KR100312820B1 - Advanced Waste Water Treatmant Methods with using Fermented Primary Sludge - Google Patents

Abstract

In the present invention, in the treatment of sewage or waste water, a fermentation tank is provided in a treatment process consisting of a biological reaction tank and a sedimentation basin, and the raw sludge generated by precipitation of solids contained in the influent wastewater in the first settler is fermented in the fermentation tank, acetate The fermentation broth containing a series of organic acids and the like is used as an electron donor for denitrification of nitrogen oxides by the post-denitrification method, while dissolved organic matter contained in the effluent of the first settler may be The present invention relates to an advanced sewage treatment method, which is used to maintain anaerobic conditions for denitrification or phosphorus release, which contributes to the treatment and disposal of fresh sludge, which produces odors with economical and effective nitrogen and phosphorus removal.

Description

Advanced Waste Water Treatmant Methods with using Fermented Primary Sludge}

The present invention relates to a method for removing nutrients from sewage or wastewater, and more particularly, biological treatment consisting of a reaction tank and a sedimentation basin to remove nitrogen and phosphorus from sewage or wastewater treated in an urban sewage treatment plant or an industrial wastewater treatment plant. In the wastewater advanced treatment method, a fermentation tank is installed in the process and fresh sludge generated in the first settler is fermented with organic acid in the fermentation tank, and nitrogen and phosphorus can be removed with high efficiency by using a sludge fermentation solution containing organic acid. It is about.

Contaminants in sewage can be classified into organic matter expressed as biochemical oxygen demand (BOD) and nutrients such as nitrogen and phosphorus. Up to now, sewage treatment plants have been mainly treated with organic matter, and much of nitrogen and phosphorus have not been removed, but they have been discharged to rivers, lakes, or oceans.

If the sewage is discharged with nitrogen and phosphorus, it will cause eutrophication in rivers and lakes, and if it enters the ocean, it can cause red tide. Severe eutrophication causes odors and water pollution, as well as limiting the use of drinking water and waterways. Therefore, in order to prevent eutrophication of the water system as above, it is necessary to sufficiently remove nutrient nitrogen compounds or phosphates from the sewage treatment plant.

The principle of biological denitrification first converts ammonia nitrogen to nitrate by nitrification ( Nitrosomonas , Nitrobactor ) in aerobic state. In the anoxic state, nitrate-type combined oxygen is used for dissolved oxygen, and nitrogen is removed from the sewage due to the characteristics of microorganisms which reduce to free nitrogen. At this time, organic matter is used as an electron donor.

The method of supplying organic materials for denitrification in anoxic state is very important in biological denitrification process. Almost all nitrification and denitrification methods developed so far are divided into total denitrification using organic materials contained in sewage and post denitrification using organic alcohols such as methyl alcohol from the outside.

However, in the total denitrification method, the denitrification efficiency is low when the concentration of dissolved organic matter that is readily available to microorganisms in the influent sewage is low. However, in order to use as an electron donor for denitrification, organic materials that are easily decomposed, such as methyl alcohol, need to be injected into an oxygen-free reaction tank, which is a great cost burden.

Therefore, the present invention was devised to solve the above-mentioned problems, and in particular, while utilizing the advantages of the post-denitrification method with high nitrogen removal efficiency and small anoxic reaction tank, it solves the problem of operating cost required for procurement of methyl alcohol. The sediment fermentation liquor produced by fermenting fresh sludge, which is suffering from odors and poor dehydration efficiency, is treated by sedimentation of solids contained in influent wastewater from the first settler. It provides advanced wastewater treatment method using fresh sludge which can improve nitrogen and phosphorus removal efficiency.In addition, advanced wastewater that also removes nitrogen by total denitrification by using dissolvable dissolved organic matter contained in influent wastewater. The purpose is to provide a treatment method.

Raw sludge produced by sedimentation of sewage wastewater consists of a mixture of high molecular weight organic compounds such as fibrin, hemicellulose, starch, protein and fat. When fermented in anaerobic state, acetic acid is produced through propionic acid, butyric acid and ethanol. It is decomposed into methane gas and carbon dioxide. In the anaerobic fermentation process of organic matter, the methane fermentation step is very difficult and unsuccessful, but it is very easy up to the organic acid fermentation step, which is the first step of methane fermentation.

In the present invention, in view of the composition and anaerobic fermentation characteristics of the fresh sludge, the organic sludge contained in the sewage water flowing into the treatment plant and precipitated in the first settler is transferred to the fermenter, the raw sludge, the raw sludge is fermented The resulting acetic acid-based organic acid was used as an electron donor for the denitrification by the post-nitrogenation of nitrogen oxides in an oxygen-free reactor.

In addition, in the present invention, the solids contained in the influent wastewater are removed from the first settler and the dissolved organic matter contained in the effluent from the first settler is also introduced into a subsequent anoxic or anaerobic reactor to be used for denitrification by a total denitrification method or phosphorus. It was used to maintain anaerobic conditions for release to maximize the utilization of organic substances that may be deficient in denitrification.

In Korea, due to the long extension of sewage pipes, a considerable amount of organic matter is introduced into the state where it is difficult to dissolve and settle, so the raw sludge produced in the first settler does not meet the organic material requirement in the denitrification reaction or the nitrification process because the organic inflow concentration is low. In order to sufficiently remove the nitrogen oxides generated in the present invention, there is a problem that the denitrification efficiency is low due to the lack of organic material, so that the total denitrification used in the dissolved organic matter in the influent sewage is performed in parallel.

As in the present invention, the raw sludge fermented from sludge fermented in the first settler is used as an electron donor for denitrification by the post-denitrification method, and the anaerobic conditions for the release of phosphorus from the dissolved organic matter contained in the influent wastewater. When used for the denitrification reaction by the maintenance and total denitrification method, the efficiency of nitrogen and phosphorus removal in the sewage treatment plant is improved first, the eutrophication of the effluent system is improved, the sludge generation amount is reduced, and the landfill demand and leachate generation due to the sludge landfill Secondary pollution such as air pollution by incineration can be reduced.

1 is a schematic process diagram of a first embodiment according to the present invention;

2 is a schematic process diagram of a second embodiment according to the present invention;

3 is a schematic process diagram of a third embodiment according to the present invention.

-Explanation of symbols for the main parts of the drawing-

1a: first rechargeable battery 1b: second rechargeable battery

2: anaerobic reactor 3a: first aerobic reactor

3b: second aerobic reactor 4: anoxic reactor

4a: 1st anoxic reactor 4b: 2nd anoxic reactor

5: fermentation tank 6: return sludge

7: Internal circulating water 8: Fresh sludge

9: sludge fermentation liquid

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

<Description of Embodiment 1 of FIG. 1>

1 is a schematic process diagram of a first embodiment of a method for treating wastewater using advanced fermentation sludge according to the present invention.

As shown, in the present embodiment, the influent sewage → the first settler (1a) → the anaerobic reactor (2) → the first aerobic reactor (3a) → the anaerobic reactor (4) → the second aerobic reactor (3b) → the second settler (1b) → The fermentation tank (5) is provided in the process consisting of the effluent water, and the fresh sludge (8) generated by the precipitation of organic solids contained in the inflow and wastewater from the first settler (1a) is transferred to the fermentation tank (5). And the sludge fermentation liquid 9 produced by fermentation is injected into the anoxic reaction tank 4, and the activated sludge precipitated in the second settler 1b is returned to the first aerobic reaction tank 3a as the return sludge 6a. The process consists of. Hereinafter, the operation of the individual unit process will be described.

In the first sedimentation cell (1a), which is a solid-liquid separation process, dissolved organic matter contained in the influent sewage water is overflowed into the anaerobic reaction tank (2), which is a subsequent process along the sewage water, and the sedimentable solids are precipitated and taken out as fresh sludge (8). It is transferred to the fermentation tank (5).

In the anaerobic reaction tank 2, anaerobic conditions are maintained under aerobic agitation and phosphorus release reaction is performed from activated sludge returned from the second settler 1b. As described above, the anaerobic reactor 2 corresponds to a preliminary reaction necessary to allow a larger amount of phosphorus to be taken up in the first aerobic reactor 3a.

In the first aerobic reactor (3a), the reaction liquid introduced from the anaerobic reactor (2) is aeration mixed, organic matter in the sewage is aerobic decomposed by catabolism and assimilation of activated sludge microorganisms under aerobic conditions, and ammonia nitrogen is It is oxidized to nitric acid nitrogen (NO ₂ , NO ₃ ) by the metabolism of nitrifying microorganisms. In addition, in the first aerobic reactor 3a, a larger amount of phosphorus is excessively ingested in the activated sludge microorganism than the one released in the anaerobic reactor 2, so that the phosphorus is removed from the wastewater.

In the oxygen-free reaction tank (4), the combined oxygen in the form of nitrate-nitrogen nitrogen introduced from the first aerobic reaction tank (3a) by aerobic microorganisms is reduced to free nitrogen by the aerobic microorganism in which oxygen is not supplied and only stirring is performed to free oxygen. The denitrification reaction proceeds mainly. In order to reduce the nitrogen nitrate to be used as the electron acceptor to reduce the free nitrogen, an organic substance, which is an electron donor, must be injected. In the past, methyl alcohol was mainly purchased and used, unlike in the present invention.

In order to solve the excessive economic burden caused by the use of methyl alcohol in the present invention was improved so that the decomposing acetate-based organic acid produced by fermenting the fresh sludge 8 generated in the first settler (1a) as an electron donor . In addition to fresh sludge, fermentation of surplus activated sludge and denitrification can reduce the problems of sludge, which has a lot of difficulties in disposal.

The second aerobic reaction tank 3b is a reaeration process in which the reaction liquid introduced from the oxygen-free reaction tank 4 is converted into an aerobic state. As a result, the remaining organic matter is decomposed by aerobic microorganisms, denitrification is completed, free nitrogen present in water is degassed (Air Stripping), released into the atmosphere, and deteriorated under anoxic conditions of the previous stage. It is a process to improve sedimentation.

The final settler 1b is a solid-liquid separation process in which the solid precipitates from the solid suspension mixture to be separated and clean symbolic water is separated. The symbolic water flows out as treated water and the activated sludge, which is the precipitated solid, is the anaerobic sludge as a return sludge. It may be returned to the reactor 2 and some excess may be discarded.

In the fermentation tank 5, the organic substance contained in the fresh sludge 8 precipitated and separated in the first settler 1a is fermented to produce an acetate-based organic acid. The organic material fermented in this process is injected into the anoxic reactor 4 as described above and used as an electron donor for denitrification.

Raw sludge is composed of a mixture of high molecular organic compounds such as fibrin, semi-fibre, starch, protein, and fat. When fermented under anaerobic conditions, acetic acid is produced through propionic acid, butyric acid, ethanol, etc., and finally decomposed into methane gas. Fermentation has been used mainly for sludge reduction and stabilization of sewage treatment plants.

The fermentation tank 5 in which the raw sludge is fermented according to the present invention is basically a unit process of the same principle as the anaerobic digestion tank that has been mainly used for sludge reduction and methane gas production in a conventional sewage treatment plant, and the operation mode is merely changed. Therefore, by using the existing sludge digestion tank as a fermentation tank, the advanced treatment method according to the present invention can be easily adopted in the sewage treatment plant in operation. In the existing sludge digestion tank, organic matter was finally decomposed to the gas generation stage such as methane through the organic acid fermentation stage. However, in the present invention, the reaction of the conventional sludge digestion process is shortened by one step to terminate the reaction in the organic acid fermentation step, and the organic acid produced therein is used for denitrification instead of methyl alcohol, which has been used in the post-denitrification method. Nitrogen removal efficiency is improved and economically very advantageous.

In order to be rapidly denitrified, the respiration of microorganisms must be vigorous, and the respiration of microorganisms is closely related to the types and amounts of organic substances available to the microorganisms, and thus, the organic substances that can be easily used by the microorganisms must be sufficiently supplied. Up to now, the post-denitrification method used methyl alcohol, which is easily used by microorganisms, and relatively inexpensive. However, experimental results show that acetate, which has a relatively simple molecular structure, is most advantageous, and then butyl. It was confirmed that the order of salts and alcohols. Organic matter produced after fermentation is the most acetate and then consists of butyl salt, propyl salt and alcohols can be effectively used for denitrification.

In particular, the sludge digester that has been used up to now has been frequently failed to operate in the difficult methane fermentation stage even though it is easily completed until the organic acid fermentation stage. On the other hand, in the present invention, since the fermentation broth from which the reaction is completed in the organic acid fermentation step is used for denitrification, the risk of failure is less than that of methane fermentation and is a stable method.

As the organic acid fermentation proceeds in the fermentation tank 5, hydrogen ion concentration is excessively increased, and an alkaline agent may be required for effective fermentation. In addition, emulsified hydrogen gas or the like may cause odors, so ferric salt (Fe ⁺⁺ ) may be added or the generated gas may be blown into the first aerobic reactor 3a to cause odor decomposition material to be oxidized by aerobic microorganisms. have.

The fermentation broth completed fermentation in the fermentation tank 5 may include inorganic solids or organic solids that cannot be decomposed. If such solids are not removed and injected into the oxygen-free reaction tank 4, the solid organic matter is gradually decomposed and organic matter is eluted from the second aerobic reaction tank 3b close to the second settling battery 1b or the second settling battery 1b. It can also adversely affect water quality. In addition, since the inorganic solid is circulated in the water treatment process through the conveying sludge (6), the active sludge is reduced in the composition ratio of active microorganisms that contribute to the decomposition of organic matter, the sludge activity is also reduced. Therefore, it is preferable to use a filtrate in which the solids are separated by adding solid-liquid separation means [not shown] to the fermentation tank 5.

As a solid-liquid separation means, an additional sedimentation basin or dehydrator is installed after the fermentation tank (5), or two or more fermentation tanks are connected in series to allow the fermentation broth to flow out of the fermentation tank to stop the agitation so that precipitation occurs and the flow direction of the inflow / outflow There is a method of changing and using.

<Description of Embodiment 2 of FIG. 2>

Figure 2 relates to a second embodiment of the advanced wastewater treatment method using the organic waste according to the present invention.

As shown, in this embodiment, the influent sewage → the first settler 1a → the first anaerobic reactor 4a → the first aerobic reactor 3a → the second anoxic reactor 4b → the second aerobic reactor 3b. → a fermentation tank (5) is provided in the process consisting of the second settler (1b) → effluent water, the fresh sludge (8) generated by the precipitation of organic solids contained in the influent wastewater from the first settler (1a) is fermentation tank ( 5) fermented and sludge fermented liquor (9) is injected into the second anoxic reaction tank (4b), the activated sludge precipitated in the second settler (1b) as the return sludge (6) the first anoxic reaction tank (4a) And the reaction liquid of the first aerobic reaction tank 3a is internally circulated to the first anoxic reaction tank 4a.

In this embodiment, post-denitrification by the second anoxic reaction tank 4b and total denitrification by the first anoxic reaction tank 4a into which internal circulating water flows from the first aerobic reaction tank 3a are performed together. Therefore, the dissolved organic matter contained in the symbolic water of the first settler 1a is also used as an electron donor for the denitrification reaction, so that organic matter can be utilized to the fullest. Therefore, organic matter contained in the influent wastewater is mainly composed of dissolved organic matter. This is an advantageous method when the denitrification efficiency is not satisfied only by post-denitration by the fresh sludge fermentation liquor drawn out after precipitation in the first settler 1a.

<Description of Embodiment 3 of FIG. 3>

Figure 3 relates to a third embodiment of the advanced sewage treatment method using the organic waste according to the present invention.

As shown, in the present embodiment, an anaerobic reaction tank 2 is additionally installed as a subsequent process of the first settler 1a in the front step of the first aerobic reaction tank 3a in the process constituting the second embodiment. The order of the process is influent sewage → first settler (1a) → anaerobic reactor (2) → first anoxic reactor (4a) → first aerobic reactor (3a) → second anoxic reactor (4b) → second aerobic reactor (3b) ) 2nd sedimentation battery 1b → effluent water.

In the present embodiment, an anaerobic reaction tank 2 is further provided, except that the return sludge 6 is introduced into the anaerobic reaction tank 2 from the second settler 1b to increase the emission efficiency of phosphorus. The structure of the process and the operation of the unit process are the same.

The first aerobic reactor 3a of each embodiment described above is a very important unit process in which nitrification reaction, which is an essential step reaction for denitrification, is performed.

The nitrifying microorganisms contributing to this important nitrification reaction is very easy to wash out because the yield coefficient (Yield Coefficient) is much lower than other aerobic microorganisms should be maintained in a high concentration of microorganisms in the first aerobic reaction tank (3a). In order to maintain a high microbial concentration, the solids retention time (SRT) must be long. Therefore, when microorganisms are suspended and proliferated in the first aerobic reactor 3a, the capacity of the first aerobic reactor 3a is increased, which is economically disadvantageous. The method of reducing the economic efficiency and increasing the nitrification efficiency includes filling the first aerobic reactor 3a with a biofilm contact material in which biofilms are formed and biofilms are formed, or nitrification so that nitrification microorganisms can be multiplyed. It is also desirable to fill a carrier in which the microorganisms are immobilized.

As described above, if the nitrogen and phosphorus removal method using the fermented sludge according to the present invention using the raw sludge generated in the first settler as an electron donor for denitrification reaction is economical without purchasing methyl alcohol or the like. Phosphorus method can maximize the advantages of the post-denitrification method, while it is possible to add a total denitrification method, it is possible to effectively remove nitrogen and phosphorus which seriously affects the eutrophication of the lake. In addition, sludge that is struggling with treatment can be used as a resource for nitrogen and phosphorus removal. Particularly, sludge that does not need to be transported, such as sludge that causes secondary environmental pollution, such as burden of transportation costs due to long-distance transportation of dehydrated sludge that is perishable, odor generation in landfill, leachate in landfill, and air pollution due to incineration. It is more economical because it can be effectively disposed of in sewage treatment plants.

Claims (5)

A first settler (1a) in which solids contained in influent wastewater are separated and sedimented, an anaerobic reactor (2) in which phosphorus is released from activated sludge, and a first aerobic reactor (3a) in which aerobic decomposition of organic matter and nitrification of organic nitrogen and ammonia nitrogen (3a) ), The anoxic reaction tank 4 in which the denitrification reaction of the nitrogen oxide oxidized in the first aerobic reaction tank 3a and the organic matter contained in the effluent of the anoxic reaction tank 4 are aerobicly decomposed and degassed in nitrogen and activated sludge. The second aerobic reaction tank (3b) in which phosphorus is excessively ingested, the second precipitated battery (1b) in which solids and symbolic water are separated from the effluent of the second aerobic reaction tank (3b) in sequence, and precipitated in the second settler (1b) In the wastewater treatment method comprising a series of processes in which solids are introduced into the anaerobic reactor 2 as a return sludge 6, The fermentation tank 5 is provided, the fresh sludge 8 withdrawn from the first settler 1a is transferred to the fermentation tank 5 and fermented, and the fresh sludge 8 is fermented and produced in the fermentation tank 5. Fermentation broth containing organic acid (9) is injected into the oxygen-free reaction tank (4) is used for the advanced sewage treatment method using the fermentation sludge, characterized in that used as an electron donor for the denitrification reaction. The liquid fermentation broth (9) according to claim 1, wherein the fermentation broth (9) produced in the fermentation broth (5) is injected into the anoxic reaction tank (4), wherein the liquid fermentation broth (9) undergoes a solid-liquid separation step to remove solids in the fermentation broth. Advanced sewage treatment method using fermentation sludge, characterized in that it is injected into the oxygen-free reaction tank (4) The first settler 1, in which the solids contained in the influent wastewater are sedimented and separated, the first anoxic reactor 4a in which the nitrogen oxides are denitrified, and the first aerobic reactor, in which the organic matter is aerobicly decomposed and the organic nitrogen and ammonia nitrogen are nitrified. (3a), the remaining organic matter contained in the effluent of the second anoxic reaction tank 4b and the second anoxic reaction tank 4b in which the denitrification reaction of the nitrogen oxide oxidized in the first aerobic reaction tank 3a is performed is subjected to aerobic decomposition and nitrogen The second aerobic reaction tank (3b) in which phosphorus is excessively ingested in the degassing and activated sludge of the second, and the second settler (1b) in which solids and symbolic water are separated from the effluent of the second aerobic reaction tank (3b) in sequence, The solid precipitated in the settling basin 1b flows into the first anoxic reaction tank 4a as the return sludge 6, and the reaction solution of the first aerobic reaction tank 3a is the first anoxic reaction tank as the internal circulating water 7. 4a) a series of inflows In the wastewater treatment method comprising the process, The fermentation tank 5 is provided, the fresh sludge 8 withdrawn from the first settler 1a is transferred to the fermentation tank 5 and fermented, and the fresh sludge 8 is fermented and produced in the fermentation tank 5. Fermentation broth (9) containing organic acids is injected into the second anoxic reactor (4b) and used as an electron donor for denitrification. The liquid fermentation broth (9) according to claim 3, wherein the fermentation broth (9) produced in the fermentation broth (5) is injected into the second anoxic reaction tank (4b) through a solid-liquid separation step to remove solids in the fermentation broth. Advanced wastewater treatment method using a fermentation sludge, characterized in that the injection into the second anoxic reaction tank (4b) The anaerobic reaction tank (2) for discharging phosphorus from activated sludge as a subsequent step of the first settler (1a) is further installed in the previous step of the first anoxic reaction tank (4a). Advanced wastewater treatment method using fermented sludge, characterized in that the return sludge 6 is introduced into the anaerobic reaction tank (2) in (1b)