Method and device for concentrating liquid waste

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]

[0001] The present invention relates to a method and an apparatus for concentrating liquid waste, and in particular to a method and an apparatus for concentrating liquid waste, which form coagulated flocs from liquid waste and obtain concentrated sludge and separated liquid from the liquid waste containing the coagulated flocs. [Background technology]

[0002] Liquid waste is sludge that is formed when suspended solids in water settle or float to the surface and become muddy, or liquid waste that is generated during the treatment process of human waste, septic tank sludge, water purification, sewage treatment, and private wastewater. There are two types of liquid waste: organic sludge and inorganic sludge. The former is organic waste that is collected as sludge or industrial waste generated in facilities that treat organic wastewater from sewage treatment plants, food factories, paper and pulp factories, etc. The main component of organic waste is organic matter that includes mineral oil and animal and vegetable oil.

[0003] The latter includes drinking water sludge, which is a coagulation and settling sludge from civil engineering sites and water purification plants, and sludge generated in facilities that treat wastewater containing large amounts of sand and metal components, such as in metal plating factories.

[0004] In addition, digested sludge discharged from digesters and methane fermenters that decompose organic matter such as biomass and sewage sludge under anaerobic conditions is also a liquid waste.

[0005] To reduce the volume of sludge, it is thickened or thickened and dewatered.

[0006] Thickening is the process of increasing the concentration of sludge to produce thickened sludge.

[0007] Dewatering is the process of squeezing water from thickened sludge using mechanical pressure, resulting in a dewatered cake with a low moisture content.

[0008] In the dehydration of sludge, the higher the concentration of the sludge, the more efficient the dehydration of the sludge. Therefore, various methods have been proposed for thickening the sludge prior to the dehydration.

[0009] FIG. 6 is a schematic diagram showing a process flow of a conventional method for concentrating and dehydrating liquid waste.

[0010] As mentioned above, thickening is generally used as a pretreatment to increase the concentration of sludge before it is fed to the dehydrator. After the sludge is conditioned in the coagulation tank by adding a polymer coagulant to create coagulated flocs, the conditioned sludge is separated in the thickener into thickened sludge and separated liquid.

[0011] The rate at which polymer flocculants are added to sludge is generally 0.2 to 5 wt% relative to the solid matter in the sludge.

[0012] The concentrated sludge is dehydrated in a dehydrator to further reduce the volume. A polymer flocculant is used in this dehydration process as an aqueous solution in which it is dissolved in water. The concentration of the aqueous solution is not particularly limited, but is usually 0.05 to 0.8 wt%.

[0013] The dehydrator produces the dehydrated filtrate and the dehydrated cake, which is either transported to a landfill or incinerated in a company's own incinerator. In sewage treatment, the separated liquid and the dehydrated filtrate are sent to the sewage treatment process as return water for water treatment.

[0014] Thickening is also used as a pretreatment process to increase the concentration of sludge supplied to an anaerobic digester in order to improve the anaerobic treatment performance in the anaerobic digester or methane fermenter.

[0015] FIG. 7 is a schematic diagram showing a process flow of a conventional method for concentrating liquid waste as a pretreatment for anaerobic digestion.

[0016] As shown in the diagram, a polymer coagulant is added to the sludge in a coagulation tank, and after conditioning to create coagulated flocs, the conditioned sludge is separated into thickened sludge and separated liquid in a thickener. The organic matter in the thickened sludge is broken down into methane gas and carbon dioxide gas in an anaerobic digester. The methane gas is used as boiler fuel, etc. The separated liquid is sent to the sewage treatment process for water treatment.

[0017] The sludge from the anaerobic digester (digested sludge) is also periodically removed from the anaerobic digester and thickened and dewatered as shown in Figure 6.

[0018] Conventionally, gravity thickeners and granular thickeners have been used to thicken sludge.

[0019] FIG. 8 is a schematic diagram showing a conventional treatment flow of liquid waste using a gravity concentrator.

[0020] As shown in the figure, a polymer coagulant is added to the sludge in the coagulation tank to condition it and create coagulated flocs. The conditioned sludge is then separated into thickened sludge and separated liquid in the gravity thickening tank. The thickened sludge is sent to a dehydrator or anaerobic digester.

[0021] The conditioned sludge flows into the gravity thickener tank, where solids and liquids are separated. The separated liquid is discharged from the separated liquid outlet pipe. The sludge that settles in the gravity thickener tank is stirred by a picket fence inside the tank, and the water between the sludge particles is discharged to obtain thickened sludge. The thickened sludge is discharged from the bottom of the tank.

[0022] FIG. 9 is a schematic diagram showing a treatment flow of liquid waste using a conventional granulation concentrator.

[0023] As shown in the figure, the granulation thickener uses an agitator and draft tube to mix the sludge flowing in from the bottom of the tank with a polymer coagulant, turning the flocs into large granules. The granules and separated liquid are separated by a screen, and the separated liquid is discharged from the separated liquid outlet pipe. The granules become concentrated sludge, and are discharged from the granulation thickener through the concentrated sludge outlet pipe.

[0024] Patent Document 1 also discloses a sludge concentration apparatus including a coagulation reaction tank in which sludge is reacted with a coagulant to produce coagulated sludge, a concentrator that thickens the coagulated sludge extracted from the coagulation reaction tank to form concentrated sludge, a sludge supply path that supplies coagulated sludge from the coagulation reaction tank to the concentrator, a sludge circulation path that circulates a portion of the concentrated sludge formed by the concentrator to the coagulation reaction tank, a discharge path that discharges the remainder of the concentrated sludge formed by the concentrator to the outside, and a first coagulant injection device that inputs the coagulant into the coagulation reaction tank.

[0025] According to the sludge thickening apparatus of Patent Document 1, a portion 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. This increases the density and mechanical strength of the coagulated flocs, and further reduces the water content of the dehydrated cake after dewatering.

[0026] Patent Document 2 discloses a method for producing pure water, comprising: (1) a coagulation step of adding an inorganic coagulant to raw water and adding returned sludge containing a polymer coagulant to carry out a coagulation reaction; (2) a solid-liquid separation step of separating the coagulated flocs produced in the coagulation step into solid and liquid; (3) a desalination step of passing treated water obtained from the solid-liquid separation step through a reverse osmosis membrane device and / or an ion exchange device for desalting; (4) a sludge return step of returning a portion of the coagulated sludge discharged from the solid-liquid separation step to the coagulation step; and (5) a step of adding a polymer coagulant to the coagulated sludge returned to the coagulation step.

[0027] According to the pure water production method of Patent Document 2, the SS concentration in the sedimentation or flotation treated water is reduced, improving the quality of the treated water. [Prior art documents] [Patent documents]

[0028] [Patent Document 1] JP 2020-001016 A [Patent Document 2] Japanese Patent Application Publication No. 11-104696 Summary of the Invention [Problem to be solved by the invention]

[0029] According to Patent Document 1, compared with conventional thickening methods in which a portion of the thickened sludge is not returned to the coagulation reaction tank, the density and mechanical strength of the coagulated flocs are increased, and the water content of the dehydrated cake after dewatering can be further reduced. However, the addition of a polymer coagulant to the coagulation reaction tank increases the viscosity inside the tank, which may reduce the dispersibility of the thickened sludge, sludge, and polymer coagulant in the coagulation reaction tank, resulting in insufficient mixing.

[0030] Therefore, the coagulation reaction is greatly influenced by the operating conditions of the coagulation reaction tank, such as the stirring conditions in the coagulation reaction tank and the amount of thickened sludge returned, which affects the thickening ability.

[0031] In Patent Document 2, a polymer flocculant is added to a portion of the flocculated sludge discharged in the solid-liquid classification process and returned to the flocculation process, but since the object to be treated is not liquid waste (sludge) to be disposed of but raw water that is the raw material for pure water, the viscosity of the flocculation process is low and the problem of non-uniform dispersion does not occur. In addition, the object to be treated is raw water, and the technical field is different.

[0032] The object of the present invention, made in consideration of the above problems, is to provide a sludge thickening method and thickening apparatus which improves dispersibility during the coagulation reaction and enables stable thickening even with slight differences in operating conditions. [Means for solving the problem]

[0033] As a result of intensive research into achieving the above-mentioned object, the inventors have discovered that in a sludge thickening method involving flocculation in a coagulation tank, thickening of sludge in a thickener, and returning a part of the thickened sludge to the flocculation step, by adding a polymer flocculant to the returned thickened sludge before it is mixed with the sludge to be treated, it is possible to make the flocculated flocs in the coagulation tank larger and denser, and by not adding a polymer flocculant to the coagulation tank, it is possible to suppress an increase in viscosity within the coagulation tank. As a result, they have discovered that the concentration efficiency in the thickener is stably improved even with slight differences in operating conditions, and have completed the present invention.

[0034] That is, the above-mentioned object can be achieved by a method for concentrating liquid waste, comprising: a flocculation step of forming flocs from liquid waste; a concentration step of concentrating the liquid waste containing the flocs to obtain concentrated sludge and separated liquid; an extraction step of extracting at least a part of the concentrated sludge obtained in the concentration step; and a return step of adding a polymer flocculant to the extracted concentrated sludge and returning the obtained flocculated concentrated sludge to the flocculation step, wherein the formation of the flocs in the flocculation step is achieved by mixing the returned flocculated concentrated sludge with the liquid waste.

[0035] A preferred embodiment of the method for concentrating liquid waste according to the present invention is as follows. (1) After the removing step, a dewatering step is further included in which the remaining portion of the removed thickened sludge is dewatered.

[0036] According to this, by dewatering the concentrated sludge having a high concentration, it is possible to improve the dewatering performance more than before. (2) The polymer flocculant is a polymer flocculant for water supply. By using a polymer flocculant for water supply as the polymer flocculant, large and strong flocs can be produced from the water supply sludge, thereby improving the thickening property of the obtained thickened sludge. (3) The polymer flocculant is a water supply polymer flocculant that does not contain acrylamide monomers. This improves the concentration of concentrated sludge obtained from water supply sludge, and prevents carcinogenic acrylamide monomers from being returned to the upstream process of the water purification process, even if the separated water produced during concentration is returned to the upstream process of the water purification process.

[0037] The above object can also be achieved by an apparatus for concentrating liquid waste, comprising: flocculation means for forming flocs from liquid waste; concentration means for concentrating the liquid waste containing the flocs to obtain concentrated sludge and separated liquid; piping means for removing at least a portion of the concentrated sludge obtained by the concentration means; mixing means for adding and mixing a polymer flocculant with the concentrated sludge removed by the piping means to obtain coagulated concentrated sludge; and return means for returning the coagulated concentrated sludge obtained by the mixing means to the flocculation means.

[0038] A preferred embodiment of the liquid waste concentrating device according to the present invention is as follows. (1) The concentrating means is a gravity concentrating device, or the flocculating means and the concentrating means are a granulating concentrating device. Effect of the Invention

[0039] According to the present invention, instead of directly adding a polymer flocculant to liquid waste to form flocs, a polymer flocculant is added to and mixed with at least a part of concentrated sludge to obtain flocculated thickened sludge, and this flocculated thickened sludge is mixed with liquid waste to form flocs, so that the increase in viscosity during flocculation is suppressed and dispersibility during the flocculation reaction is improved compared to the case where a polymer flocculant is directly added to liquid waste. Furthermore, since flocs are formed using the flocculated thickened sludge as a nucleus, the flocs are larger and stronger than before.

[0040] Therefore, even if the conditions of the flocculation reaction are somewhat different, stable concentration of liquid waste is possible. [Brief description of the drawings]

[0041] [Figure 1] 1 is a flow chart for explaining an example of a method for concentrating liquid waste according to the present invention. [Diagram 2] FIG. 1 is a schematic diagram showing a typical example of a treatment flow according to a method for concentrating liquid waste of the present invention. [Diagram 3] FIG. 1 is a schematic diagram showing a liquid waste treatment device 10 of the present invention. [Figure 4] FIG. 2 is a schematic diagram showing a liquid waste treatment device in which the concentrating means is a gravity concentrating device. [Diagram 5] FIG. 2 is a schematic diagram showing a liquid waste treatment device in which the flocculation means and the concentration means are granulation concentration devices. [Figure 6] FIG. 1 is a schematic diagram showing a process flow of a conventional method for concentrating and dehydrating liquid waste. [Figure 7] FIG. 1 is a schematic diagram showing a process flow of a conventional method for concentrating liquid waste as a pretreatment for anaerobic digestion. [Figure 8] FIG. 1 is a schematic diagram showing a conventional treatment flow of liquid waste using a gravity concentration device. [Figure 9] FIG. 1 is a schematic diagram showing a conventional treatment flow of liquid waste using a granulation concentrator. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0042] <Method of concentrating liquid waste> FIG. 1 is a flow chart for explaining one 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 treatment flow according to the method for concentrating liquid waste of the present invention.

[0043] As shown in FIG. 1, the present invention includes an aggregation step (S100), a concentration step (S110), a removal step (S120), and a return step (S130).

[0044] (Liquid waste) Liquid waste includes wastewater with a suspended solids concentration of 1000 mg / L or more, sludge that has become muddy (slurry-like) due to the settling or floating of suspended organic and inorganic matter in water, hydrolysis products of inorganic coagulants and powdered activated carbon added as water treatment chemicals, etc., solid particles, algae, fungi, and hydrolysis products of inorganic coagulants, water supply sludge, sewage and septic tank sludge, and liquid waste generated during water treatment processes such as water purification, sewage treatment, and public wastewater treatment.

[0045] The method for concentrating liquid waste according to the present invention will be described below with reference to FIGS.

[0046] [Agglutination process (S100)] In this process, flocculated flocs are formed from the liquid waste. The flocs are formed by mixing the returned flocculated and concentrated sludge (concentrated sludge to which a polymer flocculant has been added) with the liquid waste. The flocculated and concentrated sludge will be described later. This process is generally carried out in a flocculation tank.

[0047] The sludge concentration (SS concentration) in the coagulation tank into which the coagulated and concentrated sludge and liquid waste flow is preferably 5.0 to 20 g / L, and the SS concentration is more preferably 10 to 20 g / L. Therefore, by monitoring the sludge concentration in the coagulation tank, the optimal return flow rate of the coagulated and concentrated sludge can be determined in the return step (S130) described later.

[0048] A mixing tank for adding and mixing an inorganic flocculant may be provided upstream of the flocculation tank.

[0049] When inorganic coagulants are added in the mixing tank, commercially available products such as aluminum sulfate, polyaluminum chloride (PAC), polyferric sulfate (polyferric), ferric chloride, or a mixture of these can be used. In addition, when these inorganic coagulants are used, the pH of the liquid waste during conditioning drops, so commercially available caustic soda, etc. is used as an alkaline agent to adjust the pH to the appropriate coagulation pH.

[0050] In addition to or instead of the inorganic coagulant added in the mixing tank, an organic coagulant may be added. When an organic coagulant is added in the mixing tank, a commercially available product may be used as the organic coagulant, and one or more of the following may be used: polyalkylpolyamine, polyethyleneimine, diallyldimethylammonium chloride, ethylenediamine epichlorohydrin polycondensate, dicyandiamide-ammonium chloride-formaldehyde polycondensate, polyethylene-polyamine-dimethylamine-epichlorohydrin polycondensate, and dialkylamine-epichlorohydrin polycondensate.

[0051] The organic coagulant may be used without dilution or after diluting with water etc. When an organic coagulant is added, the addition rate of the organic coagulant to the liquid waste is generally 0.1% to 10% by mass, preferably 0.5% to 5% by mass, relative to the solid matter TS of the sludge (liquid waste).

[0052] The liquid waste in the coagulation tank is mixed with the coagulated and thickened sludge, and after conditioning to form coagulated flocs, the liquid waste containing the coagulated flocs is transferred to the thickening step (S110) (this concludes the coagulation step (S100)).

[0053] [Concentration process (S110)] In this process, the liquid waste containing the flocs is thickened to obtain thickened sludge and separated liquid. As the thickener used for thickening, for example, a gravity thickener such as a gravity thickener, a centrifugal thickener, a screen thickener, a belt-type filtration thickener, a granulation thickener, a flotation thickener, or other commercially available thickeners can be used.

[0054] When the liquid waste is coagulation-sedimentation sludge generated from the coagulation-sedimentation process of a water purification plant, that is, drinking water sludge, the thickener used in this process is generally a gravity thickener.

[0055] The sludge concentration (SS) of liquid waste before thickening is 5g / L to 15g / L, but the sludge concentration (SS) of the thickened sludge after thickening is 20-40g / L, depending on the sludge properties, type of thickener, and operating conditions.

[0056] The concentrated sludge having a high sludge concentration of 20 to 40 g / L may be transferred to an anaerobic digestion tank as desired. In this case, the high concentration of the concentrated sludge increases the retention time in the anaerobic digestion tank, thereby improving the anaerobic digestion performance (concentration step (S110)).

[0057] [Removal process (S120)] In this step, at least a part of the concentrated sludge obtained in the concentration step (S110) is taken out. To take out the concentrated sludge, for example, a return line including a dedicated return pipe connected at one end to the concentrator and at the other end to the coagulation tank or an upstream position of the coagulation tank, and a return pump provided in the return pipe can be used. This allows the coagulated and concentrated sludge obtained by adding a polymer coagulant to be returned to the coagulation tank at a stable sludge flow rate in the subsequent return step (S130).

[0058] The amount of thickened sludge to be removed is based on a suitable mixing ratio of the coagulated thickened sludge and liquid waste, which will be described later, and an amount required for this mixing ratio is removed (this is the removal step (S120)).

[0059] [Return process (S130)] In this step, a polymer flocculant is added to the extracted thickened sludge, and the resulting flocculated and thickened sludge is returned to the flocculation step (S100).

[0060] The polymer flocculant may be added to the suction or discharge part of the return pump (not shown) for the thickened sludge, to a line mixer provided in the return piping, or to a mixing tank provided at the mixing site in Figure 2. The mixing tank provided in the return piping may be mechanical or may be agitated by a water current caused by the thickened sludge.

[0061] The residence time of the concentrated sludge in the mixing tank installed in the return pipe varies depending on the stirring method, stirring strength, 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 more, the polymer flocculant and the concentrated sludge are mixed sufficiently. On the other hand, if the residence time is 3 minutes or less, the possibility of the concentrated sludge flocculating matter accumulating in the mixing tank installed in the return pipe and the possibility of the flocculating property decreasing can be reduced.

[0062] The polymer flocculant may be a commercially available product, and may be an anionic polymer flocculant, a cationic polymer flocculant, or an amphoteric polymer flocculant, either alone or in combination. The polymer flocculant may be in powder form, liquid form (dispersion form, emulsion form), or the like.

[0063] The anionic polymer flocculant can be any one or more selected from the group consisting of polyacrylic acid, sodium polyacrylate, potassium polyacrylate, ammonium polyacrylate, polymethacrylic acid, sodium polymethacrylate, potassium polymethacrylate, and ammonium polymethacrylate.

[0064] Also usable are polyacrylamide-based polymer flocculants, which are copolymers of acrylamide monomers and (meth)acrylates.

[0065] When the liquid waste is coagulation-sedimentation sludge generated from the coagulation-sedimentation process of a water purification plant, that is, drinking water sludge, a polymer coagulant for water supply is used as the polymer coagulant.

[0066] 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 process. On the other hand, since acrylamide is carcinogenic, from the viewpoint of avoiding the separation liquid and dehydration filtrate in the concentration process (S110) in which acrylamide monomers remain being returned as return water to the previous process of water purification treatment, polymer flocculants for water supply such as polyacrylic acid and sodium polyacrylate that do not contain acrylamide monomers are suitable.

[0067] The cationic polymer flocculant has a cationic monomer as an essential component, and one or more selected from homopolymers or copolymers of cationic monomers, copolymers of cationic monomers and nonionic monomers, etc. Examples of the cationic monomer include dimethylaminoethyl acrylate, dimethylaminoethyl methacrylate, diethylaminoethyl acrylate, diethylaminoethyl methacrylate, or alkali metal salts or quaternary ammonium salts thereof.

[0068] The amphoteric polymer flocculant is a copolymer of a cationic monomer, an anionic monomer and a nonionic monomer, and has a cationic unit, an anionic unit and a nonionic unit in the molecule.

[0069] When the liquid waste is sludge after biological treatment, the polymer flocculant may be a cationic polymer flocculant or an amphoteric polymer flocculant having any cationic degree or molecular weight.

[0070] When the liquid waste is water supply sludge, it is preferable to add a water supply polymer flocculant of poly(meth)acrylate having a 0.1% salt viscosity of 2 to 5 mPa s and an anion equivalent of -9.0 or less to the concentrated sludge, but the water supply polymer flocculant is not limited to this. Water supply polymer flocculants containing acrylamide monomers and those not containing acrylamide monomers can both be used depending on the purpose.

[0071] The salt viscosity is the value measured at 25°C using a Brookfield viscometer on a sample prepared by dissolving poly(meth)acrylate in a 1N aqueous sodium chloride solution to a concentration of 0.1% by mass, and the unit of viscosity is mPa s.

[0072] The anion equivalent is a value that can be determined by the following measurement method, and is expressed in units of meq / g. Prepare a 0.1% aqueous solution of poly(meth)acrylate, add 5 ml of methyl glycol chitosan solution (N / 200), stir, add 2-3 drops of touidine blue indicator, and titrate with potassium polyvinyl sulfate solution (PVSK, N / 400). The end point is the point at which the color changes and is maintained for 10 seconds or more. A blank test is performed using the same procedure as above, but without adding the sample, and the anion equivalent Av is calculated using the following formula.

[0073] Anion equivalent (Av) [meq / g] = (Blank titer ml - Sample titer ml) x 1 / 2 x Titer of PVSK

[0074] The addition rate of polymer coagulant to concentrated sludge is 0.02 wt / wt% or more vs. SS and 2.0 wt / wt% or less vs. SS. If the addition rate of polymer coagulant is 0.02 wt / wt% or more vs. SS, the polymer coagulant solution mixes well with the concentrated sludge, strong coagulated flocs are formed in the coagulation tank, and thickening performance is improved. If the addition rate of polymer coagulant is 2.0 wt / wt% or less vs. SS, strong coagulated flocs are formed in the coagulation tank from the coagulated concentrated sludge and liquid waste while reducing the amount of polymer coagulant used, and thickening performance is improved.

[0075] By monitoring the predetermined polymer flocculant addition rate to the thickened sludge ("wt / wt% vs SS" or "wt / wt% vs TS"), the sludge concentration and sludge flow rate in the coagulation tank into which the coagulated thickened sludge and liquid waste flow in, and the thickened sludge concentration, the optimal return flow rate of the coagulated thickened sludge to be returned to the coagulation process (S100) can be determined.

[0076] In addition, by installing a sludge flow meter or a sludge concentration meter in the return piping of the return process (S130) to monitor the return flow rate and sludge concentration, the amount of coagulated and concentrated sludge returned to the coagulation process (S100) can be controlled, and stable concentration can be achieved.

[0077] The sludge concentration can be detected using commercially available sludge concentration meters such as a near-infrared sludge concentration meter, a laser light sludge concentration meter, or a microwave sludge concentration meter. The sludge flow rate can be detected using commercially available electromagnetic flow meters or ultrasonic flow meters. The pump that returns the coagulated and concentrated sludge can be a commercially available product, and the flow rate can be adjusted to a set value by controlling the rotation speed before being returned.

[0078] According to the method for concentrating liquid waste of the present invention, the formation of flocs from the liquid waste in the coagulation step (S100) is achieved by mixing the returned coagulated and concentrated sludge with the liquid waste, rather than by adding a polymer coagulant directly to the liquid waste, so that the increase in viscosity during the coagulation reaction is suppressed more than in the past, and the dispersibility during the coagulation reaction is improved. Therefore, compared to the conventional method of setting the injection rate of the polymer coagulant based on the flow rate of the sludge (liquid waste) flowing into the coagulation tank, it is possible to always add the polymer coagulant in an optimal amount regardless of the properties of the liquid waste.

[0079] This makes it possible to optimize the amount of polymer flocculant used and perform efficient treatment while achieving high flocculation effect and concentration in a stable and continuous manner.

[0080] If the coagulated and concentrated sludge with the optimal amount of polymer coagulant added is returned to the coagulation step (S100), there is no need to add additional polymer coagulant in the coagulation step (S100).In fact, if additional polymer coagulant is added in the coagulation step (S100), it will take time to disperse and homogenize the sludge in the coagulation tank due to the viscosity of the polymer coagulant solution, which may actually result in a decrease in coagulation and concentration.

[0081] Indicators of sludge concentration include SS (suspended solids) and TS (total solids). In sludge with a low dissolved salt concentration (concentration of dissolved salts such as salt), such as sewage, the measured values ​​of SS and TS are the same, but in sludge with a high dissolved salt concentration, such as sewage treatment, the values ​​of SS and TS may differ, and SS is used as the sludge concentration.

[0082] In the present invention, SS and TS are defined as follows. SS:K 0102:2019 Industrial wastewater test method 14.1 Suspended solids TS:K 0102:2019 Industrial wastewater test method 14.2 Total evaporation residue

[0083] Although an example of the method for concentrating liquid waste according to the present invention has been described above with reference to Figs. 1 and 2, the present invention is not limited to this example.

[0084] For example, at least a portion of the concentrated sludge obtained in the concentration step (S110) is removed and returned to the flocculation step (S100) as condensed concentrated sludge, but the remainder of the concentrated sludge obtained in the concentration step (S110) may be dewatered.

[0085] As shown in Fig. 1, the method for concentrating liquid waste of the present invention includes a dehydration step (S140) as an optional step. The dehydration step (S140) will be described below.

[0086] [Dehydration process (S140)] In this step, the remaining part of the concentrated sludge removed after the removing step (S120) is dewatered.

[0087] Dewatering involves applying mechanical pressure to the thickened sludge to squeeze out water from the thickened sludge, resulting in a dewatered cake with a low moisture content.

[0088] The dehydrator used in this step may be a conventionally known device, and examples thereof include a belt press dehydrator, a centrifugal dehydrator, a pressurized dehydrator, a vacuum dehydrator, a granulation and conditioning type high-efficiency direct dehydration method, a multiple disk type dehydrator, a screw press type dehydrator, and an electro-osmosis type dehydrator.

[0089] The obtained dehydrated cake is disposed of by being transported to a landfill or incinerated in an incinerator, as in the conventional manner (the above is the dehydration step (S140)).

[0090] According to the method for concentrating liquid waste of the present invention, which includes the dewatering step (S140), the concentrated sludge obtained after the concentration step (S110) contains large and strong flocs, so that the dewatering performance in the dewatering step (S140) is improved and the moisture content of the obtained dewatered cake is lower than in the past. Therefore, the transportation cost of the dewatered cake and the fuel cost for incineration can be reduced compared to the past.

[0091] Furthermore, in the method for concentrating liquid waste 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, but other additives may also be used. For example, a short fiber agent may be added to the liquid waste to improve the concentrating ability.

[0092] Examples of the staple fiber agent include natural staple fibers such as waste paper and cotton, chemically synthesized staple fibers, and recycled staple fibers. Staple fibers made of recycled thread from plastic waste and staple fibers made of viscose rayon are preferred.

[0093] Among them, short fiber medicines made of viscose rayon (for example, Evergloss U-700 series, manufactured by Suing Co., Ltd.) have excellent concentration effect.

[0094] From the viewpoint of excellent dispersibility in liquid waste and affinity with liquid waste (sludge), a short fiber agent having a fiber length of 5 to 10 mm and a moisture content of 30 to 80 wt / wt% is suitable.

[0095] The addition rate of the short fiber-like chemical is 0.02 to 1.0 wt / vol % based on the liquid waste, and preferably 0.1 to 0.5 wt / vol %.

[0096] By adding 0.02 wt / vol% or more of short fiber chemicals to the liquid waste, the liquid waste and fibers can form stronger flocs, improving the concentration in the concentration step (S110). This results in a more concentrated concentrated sludge, which reduces the SS and BOD concentrations in the separated liquid.

[0097] In addition, by setting the addition rate of the short fiber chemical agent to less than 1.0 wt / vol% per liquid waste, the short fiber chemical agent can be uniformly mixed and dispersed in the liquid waste, effectively capturing the oil and SS in the liquid waste, and is also economically advantageous.

[0098] <Liquid waste concentrator> 3 is a schematic diagram showing a liquid waste treatment device 10 of the present invention. As shown in the figure, the liquid waste treatment device 10 of the present invention has a flocculation means 20, a concentration means 30, a piping means 40, a mixing means 50, and a return means 60.

[0099] The flocculation means 14 is a means for forming flocs from the liquid waste, and is generally a flocculation tank. The mixed liquid waste and the returned flocculated and concentrated sludge are agitated in the flocculation tank, and flocs grow and are formed.

[0100] A mixing tank may be provided upstream of the coagulation tank to add and mix an inorganic coagulant. Also, an organic coagulant may be added in addition to or instead of the inorganic coagulant added in the mixing tank.

[0101] The sludge concentration (SS concentration) in the coagulation tank, the return flow rate of the coagulated and concentrated sludge, the inorganic coagulant, and the organic coagulant are as described in the above method for concentrating liquid waste, and therefore will not be described here. Downstream of the coagulation means 20, a concentration means 30 is provided.

[0102] The thickening means 30 is a means for thickening the liquid waste containing the flocs to obtain thickened sludge and separated liquid.

[0103] As the concentrating means 30, any conventionally known concentrating means can be used, for example, commercially available concentrating devices such as gravity concentrators such as gravity concentrators, centrifugal concentrators, screen concentrators, belt-type filtration concentrators, granulation concentrators, and flotation concentrators.

[0104] Among them, it is preferable that the concentrating means 30 is a gravity concentrating device, or that the flocculating means 20 and the concentrating means 30 are a granulation concentrating device.

[0105] Fig. 4 is a schematic diagram showing a liquid waste treatment device in which the thickening means is a gravity thickener. As shown in the figure, the gravity thickener introduces liquid waste (conditioned sludge) containing coagulated flocs from the coagulation tank into a center well, and gently stirs the conditioned sludge to separate water and air bubbles from it by rotating the picket fence and sludge scraper plate with a drive unit. The sludge is separated by gravity into thickened sludge and separated liquid, and the separated liquid is drawn out from the separated liquid outlet pipe, and the thickened sludge is drawn out from the thickened sludge withdrawal pipe below the gravity thickener.

[0106] According to the present invention, since the flocculation is strong, even if the sludge is stirred with a picket fence in the tank, the sludge does not break down, and the water between the sludge particles is easily discharged, so that highly concentrated sludge can be obtained. Since highly concentrated concentrated sludge is obtained, the flow rate of the concentrated sludge to be returned can be reduced, and the power cost of the return pump (not shown) can be reduced. Furthermore, if a dehydration facility is provided in the downstream stage, the dehydration performance of the dehydrator is improved and the retention time of the concentrated sludge in anaerobic digestion is extended, improving the organic matter removal effect.

[0107] Fig. 5 is a schematic diagram showing a liquid waste treatment device in which the flocculation means and the concentration means are a granulation concentration device. As shown in the figure, the granulation concentration device has a granulation concentration tank equipped with an agitator having an agitating blade, and liquid waste is introduced into the tank through a sludge inlet pipe provided at the bottom, and flocculated and concentrated sludge is introduced through a return pipe also provided at the bottom.

[0108] The liquid waste and coagulated thickened sludge are mixed and stirred in a draft tube and an agitator to form coagulated flocs, which then form larger granules. From there, the mixture is separated into granulated thickened sludge and separated liquid by a screen. The granulation thickening device produces strong and large coagulated flocs, which allows the openings of the screen, which is prone to clogging, to be enlarged, resulting in stable thickening and highly concentrated thickened sludge.

[0109] If the liquid waste is organic sludge, the separated liquid is sent to a sewage treatment process or the like for water treatment. If the liquid waste is inorganic sludge, the separated liquid is returned as return water, for example to a previous process of water purification treatment, or is discharged. The concentrated sludge is taken out from the piping means.

[0110] The piping means 40 is a means for taking out at least a part of the concentrated sludge obtained by the concentration means 30, and may be, for example, a return line including a dedicated return pipe having one end connected to the concentration means 30 and the other end connected to the bottom of the concentration means 30 when the concentration means 30 is a granulation concentration device or the coagulation means 20 or the concentration means 30 is a granulation concentration device, and a return pump provided on the return pipe. A mixing means 50 is provided on the return line.

[0111] The mixing means 50 is a means for adding and mixing a polymer flocculant with the thickened sludge taken out by the piping means 40 to obtain a flocculated thickened sludge. Examples of the mixing means 50 include a line mixer or a mixing tank provided at the suction or discharge part of a return pump (not shown) for the thickened sludge or in the middle of the return piping. The mixing in the mixing tank may be mechanical or may be a water current caused by the thickened sludge. The residence time in the mixing tank and the polymer flocculant to be added are as explained in the method for concentrating liquid waste, and therefore will not be explained here.

[0112] The return means 60 is a means for returning to the flocculation means the coagulated and concentrated sludge obtained by the mixing means 50. The specific configuration of the return means 60 is as described above for the piping means 40 as the return line.

[0113] In addition, a sludge flow meter and a sludge concentration meter may be installed in the return piping of the return line to monitor the return flow rate and sludge concentration. The detection of the sludge concentration is as explained in the above-mentioned method for concentrating liquid waste, and therefore the explanation thereof will be omitted here.

[0114] Furthermore, as shown in FIG. 3, in the liquid waste treatment device 10 of the present invention, the return piping branches into a return means 60 which removes at least a portion of the concentrated sludge from the concentration means 30 and then returns it to the flocculation means 20 via the mixing means 50, and a piping which transports the remainder of the concentrated sludge downstream, and a dewatering means (not shown) may be provided at the end of the piping.

[0115] The dewatering means applies mechanical pressure to the concentrated sludge to squeeze out water from the concentrated sludge and obtain a dewatered cake with a low water content. Any conventionally known means can be used as the dewatering means. The obtained dewatered cake is transported to an outside place for disposal in a landfill or incinerated in an incinerator.

[0116] According to the liquid waste treatment device of the present invention including the dewatering means, strong flocs can be obtained, which improves the dewatering performance when dewatering the concentrated sludge, and the moisture content of the dewatered cake is lower than before. This reduces the transportation cost when removing the waste, and also reduces the fuel cost required for incineration.

[0117] The present invention will now be described more specifically with reference to examples. EXAMPLES

[0118] 1. Example 1 The excess sludge (liquid waste) (pH 6.5, SS 10g / L) from the standard activated sludge treatment facility of a separate sewerage treatment plant was used as the target. 3 A concentration test was carried out using a wire screen with a slit width of 1 mm at a temperature of 20-25°C for 10 min / day. The sludge concentration of the concentrated sludge and the SS concentration of the separated liquid were measured.

[0119] [Table 1]

[0120] The excess sludge (liquid waste) in the coagulation tank in Table 1 was mixed with coagulated concentrated sludge, which had been prepared in advance and to which a cationic polymer coagulant (EvaGrose C-104G, manufactured by Suing Co.) had been added at 0.02-0.5 wt% per SS weight of the excess sludge (0.03-0.74 wt% per SS weight of the concentrated sludge), and the coagulated flocs were then concentrated using a screen.

[0121] The thickened sludge prepared in advance was thickened in advance using the thickening test equipment in Table 1 after conditioning the excess sludge with a cationic polymer coagulant at a rate of 0.3 wt / wt% relative to SS (SS 38 g / L, test number No. 11 in Table 2).

[0122] We also conducted tests in which the polymer flocculant was added directly to the coagulation tank without returning the concentrated sludge to the coagulation tank, and in which the polymer flocculant was added directly to the coagulation tank and then concentrated sludge without the addition of polymer flocculant was added.

[0123] The results are shown in Table 2.

[0124] 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 SS in the flocculation tank.

[0125] (i) "Polymer flocculant added to concentrated sludge" in Table 2 corresponds to the case where the required amount of polymer flocculant is added to the concentrated sludge using the method of the present invention, and the concentrated sludge containing the polymer flocculant (flocculated concentrated sludge) is returned to the coagulation tank.

[0126] The polymer flocculant addition rate relative to the SS weight of the thickened sludge is also shown in parentheses (Test Nos. 1 to 9).

[0127] (ii) in Table 2, “Polymer coagulant added to coagulation tank without returning thickened sludge”, refers to the case where polymer coagulant was added to the coagulation tank without adding thickened sludge or returning thickened sludge to the coagulation tank (Test Nos. 10 to 13).

[0128] (iii) in Table 2, "Concentrated sludge is returned and polymer coagulant is added to the coagulation tank," refers to the case where concentrated sludge without adding polymer coagulant was returned to the concentrated sludge in the coagulation tank and polymer coagulant was added to the coagulation tank (Test Nos. 14 to 17).

[0129] [Table 2]

[0130] A polymer flocculant was added to the thickened sludge at a rate of 0.3 wt / wt% relative to the SS weight in the coagulation tank, and the resulting coagulated thickened sludge was returned to the coagulation tank so that the SS in the coagulation tank was 20 g / L.The coagulated thickened sludge and excess sludge were coagulated in the 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).

[0131] Neither the coagulated thickened sludge nor the thickened sludge was returned to the coagulation tank, but a polymer coagulant was added to the coagulation tank at a polymer coagulant addition rate of 0.3 wt / wt% to SS based on the SS weight in the coagulation tank, and the sludge was coagulated and screen thickened. The SS of the thickened sludge was 38 g / L, and the SS of the separated liquid was 220 mg / L (Test No. 11).

[0132] The concentrated sludge without the addition of polymer coagulant was returned to the coagulation tank, the SS in the coagulation tank was adjusted to 20 g / L, and polymer coagulant was added to the coagulation tank at a rate of 0.4 wt / wt% to SS based on the weight of the SS in the coagulation tank. The sludge was coagulated and thickened with a screen, and the SS of the concentrated sludge was 44 g / L, and the SS of the separated liquid was 300 mg / L (Test No. 15).

[0133] As in the present invention, by adding the required amount of polymer coagulant to the concentrated sludge, returning the concentrated sludge containing the polymer coagulant (coagulated concentrated sludge) to the coagulation tank, and conditioning the excess sludge (liquid waste) in the coagulation tank and screen concentrating it, the SS concentration of the concentrated sludge obtained was increased even if the amount of polymer coagulant added was reduced, and the SS concentration of the separated liquid was also reduced.

[0134] 2. Example 2 0.5 L of the concentrated sludge obtained in Example 1 was taken and conditioned with the polymer flocculant used in Example 1. The addition rate of the polymer flocculant to the concentrated sludge was 0.5 to 2.0 wt / wt% relative to SS. After conditioning, the filter cloth area was 100 cm 2 The conditioned concentrated sludge was placed on the filter cloth, and a pressure dehydration test was performed using a pressure dehydration tester by applying uniaxial pressure of 50 kPa for 10 minutes. After the pressure dehydration test, the dehydrated cake was taken out and the moisture content was measured. In addition, the SS of the dehydrated filtrate discharged from the filter cloth was measured.

[0135] The results are shown in Table 3.

[0136] The following three types of concentrated sludge were used in the dewatering test. The concentrated sludge preparation methods (i) to (iii) shown in the column of polymer flocculant addition rate for concentrated sludge in Table 3 and the concentrated sludge concentrations are as follows:

[0137] (i) This is thickened sludge obtained by adding a polymer flocculant to thickened sludge, and corresponds to test number No. 5 in Table 2 (Example 1), and the thickened sludge concentration is SS 65 g / L.

[0138] (ii) This is thickened sludge obtained by adding a polymer flocculant to a coagulation tank without returning the thickened sludge, and corresponds to test number 11 in Table 2 (Example 1), and the thickened sludge concentration is SS 38 g / L.

[0139] (iii) This is thickened sludge obtained by returning the thickened sludge and adding a polymer flocculant to the coagulation tank, and corresponds to test number 15 in Table 2 (Example 1), and the thickened sludge concentration is SS 44 g / L.

[0140] [Table 3]

[0141] When a polymer flocculant was added to the concentrated sludge of test number 5 in Table 2 (Example 1) at 1.0 wt / wt% relative to SS and pressure dewatered after conditioning, the moisture content of the dehydrated cake was 80% and the SS of the dehydrated filtrate was 310 mg / L (test number 2).

[0142] When a polymer flocculant was added to the concentrated sludge of Test No. 11 in Table 2 (Example 1) at 1.5 wt / wt% relative to SS and the sludge was conditioned and then pressurized dehydrated, the moisture content of the dehydrated cake was 82% and the SS of the dehydrated filtrate was 380 mg / L (Test No. 6).

[0143] When a polymer flocculant was added to the concentrated sludge of test number 15 in Table 2 (Example 1) at 1.5 wt / wt% relative to SS and pressure dewatered after conditioning, the moisture content of the dewatered cake was 82% and the SS of the dewatered filtrate was 350 mg / L (test number 10).

[0144] As in the present invention, the required amount of polymer flocculant is added to the thickened sludge, the thickened sludge containing the polymer flocculant (flocculated thickened sludge) is returned to the coagulation tank, and the excess sludge (liquid waste) is refined in the coagulation tank and the thickened sludge obtained by screen thickening is dewatered, thereby making it possible to obtain a dehydrated cake with a low moisture content even if the amount of polymer flocculant added is reduced.

[0145] The thickened sludge obtained in the present invention contributes to improving the dewatering performance in the subsequent stage.

[0146] 3. Example 3 In the rapid filtration equipment of a water purification facility, river water with a turbidity of 3 to 5 degrees was used as raw water for drinking water, and a PAC injection rate of 20 mg / L was used to coagulate and sediment the water. The coagulated and sedimented sludge discharged from the sedimentation tank (pH 6.5, SS 5.1 g / L or less, drinking water sludge (liquid waste)) was subjected to a concentration test using the concentration test device shown in Table 1.

[0147] The water supply sludge (liquid waste) and the coagulated and concentrated sludge, which had been prepared in advance by adding an anionic water supply polymer coagulant (EvaGrose WA-200, manufactured by Suing Co., Ltd.) that does not contain acrylamide at 0.2-0.4 wt% per SS weight of the water supply sludge (0.35-0.81 wt% per SS weight of the concentrated sludge), were added to the coagulation tank shown in Table 1, mixed, and the coagulated flocs were concentrated using a screen.

[0148] The thickened sludge that had been prepared in advance was made by conditioning the drinking water sludge with the same non-acrylamide anionic water supply polymer flocculant at a rate of 0.4 wt / wt% versus SS, and then thickening it using the thickening test equipment shown in Table 1 (SS 36 g / L, test number No. 7 in Table 4).

[0149] In addition, similarly to Example 1, tests were also conducted in which the concentrated sludge was not returned to the coagulation tank and a polymer coagulant was added directly to the coagulation tank, and in which a polymer coagulant was added directly to the coagulation tank and then concentrated sludge without added polymer coagulant was added.

[0150] The results are shown in Table 4.

[0151] (i) "Polymer flocculant added to concentrated sludge" in Table 4 corresponds to the case where the required amount of polymer flocculant is added to previously prepared concentrated sludge using the method of the present invention, and the concentrated sludge containing the polymer flocculant (flocculated concentrated sludge) is returned to the coagulation tank.

[0152] The polymer flocculant addition rate relative to the SS weight of the concentrated sludge is also shown in parentheses in Table 4 (Test Nos. 1 to 5).

[0153] (ii) in Table 4, "Polymer coagulant added to coagulation tank without returning concentrated sludge," refers to the case where polymer coagulant was not added to the concentrated sludge, and the concentrated sludge was not returned to the coagulation tank, but a polymer coagulant was added to the coagulation tank (Test Nos. 6 to 8).

[0154] (iii) in Table 4, "Concentrated sludge is returned and polymer coagulant is added to the coagulation tank," refers to the case where concentrated sludge without adding polymer coagulant was returned to the coagulation tank and polymer coagulant was added to the coagulation tank (Test Nos. 9 to 11).

[0155] [Table 4]

[0156] A polymer flocculant was added to the thickened sludge at a rate of 0.3 wt / wt% relative to the SS weight in the coagulation tank, and the resulting coagulated thickened sludge was returned to the coagulation tank so that the SS in the coagulation tank was 10 g / L. When the coagulated thickened sludge and excess sludge (liquid waste) were coagulated in the coagulation tank and screen-thickened, the SS of the thickened sludge was 44 g / L, and the SS of the separated liquid was 100 mg / L (Test No. 2).

[0157] Neither the coagulated thickened sludge nor the thickened sludge was returned to the coagulation tank, but a polymer coagulant was added to the coagulation tank at a polymer coagulant addition rate of 0.4 wt / wt% to SS based on the SS weight in the coagulation tank, and the sludge was coagulated and screen thickened. The SS of the thickened sludge was 36 g / L, and the SS of the separated liquid was 260 mg / L (Test No. 7).

[0158] The concentrated sludge without the addition of polymer coagulant was returned to the coagulation tank, the SS in the coagulation tank was adjusted to 10 g / L, and polymer coagulant was added to the coagulation tank at a polymer coagulant addition rate of 0.4 wt / wt% relative to the SS weight in the coagulation tank, and the sludge was coagulated and screen-concentrated. The SS of the concentrated sludge was 39 g / L, and the SS of the separated liquid was 330 mg / L (Test No. 10).

[0159] As in the present invention, by adding the required amount of polymer flocculant to the concentrated sludge, returning the concentrated sludge containing the polymer flocculant (flocculated concentrated sludge) to the coagulation tank, and conditioning the water supply sludge (liquid waste) in the coagulation tank and screen concentrating it, the SS concentration of the concentrated 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

1. a flocculation step for forming flocs from the liquid waste; a concentration step of concentrating the liquid waste containing the flocs to obtain concentrated sludge and a separated liquid; A removal step of removing at least a portion of the concentrated sludge obtained in the concentration step; a suspended solids concentration measuring step of measuring a suspended solids concentration (SS concentration) of the extracted concentrated sludge; A returning step of adding a polymer flocculant to the extracted concentrated sludge in an amount corresponding to the measurement result of the SS concentration measuring step, and returning the obtained flocculated concentrated sludge to the flocculation step, 2. A method for concentrating liquid waste, comprising the steps of: forming the flocs in the flocculation step by mixing the returned flocculated and concentrated sludge with the liquid waste.

2. 2. The method for concentrating liquid waste according to claim 1, further comprising a dehydration step of dehydrating the remaining part of the concentrated sludge removed after the removing step.

3. 3. The method for concentrating liquid waste according to claim 1, wherein the polymer flocculant is a polymer flocculant for water supply.

4. 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.

5. A method for concentrating liquid waste as described in claim 1 or 2, characterized in that the suspended solids concentration (SS concentration) of the liquid waste is 1000 mg / L or more.

6. A method for concentrating liquid waste as described in claim 1 or 2, characterized in that in the coagulation process, no coagulant is added except for the polymer coagulant contained in the coagulated concentrated sludge.

7. a flocculation means for forming flocs from the liquid waste; a concentrating means for concentrating the liquid waste containing the flocs to obtain concentrated sludge and a separated liquid; A piping means for extracting at least a portion of the concentrated sludge obtained by the concentration means; a sludge concentration meter provided in the middle of the piping means and capable of measuring a suspended solids concentration (SS concentration) of the concentrated sludge in the piping means; a mixing means for adding and mixing the concentrated sludge taken out by the piping means with an amount of polymer flocculant corresponding to the measurement result by the sludge concentration meter to obtain a flocculated concentrated sludge; A returning means for returning the flocculated and concentrated sludge obtained by the mixing means to the flocculation means; 1. A liquid waste concentrating apparatus comprising:

8. The liquid waste concentrating apparatus as described in claim 7, characterized in that the flocculation means and the concentrating means are granulation concentrating apparatus.

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