KR101683271B1 - Apparatus for processing waste water with algae - Google Patents

Abstract

A wastewater treatment apparatus using algae is disclosed. The wastewater treatment apparatus includes a methane fermentation tank for decomposing organic matters in the wastewater by anaerobic reaction to produce methane (CH ₄ ), an organic matter removal tank for removing organic matter from the methane fermentation tank of the methane fermentation tank, , A nitrification tank for oxidizing ammonia nitrogen using oxygen generated from the algae production tank, a sedimentation tank for solid-liquid separation of algae and nitrifying microorganisms produced from the algae production tank and the nitrification tank, A thermal hydrolysis reaction tank for thermally hydrolyzing the solid matter, and a denitrification tank for denitrifying the liquid matter obtained by solid-liquid separation. According to this, the hydrolysis process increases the decomposition rate and efficiency of the organic substances present in the wastewater. In addition, it is possible to reduce the concentration of solids in the algae reaction tank by removing organic matters and solids that remain before entering the algae tank after the anaerobic treatment, thereby increasing the light transmittance required to generate algae.

Description

[0001] The present invention relates to an apparatus for treating wastewater using algae,

The present invention relates to a wastewater treatment apparatus capable of increasing the amount of methane produced by treating wastewater using algae and utilizing the produced algae. More particularly, the present invention relates to a wastewater treatment apparatus for growing algae using nutrients in wastewater, The present invention relates to a wastewater treatment apparatus capable of not only increasing methane production of an anaerobic digestion tank but also purifying wastewater.

There are various methods of treating wastewater containing high concentration of organic matter, but anaerobic treatment method is mainly used in consideration of economic efficiency and efficiency. A representative technique of the anaerobic treatment method is an anaerobic digestion process, which refers to a technique of converting organic matter (C) into methane gas (CH ₄ ) by decomposing acid-producing microorganisms and methanogenic microorganisms by maintaining an anaerobic state without air. Unlike aerobic technology, anaerobic technology does not require oxygen to treat organic matter, so it has the advantage of obtaining methane (CH ₄ ), which is an economical and useful natural gas. However, when anaerobic treatment is performed on wastewater, organic matter can be removed, but nitrogen and phosphorus are not removed, and nitrogen and phosphorus, which are combined with organic matter, are eluted, and nitrogen and phosphorus load are increased in subsequent processing steps.

Phosphorus present in wastewater can be chemically removed. The dissolved phosphorus is converted into a solid form using a flocculant such as aluminum sulfate or iron chloride, and then removed by solid-liquid separation as shown in the following reaction formula.

Al ^{3 +} + PO ₄ ^{3 -} = AlPO ₄ (↓)

Fe ^{3 +} + PO ₄ ^{3 -} = FePO ₄ (↓)

In the case of nitrogen, it can be removed physically and chemically, but it is removed by biological methods for economic reasons. First, the ammonia nitrogen in the reduced state is oxidized by the nitrifying microorganism under the oxidizing condition. Nitrification consists of two steps and is as follows.

NH ₄ ⁺ + 1.5 O ₂ → NO ₂ ^- + 2H ⁺ + H ₂ O (Step 1)

NO ₂ ^- + 0.5O ₂ → NO ₃ ^- (Step 2)

NH ₄ ⁺ + ₂ O ₂ ? NO ₃ ^- + 2H ⁺ + H ₂ O (total)

As shown in the above equation, 1 g of ammonia nitrogen is converted into nitrite nitrogen, which consumes 3.43 g of oxygen and is further oxidized to nitrate nitrogen, which consumes 1.14 g of oxygen, resulting in 1 g of ammonia nitrogen being oxidized as a whole 4.57 g of oxygen is consumed. Therefore, a system that can supply the required oxygen is necessary for nitrification and it is the main cause of the increase of the maintenance cost.

The oxidized nitrogen is converted into nitrogen gas (N ₂ ) after being subjected to the reduction reaction and released into the air to complete the nitrogen removal. This reaction is called denitrification. The denitrification is accomplished by using nitrogen as the electron acceptor in which denitrifying microorganisms are oxidized under oxygen-free reducing conditions. At this time, an electron donor is required and organic materials such as methanol are used. The denitrification reaction with methanol as an electron donor is expressed as follows.

_{^{6NO 3 - + 5CH 3 OH →}} 3N 2 + 5CO 2 + 7H 2 O + 6OH -

The denitrification can be carried out in nitrate nitrogen (NO ₃ ^- N) and nitrite nitrogen (NO ₂ ^- N) states.

0.25O ₂ + H ⁺ + e ^- & gt ^; 0.5H ₂ O

0.33NO ₂ ^- + 1.33H ⁺ + e ^{- -} > 0.17N ₂ + 0.67H ₂ O

0.20NO ₃ ^- + 1.2H ⁺ + e ^- > 0.1N ₂ + 0.6H ₂ O

As can be seen from the above equation, in order for 1 g of nitrite nitrogen (NO ₂ ^- ) to be reduced, 1.73 g of COD is consumed and 2.86 g of COD is consumed to reduce 1 g of nitrate nitrogen (NO ₃ ^- ). These organic materials are called external carbon sources because they must be injected to the outside using methanol or acetic acid. As the amount of nitrogen to be reduced is increased, the amount of the external carbon source required increases, which causes an increase in the economic burden.

To solve this problem, a recently developed process is a nitrification-independent denitrification process (Fig. 1). This process is called an autotrophic denitrification because it uses ammonia nitrogen, which is an inorganic substance, instead of using organic materials for denitrification. In this process, 50% of wastewater is nitrified and ammonia nitrogen existing in the remaining 50% is used as an electron donor. This can be expressed as:

NH ₄ ⁺ + NO ₂ ^- > N ₂ + H ₂ O

As can be seen from the above equation, since the external carbon source is not consumed for denitrification, the external carbon source necessary for the conventional process can be reduced by 100%. Also, in the case of nitrification, only 50% of the flow rate is nitrified, resulting in a 37% reduction in oxygen consumption compared to the conventional process. Therefore, it can be said that the process is economically superior to the existing process. However, this process requires a long period of time to grow and maintain the microorganisms, and the operation conditions are very difficult.

Although the above-described techniques have focused on removing nitrogen and phosphorus in wastewater as pollutants, efforts have recently been made to recover the energy by growing algae using nitrogen and phosphorus in wastewater.

Birds are generally represented by C ₁₀₆ H ₂₆₃ O ₁₁₀ N ₁₆ P. They can produce 111 kg of algae and 138 kg of COD using 1 kg of phosphorus and produce 16 kg of algae and 20 kg of COD when 1 kg of nitrogen is utilized. Generally, since the concentrations of nitrogen and phosphorus in sewage are 45 and 6 mg / L, production of COD of 900 and 828 mg / L is possible through the production of algae, and production of COD of 20,000 mg / L by utilizing the anaerobic digester tank of sewage treatment plant It is possible to produce 100,000 mg / L COD using livestock manure, so the potential for recovering resources is very high. Recently, due to the development of LED technology, a method for providing light required for bird growth has been improved, and various technologies using algae have been developed.

2. Description of the Related Art In recent years, the development of a technology (FIG. 2) for increasing production of methane by producing algae using nitrogen and phosphorus in treated water and recirculated water in a sewage disposal plant in the United States and injecting them into an anaerobic digester has been developed. However, since this process has no step to remove nitrogen and phosphorus, there is a problem that accumulation of nitrogen and phosphorus occurs when operated for a long period of time.

The method of treating wastewater by using algae utilizes the symbiosis of algae and bacteria. Bacteria oxidize organic matter in wastewater using oxygen to produce carbon dioxide, and algae produce new algae and oxygen by photosynthesis under light conditions using carbon dioxide. Symbiosis is achieved by the bacteria again using the oxygen produced by the algae. The activated-algae process is called activated-algae, which uses the symbiosis of bacteria and algae. However, the existing activated-algae process has a limitation of the depth through which the light necessary for algal growth is transmitted. In winter, Failed to apply on site.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and it is an object of the present invention to provide a method and apparatus for recovering and recycling algae using nitrogen and phosphorus present in wastewater, And it is an object of the present invention to provide a method which can be economically removed without supplying an external carbon source.

The apparatus for treating wastewater according to the present invention comprises a methane fermentation tank for decomposing organic matter in wastewater through an anaerobic reaction to produce methane (CH ₄ ), an organic matter removal tank for removing organic matter by flowing a supernatant of the methane fermentation tank, A nitrification tank for oxidizing ammonia nitrogen by using oxygen generated from the algae production tank, an algae production tank and a nitrification microorganism produced from the algae production tank and the nitrification tank by solid-liquid separation A denitrification tank for denitrifying the liquid material obtained by solid-liquid separation; and a denitrification tank for denitrifying the liquid material obtained by solid-liquid separation.

It is preferable that the organic matter removing tank is used to simultaneously remove solids and organic matter using an upflow denitrification filter using an auxiliary filter medium.

A part of the solid matter separated by solid-liquid separation from the settling tank is returned to the algae-producing tank.

The carbon source hydrolyzed and recovered in the thermal hydrolysis reactor flows into the denitrification tank, and a part of the carbon source is introduced into the methane fermentation tank.

The methane generated in the methane fermentation tank is used for generation of electricity by combustion, and the carbon dioxide generated during methane combustion is supplied as a carbon source of the algae production tank.

An acid fermentation tank may be provided at the front end of the methane fermentation tank to ferment algae such as wastewater.

The wastewater treatment apparatus according to the present invention enhances the decomposition rate and efficiency of the organic matter present in the wastewater through the hydrolysis process. In addition, after the anaerobic treatment, the remaining organic matter and solids are removed before entering into the bird reactor, thereby reducing the solids concentration in the algae reactor, thereby increasing the light transmittance required for algae production and increasing the purity of the algae produced. In addition, the removal efficiency of nitrogen is improved by removing organic matter remaining in the oxidized nitrogen contained in the return water. Since the organic matter and solids were removed from the shear stage, the algal reaction tank was dominated by algae, and the growth of solids and microorganisms, which interfere with light transmission, was minimized and the light transmission efficiency was increased. The inorganic carbon required for algae production recycles methane generated from the methane fermenter and carbon dioxide from boilers that burn dehydrated solids. Oxygen required for nitrogen oxidation uses oxygen generated during the generation of algae so that no additional oxygen is required. The carbon source required for denitrification is obtained through hydrolysis of algae. In general, the C / N ratio of the algae is 71, which is very high as the carbon source, compared to the C / N ratio of the excess sludge of 5.1. Thereby improving the economic efficiency.

1 is a conceptual diagram of a conventional high-concentration wastewater treatment process.
FIG. 2 is a conceptual diagram of a high-concentration wastewater treatment process using existing algae.
3 is an embodiment according to the present invention.
4 is an embodiment for simultaneously fermenting algae and sludge according to the present invention.

In order to solve the above technical problems, the wastewater treatment apparatus is capable of removing nitrogen and phosphorus contained in wastewater by increasing the recovery of methane by producing algae using high concentration wastewater.

Technology to simultaneously produce algae and nitrogen / phosphorus by producing algae using nitrogen and phosphorus in wastewater and oxidizing nitrogen in wastewater by using oxygen generated in the process of algae to remove it from the subsequent denitrification process to be. Since no separate oxygen supply is required for nitrification, there is no need for a system for oxygen supply, which saves initial investment and saves maintenance expenses because there is no need to consume electricity to operate the system. In addition, the solids in wastewater and wastewater can be rapidly and efficiently hydrolyzed to increase the efficiency of the anaerobic process, and the hydrolyzed organic matter can be used as a carbon source for nitrogen removal.

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

3 is a schematic view of a wastewater treatment system according to the present invention. The wastewater treatment apparatus according to the present invention includes a methane fermentation tank 10, an organic matter removal tank 20, a bird producing tank 30, a nitrification tank 40, a settling tank 50, a denitrifying tank 60, (70).

The high concentration wastewater first decomposes the organic matter in the wastewater through the anaerobic reaction in the methane fermentation tank 10 to produce methane (CH ₄ ). The supernatant of the methane fermentation tank 10 flows into the subsequent organic material removal tank 20, and the organic material is removed by the nitrate nitrogen returned from the settling tank 50. The denitrification process is most suitable for the organic matter removing tank 20, because the solids and the organic substances are removed at the same time, so that the inflow of the organic substances and the solids into the subsequent algae producing tank 30 can be minimized. The inflow of the organic matter and the solids into the alga generation tank 30 is minimized, so that the algae can be dominant in the algae generation tank 30 and the transmission of light due to the accumulation of solid matter can be prevented.

The algae-producing tank 30 receives the effluent of the organic material removing tank 20 and generates algae using nitrogen, phosphorus, carbon dioxide, and light, and generates oxygen as a by-product. The generated oxygen is used to oxidize the ammonia nitrogen in the subsequent nitrification tank 40. The algae and the nitrifying microorganisms generated in the algal production tank 30 and the nitrification tank 40 are subjected to solid-liquid separation in the sedimentation tank 50 and part of them are transferred to the algal production tank 30, The carbon source is recovered through hydrolysis to be used in the denitrification tank 70 and a part of the carbon source is introduced into the methane fermentation tank 10 to increase the methane production. Methane produced in the methane fermentation tank 10 is used to generate electricity by generating heat by combustion, and carbon dioxide generated during methane combustion is supplied as a carbon source of the algal-producing tank 30.

4 is a schematic view showing another embodiment of the present invention in which the methane fermentation tank 10, the organic matter removal tank 20, the algae generation tank 30, the nitrification tank 40, the settling tank 60, And a deasphalted tank 60. In addition, an acid fermentation tank 80 is provided at the upstream of the methane fermentation tank 10.

The algae are introduced into the acid fermentation tank 80 without being hydrolyzed separately to simplify the process and improve the efficiency of the methane fermentation tank 10 by performing fermentation like wastewater. The carbon source necessary for the denitrification can increase the denitrification rate by using the organic acid generated in the acid fermentation tank 80. In addition, solid matter generated through dehydration can recover heat and carbon dioxide through combustion and be recycled.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims. Accordingly, the true scope of the present invention should be determined by the technical idea of the appended claims.

Claims (7)

A methane fermenter that decomposes organic matter in the wastewater through an anaerobic reaction to produce methane (CH ₄ )
An organic matter removing tank through which a supernatant of the methane fermentation tank flows and organic substances are removed,
An algae generating tank for generating algae using the effluent of the organic material removing tank,
A nitrification tank for oxidizing ammonia nitrogen using oxygen generated from the algae production tank,
A sedimentation tank for solid-liquid-separating the algal-producing tank and the nitrifying microorganisms produced from the nitrifying tank,
A thermal hydrolysis reaction tank for thermally hydrolyzing the solid obtained by solid-liquid separation, and
A denitrification tank for denitrifying the liquid material obtained by solid-liquid separation
And a control unit for controlling the wastewater treatment unit.
The method according to claim 1,
Wherein the organic matter removing unit is configured to simultaneously remove solid matter and organic matter using an upflow denitrification filter using an auxiliary filter medium.
The method according to claim 1,
And a part of the solid matter separated by solid-liquid separation from the settling tank is transported to the algae-producing tank.
The method according to claim 1,
And the carbon source hydrolyzed and recovered in the thermal hydrolysis tank is introduced into the denitrification tank.
5. The method of claim 4,
And a part of the carbon source is introduced into the methane fermentation tank.
The method according to claim 1,
Wherein methane generated in the methane fermentation tank is used for generation of electricity and carbon dioxide generated during methane combustion is supplied as a carbon source of the algae production tank.
The method according to claim 1,
Further comprising an acid fermentation tank provided at a front end of the methane fermentation tank,
Wherein the acid fermentation tank ferments algae like wastewater.

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