JP2014205096A - Chemical denitrification processing method using solid organism-derived substance - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide means for economically reducing contaminant in an oxidation state in concentrated nitric acid drainage without applying biological treatment.SOLUTION: Chemical processing is performed to contaminant in an oxidation state in drainage by reducing the contaminant by adding a solid organism-derived substance being an object to be discarded in a reduced state to drainage in an oxidation state. For example, by adding a solid organism-derived substance such as garbage, livestock feed and waste food to nitrate nitrogen being contaminant in concentrated nitric acid drainage having pH at 3 or less without applying biological treatment, nitrate nitrogen is chemically reduced to nitrogen gas, and can be denitrified.

Description

The present invention is used for treatment of industrial wastewater and the like, and relates to maintenance of water quality after treatment. Especially in the treatment of pollutants in wastewater that is oxidized and strongly acidic, such as nitrate nitrogen and nitrite nitrogen contained in wastewater, a reduction treatment method that uses only chemical treatment without biological treatment. provide.

Concentrated nitric acid drainage discharged from the degreasing / acid cleaning process is strongly acidic and a large amount is generated, so that the treatment is not easy. Conventional treatment methods include neutralization, dilution, biological treatment with denitrifying bacteria, etc., all of which require a large amount of alkali, greatly increase the amount of treated water, or treatment performance depending on the degree of biological activity. There are issues such as destabilization. In general, biological treatment using microorganisms is basically used, and as a complementary treatment, neutralization, dilution, and volatilization methods are often combined.

Japanese Unexamined Patent Application Publication No. 2008-136942 proposes a denitrification method using anaerobic bacteria, and Japanese Unexamined Patent Application Publication No. 2011-240327 proposes a method of extracting and denitrifying only granular bacteria in food wastewater. As a supplement to biological treatment methods, Japanese Patent Application Laid-Open No. 09-206790 and Japanese Patent No. 4037491 show contrivances in organic matter addition methods when wastewater is biologically reduced and denitrified. ing. In JP-A-55-129199, JP-A-62-171792, and JP-A-10-137788, a treatment for denitrification by mixing nitric acid wastewater as an oxidizing agent when biologically treating BOD-containing wastewater such as sewage. A law has been proposed. However, in the case of a biological treatment method, it is necessary to prepare an environment in which microorganisms can grow, so that it is difficult to treat a large amount of waste nitric acid, particularly a high concentration of waste nitric acid.

In the case of the chemical denitrification treatment method, the method mainly uses a reducing agent or a catalyst that promotes a reduction reaction. Japanese Patent Laid-Open No. 2006-263705 and Japanese Patent No. 4706828 use ferrous iron as a reducing agent, and Japanese Patent Laid-Open No. 2000-334478 and Japanese Patent No. 3145582 use the reducing power of hydrogen. Japanese Patent Application Laid-Open No. 05-138177 uses sodium bisulfite as a reducing agent. JP 2012-076019, JP 11-047793, JP 3652618, etc. use a reduction catalyst.

JP2008-136942 JP2011-240327 JP 09-206790 Patent 4037491 JP 55-129199 JP 62-171792 JP 10-137788 A JP 2006-263705 Patent 4706828 JP2000-334478 Patent 3155582 JP 05-138177 JP2012-076019 JP 11-047793 A Patent 3652618

In the case of a biological treatment method, the function of microorganisms varies depending on the temperature and components, and the treatment performance tends to become unstable. In addition, the quality of the wastewater is not constant, and there is a problem that it is difficult to maintain and maintain the microbial growth environment. In particular, when concentrated nitric acid flows in, a large amount of microorganisms may be killed. In the case of a large amount of processing, concentrated nitric acid must be diluted, resulting in a problem that the processing apparatus becomes large.

The neutralization treatment and dilution treatment, which are techniques for complementing biological treatment, also use a large amount of the alkali neutralizing agent and dilution water, so that the amount of treated water increases. In addition, when it is premised on dilution, the chance of contact of nitrate nitrogen and nitrite nitrogen in the waste water with the reducing bacteria is reduced, and the treatment speed is reduced. Therefore, it is necessary to volatilize in the air over a long time during the treatment process. When a neutralizing agent is mixed, a large amount of metal salt is produced, and a new problem of removing the metal salt arises.

In chemical denitrification treatment methods, methods using reducing agents such as ferrous iron, hydrogen, and sodium bisulfite have been proposed, but they are all expensive, and when treating a large amount of concentrated nitric acid wastewater. Not realistic.

A method of reducing nitric acid wastewater using BOD-containing wastewater has also been proposed, but because microbial treatment is premised, the amount of nitric acid wastewater mixed is 1 / kg of total organic matter in 1 kg of BOD-containing wastewater. It is limited from 10 and _{1 / 2kg-N-NO 3} . Since most of the BOD-containing wastewater is water, it is dilute as a reducing agent, resulting in an increase in the amount of treated water. Therefore, it cannot cope with highly concentrated nitric acid waste water that affects the growth environment of microorganisms.

Also, if the source of BOD-containing wastewater and nitric acid wastewater are separated, it is necessary to transport either raw water. In either case, a large amount of water must be transported, which increases the transportation cost. .

In the process of diligently developing a treatment method for concentrated nitric acid wastewater having a pH of 3 or less using a variety of methods, the chemical treatment method is more stable than the biological treatment, and the equipment This is advantageous when considering reduction, and the idea has been reached that the development of an inexpensive reducing agent is indispensable. In the case of biological treatment, the processing performance is unstable because the microorganisms rely on a reduction reaction, and concentrated nitric acid cannot be treated directly, resulting in an increase in the amount of treated water and a dilute nitrogen component, It was judged that it was difficult to solve the fundamental problem in that the reduction reaction rate was slow. On the other hand, even in the case of chemical methods, the development of an inexpensive reducing agent was an essential requirement. It is a necessary condition that the reducing agent works under a strong acid.

As a result of investigating inexpensive reducing agents and focusing on their reactivity and availability, biodegradable biological materials are left in the living environment in a reduced or overreduced state. I noticed. Organic substances in living environment such as biologically derived substances, specifically leftover food, feed, waste food, sewage sludge, waste animals and plants, organic solid waste with biodegradability, are not originally used for chemical reactions, Some of the so-called raw garbage is composted for effective use, or most is incinerated. The chemical reactivity of the biological material has hardly been studied. The inventors have noticed that organisms such as animals and plants use reducing substances for life support in the course of searching for inexpensive reducing agents. In the first place, plants that are producers in the food chain reduce carbon dioxide by photosynthesis and synthesize sugar. Furthermore, animals metabolize the sugars to further reduce them and synthesize polysaccharides, proteins, lipids, and the like. Among them are antioxidants that can be said to be in a hyperreduced state.

The inventors have realized that the use of a biologically-derived substance that is left in such a reduced state is most effective in solving the present problem, and has reached the present invention. In other words, most biological substances are in an amorphous state, so the water molecule permeation rate is high, the density is around 1, and it is found to be a porous body (large specific surface area). Found that it was excellent. Treatment of concentrated nitric acid wastewater from solid biological substances that are subject to disposal, especially processed foods that have undergone artificial treatment, such as leftover food, feed, waste food, sewage sludge, waste animals and plants, organic solid waste, etc. By using as a reducing agent, the concentrated nitric acid waste water can be stably treated without diluting and without increasing the size of the treatment apparatus.

The greatest feature of the present invention is that a solid biological substance is used as a reducing agent. Because it is solid, the increase in the amount of wastewater due to treatment is negligible, and since the biological material itself is amorphous, porous and hydrophilic, the effect of having a moderately fast reaction rate is a chemical. This is a feature that does not appear in the reducing agent.

In addition, when using biological substances, reduce acid concentration is reduced by using coexisting concentrated nitric acid with reducing agents such as urea and nylon nonwoven fabric and catalyst under strong acidity, or using cheap iron, and then using biological substances. It was also found that the most efficient treatment can be achieved by reduction and finally precipitation with a basic substance. A part of the added iron remains in the treatment liquid as divalent or trivalent iron ions, but precipitates as ferric hydroxide by the addition of a basic substance. When a ferric hydroxide colloid is separately added during the precipitation, heavy metals can be selectively precipitated.

Since it is a chemical treatment method that does not rely on microorganisms, there is no limit to the amount or concentration of concentrated nitric acid, daily maintenance is easy, and the treatment apparatus can be automated. It is also easy to respond to fluctuations in the quality of wastewater, and the fluctuations in the quality of wastewater are tracked by conductivity, acid concentration, oxidation-reduction potential, etc., and chemical reactants such as reducing agents, catalysts, iron, basic substances, etc. What is necessary is just to control the input amount.

Since concentrated nitric acid is not diluted, the chance of contact between nitrate nitrogen and nitrite nitrogen and the reducing reactant is increased, and the reduction reaction rate is increased. Therefore, it is not necessary to rely on nitrogen gas volatilization over time during the treatment process.

Since the main reducing agent is a solid biological material that is a material to be discarded, the cost is extremely low, and in some cases, it may be possible to collect the processing costs. In particular, waste food and fruits are effective because they have a large impact on the environment.

Since the biological material to be used has a moisture ratio smaller than that of BOD-containing wastewater such as sewage, the transportation cost can be minimized even when transported. In addition, although the biologically derived substance to be used is a substance to be discarded, its quality is generally clear and stable, and it is suitable as a chemical reaction material. By blending a plurality of solid biological substances, the quality can be further stabilized and made easy to use.

Concentrated nitric acid has been difficult to treat due to its strong acidity and large amount of treatment, but according to the present invention, it can be treated without depending on a dilution method or a biological treatment method. By using a solid biological material that is a target for disposal, concentrated nitric acid can be processed inexpensively and compactly, and its processing equipment can be saved and reduced in size, and at the same time adversely affects the environment. It becomes possible to treat organic solid waste.

As a basic treatment method, a biogenic substance as a reducing agent is added to concentrated nitric acid wastewater having a pH of 3 or less and stirred, and nitrate nitrogen and nitrite nitrogen in the concentrated nitric acid wastewater are reduced. Reduced by contact with the derived material, removed as nitrogen gas, and denitrified.

The biological material used as the reducing agent is a biological material that is a solid material to be discarded, and specifically includes leftover rice, feed, waste food, sewage sludge, waste animals and plants, organic solid waste, and the like. In particular, it is desirable to be a material subject to disposal that can collect disposal costs (so-called reverse-paid collection), but other biological materials that are unclear as to whether it is waste or not can be used for wastewater treatment. It can be considered as a material to be discarded. The solid biological material is an organic solid synthesized by a living body in a broad sense, and includes all of them.

The contact method between the biological substance and nitrate nitrogen or nitrite nitrogen in the concentrated nitric acid wastewater may be any of the aeration method, the stirring method, the rotating disk method, or the circulating flowing water method, preferably the aeration method or Stir by the stirring method and contact.

When the pH of the concentrated nitric acid waste water is less than 2, urea may be added together with the nylon nonwoven fabric and iron may be further added to raise the pH to 2 or more. Urea is used as a reduction aid, and nylon nonwoven fabric is used as a reduction catalyst. Urea is used in powder form, and nylon non-woven fabric is used in cloth form. Preferably, the catalyst efficiency can be increased by cutting into 1 to 20 cm square. Iron is used for reducing acidity and using hydrogen generated by the reaction as a reduction aid. Iron can be iron scrap as a material to be discarded or iron powder.

After the reduction treatment, the treated water can be easily handled by adding an inorganic basic substance and adjusting the pH to 7-10. By producing a precipitate and separating the precipitated sludge, the supernatant water can be sent to the next gentle processing step. Specific examples of the inorganic basic substance include sodium hydroxide, calcium hydroxide, magnesium hydroxide, and calcium oxide.

The concentrated nitric acid prepared for the experiment had a pH of 1.4, an electrical conductivity of 13.5 mS / cm, and a redox potential of 748 mV. The nitrate nitrogen concentration in the concentrated nitric acid was determined by measuring the absorbance using a spectrophotometer U-3000 and determining the nitric acid concentration from a calibration curve. The nitrate nitrogen concentration was calculated from the nitric acid concentration according to the following formula. Nitrate nitrogen concentration = 0.222 × nitric acid concentration. As a result, the nitrate nitrogen concentration was 0.8 mol / L.

0.25 wt% urea, 0.50 wt% nylon non-woven fabric (NO5070 manufactured by Asahi Kasei Fibers Co., Ltd.) and 1 wt% iron wire (1 mm diameter x 20 cm length) in 5 L of concentrated nitric acid waste water Was added and aerated from the bottom of the water tank, and the inside of the tank was stirred for 24 hours. Treated water 1 after treatment had a pH of 2.8, an electrical conductivity of 9.7 mS / cm, and an oxidation-reduction potential of 249 mV.

2.25% by weight of remaining rice (cooked white rice) was added, aerated from the bottom of the water tank, and stirred in the tank for 30 minutes. The treated water 2 after the treatment had a pH of 3.1, an electrical conductivity of 9.8 mS / cm, and a redox potential of 247 mV.

10% by weight of calcium hydroxide was added, aerated from the bottom of the water tank, and the inside of the tank was stirred for 600 minutes. The treated water 3 after the treatment had a pH of 8.4, an electric conductivity of 9.7 mS / cm, and an oxidation-reduction potential of -339 mV. The nitrate nitrogen concentration in the treated water 3 was calculated from the result of measuring the absorbance with a spectrophotometer. As a result, it was 0.06 mol / L, and the removal rate from the raw water was 92.5%. During the treatment, no ammonia gas odor was generated, and it was confirmed that denitrification with nitrogen gas was appropriately performed.

Claims (4)

In a wastewater treatment method in which denitrification is performed as nitrogen gas by chemically reducing concentrated nitric acid wastewater having a pH of 3 or less, a solid biological substance, which is a target substance for disposal, is mixed with the wastewater without biological treatment. A chemical denitrification method characterized by reducing and denitrifying nitrogen gas. An oxidation-reduction treatment method characterized by using, as a living body-derived substance according to claim 1, residual rice, feed, waste food, sewage sludge, waste animals and plants, or organic solid waste. 3. The chemical denitrification method according to claim 1, wherein when the pH of the concentrated nitric acid wastewater is less than 2, urea is added together with the nylon nonwoven fabric and iron is further added to raise the pH to 2 or more. 4. The chemical denitrification method according to claim 3, wherein after the reduction treatment, an inorganic basic substance is added to adjust the pH to 7 to 10.