JP2023080648A - Liquid waste concentration method and apparatus - Google Patents

Abstract

To provide a method of concentration of liquid waste and a concentration apparatus that improve dispersibility during a coagulation reaction and enable stable concentration even under slightly different operating conditions.SOLUTION: A method of concentrating liquid waste has a coagulation process (S100), a concentration process (S110), an extraction process (S120), and a return process (S130). The formation of coagulation flocs in the coagulation process (S100) is realized by mixing the returned coagulation thickened sludge into the liquid waste. This improves dispersion during the coagulation reaction and enables stable concentration of liquid waste even if the conditions of the coagulation reaction vary slightly. The present invention also provides an apparatus for concentrating liquid waste.SELECTED DRAWING: Figure 1

Description

TECHNICAL FIELD The present invention relates to a liquid waste concentration method and a liquid waste concentration apparatus, and more particularly to a liquid waste in which flocculated flocs are formed from the liquid waste, and thickened sludge and a separated liquid are obtained from the liquid waste containing the flocculated flocs. The present invention relates to a method for concentrating substances and an apparatus for concentrating liquid waste.

Liquid waste is sludge that has become muddy due to sedimentation or floating of suspended solids in water, and liquid waste that is generated during treatment processes such as night soil, septic tank sludge, water treatment, sewage treatment, and private wastewater treatment. There are two types of liquid waste: organic sludge and inorganic sludge. The former is organic waste collected as sludge and industrial waste generated by facilities that treat organic wastewater from sewage treatment plants, food factories, paper and pulp factories, and the like. The main components of organic waste are organic matter including mineral oil, animal and vegetable oils.

The latter is clean water sludge, which is coagulated sedimentation sludge at civil engineering sites and water purification plants, and sludge generated at equipment for treating wastewater containing a large amount of sand, metal components, etc., such as in metal plating factories.

In addition, digested sludge discharged from a digestion tank or a methane fermentation tank that decomposes organic matter such as biomass and sewage sludge under anaerobic conditions is also a liquid waste.

Thickening or thickening and dehydration are performed to reduce the volume of sludge.

Thickening is a process of increasing the concentration of sludge to obtain thickened sludge.

Dewatering is the process of applying mechanical pressure to squeeze water out of thickened sludge, resulting in a dewatered cake with a low water content.

In sludge dehydration, the higher the sludge concentration, the higher the sludge dehydration efficiency. Therefore, various methods for concentrating sludge prior to dehydration have been proposed.

FIG. 6 is a schematic diagram showing a processing flow of a conventional liquid waste concentration/dehydration method.

As mentioned above, thickening is commonly used as a pretreatment to increase the sludge concentration fed to the dehydrator. Sludge is added with a polymer flocculating agent in a flocculating tank, and after conditioning to form flocculated sludge, the sludge after conditioning is separated into concentrated sludge and a separated liquid in a thickener.

The addition rate of the polymer flocculant to the sludge is generally 0.2 to 5 wt% relative to the solid matter of the sludge.

The thickened sludge is dehydrated in a dehydrator to further reduce the volume. For this dehydration treatment, an aqueous solution in which a polymer flocculant is dissolved in water is used. Although the concentration of the aqueous solution is not particularly limited, it is usually 0.05 to 0.8 wt%.

A dehydrated filtrate and a dehydrated cake are carried out from the dehydrator, and the dehydrated cake is carried out for landfill disposal or the like, or is incinerated in an incinerator of its own. In the sewage treatment, the separated liquid and the dehydrated filtrate are sent to the sewage treatment process as return water for water treatment.

In addition, concentration is used as a pretreatment for increasing the concentration of sludge supplied to an anaerobic digestion tank or methane fermentation tank in order to improve the anaerobic treatment performance of the anaerobic digestion tank or methane fermentation tank.

FIG. 7 is a schematic diagram showing a processing flow of a conventional method for concentrating liquid waste as pretreatment for anaerobic digestion.

As shown in the figure, a polymer flocculant is added to sludge in a flocculation tank, and after conditioning to form flocculated sludge, the sludge after conditioning is separated into thickened sludge and a separated liquid in a thickener. Organic matter in thickened sludge is decomposed into methane gas and carbon dioxide gas in an anaerobic digester. Methane gas is used as boiler fuel. The separated liquid is sent to a sewage treatment process for water treatment.

The sludge in the anaerobic digestion tank (digested sludge) is also periodically withdrawn from the anaerobic digestion tank as digested sludge, and concentrated and dewatered as shown in FIG.

Gravity thickeners and granulation thickeners have been conventionally used to thicken sludge.

FIG. 8 is a schematic diagram showing a processing flow of liquid waste using a conventional gravity concentrator.

As shown in the figure, a polymer flocculant is added to the sludge in the flocculation tank, and after conditioning to form flocculated sludge, the sludge after conditioning is separated into thickened sludge and separated liquid in the gravity thickening tank. Thickened sludge is sent to a dehydrator or an anaerobic digester.

The conditioned sludge flows into the gravity thickener and undergoes solid-liquid separation. The separated liquid is discharged from the separated liquid outflow tube. The sludge settled in the gravity thickening tank is agitated by a picket fence in the tank to discharge water between sludge particles to obtain thickened sludge. Thickened sludge is discharged from the bottom of the water tank.

FIG. 9 is a schematic diagram showing a processing flow of liquid waste using a conventional granulating and concentrating apparatus.

As shown in the figure, the granulation and concentration apparatus mixes the sludge flowing from the bottom of the water tank with the polymer flocculant using a stirrer and a draft tube, thereby turning flocculated flocs into large granules. The granules and the separated liquid are separated by a screen, and the separated liquid is discharged from the separated liquid outflow tube. The granules become thickened sludge and are discharged outside from the granulation and thickening device through the thickened sludge outflow pipe.

Further, Patent Document 1 discloses a flocculation reaction tank that reacts sludge with a flocculant to generate flocculated sludge, a thickener that thickens flocculated sludge extracted from the flocculation reaction tank to form thickened sludge, and flocculation. A sludge supply channel that supplies flocculated sludge from the reaction tank to the thickener, a sludge circulation channel that circulates part of the thickened sludge formed by the thickener to the flocculation reaction tank, and a remaining thickened sludge formed by the thickener. , a sludge thickener comprising a discharge path for discharging to the outside and a first coagulant charging device for charging the coagulant into the coagulation reaction tank.

According to the sludge thickener of Patent Document 1, part of the thickened sludge is returned to the coagulation reaction tank, so that the retention time of the thickened sludge in the coagulation reaction tank can be extended, thereby increasing the compactness of the coagulated flocs. The mechanical strength is increased, and the water content of the dehydrated cake after dehydration can be further reduced.

Patent Document 2 describes (1) a flocculation step in which an inorganic flocculant is added to raw water and a return sludge containing a polymer flocculant is added to cause a flocculation reaction, and (2) the flocculated flocs produced in the flocculation step are solidified. A solid-liquid separation step of liquid separation, (3) a desalination step of passing the treated water obtained from the solid-liquid separation step through a reverse osmosis membrane device and/or an ion exchange device to desalinate it, (4) a solid-liquid separation step and (5) a step of adding a polymer flocculant to the flocculated sludge returned to the flocculation step.

According to the pure water production method of Patent Document 2, the SS concentration of the sedimentation or flotation treated water is reduced, and the water quality of the treated water is improved.

Japanese Patent Application Laid-Open No. 2020-001016 JP-A-11-104696

According to Patent Document 1, compared with the conventional concentration method in which part of the thickened sludge is not returned to the coagulation reaction tank, the compactness and mechanical strength of the coagulated floc are increased, and the water content of the dehydrated cake after dehydration is increased. Although it can be further reduced, the addition of the polymer flocculant to the flocculation reaction tank increases the viscosity in the tank, and the dispersibility of the thickened sludge, sludge, and polymer flocculant in the flocculation reaction tank decreases. , there is a risk of insufficient mixing.

Therefore, the agglomeration reaction is greatly influenced by the operating conditions of the flocculation reaction tank, such as the stirring conditions of the flocculation reaction tank and the return amount of thickened sludge, and the thickening property is affected.

In Patent Document 2, a polymer flocculant is added to a part of the flocculated sludge discharged in the solid-liquid classification process and returned to the flocculation process, but the liquid waste (sludge) that should be disposed of is the object of treatment. However, since it is raw water that is a raw material for pure water, the aggregation process also has a low viscosity, and the problem of non-uniform dispersion does not occur. Moreover, the object to be treated is raw water, and the technical field is also different.

An object of the present invention, which has been made in view of the above problems, is to provide a sludge thickening method and a sludge thickening apparatus that improve dispersibility during a flocculation reaction and enable stable thickening even with slight differences in operating conditions. That's what it is.

The present inventors have made intensive studies to achieve the above object, and found that in a sludge thickening method involving flocculation in a flocculation tank, thickening of sludge in a thickener, and return of part of the thickened sludge to the flocculation process, By adding a polymer flocculant to the thickened sludge to be returned before mixing it with the sludge to be treated, the flocculated flocs in the flocculation tank can be made larger and denser, and the polymer flocculation in the flocculation tank can be increased. It was found that the viscosity increase in the flocculation tank can be suppressed by not adding any agent, and as a result, the concentration efficiency in the concentrator can be stably improved even if the operating conditions are slightly different, and the present invention is completed. reached.

That is, the above object is provided by a flocculation step of forming flocculated flocs from liquid waste, a concentration step of concentrating the liquid waste containing the flocculated flocs to obtain concentrated sludge and a separated liquid, and the a taking-out step of taking out at least part of the thickened sludge; and a returning step of adding a polymer flocculant to the taken-out thickened sludge and returning the obtained flocculated thickened sludge to the flocculation step, wherein the flocculation step The formation of the flocculated flocs in A. above can be achieved by the method for concentrating liquid waste, characterized in that the flocculated and thickened sludge returned is mixed with the liquid waste.

Preferred embodiments of the method for concentrating liquid waste according to the present invention are as follows.
(1) After the removal step, the method further includes a dehydration step for dewatering the remaining thickened sludge that has been removed.

According to this, the dehydration performance can be improved more than before by dehydrating thickened sludge that has become highly concentrated.
(2) The polymer flocculant is a polymer flocculant for water supply. By using a polymer flocculant for water supply as a polymer flocculant, it is possible to form large and strong flocculated flocs from tap water sludge, thus improving the thickening property of the obtained thickened sludge.
(3) The polymer flocculant is a water supply polymer flocculant that does not contain an acrylamide monomer. As a result, the concentration of thickened sludge obtained from tap water sludge is improved, and even if the separated water generated during concentration is returned to the first stage of water purification treatment, the carcinogenic acrylamide monomer will be removed from the water purification treatment. There is no need to return to the previous stage of the process.

Further, the above objects are provided by: flocculating means for forming flocculated flocs from liquid waste; concentrating means for concentrating the liquid waste containing the flocculated flocs to obtain concentrated sludge and a separated liquid; Piping means for taking out at least part of the thickened sludge, mixing means for adding and mixing a polymer flocculant to the thickened sludge taken out by the piping means to obtain flocculated thickened sludge, and flocculation obtained by the mixing means. and return means for returning the thickened sludge to the flocculating means.

Preferred embodiments of the liquid waste concentrator according to the present invention are as follows.
(1) The concentration means is a gravity concentration device, or the flocculation means and concentration means are a granulation concentration device.

According to the present invention, instead of directly adding a polymer flocculant to liquid waste to form flocculated flocs, a polymer flocculant is added to and mixed with at least a part of thickened sludge to obtain flocculated thickened sludge. Since flocculated flocs are formed by mixing this flocculated thickened sludge with the liquid waste, the increase in viscosity during flocculation formation is suppressed compared to the case where the polymer flocculant is directly added to the liquid waste. and improves dispersibility during the aggregation reaction. Furthermore, since the flocculated flocs are formed with the flocculated thickened sludge as the nucleus, the flocculated flocs are larger and stronger than before.

Therefore, it is possible to stably concentrate the liquid waste even if the aggregation reaction conditions are slightly different.

BRIEF DESCRIPTION OF THE DRAWINGS It is a flowchart for demonstrating an example of the concentration method of the liquid waste of this invention. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic diagram showing a representative example of a processing flow according to the method for concentrating liquid waste of the present invention. 1 is a schematic diagram showing a liquid waste treatment apparatus 10 of the present invention; FIG. FIG. 2 is a schematic diagram showing a liquid waste treatment apparatus in which the concentrating means is a gravity concentrator. FIG. 2 is a schematic diagram showing a liquid waste treatment apparatus in which the aggregating means and the concentrating means are granulating and concentrating devices; 1 is a schematic diagram showing a processing flow of a conventional liquid waste concentration/dehydration method. FIG. 1 is a schematic diagram showing a processing flow of a conventional method for concentrating liquid waste as pretreatment for anaerobic digestion. FIG. FIG. 2 is a schematic diagram showing a processing flow of liquid waste using a conventional gravity concentrator. FIG. 2 is a schematic diagram showing a processing flow of liquid waste using a conventional granulating and concentrating apparatus.

<Method for Concentrating Liquid Waste>
FIG. 1 is a flow chart for explaining an example of the method for concentrating liquid waste of the present invention, and FIG. 2 is a schematic diagram showing a representative example of the processing flow according to the method for concentrating liquid waste of the present invention.

The present invention, as shown in FIG. 1, has a flocculation step (S100), a concentration step (S110), a removal step (S120), and a return step (S130).

(liquid waste)
Liquid waste includes waste liquid with a suspended solid concentration of 1000 mg/L or more, suspended suspended solids of organic and inorganic substances in water, hydrolysis products of inorganic flocculants added as water treatment chemicals, powdered activated carbon, etc. Or sludge that has risen to become muddy (slurry), solid particles, algae and fungi, water supply sludge containing hydrolysis products of inorganic flocculants, night soil and septic tank sludge, water purification treatment, sewage treatment, It is a liquid waste generated in the process of water treatment such as private sector wastewater.

The liquid waste concentration method of the present invention will be described below with reference to FIGS. 1 and 2. FIG.

[Aggregation step (S100)]
In this step, agglomerated flocs are formed from liquid waste. Formation of flocculated flocs is achieved by mixing returned flocculated thickened sludge (thickened sludge to which polymer flocculant has been added) into the liquid waste. The coagulated thickened sludge will be described later. This step is generally performed in a coagulation tank.

The sludge concentration (SS concentration) of the coagulation tank into which the coagulated thickened sludge and the liquid waste flow is preferably 5.0 to 20 g/L, and more preferably 10 to 20 g/L. Therefore, by monitoring the sludge concentration in the coagulation tank, it is possible to determine the optimum return flow rate of the coagulated and thickened sludge in the return step (S130), which will be described later.

A mixing tank for adding and mixing the inorganic coagulant may be provided in the preceding stage of the coagulation tank.

When an inorganic flocculant is added in the mixing tank, the inorganic flocculant is commercially available aluminum sulfate, polyaluminum chloride (PAC), polyferric sulfate (polyiron), ferric chloride, or a mixture thereof. can. In addition, since the use of these inorganic flocculants lowers the pH of the liquid waste during refining, commercially available caustic soda or the like is used as an alkaline agent to adjust the flocculation pH to an appropriate level.

In addition to the inorganic coagulant added in the mixing tank, or instead of the inorganic coagulant, an organic coagulant may be added. When an organic coagulant is added in the mixing tank, a commercially available organic coagulant can be used, such as polyalkylpolyamine, polyethyleneimine, diallyldimethylammonium chloride, ethylenediamine epichlorohydrin polycondensate, dicyandiamide/ammonium chloride/formaldehyde. One or more of polycondensates, polyethylene/polyamine/dimethylamine/epichlorohydrin polycondensates, dialkylamine/epichlorohydrin polycondensates, and the like can be used.

The organic coagulant can be used without diluting the product, or after being diluted with water or the like. When the organic coagulant is added, the addition rate of the organic coagulant to the liquid waste is generally 0.1% by mass to 10% by mass with respect to the solid matter TS of the sludge (liquid waste), preferably is 0.5% by mass to 5% by mass.

After the liquid waste in the flocculation tank is mixed with the flocculated thickened sludge and subjected to refining to form flocculated flocs, the liquid waste containing the flocculated flocs is transferred to the concentration step (S110) (the flocculation step (S100 )).

[Concentration step (S110)]
In this step, liquid waste containing flocculated flocs is concentrated to obtain concentrated sludge and separated liquid. As a thickener used for concentration, for example, a commercially available thickener such as a gravity thickener such as a gravity thickener, a centrifugal thickener, a screen thickener, a belt-type filtration thickener, a granulation thickener, and a flotation thickener can be used.

When the liquid waste is coagulated sedimentation sludge generated from a coagulating sedimentation treatment process in a water purification plant, that is, tap water sludge, the thickener used in this process is generally a gravity thickening tank.

The sludge concentration of the liquid waste before thickening, SS, is 5 g/L to 15 g/L. 20 to 40g/L.

Thickened sludge with a high sludge concentration of 20-40 g/L may optionally be transferred to an anaerobic digester. In this case, the high sludge concentration in the concentrated concentration lengthens the retention time in the anaerobic digestion tank, and the anaerobic digestion performance can be improved (concentration step (S110)).

[Extraction step (S120)]
In this step, at least part of the thickened sludge obtained in the thickening step (S110) is taken out. For taking out thickened sludge, for example, a dedicated return pipe having one end connected to the thickener and the other end connected to the coagulation tank or an upstream position of the coagulation tank, and a return pump provided in the return pipe , can be used. According to this, in the subsequent return step (S130), the flocculated thickened sludge obtained by adding the polymer flocculant can be returned to the flocculation tank at a stable sludge flow rate.

The amount of thickened sludge to be taken out is based on a suitable mixing ratio of flocculated thickened sludge and liquid waste, which will be described later, and is taken out in an amount necessary for this mixing ratio (above, taking-out step (S120)). .

[Returning step (S130)]
In this step, a polymer flocculant is added to the thickened sludge taken out, and the obtained flocculated thickened sludge is returned to the flocculation step (S100).

The place where the polymer flocculant is added is the suction part and the discharge part of the thickened sludge return pump (not shown), the line mixer provided in the middle of the return pipe, and the mixing tank provided at the mixing part in FIG. It may be added in this mixing tank. Agitation in the mixing tank provided in the middle of the return pipe may be mechanical agitation or agitation by a water flow of thickened sludge.

The retention time of the thickened sludge in the mixing tank provided in the middle of the return pipe varies depending on the stirring method, stirring intensity, return flow rate and its concentration, but can be, for example, 0.5 to 3 minutes. If the residence time is 0.5 minutes or longer, the polymer flocculant and thickened sludge are sufficiently mixed. On the other hand, if the residence time is 3 minutes or less, it is possible to reduce the possibility that thickened sludge aggregates will accumulate in the mixing tank provided in the middle of the return pipe and the possibility that the flocculation property will deteriorate.

Commercially available polymer flocculants can be used, and anionic polymer flocculants, cationic polymer flocculants, or amphoteric polymer flocculants can be used either alone or in combination. Further, the polymer flocculant can be used in powder form, liquid form (dispersion form, emulsion form), or the like.

The anionic polymer flocculant is selected from the group consisting of polyacrylic acid, sodium polyacrylate, potassium polyacrylate, ammonium polyacrylate, polymethacrylic acid, sodium polymethacrylate, potassium polymethacrylate, and ammonium polymethacrylate. It is possible to use any one or more of

Polyacrylamide-based polymer flocculants can also be used, which are copolymers of acrylamide monomers and (meth)acrylates.

When the liquid waste is coagulated sedimentation sludge generated from a coagulating sedimentation treatment process in a water purification plant, that is, tap water sludge, a polymer flocculant for water supply is used as the polymer flocculant.

Polymer flocculants for water supply are standardized by the Japan Water Works Association (JWWA K163:2019, polyacrylamide for water supply). As the polymer flocculant for water supply, polyacrylamide for water supply can be used in this step. On the other hand, since acrylamide is carcinogenic, from the viewpoint of avoiding that the separated liquid and dehydrated filtrate in the concentration step (S110) in which acrylamide monomer remains are returned to the first step of water purification treatment as returned water, acrylamide Polymeric flocculants for water supply such as polyacrylic acid and sodium polyacrylate that do not contain monomers are suitable.

The cationic polymer flocculant contains a cationic monomer as an essential component, and at least one of homopolymers or copolymers of cationic monomers, copolymers of cationic monomers and nonionic monomers, and the like. can be selected and used. Cationic monomers include dimethylaminoethyl acrylate, dimethylaminoethyl methacrylate, diethylaminoethyl acrylate, diethylaminoethyl methacrylate, alkali metal salts and quaternary ammonium salts thereof.

Amphoteric polymer flocculants are obtained by copolymerizing cationic monomers, anionic monomers and nonionic monomers, and have cationic units, anionic units and nonionic units in the molecule.

When the liquid waste is sludge after biological treatment, a cationic polymer flocculant or an amphoteric polymer flocculant having any cationic degree or molecular weight can be used as the polymer flocculant.

When the liquid waste is tap water sludge, poly (meth) having a 0.1% salt viscosity of 2 to 5 mPa s and an anion equivalent of −9.0 or less is used as a polymer flocculant for concentrated sludge. Although it is preferable to add an acrylate polymer flocculant for water supply, the polymer flocculant for water supply is not limited to this. Both a polymer flocculant for water supply containing an acrylamide monomer and a polymer flocculant for water supply not containing an acrylamide monomer can be used depending on the intended purpose.

The salt viscosity was measured by using a Brookfield viscometer at 25° C. for a sample obtained by dissolving a poly(meth)acrylic acid salt in a 1N sodium chloride aqueous solution to a concentration of 0.1% by mass. value, and the unit is mPa·s.

The anion equivalent is a value that can be determined by the following measurement method, and the unit is meq/g. Prepare a 0.1% aqueous solution of poly (meth) acrylate, add 5 ml of methyl glycol chitosan solution (N / 200), stir, add 2 to 3 drops of toydin blue indicator, add potassium polyvinyl sulfate solution ( PVSK, N/400), and the end point is when the color changes and is maintained for 10 seconds or more. A blank test is performed without adding a sample by the same procedure as above, and the anion equivalent Av is calculated by the following formula.

Anion equivalent (Av) [meq/g] =
(blank titer ml - sample titer ml) x 1/2 x PVSK titer

The addition rate of the polymer flocculant to the concentrated sludge is 0.02 wt/wt% vs. SS or more and 2.0 wt/wt% vs. SS or less. If the addition rate of the polymer flocculant is 0.02 wt/wt% vs. SS or more, the solution of the polymer flocculant mixes well with the thickened sludge, forming strong flocculated flocs in the flocculation tank and improving the concentration performance. improves. By setting the addition rate of the polymer flocculant to 2.0 wt/wt% vs. SS or less, the amount of the polymer flocculant used is suppressed, and the flocculated thickened sludge and liquid waste are flocculated to form strong flocculated flocs in the flocculation tank. is generated to improve the concentration performance.

Polymer flocculant addition rate ("wt/wt% vs. SS" or "wt/wt% vs. TS") set in advance to thickened sludge, and sludge concentration in the flocculation tank into which flocculated thickened sludge and liquid waste flow By monitoring the sludge flow rate and thickened sludge concentration, the optimum return flow rate of the coagulated and thickened sludge to be returned to the coagulation step (S100) can be determined.

In addition, by installing a sludge flow meter and a sludge concentration meter in the middle of the return pipe of the return process (S130) and monitoring the return flow rate and sludge concentration, the amount of coagulated and thickened sludge returned to the coagulation process (S100) Controllable and stable concentration can be achieved.

A commercially available sludge concentration meter such as a near-infrared light type sludge concentration meter, a laser light type sludge concentration meter, or a microwave sludge concentration meter can be used to detect the sludge concentration. A commercially available electromagnetic flowmeter, ultrasonic flowmeter, or the like can be used to detect the sludge flow rate. The pump for returning the coagulated and thickened sludge may be a commercially available product, and the sludge can be returned after being adjusted to a set flow rate by controlling the rotation speed.

According to the method for concentrating liquid waste of the present invention, the formation of flocculated flocs from the liquid waste in the flocculation step (S100) is performed by adding the polymer flocculant directly to the liquid waste, instead of flocculating the returned flocculation. Since the thickened sludge is mixed with the liquid waste, the increase in viscosity during the flocculation reaction is suppressed more than before, and the dispersibility during the flocculation reaction is improved. Therefore, compared to the conventional method of setting the injection rate of the polymer flocculant based on the flow rate of sludge (liquid waste) flowing into the flocculation tank, the optimal addition amount is always high regardless of the properties of the liquid waste. It becomes possible to add a molecular flocculant.

As a result, it is possible to stably and continuously obtain a high flocculation effect and concentration while performing efficient treatment by optimizing the amount of polymer flocculant used.

If the coagulated thickened sludge with the optimum added amount of polymer flocculant is returned to the flocculation step (S100), there is no need to additionally add the polymer flocculant in the flocculation step (S100). Rather, if the polymer flocculant is additionally added in the flocculation step (S100), it will take time to homogenize the dispersion in the flocculation tank due to the viscosity of the polymer flocculant solution, and there is a possibility that the flocculation and concentration properties will rather decrease. be.

SS (suspended solids) and TS (total solids) are available as indexes 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 common salt) such as sewage, but the values of SS and TS of sludge with a high concentration of dissolved salts such as night soil treatment are different. If different, the sludge concentration is taken from SS.

In the present invention, SS and TS follow the definitions below.
SS:K 0102:2019 Industrial Effluent Test Method 14.1 Suspended Solids TS:K 0102:2019 Industrial Effluent Test Method 14.2 Total Evaporation Residue

An example of the liquid waste concentration method of the present invention has been described above with reference to FIGS. 1 and 2, but the present invention is not limited to this example.

For example, at least part of the thickened sludge obtained in the concentration step (S110) is taken out and returned to the flocculation step (S100) as condensed thickened sludge, but the remainder of the thickened sludge obtained in the concentration step (S110) may be dehydrated.

As shown in FIG. 1, the liquid waste concentration method of the present invention includes a dehydration step (S140) as an optional step. The dehydration step (S140) will be described below.

[Dehydration step (S140)]
In this step, the remainder of the thickened sludge taken out after the taking out step (S120) is dewatered.

Dehydration involves applying mechanical pressure to the thickened sludge to squeeze water out of the thickened sludge to obtain a dehydrated cake with a low water content.

As the dehydrator used in this step, conventionally known devices can be used. A disk type dehydrator, a screw press type dehydrator, an electroosmotic dehydrator and the like can be mentioned.

The obtained dehydrated cake is disposed of by carrying it out and landfilling it, or by incinerating it in an incinerator, as in the conventional case (above, the dehydration step (S140)).

According to the liquid waste concentration method of the present invention including the dehydration step (S140), the thickened sludge obtained after the concentration step (S110) contains large and firm flocs, so the dehydration performance in the dehydration step (S140) is also improved. The moisture content of the obtained dehydrated cake is lower than before. Therefore, the cost of transporting the dehydrated cake and the cost of fuel for incineration can be reduced.

Furthermore, in the liquid waste concentration method of the present invention, a polymer flocculant is added to the concentrated sludge, and an inorganic flocculant or an organic coagulant is optionally added to the liquid waste. additives may be used. For example, short fibrous chemicals may be added to the liquid waste to improve concentration.

Short fibrous agents include, for example, natural short fibers such as used paper and cotton, chemically synthesized short fibers, and regenerated short fibers. Short fibers regenerated from plastic waste and staple fibers made of viscose rayon are suitable.

Among them, a short fibrous drug (for example, Evergulose U-700 series, manufactured by Swing Co., Ltd.), which is a short fiber material made of viscose rayon, has an excellent concentration effect.

From the standpoint of excellent dispersibility in liquid waste and affinity with liquid waste (sludge), a short fibrous agent having a fiber length of 5 to 10 mm and a water content of 30 to 80 wt/wt% is suitable.

The addition rate of the short fibrous chemical is 0.02 to 1.0 wt/vol%, preferably 0.1 to 0.5 wt/vol%, based on the liquid waste.

By setting the addition rate of the short fibrous chemical to be 0.02 wt/vol% or more per liquid waste, it is possible to obtain even stronger aggregated flocs by the liquid waste and fibers, and the concentration in the concentration step (S110) improve sexuality. Therefore, thickened sludge with a higher concentration can be obtained, and the SS concentration and BOD concentration of the separated liquid can be reduced.

In addition, since the addition rate of the short fiber chemical is less than 1.0 wt/vol% per liquid waste, the short fiber chemical can be uniformly mixed and dispersed in the liquid waste, and the oil content and SS of the liquid waste can be reduced. can be effectively captured and is economically advantageous.

<Liquid Waste Concentrator>
FIG. 3 is a schematic diagram showing a liquid waste treatment apparatus 10 of the present invention. As illustrated, the liquid waste treatment apparatus 10 of the present invention has flocculation means 20 , concentration means 30 , piping means 40 , mixing means 50 and return means 60 .

The flocculating means 14 is means for forming flocculated flocs from liquid waste, and is generally a flocculating tank. The liquid waste mixed in the coagulation tank and the returned coagulated thickened sludge are agitated to grow and form coagulated flocs.

A mixing tank for adding and mixing the inorganic coagulant may be provided in the preceding stage of the coagulation tank. In addition to the inorganic coagulant added in the mixing tank, or instead of the inorganic coagulant, an organic coagulant may be added.

The sludge concentration (SS concentration) in the coagulation tank, the return flow rate of the coagulated and thickened sludge, the inorganic coagulant, and the organic coagulant are as described in the method for concentrating the liquid waste, and the description thereof is omitted here. . Concentrating means 30 is provided downstream of the aggregation means 20 .

The concentrating means 30 is means for concentrating liquid waste containing flocculated flocs to obtain concentrated sludge and separated liquid.

As the concentration means 30, conventionally known concentration means can be used, for example, a gravity concentration device such as a gravity concentration tank, a centrifugal concentration machine, a screen concentration machine, a belt-type filtration concentration machine, a granulation concentration tank, a flotation concentration, and the like. Commercially available concentrators can be used.

Among them, it is preferable that the concentration means 30 is a gravity concentration device, or the aggregation means 20 and the concentration means 30 are granulation concentration devices.

FIG. 4 is a schematic diagram showing a liquid waste treatment apparatus in which the concentrating means is a gravity concentrator. As shown in the figure, the gravity thickener introduces liquid waste (conditioned sludge) containing flocculated flocs from the flocculating tank into the center well, and rotates the picket fence and the sludge scraping plate with a driving device. and gently agitate to separate water and air bubbles in the conditioned sludge. Sludge is separated by gravity into thickened sludge and separated liquid, the separated liquid is withdrawn from the separated liquid outflow pipe, and the thickened sludge is withdrawn from the thickened sludge withdrawal pipe below the gravity thickener.

According to the present invention, since the flocculated floc is strong, even if the sludge is agitated by the picket fence in the tank, the sludge will not break, the water between the sludge particles will be easily discharged, and highly concentrated thickened sludge will be produced. Obtainable. Since highly concentrated thickened sludge can be obtained, the flow rate of thickened sludge to be returned can be reduced, resulting in a reduction in the power cost of the return pump (not shown). Further, when a dehydration facility is provided in the latter stage, the dehydration performance of the dehydrator is improved and the retention time of the thickened sludge in the anaerobic digestion is increased, thereby improving the organic substance removal effect.

FIG. 5 is a schematic diagram showing a liquid waste treatment apparatus in which the aggregating means and the concentrating means are granulation and concentrating apparatuses. As shown in the figure, the granulation and concentration apparatus has a granulation and concentration tank equipped with a stirrer having agitating blades. Agglomerated thickened sludge is allowed to flow in from the provided return pipe.

Liquid waste and flocculated thickened sludge are agitated and mixed by a draft tube and an agitator to form flocculated flocs, which are further formed into larger granules. From there, it is separated into granulated thickened sludge and separated liquid by a screen. According to the granulation and thickening apparatus, since strong and large flocs are generated, the opening of the screen, which tends to be clogged, can be enlarged, and stable thickening and high-concentration thickened sludge can be obtained.

When the liquid waste is organic sludge, the separated liquid is sent to a sewage treatment process or the like for water treatment. When the liquid waste is inorganic sludge, the separated liquid is returned as return water to, for example, the first step of water purification treatment, or discharged. Thickened sludge is removed from the piping means.

The piping means 40 is means for taking out at least part of the thickened sludge obtained by the thickening means 30. For example, one end is connected to the thickening means 30, and the other end is the flocculating means 20 or the flocculating means 20 and the thickening means 30. In the case of a granulation concentrator, a return line including a dedicated return pipe whose other end is connected to the bottom of the concentration means 30 and a return pump provided in the return pipe can be used. A mixing means 50 is provided in the return line.

The mixing means 50 is means for adding and mixing a polymer flocculant to the thickened sludge taken out by the piping means 40 to obtain flocculated thickened sludge. The mixing means 50 includes, for example, a suction part and a discharge part of a return pump (not shown) for thickened sludge, or a line mixer or a mixing tank provided in the middle of the return pipe. Agitation in the mixing tank may be mechanical agitation or agitation by a water flow of thickened sludge. The residence time in the mixing tank and the polymer flocculant to be added are as described in the method for concentrating liquid waste, and the description thereof is omitted here.

The returning means 60 is means for returning the coagulated thickened sludge obtained by the mixing means 50 to the coagulating means. The specific configuration of the return means 60 is as described for the return line in the piping means 40 above.

Also, a sludge flow meter and a sludge concentration meter may be installed in the middle of the return pipe of the return line to monitor the return flow rate and the sludge concentration. The detection of the sludge concentration and the like are as explained in the method for concentrating the liquid waste, and the explanation thereof is omitted here.

Further, as shown in FIG. 3, in the liquid waste treatment apparatus 10 of the present invention, the return pipe takes out at least part of the thickened sludge from the thickening means 30 and then returns it to the flocculating means 20 via the mixing means 50. Although it branches into means 60 and a pipe for transferring the rest of the thickened sludge downstream, a dehydration means (not shown) may be provided at the end of the pipe.

The dewatering means applies mechanical pressure to the thickened sludge to squeeze water out of the thickened sludge to obtain a dehydrated cake with a low water content. Conventionally known means can be used as the dehydration means. The obtained dehydrated cake is carried out to the outside for landfill disposal or the like, or is incinerated in an incinerator.

According to the liquid waste treatment apparatus of the present invention including the dehydration means, since strong flocculated flocs can be obtained, the dehydration performance when dewatering thickened sludge is also improved, and the water content of the dehydrated cake is lower than before. descend. Therefore, it is possible to reduce the cost of transportation when carrying out, and further reduce the cost of fuel necessary for incineration.

EXAMPLES Hereinafter, the present invention will be described more specifically with reference to Examples.

1. Example 1
Excess sludge (liquid waste) (pH 6.5, SS 10g/L) from the standard activated sludge treatment facility of a separate sewage treatment plant was tested using the concentration test equipment shown in Table 1. The excess sludge flow rate was 4.5m ³ / Concentration tests were conducted using a screen with a wire slit width of 1 mm at a liquid temperature of 20 to 25°C. The sludge concentration of the thickened sludge and the SS concentration of the separated liquid were measured.

Excess sludge (liquid waste) in the flocculation tank shown in Table 1 was mixed with pre-prepared thickened sludge with a cationic polymer flocculant (Ebergrose C-104G, manufactured by Swing) in an amount of 0.00 per SS weight of excess sludge. 02 to 0.5 wt% (0.03 to 0.74 wt% per SS weight of the thickened sludge) was added and mixed to flocculate flocculated flocs, which were then concentrated with a screen.

Pre-prepared thickened sludge is thickened sludge (SS 38g/ L, Test No. 11) in Table 2.

In addition, when the thickened sludge is not returned to the flocculation tank and the polymer flocculant is added directly to the flocculation tank, or when the polymer flocculant is added directly to the flocculation tank and further concentration is performed without adding the polymer flocculant. A case where sludge was added was also tested.

Table 2 shows the results.

The polymer flocculant addition rate (wt/wt% vs. SS) in Table 2 is the addition rate of the polymer flocculant relative to the weight of the flocculating tank SS.

(i) "Add polymer flocculant to thickened sludge" in Table 2 is the method of the present invention, adding the required amount of polymer flocculant to thickened sludge to obtain thickened sludge containing a polymer flocculant ( coagulated thickened sludge) is returned to the coagulation tank.

The addition rate of the polymer flocculant to the SS weight of the thickened sludge is also shown in parentheses (Test Nos. 1 to 9).

(ii) in Table 2, "adding a polymer flocculant to the flocculation tank without returning the thickened sludge" means that no polymer flocculant is added to the thickened sludge and the thickened sludge is not returned to the flocculation tank, (Test Nos. 10 to 13).

(iii) “Return thickened sludge and add polymer flocculant to flocculation tank” in Table 2 returns thickened sludge without polymer flocculant added to the thickened sludge in the flocculation tank, adding the polymer flocculant. This is the case when added to the flocculation tank (Test Nos. 14 to 17).

The flocculated thickened sludge obtained by adding a polymer flocculant to thickened sludge at an addition rate of 0.3 wt / wt% vs. SS with respect to the SS weight in the flocculation tank is added to the flocculation tank so that the SS in the flocculation tank becomes 20 g / L. When the sludge was returned and the coagulated thickened sludge and excess sludge were coagulated in a coagulation tank and screen-thickened, the SS of the thickened sludge was 65 g/L and the SS of the separated liquid was 110 mg/L (Test No. 5).

Neither coagulated thickened sludge nor thickened sludge is returned to the flocculation tank, and a polymer flocculant with a polymer flocculant addition rate of 0.3 wt / wt% relative to the SS weight in the flocculation tank is added to the flocculation tank to flocculate. The SS of the thickened sludge was 38 g/L, and the SS of the separated liquid was 220 mg/L (Test No. 11).

The thickened sludge to which no polymer flocculant is added is returned to the flocculation tank, the SS in the flocculation tank is adjusted to 20 g / L, and the polymer flocculant addition rate is 0.4 wt / wt% with respect to the SS weight in the flocculation tank. When the SS polymer flocculant was added to the flocculation tank, flocculated and screen-concentrated, the SS of the thickened sludge was 44 g/L and the SS of the separated liquid was 300 mg/L (Test No. 15).

As in the present invention, the required addition amount of the polymer flocculant is added to the thickened sludge, the thickened sludge containing the polymer flocculant (flocculated thickened sludge) is returned to the flocculation tank, and the surplus sludge (liquid waste ) was refined and screen-condensed, the SS concentration of the thickened sludge obtained was increased even when the amount of polymer flocculant added was reduced, and the SS concentration of the separated liquid was also reduced.

2. Example 2
0.5 L of the thickened sludge obtained in Example 1 was collected and refined with the polymer flocculant used in Example 1. The addition rate of the polymer flocculant to the thickened sludge was 0.5-2.0 wt/wt% vs. SS. After refining, the refined thickened sludge was placed on a filter cloth having a filter cloth area of 100 cm ² , and was uniaxially pressurized at a pressure of 50 kPa for 10 minutes to perform a pressure dehydration test with a pressure dehydration tester. After the pressure dehydration test, the dehydrated cake was taken out and the moisture content was measured. Also, the SS of the dehydrated filtrate discharged from the filter cloth was measured.

Table 3 shows the results.

The following three types of thickened sludge were used in the dehydration test. That's right.

(i) Thickened sludge obtained by adding a polymer flocculant to thickened sludge, test number No. in Table 2 (Example 1). 5, and the thickened sludge concentration is SS65g/L.

(ii) Thickened sludge obtained by using a polymer flocculant in a flocculation tank without returning the thickened sludge, test number No. 1 in Table 2 (Example 1). 11, and the thickened sludge concentration is SS38g/L.

(iii) Thickened sludge obtained by returning the thickened sludge and adding a polymer flocculant to the flocculation tank. 15, and the thickened sludge concentration is SS44g/L.

Test No. in Table 2 (Example 1). Add 1.0wt/wt% of polymer flocculant to the thickened sludge in step 5 and dehydrate under pressure after refining. There was (test number No. 2).

Test No. in Table 2 (Example 1). 1.5 wt/wt% of the polymer flocculant is added to the thickened sludge of No. 11, and pressure dewatering is performed after refining. There was (test number No. 6).

Test No. in Table 2 (Example 1). 1.5 wt/wt% of polymer flocculant is added to the thickened sludge of No. 15, and pressure dewatering is performed after refining. There was (test number No. 10).

As in the present invention, the necessary amount of polymer flocculant is added to the thickened sludge, the thickened sludge containing the polymer flocculant (flocculated thickened sludge) is returned to the flocculation tank, and the excess sludge (liquid waste) is returned to the flocculation tank. By dewatering the thickened sludge obtained by refining and screen-concentrating the material), a dehydrated cake with a low moisture content can be obtained even if the amount of polymer flocculant added is reduced.

The thickened sludge obtained by the present invention contributes to the improvement of dehydration performance in the latter stage.

3. Example 3
In the rapid filtration equipment of the water purification plant, river water with a turbidity of 3 to 5 degrees is treated with PAC injection rate of 20 mg / L as tap water, and the coagulated sedimentation sludge discharged from the sedimentation tank (pH 6.5, SS 5.1 g/L) or less, a concentration test was performed using the concentration test apparatus shown in Table 1 for tap water sludge (liquid waste).

Water supply sludge (liquid waste) in the flocculation tank in Table 1, and pre-prepared thickened sludge containing an acrylamide-free anionic polymer flocculant for water supply (Evergross WA-200, manufactured by Swing Co., Ltd.) 0.2 to 0.4 wt% per SS weight of tap water sludge (0.35 to 0.81 wt% per SS weight of thickened sludge) added flocculated thickened sludge, mixed and flocculated. was concentrated with

The thickened sludge prepared in advance was mixed with the same acrylamide-free anionic water-use polymer flocculant added to the tap water sludge at a rate of 0.4 wt/wt% vs. SS. thickened sludge (SS 36 g/L, test number No. 7 in Table 4).

Further, as in Example 1, when the thickened sludge is not returned to the flocculation tank and the polymer flocculant is added directly to the flocculation tank, or the polymer flocculant is added directly to the flocculation tank, A test was also conducted in the case of adding thickened sludge to which no molecular flocculant was added.

Table 4 shows the results.

In Table 4, (i) “Add polymer flocculant to thickened sludge” is the method of the present invention, adding the necessary amount of polymer flocculant to thickened sludge prepared in advance to obtain polymer flocculation. This is the case where the thickened sludge containing the agent (coagulated thickened sludge) is returned to the coagulation tank.

The addition rate of the polymer flocculant to the SS weight of the thickened sludge is also shown in parentheses in Table 4 (Test Nos. 1 to 5).

(ii) in Table 4, "adding a polymer flocculant to the flocculation tank without returning the thickened sludge" means that no polymer flocculant is added to the thickened sludge and the thickened sludge is not returned to the flocculation tank. (Test Nos. 6 to 8).

(iii) “Return the thickened sludge and add the polymer flocculant to the flocculation tank” in Table 4 returns the thickened sludge to the flocculation tank without adding the polymer flocculant to the thickened sludge, and adds the polymer flocculant. This is the case where it was added to the flocculation tank (Test Nos. 9 to 11).

The flocculated thickened sludge obtained by adding a polymer flocculant to thickened sludge at an addition rate of 0.3 wt / wt% vs. SS with respect to the SS weight in the flocculation tank is added to the flocculation tank so that the SS in the flocculation tank becomes 10 g / L. When the coagulated thickened sludge and excess sludge (liquid waste) were returned and coagulated in the coagulation tank and screen-condensed, the SS of the thickened sludge was 44 g/L, and the SS of the separated liquid was 100 mg/L (Test No. No. 2).

Neither coagulated thickened sludge nor thickened sludge is returned to the flocculation tank, and a polymer flocculant with a polymer flocculant addition rate of 0.4 wt / wt% relative to the SS weight in the flocculation tank is added to the flocculation tank to flocculate. The SS of the thickened sludge was 36 g/L, and the SS of the separated liquid was 260 mg/L (Test No. 7).

The thickened sludge to which no polymer flocculant is added is returned to the flocculation tank, the SS in the flocculation tank is adjusted to 10 g / L, and the polymer flocculant addition rate is 0.4 wt / wt% with respect to the SS weight in the flocculation tank. When the SS polymer flocculant was added to the flocculation tank, flocculated and screen-concentrated, the SS of the thickened sludge was 39 g/L, and the SS of the separated liquid was 330 mg/L (Test No. 10). .

As in the present invention, the necessary amount of polymer flocculant is added to the thickened sludge, the thickened sludge containing the polymer flocculant (flocculated thickened sludge) is returned to the flocculation tank, and the water supply sludge (liquid state) is returned to the flocculation tank. By refining and screen-concentrating waste), the SS concentration of the thickened sludge obtained was increased even when the amount of polymer flocculant added was reduced, and the SS concentration of the separated liquid was also reduced.

Claims (6)

an agglomeration step of forming agglomerated flocs from liquid waste;
a concentration step of concentrating the liquid waste containing the flocculated flocs to obtain concentrated sludge and a separated liquid;
A taking-out step of taking out at least part of the thickened sludge obtained in the thickening step;
a return step of adding a polymer flocculant to the thickened sludge taken out and returning the obtained flocculated thickened sludge to the flocculation step;
A method for concentrating liquid waste, wherein the formation of the flocculated flocs in the flocculation step is performed by mixing the returned flocculated thickened sludge with the liquid waste. 2. The method for concentrating liquid waste according to claim 1, further comprising a dehydration step of dehydrating the remaining thickened sludge that has been removed after the removal step. 3. The method for concentrating liquid waste according to claim 1, wherein the polymer flocculant is a polymer flocculant for water supply. 4. The method for concentrating liquid waste according to claim 3, wherein the polymer flocculant is a polymer flocculant for water supply that does not contain an acrylamide monomer. flocculation means for forming flocculation from liquid waste;
Concentrating means for concentrating the liquid waste containing the flocculated flocs to obtain concentrated sludge and a separated liquid;
Piping means for taking out at least part of the thickened sludge obtained by the thickening means;
mixing means for adding and mixing a polymer flocculant to the thickened sludge taken out by the piping means to obtain flocculated thickened sludge;
a returning means for returning the coagulated thickened sludge obtained by the mixing means to the coagulating means;
A concentrating device for liquid waste, characterized by comprising: 6. The apparatus for concentrating liquid waste according to claim 5, wherein said concentrating means is a gravity concentrator, or said flocculating means and said concentrating means are granulation concentrators.

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