity of the wastewater, and cohesive pressurizing the wastewater to remove heavy metals of the wastewater; An electrolysis device having an anode and a cathode having metal electrodes, in which an electrolyte and a liquid catalyst are injected into an electrolytic cell into which the waste water flows into the electrolysis step to electrically decompose the waste water; And A post-treatment step of flocculating pressure flotation to remove the unreacted liquid catalyst and untreated heavy metal in the electrolyzed wastewater; To Nitrogen removal method of the plating wastewater comprising a. 2. The method of claim 1, wherein the electrolysis step comprises electrolyzing cyan and ammonia nitrogen by the positive electrode and simultaneously electrolyzing nitrate nitrogen by the negative electrode. 2. The method of claim 1, wherein the electrolyte is injected with sodium chloride (NaCl) into the electrolyte. The liquid catalyst of claim 1, wherein the liquid catalyst comprises one of zinc (Zn), tin (Sn), copper (Cu), lead (Pb), iron (Fe), antimony (Sb), and aluminum (Al). Nitrogen removal method of the plating wastewater, characterized in that the single- or complex-based liquid catalyst containing. The liquid catalyst of claim 4, wherein the liquid catalyst uses the metal in the form of a compound of any one of Mx (SO ₄ ) y, Mx (Cl) y, Mx (CO ₃ ) y, and Mx (OH) y. Nitrogen removal method of the plating wastewater characterized in that it is dissolved in hydrochloric acid or sulfuric acid (M is one of the metals of claim 3, x, y is an integer of 2 or more depending on the combination of the compound). The method of claim 5, wherein when the liquid catalyst is a compound of the form of Mx (Cl) y, the step of injecting the electrolyte can be omitted (M is the metal of claim 3 One, x, y is an integer of 2 or more depending on the combination of the compounds).

Images