JP2021191570A - Wastewater treatment method - Google Patents

Abstract

To provide a wastewater treatment method capable of obtaining an excellent coagulation treatment effect, improvement of treated water quality and improvement of solid-liquid separability in the solid-liquid separation step by using a coagulation auxiliary agent in the returned sludge, and capable of achieving compactness of sedimentation equipment, increase in the amount of treated water in the existing sedimentation equipment, and high performance of water quality improvement.SOLUTION: A wastewater treatment method including a biological treatment step, includes a solid-liquid separation step in a subsequent stage of the biological treatment step. The wastewater treatment method includes adding a coagulation auxiliary agent to sludge drawn from the solid-liquid separation step in a subsequent stage of the biological treatment step or concentrated sludge obtained by concentrating the sludge, and then returning the sludge or the concentrated sludge containing the coagulation auxiliary agent to the biological treatment step.SELECTED DRAWING: Figure 5

Description

The present invention relates to a wastewater treatment method. In particular, in organic wastewater treatment, it is related to sewage treatment including rainy weather sewage and sunny weather sewage, and factory wastewater treatment. The present invention relates to a wastewater treatment method capable of solving problems such as deterioration of properties and obtaining an excellent wastewater treatment effect.

In addition to sewage in rainy weather, which is a mixture of rainwater and sewage from combined sewerage, sewage in combined sewerage and diversion type sewerage in fine weather, urine, septic tank sludge, landfill leachate, and organic wastewater discharged from private business establishments. BOD (Biochemical Oxygen Demand: biochemical oxygen demand) and suspended solids (hereinafter referred to as SS) are removed by biological treatment. The obtained treated water is discharged into public water areas, or is highly treated again and reused.

Sewage in rainy weather is not discharged as untreated sewage to public water areas, but is generally stored in a storage facility (reservoir in rainy weather) and treated at a sewage treatment plant after rainfall. When the reservoir is full in rainy weather, it is common for sewage diluted with rainwater to be discharged after sedimentation and disinfection treatment with simple treated water.

In the biological treatment of wastewater from private business establishments, bulking by filamentous fungi may cause solid-liquid separation problems in the settling tank, and polymer coagulants, organic coagulants and anti-bulking agents are used as countermeasures. It is known.

FIG. 1 shows an example of the sewage treatment flow of the combined sewerage system in fine weather.

The sewage first passes through a sand basin, and SS, insoluble COD (Chemical Oxygen Demand) and BOD contained in the sewage are removed by solution separation. The first settling pond treated water flows into the reaction tank, the organic matter of the sewage is decomposed and removed by the activated sludge in the reaction tank, and the final settling pond in the latter stage is solid-liquid separated into the treated water and the sludge mainly composed of activated sludge. The treated water is discharged into public water areas, or the treated water is highly treated and used as washing water for sewage treatment plants. The sludge is returned to the front stage of the reaction tank as returned sludge, and the concentration of activated sludge in the reaction tank is maintained, so that stable biological treatment is performed in the reaction tank.

The sludge that is not used for the returned sludge is extracted from the final settling basin as surplus sludge and treated with sludge such as concentration and dehydration. Concentration includes gravity concentration and mechanical concentration. In mechanical concentration, no chemical injection or polymer flocculant is added to excess sludge, and the sludge is concentrated by a belt concentrator or a centrifugal concentrator. The excess sludge concentration is about 1% by weight, while the concentrated sludge concentration is several% by weight. Excess sludge in sewage is concentrated and then dehydrated by a dehydrator. Excess sludge discharged from wastewater treatment facilities of private business establishments is often directly dehydrated without concentration.

FIG. 2 shows a conventional sewage treatment flow in rainy weather.

Rainy weather sewage from the combined sewerage system is discharged from a pumping station or the like to a public water area by the time it reaches the sewage treatment plant. The sewage in rainy weather that reaches the sewage treatment plant first passes through the settling basin, and the treated water in the first settling basin is biologically treated with 1Q of sewage in rainy weather (maximum amount of sewage in the planned time in rainy weather. Sewage in rainy weather is simply treated and discharged into public water areas. Simple treatments include SS removal by the first settling basin and disinfection of the first settling basin treated water.

On the other hand, in order to reduce the load of the discharged water to the public water area, there is a technology to first apply the confluence improvement technology to the settling basin treated water and then discharge it to the public water area. Confluence improvement technology is applied to pump stations, rainwater spouts, and first settling basins, and is discharged from pump stations, rainwater spouts, and first settling basins by contaminant removal, high-speed filtration, coagulation separation, disinfection, and measurement / control technology. The purpose is to improve the quality of the first settling basin treated water in rainy weather and sewage in rainy weather. Confluence improvement technology for contaminants includes removal facilities for contaminants installed at the rainwater spout, installation of stormwater stagnation ponds and stormwater storage pipes, reinforcement of shield pipes, diversion of combined sewers, etc. So, there is a merging improvement technology that involves all processing equipment and equipment.

FIG. 3 shows an example of a sewage treatment flow (method for treating activated sludge in rainy weather) for biologically treating a conventional amount of sewage in rainy weather 3Q (three times 1Q; the same applies hereinafter).

The activated sludge treatment method for sewage in rainy weather is a technology for improving the pollution of combined sewage at the initial stage of rainfall, and uses the activated sludge treatment equipment of the existing sewage treatment plant. Previously, only 1Q was biologically treated, and the remaining 2Q (twice as much as 1Q; the same applies hereinafter) was first discharged after sedimentation in a settling basin, but with this rainy weather sewage activated sludge treatment method, 1Q out of 3Q is reacted. It is flowed into the first stage of the tank and treated as before, and the remaining 2Q, which had been discharged after sedimentation in the first settling basin, is put into 1/4 of the second stage of the reaction tank for biological treatment.

If the sewage in the rain exceeds 3Q, the sewage in the rain is simply treated by the confluence improvement technology and then discharged into the public water area.

FIG. 4 shows a conventional biological treatment flow of wastewater.

In particular, when biologically treating water to be treated at private business establishments, bulking occurs due to sudden load fluctuations of organic substances due to changes in the types of products manufactured at private business establishments and an increase in the amount of wastewater. The carryover of the treated water SS in the settling tank and the settling concentration of sludge may decrease. Most of the causes of solid-liquid separation disorders in the settling tank are bulking due to filamentous fungi. At that time, there is a technique of adding a polymer flocculant or an anti-bulking agent to the returned sludge and returning the returned sludge containing the polymer flocculant or the anti-bulking agent to the front stage of the biological treatment tank.

According to the case of Osaka City (https://www.nissuicon.co.jp/jigyou/gesuidou/utenji-kasseiodei/), 1Qsh out of 3Qsh of sewage in rainy weather is used in the reaction tank (" It is also called "reaction tank".) In the first stage, the conventional organic matter is biologically treated, and the remaining 2Qsh of sewage in rainy weather, which has been settled and discharged until now, is stepped into 1/4 of the second stage of the reaction tank for treatment. The organic matter adsorbed in the latter stage of the reaction vessel is settled in the final settling basin and returned to the reaction vessel for biological treatment. By utilizing the biosoaption method, which is one of the sewage activated sludge methods, the activated sludge recovers its adsorptive power again in the latter stage of the reaction tank, so that stable treatment can be continued. The sewage activated sludge method in rainy weather also uses this principle to reduce the amount of pollution in the early stage of rainy weather.

Patent Document 1 (Japanese Unexamined Patent Publication No. 11-104696) describes (1) an agglutination step of adding an inorganic agglutinating agent to raw water and adding a return sludge containing a polymer agglutinating agent to cause an agglutination reaction (2). ) Solid-liquid separation step of solid-liquid separation of agglutinated flocs generated in the agglutination step, (3) Desalting by passing the treated water obtained from the solid-liquid separation step through a reverse osmosis membrane device and / or an ion exchange device. A salt step, (4) a sludge return step of returning a part of the agglutinated sludge discharged from the solid-liquid separation step to the agglutination step, and (5) a step of adding a polymer flocculant to the agglutinating sludge returned to the agglutination step. A method for producing pure water is disclosed.

The pure water production method consists of a coagulation step, a solid-liquid separation step, and a desalting step. It is possible to provide a pure water production system capable of suppressing contamination of the osmosis membrane and the ion exchange resin and reducing the cleaning frequency thereof.

In Patent Document 2 (Japanese Unexamined Patent Publication No. 8-103788), regarding the addition of a drug to the return sludge line, "By adding the drug to the return sludge line, a small amount of filamentous fungi is not completely eradicated at one time. Filamentous bacteria and actinomycetes can be sterilized one by one, which can effectively suppress bulking and squamming without deteriorating the quality of treated water such as COD and SS. Add chemicals to the return sludge line. In that case, the amount of the drug added is calculated with respect to the flow rate of the returned sludge. "

Non-Patent Document 1 (Takahiro Yamamoto, Takaaki Nakamura, "Improvement of combined sewerage system using existing facilities in Osaka City-Development and practical application of activated sludge treatment method for sewage in rainy weather-", EICA: Journal of Environmental System Measurement and Control Society / According to the editorial committee of the academic journal "EICA", 2005, Vol. 10, No. 2, pp. 9, 12), the 3W treatment method used the conventional simple treatment discharge method to use sewage in rainy weather as a method for reducing the discharge load. It is disclosed that it is valid. In the 3W treatment method, 1Q is used for activated sludge treatment, and the excess water amount up to 2Q, which has been simply treated and discharged in the past, is allowed to flow into the final stage of the reaction tank for activated sludge treatment.

Japanese Unexamined Patent Publication No. 11-104696 Japanese Unexamined Patent Publication No. 8-103788

Takahiro Yamamoto, Takaaki Nakamura, "Improvement of combined sewerage system using existing facilities in Osaka City-Development and practical application of activated sludge treatment method for sewage in rainy weather-", EICA: Journal of Environmental System Measurement and Control Society / Journal of the Society "EICA" Editorial Board, 2005, Vol. 10, No. 2, pp. 9, 12

The issues of solid-liquid separation of the first sedimentation basin of sewage in rainy weather are as follows.
(1) When the sewage in rainy weather flows in at a design amount of 1Q or more, the solid-liquid separability in the first settling basin deteriorates.
(2) As the solid-liquid separability in the first settling basin deteriorates, the treated water in the first settling basin of 1Q or more is discharged into the public water area, but the quality of the discharged water deteriorates.

The problems in biological treatment of sewage in rainy weather are as follows.
(1) Since the amount of inflow water is three times the designed amount of water, it is difficult to separate solid and liquid in the final settling basin after biological treatment, and the treated water SS in the final settling basin increases and the concentration of returned sludge decreases.
(2) When 2Q is poured into the final stage of the reaction tank, the BOD sludge load of the reaction tank increases and the cohesiveness of the activated sludge decreases, so that the solid-liquid separability in the final settling basin decreases.

The challenges in biological treatment of wastewater from private businesses are as follows.
(1) Due to load fluctuations in biological treatment, solid-liquid separability in the settling tank at the subsequent stage of the biological treatment tank deteriorates due to bulking.
(2) The anti-bulking agent is added to the returned sludge and returned to the front stage of the biological treatment tank, but the effect of the anti-bulking agent is reduced and the activated sludge in the biological treatment tank is damaged during the stay in the biological treatment tank.

The present invention has been made in view of the above circumstances, and by using a coagulation auxiliary agent for the returned sludge, an excellent coagulation treatment effect in the solid-liquid separation step, improvement of treated water quality, and solid-liquid separability. It is an object of the present invention to provide a wastewater treatment method that can achieve the improvement of the water quality, the compactness of the settling device, the increase of the treated water amount in the existing settling device, and the improvement of the water quality.

Further, in some embodiments of the present invention, it is possible to improve the water quality of the first settling pond treated water of the rainy weather sewage discharged into the public water area and the biologically treated water and the discharged water of the rainy weather sewage. The subject is to provide a wastewater treatment method.

The present invention has been made in view of the above circumstances, and is specified as follows.
(1)
It is a wastewater treatment method that includes a biological treatment process.
The wastewater treatment method includes a solid-liquid separation step after the biological treatment step.
After adding a coagulation aid to the sludge extracted from the solid-liquid separation step after the biological treatment step or the concentrated sludge in which the sludge is concentrated, the sludge containing the coagulation aid or the concentrated sludge is added to the biological treatment step. Waste treatment methods, including returning.
(2)
The wastewater treatment method according to (1), further comprising a solid-liquid separation step before the biological treatment step.
(3)
The solid-liquid separation step prior to the biological treatment step is performed in the first settling basin where sewage flows in during rainy weather.
The wastewater treatment method according to (2), wherein the sludge containing the coagulation aid or the concentrated sludge is mixed with sewage in rainy weather and returned to the first settling basin.
(4)
The biological treatment step is performed in a plurality of reaction tanks and is carried out in a plurality of reaction tanks.
The solid-liquid separation step after the biological treatment step is performed in the final settling basin.
The sludge extracted from the final settling basin is returned sludge and surplus sludge, and a part of the returned sludge is returned to the reaction tank at the front stage among the plurality of reaction tanks and aggregated in another part of the returned sludge. The wastewater treatment method according to any one of (1) to (3), wherein the auxiliary agent is added and then returned to the reaction tank in the final stage among the plurality of reaction tanks.
(5)
The wastewater treatment method according to (4), further comprising adding a coagulation aid to a part of the concentrated sludge in which the excess sludge is concentrated and then returning the sludge to the final reaction tank among the plurality of reaction tanks.
(6)
The biological treatment step is performed in a plurality of reaction tanks and is carried out in a plurality of reaction tanks.
The solid-liquid separation step after the biological treatment step is performed in the final settling basin.
The sludge extracted from the final settling basin is returned sludge and surplus sludge, and all of the returned sludge is returned to the first reaction tank among the plurality of reaction tanks, and a part of the concentrated sludge in which the surplus sludge is concentrated. The wastewater treatment method according to any one of (1) to (3), wherein the sludge assisting agent is added to the sludge and then returned to the reaction tank in the final stage among the plurality of reaction tanks.
(7)
The wastewater treatment method according to any one of (4) to (6), further comprising adding a coagulation aid to the returned sludge returned to the reaction tank at the front stage among the plurality of reaction tanks.

According to the present invention, by using a coagulation auxiliary agent for the returned sludge and / or the concentrated sludge of the surplus sludge, an excellent coagulation treatment effect in the solid-liquid separation step, improvement of treated water quality, and improvement of solid-liquid separability. It is possible to provide a wastewater treatment method that can achieve compactness of the settling device, an increase in the amount of treated water in the existing settling device, and improvement of the water quality of the settling device outlet water and the biologically treated water.

It is a figure which shows the sewage treatment flow of a combined sewer in a sunny day. It is a figure which shows the conventional sewage treatment flow in rainy weather. It is a figure which shows the sewage treatment flow which biologically treats the conventional sewage amount 3Q in rainy weather. It is a figure which shows the biological treatment flow of the conventional wastewater. It is a figure which shows an example of the treatment flow of the sewage in rainy weather of this invention. It is a figure which shows an example of the treatment flow of the sewage in rainy weather of this invention. It is a figure which shows an example of the treatment flow of the sewage in rainy weather of this invention. It is a figure which shows an example of the sewage treatment flow of the sewage in rainy weather of this invention. It is a figure which shows an example of the sewage treatment flow of the sewage in rainy weather of this invention. It is a figure which shows an example of the polymer coagulant injection control flow to the first sedimentation basin of this invention. It is a figure which shows an example of the polymer coagulant injection control flow to the reaction tank of this invention.

Next, a mode for carrying out the present invention will be described in detail with reference to the drawings. It is understood that the present invention is not limited to the following embodiments, and design changes, improvements, etc. may be appropriately made based on ordinary knowledge of those skilled in the art without departing from the spirit of the present invention. Should be. In addition, each specific feature of each embodiment disclosed in the present specification is not independent of each other, and may be appropriately combined based on the ordinary knowledge of those skilled in the art without departing from the spirit of the present invention. It should be understood that it can be done. For example, the method for improving the solid-liquid separation performance in the first settling basin and the method for improving the solid-liquid separation performance in the final settling basin of the present invention can be naturally combined.

In the present invention, the treated water includes sewage, human waste, septic tank sludge, organic wastewater discharged from landfill leachate and private business establishments, and first settling of sewage in rainy weather and sewage in rainy weather in a combined sewerage system. Contains water. The purpose of the treatment is to remove suspended solids, COD, BOD and Escherichia coli which are pollutants of the water to be treated.

(Coagulation aid)
In the present invention, as the coagulation aid, an organic coagulation aid such as an organic polymer coagulant or an organic coagulant described later and an inorganic coagulant can be preferably used. As the coagulation aid, an organic coagulation aid is preferable. In addition, in this specification, even if it can be used as an anti-bulking agent, the one having an aggregation effect is included in the concept of an aggregation aid.

(Organic polymer flocculant)
Organic polymer flocculants (hereinafter referred to as "polymer flocculants") that can be used in the present invention include cationic, anionic, nonionic, and amphoteric depending on the charged state, and are the target first sedimentation reservoirs. It may be appropriately selected according to the treated water, returned sludge, concentrated sludge and active sludge. In particular, when used in activated sludge produced by biological treatment in the present invention, it is preferable to select and use one or more of a cationic polymer flocculant and an amphoteric polymer flocculant. One type of polymer flocculant may be used alone, or two or more types may be used in combination.

The cationic polymer flocculant has a cationic monomer as an essential component, and is a copolymer of a cationic monomer or a copolymer of a cationic monomer and the above-mentioned nonionic monomer. As the cationic monomer, dimethylaminoethyl acrylate, dimethylaminoethyl methacrylate, diethylaminoethyl acrylate, diethylaminoethyl methacrylate or a quaternary ammonium salt thereof, or a cationic polymer flocculant containing an amidine unit in the molecule can also be used. ..

Further, in some embodiments of the present invention, an amphoteric polymer flocculant obtained by copolymerizing a cationic monomer unit, an anionic monomer unit and a nonionic monomer unit can be used.

The molecular weight of the polymer flocculant is preferably 2 million to 15 million, and there are powdered products and liquid products. The polymer flocculant can be used by any method, but if the product itself is added to wastewater or sludge, whether it is a powdered product or a liquid product, the polymer flocculant component may solidify or the polymer flocculant may be poorly dissolved. Since it cannot exert the agglutination effect, it is used in an aqueous solution. Since it usually takes time to dissolve, powdered products and liquid products are generally dissolved in dissolved water such as tap water, industrial water, and treated water for wastewater treatment, and prepared as a polymer flocculant solution before use. Will be done. The dissolution concentration of the polymer flocculant is usually about 0.01 to 0.5% by weight, and can be, for example, 0.1 to 0.3% by weight.

(Organic coagulant)
Organic coagulants are more cationic than polymer flocculants, have a small molecular weight of 1 million or less, and are generally liquid products. Since the organic coagulant has a lower molecular weight than a polymer flocculant such as a cationic polymer flocculant, the viscosity of the product is also low. Therefore, there is no need for dissolution or dilution work to adjust the concentration and viscosity, and the product can be used as it is.

The type of the organic coagulant is not particularly limited, and one or more known ones can be used, and examples thereof include a condensation polymer, a dicyandiamide / formarin condensate, polyethyleneimine, polyvinylimidazolin, and polyvinylpyridine. Dialylamine salt / sulfur dioxide copolymer, polydimethyldiallylammonium salt, polydimethyldiallylammonium salt / sulfur dioxide copolymer, polydimethyldiallylammonium salt / acrylamide copolymer, polydimethyldiallylammonium salt / diallylamine hydrochloride derivative co-weight There are coalesced and allylamine salt polymers.

Specific examples of the condensation polyamine include a condensate of alkylene dichloride and alkylene polyamine, a condensate of aniline and formarin, a condensate of alkylene diamine and epichlorohydrin, and a condensate of ammonia and epichlorohydrin. Examples of the alkylene diamine that condenses with epichlorohydrin include dimethylamine, diethylamine, methylpropylamine, methylbutylamine, dibutylamine and the like.

(Anti-bulking agent)
In some embodiments of the present invention, it is preferable to further add an anti-bulking agent to a part of the returned sludge and / or the concentrated sludge.

The anti-bulking agent is an agent for dealing with bulking caused by filamentous fungi, and can be added to a part of returned sludge and / or concentrated sludge. The anti-bulking agent applicable to the present invention preferably has a molecular weight of 5000 to 15 million. Therefore, in some embodiments of the present invention, it is preferable to add an anti-bulking agent to a part of the returned sludge and / or the concentrated sludge, and in particular, the returned sludge and / or the concentrated sludge to be returned to the final stage of the reaction tank. It is preferable to add it to a part of.

Anti-bulking agents include benzalkonium chloride, benzethonium chloride and mixtures thereof, which are bactericidal agents and are quaternary ammonium salts having a high bactericidal effect, cationic polymer flocculants, and organic coagulants. The bactericidal agent contracts, cuts, and lyses the sheath of the filamentous fungus that causes bulking, thereby alleviating or eliminating bulking. Since the cationic polymer flocculant and the organic coagulant can aggregate activated sludge containing filamentous fungi, the sedimentation property is improved.

Since the cationic and amphoteric polymer flocculants and the organic coagulant are treated as coagulation aids in the present invention, the anti-bulking agent added in the preferred embodiment means an anti-bulking agent other than the anti-aggregation agent.

(Precipitation device)
In the present invention, the configuration of the settling device is not particularly limited as long as the effect of the present invention can be achieved, but the structure and the like of a general settling device to which the present invention can be applied will be described as follows.

The settling device for solid-liquid separation of the mixed liquid containing activated sludge after biological treatment includes a cross-flow type settling basin and an upward-flow type settling tank. Generally, the cross-flow sedimentation basin is used for solid-liquid separation of sewage treatment, and the upward-flow sedimentation tank is used for solid-liquid separation of wastewater treatment of private business establishments.

In the cross-flow type settling basin, inflow water flows in from the inflow part of the cross-flow type settling basin, and aggregated flocs and SS settle while reaching the outflow part of the treated water on the opposite side, and solid-liquid separation is performed. The flow direction of the treated water is approximately horizontal.

The upward flow type settling tank guides the inflow water to the center well in the center of the upward flow type settling tank, and evenly flows out from the lower part of the center well to the entire settling tank, and separates the treated water and sludge into solid and liquid. The flow direction of the treated water is approximately upward.

FIG. 5 shows an example of the treatment flow of sewage in rainy weather of the present invention, and shows a method for improving the solid-liquid separation performance in the first settling basin.

As shown in FIG. 5, the return sludge of the final settling pond and the coagulation auxiliary agent are mixed in the return sludge pipe and the mixing tank provided in the middle of the return sludge pipe, and the return sludge containing the coagulation auxiliary agent is mixed with the sewage in rainy weather. First, solid-liquid separation is performed in the settling pond, and SS, COD, BOD, and Escherichia coli, which are pollutants of sewage in rainy weather, are removed as the first settled sludge together with the returned sludge.

Initially, the treated water from the settling basin can be disinfected and discharged into public water areas. Alternatively, the first settling basin treated water flows into the reaction tank and is biologically treated in the reaction tank by the activated sludge of the returned sludge that is returned to the front stage of the reaction tank as before. The activated sludge mixture is solid-liquid separated in the final settling pond to become sludge and treated water, the sludge becomes returned sludge and surplus sludge, and the treated water is discharged after disinfection or is highly treated and effectively utilized. ..

In the front part of the first settling basin, sewage in rainy weather and returned sludge to which a coagulation aid is added are mixed, and the treated water and sludge are separated into solid and liquid in the first settling basin. Initially, the settling basin treated water is discharged to a public water area after disinfection by bypassing the biological treatment step (in the figure, it is performed by bypassing in the reaction tanks (1) to (4)). The sludge is concentrated as initial sludge or mixed with excess sludge for dehydration and sludge digestion.

In addition, the treated water in the first settling pond is flowed into the reaction tank of the biological treatment step in the subsequent stage, and is biologically treated with the activated sludge in the reaction tank. Escherichia coli is removed. The activated sludge mixture in the reaction tank flows out from the final stage of the reaction tank, is solid-liquid separated into treated water and sludge in the final settling basin, and the treated water is discharged or highly treated. A part or all of the sludge is returned to the front stage portion of the reaction tank (1) as a return sludge in order to maintain the activated sludge concentration (MLSS: Mixed Liquor Suspended Solids) of the reaction tank. In addition, a part of the sludge that is solid-liquid separated in the final settling basin is concentrated or dehydrated as excess sludge.

In the first settling basin, pollutants are removed from the sewage in rainy weather, and the sewage in rainy weather with a reduced pollutant load in the reaction tank can be biologically treated in the reaction tank. The quality of biologically treated water is stable and good biological treatment is possible.

The sludge extracted from the final settling basin is a two-system return sludge line, which is in the front stage of the first settling basin (return sludge [2] in the figure) and the front stage of the reaction tank (return sludge [1] in the figure). Each will be returned. The remaining sludge drawn from the final settling basin is treated as excess sludge by sludge treatment such as concentration and dehydration.

Inorganic flocculants such as commercially available polyiron and sulfate bands can be used in addition to the flocculation aids added to sewage in rainy weather, but organic matter-based pollutants have better coagulation of organic matter and activated sludge than inorganic flocculants. Organic aggregation aids are effective.

Return sludge containing a polymer flocculant or an organic coagulant is added to the sewage in rainy weather, and the SS and BOD are removed in the first settling basin. It can be discharged into public water areas without the need for it. The first settling basin treated water from which SS and BOD have been removed in the first settling basin has better water quality than the first settling basin treated water in which sewage in rainy weather or sewage in rainy weather is simply settled in the first settling basin, and is discharged to public water areas. The pollutant load of the discharged water can be significantly reduced.

Soluble BOD and soluble COD, which are pollutants of sewage in rainy weather and are soluble organic substances, are adsorbed on the returned sludge returned from the final sedimentation pond. Hereinafter, it is removed as the first sedimentation sludge). On the other hand, SS of sewage in rainy weather, insoluble BOD, insoluble COD, and Escherichia coli, which are insoluble organic substances, are adsorbed and adhered to the surface of the returned sludge containing a coagulation aid, and are taken up as initial sludge. Will be removed.

Initially settled sludge that has taken in pollutants from sewage in rainy weather is dehydrated together with excess sludge and used as sewage sludge fuel, or sludge is reduced or gasified by digestion or methane fermentation.

In the present embodiment, when the pollutant of the sewage in rainy weather is removed more than before, the BOD concentration of the first settling pond treated water which is the inflow water of the reaction tank becomes a low value, so that the MLSS concentration of the reaction tank in the activated sludge treatment becomes low. Since the operation can be performed at a low level, the return flow rate of the returned sludge can be reduced, and the power cost thereof can be reduced. Further, since the BOD concentration and the MLSS concentration of the first settling basin treated water are low, the amount of air can be reduced and the blower power cost can be reduced.

In the present embodiment, separately from the existing drawn sludge pump, a return sludge pump that returns the return sludge to the first stage of the settling basin and a pipe for returning to the first stage of the first settling basin are separately provided (in the figure, the return sludge [return sludge [ 2]).

The reason for deploying a return sludge pump or the like in addition to the drawn sludge pump is that it is difficult to adjust the returned sludge flow rate when the returned sludge is first returned to the first stage of the settling basin and the reaction tank with only one drawn sludge pump. If a plurality of drawn sludge pumps have already been deployed, one of them can be used as a return sludge pump for first returning to the front stage of the settling basin.

The first stage of the return sludge is from the sewage inflow pipe to the inflow part of the first settling basin in rainy weather. The first settling basin inflow part is from the inflow part of the inflow water to just before the solid-liquid separation part. The settling basin is from the inflow (raw water) pipe to the center well (including the center well).

As a place to add the coagulation auxiliary agent, it may be added to a line mixer or a mixing tank provided in the suction part or discharge part of the return sludge pump or in the middle of the return sludge piping. The stirring of the mixing tank provided in the middle of the return sludge piping may be mechanical stirring or stirring by a water flow of the return sludge.

The residence time of the returned sludge in the mixing tank provided in the middle of the returned sludge piping varies depending on the stirring method, stirring strength, return flow rate of the coagulated sediment sludge and its concentration, but can be, for example, 0.2 to 3 minutes. .. If the residence time is 0.2 minutes or more, the mixing of the coagulation aid and the returned sludge is sufficient. On the other hand, if the residence time is 3 minutes or less, there is a possibility that agglomerates of the return sludge may be accumulated in the mixing tank provided in the middle of the return sludge piping and the cohesiveness at the inflow part of the first settling basin may be lowered. It can be kept low.

If the coagulation aid is added in the optimum amount to the returned sludge and first returned to the stage before the settling basin, there is no need to add an additional coagulation aid. Even if additional addition is made, it takes time to make the dispersal auxiliary agent uniform in the pre-stage of the first settling basin and inside the first settling basin, so the processability may be deteriorated.

The concentration of the returned sludge added to the sewage in the rainy weather that initially flows into the settling basin is preferably 50 to 1000 mg / L, more preferably 100 to 500 mg / L with respect to the amount of sewage in the rainy weather.

Further, assuming that the general SS concentration of sewage in rainy weather is 100 mg / L, the ratio of the return sludge concentration / SS concentration of sewage in rainy weather is preferably 0.5 to 10, more preferably 1 to 5.

The preferable range of the ratio of the return sludge concentration / SS concentration of sewage in rainy weather is determined in consideration of the general SS concentration of 100 mg / L of sewage in rainy weather. When the ratio of the return sludge concentration / SS concentration of sewage in rainy weather is 0.5 or more, solid-liquid separation in the first settling basin becomes easy. That is, the return sludge concentration is sufficiently high with respect to the SS concentration of sewage in rainy weather. This is because the activated sludge of the returned sludge for adsorbing and adsorbing SS and soluble BOD of sewage in rainy weather is sufficient. On the other hand, if the ratio of the return sludge concentration / SS concentration of sewage in rainy weather is 10 or less, the SS concentration of the inflow water of the first settling basin will increase, so the possibility that solid-liquid separation in the first settling basin will be difficult should be kept low. Can be done. In other words, when the SS concentration of the first settling pond inflow water increases in consideration of the returned sludge concentration, sludge caused by the inflow SS accumulates in the first settling pond, the sludge interface rises, and the sludge becomes sludge in the first settling pond treated water. Since the resulting SS may flow out, the ratio of the return sludge concentration / the SS concentration of the sewage in rainy weather is preferably 10 or less.

Further, the addition rate of the coagulation aid to the sewage in the rainy weather that initially flows into the settling basin is preferably 0.05 to 5.0% by weight with respect to the sludge weight of the returned sludge, that is, SS, and 0. More preferably, it is 5 to 3.0% by weight vs. SS.

When the coagulation aid is first injected into the inflow portion of the sedimentation basin as in the prior art, the coagulation aid injection rate was calculated by the weight of the coagulation aid (mg / L) with respect to the amount of sewage in rainy weather. As described above, when the coagulation auxiliary agent is added to the returned sludge, it is preferable to use "% by weight vs. SS" used for dehydration of sludge treatment as an index as the coagulation auxiliary agent addition rate. In the present invention, the agglutination auxiliary agent agglomerates the sludge particles of SS of sewage in rainy weather and sludge returned sludge, and the addition rate of the agglutination auxiliary agent should be determined with respect to the weight of solid matter such as SS. The injection rate of the coagulation aid to the amount of water, mg / L, does not consider SS or sludge solids.

Since the SS concentration in the inflow part of the first settling basin including the SS of the returned sludge changes depending on the return conditions of the returned sludge, the weight of the coagulation aid (in mg / L treated water as the unit) with respect to the amount of sewage in rainy weather is the coagulation aid. Proper control and control of injection volume is not possible.

There are SS (suspended solids) and TS (Total Solids: total evaporation residue) as indicators of sludge concentration. In addition, the measured values of SS and TS are the same for sludge with a low concentration of dissolved salts (concentration of dissolved salts such as salt) such as sewage, but the values of SS and TS of sludge are high for urine treatment with a high concentration of dissolved salts. If different, the sludge concentration adopts SS.

In the present invention, SS and TS follow the following definitions.
SS: JIS K 0102: 2019 Factory effluent test method 14.1 Suspended solids TS: JIS K 0102: 2019 Factory effluent test method 14.2 Total evaporation residue

FIG. 6 shows another example of the treatment flow of the sewage activated sludge treatment method in rainy weather of the present invention. This is a method to improve the solid-liquid separation performance in the final settling basin.

First, 1Q of the settling basin treated water is made to flow into the first tank (reaction tank (1)) of the reaction tank, and the sludge returned from the final settling basin is returned to the first tank as before. The 2Q of the first settling basin treated water is also flowed into the final stage of the reaction tank (the fourth tank in the figure, but not limited to the fourth tank), and the sludge returned from the final settling basin is also returned to the final stage (the sludge returned from the final settling basin is also returned to the final stage). Return sludge in the figure [2]). A coagulation aid is added to the returned sludge returned to the fourth tank, which is the final stage. The agglutination aid is added to the mixing tank or the return pipe, and the return sludge and the agglutination aid are mixed and homogenized by the time it enters the fourth tank, which is the final stage of the reaction tank. Activated sludge mixture containing 3Q of treated water from the first settling basin flows into the final settling basin, but the sludge in the final settling basin has good cohesiveness and sedimentation concentration due to the adhesion auxiliary agent attached to the returned sludge. It is easy to separate solid and liquid into treated water.

The place where the returned sludge containing the coagulation auxiliary agent is added to the reaction tank may be an inflow pipe or a pipe from the activated sludge mixed liquid outflow portion of the final stage reaction tank or the final stage reaction tank to the final settling basin.

For the aggregation of activated sludge in the activated sludge mixture in the final stage reaction tank, the weight ratio of the added aggregate auxiliary agent per weight of the returned sludge returned to the final stage reaction tank, and the returned sludge containing the activated sludge mixture and the aggregated auxiliary agent. Mixing time with and stirring strength are important. As for the stirring strength, air stirring in the reaction tank or stirring by the pipe flow rate is sufficient. The mixing time is preferably 3 minutes to 3 hours. Aggregation of activated sludge is sufficient for 3 minutes or more, and if it is contained within 3 hours, redispersion of aggregates of activated sludge can be prevented.

FIG. 7 shows another example of the treatment flow of sewage in rainy weather of the present invention. This is a method to improve the solid-liquid separation performance in the first settling basin.

In FIG. 7, in the first stage of the settling basin, sewage in rainy weather and concentrated sludge of excess sludge to which a coagulation aid is added are mixed, solid-liquid separated in the first settling basin, and BOD and COD which are pollutants of sewage in rainy weather. And Escherichia coli and SS are removed. The pollutants are removed from the sewage in rainy weather, and the sewage in rainy weather with reduced load is biologically treated in the reaction tank. In the figure, the reaction tank has a four-tank structure of (1) to (4), but is not limited to this. In the final settling basin, the treated water and sludge are separated into solid and liquid, and the treated water is discharged or highly treated. The sludge drawn from the final settling basin is returned sludge and excess sludge, and the returned sludge is returned to the reaction tank. Excess sludge is concentrated into concentrated sludge, and a part of it is added and mixed with agglutination aid as described above and first returned to the front stage of the settling basin, but the rest without the agglutination aid is added. Sludge is treated.

In sludge treatment such as concentration and dehydration of excess sludge, excess sludge is concentrated by gravity or mechanically and dehydrated. By adding a coagulation aid to a part of the concentrated sludge of these surplus sludges, it is possible to improve the solid-liquid separability in the first settling basin by mixing it with sewage in rainy weather at the stage before the first settling basin. .. Further, the concentrated sludge of the surplus sludge has a higher sludge concentration than the surplus sludge and the returned sludge, and therefore, the return flow rate of the concentrated sludge of the surplus sludge is smaller than that of the returned sludge.

Since it is the concentrated sludge of excess sludge that is returned to the first stage of the first settling basin, the conditions for returning it to the first stage of the first settling basin (specifically, the SS concentration of the inflow part of the first settling basin, the addition rate of the coagulation aid, etc.). ) Is the same as the embodiment shown in FIG.

The excess sludge drawn from the final settling basin is either concentrated by itself and then mixed with the initial settling sludge and dehydrated, or the excess sludge is dehydrated without being concentrated.

In the present invention, the concentrated sludge of the surplus sludge is a sludge concentrated alone without being mixed with the initial sludge. Sludge mixed with initial sludge other than surplus sludge cannot be returned to the initial settling basin or biological treatment of the present invention because the amount of activated sludge is small. Since excess sludge and concentrated sludge of excess sludge will decay over time, it is preferable to first aerate them before returning them to a settling basin or biological treatment. Aeration may be performed by any method such as oxygen supply by a diffuser pipe or pump circulation. In addition, for the purpose of use in emergencies such as sewage treatment in rainy weather, the concentration of excess sludge and excess sludge by adding oxides such as nitrates, nitrites, and hydrogen peroxide, which are low in decomposition and have good storage stability even when stored. Preventing sludge from decaying is also effective.

The injection rate of the oxide as a product is 50 to 1000 mg / L, preferably 100 to 500 mg / L with respect to the flow rate of the concentrated sludge of the excess sludge. If it is 50 mg / L or more, the concentrated sludge of excess sludge becomes aerobic. If it is 1000 mg / L or less, it is possible to avoid an excessive increase in the product storage amount of the oxide and an excessive increase in the injection equipment.

The above oxide is added before the addition of the coagulation aid of the present invention. In other words, by adding an oxide product to the suction part and discharge part of the sludge pump that returns concentrated sludge of excess sludge, the reactivity between the concentrated sludge of excess sludge and the oxide is high, so even the addition of a coagulation aid. The concentrated sludge of excess sludge becomes aerobic, and the above oxide does not remain.

There are two methods for concentrating excess sludge: a chemical-free injection method and a method in which a polymer flocculant is added to the excess sludge in the existing concentration process to concentrate the sludge. Further, there is a method of concentrating with a gravity type concentrating tank or a mechanical type concentrating tank, for example, a centrifugal concentrator or a belt type filtration concentrator.

The concentration of concentrated sludge varies depending on the difference between chemical injection and non-chemical injection and the concentration method, but is generally 1 to 3% by weight. Even when a polymer flocculant is used for concentration and the concentrated sludge containing the polymer flocculant is returned to the first stage of the settling basin, a coagulation aid that can sewage in rainy weather can be separated into solid and liquid well in the first settling basin. Should be used.

FIG. 8 shows another example of the treatment flow of sewage in rainy weather of the present invention. This is a method to improve the solid-liquid separation performance in the final settling basin.

In the embodiment shown in FIG. 8, in addition to the existing return sludge return, another return sludge facility is provided, a coagulation aid is added to the return sludge, and the return sludge is returned to the final stage of the reaction tank. In the final stage reaction tank, the returned sludge containing the coagulation aid and the activated sludge in the final stage reaction tank are mixed to generate coagulated flocs with good settling property, and the solid-liquid separability in the final settling basin is improved. Can be done.

A coagulation aid may be added to the existing return sludge that is returned to the front stage of the reaction tank, but the agglomeration flocs may be destroyed by strong stirring in the reaction tank or the reaction tank may stay until it flows into the final settling basin. Since the aggregation effect of the aggregation aid as an agent may decrease over time, it is preferable not to add the aggregation aid to the returned sludge returned to the front stage of the reaction tank. The same applies to the embodiments shown in FIGS. 5 to 7.

In the embodiment shown in FIG. 8, the sludge return ratio to the front stage of the reaction tank is preferably 0.03 to 0.5, and the sludge return ratio to the final stage of the reaction tank is 0.03 to 0.5. It is preferable to have. This sludge return ratio can be applied not only to the return sludge but also to the return of concentrated sludge of excess sludge. If the sludge return ratio to the front stage of the reaction tank is 0.03 or more, the biological treatment becomes more stable, and if the sludge return ratio to the front stage of the reaction tank is 0.5 or less, it flows into the final settling basin. Since the amount of sludge is suppressed, the burden of solid-liquid separation in the final settling basin is reduced. Further, if the sludge return ratio to the final stage of the reaction tank is 0.03 or more, the return sludge flow rate is sufficient, and the sludge containing the coagulation aid is sufficient in the final settling basin, so that coagulation is good. Therefore, solid-liquid separation in the final settling basin is stable. When the sludge return ratio to the final stage of the reaction tank is 0.5 or less, the amount of sludge flowing into the final settling basin is suppressed, so that solid-liquid separation in the final settling basin is good.

The sludge return ratio (sewerage facility planning design guideline and explanation Part 2 Chapter 4 Water Treatment Facility 4.6.4 (2009)) is calculated as follows.
Sludge return ratio = MLSS of reaction tank / (SS of return sludge-MLSS of reaction tank)
In the formula, the unit of MLSS of the reaction tank and SS of the returned sludge is mg / L.

In addition to sewage, this treatment flow can also be applied to measures against bulking of wastewater from private business establishments.
In private business wastewater treatment, there is no initial settling basin for sewage treatment, and organic wastewater is biologically treated in a biological treatment tank equivalent to a reaction tank for sewage treatment. Unlike the reaction tank for sewage treatment, the biological treatment tank is often not divided into multiple parts. In this case, the final stage of the biological treatment tank is from the outflow part of the activated sludge mixture in the biological treatment tank to the inflow part of the settling tank. Point to.

A part of the returned sludge extracted from the settling tank can be returned to the front stage of the biological treatment tank, and a bulking inhibitor can be added to a part of the returned sludge and returned to the final stage of the biological treatment tank. By returning to the final stage of the biological treatment tank, the sludge of the activated sludge mixture in the biological treatment tank is aggregated by the returned sludge containing the anti-bulking agent, and the solid-liquid separability is improved in the settling tank.

In the present invention, one or more kinds of various bactericidal agents such as commercially available inorganic oxidizing agents and cationic surfactants can be added to a part of the returned sludge and returned to the final stage of the biological treatment tank. .. Preferably, a commercially available anti-bulking agent and the anti-bulking agent of the present invention can be mixed, added to a part of the returned sludge, and returned to the final stage of the biological treatment tank. More preferably, the anti-bulking agent of the present invention, which can reduce the damage to the activated sludge caused by the commercially available anti-bulking agent, can be added to a part of the returned sludge and returned to the final stage of the biological treatment tank.

The coagulation aid addition rate is preferably 0.05 to 5.0% by weight vs. SS, and is preferably 0.05 to 1.0% by weight vs. SS, with respect to the sludge weight of the returned sludge, that is, SS. More preferred.

FIG. 9 shows another example of the sewage treatment flow of the sewage in rainy weather of the present invention.

In the embodiment shown in FIG. 9, in addition to the return of the existing returned sludge, a coagulation aid such as a polymer flocculant or an organic coagulant is added to a part of the concentrated sludge from the excess sludge concentration facility to concentrate it. Return the sludge to the final stage of the reaction tank.

Since the concentrated sludge concentration is several times higher than the returned sludge concentration, the return flow rate to the reaction tank in the final stage can be smaller in the concentrated sludge return flow rate than in the return sludge flow rate.

Since it is the concentrated sludge of excess sludge that is returned to the reaction tank, the conditions for returning it to the reaction tank are the same as those of the embodiment shown in FIG.

FIG. 10 shows an example of the polymer coagulation aid injection control flow of the present invention in the addition of return sludge to the first settling basin.

The procedure for controlling the SS weight of the inflow portion of the first settling basin and controlling the injection of the coagulation aid is as follows.
(1) Measure the flow rate of sewage in rainy weather. Alternatively, set a predicted value based on experience in operation management.
(2) First, set the SS concentration of the inflow part of the settling basin. Alternatively, set a predicted value based on experience in operation management.
(3) Calculate the SS weight of the first settling basin inflow part from the set values of the sewage flow rate in rainy weather and the SS concentration of the first settling basin inflow part. Only the sewage flow rate in rainy weather).
(4) Estimate the SS concentration from the SS concentration measurement of the returned sludge or the value recorded in the operation management record.
(5) First, the return sludge flow rate is calculated from the SS weight of the inflow part of the settling basin and the SS concentration of the return sludge.
(6) Calculate the SS weight of the returned sludge from the flow rate of the returned sludge and the concentration of the returned sludge.
(7) Aggregation aid addition rate with respect to SS weight of returned sludge The addition weight of the aggregation aid is calculated from the set value.
(8) A coagulant auxiliary agent solution suitable for the weight of the polymer flocculant or the organic coagulant is added to the returned sludge by a chemical injection pump.

As the sludge concentration detecting means, a commercially available sludge densitometer such as a near-infrared light type sludge densitometer, a laser light type sludge densitometer, and a microwave sludge densitometer can be used. As the sludge flow rate detecting means, a commercially available electromagnetic flow meter, ultrasonic flow meter, or the like can be used. The pump that returns the sludge may be a commercially available product, and can be adjusted to the set flow rate by controlling the rotation speed and returned.

FIG. 11 shows an example of the polymer coagulation aid injection control flow of the present invention in the addition of returned sludge to the final stage of the reaction tank.

The procedure for controlling the SS weight at the final stage of the reaction tank and controlling the injection of the polymer flocculant or organic coagulant is as follows.
(1) First, the flow rate of the settling basin treated water or the treated water (hereinafter referred to as "treated water") is measured.
(2) Measure the SS (MLSS) concentration of the reaction tanks other than the final stage. Or set the control value.
(3) The SS weight to be returned to the reaction tank is calculated from the difference between the set SS concentration in the final stage of the reaction tank and the measured SS concentration in the reaction tanks other than the final stage.
(4) Measure the SS concentration of the returned sludge.
(5) The flow rate of the returned sludge returned to the final stage of the reaction tank is calculated from the SS weight required in the reaction tank and the SS concentration of the returned sludge.
(6) The weight of the agglutination aid added is determined by the SS weight returned to the final stage of the reaction tank and the set value of the agglutination aid addition rate.
(7) The amount of the coagulation aid solution to be added to the returned sludge is determined from the weight of the coagulation aid added and the dissolution concentration.
(8) Start the coagulation aid injection pump and add the coagulation aid solution to the returned sludge.

Hereinafter, examples for better understanding the present invention and its advantages will be illustrated, but the present invention is not limited to the examples.

(Conventional example 1: Solid-liquid separation in the first settling basin of sewage in simulated rainy weather)
As the simulated rainy weather sewage, the first settling basin inflow sewage in fine weather was diluted 2-fold with dechlorinated tap water and used for the test. The pH of the simulated rainy sewage was 7.4, the SS was 100 mg / L, and the BOD was 100 mg / L.

A polymer flocculant (Ebagulose B-094, amphoteric, molecular weight 5 million, manufactured by Swing Corporation) was added to simulated rainy sewage in a coagulation tank, and the test was conducted under the conditions shown in Table 1. As the polymer flocculant, a polymer flocculant-dissolved solution previously dissolved in tap water with dechlorinated water so that the dissolution concentration was 0.1% by weight was used.

Table 2 shows the treatment results when a polymer flocculant (Ebagulose B-094, amphoteric, molecular weight 5 million, manufactured by Swing Corporation) was added to the simulated rainy sewage.

In the simulated rainy weather sewage volume 1Q, the SS removal rate was 50% and the BOD removal rate was 28% by adding 2 mg / L of the polymer flocculant, but when the simulated rainy weather sewage volume was increased in 2Q, It was found that the removal rate of SS and BOD decreased significantly, and the concentration of SS and BOD in the first settling basin treated water of the simulated rainy sewage increased.

(Conventional Example 2: Solid-liquid separation in the first settling basin by adding return sludge to sewage in simulated rainy weather)
The simulated rainy weather sewage of Conventional Example 1 is provided with a mixing tank having the same shape as the coagulation tank of Table 1 and having the same effective capacity, the return sludge of Conventional Example 2 is added to the mixing tank, and then the coagulation tank of Table 1 is provided. After adding a polymer flocculant (Ebagulose B-094, amphoteric, molecular weight 5 million, manufactured by Swing Corporation) to the flocculation tank, the test was conducted under the conditions shown in Table 1. The returned sludge of Conventional Example 2 used in the test was sludge collected from the terminal treatment plant, and its properties were 6000 mg / L for SS, 5800 mg / L for TS, and 82% for VSS / SS. Table 3 shows the treatment results when the returned sludge and the polymer flocculant were directly added to the simulated rainy sewage.

(Example 1: Return sludge to which a polymer flocculant is added is added to sewage in simulated rainy weather, and solid-liquid separation is first performed in a settling basin).
The returned sludge of Conventional Example 2 to which a polymer flocculant (Ebagrose B-094, amphoteric, molecular weight 5 million, manufactured by Swing Corporation) was added to the simulated rainy sewage of Conventional Example 1 was applied to the simulated rainy sewage amount. 100 to 300 mg / L was added as SS, and the test was conducted under the conditions shown in Table 1. The addition rate of the polymer flocculant was the addition rate per SS weight of the returned sludge, which was 0.7 to 3.0% by weight vs. SS. The injection rate of the polymer flocculant with respect to the amount of treated water was 1 to 6 mg / L. Table 4 shows the treatment results of adding the returned sludge to which the polymer flocculant was added to the simulated rainy weather sewage.

By mixing the returned sludge to which the polymer flocculant is added and the simulated rainy weather sewage, the SS of the simulated rainy weather sewage is effectively taken into the returned sludge to which the polymer flocculant is added, so that the treated water amount is from 1Q. It was found that the SS removal rate and the BOD removal rate in the first settling tank did not decrease even if the increase was increased to 3Q, and the SS and BOD removal performance could be maintained.

(Conventional Example 3: Activated sludge treatment of simulated first settling tank treated water by 3W method)
The simulated rainy sewage of Conventional Example 1 was solid-liquid separated using the equipment shown in Table 1 with no chemical injection at the simulated rainy sewage volume of 3Q, and the obtained treated water was used as the simulated first settling tank treated water. The properties were pH 7.3, SS 62 mg / L, and BOD 78 mg / L.

Using the biological treatment equipment shown in Table 5, the simulated initial settling tank treated water volume 3Q was subjected to a biological treatment test in the biological treatment tank. 1Q of the simulated first settling tank treated water was added to the first tank of the biological treatment tank, and the remaining 2Q was added to the fourth tank. The sludge returned from the final settling tank was returned to the first tank of the biological treatment tank, and the MLSS was maintained at 2000 mg / L from the first tank to the third tank of the biological treatment tank. The MLSS of the 4th tank into which the simulated first settling tank treated water volume 2Q flows was about 700 mg / L. The BOD sludge load of the entire biological treatment tank was 0.35 kg / kg day.

Table 6 shows the biological treatment test results of the simulated first settling tank treated water by the 3W method.
When the simulated first settling tank treated water with SS62 mg / L and BOD78 mg / L was biologically treated with a BOD sludge load of 0.35 kg / kg days, the SS removal rate was 23% and the BOD removal rate was 63%. The SS removal rate was lower than the BOD removal rate because the liquid separability deteriorated.

(Example 2)
In comparison with the conventional examples 3 and 3W method, 2Q of the simulated initial settling tank treated water volume 3Q is flowed into the 4th tank of the biological treatment tank, and the returned sludge containing a polymer flocculant and an organic coagulant is contained in the 4th tank. Was returned, and the MLSS concentration in the 4th tank was maintained at 2000 mg / L.

Using the simulated first settling tank treated water of the simulated rainy sewage of the conventional example 3, the specifications of the biological treatment device in Table 5 and the MLSS concentration of the 4th tank of the biological treatment tank among the test conditions in Table 5 are the first tank. In the same manner as in the third tank, the simulated first settling tank treated water was subjected to a biological treatment test with a water volume of 3Q at 2000 mg / L.

The simulated initial settling tank treated water volume 3Q was tested in the same manner as in Conventional Example 3 by inflowing 1Q into the first tank of the biological treatment tank and 2Q into the fourth tank of the biological treatment tank.

The returned sludge is returned so that the MLSS concentration of the first biological treatment tank is 2000 mg / L, and the MLSS concentration of the fourth biological treatment tank into which 2Q flows is high so that it is 2000 mg / L. The returned sludge containing a molecular flocculant and an organic coagulant was returned. The BOD sludge load was 0.29 kg / kg day for the entire biological treatment tank.

Ebagulose C-104G (cationic, molecular weight 4 million, manufactured by Swing Corporation) is used as a polymer flocculant, and Evagrose L-51 and Evagrose L-305 (both cationic,) are used as organic coagulants. A molecular weight of 300,000, manufactured by Swing Corporation) was used. A polymer flocculant solution was used in which the cationic polymer flocculant was previously dissolved in tap water dechlorinated so that the dissolution concentration was 0.1% by weight. In addition, since the weight of the organic coagulant added is small for a small-scale test, it was previously dissolved in tap water with dechlorinated water so that the dissolution concentration was 0.1% by weight, as with the polymer flocculant. An organic coagulant solution was used.

Table 7 shows the results of the biological treatment test of the simulated first settling tank treated water. The SS removal rate of the final settling tank treated water, which is an index of solid-liquid separability, was Ebagulose C-104G as a polymer flocculant> Evagulose L-305 as an organic coagulant> Evagrose L-51 as an organic coagulant. Increasing the addition rate of any of the coagulation aids improved the SS removal rate.

The polymer flocculant and the organic coagulant are added to the returned sludge returned to the fourth tank of the biological treatment tank, and the chemical addition rate is the addition rate per SS weight of the returned sludge.

By returning the returned sludge containing the polymer flocculant and the organic coagulant so that the MLSS concentration of the fourth biological treatment tank becomes 2000 mg / L as compared with the conventional example 3, the entire biological treatment tank is returned. The BOD sludge load decreased to 0.29 kg / kg day, the biological treatment performance by activated sludge was improved, and the BOD removal rate was increased. In addition, due to the coagulation effect of activated sludge by the polymer flocculant and the organic coagulant, the outflow of SS from the final settling tank could be suppressed, and the SS removal rate of the final settling tank treated water was also improved.

(Example 3)
In comparison with the conventional examples 3 and 3W method, the entire amount of the simulated first settling tank treated water of the simulated rainy sewage was made to flow into the first tank of the biological treatment tank for activated sludge treatment.

Using the simulated first settling tank treated water of the simulated rainy sewage of the conventional example 3, the specifications of the biological treatment device in Table 5 and the MLSS concentration among the test conditions in Table 5 were 2000 mg / from the first tank to the fourth tank. When L was set, the simulated first settling tank treated water was subjected to a biological treatment test at a ^{water volume of 3Q and 9.8 m 3 / day.}

In the simulated initial settling tank treated water volume 3Q, the entire amount of 3Q is flowed into the first tank of the biological treatment tank, and the returned sludge containing the polymer flocculant and the organic coagulant is returned only to the first tank of the biological treatment tank. The MLSS concentration in the first to fourth tanks of the biological treatment tank was adjusted to 1000 to 2000 mg / L with the returned sludge. The BOD sludge load was 0.29 to 0.58 kg / kg day for the entire biological treatment tank.

Ebagulose C-104G (cationic, molecular weight 4 million, manufactured by Swing Corporation) is used as the polymer flocculant, and the addition rate is 0.09 to 0.57% by weight per SS weight of the returned sludge. there were.

Table 8 shows the results of the biological treatment test of the simulated first settling tank treated water. The BOD removal rate of the final settling tank treated water is 82 to 83% for a BOD sludge load of 0.58 kg / kg day, 86 to 89% for a BOD sludge load of 0.39 kg / kg day, and a BOD sludge load of 0 for the entire biological treatment tank. It became 88 to 91% at .29 kg / kg day, and when the MLSS concentration in the biological treatment tank was increased, the BOD sludge load was reduced and the BOD removal rate of the final settling tank treated water was improved. It was found that increasing the addition rate of the polymer flocculant can suppress the outflow of SS from the final settling tank and improve the SS removal rate of the final settling tank treated water.

Claims (7)

It is a wastewater treatment method that includes a biological treatment process.
The wastewater treatment method includes a solid-liquid separation step after the biological treatment step.
After adding a coagulation aid to the sludge extracted from the solid-liquid separation step after the biological treatment step or the concentrated sludge in which the sludge is concentrated, the sludge containing the coagulation aid or the concentrated sludge is added to the biological treatment step. Waste treatment methods, including returning. The wastewater treatment method according to claim 1, further comprising a solid-liquid separation step in front of the biological treatment step. The solid-liquid separation step prior to the biological treatment step is performed in the first settling basin where sewage flows in during rainy weather.
The wastewater treatment method according to claim 2, wherein the sludge containing the coagulation aid or the concentrated sludge is mixed with sewage in rainy weather and returned to the first settling basin. The biological treatment step is performed in a plurality of reaction tanks and is carried out in a plurality of reaction tanks.
The solid-liquid separation step after the biological treatment step is performed in the final settling basin.
The sludge extracted from the final settling basin is returned sludge and surplus sludge, and a part of the returned sludge is returned to the reaction tank at the front stage among the plurality of reaction tanks and aggregated in another part of the returned sludge. The wastewater treatment method according to any one of claims 1 to 3, wherein the auxiliary agent is added and then returned to the reaction tank in the final stage among the plurality of reaction tanks. The wastewater treatment method according to claim 4, further comprising adding a coagulation aid to a part of the concentrated sludge in which the excess sludge is concentrated and then returning the sludge to the final reaction tank among the plurality of reaction tanks. The biological treatment step is performed in a plurality of reaction tanks and is carried out in a plurality of reaction tanks.
The solid-liquid separation step after the biological treatment step is performed in the final settling basin.
The sludge extracted from the final settling basin is returned sludge and surplus sludge, and all of the returned sludge is returned to the first reaction tank among the plurality of reaction tanks, and a part of the concentrated sludge in which the surplus sludge is concentrated. The wastewater treatment method according to any one of claims 1 to 3, wherein the sludge assisting agent is added to the sludge and then returned to the reaction tank in the final stage among the plurality of reaction tanks. The wastewater treatment method according to any one of claims 4 to 6, further comprising adding a coagulation aid to the returned sludge returned to the reaction tank at the front stage among the plurality of reaction tanks.

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